Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H36: Advances in Scanned Probe Microscopy IIFocus
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Sponsoring Units: GIMS Chair: Christopher Gutierrez, NIST Room: 299 |
Tuesday, March 14, 2017 2:30PM - 3:06PM |
H36.00001: Revealing Energy Level Structure of Individual Quantum Dots by Single-Electron Sensitive Electrostatic Force Spectroscopy Invited Speaker: Peter Grutter The ground and excited electronic level structure of quantum systems is of fundamental importance for their optical, electric and chemical properties. Single-electron sensitive electrostatic force measurement with AFM has been demonstrated to be capable of quantitative energy level spectroscopy of individual and coupled semiconductor quantum dots (QD). In our experiments the oscillation of a dc biased AFM tip modulates the charge state of a QD. The QD is separated from a back gate via a tunnelling barrier. The resulting charge dynamics leads to measurable changes in cantilever resonance frequency and dissipation. The tip of our AFM can thus be described as a movable gate to address a QD of choice and is at the same time a charge detector with single electron sensitivity. Key to the experimental implementation is that the QD-back electrode tunnelling barrier is engineered to have a QD-back electrode tunnelling rate similar to the AFM cantilever mechanical resonance frequency. Furthermore, one needs to correct for the frequency dependent phase transfer function to obtain `true' dissipation values. The changes in dissipation and frequency measured by AFM are quantitatively described by the back-action of the single electron on the capacitive coupled AFM tip. In particular, we find that the ratio of the measured frequency shift to dissipation directly yields the QD-back electrode tunnelling rate. This allows an experimental determination of the energy dependence of single electron tunnelling rates, yielding quantitative information on the continuous DOS of gold nanoparticles, the discrete degenerate energy levels in single and coupled InAs QDs or possibly even homo- and lumo orbitals of single molecules coupled to an electrode. [Preview Abstract] |
Tuesday, March 14, 2017 3:06PM - 3:18PM |
H36.00002: Robust High-Resolution Imaging and Quantitative Force Spectroscopy in Vacuum with Tuned-Oscillator Atomic Force Microscopy. Udo Schwarz, Omur Dagdeviren, Jan Götzen, Hendrik Hölscher, Eric Altman Atomic force microscopy and spectroscopy are based on locally detecting the interactions between a surface and a sharp probe tip. For highest resolution imaging, noncontact modes that avoid tip-sample contact are used; control of the tip's vertical position is accomplished by oscillating the tip and detecting perturbations induced by its interaction with the surface potential. Due to this potential's nonlinear nature, however, achieving reliable control of the tip-sample distance is challenging, so much so that despite its power vacuum-based noncontact atomic force microscopy has remained a niche technique. Here we introduce a new pathway to distance control that prevents instabilities by externally tuning the oscillator's response characteristics [1]. A major advantage of this operational scheme is that it delivers robust position control in both the attractive and repulsive regimes with only one feedback loop, thereby providing an easy-to-implement route to atomic resolution imaging and quantitative tip-sample interaction force measurement. [1] O. E. Dagdeviren et al, Nanotechnology 27, 065703 (2016) [Preview Abstract] |
Tuesday, March 14, 2017 3:18PM - 3:30PM |
H36.00003: Ultra-sensitive magnetic microscopy with an atomic magnetometer and flux guides Young Jin Kim, Igor Savukov Many applications in neuroscience, biomedical research, and material science require high-sensitivity, high-resolution magnetometry. In order to meet this need we recently combined a cm-size spin-exchange relaxation-free Atomic Magnetometer (AM) with a flux guide (FG) to produce ultra-sensitive FG-AM magnetic microscopy. The FG serves to transmit the target magnetic flux to the AM thus enhancing both the sensitivity and resolution to tiny magnetic objects. In this talk, we will describe existing and next generation FG-AM devices and present experimental and numerical tests of its sensitivity and resolution. We demonstrate that an optimized FG-AM has sufficient resolution and sensitivity for the detection of a small number of neurons, which would be an important milestone in neuroscience. In addition, as a demonstration of one possible application of the FG-AM device, we conducted high-resolution magnetic imaging of micron-size magnetic particles. We will show that the device can produce clear microscopic magnetic image of 10 $\mu$m-size magnetic particles. [Preview Abstract] |
Tuesday, March 14, 2017 3:30PM - 3:42PM |
H36.00004: Optimal Control-Enabled Imaging and Spectroscopy using a Nanowire Magnetic Resonance Force Microscope William Rose, Holger Haas, Angela Chen, David Cory, Raffi Budakian Magnetic resonance imaging (MRI) is a powerful non-invasive technique that has transformed our ability to study the structure and function of biological systems. Key to its success has been the unique ability to combine imaging with magnetic resonance spectroscopy. Although it remains a significant challenge, there is considerable interest in extending MRI spectroscopy to the nanometer scale because it would provide a fundamentally new route for determining the structure and function of complex biomolecules. We present data taken with a nanowire magnetic resonance force microscopy (MRFM) setup. We show how the capabilities of this very sensitive spin-detection system can be extended to include spectroscopy and nanometer-scale imaging by combining optimal control theory (OCT) techniques with magic echo sequences. We apply OCT-based dynamical-decoupling pulses to nanoscale ensembles of proton spins in polystyrene, and demonstrate a 500-fold line-narrowing of the proton spin resonance, from 30 kHz to 60 Hz. We further demonstrate 1-D imaging over a 35-nm region with an average voxel size of 2.2 nm. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H36.00005: Simulating contrast inversion in atomic force microscopy imaging with real-space pseudopotentials Alex Lee, Yuki Sakai, James Chelikowsky Atomic force microscopy measurements have reported contrast inversions for systems such as Cu$_2$N and graphene that can hamper image interpretation and characterization. Here, we apply a simulation method based on \emph{ab initio} real-space pseudopotentials to gain an understanding of the tip-sample interactions that influence the inversion. We find that chemically reactive tips induce an attractive binding force that results in the contrast inversion. The inversion is tip height dependent and not observed when using less reactive CO-functionalized tips. [Preview Abstract] |
Tuesday, March 14, 2017 3:54PM - 4:06PM |
H36.00006: Scanning SQUID microscopy in cryogen-free refrigerators David Low, Brian T. Schaefer, Matt Ferguson, Alexander Jarjour, Katja C. Nowack Scanning magnetic probe microscopy becomes more challenging in cryogen-free systems due to vibrations introduced at the sample by the cryocooler. We are implementing superconducting quantum interference device (SQUID) microscopes in two cryogen-free systems: a Montana Instruments Nanoscale Workstation and a BlueFors Cryogenics LD400 dilution refrigerator. We evaluate the vibrations in our microscopes from magnetic flux noise spectral densities measured near a localized source of magnetic field following a recently developed method by Schiessl et al. (arXiv:1610.00285) and outline methods intended to reduce vibrations. [Preview Abstract] |
Tuesday, March 14, 2017 4:06PM - 4:18PM |
H36.00007: Electron Spin Resonance with Scanning SQUID Sensor Zheng Cui, Sean Hart, Rahim Ullah, John R. Kirtley, K. A. Moler Electron spin resonance (ESR) is a powerful technique for the study of electron properties in materials, such as spin-orbit coupling, hyperfine interactions, as well as other relaxation processes. Conventional ESR is performed in large magnetic fields (up to several Tesla) with large sample volumes (several milliliters). Disadvantages of the conventional technique include resonance-linewidth broadening due to inhomogeneity in large samples and incompatibility of large magnetic fields with certain samples (e.g. low-$H_c$ superconductors). A Superconducting QUantum Interference Device (SQUID) is an ultrasensitive magnetic flux detector that can measure spin resonance in low fields and small samples. With a magnetic sensitivity of 1000 Bohr magnetons, our scanning SQUID sensor can detect the ESR signal from $10^8$ electron spins at 4.2 Kelvin and 1 Gauss of magnetic field. The scanning capability will enable us to locate and study microscopic devices as well as to spatially resolve micron-scale variations in bulk samples. We will demonstrate scanning SQUID low-field ESR measurements on well-known materials such as DPPH (2,2-diphenyl-1-picrylhydrazyl). $\left[1\right]$ L. R. Narasimhan, M. Takigawa, M. B. Ketchen, APL, 65, 1305-1307 (1994). [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:30PM |
H36.00008: Quantum State Absorptions Coupled To Resonance Raman Spectroscopy Could Result In A General Explanation of TERS From Multiprobe NSOM {\&} Raman Scattering Aaron Lewis, Zachary Schultz, John Parthenios, Rimma Dekhter, Dimitris Anestopoulos, Spiridon Grammatikopoulos, Kostantinos Papagelis, James Marr, Costas Galiotis, Dimitry Lev Tip enhanced Raman scattering (TERS) amplifies the intensity of vibrational Raman scattering by employing the tip of a probe interacting, in ultra close proximity, with a surface. Although a general understanding of the TERS process is still to be fully elucidated, scanning tunneling microscopy (STM) feedback is often applied with success in TERS to keep a noble metal probe in intimate proximity with a noble metal substrate. Since such STM TERS is a common modality, the possible implications of plasmonic fields that may be induced by the tunneling process are investigated. In addition, TERS of a 2D resonant molecular system, a MoS$_{\mathrm{2}}$ bilayer crystal and a 2D non-resonant, lipid molecular bilayer are compared. Data with multiple excitation wavelengths and surfaces for the resonant system in the near- (TERS) and far-field are reported. An interpretation based on weak coupling interactions within the framework of conventional resonance Raman scattering can explain the observed TERS enhancements. The none-resonant molecular lipid system, on the other hand, requires strong coupling for a full understanding of the reported observations. [Preview Abstract] |
(Author Not Attending)
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H36.00009: Hyperbolic surface polaritons in hexagonal boron nitride Siyuan Dai, Yafang Yang, Qiong Ma, Kenji Watanabe, Takashi Taniguchi, Pablo Jarillo-Herrero, Michael Fogler, D. N. Basov Hexagonal boron nitride (hBN) is a natural hyperbolic material ($\varepsilon_{\mathrm{z}}\varepsilon_{\mathrm{xy}}$ \textless 0) which supports volume-confined hyperbolic polaritons (HPs). In this work, we report on the observation of hyperbolic surface polaritons (HSPs) confined along sidewalls of the hBN slab. We have systematically studied the wavelength, damping and momentum-frequency dispersion of the HSPs by infrared nano-imaging using the scattering-type scanning near-field optical microscopy. We investigate the reflection, transmission and scattering of HSPs at the hBN slab corner with various angles. The surface confined nature of HSPs further allows the propagation steering though engineering of the hBN slab geometry. [Preview Abstract] |
Tuesday, March 14, 2017 4:42PM - 4:54PM |
H36.00010: Nanoscale thermal imaging of VO$_2$ via Poole-Frenkel conduction Alyson Spitzig, Jason D. Hoffman, Adam E. Pivonka, Harry Mickalide, Alex Frenzel, Jeehoon Kim, Changhyun Ko, You Zhou, Kevin O'Connor, Eric W. Hudson, Shriram Ramanathan, Jennifer E. Hoffman We present a novel method for nanoscale thermal imaging of insulating thin films. We demonstrate this method on VO$_2$, which undergoes a sharp insulator-to-metal transition at 340 K. We sweep the voltage applied to a conducting atomic force microscope tip in contact mode at room temperature and measure the resultant current through a VO$_2$ film. The Poole-Frenkel (PF) conduction mechanism, which dominates in the insulating state of VO$_2$, is fit to extract the local temperature of the film using fundamental constants and known film properties. We measure the local electric field and temperature immediately preceding the insulator-to-metal transition in VO$_2$ to determine whether the transition can be triggered by an applied electric field alone. We calculate an average temperature of 334 $\pm$ 5 K, implying that Joule heating has locally warmed the sample very close to the transition temperature. Our thermometry technique opens up the possibility to measure the local temperature of any film dominated by the PF conduction mechanism, and presents the opportunity to extend our technique to other conduction mechanisms. [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:06PM |
H36.00011: Scanning thermal microscopy using electrical measurements Abhay Shastry, Sosuke Inui, Charles Stafford The local temperature and voltage of a quantum system out of equilibrium is defined via a floating probe\footnote{Abhay Shastry and Charles Stafford, Physical Review B 94, 155433 (2016)} operating in the tunneling regime. However, experimental difficulties in thermally isolating the probe have limited the spatial resolution of scanning thermal microscopy. We now propose a method to measure the temperature using only electrical measurements in systems obeying the Wiedemann-Franz law. The method significantly advances the spatial resolution and accuracy of scanning thermal microscopy, bringing it to the previously inaccessible tunneling regime. [Preview Abstract] |
Tuesday, March 14, 2017 5:06PM - 5:18PM |
H36.00012: Ultrasensitive Force Controlled Live Cell Optical Imaging and Voltage Sensing Aaron Lewis, Aaron Brahami, Hadas Levy, Efrat Zlotkin-Rivkin, Dimitry Lev, Talia Yeshua, Oleg Fedosyeyev, Benjamin Aroeti Force controlled optical and scanned probe imaging of voltage sensing of living cell membranes is demonstrated by overcoming limitations inherent in atomic force microscopy (AFM) since its inception in 1986...................$^{1}$. This work and the advances that have allowed it permit a whole genre of functional biological imaging with stiff scanned probe imaging cantilevers having force constants ranging from 1-10N/m. To achieve these innovations, several constraints had to be overcome that have restricted live cell AFM imaging to only highly limiting ultrasoft (0.05N/m) cantilevers. The limitations extend even to structural topographic imaging with these soft cantilevers having inherent geometric and other shortcomings. This is exemplified by difficulties in imaging fine cell protrusions, such as microvilli that can emanate from cell membranes. The progress reported here demonstrates both ultimate topographic imaging and new functional applications that should have a significant impact on biological imaging of living and other ultrasoft systems. [Preview Abstract] |
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