Matthew Ray, Tenor Trombone

Cavatine / C. Saint-Saëns; With Malice Toward None / John Williams; Sonatina for Trombone and Piano / Kazimierz Serocki; Brass Quintet No. 1 / Victor Ewal

ASSEMBLY AND MODIFICATION OF A HYPERTHERMAL AND LOW ENERGY ION BEAMLINE FOR DETECTING ELECTRON-HOLE PAIR PRODUCTION IN SCHOTTKY DIODES

A hyperthermal and low energy ion beamline to measure electron-hole pair production due to ion bombardment of Schottky diodes has been modified and assembled. A brief overview of the instrument is given and the reason for operating the ion beamline in the hyperthermal and low energy regime is discussed. The capabilities of the ion beamline are unique and provide the means to measure quantities that offer insight into various energy exchange mechanisms that occur at surfaces. Combined with the ability to accept Schottky diode samples, the beamline is capable of measuring both charge transfer and electron-hole pair production caused by ion bombardment of the sample. Details of assembly and modification of the ion beamline as well as theory of operation are discussed. Data verifying the precision of the beamline mass and charge selection processes is provided along with a profile of the ion beam. The beamline has been upgraded to enhance reliability by replacing diffusion pumps with turbomolecular vacuum pumps. Also, the scattering chamber has been outfitted with a load lock system to drastically reduce sample turnaround time, an important feature for the Schottky diode experiments. The theory of Schottky barriers and Schottky diodes is also discussed. Current and voltage measurements were taken on the Schottky diode device and were used to calculate the Schottky barrier height. Using an Ar high flux ion beam and Na low flux ion beam, preliminary electron hole pair measurements on a Schottky diode are presented. A possible explanation of results is provided by considering an analogue to Schottky diodes, metal-insulator-metal tunnel junctions [1]

The dynamics of energy and charge transfer in low and hyperthermal energy ion-solid interactions

The energy and charge transfer dynamics for low and hyperthermal energy (10 eV to 2 keV) alkali and noble gas ions impacting noble metals as a function of incident energy, species and scattering geometry has been studied. The experiments were performed in an ultra-high vacuum scattering chamber attached to a low and hyperthermal energy beamline. The energy transfer was measured for K+ scattered from a Ag(001) surface along the [110] crystalline direction at a fixed laboratory angle of 90°. It was found that as the incident energy is reduced from 100 to 10 eV, the normalized scattered energy increased. Previous measurements have shown a decrease in the normalized energy as the incident ion energy is reduced due to an attractive image force. Trajectory analysis of the data using a classical scattering simulation revealed that instead of undergoing sequential binary collisions as in previous studies, the ion scatters from two surface atoms simultaneously leading to an increased normalized energy. Additionally, charge transfer measurements have been performed for Na+ scattering from Ag(001) along the [110] crystalline direction at a fixed laboratory angle of 70°. It was found that over the range of energies used (10 eV to 2 keV), the neutralization probability of the scattered ions varied from ~30% to ~70% depending on the incident velocity, consistent with resonant charge transfer. A fully quantum mechanical model that treats electrons independently accurately reproduces the observed data. Measurements of electron-hole pair excitations were used to explore the pathways which a solid uses to dissipate the energy imparted by the incident ion beam. Ultrathin film (10 nm) metal-oxide-semiconductor (Au/SiO2 /n-Si) devices were used to detect the electron-hole pairs for cases when the ion deposited all of its translational energy into the solid. The incident ions were incident at an angle normal to the surface of the device to maximize energy deposition and consequently electron-hole pair production. The rectifying metal-oxide-semiconductor device separates the electrons from the holes, allowing a current associated with electron-hole pair production to be measured. In these experiments a number of ion species (He,+ , Li+ , Ar+ , K+ ) were made incident on multiple devices and the incident energy ranged from 100 eV to 2 keV. It was found that electron-hole pair production increased with incident ion velocity consistent with a kinetic electron excitation model where the electrons in the metal are partially confined to the surface

The Effects of Single-Walled Carbon Nanotubes on Plant Growth

Nanotechnology is not only being used to enhance commercial goods but the research into the use of nanomaterials as soil and groundwater remediation options has been underway for some time. The research to date suggests that once CNTs have been taken up by humans, or other species they may cause inflammation, oxidative stress, cell damage, or adverse effects on cell performance. However, when considering the interactions between CNTs and plants cells or developing plants the outcomes are less certain and may be counterintuitive. Interactions between developing plants seem to show neutral or positive short-term effects. Research conducted thus far shows un-functionalized single-walled carbon nanotubes, when suspended in an aquatic environment, seem to enhance the growth of plant life in the short term

Interfacing peripheral nerve with macro-sieve electrodes following spinal cord injury

Macro-sieve electrodes were implanted in the sciatic nerve of five adult male Lewis rats following spinal cord injury to assess the ability of the macro-sieve electrode to interface regenerated peripheral nerve fibers post-spinal cord injury. Each spinal cord injury was performed via right lateral hemisection of the cord at the T9–10 site. Five months post-implantation, the ability of the macro-sieve electrode to interface the regenerated nerve was assessed by stimulating through the macro-sieve electrode and recording both electromyography signals and evoked muscle force from distal musculature. Electromyography measurements were recorded from the tibialis anterior and gastrocnemius muscles, while evoked muscle force measurements were recorded from the tibialis anterior, extensor digitorum longus, and gastrocnemius muscles. The macro-sieve electrode and regenerated sciatic nerve were then explanted for histological evaluation. Successful sciatic nerve regeneration across the macro-sieve electrode interface following spinal cord injury was seen in all five animals. Recorded electromyography signals and muscle force recordings obtained through macro-sieve electrode stimulation confirm the ability of the macro-sieve electrode to successfully recruit distal musculature in this injury model. Taken together, these results demonstrate the macro-sieve electrode as a viable interface for peripheral nerve stimulation in the context of spinal cord injury

Pulsar Timing with the Fermi LAT

We present an overview of precise pulsar timing using data from the Large Area Telescope (LAT) on Fermi. We describe the analysis techniques including a maximum likelihood method for determining pulse times of arrival from unbinned photon data. In addition to determining the spindown behavior of the pulsars and detecting glitches and timing noise, such timing analyses allow the precise determination of the pulsar position, thus enabling detailed multiwavelength follow up.Comment: 6 page, 3 figures, to appear in AIP Conference Proceedings of Pulsar Conference 2010 "Radio Pulsars: a key to unlock the secrets of the Universe", Sardinia, October 201

Looking for Stars and Finding the Moon: Effects of Lunar Gamma-ray Emission on Fermi LAT Light Curves

We are conducting a search for new gamma-ray binaries by making high signal-to-noise light curves of all cataloged Fermi LAT sources and searching for periodic variability using appropriately weighted power spectra. The light curves are created using a variant of aperture photometry where photons are weighted by the probability that they came from the source of interest. From this analysis we find that the light curves of a number of sources near the ecliptic plane are contaminated by gamma-ray emission from the Moon. This shows itself as modulation on the Moon's sidereal period in the power spectra. We demonstrate that this contamination can be removed by excluding times when the Moon was too close to a source. We advocate that this data screening should generally be used when analyzing LAT data from a source located close to the path of the Moon.Comment: 2012 Fermi Symposium proceedings - eConf C12102