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D T Nguyen, S D Findlay, J Etheridge
We assess a selection of electron probes in terms of the spatial resolution with which information can be derived about the structure of a specimen, as opposed to the nominal image resolution. Using Ge [001] as a study case, we investigate the scattering dynamics of these probes and determine their relative merits in terms of two qualitative criteria: interaction volume and interpretability. This analysis provides a 'menu of probes' from which an optimum probe for tackling a given materials science question can be selected...
September 7, 2017: Ultramicroscopy
Charles Bevis, Robert Karl, Jonathan Reichanadter, Dennis F Gardner, Christina Porter, Elisabeth Shanblatt, Michael Tanksalvala, Giulia F Mancini, Henry Kapteyn, Margaret Murnane, Daniel Adams
The ability to record large field-of-view images without a loss in spatial resolution is of crucial importance for imaging science. For most imaging techniques however, an increase in field-of-view comes at the cost of decreased resolution. Here we present a novel extension to ptychographic coherent diffractive imaging that permits simultaneous full-field imaging of multiple locations by illuminating the sample with spatially separated, interfering probes. This technique allows for large field-of-view imaging in amplitude and phase while maintaining diffraction-limited resolution, without an increase in collected data i...
September 6, 2017: Ultramicroscopy
Tijana Djordjević, Ivan Radović, Vito Despoja, Keenan Lyon, Duško Borka, Zoran L Mišković
We present an analytical modeling of the electron energy loss (EEL) spectroscopy data for free-standing graphene obtained by scanning transmission electron microscope. The probability density for energy loss of fast electrons traversing graphene under normal incidence is evaluated using an optical approximation based on the conductivity of graphene given in the local, i.e., frequency-dependent form derived by both a two-dimensional, two-fluid extended hydrodynamic (eHD) model and an ab initio method. We compare the results for the real and imaginary parts of the optical conductivity in graphene obtained by these two methods...
September 4, 2017: Ultramicroscopy
X Shen, R K Li, U Lundström, T J Lane, A H Reid, S P Weathersby, X J Wang
To understand and control the basic functions of physical, chemical and biological processes from micron to nano-meter scale, an instrument capable of visualizing transient structural changes of inhomogeneous materials with atomic spatial and temporal resolutions, is required. One such technique is femtosecond electron microdiffraction, in which a short electron pulse with femtosecond-scale duration is focused into a micron-scale spot and used to obtain diffraction images to resolve ultrafast structural dynamics over a localized crystalline domain...
September 1, 2017: Ultramicroscopy
Bret E Dunlap, Timothy J Ruggles, David T Fullwood, Brian Jackson, Martin A Crimp
In this work, the relative capabilities and limitations of electron channeling contrast imaging (ECCI) and cross-correlation electron backscattered diffraction (CC-EBSD) have been assessed by studying the dislocation distributions resulting from nanoindentation in body centered cubic Ta. Qualitative comparison reveals very similar dislocation distributions between the CC-EBSD mapped GNDs and the ECC imaged dislocations. Approximate dislocation densities determined from ECC images compare well to those determined by CC-EBSD...
September 1, 2017: Ultramicroscopy
Sergei Lopatin, Bin Cheng, Wei-Ting Liu, Meng-Lin Tsai, Jr-Hau He, Andrey Chuvilin
The performance of a monochromated transmission electron microscope with Wien type monochromator is optimized to achieve an extremely narrow energy spread of electron beam and an ultrahigh energy resolution with spectroscopy. The energy spread in the beam is improved by almost an order of magnitude as compared to specified values. The optimization involves both the monochromator and the electron energy loss detection system. We demonstrate boosted capability of optimized systems with respect to ultra-low loss EELS and sub-angstrom resolution imaging (in a combination with spherical aberration correction)...
September 1, 2017: Ultramicroscopy
W Xu, J H Dycus, J M LeBeau
Transmission electron microscopy specimens typically exhibit local distortion at thin foil edges, which can influence the absorption of X-rays for quantitative energy dispersive X-ray spectroscopy (EDS). Here, we report a numerical, three-dimensional approach to model the geometry of general specimens and its influence on quantification when using single and multiple detector configurations. As a function of specimen tilt, we show that the model correctly predicts the asymmetric nature of X-ray counts and ratios...
September 1, 2017: Ultramicroscopy
Rickard R Shen, Pål Efsing
Plastic strain estimation using electron backscatter diffraction (EBSD) based on kernel average misorientation (KAM) is affected by random orientation measurement error, EBSD step length, choice of kernel and average grain size. These sensitivities complicate reproducibility of results between labs, but it is shown in this work how these drawbacks can be overcome. The modifications to KAM were verified against a similar misorientation metric based on grain orientation spread (GOS), which does not show sensitivity to these factors...
August 31, 2017: Ultramicroscopy
Emad Oveisi, Antoine Letouzey, Sandro De Zanet, Guillaume Lucas, Marco Cantoni, Pascal Fua, Cécile Hébert
Deriving accurate three-dimensional (3-D) structural information of materials at the nanometre level is often crucial for understanding their properties. Tomography in transmission electron microscopy (TEM) is a powerful technique that provides such information. It is however demanding and sometimes inapplicable, as it requires the acquisition of multiple images within a large tilt arc and hence prolonged exposure to electrons. In some cases, prior knowledge about the structure can tremendously simplify the 3-D reconstruction if incorporated adequately...
August 30, 2017: Ultramicroscopy
William Osborn, Lawrence H Friedman, Mark Vaudin
We present a new methodology to accurately measure strain magnitudes from 3D nanodevices using Electron Backscatter Diffraction (EBSD). Because the dimensions of features on these devices are smaller than the interaction volume for backscattered electrons, EBSD patterns from 3D nanodevices will frequently be the superposition of patterns from multiple material regions simultaneously. The effect of this superposition on EBSD strain measurement is demonstrated, along with an approach to separate EBSD patterns from these devices via subtraction...
August 29, 2017: Ultramicroscopy
Qiwei Shi, Stéphane Roux, Félix Latourte, François Hild, Dominique Loisnard, Nicolas Brynaert
In situ SEM mechanical tests are key to study crystal plasticity. In particular, imaging and diffraction (EBSD) allow microstructure and surface kinematics to be monitored all along the test. However, to get a full benefit from different modalities, it is necessary to register all images and crystallographic orientation maps from EBSD into the same frame. Different correlative approaches tracking either Pt surface markings, crystal orientations or grain boundaries, allow such registrations to be performed and displacement as well as rotation fields to be measured, a primary information for crystal plasticity identification...
August 24, 2017: Ultramicroscopy
Ebrahim Najafi, Bolin Liao, Timothy Scarborough, Ahmed Zewail
Understanding the mechanical properties of organic semiconductors is essential to their electronic and photovoltaic applications. Despite a large volume of research directed toward elucidating the chemical, physical and electronic properties of these materials, little attention has been directed toward understanding their thermo-mechanical behavior. Here, we report the ultrafast imaging of surface acoustic waves (SAWs) on the surface of the Poly(3-hexylthiophene-2,5-diyl) (P3HT) thin film at the picosecond and nanosecond timescales...
August 24, 2017: Ultramicroscopy
Thilo Kramer, Daniel Mierwaldt, Malte Scherff, Mike Kanbach, Christian Jooss
Non-volatile resistance change under electric stimulation in many metal-oxides is a promising path to next generation memory devices. However, the underlying mechanisms are still not fully understood. In situ transmission electron microscopy experiments provide a powerful tool to elucidate these mechanisms. In this contribution, we demonstrate a TEM lamella geometry for in situ biasing with two fixed electrode contacts ensuring low and stable contact resistances. We use Pr1-xCaxMnO3-δ sandwiched by Pt electrodes as model system...
August 23, 2017: Ultramicroscopy
Kenneth H Downing, Robert M Glaeser
The extent to which the resolution varies within a three-dimensional (3-D) reconstruction, when the diameter of an object is large, is investigated computationally. Numerical simulation is used to model ideal three-dimensional point-spread functions at different radial positions within an object. It is shown that reconstructed density maps are affected less than might have been expected when particles are larger than the depth of field. This favorable outcome is attributed mainly to the fact that a point which lies outside the depth of field relative to the center, for some orientations of the object, will also lie within the depth of field for other orientations...
August 19, 2017: Ultramicroscopy
Cecilie S Granerød, Wei Zhan, Øystein Prytz
Band gap variations in thin film structures, across grain boundaries, and in embedded nanoparticles are of increasing interest in the materials science community. As many common experimental techniques for measuring band gaps do not have the spatial resolution needed to observe these variations directly, probe-corrected Scanning Transmission Electron Microscope (STEM) with monochromated Electron Energy-Loss Spectroscopy (EELS) is a promising method for studying band gaps of such features. However, extraction of band gaps from EELS data sets usually requires heavy user involvement, and makes the analysis of large data sets challenging...
August 17, 2017: Ultramicroscopy
David L J Engberg, Lars J S Johnson, Jens Jensen, Mattias Thuvander, Lars Hultman
Mass spectral overlaps in atom probe tomography (APT) analyses of complex compounds typically limit the identification of elements and microstructural analysis of a material. This study concerns the TiSiN system, chosen because of severe mass-to-charge-state ratio overlaps of the (14)N(+) and (28)Si(2+) peaks as well as the (14)N2(+) and (28)Si(+) peaks. By substituting (14)N with (15)N, mass spectrum peaks generated by ions composed of one or more N atoms will be shifted toward higher mass-to-charge-state ratios, thereby enabling the separation of N from the predominant Si isotope...
August 12, 2017: Ultramicroscopy
Z Hafsi, O Mansour, A Kadoun, L Khouchaf, C Mathieu
The effect of the electron beam skirting on the emission and detection of the backscattered electrons (BSE) in a low vacuum scanning electron microscope is investigated at low energy regime. Monte Carlo computed dependencies of the BSE distribution on the water vapor and air pressure shown a significant increase of the extent of the BSE exit zone. The pressure variation has however a little effect when helium gas is used. A new approach based on the comparison between the sizes of the skirt and the BSE exit zone on the specimen surface provides a useful tool to determine the operating pressure range that ensures minimal degradation of the lateral resolution in BSE imaging mode...
August 12, 2017: Ultramicroscopy
Hassan N Al-Obaidi, Ali S Mahdi, Imad H Khaleel
Accumulation of charges (electrons) at the specimen surface in scanning electron microscope (SEM) lead to generate an electrostatic potential. By using the method of image charges, this potential is defined in the chamber's space of such apparatus. The deduced formula is expressed in terms a general volumetric distribution which proposed to be an infinitesimal spherical extension. With aid of a binomial theorem the defined potential is expanded to a multipolar form. Then resultant formula is adopted to modify a novel mirror plot equation so as to detect the real distribution of trapped charges...
August 12, 2017: Ultramicroscopy
Vilém Neděla, Eva Tihlaříková, Jiří Runštuk, Jiří Hudec
A new Combined System for high-efficiency detection of Secondary and Backscattered Electrons (CSSBE) in the ESEM consists of three detectors: an ionisation SE detector, an improved scintillation BSE detector, and a new Ionisation Secondary Electron Detector with an electrostatic Separator (ISEDS). The ISEDS optimizes conditions for electron-gas ionisation phenomena in the ESEM to achieve a strongly amplified signal from the secondary electrons with a minimal contribution from backscattered and beam electrons...
August 12, 2017: Ultramicroscopy
Joshua A Taillon, Christopher Pellegrinelli, Yi-Lin Huang, Eric D Wachsman, Lourdes G Salamanca-Riba
FIB/SEM nanotomography (FIB-nt) is a powerful technique for the determination and quantification of the three-dimensional microstructure in subsurface features. Often times, the microstructure of a sample is the ultimate determiner of the overall performance of a system, and a detailed understanding of its properties is crucial in advancing the materials engineering of a resulting device. While the FIB-nt technique has developed significantly in the 15 years since its introduction, advanced nanotomographic analysis is still far from routine, and a number of challenges remain in data acquisition and post-processing...
August 9, 2017: Ultramicroscopy
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