Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session T24: Focus Session: Advances in Scanned Probe Microscopy III: Scanning Probes Spectroscopic Techniques |
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Sponsoring Units: GIMS Chair: Duming Zhang, National Institute of Standards and Technology Room: 504 |
Thursday, March 6, 2014 11:15AM - 11:51AM |
T24.00001: Electric Field Control of Topological Insulator Surface States Invited Speaker: Tong Zhang Electrical-field control of the carrier density of topological insulators (TIs) has greatly expanded the possible practical use of these materials. However, the combination of low-temperature local probe studies and a gate tunable TI device remains challenging. We have overcome this limitation by scanning tunneling microscopy measurements on in-situ molecular-beam epitaxy grown TI films on SrTiO3 substrates with pre-patterned electrodes. We are able to continuously tune the carrier density and observe the local electronic structure of pristine TI films. In the talk I present our recent results on back-gated Bi2Se3 and Sb2Te3 films. In Bi2Se3 films, we found that both DOS and the wavelength of the standing waves vary with gate voltage, due to the shifting of the Fermi level. In 3 nm thick Sb2Te3 film, a gap opening at Dirac point due to the coupling of top and bottom surface is observed. Moreover, the surface state band gap was found to be tunable by back gate, indicating the possibility of observing a topological phase transition in this system. Our results are well explained by an effective model of 3D topological insulator with structure inversion asymmetry, indicating that 3 nm thick Sb2Te3 films are topologically nontrivial and belong to the quantum spin Hall insulator class. [Preview Abstract] |
Thursday, March 6, 2014 11:51AM - 12:03PM |
T24.00002: MultiProbe Electrical Measurements of Carbon Nanotubes With On-line Raman Scattering Dalia Yablon, Talia Yeshua, Christian Lehmann, Stephanie Reich, Kristin Strain, Eleano Campbell A multiprobe scanning probe microscope (SPM) system has been used to perform multiprobe electrical measurement of carbon nanotubes. In this system two probes can be used across an isolated carbon nanotube. A variety of probes have been developed that are compatible with multiprobe operation. These include probes for writing single single walled carbon nanotubes which have a high degree of alignment and this is demonstrated with on-line Raman. The interconnection of the multiprobe system with the Raman System will be described in detail. The combination has the potential to cross the fabrication/measurement gap that will allow for both production and nanocharacterization of such single molecule carbon nanotube molecular devices both with chemically sensitive Raman measurements (with and without plasmonic enhancement) and with on-line electrical transport on isolated carbon nanotubes. [Preview Abstract] |
Thursday, March 6, 2014 12:03PM - 12:15PM |
T24.00003: Rotational Excitation Spectroscopy with the Scanning Tunneling Microscope -- Distinction of Nuclear Spin States Fabian Donat Natterer, Fran\c{c}ois Patthey, Harald Brune The appeal of inelastic electron tunneling spectroscopy with the scanning tunneling microscope (STM) stems from its unmatched spatial resolution and the ability to measure the magnetic, electronic and vibrational properties of individual atoms and molecules. Rotational excitations of molecules could provide additional information of surface processes but have hitherto remained elusive. Here we demonstrate rotational excitation spectroscopy (RES) with the STM for hydrogen and its isotopes on graphene and hexagonal boron nitride. Since the Pauli principle imposes restrictions on the allowed rotational levels $J$ for molecules with identical nuclei, a certain alignment of the nuclear spins entails a specific set of rotational levels. Conversely, measuring the rotational levels allows characterizing the molecular nuclear spin state. We measured excitation energies at 44 meV and 21 meV, corresponding to rotational transitions $J=0\rightarrow2$ for hydrogen and deuterium. We thereby identify the nuclear spin isomers para-H$_2$ and ortho-D$_2$. For HD, we observe $J=0\rightarrow1$ and $J=0\rightarrow2$ transitions, as expected for heteronuclear diatomics. Our measurements demonstrate the potential of STM-RES in the study of nuclear spin states with unprecedented spatial resolution. [Preview Abstract] |
Thursday, March 6, 2014 12:15PM - 12:27PM |
T24.00004: Magnetic properties of single Ni atoms on Cu2N Henning Prueser, Toby G. Gill, Ben Warner, Cyrus F. Hirjibehedin When a magnetic atom is placed onto a conducting surface its properties may change considerably due to interactions with the substrate. This interaction may be reduced by introducing a thin decoupling layer between the atom and the underlying metal. One general consequence of placing a magnetic atom on a surface is magnetic anisotropy, where angular momentum along a certain direction is energetically preferred. Although recent studies of atomic scale nanostructures have been able to measure the magnetic anisotropy for atomically precise configurations, a clear understanding of the dramatic differences observed for different atomic spins has not yet emerged. Using scanning tunneling microscopy and spectroscopy, we study the case of single Ni atoms deposited on copper nitride (Cu2N) islands formed in a Cu(001) surface. As in prior studies, we find that the observed magnetic behavior strongly depends on the binding site of the adsorbate. For Ni, however, surprisingly large anisotropy is observed on a nitrogen binding site; this is in stark contrast to the behavior observed for Mn, Fe, and Co, which display evidence of magnetic anisotropy on Cu sites. We explore the possible origins for this behavior as well as the implications for other transition metal adsorbates. [Preview Abstract] |
Thursday, March 6, 2014 12:27PM - 12:39PM |
T24.00005: Plasmons and Electrons as Nanosecond-Fast Sensors for Scanning Tunneling Microscopy Sebastian Loth The ability to measure the fast dynamical evolution of atomic-scale systems often holds the key to their understanding. We combine fast pump-probe spectroscopy tools with low-temperature scanning tunneling microscopy to study atomically assembled arrays of magnetic atoms. The dynamical information quantifies spin lifetimes, magnetic stability and even allows identifying the cross-over between quantum spins and classical magnetism [1]. The spin relaxation times of transition metal atoms can be measured by all-electronic pump probe spectroscopy in which nanosecond-fast voltage pulses excite the spins and probe the average time-dependent response by variations in the spin-polarized tunnel current. In addition, the fast evolution of the local electrostatic potential can be mapped by detecting plasmonic light emission from the STM tunnel junction with time correlating single photon counting [2]. The combination of electrical stimulus and optical detection provides precise control of the excitation process of individual atoms enabling new experiments to probe charge and spin dynamics in the scanning tunneling microscope. [1] S. Loth, S. Baumann, C. P. Lutz, D. M. Eigler, A. J. Heinrich, Science 335, 196 (2012). [2] C. Grosse, M. Etzkorn, K. Kuhnke, S. Loth, K. Kern, Appl. Phys. Lett. 103, 183108 (2013). [Preview Abstract] |
Thursday, March 6, 2014 12:39PM - 12:51PM |
T24.00006: Controlling Spin Dynamics of Magnetic Spin Chains at the Atomic Scale Shichao Yan, Deung-Jang Choi, Jacob Burgess, Steffen Rolf-Pissarczyk, Sebastian Loth By combining radio-frequency circuitry with sub-Kelvin Scanning Tunneling Microscopy (STM), fast electric pump-probe pulses of nanosecond duration can be introduced into the tunneling junction with high fidelity. We apply this technique to study dynamics of Fe trimers which can be assembled with the tip of the STM by placing Fe atoms in a regular pattern on copper nitride surface on Cu(100). The spin relaxation time of Fe trimers is found to be extremely sensitive to variations in their environment. This sensitivity can be used to sense the presence of another spin. By attaching a transition metal atom to the STM tip and approaching it to the nanostructure on the surface we deduce the coupling strength between the magnetic atoms. Furthermore, the magnetic state of long-lived spin chains can be sensed even at several nanometers distance by minute changes of the Fe trimer's spin relaxation time. This work paves the way to study and control spin dynamics of nanostructures with precisely tunable spin environments. [Preview Abstract] |
Thursday, March 6, 2014 12:51PM - 1:03PM |
T24.00007: Quantifying many-body effects by high-resolution Fourier transform scanning tunneling spectroscopy Stephanie Grothe, Steve Johnston, Shun Chi, Pinder Dosanjh, Sarah A. Burke, Yan Pennec The properties of solids are influenced by many-body effects that arise from the interactions of the electrons with each other and with the multitude of collective lattice, spin or charge excitations. We apply the technique of Fourier transform scanning tunneling spectroscopy (FT-STS) to probe the many-body effects of the Ag(111) surface state. A renormalization of the otherwise parabolic dispersion induced by electron-phonon interactions is revealed that has not previously been resolved by any technique, allowing us to extract the real part of the self-energy. Furthermore, we show how variations in the intensity of the FT-STS signal are related to the imaginary part of the self-energy. We accurately modeled the experimental data with the T-matrix formalism for scattering from a single impurity, assuming that the surface electrons are dressed by electron-electron and electron-phonon interactions. A Debye energy of $\hbar\Omega_D = 14 \pm 1$ meV and an electron-phonon coupling strength of $\lambda= 0.13 \pm 0.02$ was extracted. Our results advance FT-STS as a tool to simultaneously extract real and imaginary parts of the self-energy for both occupied and unoccupied states with a momentum and energy resolution competitive with angle-resolved photoemission spectroscopy. [Preview Abstract] |
Thursday, March 6, 2014 1:03PM - 1:15PM |
T24.00008: ABSTRACT WITHDRAWN |
Thursday, March 6, 2014 1:15PM - 1:27PM |
T24.00009: Current and Susceptibility Imaging with Scanning SQUIDs Christopher Watson, Katja Nowack, Eric Spanton, John Kirtley, Kathryn Moler Spatial variations in conductivity and magnetic susceptibility herald both global effects, including the existence of topological phases, and local features, such as those associated with material defects. Recent reports study these phenomena via local imaging of the magnetic field associated with the resultant current distribution, making use of scanning SQUID (Superconducting QUantum Interference Device) microscopy. Here we explore the utility of this technique and the extent to which the spatial resolution may be improved by a reduction of the sensor size and thorough characterization and calibration of the sensor height and point spread function. SQUID current imaging offers a crucial local complement to global transport measurements in exploring the wealth of conductance phenomena present in quantum material systems. [Preview Abstract] |
Thursday, March 6, 2014 1:27PM - 1:39PM |
T24.00010: Visualizing the Subsurface of Soft Matter: Simultaneous Topographical Imaging, Depth Modulation, and Compositional Mapping with Triple Frequency Atomic Force Microscopy Santiago Solares, Daniel Ebeling, Babak Eslami Characterization of subsurface morphology and mechanical properties with nanoscale resolution and depth control is of significant interest in soft matter fields like biology and polymer science, where buried structural and compositional features can be important. However, controllably ``feeling'' the subsurface is a challenging task for which the available imaging tools are relatively limited. This presentation describes a trimodal atomic force microscopy (AFM) imaging scheme, whereby three eigenmodes of the microcantilever probe are used as separate control ``knobs'' to simultaneously measure the topography, modulate sample indentation by the tip during tip-sample impact, and map compositional contrast, respectively. This method is illustrated through computational simulation and experiments conducted on ultrathin polymer films with embedded glass nanoparticles. By actively increasing the tip-sample indentation using a higher eigenmode of the cantilever, one is able to gradually and controllably reveal glass nanoparticles that are buried tens of nanometers deep under the surface, while still being able to refocus on the surface. [Preview Abstract] |
Thursday, March 6, 2014 1:39PM - 1:51PM |
T24.00011: Vertical NC-AFM Atom Manipulation without Tip Change Joseph Bamidele, Robert Turansky, Yasuhiro Sugawara, Ivan Stich, Lev Kantorovich We present a joint experimental and theoretical study of vertical manipulation of ``super''-Cu atoms on the oxygen-terminated $p$(2 $\times$ 1) Cu(110) surface with Non-Contact Atomic Force Microscopy (NC-AFM). Using NC-AFM we find that, using an O-terminated tip [1] vertical manipulation events consisting of removal are very rare, and, contrary, deposition processes of Cu atoms are very frequent. Interestingly, no change of contrast is observed, meaning that the vertical manipulation retains the tip apex unchanged. The experiments are supported by theoretical study using DFT calculations in conjunction with nudged elastic band method for calculating transition barriers, as well as kinetic Monte Carlo (KMC) simulations for accessing the tip-related time-scales. We propose detailed mechanism of the vertical manipulation, which fully explain experimental observations, including the removal/deposition probabilities. The mechanism consists of several stages: two stochastic (thermal with an energy barrier) and one conservative (dragging), which happens in between. KMC simulations confirm the viability of this mechanism and give statistics information. \\[4pt] [1] J. Bamidele \textit{et al.}; Phys. Rev. B \textbf{86}, 155422 (2012)$.$ [Preview Abstract] |
Thursday, March 6, 2014 1:51PM - 2:03PM |
T24.00012: Three-dimensional atomic force microscopy: interaction force vector by direct observation of tip trajectory Gavin King, Krishna Sigdel, Justin Grayer The prospect of a robust three dimensional atomic force microscope (AFM) holds significant promise in nanoscience. Yet, in conventional AFM, the tip-sample interaction force vector is not directly accessible. We scatter a focused laser directly off an AFM tip apex to rapidly and precisely measure the tapping tip trajectory in three dimensional space. This data also yields three dimensional cantilever spring constants, effective masses, and hence, the tip-sample interaction force components. Significant lateral forces representing 49{\%} and 13{\%} of the normal force were observed in common tapping mode conditions as a silicon tip intermittently contacted a glass substrate in aqueous solution; as a consequence, the direction of the force vector tilted considerably more than expected. When addressing the surface of a lipid bilayer, the behavior of the force components differed significantly from that observed on glass. This is attributed to the lateral mobility of the lipid membrane coupled with its elastic properties. Direct access to interaction components $F_{\mathrm{x}}$, $F_{\mathrm{y}}$, and $F_{\mathrm{z}}$ provides a more complete view of tip dynamics that underlie force microscope operation and can form the foundation of a three-dimensional AFM in a plurality of conditions. [Preview Abstract] |
Thursday, March 6, 2014 2:03PM - 2:15PM |
T24.00013: PiezoForce and Contact Resonance Microscopy Correlated with Raman Spectroscopy applied to a Non-linear Optical Material and to a Lithium Battery Material Aaron Lewis, Gabi Zeltzer, Oleg Zinoviev, Michael Roth, Bernhard Roling, Aaron Lewis, Rimma Dekhter A non-linear optical material (KTP) and a lithium-ion conductive glass ceramic (LICGC) for lithium batteries have been studied with Raman Spectroscopy on-line with Piezo Force and Contact Resonance Microscopies. This is allowed by a unique design of the scanned probe microscopy platform used in these studies and the electrical probes that have been developed that keep the optical axis completely free from above so that such combinations are feasible. The integration allows the investigation of alterations in the strain induced in the chemical structure of the materials as a result of the induction of piezo force. The combination of chemical characterization with both piezo force and contact resonance [1] microscopy allows for the monitoring of structural and ionic changes using Raman scattering correlated with these modalities. In KTP, it has been seen that the largest changes take place in TiO6 octahedral structure symmetric and antisymmetric stretch in the interfaces between the regions of the poling of the structure. In the LICGC, defined Raman changes are observed that are related to the contact resonance frequency. The combination adds considerable insight into both the techniques of Piezo Force Microscopy and Contact Resonance Microscopy. [Preview Abstract] |
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