Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H26: Advances in Scanned Probe Microscopy II: High Frequency, and Optical and Low Temperature MeasurementsFocus
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Sponsoring Units: GIMS Room: BCEC 160B |
Tuesday, March 5, 2019 2:30PM - 3:06PM |
H26.00001: What limits time resolution in AFM? Invited Speaker: Peter Grutter Developing a technique that combines nanometer spatial and sub-femtosecond temporal sensitivity is a crucial step towards exposing the inner mechanisms of chemical reactions, single molecule motion, electron dynamics in solids, and the effects of defects or trap states on electron motion and behavior, amongst many other questions relating to the most fundamental processes in molecular systems. |
Tuesday, March 5, 2019 3:06PM - 3:18PM |
H26.00002: Subsurface Second Harmonic Speckle Defect Microscopy Farbod Shafiei, Tommaso Orzali, Alexey Vert, P Y Hung, Gennadi Bersuker, Michael C Downer Growing crystals epitaxialy over substrates is a critically important process for opto-electronic applications. Due to generally occurred atomic-level mismatches between the crystal and substrate, these semiconductor thin films are vulnerable to varieties of defects (like threading dislocation in GaAs-Si), which act as scattering sites for electrons and photons. Multi-scattering from these defects can result in the localization of the light. We demonstrate that a signature of this localization (in the case of III-V films) can be picked by a fiber scanning probe microscope in nonlinear regime. The size of these light localizations, which optically appear like speckles, have strong correlation to the density of the film dislocations. We introduce this noninvasive optical technique capable of identifying the presence of threading dislocations, their density, as well as orientation and structural arrangements of these defects. |
Tuesday, March 5, 2019 3:18PM - 3:30PM |
H26.00003: Optical evolution of dislocation speckle imaging inside and outside of thin films Farbod Shafiei, Tommaso Orzali, Alexey Vert, Man Hoi Wong, Gennadi Bersuker, Michael C Downer We have employed a fiber scanning probe microscopy to study light localization due to multi-scattering of light by dislocation defects in III-V films (in particular, GaAs-Si). By sputtering the film down to the semiconductor-substrate interface we observe how the nonlinear optical signature of the dislocation defects changes with the increasing density of a dislocation area. The same probe microscopy approach was used to track the evolution of the propagating optical fields from these dislocation speckles, outside the thin film. Such approach can be used as an extremely high resolution monitoring tool of propagating electromagnetic fields. |
Tuesday, March 5, 2019 3:30PM - 3:42PM |
H26.00004: Vibration measurements of a scanning SQUID microscope in a cryogen-free dilution refrigerator David Low, George Ferguson, Alexander B Jarjour, Rachel Resnick, Brian Schaefer, Eric N Smith, Katja Nowack Scanning probe microscopy is more challenging in cryogen-free systems due to vibrations introduced at the sample by the cryocooler. We built a cryogen-free scanning superconducting quantum interference device (SQUID) magnetic probe microscope operating in a cryogen-free dilution refrigerator with a base temperature of 10 mK. We report characterization of both the vibrations at the mixing chamber plate and of probe-to-sample vibrations. For the latter, we follow Schliessl et al. (Appl. Phys. Lett. 109, 232601 (2016)) and measure noise spectra at multiple locations above a sample where strong magnetic field gradients are present. This allows us to disentangle vibrations in different spatial directions. We find that the most pronounced vibrations are below 10 nm/Hz1/2 and occur at low harmonics of the pulse tube cycle. We will also discuss future improvements to our microscope and refrigerator that will further reduce the vibrations in our system. |
Tuesday, March 5, 2019 3:42PM - 3:54PM |
H26.00005: Upgrading a low-temperature scanning tunneling microscope for electron spin resonance experiments Fabian Natterer, François Patthey, Tobias Bilgeri, Patrick Forrester, Nicolas Weiss, Harald Brune We describe the upgrade of a helium-3 STM to an electron spin resonance enabled apparatus [1]. We are able to transmit RF power to the tunnel junction at frequencies of up to 30 GHz. Our apparatus is benchmarked via magnetic field sweep ESR on the model system TiH/MgO/Ag(100)[2] for which we find a magnetic moment of (1.004±0.001) μB. We can chose a DC mode for regular STM operation or an ultra-fast mode for pump-probe spectroscopy or the reading of spin-states. In both modes, simultaneous radiofrequency excitation is possible, which we add via a resistive pick-off tee to the bias voltage path. We discuss our transmission, indicate potential pitfalls in the upgrade and demonstrate how to synchronize the arrival times of RF and DC pulses coming from different paths to the STM junction, a prerequisite for future pulsed ESR experiments. |
Tuesday, March 5, 2019 3:54PM - 4:06PM |
H26.00006: An Ultra-High Vacuum Cryogen-free Low Temperature Proximal Probe System for the Exploration of Low Dimensional Materials and Nano-devices Angela Coe, Guohong Li, Eva Andrei We introduce a new design concept that combines into one instrument, several scanning probe microscopy modules, ultra-high vacuum, low temperature, magnetic field, and cryogen free operation. The integration of these capabilities is made possible by the realization of an ultra-compact scanning probe microscopy (SPM) head with a modular design for accommodating interchangeable probes including STM, AFM, and MFM. A novel transfer mechanism makes it possible to transfer the SPM head between various chambers of a compact UHV system for loading probes, tips, and samples. The instrument is equipped with stages for sputtering, e-beam film deposition, and exfoliation for in-situ sample preparation and tip conditioning. Following the UHV room-temperature assembly, the entire SPM with the loaded sample is transferred without breaking vacuum to a variable temperature cryogen-free cryostat and magnet. The integration of all these capabilities into one instrument enables in-situ nano-scale characterization of low dimensional systems and devices in an ultra-clean environment, and under controlled temperature and field conditions. |
Tuesday, March 5, 2019 4:06PM - 4:18PM |
H26.00007: Low temperature magnetic force microscope with simple design. Jeffrey Vit, Kwok-Wai Ng, Alejandro De Lozanne We present a new design for a magnetic force microscope that will operate at variable temperatures down to liquid helium in fields up to 8 Tesla. As with our previous designs, the temperature/field design goals are achieved most efficiently by maintaining everything within a one-inch cylinder.[Rev. Sci. Instrum. 78, 053710 (2007)] Unlike other designs, this one has an open architecture that results in simplified machining, assembly, modification/repair, and daily operation. The new microscope has three homemade stick-slip stages that provide several millimeters of relative travel between tip and sample. |
Tuesday, March 5, 2019 4:18PM - 4:30PM |
H26.00008: Advances in SQUID-detected Magnetic Resonance Force Microscopy Martin De Wit, Gesa Welker, Frederik Hoekstra, Tjerk Oosterkamp Magnetic Resonance Force Microscopy (MRFM) is a technique that combines magnetic resonance protocols with an ultrasensitive cantilever to measure the forces exerted by extremely small numbers of spins. The fundamental limit for the sensitivity of MRFM is given by the thermal force noise, so experiments should be performed at the lowest possible temperature. For this reason, we have developed a three stage mechanical low pass filter, which combines good vibration isolation (expected attenuation > 100 dB at 100 Hz) with a high thermal conductance (cooling power 113 μW at 100 mK). The MRFM can be operated at temperatures around 20 mK thanks to a SQUID-based detection scheme and the mechanical generation of the alternating B1 fields required for the magnetic resonance. We use these technical advances to perform MRFM experiments on a thin copper film, where we obtain frequency-shift signals from the Boltzmann polarization of spins in a volume as small as (40 nm)3. We propose an experiment on a sample containing protons where magnetic resonance imaging with a voxel size < (10 nm)3 should be possible. |
Tuesday, March 5, 2019 4:30PM - 4:42PM |
H26.00009: Incommensurate surface superstructure observed on epitaxially grown Al(111) films by scanning tunneling microscopy at mK temperature Sungmin Kim, Johannes Schwenk, William G Cullen, Young Kuk, Joseph A Stroscio Superconducting aluminum samples are generally used as a standard reference for testing the energy resolution of cryogenic scanning tunneling microscopes operating at ultra-low temperatures by measuring its superconducting tunneling gap spectrum. However, only a few of the atomic structure of the aluminum surface have been reported in those studies because of the difficulties in preparing atomically clean surfaces due to its strong reactivity. In this presentation, we report the observation of an incommensurate superstructure on Al(111) films grown epitaxially on graphene on SiC substrates. The observed superstructure has 3-fold symmetry with a 3.3 periodicity. The superstructure closely resembles a charge density wave structure, for example, similar to that typically observed on NbSe2. We therefore speculate that possibly Al(111) may support a surface CDW at ultra-low temperatures due to same electron-phonon coupling which is responsible its superconductivity. Other possible explanations for a surface or bulk CDW phase include such soft phonons resulting from strain effects [1], which will be discussed. |
Tuesday, March 5, 2019 4:42PM - 4:54PM |
H26.00010: Photonic crystal fiber assisted nano-antenna for tip-enhanced Raman spectroscopy Khant Minn, Blake Birmingham, Brynna R Neff, Marlan O Scully, Howard Ho Wai Lee, Zhenrong Zhang Metallic plasmonic nano-probes can efficiently excite and detect the near-field at nanoscale for near-field imaging and sensing applications such as tip-enhanced Raman spectroscopy (TERS). In this paper, we report the design, fabrication and far-field characterization of a photonic-plasmonic probe. In our device, light in a photonic crystal fiber (PCF) couples with the surface plasmons of a nano-antenna. The needle-shaped antenna is grown by electron beam assisted chemical deposition of platinum on the PCF’s end facet. Plasmonic resonance conditions can be optimized by controlling the deposition parameters, height, and base diameter of the antenna. Far field emission to the side of the probe, optical spectra and mode profiles transmitted through the probe demonstrate the excitation of surface plasmons on the antennae. The probe can be implemented into TERS setup to obtain spectroscopic information at the nanoscale. |
Tuesday, March 5, 2019 4:54PM - 5:06PM |
H26.00011: Cryogen-free variable temperature scanning SQUID microscope Logan Bishop-Van Horn, Zheng Cui, John Kirtley, Kathryn Ann Moler Scanning Superconducting QUantum Interference Device (SQUID) microscopy is a powerful tool for imaging local magnetic properties, but it requires a low-vibration cryogenic environment, traditionally achieved by thermal contact with a bath of liquid helium or the mixing chamber of a “wet” dilution refrigerator. We mount a SQUID microscope on the 3 K plate of a Bluefors pulse tube cryocooler and characterize its vibrational spectrum by measuring SQUID noise in a region of sharp flux gradient. By implementing passive vibration isolation, we reduce relative sensor-sample vibrations to 20 nm in-plane and 15 nm out-of-plane. A variable-temperature sample stage that is thermally isolated from the SQUID sensor enables measurement at sample temperatures from 2.8 K to 110 K. We demonstrate these advances by imaging inhomogeneous susceptibility and vortex pinning in optimally doped YBCO above 90 K. Together with sub-micron spatial resolution and 350×350 μm2 scan range, these advances position us for further studies of magnetic and superconducting materials and devices over a temperature range not previously accessible to scanning SQUID microscopy. |
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