Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session L23: Advances in Scanned Probe Microscopy IV: Correlative and Analytical Measurements in Scanning Probe Microscopy |
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Sponsoring Units: GIMS Room: BCEC 158 |
Wednesday, March 6, 2019 11:15AM - 11:27AM |
L23.00001: Cryogenic Nitrogen-Vacancy Scanning Microscope Uri Vool, Assaf Hamo, Ziwei Qiu, Tony Zhou, Amir Yacoby The Nitrogen-Vacancy (NV) electron spin is a quantum sensor of magnetic field, with high sensitivity in a wide range of frequencies and extremely high spatial resolution. Most NV magnetometry experiments are performed by stationary NVs in a bulk crystal measuring a nearby sample. This limits the spatial resolution to the optical diffraction limit and strongly limits the sample which can be measured. Recently, a scanning technique was developed to overcome these issues, in which the NV is located on a tip that can be scanned over a sample. |
Wednesday, March 6, 2019 11:27AM - 11:39AM |
L23.00002: Nanoscale CVD Graphene Hall Probes for high resolution Scanning Probe Microscopy David Collomb, Penglei Li, Simon Bending, Daniel Wolverson Advances in magnetic imaging are one of many improvements in instrumentation which have enabled scientists to pioneer and develop their next big research ideas. One important technique, scanning Hall probe microscopy (SHPM), involves rastering a Hall sensor over a surface to create a magnetic field map across the sample. However, SHPM has typically relied on the low temperature performance of GaAs-based Hall probes, whose figures-of-merit become much worse at room temperature. This tends to exclude SHPM from numerous applications under ambient conditions such as susceptometry for non-destructive evaluation and characterisation of ferromagnetic data storage media. Making use of graphene's high carrier mobility and facile CVD growth techniques, we have fabricated graphene Hall devices with nanoscale lateral dimensions for sub-100nm spatial resolution imaging while maintaining excellent room temperature minimum detectable fields in the μT/√Hz range. We will illustrate the imaging performance of such probes, including; low frequency noise performance and magnetic sensitivity, for devices with different active areas, carrier densities and drive currents. |
Wednesday, March 6, 2019 11:39AM - 11:51AM |
L23.00003: Near-field correlative nanoscopy accesses physical constants in complex functional materials Stefan Mastel, Tobias Gokus, Alexander Govyadinov, Andreas Huber Nanoscale characterization methods play a key role in the analysis, development and optimization of nanoscopic materials and devices. Often several characterization techniques are required to gain a comprehensive understanding of the various material properties of complex functional materials. Here we introduce the combined nanoscale analysis of complex material systems by correlating infrared scattering-type Scanning Near-field Optical Microscopy (s-SNOM) with information obtained by other Scanning Probe Microscopy (SPM) based techniques. For example near-field reflection/absorption imaging at 1500 cm-1 of a only 50 nm thin phase-separated PS/LDPE polymer film allows to selectively highlight the distribution of PS in the blend, while atomic force microscopy modes simultaneously map the mechanical properties like adhesion. Further, results will be presented that correlate the nanoscale near-field optical response of semiconducting samples like SRAM devices in different frequency ranges (mid-IR & THz) to Kelvin Probe Force Microscopy and Electrostatic Force Microscopy measurements. Thus, neaspec s-SNOM systems represent an ideal platform to characterize complex material systems by different near-field optical and SPM-based mechanical and electrical methods at the nanoscale. |
Wednesday, March 6, 2019 11:51AM - 12:03PM |
L23.00004: Magnetic force sensing using a self-assembled GaAs nanowire with a MnAs tip Nicola Rossi, Boris Gross, Florian Dirnberger, Dominique Bougeard, Martino Poggio We present a scanning magnetic force sensor based on an individual magnet-tipped GaAs nanowire (NW) grown by molecular beam epitaxy [1]. Its magnetic tip consists of a final segment of single-crystal MnAs formed by sequential crystallization of the liquid Ga catalyst droplet [2]. We characterize the mechanical and magnetic properties of such NWs by measuring their flexural mechanical response in an applied magnetic field [3]. Comparison with numerical simulations allows the identification of their equilibrium magnetization configurations, which in some cases include magnetic vortices. We determine a NW's performance as a scanning probe [4], by measuring its dynamical response to the magnetic field of a micrometric current-carrying wire. The NWs' tiny tips and their high force sensitivity make them promising for imaging weak magnetic field patterns on the nanometer-scale, as required for mapping mesoscopic transport and spin textures or in nanometer-scale magnetic resonance. |
Wednesday, March 6, 2019 12:03PM - 12:15PM |
L23.00005: The Correlation between Location Confidence and Alkanethiol Chain Tilt Direction in Alkanethiol Self-Assembled Monolayers (SAMs) Mitchell Yothers, Soumya Bhattacharya, Lloyd Bumm Accurate measurements of structures at the nanoscale are of fundamental importance for nanofabrication. Using alkanethiol self-assembled monolayers (SAMs) as a model system, we demonstrate a way to measure the alkanethiol chain tilt direction from constant-current scanning tunneling microscope (STM) images. These measurements are made with a real-space image post-processing technique that compensates for image distortion using a physical model. Using this measurement, we are also able to establish the chain tilt direction without guest molecules, by using the position uncertainty of molecules about their expected lattice site position. In particular, we will show the direction of maximum position uncertainty is anticorrelated with the alkanethiol chain tilt direction. This anticorrelation is consistent across different STM tips and alkanethiol chain lengths. |
Wednesday, March 6, 2019 12:15PM - 12:27PM |
L23.00006: A differential photon-rate meter for real-time peak tracking in optically detected magnetic resonance at low photon-count rates Kapildeb Ambal The optically detected magnetic resonance of the NV- center in diamond provides a mechanism for precise, nanoscale magnetometry. As an alternative to measuring and fitting complete resonance spectra, resonance peak locking and tracking methods provide real-time and continuous measurements of the magnetic field. But the weak photoluminescence from small ensembles of NV- center including single NV- centers poses a problem for peak tracking. The emitted light requires single-photon detection which produces a narrow (≈ 20 ns) voltage pulse per detected photon. The discrete voltage pulses are not amenable for demodulation by regular lockin amplifiers. Here, we address active feedback control and real-time field tracking with photon detection rates in the range of 4 X 103 s-1 to 1 X 106 s-1, which are typical of single NV- centers, and we present a custom differential rate meter with phase sensitive detection. Without compromising signal-to-noise, this real-time data processing scheme provides all the typical functionalities of a lock-in amplifier needed for real-time peak locking and tracking. We demonstrate continuous field measurements at sweep rates exceeding 50 μT/s. This scheme covers a broad magnetic field range, limited by the frequency range of the microwave generator. |
Wednesday, March 6, 2019 12:27PM - 12:39PM |
L23.00007: The tip shape dependence of the STM-induced luminescence Songbin Cui, Ungdon Ham, Tae-Hwan Kim Photon signal enhancement due to surface plasmon coupling becomes an important issue in high-resolution microscopy/spectroscopy, such as scanning tunneling microscopy (STM) induced luminescence, surface/tip enhanced Raman spectroscopy, and so on. Such enhancement is significantly varied by modifying the plasmonic nanocavities. The gap-mode plasmonic nanocavity between an STM tip and surface realizes sub-molecular photon spectroscopy. The plasmonic resonant modes are known to be modified by tip indentation. However, the tip shape dependence of the plasmonic nanocavity remains unclear. In this work, we experimentally present the role of tip shape in surface plasmonic light emission. We have used Ag tips and a Ag(100) substrate, and STM-induced photon signals have been measured from the two opposite sides of the STM tip simultaneously. We found that changing small parts of the tip can differ the photon spectrum significantly due to tip shape asymmetry. This finding can help us to tune the plasmonic photon emission spectra more efficiently and give a new insight by using the symmetric or asymmetric STM tip induced luminescence. |
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