Theses

The amount of twin formation of electroplated and thermally treated copper thin films was evaluated by electron back-scattering diffraction (EBSD) analysis. The result establishes the importance of twin formation in the analysis of stress-induced voiding, and indicates that with the inclusion of a copper alloy co-element, twin formation was significantly reduced relative to pure-copper. Furthermore, the thermal stress hysteresis curve of the Cu-Sn(0.01wt%) thin film indicated a higher flow stress than that of purecopper. These indications are consistent with the theory of suppressed grain deformation and reduced grain boundary elimination by particle pinning of grain boundaries during microstructure evolution of electroplated copper thin film. With the growth of the grains inhibited, both boundary filling and vacancy generation issues are suppressed, and the number of twin boundaries as void nucleation sites are reduced. Thus, the copper alloy film is believed to be more resistant to stress-induced voiding.

A program was created to model the effects of surface roughness on reflectance from circular conducting surfaces. Despite tests indicating a correct computational model, ill-conditioned surface impedance matrices mean that the results can’t be trusted.

This report is a synthesis of my experiences in the applied physics program preparing to enter a career in science communication. I compare my experiences in academic writing and professional writing to my experiences in my physics classes. For academic and professional writing, I go through how I was hired in the positions, my main responsibilities, and what I learned. My positions in academic writing included being a writer in the dean’s office in CPMS, being a writing tutor in the Research and Writing Center and being an intern for the technical writing company Niche. For most of these jobs, I learned how to be independent, how to talk to scientists, how to collaborate with others, and how to write well. I then synthesize these experiences and compare them to my academic training, noting that I received a lack of training in a competitive news environment, and a lack of training in searching out my own ‘beat’ for science stories. I compare my professional training to the academic training I received and note that I feel very prepared to tackle complex scientific issues, and confident in my ability to belong in a male-dominated science environment. I then advise future students on a potential roadmap for those that are interested in pursuing a similar path, such as taking many science classes, and participating in research. I also advise future students to seek internships sooner rather than later.

Aluminum is a great potential material for thin-film mirrors in space telescopes as it has a high reflectance range. However, when aluminum oxidizes, the reflectance range no longer includes light beyond ~120 nm wavelengths as the reflectivity drops below 5%. In order to maximize reflectance in the ultraviolet and open potential data such as Lyman series lines, there needs to be a way to keep that high reflectance range. This research explores potential storage environments that slow the oxidation of thin aluminum films through use of oxygen absorbers, where the film and oxide thicknesses are tracked through use of ellipsometry. Results show that 3000 cubic centimeters (cc) of oxygen absorbers can slow the oxidation of aluminum samples by 3.6 times, 6000 ccs by 3.0 times, 9000 ccs by 2.4 times.

Aluminum is a useful material for broadband mirrors due to its high reflectance across many wavelengths, including the far-ultraviolet. Its high reflectance in the far-ultraviolet makes it a promis- ing candidate for use in the next generation of space telescopes. However, oxidation of aluminum poses a problem because it dramatically reduces aluminum reflectance in the far-ultraviolet. One potential solution is thin film fluoride coatings on the aluminum mirrors, though it is difficult to test these mirrors for FUV reflectance as FUV light is difficult to produce and is absorbed in the atmosphere. Here a method is developed for obtaining at-wavelength reflectance measurements using a plasma as the light source, a monochromator, and vacuum chamber. Reflectance was measured, though the values were lower than expected. The method requires further developement to acquire reliable measurements.

Aluminum is the best choice of materials for coating broadband mirrors. Comparative studies of optical instruments containing aluminum-coated mirrors can be challenging because aluminum oxidizes so quickly in air. Fluoride capping layers have been used to prevent oxidation, but they also decrease the range of high reflectance in the far UV. Aluminum’s rapid oxidation is an obstacle to making successive, reproducible measurements, making joint work between laboratories more difficult. In this experiment we studied the effects of storage in cryogenic (liquid nitrogen, hexane, and liquid oxygen) and low-oxygen (dry ice and argon) on the retardation of the oxidation of the aluminum mirrors. We observed that all storage conditions that we tested slowed oxidation by two orders of magnitude. While more work is needed to quantify the retardation effects more specifically, especially for hexane and argon, our data suggests that any of these environments could prove useful in mitigating aluminum oxidation during storage.

The Brigham Young University (BYU) Molten Salt Micro Reactor (MSMR), is a concept design for a small, modular, molten salt fueled nuclear reactor that has no active components making it class A passively safe. \cite{LARSEN} Previously, the reactor models that have been created for neutronics simulations have been coded and changed by hand. A new coding library is presented that automates most of the modeling process, allowing engineers to change the design rapidly. The modeling code was verified through comparison with previous modeling work. The new software will allow rapid design iterations and the generation of a training data set for future machine learning work.

Starshades and other sensitive optical devices require dust mitigation techniques to protect their surfaces. We investigate coating these surfaces with a photodegradable polymer film that will vaporize when exposed to ultraviolet light. A series of experiments was conducted in which we studied this phenomenon in vacuum after applying a photo-depolymerizing coating. Poly (2-methyl, 1-pentene) sulfone is shown to degrade in vacuum when exposed to 172 nm UV light. Future studies will examine whether the coating can be used to remove dust contaminants from sensitive optical devices upon photoirradiation.

Electron Cryotomography (Cryo-ET) is an important imaging technique used by scientists. It uses cryogenic sample preparation, an electron microscope, and powerful image processing software to create high-resolution 3D views of cells and the structures within them. Cryo-ET has been a valuable tool for discovering many novel features about the functions of a wide variety of bacterial species. I was closely involved in two Cryo-ET research projects during my time at BYU. This paper will discuss both projects, as well as the principles of Cryo-ET and potential future applications of such research.

This is a manual that is meant to be used for, and should be used alongside, general training purposes. It will give general instructions how to use the machines in an Eyeglass World lab and will describe the standard method for the average job. It’s not meant to be an exhaustive list of every possibility or every circumstance that you might encounter, and can be used as a resource to answer, and help remind about, the standard procedures of each machine. The instructions are designed for the listed model numbers for each machine. Differently designed machines may be similar, but these instructions may not be perfectly applicable to newer models. Please adjust accordingly.

Aluminum (Al) is the best choice for next generation broadband mirrors because it has high reflectance over a wide range of wavelengths. However, the far ultraviolet ( λ < 120 nm) range has not been explored much since aluminum oxide is absorptive in that range. Fluoride protective layers have been used in the past to prevent oxidation, but limit the range of wavelengths that can be clearly observed. These protective layers also make studying the reflectance of Al in the UV range difficult. This paper explores the rate at which aluminum oxidizes in different storage environments. Samples were stored in liquid nitrogen (LN2), hexane and dry ice environments. Oxide thicknesses were measured using variable-angle, spectroscopic ellipsometry (VASE). Rates of oxidation during storage were compared with oxidation in ambient lab air. It is shown that LN2 retards oxidation by a factor of 500, hexane by a factor of 200 and dry ice by a factor of 40. The results shows that aluminum oxidation can be significantly retarded. This opens up possibilities of ultra-thin protective layers, which would allow the far uv to be observed by space telescopes.

I studied angular-dependent extreme ultraviolet (XUV) transmission and reflection data from an XUV-absolute photodiode to obtain indices of refraction of the diode’s surface SiO2.layer. These parameters were also measured for an aluminum fluoride thin film that covered half the diode’s surface. Measurements were made at the Advanced Light Source (ALS) by BYU students. Various multilayer optical models were explored to extract the thickness of the AlF3 and SiO2 layers and the indices of refraction of SiO2. This study looked at wavelengths from 12 nm to 49.5 nm. I found the indices of refraction SiO2 to be close to the literature values at the shorter wavelengths (up to about 20 nm) but then the indices of refraction increasingly deviated as the wavelengths approached the upper limit of wavelengths measured—49.5 nm.

Lithium fluoride (LiF) has the highest band gap of any solid material and thus has many applications in far ultraviolet (FUV) optics. However, LiF is difficult to work with because of its hygroscopic nature, meaning it can absorb water out of air. Surprisingly, little is known about what happens microscopically and structurally to LiF thin films when exposed to humid air. To shed light on this, LiF was deposited on bare Si wafers by resistive heating evaporation and stored in various levels of humidity. Samples were characterized using variable-angle, spectroscopic ellipsometry (VASE), atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). Results show that LiF films exposed to a relative humidity (RH) above 90% undergo irreversible changes. These changes include optical properties as determined by VASE, the surface structure as determined by SEM, and the surface roughness as determined by AFM. On the other hand, samples stored at a dew point of -22° C (4% RH room temperature), showed only small changes in ellipsometric constants. The ones stored at intermediate humidity 4° C (21% RH at room temperature) showed larger changes in ellipsometric constants. SEM also showed that deliquescence as well as efflorescence occur in LiF thin films under higher humidity conditions.

Miniature spectrometers are of great interest to NASA as necessary instrumentation is scaled down and optimized for specific space applications. Semiconductor nanocrystals called quantum dots (QD) are being used to create a miniature high-resolution filter-based spectrometer, with the goal of use in space within five years. Computational imaging techniques—such as automated image analysis and mathematical spectrum reconstruction algorithms—are two of the key aspects to making the QD spectrometer a reality. This thesis discusses the process of developing these computational methods, along with the improvements that have occurred from previous work.

Uranium, a nuclear fuel source, can oxidize and degrade in reactor conditions. Previous studies have shown oxidation resistance in a uranium-niobium alloy. The nature of the oxides that form on U-6Nb after long exposure to air was explored using neutron diffraction at Los Alamos National Laboratory. We deposited thin films of uranium-niobium alloys for oxidation studies. We used ellipsometry to quantify the oxide growth over time as a function of niobium content. We found that the oxide thickness increases linearly with the logarithmic of time. This study also supports the hypothesis that uranium and niobium oxides form a protective passivation layer on a uranium alloy, preventing oxidation and extending the life of the fuel.

A revolutionary solution for colorblindness was devised by Dr. Don McPherson who invented color corrective glasses for the colorblind to see colors in 2012. We are hoping to create greater empathy for colorblind individuals and to assist in creating a more colorblind-accessible environment. Hence, converse to the colorblind corrective glasses, in this project we assumed a person with healthy color vision would perceive the world as a red-green colorblind person if only 540 nm to 570 nm of wavelengths were let through by the dichroic filters. We report on the creation of googles that causes people wearing them to lose red-green discrimination. In short, our goal is to allow non-colorblind individuals to experience red/green colorblindness. Seventeen volunteers completed Ishihara colorblind tests, sixteen of them with healthy color vision were diagnosed as severely red/green colorblind while taking the test with colorblind goggles on.

NASA is preparing to send new telescopes into space with the capacity to see into the far ultraviolet (UV) spectrum. Many materials lose their reflectance the farther into the UV that they go, but Al is a prime candidate because of its good reflectance in the far ultraviolet. As such, mirrors with Al bases and protective layers are being researched as candidates for the thin film mirrors needed on future telescopes. Without a protective layer, Al oxidizes and loses much of its far-ultraviolet reflectance. Prior to sending telescopes into space, many components are placed in storage for extended periods of time. While in storage, thin films may degrade depending on the temperature or humidity of the environment. We stored multiple Al coated with 30 nm AlF3 bilayer mirrors in a 327 K oven in dry air (276 K dew point) to simulate a hot storage room. The Al layers for all samples are 20 nm. Using spectroscopic ellipsometry over the 190 to 1700 nm range to periodically measure samples, we found that there was no significant change in the ~30 nm AlF3 capping layer over a period of 2500 hours.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 eects 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.

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.

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.

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 ).

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.