Microsegregation of an Aluminum and Magnesium Alloy at High Solidification Rates

1981 ◽  
Vol 8 ◽  
Author(s):  
L.J. Masur ◽  
J.T. Burke ◽  
T.Z. Kattamis ◽  
M.C. Flemings
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
Coarse Grained ◽  
Specimen Preparation ◽  
Second Phase ◽  
Solute Redistribution ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Compositional Changes ◽  
Rapidly Solidified ◽  
Zn Alloys

ABSTRACTResults are presented of an on-going study of structure and solute redistribution in ribbon cast Al-Cu and Mg-Zn alloys. Regions found in these ribbons are (1) an apparently chemically homogeneous coarse-grained zone adjacent the chill, (2) a transition cellular region, and (3) a dendritic zone, usually equiaxed. In both alloys, structure in the equiaxed region becomes coarser with increasing distance from the chill. In Mg-Zn alloys, the amount of nonequilibrium second phase increases essentially linearly with distance in the cellular and dendritic regions. Scanning transmission electron microscopy can accurately measure solute distribution across rapidly solidified cells or dendrites, but the possibility of surface compositional changes during specimen preparation must be recognized.

Redistribution Effects for OMVPE InP/GaAs

1988 ◽  
Vol 144 ◽  
Author(s):  
OH Tae-IL ◽  
Wallace B. Leigh
Keyword(s):  
Electron Diffraction ◽  
Cross Sections ◽  
Scanning Transmission Electron Microscopy ◽  
Field Investigation ◽  
Second Phase ◽  
X Ray ◽  
Substrate Side ◽  
Gaas Substrates ◽  
Transmission Electron ◽  
Scanning Transmission

ABSTRACTWe have analyzed the redistribution parameters for InP grown by organometallic vapor phase epitaxy (OMVPE) on GaAs substrates. The layers, grown using (trimethyl Indium) TMIn at atmospheric pressure, have been characterized for epitaxial quality using photoluminescence, energy dispersed x-ray analysis, and optical microscopy. In order to better understand the effects of inter-diffusion and inter-mixing for the GaAs into the InP epitaxial layer, the layer-substrate interface was first probed by growing consecutive samples of InP for increasingly longer growth times, and thus characterizing the layers as one moves away from the interface. For more detailed analysis, cross-sections of the InP/GaAs interface were prepared for scanning transmission electron microscopy (STEM). Energy dispersed x-ray analysis has shown that all elements In, Ga, As, and P, are present on the epitaxial side of the interface, while only Ga and As are present on the substrate side. A combination of electron diffraction and luminescence measurements show the epitaxy is at least 80% InP at the interface and essentially 100% InP at a distance of 6000Å into the epilayer. Electron diffraction and bright field investigation at the interface show the existence of a second phase, existing in a mostly InP matrix. The effects of redistribution in heteroepitaxial InP/GaAs will be discussed.

Recent Advances in FIB Technology for Nano-prototyping and Nano-characterisation

2007 ◽  
Vol 1020 ◽  
Author(s):  
Debbie J Stokes ◽  
Laurent Roussel ◽  
Oliver Wilhelmi ◽  
Lucille A Giannuzzi ◽  
Dominique HW Hubert
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Specimen Preparation ◽  
Nano Materials ◽  
Transmission Electron ◽  
Scanning Transmission

AbstractCombined focused ion beam (FIB) and scanning electron microscopy (SEM) methods are becoming increasingly important for nano-materials applications as we continue to develop ways to exploit the complex interplay between primary ion and electron beams and the substrate, in addition to the various subtle relationships with gaseous intermediaries.We demonstrate some of the recent progress that has been made concerning FIB SEM processing of both conductive and insulating materials for state-of-the-art nanofabrication and prototyping and superior-quality specimen preparation for ultra-high resolution scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) imaging and related in situ nanoanalysis techniques.

scholarly journals Towards Automating Structural Discovery in Scanning Transmission Electron Microscopy

2021 ◽  
Author(s):  
Nicole Creange ◽  
Ondrej Dyck ◽  
Rama K Vasudevan ◽  
Maxim Ziatdinov ◽  
Sergei V Kalinin
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Topological Defects ◽  
Functional Materials ◽  
Bayesian Optimization ◽  
Second Phase ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission

Abstract Scanning transmission electron microscopy (STEM) is now the primary tool for exploring functional materials on the atomic level. Often, features of interest are highly localized in specific regions in the material, such as ferroelectric domain walls, extended defects, or second phase inclusions. Selecting regions to image for structural and chemical discovery via atomically resolved imaging has traditionally proceeded via human operators making semi-informed judgements on sampling locations and parameters. Recent efforts at automation for structural and physical discovery have pointed towards the use of ‘active learning’ methods that utilize Bayesian optimization with surrogate models to quickly find relevant regions of interest. Yet despite the potential importance of this direction, there is a general lack of certainty in selecting relevant control algorithms and how to balance a priori knowledge of the material system with knowledge derived during experimentation. Here we address this gap by developing the automated experiment workflows with several combinations to both illustrate the effects of these choices and demonstrate the tradeoffs associated with each in terms of accuracy, robustness, and susceptibility to hyperparameters for structural discovery. We discuss possible methods to build descriptors using the raw image data and deep learning based semantic segmentation, as well as the implementation of variational autoencoder based representation. Furthermore, each workflow is applied to a range of feature sizes including NiO pillars within a La:SrMnO3 matrix, ferroelectric domains in BiFeO3, and topological defects in graphene. The code developed in this manuscript are open sourced and will be released at github.com/creangnc/AE_Workflows.

High-Quality, Smooth Fe3O4 Thin Films on Si By Controlled Oxidation of Fe in CO/CO2

2012 ◽  
Vol 1430 ◽  
Author(s):  
Fengyuan Shi ◽  
Hua Xiang ◽  
M. S. Rzchowski ◽  
Y. A. Chang ◽  
P.M. Voyles
Keyword(s):  
Magnetic Field ◽  
Crystal Structure ◽  
Thin Films ◽  
Scanning Transmission Electron Microscopy ◽  
Defect Density ◽  
Second Phase ◽  
High Quality ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Electron Energy Loss

ABSTRACTWe fabricated Fe3O4 thin films on TiN buffered Si by CO/CO2 oxidation at 160 °C. The easy saturation of the magnetization at high magnetic field and high resolution scanning transmission electron microscopy (HRSTEM) images show low defect density, smooth Fe3O4 thin films. Oxidation at 400 °C resulted in an undesirable second phase in between the TiN and the un-oxidized Fe, but changes in total gas pressure did not lead to a second phase. The crystal structure of this second phase is similar to Fe2TiO4 (ulvöspinel) from HRSTEM and STEM electron energy loss spectroscopy. Fe3O4 thin films grown at 160 °C follow a power law growth model with an exponent of 0.23±0.03.

Preparation of Titanium Microgrids for Scanning Transmission Electron Microscopy

1977 ◽  
Vol 35 ◽  
pp. 322-323
Author(s):  
M.L. Collins ◽  
N.W. Parker
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Scanning Transmission Electron Microscopy ◽  
Single Atom ◽  
Specimen Preparation ◽  
Transmission Microscopy ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission

The ideal supporting microgrid for high resolution scanning transmission electron microscopy should be: 1) made of material of low atomic number, 2) uniformly flat for ease in focusing, 3) resistant to any treatments necessary for cleaning and specimen preparation, and 4) a good electrical and thermal conductor. In the past, microgrid supports have been made of fenestrated plastic films strengthened by carbon or metal coatings. While adequate for most work, they cannot be baked at temperatures greater than 50°C. which may be necessary in some cases to completely eliminate contamination for single atom imaging using the STEM. To provide a reliably non-contaminating substrate support for high resolution scanning transmission microscopy, we have developed a simple technique for the preparation of microgrids of titanium metal. As can be seen in table 1, titanium posesses many attractive features.

Enhancement of Contrast in the CEM and STEM Using Bumpy Specimens and Employing the “Dappled Field” Mode of Operation

1974 ◽  
Vol 32 ◽  
pp. 552-553 ◽  
Author(s):  
L. Gandolfi ◽  
J. Reiffel
Keyword(s):  
Operating Mode ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Specimen Preparation ◽  
Field Mode ◽  
Preparation Methods ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Mode Of Operation ◽  
Scanning Transmission

Calculations have been performed on the contrast obtainable, using the Scanning Transmission Electron Microscope, in the observation of thick specimens. Recent research indicates a revival of an earlier interest in the observation of thin specimens with the view of comparing the attainable contrast using both types of specimens.Potential for biological applications of scanning transmission electron microscopy has led to a proliferation of the literature concerning specimen preparation methods and the controversy over “to stain or not to stain” in combination with the use of the dark field operating mode and the same choice of technique using bright field mode of operation has not yet been resolved.

High-Voltage Scanning Electron Microscopy

1970 ◽  
Vol 28 ◽  
pp. 6-7
Author(s):  
J. M. Cowley
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Wave Optics ◽  
Contrast Effects ◽  
Transmission Electron ◽  
Mode Of Operation ◽  
Scanning Transmission ◽  
Types Of Information ◽  
Voltage Scanning

The comparison of scanning transmission electron microscopy (STEM) with conventional transmission electron microscopy (CTEM) can best be made by means of the Reciprocity Theorem of wave optics. In Fig. 1 the intensity measured at a point A’ in the CTEM image due to emission from a point B’ in the electron source is equated to the intensity at a point of the detector, B, due to emission from a point A In the source In the STEM. On this basis it can be demonstrated that contrast effects In the two types of instrument will be similar. The reciprocity relationship can be carried further to include the Instrument design and experimental procedures required to obtain particular types of information. For any. mode of operation providing particular information with one type of microscope, the analagous type of operation giving the same information can be postulated for the other type of microscope. Then the choice between the two types of instrument depends on the practical convenience for obtaining the required Information.

Imaging and diffraction modes in Scanning Transmission Electron Microscopy

1986 ◽  
Vol 44 ◽  
pp. 684-687
Author(s):  
J. M. Cowley ◽  
R. Glaisher ◽  
J. A. Lin ◽  
H.-J. Ou
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
High Efficiency ◽  
Fiber Optic ◽  
Image Intensifier ◽  
Detector System ◽  
Detector Plane ◽  
Secondary Electrons ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Special Detector

Some of the most important applications of STEM depend on the variety of imaging and diffraction made possible by the versatility of the detector system and the serial nature, of the image acquisition. A special detector system, previously described, has been added to our STEM instrument to allow us to take full advantage of this versatility. In this, the diffraction pattern in the detector plane may be formed on either of two phosphor screens, one with P47 (very fast) phosphor and the other with P20 (high efficiency) phosphor. The light from the phosphor is conveyed through a fiber-optic rod to an image intensifier and TV system and may be photographed, recorded on videotape, or stored digitally on a frame store. The P47 screen has a hole through it to allow electrons to enter a Gatan EELS spectrometer. Recently a modified SEM detector has been added so that high resolution (10Å) imaging with secondary electrons may be used in conjunction with other modes.

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