High-angular-resolution electron energy loss spectroscopy of hexagonal boron nitride

High-angular-resolution electron energy loss spectroscopy (EELS) is used to study the anisotropic behavior of the boron and nitrogen K ionization edges in h-BN. This work makes significant progress toward improving the anisotropy measurements. The authors show experimentally by EELS the vanishment of the p* peak existing in these K edges in agreement with electronic structure calculations and previous soft x-ray absorption spectroscopy measurements

The Nascent Specter: Vision, Corporeality, Reproduction, and Modernity in Henry James and Photographic Theory

Honors (Bachelor's)EnglishUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/107800/1/rzaluzec.pd

Nanometer-scale sharpness in corner-overgrown heterostructures

A corner-overgrown GaAs/AlGaAs heterostructure is investigated with transmission and scanning transmission electron microscopy, demonstrating self-limiting growth of an extremely sharp corner profile of 3.5 nm width. In the AlGaAs layers we observe self-ordered diagonal stripes, precipitating exactly at the corner, which are regions of increased Al content measured by an XEDS analysis. A quantitative model for self-limited growth is adapted to the present case of faceted MBE growth, and the corner sharpness is discussed in relation to quantum confined structures. We note that MBE corner overgrowth maintains nm-sharpness even after microns of growth, allowing the realization of corner-shaped nanostructures.Comment: 4 pages, 3 figure

Sample Preparation Methodologies for In Situ Liquid and Gaseous Cell Analytical Transmission Electron Microscopy of Electropolished Specimens

AbstractIn recent years, an increasing number of studies utilizingin situliquid and/or gaseous cell scanning/transmission electron microscopy (S/TEM) have been reported. Because of the difficulty in the preparation of suitable specimens, these environmental S/TEM studies have been generally limited to studies of nanoscale structured materials such as nanoparticles, nanowires, or sputtered thin films. In this paper, we present two methodologies which have been developed to facilitate the preparation of electron-transparent samples from conventional bulk metals and alloys forin situliquid/gaseous cell S/TEM experiments. These methods take advantage of combining sequential electrochemical jet polishing followed by focused ion beam extraction techniques to create large electron-transparent areas for site-specific observation. As an example, we illustrate the application of this methodology for the preparation ofin situspecimens from a cold-rolled Type 304 austenitic stainless steel sample, which was subsequently examined in both 1 atm of air as well as fully immersed in a H2O environment in the S/TEM followed by hyperspectral imaging. These preparation techniques can be successfully applied as a general procedure for a wide range of metals and alloys, and are suitable for a variety ofin situanalytical S/TEM studies in both aqueous and gaseous environments.</jats:p

Radiation effects in Zr and Hf containing garnets

Garnets have been considered as host phases for the safe immobilisation of high-level nuclear waste, as they have been shown to accommodate a wide range of elements across three different cation sites, such as Ca, Y, Mn on the a-site, Fe, Al, U, Zr, and Ti on the b-site, and Si, Fe, Al on the c-site. Garnets, due to their ability to have variable composition, make ideal model materials for the examination of radiation damage and recovery in nuclear materials, including as potential waste forms. Kimzeyite, Ca3Zr2FeAlSiO12, has been shown naturally to contain up to 30 wt% Zr, and has previously been examined to elucidate both the structure and ordering within the lattice. This study examines the effects of radiation damage and recovery using in-situ ion beam irradiation with 1 MeV Kr ions at the IVEM-TANDEM facility, Argonne National Laboratory. The complementary Hf containing system Ca3Hf2FeAlSiO12 was also examined, and found to have a different response to irradiation damage. A sample of irradiated Ca3Zr2FeAlSiO12, at 1000 K, was characterised using aberration corrected (S)TEM and found to contain discreet, nano-sized, crystalline Fe rich particles, indicating a competing process during recovery is occurring

Precise determination of atom configuration in partially disordered spinel compounds by HARECSX.

Electron channeling enhanced x-ray spectroscopy has been being widely used to determine ordered arrangement of component atoms in multinary inorganic or metallic crystals. Recent theoretical advancements in the modeling of characteristic x-ray emission by inelastic scattering of incident electrons under dynamical diffraction conditions has achieved remarkable progress, and it has enabled scientists to analyze the experimental intensity of x-ray emission in precise detail. In this study, the ion configuration in magnesium aluminate spinel (MgO{center_dot}nAl{sub 2}O{sub 3}) has been examined by measurements of characteristic x-ray emission as a function of incident electron beam direction at high angular resolution, a technique which we have termed HARECXS (high angular resolution electron channeling x-ray spectroscopy). This paper reports the results and emphasizes the applicability of HARECXS to partially disordered materials

HVEM-Tandem and EELS study of radiation damage in zirconolite

Zirconolite (CaZrTi{sub 2}O{sub 7}) is the major host phase for actinides in Synroc, a promising waste form for the immobilization of high-level radioactive waste. The effect of radiation damage on the structure and durability of zirconolite are important to predictive modeling of zirconolite`s behavior in the repository environment and risk assessment. In this study, radiation damage effects in zirconolite were investigated by irradiating samples with 1.5 MeV Kr{sup +} ions using the HVEM-Tandem at Argonne National Laboratory (ANL) and energy loss electron spectroscopy (EELS). The HVEM-Tandem consists of a modified AEI high voltage transmission electron microscope interfaced to a 2 MV tandem ion accelerator. EELS spectra were collected using a Philips 420 TEM, operated at 120 kV, fitted with a Gatan Model 607 Serial EELS. EELS data were recorded at resolutions of {approximately} 1.0 eV and at a dispersion of about {approximately} 0.25 eV. Selected area diffraction patterns (SADs) of individual grains of various zirconolites were monitored as a function of dose to establish the critical dose for amorphization (D{sub c}). The authors found that (1) D{sub c}(zirconolite) is independent of the atomic weight of dopants in zirconolite and the mean atomic weight of the sample and that (2) the Bragg reflections in SAD patterns which persist to the highest doses are firstly those resulting from the fluorite sublattice and secondly the four (110)-type reflections which lie on the innermost of the two diffuse rings representative of amorphous zirconolite

Effects of ion implantation and temperature on radiation-induced segregation in Ni-9Al alloys

Effects of Ne and Sc implantation on radiation-induced segregation (RIS) in Ni-9at.%Al were studied in-situ using the high-voltage electron microscope/Tandem accelerator at ANL. A highly-focused 900- keV electron beam generated radial defect fluxes which, in turn, induced transport of Al atoms toward the center of the electron- irradiated area via the inverse Kirkendall effect. Radial segregation rate of Al atoms was monitored by measuring the diameter of the {gamma}{prime}-Ni{sub 3}Al zone which formed in the Al-enriched area during irradiation. Ne and Sc implantation effects on RIS were investigated at 550 C; Ne effects were also examined at 625 C to determine effect of temperature on ability of Ne to act as defect trapping sites, causing RIS suppression. It was found that the RIS suppression effect of Ne increased with irradiation temperature and that Sc had a small RIS suppression effect which increased with Sc implantation dose. Ne bubbles which formed during implantation are believed to be responsible for its strong suppression effect. 6 figs, 12 ref