Noise Removal by Crystallographic Averaging and Information Content of an Image With Respect to Detections of Plane Symmetries (original) (raw)
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Advanced Structural and Chemical Imaging, 2015
Crystallographic image processing (CIP) techniques may be utilized in scanning probe microscopy (SPM) to glean information that has been obscured by signals from multiple probe tips. This may be of particular importance for scanning tunneling microscopy (STM) and requires images from samples that are periodic in two dimensions (2D). The image-forming current for double-tips in STM is derived with a slight modification of the independent-orbital approximation (IOA) to allow for two or more tips. Our analysis clarifies why crystallographic averaging works well in removing the effects of a blunt STM tip (that consists of multiple mini-tips) from recorded 2D periodic images and also outlines the limitations of this image-processing technique for certain spatial separations of STM double-tips. Simulations of multiple mini-tip effects in STM images (that ignore electron interference effects) may be understood as modeling multiple mini-tip (or tip shape) effects in images that were recorde...
MRS Proceedings, 2014
A statistically sound procedure for the unambiguous identification of the underlying Bravais lattice of an image of a 2D periodic array of objects is described. Our Bravais lattice detection procedure is independent of which type of microscope has been utilized for the recording of the image data. It is particularly useful for the correction of Scanning Tunneling Microscope (STM) images that suffer from a blunt scanning probe tip artifact, i.e. simultaneously recording multiple mini-tips. The unambiguous detection of the type of translation symmetry presents a first step towards making objective decisions about which plane symmetry a 2D periodic image is best modeled by. Such decisions are important for the application of Crystallographic Image Processing (CIP) techniques to images from Scanning Probe Microscopes (SPMs).
Progress in Crystallographic Image Processing for Scanning Probe Microscopy
Microscopy and Microanalysis, 2015
Crystallographic Image Processing (CIP) originated with the electron crystallography community. Nobel Laureate Sir Aaron Klug (OM, FRS) and coworkers pioneered the technique for the analysis of long-range ordered biological materials in parallel illumination Transmission Electron Microscopes (TEMs). Corrections for the effects of the TEM's phase contrast transfer function and for less than optimal imaging conditions are part of this kind of CIP. There are also "electron microscope independent" 2D crystallography foundations to this kind of image processing.
Crystallographic Image Processing for Scanning Probe Microscopes
Microscopy and Microanalysis, 2012
Scanning probe microscopy (SPM) images of regularly arranged spatially periodic objects can be processed crystallographically. The resulting information may be used to remove from the SPM image distortions that are due to a "less than perfect" imaging process. The combined effects of these distortions result in a point spread function that gives a quantitative measure of the microscope's performance for a certain set of experimental conditions. On the basis of highly symmetric "calibration samples", the point spread function of the microscope may be extracted and utilized for the correction of SPM images of unknowns that were recorded under essentially the same experimental conditions. We concentrate in this paper on more theoretical aspects of our method. A "blunt" scanning tunnelling microscopy (STM) tip that consists of multiple "mini-tips" with electron orbital dimensions may be "symmetrized" on the basis of prior knowledge on the plane symmetry of a two-dimensional periodic array. This is illustrated with the crystallographic processing of a STM image of a regular array of fluorinated cobalt phthalocyanine molecules on graphite and backed up conceptually by simple simulations. Keywords scanning probe microscopy; scanning tunnelling microscopy; 2D periodic symmetry; point spread function 1 "Traditional" refers here to SPMs that have just one "kind" of a probe-sample interactions signal attached to each 2D scanning increment. Nontraditional SPMs are defined by having two or more such kinds of signals attached to each 2D scanning increment. Examples of non-traditional SPMs are spin-polarized STMs and critical dimension SPMs. Utilizing "black-white" and "colour symmetries" (e.g. Shubnikov AV, Below NV. et al.,
Ultramicroscopy, 2010
We report a local crystal structure analysis with a high precision of several picometers on the basis of scanning transmission electron microscopy (STEM). Advanced annular dark-field (ADF) imaging has been demonstrated using software-based experimental and data-processing techniques, such as the improvement of signal-to-noise ratio, the reduction of image distortion, the quantification of experimental parameters (e.g., thickness and defocus) and the resolution enhancement by maximum-entropy deconvolution. The accuracy in the atom position measurement depends on the validity of the incoherent imaging approximation, in which an ADF image is described as the convolution between the incident probe profile and scattering objects. Although the qualitative interpretation of ADF image contrast is possible for a wide range of specimen thicknesses, the direct observation of a crystal structure with deep-sub-angstrom accuracy requires a thin specimen (e.g., 10 nm), as well as observation of the structure image by conventional high-resolution transmission electron microscopy.
Crystallographic STM image processing of 2D periodic and highly symmetric molecule arrays
2011
Crystallographic Image Processing (CIP) is applied to experimental Scanning Tunneling Microscopy (STM) images of regular (2D periodic) arrays of organic molecules on noble metal substrates. The crystallographically averaged (surface) lattices, structural motifs, and plane symmetry groups of the arrays are determined. An assessment of the samples with the goal of utilizing highly symmetric molecular arrays as calibration samples for STM is made. A brief introduction to the CIP procedures is given in an appendix.
AIP Advances
The crystallographic structures of disordered materials are typically analyzed using diffractometry techniques, such as x-ray diffraction (XRD), neutron diffraction (ND), and electron diffraction (ED). Here, we demonstrate a novel technique to analyze the local structure of disordered materials via scanning transmission electron microscopy (STEM) under a contrast variation scheme. Contrast variation is a scheme used for the analysis of bulk materials, which combines two different diffractometry techniques with discrete scattering factors, such as ND and XRD. The STEM image contrasts of annular dark-field (ADF) and annular bright-field (ABF) imaging, which are characterized by different atomic number dependences, are simultaneously utilized. Simulated STEM images of amorphous SiO2 are examined using Fourier transform and autocorrelation operations, revealing that the Fourier transforms of ADF and ABF images are consistent with the results of conventional XRD/ED and ND techniques, res...
Accurate Nanoscale Crystallography in Real-Space Using Scanning Transmission Electron Microscopy
Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada, 2015
Here, we report reproducible and accurate measurement of crystallographic parameters using scanning transmission electron microscopy. This is made possible by removing drift and residual scan distortion. We demonstrate real-space lattice parameter measurements with <0.1% error for complex-layered chalcogenides Bi2Te3, Bi2Se3, and a Bi2Te2.7Se0.3 nanostructured alloy. Pairing the technique with atomic resolution spectroscopy, we connect local structure with chemistry and bonding. Combining these results with density functional theory, we show that the incorporation of Se into Bi2Te3 causes charge redistribution that anomalously increases the van der Waals gap between building blocks of the layered structure. The results show that atomic resolution imaging with electrons can accurately and robustly quantify crystallography at the nanoscale.
Ultramicroscopy 153 (2015) 32–39, 2015
In many cases, the three-dimensional reconstructions from atom probe tomography (APT) are not sufficiently accurate to resolve crystallographic features such as lattice planes, shear bands, stacking faults, dislocations or grain boundaries. Hence, correlative crystallographic characterization is required in addition to APT at the exact same location of the specimen. Also, for the site-specific preparation of APT tips containing regions of interest (e.g. grain boundaries) correlative electron microscopy is often inevitable. Here we present a versatile experimental setup that enables performing correlative focused ion beam milling, transmission electron microscopy (TEM), and APT under optimized characterization conditions. The setup was designed for high throughput, robustness and practicability. We demonstrate that atom probe tips can be characterized by TEM in the same way as a standard TEM sample. In particular, the use of scanning nanobeam diffraction provides valuable complementary crystallographic information when being performed on atom probe tips. This technique enables the measurement of orientation and phase maps as known from electron backscattering diffraction with a spatial resolution down to one nan-ometer.