Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session A10: Advances in Scanned Probe Microscopy 1: Novel Approaches and Ultrasensitive DetectionFocus
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Sponsoring Units: GIMS Chair: Roger Proksch, Asylum Research Room: 108 |
Monday, March 2, 2020 8:00AM - 8:12AM |
A10.00001: Scanning Probe Microscope in an Ultra-High Vacuum Cryogen-free Environment Angela Coe, Guohong Li, Eva Andrei Our new design concepts expand the use of scanning probe microscopy (SPM) into an ultra-high vacuum cryogen-free system. Typical cryogen-free systems are too noisy to effectively operate SPM, which require a low noise environment. We have created an internal vibration isolation unit that is able to connect to existing cryogen-free cryostats making their noise level low enough to operate SPMs. Our SPM is a modular design that can accommodate interchangeable probes, including STM, AFM, and MFM. The instrument is equipped with stages for sputtering, e-beam film deposition, and exfoliation for in-situ sample preparation and tip conditioning. The SPM is assembled at room temperature in ultra-high vacuum and a novel low-profile vertical transfer mechanism makes it possible to transfer the SPM, 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. |
Monday, March 2, 2020 8:12AM - 8:24AM |
A10.00002: Graphene-based Hall probe magnetic imaging David Collomb, Penglei Li, Simon J Bending Hall probe microscopy is a powerful tool for mapping magnetic fields across a sample surface, and can be used to investigate key properties of magnetic and superconducting materials. However, to date the technique has not been widely used under ambient conditions because the figures-of-merit of available GaAs-based Hall probes degrade substantially at room temperature. To address this we have recently demonstrated sub-100nm CVD graphene Hall devices with room temperature field resolutions in the μT/√Hz range, greatly exceeding the performance of GaAs-based Hall probes.1 Additionally, we have demonstrated improved stability and increased mobility in graphene devices encapsulated in HSQ.2 We build upon these developments to optimise CVD graphene Hall probes for high resolution ambient magnetic imaging. We also report progress made in extending the technique to include local susceptometry mapping for, e.g., characterisation of ferromagnetic data storage media. |
Monday, March 2, 2020 8:24AM - 8:36AM |
A10.00003: Optimal isolation of structures from the external vibrations by particulate media
Hasson Tavossi, Department of Engineering Technology, Savannah State University, 3219 College St. Savannah, GA 31404. Hasson Tavossi
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Monday, March 2, 2020 8:36AM - 8:48AM |
A10.00004: Imaging electrons at the nanoscale with a cooled scanning probe microscope Andrew Smeltzer, Sagar Bhandari, Robert Taylor, Andrew Merritt The ability to measure and manipulate electrons at the nanoscale gives insight into nanoscale physics and paves way for its applications in electronics and photonics. We present a design and implementation of a scanning probe microscope that is cooled to liquid nitrogen temperature, to image electrons at the nanoscale. The imaging technique relies on a conductive scanning tip that acts as a local, movable electrostatic gate. The tip creates a local change in density of electrons in the material directly underneath it deflecting the electrons away from their original path. This changes the conductance of the device. The conductance is measured as a function of tip position while the tip moves across the material. The conductance change vs. tip position gives the map of the electron flow in the material. To align the tip within a micron of the sample at liquid nitrogen temperature, we use a home-built coarse positioning system. By applying high voltages to a piezo tube, the tip is raster scanned over the sample. With this method, we plan to image the viscous flow of electrons in graphene at liquid nitrogen temperature. Our design also allows us to image electronic flow in other nanoscale materials such as 2D semiconductors and topological insulators. |
Monday, March 2, 2020 8:48AM - 9:00AM |
A10.00005: Our software eliminates up to 80% of vibrational noise in a scanning tunneling microscope Jonathan Goettsch, Harris Pirie, Bryce Primavera, Albert Chien, Jennifer E. Hoffman Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are globally employed techniques to measure the electronic structure of condensed matter systems with atomic precision. They require extremely stable environments to operate: modern microscopes typically use a combination of pneumatic isolators and massive inertial blocks to reduce ambient vibrations to the picometer scale. However, improvements beyond this benchmark are challenging and even the best microscopes are still limited by residual vibrations. Here we demonstrate a software algorithm that cancels up to 80% of vibrational noise over a 300 Hz bandwidth, even in modern ultra-lowvibration laboratories. Our scheme relies on a precisely calibrated transfer function to accurately propagate geophone-recorded vibrations to the STM tip. These vibrations are then subtracted from spectroscopic and topographic measurements by post processing. Our algorithm mitigates STM vibrational noise in a wide range of experimental environments, including those with high-amplitude noise. |
Monday, March 2, 2020 9:00AM - 9:12AM |
A10.00006: Progress on the Scanning Majorana Microscope Eric Goodwin, Michael Gottschalk, Alex Levchenko, Stuart Tessmer Quantum dots have proven to be powerful probes for studying a variety of mesoscopic effects. In general, lithographically-defined surface quantum dots and scanning single-electron-transistor (SET) quantum dot microscopes fulfill different niches, in part due to the inability to bring the scanning SET close enough to the surface to provide strong coupling. We show significant progress on a new type of scanning quantum dot microscope which we call the Scanning Majorana Microscope (SMM). This novel probe is capable of resolving single electons entering a quantum dot situated at the tip's apex; and importantly, we are able to position the quantum dot within tunneling range (~1nm) of the surface of a sample. With the ability to strongly couple surface states to the quantum dot and study how the single-electron signal evolves as a function of coupling strength, this probe represents a new tool to study mesoscopic systems, including candidate Majorana states. |
Monday, March 2, 2020 9:12AM - 9:48AM |
A10.00007: Single-Atom Spin Resonance for Quantum Sensing in an STM Invited Speaker: Christopher Lutz We use a low-temperature scanning tunneling microscope (STM) to perform electron spin resonance (ESR) of individual magnetic atoms on a surface, and employ these atoms as atomic-scale magnetic sensors1. This technique combines the single-atom control of STM with the high energy resolution of ESR. We drive spin resonance by using the large electric field available in the tunnel junction1,2, and sense the spin by means of magnetoresistance, using a spin-polarized STM tip. Magnetic coupling between two iron atoms placed a few nanometers apart on an MgO film shows inverse-cube distance dependence, indicating magnetic dipolar interaction3. This yields a precise measure of the magnetic moment of the iron atom, which is then used to probe other atoms, such as the bistable magnetic bits formed by individual holmium atoms4. We also use STM to drive ESR of titanium5 and copper atoms6, which show free spin-1/2 behavior, in contrast to the high spin and large magnetic anisotropy of iron. Assembled arrays of low-spin atoms show exchange coupling that results in highly entangled magnetic states for quantum simulation of many-body states5. ESR also reveals hyperfine coupling between the nucleus and the electrons of each atom6,7. Furthermore, pulsed ESR allows us to perform coherent manipulation of atomic spins in order to observe Rabi oscillation, Ramsey fringes, and spin echoes8. The combination of STM with ESR thus provides a versatile tool for exploring nano-scale quantum magnetism. |
Monday, March 2, 2020 9:48AM - 10:00AM |
A10.00008: Sputtered Mo-Re SQUID-on-Tip for High-Field Magnetic and Thermal Nanoimaging Kousik Bagani, Jayanta Sarkar, Aviram Uri, Michael Rappaport, Martin E Huber, Eli Zeldov, Yuri Myasoedov Scanning nanoscale superconducting quantum interference devices (SQUIDs) have attracted attention as highly sensitive microscopic magnetic and thermal characterization tools of quantum and topological states of matter and devices. We present here a technique of collimated differential-pressure magnetron sputtering for the versatile self-aligned fabrication of SQUID-on-tip (SOT), which cannot be produced by conventional sputtering methods due to their diffusive, rather than the required directional point source, deposition. The technique provides access to a broad range of high Hc2 superconducting materials, alloys and possibly even high-Tc superconductors. This advancement is crucial for expanding the ranges of operating temperatures and magnetic fields essential of SOTs for the study of magnetic phenomena and dissipation mechanisms in a wide variety of quantum systems, unconventional superconductors, and topological materials. As a first example, we have fabricated Mo-Re SOTs with sub-50-nm diameter, that operates up to an unprecedentedly high magnetic field of 5 T with spin sensitivity better than 1.2 μ0/Hz1/2 up to 3 T at 4.2 K, and thermal sensitivity better than 4 μK/Hz1/2 up to 5 T—about five times higher than any previous report [1]. |
Monday, March 2, 2020 10:00AM - 10:12AM |
A10.00009: Spin-polarized Seebeck effect at the nanoscale measured with scanning tunneling thermovoltage microscopy Jewook Park, Felix Luepke, Jun Jiang, Xiaoguang Zhang, An-Ping Li Spin caloritronic effects have gained recent interest due to, e.g., potential low-power applications of magnetic tunnel junctions in which a temperature gradient-driven tunneling of electrons gives rise to a spin-dependent thermovoltage due to the Seebeck effect. Here, we report spatial mapping of the spin-resolved thermovoltage in a tunneling junction formed by ferromagnetic Co islands on a Cu(111) substrate and the magnetic tip of a scanning tunneling microscope. Our measurements reveal variations of the thermovoltage as function of spin polarization, island size, and stacking orientation of the islands with respect to the substrate. This method allows to reveal nanoscopic heterogeneities of both, the magnetic structures and the spin-dependent thermoelectric power. |
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