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Journal of Visualized Experiments : JoVE Jul 2021The modern aberration-corrected scanning transmission electron microscopes (AC-STEM) have successfully achieved direct visualization of atomic columns with sub-angstrom...
The modern aberration-corrected scanning transmission electron microscopes (AC-STEM) have successfully achieved direct visualization of atomic columns with sub-angstrom resolution. With this significant progress, advanced image quantification and analysis are still at the early stages. In this work, we present the complete pathway for the metrology of atomic resolution scanning transmission electron microscopy (STEM) images. This includes (1) tips for acquiring high-quality STEM images; (2) denoising and drift-correction for enhancing measurement accuracy; (3) obtaining initial atomic positions; (4) indexing the atoms based on unit cell vectors; (5) quantifying the atom column positions with either 2D-Gaussian single peak fitting or (6) multi-peak fitting routines for slightly overlapping atomic columns; (7) quantification of lattice distortion/strain within the crystal structures or at the defects/interfaces where the lattice periodicity is disrupted; and (8) some common methods to visualize and present the analysis. Furthermore, a simple self-developed free MATLAB app (EASY-STEM) with a graphical user interface (GUI) will be presented. The GUI can assist in the analysis of STEM images without the need for writing dedicated analysis code or software. The advanced data analysis methods presented here can be applied for the local quantification of defect relaxations, local structural distortions, local phase transformations, and non-centrosymmetry in a wide range of materials.
Topics: Microscopy, Electron; Microscopy, Electron, Scanning Transmission
PubMed: 34279511
DOI: 10.3791/62164 -
Optics Letters Jun 2023An interferogram demodulation method based on azimuthal complex spectrum analysis is proposed for achieving picometer-scale accuracy with an optical vortex...
An interferogram demodulation method based on azimuthal complex spectrum analysis is proposed for achieving picometer-scale accuracy with an optical vortex interferometer (OVI). The OVI uses conjugated p-radial-order Laguerre-Gaussian beams to produce a high-order petal-like interferogram. A camera with a multi-ring pattern written on its sensor is used to convert the interferogram into multiple azimuthal intensity profiles. A phase shift subjected to either uniform surface displacement or axisymmetric non-uniform surface deformation can be retrieved from the complex spectra of the azimuthal intensity profiles at the main frequency components. The experiment verified that the measurement error is 84 pm for a displacement of 10 nm and 0.359 nm for a deformation magnitude of 100 nm. The effect of surface misalignment on the measurement result is also discussed. The proposed method provides an effective and highly accurate method of interferogram demodulation for the OVI and extends the applicability of OVI from uniform surface displacement measurement to axisymmetric non-uniform surface deformation measurement.
PubMed: 37262235
DOI: 10.1364/OL.494198 -
Physical Review Letters Dec 2021Laser-induced tunneling ionization is one of the fundamental light-matter interaction processes. An accurate description of the tunnel-ionized electron wave packet is...
Laser-induced tunneling ionization is one of the fundamental light-matter interaction processes. An accurate description of the tunnel-ionized electron wave packet is central to understanding and controlling subsequent electron dynamics. Because of the anisotropic molecular structure, tunneling ionization of molecules involves considerable challenges in accurately describing the tunneling electron wave packet. Up to now, some basic properties of the tunneling electron from molecules still remain unexplored. Here, we demonstrate that the tunneling electron from a molecule is not always emitted from the geometric center of the molecule along the tunnel direction. Rather, the photoemission position depends on the molecular orientation. Using a photoelectron holographic technique, we determine the photoemission position for a nitrogen molecule relative to the molecular geometric center to be 95±21 pm when the molecular axis is oriented along the tunnel direction. Our Letter poses, and answers experimentally, a fundamental question as to where the molecular photoionization actually begins, which has significant implications for time-resolved probing of valence electron dynamics in molecules.
PubMed: 35029482
DOI: 10.1103/PhysRevLett.127.263202 -
Light, Science & Applications Jun 2023Miniaturization of optical spectrometers is important to enable spectroscopic analysis to play a role in in situ, or even in vitro and in vivo characterization systems....
Miniaturization of optical spectrometers is important to enable spectroscopic analysis to play a role in in situ, or even in vitro and in vivo characterization systems. However, scaled-down spectrometers generally exhibit a strong trade-off between spectral resolution and operating bandwidth, and are often engineered to identify signature spectral peaks only for specific applications. In this paper, we propose and demonstrate a novel global sampling strategy with distributed filters for generating ultra-broadband pseudo-random spectral responses. The geometry of all-pass ring filters is tailored to ensure small self- and cross-correlation for effective information acquisition across the whole spectrum, which dramatically reduces the requirement on sampling channels. We employ the power of reconfigurable photonics in spectrum shaping by embedding the engineered distributed filters. Using a moderate mesh of MZIs, we create 256 diverse spectral responses on a single chip and demonstrate a resolution of 20 pm for single spectral lines and 30 pm for dual spectral lines over a broad bandwidth of 115 nm, to the best of our knowledge achieving a new record of bandwidth-to-resolution ratio. Rigorous simulations reveal that this design will readily be able to achieve single-picometer-scale resolution. We further show that the reconfigurable photonics provides an extra degree of programmability, enabling user-defined features on resolution, computation complexity, and relative error. The use of SiN integration platform enables the spectrometer to exhibit excellent thermal stability of ±2.0 °C, effectively tackling the challenge of temperature variations at picometer-scale resolutions.
PubMed: 37357227
DOI: 10.1038/s41377-023-01195-2 -
Optics Letters Jul 2019We propose a simple compact interferometer using twisted light to detect picometer displacement on a solid or liquid surface. The heart of the interferometer lies in...
We propose a simple compact interferometer using twisted light to detect picometer displacement on a solid or liquid surface. The heart of the interferometer lies in producing a daisy petal pattern formed by interference between two oppositely charged twisted beams. The sample being probed is an active component of the interferometer. By analyzing the rotation of the petal pattern, caused by the relative displacement between the cylindrical lens (CL) and solid/liquid surface, we exhibit picometer resolution in displacement measurements. Remarkably, we explore the significance of a radial quantum number in the measurement of surface displacement and surface tilt angle. We also investigate the arbitrary surface deformation profile with similar precision by modifying the set-up. We perform simulations in realistic experimental settings and show that they are in excellent agreement with the predictions of analytic expressions. The proposed set-up can be further miniaturized by a small focal length CL and will open routes for tremendous applications in picometer-scale displacement measurement of a solid or liquid interface by various excitations.
PubMed: 31305580
DOI: 10.1364/OL.44.003594 -
Applied Optics Nov 2020A two-dimensional (2D) picometer comb, a novel optical element made by picometer-differential four times exposed in two perpendicular directions, is proposed to generate...
A two-dimensional (2D) picometer comb, a novel optical element made by picometer-differential four times exposed in two perpendicular directions, is proposed to generate the dot array projection pattern for three-dimensional (3D) shape reconstruction and other applications. Not only does a 2D picometer comb generate a stable light field distribution with extremely long depth of field and small divergence angle as a one-dimensional picometer comb, it also has new properties, such as periodicity of diffraction field in two perpendicular directions and high concentration of energy of points, which is particularly suitable for providing dot array structured light. We demonstrate that the diffraction field of a 2D picometer comb provides a solution for non-defocusing 3D reconstruction with a dot array. In fabrication of a 2D picometer comb, we can modulate the holography by changing the angle of two beams slightly, so its period can be measured at picometer accuracy. A 2D picometer comb can be made to any scale, then it can be integrated to mobile devices, such as a mobile phone, for 3D shape reconstruction. Furthermore, the concept of a 2D picometer comb would be applied to generate a picometer light field for opening the door of pico-optics in the future.
PubMed: 33361990
DOI: 10.1364/AO.408925 -
Applied Optics Apr 2019Future space observatory missions are forecasting the need for sensing and controlling wavefront error and system alignment stability to picometer scale. Picometer...
Future space observatory missions are forecasting the need for sensing and controlling wavefront error and system alignment stability to picometer scale. Picometer stability performance demands precision knowledge of the mirror and metering structure materials to the same degree. A high-speed electronic speckle pattern interferometer was designed and built to demonstrate measurements of both static and dynamic responses of picometer amplitudes in materials of diffuse surface subjected to very low energy disturbances. This paper describes the details of a test to impart a dynamic disturbance of picometer scale and measure the response of a composite material. The results of the test are also reported and show conclusively that sub-picometer scale effects can be accurately measured in an open test environment outside a vacuum chamber.
PubMed: 31044790
DOI: 10.1364/AO.58.003156 -
Nano Letters May 2024Diamond is considered the most promising next-generation semiconductor material due to its excellent physical characteristics. It has been more than three decades since...
Diamond is considered the most promising next-generation semiconductor material due to its excellent physical characteristics. It has been more than three decades since the discovery of a special structure named n-diamond. However, despite extensive efforts, its crystallographic structure and properties are still unclear. Here, we show that subdisordered structures in diamond provide an explanation for the structural feature of n-diamond. Monocrystalline diamond with subdisordered structures is synthesized via the chemical vapor deposition method. Atomic-resolution scanning transmission electron microscopy characterizations combined with the picometer-precision peak finder technology and diffraction simulations reveal that picometer-scale shifts of atoms within cells of diamond govern the subdisordered structures. First-principles calculations indicate that the bandgap of diamond decreases rapidly with increasing shifting distance, in accordance with experimental results. These findings clarify the crystallographic structure and electronic properties of n-diamond and provide new insights into the bandgap adjustment in diamond.
PubMed: 38722094
DOI: 10.1021/acs.nanolett.4c01857 -
Physical Review Letters Mar 2019The Laser Interferometer Space Antenna (LISA) and its metrology chain have to fulfill stringent performance requirements to enable the space-based detection of...
The Laser Interferometer Space Antenna (LISA) and its metrology chain have to fulfill stringent performance requirements to enable the space-based detection of gravitational waves. This implies the necessity of performance verification methods. In particular, the extraction of the interferometric phase, implemented by a phasemeter, needs to be probed for linearity and phase noise contributions. This Letter reports on a hexagonal quasimonolithic optical bench implementing a three-signal test for this purpose. Its characterization as sufficiently stable down to picometer levels is presented as well as its usage for a benchmark phasemeter performance measurement under LISA conditions. These results make it a candidate for the core of a LISA metrology verification facility.
PubMed: 30932596
DOI: 10.1103/PhysRevLett.122.081104 -
Applied Optics Jun 2020The accuracy of optical three-dimensional (3D) shape measurement is always influenced by the defocusing of a projection or imaging system. In this paper, a novel optical...
The accuracy of optical three-dimensional (3D) shape measurement is always influenced by the defocusing of a projection or imaging system. In this paper, a novel optical element made by picometer-differential twice-exposed holography, called a picometer comb, is proposed to generate the projection pattern for 3D shape measurement. Two interference fields with picometer-scale period difference are recorded on a substrate to fabricate the picometer comb by twice-exposed laser holography; this element reconstructs the diffraction field, which is essentially the interference between the holograms of two object waves with a slight angle. This picometer comb has the advantage of the generation of a stable light field distribution with extremely long depth of field and small divergence angle. We demonstrate that this diffraction field provides a solution for non-defocusing 3D shape measurement.
PubMed: 32543543
DOI: 10.1364/AO.392306