Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session T46: Focus Session: Advances in Scanned Probe Microscopy 1: Scanning Probe Spectroscopy & Novel Applications to C-based Systems |
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Sponsoring Units: GIMS Chair: Alexander Otte, Delft University of Technology Room: Hilton Baltimore Holiday Ballroom 5 |
Thursday, March 21, 2013 8:00AM - 8:12AM |
T46.00001: A Josephson STM with two niobium tips Anita Roychowdhury, Rami Dana, Michael Dreyer, James Robert Anderson, Christopher J. Lobb, Frederick C. Wellstood We are developing a dual-tipped scanning tunneling microscope (STM) that operates at milliKelvin temperatures. The two tips can be connected and brought into tunneling with a superconducting sample to form a SQUID loop. Our scheme involves holding one of the tips fixed while the other is scanned to image spatial variations in the gauge invariant phase difference on the superconducting surface. We have developed a novel technique to fabricate sharp Niobium tips using a reactive ion etcher. The tips have been tested at 4 K and exhibit both a superconducting gap and atomic resolution on Au(111) and Bi$_2$Se$_3$ samples. We will describe the experimental setup, our tip fabrication technique, and present initial results. [Preview Abstract] |
Thursday, March 21, 2013 8:12AM - 8:24AM |
T46.00002: Electron-Hole Asymmetries in the Locally Inverted $\alpha^2 F(\omega)$ Spectrum of a Conventional Superconductor by STM Francis Niestemski, Steven Johnston, Alex Contryman, Charlie Camp, Tom Devereaux, Hari Manoharan Utilizing scanning tunneling microscopy to create a superconductor-vacuum-superconductor junction, we invert the measured spectroscopy of the archetypal elemental superconductor Pb utilizing strong-coupling Eliashberg theory to obtain a local $\alpha^ 2F(\omega)$. This is the STS vacuum analogue of the pioneering McMillan and Rowell sandwich junction [W. L. McMillan and J. M. Rowell Phys. Rev. Lett. 14, 108-112 (1965)]. We find broad underlying agreement with McMillan and Rowell highlighted by previously unobserved electron-hole asymmetries and new fine structure which we discuss in terms of both conventional and unconventional superconducting bosonics. [Preview Abstract] |
Thursday, March 21, 2013 8:24AM - 8:36AM |
T46.00003: Intermodulation Spectroscopy applied to AFM David Haviland, Daniel Platz, Daniel Forchheimer, Erik Thol\'en Measurement of surface forces at the single atom level is usually achieved by exploiting the enhanced sensitivity of a high quality factor resonator in ultrahigh vacuum, with small measurement bandwidth and therefore slow measurement speed. Frequency modulation AFM allows one to overcome this limitation, at the price of one extra feedback loop and very limited quantitative information about the interaction forces between the tip and the surface while imaging. We have introduced a multi-frequency method called Intermodulation AFM (ImAFM), which can be seen as containing features of both the amplitude modulation and frequency modulation AFM methods. In this talk we describe ImAFM in its most general form, where the nonlinear tip surface interaction is seen as transferring an input drive frequency comb, to an output frequency comb. These frequency combs can represent either amplitude modulated or frequency modulated signals, or both. It is demonstrated how the method optimally exploits the frequency band near resonance to extract as much information as is possible for a given measurement bandwidth. With this frequency-domain information one can reconstruct both conservative and dissipative tip-surface interactions with unprecedented accuracy and speed. [Preview Abstract] |
Thursday, March 21, 2013 8:36AM - 8:48AM |
T46.00004: Interaction imaging with amplitude-dependence force spectroscopy Daniel Platz, Daniel Forchheimer, Erik Thol\'{e}n, David Haviland The ultimate goal in atomic force microscopy (AFM) is the combination of imaging with accurate force measurement. Dynamic AFM offers only qualitative information about the tip-surface interaction while imaging, because the sharp cantilever resonance efficiently filters out the high frequency components of the tip-surface. Traditional force measurements are based on slow, point-wise surface approaches and are incompatible with imaging. Here, we present a method called amplitude-dependence force spectroscopy (ADFS) that enables quantitative dynamic force reconstruction at every point of an AFM image, while scanning at normal speeds. ADFS breaks with the paradigm of constant tip oscillation amplitude, as the oscillation amplitude is rapidly modulated at every image point. The measured response gives the amplitude-dependence of the Fourier component of the force at the resonant frequency, which allows for a model-free reconstruction of the tip-surface. We have made rigorous tests of ADS using numerical simulations and have used it for a detailed study of the mechanical properties of polymer surfaces. The amplitude-dependence of the response in dynamic AFM provides a new and coherent framework for the description of conservative and dissipative tip-surface forces. [Preview Abstract] |
Thursday, March 21, 2013 8:48AM - 9:00AM |
T46.00005: Quantitative Atomic-Resolution Surface Force Field Spectroscopy in Three Dimensions: A {\it {How-To}} Guide for Collecting Meaningful Data Mehmet Z. Baykara, Omur E. Dagdeviren, Todd C. Schwendemann, Harry M\"{o}nig, Eric I. Altman, Udo D. Schwarz Three-dimensional atomic force microscopy (3D-AFM) is being increasingly used to measure the chemical interactions between an atomically sharp probe tip and surfaces of interest in terms of atomic-scale forces and energies in three dimensions. Since the results provided by 3D-AFM may be affected by piezo nonlinearities, thermal and electronic drift, tip asymmetries, and elastic deformation of the tip's apex, these effects need to be considered during data interpretation. In this talk, we analyze the impact of these effects on the data, compare different methods to record atomic-resolution surface force fields, and determine the approaches that suffer the least from associated artifacts. We conclude that efforts to reduce unwanted influence of tip properties on recorded data are indispensable to extract detailed information about atomic-scale properties of the surface. [Preview Abstract] |
Thursday, March 21, 2013 9:00AM - 9:12AM |
T46.00006: Virtual Scanning Tunneling Microscopy: A local spectroscopic probe of high mobility 2D electron systems Matthew Pelliccione, John Bartel, Adam Sciambi, Loren Pfeiffer, Ken West, David Goldhaber-Gordon Many scanning probe techniques have been utilized in recent years to measure local properties of high mobility two-dimensional (2D) electron systems in GaAs. However, most techniques lack the ability to tunnel into the buried 2D system and measure local spectroscopic information. We report scanning gate measurements on a bilayer GaAs/AlGaAs heterostructure that allows for a local modulation of tunneling between two 2D electron layers. We call this technique Virtual Scanning Tunneling Microscopy (VSTM) [1] as the influence of the scanning gate is analogous to an STM tip, except at a GaAs/AlGaAs interface instead of a surface. We present measurements that highlight the spatial resolution and spectroscopic capabilities of the technique. \newline [1] A. Sciambi, M. Pelliccione \textit{et al.}, Appl. Phys. Lett. \textbf{97}, 132103 (2010). [Preview Abstract] |
Thursday, March 21, 2013 9:12AM - 9:24AM |
T46.00007: Tuning 2D-2D tunneling in high mobility electron systems John Bartel, Matthew Pelliccione, Adam Sciambi, Loren Pfeiffer, Ken West, David Goldhaber-Gordon We present measurements on GaAs/AlGaAs bilayer two-dimensional electron systems (2DES) where the tunnel coupling between the 2DES is tunable with a gate. By designing a GaAs/AlGaAs heterostructure with a relatively low energy barrier between the 2DES, reducing the electron density with a gate lowers the effective barrier height between the 2DES and increases the tunnel coupling. We describe the fabrication process developed to realize these samples, along with measurements that take advantage of this tunable tunnel coupling to realize a novel transistor where the gate lies outside the channel region [1]. In addition, the suitability of these devices for scanning gate measurements will be discussed. \newline [1] A. Sciambi, M. Pelliccione \textit{et al.}, Phys. Rev. B \textbf{84}, 085301 (2011). [Preview Abstract] |
Thursday, March 21, 2013 9:24AM - 10:00AM |
T46.00008: Gate Map Tunneling Spectroscopy of Interactions in Graphene Invited Speaker: Jungseok Chae The local electron density of states (LDOS) in semiconductors and semimetals like graphene can be adjusted with respect to the Fermi energy by using an electric field applied by a nearby gate electrode. In this way interaction physics can be turned on and off as the electron density is modulated at the Fermi level in an applied magnetic field. Interaction physics in graphene has been an interesting subject since the first isolation of single layer graphene, due the singular nature of the Dirac point in the graphene spectrum. The electronic density of states at the Dirac point vanishes and the long-range Coulomb interactions are not effectively screened, which gives rise to a rich spectrum of interaction-driven physics in magnetic fields at low temperatures. In this talk, I will present recent experimental results in graphene on boron nitride substrates using gate mapping tunneling spectroscopy [1]. Gate map tunneling spectroscopy consists of series of single tunneling spectra obtained as a back gate voltage is varied to change the carrier density at the Fermi level. The gate maps show clear variations of the tunneling spectrum as a function of carrier density. The formation of Landau levels (LLs) in magnetic fields up to 8 T is observed to form a staircase pattern in maps of the tunneling conductance in the 2-dimensional tunneling bias voltage-gate voltage plane. LLs modulate the LDOS at the Fermi level as the carrier density is varied with the gate potential. An analysis of the LL peak positions shows that the graphene energy-momentum remains linear at low energies, but that the dispersion velocity is enhanced due to interactions as the density is lowered approaching the Dirac point. Interaction effects are also strongly seen near zero density by the opening of large Coulomb gaps in the tunneling spectra, which will be discussed in terms of the competing effects of residual substrate induced disorder and interactions. \\[4pt] [1] J. Chae \textit{et. al}., PRL \textbf{197}, 116802 (2012) [Preview Abstract] |
Thursday, March 21, 2013 10:00AM - 10:12AM |
T46.00009: Thermoelectric microscopy for imaging disorder in epitaxial graphene Sanghee Cho, Stephen Kang, Wondong Kim, Ho-Ki Lyeo, Eui-Sup Lee, Sung-Jae Woo, Yong-Hyun Kim, Ki-Jeong Kong, Ilyou Kim, Hyeong-Do Kim, Tong Zhang, Joseph Stroscio Thermopower, an electron transport property, is a measure of thermal energy relative to the Fermi-energy E$_{F}$ and thus reflects the asymmetry in the density of states (DOS) with respect to E$_{F}$. We use thermopower as a microscopic probe of electronic properties of epitaxial graphene grown on SiC(0001), for which a scanning probe microscopy method has been developed by modifying a ultra-high-vacuum atomic force microscope. This method has a particular sensitivity to the electronic states near E$_{F}$. We thereby could image structural defects and strain fields that cause distortions in the electronic states near E$_{F}$. Such a capability allowed us to explore how the structural disorder is correlated and how the correlation evolves by responding to inherent strain in epitaxial graphene. Furthermore, striking images of atomically varying states and the finding of one-dimensional quantum confinement will be presented, demonstrating the ability to probe local DOS at the extreme scale. [Preview Abstract] |
Thursday, March 21, 2013 10:12AM - 10:24AM |
T46.00010: Noise Analysis on Graphene Devices via Scanning Noise Microscopy Duckhyung Cho, Moon Gyu Sung, Hyungwoo Lee, Kwang Heo, Kyung-Eun Byun, Taekyeong Kim, David H. Seo, Sunae Seo, Seunghun Hong Until now, the studies about low-frequency noises in electronic devices have mostly relied on the scaling behaviour analysis of current noise measured from multiple devices with different resistance values. However, the fabrication of such multiple devices for noise analysis is a labor-intensive and time-consuming work. Herein, we developed the scanning noise microscopy (SNM) method for nanoscale noise analysis of electronic devices, which allowed us to measure the scaling behaviour of electrical current noises in a graphene-strip-based device. In this method, a conductive atomic force microscopy probe made a direct contact on the graphene strip channel in the device to measure the noise spectra through it. The SNM method enabled the investigation of the noise scaling behaviour using only a single device. In addition, the nanoscale noise map was obtained, which allowed us to study the effect of structural defects on the noise characteristics of the graphene strip channel. Our method should be a powerful strategy for nanoscale noise analysis and play a significant role in basic research on nanoscale devices. [Preview Abstract] |
Thursday, March 21, 2013 10:24AM - 10:36AM |
T46.00011: Electronic state of carbon material surface by non-contact scanning nonlinear dielectric microscopy Shin-ichiro Kobayashi, Yasuo Cho Non-contact scanning nonlinear dielectric microscopy (NC-SNDM) can detect both topography and microscopic electric dipole moment of semiconducting surfaces. Recently, we clearly observed the atomic surface of graphite and fullerene (C$_{60})$ molecule on Si(111)-(7$\times$7) surface (7$\times$7 surface) by using second-order amplitude in SNDM signal as a feedback signal. SNDM signal of graphite by NC-SNDM originates from the electrochemical capacitance with tunneling and is related to the density of state (DOS) of an atomic or molecular surface [1,2]. However, a linear DOS was considered to investigate the origin of SNDM signals only when considering the electronic state of graphite surface, interface between C$_{60}$ and 7$\times$7 surface and internal structure of C$_{60}$ on 7$\times$7 surface in NC-SNDM. To resolve this problem, we introduce the general electrochemical capacitance induced by tunneling effect for analysis of NC-SNDM and discuss not only the influence of probe tip on SNDM signal and the origin of current signal but also the characteristics of SNDM signals obtained from graphite and from C$_{60}$ on 7$\times$7 surface \\[4pt] [1] S. Kobayashi and Y. Cho, Phys. Rev. B, 82, 245427(2010).\\[0pt] [2] S. Kobayashi and Y. Cho, Surf. Sci., 606, 174(2011). [Preview Abstract] |
Thursday, March 21, 2013 10:36AM - 10:48AM |
T46.00012: Contactless Probing of the Carrier Transport in Carbon Nanotubes Using Dielectric Force Microscopy Yize Li, Jun Ge, Jia Liu, Jie Zhang, Wei Lu, Liwei Chen We have developed a scanning probe microscopy (SPM) based technique which is named as dielectric force microscopy (DFM) to manipulate and probe the majority carriers in 1-dimentional nanoelectronic materials. We have demonstrated its success in distinguishing semiconducting single-walled carbon nanotubes (SWNTs) from metallic ones, locating semiconducting-metallic junction in SWNTs, determining the majority carrier types in SWNTs and ZnO nanowires, and detecting the electronic doping of SWNTs by gaseous ammonia. To achieve a quantitative measure of the intrinsic carrier transport, we have performed DFM measurement on individual SWNTs, fabricated field effect transistor devices with the individual SWNT serving as the channel, and carried out electrical transport experiment. The results from DFM and transport measurements are quantitatively correlated in an almost perfect fashion allowing the extraction of intrinsic carrier transport properties especially carrier mobility from DFM data without making metal contacts. Furthermore, we have successfully detected the location and behavior of local transport barriers in SWNTs utilizing the nanometer scale resolution feature of DFM. [Preview Abstract] |
Thursday, March 21, 2013 10:48AM - 11:00AM |
T46.00013: Quantitative Kelvin Probe Force Microscopy of a Single-Walled Carbon Nanotube Transistor Elliot Fuller, Brad Corso, Tolga Gul, Philip Collins Kelvin Probe Force Microscopy (KPFM) is well-suited to measuring the surface potentials of nanoscale devices, including organic thin film, graphene, and silicon nanowire field effect transistors (FETs). However, a primary limitation of KPFM is long-range capacitive coupling of the probe to parts of the sample that are distant from the immediate vicinity of the probe tip. This coupling complicates quantitative measurements and limits most KPFM work to qualitative observations of work function variations. Here, we address these problems to extract potentials along current-carrying, single-walled carbon nanotube (SWNT) FETs. As a low carrier density channel only 1 nm in diameter, SWNTs have extremely weak coupling to a KPFM probe tip, and therefore they provide a unique, limiting geometry that tests the resolving power of KPFM. By directly measuring this SWNT coupling and other, spatially-varying capacitive couplings to the probe tip, we have developed a robust and quantitative method for separating the desired signal, the local surface potential, from other electrostatic effects. The technique can be readily applied to other nanoscale devices to correctly extract work functions, potential gradients, and inhomogeneities in electrochemical potential. [Preview Abstract] |
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