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Matthieu Picher, Kerstin Bücker, Thomas LaGrange, Florian Banhart
We implement a parametric study with single electron pulses having a 7 ns duration to find the optimal conditions for imaging, diffraction, and electron energy-loss spectroscopy (EELS) in the single-shot approach. Photoelectron pulses are generated by illuminating a flat tantalum cathode with 213 nm nanosecond laser pulses in a 200 kV transmission electron microscope (TEM) with thermionic gun and Wehnelt electrode. For the first time, an EEL spectrometer is used to measure the energy distribution of single nanosecond electron pulses which is crucial for understanding the ideal imaging conditions of the single-shot approach...
March 13, 2018: Ultramicroscopy
W Verhoeven, J F M van Rens, E R Kieft, P H A Mutsaers, O J Luiten
Ultrashort, low-emittance electron pulses can be created at a high repetition rate by using a TM110 deflection cavity to sweep a continuous beam across an aperture. These pulses can be used for time-resolved electron microscopy with atomic spatial and temporal resolution at relatively large average currents. In order to demonstrate this, a cavity has been inserted in a transmission electron microscope, and picosecond pulses have been created. No significant increase of either emittance or energy spread has been measured for these pulses...
March 10, 2018: Ultramicroscopy
A Scholl, M A Marcus, A Doran, J R Nasiatka, A T Young, A A MacDowell, R Streubel, N Kent, J Feng, W Wan, H A Padmore
Aberration correction by an electron mirror dramatically improves the spatial resolution and transmission of photoemission electron microscopes. We will review the performance of the recently installed aberration corrector of the X-ray Photoemission Electron Microscope PEEM-3 and show a large improvement in the efficiency of the electron optics. Hartmann testing is introduced as a quantitative method to measure the geometrical aberrations of a cathode lens electron microscope. We find that aberration correction leads to an order of magnitude reduction of the spherical aberrations, suggesting that a spatial resolution of below 100 nm is possible at 100% transmission of the optics when using x-rays...
March 10, 2018: Ultramicroscopy
Yeomin Yoon, Suwoo Noh, Jiseong Jeong, Kyihwan Park
The topology image is constructed from the 2D matrix (XY directions) of heights Z captured from the force-feedback loop controller. For small height variations, nonlinear effects such as hysteresis or creep of the PZT-driven Z nano scanner can be neglected and its calibration is quite straightforward. For large height variations, the linear approximation of the PZT-driven Z nano scanner fail and nonlinear behaviors must be considered because this would cause inaccuracies in the measurement image. In order to avoid such inaccuracies, an additional strain gauge sensor is used to directly measure displacement of the PZT-driven Z nano scanner...
March 8, 2018: Ultramicroscopy
Shibabrata Basak, Jacob Jansen, Yoones Kabiri, Henny W Zandbergen
The key to understanding the performance of Li-O2 batteries is to study the chemical and structural properties of their discharge product(s) at the nanometer scale. Using TEM for this purpose poses challenges due to the sensitivity of samples to air and electron beams. This paper describes our use of in situ EELS to evaluate experimental procedures to reduce electron-beam degradation and presents methods to deal with air sensitivity. Our results show that Li2 O2 decomposition is dependent on the total dose and is approximately 4-5 times more pronounced at 80 than at 200 kV...
March 6, 2018: Ultramicroscopy
Hidehito Adaniya, Martin Cheung, Cathal Cassidy, Masao Yamashita, Tsumoru Shintake
A new SEM-based in-line electron holography microscope has been under development. The microscope utilizes conventional SEM and BF-STEM functionality to allow for rapid searching of the specimen of interest, seamless interchange between SEM, BF-STEM and holographic imaging modes, and makes use of coherent low-energy in-line electron holography to obtain low-dose, high-contrast images of light element materials. We report here an overview of the instrumentation and first experimental results on gold nano-particles and carbon nano-fibers for system performance tests...
March 6, 2018: Ultramicroscopy
W Xu, J M LeBeau
We establish a series of deep convolutional neural networks to automatically analyze position averaged convergent beam electron diffraction patterns. The networks first calibrate the zero-order disk size, center position, and rotation without the need for pretreating the data. With the aligned data, additional networks then measure the sample thickness and tilt. The performance of the network is explored as a function of a variety of variables including thickness, tilt, and dose. A methodology to explore the response of the neural network to various pattern features is also presented...
March 5, 2018: Ultramicroscopy
J Bogdanowicz, A Kumar, C Fleischmann, M Gilbert, J Houard, A Vella, W Vandervorst
This paper demonstrates the increased light absorption efficiency of semiconducting atom probe tips resulting from focused-ion-beam (FIB) preparation. We use transmission electron microscopy to show that semiconducting tips prepared with FIB are surrounded with an amorphized shell. Photomodulated optical reflectance measurements then provide evidence that FIB-induced damage leads to an increase in both sub- and supra-bandgap light absorption efficiency. Using laser-assisted atom probe tomography (La-APT) measurements, we finally show that, for a nanoscale tip geometry, the laser-induced heating of a tip during La-APT is enhanced by the FIB preparation...
March 5, 2018: Ultramicroscopy
Mohamed Aymen Mahjoub, Guillaume Monier, Luc Bideux, Bernard Gruzza, Christine Robert-Goumet
A non-destructive new imaging technique called Multi-Mode Elastic Peak Electron Microscopy (MM-EPEM), hypersensitive to surface chemistry and with an in-depth resolution of one atomic monolayer was developed. This method consists on performing several MM-EPEM images containing n × n pixels associated to an intensity of the elastic backscattered electrons by varying the incident electron energy in the range 200-2000 eV. This approach allows obtaining depth sampling information of the analyzed structures...
February 28, 2018: Ultramicroscopy
John S Mangum, Lisa H Chan, Ute Schmidt, Lauren M Garten, David S Ginley, Brian P Gorman
Site-specific preparation of specimens using focused ion beam instruments for transmission electron microscopy is at the forefront of targeting regions of interest for nanoscale characterization. Typical methods of pinpointing desired features include electron backscatter diffraction for differentiating crystal structures and energy-dispersive X-Ray spectroscopy for probing compositional variations. Yet there are situations, notably in the titanium dioxide system, where these techniques can fail. Differentiating between the brookite and anatase polymorphs of titania is either excessively laborious or impossible with the aforementioned techniques...
February 23, 2018: Ultramicroscopy
Andreas Mittelberger, Christian Kramberger, Jannik C Meyer
The performance of the detector is of key importance for low-dose imaging in transmission electron microscopy, and counting every single electron can be considered as the ultimate goal. In scanning transmission electron microscopy, low-dose imaging can be realized by very fast scanning, however, this also introduces artifacts and a loss of resolution in the scan direction. We have developed a software approach to correct for artifacts introduced by fast scans, making use of a scintillator and photomultiplier response that extends over several pixels...
February 17, 2018: Ultramicroscopy
M Radek, J-G Tenberge, S Hilke, G Wilde, M Peterlechner
Electron microscopy images are interference patterns and can generally not be interpreted in a straight forward manner. Typically, time consuming numerical simulations have to be employed to separate specimen features from imaging artifacts. Directly comparing numerical predictions to experimental results, realistic simulation box sizes and varying imaging parameters are needed. In this work, we introduce an accelerated multislice algorithm, named STEMcl, that is capable of simulating series of large super cells typical for defective and amorphous systems, in addition to parameter series using the massive parallelization accessible in today's commercial PC-hardware, e...
February 16, 2018: Ultramicroscopy
Misa Hayashida, Kai Cui, Marek Malac, Ray Egerton
We measured the linear thermal expansion coefficients of amorphous 5-30 nm thick SiN and 17 nm thick Formvar/Carbon (F/C) films using electron diffraction in a transmission electron microscope. Positive thermal expansion coefficient (TEC) was observed in SiN but negative coefficients in the F/C films. In case of amorphous carbon (aC) films, we could not measure TEC because the diffraction radii required several hours to stabilize at a fixed temperature.
February 16, 2018: Ultramicroscopy
Shahedul Hoque, Hiroyuki Ito, Ryuji Nishi
In our previous works, we have proposed N-SYLC (N-fold symmetric line currents) models for aberration correction. In this paper, we propose "in-lens N-SYLC" model, where N-SYLC overlaps rotationally symmetric lens. Such overlap is possible because N-SYLC is free of magnetic materials. We analytically prove that, if certain parameters of the model are optimized, an in-lens 3-SYLC (N = 3) doublet can correct 3rd order spherical aberration. By computer simulation, we show that the required excitation current for correction is less than 0...
February 16, 2018: Ultramicroscopy
E Di Russo, I Blum, J Houard, M Gilbert, G Da Costa, D Blavette, L Rigutti
A systematic study of the biases occurring in the measurement of the composition of GaN by Atom Probe Tomography was carried out, in which the role of surface electric field and laser pulse intensity has been investigated. Our data confirm that the electric field is the main factor influencing the measured composition, which exhibits a deficiency of N at low field and a deficiency of Ga at high field. The deficiency of Ga at high field is interpreted in terms of preferential evaporation of Ga. The detailed analysis of multiple evaporation events reveals that the measured composition is not affected by pile-up phenomena occurring in detection system...
February 6, 2018: Ultramicroscopy
Siavash Maraghechi, Johan P M Hoefnagels, Ron H J Peerlings, Marc G D Geers
High resolution scanning electron microscopy (HR-SEM) is nowadays very popular for different applications in different fields. However, SEM images may exhibit a considerable amount of imaging artifacts, which induce significant errors if the images are used to measure geometrical or kinematical fields. This error is most pronounced in case of full field deformation measurements, for instance by digital image correlation (DIC). One family of SEM artifacts result from positioning errors of the scanning electron beam, creating artifactual shifts in the images perpendicular to the scan lines (scan line shifts)...
February 3, 2018: Ultramicroscopy
Elena Pascal, Saransh Singh, Patrick G Callahan, Ben Hourahine, Carol Trager-Cowan, Marc De Graef
Transmission Kikuchi diffraction (TKD) has been gaining momentum as a high resolution alternative to electron back-scattered diffraction (EBSD), adding to the existing electron diffraction modalities in the scanning electron microscope (SEM). The image simulation of any of these measurement techniques requires an energy dependent diffraction model for which, in turn, knowledge of electron energies and diffraction distances distributions is required. We identify the sample-detector geometry and the effect of inelastic events on the diffracting electron beam as the important factors to be considered when predicting these distributions...
February 2, 2018: Ultramicroscopy
Jinsen Tian, Jing Wu, Yu-Lung Chiu
The intensity profiles of backscattered and secondary electrons from a pure Mg sample have shown a variation with sample thickness and acceleration voltage in the range of 5-30 kV, depending on the specimen holder used. The intensities of backscattered electron (BSE) and secondary electron (SE) signals increases with the sample thickness until saturation when using a scanning transmission electron microscopy (STEM) holder with a closed tube below the sample. However the SE signal increases to the maximum and then decreases with the sample thickness when using a transmission Kikuchi diffraction (TKD) holder with no shielding below the sample whereas the BSE signal again increases until saturation...
February 2, 2018: Ultramicroscopy
Niels de Jonge
The sample dependent spatial resolution was calculated for transmission electron microscopy (TEM) and scanning TEM (STEM) of objects (e.g., nanoparticles, proteins) embedded in a layer of liquid water or amorphous ice. The theoretical model includes elastic- and inelastic scattering, beam broadening, and chromatic aberration. Different contrast mechanisms were evaluated as function of the electron dose, the detection angle, and the sample configuration. It was found that the spatial resolution scales with the electron dose to the -1/4th power...
February 1, 2018: Ultramicroscopy
Philip J B Koeck
I suggest an electrostatic phase plate designed to broaden the contrast transfer function of a transmission electron microscope operated close to Scherzer defocus primarily in the low resolution direction. At higher defocus the low frequency behavior is equal to that close to Scherzer defocus, but CTF-correction becomes necessary to extend image interpretation to higher resolution. One simple realization of the phase plate consists of two ring shaped electrodes symmetrically surrounding the central beam. Since no physical components come into contact with the central beam and charge on the electrodes is controlled by an external voltage supply, problems with uncontrolled charging are expected to be reduced...
February 1, 2018: Ultramicroscopy
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