The production and control of antihydrogen at very low temperatures provided a key tool to test the validity for the antimaterial of the fundamental principles of the interactions of nature such as the weak principle of equivalence (WEP), and CPT symmetry (Charge, Parity, and Time reversal). The work presented in this dissertation studies the collisions of electrons and positrons in strong magnetic fields that generate magnetobound positronium (positron-electron system temporarily bound due to the presence of a magnetic field) and its possible role in the generation of antihydrogen.

In this work, we demonstrate the mechanism for etching exfoliated graphene on SiO2 and other technological important substrates (Si, SiC and ITO), using low-energy electron sources. Our mechanism is based on helium ion sputtering and vacancy formation. Helium ions instead of incident electrons cause the defects that oxygen reacts with and etches graphene. We found that etching does not occur on low-resistivity Si and ITO. Etching occurs on higher resistivity Si and SiC, although much less than on SiO2. In addition, we studied the degradation mechanism of MoS2 under ambient conditions using as-grown and preheated mono- and thicker-layered MoS2 films. Thicker-layered MoS2 do not exhibit the growth of dendrites that is characteristic of monolayer degradation. Dendrites are observed to stop at the monolayer-bilayer boundary. Raman and photoluminescence spectra of the aged bilayer and thicker-layered films are comparable to those of as-grown films. We found that greater stability of bilayers and thicker layers supports a previously reported mechanism for monolayer degradation involving Förster resonance energy transfer. As a result, straightforward and scalable 2D materials integration, or air stable heterostructure device fabrication may be easily achieved. Our proposed mechanisms for etching graphene and ambient degradation of MoS2 could catalyze research on realizing …

This work explores two very different structural systems: n-type hydrogenated amorphous silicon (a-Si:H) and gold nanoparticles (AuNPs) suspended in a matrix of organic ligands. For a-Si:H, examination of the gas-phase concentration of dopant (1-6% PH3/SiH4) and argon diluent effects includes the temperature dependent conductivity, low-frequency electronic noise, and Raman spectroscopy to examine structure. It is found that a-Si:H samples grown with high dopant concentration or with argon dilution exhibit an anomalous hopping conduction mechanism with an exponent of p=0.75. An experimental approach is used to determine correlations between conduction parameters, such as the pre-exponential factor and the characteristic temperature, rather than an analysis of existing models to explain the anomalous conduction. From these results, the anomalous conduction is a result of a change in the shape of the density of states and not a shift of the Fermi level with dopant. Additionally, it is found that argon dilution increases the carrier mobility, reduces the doping efficiency, and causes a degradation of the short-range order. With AuNPs, a comparison of temperature dependent conductivity and low-frequency noise shows that the temperature coefficient of resistance (TCR) is independent of the length of interparticle distance while the noise magnitude decreases.

This study produced and analyzed shaped tungsten wire tips formed through electrochemical etching. Specifically, the cone length and the radius of curvature of the tip were analyzed. Having the tips move dynamically through an electrolytic solution, such as potassium hydroxide, and tuning the initial starting depth of the tungsten wire along with the dynamic speed of the tungsten wire as it passed throughout the solution allowed various types of tip profiles to be produced. The tip's radius of curvature was able to be reproduced with an accuracy between 88 - 92 %. The method provided would be applicable for the production of various styles of liquid-metal ion source (LMIS) probes and scanning probe microscope (SPM) tips.