Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q31: Microscopy 1: Electrons, THz, OpticalRecordings Available
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Sponsoring Units: GIMS Chair: Melissa Santala, Oregon State Room: McCormick Place W-192A |
Wednesday, March 16, 2022 3:00PM - 3:36PM |
Q31.00001: New Approaches to Atomic-Resolution Structural Analysis by Analytical Scanning Transmission Electron Microscopy Invited Speaker: Robert F Klie Over the last two decades, we have witnessed a paradigm change in the way we characterize materials using electron microscopy, starting with the first implementation of aberration correctors followed by faster, more sensitive CMOS detectors, monochromated electron sources for electron spectroscopy and, most recently, magnetic field-free lenses. As the result of these transformational discoveries, we are now able to study materials with unprecedented resolution, sensitivity and precision. |
Wednesday, March 16, 2022 3:36PM - 3:48PM |
Q31.00002: Scanning Transmission Electron Microscopy based Atomic Scale Fabrication Enhanced by In-operando Optical and Thermal Excitation Stephen Jesse, Ondrej Dyck, Andrew R Lupini The scanning transmission electron microscope (STEM) has been at forefront of providing atomic resolution structural and functional imaging of materials. This is made possible by a combination of highly tuned electron optics which focus the electron beam to sub-Angstrom levels, scanning systems which can rapidly and accurately steer the beam, and extremely sensitive detectors and spectrometers that allow one to measure the flux, scattering, and energy of transmitted electrons. More recently, it has been shown that this same remarkable system can be used as a platform to induce material transformations controllably, thus enabling new opportunities to fabricate structures at the atomic scale. We have recently worked to enhance these fabrication capabilites by developing methods that to locally heat the sample or nearby materials while in the microscope using current or optical excitation to influence the mobility of defects, adatoms, or nanoparticles or to induce melting, evaporation, or ablation of material that can be used as dopants. This presentation will discuss recent results to create ordered arrays of dopants in single layer 2D materials with the ultimate goal of building, from the atomic scale up, materials systems for quantum information science applications. |
Wednesday, March 16, 2022 3:48PM - 4:00PM |
Q31.00003: Mapping conductivity with secondary electron EBIC in a STEM Ondrej Dyck, Jacob Swett, Charalambos Evangeli, Andrew R Lupini, Jan Mol, Stephen Jesse Recent work has established secondary electron (SE) e-beam induced current (SEEBIC) imaging in a scanning transmission electron microscope (STEM) as a viable way to image electrical conductivity and connectivity with high spatial resolution. This technique relies on SE emission to generate a current in the sample measured by a transimpedance amplifier. STEM SEEBIC has been shown to be able to reach atomic resolution and can distinguish single layers of graphene. In this talk, I will discuss the basic operational principles of STEM SEEBIC, illustrate its usefulness for examining operando graphene nanodevices, discuss various sources of SEEBIC image contrast, and discuss the role of substrate contributions to the signal. Because STEM SEEBIC does not rely on the collection of primary scattered electrons, this signal can be collected independently and in parallel with other standard STEM-based characterization modalities such as annular dark field (ADF) imaging or electron energy loss spectroscopy (EELS). This enables a complementary information channel to be acquired which is closely linked to the electron density and electronic properties of the sample. |
Wednesday, March 16, 2022 4:00PM - 4:12PM |
Q31.00004: Enhancing Symmetry Breaking Defects in Materials with a STEM Phase Plate Stephanie M Ribet, Colin L Ophus, Vinayak P Dravid, Roberto dos Reis Local and extended defects are thermodynamically required in any physical system, and they disproportionally impact material properties. Because many important defects break long range order in materials, we aim to develop a high-resolution electron microscopy technique to amplify local crystal symmetry breaking signals. Scanning transmission electron microscopy (STEM) is a natural tool to establish form-function relationships in these materials at the relevant length scales. The small probe size and versatile nature of STEM allows multimodal signals to be leveraged for advanced characterization. For example, researchers have demonstrated how a 4D-STEM approach can leverage information encoded in reciprocal space to investigate a material's symmetry.[1] The incorporation of a phase plate in the probe forming aperture of a STEM can efficiently enhance signals from a wide range of spatial frequencies.[2] In this study, we optimize the geometry of STEM phase plates given the local symmetry of crystalline structures, with the goal of more easily observing defects. We will present STEM simulations and calculations that demonstrates this effect in a variety of systems. |
Wednesday, March 16, 2022 4:12PM - 4:24PM |
Q31.00005: Kinetic and thermodynamic measurements of the crystallization of phase change materials using transmission electron microscopy and nanocalorimetry Isak McGieson Phase change materials (PCM) are semiconducting alloys with distinct optical and electrical properties in the amorphous and crystalline phases that make them useful for memory applications. The thermodynamics and kinetics of the crystallization of PCMs far from equilibrium conditions are of technological and scientific interest but can be difficult to probe experimentally due to small grain sizes and very rapid crystal growth. In this work, the crystallization of an amorphous PCM, Ag3In4Sb76Te17, was investigated using transmission electron microscopy (TEM) imaging and a nanocalorimeter designed for use in a TEM. In situ TEM imaging was used to resolve crystal growth of small grains. Nanocalorimetry experiments were run at multiple heating rates (up to 104 K/s) and a Kissinger analysis was used to find the activation energy of crystallization. The thermodynamic measurements allowed the enthalpy of fusion to be calculated for temperatures far below the equilibrium melting temperature. Current TEM imaging experiments have demonstrated the viability of planned experiments for the simultaneous collection of kinetic and thermodynamic data over a broad set of heating rates. |
Wednesday, March 16, 2022 4:24PM - 4:36PM |
Q31.00006: Atomic scale direct-write dopant patterning on graphene Andrew R Lupini, Ondrej Dyck, Mina Yoon, Sergei V Kalinin, Jacob Swett, Stephen Jesse The properties of many devices and potential technologies depend on the precise position of a few dopant atoms, meaning that one of the requirements for future generations of nanofabrication will be the ability to insert dopants at well-defined locations. The problem is that most fabrication methods do not achieve the atomic scale position resolution that new quantum devices will require. |
Wednesday, March 16, 2022 4:36PM - 4:48PM |
Q31.00007: Terahertz microspectroscopy: far-field spectral fidelity degradation and recovery Tim LaFave, Andrea G Markelz Terahertz near-field microspectroscopy is an emerging technique essential for characterization of novel materials and biomolecules. A popular technique utilizes a subwavelength aperture and a detector placed in the far-field. Growing interest in this technique is due to the advent of high-power frequency tunable THz sources and high sensitivity room temperature THz detectors. Severe limitations are found with resulting spectral artifacts arising from diffraction, sample geometry, aperture size, and nearby resonances. We model transmission of a focused 400 μm diameter Gaussian beam through c-cut single crystal sucrose, with a well-defined resonance at 1.985 THz, mounted on 150 μm and 200 μm diameter apertures using HFSS. Modeling is validated with Beer’s Law with respect to sample thickness. Spectral fidelity is found to deteriorate beyond ~750 μm from the aperture, illustrating the need for near-field detection. We find that spectral fidelity may extended to the far-field with a low-loss THz waveguide that may facilitate a thermally-sensitive THz detector. This work is anticipated to be of great interest to a broad community in which far-field detection is commonly used and value to the growing interest in the design and development of compact THz microspectroscopy instruments. |
Wednesday, March 16, 2022 4:48PM - 5:00PM |
Q31.00008: Traceable localization in optical microscopy Craig R Copeland, Ronald G Dixson, Andrew C Madison, Adam L Pintar, B. Rob Ilic, Samuel M Stavis Localization microscopy enables resolution beyond the limit of optical diffraction, engendering many opportunities across the physical and life sciences. With enough signal photons, the localization precision of sparse images can extend into the subnanometer scale. Supporting accuracy is challenging, however, as systematic errors can be orders of magnitude larger across an imaging field. To solve this critical but often ignored problem, we are developing arrays of nanoscale apertures into traceable standards for localization microscopy. We fabricate aperture arrays by electron-beam lithography and measure aperture positions by critical-dimension atomic-force microscopy. Correlative measurements by optical microscopy reveal localization errors due to optical aberrations, which we correct by a Zernike model. Statistical analysis of aperture positions correlates surface structure and optical transmission to within a few nanometers. Our calibration establishes the new concept of a localization uncertainty field, with localization errors and scale uncertainty yielding regions of position traceability to within a 68 % coverage interval of ± 1.0 nm. In this way, our study achieves new traceability in localization microscopy, enabling reliable position data for meaningful comparison. |
Wednesday, March 16, 2022 5:00PM - 5:12PM |
Q31.00009: Rapid simulations of hyperspectral near-field images of three-dimensional heterogeneous surfaces Xinzhong Chen, Ziheng Yao, Stefan G Stanciu, Dmitri N Basov, Rainer Hillenbrand, Mengkun Liu The scattering-type scanning near-field optical microscope (s-SNOM) has emerged as a powerful tool for resolving nanoscale inhomogeneities in laterally heterogeneous samples. However, most analytical models used to predict the scattering near-field signals are assuming homogenous landscapes (bulk materials), resulting in inconsistencies when applied to samples with more complex configurations. In this work, we combine the point-dipole model (PDM) to the finite-element method (FEM) to account for the lateral and vertical heterogeneities while keeping the computation time manageable. Full images, spectra, or hyperspectral line profiles can be simulated by calculating the self-consistent dipole radiation demodulated at higher harmonics of the tip oscillation, mimicking real experimental procedures. Using this formalism, we clarify several important yet puzzling experimental observations in near-field images on samples with rich typography and complex material compositions, heterostructures of two-dimensional material flakes, and plasmonic antennas. The developed method serves as a basis for future investigations of nano-systems with nontrivial topography. |
Wednesday, March 16, 2022 5:12PM - 5:24PM |
Q31.00010: Development of Image Corrections for Photoemission Electron Microscopy (PEEM) and its Application to Graphene Henry Bell, Falk Niefind, Randolph E Elmquist, Sujitra Pookpanratana The PEEM is a full-field electron microscope that utilizes the photoelectric effect to image a surface. Due to its resolution on the order of 10 nanometers and its ability to image both the morphology of a surface and its band structure it is a useful tool in understanding the properties of materials for use in electronic devices. To correct for random sample misalignment and experimental frame of reference in the spectroscopy mode of the PEEM, the 3D dataset must be rotated in both the momentum and energy axis which requires pixel calibration and energy alignment. I have created custom Python scripts to both automate this process and standardize the calibration and correction procedure to streamline data analysis for users of the PEEM. Graphene was utilized as an initial calibration material due to its distinct electronic band structure. The 6 Dirac cones of graphene were used as iso-energy points to align the frames on the energy axis and a series of matrix operations were utilized to rotate the image in the momentum axis to correct for sample misalignment. I used the corrected dataset to estimate the Fermi velocity and compare to other graphene samples measured in the PEEM. We are also looking to extend our experiments by investigating nitrogen dilute doped GaAs. |
Wednesday, March 16, 2022 5:24PM - 5:36PM |
Q31.00011: Reconstruction of Nano-Plasmonic Excitations Using Ultrafast Transmission Electron Microscopy John H Gaida, Hugo Lourenço-Martins, Sergey Yalunin, Armin Feist, Murat Sivis, Thorsten Hohage, F. Javier García de Abajo, Claus Ropers Photon-induced Near-field Electron Microscopy (PINEM) in Ultrafast Transmission Electron Microscopes can be used to map the ultrafast evolution of optical near fields [1] and the structural dynamics of materials [2] on nanometer length scales using femtosecond electron pulses. In particular, PINEM enables mapping the responses of nanostructures to external stimuli [3, 4], which can be useful to address the yet elusive problem of comprehensively studying the dependence of plasmonic fields on the polarization state of the driving laser field. |
Wednesday, March 16, 2022 5:36PM - 5:48PM |
Q31.00012: A scanning NV center magnetometry probe fabricated by a focused ion beam Yuta Kainuma, Aoi Ideguchi, Kunitaka Hayashi, Toshu An Utilizing the NV (Nitrogen-Vacancy) center in diamond as a scanning magnetometry probe is gaining much attention owing to its potential for high magnetic field sensitivity with nanometer-scale spatial resolution. The scanning NV magnetometry probe has been fabricated by using complicated methods such as electron beam lithography. We introduce an alternative method for this by using laser cutting and forcused ion beam (FIB) milling. By using laser cutting, a thin diamond bulk sample, which has NVs near-surface can be flexibly fabricated into blocks of several tenths of micrometers size. Successively, with a donut-shaped FIB milling pattern, avoiding the damage of NV states by Ga+ ion in FIB fabrication at the probe center position, a diamond pillar probe hosting NVs near the surface with a diameter of about 1 – 2 micrometer was fabricated. With this probe, a micrometer scale magnetic structure imaging from a magnetic tape was demonstrated via stray magnetic field detection. For improvement of the NV probe's magnetic sensing ability, reducing the diameter of the probe to less than one hundred nanometers, without NVs’ damage is required. For this, protection of NV layers at the probe by a PtPd metal film deposition during FIB fabrication was examined. |
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