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Full-Text Articles in Physical Sciences and Mathematics
Cryostat System For Spacecraft Materials Testing, Justin Dekany
Cryostat System For Spacecraft Materials Testing, Justin Dekany
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
An existing space environment simulation test chamber used in the study of electron emission, sample charging and discharge, electrostatic discharge and arcing, electron transport, and luminescence of spacecraft materials now has extended temperature control capabilities. By incorporating a two-stage, closed-cycle helium cryostat, it is now possible to simulate the temperature typical spacecraft will experience when in orbit, ranging from < 40 K to > 450 K. The system was designed to maintain compatibility with an existing ultrahigh vacuum chamber that can simulate diverse space environments. This vacuum chamber can simulate space environment conditions by producing the same pressure, amount of electrons, electromagnetic radiation and temperature …
Defects Density Of States Model Of Cathodoluminescent Intensity And Spectra Of Disordered Sio2, Amberly Evans Jensen, Jr Dennison
Defects Density Of States Model Of Cathodoluminescent Intensity And Spectra Of Disordered Sio2, Amberly Evans Jensen, Jr Dennison
Journal Articles
Electron beam measurements show that disordered SiO2 exhibits electron-induced luminescence, and that it varies with incident beam energy and current density, sample temperature, and wavelength. A simple model based on the electronic band structure and defect density of states—initially used to explain electron transport in highly disordered insulating materials—has been extended to predict the relative cathodoluminescent intensity and spectral radiance for disordered SiO2 as a function of these variables. Due to the large band gap of insulating SiO2, thermal excitation from the valence to conduction band is highly improbable; excitation is through collisions of the incident …
Low Temperature Cathodoluminescence In Disordered Sio2, Amberly Evans Jensen, Jr Dennison, Gregory Wilson, Justin Dekany
Low Temperature Cathodoluminescence In Disordered Sio2, Amberly Evans Jensen, Jr Dennison, Gregory Wilson, Justin Dekany
Graduate Student Publications
In recent charging studies, a discernible glow was detected emanating from sample surfaces undergoing electron beam bombardment that resulted from a luminescent effect termed cathodoluminescence. This suggests that some of the materials used as optical elements, structural components, and thermal control surfaces in the construction of space-based observatories might luminesce when exposed to sufficiently energetic charged particle fluxes from the space plasma environment. A central focus of our experiments was the temperature dependence of the luminescent behavior. Here, an overview of our experimental results is given, as well as a qualitative model to describe the luminescent behavior. We look at …
Ultrahigh Vacuum Cryostat System For Extended Low Temperature Space Environment Testing, Justin Dekany, Robert H. Johnson, Gregory Wilson, Amberly Evans Jensen, Jr Dennison
Ultrahigh Vacuum Cryostat System For Extended Low Temperature Space Environment Testing, Justin Dekany, Robert H. Johnson, Gregory Wilson, Amberly Evans Jensen, Jr Dennison
Graduate Student Publications
The range of temperature measurements have been significantly extended for an existing space environment simulation test chamber used in the study of electron emission, sample charging and discharge, electrostatic discharge and arcing, electron transport, and luminescence of spacecraft materials. This was accomplished by incorporating a new two- stage, closed-cycle helium cryostat which has an extended sample temperature range from450 K, with long-term controlled stability of
Low-Temperature Charge Transport In Ga-Acceptor Nanowires Implanted By Focused-Ion Beams, S. J. Robinson, C. L. Perkins, T. -C. Shen, J. R. Tucker, T. Schenkel, X. W. Wang, T. P. Ma
Low-Temperature Charge Transport In Ga-Acceptor Nanowires Implanted By Focused-Ion Beams, S. J. Robinson, C. L. Perkins, T. -C. Shen, J. R. Tucker, T. Schenkel, X. W. Wang, T. P. Ma
T. -C. Shen
Ga-acceptor nanowires were embedded in crystalline Si using focused-ion beams. The dc current-voltage characteristics of these wires after annealing are highly nonlinear at low temperatures. A conductance threshold of less than 50mV is observed independent of Ga+ dosage and implant beam overlap. These features suggest a Coulomb blockade transport mechanism presumably caused by a network of Ga precipitates in the substrate. This granular scenario is further supported by measurements of gated nanowires. Nanowires with metallic conductance at low temperatures could be achieved by reducing the current density of the focused-ion beams.
Ion Beam Mixing In Ag-Pd Alloys, J L. Klatt, R S. Averback, David Peak
Ion Beam Mixing In Ag-Pd Alloys, J L. Klatt, R S. Averback, David Peak
All Physics Faculty Publications
Ion beam mixing during 750 keV Kr+ irradiation at 80 K was measured on a series of Ag‐Pd alloys using Au marker atoms. The mixing in pure Ag was the greatest and it decreased monotonically with increasing Pd content, being a factor of 10 higher in pure Ag than in pure Pd. This large difference in mixing cannot be explained by the difference in cohesion energy between Ag and Pd in the thermodynamic model of ion beam mixing proposed by Johnson et al. [W. L. Johnson, Y. T. Cheng, M. Van Rossum, and M‐A. Nicolet, Nucl. …