Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session J20: Surfaces: Novel Instrumentation and Techniques |
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Sponsoring Units: DCMP Chair: Jianhua Gu, West Virginia University Room: LACC 407 |
Tuesday, March 22, 2005 11:15AM - 11:27AM |
J20.00001: Coherent Atom Beams to Probe Surface Dynamics Forest Patton, Stephen Kevan We are developing a probe of surface dynamics for time scales and size scales on the order of 1ms and 1 nm respectively. This is done by quasielastic scattering of a coherent thermal atom beam off a surface. Helium atoms and hydrogen molecules have de Broglie wavelengths of about 1 angstrom making them natural choices for nanoscale probes. Scattered coherent atoms interfere with themselves to create a speckle pattern. As in dynamic light scattering, monitoring the change in the reflected speckle pattern will probe the time scales of surface dynamical processes. We have created a continuous coherent beam of atoms. We have measured diffraction from single slits, pinholes, and sets of randomly oriented pinholes (to simulate a speckle pattern). We are at the stage where we are trying to reflect the beam off of a sample. The set up includes using a high voltage ionization tip and channel electron multiplier as detector, a micron sized glass capillary nozzle with 1000 PSI stagnation pressure, and micron sized skimmers and pinholes to create the conditions for coherence. [Preview Abstract] |
Tuesday, March 22, 2005 11:27AM - 11:39AM |
J20.00002: Atom-by-atom extraction by controlling a scanning tunneling microscope tip- cluster interaction Aparna Deshpande, Danda Acharya, Joel Vaughn, Kai-F Braun, Saw-W Hla, Handan Yildirim, Abdelkader Kara, Talat Rahman We present a novel atom-by-atom extraction scheme using scanning tunneling microscope (STM) manipulations on a Ag(111) surface at 6K under an ultra-high-vacuum condition. At the initial step, a silver nanocluster is deposited on the surface by gently touching the silver coated tip onto the surface. Individual silver atoms from the cluster are then extracted by precisely controlling the tip-cluster interactions. The recorded STM tip height signals reveal atomistic details of the atom extraction dynamics. The experimental findings are corroborated by total energy calculations based on interaction potentials using the embedded atom method. [Preview Abstract] |
Tuesday, March 22, 2005 11:39AM - 11:51AM |
J20.00003: Laser Speckle Interferometry for Measuring Three-Dimensional Mesoscopic Deformations in Polycrystalline Surfaces Timothy Smith, Lori Bassman, Zamir Lalji, Eric Flynn, Tommy Leung, Sean Cramer, Nick vonGersdorff, Scott Greenfield, Aaron Koskelo A speckle interferometric microscope has been constructed to simultaneously measure mesoscopic deformations in all three directions at a surface. The purpose is to understand mesoscale mechanics in polycrystalline materials using direct observation. The microscope uses three different wavelength lasers to separate dimensional data (out-of-plane and two in-plane directions) while capturing the intensity of speckle reflected from a surface as a function of position and time. Images are captured before and after deformation, with an intermediate image taken before deformation but with a mirror in one arm of each interferometer tilted. Post-processing exploits the mirror tilts to produce carrier fringes that isolate deformation data in Fourier space and increase sensitivity by orders of magnitude over traditional interferometry. Data are taken with 1 $\mu $m spatial resolution, and 10 nm deformations have been resolved. Experiments underway are using the system to study polycrystalline creep. [Preview Abstract] |
Tuesday, March 22, 2005 11:51AM - 12:03PM |
J20.00004: Ultrafast Electron Diffraction for Interfaces and Nanometer Scale Materials Chong-Yu Ruan Surfaces are essential in many fundamental processes in materials and biology. Atomic interfaces can be modified with layered structures to engineer properties for nanometer scale sensing and electronics, or be used as templates for monolayer-assemblies with control from surface chemistry. Ultrafast electron diffraction (UED) can be applied to resolve, for these materials, both structures and dynamics to elucidate the underlying mechanisms and functions. I will outline the recent developments of surface UED in which crystalline substrates were used as templates for making chemically modified layers or supramolecular assemblies; their local structures and periodic orders in the long range reflect their affinities to the substrates. With controls of laser fluences, energies, and surface characters, strongly driven (either from charges or from thermal strains) restructuring of the surfaces and adspecies were observed with sub-angstrom displacement of atoms following the ultrashort laser impulse in the far-from-equilibrium regime at short time and at near-equilibrium at long times. [Preview Abstract] |
Tuesday, March 22, 2005 12:03PM - 12:15PM |
J20.00005: Towards a direct method for low energy electron diffraction Dilano Saldin, Valentin Shneerson, Klaus Heinz A direct method for crystallography is an algorithm that leads directly from a set of measured diffraction intensities to an atomic-scale structure without the need for guesswork or iterative model building. Recently there has been considerable progress towards the development of such a method in the area of surface x-ray diffraction, where knowledge of the bulk structure allows the problem to be treated as one of structure completion. The algorithm involves iteratively satisfying constraints in real and reciprocal space. Extension of such a methodology to LEED is much more difficult as there is no invertible Fourier transform relationship between relevant quantities in the two spaces, due to multiple scattering. Nevertheless, we have made significant progress towards the solution of this inverse problem. We will describe the algorithm and give examples of practical applications to measured experimental data. [Preview Abstract] |
Tuesday, March 22, 2005 12:15PM - 12:27PM |
J20.00006: Single electron manipulation and imaging by Electrostatic Force Microscopy Ezra Bussmann, Clayton Williams A new scanning probe method capable of detecting single electron tunneling events to/from individual electronic states at the surface of an insulator has recently been demonstrated [1,2]. The approach has now been used to demonstrate the manipulation and imaging of single electrons at an oxide surface. With a positive bias voltage on the sample, single electron tunneling events are observed when the probe is brought within tunneling range. Subsequent imaging clearly shows a localized change in the surface potential each time an electron tunnels. When the polarity of the bias voltage is reversed, the electron at the surface tunnels back into the probe, with a corresponding change observed in the image of the surface. This method provides a means to characterize individual electron traps in insulator films. The details of the experiment and corresponding theory will be presented and the manipulation results will be discussed. 1. L. J. Klein and C.C. Williams, Appl. Phys. Lett. \textbf{81}, 4589 (2002). 2. E. Bussmann, D.J. Kim, and C. C. Williams, Appl. Phys. Lett. \textbf{85}, 2538 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 12:27PM - 12:39PM |
J20.00007: Localized Single Electron Tunneling Spectroscopy Measurements on SiO2 Ezra Bussmann, Clayton Williams A new scanning probe method capable of detecting single electron tunneling events to/from individual electronic states at the surface of an insulator has recently been demonstrated [1,2]. The approach has now been developed for performing local electronic spectroscopy measurements. The surface is imaged in dynamic force microscopy mode. After imaging, single electron tunneling force spectroscopy at specific locations on the surface is performed either by scanning the probe at fixed bias voltage toward the surface, or moving the tip within tunneling range and scanning the bias voltage on the probe. When this is done, single electron tunneling events are observed to occur only a specific sites on the surface, at particular gaps and voltages. A theory has been developed to extract the energy of the electronic state to/from which the single electron tunneling occurs. 1. L. J. Klein and C.C. Williams, Appl. Phys. Lett. \textbf{81}, 4589 (2002). 2. E. Bussmann, D.J. Kim, and C. C. Williams, Appl. Phys. Lett. \textbf{85}, 2538 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 12:39PM - 12:51PM |
J20.00008: Observation of all dangling bond states and potential variation among them by noncontact atomic force microscopy Yukio Hasegawa, Toyoaki Eguchi, K. Akiyama, T. An, M. Ono, Y. Fujikawa, T. Sakurai, T. Hashimoto, Y. Morikawa, K. Terakura, M. Lagally High-resolution non-contact atomic force microscope (AFM) images were successfully taken on the Ge(105)-(1x2) structure formed on the Si(105) substrate and revealed all dangling bonds of the surface regardless to their electronic situation, surpassing the scanning tunneling microscopy, whose images were strongly deviated from the atomic structure by the electronic states involved. An atomically resolved electrostatic potential profile by a Kelvin probe method with AFM shows potential variations among the dangling bond states, directly observing a charge transfer between them. These results clearly demonstrate that high-resolution non-contact AFM with a Kelvin probe method is an ideal tool for analyses of atomic structures and electronic properties of surfaces. [Preview Abstract] |
Tuesday, March 22, 2005 12:51PM - 1:03PM |
J20.00009: Attonewton force detection near a surface Seppe Kuehn, Sean Garner, John Marohn Magnetic resonance force microscopy (MRFM) is a promising new technique for acquiring magnetic resonance images of a single molecule; to date we have demonstrated an unprecedented sensitivity of $\sim $10$^{5}$proton spins. Moving forward requires that force microscopy enter a new regime, where attonewton (10$^{-18}$ N) forces are measured near a surface. To facilitate this we operate custom fabricated, low spring constant, high quality factor cantilevers with their motion parallel to the sample surface. We observe that cantilever force sensitivity degrades with decreasing tip-sample separation due to energy losses. Our measurements indicate that this effect is dependent on tip size, composition, and tip-sample voltage. Theoretical models suggest that this effect might be due to dielectric fluctuations within the sample or inhomogeneous charge distributions on the surface. We have designed experiments to test these hypotheses and to elucidate the detailed mechanism of energy losses between a cantilever and a surface. [Preview Abstract] |
Tuesday, March 22, 2005 1:03PM - 1:15PM |
J20.00010: Contact-Less Electrical Characterization of Fully Depleted Silicon-on-Insulator Emma Tevaarwerk, Peng Peng Zhang, Olivia Castellini, Don Savage, M.G. Lagally, M.A. Eriksson Ultra-thin (10 nm) silicon-on-insulator (SOI) has recently emerged as an important substrate, and at nominal doping levels of 10\^{}15 per cubic centimeter will be fully depleted of free carriers by interface states at the silicon-silicon dioxide interface[1]. Therefore, when imaged with contact-less characterization techniques such as electric force microscopy, one might expect the ultra-thin silicon layer to behave as if it has no free carriers. However, our electric force microscopy measurements show that the layer possesses sufficient free charge to have a 2D resistivity of at least 800 TOhm/square, and that the silicon layer behaves as a metal when charge is deposited on it [2, 3]. We believe that thermally activated charge hopping at silicon-silicon dioxide interface provides free carriers even when there are no free carriers from the silicon bulk. We discuss the implications of this conduction path to imaging of 10 nm SOI by electric force microscopy. Research supported by DOE and AFOSR. [1] S. Henaux, et al. J. Electrochem. Soc. 146, 2737 (1999), [2] Tevaarwerk, et al, Appl. Phys. Lett. 80, 4626 (2002) , [3] P. Zhang, et al, in preparation. [Preview Abstract] |
Tuesday, March 22, 2005 1:15PM - 1:27PM |
J20.00011: High-throughput resistivity apparatus for characterization of combinatorial libraries Kevin Hewitt, Philip Casey, Manfred Jericho, Rong Sun A combinatorial apparatus, capable of measuring the resistance versus temperature of 49 samples prepared by thin film deposition techniques has been designed and tested. Magnetron sputtering is used to deposit films through an aluminum mask consisting of 8 mm diameter holes cut on a 7 x 7 grid. Electrical contact to the thin film samples are made in a standard van der Paaw geometry using 196 spring-loaded, gold-coated pins - four pins for each of the 49 samples. The system is able to characterize the resistivity of any conductor, semiconductor or superconductor library from 32 K to 350 K. The resistivity of a highly conductive metal (silver) and semi-conductor (multi-layer film of Si-Ge) are presented to highlight the capabilities of the apparatus. [Preview Abstract] |
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