Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N31: Advances in scanned probe microscopyRecordings Available
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Sponsoring Units: GIMS Chair: Chris Jacobsen, Argonne Lab/Northwestern U Room: McCormick Place W-192A |
Wednesday, March 16, 2022 11:30AM - 11:42AM |
N31.00001: UHV Compatible Negative Stiffness Vibrational Isolator for STM Arnav Srivastava, Wan-Ting Liao, Jennifer Hoffman A scanning tunneling microscope (STM) images electronic structure at the picometer scale; it is thus extremely sensitive to even small ambient and environmental vibrations. Here we describe an ultra-high vacuum (UHV) compatible vibration isolation stage for the STM that uses a negative stiffness mechanism (NSM). NSM isolators have demonstrated lower resonant frequencies than pneumatic and eddy current vibration isolation, but they have not been available for compact in-vacuum use commercially. We used COSMOL Multiphysics finite-element analysis to simulate structural stability and natural frequency of our new design. We used a vibrometer and accelerometer to demonstrate the new system performance. Here we present and compare our simulation and measurement results. |
Wednesday, March 16, 2022 11:42AM - 11:54AM |
N31.00002: Adding RF capabilities to a mK-STM for capacitance measurements Michael Dreyer, Jonathan J Marbey, Robert E Butera Scanning tunneling microscopy (STM) typically operates at a low bandwidth of a few kHz. There are several reasons to expand the bandwidth into the radio frequency (RF) range such as noise measurements, electron spin resonance (ESR), scanning on insulators, or measuring the tip-sample capacitance. This capability has been achieved by many research groups in different systems and environments. Conventionally, the low frequency tunneling signal is separated from a superimposed RF signal and the STM tip acts as a near field antenna. |
Wednesday, March 16, 2022 11:54AM - 12:06PM |
N31.00003: Resolving nanoscale mechanical properties of multi-layered low-k dielectric films by contact resonance atomic force microscopy Gheorghe Stan, Sean W King The continuous advances in semiconductor device fabrication demand various characterization techniques capable of proving quantitative measurements at the nanoscale. A prominent scanning probe-based technique for nanoscale elastic property measurements is contact resonance atomic force microscopy (CR-AFM). CR-AFM uses the sensitivity of the eigenmodes of an AFM cantilever to the contact mechanics established between the apex of the AFM probe and the sample tested. While the applicability of CR-AFM has been examined on a large variety of compliant and stiff materials, new methodological approaches are expected to improve its measurement accuracy and ease of applicability. This is especially relevant to single and multi-layered coated specimens that are part of advanced semiconductor devices. In this work we examined CR-AFM measurements on a series of thin low-k dielectric films assembled in a stiff/compliant/substrate structure. The thickness of the top layer was used as a control parameter to vary the structural complexity and mechanical stiffness of the system. The measurements were analyzed both by analytical models and finite element analysis to observe the contributions of various geometrical factors and approximations that usually are mitigated by calibration procedures. It was found that the finite element analysis provides a more detailed yet inclusive analysis of the mechanics of the system and can be used to separate among the mechanical properties of layered structures. |
Wednesday, March 16, 2022 12:06PM - 12:18PM |
N31.00004: Characterizing Charged Defects in Oxide-on-Silicon using Kelvin Probe Force Microscopy Leah Tom, Zachary J Krebs, Justin T White, Wyatt A Behn, Mark A Eriksson, Victor W Brar, Sue N Coppersmith, Mark G Friesen While silicon-based quantum dot qubits are a promising platform for quantum computing, due to their long coherence times, charge noise from oxide layers below the gate electrodes hinders critical improvements in qubit operations. To characterize the microscopic origin of charge noise in these gate oxides, we perform Kelvin Probe Force Microscopy (KPFM) measurements on a thin aluminum-oxide layer grown atop silicon dioxide and bulk silicon. These experiments reveal defects in the oxide that exchange charges with the AFM tip when its bias voltage is swept. By repeating such scans while rastering the tip over the sample, and comparing them to electrostatic simulations of the tip and sample, we can identify the depths of the charged defects. We further investigate the binding energies of the defects, making use of the charging voltages from our experiments. These results will be useful for understanding and potentially improving qubit gate operations. |
Wednesday, March 16, 2022 12:18PM - 12:30PM |
N31.00005: Using functionalized tips mounted on noncontact atomic force microscope to break chemical bonds within molecules – a computational perspective Dingxin Fan, James R Chelikowsky “What would the properties of materials be if we could really arrange the atoms the way we want them? […] I can hardly doubt that when we have some control of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of different things that we can do.” – Richard P. Feynman (1959). Feynman’s idea has been, partially, realized through the use of noncontact atomic force microscope (nc-AFM). |
Wednesday, March 16, 2022 12:30PM - 12:42PM |
N31.00006: Scanning Probe Microscopy Combined with Low Temperature Cryogen-free Operation in an Ultra-High Vacuum High Field Environment Angela M Coe, Guohong Li, Eva Y Andrei Scanning probe microscopy (SPM) is combined with cryogen-free operation in our innovative ultra-high vacuum (UHV) system with low temperatures reaching 4K and high magnetic fields up to 9T. Utilizing a unique internal vibration isolator and custom probe head, we have sufficiently reduced the vibration level of the cryostat pulse tube to operate SPMs thus solving the problem that typical cryogen-free systems are too noisy to operate SPMs. Our custom probe head is modular and accommodates interchangeable probes, such as STM, AFM, and MFM. Sample and probe conditioning is incorporated into the UHV system, particularly ion sputtering, e-beam film deposition, exfoliation, and heat treatment. The SPM head is transferable about the entire system, allowing for sample and probe insertion at room temperature with optical access. A novel low-profile vertical transfer mechanism enables transport of the SPM to the cryogen-free cryostat. By incorporating all these capabilities into one instrument, nano-scale characterization of low dimensional systems can be explored in an ultra-clean environment with controlled temperature and magnetic field. |
Wednesday, March 16, 2022 12:42PM - 12:54PM |
N31.00007: Scattering-Type Scanning Near-Field Optical Microscopy with Akiyama Piezo-Probes Michael Dapolito, Xinzhong Chen, Chaoran Li, Makoto Tsuneto, Shuai Zhang, Xu Du, Adrian Gozar, Mengkun Liu Recent developments of the scattering-type scanning near-field optical microscope at cryogenic temperatures (cryogenic s-SNOM or cryo-SNOM) have led to many breakthroughs in the studies of low energy excitations in quantum materials. However, the simultaneous demands on vibration isolation, low base temperature, precise nano-positioning, and optical access make the construction of a cryo-SNOM a daunting task. Adding to the overhead space required for a cryo-SNOM is the atomic force microscopy (AFM) control, which predominantly utilizes a laser-based detection scheme for determining the cantilever tapping motion. Here we provide an alternative and simplified route for performing s-SNOM using metal-coated Akiyama probes, where the cantilever tapping motion is detected through a piezoelectric signal. The Akiyama-based cryo-SNOM attains high spatial resolution, good near-field contrast, and is able to perform imaging with a significantly more compact system compared to other cryo-SNOM techniques. This system can also easily accommodate far-infrared wavelengths and high magnetic fields in the future. |
Wednesday, March 16, 2022 12:54PM - 1:06PM |
N31.00008: Advanced numerical modeling of light-matter interactions at nanometer length scales Haoyue Jiang, Patrick McArdle, David J Lahneman, Mumtaz Qazilbash, Tetiana Slusar, Hyun-Tak Kim, Amlan Biswas, Jingyi Chen Scattering-type, scanning near-field infrared microscopy (S-SNIM) is a cutting-edge experimental technique that allows infrared spectra to be obtained at nanometer scale spatial resolution well beyond the diffraction limit of light. Effective extraction of meaningful information from experimental data relies on accurate modeling of the light-probe-sample interaction. This is especially true in media with more intricate geometries and optical properties such as thin films, nanostructures, and anisotropic materials because analytical models are inadequate for these systems. Here we demonstrate advanced, fully numerical methods to simulate the near-field infrared response of different systems and compare directly with experimental data. We will present spectra of thin films (e.g. SiO2 films on Si substrates and surface metallicity of SrTiO3), spectra and imaging of nanostructures (e.g. nano-platelets of Cu2S), and the near-field infrared response of materials with anisotropic dielectric function (e.g. rutile TiO2). This work demonstrates fully numerical simulations as a universal and reliable way forward for modeling of experimental S-SNIM spectra from a diverse range of systems. |
Wednesday, March 16, 2022 1:06PM - 1:18PM |
N31.00009: Compensation of electrostatically-induced background in s-SNOM. Artem Danilov Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) and nano-FTIR are modern techniques for nanoscale imaging and spectroscopy across Visible, IR and THz regions with wavelength-independent spatial resolution <20 nm. s-SNOM is based on the atomic force microscopy (AFM), where a sharp AFM tip is illuminated by focused light beam. The tip acts as an antenna that receives the incoming light and channels it into a strong nanoscale hotspot at its apex. The near-field interaction of this hotspot with the sample directly below the tip modifies the tip scattering properties. We pioneered technologies for background-free detection for this tip scattering, providing means for reliable nanoscale analysis. However, here we show that despite advanced background suppression techniques, scattering SNOM could be a subject for traditional AFM-related artefact related to electrostatic influences. |
Wednesday, March 16, 2022 1:18PM - 1:30PM |
N31.00010: Modifying plasmon resonances at nanocavities by molecular adsorption: A Scanning Tunnelling Microscopy Study Óscar Jover Arrate, Koen Lauwaet, Roberto Otero Scanning Tunnelling Microscopy (STM) is a promising tool to study the properties of plasmonic nano and pico-cavities[1], as it allows atomic-scale control of the cavity size. STM electroluminescence spectra contains information about the optical properties of the cavity but also about the electronic structure of the system. Recently, our group has developed a normalization technique to separate these two factors by combining luminescence and I(V) measurements[2]. In this work, we use this technique to investigate the optical modifications in nanocavities between an Au tip and noble metal surfaces, due to the adsorption of two different organic molecules (5,12-Bis(phenylethynyl)naphthacene (BPEN), 9,10-bis(phenylethynyl)anthracene (BPEA)). Our results show that most of the changes in the raw spectra can be attributed to electronic structure factors, but still true optical modifications in the gap plasmonic modes due to the presence of the molecules can be observed in the normalized spectra. As possible origins for such changes, Pauli repulsion from the molecule electron density or coupling of plasmonic and excitonic modes will be discussed. |
Wednesday, March 16, 2022 1:30PM - 1:42PM |
N31.00011: Scanning Gradiometry of Magnetic and Electric Fields with a Single Nitrogen-Vacancy Sensor William S Huxter, Marius L Palm, Miranda L Davis, Christian L Degen We report on the development of quantum sensing protocols for the quantitative measurement of magnetic and electric field gradients with nanoscale spatial resolution. With a single nitrogen-vacancy (NV) center at the apex of a scanning diamond probe, we synchronize coherent spin manipulations and optical readout measurements with the mechanical oscillations of the scanning probe. This process converts the sample's static magnetic/electric field into an AC gradient field which can be measured with increased sensitivity while rejecting low frequency noise. We switch between measuring magnetic and electric field gradients by changing the alignment of a milli-Tesla strength bias magnet with respect to the NV symmetry axis. Notably, this technique provides roughly an order of magnitude improvement in magnetic field sensitivity and provides a method to overcome the significant electric field screening currently hindering static field NV electrometry. We demonstrate our scanning gradiometry technique by imaging magnetic and electric field gradients of several well-studied material systems. |
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