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Articles 1 - 30 of 50
Full-Text Articles in Engineering
Underlying Substrate Effect On Electrochemical Activity For Hydrogen Evolution Reaction With Low-Platinum-Loaded Catalysts, Baleeswaraiah Muchharla, Peter V. Sushko, Kishor K. Sadasivuni, Wei Cao, Akash Tomar, Hani Elsayed-Ali, Adetayo Adedeji, Abdennaceur Karoui, Joshua M. Spurgeon, Bijandra Kumar
Underlying Substrate Effect On Electrochemical Activity For Hydrogen Evolution Reaction With Low-Platinum-Loaded Catalysts, Baleeswaraiah Muchharla, Peter V. Sushko, Kishor K. Sadasivuni, Wei Cao, Akash Tomar, Hani Elsayed-Ali, Adetayo Adedeji, Abdennaceur Karoui, Joshua M. Spurgeon, Bijandra Kumar
Electrical & Computer Engineering Faculty Publications
Platinum is known as the best catalyst for the hydrogen evolution reaction (HER) but the scarcity and high cost of Pt limit its widespread applicability. Herein, the role of the underlying substrate on the HER activity of dispersed Pt atoms is uncovered. A direct current magnetron sputtering technique is utilized to deposit transition metal (TM) thin films of W, Ti, and Ta as underlying substrates for extremely low loading of Pt (
Broadband Dielectric Spectroscopic Detection Of Ethanol: A Side-By-Side Comparison Of Zno And Hkust-1 Mofs As Sensing Media, Papa K. Amoah, Zeinab Mohammed Hassan, Pengtao Lin, Engelbert Redel, Helmut Baumgart, Yaw S. Obeng
Broadband Dielectric Spectroscopic Detection Of Ethanol: A Side-By-Side Comparison Of Zno And Hkust-1 Mofs As Sensing Media, Papa K. Amoah, Zeinab Mohammed Hassan, Pengtao Lin, Engelbert Redel, Helmut Baumgart, Yaw S. Obeng
Electrical & Computer Engineering Faculty Publications
The most common gas sensors are based on chemically induced changes in electrical resistivity and necessarily involve making imperfect electrical contacts to the sensing materials, which introduce errors into the measurements. We leverage thermal- and chemical-induced changes in microwave propagation characteristics (i.e., S-parameters) to compare ZnO and surface-anchored metal-organic-framework (HKUST-1 MOF) thin films as sensing materials for detecting ethanol vapor, a typical volatile organic compound (VOC), at low temperatures. We show that the microwave propagation technique can detect ethanol at relatively low temperatures (<100 >°C), and afford new mechanistic insights that are inaccessible with the traditional dc-resistance-based measurements. In addition, …
Solution Atomic Layer Deposition Of Smooth, Continuous, Crystalline Metal-Organic Framework Thin Films, Maïssa K.S. Barr, Soheila Nadiri, Dong-Hui Chen, Peter G. Weidler, Sebastian Bochmann, Helmut Baumgart, Julien Bachmann, Engelbert Redel
Solution Atomic Layer Deposition Of Smooth, Continuous, Crystalline Metal-Organic Framework Thin Films, Maïssa K.S. Barr, Soheila Nadiri, Dong-Hui Chen, Peter G. Weidler, Sebastian Bochmann, Helmut Baumgart, Julien Bachmann, Engelbert Redel
Electrical & Computer Engineering Faculty Publications
For the first time, a procedure has been established for the growth of surface-anchored metal–organic framework (SURMOF) copper(II) benzene-1,4-dicarboxylate (Cu-BDC) thin films of thickness control with single molecule accuracy. For this, we exploit the novel method solution atomic layer deposition (sALD). The sALD growth rate has been determined at 4.5 Å per cycle. The compact and dense SURMOF films grown at room temperature by sALD possess a vastly superior film thickness uniformity than those deposited by conventional solution-based techniques, such as dipping and spraying while featuring clear crystallinity from 100 nm thickness. The highly controlled layer-by-layer growth mechanism of sALD …
Charge Transport, Conductivity And Seebeck Coefficient In Pristine And Tcnq Loaded Preferentially Grown Metal Organic Frameworks, Xin Chen, Kai Zhang, Zeinab Mohammed Hassan, Engelbert Redel, Helmut Baumgart
Charge Transport, Conductivity And Seebeck Coefficient In Pristine And Tcnq Loaded Preferentially Grown Metal Organic Frameworks, Xin Chen, Kai Zhang, Zeinab Mohammed Hassan, Engelbert Redel, Helmut Baumgart
Electrical & Computer Engineering Faculty Publications
This investigation on Metal-Organic Framework (MOF) HUKUST-1 films focuses on comparing the undoped pristine state and with the case of doping by TCNQ infiltration of the MOF pore structure. We have determined the temperature dependent charge transport and p-type conductivity for HKUST-1 films. Furthermore, the electrical conductivity and the current-voltage characteristics have been characterized in detail. Because the most common forms of MOFs, bulk MOF powders, do not lend themselves easily to electrical characterization investigations, here in this study the electrical measurements were performed on dense, compact surface-anchored metal-organic framework (SURMOF) films. These monolithic, well-defined, and (001) preferentially oriented MOF …
Generation Of Excited Species In A Streamer Discharge, Shirshak K. Dhali
Generation Of Excited Species In A Streamer Discharge, Shirshak K. Dhali
Electrical & Computer Engineering Faculty Publications
At or near atmospheric pressure, most transient discharges, particularly in molecular gases or gas mixture containing molecular gases, result in a space charge dominated transport called a streamer discharge. The excited species generation in such discharges forms the basis for plasma chemistry in most technological applications. In this paper, we simulate the propagation of streamers in atmospheric pressure N2 to understand the energy partitioning in the formation of various excited species and compare the results to a uniform Townsend discharge. The model is fully two-dimensional with azimuthal symmetry. The results show a significantly larger fraction of the energy goes …
Gold/Qds-Embedded-Ceria Nanoparticles: Optical Fluorescence Enhancement As A Quenching Sensor, Nader Shehata, Effat Samir, Ishac Kandas
Gold/Qds-Embedded-Ceria Nanoparticles: Optical Fluorescence Enhancement As A Quenching Sensor, Nader Shehata, Effat Samir, Ishac Kandas
Electrical & Computer Engineering Faculty Publications
This work focuses on improving the fluorescence intensity of cerium oxide (ceria) nanoparticles (NPs) through added plasmonic nanostructures. Ceria nanoparticles are fluorescent nanostructures which can emit visible fluorescence emissions under violet excitation. Here, we investigated different added plasmonic nanostructures, such as gold nanoparticles (Au NPs) and Cadmium sulfide/selenide quantum dots (CdS/CdSe QDs), to check the enhancement of fluorescence intensity emissions caused by ceria NPs. Different plasmonic resonances of both aforementioned nanostructures have been selected to develop optical coupling with both fluorescence excitation and emission wavelengths of ceria. In addition, different additions whether in-situ or post-synthesis have been investigated. We found …
Thermoelectric Porous Mof Based Hybrid Materials, Engelbert Redel, Helmut Baumgart
Thermoelectric Porous Mof Based Hybrid Materials, Engelbert Redel, Helmut Baumgart
Electrical & Computer Engineering Faculty Publications
Porous hybrid materials and MOF (Metal-Organic-Framework) films represent modern designer materials that exhibit many requirements of a near ideal and tunable future thermoelectric (TE) material. In contrast to traditional semiconducting bulk TE materials, porous hybrid MOF templates can be used to overcome some of the constraints of physics in bulk TE materials. These porous hybrid systems are amenable for simulation and modeling to design novel optimized electron-crystal phonon-glass materials with potentially very high ZT (figure of merit) numbers. Porous MOF and hybrid materials possess an ultra-low thermal conductivity, which can be further modulated by phonon engineering within their complex porous …
Effect Of Layer Thickness On Structural, Morphological And Superconducting Properties Of Nb3Sn Films Fabricated By Multilayer Sequential Sputtering, M. N. Sayeed, U. Pudasaini, C. E. Reece, G. V. Eremeev, H. E. Elsayed-Ali
Effect Of Layer Thickness On Structural, Morphological And Superconducting Properties Of Nb3Sn Films Fabricated By Multilayer Sequential Sputtering, M. N. Sayeed, U. Pudasaini, C. E. Reece, G. V. Eremeev, H. E. Elsayed-Ali
Electrical & Computer Engineering Faculty Publications
Superconducting Nb3Sn films can be synthesized by controlling the atomic concentration of Sn. Multilayer sequential sputtering of Nb and Sn thin films followed by high temperature annealing is considered as a method to fabricate Nb3Sn films, where the Sn composition of the deposited films can be controlled by the thickness of alternating Nb and Sn layers. We report on the structural, morphological and superconducting properties of Nb3Sn films fabricated by multilayer sequential sputtering of Nb and Sn films on sapphire substrates followed by annealing at 950 °C for 3 h. We have investigated the …
Observation Of Reduced Thermal Conductivity In A Metal-Organic Framework Due To The Presence Of Adsorbates, Hasan Babaei, Mallory E. Decoster, Minyoung Jeong, Zeinab M. Hassan, Timur Islamoglu, Helmut Baumgart, Alan J.H. Mcgaughey, Engelbert Redel, Omar K. Farha, Patrick E. Hopkins, Jonathan A. Malen, Christopher E. Wilmer
Observation Of Reduced Thermal Conductivity In A Metal-Organic Framework Due To The Presence Of Adsorbates, Hasan Babaei, Mallory E. Decoster, Minyoung Jeong, Zeinab M. Hassan, Timur Islamoglu, Helmut Baumgart, Alan J.H. Mcgaughey, Engelbert Redel, Omar K. Farha, Patrick E. Hopkins, Jonathan A. Malen, Christopher E. Wilmer
Electrical & Computer Engineering Faculty Publications
Whether the presence of adsorbates increases or decreases thermal conductivity in metal-organic frameworks (MOFs) has been an open question. Here we report observations of thermal transport in the metal-organic framework HKUST-1 in the presence of various liquid adsorbates: water, methanol, and ethanol. Experimental thermoreflectance measurements were performed on single crystals and thin films, and theoretical predictions were made using molecular dynamics simulations. We find that the thermal conductivity of HKUST-1 decreases by 40 – 80% depending on the adsorbate, a result that cannot be explained by effective medium approximations. Our findings demonstrate that adsorbates introduce additional phonon scattering in HKUST-1, …
A Review: Thermal Stability Of Methylammonium Lead Halide Based Perovskite Solar Cells, Tanzila Tasnim Ava, Abdullah Al Mamun, Sylvain Marsillac, Gon Namkoong
A Review: Thermal Stability Of Methylammonium Lead Halide Based Perovskite Solar Cells, Tanzila Tasnim Ava, Abdullah Al Mamun, Sylvain Marsillac, Gon Namkoong
Electrical & Computer Engineering Faculty Publications
Perovskite solar cells have achieved photo-conversion efficiencies greater than 20%, making them a promising candidate as an emerging solar cell technology. While perovskite solar cells are expected to eventually compete with existing silicon-based solar cells on the market, their long-term stability has become a major bottleneck. In particular, perovskite films are found to be very sensitive to external factors such as air, UV light, light soaking, thermal stress and others. Among these stressors, light, oxygen and moisture-induced degradation can be slowed by integrating barrier or interface layers within the device architecture. However, the most representative perovskite absorber material, CH3 …
Microstructural Evaluation Of Aluminium Alloy A365 T6 In Machining Operation, Bankole I. Oladapo, S. Abolfazl Zahedi, Francis T. Omigbodun, Edwin A. Oshin, Victor A. Adebiyi, Olaoluwa B. Malachi
Microstructural Evaluation Of Aluminium Alloy A365 T6 In Machining Operation, Bankole I. Oladapo, S. Abolfazl Zahedi, Francis T. Omigbodun, Edwin A. Oshin, Victor A. Adebiyi, Olaoluwa B. Malachi
Electrical & Computer Engineering Faculty Publications
The optimum cutting parameters such as cutting depth, feed rate, cutting speed and magnitude of the cutting force for A356 T6 was determined concerning the microstructural detail of the material. Novel test analyses were carried out, which include mechanical evaluation of the materials for density, glass transition temperature, tensile and compression stress, frequency analysis and optimisation as well as the functional analytic behaviour of the samples. The further analytical structure of the particle was performed, evaluating the surface luminance structure and the profile structure. The cross-sectional filter profile of the sample was extracted, and analyses of Firestone curve for the …
N-I-P Nanocrystalline Hydrogenated Silicon Solar Cells With Rf-Magnetron Sputtered Absorbers, Dipendra Adhikari, Maxwell M. Junda, Corey R. Grice, Sylvain X. Marsillac, Robert W. Collins, Nikolas J. Podraza
N-I-P Nanocrystalline Hydrogenated Silicon Solar Cells With Rf-Magnetron Sputtered Absorbers, Dipendra Adhikari, Maxwell M. Junda, Corey R. Grice, Sylvain X. Marsillac, Robert W. Collins, Nikolas J. Podraza
Electrical & Computer Engineering Faculty Publications
Nanocrystalline hydrogenated silicon (nc-Si:H) substrate configuration n-i-p solar cells have been fabricated on soda lime glass substrates with active absorber layers prepared by plasma enhanced chemical vapor deposition (PECVD) and radio frequency magnetron sputtering. The cells with nanocrystalline PECVD absorbers and an untextured back reflector serve as a baseline for comparison and have power conversion efficiency near 6%. By comparison, cells with sputtered absorbers achieved efficiencies of about 1%. Simulations of external quantum efficiency (EQE) are compared to experimental EQE to determine a carrier collection probability gradient with depth for the device with the sputtered i-layer absorber. This incomplete …
Improved Gas Sensing Performance Of Ald Azo 3-D Coated Zno Nanorods, P. Lin, X. Chen, K. Zhang, H. Baumgart
Improved Gas Sensing Performance Of Ald Azo 3-D Coated Zno Nanorods, P. Lin, X. Chen, K. Zhang, H. Baumgart
Electrical & Computer Engineering Faculty Publications
This paper reports an enhancement on the sensing performance of ZnO nanorod ethanol sensors with a new approach by utilizing nested coatings of Aluminum doped ZnO (AZO) thin films by Atomic Layer Deposition (ALD) technology. ZnO nanorods were grown by the hydrothermal method with the ZnO seed layer synthesized on Silicon wafers by ALD. To enhance the sensing performance of ZnO nanorod ethanol sensors, multiple coated AZO thin film 3-D coatings were deposited on the surface of the intrinsic ZnO nanorods by ALD.To investigate the sensing performance of the ZnO nanorods sensor for the detection of ethanol vapor, a gas …
Characterization And Analysis Of Ultrathin Cigs Films And Solar Cells Deposited By 3-Stage Process, Grace Rajan, Krishna Aryal, Shankar Karki, Puruswottam Aryal, Robert W. Collins, Sylvain Marsillac
Characterization And Analysis Of Ultrathin Cigs Films And Solar Cells Deposited By 3-Stage Process, Grace Rajan, Krishna Aryal, Shankar Karki, Puruswottam Aryal, Robert W. Collins, Sylvain Marsillac
Electrical & Computer Engineering Faculty Publications
In view of the large-scale utilization of Cu(In,Ga)Se2 (CIGS) solar cells for photovoltaic application, it is of interest not only to enhance the conversion efficiency but also to reduce the thickness of the CIGS absorber layer in order to reduce the cost and improve the solar cell manufacturing throughput. In situ and real-time spectroscopic ellipsometry (RTSE) has been used conjointly with ex situ characterizations to understand the properties of ultrathin CIGS films. This enables monitoring the growth process, analyzing the optical properties of the CIGS films during deposition, and extracting composition, film thickness, grain size, and surface roughness which …
Novel Contact Materials For Improved Performance Cdte Solar Cells, Angus Rocket, Robert Collins, Sylvain Marsillac
Novel Contact Materials For Improved Performance Cdte Solar Cells, Angus Rocket, Robert Collins, Sylvain Marsillac
Electrical & Computer Engineering Faculty Publications
This program has explored a number of novel materials for contacts to CdTe solar cells in order to reduce the back contact Schottky barrier to zero and produce an ohmic contact. The project tested a wide range of potential contact materials including TiN, ZrN, CuInSe2:N, a-Si:H and alloys with C, and FeS2. Improved contacts were achieved with FeS2. As part of understanding the operation of the devices and controlling the deposition processes, a number of other important results were obtained. In the process of this project and following its conclusion it led to research …
Light Soaking Phenomena In Organic-Inorganic Mixed Halide Perovskite Single Crystals, Hye Ryung Byun, Dae Young Park, Hye Min Oh, Gon Namkoong, Mun Seok Jeong
Light Soaking Phenomena In Organic-Inorganic Mixed Halide Perovskite Single Crystals, Hye Ryung Byun, Dae Young Park, Hye Min Oh, Gon Namkoong, Mun Seok Jeong
Electrical & Computer Engineering Faculty Publications
Recently, organic inorganic mixed halide perovskite (MAPbX3; MA = CH3NH3+, X = Cl-, Br-, or I-) single crystals with low defect densities have been highlighted as candidate materials for high-efficiency photovoltaics and optoelectronics. Here we report the optical and structural investigations of mixed halide perovskite (MAPbBr3-xIx) single crystals. Mixed halide perovskite single crystals showed strong light soaking phenomena with light illumination conditions that were correlated to the trapping and detrapping events from defect sites. By systematic investigation with optical analysis, we found that the …
Impact Of Trucking Network Flow On Preferred Biorefinery Locations In The Southern United States, Timothy M. Young, Lee D. Han, James H. Perdue, Stephanie R. Hargrove, Frank M. Guess, Xia Huang, Chung-Hao Chen
Impact Of Trucking Network Flow On Preferred Biorefinery Locations In The Southern United States, Timothy M. Young, Lee D. Han, James H. Perdue, Stephanie R. Hargrove, Frank M. Guess, Xia Huang, Chung-Hao Chen
Electrical & Computer Engineering Faculty Publications
The impact of the trucking transportation network flow was modeled for the southern United States. The study addresses a gap in existing research by applying a Bayesian logistic regression and Geographic Information System (GIS) geospatial analysis to predict biorefinery site locations. A one-way trucking cost assuming a 128.8 km (80-mile) haul distance was estimated by the Biomass Site Assessment model. The "median family income," "timberland annual growth-to-removal ratio," and "transportation delays" were significant in determining mill location. Transportation delays that directly impacted the costs of trucking are presented. A logistic model with Bayesian inference was used to identify preferred site …
Simulation Study Of Hemt Structures With Hfo2 Cap Layer For Mitigating Inverse Piezoelectric Effect Related Device Failures, Deepthi Nagulapally, Ravi P. Joshi, Aswini Pradhan
Simulation Study Of Hemt Structures With Hfo2 Cap Layer For Mitigating Inverse Piezoelectric Effect Related Device Failures, Deepthi Nagulapally, Ravi P. Joshi, Aswini Pradhan
Electrical & Computer Engineering Faculty Publications
The Inverse Piezoelectric Effect (IPE) is thought to contribute to possible device failure of GaN High Electron Mobility Transistors (HEMTs). Here we focus on a simulation study to probe the possible mitigation of the IPE by reducing the internal electric fields and related elastic energy through the use of high-k materials. Inclusion of a HfO2 "cap layer" above the AlGaN barrier particularly with a partial mesa structure is shown to have potential advantages. Simulations reveal even greater reductions in the internal electric fields by using "field plates" in concert with high-k oxides
Polarization Of Bi2te3 Thin Film In A Floating-Gate Capacitor Structure, Hui Yuan, Kai Zhang, Haitao Li, Hao Zhu, John E. Bonevich, Helmut Baumgart, Curt A. Richter, Qiliang Li
Polarization Of Bi2te3 Thin Film In A Floating-Gate Capacitor Structure, Hui Yuan, Kai Zhang, Haitao Li, Hao Zhu, John E. Bonevich, Helmut Baumgart, Curt A. Richter, Qiliang Li
Electrical & Computer Engineering Faculty Publications
Metal-Oxide-Semiconductor (MOS) capacitors with Bi2Te3 thin film sandwiched and embedded inside the oxide layer have been fabricated and studied. The capacitors exhibit ferroelectric-like hysteresis which is a result of the robust, reversible polarization of the Bi2Te3 thin film while the gate voltage sweeps. The temperature-dependent capacitance measurement indicates that the activation energy is about 0.33 eV for separating the electron and hole pairs in the bulk of Bi2Te3, and driving them to either the top or bottom surface of the thin film. Because of the fast polarization speed, potentially excellent …
Stm Study Of Pulsed Laser Assisted Growth Of Ge Quantum Dot On Si(1 0 0)-(2 × 1), Ali Orguz Er, Hani E. Elsayed-Ali
Stm Study Of Pulsed Laser Assisted Growth Of Ge Quantum Dot On Si(1 0 0)-(2 × 1), Ali Orguz Er, Hani E. Elsayed-Ali
Electrical & Computer Engineering Faculty Publications
Ge quantum dot formation on Si(1 0 0)-(2 × 1) by nanosecond pulsed laser deposition under laser excitation was investigated. Scanning tunneling microscopy was used to probe the growth mode and morphology. Excitation was performed during deposition using laser energy density of 25-100 mJ/cm 2. Faceted islands were achieved at a substrate temperature of ∼250 °C only when using laser excitation. The island morphology changes with increased laser excitation energy density although the faceting of the individual islands remains the same. The size of the major length of islands increases with the excitation laser energy density. A purely electronic …
Physical Analysis Of Vo2 Films Grown By Atomic Layer Deposition And Rf Magnetron Sputtering, Madhavi Tangirala, Kai Zhang, David Nminibapiel, Venkateswara Pallem, Christian Dussarrat, Wei Cao, Thomas N. Adam, Corbet S. Johnson, Hani E. Elsayed-Ali, Helmut Baumgart
Physical Analysis Of Vo2 Films Grown By Atomic Layer Deposition And Rf Magnetron Sputtering, Madhavi Tangirala, Kai Zhang, David Nminibapiel, Venkateswara Pallem, Christian Dussarrat, Wei Cao, Thomas N. Adam, Corbet S. Johnson, Hani E. Elsayed-Ali, Helmut Baumgart
Electrical & Computer Engineering Faculty Publications
Among the many vanadium suboxides and different stoichiometries, VO2 has received considerable attention due to its remarkable metal-insulator transition (MIT) behavior, which causes a significant reversible change in its electrical and optical properties occurring across the phase transition at 67°C. The initially amorphous VO2 thin films were fabricated by the emerging, Atomic Layer Deposition (ALD) technique with (tetrakis[ethylmethylamino]vanadium) {V(NEtMe)4} as precursor and H2O vapor as oxidation agent. For benchmarking we have also used the RF Magnetron Sputtering technique to deposit metallic vanadium thin films, which were later oxidized during furnace annealing. Post annealing of …
Atmospheric Pressure He-Air Plasma Jet: Breakdown Process And Propagation Phenomenon, Asma Begum, Mounir Laroussi, Mohammad Rasel Pervez
Atmospheric Pressure He-Air Plasma Jet: Breakdown Process And Propagation Phenomenon, Asma Begum, Mounir Laroussi, Mohammad Rasel Pervez
Electrical & Computer Engineering Faculty Publications
In this paper He-discharge (plasma jet/bullet) in atmospheric pressure air and its progression phenomenon has been studied experimentally using ICCD camera, optical emission spectroscopy (OES) and calibrated dielectric probe measurements. The repetitive nanosecond pulse has applied to a plasma pencil to generate discharge in the helium gas channel. The discharge propagation speed was measured from the ICCD images. The axial electric field distribution in the plasma jet is inferred from the optical emission spectroscopic data and from the probe measurement. The correlation between the jet velocities, jet length with the pulse duration is established. It shows that the plasma jet …
Growth Analysis Of (Ag,Cu)Inse2 Thin Films Via Real Time Spectroscopic Ellipsometry, S. A. Little, V. Ranjan, R. W. Collins, S. Marsillac
Growth Analysis Of (Ag,Cu)Inse2 Thin Films Via Real Time Spectroscopic Ellipsometry, S. A. Little, V. Ranjan, R. W. Collins, S. Marsillac
Electrical & Computer Engineering Faculty Publications
In situ and ex situ characterization methods have been applied to investigate the properties of (Ag,Cu)InSe2 (ACIS) thin films. Data acquired from real time spectroscopic ellipsometry (RTSE) experiments were analyzed to extract the evolution of the nucleating, bulk, and surface roughness layer thicknesses. The evolution of these layer thicknesses suggests a transition from Volmer-Weber to Stranski-Krastanov type behavior when Cu is replaced by Ag. The complex dielectric functions of ACIS at both deposition and room temperature as a function of film composition were also extracted from the RTSE data, enabling parameterization of the alloy optical properties.
Analysis Of Interband, Intraband, And Plasmon Polariton Transitions In Silver Nanoparticle Films Via In Situ Real-Time Spectroscopic Ellipsometry, S. A. Little, R. W. Collins, S. Marsillac
Analysis Of Interband, Intraband, And Plasmon Polariton Transitions In Silver Nanoparticle Films Via In Situ Real-Time Spectroscopic Ellipsometry, S. A. Little, R. W. Collins, S. Marsillac
Electrical & Computer Engineering Faculty Publications
The dielectric function of Ag nanoparticle films, deduced from an analysis of in situ real-time spectroscopic ellipsometry (RTSE) measurements, is found to evolve with time during deposition in close consistency with the film structure, deduced in the same RTSE analysis. In the nucleation regime, the intraband dielectric function component is absent and plasmon polariton behavior dominates. Only at nuclei contact, does the intraband amplitude appear, increasing above zero. Both intraband and plasmon amplitudes coexist during surface smoothening associated with coalescence. The intraband relaxation time increases rapidly after surface smoothening is complete, also in consistency with the thin film structural evolution.
Low Temperature Epitaxial Growth Of Ge Quantum Dot On Si (100) - (2×1) By Femtosecond Laser Excitation, Ali Oguz Er, Wei Ren, Hani E. Elsayed-Ali
Low Temperature Epitaxial Growth Of Ge Quantum Dot On Si (100) - (2×1) By Femtosecond Laser Excitation, Ali Oguz Er, Wei Ren, Hani E. Elsayed-Ali
Electrical & Computer Engineering Faculty Publications
Low temperature epitaxy of Ge quantum dots on Si (100) - (2×1) by femtosecond pulsed laser deposition under femtosecond laser excitation was investigated. Reflection high-energy electron diffraction and atomic force microscopy were used to analyze the growth mode and morphology. Epitaxial growth was achieved at ∼70 °C by using femtosecond laser excitation of the substrate. A purely electronic mechanism of enhanced surface diffusion of the Ge adatoms is proposed. © 2011 American Institute of Physics. [doi:10.1063/1.3537813]
Precise Control Of Highly Ordered Arrays Of Nested Semiconductor/Metal Nanotubes, Diefeng Gu, Helmut Baumgart, Kandabara Tapily, Pragya Shrestha, Gon Namkoong, Xianyu Ao, Frank Müller
Precise Control Of Highly Ordered Arrays Of Nested Semiconductor/Metal Nanotubes, Diefeng Gu, Helmut Baumgart, Kandabara Tapily, Pragya Shrestha, Gon Namkoong, Xianyu Ao, Frank Müller
Electrical & Computer Engineering Faculty Publications
Lithographically defined microporous templates in conjunction with the atomic layer deposition (ALD) technique enable remarkable control of complex novel nested nanotube structures. So far three-dimensional control of physical process parameters has not been fully realized with high precision resolution, and requires optimization in order to achieve a wider range of potential applications. Furthermore, the combination of composite insulating oxide layers alternating with semiconducting layers and metals can provide various types of novel applications and eventually provide unique and advanced levels of multifunctional nanoscale devices. Semiconducting TiO2 nanotubes have potential applications in photovoltaic devices. The combination of nanostructured semiconducting materials …
Nonuniformity In Lattice Contraction Of Bismuth Nanoclusters Heated Near Its Melting Point, A. Esmail, M. Abdel-Fattah, Hani E. Elsayed-Ali
Nonuniformity In Lattice Contraction Of Bismuth Nanoclusters Heated Near Its Melting Point, A. Esmail, M. Abdel-Fattah, Hani E. Elsayed-Ali
Electrical & Computer Engineering Faculty Publications
The structural properties of bismuth nanoclusters were investigated with transmission high-energy electron diffraction from room temperature up to 525 ± 6 K. The Bi nanoclusters were fabricated by thermal evaporation at room temperature on transmission electron microscope grids coated with an ultrathin carbon film, followed by thermal and femtosecond laser annealing. The annealed sample had an average cluster size of ∼14 nm along the minor axis and ∼16 nm along the major axis. The Debye temperature of the annealed nanoclusters was found to be 53 ± 6 K along the [012] direction and 86 ± 9 K along the [110] …
Rf And Structural Characterization Of Srf Thin Films, A.M. Valente-Feliciano, H.L. Phillips, C.E. Reece, J. Spradlin, X. Zhao, D. Gu, H. Baumgart, D. Beringer, R.A. Lukaszew, B. Xiao, K. Seo
Rf And Structural Characterization Of Srf Thin Films, A.M. Valente-Feliciano, H.L. Phillips, C.E. Reece, J. Spradlin, X. Zhao, D. Gu, H. Baumgart, D. Beringer, R.A. Lukaszew, B. Xiao, K. Seo
Electrical & Computer Engineering Faculty Publications
In the past years, energetic vacuum deposition methods have been developed in different laboratories to improve Nb/Cu technology for superconducting cavities. JLab is pursuing energetic condensation deposition via Electron Cyclotron Resonance. As part of this study, the influence of the deposition energy on the material and RF properties of the Nb thin film is investigated. The film surface and structure analyses are conducted with various techniques like X-ray diffraction, Transmission Electron Microscopy, Auger Electron Spectroscopy and RHEED. The microwave properties of the films are characterized on 50 mm disk samples with a 7.5 GHz surface impedance characterization system. This paper …
Electronic And Structural Properties Of Molybdenum Thin Films As Determined By Real Time Spectroscopic Ellipsometry, J. D. Walker, H. Khatri, V. Ranjan, Jian Li, R. W. Collins, S. Marsillac
Electronic And Structural Properties Of Molybdenum Thin Films As Determined By Real Time Spectroscopic Ellipsometry, J. D. Walker, H. Khatri, V. Ranjan, Jian Li, R. W. Collins, S. Marsillac
Electrical & Computer Engineering Faculty Publications
Walker, J.D., Khatri, H., Ranjan, V., Li, J., Collins, R.W., & Marsillac, S. (2009). Electronic and structural properties of molybdenum thin films as determined by real-time spectroscopic ellipsometry. Applied Physics Letters, 94(14). doi: 10.1063/1.3117222
Activation Energy Of Surface Diffusion And Terrace Width Dynamics During The Growth Of In (4×3) On Si (100) - (2×1) By Femtosecond Pulsed Laser Deposition, M. A. Hafez, H. E. Elsayed-Ali
Activation Energy Of Surface Diffusion And Terrace Width Dynamics During The Growth Of In (4×3) On Si (100) - (2×1) By Femtosecond Pulsed Laser Deposition, M. A. Hafez, H. E. Elsayed-Ali
Electrical & Computer Engineering Faculty Publications
The nucleation and growth of indium on a vicinal Si (100) - (2×1) surface at high temperature by femtosecond pulsed laser deposition was investigated by in situ reflection high energy electron diffraction (RHEED). RHEED intensity relaxation was observed for the first ∼2 ML during the growth of In (4×3) by step flow. From the temperature dependence of the rate of relaxation, an activation energy of 1.4±0.2 eV of surface diffusion was determined. The results indicate that indium small clusters diffused to terrace step edges with a diffusion frequency constant of (1.0±0.1) × 1011 s-1. The RHEED specular …