Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session U9: Scanning Probe Microscopy |
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Sponsoring Units: GIMS Chair: Karen Waldrip, Sandia National Laboratories Room: Baltimore Convention Center 301 |
Thursday, March 16, 2006 8:00AM - 8:12AM |
U9.00001: An \textit{in-situ} Study of Martensitic Transformation in Shape Memory Alloys using PEEM Gang Xiong, T. Droubay, A. Joly, W. Hess, M. Cai, S. Langford, J. Dickinson, M. Wu, Q. He, W. Huang The thermally-induced martensitic transformation in a polycrystalline CuZnAl and NiTi thin film shape memory alloy (SMA) was probed using photoemission electron microscopy (PEEM). Ultra-violet photoelectron spectroscopy (UPS) measurements indicate that the apparent surface work function changes reversibly during transformation, presumably due to the contrasting electronic structures of the martensitic and austenitic phases. \textit{In situ} PEEM images provide information on the spatial distribution of these phases and the microstructural evolution during transformation. The evolution of the photoemission intensities obtained from PEEM images during transformation can provide quantitative information on fractional percentages of austenite and martensite phases as the transformation proceeds. PEEM offers considerable potential for improving our understanding of martensitic transformations in shape memory alloys in real time. [Preview Abstract] |
Thursday, March 16, 2006 8:12AM - 8:24AM |
U9.00002: Investigation of ferroelectric materials with scanning microwave microscope Jewook Park, Jonghoon Cho, Sangyun Lee, Kookrin Char By using scanning microwave microscope (SMM), we investigated dielectric properties of ferroelectric materials in high frequency regime (1.5GHz). Our SMM had the capability to measure a complex dielectric constant of the samples from the shift of resonant frequency (fr) and Q value of the probing resonator. In order to obtain non-linear dielectric constants of the ferroelectric samples, we applied oscillating electric field perpendicular to the sample and measured the 1$^{st}$ order derivative of the resonant frequency of the resonator (dfr/dE) with respect to the applied field. In this way we could image the ferroelectric domain and the domain boundary structure of the triglycine sulfate single crystal using the dfr/dE and the fr signal, respectively. Moreover we observed the ferroelectric responses from the tunable dielectric Ba$_{0.6}$Sr$_{0.4}$TiO$_{3}$ thin film under the additional DC voltage bias to the film. [Preview Abstract] |
Thursday, March 16, 2006 8:24AM - 8:36AM |
U9.00003: Plasmon-based Enhanced NSOM Spectroscopy. A.T. Chang, C.L. Nehl, F. Tam, N.J. Halas, J.H. Hafner, K.F. Kelly Surface enhanced Raman spectroscopy is a well established technique for enhancing the Raman signal of a particular sample, allowing for spectroscopy of far lower quantities of the molecule of interest than other procedures allow. This enhancement is mainly caused by the enhancement of the incident electric field by exciting the plasmon resonance of the surface. By attaching metal nanoparticles on an NSOM probe, we demonstrate that the plasmon-based enhancement can come from the probe itself instead of the surface, resulting in a powerful tool for the chemical analysis at the nanometer scale. [Preview Abstract] |
Thursday, March 16, 2006 8:36AM - 8:48AM |
U9.00004: Dielectrophoretic Force Microscopy Al Hilton, Brian Lynch, Garth Simpson Dielectrophoretic force microscopy, a novel scanning probe microscopy technique in which a tip-sample dielectrophoretic force is incorporated into the feedback mechanism of a standard atomic force microscope, is shown to allow for the facile noncontact imaging of the dieelctric properties of systems in aqueous media. By tuning the ac frequency, dielectric spectroscopy can be performed at solid/liquid interfaces with high spatial resolution. In studies of cells, the frequency-dependent dielectrophoretic force is sensitive to biologically relevant electrical properties, including local membrane capacitance and ion mobility. Additionally, the presence of a dielectrophoretic force reduces the mechanical tip-sample contact forces that frequently hinder microscopy studies of soft, deformable systems. Consequently, dielectrophoretic force microscopy is well suited for \textit{in situ} scanning probe microscopy studies of biological systems. [Preview Abstract] |
Thursday, March 16, 2006 8:48AM - 9:00AM |
U9.00005: Spectral density of fluctuations for a driven, nonlinear micromechanical oscillator at kinetic phase transition Corey Stambaugh, Ho Bun Chan We measure the spectral densities of fluctuations of an underdamped nonlinear micromechanical torsional oscillator. By applying a sufficiently large periodic driving force, two stable dynamical states occur within a particular range of drive frequency. White noise is injected into the driving force allowing the system to overcome the activation barrier and to switch between the two states. While the system predominately resides in one of the two states for most excitation frequencies, a narrow range of frequencies exist where the population levels are approximately equal and the system is at a `kinetic phase transition' that bears resemblance to the phase transition of thermal equilibrium systems. By examining the power spectral densities of the measured oscillation amplitude, the fluctuation characteristics of the system can be studied. At the `kinetic phase transition' a supernarrow peak, centered at the excitation frequency, arises as a result of noise-induced transitions between the two dynamic states. Smaller, secondary peaks associated with fluctuations about the two attractors are also examined. Its dependence on noise and excitation frequency is shown to be distinct from that of the supernarrow peak. [Preview Abstract] |
Thursday, March 16, 2006 9:00AM - 9:12AM |
U9.00006: Nonlinear coupling of nano mechanical resonators to Josephson quantum circuits Xingxiang Zhou, Ari Mizel We study a technique to couple the position operator of a nano mechanical resonator to a SQUID device by modulating its magnetic flux bias. By tuning the magnetic field properly, either linear or quadratic couplings can be realized, with a discretely adjustable coupling strength. This allowes us to realize nonlinear dynamics on the nano mechanical resonator by coupling it to a Josephson quantum circuits. As an example we show how squeezing of the nano mechanical resonator can be realized with this technique. We also propose a simple method to measure the uncertainty in the position of the nano mechanical resonator without quantum state tomography. [Preview Abstract] |
Thursday, March 16, 2006 9:12AM - 9:24AM |
U9.00007: Nanomanipulation with dynamic AFM Ivan Stich, Peter Dieska, Ruben Perez Nanomanipulation [1] is one of the most important current issues in dynamic AFM (DAFM). Following the first vertical manipulation on Si(111)-(7x7) [1] a lateral manipulation was documented by interchange manipulation of Sn and Ge adatoms on the Ge(111)- c(2x8) surface [2]. However, the atomistic details and nature of these processes remain unclear. In order to shed light on these experiments we have performed DFT simulations on two model systems: (1) anionic antisite defect on the InP(110) surface [3], and (2) the Sn-covered Ge(111)-c(2x8) surface. In (1) the P defect atom moves vertically in a double well potential with two minima, which opens the possibility to vertically manipulate the defect atom from one minimum into the other. We will addresses issues such as whether the experiments can be performed in both attractive and repulsive interaction regimes and whether the basic atomistic mechanism is related to lowering of the barriers by the presence of the tip, or by a purely mechanical effect where the atom is pushed over a barrier. In (2) we will show how presence of the tip can affect the charge transfer processes between the different dangling bonds and hence induce atomic manipulation. [1] N. Oyabu et al., Phys. Rev. Lett. 90, 176102 (2003) [2] Y. Sugimoto et al., Nature Mater. 4, 156 (2005); N. Oyabu et al., Nanotechnology 16, S112 (2005). [3] P. Dieska, I. Stich, R. Perez, Phys. Rev. Lett. 95 126103 (2005) [Preview Abstract] |
Thursday, March 16, 2006 9:24AM - 9:36AM |
U9.00008: Assembly of Nanoparticle-Attached AFM Tips for Nano-Optical Applications Taekyeong Kim, Sung Myung, Narae Cho, Seunghun Hong The well-defined geometry and chemical properties of the end of atomic force microscopy tips are critical components for various tip-enhanced nano-optical applications such as nanoscale Raman and FRET imaging. However, conventional AFM tip fabrication method often results in a large variation of tip shapes and chemical properties. Recent nanotechnology allows us to synthesize `nanoparticles' (e.g. Au, Ag, CdSe, etc). We developed a method to mass-produce `AFM tips with well-defined geometry and chemical properties' by assembling a single nanoparticle at the end of the tip via self-assembly strategy. In this way, only the end part of the tip is functionalized with organic molecules which attract nanoparticles in the solution. When the functionalized tip is placed in the nanoparticle solution, nanoparticles are selectively assembled only onto the end of the tip. We assembled a nanoparticle (e.g. 50nm diameter Au nanoparticle) at the end of the tip and demonstrated AFM imaging using these tips. Our method allows us to assemble nanoparticles at the end of the tip, and it can be scaled up for large scale assembly. [Preview Abstract] |
Thursday, March 16, 2006 9:36AM - 9:48AM |
U9.00009: Investigation of Electrical Behaviors of Nanostructures through Scanning-Probe Microscopy Beverly Clark III, Hans Hallen A scanning-probe microscope with two electrically-isolated electrodes fabricated on one probe is used to locally investigate electrical behavior of nanostructures. The split-tip probe, which we have recently developed, is optimized for light coupling into a particular region of a nanostructure while non-contact measurements are simultaneously made between the two electrodes. The capacitance is influenced by the presence of a conducting region on the surface beneath the electrodes. The capacitance coupled or scanning conductivity mode allows rapid characterization of large numbers of molecules so that molecules of interest can be identified for further study. Finite element models aid in the quantification and understanding of the data. [Preview Abstract] |
Thursday, March 16, 2006 9:48AM - 10:00AM |
U9.00010: Scanning Tunneling Potentiometry for Nanoscale Transport Studies Michael Rozler, M.R. Beasley We have developed a scanning tunneling potentiometry (STP) system for study of electrical transport on nanometer length scales. A novel biasing scheme is used to achieve electrochemical potential resolution at the theoretical limits of this measurement - the thermal noise of the tunnel junction. We apply this technique to several materials in order to explore the capabilities of the instrument. These include thin films of Au, the ``bad metal'' SrRuO$_{3}$ and amorphous indium oxide. Homogeneity of transport in these systems is discussed. Work supported initially by the AFOSR and currently by the NSF. [Preview Abstract] |
Thursday, March 16, 2006 10:00AM - 10:12AM |
U9.00011: Alpha Control - A new Concept in SPM Control \newline P. Spizig, D. Sanchen, G. Volswinkler, W. Ibach, J. Koenen Controlling modern Scanning Probe Microscopes demands highly sophisticated electronics. While flexibility and powerful computing power is of great importance in facilitating the variety of measurement modes, extremely low noise is also a necessity. Accordingly, modern SPM Controller designs are based on digital electronics to overcome the drawbacks of analog designs. While todays SPM controllers are based on DSPs or Microprocessors and often still incorporate analog parts, we are now introducing a completely new approach: Using a Field Programmable Gate Array (FPGA) to implement the digital control tasks allows unrivalled data processing speed by computing all tasks in parallel within a single chip. Time consuming task switching between data acquisition, digital filtering, scanning and the computing of feedback signals can be completely avoided. Together with a star topology to avoid any bus limitations in accessing the variety of ADCs and DACs, this design guarantees for the first time an entirely deterministic timing capability in the nanosecond regime for all tasks. This becomes especially useful for any external experiments which must be synchronized with the scan or for high speed scans that require not only closed loop control of the scanner, but also dynamic correction of the scan movement. Delicate samples additionally benefit from extremely high sample rates, allowing highly resolved signals and low noise levels. [Preview Abstract] |
Thursday, March 16, 2006 10:12AM - 10:24AM |
U9.00012: Theory of Q-Controlled Dynamic Force Microscopy in Liquids Hendrik Holscher, Udo D. Schwarz The so-called Q-control method allows the active modification of the effective cantilever damping in dynamic force microscopy (DFM) by increasing or decreasing the Q-value of the cantilever. This feature has been used in recent years in numerous experimental studies to improve the apparent imaging capabilities of DFM in liquids. However, it is striking that an in-depth analytic description that would allow a rigorous theoretical explanation of the various features of Q-controlled dynamic force microscopy (QC-DFM) is still missing. Here, we present an analysis of QC-DFM based on the analytical solution of the equation of motion considering a model tip-sample interaction force. Explicit formulas allowing for the calculation of relevant parameters such as amplitude, surface deformation, and maximum forces during an individual oscillation cycle are given. It is found that higher effective Q-factors assist in reducing the maximum tip-sample forces. This helps suppressing unwanted deformations of the sample surface, leading to the reported enhanced image quality. Finally, the results are discussed in relation to the situation in air. [Preview Abstract] |
Thursday, March 16, 2006 10:24AM - 10:36AM |
U9.00013: Simulation of contact and non-contact AFM images of H-terminated Si(100) surface with a CH3 impurity Akira Masago, Satoshi Watanabe, Katsunori Tagami, Masaru Tsukada Using a density-functional-based tight-binding method, we have investigated whether atomic force microscope (AFM) images with atomic resolution can be obtained for hydrogen-terminated silicon (100) 1x1 surface including a methyl. We have simulated contact mode images of this surface using a silicon tip with and without a hydrogen atom at the apex. For the silicon tip without hydrogen at the apex, we obtained good images with anisotropic spots reflecting the symmetry of a methyl for large tip-sample distance. For the silicon tip with hydrogen at the apex, we found that better images with atomic resolution, showing internal hydrogen and carbon atoms of a methyl, are expected if the forces can be measured precisely. We have also examined non-contact mode images. Although a force line profile of non-contact mode is smoother than one of contact mode, their difference is not so large. [Preview Abstract] |
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