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Vanderbilt University
1.
Greaving, Jason James.
Fabrication and Characterization of Diamond Thin Films as Nanocarbon Transistor Substrates.
Degree: MS, Interdisciplinary Materials Science, 2013, Vanderbilt University
URL: http://hdl.handle.net/1803/12896 
► As the limits of silicon based transistors are approached, carbon nano-electronics represents a promising alternative to traditional semiconducting transistors. Silicon-dioxide hinders the electron transport through…
(more)
▼ As the limits of silicon based transistors are approached, carbon nano-electronics represents a promising alternative to traditional semiconducting transistors. Silicon-dioxide hinders the electron transport through carbon transistors as well as obscuring information about their transport. Diamond is a promising new dielectric for use with carbon transistors which may remedy these problems.
This project is concerned with the development of diamond thin films for use as dielectric substrates in FETs. Diamond films were grown, trying to minimize thickness and conductivity. Diamond was chosen as a material due to its wide band gap, as well as its radiation hardness. This would allow inspection of the effects of radiation on the transistor elements in our FETs. These films were characterized using a number of techniques to assess their viability as dielectric substrates. Once the viability was established, the surface was modified to create an optimal interface for the transistors that would be transferred to the surface. Finally, transfer of carbon based transistors was attempted.
Advisors/Committee Members: Norman Tolk (committee member), Jim Davidson (Committee Chair).
Subjects/Keywords: diamond; transistor; CVD
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APA (6th Edition):
Greaving, J. J. (2013). Fabrication and Characterization of Diamond Thin Films as Nanocarbon Transistor Substrates. (Thesis). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/12896
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Greaving, Jason James. “Fabrication and Characterization of Diamond Thin Films as Nanocarbon Transistor Substrates.” 2013. Thesis, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/12896.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Greaving, Jason James. “Fabrication and Characterization of Diamond Thin Films as Nanocarbon Transistor Substrates.” 2013. Web. 15 Apr 2021.
Vancouver:
Greaving JJ. Fabrication and Characterization of Diamond Thin Films as Nanocarbon Transistor Substrates. [Internet] [Thesis]. Vanderbilt University; 2013. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/12896.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Greaving JJ. Fabrication and Characterization of Diamond Thin Films as Nanocarbon Transistor Substrates. [Thesis]. Vanderbilt University; 2013. Available from: http://hdl.handle.net/1803/12896
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Vanderbilt University
2.
Garnett, Joy Carleen.
Maxwell Fisheye Lens As A Waveguide Crossing For Integrated Photonics.
Degree: MS, Interdisciplinary Materials Science, 2013, Vanderbilt University
URL: http://hdl.handle.net/1803/12460
► Integrated silicon (Si) photonics represents one of the key technologies for developing compact high speed optical systems for computing and telecommunications. In such systems, electric…
(more)
▼ Integrated silicon (Si) photonics represents one of the key technologies for developing compact high speed optical systems for computing and telecommunications. In such systems, electric buses are replaced with integrated Si waveguides which transport light across the chip. In order to implement high density networks, it is inevitable that waveguides will need to be crossed to transport information across orthogonal directions. However, when two or more waveguides cross, light is scattered due to the abrupt change in the modal index resulting in losses of up to 40 percent. This loss occurs to both the environment as well as the overlapped waveguide, causing cross-talk into the other channel resulting in false signals.
Current Si based waveguide crosses require either a large footprint or are limited in the number of waveguides that can be crossed simultaneously. In this work, we develop integrated gradient index elements based on the Maxwell Fisheye (MFE) to provide low-loss and massively parallel optical waveguide crossings. To realize a crossing, waveguides which are modal index matched to the MFE are coupled across the lens wherein the output of one waveguide is imaged to the input of its partner on the opposite side. Based on this methodology, we present full-wave modeling of the device demonstrating a 0.1 dB loss (97.7% transmission) per
crossing for an overall waveguide cross footprint of 28.26 square microns, among the most efficient designs to date. We also propose how this device can be realized using smoothly tapered Si waveguides to provide
the required 2D gradient refractive index profile.
Advisors/Committee Members: Dr. Jason Valentine (Committee Chair), Dr. Norman Tolk (Committee Chair).
Subjects/Keywords: integrated optics; Maxwell Fisheye; gradient optics; metamaterials; gradient lens
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APA (6th Edition):
Garnett, J. C. (2013). Maxwell Fisheye Lens As A Waveguide Crossing For Integrated Photonics. (Thesis). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/12460
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Garnett, Joy Carleen. “Maxwell Fisheye Lens As A Waveguide Crossing For Integrated Photonics.” 2013. Thesis, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/12460.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Garnett, Joy Carleen. “Maxwell Fisheye Lens As A Waveguide Crossing For Integrated Photonics.” 2013. Web. 15 Apr 2021.
Vancouver:
Garnett JC. Maxwell Fisheye Lens As A Waveguide Crossing For Integrated Photonics. [Internet] [Thesis]. Vanderbilt University; 2013. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/12460.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Garnett JC. Maxwell Fisheye Lens As A Waveguide Crossing For Integrated Photonics. [Thesis]. Vanderbilt University; 2013. Available from: http://hdl.handle.net/1803/12460
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Vanderbilt University
3.
Wiggins, Brenden Wayne.
Investigations of the semi-insulating LiIn_(1-x)Ga_(x)Se_(2) solid solution for neutron detection.
Degree: PhD, Physics, 2016, Vanderbilt University
URL: http://hdl.handle.net/1803/13465
► Synthesis and single crystal growth methods for Li-containing chalogenides, specifically LiIn1-xGaxSe2, single crystals are discussed. This study elucidates the possibility of improving neutron detection by…
(more)
▼ Synthesis and single crystal growth methods for Li-containing chalogenides, specifically LiIn1-xGaxSe2, single crystals are discussed. This study elucidates the possibility of improving neutron detection by reducing the indium capture contribution; with the incorporation of the lithium-6 isotope, gallium substitution may overcome the neutron detection efficiency limitation of 6LiInSe2 due to predominant capture by the indium-115 isotope. As a figure of merit, the ternary parent compounds LiInSe2 and LiGaSe2 were included in this study. Quality crystals can be obtained utilizing the vertical Bridgman method producing quaternary compounds with tunable optical properties. Quaternary crystals of varying quality depending on gallium concentration, approximately 5 x 5 x 2 mm3 or larger in volume, were harvested, analyzed and revealed tunable absorption characteristics between 2.8-3.4 eV. The electronic structure and optical properties of the LiIn1–xGaxSe2 (x=0, 0.25, 0.5, 0.75, 1) solid solution were studied by density functional theory (DFT) with pure functionals. The exchange-correlation is treated within the local density approximation (LDA) and generalized-gradient approximation (GGA). The electronic structures for each respective compound are discussed in detail. Calculations reveal that gallium incorporation can be used to tune the optical-electrical properties of the solid solution and correlates with the lattice parameter. The band gap trend of the LiIn1–xGaxSe2 system follows a nonlinear behavior between the LiInSe2 and LiGaSe2 ternary boundaries. The bowing parameter is estimated to be on the order of 0.1–0.3eV at the -point. Low-temperature optical absorption revealed a 30% change in the temperature dependence of the band gap for the intermediate compound LiIn0.6Ga0.4Se2 compared to ternary boundaries and suggests the heat capacity to be another control element through strain.
Advisors/Committee Members: Norman Tolk (committee member), Kalman Varga (committee member), Keivan Stassun (Committee Chair), Arnold Burger (Committee Chair), Ashley Stowe (Committee Chair).
Subjects/Keywords: crystal growth; optical; scintillation; lithium; neutron; DFT
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APA (6th Edition):
Wiggins, B. W. (2016). Investigations of the semi-insulating LiIn_(1-x)Ga_(x)Se_(2) solid solution for neutron detection. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/13465
Chicago Manual of Style (16th Edition):
Wiggins, Brenden Wayne. “Investigations of the semi-insulating LiIn_(1-x)Ga_(x)Se_(2) solid solution for neutron detection.” 2016. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/13465.
MLA Handbook (7th Edition):
Wiggins, Brenden Wayne. “Investigations of the semi-insulating LiIn_(1-x)Ga_(x)Se_(2) solid solution for neutron detection.” 2016. Web. 15 Apr 2021.
Vancouver:
Wiggins BW. Investigations of the semi-insulating LiIn_(1-x)Ga_(x)Se_(2) solid solution for neutron detection. [Internet] [Doctoral dissertation]. Vanderbilt University; 2016. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/13465.
Council of Science Editors:
Wiggins BW. Investigations of the semi-insulating LiIn_(1-x)Ga_(x)Se_(2) solid solution for neutron detection. [Doctoral Dissertation]. Vanderbilt University; 2016. Available from: http://hdl.handle.net/1803/13465
Vanderbilt University
4.
Krejci, Alexander James.
Studying and Controlling Order Within Nanoparticle Monolayers Fabricated Through Electrophoretic Deposition.
Degree: PhD, Physics, 2013, Vanderbilt University
URL: http://hdl.handle.net/1803/12917
► Electrophoretic deposition (EPD) is introduced in a new light: as a process for the fabrication nanoparticle monolayers (NPMs).Using EPD, NPMs are fabricated from a variety…
(more)
▼ Electrophoretic deposition (EPD) is introduced in a new light: as a process for the fabrication nanoparticle monolayers (NPMs).Using EPD, NPMs are fabricated from a variety of different types of NPs such as iron oxide, cobalt ferrite, TiO2, indium tin oxide, and more, and these NPMs display local order between NPs As order between NPs within an array has been shown to affect the properties of said array, the mechanisms that generate order are investigated.
Order within two systems is studied, one incorporating superparamagnetic iron oxide NPs and the other incorporating ferromagnetic cobalt ferrite NPs. In the iron oxide NPMs, magnetic dipole interactions are shown to have little effect on the order within the NPM. We observe that the order within the iron oxide NPM is generated during the drying of the film after NPs have deposited. From this it is inferred that capillary forces likely generate order. Within the cobalt ferrite NPMs, the magnetic easy axes of the NPs are observed to align, indicating that magnetic interactions likely generate order.
Advisors/Committee Members: Shane Hutson (committee member), Janet Macdonald (committee member), Norman Tolk (committee member), Kalman Varga (committee member), James H. Dickerson (Committee Chair).
Subjects/Keywords: monolayer; nanoparticles; iron oxide; hexagonal packing; x-ray scattering; voronoi; order parameter; electrophoretic; cobalt ferrite; superparamagnetism; ferromagnetism
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APA (6th Edition):
Krejci, A. J. (2013). Studying and Controlling Order Within Nanoparticle Monolayers Fabricated Through Electrophoretic Deposition. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/12917
Chicago Manual of Style (16th Edition):
Krejci, Alexander James. “Studying and Controlling Order Within Nanoparticle Monolayers Fabricated Through Electrophoretic Deposition.” 2013. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/12917.
MLA Handbook (7th Edition):
Krejci, Alexander James. “Studying and Controlling Order Within Nanoparticle Monolayers Fabricated Through Electrophoretic Deposition.” 2013. Web. 15 Apr 2021.
Vancouver:
Krejci AJ. Studying and Controlling Order Within Nanoparticle Monolayers Fabricated Through Electrophoretic Deposition. [Internet] [Doctoral dissertation]. Vanderbilt University; 2013. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/12917.
Council of Science Editors:
Krejci AJ. Studying and Controlling Order Within Nanoparticle Monolayers Fabricated Through Electrophoretic Deposition. [Doctoral Dissertation]. Vanderbilt University; 2013. Available from: http://hdl.handle.net/1803/12917
Vanderbilt University
5.
Russakoff, Arthur Gerald.
The Interaction of Small Molecules and Short Intense Laser Fields.
Degree: PhD, Physics, 2015, Vanderbilt University
URL: http://hdl.handle.net/1803/15339
► The advent of short intense laser fields promises unprecedented quantum control over chemical reactions. Laser fields of femtosecond duration are now readily available on the…
(more)
▼ The advent of short intense laser fields promises unprecedented quantum control over chemical reactions. Laser fields of femtosecond duration are now readily available on the tabletop. In this dissertation we investigate the interaction of these laser fields with small molecules through simulations using the time-dependent density-functional theory (TDDFT) coupled with the Ehrenfest dynamics. We also investigate time propagation algorithms to improve the computational efficiency of solving the time-dependent Kohn-Sham equations of the TDDFT. In particular we construct the time propagator with two subspace methods, using either the Lanczos basis or the eigenbasis of the Kohn-Sham Hamiltonian, and compare the accuracy and computational efficiency of these methods to the highly accurate fourth-order Taylor expansion of the propagator. In the application of the simulations we consider a range of laser durations and intensities, the effects of molecular alignment, the coupling of the dynamics between the electrons and the nuclei, and the role of electronic excitation. The systems examined are acetylene (C2H2) and ethylene (C2H4) interacting with linearly polarized pulses, and circularly polarized pulses interacting with acetylene and the hydrogen molecule (H2).
Advisors/Committee Members: Norman Tolk (committee member), Greg walker (committee member), Volker Oberacker (committee member), Richard Haglund (committee member), Kalman Varga (Committee Chair).
Subjects/Keywords: molecular dynamics; ehrenfest dynamics; time dependent density functional theory; physics; femtosecond; attosecond; density functional theory
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APA (6th Edition):
Russakoff, A. G. (2015). The Interaction of Small Molecules and Short Intense Laser Fields. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/15339
Chicago Manual of Style (16th Edition):
Russakoff, Arthur Gerald. “The Interaction of Small Molecules and Short Intense Laser Fields.” 2015. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/15339.
MLA Handbook (7th Edition):
Russakoff, Arthur Gerald. “The Interaction of Small Molecules and Short Intense Laser Fields.” 2015. Web. 15 Apr 2021.
Vancouver:
Russakoff AG. The Interaction of Small Molecules and Short Intense Laser Fields. [Internet] [Doctoral dissertation]. Vanderbilt University; 2015. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/15339.
Council of Science Editors:
Russakoff AG. The Interaction of Small Molecules and Short Intense Laser Fields. [Doctoral Dissertation]. Vanderbilt University; 2015. Available from: http://hdl.handle.net/1803/15339
Vanderbilt University
6.
Paxton, William Francis.
Thermionic Electron Emission Properties of Nitrogen-Incorporated Polycrystalline Diamond Films.
Degree: PhD, Electrical Engineering, 2013, Vanderbilt University
URL: http://hdl.handle.net/1803/11438
► Thermionic energy conversion (TEC) is a potentially practical method for the efficient conversion of thermal energy directly into electrical energy. Standard TEC configurations consist of…
(more)
▼ Thermionic energy conversion (TEC) is a potentially practical method for the efficient conversion of thermal energy directly into electrical energy. Standard TEC configurations consist of a cathode and an anode separated by some interelectrode gap and electrical connections between the two. When thermal energy is imparted to the cathode, electrons with sufficient energy are thermionically emitted and traverse the interelectrode gap. These electrons are then collected by the cooler anode and cycled back to the cathode through an external load. From this simple description, it is clear that the performance of a TEC device depends on the cathode’s ability to undergo thermionic emission which leads to the purpose of this research.
Diamond has several favorable material properties for use in TEC such as low to negative electron affinity, high thermal conductivity, and radiation tolerance. This research investigated diamond’s thermionic emission properties such that an all-diamond TEC device could be realized. A fabrication method was first developed to deposit nitrogen-incorporated diamond thermionic cathodes using microwave plasma-enhanced chemical vapor deposition. Raman spectroscopy indicated that the diamond samples were predominantly diamond with minimal other carbonaceous content. A testing apparatus was then designed capable of accurately studying the thermionic emission operation of the fabricated diamond cathodes in both vacuum and various low pressure gaseous environments. Potential failure mechanisms of diamond cathodes that would inhibit implementation into practical thermionic devices were then identified. To overcome these failure mechanisms, portions of the research were directed toward a better understanding of the emission process from diamond as well as factors that influence it. Finally, new methods were developed that allowed for increased performance, reliability, and operational lifetime. The results obtained in this research were then used to predict the performance of an all-diamond thermionic energy converter.
Advisors/Committee Members: Weng P. Kang (committee member), Norman Tolk (committee member), Greg Walker (committee member), Mike Alles (committee member), Jim Davidson (Committee Chair).
Subjects/Keywords: Diamond; Thermionic Emission; Energy Conversion; Nitrogen
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APA (6th Edition):
Paxton, W. F. (2013). Thermionic Electron Emission Properties of Nitrogen-Incorporated Polycrystalline Diamond Films. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/11438
Chicago Manual of Style (16th Edition):
Paxton, William Francis. “Thermionic Electron Emission Properties of Nitrogen-Incorporated Polycrystalline Diamond Films.” 2013. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/11438.
MLA Handbook (7th Edition):
Paxton, William Francis. “Thermionic Electron Emission Properties of Nitrogen-Incorporated Polycrystalline Diamond Films.” 2013. Web. 15 Apr 2021.
Vancouver:
Paxton WF. Thermionic Electron Emission Properties of Nitrogen-Incorporated Polycrystalline Diamond Films. [Internet] [Doctoral dissertation]. Vanderbilt University; 2013. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/11438.
Council of Science Editors:
Paxton WF. Thermionic Electron Emission Properties of Nitrogen-Incorporated Polycrystalline Diamond Films. [Doctoral Dissertation]. Vanderbilt University; 2013. Available from: http://hdl.handle.net/1803/11438
Vanderbilt University
7.
Gilbert Corder, Stephanie Nicole.
Ultrafast relaxation dynamics and optical properties of GaAs and GaAs-based heterostructures.
Degree: PhD, Interdisciplinary Materials Science, 2014, Vanderbilt University
URL: http://hdl.handle.net/1803/14568
► Three previously unreported photo-carrier relaxation pathways are presented and discussed in GaAs-based systems. In bulk GaAs, a transient bleach of the spin-split exciton transition 1s->2p…
(more)
▼ Three previously unreported photo-carrier relaxation pathways are presented and discussed in GaAs-based systems. In bulk GaAs, a transient bleach of the spin-split exciton transition 1s->2p is reported following photo-excitation at low temperatures and is likely caused by final state blocking of the 2p_1 exciton level. The bleach of the 1s->2p_-1 transition is delayed with respect to that of the free carriers and 1s->2p_+1, suggesting electronic relaxation occurs through two simultaneous mechanisms: elastic scattering between quantized conduction band states and spin-dependent relaxation through the 2p_1 exciton states. For ErAs:GaAs composites, the response at short time delays is completely dependent on the occupation of the interface trap state between the ErAs nanoparticles and the GaAs matrix. Occupation of the interface state depends on the photo-carrier energy, carrier density, and trap density. Carrier scattering from the interface state plays a large role in the response as it prevents full relaxation of the system on ultrashort timescales. The composite ErAs:GaAs systems also exhibit an oscillatory response highly suggestive of surface plasmon polaritons at the interface between the semi-metallic ErAs and semiconducting GaAs, which couple to the GaAs phonon modes. The oscillation frequencies are observed to follow the same trend with volume fraction as the static absorption resonance peaks, suggesting different nanoparticle size distributions exist with different ErAs incorporation.
Advisors/Committee Members: Jimmy Davidson (committee member), Kalman Varga (committee member), Richard Haglund (committee member), Timothy Hanusa (committee member), Norman Tolk (Committee Chair).
Subjects/Keywords: Ultrafast dynamics; gallium arsenide; carrier relaxation; spectroscopy; semiconductors; photonics; optics
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APA (6th Edition):
Gilbert Corder, S. N. (2014). Ultrafast relaxation dynamics and optical properties of GaAs and GaAs-based heterostructures. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/14568
Chicago Manual of Style (16th Edition):
Gilbert Corder, Stephanie Nicole. “Ultrafast relaxation dynamics and optical properties of GaAs and GaAs-based heterostructures.” 2014. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/14568.
MLA Handbook (7th Edition):
Gilbert Corder, Stephanie Nicole. “Ultrafast relaxation dynamics and optical properties of GaAs and GaAs-based heterostructures.” 2014. Web. 15 Apr 2021.
Vancouver:
Gilbert Corder SN. Ultrafast relaxation dynamics and optical properties of GaAs and GaAs-based heterostructures. [Internet] [Doctoral dissertation]. Vanderbilt University; 2014. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/14568.
Council of Science Editors:
Gilbert Corder SN. Ultrafast relaxation dynamics and optical properties of GaAs and GaAs-based heterostructures. [Doctoral Dissertation]. Vanderbilt University; 2014. Available from: http://hdl.handle.net/1803/14568
Vanderbilt University
8.
Marvel, Robert Edward.
Physics and Processing of Vanadium Dioxide for Optical Devices.
Degree: PhD, Interdisciplinary Materials Science, 2016, Vanderbilt University
URL: http://hdl.handle.net/1803/10429
► This dissertation examines the fundamental physical properties and material processing methods required to design and fabricate the next generation of optical modulators based on the…
(more)
▼ This dissertation examines the fundamental physical properties and material processing methods required to design and fabricate the next generation of optical modulators based on the vanadium dioxide metal-insulator transition. All-optical devices capable of performing at GHz speeds, which are only limited by the laser pulse duration, were designed, fabricated and tested. Broad-band pump-probe experiments examined the femtosecond phase transition dynamics in vanadium dioxide when excited at a range of wavelengths from 400 nm to 1500 nm and indicate that THz modulation speeds could be achieved. In addition, fabrication methods and doping were explored as paths to tune the phase transition properties. The optical modulator design and material performance are discussed in the context of current state-of-the-art technology.
Advisors/Committee Members: Timothy Hanusa (committee member), Norman Tolk (committee member), Bridget Rogers (committee member), Richard Haglund (Committee Chair), Jason Valentine (Committee Chair).
Subjects/Keywords: laser spectroscopy; optical devices; vanadium dioxide; optical properties
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APA (6th Edition):
Marvel, R. E. (2016). Physics and Processing of Vanadium Dioxide for Optical Devices. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/10429
Chicago Manual of Style (16th Edition):
Marvel, Robert Edward. “Physics and Processing of Vanadium Dioxide for Optical Devices.” 2016. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/10429.
MLA Handbook (7th Edition):
Marvel, Robert Edward. “Physics and Processing of Vanadium Dioxide for Optical Devices.” 2016. Web. 15 Apr 2021.
Vancouver:
Marvel RE. Physics and Processing of Vanadium Dioxide for Optical Devices. [Internet] [Doctoral dissertation]. Vanderbilt University; 2016. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/10429.
Council of Science Editors:
Marvel RE. Physics and Processing of Vanadium Dioxide for Optical Devices. [Doctoral Dissertation]. Vanderbilt University; 2016. Available from: http://hdl.handle.net/1803/10429
Vanderbilt University
9.
Musho, Terence David.
Quantum Simulation of Nanoscale Transport in Direct Energy Conversion Materials: From Thermal-Field Emitters to Thermoelectrics.
Degree: PhD, Interdisciplinary Materials Science, 2012, Vanderbilt University
URL: http://hdl.handle.net/1803/11426
► In the ongoing struggle to resolve our current energy crisis, many agencies and researchers have spearheaded the application of direct energy conversion materials, such as…
(more)
▼ In the ongoing struggle to resolve our current energy crisis, many agencies and researchers have spearheaded the application of direct energy conversion materials, such as thermoelectric and thermionic devices for waste heat recovery and power generation. However, the current state-of-the-art direct energy conversion materials are plagued by extremely low efficiencies that prevent a widespread solution. Recent effort to improve the efficiencies of these direct energy conversion materials has demonstrated a drastic increase through the inclusion of nanoscale features. With new advances in nanoscale materials comes the need for new models that can capture the underlying physics. Thus, this research has developed a necessary tool and a unique modeling approach (based on NEGF quantum simulations) that couples both the electrical and thermal response of nanoscale transport accounting for both the dissipative interactions of electron-phonon and phonon-phonon scattering. Through the aid of high performance computing techniques, the models developed in this research are able to explore the large design space of nano-structured thermoelectrics and thermionic materials. The models allow computational predictions to drive innovation for new, optimized, direct energy conversion materials.
A specific device innovation that has come from this research is the development of variably spaced superlattice (VSSL) devices, which are the next progression in band engineering thermoelectric materials. Computational findings of VSSL materials predict a seven times increase in ZT at room temperature when compared to traditional superlattice devices. Other thermoelectric materials studied include nanocrystalline composites (NCC) which were predicted to outperform equivalent superlattice structures as a results of decreases electron filtering. In addition to thermoelectric materials, this research has developed a quantum modeling technique to investigate and optimize nano-tipped thermionic and thermal-field devices. Results have provided incite into the applicability of Richardson's theory in characterizing the emission from wide-band gap thermionic materials. Ultimately, the quantum models developed in this research are a necessary tool for understanding nanoscale transport and innovating new nanostructured materials.
Advisors/Committee Members: Alvin Strauss (committee member), Kalman Varga (committee member), Norman Tolk (committee member), Ron Schrimpf (committee member), D. Greg Walker (Committee Chair).
Subjects/Keywords: nanostructure; thermoelectric; thermionic; direct energy conversion; NEGF; quantum; nanoscale
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APA (6th Edition):
Musho, T. D. (2012). Quantum Simulation of Nanoscale Transport in Direct Energy Conversion Materials: From Thermal-Field Emitters to Thermoelectrics. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/11426
Chicago Manual of Style (16th Edition):
Musho, Terence David. “Quantum Simulation of Nanoscale Transport in Direct Energy Conversion Materials: From Thermal-Field Emitters to Thermoelectrics.” 2012. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/11426.
MLA Handbook (7th Edition):
Musho, Terence David. “Quantum Simulation of Nanoscale Transport in Direct Energy Conversion Materials: From Thermal-Field Emitters to Thermoelectrics.” 2012. Web. 15 Apr 2021.
Vancouver:
Musho TD. Quantum Simulation of Nanoscale Transport in Direct Energy Conversion Materials: From Thermal-Field Emitters to Thermoelectrics. [Internet] [Doctoral dissertation]. Vanderbilt University; 2012. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/11426.
Council of Science Editors:
Musho TD. Quantum Simulation of Nanoscale Transport in Direct Energy Conversion Materials: From Thermal-Field Emitters to Thermoelectrics. [Doctoral Dissertation]. Vanderbilt University; 2012. Available from: http://hdl.handle.net/1803/11426
Vanderbilt University
10.
Nicholl, Ryan John Thomas.
Non-Hookean Mechanics of Crystalline Membranes.
Degree: PhD, Physics, 2017, Vanderbilt University
URL: http://hdl.handle.net/1803/13212
► Graphene is the simplest crystalline membrane and therefore the ideal material to test mechanics at the ultimate, atomic thickness limit. It is well known from…
(more)
▼ Graphene is the simplest crystalline membrane and therefore the ideal material to test mechanics at the ultimate, atomic thickness limit. It is well known from experiments performed at high stress that graphene is one of the stiffest materials ever studied. At the same time, any thin material is always crumpled. In the case of graphene, crumpling can arise from static wrinkling or thermal fluctuations (flexural phonons). In this dissertation, we experimentally studied the effect of this crumpling on stretching and bending graphene. First, we developed a method to measure the mechanical response of suspended graphene at low stress. We found that the stretching stiffness of graphene is reduced by up to 10 times because of crumpling. We probed the contribution to stretching due to flexural phonons through temperature-dependent measurements. We probed the contribution due to static wrinkling by measuring changes in mechanical response when modifying membrane geometry in-situ. From this, we found that static wrinkles are the dominant source of crumpling. Second, we observed nonlinear stress-strain curves while applying high stress to our suspended graphene samples. We studied this nonlinearity in detail by comparing two complementary measurements of strain obtained from interferometric profilometry and Raman spectroscopy. This allowed us to measure the strength of crumpling and compare our data to recent theory. We found that stress/strain relationship in crumpled in graphene is described by a non-linear Hooke’s law with an exponent of ~0.14, which is good agreement with theory. Finally, we developed process flows to fabricate graphene cantilevers, stable in vacuum and air. We estimated that their bending rigidities are at least 100 times higher than what is expected for flat graphene. It is likely that this increase in the bending rigidity is also associated with crumpling.
Advisors/Committee Members: Greg Walker (committee member), Kalman Varga (committee member), Norman Tolk (committee member), Nickolay Lavrik (committee member), Kirill Bolotin (Committee Chair).
Subjects/Keywords: mechanics; crumpling; 2D materials; graphene
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APA (6th Edition):
Nicholl, R. J. T. (2017). Non-Hookean Mechanics of Crystalline Membranes. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/13212
Chicago Manual of Style (16th Edition):
Nicholl, Ryan John Thomas. “Non-Hookean Mechanics of Crystalline Membranes.” 2017. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/13212.
MLA Handbook (7th Edition):
Nicholl, Ryan John Thomas. “Non-Hookean Mechanics of Crystalline Membranes.” 2017. Web. 15 Apr 2021.
Vancouver:
Nicholl RJT. Non-Hookean Mechanics of Crystalline Membranes. [Internet] [Doctoral dissertation]. Vanderbilt University; 2017. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/13212.
Council of Science Editors:
Nicholl RJT. Non-Hookean Mechanics of Crystalline Membranes. [Doctoral Dissertation]. Vanderbilt University; 2017. Available from: http://hdl.handle.net/1803/13212
Vanderbilt University
11.
Jarrahi, Zeynab.
Effect of Substrate and Morphology on the Relaxation Dynamics of Carriers and Phonons in Graphene.
Degree: PhD, Physics, 2016, Vanderbilt University
URL: http://hdl.handle.net/1803/12764
► Graphene, the two dimensional allotrope of the carbon family, exhibits extremely high electron mobility, thermal conductivity and fascinating ultrafast carrier-carrier and carrier-phonons interactions. However, being…
(more)
▼ Graphene, the two dimensional allotrope of the carbon family, exhibits extremely high electron mobility, thermal conductivity and fascinating ultrafast carrier-carrier and carrier-phonons interactions. However, being merely one atom thick, introducing a substrate or altering the morphological form of graphene can affect both its equilibrium and non-equilibrium dynamics and inevitably influence the performance of graphene-based devices. In the first part of this dissertation, we use fluence and energy dependent ultrafast pump-probe spectroscopy to determine the effect of substrate on the femtosecond transient electron and phonon dynamics of single layer graphene transferred on sapphire, quartz and single crystalline diamond. Using a multi-channel cooling theory involving surface phonons of the substrate, intrinsic optical phonons of graphene and the corresponding competing scattering rates, we proceed to explain the strong substrate-dependent dynamics of graphene observed in our experiments. We stipulate that the sub-nm surface roughness of the studied substrates, enable a strong coupling between the phototexcited carriers in graphene and the surface vibrational modes of the polar substrates. We show that this additional energy relaxation pathway can compete with the intrinsic phonons of graphene to not only reduce the transient electron temperature but also the carrier and optical phonon lifetimes in graphene.
In the second part of this dissertation, we introduce a methodology for fabrication of a novel quasi-one dimensional morphology of graphene called curled graphene ribbons (CGR). Our gate dependent scanning photocurrent measurements reveal an astounding two orders of magnitude enhancement in the photocurrent response of CGR which we attributed to the photothermoelectric effect (PTE).Understanding how the equilibrium and non-equilibrium dynamics of carriers and phonons in graphene are altered by the interface or morphology and deciphering the various energy relaxation pathways, will pave the way towards realization of higher performance graphene based electronics and optoelectronics.
Advisors/Committee Members: Kalman Varga (committee member), Volker Oberacker (committee member), Jim Davidson (committee member), Richard Mu (committee member), Norman Tolk (Committee Chair).
Subjects/Keywords: Interface; Surface phonons; Optoelectronics; Graphene; Ultrafast Spectroscopy
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APA (6th Edition):
Jarrahi, Z. (2016). Effect of Substrate and Morphology on the Relaxation Dynamics of Carriers and Phonons in Graphene. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/12764
Chicago Manual of Style (16th Edition):
Jarrahi, Zeynab. “Effect of Substrate and Morphology on the Relaxation Dynamics of Carriers and Phonons in Graphene.” 2016. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/12764.
MLA Handbook (7th Edition):
Jarrahi, Zeynab. “Effect of Substrate and Morphology on the Relaxation Dynamics of Carriers and Phonons in Graphene.” 2016. Web. 15 Apr 2021.
Vancouver:
Jarrahi Z. Effect of Substrate and Morphology on the Relaxation Dynamics of Carriers and Phonons in Graphene. [Internet] [Doctoral dissertation]. Vanderbilt University; 2016. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/12764.
Council of Science Editors:
Jarrahi Z. Effect of Substrate and Morphology on the Relaxation Dynamics of Carriers and Phonons in Graphene. [Doctoral Dissertation]. Vanderbilt University; 2016. Available from: http://hdl.handle.net/1803/12764
Vanderbilt University
12.
Wade, Travis Charles.
TEM Study of Nanostructured Cold Cathode Diamond Field Emitter Tips.
Degree: PhD, Interdisciplinary Materials Science, 2011, Vanderbilt University
URL: http://hdl.handle.net/1803/14355
► This dissertation furthers the understanding of diamond as a material for cold cathode field emission. Although diamond has proven to be an excellent emitter with…
(more)
▼ This dissertation furthers the understanding of diamond as a material for cold cathode field emission. Although diamond has proven to be an excellent emitter with orders of magnitude more current at lower fields than competing technologies, fabrication yield has been a persistent issue. Irregularities in emission behavior between tips have historically been attributed to anomalies in the fabrication process which results in “sharp” or “less sharp” diamond tips. However, differences are observed in electron emission thresholds even between tips that appear by conventional analysis to be equally well formed. By enabling analysis of the emitter surface and sub-surface, the methods developed herein permit analysis of diamond tip growth and provide a feedback mechanism for optimization of field emitter properties. This dissertation contains first-time measurements of sharp-tipped diamond cold cathode field emitters imaged by transmission electron microscopy. These preliminary observations correlate hitherto unknown diamond cold cathode emitter nanostructure with emission behavior.
Advisors/Committee Members: Weng P Kang (committee member), Kalman Varga (committee member), Charles Lukehart (committee member), Greg Walker (committee member), Jim Davidson (Committee Chair), Norman Tolk (Committee Chair).
Subjects/Keywords: CVD; field emission; nanostructured; nanoscience; cold cathode; FIB; diamond; TEM
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APA (6th Edition):
Wade, T. C. (2011). TEM Study of Nanostructured Cold Cathode Diamond Field Emitter Tips. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/14355
Chicago Manual of Style (16th Edition):
Wade, Travis Charles. “TEM Study of Nanostructured Cold Cathode Diamond Field Emitter Tips.” 2011. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/14355.
MLA Handbook (7th Edition):
Wade, Travis Charles. “TEM Study of Nanostructured Cold Cathode Diamond Field Emitter Tips.” 2011. Web. 15 Apr 2021.
Vancouver:
Wade TC. TEM Study of Nanostructured Cold Cathode Diamond Field Emitter Tips. [Internet] [Doctoral dissertation]. Vanderbilt University; 2011. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/14355.
Council of Science Editors:
Wade TC. TEM Study of Nanostructured Cold Cathode Diamond Field Emitter Tips. [Doctoral Dissertation]. Vanderbilt University; 2011. Available from: http://hdl.handle.net/1803/14355
Vanderbilt University
13.
Bennett, William Geoffrey.
Single Event Upset Mechanisms in Emerging Memory Technologies.
Degree: PhD, Electrical Engineering, 2014, Vanderbilt University
URL: http://hdl.handle.net/1803/12858
► The commercial memory industry, now more than ever, is looking at CMOS Flash alternatives to provide continued scaling of data storage elements. Meanwhile, radiation tolerant…
(more)
▼ The commercial memory industry, now more than ever, is looking at CMOS Flash alternatives to provide continued scaling of data storage elements. Meanwhile, radiation tolerant memory researchers and designers are investigating these new technologies to see if they could provide higher reliability in radiation environments compared to their CMOS counterparts. New reliability concerns can arise with continued scaling and the introduction of new materials. Presented are various single event effects (SEE) for a Hf/HfO2 1T1R resistive random access memory (RRAM), as well as SEE in highly scaled nodes with tightly space junctions. Single-event upsets (SEUs), where incident ions change the state of a stored bit in memory (1 to 0, or 0 to 1) were first discovered in RRAMs using backside two photon absorption at
Vanderbilt University. SEUs occur when charge generated in the access transistor generate a voltage pulse across the RRAM capable of writing to the cell. For verification of this susceptibility, ions from Lawrence Berkeley National Lab’s 88” cyclotron were used. This allowed for the demonstration of not only SEUs, but also multiple-event upsets (MEUs), where cumulative effects from multiple ions add together to produce a single upset. Tightly spaced silicon junctions were also investigated, showing a strong interaction between adjacent junctions and a higher likelihood of interaction when using alternate SEU testing sources. These results culminated in modeling work that estimated the susceptibility of future RRAM technology nodes, and the results show that they may be more tolerant than many unhardened memory cells.
Advisors/Committee Members: Dr. Robert Reed (committee member), Dr. Robert Weller (committee member), Dr. Arthur Witulski (committee member), Dr. Norman Tolk (committee member), Dr. Ronald Schrimpf (Committee Chair).
Subjects/Keywords: single event upsets; multiple event upsets; RRAM; resistive random access memory; charge sharing; charge competition; multiple node charge collection; two photon absorption; heavy ion irradiation
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APA (6th Edition):
Bennett, W. G. (2014). Single Event Upset Mechanisms in Emerging Memory Technologies. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/12858
Chicago Manual of Style (16th Edition):
Bennett, William Geoffrey. “Single Event Upset Mechanisms in Emerging Memory Technologies.” 2014. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/12858.
MLA Handbook (7th Edition):
Bennett, William Geoffrey. “Single Event Upset Mechanisms in Emerging Memory Technologies.” 2014. Web. 15 Apr 2021.
Vancouver:
Bennett WG. Single Event Upset Mechanisms in Emerging Memory Technologies. [Internet] [Doctoral dissertation]. Vanderbilt University; 2014. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/12858.
Council of Science Editors:
Bennett WG. Single Event Upset Mechanisms in Emerging Memory Technologies. [Doctoral Dissertation]. Vanderbilt University; 2014. Available from: http://hdl.handle.net/1803/12858
Vanderbilt University
14.
Jones, Jennifer Ann.
Linear and Nonlinear Optical Study of Multilayer Ferroelectric Polymer Systems.
Degree: PhD, Interdisciplinary Materials Science, 2015, Vanderbilt University
URL: http://hdl.handle.net/1803/10863
► Multilayer polymer systems are a focus of increasing research effort motivated by the possibility to realize compact and flexible energy storage and energy harvesting devices.…
(more)
▼ Multilayer polymer systems are a focus of increasing research effort motivated by the possibility to realize compact and flexible energy storage and energy harvesting devices. However, the performance and stability of these polymer systems are highly dependent on temperature. In this study the structure of monolayer ferroelectric polyvinylidene fluoride (PVDF) thin films and the relaxation dynamics as a function of temperature are characterized using XRD, FTIR and second harmonic generation (SHG). Multilayered ferroelectric polyvinylidene fluoride (PVDF) systems are fabricated using enabling technology in co-extrusion for increased energy storage and energy harvesting efficiency as well as increased stability at elevated temperatures. To understand the physics of why these multilayered systems perform better than single layer PVDF characterization techniques using second harmonic generation (SHG), electric field induced second harmonic (EFISH) and Raman laser spectroscopy are developed. Results show that the combination of Raman and SHG is a very sensitive, non-destructive and versatile technique that can be used to study the ferroelectric and structural properties of these systems. The addition of the EFISH technique allows the interrogation of structural and dielectric properties within individual layers and at the interfaces.
Advisors/Committee Members: Dr. Jimmy Davidson (committee member), Dr. Deyu Li (committee member), Dr. Eva Harth (committee member), Dr. Kane Jennings (Committee Chair), Dr. Norman Tolk (Committee Chair).
Subjects/Keywords: ferroelectric; SHG; thin film; polymer
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APA (6th Edition):
Jones, J. A. (2015). Linear and Nonlinear Optical Study of Multilayer Ferroelectric Polymer Systems. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/10863
Chicago Manual of Style (16th Edition):
Jones, Jennifer Ann. “Linear and Nonlinear Optical Study of Multilayer Ferroelectric Polymer Systems.” 2015. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/10863.
MLA Handbook (7th Edition):
Jones, Jennifer Ann. “Linear and Nonlinear Optical Study of Multilayer Ferroelectric Polymer Systems.” 2015. Web. 15 Apr 2021.
Vancouver:
Jones JA. Linear and Nonlinear Optical Study of Multilayer Ferroelectric Polymer Systems. [Internet] [Doctoral dissertation]. Vanderbilt University; 2015. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/10863.
Council of Science Editors:
Jones JA. Linear and Nonlinear Optical Study of Multilayer Ferroelectric Polymer Systems. [Doctoral Dissertation]. Vanderbilt University; 2015. Available from: http://hdl.handle.net/1803/10863
Vanderbilt University
15.
Gregory, Justin Mark.
Effect of Electron and Phonon Excitation on the Optical Properties of Indirect Gap Semiconductors.
Degree: PhD, Interdisciplinary Materials Science, 2013, Vanderbilt University
URL: http://hdl.handle.net/1803/10889
► The interaction of electrons and phonons with the properties of semiconducting crystals continues to be a fascinating and highly fruitful field of study. This dissertation…
(more)
▼ The interaction of electrons and phonons with the properties of semiconducting crystals continues to be a fascinating and highly fruitful field of study. This dissertation addresses two research problems under the general heading of electron and phonon effects on the optical properties of indirect gap semiconductors.
The first problem concerns nonlinear (multi-photon) absorption in germanium crystals, a topic of interest for the telecommunications industry as well as to the basic scientist. Using a combination of infrared transmittance experiments and numerical analysis, the two- and three-photon absorption coefficients β and γ for germanium have been evaluated over the range of wavelengths from 2.8 µm to 5.2 μm. The ratios of the coefficients across the direct/indirect gap transitions and between the two-and three-photon cases, which are less susceptible to experimental uncertainties than the absolute coefficients, have also been determined. Comparison with theoretical studies shows excellent agreement.
The second problem addresses the optical characteristics of ion-bombarded diamond crystals, which is a swiftly developing field due to diamond’s current status as the material of choice for hosting photonic and quantum information devices. The ultrafast optical technique known as coherent acoustic phonon interferometry has been applied to He ion irradiated diamond crystals for the purpose of determining the optical modification induced by the implantation damage. The experimental results provide information about the variation at in the complex refractive indices of the implanted specimens as well as the variation in the photoelastic tensor. A simple phenomenological model quantitatively describing the damage-induced optical modification has been developed which accurately predicts the experimental observations, and may prove to be a useful tool for quantum device design.
Advisors/Committee Members: Jim Davidson (committee member), Leonard Feldman (committee member), Timothy Hanusa (committee member), Sokrates Pantelides (committee member), Ronald Schrimpf (committee member), Norman Tolk (Committee Chair).
Subjects/Keywords: ion implantation; diamond; multiphoton absorption; germanium; refractive index; photoelasticity
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APA (6th Edition):
Gregory, J. M. (2013). Effect of Electron and Phonon Excitation on the Optical Properties of Indirect Gap Semiconductors. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/10889
Chicago Manual of Style (16th Edition):
Gregory, Justin Mark. “Effect of Electron and Phonon Excitation on the Optical Properties of Indirect Gap Semiconductors.” 2013. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/10889.
MLA Handbook (7th Edition):
Gregory, Justin Mark. “Effect of Electron and Phonon Excitation on the Optical Properties of Indirect Gap Semiconductors.” 2013. Web. 15 Apr 2021.
Vancouver:
Gregory JM. Effect of Electron and Phonon Excitation on the Optical Properties of Indirect Gap Semiconductors. [Internet] [Doctoral dissertation]. Vanderbilt University; 2013. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/10889.
Council of Science Editors:
Gregory JM. Effect of Electron and Phonon Excitation on the Optical Properties of Indirect Gap Semiconductors. [Doctoral Dissertation]. Vanderbilt University; 2013. Available from: http://hdl.handle.net/1803/10889
Vanderbilt University
16.
Steigerwald, Andrew David.
Studies of radiation damaged gallium arsenide using coherent acoustic phonon spectroscopy.
Degree: PhD, Interdisciplinary Materials Science, 2010, Vanderbilt University
URL: http://hdl.handle.net/1803/12395
► The operation and properties of semiconductor devices depends critically on a material’s electronic structure. Point defects, such as vacancy and interstitial defects that arise from…
(more)
▼ The operation and properties of semiconductor devices depends critically on a material’s electronic structure. Point defects, such as vacancy and interstitial defects that arise from operation in radiative atmospheres or during less-than-ideal growth processes, have a significant influence on electronic material properties and tend to degrade device operation. Here we show that a novel ultrafast time-resolved pump-probe technique, known as coherent acoustic phonon spectroscopy, is capable of non-destructive, quantitative, depth-dependent measurement of point defect profiles arising from ion irradiation in gallium arsenide. In the CAP response, defects are observable through reduction of the CAP oscillation amplitude, which is demonstrated to be connected to a decrease in the photoelastic constant at the 1.42 eV GaAs band-edge caused by defect-induced lattice strain. Finally, we present theoretical calculations that support our proposed model and agree well with experimental observations
Advisors/Committee Members: Kalman Varga (committee member), Richard Mu (committee member), Sandra Rosenthal (committee member), Jim Davidson (committee member), Norman Tolk (Committee Chair).
Subjects/Keywords: ultrafast; nanoscale; picosecond ultrasonics; point defects
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APA (6th Edition):
Steigerwald, A. D. (2010). Studies of radiation damaged gallium arsenide using coherent acoustic phonon spectroscopy. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/12395
Chicago Manual of Style (16th Edition):
Steigerwald, Andrew David. “Studies of radiation damaged gallium arsenide using coherent acoustic phonon spectroscopy.” 2010. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/12395.
MLA Handbook (7th Edition):
Steigerwald, Andrew David. “Studies of radiation damaged gallium arsenide using coherent acoustic phonon spectroscopy.” 2010. Web. 15 Apr 2021.
Vancouver:
Steigerwald AD. Studies of radiation damaged gallium arsenide using coherent acoustic phonon spectroscopy. [Internet] [Doctoral dissertation]. Vanderbilt University; 2010. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/12395.
Council of Science Editors:
Steigerwald AD. Studies of radiation damaged gallium arsenide using coherent acoustic phonon spectroscopy. [Doctoral Dissertation]. Vanderbilt University; 2010. Available from: http://hdl.handle.net/1803/12395
Vanderbilt University
17.
Halabica, Andrej.
Coherent acoustic phonons in metal/dielectric superlattices.
Degree: PhD, Physics, 2009, Vanderbilt University
URL: http://hdl.handle.net/1803/14424
► Pulsed infrared laser annealing experiments on metal implanted dielectric matrices were performed, using a free electron laser as a source of infrared radiation at 8…
(more)
▼ Pulsed infrared laser annealing experiments on metal implanted
dielectric matrices were performed, using a free electron laser as a
source of infrared radiation at 8 and 9 *m wavelengths. This was
the first study where such wavelengths were used for laser annealing
of composite materials. Our results show that the annealing
successfully modified nanocomposites consisting of Au and Ag
nanoparticles embedded in a dielectric matrix. Fast nucleation and
growth of Au nanoparticles in both SiO2 and Al2O3 matrices
were observed, while nanoparticle dissolution due to this rapid
thermal annealing process was observed in Ag-implanted SiO2.
These experiments demonstrate the unique effects of fast thermal
heating of the matrix on the size and size distribution of embedded
metal nanoparticles, using photons with energies far below the bulk
bandgap of the matrix.
A set of composite materials in the form of Au/Al2O3
superlattices was also prepared using electron beam evaporation.
Time-resolved femtosecond laser spectroscopy was successfully
applied to study the vibrational properties of these multilayers. A
comprehensive experimental and computational study of the effects of
varying Au layer thickness on the excitability and detectability of
the first and second surface acoustic phonon mode was undertaken.
The frequency of these modes was compared to the theoretical
calculation and the slight differences were attributed to the effect
of the nanoparticle structure of the Au films, which was confirmed
using TEM and optical spectroscopy. In addition to the surface
modes, propagating phonon modes were observed in the Au(5
nm)/Al2O3(45 nm) superlattice. These belong to the lowest
minibranch of the zone-folded longitudinal phonon dispersion curve
and travel in the form of a propagating pulse, which is reflected at
the substrate and surface interfaces. By detecting two echoes of the
pulse, it was possible to experimentally determine the effective
sound velocity in the superlattice.
Advisors/Committee Members: Sharon Weiss (committee member), Robert Magruder (committee member), Norman Tolk (committee member), Sokrates Pantelides (committee member), Richard Haglund (Committee Chair).
Subjects/Keywords: laser annealing; superlattice; coherent acoustic phonons; surface modes; nanoparticles
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APA (6th Edition):
Halabica, A. (2009). Coherent acoustic phonons in metal/dielectric superlattices. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/14424
Chicago Manual of Style (16th Edition):
Halabica, Andrej. “Coherent acoustic phonons in metal/dielectric superlattices.” 2009. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/14424.
MLA Handbook (7th Edition):
Halabica, Andrej. “Coherent acoustic phonons in metal/dielectric superlattices.” 2009. Web. 15 Apr 2021.
Vancouver:
Halabica A. Coherent acoustic phonons in metal/dielectric superlattices. [Internet] [Doctoral dissertation]. Vanderbilt University; 2009. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/14424.
Council of Science Editors:
Halabica A. Coherent acoustic phonons in metal/dielectric superlattices. [Doctoral Dissertation]. Vanderbilt University; 2009. Available from: http://hdl.handle.net/1803/14424
Vanderbilt University
18.
Wang, Wei.
Carrier Dynamics at Si-Dielectric Interfaces Studied by Second-Harmonic-Generation.
Degree: PhD, Physics, 2002, Vanderbilt University
URL: http://hdl.handle.net/1803/14469
► This dissertation describes research on the application of intense, tunable, ultrafast lasers to studies of the silicon-dielectric system. Recently developed and now commercially available ultra-fast…
(more)
▼ This dissertation describes research on the application of intense, tunable, ultrafast lasers to studies of the silicon-dielectric system. Recently developed and now commercially available ultra-fast lasers are excellent tools for studying nonlinear optical effects in materials. Second-harmonic-generation (SHG) has come to be recognized as a uniquely useful nonlinear optical effect. For reasons of symmetry, SHG is sensitive to interfaces between materials with inversion symmetry. This technique yields rich information on electronic structure, local fields, symmetry and carrier dynamics at interfaces. It also has the advantages of being contactless and non-intrusive. It is therefore a promising tool for the investigation of mature Si-dielectric interfaces. In this thesis, we present first SHG measurements of the Si-high-k dielectric material system. Our data show features that are drastically different from the Si-SiO2 system. Unlike the Si-SiO2 system, where a rapid initial rise in SHG intensity is followed by a gradual increase until saturation, SHG from Si/ZrSiOx gradually decreases to a stable level after an initial quick rise. We attribute this difference to different carrier dynamics in these two systems. While in the SiO2 system, electron injection dominates the process, holes and electrons have a much more equal role in ZrSiOx. This arises from characteristically different band offset relationships in these two systems. Wavelength-dependent SHG measurements reveal a threshold of about 1.4 eV. A band diagram at the Si/ZrSiOx interface is then constructed with a conduction band offset of about 2.8 eV, which is well above the minimum 1 eV value determined by many calculations to prevent carrier tunneling. This lends strong support to ZrSiOx as a candidate for gate oxide in future generation semiconductor devices.
Advisors/Committee Members: Royal Albridge (committee member), Jim Davidson (committee member), Tom Weiler (committee member), Sokrates Pantelides (committee member), Norman Tolk (Committee Chair).
Subjects/Keywords: second-harmonic-generation (SHG); high-k dielectric; carrier dynamic; nonlinear optics; Si
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APA (6th Edition):
Wang, W. (2002). Carrier Dynamics at Si-Dielectric Interfaces Studied by Second-Harmonic-Generation. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/14469
Chicago Manual of Style (16th Edition):
Wang, Wei. “Carrier Dynamics at Si-Dielectric Interfaces Studied by Second-Harmonic-Generation.” 2002. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/14469.
MLA Handbook (7th Edition):
Wang, Wei. “Carrier Dynamics at Si-Dielectric Interfaces Studied by Second-Harmonic-Generation.” 2002. Web. 15 Apr 2021.
Vancouver:
Wang W. Carrier Dynamics at Si-Dielectric Interfaces Studied by Second-Harmonic-Generation. [Internet] [Doctoral dissertation]. Vanderbilt University; 2002. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/14469.
Council of Science Editors:
Wang W. Carrier Dynamics at Si-Dielectric Interfaces Studied by Second-Harmonic-Generation. [Doctoral Dissertation]. Vanderbilt University; 2002. Available from: http://hdl.handle.net/1803/14469
Vanderbilt University
19.
Miller, Jerome Keith.
Probing III-V semiconductor heterostructures using time resolved pump-probe techniques.
Degree: PhD, Physics, 2006, Vanderbilt University
URL: http://hdl.handle.net/1803/13931
► In this dissertation, we applied tunable, ultra-fast lasers along with a pump-probe experimental technique to study electron and phonon dynamics. With one channel, Second Harmonic…
(more)
▼ In this dissertation, we applied tunable, ultra-fast lasers along with a pump-probe experimental technique to study electron and phonon dynamics. With one channel, Second Harmonic Generation can be monitored, which is a contactless and non-invasive probe that provides time resolved information on carrier dynamics and transport near interfaces. With another channel, differential reflectivity can be monitored, which gives information on coherent longitudinal acoustic phonons as they propagate into the heterostructure.
We have studied ultra-fast carrier dynamics in GaAs/GaSb and GaAs/GaSb/InAs heterostructures using a pump-probe electric-field induced second harmonic (EFISH) generation technique. We observed a complicated evolution of the interfacial fields originating from the redistribution of carriers between the interfaces. The ability of the EFISH signal to monitor spatially separated regions makes pump-probe SHG a unique tool for studying relaxation and transport phenomena in multilayer semiconductor structures.
We report the first studies of long-lived oscillations in femtosecond optical pump-probe measurements on GaSb/GaAs systems. The oscillations arise from a photo-generated Coherent Longitudinal Acoustic Phonon (CLAP) wave, which travels from the top surface of GaSb across the interface into the GaAs substrate, thus providing information on the optical properties of the material as a function of time/depth. Wavelength-dependent studies of the oscillations near the bandgap of GaAs indicate strong correlations to the optical properties of GaAs.
We report the first use of CLAP waves to probe buried GaxIn1-xAs layers in GaAs. There are two features that can be observed when the CLAP wave enters the buried layer: (1) there is a reduction in the amplitude of the oscillations due to absorption of the probe light and (2) there is a phase change that is caused by the difference in the index of refraction and the speed of sound in GaAs and GaxIn 1-xAs. This technique is shown to be a new, non-invasive tool to measure layer thicknesses as a function of depth. A simple model has also been developed that satisfactorily characterizes our experimental results.
Advisors/Committee Members: Royal Albridge (committee member), Steven Csorna (committee member), Thomas Kephart (committee member), Ronald Schrimpf (committee member), Norman Tolk (Committee Chair).
Subjects/Keywords: Second Harmonic Generation; Phonon Dynamics; Differential Reflectivity; Pump-Probe; Ultra-fast; CLAP waves
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APA (6th Edition):
Miller, J. K. (2006). Probing III-V semiconductor heterostructures using time resolved pump-probe techniques. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/13931
Chicago Manual of Style (16th Edition):
Miller, Jerome Keith. “Probing III-V semiconductor heterostructures using time resolved pump-probe techniques.” 2006. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/13931.
MLA Handbook (7th Edition):
Miller, Jerome Keith. “Probing III-V semiconductor heterostructures using time resolved pump-probe techniques.” 2006. Web. 15 Apr 2021.
Vancouver:
Miller JK. Probing III-V semiconductor heterostructures using time resolved pump-probe techniques. [Internet] [Doctoral dissertation]. Vanderbilt University; 2006. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/13931.
Council of Science Editors:
Miller JK. Probing III-V semiconductor heterostructures using time resolved pump-probe techniques. [Doctoral Dissertation]. Vanderbilt University; 2006. Available from: http://hdl.handle.net/1803/13931
Vanderbilt University
20.
Kalavagunta, Aditya.
Understanding the impact of bulk traps on GaN HEMT DC and RF characteristics.
Degree: PhD, Electrical Engineering, 2009, Vanderbilt University
URL: http://hdl.handle.net/1803/11752
► The demand for high power high frequency semiconductor devices has led to the development of microwave power devices using GaN and SiC. AlGaN/GaN HEMTs have…
(more)
▼ The demand for high power high frequency semiconductor devices has led to the development of microwave power devices using GaN and SiC. AlGaN/GaN HEMTs have shown power densities of 9.8 W/mm at 8 GHz. Although these results are very encouraging, significant work needs to be done to improve performance. It is generally recognized that trapping effects limit the performance of these devices. In this dissertation we study the impact of bulk traps on three distinct characteristics of these devices. These 3 mechanisms are: degradation in the IV characteristics, self-heating and gate-lag.
Displacement-damage induced degradation in AlGaN/AlN/GaN HEMTs with polarization charge induced 2DEGs is examined using simulations and experiments. Carrier removal in the unintentionally doped AlGaN layer changes the space charge in the structure and this changes the band bending. The band bending decreases the 2DEG density, which in turn reduces the drain current in the device. The effect of the defect energy levels on the 2DEG density is also studied. The interplay between band bending, mobility degradation, and the charged defects is analyzed and quantified.
Experiments and TCAD simulations are used to study the relationship between bulk traps, self-heating and mobility degradation in AlGaN/AlN/GaN HEMTs. Bulk traps in the GaN channel region and other regions of the device degrade the 2DEG density and the mobility in the device. This in turn degrades the performance of the device. Mobility degradation is closely coupled with the self-heating in the device. The interplay between bulk traps, mobility degradation and self-heating is analyzed and quantified.
Experiments and simulations showing the impact of proton irradiation induced bulk traps on gate lag in AlGaN/AlN/GaN HEMTs are analyzed. Pre-existing donor-like surface traps in the gate-drain and source-gate access regions cause the majority of the gate-lag in the device. The simulations indicate that these traps at the AlGaN/Nitride surface are very close to the valence band. Gate lag increases with increased bulk traps. This is due to the reduction in the 2DEG density as a result of band bending and mobility degradation. The experiments and simulations did not indicate any substantial hot electron induced current collapse due to bulk traps.
Advisors/Committee Members: Dr Ron Schrimpf (committee member), Dr Dan Fleetwood (committee member), Dr Robert Weller (committee member), Dr Norman Tolk (committee member), Dr Robert Reed (Committee Chair).
Subjects/Keywords: bulk traps; HEMTs; gallium nitride; DC and RF characteristics; Modulation-doped field-effect transistors – Computer simulation; Gallium nitride
Record Details
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Record Details
Similar Records
Cite
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❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Kalavagunta, A. (2009). Understanding the impact of bulk traps on GaN HEMT DC and RF characteristics. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/11752
Chicago Manual of Style (16th Edition):
Kalavagunta, Aditya. “Understanding the impact of bulk traps on GaN HEMT DC and RF characteristics.” 2009. Doctoral Dissertation, Vanderbilt University. Accessed April 15, 2021.
http://hdl.handle.net/1803/11752.
MLA Handbook (7th Edition):
Kalavagunta, Aditya. “Understanding the impact of bulk traps on GaN HEMT DC and RF characteristics.” 2009. Web. 15 Apr 2021.
Vancouver:
Kalavagunta A. Understanding the impact of bulk traps on GaN HEMT DC and RF characteristics. [Internet] [Doctoral dissertation]. Vanderbilt University; 2009. [cited 2021 Apr 15].
Available from: http://hdl.handle.net/1803/11752.
Council of Science Editors:
Kalavagunta A. Understanding the impact of bulk traps on GaN HEMT DC and RF characteristics. [Doctoral Dissertation]. Vanderbilt University; 2009. Available from: http://hdl.handle.net/1803/11752
. 
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