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Full-Text Articles in Physics
Free Charge Carrier Properties In Two-Dimensional Materials And Monoclinic Oxides Studied By Optical Hall Effect, Sean Knight
Free Charge Carrier Properties In Two-Dimensional Materials And Monoclinic Oxides Studied By Optical Hall Effect, Sean Knight
Department of Electrical and Computer Engineering: Dissertations, Theses, and Student Research
In this dissertation, optical Hall effect (OHE) measurements are used to determine the free charge carrier properties of important two-dimensional materials and monoclinic oxides. Two-dimensional material systems have proven useful in high-frequency electronic devices due to their unique properties, such as high mobility, which arise from their two-dimensional nature. Monoclinic oxides exhibit many desirable characteristics, for example low-crystal symmetry which could lead to anisotropic carrier properties. Here, single-crystal monoclinic gallium oxide, an AlInN/GaN-based high-electron-mobility transistor (HEMT) structure, and epitaxial graphene are studied as examples. To characterize these material systems, the OHE measurement technique is employed. The OHE is a physical …
Ordered Growth Of Ferroelectric Diisopropylammonium-Bromide Microcrystals Through Slotted-Jar Growth And Lithographically Controlled Wetting, Andrew J. Fanning
Ordered Growth Of Ferroelectric Diisopropylammonium-Bromide Microcrystals Through Slotted-Jar Growth And Lithographically Controlled Wetting, Andrew J. Fanning
Honors Theses
Organic molecular ferroelectrics show promise for industry applications because of their switchable high spontaneous polarization value, mechanical flexibility, and cost-effectiveness. Since these materials, namely diisopropylammonium bromide, exhibit ferroelectricity only in tandem with a high level of crystallinity, novel methods must be explored in order to ensure that high levels of crystallinity are achieved. This project seeked to perfect the methods of Slotted Jar Growth and Lithographically Controlled Wetting (LCW). Slotted Jar Growth uses temperature driven solution saturation to grow crystals on a desired substrate. LCW drives the growth of microscopic diisopropylammonium bromide crystals, in their ferroelectric phase, through the use …
Nv Center Detection Of Electric Fields And Low-Intensity Light, Nicholas Harmon, Michael Flatte
Nv Center Detection Of Electric Fields And Low-Intensity Light, Nicholas Harmon, Michael Flatte
Faculty Works
Nitrogen vacancy (NV) center spins in diamond are attractive candidates for quantum information processing and sensitive, nanoscale magnetometers due to their long spin coherence times under ambient conditions [1]. The ground state of the NV spin is also sensitive to electric fields [2]. We present a theory of quantum detection using positive operator valued measurements (POVMs) wherein the presence of an electric field is determined by spin-dependent fluorescence of an NV center. The predicted sensitivity to small electric fields can also be used for photon detection. Photons incident upon a chromophore near the diamond interface may induce a charge polarization …
Optically Trapped Fluorescent Nanodiamonds, Viva Horowitz
Optically Trapped Fluorescent Nanodiamonds, Viva Horowitz
Scholarly Projects
The nitrogen-vacancy (NV) color center in diamond is gaining significant interest for applications in nanoscale sensing. The optical addressability of the magnetically sensitive spin states and the ability to coherently control these states at room temperature makes this system an exciting candidate for spin-based magnetometry. I constructed an optical tweezers apparatus combined with a confocal fluorescence apparatus. Using the optical apparatus, we demonstrate three-dimensional position control of nanodiamonds in solution with simultaneous readout of ground-state electron-spin resonance (ESR) transitions in an ensemble of diamond nitrogen-vacancy (NV) color centers. Despite the motion and random orientation of NV centers suspended in the …
Decay Of Nuclear Hyperpolarization In Silicon Microparticles, M. Lee, M. C. Cassidy, C. Ramanathan, C. M. Marcus
Decay Of Nuclear Hyperpolarization In Silicon Microparticles, M. Lee, M. C. Cassidy, C. Ramanathan, C. M. Marcus
Dartmouth Scholarship
We investigate the low-field relaxation of nuclear hyperpolarization in undoped and highly doped silicon microparticles at room temperature following removal from high field. For nominally undoped particles, two relaxation time scales are identified for ambient fields above 0.2 mT. The slower, T1,s, is roughly independent of ambient field; the faster, T1,f, decreases with increasing ambient field. A model in which nuclear spin relaxation occurs at the particle surface via a two-electron mechanism is shown to be in good agreement with the experimental data, particularly the field independence of T1,s. For boron-doped particles, a single relaxation time scale is observed. This …
Phonons Of Single Quintuple Bi2te3 And Bi2se3 Films And Bulk Materials, Wei Cheng, Shang-Fen Ren
Phonons Of Single Quintuple Bi2te3 And Bi2se3 Films And Bulk Materials, Wei Cheng, Shang-Fen Ren
Faculty publications – Physics
Phonons of single quintuple films of Bi2Te3 and Bi2Se3 and corresponding bulk materials are calculated in detail by MedeA (a trademark of Materials Design) and Vienna ab initio simulation package (VASP). The calculated results with and without spin-orbit couplings are compared, and the important roles that the spin-orbit coupling plays in these materials are discussed. A symmetry breaking caused by the anharmonic potentials around Bi atoms in the single quintuple films is identified and discussed. The observed Raman intensity features in Bi2Te3 and Bi2Se3 quintuple films are explained.
Microscopic Theory Of The Low Frequency Raman Modes In Germanium Nanocrystals, Shang-Fen Ren, Peter Y. Yu
Microscopic Theory Of The Low Frequency Raman Modes In Germanium Nanocrystals, Shang-Fen Ren, Peter Y. Yu
Faculty publications – Physics
We have studied the Raman intensities of low-frequency phonon modes in germanium (Ge) nanocrystals (NC) with varying sizes by using a microscopic valence force field model. The results are compared with the predictions of the continuum model of Lamb using a projection method. We found that the l=0 spheroidal Lamb modes are Raman active in the parallel polarization scattering geometry, while the l=2 spheroidal Lamb modes are active in the crossed polarization geometry. This result agrees with the group theory prediction that the torsional Lamb modes are not Raman active, but is in disagreement with the identification of torsional Lamb …
Microscopic Investigation Of Phonon Modes In Sige Alloy Nanocrystals, Shang-Fen Ren, Wei Cheng, Peter Y. Yu
Microscopic Investigation Of Phonon Modes In Sige Alloy Nanocrystals, Shang-Fen Ren, Wei Cheng, Peter Y. Yu
Faculty publications – Physics
Phonon modes in spherical silicon germanium alloy (SiGe) nanocrystals containing up to 1147 atoms (3.6 nm) have been investigated as a function of the Si concentration. Microscopic details of phonon modes, including phonon frequencies and vibrational amplitudes, phonon density-of-states are calculated directly from the dynamic matrices. In particular, the dependence of phonon frequency on the configuration (such as a different ratio of Si to Ge atoms), and location (surface or interior) of clusters of atoms in SiGe alloy nanocrystals have been investigated. Low frequency surface phonons that are related to the spheroidal and torsional modes of a continuum sphere are …
Theoretical Investigation Of The Surface Vibrational Modes In Germanium Nanocrystals, Shang-Fen Ren, Wei Cheng, Peter Y. Yu
Theoretical Investigation Of The Surface Vibrational Modes In Germanium Nanocrystals, Shang-Fen Ren, Wei Cheng, Peter Y. Yu
Faculty publications – Physics
We have used a microscopic lattice dynamical model to study phonon modes in germanium (Ge) NC with size varying between 47 to 7289 atoms (diametersimilar to6.8 nm). By separating these atoms into bulk and surface atoms we have found that surface modes can exist in Ge NC both at low frequencies (<50>cm(-1)) and at high frequency (similar to260 cm(-1)). The latter mode is a resonant mode which occurs in the "pseudogap" between the acoustic and optical phonon branches in bulk Ge. From the low frequency surface modes we have been able to reconstruct the spheroidal and torsional Lamb modes …
Calculations Of Surface Effects On Phonon Modes And Raman Intensities Of Ge Quantum Dots, Shang-Fen Ren, Wei Cheng
Calculations Of Surface Effects On Phonon Modes And Raman Intensities Of Ge Quantum Dots, Shang-Fen Ren, Wei Cheng
Faculty publications – Physics
Phonon modes and Raman intensities of Ge quantum dots (QDs) with two different types of surfaces, a free standing surface or a fixed surface, in a size range from five atoms to 7 nm in diameter, are calculated by using a microscopic valence force field model. The results are compared, and the effects of surfaces on phonon properties of QDs are investigated. It is found that phonon modes and Raman intensities of QDs with these two different types of surfaces have obvious differences which clearly reveal the effects of the surfaces of QDs. The calculated results agree with existing experimental …
Calculations On The Size Effects Of Raman Intensities Of Silicon Quantum Dots, Wei Cheng, Shang-Fen Ren
Calculations On The Size Effects Of Raman Intensities Of Silicon Quantum Dots, Wei Cheng, Shang-Fen Ren
Faculty publications – Physics
Raman intensities of Si quantum dots (QD's) with up to 11489 atoms (about 7.6 nm in diameter) for different scattering configurations are calculated. First, phonon modes in these QD's, including all vibration frequencies and vibration amplitudes, are calculated directly from the lattice-dynamic matrix by using a microscopic valence force field model combined with the group theory. Then the Raman intensities of these quantum dots are calculated by using a bond-polarizability approximation. The size effects of the Raman intensity in these QD's are discussed in detail based on these calculations. The calculations are compared with the available experimental observations. We are …
Phonon Modes In Inas Quantum Dots, Shang-Fen Ren, G Qin, Deyu Lu
Phonon Modes In Inas Quantum Dots, Shang-Fen Ren, G Qin, Deyu Lu
Faculty publications – Physics
Phonon modes in spherical InAs quantum dots (QDs) with up to 11 855 atoms (about 8.5 nm in diameter) are calculated by using a valence force field model, and all the vibration frequencies and vibration amplitudes of the QDs are calculated directly from the lattice-dynamic matrix. The projection operators of the irreducible representations of the group theory are employed to reduce the computational intensity, which further allows us to investigate the quantum confinement effect of phonon modes with different symmetries. It is found that the size effects of phonon modes depend on the symmetry of the modes. For zinc-blende structure, …
Electrons In Image States Near Roughened Metal Surfaces, Brian K. Clark, Brian W. Gregory, Jean M. Standard
Electrons In Image States Near Roughened Metal Surfaces, Brian K. Clark, Brian W. Gregory, Jean M. Standard
Faculty Publications – Chemistry
Electrons near roughened Ag and Au surfaces with chemisorbed dielectric overlayers of alkanethiol or alkaneselenol self-assembled monolayers are shown to move within the sulfur or selenium head-group layer on the metal terraces. The electrons exist in image states with respect to Ag or Au step edges. There is no substantial image force between the electrons and the terraces.