Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session A45: Frontiers in Coherent Diffractive Imaging and Electron MicroscopyFocus
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Sponsoring Units: GIMS Chair: Jianwei (John) Miao Room: Room 315 |
Monday, March 6, 2023 8:00AM - 8:36AM |
A45.00001: Coherent Imaging and Nanoscale Materials Characterization using Ultrafast Laser-Generated X-rays Invited Speaker: Henry C Kapteyn Next-generation nano and quantum systems and devices are becoming increasingly complex, with their behavior governed by interface quality or precise chemical, interfacial or dopant composition. Furthermore, characterizing their functional as well as structural properties is becoming increasingly challenging as these structures shrink, requiring new capabilities and techniques. |
Monday, March 6, 2023 8:36AM - 8:48AM |
A45.00002: Secondary Electron Metrology for Enhanced Charged Particle Microscopy Akshay Agarwal, Leila Kasaei, Albert Schultz, Leonard C Feldman, Vivek K Goyal Scanning electron microscopy and helium ion microscopy are widely used for nanoscale imaging. In each case, a high energy beam of electrons or ions is raster scanned over the sample. At each pixel, the beam generates secondary electrons (SEs) often detected by an Everhart-Thornley detector (a scintillator at high voltage followed by a light pipe-photomultiplier couple). The detector produces a voltage pulse whose magnitude is expected to be proportional to the number of detected SEs. The ideal image would be a pixelwise map of the yield of SEs, i.e., the average number of SEs emitted per incident particle. However, this goal is not realized because the gains and efficiencies of detector components are highly variable and generally unknown. In this work, we present methods for SE yield mapping by accurate characterization of the response of the detector to single SEs using two approaches. First, we present a model that assumes a Gaussian detector response and demonstrate model parameter extraction by imaging samples with a range of SE yields. Second, we describe how the detector response can be obtained empirically by imaging a sample with low SE yield. Finally, we discuss pixelwise estimators for the SE yield and their experimental implementation. Emphasis on quantitative electron detection, combined with advanced statistical analyses is expected to enable new limits of resolution and material analysis. |
Monday, March 6, 2023 8:48AM - 9:00AM Author not Attending |
A45.00003: Scanning multiprobe microscopy Patrick R Forrester, Yuan Cao, Zhuozhen Cai, Myungchul Oh, Yonglong Xie, Kevin P Nuckolls, Ali Yazdani, Amir Yacoby Scanning probe microscopy (SPM) techniques broadly fit into two paradigms: scanning tip-based methods and scanning chip-based methods. Tip-based architectures can facilitate exceptionally close tip-sample distances enabling high spatial and signal resolution. However, few sensors can be implemented this way. Chip-based approaches allow for a broader variety of more intricate sensors (or ensembles thereof) with stricter limitations on sensor-sample distances. In this talk, I will discuss the development of a new SPM paradigm-scanning multiprobe microscopy-that marries the broad functional possibilities of chip-based SPM and the exceptionally small sensor-sample distances of tip-based techniques. This multiprobe microscope permits simultaneous operation of several arbitrary mesoscopic probes and is wafer-scale compatible. I will highlight relevance to open questions in condensed matter physics and quantum information science. |
Monday, March 6, 2023 9:00AM - 9:12AM |
A45.00004: A Hybrid Dilution Refrigerator as a Platform for Low-Vibration Quantum Imaging Jacob Franklin, Joshua Bedard, Ilya Sochnikov Noise resulting from vibrations between a probe and a sample are oftentimes the leading source of error in microscopies using ultra-high precision probes, such as scanning SQUID microscopy. In our Bluefors LD250 dilution refrigerator, we have installed a helium battery that enables a hybrid cooling mode, in which cooling is possible for 2-4 hours without operation of the typical, vibration-causing pulse tube. We present here vibrational noise analysis using scanning SQUID images of local magnetic field sources and compare the vibrations in the normal cooling mode and the hybrid cooling mode. Our showcasing of specific material studies demonstrates the advantage of the new approach for quantum imaging at ultra-low temperatures. |
Monday, March 6, 2023 9:12AM - 9:24AM |
A45.00005: Development of a broadband cryogenic magnetic scanning near-field optical microscope Samuel J Haeuser, Richard H Kim, Joongmok Park, Jigang Wang We have developed a versatile near-field microscopy platform that can operate at high magnetic fields and below liquid-helium temperatures. We use this platform to demonstrate an extreme condition nanoscope operation and obtain the first cryogenic magneto time-domain nano-spectroscopy/imaging at temperatures as low as 1.8 K and magnetic fields up to 5 T simultaneously. Our cryogenic magneto scanning near-field optical microscopy, or cm-SNOM, instrument comprises: a broadband spectrum ranging from THz to mid-IR, a 5 T split pair magnetic cryostat with a custom-made insert, and an atomic force microscope (AFM) unit that accepts ultrafast excitation. We demonstrate the ultrafast and ultrabroadband cm-SNOM operation with a CW IR laser source, tunable femtosecond IR pulses, and single-cycle THz pulses. We apply the cm-SNOM to obtain measurements of superconducting, topological, and magneto-plasmonic materials. The new capabilities for studying these quantum materials, which require the extreme environment of cryogenic operation and applied magnetic fields simultaneously in nanometer space, femtosecond time, across broadband energy scales, represent a leap forward in near-field microscopy. |
Monday, March 6, 2023 9:24AM - 9:36AM |
A45.00006: Gaussian Process Regression Aided Spiral Scanning on Polaritonic Media Matthew Fu, Suheng Xu, Shuai Zhang, Frank Ruta, Jordan Pack, Samuel L Moore, Daniel J Rizzo, Bjarke S Jessen, Cory R Dean, Mengkun Liu, Dimitri Basov Integration time and signal-to-noise are inextricably linked when performing scanning probe measurements such as in scanning near-field optical microscopy (SNOM). Since these measurements define a large lower bound on the measurement time, we used a combination of Gaussian process regression with sparse spiral scanning in order to bypass this constraint. Our study demonstrates that this approach, when used to image graphene/α-RuCl3 charge-transfer polaritons and hBN phonon polaritons, results in key features such as damping and dispersion that are in good agreement with those extracted from traditional raster scans with the same integration time per pixel and dimensions. Most significantly, the gaussian process aided sparse spiral scan has roughly 9 times less data than raster scans and offers a commensurate 9 times decrease in measurement time to raster scans. |
Monday, March 6, 2023 9:36AM - 9:48AM |
A45.00007: Physics-informed Bayesian Optimization of an Electron Microscope Desheng Ma, Chenyu Zhang, Yu-Tsun Shao, Zhaslan Baraissov, Cameron J Duncan, Adi Hanuka, Auralee Edelen, Jared Maxson, David A Muller Precise control of the electron beam shape is critical for the successful application of scanning transmission electron microscopes (STEM) to understanding materials at atomic level. However, the nature of magnetic lenses introduces various orders of aberrations and makes aberration corrector tuning a complex and time-consuming procedure. Here we approach the problem from the perspective of accelerator physics and demonstrate the equivalence between aberration correction and beam emittance minimization in phase space. We show a deep neural network can accurately capture phase space variations from electron Ronchigrams, enabling a rapidly-executing beam quality measurement tool. A Bayesian approach is adopted to optimize for the system for minimum emittance growth and provides the full posterior of the response over control parameters to account for uncertainties at each query. Furthermore, a deep kernel is implemented and shown to effectively learn the correlations between input dimensions, which can generalize to other accelerator tuning tasks as well. Both simulation and experimental results show the proposed method outperforms existing alignment approaches. This new scheme enables fully automated aberration corrector tuning, achieving greater speed and less human bias. |
Monday, March 6, 2023 9:48AM - 10:00AM |
A45.00008: Transmission Kikuchi Diffraction Simulation for Cross-Correlation Analysis Yueyun Chen, Matthew H Mecklenburg, Brian C Regan Transmission Kikuchi diffraction (TKD) is a scanning electron microscopy technique combining imaging and diffraction to identify phases and map crystal orientations. TKD allows for real space and reciprocal space to be detected simultaneously. Using a Hough transform-based indexing routine, the diffraction information can be analyzed in real-time from a region of the crystal only a few nanometers wide. The TKD patterns also contain information that is subtler, such as temperature and strain, that come from small changes in lattice parameters. Extracting these details requires more sensitivity than can be achieved with the traditional Hough method. New cross-correlation based techniques, where the experimental patterns are compared with simulated ones, can achieve the necessary sensitivity. But results vary depending on how faithfully the diffraction patterns are simulated. For instance, one can choose to take a kinematic or a dynamical approach, to account for the Debye-Waller effect, or to consider the background intensity from inelastically scattered electrons. In this work, we compare different simulation methods and propose a TKD pattern simulation routine that balances sensitivity with computational cost. The result is a measurement of spatially varying strain in materials at a precision on the parts-per thousand level. |
Monday, March 6, 2023 10:00AM - 10:12AM |
A45.00009: On the Absence of Knock-On Damage in Lithium Metal at Cryogenic Temperatures Matthew H Mecklenburg, Xintong Yuan, Ambarneil Saha, Yuzhang Li Knock-on damage and sputtering (both electron-nuclear scattering) along with radiolysis (electron-electron scattering), are the three main types of damage that occur when the electron beam interacts with the sample in a transmission electron microscope (TEM). The kinetic threshold of knock-on damage gives an electron beam kinetic energy below which crystals such as graphite (120 keV) and silicon (200 keV) are effectively stable under this β radiation exposure, independent of temperature. These thresholds are well within the typical kinetic energies used in modern TEMs, whose kinetic energies are between 30 keV and 300 keV. The atomic nuclei, once ejected from a crystal, have their own kinetic energy that is the related to the incident electron beam’s kinetic energy and the threshold energy in the crystal. In lithium, imaged under a 300 keV beam, this produces at most a lithium nuclei with a kinetic energy of about 110 eV (given a 9 eV potential well or activation energy), which is much greater than the thermal energy at room temperature. Cryogenic temperatures should offer no protection in lithium metal bombarded by 300 keV electrons, where the threshold kinetic energy is 30 keV. Yet, despite these basic kinetics, lithium can remain undamaged at liquid nitrogen temperatures for fluences over 1000 electrons/Å2, and is damaged easily at room temperature. We will examine this mystery in more detail, with both experimental evidence and possible theoretical explanations. |
Monday, March 6, 2023 10:12AM - 10:24AM |
A45.00010: Dynamical Electron Diffraction: An Analytic Solution for Five Beams Tristan O'Neill, Brian C Regan, Matthew H Mecklenburg In the kinematical limit, an electron beam transiting a crystal diffracts once and then leaves. However, in thicker crystals an electron beam diffracts multiple times in what is called dynamical diffraction. Beams undergoing multiple diffraction interact with each other via the pendell?sung effect, producing intricate interference patterns inside the convergent beam electron diffraction (CBED) disks. In the case of two or three beams, the diffraction patterns can be solved analytically in terms of coupled harmonic oscillators. Here we show that, using a more sophisticated matrix analysis, the five beam case can also be solved under certain conditions. Applying this result to a four dimensional scanning transmission electron microscopy (4DSTEM) data hypercube, we determine a sample's thickness and extinction distance. The five-beam solution provides a possible path for high precision interrogation of crystalline samples. |
Monday, March 6, 2023 10:24AM - 10:36AM |
A45.00011: Visualization Interface for Single Crystal Neutron Spectroscopy Andrei T Savici, Igor A Zaliznyak Analysis and visualization for single crystal neutron spectroscopy experiments have been historically performed using data pre-histogrammed in energy transfer. To obtain the dynamic structure factor, each histogram bin, for each detector, is transformed to energy and momentum transfer. For further analysis and visualization, the data is re-histogrammed in energy-momentum space, such that every reciprocal space region contains the average of the contributing histogram bins [1,2]. The main deficiencies of such existing approach are (i) the large amount of memory resources needed to store the histogram bins with zero neutron counts, and (ii) the difficulty of error propagation in re-histogramming, which result in the absence of weighting of contributions with different statistical significance. Based on the lessons learned from single crystal diffraction [3,4], we have developed a different approach, where the histogramming to energy-momentum space is based on neutron detection events and accounts for their statistical significance. The algorithm is implemented in the Mantid software [5] and provides options for processing and correcting both upolarized and polarized data. Here, we will emphasize the experience we gained with implementing straight forward python scripting based data processing and visualization, using the event approach. We will present plans for a future graphical user interface. |
Monday, March 6, 2023 10:36AM - 10:48AM |
A45.00012: Broadband Infrared Confocal Imaging for applications in Additive Manufacturing. Kaitlin Lyszak We address new measurement challenges relating to 3D printing in metal powder using the powder bed fusion technique. Using a combination of confocal microscopy principles and fast, sensitive mid-infrared collection techniques, we present a compact and versatile method of measuring and analyzing broadband thermal emissions from the vicinity of the molten metal pool during the additive manufacturing process. We demonstrate the benefits of this instrumentation and potential for scientific research as well as in-situ monitoring. Our compact microscope collection optics can be implemented in various powder bed fusion machines under vacuum or inert atmospheric environments to enable extensions such as multi-color pyrometry or spectroscopic studies of additive manufacturing processes. |
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