NanoImaging Research Laboratory
The NanoImaging Lab has just completed its third year of operation. The Lab is divided
into three facilities: Microscopy, Fabrication and Evaluation of Imaging Devices, and
Nanoparticle Synthesis.
Microscopy. In this facility we characterize materials by imaging, electron diffraction,
and x-ray microanalysis. Ongoing work focuses on correlating polymer particle size and
structure with synthesis methods. Prof Matt Miri’s group, Chemistry, is synthesizing
high-density polyethylene particles in a starch binder with a goal of developing largely
biodegradable plastic film. We are using the TEM to image the polymer particles to
characterize their size, size distribution, and morphology. We also use the SEM to image
cross sections of films designed to mimic what would happen if the material were used to
fabricate plastic bags.
We have also initiated a collaboration with Prof Benjamin Varela in Mechanical
Engineering. Prof Varela’s research interest is in the use of geopolymers (ceramics) as
construction materials. We have used the SEM to both image the material and provide
elemental analysis via x-ray microanalysis. Examples are given in Fig. 1.
Fig. 1. Example SEM images of ceramic material with different elemental compositions
Prof Davide Mariotti’s research is in nanofabrication and we are imaging materials and
devices fabricated by his students. We have also worked with R. DiLeo, NanoPower
Research Labs, to image a complex between tin and carbon nanotubes, as illustrated in
Fig. 2.
Fig. 2. Image of a tin-CNT complex. The dark areas are the tin clusters adsorbed to the bundle of
carbon nanotubes.
Fabrication and Evaluation of Imaging Devices. We continue to build our expertise in
fabrication of organic-based light-emitting devices (LEDs). Our ultimate goal is to
fabricate hybrid devices in which inorganic nanocrystals are the light-emitting element
and the organic layers are used for strictly electron and hole transport. A necessary
prerequisite to that goal is building devices that use the organic material to emit light.
These are commonly called organic light-emitting devices (OLEDs), which are further
characterized on the basis of whether the devices use small molecules that are vacuum
evaporated to form the device structure (SMOLEDs) or polymeric materials that are
typically fabricated by spin-coating techniques (PLEDs). We are just beginning our study
of PLED devices.
We have made much progress in the SMOLED category and are now reproducibly
fabricating devices whose optoelectronic characteristics are consistent with those
published in the scientific literature. Figure 3 shows some of our results, including a
schematic cross section of the device on the right-hand side. Holes are injected from the
left-hand side of the device via the indium tin oxide (ITO) layer and the polymer buffer
layer (PSS:PEDOT) and finally into the hole transport layer (TPD). Meanwhile electrons
are injected from the right-hand side via the aluminum cathode and LiF layers into the
electron transport layer (Alq3). With balanced charge injection, which is part of the
optimization of the device structure, the electrons and holes meet in the Alq3 layer and
form an exciton, which decays by emitting a photon (green in this device structure).
The data shown in the left-hand side of Fig. 3 pertain to an experiment in which we
varied the placement of the LiF buffer layer. LiF was deposited either under the cathode,
above the PEDOT:PSS layer, placed at both sites, or placed below the cathode and
between the TPD and Alq3 layers. The best device was that with LiF only below the
cathode. Personnel involved: Omkar Vyavahare and Nikita Surve, both graduate students
in the Materials Science & Engineering program.
Fig. 3. (Left) Device efficiency vs applied voltage for different locations of the LiF buffer layer (see
text for details). (Right) Basic device schematic showing one possible location for the LiF buffer
layer.
Nanocrystal Synthesis. We are synthesizing nanocrystals composed of CeO2, which are
currently intended for a nonimaging application. These are grown by an aqueous
precipitation route that is “green” and inherently scalable. The techniques we are
developing can be readily applied to other compositions that have more imaging
relevance.
Of importance to the potential application is whether or not the nanocrystals we produce
are crystalline. With the help of M. Rodriguez at SUNY Albany we were able to obtain
high-resolution TEM pictures of our material as shown in Fig. 4. These images show
lattice planes characteristic of crystalline material. Electrons moving down the columns
are retarded in phase via their interaction with the crystal atoms, whereas those electrons
moving down the spaces between lattice plans are not. The result is an interference
pattern characteristic of crystalline material. Measurement of spacing between the planes,
as well as fast Fourier transforms of the individual particles, show that the imaged planes
are characteristic of the (111) planes for CeO2.
Fig. 4. High-resolution TEM image of CeO2 nanocrystals.
As crystal size decreases the general expectation is that the lattice constant of the crystal
should decrease due to surface tension and other forces. But, just the opposite is seen in
CeO2. The published literature supports the observation, but the mechanism causing this
effect is controversial. Some have suggested that the expansion is due to reduction of the
crystal to Ce2O3, a form that would be useless for our intended application of this
material. We have extended the particle size down to 1.1 nm diameter, smaller than any
other published result. Our electron diffraction analysis shows that the material is still
CeO2 at this size, hopefully clearing up the disputed interpretation of the lattice
expansion. Personnel involved: Gary DiFrancesco, Associate Scientist. Project supported
by Cerion Energy, Inc.
Course and Outreach Support. The Microscopy Facility has become a popular resource
for supporting various CIS/COS/COE courses. In the last year it has been used to support
Introduction to Electron Microscopy, Imaging Science Fundamentals (two sections),
Frontiers in Science, and Introduction to Nanotechnology. In addition, the Microscopy
Facility has supported outreach events including one CIS Open Houses, the CIS High
School Intern program, and a cooperative venture between CIS and the Rush-Henrietta
School District.
Publications and Patents
R. K. Hailstone, A. G. DiFrancesco, J. G. Leong, T. D. Allston, K. J. Reed, “A Study
of Lattice Expansion in CeO2 by Transmission Electron Microscopy”, J. Physical
Chemistry C, 113, 15155-15159 (2009).
R. K. Hailstone, A. G. DiFrancesco, J. G. Leong, T. D. Allston, K. J. Reed,
“Preparation and Characterization of CeO2 Nanoparticles”, Fall MRS Proceedings,
(2008).
O. Vyavahare, R. K. Hailstone, “Enhanced Performance of Organic Light-Emitting
Diodes Using a LiF Buffer Layer”, Spring MRS Proceedings (2009).
A. G. DiFrancesco, T. D. Allston, R. K. Hailstone, A. Langner, K. J. Reed, “Fuel
Additive Containing Lattice Engineered Cerium Dioxide Nanoparticles”, US Patent App
PCT/US08/87133, December (2008).
Grants and Contracts FY09
Cerion Energy, $135k
Facilities
Microscopy: JEOL 6400V scanning electron microscope with a LaB6 electron gun and
energy dispersive X-ray analysis for elemental detection. JEOL 2000FX transmission
electron microscope with energy dispersive X-ray analysis for elemental detection (See
frontpiece for a picture). JEOL 100CX II transmission electron microscope. Reichert
Jung ultramicrotome for cross-section preparation. Nikon 9000 Film Scanner.
Device Fabrication and Evaluation: Denton vacuum coater, Laurell spin coater, Keithly
digital source meter for I-V curves, Ocean Optics monochromator for
electroluminescence spectra and radiance measurement.
Nanocrystal Synthesis: Three- and nine-liter reactors for precipitation of inorganic
nanocrystals, with extensive process control by Labview software. Brookhaven dynamic
light scattering instrument for particle size measurement.
In the zip file, the figure labeled “overleaf” is for the image facing the first page
discussing the NanoImaging Lab in the annual report.
The figure caption for this overleaf is:
Transmission electron microscope operating at 200 kV.