Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z32: Interactions and Thin Films |
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Sponsoring Units: DMP Chair: Arthur Smith, Ohio University Room: E142 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z32.00001: Long-range repulsive interaction induced Cs superlattices on graphene/SiC Xu-Cun Ma, Can-Li Song, Yi-Lin Wang, Ye-Ping Jiang, Li-Li Wang, Ke He, Xi Chen, Jin-Feng Jia, Qi-Kun Xue The adsorption behavior of Cs on graphenes formed on 6H-SiC(0001) substrate has been investigated by low-temperature scanning tunneling microscopy. At low coverages ($<$0.032 nm$^{-2})$, individual Cs atoms absorb preferentially on distinct sites of the mori\'e pattern, which is formed by the first carbon buffer layer and underlying SiC substrate. At higher coverages ($>$0.33 nm$^{-2})$, short-range ordered structures are presented. Specially, when the coverage is appropriate, Cs atoms can spontaneously form two hexagonal superlattices with a lattice constant of 1.86 nm and 3.24 nm, respectively. By analyzing the coverage-dependent Cs-Cs interatom distance distributions, a long-range repulsive electrostatic interaction between Cs atoms is revealed. The occurrence of Cs superlattices results from the inhomogeneous surface potential on the few layer graphene and electrostatic repulsion between Cs atoms. [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z32.00002: Simulation tactic on dynamic cluster surface interaction Iat Neng Chan, Siu-Long Lei The wave function of time dependent Schrodinger Equation for few surface atoms is simulated to visualize the dynamics of external interaction detail in three dimensions. Instead of finding the solution of continuous variation, step consequence assembled from independent stable moments is used to approach a desired precision as close as possible. The function is plotted in a serious setting of time interval. The graphic distribution shows a similarity as the orbit structures during stable moments. In the computation, the singularity is artificially and logically avoided. Other factors such as spin are not yet considered. For modeling the dynamic interaction, external features such as particles or charges or radiation are integrated as an adjustable environment in the calculation route. Under these stimulations, the change of distribution can be seen and the effects of interaction are imitated roughly. Based on the obtained results, more subjects mainly on the exchanges between the surface states and the incoming factors are under investigated. [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z32.00003: Substrate mediated smooth growth of para-sexiphenyl on graphene Bene Poelsema, Gregor Hlawacek, Fawad S. Khokhar, Raoul van Gastel, Christian Teichert We report on the layer-by-layer growthof lying para-sexiphenyl (6P) molecules on metal supported graphene flakes. The formation of multilayers has been monitored in situ by means of LEEM. $\mu $-LEED has been used to reveal a bulk-like structure of the submonolayer, monolayer and multilayer regime. Graphene is a flexible, highly conductive and transparent electrode material, making it a promising technological substrate for organic semiconductors. 6P is a blue light emitting molecule with a high charge carrier mobility. The combination of an established deposition technique with the unique properties of organic semiconductors and graphene is an enabler for future flexible and cost efficient devices based on small conjugated molecules\textbf{.} [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z32.00004: Investigation of Stability of Single Mn Monolayers on and in w-GaN(000-1) Abhijit Chinchore, Meng Shi, Kangkang Wang, Jeongihm Pak, Arthur Smith There has been much interest in dilute magnetic semiconductors involving GaN. Recently, it has become of interest to consider the possible advantages of delta-doped magnetic layers, rather than a random alloy. Here we investigate experimentally the growth of single Mn monolayers on top of GaN as well as the re-deposition of GaN on the Mn monolayer, using a combination of N-plasma molecular beam epitaxy and reflection high energy electron diffraction (RHEED). The single Mn monolayers form a novel rt3 x rt3 R-30deg structure.[1] Upon nitrogen plasma exposure, this periodicity is removed as seen in RHEED. However, even after heating to as high as 700 C, Auger electron spectroscopy shows very little change in the Mn peak intensity. Furthermore, a rapid reduction of Mn Auger electron peak intensity after only 3-5 GaN bilayers of redeposition is seen, showing that Mn is fully covered by the subsequent GaN layers. Therefore the Mn monlayer appears to be quite stable within the GaN (000-1) surface. This work has been supported by DOE (Grant No.DE-FG02-06ER46317) and NSF (Grant No.0730257). Equipment support from ONR is also acknowledged. [1] Chinchore et al., Applied Physics Letters \textbf{93(18)}, 181908 (2008). [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z32.00005: Growth and Investigation of Mn delta-doped superlattices in w-GaN(000-1) Meng Shi, Abhijit Chinchore, Kangkang Wang, Jeongihm Pak, Arthur Smith, David Rench, Nitin Samarth It is of great interest to form novel spintronic systems involving magnetic layers in semiconductor hosts. Recently, the possibility to form delta-doped magnetic layers in wurtzite GaN has been postulated theoretically [1]. In this work, we deposit single Mn monolayers on w-GaN(000-1) followed by a thin spacer layer of GaN, and then this process is repeated many times in order to form a superlattice of the form Mn/GaN/Mn/GaN/Mn? Samples having different GaN interlayer spacings and repetitions of 50 to 100 have been grown. Reflection high energy electron diffraction data acquired during deposition indicates good quality growth for many repetitions. Magnetic property measurements are currently in progress, and results will be presented. This work has been supported by DOE (Grant No.DE-FG02-06ER46317) and NSF (Grant No.0730257). Equipment support from ONR is also acknowledged. \\[4pt] [1] Cui X.Y. et al, JAP 106, 043711 (2009) [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z32.00006: Out-of-plane nesting of spin spiral in ultrathin Fe/Cu(001) films revealed by SX-ARPES Jun Miyawaki, Ashish Chainani, Yasutaka Takata, Mattia Mulazzi, Masaki Oura, Yasunori Senba, Haruhiko Ohashi, Shik Shin We investigate the origin of the spin spiral (SS) state in epitaxial ultrathin Fe films on Cu(001) using soft x-ray (SX)-ARPES. Fe/Cu(001) films exhibit a SS, in contrast to the ferromagnetic bulk bcc Fe. We study the in-plane and out-of-plane Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films. It was found that the SS is due to nested regions confined to out-of-plane FSs, which are drastically modified compared to in-plane FSs. From precise reciprocal space maps along $k_z$ in successive Brillouin zones, we identify the associated real space compressive strain of 1.5$\pm$0.5\% along {\it c}-axis. An autocorrelation analysis quantified the incommensurate ordering vector $\mathbf{q}$=(2$\pi/a$) (0,0,$\sim$0.86), favoring a SS. These results are consistent with magneto-optic Kerr effect [1] and surface x-ray diffraction experiments [2] on the Fe/Cu(001) films, and suggest the importance of in-plane and out-of-plane FS mapping for ultrathin films. [1] D.~Qian, {\it et al.}, Phys.~Rev.~Lett.~{\bf 87}, 227204 (2001). [2] H.~L.~Meyerheim, {\it et al.}, Phys.~Rev.~B {\bf 71}, 035409 (2005). [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z32.00007: Effective mass anomalies in strained silicon thin films Jun Yamauchi The most fundamental shape of nanostructures may be a slab or thin film. Semiconductor slabs sandwiched insulators are a most basic model for the channel region of modern devices such as multi-gate and SOI (silicon on insulator) MOSFET. The aim of this presentation is to make systematic investigation of the shape effect on the electronic structures in the semiconductor slabs using a density functional pseudoptentital method. Hydrogen terminated silicon thin films are used as a model of the slabs sandwiched by insulators. Adopted parameters are biaxial strain and crystal direction, as well as the thickness of the film. Among the calculated results, a remarkable feature is that the longitudinal effective mass component of the conduction band reveals anomaly on certain parameter lines in the $<110>$ and $<111>$ confinement cases. This anomaly is due to the confinement effect and lowering of the crystal symmetry by the strain. It is found that the confinement effect is semi-quantitatively explained by an extension of simple zero-point energy model using the first-principles k.p perturbation calculation. [1] J. Yamauchi, IEEE Electron Device Letters vol.29 186 (2008); J. Comp. Theor. Nanoscience (in press). [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z32.00008: Surface electronic structure of single-crystalline zirconium diboride thin films Y. Yamada-Takamura, F. Bussolotti, A. Fleurence, S. Bera, R. Friedlein Single-crystalline thin films of zirconium diboride (ZrB$_{2})$ with a simple crystal structure consisting of alternating hexagonal close-packed Zr and honeycomb B layers have been epitaxially grown on Si(111) by chemical vapor epitaxy. Oxide layers formed upon exposure to air can be removed by heating in ultra-high vacuum resulting in oxide-free and atomically-flat surfaces making the ZrB$_{2}$ films ideal for the epitaxial growth of heterostructures in other setups. The electronic structure of the as obtained ZrB$_{2}$(0001)-(2$\times $2) surface has been studied using angle-resolved ultraviolet photoelectron spectroscopy. Along the $\bar {\Gamma }\bar {M}$ direction two parabolic features in the vicinity of the Fermi level are clearly resolved. While the dispersion of these Zr-derived surface states is similar to those observed at (1x1) single crystal surfaces and calculated dispersion curves for a Zr-terminated slab model, a pronounced intensity change at the zone boundary is a strong indication of a back-folding of electronic bands into the reduced Brillouin zone. The origin of the (2$\times $2) reconstruction is likely the presence of Si atoms on the surface. A flat band at 0.25 eV is accordingly assigned to localized Si-derived states [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z32.00009: ABSTRACT WITHDRAWN |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z32.00010: Elastic properties of polycrystalline aluminum and silver films down to 6 mK Andrew Fefferman, Robert Pohl, Jeevak Parpia Many mechanical resonators, from nanoscale beams to gravitational wave detectors, are coated with polycrystalline or amorphous films, and it is important to understand the contribution of the film to the elastic properties of the composite structure. We have made elastic measurements on high purity micron-thick polycrystalline aluminum and silver films with the double paddle resonator technique, using a single crystal silicon substrate with internal friction $Q^{-1}\approx 2\times10^{-8}$ below a few kelvin. We observed large $Q^{-1} \approx 10^{-4}$ in both films, indicating that these films can contribute substantially to the damping of mechanical resonators, even at very low temperatures. In aluminum, we also observed remarkable agreement between the relative change in sound speed $\delta v/v_0$ and $Q^{-1}$ of the aluminum and the predictions of the tunneling model for an amorphous superconductor well below $T_c$. This agreement might be due to tunneling of dislocation kinks in a modulated kink-Peierls potential. However, previous measurements on polycrystalline bulk metal and films have shown that other glassy properties such as the thermal conductivity and heat capacity are not in agreement with the tunneling model predictions. [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z32.00011: Effects of crystallinity in resistance switching behavior of epitaxial NiO films S.R. Lee, H.M. Kim, K. Char, H.W. Park, D.H. Kwon, M. Kim, M.R. Jo, Y.D. Park, D.C. Kim, S. Seo, R. Jung We fabricated epitaxial NiO films (epi-NiO) on (100) SrRuO$_3$ (SRO) films at room temperature (NiO-RT), 500 $^{\circ}$C (NiO-500), and 700 $^{\circ}$C (NiO-700). Crystallinity of epi-NiO was characterized by X-ray diffraction spectra, which indicates that NiO grown at a higher temperature shows a better crystallinity. I-V properties and associated resistance switching (RS) are investigated by using Pt and SRO as top and bottom electrodes; NiO-RT and NiO-500 exhibit bipolar RS, while the RS phenomenon is not observed in NiO-700. Temperature dependence of initial I- V curves shows that pristine Pt/NiO-500 and Pt/NiO-700 are in an insulating and a metallic state, respectively. The Pt/epi-NiO interfaces are further investigated by transmission electron microscopy and its results will be presented. Our experimental results suggest that crystallinity of epi-NiO is a key parameter for bistability of oxygen states at the Pt/epi-NiO interfaces, which results in distinctive I-V characteristics and associated RS behavior. The implication of our work on the microscopic origin of general switching behavior in NiO will be discussed. [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z32.00012: Structural and Electronic Properties of Mn$_{x}$Ga$_{1-x }$Monolayers on Wurzite GaN(0001) Surface Kangkang Wang, Abhijit Chinchore, Meng Shi, Arthur Smith Ferromagnetic (FM) metal/semiconductor bilayers are of great interest due to their importance in novel spintronics applications, such as spin injection and spin light-emitting diodes$^{[1]}$. It has been reported$^{[2]}$ that $\delta $-MnGa, a FM alloy with T$_{C}$ higher than room temperature (RT), can be grown epitaxial on top of w-GaN(0001) with sharp interface and controllable magnetism. Using molecular beam epitaxy, we deposit up to 3 monolayers (ML's) of Mn onto w-GaN(0001) ``1x1'' surface, which forms Mn$_{x}$Ga$_{1-x}$ with x varying from 0 to $\sim $ 0.6. Mn-induced surface reconstructions and formation of Mn$_{x}$Ga$_{1-x }$crystalline phases are observed by reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy as well as \textit{in-situ} RT-STM. The data suggests large-period reconstructions upon deposition of $<$ 0.25ML Mn and quick formation of $\delta $-MnGa at $\sim $1 ML of Mn. Structural and electronic properties at representative stages will be presented, as well as possible magnetic properties of MnGa ML's. This work has been supported by DOE (Grant No.DE-FG02-06ER46317) and NSF (Grant No.0304314). Equipment support from ONR is also acknowledged. [1] S.A.Wolf \textit{et al}, Science \textbf{294}, 1488 (2001) [2] E.Lu \textit{et al}, Phys.Rev.Lett. \textbf{97}, 146101 (2006) K.K.Wang \textit{et al, M}ater.Res.Soc.Symp.Proc.1118-K06-06 (2009) [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z32.00013: Structural Characterization of $Y_{2}O_{3}$ Films Grown on Sapphire by MBE Shawn Penson, Scott Webster, Raveen Kumaran, Wei Li, Thomas Tiedje Yttrium oxide is a hard, thermally stable, transparent oxide, making it an excellent host for rare earth ions used in solid state laser waveguides. The structural quality of the these thin films can be expected to affect the emission cross section of the active ions and losses in the waveguide due to absorption and scatter. $Y_{2}O_{3}$ films were deposited on A, M, R and C plane sapphire substrates by molecular beam epitaxy. X-ray diffraction and transmission electron microscopy measurements were performed in order to determine the structure of the films. The films exhibited a textured mosaic structure (111) oriented with all substrates. The grains were found to be twinned with strong in plane orientations on A,R and C plane substrates but randomly oriented on M-plane. Grain size and tilt were dependent on the orientation of the sapphire substrate. R-plane substrates gave the highest quality films with larger grains and less mosaic tilt. This is likely due to better lattice matching between the substrate and film. [Preview Abstract] |
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