Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F10: Advances in Scanned Probe Microscopy 3: Scanning Probes Spectroscopic TechniquesFocus
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Sponsoring Units: GIMS Chair: Stephen Jesse, University of Tennessee Room: 108 |
Tuesday, March 3, 2020 8:00AM - 8:36AM |
F10.00001: Direct and converse flexoelectricity: the effect of strain and electric field gradients on nanoscale electromechanical responses Invited Speaker: Neus Domingo Surface electromechanics at the nanoscale are typically studied by Piezoresponse Force Microscopy (PFM), based on the inverse piezoelectric effect. As a first approach, generally only homogeneous responses are taken into account, but it has been realized that the effect of gradients in electro-mechanical phenomena at the nanoscale can become dominating: the generation of electrical signals after the application of mechanical strain gradients with an AFM tip has been proved, and it has been shown that it is possible to write ferroelectric domains [1] or to move oxygen vacancies and charges. |
Tuesday, March 3, 2020 8:36AM - 8:48AM |
F10.00002: New modalities for cryogenic nano-imaging and -spectroscopy Sven A. Doenges, Kyoung-Duck Park, tao jiang, Fabian Menges, Markus B. Raschke Scanning nano-optical imaging and -spectroscopy have emerged as powerful tools in investigating and understanding heterogeneities and underlying physics in a wide range of organic, layered van der Waals, and correlated electron materials. However, the extension to variable and low temperatures has remained a major experimental challenge, yet highly desirable with many fundamental properties and phase transitions only emerging far below room temperature. Here, we present the development of cryogen-free variable temperature infrared nano-imaging and spectroscopy, as well as variable temperature tip-enhanced photoluminescence and nano-Raman spectroscopy in different instruments based on closed cycle cryocoolers with an exchange gas cooled low vibration interface. At the example of surface plasmon polariton nano-imaging in graphene, we establish infrared scattering scanning near-field optical microscopy (s-SNOM) at temperatures as low as 15 K with spatial resolution of 10 nm. Further, we demonstrate tip-enhanced photo-luminescence (TEPL) and tip-enhanced Raman spectroscopy (TERS) of different excitonic systems based on 2D transition metal dichalcogenide (TMD) heterostructures. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F10.00003: Bulk ferromagnetic tips for spin-polarized scanning tunneling microscopy Masahiro Haze, Hung-Hsiang Yang, Kanta Asakawa, Ryosuke Yamamoto, Nobuyuki Watanabe, Yasuo Yoshida, Yukio Hasegawa To develop nano-controlled magnetic materials for condensed matter physics and device applications, it has been required to investigate magnetic structures in atomic scales. While spin-polarized scanning tunneling microscopy (SP-STM) is one of the powerful tools, the usage is still hampered because of the issue on its probe. Tips coated with magnetic thin films are often used, but fabricating stable and reliable ones is not easy unless well equipped. Among the bulk magnetic probes, which can be prepared rather easily, chemically etched antiferromagnetic Cr tips are most commonly used. However, antiferromagnetic probes have disadvantages that the magnetization direction cannot be controlled and defined. On the other hand, bulk ferromagnetic probes are good choices if target materials are robust against stray fields such as antiferromagnetic materials. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F10.00004: Fourier transform infrared scanning tunneling microscopy: Measuring vibrational modes at the nanoscale Kristopher Barr, Naihao Chiang, Andrew Ira Guttentag, Paul S Weiss Scanning probe microscopy has enabled unprecedented surface imaging capability down to atomic resolution. Recent advances in photon technologies has led to successful integration of optical spectroscopy with various scanning probe microscopy. In this work, we use the scanning tunneling microscope tip as a nano antenna and a multiplexed signal from a bench-top Fourier-transform interferometer to discover vibrational modes at the nanoscale. By back illuminating our gold on sapphire samples, we are able to excite molecular self-assembled monolayers into vibrationally excited states evanescently, thus creating a perturbation in the conductance of the STM junction. We use cyanide on gold as a proof-of-concept system because of its distinct vibrational spectra, its stability under ambient conditions, and our control of the molecules interactions. In previous work, we have demonstrated direct control of the gold cyanide molecular packing structures – cubic or hexagonal close packed – and can contribute a vibrational mode from Raman and infrared spectroscopy to each phase. This custom-built instrument performs operates at ambient temperature and pressure, enabling us to image chemical structure with single-molecule resolution on a variety of systems. |
Tuesday, March 3, 2020 9:12AM - 9:24AM |
F10.00005: Role of steps on Pb atomic-layer superconductivity Yudai Sato, Fumikazu Oguro, Kanta Asakawa, Takashi Uchihashi, Yukio Hasegawa Atomic-layer superconductors [1] exhibit various unique characteristics. One of the features is the enhancement of the in-plane critical magnetic field. The presence of steps, which work as a Josephson barrier [2], is inevitable. It is thus expected that the weakened coupling between terraces confines cooper pairs within the terraces and modifies superconductivity depending on the terrace width. |
Tuesday, March 3, 2020 9:24AM - 9:36AM |
F10.00006: GHz-THz near-field imaging of extreme subwavelength metal structures Xinzhong Chen, Xiao Liu, Xiangdong Guo, Shu Chen, Hai Hu, Elizaveta Nikulina, Ziheng Yao, Hans Bechtel, Michael Martin, G Carr, Qing Dai, Songlin Zhuang, Qing Hu, Yiming Zhu, Rainer Hillenbrand, Mengkun Liu, Guanjun You Modern scattering-type scanning near-field optical microscopy (s-SNOM) has become an indispensable tool in material research. In this talk we present a home-built GHz-THz s-SNOM using Schottky diodes as both light source and detector, achieving unprecedented spatial resolution at long wavelength (~2 mm). We systematically investigated a series of extreme subwavelength metallic nanostructures at the micrometer scale. The near-field material contrast is found to be greatly impacted by the lateral size and connectivity of the nanostructures, which is drastically different from the cases at shorter wavelengths (e.g. IR s-SNOM). The observed phenomena can be explained by a quasi-static analysis and full-wave electromagnetic simulations. Our results reveal that s-SNOM with long wavelength excitation is an ideal candidate for investigating the electrostatic behavior of metallic devices. |
Tuesday, March 3, 2020 9:36AM - 9:48AM |
F10.00007: Ultrafast infrared nano-spectroscopic imaging of heterogeneous photoinduced dynamical processes Jun Nishida, Samuel C. Johnson, Sven A. Doenges, Amani H Alfaifi, Sean Shaheen, Markus B. Raschke Low-energy responses and interactions at mid-infrared frequencies often play central roles in photoinduced dynamical phenomena, ranging from phase transitions in quantum materials to polaron formations in photovoltaic materials. However, the spatial heterogeneities and temporal evolution associated with such low-energy processes in the photoinduced transient state has remained elusive. Here, we develop and apply ultrafast infrared scattering scanning near-field optical microscopy (IR s-SNOM) to characterize photoinduced dynamics with far-from-equilibrium excitation and ultrahigh spatio-temporal-spectral resolution. For unambiguous determination of nano-scale phase and spectral responses, we develop optical pump - infrared probe nano-imaging with heterodyne detection. We demonstrate the performance of ultrafast IR s-SNOM to probe transient quantum states of the photoinduced heterogeneous metallic phase in vanadium oxide microrods, as well as spatially varying polaron-molecule coupling in lead halide perovskite films. The approach of ultrafast heterodyne IR s-SNOM with strong pump excitation is generally applicable to a wide range of strong transient field phenomena, providing for fundamental insight into heterogeneous electronic, structural, and dynamical properties of materials. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F10.00008: Calibrating atomic force microscope detectors on soft surfaces Daniel Forchheimer, Daniel Platz, Riccardo Borgani, David Haviland Quantitative force microscopy requires independant means of calibrating both cantilever stiffness and detector responsivity (i.e. the factor mapping cantilever deflection in nanometers to photo-detector signal in Volts). The conventional methods slowly approach the surface while observing either static bending or change in oscillation amplitude. Detector responsivity is then obtained under the assumption that the surface does not deform during the region of approach used for calibration. This assumption may be satisfied for large force and stiff sample, both of which risk damaging the tip. Here we present a new method for detector calibration based on Intermodulation AFM where the tip-surface force versus cantilever deflection is continuously monitored during the slow approach. This method allows us to calibrate the detector without the previously mentioned assumptions. We can therefore calibrate on any surface, hard or soft, or directly on the sample with the same magnitude of force used for quantitative imaging. We present the theory of this method and its experimental implementation on a variety of different surfaces. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F10.00009: The influence of time and temperature on viscoelastic properties of nanoscale domains within polymer composites Bede Pittenger, Sergey Osechinskiy, John Thornton, Sophie Loire, Thomas Mueller The behavior of polymer composites is controlled by the properties of the components as well as the microstructure of the material. Because confinement effects and interphase formation can alter properties of the microphases, only measurements performed directly on the composite can provide the needed local property distribution. Mechanical properties of polymers are generally time dependent, so a full understanding requires measurements over a range of frequencies and temperatures. Ideally, one would like to observe the mechanical behavior of these microscopic domains while they pass through their glass transitions to appreciate the influence of size effects and confinement on time dependent mechanical properties. |
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F10.00010: Cryogenic Scattering-type Scanning Near-field Optical Microscopy Fanwei Liu, Xi Chen, Mengkun Liu, Hanqing Mao, Sidan Chen, Xinzhong Chen, Ziheng Yao Scattering-type scanning near field optical microscopy (s-SNOM) has become an important branch of modern optical techniques in the past decade, which allows nanoscale imaging over a broad spectral range. This informative technique is feasible to study the electrodynamics of correlated quantum materials with a spatial resolution down to 10 nm. As a powerful scanning probe microscopy, although the importance of cryo-SNOM has been universally recognized, the realization remains to be a challenging task. Based on the experience of cryo-AFM, we built a set of s-SNOM operating with variable sample temperature down to 10 K. The scanning probe is located in ultra high vacuum chamber with He-bath cryostat maintaining low temperature and combined with a molecule beam epitaxy (MBE) system. The nine home-made positioners of the scanning system function well at low temperature. The system is equipped with CO2 laser which can provide long-time stable light source. Our cryo-SNOM has been tested at liquid nitrogen temperature, which shows good performance and is promising to work well below 10K. |
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