Selected Publications

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By R. Vanfleet (et al.)
Abstract: Re-distribution of Mn atoms implanted into Czochralski silicon (CzSi: Mn) and floating zone silicon (FzSi: MN) after thermal annealing between 300 and 1,000 degrees C have been investigated by secondary ion mass spectroscopic technique. The motivation behind our study comes from recent report of strong magnetic ordering up to 400 K of Mn(+) implanted silicon samples reported by Bolduc et al. (Phys Rev B 71: 033302, 2005). Our silicon substrates were implanted with 160 keV Mn(+) ion to a dose of 1 x 10(16) cm(-2) at either room temperature or at 340 degrees C. The Mn profiles after annealing above 900 degrees C showed multiple concentration peaks for the 340 degrees C implanted samples, but not for the samples implanted at room temperature. We also carried out cross sectional TEM and ferromagnetic resonance measurements to correlate the micro-structural and magnetization data with the Mn depth profile obtained by SIMS.
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By R. R. Vanfleet (et al.)
Abstract: Antiphase domains are seen in single crystal gamma lithium aluminate (gamma-LiAlO(2)) with 16.7 nm periodicity in the < 110 > direction. Alternate domains have a 1/2 [001] shift. Beta phase lithium aluminate (beta-LiAlO(2)) is seen to form on the surface of the as-received wafers with an epitaxial strain limited relationship with the bulk gamma phase. The orthorhombic beta phase aligns with the a and b axes (0.528 and 0.630 nm) matching with the tetragonal gamma phase's a and c axes (0.5168 and 0.6268 nm). The gamma and beta phases are seen to have different etch rates. The beta phase converts back to the gamma phase above 450 degrees C. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3014193]
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By Guillermo Acosta, Richard Vanfleet, David D. Allred, and R. S. Turley
Abstract: When considering the optical performance of thin films in the Extreme Ultraviolet (EUV), developing an accurate physical description of a thin film coating is necessary to be able to successfully model optical performance. With the short wavelengths of the EUV, film interfaces and sample roughness warrant special attention and care. The surfaces of thin film samples are routinely measured by Atomic Force Microscopy, from which roughness can be determined. However, characterizing the quality of interfaces below the surface is much more challenging. In a recent study of scandium oxide thin films, High Resolution Transmission Electron Microscopy and Annular Dark Field Scanning Transmission Electron Microscopy (ADF STEM) were used to study the cross section of the samples. ADF STEM data analyzed along a path into the volume of the sample (normal to the interfaces) reveals information of sample density versus depth. This density-depth profile reflects the presence of subsurface film interfaces in the volume of the sample. Additionally, information from the ADF STEM profile can be used to gauge the roughness of the subsurface interfaces, which is used to refine the sample description during modeling. We believe this is the first use of ADF STEM in this capacity. This characterization technique may provide key insight to subsurface interface quality, which is particularly important when optimizing the performance of multilayer coatings in the EUV.
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By R. Vanfleet (et al.)
Abstract: The magnetic properties and microstructure of p-type Si (100) implanted with 1.0 x 10(15) cm(-2) of Cr ions at 200 keV have been investigated by a superconducting quantum interference device (SQUID) magnetometer, scanning electron microscope (SEM) and transmission electron microscopy (TEM). The magnetic hysteresis loops and saturation magnetization of 0.67-0.75 emu/g in a wide temperature range are observed in the as-implanted sample. Annealing of the as-implanted sample modifies the microstructure and therefore weakens the magnetic exchange interaction. TEM observations show that the as-implanted silicon layer is amorphous. After annealing at temperature >= 800 degrees C, the SEM showed that the implanted profile layer became blurred and narrow, the ferromagnetism was weakened, which should have resulted from the re-crystallization of the implanted amorphous layer. These results were further compared with magnetic hysteresis observed in Mn-implanted silicon. (C) 2008 Elsevier Ltd. All rights reserved.
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By R. Vanfleet (et al.)
Abstract: To better understand the mechanism of the reported “quasi‐ferromagnetism” observed in Si ions self‐implanted or irradiated silicon, we carry out high resolution transmission electron microscopy (HRTEM), magnetization measurements using superconducting quantum interference device (SQUID) magnetometer, and ferromagnetic resonance (FMR) measurements of the magnetic interaction of the defect‐associated sites in silicon damaged by silicon self‐implantation or energetic particle beams. The SQUID measurements showed that the silicon self‐implanted sample has paramagnetic ordering. FMR measurements indicated the He++ irradiated sample has a ferromagnetic interaction and yields a Lande g‐factor of 2.35.
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By R. R. Vanfleet (et al.)
Abstract: A scanning transmission electron microscope (STEM) study of silicon-germanium alloying using annular dark field (ADF) or Z-contrast imaging and electron energy loss spectroscopy (EELS) is presented. Results and techniques are discussed. Growth of 11 equivalent monolayers of germanium on silicon at 650 degrees C results in dome-shaped islands or quantum dots that contain up to similar to 40% silicon. The interface between the as-grown island and substrate shows a highly disordered or amorphous zone similar to 1.5-nm wide directly under the island. Annealing for 60 min at 650 degrees C gives larger pyramidal islands with diffuse crystalline interfaces and an equilibrium distribution of up to similar to 70% silicon in the islands.