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 Y45: Advances in Scanned Probe Microscopy |
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Sponsoring Units: GIMS Chair: Marlou Slot, National Institute of Standards and Technology Room: Room 315 |
Friday, March 10, 2023 8:00AM - 8:12AM |
Y45.00001: Direct Imaging of Quantum Scars in a Stadium-shaped Graphene Quantum Dot Zhehao Ge, Sergey Slizovskiy, Peter Polizogopoulos, Takashi Taniguchi, Kenji Watanabe, Vladimir Falko, Jairo Velasco Jr. Wavefunction scarring (or quantum scars) refers to the enhancement of quantum probability density in the vicinity of classical periodic orbits of a chaotic system, which is a fundamental phenomenon connecting quantum and classical mechanics. Quantum scars are not only appealing to fundamental physics but also crucial for understanding the behavior of nanodevices, such as the conductance fluctuations of open quantum dots. More recently, the many-body version of quantum scars observed in atomic chains have also demonstrated their potential importance in quantum information. Quantum scars were first predicted to exist in stadium-shaped quantum billiards (a canonical chaotic system in classical mechanics) about 40 years ago, which has spurred extensive experimental attempts to image such states since then. Although clear scarred wavefunctions have been visualized in analog experiments such as microwave cavity experiments, unambiguous direct imaging of such states is still lacking in a real quantum system. In this talk, I will show our recent experimental progress on direct imaging of quantum scars in an electrostatically defined stadium-shaped graphene quantum dot with a low-temperature scanning tunneling microscope. |
Friday, March 10, 2023 8:12AM - 8:24AM |
Y45.00002: Decay rate spectroscopy for a direct probe of Josephson and Andreev currents on the atomic scale Wonhee Ko, Jose Lado, Eugene F Dumitrescu, Sang Yong Song, Petro Maksymovych The tunneling current in superconducting tunnel junctions involves several mechanisms in addition to the normal-electron tunneling, such as Josephson tunneling and Andreev reflection. Identification of the tunneling mechanisms as a function of external parameters, such as barrier height, bias voltage, temperature, and so on, is the key to elucidating the characteristics of the superconductors, such as paring symmetry and topology. Here, we present a new method to identify distinct tunneling modes based on the decay rate of tunneling current measured by scanning tunneling microscopy (STM) [1,2]. Precise control of the tip-sample distance in picometer resolution allows us to quantify the decay rate as a function of bias and tip height, with which we identified the crossover of tunneling modes between single-charge quasiparticle tunneling, (multiple) Andreev reflection, and Josephson tunneling. The method was both applied to S-I-S [1] and S-I-N [2] junctions, to unambiguously identify Josephson and Andreev currents. Moreover, mapping decay rates in the atomic resolution with STM revealed the intrinsic modulation of Andreev reflection and Josephson current. The result shows that the decay rate spectroscopy will be crucial for addressing the superconducting characteristics of the materials and their applicability for Josephson-junction devices. |
Friday, March 10, 2023 8:24AM - 8:36AM |
Y45.00003: Nanoscale Visualization of the Electrostatic Barrier at a Material Interface Utilizing Scanning Probe Microscopy and Computational Modeling Vincent P LaBella Electrostatic barriers at material interfaces are the foundation of current and futuristic electronic and optoelectronic devices. Visualization of the electrostatic barrier at an interface can be accomplished with nanoscale resolution utilizing ballistic electron emission microscopy (BEEM), an STM-based technique [1]. A spatial map of the barrier is formed by collecting tens of thousands of BEEM spectra on a regularly spaced grid and fitting them to extract the local barrier height. These maps and histograms that display the frequency of specific barrier energy, provide insight into the physical and chemical composition of the interface as well as the hot electron scattering. Computational modeling of the histograms simulates the distributions of barrier heights and provides quantitative information such as scattering rates and relative presence of different barrier height energies. A discussion of the ultimate spatial and energetic resolution will be presented, along with numerous examples such as incomplete silicide formation, multiple metal species at the interface, and monolayer thick dielectric layers [2,3]. |
Friday, March 10, 2023 8:36AM - 8:48AM |
Y45.00004: Improved control of Hydrogen Depassivated Lithography (HDL) with Scanning Tunnelling Microscope ultrafast feedback loop Richa Mishra, James H.G. Owen, John N. Randall, Ehud Fuchs, S.O.Reza Moheimani The principle of scanning tunneling microscopy is based on the quantum mechanical phenomena called “tunneling” where electrons tunnel from the apex of a sharp tip to a conducting surface at a certain bias voltage. Conventionally, the STM works mostly in constant-current imaging mode, whereby a controller adjusts the tip height to keep the natural logarithm of the tunneling current constant. The controller output is then plotted to obtain the topography of the sample surface. This constant current imaging mode not only provides the topography of the surface but also gives insight into electrical and chemical properties of the sample. But, obtaining I-V curve information by this process is slow and prone to failure due to repeated freezing of the tip and controller being disengaged. |
Friday, March 10, 2023 8:48AM - 9:00AM |
Y45.00005: Piezo stack fabrication and characterization for scanning probe microscopy Diego J Panzardi Serra A scanning probe microscope (SPM) must accurately move a tiny sensor across a macroscopic distance to approach within a few nanometers of a sample surface. A typical SPM employs a stepper motor composed of piezoelectric shear actuators, in which individual piezo plates are combined in stacks to increase their total shear. Although pre-fabricated piezo stacks are commercially available, they are typically costly, especially when custom dimensions are required to fit a novel microscope design. Here we describe a procedure to reliably fabricate arbitrary-sized stacks of soft lead zirconate titanate (PZT) piezo ceramic plates. To verify the reproducibility of our procedure, we designed a capacitance sensing unit that can measure the shear of each stack with 50 nanometer accuracy . We confirm our capacitive characterization with a Michelson interferometer. |
Friday, March 10, 2023 9:00AM - 9:12AM |
Y45.00006: Acoustic-Vibration Coupling in an Ultra-Quiet Cylindrical Laboratory Rodrick N Shumba, Juliet Nwagwu, Wan-Ting Liao, Joseph D Gibbons, Jennifer E Hoffman Atomic-scale fabrication and imaging techniques require an ultra-quiet environment to reach optimal resolution. Scanning tunneling microscopy (STM) is among the most demanding, with exponential sensitivity to perturbations in the tip-sample distance. To reduce vibration noise, STM facilities typically employ a massive inertial block floating on soft pneumatic springs; however these blocks are prone to coherent acoustic standing waves coupling to their vibrations because of their flat sides. We describe a new low-vibration facility at Harvard University that employs a cylindrical, rather than prismatic block, designed to minimize the coupling of acoustic standing waves between the straight walls and the curved block face. Here, we use a movable microphone to measure the acoustic response throughout the room, to map out the spatial eigenmodes. We compare the measured acoustic modes to COMSOL Multiphysics simulations of the room. Finally, we use an accelerometer to measure the vibration response of the cylinder and compute the acoustic-vibration transfer function. |
Friday, March 10, 2023 9:12AM - 9:24AM |
Y45.00007: Cryogen-Free Cooling Combined with Scanning Probe Microscopy in an Ultra-High Vacuum High Field environment Angela M Coe, Guohong Li, Eva Y Andrei We merged cryogen-free operation with scanning probe microscopy (SPM) in our ground-breaking ultra-high vacuum (UHV) system reaching low temperatures (4K) and high magnetic fields (9T). This achievement is owed to the creation of a unique internal vibration isolator (Patent Application US17/996,246) and custom probe head (U.S. Patent No. 11,474,127), which reduced the vibration level of the cryostat pulse tube to operate SPMs, solving the noise problem of typical cryogen-free systems. The modular design of our probe head accommodates interchangeable probes, such as STM, AFM, and MFM. Conditioning of sample and probe is incorporated into the UHV system, particularly ion sputtering, e-beam film deposition, exfoliation, and heat treatment. The compact SPM head is transferable about the entire system, allowing for sample and probe insertion at room temperature with optical access. Transport of the SPM to the cryogen-free cryostat is enabled by a novel low-profile vertical transfer mechanism (Patent Application PCT/US2019/027929). Incorporating all these capabilities into one instrument permits exploration of nano-scale characterization of low dimensional systems in an ultra-clean environment with controlled temperature and magnetic field. |
Friday, March 10, 2023 9:24AM - 9:36AM |
Y45.00008: Cryogenic atomic force microscopy system integrated in cryogen-free dilution refrigerator for single-electron sensitive electric force microscopy/spectroscopy Yoichi Miyahara, Binod D.C., Noah Austin-Bingamon We present a cryogenic atomic force microscopy (AFM) system which is integrated in a cryogen-free dilution refrigerator with magnetic field up to 9 T. A large internal volume of the cryostat allows the AFM unit to be installed on an efficient internal vibration isolation system, enabling good mechanical stability. Combined with the rigid design of coarse positioners, the influence from the pulse tube cooler is minimized. The AFM is equipped with a fiber-optic interferometer which is used for both detecting the cantilever deflection and exciting the cantilever oscillation [1]. The capability of optically exciting cantilever oscillation enables tunable cantilever quality factor and the clean cantilever resonance, which is crucial for single-electron sensitive electric force microscopy/spectroscopy [2,3]. We will present the details of the system and its performance. |
Friday, March 10, 2023 9:36AM - 9:48AM |
Y45.00009: Fabry Perot fiber interferometer for millikelvin AFM cantilever detection Federico Maccagno, Aaron J Coe, Benjamin H November, Stefan Ulrich, Jennifer Hoffman We describe the design and construction of a position detection system for pendulum geometry non-contact atomic force microscopy (nc-AFM) suitable for a millikelvin ultra-high vacuum environment. We use a single fiber-optic cable to create a Fabry-Perot interferometer to detect the oscillation frequency and amplitude of an inverted-geometry silicon cantilever. Our detector achieves sub-nanometer resolution while dissipating less than 250uW, which makes it suitable for operation in a dilution refrigerator. We use a compensating piezo to solve phase-slippage of the laser signal, enabling stable positional accuracy over the hours necessary to acquire an AFM image. Furthermore, the fiber-cantilever alignment can be remotely calibrated with our unique XYZ piezo walker that uses metal-ceramic sliding surfaces for more robust operation in ultra high vacuum and cryogenic temperatures. Our entire detection system, including XYZ alignment walkers, occupies a minimal in-situ footprint of 24mm x 28mm x 52mm, located near the tip-sample junction. |
Friday, March 10, 2023 9:48AM - 10:00AM |
Y45.00010: True Atomic-Resolution Surface Imaging under Ambient Conditions via High-Speed Conductive Atomic Force Microscopy Saima Aktar Sumaiya, Mehmet Z Baykara A wide range of physical phenomena are governed by the atomic-scale structure and properties of material surfaces. Yet, the principal tools utilized to characterize surfaces at the atomic level rely on strict environmental conditions such as ultrahigh vacuum and low temperature. Results obtained under such well-controlled, pristine conditions bear little relevance for the great majority of processes and applications that often occur under ambient conditions. Here, we report true atomic-resolution surface imaging via conductive atomic force microscopy (C-AFM) under ambient conditions, performed at high scanning speeds [1]. Our approach delivers atomic-resolution maps on a variety of surfaces, most prominently from the 2D materials family. With our method, we are able to resolve single atomic vacancies, in addition to other types of defects. Our findings demonstrate that C-AFM can be utilized as a powerful tool for atomic-resolution imaging of surface structure under ambient conditions, with wide-ranging applicability. |
Friday, March 10, 2023 10:00AM - 10:12AM |
Y45.00011: BE PFM and BE CRF for functional studies of free-standing ferroelectric membranes and thin films Neus Domingo Marimon, David Pesquera Herrero, Liam Collins, Kyle Kelley, Stephen Jesse, Marti Checa Classical AFM based tools to study electromechanical phenomena with nanoscale resolution are challenging to be applied on free-standing membranes, due to the mechanical instability of the systems. In this framework, resonant contact modes, such as Contact Resonance Frequency (CRF) and DART Piezoresponse Force Microscopy (DART-PFM), couple to geometrically induced vibrational modes of the suspended membranes and interfere the measurement of piezoelectric properties. Here, I will show on one hand how all the mechanical information of CRF is embedded into the DART-PFM signal. Then, I will discuss the risks, signal artifacts and common experimental concerns arising in this type of measurements and how the application of BE PFM and BE CRF, in a single and multifrequency approach can be applied to overcome the exposed issues. I will show the results obtained on the study of free-standing BaTiO3 membranes with thicknesses in the range of 20 nm to 70 nm with different suspended geometries as well as on corrugated membranes laying on conductive substrates. I will then discuss how the strain and more specifically the strain gradient induced by these geometries impacts on the configuration of ferroelectric domains and enhancement of polarization, and the opportunities this opens to create complex structures with pre-designed functionalities. |
Friday, March 10, 2023 10:12AM - 10:24AM |
Y45.00012: Selectivity in single-molecule reactions by tip-induced redox chemistry Leo Gross Selective and reversible bond formation and dissociation can be controlled by tip-induced reduction-oxidation reactions on a surface. Molecular rearrangements leading to different constitutional isomers are selected by the polarity and magnitude of applied voltage pulses from the tip of a combined scanning tunneling microscope (STM) / atomic force microscope (AFM). Combining STM, AFM and Kelvin probe force microscopy data and measurements of reaction yields as a function of voltage and current, we obtain insights into the reaction mechanism and find that the energy landscape of the isomers in different charge states is important to rationalize the selectivity of the reactions. |
Friday, March 10, 2023 10:24AM - 10:36AM |
Y45.00013: Photothermally driven AFM of soft matter samples Edward Nelson, Patrick Frederix, Gotthold Fläschner, Dominik Ziegler, Jonathan Adams, Hans Gunstheimer Since its invention in 1986, the atomic force microscope (AFM) has evolved into a multifunctional toolbox. Although there have been many developments towards improving the fundamental elements of an AFM – the scanner, controller, deflection detection system, and AFM cantilevers – most AFM systems still rely on a dither piezo to induce oscillation of the tip. |
Friday, March 10, 2023 10:36AM - 10:48AM Author not Attending |
Y45.00014: On-Surface Synthesis of Organic Molecules and Nanoarchitectures by Scanning Probe Manipulation Andre Schirmeisen, Qigang Zhong, Alexander Ihle, Hermann Wegner, Sebastian Ahles, Daniel Ebeling On-surface synthesis is at the verge of emerging as the method of choice for the generation and visualization of new molecules and molecular assemblies. In particlar constructing low-dimensional covalent assemblies with tailored size and connectivity is challenging yet often key for applications in molecular electronics where optical and electronic properties of the quantum materials are highly structure dependent. We present a versatile approach for building such structures block by block on bilayer sodium chloride (NaCl) films on Cu(111) with the tip of an atomic force microscope, while tracking the structural changes with single-bond resolution. Covalent homo-dimers in cis and trans configurations and homo-/hetero-trimers were selectively synthesized by a sequence of dehalogenation, translational manipulation and intermolecular coupling of halogenated precursors. Further demonstrations of structural build-up include complex bonding motifs, like carbon–iodine–carbon bonds and fused carbon pentagons. Further we present an example for the on-surface synthesis of an structurally elusive molecule, P3N3, the inorganic aromatic analogue of benzene, not obtainable via traditional synthetic methods. Our work presents strategies for synthesizing elusive molecules as well as covalent nanoarchitectures, studying structural modifications and revealing pathways of intermolecular reactions. |
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