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Department Library

2020

James Erikson (Senior Thesis, April 2020, Advisor: David Allred, John Colton )

Abstract

Temperature is an important parameter in many processes being studied with microfluidic devices. As such, improved temperature sensing methods compatible with the size and sensitivity required for microfluidics need to be found. This work investigates the photoluminescence lifetime of Rhodamine B and CdTe quantum dots for potential use in microfluidic devices. Lifetime values were sampled over a range of known temperatures through time-correlated single photon counting. Spectral measurements were also taken at each temperature. In Rhodamine B, lifetime was obtained through numerical deconvolution, however, results obtained in this way were unreliable due to variability within the sample itself over time. Similar methods proved similarly unreliable for CdTe quantum dots, which also show variability over time, though to a lesser extent. Through the application of machine learning algorithms, temperatures in CdTe quantum dots can be accurately determined with uncertainties ranging from 7.7 K at cryogenic temperatures to 0.1 K near room temperature. This success shows that temperature dependent photoluminescence is a valid option for future applications in microfluidic devices.

2019

Daniel Jones (Senior Thesis, April 2019, Advisor: David Allred, Joseph Moody )

Abstract

Geosynchronous satellites (GEOs) need to be monitored to track their health, effects of space aging, and unexpected maneuvers. This can be accomplished by creating photometric and polarimetric signatures from light curves. To develop our understanding about how the light curves reveal the needed information, we began by studying the 101 W satellite cluster. To create the light curves, observations were taken through Johnson V, B, R, and I filters as well as polarized filters using the telescopes at the Remote Observatory for Variable Object Research (ROVOR) in Delta, UT and at the Optical Delving Infrared iNnovation (ODIN) laboratory at the Kirtland Airforce Base in Albuquerque, NM. To determine the effects of aging, three signatures were compared with archived data for the respective GEOs. We found that dimming and/or reddening occurred. The dimming was equal to 0.1-0.2 mags and the B-V color increased by about 0.1 indicating a reddening by that amount. Using the polarized data, the Stokes parameters were calculated. An increased understanding of the satellite's structure and movements can be obtained by analyzing how these parameters change in a night.

Nick Steil (Capstone, December 2019, Advisor: David Allred )

Abstract

This paper delves into the connections between physics and finance, at the surface two seemingly unrelated fields. Central to the nature of the scientific method as an integral part of the physics education, I will connect elements of the method to the field of finance. The skills of building models to mathematically describe a law of physics based on certain assumptions is a skill that translates to build financial models to price assets. Both fields rely on the need for data to work in harmony with derived models to better understand the subject.

2018

Alexandra Davis (Senior Thesis, December 2018, Advisor: David Allred )

Abstract

One of NASA’s overarching goals is the Origins project, which explores both the universe and ways to better understand it. Of special concern is the extreme or vacuum ultraviolet (VUV or XUV, respectively) range, far past 10 eV (the current telescopes’ observation limit). The growth rate of the aluminum oxide (Al2O3) under various protective coatings—specifically aluminum fluoride, First Contact Opticlean, and liquid nitrogen—is tested. Ellipsometry and SEM are used to understand more about the chemical composition of the created mirrors as a function of time. Results show a 9nm layer of AlF3 on aluminum is a stable barrier layer against oxidation of aluminum.

Jesse Richmond (Senior Thesis, April 2018, Advisor: David Allred )

Abstract

The Labeled Release experiment of the Viking landers led to the hypothesis that martian soil is highly oxidized. Hydrogen peroxide has been suggested as the primary oxidant, but no definitive theory exists as to how it forms in the martian environment. We propose that ultraviolet radiation interacts with carbon dioxide, water, and other trace substances in the martian atmosphere to form this hydrogen peroxide. We tested this theory by constucting a Mars-like atmosphere within a vacuum system and then exposing it to ultraviolet radiation from a UV lamp. The resulting products were then collected into a cold trap and analyzed by a mass spectrometer. Initial results do seem to indicate that hydrogen peroxide was generated by the interaction, as well as other substances. If correct, this data further expands our knowledge of the martian environment and explains why no martian organics have been discovered thus far.

2017

Stephanie Thomas (Senior Thesis, May 2017, Advisor: David Allred )

Abstract

Pure aluminum mirrors optimize the reflectance of broadband mirrors for space-based telescopes; however, they oxidize instantly in atmospheric conditions, decreasing reflectance in the far-UV from 90% to 20%. The largely untried method of Removable Volatile Aluminum Protection (REVAP) overcoats freshly deposited Al mirrors with a barrier layer of cadmium or zinc intended for removal in vacuum. I use ellipsometry and energy dispersive x-ray spectroscopy (EDS) periodically to observe how the barrier layers interact with the Al and how the composition of the mirrors changes with time. Preliminary EDS results show Cd may have prevented aluminum oxidation in some samples. Cd and Zn exhibit low adhesion to Al, making REVAP with them unfavorable. EDS measurements on samples after attempting re-evaporation shows uneven removal of Cd and Zn.

Spencer Willett (Senior Thesis, August 2017, Advisor: David Allred )

Abstract

The LUVOIR telescope, a potential future telescope for NASA, will benefit from having a broadband mirror coated with aluminum that can allow for reflectance from the visible and infrared all the way down to the far-UV. The aluminum thin-film will need to remain unoxdized in order to reflect into the far-UV range. The application of polymers to protect the aluminum from oxidizing was investigated. We used a magnetron sputtering system and a plasma cleaner to determine whether various polymers could be removed via hydrogen etching of the thin-film. Ellipsometry was used to determine the thicknesses of the polymer thin films before and after etching occurred. The results show that controlled etching can occur with various gases. The results also show that the etching process was reasonably controlled.

2015

Brandon McKeon (Senior Thesis, April 2015, Advisor: David Allred )

Abstract

Silicon dioxide (SiO2) is useful in microelectronics, micro-fabrication and optics. It has traditionally been deposited through low-pressure chemical vapor deposition (LPCVD) at high temperatures (about 900 to 1000 C). Various reactants have been used in this process, such as dichlorosilane and oxygen, or silane and nitrous oxide in different combinations. We explore the reaction of dichlorosilane and nitrous oxide in SiO2 LPCVD by varying the temperature from 850 to 950 C and the pressure from 0.30 to 1.05 Torr. Films with mirror-like surfaces are deposited in an ambient temperature of 900 C, with a gas ratio of 3.33 parts nitrous oxide for every one part dichlorosilane, and at a pressure between 0.35 and 0.69 Torr, while pressures outside of this range result in foggy surfaces or no deposition. These results are in good agreement with previous work and indicate that careful control of pressure is necessary for depositing uniform films for use in optical applications.

2014

Jason Kyle Anderson (Senior Thesis, April 2014, Advisor: David Allred )

Abstract

Traditional microfabrication processes are confined to a small set of materials due to limitations on etching and confined to low-aspect-ratio fabrication due to limits in both etching and stability of thicker film deposition processes. Carbon Nanotube Templated Microfabrication (CNT-M) technology has introduced a dramatically different approach to microfabrication that fabricates without significant etch processes. This is achieved by forming the desired structure in carbon nanotubes (CNT) and then filling or infiltrating that structure with the material of choice. This technology has been developed at BYU using materials like silicon and carbon. Microfabrication with metals is needed because of their higher density and improved electrical and mechanical properties compared to traditional microfabrication materials. A suitable metals process has not yet been found. We endeavored to develop atomic layer deposition (ALD) of W using atomic H as the agent for abstracting the nonmetal atoms such as C, O or F that act as ligands for the gaseous form of W used to bring the W into the deposition. We used tungsten hexafluoride (WF6) and molecular hydrogen as our reactants, flowing them in alternating cycles onto carbon nanotube samples in a vacuum chamber. We did not achieve significant W deposition in the initial process, so we incorporated a microwave generator to replace the H2 with hydrogen plasma. This somewhat improved deposition, but an even bigger improvement in deposition came when the samples were ozone treated before deposition. This process achieved a final product composed of 60% W as measured using and EDAX system in an SEM. This deposition was still too limited to allow for mechanical and electrical tests of the samples, which were too fragile for liftoff from the substrate.

Collin Brown (Senior Thesis, April 2014, Advisor: David Allred )

Abstract

Abstract Text: The fabrication of microelectromechanical systems (MEMS) is generally limited by the same processes and materials used in the semiconductor industry. We have been investigating the infiltration of patterned carbon nanotube (CNT) forests to find more materials and potentially easier methods to make MEMS. Our goal is to fill in the void between the nanotubes in the CNT forest with deposited metal, creating a solid metal-carbon hybrid in the same shape as the CNT forest. Previous students here at BYU investigated the infiltration of molybdenum and tungsten metal using molybdenum carbonyl and tungsten carbonyl, respectively, as precursors in chemical vapor deposition (CVD). The current topic of research is infiltration by atomic layer deposition (ALD) using tungsten hexafluoride and hydrogen (including atomic hydrogen via microwave plasma) as precursors. In the course of this research, we have seen the tungsten deposited as a crust over the top of the CNT forest, penetrating only microns into the forest.

2013

Jordan Bell (Senior Thesis, April 2013, Advisor: David Allred )

Abstract

The thickness uniformity of thin films across a substrate's surface is of interest in many important applications, including the manufacture of multilayer mirrors and antireflective coatings. This thesis explores the thickness profile of films deposited by DC magnetron sputtering on large stationary substrates, then uses that data in a computer model to predict thickness uniformity for substrates undergoing "planetary" motion. We tested the ability of the model to make predictions by producing a sample under planetary rotation and measuring its thickness profile. We found that the model gave a good approximation to the actual thickness profile, but actually underestimated the thickness uniformity.

James Schwab (Capstone, April 2013, Advisor: David Allred )

Abstract

Brigham Young University's Department of Physical and Astronomy's Thin Film Research Group has been studying the apparent expansion of yttrium oxide and scandium oxide when exposed to 7.27 eV excimer lamp. These films have more than tripled their initial thickness because of the exposure. Such expansion is quite unexpected. The excimer lamp used is very similar to UV cleaning lamps used to clean films and semiconductors in industry. It is therefore very important to understand this phenomenon. It has been previously found that reactively sputtered samples exhibit this expansion. Samples were grown and then analyzed using a tunneling electron microscope, ellipsometry, and spectral analysis. More samples were prepared and tested in various atmospheres in an attempt to isolate the catalysts or reactants needed for the phenomenon to occur. Evidence suggests that the presence of a gaseous species; perhaps oxygen or ozone is required in addition to the lamp for growth to occur.

2012

Richard Hansen (Honors Thesis, July 2012, Advisor: David Allred )

Abstract

Microelectromechanical systems (MEMS) fabrication traditionally uses the same limited methods and materials as those used in the silicon-based microelectronics industry. In order to make MEMS out of a much richer suite of materials, such as metals, Brigham Young University researchers developed a process termed carbon-nanotube-templated microfabrication (CNT-M). In CNT-M, we grow a patterned carbon nanotube (CNT) forest and fill in the spaces between CNTs by atomistic deposition, thus creating a CNT-composite material while preserving the original pattern of the CNT forest. Through chemical vapor deposition, we have made metallic microstructures by infiltrating CNT forests with a tungsten or a molybdenum carbonyl precursor. We were able to infiltrate the CNT forests more completely by using the molybdenum carbonyl precursor, and we determined the electrical and mechanical properties of the resulting composite material. Using cloverleaf test structures and the van der Pauw method, we found that the composite material has a resistivity between 749 and 935 uΩ·cm. By mechanically deflecting cantilever beams with an Instron materials testing apparatus, we found that the CNT composite has a Young’s modulus between 9.17 and 56.2 GPa, a yield strength between 106 and 221 MPa, and a maximum percent strain between 0.4 and 1.5%. These results characterize the material as being both electrically conductive and mechanically strong. Therefore, this simple, yet effective, method for creating metallic microstructures could open the door to new possibilities for MEMS.

Stuart Harper (Senior Thesis, October 2012, Advisor: David Allred )

Abstract

A statistical analysis of noise data from various-sized solid propellant rocket motors is presented. Time waveform data sampled at 204.8kHz using 6.35mm and 3.18mm microphones were collected near motors with nozzle exit diameters ranging from 0.13m to 1.22m. Non-Gaussian features of the data are explored by calculating estimates of the probability density functions of the data, its standard deviation, its skewness, and its kurtosis. This is carried out for both the pressure waveform and its first order time difference to reveal the formation of acoustic shocks within the noise. The analysis shows greater similarity between different rocket statistics for the pressure than for the time derivative.

2011

Alison Wells (Senior Thesis, August 2011, Advisor: David Allred )

Abstract

Brigham Young University's Thin Films Research Group has been studying the exposure of reactively sputtered yttrium (Y2O3) and scandium (Sc2O3) oxide films to a 7.2 eV vacuum ultraviolet (VUV) excimer lamp. Our results show that a dramatic increase occurs to the film when it is subjected to the UV light. In some cases the film swells to nearly seven times the original thickness, which is an unexpected result. The light source used in our research is similar to those used for cleaning in the semiconductor industry. Therefore, it is important to determine the cause of growth. It has been determined that reactively sputtered samples can exhibit film growth, whereas oxide films from air oxidation of metal films do not. We have experimentally determined that the film growth is not connected to new deposition or oxidation of the silicon substrate. The growth can then be attributed to change rendered to the sample itself. Pressure from water vapor within voids does not appear to be the cause---neither does surface interaction with gas species (ozone and atomic oxygen) by themselves. Evidence suggests that atomic oxygen and/or ozone created by the lamp with VUV photons present at the same time are altering the structure of our samples and are driving the film growth.

2010

Devon Mortensen (Senior Thesis, August 2010, Advisor: David Allred )

Abstract

Brigham Young University's Thin Films Research Group has recently discovered that exposure of reactively sputtered yttria (Y2O3) films to 7.2 eV vacuum-ultraviolet (VUV) light results in a dramatic increase in the films' thicknesses. In some cases films swelled to nearly seven times their original thickness. Due to the high chemical stability of Y2O3, this result was entirely unexpected. Determining the cause of this growth is an important issue since yttria is being considered as a material component in semiconductor devices and the light source used in this research is similar to cleaning lamps used in industry. We have experimentally determined that the film growth is not due to new deposition and is therefore a result of a change rendered to the sample itself. The growth cannot be attributed to oxidization of the yttria or the silicon substrate. Evidence suggests that VUV radiation is altering the structure of our Y2O3 samples, which is the main mechanism driving film growth.

2009

Jon Brame (Senior Thesis, April 2009, Advisor: David Allred )

Abstract

The goal of this project is to enable fabrication of a transistor device using silicon nanowires (SiNW) as semiconductors. In order to be able to establish electrical contact with the nanowires the SiNW growth is con ned to certain areas that can be contacted using electron-beam lithography (EBL). This is done by controlling the deposition of SiNW catalyst through angle-evaporation onto pillars on the device. The nanowires then grow from the sidewalls of the pillars and can be contacted using EBL.

Michael Rasmussen (Senior Thesis, April 2009, Advisor: David Allred )

Abstract

2008

Bryan Hicks (Capstone, April 2008, Advisor: David Allred )

Abstract

Making semiconductor devices based on single-walled carbon nanotubes (SWCNT) is one of the more compelling potential applications of these long but ultrathin structures. We see asymmetric voltage-current behavior across a random network of SWCNTs contacted by asymmetric metal electrodes (Au/Al). No effort was made to align the SWCNTs or to eliminate metallic nanotubes in our devices, procedures which are common in other devices [1]. Current rectification was, nonetheless, observed in the source-drain bias range of -3V to +3V. Rectification was somewhat surprising since, although metallic tubes are in the minority (~ 1/3), they could potentially act as shunts and mask the electric properties of the semiconducting majority. No correlation between electrode spacing and current rectification was observed. The lowest leakage current measured was 1% of the maximum current carrying capacity. Maximum forward-biased current capacities range between 8μA and 841μA.

Elisabeth Strein (Senior Thesis, August 2008, Advisor: David Allred )

Abstract

Cleaning techniques for Si/SiO2 ultrathin films are presented. With the re- moval of adventitious carbon on the surface, Si/SiO2 ultrathin films can serve as calibration standards in vacuum ultraviolet re ectance characterization (the range from 8 to 60 nm). Our group anticipates using these standards when making a mirror that will be sent to the moon and will be used to study the earth's magnetosphere. Data are presented for the samples that demon- strate the elimination of adventitious carbon contamination via oxygen rad- icals and chemical treatments. Data are determined by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. Additionally, I found that the antechamber of the XPS system deposits hydrocarbon onto the surface of samples. I adapted a plasma cleaner so that it minimized the e ects of this instrumental contamination. I found that samples must be cleaned with the lamp for at least five minutes or cleaned with the two-step chemical RCA clean. I found a correlation between the ellipsometry data and the XPS data. Finally I stored samples and found that carbon begins to redeposit on the sample surface within 2 hours of cleaning it. Storage data are presented.

2007

Guillermo Antonio Acosta (PhD Dissertation, December 2007, Advisor: David Allred )

Abstract

This study reports on the physical and optical characterization of scandium oxide thin films. Thin films of scandium oxide, 20-40 nm thick, were deposited on silicon wafers, quartz slides, and silicon photodiodes by reactively sputtering scandium in an oxygen environment. These samples were characterized using ellipsometry, high-resolution transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis. A 28.46 nm thick scandium oxide thin film was measured in the Extreme Ultraviolet (EUV) from 2.7 to 50 nm (459.3 to 24.8 eV) using synchrotron radiation at the Advanced Light Source Beamline 6.3.2 at the Lawrence Berkeley National Laboratory. In these measurements, a new method for data collection was used, in which the reflection and transmission data were collected simultaneously. Analysis of the EUV reflection and transmission data was performed using a front-side reflection, matrix-multiplication technique, which is novel among EUV analytical practice. During data analysis, a new weighting scheme was used, named “adaptive weighting”. This analysis provides the first experimentally determined optical constants n and k for scandium oxide thin films from 4.5-30 nm. Also, the positions of the L2 and L3 electronic transitions of scandium oxide have been measured, at 3.069 and 3.101 nm (404.0 and 399.9 eV), respectively, while the measurements near the M transition suggest it to be at approximately 31.5 nm (39.4 eV). Comparing the electronic transition positions of scandium oxide to those of scandium show that the oxidation of scandium shifts the positions to lower energies. For L2 the shift is about 1.8 eV, for L3 the shift is about 1.4 eV, and for M the shift is about 1.9 eV. The binding energies of scandium oxide are greater than those of scandium, as is expected for an oxide compared to its parent metal. This trend in the shift of the transition positions is unexpected, and warrants further investigation.

Robert Gillis (Capstone, August 2007, Advisor: David Allred )

Abstract

We use spectroscopic ellipsometry on thin films of thorium oxide deposited on silicon wafers to determine the optical constants (n and k) of thorium oxide more precisely over the spectral range of 0.73-9.43 eV. We particularly focused on the 6.5-9.43 eV range. We found evidence of indirect band gaps at 7.5 and 7.9 eV. Our measurements also support the theory that the direct band gap is at 5.9 eV as claimed by William R. Evans in his senior thesis rather than 4 eV as clamed in T.R. Griffiths, and James Dixon (J. of Chemical Society, Faraday Transactions, 88, 1149-1160, 1992, and ref. cited within, especially ref. 2-9 ).

Jacqualine Jackson (Honors Thesis, April 2007, Advisor: David Allred )

Abstract

It is difficult to measure the reflectance of thin films accurately in the extreme ultraviolet due to lack of precision instrumentation in this range and the effects of surface roughness. However, this has little effect on transmittance measurements. Whereas the real part of the refractive index is dependant on both transmittance and reflectance, the imaginary part can be determined from transmittance data alone. It is possible to use Kramers-Kronig analysis to calculate the real part if the imaginary part is known over a sufficiently broad range. We show that the delta calculated from reflection and transmission data without taking into account roughness may underestimate the real part of the refractive index of the scandium oxide samples we are studying by up to 40% near 270 eV.

2006

S. Andrew Ning (Honors Thesis, August 2006, Advisor: David Allred )

Abstract

2005

William Ray Evans (Honors Thesis, January 2005, Advisor: David Allred )

Abstract

2004

Guillermo Antonio Acosta (Masters Thesis, August 2004, Advisor: David Allred )

Abstract

A technique has been developed which allows for atomic force microscopy to be used to measure the thickness of thin film samples. This technique involves the fabrication of a distinct, abrupt step in the film surface, using a device called the Abruptor. The step can then be scanned with an AFM, revealing the height of the step. Films with thickness form 6-15 nm are now routinely measured in this way, while it is possible to measure thinner samples. The thinnest measured film so far is approximately 3.6nm. Use of this technique has provided insight to the swelling of films die to oxidation, the degree of non-uniformity of film thickness due to deposition geometry, and has the potential for use in the study nanoscale hydrocarbon contaminants on surfaces.

Kristi Adamson (Senior Thesis, April 2004, Advisor: David Allred )

Abstract

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Paul Archer (Senior Thesis, June 2004, Advisor: David Allred )

Abstract

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Luke Bissell (Senior Thesis, August 2004, Advisor: David Allred )

Abstract

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Jedediah Edward Jensen Johnson (Honors Thesis, August 2004, Advisor: David Allred )

Abstract

Richard Sandberg (Senior Thesis, August 2004, Advisor: David Allred )

Abstract

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2003

Ryan Camacho (Senior Thesis, May 2003, Advisor: David Allred )

Abstract

Ross Robinson (Senior Thesis, August 2003, Advisor: David Allred )

Abstract

2001

Joseph S. Choi (Honors Thesis, June 2001, Advisor: David Allred )

Abstract

Cort Johnson (Senior Thesis, April 2001, Advisor: David Allred )

Abstract

Matthew B Squires (Masters Thesis, August 2001, Advisor: David Allred )

Abstract

I have built a variable angle reflectometer capable of measuring absolute reflectance between 2.5 degrees and 85 degrees grazing incidence for use in the extreme ultraviolet, and it is possible to perform surface scans over a sample 5cm square. The measurement system was constructed to be modular for future applications. The data collection and analysis is automated using LabVIEW and data acquisitions hardware. The data is corrected for time variables in the intensity of the plasma source. The optical constants of fused industrial diamond and highly oriented pyrolytic graphite (HOPG) have been measured using the variable angle reflectometer. Qualitatively the measured values reasonably agree with previously published data for diamond and graphite. However, the measured data points are sparse and have only been measured at bright spectral lines if H, He and N. the small size and unknown quality of the graphite and diamond made it difficult to quantitatively compare the measured optical properties to other published data. I have analyzed the atomic scattering factors (ASF) of diamond and graphite, calculated from the n and k values reported in the Handbook of Optical Constants I & II (ed. E. Palik), by calculating the relative difference between the ASF of diamond and graphite. The relative error in f1 at 8 eV is about 100% and between 15.5.-25 eV it is about 25%. This large of a difference at 25 eV is greater than expected because the nearest resonance in the carbon spectrum is at 8 eV. At 30 eV this difference is about 10 times greater than the difference between the energies of the single and double bonds in carbon. The mechanisms that determine the optical properties of carbon are significantly affected by the crystal structure of the bulk carbon. There is a relative difference of 100% between the f2 values about 8 eV. This is due to the near zero absorption of diamond below its band gap. At energies above 15.5 eV the average error is about 25%. This analysis shows that, at least for carbon, the energies of the valence electrons significantly affects the electronic structure at energies several times that of the binding energies.

1999

Matthew B. Squires (Honors Thesis, March 1999, Advisor: David Allred )

Abstract

1998

Pavel Leonidovich Brovkin (Masters Thesis, April 1998, Advisor: David Allred )

Abstract

An important problem in the development of x-ray detectors is minimizing the input capacitance of the preamplifiers. The maximum signal is transmitted to the FET in a charge-sensitive preamplifier when the capacitance of the detector and the FET are equal. This thesis targets the designing of a minimized small gate capacitance JFET and on a consideration of manufacturing and testing against theory by fabricating some device structures. In this thesis, I show that gate length ι is one of the most important geometrical parameters for creating a low capacitance and high gain device. Another important consideration concerns the etching technique. Even with alignment within 0.5μm, if etching technique does not involve a careful consideration of chemical concentration and timing relative to thickness of the oxide, the device cannot be successfully fabricated. Third, the shallow gate necessary for successful low-capacitance device can only be achieved by using low energy ion implantation.

Adam Fennimore (Honors Thesis, February 1998, Advisor: David Allred )

Abstract

1996

Gregory B. Thompson (Senior Thesis, June 1996, Advisor: David Allred )

Abstract

1993

Ming Cai (PhD Dissertation, December 1993, Advisor: David Allred )

Abstract

Mo/Si multilayer mirrors provide to date the highest reflectivity for soft x-rays in the range of 13 to 15 nm. It has potential applications for soft x-ray lithography. This dissertation has characterized the annealing behaviors of Mo/Si multilayers by Raman spectroscopy and other correlated characterization techniques. The first part of the dissertation shows how the Raman spectroscopy system is improved by using a CCD detector. Several algorithms have been developed to eliminate the cosmic noise which is unique to this kind of detector. With this high quantum efficiency detector, we can study very low-light-level Raman spectroscopy with much faster data acquisition speed. The major accomplishment of the research reported here is the characterization of the annealing behavior of Mo/Si multilayers. Two peaks, located at 323 and 438 cm-1, have been observed both in polycrystalline molybdenum silicide powder and one-hour 1000 annealed Mo/Si multilayers. This indicates that silicide has been formed at interfaces and is detectable, which provides the foundation for further studies. After high temperature annealing, in addition to the formation of silicide interfaces, the amorphous Si layers have crystalized. At this stage, the layer structure has been completely destroyed and the roughnesses of the interfaces and the surface have been increased. Both of these conditions will degrade the performance of the multilayer system. Further annealing studies show that the crystallization of Si layers and the formation of silicide through interdiffusion proceed concurrently during the annealing process.

1991

Cheryl Barnett Davis (Masters Thesis, December 1991, Advisor: David Allred )

Abstract

ZnxCd1-xTe crystals and films were studied by low temperature photoluminescence. The percentage of zinc was varied from zero (x=0) to 10 percent (x = 0.1). The spectral region from 0.7 eV to 1.8 eV was investigated. Features in the spectrum that had not been extensively examined before, including the phonon replica/defect band and the mid-gap peak, were investigated. The phonon replica/defect band is usually centered at 1.44 eV, and its width varies from 150 to 190 meV. In previous studies this peak has been termed the defect band. Examination of this peak shows that its intensity is affected by defects but its structure shows phonon replicas superimposed on the defect band. The number of phonon replicas varies. In samples with low zinc content the phonon replica peaks are easy to distinguish, but at higher concentrations they are difficult to discern. The mid-gap peak centered at 1.0 eV has not been extensively studied in these materials. This peak is noted in some samples but not in others. Its intensity relative to other peak intensities increases rapidly with power. The exact source of this peak was not determined, but various possibilities have been analyzed.

Fang Yuan (PhD Dissertation, December 1991, Advisor: David Allred )

Abstract

Boron, a low Z element, is useful for x-ray optics since it has a low atomic absorption coefficient. Boron films prepared by chemical vapor deposition were characterized optically, electronically and mechanically. Auger, infrared and hydrogen effusion analyses showed that the films are amorphous hydrogenated boron. The hydrogen content ranges from 8% to 71%. The measurements of the complex refractive index and the resistance vs. temperature determined that they are typical amorphous semiconductors with the energy gap ranging form 1.09 eV to 1.36 eV, decreasing with increasing hydrogen content. The Young’s modulus and hardness were found to be 3.05 x 1013 dyne/cm2 and around 2500 Vickers, respectively. A method of measuring optical index of boron films is proposed and described, as well as a model that determines their Young’s modulus and predicts the bending of the boron/silicone structure. The chemical tests suggested that boron films are stable in nonoxidizing bases and concentrated acids. Some oxidizing bases such as a basic ferricyanide solution are good etchants for CVD boron films. Boron coating on beryllium windows as a corrosion barrier layer and self-supporting boron windows are set forth as potential products of x-ray imaging.