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Center for Micro-Magnetic and
Electronic Devices (CMMED), Department Electrical & Computer Engineering,
University of Kentucky (November 99 – Present) This
project involves the template free fabrication of Nano-porous architectured
metal oxide films by sol-gel method and their characterization by High
Resolution FE-SEM. The films were fabricated using sol-gel method on a
magnetically soft metglas substrate 2826MB. By controlling the humidity,
concentration of the sol, water/acid content and flow rate during drying,
smooth TiO2 films showing a nano-porous architecture over large
areas (4cm X 2 cm) were fabricated. By varying the deposition conditions, it
was possible to fabricate films with ordered pores. Since these films are
deposited on a sensor platform, they can be used as humidity sensors. The
complete details of this project can be found in ''Fabrication of Nano-porous
TiO2 films through Benard-Marangoni Convection''. Materials Research Innovations,
5(3-4), 178-184, 1 Feb 2002.
(a)
individual droplets
(b) coalescence of the droplets (c) porous
films Project # 2 Fabrication of metal oxide nano wires and
nano tubes and porous alumina membranes This
project deals with the synthesis of metal oxide nano wires by a combination
of anodization and sol-gel. The method involves the fabrication of porous
alumina template by anodization, infiltrating the pores by metal oxide sol,
evaporation, baking at high temperature, and finally removal of the alumina
template by chemical etching, leaving metal oxide nano wires. We also make
titania nano tubes by anodization of a titania sheet.
Porous Anodic Alumina Template TiO2
nano wires
FE-SEM cross-sectional images of
titanium oxide nano tubes fabricated by anodization Project # 3 Hybrid
organic-inorganic hetero-junction thin film opto-electronic devices
involving organic (Pentacene) and inorganic (CdS) layers deals with
fabrication of inorganic nano-crystalline CdS layers by a chemical method and
depositing an organic layer on top of it, to fabricate a hetero-junction
device. Inorganic semiconductors like Silicon and Gallium Arsenide have been
the backbone of the semiconductor industry for the last four decades.
However, organic semiconductors like pentacene offer the advantages of low
cost,
Light
weight and flexible substrate (c) Low cost, large area processing: Inexpensive substrates and low temperature
processing are expected to substantially reduce the cost of manufacturing
solar modules. These solar cells hold
the promise of inexpensive large scale production. Apart from design and
fabrication of novel solar cells we are also involved in characterization of
these cells and modeling their junction properties. We are Collaborating with Prof. John Anthony’s
group on this project. Project # 4 Fabrication
and characterization of Nano-porous CdS and CdTe films by a soft chemistry
route. We use a novel deposition technique to fabricate
nano-porous semiconductor films. These films are potential partners in a
hetero-junction solar cell. Due to nanoporous structure of the cell, the
distance that photo excited electrons must travel within their life time can
be reduced to less than 50 nm. The enlarged p-n junction area is also
beneficial with regard to light scattering and boosts the light absorbing
capacity of the thin film cells.
Porous CdS
films Porous
CdTe film Kalyan
and Vivek are working with me on this project Project # 5 Novel method
for fabricating semi conducting nano fibers. We
use a combination of solution chemistry, high temperature and pressure to
synthesize semi conducting nano fibers.
CdS Fibers Kalyan
and Vivek are working with me on this project. This
Project involves fabrication of a magnetic nano dot array on a conducting
substrate. We are Collaborating in
this project with Prof.
Lance Delong from Physics Department, Thus
project involves fabrication of nano scale hetero-junctions in a nano
channel, studying transport and modeling. Kalyan and Vivek are working with
me on the experimental aspects of this project. Gerald and Dr. Aguilera are
working on the modeling aspects of this project. Project # 8
Evaluation of nano-crystalline CdS films prepared by size tailoring for window
layer in a solar cell. Performance of CdS/CdTe
cells can be improved by incorporating nano-technology in to their device
designs.
FE-SEM images of CdS films
prepared by solution growth, sonochemical and microwave assisted
synthesis Optical
Absorption of nano CdS by solution growth, Sonochemical and Microwave
assisted synthesis Collaborators in this
project are Dr. Vijay K Rangari
and Dr. Shaik Jeelani from Center
for Advanced Materials, Project # 9 Nano-structured CdTe films
for EL display devices This project deals with
incorporating nano-structured films in to El displays, device
characterization and modeling. This project is in the initial stages and this
section will be updated soon. Kalyan
and Vivek and Praveen are working with me on the experimental aspects of this
project. Praveen, Gerald and Dr. Aguilera are working on the modeling aspects
of this project. Project # 10 Remote
Query bacterial growth monitoring and Gas Sensing Bacterial growth monitoring using an LC sensor deals
with a new technique presented for in-vivo remote query measurement of the
complex permittivity spectra of a biological culture solution. A sensor
comprised of a printed inductor-capacitor Remote Query Gas Sensors: These sensors are comprised of an inductor-capacitor
(LC) printed circuit pair, in planar form, the resonant frequency of which
changes in response to different environmental parameters including pressure
and, when made in conjunction with a humidity-responsive thin film, humidity
levels. The resonant frequency of the sensor is detected using a remotely
located loop antenna. Within the interrogation zone the sensor perturbs the
impedance spectra of the loop antenna, from which the resonant frequency of
the sensor is determined. These planar LC sensors, when coated with a
nanoporous oxide films will act as efficient gas sensors. nanoporous films
with large surface area are expected to improve the gas sensing characteristics.
The most commonly accepted mechanism of sensing for an n-type semiconductor
metal oxide involves the formation of a space-charge region on the surface of
the oxide due to electron trapping on adsorbed oxygen species. When the
sensor is exposed to a reactive gas, the gas reacts with the surface oxygen
species, decreasing their surface concentration and releasing electrons
trapped by the oxygen adsorbate, thus increasing the conductivity of the
oxide. For large grains the sensor
resistance results from the presence of the grain boundaries within the
material. As the grain size decreases to values near that of the thickness of
the space charge region (Debye thickness), ca 10-100nm for SnO2,
the so-called “all-surface” maximized sensitivities are seen. Magnetoelastic
sensors: Micro- magnetic sensors
are being used for sensing humidity, volatile organic compounds, and
bio-sensing. Magnetic soft alloy ribbons which can be excited by applying a
bias field are being used as sensors. In response to an externally applied
magnetic field impulse the sensors ring like a bell, emitting both magnetic
flux and acoustic energy with a characteristic resonant frequency. The
magnetic flux can be detected remotely, external to the test area, using a
pick-up coil, or the acoustic energy by a microphone. By monitoring changes
in the characteristic resonant frequency of the sensor multiple environmental
parameters can be measured including temperature, pressure, velocity of
ambient medium and, when immersed in a liquid, viscosity, liquid density, and
surface tension. In combination with mass changing, chemically responsive
layers, such as polymers or nanoporous ceramics, remote query chemical
sensors can be made.
Remote query mechanism
for magnetoelastic sensors The
remote query capability as illustrated above allows the magnetoelastic
sensors to be monitored from inside sealed, opaque containers such as food.
Depending upon the application magnetoelastic sensors can be sized from
micrometer to millimeter dimensional scales. Magnetoelastic sensors in combination with nano-porous metal oxide
films with their higher surface area will allow us to make better gas sensors.
By properly doping the chemically responsive layer, we can make our sensor
response to be selective. Project # 11 ferroelectric magnetic
and magneto-resistive Transition metal oxides This
work was performed under the guidance of
Prof. C.N.R. Rao at the Solid state and Structural Chemistry
Unit, Indian Institute of Science and
Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore,
India (Jan 1997-Oct 1999). The collaborators in this project were Dr. M.
Sugantha, Dr. P.N. Santhosh and Ms. P.V.
Vanitha Synthesis
of family of oxides Ln-A-MnO3 (where Ln= La, Nd, Pr, Gd, and A=
Ca, Sr and Pb) which show metal-insulator transitions, charge ordering,
colossal magnetoresistance, studying the effect of internal pressure on
charge ordering in manganites, Distinction between two types of charge
ordering by chemical melting, studying the effect of Mn+3
substitution by other 3d metal ions on CMR, substitution by Ni+3
and Co+3 on charge ordering, charge ordering in electron doped
manganites and the effect of cation size disorder on charge ordering. This
project was under the guidance of Prof. Hans Schmid at Department of Applied
Chemistry, University of Geneva, Geneva, Switzerland (1995). The
Collaborators were Dr. J.P. Rivera and Dr. Frank Kubel. The
project objectives achieved were, synthesis of the compounds belonging to Aurivillius
Phases in the Bi-Fe-Ti-O system. Investigation of the phase stability,
construction of the Phase diagram, magnetic and magneto-electric measurements
(AC and DC), Structural modeling and refinement of the 5 & 8 layered
structured compounds. This
work was carried out under the guidance of Prof. S.V. Suryanarayana at the
Materials Research Laboratory, Osmania University, Hyderabad, India
(1990-1996) I was responsible for two
major projects during the course of my Ph.D. The objective of these two
projects was to synthesize single phase and composite materials which show
simultaneous Ferro electricity, magnetism and magneto-electric effect. The
work protocol adopted was, synthesis of ferroelectric ceramic materials by
solid state reaction method, characterization by X-ray diffraction, electron
microscopy, and their property evaluation through electrical, magnetic and
magneto-electric measurements. Any
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