II MSC AE
NANO ELECTRONICS AND SCIENCE
UNIT I INTRODUCTION, SURVEY OF MODERN ELECTRONICS
Diode as Basic Element of Electronics, Field Effect of Transistors, Heterostructure
transistors, Resonant-Tunneling diodes and transistors Need for New Concepts in
Electronics, From Microelectronics towards Bimolecular Electronics
UNIT II BASIC CONCEPTS OF ELECTROMAGNETIC WAVES AND
QUANTUM MECHANICS
Electromagnetic Waves and Maxwell’s Equations, Duality of Electron, Schrödinger
Equation, Eigenvalue Problem and Electron in Quantum Well, Electrons in Multiple
Quantum Wells. Super lattices Artificial Atoms: Quantum Dots, Molecules, Energy Level
Splitting, Chemical Bonds,Optical Transitions and Lasers
UNIT III ROLE OF PATTERN FORMATION IN NANOELECTRONICS
High Resolution Lithography, Dip-Pin Lithography, NEMS, Nano-Electromechanical
Systems, Self-Assembly structures – Chemically Directed Self-Assembly,
Surface-Layer Proteins in nanolithography
UNIT IV TRADITIONAL LOW-DIMENSIONAL SYSTEMS
Quantum Well cascade Lasers and other Quantum-Well Devices, Quantum Wires,
Quantum Dots and Quantum Dot molecules, Quantum Dot Based cellular Automata,
Coulomb Effects, Single Electron Devices Nanoscale sensors and Actuators
UNIT V NEWLY EMERGED NANOSTRUCTURES
Challenges and Potential Applications of Inorganic Hetero structures, Quantum Dots
Embedded in organic Matrix, organic light emitting diodes, Quantum Wire Interconnects,
DNA and Peptides, Fullerenes and carbon nanotubes, Molecular Electronics Materials
and Biomolecules, Future Integrated circuits: Quantum computing
Text Books:
1. C.P. Poole and F.J.Owens, “ Introduction to nanotechnology”,John Wiley &
Sons,2003
2. M.A. Ratner and D.Ratner, “ Nanotechnology ; a gentle introduction to the next big
idea” ,
Prentice Hall,2002
1. Nanometer structures:theory,modeling and simulation” Editor:Akhlesh Lakhtakia,
ASME Press
2. S.E.Lyshevski,”Nano-and micro-electrochemical systems fundamentals of nano and
microengineering ,2004.
UNIT – I
SECTION – A
1. What is lower dimension devices?
Ans: Semiconductor devices which approximate a two dimensional structure
(films), a one dimensional structure (wires) or a zero dimensional strucure (dots)
have very interesting and important properties:

The theory of the behavior of electrons in structures of dimensions lower
than three is well known. Although true zero, one and two dimensional
physical structures are not possible, if one or more dimensions are less than
the de Broglie wave length of an electron the structure has the quantum
properties of a lower dimension structure.
2. Define OLED?
Ans:
OLED technology is used in commercial applications such as displays for mobile
phones and portable digital media players, car radios and digital cameras among others.
Such portable applications favor the high light output of OLEDs for readability in
sunlight and their low power drain. Portable displays are also used intermittently,
so the lower lifespan of organic displays is less of an issue. Prototypes have been
made of flexible and rollable displays which use OLEDs' unique characteristics.
Applications in flexible signs and lighting are also being developed.[71] Philips
Lighting have made OLED lighting samples under the brand name 'Lumiblade'
available online.[72]
SECTION- B
3. Explain about the lower dimensions devices?
Ans: Semiconductor devices which approximate a two dimensional structure
(films), a one dimensional structure (wires) or a zero dimensional strucure (dots)
have very interesting and important properties:


The theory of the behavior of electrons in structures of dimensions lower
than three is well known. Although true zero, one and two dimensional
physical structures are not possible, if one or more dimensions are less than
the de Broglie wave length of an electron the structure has the quantum
properties of a lower dimension structure.
The technology for producing structures with one or more dimension
sufficiently small to achieve low-dimension quantum effects (approximately
10 nm) has recently advanced enough to allow fabrication of devices based
upon low-dimension quantum effects.
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Devices operating on quantum confinement are more efficient in energy so
there is less wasted energy to be dissipated as heat.
Quasi-two dimensional devices, such as quantum well semiconductor lasers,
are now economically practial, but quasi-one and zero dimensional devices
such as quantum wires and quantum dots are not now economically
practical, perhaps because of the additional processing required to create
wires and dots. IBM, Bellcore and Phillips dropped research and
development programs for quantum wires and dots in the mid-1990s.
Electrons can be confined to one semiconductor material by sandwiching the
semiconductor material between two layers of higher energy-band gap
materials. Such a structure is called a heterojunction.
There are allowed and forbidden energy levels for a electrons in a material.
The conductivity of a material is determined by the occupancy of the
allowed energy bands. Energy bands which are filled are called valence
bands and the ones that are sparcely occupied are called conduction bands.
The conductivity of a material is determined by the occupancy of its energy
bands.
The availability of electrons to fill the energy bands depends upon the
valence electrons of the material, but can be altered by doping, the
introduction of chemically-related material into the crustal lattice of the
material. Also photo-electric photons can change the occupancy of a
material.
The development of Molecular-Beam Epitaxy (MBE) in the laste 1960's
made quasi-two dimensional structures feasible. Not only did this allow the
creation of ultrathin films but multiple layers of such films. However it was
not until 1974 that quantum well devices were produced.
The typical laser energy arrangement involves four states:
1. E3: The state to which electrons are pumped
2. E2: The upper state of two states involved in the productions of
photons
3. E1: The lower state to which electrons drop from the upper state after
emitting a photon
4. E0: The ground state to which electrons fall from E1
The key to the operation of the laser is a population inversion, a higher
population in the upper state E2 than in the lower state E1. This is achieved
by pumping to E3and the rapid exit of electrons from the lower state E1.
In conventional lasers the energy states are natural energy level of the lasing
material such as ruby crytal or helium=neon gases. In the quantum cascade
laser the energy states are determined by the physical characteristics of the
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quantum wells and can be adjusted to any desired levels. The quantum
cascade laser relies upon cascades of 25 quantum well configurations.
Quantum wires and quantum dots may be more efficient and faster than
quantum films.
It is much more difficult to fabricate quantum wires than quantum films.
One promising technology deposits semiconductor material at the bottom of
V-shaped lines, such might be found in a diffraction grating.
Laser wires generate photons through the self annihilation of exciton,
pairings of electrons and holes. Conventional lasers, by contrast, emit
photons from the annihilation of free electrons and free holes. When the
current is increased a conventional laser's emission frequency may derease,
whereas for wire or dot lasers the frequencies are stable when current is
increased.
Variations in the width of quantum wires may result in their functioning as a
chain of quantum dots. This may occur at low temperatures.
Variations in the thickness of quantum films result in clumps that function as
quantum dots. This approach offers the possibility of creating arrays of
quantum dots.
There is a possibility of using molecules as quantum dots. The problem is
creating contacts and linkages.
4. Explain the organic lights?
Ans: Organic light-emitting diode
From Wikipedia, the free encyclopedia
Demonstration of a flexible OLED device
A green emitting OLED device
An organic light emitting diode (OLED) is a light-emitting diode (LED) in
which the emissive electroluminescent layer is a film of organic compounds which
emit light in response to an electric current. This layer of organic semiconductor
material is situated between two electrodes. Generally, at least one of these
electrodes is transparent.
OLEDs are used in television set screens, computer monitors, small, portable
system screens such as mobile phones and PDAs,watches, advertising,
information, and indication. OLEDs are also used in large-area light-emitting
elements for general illumination. Due to their low thermal conductivity, they
typically emit less light per area than inorganic LEDs.
An OLED display works without a backlight. Thus, it can display deep black levels
and can be thinner and lighter than liquid crystal displays. In low ambient light
conditions such as dark rooms, an OLED screen can achieve a higher contrast ratio
than an LCD—whether the LCD uses either cold cathode fluorescent lamps or the
more recently developed LED backlight.
There are two main families of OLEDs: those based on small molecules and those
employing polymers. Adding mobile ions to an OLED creates a Light-emitting
Electrochemical Cell or LEC, which has a slightly different mode of operation.
OLED displays can use either passive-matrix (PMOLED) or active-matrix
addressing schemes. Active-matrix OLEDs (AMOLED) require a thin-film
transistor backplane to switch each individual pixel on or off, but allow for higher
resolution and larger display sizes.
History
The first observations of electroluminescence in organic materials were in the early
1950s by A. Bernanose and co-workers at the Nancy-Université, France. They
applied high-voltage alternating current (AC) fields in air to materials such as acridine
orange, either deposited on or dissolved in cellulose or cellophane thin films. The
proposed mechanism was either direct excitation of the dye molecules or excitation
of electrons.[1][2][3][4]
In 1960, Martin Pope and co-workers at New York University developed ohmic darkinjecting electrode contacts to organic crystals.[5][6][7] They further described the
necessary energetic requirements (work functions) for hole and electron injecting
electrode contacts. These contacts are the basis of charge injection in all modern
OLED devices. Pope's group also first observed direct current (DC)
electroluminescence under vacuum on a pure single crystal of anthracene and on
anthracene crystals doped with tetracene in 1963[8] using a small area silver
electrode at 400V. The proposed mechanism was field-accelerated electron
excitation of molecular fluorescence.
Pope's group reported in 1965[9] that in the absence of an external electric field, the
electroluminescence in anthracene crystals is caused by the recombination of a
thermalized electron and hole, and that the conducting level of anthracene is higher
in energy than the exciton energy level. Also in 1965, W. Helfrich and W. G.
Schneider of the National Research Council in Canada produced double injection
recombination electroluminescence for the first time in an anthracene single crystal
using hole and electron injecting electrodes,[10] the forerunner of modern double
injection devices. In the same year, Dow Chemical researchers patented a method of
preparing electroluminescent cells using high voltage (500–1500 V) AC-driven
(100–3000 Hz) electrically-insulated one millimetre thin layers of a melted
phosphor consisting of ground anthracene powder, tetracene, and graphite
powder.[11] Their proposed mechanism involved electronic excitation at the
contacts between the graphite particles and the anthracene molecules.
Device performance was limited by the poor electrical conductivity of
contemporary organic materials. This was overcome by the discovery and
development of highly conductive polymers.[12] For more on the history of such
materials, see conductive polymers.
Electroluminescence from polymer films was first observed by Roger Partridge at
the National Physical Laboratory in the United Kingdom. The device consisted of a
film of poly(n-vinylcarbazole) up to 2.2 micrometres thick located between two
charge injecting electrodes. The results of the project were patented in 1975[13] and
published in 1983.[14][15][16][17]
The first diode device was reported at Eastman Kodak by Ching W. Tang and Steven
Van Slyke in 1987.[18] This device used a novel two-layer structure with separate
hole transporting and electron transporting layers such that recombination and light
emission occurred in the middle of the organic layer. This resulted in a reduction in
operating voltage and improvements in efficiency and led to the current era of
OLED research and device production.
Research into polymer electroluminescence culminated in 1990 with J. H.
Burroughes et al. at the Cavendish Laboratory in Cambridge reporting a high
efficiency green light-emitting polymer based device using 100 nm thick films of
poly(p-phenylene vinylene).[19]
[edit] Working principle
Schematic of a bilayer OLED: 1. Cathode (−), 2. Emissive Layer, 3. Emission of
radiation, 4. Conductive Layer, 5. Anode (+)
A typical OLED is composed of a layer of organic materials situated between two
electrodes, the anode and cathode, all deposited on a substrate. The organic molecules
are electrically conductive as a result of delocalization of pi electrons caused by
conjugation over all or part of the molecule. These materials have conductivity
levels ranging from insulators to conductors, and therefore are considered organic
semiconductors. The highest occupied and lowest unoccupied molecular orbitals
(HOMO and LUMO) of organic semiconductors are analogous to the valence and
conduction bands of inorganic semiconductors.
Originally, the most basic polymer OLEDs consisted of a single organic layer. One
example was the first light-emitting device synthesised by J. H. Burroughes et al.,
which involved a single layer of poly(p-phenylene vinylene). However multilayer
OLEDs can be fabricated with two or more layers in order to improve device
efficiency. As well as conductive properties, different materials may be chosen to
aid charge injection at electrodes by providing a more gradual electronic profile,[20]
or block a charge from reaching the opposite electrode and being wasted.[21] Many
modern OLEDs incorporate a simple bilayer structure, consisting of a conductive
layer and an emissive layer. More recent developments in OLED architecture
improves quantum efficiency (up to 19%) by using a graded heterojunction [22]. In
the graded heterojunction architecture, the composition of hole and electrontransport materials varies continuously within the emissive layer with a dopant
emitter. The graded heterojunction architecture combines the benefits of both
conventional architectures by improving charge injection while simultaneously
balancing charge transport within the emissive region.[23]
During operation, a voltage is applied across the OLED such that the anode is
positive with respect to the cathode. A current of electrons flows through the device
from cathode to anode, as electrons are injected into the LUMO of the organic
layer at the cathode and withdrawn from the HOMO at the anode. This latter
process may also be described as the injection of electron holes into the HOMO.
Electrostatic forces bring the electrons and the holes towards each other and they
recombine forming an exciton, a bound state of the electron and hole. This happens
closer to the emissive layer, because in organic semiconductors holes are generally
more mobile than electrons. The decay of this excited state results in a relaxation of
the energy levels of the electron, accompanied by emission of radiation whose
frequency is in the visible region. The frequency of this radiation depends on the band
gap of the material, in this case the difference in energy between the HOMO and
LUMO.
As electrons and holes are fermions with half integer spin, an exciton may either be
in a singlet state or a triplet state depending on how the spins of the electron and hole
have been combined. Statistically three triplet excitons will be formed for each
singlet exciton. Decay from triplet states (phosphorescence) is spin forbidden,
increasing the timescale of the transition and limiting the internal efficiency of
fluorescent devices. Phosphorescent organic light-emitting diodes make use of spin–orbit
interactions to facilitate intersystem crossing between singlet and triplet states, thus
obtaining emission from both singlet and triplet states and improving the internal
efficiency.
Indium tin oxide (ITO) is commonly used as the anode material. It is transparent to
visible light and has a high work function which promotes injection of holes into the
HOMO level of the organic layer. A typical conductive layer may consist of
PEDOT:PSS[24] as the HOMO level of this material generally lies between the
workfunction of ITO and the HOMO of other commonly used polymers, reducing
the energy barriers for hole injection. Metals such as barium and calcium are often
used for the cathode as they have low work functions which promote injection of
electrons into the LUMO of the organic layer.[25] Such metals are reactive, so
require a capping layer of aluminium to avoid degradation.
Single carrier devices are typically used to study the kinetics and charge
transport mechanisms of an organic material and can be useful when trying
to study energy transfer processes. As current through the device is
composed of only one type of charge carrier, either electrons or holes,
recombination does not occur and no light is emitted. For example, electron
only devices can be obtained by replacing ITO with a lower work function
metal which increases the energy barrier of hole injection. Similarly, hole
only devices can be made by using a cathode comprised solely of
aluminium, resulting in an energy barrier too large for efficient electron
injection.[26][27]
Section –c
1. Explain about the polymer light emitting diodes?
Polymer light-emitting diodes
poly(p-phenylene vinylene),
used in the first PLED.[19]
Polymer light-emitting diodes (PLED), also light-emitting polymers (LEP),
involve an electroluminescent conductive polymer that emits light when connected to an
external voltage. They are used as a thin film for full-spectrum colour displays.
Polymer OLEDs are quite efficient and require a relatively small amount of power
for the amount of light produced.
Vacuum deposition is not a suitable method for forming thin films of polymers.
However, polymers can be processed in solution, and spin coating is a common
method of depositing thin polymer films. This method is more suited to forming
large-area films than thermal evaporation. No vacuum is required, and the emissive
materials can also be applied on the substrate by a technique derived from
commercial inkjet printing.[33][34] However, as the application of subsequent layers
tends to dissolve those already present, formation of multilayer structures is
difficult with these methods. The metal cathode may still need to be deposited by
thermal evaporation in vacuum. An alternative method to vacuum deposition is to
deposit a Langmuir-Blodgett film.
Typical polymers used in PLED displays include derivatives of poly(p-phenylene
vinylene) and polyfluorene. Substitution of side chains onto the polymer backbone may
determine the colour of emitted light[35] or the stability and solubility of the
polymer for performance and ease of processing.[36]
While unsubstituted poly(p-phenylene vinylene) (PPV) is typically insoluble, a
number of PPVs and related poly(naphthalene vinylene)s (PNVs) that are soluble
in organic solvents or water have been prepared via ring opening metathesis
polymerization.[37][38][39]
[edit] Phosphorescent materials
Ir(mppy)3, a phosphorescent dopant which emits green light.[40]
Main article: Phosphorescent organic light-emitting diode
Phosphorescent organic light emitting diodes use the principle of
electrophosphorescence to convert electrical energy in an OLED into light in a
highly efficient manner,[41][42] with the internal quantum efficiencies of such devices
approaching 100%.[43]
Typically, a polymer such as poly(n-vinylcarbazole) is used as a host material to
which an organometallic complex is added as a dopant. Iridium complexes[42] such as
Ir(mppy)3[40] are currently the focus of research, although complexes based on other
heavy metals such as platinum[41] have also been used.
The heavy metal atom at the centre of these complexes exhibits strong spin-orbit
coupling, facilitating intersystem crossing between singlet and triplet states. By using
these phosphorescent materials, both singlet and triplet excitons will be able to
decay radiatively, hence improving the internal quantum efficiency of the device
compared to a standard PLED where only the singlet states will contribute to
emission of light.
Applications of OLEDs in solid state lighting require the achievement of high
brightness with good CIE coordinates (for white emission). The use of
macromolecular species like polyhedral oligomeric silsesquioxanes (POSS) in
conjunction with the use of phosphorescent species such as Ir for printed OLEDs
have exhibited brightnesses as high as 10,000 cd/m2.[44]
[edit] Device Architectures
[edit] Structure

Bottom or top emission: Bottom emission devices use a transparent or
semi-transparent bottom electrode to get the light through a transparent
substrate. Top emission devices[45][46] use a transparent or semi-transparent
top electrode emitting light directly. Top-emitting OLEDs are better suited
for active-matrix applications as they can be more easily integrated with a
non-transparent transistor backplane.

Transparent OLEDs use transparent or semi-transparent contacts on both
sides of the device to create displays that can be made to be both top and
bottom emitting (transparent). TOLEDs can greatly improve contrast,
making it much easier to view displays in bright sunlight.[47] This technology
can be used in Head-up displays, smart windows or augmented reality applications.
Novaled's[48] OLED panel presented in Finetech Japan 2010, boasts a
transparency of 60–70%.

Stacked OLEDs use a pixel architecture that stacks the red, green, and blue
subpixels on top of one another instead of next to one another, leading to
substantial increase in gamut and color depth, and greatly reducing pixel
gap. Currently, other display technologies have the RGB (and RGBW)
pixels mapped next to each other decreasing potential resolution.

Inverted OLED: In contrast to a conventional OLED, in which the anode is
placed on the substrate, an Inverted OLED uses a bottom cathode that can be
connected to the drain end of an n-channel TFT especially for the low cost
amorphous silicon TFT backplane useful in the manufacturing of AMOLED
displays.[49]
2. Explain about the patterning technologies?
Ans:
Patterning technologies
Patternable organic light-emitting devices use a light or heat activated electroactive
layer. A latent material (PEDOT-TMA) is included in this layer that, upon activation,
becomes highly efficient as a hole injection layer. Using this process, lightemitting devices with arbitrary patterns can be prepared.[50]
Colour patterning can be accomplished by means of laser, such as radiationinduced sublimation transfer (RIST).[51]
Organic vapour jet printing (OVJP) uses an inert carrier gas, such as argon or
nitrogen, to transport evaporated organic molecules (as in Organic Vapor Phase
Deposition). The gas is expelled through a micron sized nozzle or nozzle array
close to the substrate as it is being translated. This allows printing arbitrary
multilayer patterns without the use of solvents.
Conventional OLED displays are formed by vapor thermal evaporation (VTE) and
are patterned by shadow-mask. A mechanical mask has openings allowing the
vapor to pass only on the desired location.
[edit] Backplane technologies
For a high resolution display like a TV, a TFT backplane is necessary to drive the
pixels correctly. Currently, Low Temperature Polycrystalline silicon LTPS-TFT is
used for commercial AMOLED displays. LTPS-TFT has variation of the
performance in a display, so various compensation circuits have been reported.[45]
Due to the size limitation of the excimer laser used for LTPS, the AMOLED size was
limited. To cope with the hurdle related to the panel size, amorphoussilicon/microcrystalline-silicon backplanes have been reported with large display
prototype demonstrations.[52]
[edit] Advantages
Further information: Comparison CRT, LCD, Plasma
Demonstration of a 4.1" prototype flexible display from Sony
The different manufacturing process of OLEDs lends itself to several advantages
over flat panel displays made with LCD technology.

Lower cost in the future: OLEDs can be printed onto any suitable substrate
by an inkjet printer or even by screen printing,[53] theoretically making them
cheaper to produce than LCD or plasma displays. However, fabrication of the
OLED substrate is more costly than that of a TFT LCD, until mass
production methods lower cost through scalability. Roll-roll vapourdeposition methods for organic devices do allow mass production of
thousands of devices per minute for minimal cost, although this technique
also induces problems in that multi-layer devices can be challenging to make
due to registration issues, lining up the different printed layers to the required
degree of accuracy.

Light weight & flexible plastic substrates: OLED displays can be
fabricated on flexible plastic substrates leading to the possibility of flexible
organic light-emitting diodes being fabricated or other new applications such as
roll-up displays embedded in fabrics or clothing. As the substrate used can be
flexible such as PET,[54] the displays may be produced inexpensively.

Wider viewing angles & improved brightness: OLEDs can enable a
greater artificial contrast ratio (both dynamic range and static, measured in
purely dark conditions) and viewing angle compared to LCDs because
OLED pixels directly emit light. OLED pixel colours appear correct and
unshifted, even as the viewing angle approaches 90° from normal.

Better power efficiency: LCDs filter the light emitted from a backlight,
allowing a small fraction of light through so they cannot show true black,
while an inactive OLED element does not produce light or consume
power.[55]

Response time: OLEDs can also have a faster response time than standard
LCD screens. Whereas LCD displays are capable of between 2 and 8 ms
response time offering a frame rate of ~200 Hz, an OLED can theoretically
have less than 0.01 ms response time enabling 100,000 Hz refresh rates.
3. Explain about the colour balance issues?
Ans:

Current costs: OLED manufacture currently requires process steps that
make it extremely expensive. Specifically, it requires the use of LowTemperature Polysilicon backplanes; LTPS backplanes in turn require laser
annealing from an amorphous silicon start, so this part of the manufacturing
process for AMOLEDs starts with the process costs of standard LCD, and
then adds an expensive, time-consuming process that cannot currently be
used on large-area glass substrates.

Lifespan: The biggest technical problem for OLEDs was the limited
lifetime of the organic materials.[56] In particular, blue OLEDs historically
have had a lifetime of around 14,000 hours to half original brightness (five
years at 8 hours a day) when used for flat-panel displays. This is lower than
the typical lifetime of LCD, LED or PDP technology—each currently rated
for about 25,000 – 40,000 hours to half brightness, depending on
manufacturer and model.[57][58] However, some manufacturers' displays aim to
increase the lifespan of OLED displays, pushing their expected life past that
of LCD displays by improving light outcoupling, thus achieving the same
brightness at a lower drive current.[59][60] In 2007, experimental OLEDs were
created which can sustain 400 cd/m2 of luminance for over 198,000 hours for
green OLEDs and 62,000 hours for blue OLEDs.[61]

Color balance issues: Additionally, as the OLED material used to produce
blue light degrades significantly more rapidly than the materials that produce
other colors, blue light output will decrease relative to the other colors of
light. This differential color output change will change the color balance of
the display and is much more noticeable than a decrease in overall
luminance.[62] This can be partially avoided by adjusting colour balance but
this may require advanced control circuits and interaction with the user,
which is unacceptable for some users. In order to delay the problem,
manufacturers bias the colour balance towards blue so that the display
initially has an artificially blue tint, leading to complaints of artificiallooking, over-saturated colors. More commonly, though, manufacturers
optimize the size of the R, G and B subpixels to reduce the current density
through the subpixel in order to equalize lifetime at full luminance. For
example, a blue subpixel may be 100% larger than the green subpixel. The
red subpixel may be 10% smaller than the green.

Efficiency of blue OLEDs: Improvements to the efficiency and lifetime of
blue OLEDs is vital to the success of OLEDs as replacements for LCD
technology. Considerable research has been invested in developing blue
OLEDs with high external quantum efficiency as well as a deeper blue
color.[63][64] External quantum efficiency values of 20% and 19% have been
reported for red (625 nm) and green (530 nm) diodes, respectively.[65][66]
However, blue diodes (430 nm) have only been able to achieve maximum
external quantum efficiencies in the range of 4% to 6%.[67]

Water damage: Water can damage the organic materials of the displays.
Therefore, improved sealing processes are important for practical
manufacturing. Water damage may especially limit the longevity of more
flexible displays.[68]

Outdoor performance: As an emissive display technology, OLEDs rely
completely upon converting electricity to light, unlike most LCDs which are
to some extent reflective; e-ink leads the way in efficiency with ~ 33%
ambient light reflectivity, enabling the display to be used without any
internal light source. The metallic cathode in an OLED acts as a mirror, with
reflectance approaching 80%, leading to poor readability in bright ambient
light such as outdoors. However, with the proper application of a circular
polarizer and anti-reflective coatings, the diffuse reflectance can be reduced
to less than 0.1%. With 10,000 fc incident illumination (typical test condition
for simulating outdoor illumination), that yields an approximate photopic
contrast of 5:1.

Power consumption: While an OLED will consume around 40% of the
power of an LCD displaying an image which is primarily black, for the
majority of images it will consume 60–80% of the power of an LCD –
however it can use over three times as much power to display an image with
a white background[69] such as a document or website. This can lead to
reduced real-world battery life in mobile devices.

Screen burn-in: Unlike displays with a common light source, the brightness
of each OLED pixel fades depending on the content displayed. The varied
lifespan of the organic dyes can cause a discrepancy between red, green, and
blue intensity. This leads to image persistence, also known as burn-in.[70]

UV sensitivity: OLED displays can be damaged by prolonged exposure to
UV light. The most pronounced example of this can be seen with a near UV
laser (such as a Bluray pointer) and can damage the display almost instantly
with more than 20 mW leading to dim or dead spots where the beam is
focused. This is usually avoided by installing a UV blocking filter over the
panel and this can easily be seen as a clear plastic layer on the glass.
Removal of this filter can lead to severe damage and an unusable display
after only a few months of room light exposure.
UNIT-II
Section-A
1.
Nanometer scale is --------a) 1/1000000000
2. Bottom up is built --------------c) Atom by atom
3. What is a fabrication method?
Ans: As device dimensions in ICs continue to shrink, low dielectric constant
(low-k) materials are needed as interlevel dielectrics (ILD) to increasing RCdelay.
4. Give some advantages of ALD methods?

Ans: All advantages of traditional ALD methods; conforms to surface with
uniform thickness that is easily controlled
Section –B
1.
Give some advantages of Ald methods?
Advantages/Applications
Advantages include:

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
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All advantages of traditional ALD methods; conforms to surface with
uniform thickness that is easily controlled
Creates ultra-thin membranes only a few nanometers thick for increase
permeability
Method can be used to create porous (with controlled pore size) or nonporous membranes
Method can be used to create hybrid membranes comprising robust
inorganic matrix and functional organic groups
Allows for conformal capping of only the top surface with no internal
deposition
2. Give a brief note on molecular electronics?
Molecular electronics (sometimes called moletronics) involves the study and
application of molecular building blocks for the fabrication of electronic
components. This includes both bulk applications of conductive polymers, and
single-molecule electronic components for nanotechnology.
Molecular materials for electronics
Main articles: Conductive polymer and Organic electronics
Chemical structures of some conductive polymers. From top left clockwise:
polyacetylene; polyphenylene vinylene; polypyrrole (X = NH) and polythiophene
(X = S); and polyaniline (X = NH/N) and polyphenylene sulfide (X = S).
Voltage-controlled switch, a molecular electronic device from 1974. From
Smithsonian Chip collection.[5]
3. Explain about the molecular electronics methods?
Molecular materials for electronics is a term used to refer to bulk applications of
conductive polymers.[2] Conductive polymers or, more precisely, intrinsically
conducting polymers (ICPs) are organic polymers that conduct electricity in their
bulk state.[6] Such compounds may have metallic conductivity or can be
semiconductors. The biggest advantage of conductive polymers is their
processability, mainly by dispersion. Conductive polymers are not plastics, i.e.,
they are not thermoformable, but they are organic polymers, like (insulating)
polymers. They can offer high electrical conductivity but do not show mechanical
properties as other commercially used polymers do. The electrical properties can
be fine-tuned using the methods of organic synthesis [7] and by advanced dispersion
techniques.[8]
Section – C
1. Explain about the Linear backbone polymer blacks?
The linear-backbone "polymer blacks" (polyacetylene, polypyrrole, and
polyaniline) and their copolymers are the main class of conductive polymers.
Historically, these are known as melanins. PPV and its soluble derivatives have
similarly emerged as the prototypical electroluminescent semiconducting
polymers. Today, poly(3-alkylthiophenes) are the archetypical materials for solar
cells and transistors.[7]
Conducting polymers have backbones of contiguous sp2 hybridized carbon centers.
One valence electron on each center resides in a pz orbital, which is orthogonal to
the other three sigma-bonds. The electrons in these delocalized orbitals have high
mobility when the material is "doped" by oxidation, which removes some of these
delocalized electrons. Thus the conjugated p-orbitals form a one-dimensional
electronic band, and the electrons within this band become mobile when it is
partially emptied. Despite intensive research, the relationship between
morphology, chain structure and conductivity is poorly understood yet.[9]
2. Explain about the disadvantages of processing of molecular
electronics?
Due to their poor processability, conductive polymers enjoy few large-scale
applications . They have some promise in antistatic materials[7] and they have been
incorporated into commercial displays and batteries, but there have had limitations
due to the manufacturing costs, material inconsistencies, toxicity, poor solubility in
solvents, and inability to directly melt process. Nevertheless, conducting polymers
are rapidly gaining attraction in new applications with increasingly processable
materials with better electrical and physical properties and lower costs. With the
availability of stable and reproducible dispersions, PEDOT and polyaniline have
gained some large scale applications. While PEDOT (poly(3,4ethylenedioxythiophene)) is mainly used in antistatic applications and as a
transparent conductive layer in form of PEDOT:PSS dispersions (PSS=polystyrene
sulfonic acid), polyaniline is widely used for printed circuit board manufacturing –
in the final finish, for protecting copper from corrosion and preventing its
solderability.[8] The new nanostructured forms of conducting polymers particularly,
provide fresh air to this field with their higher surface area and better
dispersability.
Unit – II
1. What are the types of bio molecules?
A diverse range of biomolecules exist, including:

Small molecules:
o Lipids, phospholipids, glycolipids, sterols, glycerolipids
o Vitamins
o Hormones, neurotransmitters
o Metabolites

Monomers, oligomers
and polymers:
2. Give definition for quantum dot cellular automata?
Ans: Quantum Dot Cellular Automata (sometimes referred to simply as
quantum cellular automata, or QCA) are proposed models of quantum
computation, which have been devised in analogy to conventional models of
cellular automata introduced by von Neumann.
3. Give definition for cellular automata?
A cellular automaton (CA) is a finite state machine consisting of a uniform
(finite or infinite) grid of cells. Each one of these cells can only be in one of
a finite number of states at a discrete time.
Section – B
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1. Give explanation for quantum dots?
Quantum-dot cells
Origin
Cellular automata are commonly implemented as software programs.
However, in 1993, Lent et al. proposed a physical implementation of an
automaton using quantum-dot cells. The automaton quickly gained
popularity and it was first fabricated in 1997. Lent combined the discrete
nature of both cellular automata and quantum mechanics, to create nanoscale devices capable of performing computation at very high switching
speeds and consuming extremely small amounts of electrical power.
2. Explain about Modern cells?
Modern cells
Today, standard solid state QCA cell design considers the distance between
quantum dots to be about 20 nm, and a distance between cells of about 60 nm. Just
like any CA, Quantum (-dot) Cellular Automata are based on the simple interaction
rules between cells placed on a grid. A QCA cell is constructed from four quantum
dots arranged in a square pattern. These quantum dots are sites electrons can
occupy by tunneling to them.
Theory behind cell
Figure 2 - A simplified diagram of a four-dot QCA cell.
Figure 3 - The two possible states of a four-dot QCA cell.
3. Describe about Grid arrangements?
 Grid arrangements
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Figure 4 - A wire of quantum-dot cells.
Grid arrangements of quantum-dot cells behave in a ways that allow for
computation. The simplest practical cell arrangement is given by placing
quantum-dot cells in series, to the side of each other. Figure 4 shows such an
arrangement of four quantum-dot cells. The bounding boxes in the figure do
not represent physical implementation, but are shown as means to identify
individual cells.
If the polarization of any of the cells in the arrangement shown in figure 4
were to be controllable (driver cell), the rest of the cells would immediately
synchronize to its polarization due to Coulombic interactions between them;
much like an instantaneous chain reaction. In this way, a wire of quantumdot cells is realizable. Although the ability to realize conductive wires does
not alone provide the means to perform computation, a complete set of
universal logic gates can be constructed using the same principle.
Section – C
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1. Explain about logic gates?
Logic gates
Majority gate
Figure 5 - QCA Majority Gate
The fundamental logic gate in QCA is the majority gate. Figure 5 shows a
majority gate with three inputs and one output. Assuming inputs A and B
exist in a “binary 0” state and input C exists in a “binary 1” state, the output
will exist in a “binary 0” state as the conjunct electrical field effect of inputs
A and B is greater than the one of input C. In other words, the majority gate
drives the output cell’s state to be equal to that of the majority of the inputs.
Now, if the polarization of input C were to be fixed to say, binary 0, the only
way the output’s state becomes binary 1, is if input A and B are also 1.
Otherwise, the output cell will exhibit a binary 0 state.
Other gates
This conditional behavior is exactly the same as that of an AND gate.
Similarly, an OR gate can be constructed using a majority gate with fixed
polarization equivalent to binary 1 at one of its inputs. In this way, if any or
both of the remaining inputs exist in the binary 1 state, the output will be
also in a binary 1 state. Although not certainly based on a majority gate
structure, a NOT gate is just as easily realizable. The key principle behind its
functionality lies on the fact that placing a cell at 45 degrees with respect of
a pair of cells of same polarity, the polarization of the cell will become
opposite to that of its driving pair. Figure 6 shows a standard implementation
of a NOT logic gate.


Figure 6 - Standard Implementation of a NOT gate.
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State transition
2. Explain about four stages?
Four stages
A QCA clock induces four stages in the tunneling barriers of the cells above
it. In the first stage, the tunneling barriers start to rise. The second stage is
reached when the tunneling barriers are high enough to prevent electrons
from tunneling. The third stage occurs when the high barrier starts to lower.
And finally, in the fourth stage, the tunneling barriers allow electrons to
freely tunnel again. In simple words, when the clock signal is high, electrons
are free to tunnel. When the clock signal is low, the cell becomes latched.
Figure 7 shows a clock signal with its four stages and the effects on a cell at
each clock stage. A typical QCA design requires four clocks, each of which
is cyclically 90 degrees out of phase with the prior clock. If a horizontal wire
consisted of say, 8 cells and each consecutive pair, starting from the left
were to be connected to each consecutive clock, data would naturally flow
from left to right. The first pair of cells will stay latched until the second pair
of cells gets latched and so forth. In this way, data flow direction is
controllable through clock zones.
Wire-crossing
Figure 8 - Basic Wire-Crossing Technique.
Wire-crossing in QCA cells is done by using a "plus-sign" pattern, as shown
in figure 8. The distances between a plus-sign pattern and a square pattern
are exactly the same, allowing for the same Coulombic interactions between
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electrons in a cell. Thus, when a wire of square cells crosses a wire of plussign cells, they do not interact, thus the signals on each wire are preserved.
Fabrication problem
Although this technique is rather simple, it represents an enormous
fabrication problem. A new kind of cell pattern potentially introduces as
much as twice the amount of fabrication cost and infrastructure; the number
of possible quantum dot locations on an interstitial grid is doubled and an
overall increase in geometric design complexity is inevitable. Yet another
problem this technique presents is that the additional space between cells of
the same orientation decreases the energy barriers between a cells ground
state and a cell’s first excited state. This degrades the performance of the
device in terms of maximum operating temperature, resistance to entropy
and switching speed.
Crossbar Network
A different wire-crossing technique, which makes fabrication of QCA
devices more practical, was presented by Christopher Graunke, David
Wheeler, Douglas Tougaw, and Jeffrey D. Will, in their paper
“Implementation of a crossbar network using quantum-dot cellular
automata”. The paper not only presents a new method of implementing wirecrossings, but it also gives a new perspective on QCA clocking.
Their wire-crossing technique introduces the concept of implementing QCA
devices capable of performing computation as a function of synchronization.
This implies the ability to modify the device’s function through the clocking
system without making any physical changes to the device. Thus, the
fabrication problem stated earlier is fully addressed by: a) using only one
type of quantum-dot pattern and, b) by the ability to make a universal QCA
building block of adequate complexity, which function is determined only
by its timing mechanism (i.e. its clocks).
Quasi-adiabatic switching, however, requires that the tunneling barriers of a
cell be switched relatively slowly compared to the intrinsic switching speed
of a QCA. This prevents ringing and metastable states observed when cells
are switched abruptly. Therefore, the switching speed of a QCA is limited
not by the time it takes for a cell to change polarization, but by the
appropriate quasi-adiabatic switching time of the clocks being used.
4. Explain about parallel to serial?
Parallel to Serial
When designing a device capable of computing, it is often necessary to convert
parallel data lines into a serial data stream. This conversion allows different
pieces of data to be reduced to a time-dependent series of values on a single
wire. Figure 9 shows such a parallel-to-serial conversion QCA device. The
numbers on the shaded areas represent different clocking zones at consecutive
90-degree phases. Notice how all the inputs are on the same clocking zone. If
parallel data were to be driven at the inputs A, B, C and D, and then driven no
more for at least the remaining 15 serial transmission phases, the output X
would present the values of D, C, B and A –in that order, at phases three, seven,
eleven and fifteen. If a new clocking region were to be added at the output, it
could be clocked to latch a value corresponding to any of the inputs by correctly
selecting an appropriate state-locking period.
The new latching clock region would be completely independent from the other
four clocking zones illustrated in figure 9. For instance, if the value of interest
to the new latching region were to be the value that D presents every 16th
phase, the clocking mechanism of the new region would have to be configured
to latch a value in the 4th phase and every 16th phase from then on, thus,
ignoring all inputs but D.
Figure 9 - Parallel to serial conversion.
Additional serial lines
Adding a second serial line to the device, and adding another latching region
would allow for the latching of two input values at the two different outputs. To
perform computation, a gate that takes as inputs both serial lines at their
respective outputs is added. The gate is placed over a new latching region
configured to process data only when both latching regions at the end of the
serial lines hold the values of interest at the same instant. Figure 10 shows such
an arrangement. If correctly configured, latching regions 5 and 6 will each hold
input values of interest to latching region 7. At this instant, latching region 7
will let the values latched on regions 5 and 6 through the AND gate, thus the
output could be configured to be the AND result of any two inputs (i.e. R and
Q) by merely configuring the latching regions 5, 6 and 7.
This represents the flexibility to implement 16 functions, leaving the physical
design untouched. Additional serial lines and parallel inputs would obviously
increase the number of realizable functions. However, a significant drawback of
such devices is that, as the number of realizable functions increases, an
increasing number of clocking regions is required. As a consequence, a device
exploiting this method of function implementation may perform significantly
slower than its traditional counterpart.
Unit – III
Section – A
1. What is Fabrication?
Ans: Fabrication
Generally speaking, there are four different classes of QCA implementations:
Metal-Island, Semiconductor, Molecular, and Magnetic.
2. What is metal island?
Ans: The Metal-Island implementation was the first fabrication technology
created to demonstrate the concept of QCA.
3. What is molecular?
Ans: A proposed but not yet implemented method is method consists of building
QCA devices out of single molecules. The main advantages of such
implementations include: highly symmetric QCA.
Section -B
1. Explain about the metal islands?
Fabrication
Generally speaking, there are four different classes of QCA implementations:
Metal-Island, Semiconductor, Molecular, and Magnetic.
Metal-Island
The Metal-Island implementation was the first fabrication technology created to
demonstrate the concept of QCA. It was not originally intended to compete with
current technology in the sense of speed and practicality, as its structural
properties are not suitable for scalable designs. The method consists of building
quantum dots using aluminum islands. Earlier experiments were implemented
with metal islands as big as 1 micrometer in dimension. Because of the
relatively large-sized islands, Metal-Island devices had to be kept at extremely
low temperatures for quantum effects (electron switching) to be observable.
Semiconductor
Semiconductor (or solid state) QCA implementations could potentially be used
to implement QCA devices with the same highly advanced semiconductor
fabrication processes used to implement CMOS devices. Cell polarization is
encoded as charge position, and quantum-dot interactions rely on electrostatic
coupling. However, current semiconductor processes have not yet reached a
point where mass production of devices with such small features (~20
nanometers) is possible. Serial lithographic methods, however, make QCA solid
state implementation achievable, but not necessarily practical. Serial
lithography is slow, expensive and unsuitable for mass-production of solid-state
QCA devices. Today, most QCA prototyping experiments are done using this
implementation technology.
[edit] Molecular
A proposed but not yet implemented method is method consists of building
QCA devices out of single molecules. The main advantages of such
implementations include: highly symmetric QCA cell structure, very high
switching speeds, extremely high device density, operation at room
temperature, and even the possibility of mass-producing devices by means of
self-assembly. A number of technical challenges, including choice of
molecules, the design of proper interfacing mechanisms, and clocking
technology remain to be solved before this method can be implemented.
Magnetic
Magnetic QCA –commonly referred to as MQCA (or QCA: M), is based on the
interaction between magnetic nanoparticles. The magnetization vector of these
nanoparticles is analogous to the polarization vector in all other
implementations. In MQCA, the term “Quantum” refers to the quantummechanical nature of magnetic exchange interactions and not to the electrontunneling effects. Devices constructed this way could operate at room
temperature.
Improvement over CMOS
Complementary metal-oxide semiconductor (CMOS) technology has been the
industry standard for implementing Very Large Scale Integrated (VLSI) devices
for the last two decades, mainly due to the consequences of miniaturization of
such devices (i.e. increasing switching speeds, increasing complexity and
decreasing power consumption). Quantum Cellular Automata (QCA) is only
one of the many alternative technologies proposed as a replacement solution to
the fundamental limits CMOS technology will impose in the years to come.
Although QCA solves most of the limitations of CMOS technology, it also
brings its own. Research suggests that intrinsic switching time of a QCA cell is
at best in the order of terahertz. However, the actual speed may be much lower,
in the order of megahertz for solid state QCA and gigahertz for molecular QCA,
due to the proper quasi-adiabatic clock switching frequency setting.
Additionally, solid-state QCA devices cannot operate at room temperature. The
only alternative to this temperature limitation is the recently proposed
“Molecular QCA” which theoretically has an inter-dot distance of 2 nm and an
inter-cell distance of 6 nm. Molecular QCA is also considered to be the only
feasible implementation method for mass production of QCA devices.
2. Give brief description about the steps for producing quantum dots embedded
matrix?
STEPS FOR PRODUCING QUANTUM DOTS EMBEDED IN MATRIX
A method for producing quantum dots embedded in a matrix on a substrate
includes the steps of:
 Depositing a precursor on the substrate, the precursor including at least one
first metal or a metal compound
 Contacting the deposited precursor and uncovered areas of the substrate
with a gas-phase reagent including at least one second metal and/or a
chalcogen
 Initiating a chemical reaction between the precursor and the reagent by
raising a temperature thereof simultaneously with or subsequent to the
contacting so that the matrix consists exclusively of elements of the reagent.
DESCRIPTION:
The present invention relates to a method for producing quantum dots embedded in
a matrix on a substrate, and to quantum dots embedded in a matrix, produced using
the method.
In objects having a size of only a few nanometers, which are known as quantum
dots, nanodots, or nanoislands, the freedom of motion of the electrons is restricted
in all three spatial directions (“zero-dimensional system”). Thus, the linear
dimension in all three directions is less than the de Broglie wavelength of the
charge carriers. Such quantum dots have a greatly modified electronic structure
from the corresponding bulk semiconductor material and, in particular, the density
of states becomes more like that for molecules. Quantum dots have a discrete
energy spectrum and, in some aspects, behave similarly to atoms, which is due to
the quantum nature of the electronic structure. However, unlike with atoms, it is
possible to influence the size and electronic structure. Due to the small electrical
capacitance of the quantum dots, the addition of a further electron to the electrons
already present in the quantum dot (“single-electron tunneling”) requires a certain
amount of energy, ranging from several tens of meV to several hundreds of meV
(“Coulomb blockade”). This effect allows for controlled quantization of the current
flow through the quantum dot. The size and shape of the quantum dots are
dependent on the production method and the elements used. At present, quantum
dots are mainly used in nanooptics and nanoelectronics, for example, in photo
detectors and semiconductor lasers, and also in solar cells. In particular, the
formation of binary, ternary, or multinary compound semiconductor quantum
structures in a semiconductor matrix is becoming increasingly important in the
manufacture of efficient solar cells.
3. Give description about background art?
BACKGROUND ART
The most frequently used method for producing quantum dots is StranskiKrastanov epitaxial growth, which is based on a strained crystal lattice of the
semiconductor growing on the substrate. As a result of this lattice strain, the
growing layer does not grow uniformly. Instead, small nanometer-sized islands
are formed, which constitute the quantum dots. Using this method, the size and
density of the quantum dots can be controlled to a certain degree, while control
of the arrangement and position is possible only to a very limited extent. Other
methods for producing quantum dots use the methodology of scanning probe
microscopy. These methods allow excellent control over the size and position
of the quantum dots. However, they are sequential methods, in which each
quantum dot must be produced individually. Therefore, such methods can be
used only to a limited extent for devices having a large number of quantum
dots.
The in-situ creation of quantum dots in a matrix is known, for example, from
U.S. 2004/0092125 A1. There, a dielectric precursor is coated onto a thin metal
layer on a substrate and gradually heated, whereby the metal layer and the
precursor are gradually stacked on each other, so that quantum dots are formed
from the precursor in the metal layer. U.S. Pat. No. 6,242,326 B1 discloses a
method for producing quantum dots, in which GaAs quantum dots are formed
from Ga droplets and coated with a passivation layer which is formed of a
buffer layer and a barrier layer. A similar method is described in KR
1020010054538 A. Japanese document JP 2006080293 A discloses a method of
self-organized formation of InAs quantum dots on a GaAs layer, the quantum
dots being embedded in a GaAs matrix. Further, it is known from U.S. Pat. No.
5,229,320 to deposit quantum dots through a porous GaAs membrane on an
AlGaAs substrate, and to subsequently grow a matrix of AIGaAs for
embedding purposes. A method for manufacturing a polymer containing
dispersed nanoparticles is known from DE 601 08 913 T2. In that approach,
first a polymer precursor is deposited, on which nanoparticles are subsequently
distributed as quantum dots. The polymer is cross-linked by application of heat,
thereby embedding the quantum dots into the matrix.
The closest prior art to the present invention is represented by DE 694 11 945
T2, which discloses a method in which, first, a soluble precursor of a metal or a
metal compound is dissolved in a vaporizable solvent. Then, the dissolved
precursor is sprayed onto a substrate as finely distributed, nanometer-sized
droplets. Thus, in this known method, the structure and distribution of the
quantum dots are no longer dependent on the material and the substrate. The
relatively severe limitations of the epitaxial growth method do not occur. The
deposited nanostructured precursor is then brought into contact with a
chalcogen-containing reagent, so that a chemical reaction occurs at room
temperature to form quantum dots of a desired material composition comprised
of the precursor and the reagent. The solvent may be vaporized before, during
or after the chemical reaction. A polymer is additionally added to the solvent,
and serves primarily to coat the dissolved precursor in the solvent and to
prevent the nanoparticles from agglomerating during spray deposition. In
addition, the polymer is deposited on the substrate, forming a matrix in which
the quantum dots are embedded. A polymer matrix of this kind which is made
of a transparent plastic has a certain refractive index for optical applications and
may be stacked with other polymer layers of different refractive indices. The
polymer is not subjected to a chemical reaction; it does not interact with the
reagent. Materials other than a polymer cannot be used in the known method to
form the matrix, because there matrix formation is merely a secondary effect,
the matrix being formed on the substrate as a simple precipitate. The main
purpose of the polymer used is to prevent the dissolved precursor particles from
agglomerating, and therefore, must have corresponding materials and
properties.
Document U.S. 2003/0129311 A1 describes a method which is similar but in
which first a porous template is formed. The pores of the polymer are
subsequently filled with a precursor solution from which the quantum dots are
then formed.
Secton – C
1. Explain about the object of the invention?
OBJECT OF THE INVENTION
Starting from the aforementioned prior art, it is an object of the present invention
to provide a method for producing quantum dots embedded in a matrix, which will
allow any polymer-free matrices to be produced in a controlled manner without
any impairing limitations to the method. The matrix composition should be
selectable independently of the quantum dot properties, but should co-determine
the material composition of the quantum dots, resulting in concordant
compositions of the quantum dots and the matrix. Further, the production of the
quantum dots should remain independent of the severe limitations of the epitaxial
growth method. In addition, the method should be simple, inexpensive and rugged,
and should preferably enable the manufacture of compound semiconductor-based
products which may be used, in particular, in solar cell technology.
The approach for achieving these objectives will become apparent from the method
claim. Advantageous embodiments of the invention are given in the dependent
claims and will be described in more detail below in connection with the invention.
The present invention provides a method for producing quantum dots embedded in
a matrix on a substrate. In this method, first, quantum dots are deposited on the
substrate from a precursor of at least one first metal or a metal compound. In this
process, the highly structured or nanostructured deposition determines the
geometry and density of the quantum dots. In this manner and through the
selection of the precursor, the electronic properties of the quantum dots are
determined independently of the substrate, which allows for the use of a variety of
different substrates, such as simple glass, metal-coated glass, monocrystalline
wafers, polycrystalline layers, films. There is no coupling, for example, to strained
lattice states in a crystalline substrate. The use of a precursor in the present
invention eliminates the link between the final structure size and the selforganization of the quantum dots during the process. There are various known
methods for depositing quantum dots, which will be mentioned further below.
After deposition of the quantum dots, the quantum dots and the substrate regions
which are not covered by the dots are brought into contact with a gas-phase
reagent. This reagent is comprised of at least one second metal and/or a chalcogen
and contains all elements of the matrix to be formed, while the matrix is composed
exclusively of elements of the reagent. The chemical reaction between the
precursor and the reagent is brought about by raising the temperature
simultaneously with or subsequent to said contact (annealing step). The contact
between the reagent and the deposited quantum dots causes the precursor to
undergo a chemical reaction leading to the final material composition of the
quantum dots.
In regions where the reagent contacts the exposed substrate, a matrix is formed
from the elements of the reagent in a corresponding stoichiometric ratio. The
matrix also deposits above the converted quantum dots, so that the quantum dots
are completely embedded in the in-situ formed matrix after the reaction with the
reagent is completed.
Thus, the method of the present invention enables quantum dots to be produced
using elemental metals or metal compounds as a precursor in a gas-phase reaction
with multinary or elemental chalcogens. In the method of the present invention, the
gas-phase reaction step serves simultaneously, i.e., in situ in one and the same
method step, to grow the matrix in the preferred form from a binary, ternary or
multinary compound semiconductor in which the quantum dots are embedded, also
in the form of a compound semiconductor (having one or more metal components
more than the matrix). The gas-phase reaction step may be carried out such that the
precursor is reacted directly to form the final product, for example, by using
increased process temperature, or such that this reaction is performed in a
subsequent, separate annealing step. The structural, electronic and optical
properties of the final product are determined by the dimensions of the precursor
structure, the precursor elements used, and the elements used in the gas-phase
reaction. There are various methods available for producing the precursor and for
the gas-phase reaction.
The deposition of metallic precursors in the form of islands of desired dimensions,
which are then converted preferably into semiconductor structures in the
subsequent gas phase-based processing step, can be done using a variety of
methods, such as evaporation, sputtering, lithographic processes, Focused Ion
Beam, scanning probe microscopy-based methods, electrochemical deposition
techniques, and the ILGAR and SILAR wet-chemical methods.
German document DE 694 11 945 T2, which represents the art closest to the
present invention, describes a method for depositing a dissolved precursor. This
method can also be used in the present invention, provided that the precursor used
is soluble. In a refinement, said method advantageously uses a liquid-phase
precursor which is dissolved in a vaporizable solvent. The precursor/solvent
mixture is then sprayed onto the substrate in the form of droplets using special
nozzles, possibly while applying an electric field. In this process, care must be
taken to prevent agglomeration of the precursor. In this invention, it is not possible
to add polymers as a separating agent, because they would also be incorporated
into the matrix, leading to unwanted effects. The solvent may be vaporized before,
during or after the initiation of the chemical reaction between the precursor and the
reagent, so that the final product of the quantum dots is obtained by a wet-chemical
or a dry-chemical reaction.
In addition to depositing the precursor in dissolved form, a solid-phase precursor
may also be used to advantage. This precursor is then deposited on the substrate in
highly structured to nanostructured form using special yet simple methods. For
example, a solid-phase precursor may be deposited on the substrate in the form of
nanoparticles simply by sprinkling them thereon. The nanoparticles may also be
selectively deposited using, for example, micromanipulators.
A similar variety of processes are available for the gas-phase reaction of the
desired elements in the reagent with the metallic precursors. The method of the
present invention preferably uses semiconducting elements. Depending on the
desired final product, which generally contains at least one metal and/or a
chalcogen, there are different combinations of elemental, binary, ternary or
multinary metallic precursors available which can be reacted with corresponding
elemental, binary, ternary or multinary chalcogenides in the reagent. Preferably,
therefore, binary, ternary or multinary compound semiconductors are formed for
the quantum structure and the matrix. Elements from groups I through VI are
preferably used for this purpose.
While the structural, electronic and optical properties of the quantum structures,
preferably compound semiconductor structures, produced are mainly dependent
on the elements used in the precursors and the gas-phase reaction, additional,
typical properties of quantum dots are to be
2. Give example of fabrication process?
Example (I)
Ternary CuGaSe 2 Quantum Dots of Elemental Cu in a Ga 2 Se 3 Matrix
Initially, metallic dots of Cu as the precursor PC having lateraled and vertical
dimensions in the nanometer range are deposited on a substrate SU of glass
(non-conductive) or of molybdenum-coated glass (conductive). The deposition
of precursor PC is done by evaporation using a suitable mask for
nanopatterning the metal being deposited. However, the deposition can also be
done using physical vapor deposition, molecular beam epitaxy, chemical
transport methods (chemical vapor deposition, metal-organic chemical vapor
deposition, etc.), or chemical or electrochemical methods (SILAR, ILGAR,
electrode position, chemical bath deposition, etc.). Substrate SU, together with
metal precursors PC, is then subjected to an annealing step, which allows
reaction with gaseous reagent RG which, in this case, contains Ga and Se.
Depending on the temperature and other process parameters, such as time and
pressure, the gaseous components react with the Cu, forming the ternary
compound CuGaSe 2 in the form of nanometer-sized quantum dots. The process
parameters are selected such that these ternary quantum dots are formed in a
matrix of a binary compound (Ga 2 Se 3 ), which is deposited simultaneously
with the reaction that forms the ternary quantum dots (see the figure). In the
process, matrix MA initially deposits on substrate SU, and then also on the
converted quantum dots QD, so that quantum dots QD are finally embedded in
matrix MA. The process kinetics determining the size and shape of the resulting
Nano-sized structures can be controlled by the process parameters, which
include, inter alia, the process temperature, the saturation conditions in the gas
phase at the corresponding substrate temperature, and the duration of the
process.
A simple method for the fabrication of metal nanoparticles is introduced.
Heating metal–organic crystals in vacuum results in the formation of welldefined metal particles embedded in a carbon matrix. The method is
demonstrated for iron phthalocyanine. At 500 °C homogeneously distributed
iron nanoparticles with a reasonably narrow size distribution form by nucleation
and ripening. After this initial phase the formation kinetics changes drastically.
The particles move in the matrix to incorporate material. The 'gluttony' phase
shows astonishing similarities with the search for nutrition of living microorganisms. Particle formation, ripening and gluttony are followed in situ by
transmission electron microscopy.
3. Explain about transconductance?
Transconductance
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Transconductance, also known as mutual conductance[citation needed], is a property
of certain electronic components. Conductance is the reciprocal of resistance;
transconductance, meanwhile, is the ratio of the current change at the output port to
the voltage change at the input port. It is written as gm. For direct current,
transconductance is defined as follows:
For small signal alternating current, the definition is simpler:
Contents
[hide]
Transconductance amplifiers
A transconductance amplifier (gm amplifier) puts out a current proportional to
its input voltage. In network analysis, the transconductance amplifier is defined as a
voltage controlled current source (VCCS) . It is common to see these amplifiers
installed in a cascode configuration, which improves the frequency response.
Unit – IV
1. What is fullerence?
Ans:
A fullerene is any molecule composed entirely of carbon, in the form of a hollow
sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and they
resemble the balls used in association football. Cylindrical ones are called carbon
nanotubes or buckytubes. Fullerenes are similar in structure to graphite, which is
composed of stacked graphene sheets of linked hexagonal rings; but they may also
contain pentagonal (or sometimes heptagonal) rings.[1]
2. Give some types of fullerences?
Ans: Types of fullerene
Since the discovery of fullerenes in 1985, structural variations on fullerenes have
evolved well beyond the individual clusters themselves. Examples include:[16]


buckyball clusters: smallest member is C20 (unsaturated version of
dodecahedrane) and the most common is C60;
nanotubes: hollow tubes of very small dimensions, having single or
multiple walls; potential applications in electronics industry;
3. Give 3 types of fullerences?
Ans:




megatubes: larger in diameter than nanotubes and prepared with walls of
different thickness; potentially used for the transport of a variety of
molecules of different sizes;[17]
polymers: chain, two-dimensional and three-dimensional polymers are
formed under high pressure high temperature conditions
nano"onions": spherical particles based on multiple carbon layers
surrounding a buckyball core; proposed for lubricants;[18]
linked "ball-and-chain" dimers: two buckyballs linked by a carbon
chain;[19]
Section- B
1. Explain about the fullerence in detail?
Ans:
A fullerene is any molecule composed entirely of carbon, in the form of a hollow
sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and they
resemble the balls used in association football. Cylindrical ones are called carbon
nanotubes or buckytubes. Fullerenes are similar in structure to graphite, which is
composed of stacked graphene sheets of linked hexagonal rings; but they may also
contain pentagonal (or sometimes heptagonal) rings.[1]
The first fullerene to be discovered, and the family's namesake, buckminsterfullerene
(C60), was prepared in 1985 by Richard Smalley, Robert Curl, James Heath, Sean O'Brien,
and Harold Kroto at Rice University. The name was an homage to Buckminster Fuller,
whose geodesic domes it resembles. The structure was also identified some five years
earlier by Sumio Iijima, from an electron microscope image, where it formed the
core of a "bucky onion."[2] Fullerenes have since been found to occur in nature.[3]
More recently, fullerenes have been detected in outer space.[4] According to
astronomer Letizia Stanghellini, "It’s possible that buckyballs from outer space
provided seeds for life on Earth.”[5]
The discovery of fullerenes greatly expanded the number of known carbon allotropes,
which until recently were limited to graphite, diamond, and amorphous carbon such as
soot and charcoal. Buckyballs and buckytubes have been the subject of intense
research, both for their unique chemistry and for their technological applications,
especially in materials science, electronics, and nanotechnology
(C60) was named after Richard Buckminster Fuller, a noted
architectural modeler who popularized the geodesic dome. Since
buckminsterfullerenes have a shape similar to that sort of dome, the name was
thought appropriate. As the discovery of the fullerene family came after
buckminsterfullerene, the shortened name 'fullerene' is used to refer to the family
of fullerenes. The suffix “ene” indicates that each C atom is covalently bonded to
three others (instead of the maximum of four), a situation that classically would
correspond to the existence of bonds involving two pairs of electrons (“double
bonds”).
Buckminsterfullerene
Types of fullerene
Since the discovery of fullerenes in 1985, structural variations on fullerenes have
evolved well beyond the individual clusters themselves. Examples include:[16]


buckyball clusters: smallest member is C20 (unsaturated version of
dodecahedrane) and the most common is C60;
nanotubes: hollow tubes of very small dimensions, having single or
multiple walls; potential applications in electronics industry;





megatubes: larger in diameter than nanotubes and prepared with walls of
different thickness; potentially used for the transport of a variety of
molecules of different sizes;[17]
polymers: chain, two-dimensional and three-dimensional polymers are
formed under high pressure high temperature conditions
nano"onions": spherical particles based on multiple carbon layers
surrounding a buckyball core; proposed for lubricants;[18]
linked "ball-and-chain" dimers: two buckyballs linked by a carbon
chain;[19]
fullerene rings.[20]
2. Explain and derive the bucky balls?
Ans:
] Buckyballs
Buckminsterfullerene
Main article: Buckminsterfullerene
Buckminsterfullerene is the smallest fullerene molecule in which no two pentagons
share an edge (which can be destabilizing, as in pentalene). It is also the most
common in terms of natural occurrence, as it can often be found in soot.
The structure of C60 is a truncated (T = 3) icosahedron, which resembles an association
football ball of the type made of twenty hexagons and twelve pentagons, with a
carbon atom at the vertices of each polygon and a bond along each polygon edge.
The van der Waals diameter of a C60 molecule is about 1.1 nanometers (nm).[21] The
nucleus to nucleus diameter of a C60 molecule is about 0.71 nm.
The C60 molecule has two bond lengths. The 6:6 ring bonds (between two
hexagons) can be considered "double bonds" and are shorter than the 6:5 bonds
(between a hexagon and a pentagon). Its average bond length is 1.4 angstroms.
Silicon buckyballs have been created around metal ions.
[edit] Boron buckyball
A type of buckyball which uses boron atoms, instead of the usual carbon, was
predicted and described in 2007. The B80 structure, with each atom forming 5 or 6
bonds, is predicted to be more stable than the C60 buckyball.[22] One reason for this
given by the researchers is that the B-80 is actually more like the original geodesic
dome structure popularized by Buckminster Fuller, which uses triangles rather than
hexagons. However, this work has been subject to much criticism by quantum
chemists[23][24] as it was concluded that the predicted Ih symmetric structure was
vibrationally unstable and the resulting cage undergoes a spontaneous symmetry
break, yielding a puckered cage with rare Th symmetry (symmetry of a
volleyball).[23] The number of six-member rings in this molecule is 20 and number of
five-member rings is 12. There is an additional atom in the center of each sixmember ring, bonded to each atom surrounding it.
[edit] Other buckyballs
Another fairly common fullerene is C70,[25] but fullerenes with 72, 76, 84 and even
up to 100 carbon atoms are commonly obtained.
In mathematical terms, the structure of a fullerene is a trivalent convex polyhedron
with pentagonal and hexagonal faces. In graph theory, the term fullerene refers to
any 3-regular, planar graph with all faces of size 5 or 6 (including the external face).
It follows from Euler's polyhedron formula, V − E + F = 2, (where V, E, F are the
numbers of vertices, edges, and faces), that there are exactly 12 pentagons in a
fullerene and V/2 − 10 hexagons.
20-fullerene
(dodecahedral
graph)
26-fullerene graph
60-fullerene
(truncated
icosahedral graph)
70-fullerene graph
The smallest fullerene is the dodecahedral C20. There are no fullerenes with 22
vertices.[26] The number of fullerenes C2n grows with increasing n = 12, 13, 14, ...,
roughly in proportion to n9 (sequence A007894 in OEIS). For instance, there are
1812 non-isomorphic fullerenes C60. Note that only one form of C60, the
buckminsterfullerene alias truncated icosahedron, has no pair of adjacent pentagons
(the smallest such fullerene). To further illustrate the growth, there are 214,127,713
non-isomorphic fullerenes C200, 15,655,672 of which have no adjacent pentagons.
Trimetasphere carbon nanomaterials were discovered by researchers at Virginia Tech
and licensed exclusively to Luna Innovations. This class of novel molecules
comprises 80 carbon atoms (C80) forming a sphere which encloses a complex of
three metal atoms and one nitrogen atom. These fullerenes encapsulate metals
which puts them in the subset referred to as metallofullerenes. Trimetaspheres have
the potential for use in diagnostics (as safe imaging agents), therapeutics and in
organic solar cells.[citation needed]
3. Describe the carbon nanotubes?
Ans: Carbon nanotubes
Main article: Carbon nanotube
Nanotubes are cylindrical fullerenes. These tubes of carbon are usually only a few
nanometres wide, but they can range from less than a micrometer to several
millimeters in length. They often have closed ends, but can be open-ended as well.
There are also cases in which the tube reduces in diameter before closing off. Their
unique molecular structure results in extraordinary macroscopic properties,
including high tensile strength, high electrical conductivity, high ductility, high
heat conductivity, and relative chemical inactivity (as it is cylindrical and "planar"
— that is, it has no "exposed" atoms that can be easily displaced). One proposed
use of carbon nanotubes is in paper batteries, developed in 2007 by researchers at
Rensselaer Polytechnic Institute.[27] Another highly speculative proposed use in the field
of space technologies is to produce high-tensile carbon cables required by a space
elevator.
[edit] Carbon nanobuds
Main article: Carbon nanobud
Nanobuds have been obtained by adding buckminsterfullerenes to carbon
nanotubes.
[edit] Fullerite
Fullerites are the solid-state manifestation of fullerenes and related compounds
and materials.
"Ultrahard fullerite" is a coined term frequently used to describe material produced
by high-pressure high-temperature (HPHT) processing of fullerite. Such treatment
converts fullerite into a nanocrystalline form of diamond which has been reported to
exhibit remarkable mechanical properties.[28]
Properties
For the past decade, the chemical and physical properties of fullerenes have been a
hot topic in the field of research and development, and are likely to continue to be
for a long time. Popular Science has published articles about the possible uses of
fullerenes in armor.[citation needed] In April 2003, fullerenes were under study for potential
medicinal use: binding specific antibiotics to the structure to target resistant bacteria
and even target certain cancer cells such as melanoma. The October 2005 issue of
Chemistry & Biology contains an article describing the use of fullerenes as lightactivated antimicrobial agents.[29]
In the field of nanotechnology, heat resistance and superconductivity are some of the
more heavily studied properties.
A common method used to produce fullerenes is to send a large current between
two nearby graphite electrodes in an inert atmosphere. The resulting carbon plasma arc
between the electrodes cools into sooty residue from which many fullerenes can be
isolated.
There are many calculations that have been done using ab-initio quantum methods
applied to fullerenes. By DFT and TD-DFT methods one can obtain IR, Raman and
UV spectra. Results of such calculations can be compared with experimental
results.
Aromaticity
Researchers have been able to increase the reactivity of fullerenes by attaching
active groups to their surfaces. Buckminsterfullerene does not exhibit
"superaromaticity": that is, the electrons in the hexagonal rings do not delocalize
over the whole molecule.
Section – C
1. Give details about aromaticity?
Ans: Aromaticity
Researchers have been able to increase the reactivity of fullerenes by attaching
active groups to their surfaces. Buckminsterfullerene does not exhibit
"superaromaticity": that is, the electrons in the hexagonal rings do not delocalize
over the whole molecule.
A spherical fullerene of n carbon atoms has n pi-bonding electrons, free to
delocalize. These should try to delocalize over the whole molecule. The quantum
mechanics of such an arrangement should be like one shell only of the well-known
quantum mechanical structure of a single atom, with a stable filled shell for n = 2,
8, 18, 32, 50, 72, 98, 128, etc.; i.e. twice a perfect square number; but this series
does not include 60. This 2(N + 1)2 rule (with N integer) for spherical aromaticity
is the three-dimensional analogue of Hückel's rule. The 10+ cation would satisfy
this rule, and should be aromatic. This has been shown to be the case using
quantum chemical modelling, which showed the existence of strong diamagnetic
sphere currents in the cation.[30]
As a result, C60 in water tends to pick up two more electrons and become an anion.
The nC60 described below may be the result of C60 trying to form a loose metallic
bond.
Chemistry
Main article: Fullerene chemistry
Fullerenes are stable, but not totally unreactive. The sp2-hybridized carbon atoms,
which are at their energy minimum in planar graphite, must be bent to form the
closed sphere or tube, which produces angle strain. The characteristic reaction of
fullerenes is electrophilic addition at 6,6-double bonds, which reduces angle strain
by changing sp2-hybridized carbons into sp3-hybridized ones. The change in
hybridized orbitals causes the bond angles to decrease from about 120° in the sp2
orbitals to about 109.5° in the sp3 orbitals. This decrease in bond angles allows for
the bonds to bend less when closing the sphere or tube, and thus, the molecule
becomes more stable.
Other atoms can be trapped inside fullerenes to form inclusion compounds known
as endohedral fullerenes. An unusual example is the egg shaped fullerene
Tb3N@C84, which violates the isolated pentagon rule.[31] Recent evidence for a
meteor impact at the end of the Permian period was found by analyzing noble
gases so preserved.[32] Metallofullerene-based inoculates using the rhonditic steel
process are beginning production as one of the first commercially-viable uses of
buckyballs.
[edit] Solubility
C60 in solution
Fullerenes are sparingly soluble in many solvents. Common solvents for the
fullerenes include aromatics, such as toluene, and others like carbon disulfide.
Solutions of pure buckminsterfullerene have a deep purple color. Solutions of C70
are a reddish brown. The higher fullerenes C76 to C84 have a variety of colors. C76
has two optical forms, while other higher fullerenes have several structural
isomers. Fullerenes are the only known allotrope of carbon that can be dissolved in
common solvents at room temperature.
Solvent
1-chloronaphthalene
1-methylnaphthalene
1,2-dichlorobenzene
1,2,4-trimethylbenzene
tetrahydronaphthalene
carbon disulfide
1,2,3-tribromopropane
xylene
bromoform
cumene
toluene
C60
51 mg/mL
33 mg/mL
24 mg/mL
18 mg/mL
16 mg/mL
8 mg/mL
8 mg/mL
5 mg/mL
5 mg/mL
4 mg/mL
3 mg/mL
C70
*
*
36.2 mg/mL
*
*
9.875 mg/mL
*
3.985 mg/mL(p-xylene)
*
*
1.406 mg/mL
Some
fullerene
structures
are not
soluble
because
they have
a small
band gap
between
the ground
and
excited
states.
These
include the
small
fullerenes
C28,[33] C36
and C50.
The C72
structure is
also in this
class, but
the
endohedral
version
with a trapped lanthanide-group atom is soluble due to the interaction of the metal
atom and the electronic states of the fullerene. Researchers had originally been
puzzled by C72 being absent in fullerene plasma-generated soot extract, but found
in endohedral samples. Small band gap fullerenes are highly reactive and bind to
other fullerenes or to soot particles.
benzene
1.5 mg/mL
1.3 mg/mL
carbon tetrachloride
0.447 mg/mL
0.121 mg/mL
chloroform
0.25 mg/mL
*
n-hexane
0.046 mg/mL
0.013 mg/mL
cyclohexane
0.035 mg/mL
0.08 mg/mL
tetrahydrofuran
0.006 mg/mL
*
acetonitrile
0.004 mg/mL
*
methanol
0.000 04 mg/mL *
water
1.3×10−11 mg/mL *
pentane
0.004 mg/mL
0.002 mg/mL
heptane
*
0.047 mg/mL
octane
0.025 mg/mL
0.042 mg/mL
isooctane
0.026 mg/mL
*
decane
0.070 mg/mL
0.053 mg/mL
dodecane
0.091 mg/mL
0.098 mg/mL
tetradecane
0.126 mg/mL
*
acetone
*
0.0019 mg/mL
isopropanol
*
0.0021 mg/mL
dioxane
0.0041 mg/mL *
mesitylene
0.997 mg/mL
1.472 mg/mL
dichloromethane
0.254 mg/mL
0.080 mg/mL
* : Solubility not measured
Solvents that are able to dissolve buckminsterfullerene (C60 and C70) are listed at
left in order from highest solubility. The solubility value given is the approximate
saturated concentration.[34] [35][36][37]
2. Explain about the hydrated fullerences?
Ans:
Solubility of C60 in some solvents shows unusual behaviour due to existence of
solvate phases (analogues of crystallohydrates). For example, solubility of C60 in
benzene solution shows maximum at about 313 K. Crystallization from benzene
solution at temperatures below maximum results in formation of triclinic solid
solvate with four benzene molecules C60·4C6H6 which is rather unstable in air. Out
of solution, this structure decomposes into usual fcc C60 in few minutes' time. At
temperatures above solubility maximum the solvate is not stable even when
immersed in saturated solution and melts with formation of fcc C60. Crystallization
at temperatures above the solubility maximum results in formation of pure fcc C60.
Millimeter-sized crystals of C60 and C70 can be grown from solution both for
solvates and for pure fullerenes.[38][39]
Hydrated Fullerene (HyFn)
C60HyFn water solution with a C60 concentration of 0.22 g/L.
Hydrated fullerene C60HyFn is a stable, highly hydrophilic, supra-molecular
complex consisting of С60 fullerene molecule enclosed into the first hydrated shell
that contains 24 water molecules: C60@(H2O)24. This hydrated shell is formed as a
result of donor-acceptor interaction between lone-electron pairs of oxygen, water
molecules and electron-acceptor centers on the fullerene surface. Meanwhile, the
water molecules which are oriented close to the fullerene surface are
interconnected by a three-dimensional network of hydrogen bonds. The size of
C60HyFn is 1.6–1.8 nm. The maximal concentration of С60 in the form of C60HyFn
achieved by 2010 is 4 mg/mL.[40] [41][42][43]
[edit] Quantum mechanics
In 1999, researchers from the University of Vienna demonstrated that waveparticle duality applied to molecules such as fullerene.[44] One of the co-authors of
this research, Julian Voss-Andreae, has since created several sculptures
symbolizing wave-particle duality in fullerenes (see Fullerenes in popular culture
for more detail).
Science writer Marcus Chown stated on the CBC radio show Quirks and Quarks in
May 2006 that scientists are trying to make buckyballs exhibit the quantum
behavior of existing in two places at once (quantum superposition).[
Unit – V
Section – A
1. Explain about the chirality?
Ans:
Safety and toxicity
Moussa et al. (1996-7)[46][47] studied the in vivo toxicity of C60 after intra-peritoneal
administration of large doses. No evidence of toxicity was found and the mice
tolerated a dose of 5 000 mg/kg of body weight (BW). Mori et al. (2006) [48] could
not find toxicity in rodents for C60 and C70 mixtures after oral administration of a
dose of 2 000 mg/kg BW and did not observe evidence of genotoxic or mutagenic
potential in vitro. Other studies could not establish the toxicity of fullerenes: on the
contrary, the work of Gharbi et al. (2005)[49] suggested that aqueous C60
suspensions failing to produce acute or subacute toxicity in rodents could also
protect their livers in a dose-dependent manner against free-radical damage.
A comprehensive and recent review on fullerene toxicity is given by Kolosnjaj et
al. (2007a,b, c).[50][51] These authors review the works on fullerene toxicity
beginning in the early 1990s to present, and conclude that very little evidence
gathered since the discovery of fullerenes indicate that C60 is toxic.
With reference to nanotubes, a recent study by Poland et al. (2008)[52] on carbon
nanotubes introduced into the abdominal cavity of mice led the authors to suggest
comparisons to "asbestos-like pathogenicity". It should be noted that this was not
an inhalation study, though there have been several performed in the past, therefore
it is premature to conclude that nanotubes should be considered to have a
toxicological profile similar to asbestos. Conversely, and perhaps illustrative of
how the various classes of molecules which fall under the general term fullerene
cover a wide range of properties, Sayes et al. found that in vivo inhalation of
C60(OH)24 and nano-C60 in rats gave no effect, whereas in comparison quartz
particles produced an inflammatory response under the same conditions.[53] As
stated above, nanotubes are quite different in chemical and physical properties to
C60, i.e., molecular weight, shape, size, physical properties (such as solubility) all
are very different, so from a toxicological standpoint, different results for C 60 and
nanotubes are not suggestive of any discrepancy in the findings.
When considering toxicological data, care must be taken to distinguish as
necessary between what are normally referred to as fullerenes: (C60, C70, ...);
fullerene derivatives: C60 or other fullerenes with covalently bonded chemical
groups; fullerene complexes (e.g., water-solubilized with surfactants, such as C60PVP; host-guest complexes, such as with cyclodextrin), where the fullerene is
physically bound to another molecule; C60 nanoparticles, which are extended solidphase aggregates of C60 crystallites; and nanotubes, which are generally much
larger (in terms of molecular weight and size) molecules, and are different in shape
to the spheroidal fullerenes C60 and C70, as well as having different chemical and
physical properties.
The above different molecules span the range from insoluble materials in
either hydrophilic or lipophilic media, to hydrophilic, lipophilic, or even
amphiphilic molecules, and with other varying physical and chemical
properties. Therefore any broad generalization extrapolating for example
results from C60 to nanotubes or vice versa is not possible, though
technically all are fullerenes, as the term is defined as a close-