Student poster projects in the department
Synthesis of Iron Pyrite Film through Low Temperature Atmospheric Pressure Chemical Vapor Deposition
Pyrite phase of FeS2 has attracted substantial attention in the field of thin film solar technology because of its high optical absorption coefficient (~5 x 105 cm-1 at hν > 1.3eV) and the band gap of 0.95 eV. In this research, we have grown highly pure iron pyrite films using a low temperature atmospheric pressure chemical vapor deposition technique. The synthesis temperature is in the range of 375-400°C and Di-tert-butyl disulfide (TBDS) is used as the sulfur precursor. TBDS is a safe and low cost sulfur source unlike H2S, which is costly, highly toxic and requires extreme care in handling. The films obtained were uniform and free from common impurity phases such as troilite and marcasite. The FeS2 films grown earlier with CVD synthesis and sulfurized using H2S had pinholes and contained secondary phases like marcasite and troilite. The FeS2 pyrite phase was confirmed using various characterization techniques that included SEM, EDS, XRD and XPS.
Development of Low Cost and Earth Abundant Zinc Phosphide based Thin Film Solar Cells
Recent trend in thin film solar cells is to use earth abundant and non-toxic materials such as zinc and iron. Zinc phosphide (Zn3P2) has been explored as a choice for solar cell absorber and is currently reviving attention. Zinc phosphide based solar cell is synthesized from earth-abundant constituents. Our group has already synthesized the zinc phosphide films and nanowires which have been published earlier. Now, the experimental parameters have been further optimized in which the zinc phosphide film and nanowires are grown at a further low temperature of 300°C and are grown using zinc film instead of zinc foil giving us the flexibility of using various substrates. In this study, Trioctylphosphine (TOP) is used as a source of phosphorous which reacts with zinc and results in the growth of Zn3P2. The zinc phosphide phase has been successfully synthesized in both bulk thin film and nanowires form. The solar cells have been made using the zinc phosphide film as the p-type absorber. And, cadmium sulfide is being used as n-type hetero junction candidate in the initial experiments. We report efficiency ~ 0.1% using this zinc phosphide based thin film solar cell. The films have been characterized using SEM/EDS, XPS, XRD and PL.
A Waveguiding Overlayer for Optical Interconnects with Integrated Source, Detector
and External Coupling
Rahul Dixit and David Klotzkin
Continually increasing bandwidth requirements have driven semiconductor manufactures to explore techniques to integrate optical interconnects, whose enormous bandwidth and high speed is very attractive. New technologies need to be developed in order to integrate optical waveguides into this semiconductor environment. This proposal develops technology for optical interconnection on Si including: high density interconnects with low loss right angle bends, grating couplers fabricated with conventional lithographic techniques, and spot-size-converted output tapers to make the high index waveguide coupler more readily to the optical fiber. The project will demonstrate realization of high-density interconnects using right-angle bends based on reflectors, rather than total internal reflection, and coupling of sources and detectors to and from the waveguide. These technologies will be realized without used of serial e-beam patterning.
CdTe Solar Cell by sputtering method
Lakshmi K. Ganta, Surya Rajendran, Tara Dhakal
Cadmium Telluride (CdTe) solar cells have been of research and commercial interest for many years. CdTe is the second most used material next to silicon in solar cells. It has been known to clock record efficiencies close to 16.5%. Our work is focused on improving the efficiency by adopting a few economical techniques. Closed Space Sublimation (CSS) has been the predominant way of depositing CdTe thin films. We adapted sputtering method and treated the thin film with Cadmium Chloride (CdCl2) and Methanol solution and annealed in oxygen to increase the grain size and later treated it with an acid solution to expose the Tellurium rich layer. All the post processing resulted in a perfect p-type layer which was later used to fabricate a thin film solar cell using Cadmium sulfide (CdS) as n-type layer. The Cell showed promising efficiency of 4.22% for a research cell. Further work is planned to increase the efficiency.
My research is focused on the development of a new method for Hidden Markov Model (HMM) decoding, which uses estimated posterior probabilities for hidden states in an HMM, in contrast to the use of prior probabilities which are used in standard Viterbi decoding. In most modern speech recognition systems, HMM's are used to model speech either at the phone or word level and, as such, are vital to recognition. The crux of my research is the development of new "Viterbi-esque" algorithms which use these posterior probabilities, along with the HMM, to hopefully obtain a gain in recognition. These new algorithms have been tested in Isolated Word Recognition (IWR) systems and so far, results seem to indicate that it may be possible to obtain such a gain. In three different IWR scenarios (of varying levels of difficulty) the new decoding algorithms have outperformed the standard HMM decoding methods, however there is still much more testing and development which needs to be done.
A Novel Hybrid Islanding Detection Method combination of SMS and Q-f for Islanding Detection of Inverter- Based DG
In this paper a novel hybrid method for islanding detection of inverter- based distributed generation is proposed. This algorithm which is a combination of Slip mode frequency-shift (SMS) and reactive power versus frequency (Q−f) as active methods detects the islanding phenomena by forcing the DG lose its stable operation and drift the frequency out of the allowed normal range of the frequency relays. A simple passive islanding detection scheme that relies on frequency relays such as under/over frequency protection (UFP/OFP) would be sufficient to detect the moment of islanding. For demonstrating the performance of the proposed method, it is evaluated under the IEEE 1547, UL 1741 anti-islanding test configuration and multiple-DG operation. The studies reported in this paper are based on time-domain simulations in the MATLAB/Simulink. The proposed hybrid method detects islanding more efficiently for loads with high quality factor (Qf); also it operates accurately in condition of load switching and does not interfere with the power system operation during normal conditions. Simulation results prove that the proposed method decreases the time of islanding detection and has less Non Detection Zone in comparison to previous methods. In addition, the technique represents to be robust under multiple-DG operations.
Birnbaum, Zachary; O'Brien, Edward; Muller, Daniel
Unmanned Aerial Vehicle Security Using Recursive Parameter Estimation
The proliferation of Unmanned Aerial Vehicles (UAVs) raises a host of new security concerns. Our research resulted in a prototype UAV monitoring system, which captures flight data and performs real-time estimation/tracking of airframe and controller parameters utilizing the Recursive Least Squares Method. Subjected to statistical validation and trend analysis, parameter estimates are instrumental for the detection of some classes of cyber attacks and incipient hardware failures that can invariably jeopardize mission success. Our results demonstrate that achieving efficient anomaly detection during flight is possible through the intelligent application of statistical methods to system behavioral profiling.
Microsystems for Harvesting Bioenergy
In the past few years microbial fuel cells (MFCs) have gained acceptance as an alternative green energy source, as they generate sustainable electric power from biodegradable organic substrates through bacterial metabolism. With the successful validation of macro-sized MFCs, recent research has focused on miniaturizing MFCs. However, the low power densities of micro- sized MFCs hinder practical applications. Our group's research focuses on improving the performance of micro-sized MFCs through optimizing the cell architecture to help decrease the energy losses especially at the anode. In addition we have developed several paper-based MFCs that can be used as an integrated power source for paper-based diagnostic devices. These paper-based MFCs offer the advantages of ease of use, low production cost, high portability and mobility, and disposability using incineration. We have also developed several MEMS MFC arrays which can be used as a compact and reliable platform for high throughput and rapid screening of electrochemically active microbes. In addition we recently started working on micro-sized microbial solar cells (MSCs) or photosynthetic fuel cells, which are a new class of MFCs that employ photosynthetic catalysts such as cyanobacteria to produce electricity.
Fraiwan is the recipient of the 2015 Outstanding PhD Researcher Award. She has been working with Professor Choi's research group since September 2012. To date, she has published 9 journal articles (7 as first author), 12 refereed conference proceedings (7 as first author), and 5 presentations.
Scalable Sentiment Classification for Big Data Analysis Using Naïve Bayes Classifier
A typical method to obtain valuable information is to extract the sentiment or opinion from a message. Machine learning technologies are widely used in sentiment classification because of their ability to "learn" from the training dataset to predict or support decision making with relatively high accuracy. However, when the dataset is large, some algorithms might not scale up well. In this paper, we aim to evaluate the scalability of Naïve Bayes classifier (NBC) in large datasets. Instead of using a standard library (e.g., Mahout), we implemented NBC to achieve fine-grain control of the analysis procedure. A Big Data analyzing system is also design for this study. The result is encouraging in that the accuracy of NBC is improved and approaches 82% when the dataset size increases. We have demonstrated that NBC is able to scale up to analyze the sentiment of millions movie reviews with increasing throughout.
A Hybrid Simulation Framework for Study of Power System Transients
This study proposed a hybrid simulation framework, which includes both discrete and
continuous states, for the study of power system transients. This framework also include
the interactions with online
transient stability analysis, diagnosis and decision making process. As an example, the the misoperation of protective relay in a 9-bus power system is studied.
OVERCOMING CHILDREN ARTICULATION ISSUES USING AUTOMATIC SPEECH RECOGNITION METHODS
Recognition of disabilities in children's language at an early age is the major goal
of this work. The Automatic Speech Recognition (ASR) system developed for this purpose
attempts to mimic the knowledge of speech therapists. In particular, the method is
based on the Goldman Fristoe Test of Articulation (GFTA) in which the therapists listen
to the children's pronunciation of words and judge whether there is a problem in their
pronunciation or not (an utterance verification problem). The word that the child
was supposed to say is known, and the ASR system should decide if the child said it
correctly or substituted/distorted one or more segments in the word. For the testing
the designed HMM model described in this report, 63 children are considered (This
set of data is called data set 1 in this report). Around half of these children were
recruited because they were diagnosed with a speech delay, that is, they had articulation
problems that children their age should not have. The main goal of this research is
to design an ASR system that could provide feedback similar to that currently given
On the Use of Gabor Filters in Designing Steganographic Distortion
With recent advances in steganography the most integral part left to steganographer is designing the distortion function. In this paper we propose a new adaptive scheme in defining the distortion function using Gabor filters in spatial domain. Compared to other embedding algorithms, our proposed method, using fine directional grid of Gabor filters, put higher emphasis on cluttered and textured areas in the image than on the edges. Our test results using the state-of-the-art steganalysis algorithms show the superiority of our approach.
Generally speaking, I am working on Digital Signal Processing (DSP) and its applications such as Data Compression in Wireless Networks. The following poster talks about Data Compression methods I have applied to reduce the amount of data transmission in wireless networks. I have chosen a method named SVD (Singular Value Decomposition) truncation to compress the data before transmission. The simulation results show the high performance of the proposed method in compression and de-noising of this type pf data in the system. Currently, I am working on Medical Sensor Networks applications like Tumor Positioning used in Radiotherapy and Medical Implant Localization systems used in Capsule Endoscopy and Telesurgery. In addition, I am also working on Indoor Mobile Positioning Systems which is a very popular topic nowadays that has received increasing attention recently.
Investigation of Amorphous Silicon/P3HT Heterojunction for Solar Cells
Michael Seymour and Alok C. Rastogi
The work presented here shows some of the experimental results obtained from analyzing the heterojunction between hydrogenated amorphous silicon (a-Si:H) and poly 3-hexylthiophene (P3HT). The goal of this study is to better understand the junction and ultimately use these materials in thin film hybrid solar cells. Two different structures were investigated; ITO/a-Si:H/P3HT/Cr/Ag and ITO/PEDOT/P3HT/a-Si:H/Cr/Ag. Surface morphology, EDAX, and transmission spectra were observed for the sputtered hydrogenated amorphous silicon layer. I-V characteristics were investigated using a Keithley 2602 Sourcemeter. Strong diode curves were obtained from both structures. There was little effect from a halogen light source. Further investigation of other parameters and effect from light is still on-going.
Sidhu, Navjot K.
This poster presents solid-state supercapacitors that have been fabricated using graphene-based electrodes and the ionic liquid based gel polymer electrolyte. Supercapacitors are electrochemical energy storage systems. Graphene acts as an excellent material for high capacitance. Their specific capacitance and cyclic performance was evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge techniques. Extensive impedance spectroscopic studies were carried out to establish specific electrical attributes of the electrolyte and electrode under various cyclic stages.These results show that even after 5000 cycles capacitance is reduced.
Zinc Oxysulfide Thin Films as Window Layer for Solar Cells
Ratheesh R. Thankalekshmi and Alok Rastogi
Thin films of ZnO doped with sulfur show electronic and optical properties which are attractive for optoelectronic device applications. Recently several investigations have been reported on the growth of homogeneous ZnO1-xSx thin films by oxidation of ZnS, reactive sputtering and atmospheric vapor transport. Nanostructure ZnO1-xSx thin films have however received limited attention. Here we report the development of ZnO1-xSx prepared with chemical spray pyrolysis technique and solution growth method. In the chemical spray pyrolysis technique, the atomized precursor solution is directed downward at the heated substrate, which upon decomposition and oxidation reaction forms a thin film. The ZnO1-xSx films prepared by the chemical spray process at 300°C over quartz substrates are highly crystalline with the ZnO1-xSx films having a preferred c-axis orientation. Optical plot shows that band edge shifts towards the lower energies by addition sulfur and a minimum of 2.78 eV is obtained for ZnO0.45S0.55 and further addition of sulfur, the band gap energy retracts initially and approaches towards that of pure ZnS. In solution growth process ZnO1-xSx are deposited over ZnO nanorods in a core-shell like nanostructure for application to thin film solar cells. ZnO films with a nanostructure dominated by arrays were deposited by hydrothermal synthesis over surface activated quartz substrates. ZnO1-xSx is deposited over ZnO nanorods by chemiplating process. Microstructure studies confirm conformal surface conversion with accumulated ZnO1-xSx growth over (0001) facets of ZnO rods. X-ray diffraction studies show c-axis orientated growth of ZnO rods. The optical absorption analysis shows concurrent band gaps corresponding to the ZnO1-xSx shell and ZnO core. The reduced band gap of ZnO1-xSx offers unique advantage in application to solar cells. It will replace Cd from conventional CdS heterojunction layer in non-toxic earth abundant materials based thin film solar cells.