Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Z10: Novel Instrumentation and Techniques in Surface Science |
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Sponsoring Units: DCMP Chair: Ray Phaneuf, University of Maryland Room: D221 |
Friday, March 25, 2011 11:15AM - 11:27AM |
Z10.00001: Development of a device-oriented UHV scanning probe microscope based on quartz sensors Jacob Tosado, William G. Cullen, Michael S. Fuhrer Scanning tunneling microscopy (STM) provides atomic-scale spatial resolution and performs local electronic spectroscopy of conducting materials. The recent emergence of graphene has highlighted the ability to tune carrier density by applying a gate voltage. However, preparation of samples as field-effect-transistors necessitates a dielectric substrate below the device, which is problematic for STM. Driven by the need to carry out high resolution imaging in ultrahigh vacuum, we are now developing an instrument which combines STM with atomic force microscopy (AFM) using a quartz sensor. This combination allows AFM approach and navigation, with uncompromised STM performance due to the very high stiffness of the quartz sensor. Primary features of the microscope design include in-situ exchange of probes and samples, with flexibility in probe and sample geometries and multiple contacts to both probe and sample. The microscope is housed in a UHV chamber with complete surface preparation and analysis capability. This talk will cover unique design features as well as testing of the microscope concept. [Preview Abstract] |
Friday, March 25, 2011 11:27AM - 11:39AM |
Z10.00002: Low-temperature STM/STS study on superconducting FeSe films Xucun Ma, Canli Song, Yilin Wang, Peng Cheng, Lili Wang, Ke He, Xi Chen, Qikun Xue By using molecular beam epitaxy (MBE) technique, we have prepared single crystalline and atomically flat FeSe thin films on graphene-terminated SiC substrate. Low temperature scanning tunneling microscopy/spectroscopy (STM/STS) measurements reveal that the local superconducting gap in the quasiparticle density of states remains robust down to two triple layers ($\sim $1.1 nm), and that the FeSe films show a novel thickness-dependent superconductivity transition behavior. We show that the superconductivity of the FeSe films can be manipulated by concise control of their surface structures. \textit{dI/dV} mapping of the vortex lattice confirms that FeSe is a typical type II superconductor. Understanding these properties may help us to unravel the mechanism of the recently discovered Fe-based superconductors and even the long-term studied cuprates. [Preview Abstract] |
Friday, March 25, 2011 11:39AM - 11:51AM |
Z10.00003: In situ coherent x-ray scattering and STM studies of hexagonally reconstructed Au(001) in Electrolytes Michael S. Pierce, Vladimir Komanicky, Andi Barbour, Daniel Hennessy, Jun-Dar Su, Alec Sandy, Hoydoo You We have studied the dynamics of Au(001) and Au(111) surfaces in situ in 0.1 M HClO4 electrolyte solution using coherent x-ray scattering experiments and STM microscopy. Our coherent x-ray scattering experiments measure a correlation time for the surface as a function of applied potentials. Coherent x-ray scattering differs from the ordinary x-ray diffraction in sensitivity to the structural and temporal details. The correlation times were obtained from measurements conducted while the surface is in equilibrium and the ordinary surface scattering intensity is constant. The correlation time changes from high $10^3$ seconds to low $10^2$ seconds. The correlation times of reconstructed surfaces at low potential are at least an order of magnitude smaller than those measured at the reconstructed surfaces in vacuum. The correlation times also change dramatically in response to the applied potential. These experiments also represent the first successful application of coherent x-ray scattering to the study of electrochemical interfaces in situ. [Preview Abstract] |
Friday, March 25, 2011 11:51AM - 12:03PM |
Z10.00004: Local transport measurements at mesoscopic length scales on epitaxial graphene using scanning tunneling potentiometry Weigang Wang, Ko Munakata, Michael Rozler, Francoise Kidwingira, Malcolm Beasley By contrast to quantum transport measurements across nanostructures (single molecular, carbon nanotube, or lithographically manufactured), local transport measurements on macroscopic samples at mesoscopic length scales are relatively uncharted territory. Scanning tunneling potentiometry (STP) is the natural tool to perform such measurements. Due to its characteristic materials parameters, thin epitaxial graphene on silicon carbide is an attractive model system for search of quantum mechanical effects in local transport. We report results of STP measurements on epitaxial graphene at room temperature. In addition to the expected residual resistivity dipoles, we have observed features in the measured potential that are counter intuitive to classical diffusive considerations. Based on these results, we conclude that a more complete theoretical description of STP measurement is necessary. Work supported by AFOSR. [Preview Abstract] |
Friday, March 25, 2011 12:03PM - 12:15PM |
Z10.00005: Possible microscopic origin of large broadening parameter in point Andreev reflection spectroscopy Jian Wei, Goutam Sheet, Venkat Chandrasekhar We report on the low frequency noise in ballistic point-contacts between a silver tip and a niobium foil. The ballistic nature is confirmed by point-contact Andreev reflection (PCAR) spectroscopy. As has been found by others, a broadening parameter $\Gamma$ needs to be introduced to fit the PCAR spectra. For contacts with higher resistance, a larger $\Gamma$ is required to fit the PCAR spectra, and we find that random two level fluctuations dominate the noise spectra. This finding suggests that two level fluctuations contribute to the broadening of the gap features. [Preview Abstract] |
Friday, March 25, 2011 12:15PM - 12:27PM |
Z10.00006: Scanning SQUID measurements of the superconducting state of $\delta$-doped SrTiO$_3$ heterostructures Julie A. Bert, Minu Kim, Chris Bell, Harold Y. Hwang, Kathryn A. Moler The discovery of interface superconductivity in complex oxide heterostructures has generated significant excitement. We used scanning SQUID microscopy to investigate the magnetic properties of one such heterostructure, $\delta$-doped structures in SrTiO$_3$ thin films. We have observed a diamagnetic response and imaged vortices providing further evidence of a two-dimensional superconducting state. Finally we measured the magnetic susceptibility from which we observe spatial inhomogeneities in the superconducting response and can estimate the temperature dependence of the magnetic penetration depth. [Preview Abstract] |
Friday, March 25, 2011 12:27PM - 12:39PM |
Z10.00007: Probing Transient Structures during interfacial charge transfer mimicking solar cells and heterogeneous catalysis Lin Chen, Xiaoyi Zhang, Grigory Smolentsev, Jianchang Guo, Klaus Attenkofer, Andrew B. Stickrath, Di-Jia Liu, Nosheen Gothard Photoinduced charge transfer at interfaces is a key process in photocatalysis and dye sensitized solar cells (DSSCs). Using X-ray transient absorption (XTA) spectroscopy, we extracted metal center surrounding transient structural information in a DSSC mimic, namely the RuN3 dye on the TiO$_{2}$ nanoparticle surfaces. Structural evolution of the adsorbed dye sensitizer and the rearrangement of the nanocrystal surface associated with the electron density shift during and after the interfacial charge injection were investigated. The other interfacial charge transfer system is a suspension of Pt nanoparticles on TiO$_{2}$ where the photoexcitation induces redox reactions and generate hydrogen fuel. The preliminary XTA results demonstrate the feasibility of the method in probing heterogeneous catalytic systems. [Preview Abstract] |
Friday, March 25, 2011 12:39PM - 12:51PM |
Z10.00008: Composition of CuAu alloy and changes upon corrosion studied by Hard X-ray Photoelectron Spectroscopy Parasmani Rajput, Blanka Detlefs, Ajay Gupta, Dieter Kolb, Jorg Zegenhagen Metals and their alloys are highly susceptible to corrosion in wet environment. Dealloying is a particular type of corrosion, attacking practically all metals in industrial use: When an alloy is coming into contact with an electrolyte, the less noble metal may go into solution, typically causing crack formation and subsequent material failure upon stress. We used bulk sensitive Hard X-ray photoelectron spectroscopy (HAXPES) with an excitation energy of 6 keV as a new powerful tool to investigate the chemical composition of alloys and changes upon dealloying, studying Cu$_{x}$Au (with x = 4.1) alloy films of 9 to 50 nm thickness. Morphology, structure and composition were further characterized by atomic force microscopy, X-ray reflectivity and quantitative X-ray fluorescence. The HAXPES analysis revealed that chemical shifts of metal core-levels, i.e. Au4$f$ and Cu3$s$, can be used as a benchmark for the alloy composition. HAXPES as a function of electron emission angle allowed depth sensitive determination of the chemical composition before and after dealloying in sulphuric acid. [Preview Abstract] |
Friday, March 25, 2011 12:51PM - 1:03PM |
Z10.00009: X-Ray Characterization of Electrodeposited Alloy Thin Films Nicholas Wozniak, Daniel McNeel, Alyssa Frey, Jennifer Hampton Particle-Induced X-ray Emission (PIXE) was used to measure the composition of electrodeposited NiFe and NiFeCu thin films. The thin films were deposited on gold-plated silicon wafers, and PIXE spectra were analyzed to obtain the Ni, Fe, Cu, and Au content in each sample. By comparing the Ni, Fe, and Cu content in a sample to the Au content in the same sample, the relative amounts of deposited material between samples could be measured. The effect of the deposition solution, deposition parameters and duration of deposition was explored. The results were compared to those measured with Energy Dispersive Spectroscopy. The results show that PIXE can measure the total deposited metal in a sample over at least four orders of magnitude with similar fractional uncertainties. The technique is also sensitive enough to observe the variations in alloy composition due to sample non-uniformity or variations in deposition parameters. [Preview Abstract] |
Friday, March 25, 2011 1:03PM - 1:15PM |
Z10.00010: Thermal conductance of interfaces with molecular layers - low temperature transient absorption study on gold nanorods supported on self assembled monolayers Wei Wang, Jingyu Huang, Catherine Murphy, David Cahill While heat transfer via phonons across solid-solid boundary has been a core field in condense matter physics for many years, vibrational energy transport across molecular layers has been less well elucidated. We heat rectangular-shaped gold nanocrystals (nanorods) with Ti-sapphire femtosecond pulsed laser at their longitudinal surface plasmon absorption wavelength to watch how their temperature evolves in picoseconds transient. We observed single exponential decay behavior, which suggests that the heat dissipation is only governed by a single interfacial conductance value. The ``RC'' time constant was 300ps, corresponding to a conductance value of 95MW/m$^{2}$K. This interfacial conductance value is also a function of ambient temperature since at temperatures as low as 80K, which are below the Debye temperature of organic layers, several phonon modes were quenched, which shut down the dominating channels that conduct heat at room temperature. [Preview Abstract] |
Friday, March 25, 2011 1:15PM - 1:27PM |
Z10.00011: Contact voltage-induced softening transition of gold-on-gold contacts at cryogenic temperatures Diana Berman, Matthew Walker, Jacqueline Krim A series of experiments were performed in vacuum environments to investigate the impact of contact voltage on the surface softening transition for gold-on-gold contacts at cryogenic temperatures [1]. The purpose of this work was twofold: (1) To examine whether asperity heating models already validated for high temperature contacts were also applicable at cryogenic temperatures, and (2) to explore the implications and validity of prior suggestions that contact temperatures between 338 and 373 K are high enough to dissociate adsorbed film and/or push them aside, but low enough to prevent asperities from becoming soft and adherent. Measurements on two distinct RF MEMS switch types were performed in the temperature range 79 - 293K and for contact voltages ranging from 0.01 to 0.13 V. Contact resistance values at all temperatures were observed to be lower for higher contact voltages associated with increased heating and softening effects. In-situ removal of adsorbed species by oxygen plasma cleaning resulted in switch adhesive failure. Switches that had not been cleaned meanwhile exhibited distinct reductions in resistance at contact temperatures close to 338 K, consistent with suggestions that films begin to desorb, disassociate, and/or be pushed aside at that temperature. Funding agencies: AFOSR, DARPA, and NSF DMR. [1] D. Berman, M. Walker, J. Krim, J. Appl. Phys., 108, 044307 (2010). [Preview Abstract] |
Friday, March 25, 2011 1:27PM - 1:39PM |
Z10.00012: Reduction of a polar oxide surface in a strong DC-field Wolfram Steurer, Svetlozar Surnev, Giovanni Barcaro, Alessandro Fortunelli, Falko P. Netzer Polar oxide surfaces are of fundamental scientific interest because of their inherent instability in bulk samples on electrostatic grounds. Here we report first experimental evidence of field-induced reduction of a polar oxide surface by applying homogeneous external DC-fields. Ultrathin Ni-oxide nanostructures immersed into an Ag(100) substrate have been grown by reactive evaporation and have subsequently been exposed to electric fields in the range of 0.5-1.6 V/nm. We achieve such high fields in a setup resembling a plate capacitor where the Ag(100) substrate (with the deposited NiO film) acts as the cathode with a counter electrode placed 800nm apart. For fields exceeding the threshold of 0.9 V/nm, oxygen atoms are torn away from the surface, thus, efficiently reducing the initially highly-ordered Ni-oxide film. The remaining Ni atoms on the surface are highly mobile and cluster together. No oxide reduction occurs if the field polarity is inverted. [Preview Abstract] |
Friday, March 25, 2011 1:39PM - 1:51PM |
Z10.00013: Interference between Surface and Bulk Scattering in Nanoscale Conductors Swarbhanu Chatterjee, Alexander Meyerovich We analyze the quasiclassical and quantum interference between the bulk and boundary scattering channels in thin high quality films. The effective transport time is calculated beyond the Matthiessen's approximation as an expansion in inverse bulk mean free path. The interference corrections to resistivity exhibit a crossover between two regimes that are characterized by distinct dependences on temperature and/or impurity concentration. In our quasiclassical approximation the results reduce to a transparent analytical expression. We discuss differences between quantum and quasiclassical approaches and experimental implications of our results. [Preview Abstract] |
Friday, March 25, 2011 1:51PM - 2:03PM |
Z10.00014: Quantitative Transmission Electron Microscopy of Nanoparticles and Thin-Film Formation in Electroless Metallization of Polymeric Surfaces Aniruddha Dutta, Helge Heinrich, Stephen Kuebler, Chris Grabill, Aniket Bhattacharya Gold nanoparticles(Au-NPs) act as nucleation sites for electroless deposition of silver on functionalized SU8 polymeric surfaces. Here we report the nanoscale morphology of Au and Ag nanoparticles as studied by Transmission Electron Microscopy (TEM). Scanning TEM with a high-angle annular dark-field detector is used to obtain atomic number contrast. From the intensity-calibrated plan-view scanning TEM images we determine the mean thickness and the volume distribution of the Au-NPs on the surface of the functionalized polymer. We also report the height and the radius distribution of the gold nanoparticles obtained from STEM images taking into consideration the experimental errors. The cross sectional TEM images yield the density and the average distance of the Au and Ag nanoparticles on the surface of the polymer. [Preview Abstract] |
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