Bulletin of the American Physical Society
Joint Fall 2011 Meeting of the Texas Sections of the APS, AAPT, and Zone 13 of the SPS
Volume 56, Number 7
Thursday–Saturday, October 6–8, 2011; Commerce, Texas
Session D3: Condensed Matter Physics and Materials Research I |
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Chair: Robert Glosser, University of Texas at Dallas Room: Sam Rayburn Center Second Floor, Room Traditions |
Friday, October 7, 2011 1:40PM - 1:52PM |
D3.00001: Band offsets of atomic layer deposited Al$_{2}$O$_{3}$, BeO and HfO$_{2}$ on Si measured by linear and nonlinear internal photoemission Ming Lei, Jung Yum, Sanjay Banerjee, Michael Downer Hf-based high-$k$ dielectrics recently replaced SiO$_{2}$ as gate oxide in some commercial transistors in order to continue down scaling complementary metal-oxide-semiconductor devices while minimizing leakage currents. Research continues on alternative high-$k$ gate oxides. The required permittivity of advanced gate dielectrics must be balanced against the barrier height for tunneling and thermionic emission leakage currents governed by the offsets of their conduction and valence bands from those of the substrate. Here we present measurements of conduction band offsets of three high-$k$ dielectrics on Si(001) substrates using linear internal photoemission (IPE), detected by measuring photocurrent from a biased MOS capacitor, and internal multi-photon photoemission (IMPE), detected by optical second-harmonic generation (SHG). We present new IPE and IMPE measurements for atomic layer deposited beryllium oxide on Si(001). Band offset measurements for Si/HfO$_{2}$, show a strong effect of post-deposition annealing on the energy barrier height. [Preview Abstract] |
Friday, October 7, 2011 1:52PM - 2:04PM |
D3.00002: Development and Characterization of a Highly Textured Bi-2212 Superconducting Ribbon Kyle Damborsky, Feng Lu, Peter McIntyre, Nathaniel Pogue, Elizabeth Sooby Development of future hadron colliders, high field NMR spectrometers, and a potential muon collider are dependent upon the availability of superconducting materials capable of producing magnetic fields greater than the upper critical fields of NbTi (12 T) and Nb3Sn (24 T) at 1.9 K. One such material is the high temperature superconductor Bi-2212 which has an upper critical field in excess of 45 T and is presently available as a fine filament round wire. The use of Bi-2212 in very high field magnet development is limited by the small fraction of the intrinsic critical current density achieved in the industry standard oxide powder in tube process wires. This approach is limited by a large porosity, parasitic phase growth, and poor connectivity due to poor texture of the superconducting grains within conductor filaments. To reduce these damaging effects, the authors report upon the development of a new process for pretexturing and compacting fine powder Bi-2212 into highly textured, high density ribbons through a roll processing technique. These ribbons may then be further formed into a round wire conductor through a modified jelly roll process. Details of the roll processing technique and jelly roll conductor will be presented along with an initial characterization of the ribbons. [Preview Abstract] |
Friday, October 7, 2011 2:04PM - 2:16PM |
D3.00003: TMAH wet etching of silicon micro- and nano-fins for selective sidewall epitaxy of III-Nitride semiconductors Lianci Liu, Denis Myasishchev, Vladimir Kuryatkov, Sergey Nikishin, Mark Holtz, Rusty Harris We describe formation of silicon micro- and nano-fins, with (111)-plane sidewall facets, for selective sidewall epitaxy of III-Nitride semiconductors. The fins are produced by wet etching (110)-oriented silicon wafers. Silicon dioxide is deposited using plasma enhanced chemical vapor deposition for producing a hard mask. The silicon dioxide is patterned using photo- and electron-beam lithography for micro- and nano-fins, respectively, followed by wet etching in hydrofluoric acid. Wet etching to produce the silicon fins is carried out using tetramethyl ammonium hydroxide (TMAH) diluted with isopropyl alcohol (IPA). Atomic force microscopy and scanning electron microscopy are used to determine morphology including the surface roughness of the area between fins and the etching rate of silicon. We tune the etching time, temperature, and percentage of IPA in order to get the best surface on both (111) and (110) planes. Adding IPA is found to alter the etch rate and improve the surface between the fins without adversely affecting the sidewall morphology. [Preview Abstract] |
Friday, October 7, 2011 2:16PM - 2:28PM |
D3.00004: Optoelectronic studies of boron-doped and gamma-irradiated diamond thin films Puskar Chapagain, Anastasiia Nemashkalo, Raul Peters, John Farmer, Sanju Gupta, Yuri M. Strzhemechny Elucidation of microscopic properties of a synthetic diamond, such as formation and evolution of bulk and surface defects, chemistry of dopants, etc. is necessary for a reliable quality control and reproducibility in applications. Employing surface photovoltage (SPV) and photoluminescence (PL) spectroscopic probes we studied diamond thin films grown on silicon by microwave plasma-assisted chemical vapor deposition with different levels of boron doping in conjunction with gamma irradiation. SPV measurements showed that while the increase of boron concentration leads to a semiconductor-metal transition, subsequent intense gamma irradiation reverts back the quasi-metallic samples to semiconducting state via compensating electrical activity of boron by hydrogen. One of the most pronounced common transitions in the SPV spectra was observed at $\sim $3.1 eV, also present in most of the PL spectra. We argue that this is a signature of the sp$^{2}$-C clusters/layers in the vicinity of grain boundaries. [Preview Abstract] |
Friday, October 7, 2011 2:28PM - 2:40PM |
D3.00005: LaF$_{3}$ and YAG:Ce$^{3+}$ nanoparticle composites for radiation detection Ryan Hall Lanthanum fluoride (LaF$_{3}$) is an attractive crystal matrix, since it is non-hygroscopic and thermally stable. Previous work with bulk crystals has shown their suitability for scintillating detectors when doped with various rare-earth elements to tune emission properties. We explore the use of doped LaF$_{3}$ nanocrystals, less than 50 nm in diameter, using a combination of Ce$^{3+}$, Tb$^{3+}$, and Eu$^{3+}$ dopants at concentrations from 1\% to 10\% by mole. These doped nanoparticles have the advantage of easy synthesis, and may be assembled through various methods depending on the desired properties. They also possess a large surface-to-volume ratio suitable for modification, such as ligands to control solubility in a variety of substances. For enhanced luminosity, we combine the LaF$_{3}$:Ce$^{3+}$ with doped yttrium aluminum garnet (Y$_{3}$Al$_{5}$O$_{12}$:Ce$^{3+}$), prepared through a glycothermal method as nanoparticles of $\sim$30 nm diameter. We propose to use the energy transfer between the Ce dopant on each crystal to effect fast, high-yield response to incident radiation. Morphology of the LaF$_{3}$ and YAG products is examined, and we quantify response to a range of photon wavelengths, toward the goal of incorporating them into a radiation detection device. [Preview Abstract] |
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