Резюмета на трудовете
към конкурса за доцент
на гл. ас. д-р инж. Георги Р. Иванов
кат. „Физика”, ХТФ, УАСГ
1. G.R. Ivanov, K. Ozanyan, P. Gladkov, “Time correlated single photon counting
method. Application to fluorescence kinetic measurements.” Yearly book, Sofia
University, (1991).
A computerized, highly sensitive system for time-correlated single photon counting is
reported. This system has over 4 orders of magnitude higher sensitivity than an alternative
Lock-in amplifier method. The system is operational in the near IR region and in the
nanosecond time domain. The time resolution is limited mainly by laser pulse back slope.
The system performance is illustrated for the case of tirne relaxation of excitonic radiative
recombinalton in Si. To achieve the necessary low dark counts noise the photomultiplier was
placed in specially designed high vacuum liquid nitrogen cooler and the temperature of the
photocathode was maintained at the optimum temperature of – 70 oC. The system
demonstrated its sensitivity by measuring a signal as low 1 photon/s or 10 -18W.
2. G. R. Ivanov, A. T. Todorov, A. G. Petrov, "New highly precise and well defined
Langmuir-Blodgett film deposition system", in Molecular Electronics vol. 7 (1991),
ed. P.I. Lazarev, Kluwer Academic Publishers, Dordrecht, Netherlands, p. 139.
Here is presented the general design and performance of a new Langmuir-Blodgett trough. It
is designed as a very precise and flexible research instrument. It has a velocity dynamic
speed range in exccess of 1:10 000, stlck-slip free movement at vclocities below 0.5x10-6
m/sec, special antivibration construction, Wilhelmy type surface pressure sensor
connected with a Lock-in amplifier, micrometer precision position scnsors, analogue feed
back loops for the surlace pressure and velocity control. It is a fully computerized instrument
with a novel algorithm for the software. For the first time we have measured such
perturbational narameters for the film quality as the unevenness of the velocity and the
acceleration specira of vibrations of the barrier and the substrate holder. Unevenness as high
as 48% can be measured while the amplitude of vibrations were in the range of 10 -4 m/sec -2
at medium speeds. These values are several times higher than the background ones.
3. G. R. Ivanov, A. T. Todorov, A. G. Petrov, "Langmuir trough with enhanced
performance", Makromol. Chem., Macromol. Symp., 46 (1991) 377.
Here is presented the general design and performance of a new Langmuir-Blodgett trough. It
is designed as a very precise flexible research instrument. It has a velocity dynamic speed
range in excess of 1:10 000, stick-slip free movement at velocities below 0.5xl0 -6 m/s,
special antivibration construction, Wilhelrny type surface pressure sensor connected to
a Lock-in amplifier, micrometer precision position sensors, analogue feed back loops for the
surface pressure and velocity control. It is a fully computerized instrument with a
productivity of 18 measurements per second with an IBM PC/AT computer. The software
has a lot of new features. For the first time we have measured such perturbational parameters
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for the film quality as the unevenness of the velocity and the acceleration spectra of
vibrations of the barrier and the substrate holder. Unevenness as high as 48% can be
measured while the amplitude of the vibrations were in the range of 10 -4 m/s2 at medium
speeds. These values are several tirnes higher than the background ones.
4. К. Г. Нушев, Г. Р. Иванов, А. Т. Тодоров, В. Й. Витков, Д. Й. Чакъров, Д. Г.
Нушев, С. К. Безуханов, А. Б. Казаков, П. Р. Парушев, „Роботизирана система за
отлагане на мономолекулярни органични филми”, Авторско свидетелство №
47827 (1993).
Изобретението се отнася до роботизирана система за отлагане на мономолекулярни
органични филми по метода на Лангмюир и Блоджет, приложим в молекулната
електроника и в технологии за свръхтънки филми. Предимство на тази система спрямо
известните такива е повишеното качество на отлагане поради виброизолираността на
работната повърхност от постамента и от зоната, където са разположени двигателите.
Освен това е разширен диапазонът на регулиране на скоростта, повишена е точността
на позициониране, постигната е повишена плавност на движението чрез използване на
задвижване с повишена коравина при отсъствие на неопределености и намалена
нелинейност. Изобретението има 3 претенции свързани с 3те различни варианта на
модулите за механично движение на изпълнителните звена.
5. G. R. Ivanov, K. G. Kostadinov, A. G. Petrov, "Aspects of Langmuir-Blodgett trough
design: computerization, pressure measurement, unevenness of motion, generated
vibrations", Thin Solid Films, 210/211 (1992) 13.
Some factors important to Langmuir-Blodgett film quality like vibrations generated within the trough, unevenness of
Some factors important to Langmuir-Blodgett film quality like vibrations generated within
the trough, unevenness of motion of the barrier or substrate holder, control of constant
pressure during deposition are evaluated. It is shown that the addition of analogue devices to
the computer control can greatly improve trough performance. Vibrations in the frequency
range from 0 to 100 Hz can be cut down to an acceleration amplitude as low as 0.02 × 10-3m
s-2. A novel translational unit design is presented by which both amplitude and frequency of
vibrations can be controlled. The unevennesss coefficient strongly depends on the
construction of the drive unit and varies from 15 to 50% for different module designs.
Integration time below 0.3 s and data acquisition rate above 10 readings per second are
recommended for precise surface pressure maintenance.ma
6. I. I. Yovchev, B. V. Vasilev, G. R. Ivanov, "A basic Langmuir-Blodgett trough
configuration", Universite de Plovdiv, Travaux Scientifiques, 30 (1995) 25, fasc. 4 Physique.
A Langmuir-Blodgett film deposition system was developed with special emphasis on
decreasing both external and generated in the system vibrations. For this purpose a marble
plate was used for both base and Teflon trough plates. Marble is known as excellent absorber
of vibrations and also its mass absorbs even very low frequency vibrations. A special
mechanical design was used also with the purpose of minimal vibration generations.
Analogue feedback for the surface pressure control was used with improved parameters and
speed of reaction.
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7. B. K. Tuleva, G. R. Ivanov, N. E. Christova, "Biosurfactant Production by a new
Pseudomonas putida Strain ", Zeitschrift fur Naturforschung, 57c (2002) 356.
Observation of both tensio-active and emulsifying activities indicated that biosurfactants
were produced by the newly isolated and promising strain Pseudomonas putida 21BN. The
biosurfactants were identified as rhamnolipids, the amphiphilic surface-active glycolipids
usually secreted by Pseudomonas spp. Their production was observed when the strain was
grown on soluble substrates, such as glucose or on poorly soluble substrates, such as
hexadecane, reaching values of 1.2 g l-1. When grown on hexadecane as the sole carbon
source the biosurfactant lowered the surface tension of the medium to 29 mN m-1 and formed
stable and compact emulsions with emulsifying activity of 69%.
8. T. Angelov, D. Radev, G. R. Ivanov, D. Antonov, I. Spirov, T. Ruskov, A. G. Petrov,
"Hydrophobic magnetic nanoparticles: synthesis and LB film preparation", J.
Optoelec. Adv. Mat., 9 (2007) 424.
Magnetic nanoparticle probes are emerging as a class of novel contrast and tracking agents
for medical and other applications. The synthesis a large scale quantity of monodispersed
magnetic nanoparticles is of great importance for using these materials in practice. In this
work, we report the synthesis of magnetite γFe2O3/ Fe3O4. The obtained nanoparticles were
investigated by IR, TEM, XRD and AFM techniques. For the first time these 30 nm particles
were deposited as Langmuir-Blodgett film. High resolution AFM study of the surface shows
lack of macro defects and a tree like aggregation of the nanoparticles. These gives possibility
of some practical applications.
9. G. R. Ivanov, J. I. Burov, "Nanodimentional Aggregates in Organic Monolayers
Studied with Atomic Force Microscopy (AFM) and Fluorescence Lifetime Imaging
Microscopy (FLIM)", Sixth Int. Conf. Balkan Physical Union; AIP Conf. Proc. 899
(2007) 257.
Organic monolayers from a fluorescently labeled phospholipid (DPPE-NBD) were deposited
on solid supports under special conditions that form stable nanometer wide bilayers cylinders
that protrude from the monolayer. This molecule was frequently used in sensor applications
due to its sensitivity to environment changes. The proposed configuration should provide
both fast response times (ultra thin film) and increased sensitivity (greatly increased surface
area). AFM can clearly distinguish between the different phases. The height difference
between the solid-expanded and the liquid-expanded phase was measured to be 1.4 nm while
the bilayer thickness was 5.6 nm. The solid domains show a 20 % decrease in fluorescence
lifetime in comparison to the monolayer as measured by FLIM. This difference in lifetimes is
explained in the model of fluorescence self quenching in the solid phase due to the molecules
being closer to each other.
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10. G. As. Georgiev, A. G. Jordanova, G. R. Ivanov, Z. I. Lalchev, "Interaction of
poloxamer F-98 with free standing phospholipid films ", J. Optoelec. Adv. Mat., 11
(2009) 1241.
The interaction of poloxamer F-98 with dimiristoylphosphatidylcholine (DMPC) is
investigated experimentally at one (monolayer) and two interacting air/water interfaces
(foam film). Monolayer tensiometry reveals the degree of co-polymer penetration in DMPC
monolayers and the alterations in monolayer compression/decompression behaviour. The
changes in the film morphology are registered by Brewster angle microscopy (BAM). Foam
film experiments show that the steric disjoining pressure arising in presence of Poloxamer F98 results in increase of film equivalent water thickness and stability. It is found that the
interaction between the co-polymer and DMPC molecules, both in monolayers and foam
films, strongly alters the interfacial properties of the mixed systems, and bears promise for
the development of new drug carrier formulations.
11. G. R. Ivanov, G. As. Georgiev, Z. I. Lalchev, "Monolayers from fluorescently
labelled phospholipids", J. Optoelec. Adv. Mat., 11 (2009) 1238.
Organic monolayers from fluorescently labeled phospholipids, mainly DPPE-NBD, were
deposited on solid supports under special conditions that form stable nanometer wide bilayer
cylinders that protrude from the monolayer. This molecule was frequently used in sensor
applications, due to its sensitivity to environmental changes. The proposed configuration
should provide both fast response times (ultra thin films) and increased sensitivity (greatly
increased surface area). Atomic Force Microscopy (AFM) can clearly distinguish between
the different phases. The height difference between the solid-expanded and the liquidexpanded phases was measured to be 1.4 nm, while the bilayer thickness was 5.6 nm. The
solid domains showed a 20 % decrease in the fluorescence lifetime in comparison to the
monolayer, as measured by Fluorescence Lifetime Imaging Microscopy. This difference in
lifetimes is explained in the model of fluorescence self quenching in the solid phase, due to
the molecules being closer to each other.
12. G. R. Ivanov, R. Tomova, S. T. Djambova, M. Nadoliiski and D. Dimova-Malinovska
"Functionalized aerogels - new nanomaterials for energy-efficient building.
Preliminary AFM, Nanoidentation and EIS studies ", J. Phys.: Conf. Ser., 253 (2010)
012077.
Aerogels are highly porous nanostructured materials with excellent thermal insulation
properties. The possibility to add additional function – to functionalize the aerogels,
especially to produce photovoltaic electricity, will make them an excellent candidate for
energy-efficient building. Going in the direction of this midterm goal we start with the
investigation of the properties of the readily available silica aerogels. Atomic Force
Microscopy reveals large areas with submicrometer roughness, which allows reliable
nanoidentation measurements. The average hardness was measured to be 2,2 MPa and the
Young’s modulus was 11 MPa, values typical for low density elastic silica aerogels.
Electrochemical Impedance Spectroscopy, measured in ambient air, shows typical capacitive
behaviour and the aerogel is best modelled by serially connected resistance of 37 kΩ and
capacitor of 170 pF. The conductivity is interpreted in terms of proton migration, strongly
dependant on air humidity.
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13. G. R. Ivanov, G. Georgiev and Z. Lalchev - Book chapter, "Fluorescently Labeled
Phospholipids - New Class of Materials for Chemical Sensors for Environmental
Monitoring ", in "Relevant Perspectives in Global Environmental Change", Julius
Ibukun Agboola (Ed.), (2011) ISBN: 978-953-307-709-3, InTech.
Reliable environmental monitoring strongly depends on the quality of chemical and
biochemical sensors. There are still some unsolved problems especially when higher
selectivity is required. In this chapter we propose a new class of materials – fluorescently
labeled phospholipids, which can be used as chemical and biochemical sensors. We focus
our attention on the most promising compound - head labeled with nitrobenzoxadiazole
(NBD) phosphatidyl ethanolamines. We were the first to study these compounds in one
component layers. Three new phenomena were discovered for this material that can be used
for successful sensor applications. In our research we use the Langmuir and Blodgett
method for investigation of organic monolayers at the air-water interface and for thin film
deposition. It can also independently be used for environmental monitoring, e.g. water
purity monitoring.
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