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Thermoelectricity and Seebeck effect have long been observed and validated in bulk materials. With the development of advanced tools of materials characterization, here we report the first observation of such an effect in the nanometer scale: in situ directional sputtering of several thermoelectric materials inside electron microscopes. The temperature gradient introduced by the electron beam creates a voltage-drop across the samples, which enhances spontaneous sputtering of specimen ions. The sputtering occurs along a preferential direction determined by the direction of the temperature gradient. A large number of nanoparticles form and accumulate away from the beam location as a result. The sputtering and re-crystallization are found to occur at temperatures far below the melting points of bulk materials. The sputtering occurs even when a liquid nitrogen cooling holder is used to keep the overall temperature at -170 °C. This unique phenomenon that occurred in the nanometer scale may provide useful clues to understanding the mechanism of thermoelectric effect. [ABSTRACT FROM AUTHOR]

This paper investigates the radial distributions of potential and electron density in free expansion plasma induced by an electron beam irradiating on the plate. The region of plasma production is assumed to be cylindrical, and the plasma expansion is assumed to be from a cylindrical source. Therefore, the one-dimensional model in cylindrical coordinates is employed in order to analyze the radial distributions of the potential and electron density. The Runge-Kutta method and the perturbation method are utilized in order to obtain the numerical and approximate solutions, respectively. The results reveal that the decrease in the initial ion energy makes most of the ions gather near the plasma production region and reduces the distribution of the average positive potential, electron, and ion density along the radial direction. The oscillation of steady-state plasma along the radial direction is also presented in this paper. The ions induce a larger amplitude of oscillation along the radial direction than do electrons because the electrons oscillate around slowly moving ions due to a far smaller electron mass than ion mass. The radial distributions of the positive potential and electron density predicted from this study are compared with the available experimental data. [ABSTRACT FROM AUTHOR]

Electron injection into a graphene sheet through a slanted armchair graphene nanoribbon (AGNR) is investigated. An incident mode, or subband, in the AGNR is valley-unpolarized. Our attention is on the valley-resolved nature of the injected electron beams and its connection to the incident mode. It is known for a normal injection that an incident mode will split symmetrically into two valley-resolved beams of equal intensity. We show, in contrast, that slanted injections result in asymmetric valley-resolved beam splitting. The most asymmetric beam splitting cases, when one of the valley-resolved beams has basically disappeared, are found and the condition derived. This is shown not due to trigonal warping because it holds even in the low incident energy regime, as long as collimation allows. These most asymmetric beam splitting cases occur at energies within an energy interval near and include the subband edge of an incident mode. The physical picture is best illustrated by a projection of the slanted AGNR subband states onto that of the 2D graphene sheet. It follows that the disappearing of a valley-resolved beam coincides with the situation that the group velocities of the projected states in the corresponding valley are in backward directions. [ABSTRACT FROM AUTHOR]

Monitor units (MUs) calculated by radiotherapy treatment planning systems need to be verified independently. At extended source-surface distances (SSDs), different output factors (OFs) can be given by different independent MU checking packages due to the calculation methods used and assumptions made within them. The accuracy of two software packages - RadCalc® (LifeLine Software Inc., Austin, USA) and eDatabook (Y. Wang, Radiation Oncology Institute, Sydney, AUS) - was determined by comparing the calculated OFs directly to measured OFs for a series of standard electron cutouts on an Elekta Synergy linear accelerator at standard and extended SSDs (100 cm and above). For the majority of the measurements made, eDatabook provided OFs closer to the measured value than RadCalc; however, in two cases, eDatabook was unable to provide a factor. RadCalc failed to calculate the OFs accurately at extended SSDs as its calculation is based on the assumption that the established effective-SSD curve can accurately predict the data where there are no measurements available. The accuracy of eDatabook is due to its use of a linear interpolation to determine the OF at an extended SSD when there are no measurement data available. [ABSTRACT FROM AUTHOR]

Imaging plates (IPs) are commonly used as passive detectors in laser-plasma experiments. We calibrated at the ELSA electron beam facility (CEA DIF) the five different available types of IPs (namely, MS-SR-TR-MP-ND) to electrons from 5 to 18 MeV. In the context of diagnostic development for the PETawatt Acquitaine Laser (PETAL), we investigated the use of stacks of IP in order to increase the detection efficiency and get detection response independent from the neighboring materials such as X-ray shielding and detector supports. We also measured fading functions in the time range from a few minutes up to a few days. Finally, our results are systematically compared to GEANT4 simulations in order to provide a complete study of the IP response to electrons over the energy range relevant for PETAL experiments. [ABSTRACT FROM AUTHOR]

Evolution in emission of secondary electrons and backscattered electrons from thermally oxidized silicon sample during a single line-scan of a focused electron beam was measured. The influence of charging-up of the sample surface on the electron emission was analytically modeled. The detected current Ic of these electrons decreased sharply at the initial scanning stage and turned steady. The ratio of Ic to incident primary-beam current (Ip) at the steady state could be expressed in terms of "scanning line density" (λin), i.e., the number of incident electrons per unit scan distance. It was found that the ratio of Ic=Ip increased monotonously with decreasing λin. Furthermore, no difference in the change of the Ic=Ip at the steady states was observed with interval, i.e., the time between consecutive single-line scans at the same position, ranging from 10 μs to 500 ms. This result indicates that attenuation of the charge at the sample surface during the single line-scan is neglectable. An analytical model was proposed for correlating Ic=Ip, the potential at the irradiated position (Vs) and kin. The calculated Ic=Ip coincided quantitatively with the experimentally determined ratio. Besides, the analytical model showed that higher magnitude and less variation in Ic=Ip during the single line-scan can be expected with lower λin, which was experimentally verified. The parameter λin can be equally controlled through Ip and the line-scan speed v. [ABSTRACT FROM AUTHOR]

Atomic resolution transmission electron microscopy records the spatially resolved scattered electron density to infer positions, density, and species of atoms. These data are indispensable for studying the relation between structure and properties in solids. Here, we show how this signal can be augmented by the lateral probability current of the scattered electrons in the object plane at similar resolutions and fields of view. The currents are reconstructed from a series of three atomic resolution TEM images recorded under a slight difference of perpendicular line foci. The technique does not rely on the coherence of the electron beam and can be used to reveal electric, magnetic, and strain fields with incoherent electron beams as well as correlations in inelastic transitions, such as electron magnetic chiral dichroism. [ABSTRACT FROM AUTHOR]

A pulsed electron beam accelerated at 12 kV with a duration of 40 µs per pulse is obtained from a Penning discharge with a hollow anode and two cathodes. The electrons are extracted through a hole in one of the cathodes and focused by a pair of coils. The electron beam has a diameter of a few mm in the cross section, while the beam current reaches peak values of 400 mA, depending on the magnetic field inside the focussing coils. This relatively inexpensive and compact device is suitable for the irradiation of small material samples placed in high vacuum. [ABSTRACT FROM AUTHOR]

Electron Beam Induced Current (EBIC) measurements were used to produce cross sectional images of superjunction power transistors. These images show how the depletion width expands under reverse bias. Superjunctions are alternating p- and n-type doped vertical columns placed between drain and source in a power transistor (Deboy et al., in: Proc. IEDM, 983-685 (1998); Lorenz et al., in: Proc. PCIM Europe, 250-258 (1998)). These columns allow a higher substrate doping of the drift region, resulting in a lower on-state resistance while still maintaining a high breakdown voltage. When the device is reverse biased, the space charge region of the superjunction should expand symmetrically due to the homogeneous doping (in the n and p region) until the complete device depletes. The depletion process was also visualized using voltage contrast (VC) measurements. Here the secondary electron signal was detected when the device was reverse biased. We show that EBIC and VC measurements can provide valuable input for process tuning and process simulations, enabling the use of smaller dimensions and higher doping levels [ABSTRACT FROM AUTHOR]

Moiré method in scanning transmission electron microscopy allows observing a magnified two-dimensional atomic column elemental map of a higher pixel resolution with a lower electron dose unlike conventional atomic column mapping. The magnification of the map is determined by the ratio between the pixel size and the lattice spacing. With proper ratios for the x and y directions, we could observe magnified elemental maps, homothetic to the atomic arrangement in the sample of SrTiO3 [0 0 1]. The map showed peaks at all expected oxygen sites in SrTiO3 [0 0 1]. [ABSTRACT FROM PUBLISHER]

We demonstrate the dual-band operation of a relativistic backward wave oscillator (RBWO) whose output is a linearly polarized TE \(_{\mathrm {\mathbf {11}}}\) -mode. The RBWO consists of two cylindrical sections with sinusoidal corrugations where the downstream section is axisymmetric and the upstream section has combined left- and right-single-fold spiral corrugations. We show that generation of 10 GHz is realized when the axisymmetric section operates as a BWO with the operating TM \(_{\mathrm {\mathbf {01}}}\) -mode and the combined spiral section operates as a Bragg reflector that converts the backward TM \(_{\mathrm {\mathbf {01}}}\) -mode to a linearly polarized forward TE \(_{\mathrm {\mathbf {11}}}\) -mode. For the same electron beam parameters, generation of 7 GHz is realized when the combined spiral section operates as a BWO with the operating TE \(_{\mathrm {\mathbf {11}}}\) -mode. We also present the possibility to change the duration of generation at each frequency within a microwave pulse by changing the electron beam current. In addition, one can change the output frequency by changing the values of the guide magnetic field near the region of cyclotron absorption. [ABSTRACT FROM PUBLISHER]

By imaging the spatial intensity distribution of the electrons from a Stoffel-Johnson (SJ) type low energy electron source for inverse photoemission spectroscopy (IPES), we find that the focus is distorted when the beam current exceeds the limiting value due to space charge effect. The space charge effect and the contact potential difference suppress the beam current at low energies (<10 eV). In this work, we show that these limitations of the SJ source can be overcome by compensation of the contact potential difference between the cathode and the lens electrodes and an uniform well focused electron beam with the set kinetic energy can be obtained. The size of the electron beam is around 1 mm full width at half maximum over the whole energy range of 5 to 30 eV generally used for IPES. The compensation of the contact potential difference also enhances the beam current substantially at low energies (<10 eV) and uniform beam current is achieved for the whole energy range. We find that the drift in the electron beam position is sensitive to the lens electrode separation and it is about 1 mm over the whole energy range. By measuring the n = 1 image potential state on Cu(100), we show that the resolution is better when the cathode filament current is set to lower values. [ABSTRACT FROM AUTHOR]

When an un-gated thermionic cathode is operated in a radio-frequency gun, some fraction of the emitted electrons will return to the cathode due to the change in sign of the electric field in the gun. This back-bombardment current causes heating of the cathode, and this reduces the ability of the cathode heater to control the bunch charge. In this paper, we investigate the fundamental factors in single-frequency back-bombardment for a short-gap electron gun. Simulations revealed that the back-bombardment power depends strongly on the operating frequency and the bunch charge. Additionally, the use of a two-frequency TM010/TM{020} electron gun to mitigate this effect was investigated which revealed that the effectiveness of this technique depends strongly upon single-frequency back-bombardment power but with the optimal reduction in back-bombardment power (62% of the baseline) occurring in the low-frequency limit. [ABSTRACT FROM PUBLISHER]

Results of one-dimensional Particle-in-Cell numerical simulations of mechanism of sub-nanosecond high-voltage pulsed discharge in nitrogen are presented. It is shown that the decrease of the cathode-anode gap changes drastically both the discharge dynamics and mechanism of runaway electrons generation responsible for the discharge initiation. It is obtained that the virtual cathode exists only during tens of picoseconds for short gaps. The conditions when the virtual cathode is not formed are found. Also, the comparison between the experimental [Rybka et al., Tech. Phys. Lett. 38, 653 (2012)] and simulation results indicates the dominant role of the virtual cathode in termination of runaway electrons generation and on separate nature of emission sources from the cathode surface. [ABSTRACT FROM AUTHOR]