Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session B24: Focus Session: Advances in Scanned Probe Microscopy I: Novel Approaches and Ultrasensitive Detection |
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Sponsoring Units: GIMS Room: 504 |
Monday, March 3, 2014 11:15AM - 11:51AM |
B24.00001: Imaging quantum transport using scanning gate microscopy Invited Speaker: Benoit Hackens Quantum transport in nanodevices is usually probed thanks to measurements of the electrical resistance or conductance, which lack the spatial resolution necessary to probe electron behaviour inside the devices. In this talk, we will show that scanning gate microscopy (SGM) yields real-space images of quantum transport phenomena inside archetypal mesoscopic devices such as quantum point contacts and quantum rings. We will first discuss the SGM technique, which is based on mapping the electrical conductance of a device as an electrically-biased sharp metallic tip scans in its vicinity. With SGM, we demonstrated low temperature imaging of the electron probability density and interferences in embedded mesoscopic quantum rings [B. Hackens et al., Nat. Phys. 2, 826 (2006)]. At high magnetic field, thanks to the SGM conductance maps, one can decrypt complex transport phenomena such as tunneling between quantum Hall edge state, either direct or through localized states [B. Hackens et al., Nat. Comm. 1, 39 (2010)]. Moreover, the technique also allows to perform local spectroscopy of electron transport through selected localized states [F. Martins et al., New J. of Phys. 15, 013049 (2013); F. Martins et al., Sci. Rep. 3, 1416 (2013)]. Overall, these examples show that scanning gate microscopy is a powerful tool for imaging charge carrier behavior inside devices fabricated from a variety of materials, and opens the way towards a more intimate manipulation of charge and quasiparticle transport. This work was performed in collaboration with F. Martins, S. Faniel, B. Brun, M. Pala, X. Wallart, L. Desplanque, B. Rosenow, T. Ouisse, H. Sellier, S. Huant and V. Bayot. [Preview Abstract] |
Monday, March 3, 2014 11:51AM - 12:03PM |
B24.00002: Design and Characterization of a millikelvin dual-tip Josephson STM A. Roychowdhury, M. Dreyer, J.R. Anderson, C.J. Lobb, F.C. Wellstood We describe the design and characterization of a dual-tip Josephson STM that operates at millikelvin temperatures. We report an effective noise temperature for the STM on the order of 200 mK.\footnote{A. Roychowdhury et. al., arXiv:1311.1855 (2013)} In addition to the expected phase diffusive super current in the ultra-small Nb-Nb junction formed by one tip and the sample,\footnote{M. Ivanchenko and L.A Zil'berman, Sov. Phys. JETP, 28, 1272 (1969)} our high resolution spectroscopy at mK temperatures reveals resonant coupling between the STM junction and the electromagnetic environment it is embedded in, as predicted by P(E) theory.\footnote{G. Ingold and H. Grabert, Phys. Rev. B., 50, 395 (1994)} We have for the first time, observed Shapiro-like steps in this limit by measuring the response of the P(E) supercurrent to microwave radiation as a function of amplitude. Fits to theory\footnote{G. Falci, V. Bubunja and G. Schon, Z. Phys. B., 85, 451 (1991)} indicate that the coupling of an ultra-small Josephson junction to its environment/circuit may be used to a) directly measure dissipation channels associated with circuit resonances and b) calibrate the frequency dependent microwave attenuation in cryogenic circuits as seen by the junction. [Preview Abstract] |
Monday, March 3, 2014 12:03PM - 12:15PM |
B24.00003: A cryogenic quantum gas scanning magnetic microscope Matthew Naides, Richard Turner, Ruby Lai, Jack DiSciacca, Benjamin Lev Atom chip trapping of quantum gases will enable single-shot, large area imaging of transport through strongly correlated and topologically non-trivial materials via detection of magnetic flux at the $10^{-7}$ flux quantum level and below. By harnessing the extreme sensitivity of atomic clocks and Bose-Einstein condensates to external perturbations, the cryogenic atom chip technology we have recently demonstrated [1] will provide a magnetic flux detection capability that surpasses other techniques, while allowing sample temperatures spanning $<$10 K to room temperature. We report on experimental progress toward developing this novel quantum gas scanning magnetic microscope [1] and describe our recent proposal [2] to image topologically protected transport through a non-ideal topological insulator in a relatively model-independent fashion. \\[4pt] [1] M. Naides, R. Turner, R. Lai, J. DiSciacca, and B. L. Lev, Trapping ultracold gases near cryogenic materials with rapid reconfigurability, arXiv:1311.2065 (2013). \\[0pt] [2] B. Dellabetta, T. L. Hughes, M. J. Gilbert, and B. L. Lev, Imaging topologically protected transport with quantum degenerate gases, Physical Review B 85, 205442 (2012). [Preview Abstract] |
Monday, March 3, 2014 12:15PM - 12:27PM |
B24.00004: First results for custom-built low-temperature (4.2 K) scanning tunneling microscope/molecular beam epitaxy and pulsed laser epitaxy system designed for spin-polarized measurements Andrew Foley, Khan Alam, Wenzhi Lin, Kangkang Wang, Abhijit Chinchore, Joseph Corbett, Alan Savage, Tianjiao Chen, Meng Shi, Jeongihm Pak, Arthur Smith A custom low-temperature (4.2 K) scanning tunneling microscope system has been developed which is combined directly with a custom molecular beam epitaxy facility (and also including pulsed laser epitaxy) for the purpose of studying surface nanomagnetism of complex spintronic materials down to the atomic scale. For purposes of carrying out spin-polarized STM measurements, the microscope is built into a split-coil, 4.5 Tesla superconducting magnet system where the magnetic field can be applied normal to the sample surface; since, as a result, the microscope does not include eddy current damping, vibration isolation is achieved using a unique combination of two stages of pneumatic isolators along with an acoustical noise shield, in addition to the use of a highly stable as well as modular `Pan'-style STM design with a high Q factor.[1] First 4.2 K results reveal, with clear atomic resolution, various reconstructions on wurtzite GaN c-plane surfaces grown by MBE, including the c(6x12) on N-polar GaN(000\underline {1}). Details of the system design and functionality will be presented. [1] Kangkang Wang, Wenzhi Lin, Abhijit V. Chinchore, Yinghao Liu, and Arthur R. Smith, Review of Scientific Instruments \textbf{82}, 053703 (2011). [Preview Abstract] |
Monday, March 3, 2014 12:27PM - 12:39PM |
B24.00005: Theory and Experiment of Scanning Thermoelectric Microscopy with Atomic Resolution Eui-Sup Lee, Sanghee Cho, Ho-Ki Lyeo, Yong-Hyun Kim Heat, a measure of entropy, is largely perceived to be diffusive and transported incoherently by charge carriers and lattice vibrations in a material, which is hard to be spatially localized. Heat transport is therefore considered a challenging means of the local imaging of a material and its electronic states. However, Cho \textit{et al.} [1] reported a series of striking wavefunction images of epitaxial graphene by measuring thermoelectric voltages with a heat-based scanning probe microscopy. Here we present how the thermoelectric signal is related to the atomic-scale wavefunctions and what the role of the temperature is at such a length scale. An exact expression of local thermoelectric voltage is deduced, and a computer-based thermoelectric imaging simulation method with first-principles wavefunction calculations is developed and performed on pristine and defective graphene. From this analysis, we find that coherent electron and heat transport through a point-like contact produces an atomic Seebeck effect. We will also discuss the connection between Seebeck coefficient and thermal properties of a material, such as electronic heat capacity and quantum of thermal conductance, by introducing the statistically defined Fermi temperature [2]. [1] S. Cho, S. D. Kang, W. Kim, E.-S. Lee, S.-J. Woo, K.-J. Kong, I. Kim, H.-D. Kim, T. Zhang, J. A. Stroscio, Y.-H. Kim, and H.-K. Lyeo, arXiv:1305.2845, Nature Mater.\textbf{ 12}, 913 (2013). [2] E.-S. Lee, S. Cho, H.-K. Lyeo, and Y.-H. Kim, arXiv:1307.3742, \textit{submitted} (2013). [Preview Abstract] |
Monday, March 3, 2014 12:39PM - 12:51PM |
B24.00006: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 12:51PM - 1:03PM |
B24.00007: Chemically Sensitive Imaging of MgP with STM Arthur Yu, Shaowei Li, Greg Czap, Wilson Ho Since its invention, the STM has been limited by its lack of sensitivity to chemical structures in molecules. Recent advances in scanning probe microscopy techniques, such as non-contact AFM and scanning tunneling hydrogen microscopy have enabled imaging of the internal structure and bonding of aromatic molecules such as pentacene and PTCDA. Here, we present a novel method of using the STM to image magnesium porphyrin molecules adsorbed on Au(110) with chemical sensitivity. In our previous study, we have shown that hydrogen molecules weakly adsorb on Au(110), exhibiting both vibrational and rotational IETS spectra. Exploiting the sensitivity of the vibrational and rotational mode energies to the local chemical environment, we perform dI/dV and d$^{2}$I/dV$^2$ imaging at different bias voltages, highlighting the various parts of the MgP molecule. In particular, we are able to image the positions of the nitrogen atoms in MgP. d$^{2}$I/dV$^{2}$ spectral mapping reveals that the origin of the chemical sensitivity comes from an energy shift of the rotational peak as the tip is scanned across the molecule, indicating a changing potential landscape for the H$_{2}$. Similar d$^{2}$I/dV$^{2}$ imaging with a CO terminated tip reveals no chemical sensitivity to nitrogen. [Preview Abstract] |
Monday, March 3, 2014 1:03PM - 1:15PM |
B24.00008: Electrostatic actuation of commercial AFM cantilevers Christian Long, Rachel J. Cannara We present an atomic force microscope (AFM) cantilever holder for electrostatic actuation of AFM cantilevers. The cantilever holder contains an electrode that is positioned behind the AFM cantilever, making this implementation of electrostatic actuation compatible with a wide variety of samples and commercially available AFM tips. Local electrostatic actuation of the cantilever eliminates the excitation of spurious mechanical resonances associated with the cantilever holder, making it an attractive alternative to piezoelectric actuation. Avoiding spurious mechanical resonances is most important for situations in which the cantilever's quality factor is low compared to the quality factors of the spurious mechanical resonances. These spurious resonances typically have quality factors of less than 50, so they are not an issue for applications such as routine tapping mode imaging in air. However, for applications where the quality factor of the cantilever is low, as is the case in contact resonance spectroscopy or in fluid environments, electrostatic actuation can be highly advantageous compared to piezoelectric actuation. [Preview Abstract] |
Monday, March 3, 2014 1:15PM - 1:27PM |
B24.00009: Combining Amplitude and frequency Modulation in Atomic Force Microscopy David Haviland, Daniel Forchheimer, Daniel Platz, Erik Tolh{\'e}n Dynamic AFM is usually sorted in to one of two general categories: Frequency Modulation (FM-AFM) or Amplitude Modulation (AM-AFM). These names refer to the way in which feedback is preformed while scanning over the surface. In either category the tip-surface interaction is viewed as a {\em passive} modulation of the response to a single drive frequency, modulating either the amplitude or phase of the response. Often an extra feedback (phase locked loop) is used to measure the response phase as a shift of resonance frequency. An alternative approach to measurement is {\em active} modulation of the drive force on the cantilever, while monitoring how this active modulation is modified by the tip-surface interaction. Such active modulation can be frequency or amplitude modulation, or both. The method is realized by driving the cantilever with a frequency comb and measuring the response at all frequencies in the comb in a phase coherent way. In comparison with single drive methods the frequency comb method can acquire much more information in the same amount of time. We will demonstrate how this technique allows one to go beyond simple linear approximations, allowing for rapid and accurate reconstruction of the non-liner tip-surface interaction in AFM. [Preview Abstract] |
Monday, March 3, 2014 1:27PM - 1:39PM |
B24.00010: 3D mapping and energy measurement of trap states in inter-layer dielectric films by Dynamic Tunneling Force Microscopy Ruiyao Wang, Sean King, Clayton Williams A novel atomic scale scanning probe microscopy method--Dynamic Tunneling Force Microscopy / Spectroscopy (DTFM/S) [1] has been employed to image the 3D distribution and energy level of individual trap states in inter-layer dielectric (ILD) and other insulating films. DTFM images of several films of different compositions, each around 5 nm thick, show a similar trap state areal density of order of 5x10$^{\mathrm{11}}$/cm$^{\mathrm{2}}$.The energy and depth of each state within tunneling range can be determined by performing the DTFM/S measurements as a function of applied voltage and probe tip height above the surface and a physical tunneling model. Nanometer scale conductance (c-AFM) and trap state imaging (DTFM) have been performed in the same location on one of the films, revealing the correlation between the observed trap states and the conductance of the film. The imaging and energy level measurement results will be presented and discussed. [1] J.P. Johnson, N. Zheng and C.C. Williams, Nanotech. 20, 055701 (2009) [Preview Abstract] |
Monday, March 3, 2014 1:39PM - 1:51PM |
B24.00011: High-sensitivity SQUIDs with dispersive readout for scanning microscopy J.M. Mol, F. Foroughi, J. Arps, E. Kammerloher, P. Bethke, G.W. Gibson, Jr., Y.K.K. Fung, B. Klopfer, K. Nowack, P.A. Kratz, M.E. Huber, K.A. Moler, J.R. Kirtley, H. Bluhm In a scanning SQUID microscope, the high magnetic flux sensitivity is utilized to image magnetic properties of sample surfaces. As an alternative to the widely used DC SQUIDs, we present Nb SQUIDs for scanning with dispersive microwave readout, featuring significantly higher bandwidth and sensitivity. An on-chip shunt capacitor in parallel with the junction and flux pickup loops forms an LC resonator whose resonance depends on the flux in the SQUID. The readout utilizes a phase-sensitive detection of the reflected drive signal at the SQUID's resonance frequency. Highest sensitivities are achieved by making use of the inherent nonlinearity of the device at high excitation powers. We present a study of the characteristics and noise measurements of our sensors at 4 K. Extrapolations from our results to 300 mK indicate that flux sensitivities as low as 50 n$\Phi_{0}$Hz$^{-1/2}$ could be possible. Using high-resolution lithography, our sensors promise sub-micron spatial resolution. Integrated into a scanning microscope, they will provide a powerful tool for the study of weak magnetic effects and quantum coherent phenomena. [Preview Abstract] |
Monday, March 3, 2014 1:51PM - 2:03PM |
B24.00012: Real-Space Imaging of Molecular Structure by Single-Molecule Inelastic Tunneling Probe Zhumin Han, Chi-lun Chiang, Chen Xu, Wilson Ho The scanning tunneling microscope is one of the most powerful tools to perform real space imaging of the electronic, magnetic, optical, and vibrational signatures of a single molecule. However, the spatial distributions of these signatures do not always relate directly to the geometric structures of the molecules. In this study, a CO molecule is transferred from the surface to a STM tip. The energy and intensity of the hindered translational mode of the CO vary when the tip is scanned across an adsorbed molecule (such as cobalt phthalocyanine). By monitoring these variations in space, we are able to resolve the geometric structure of the molecule and even subtle intramolecular and intermolecular interactions. [Preview Abstract] |
Monday, March 3, 2014 2:03PM - 2:15PM |
B24.00013: Real-space imaging of interfacial water with submolecular resolution Ying Jiang Water/solid interfaces are vital to our daily lives and also a central theme across an incredibly wide range of scientific disciplines. Resolving the internal structure, i.e. the O-H directionality, of water molecules adsorbed on solid surfaces has been one of the key issues of water science yet remains challenging. Using a low-temperature scanning tunneling microscope (STM), we report the submolecular-resolution imaging of individual water monomers and tetramers on NaCl(001) films supported by a Au(111) substrate at 5 K. The frontier molecular orbitals of adsorbed water were directly visualized, which allowed discriminating the orientation of the monomers and the H-bond directionality of the tetramers in real space. Comparison with ab initio density functional theory calculations reveals that the ability to access the orbital structures of water stems from the electronic decoupling effect provided by the NaCl films and the precisely tunable tip-water coupling. [Preview Abstract] |
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