Open Access. Powered by Scholars. Published by Universities.®
- Keyword
-
- Amplitude transmission (1)
- CVD graphene (1)
- Disclination (1)
- FDTD (1)
- Free energy (1)
-
- Ge (1)
- Graphene (1)
- Intervalley Scattering (1)
- Kinetics (1)
- Liquid crystal (1)
- Magneto-spectroscopy (1)
- Numerical Modeling (1)
- Optoelectronics (1)
- Photo-conductivity (1)
- Pump-probe experiments (1)
- Recombination (1)
- Semiconductor Physics (1)
- Simulations (1)
- Solar Cells (1)
- Solid state (1)
- Sputtering (1)
- Superconductivity nv center nitrogen vacancy pnictide iron-based magnetometry (1)
- Tellurium (1)
- Terahertz (1)
- Thin film (1)
- Time-Resolved Terahertz Spectroscopy (1)
- Topological defect (1)
- “MEEP” (1)
Articles 1 - 8 of 8
Full-Text Articles in Physics
The Interaction Of Topological Defects In Anisotropically-Elastic Nematic Liquid Crystals, Carter J. Swift
The Interaction Of Topological Defects In Anisotropically-Elastic Nematic Liquid Crystals, Carter J. Swift
Macalester Journal of Physics and Astronomy
Topological defects are very well understood so long as the medium in which they exist is isotropically-elastic. They lead to director fields which are easy to calculate and superpose linearly so that a system with any number of defects is analytically treatable. They also have an interaction which is simple in form and can be accurately described by the Peach-Koehler force. In an anisotropically-elastic medium, however, such defects are very poorly understood outside of the single-defect case which was solved by Dzyaloshinskii. In this project, numerical and approximate analytical techniques are applied in order to better understand the interaction between …
Finite-Difference-Time-Domain Simulation Of Ultrafast Experiments, Alpha Ma
Finite-Difference-Time-Domain Simulation Of Ultrafast Experiments, Alpha Ma
Macalester Journal of Physics and Astronomy
The Finite-Difference-Time-Domain (FDTD) method is a numerical method that calculates electric fields or magnetic fields by interleaving them in space and time. Using a python package called “MEEP”, I was able to write optical simulations of ultrafast experiments, especially the Terahertz Pump-Probe experiments. The goal of this project was to use FDTD simulation to measure the transmission of an electro-magnetic pulse passing through a thin film of conducting material on a dielectric substrate in order to study the characteristic conductivity of potential solar cell materials.
Nitrogen Vacancy Center Optical Magnetometry Of A Barium-Iron-Cobalt Superconductor, William Setterberg
Nitrogen Vacancy Center Optical Magnetometry Of A Barium-Iron-Cobalt Superconductor, William Setterberg
Macalester Journal of Physics and Astronomy
Experimentally probing the intrinsic properties of superconductors—such as the London penetration depth λ and the critical fields Hc1 and Hc2—poses a difficult task. Various sample- and measurement-related factors can impact the efficacy of results obtained for λ or Hc1, such as perturbations to the magnetic properties of a superconducting sample or crystalline defects. One measurement technique that can minimize the impact of both of these issues is known as Nitrogen Vacancy (NV) center magnetometry. In this work, we use NV center magnetometry to perform minimally-invasive measurements of the lower critical field Hc1 and the …
Modeling Recombination In Solar Cells, Paul Chery
Modeling Recombination In Solar Cells, Paul Chery
Macalester Journal of Physics and Astronomy
Solar cells are a competitive alternative to nonrenewable energy sources such as fossil fuels. However, the efficiency of these devices is limited by photogenerated carrier recombination. We use a finite difference numerical model to study recombination phenomena in the absorber layer of solar cells including alternate recombination models and the effects of spatial distribution of recombination centers. We compare the effect of using the constant lifetime approximation for recombination to the full Shockley-Read-Hall expression in Silicon solar cells and find that the constant lifetime approximation holds for high defect densities but not for high photon flux densities. Finally, we simulate …
Intervalley Scattering Rates In Tellurium Observed Via Time-Resolved Terahertz Spectroscopy, Joshua R. Rollag
Intervalley Scattering Rates In Tellurium Observed Via Time-Resolved Terahertz Spectroscopy, Joshua R. Rollag
Macalester Journal of Physics and Astronomy
We conducted time-resolved terahertz spectroscopy measurements on the elemental semiconductor tellurium. Pump-probe measurements were used to find the conductivity as a function of time in single crystalline tellurium samples. It was found that the excitation dynamics in tellurium changes for photon energies of 1.03 eV and 1.55 eV. The change in these excitation dynamics was attributed to intervalley scattering effects. A model using intervalley scattering and Auger recombination was fit to the data, giving a value of 2.28 ps for the intervalley scattering time constant in tellurium.
Analysis Of Spin Polarization In Half-Metallic Heusler Alloys, Alexandra Mcnichol Boldin
Analysis Of Spin Polarization In Half-Metallic Heusler Alloys, Alexandra Mcnichol Boldin
Macalester Journal of Physics and Astronomy
Half-metals have recently gained great interest in the field of spintronics because their 100% spin polarization may make them an ideal current source for spintronic devices. This project examines four Heusler Alloys of the form Co2FexMn1−xSi that are expected to be half-metallic. Two magnetic properties of these alloys were examined, the Anisotropic Magnetoresistance (AMR) and the Anomalous Hall Effect (AHE). These properties have the potential to be used as simple and fast ways to identify materials as half-metallic or non-half-metallic. The results of these measurements were also used to examine the spin …
Modelling Transient Terahertz Magneto-Spectroscopy Measurements Of P-Type Cvd Graphene Leading To A Negative Photoconductivity., Rhyan Foo Kune
Modelling Transient Terahertz Magneto-Spectroscopy Measurements Of P-Type Cvd Graphene Leading To A Negative Photoconductivity., Rhyan Foo Kune
Macalester Journal of Physics and Astronomy
Ultrafast Terahertz (THz) Magneto-Spectroscopy (UTMS) measurements were performed on p-type CVD graphene sample to investigate the intrinsic carrier dynamics of the material. We investigated static and time-resolved THz transmission measurements, in which the sample was photo-excited by a near infrared (NIR) pump pulse, in order to study its behavior in a magnetic field. In these measurements the free carriers were probed to independently measure the carrier density and scattering rate in this film. We observed, in our graphene sample, an increase in transmission related to a negative photoconductivity (decrease in conductivity after photoexcitation) consistent with previous research. This decrease is …
Kinetics Of Solid Phase Crystallization Of A-Ge Thin Films, John D. Graham
Kinetics Of Solid Phase Crystallization Of A-Ge Thin Films, John D. Graham
Macalester Journal of Physics and Astronomy
A method was developed to investigate the solid-phase crystallization (SPC) reaction undergone by germanium thin films. Amorphous films were grown by the radio-frequency (RF) magnetron sputtering and then annealed for a maximum of 6 hours at two temperatures: 446°C and 460°C. Crystallinity was measured by resistivity measurements, as well as crystal peak height and area taken from X-ray diffractometer (XRD) data. Initial data shows qualitative agreement with a nucleation-growth model for the observed kinetic process. However, observed peak narrowing phenomena suggests a comprehensive model of XRD measurements of polycrystalline thin films is needed for a rigorous interpretation of the results.