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Operating a cesium sputter source in a pulsed mode
2020
A scheme is presented for pulsing of a cesium sputter negative ion source by periodically switching on and off the high voltage driving the sputtering process. We demonstrate how the pulsed ion beam can be used in combination with a pulsed laser (6 ns pulse length) that has a 10 Hz repetition rate to study the photodetachment process, where a negative ion is neutralized due to the absorption of a photon. In such experiments, where the ion beam is used only for a small fraction of the time, we show that the pulsed mode operation can increase the lifetime of a cathode by two orders of magnitude as compared with DC operation. We also investigate how the peak ion current compares with the ion c…
Dielectric breakdown of fast switching LCD shutters
2017
Fast liquid crystal optical shutters due to fast switching, vibrationless control and optical properties have found various applications: substitutes for mechanical shutters, 3D active shutter glasses, 3D volumetric displays and more. Switching speed depends not only on properties of liquid crystal, but also on applied electric field intensity. Applied field in the shutters can exceed >10 V/micron which may lead to dielectric breakdown. Therefore, a dielectric thin film is needed between transparent conductive electrodes in order to reduce breakdown probability. In this work we have compared electrical and optical properties of liquid crystal displays with dielectric thin films with thickne…
Electrical and thermomechanical properties of CVI- Si3N4 porous rice husk ash infiltrated by Al-Mg-Si alloys
2017
Abstract The effect of following processing parameters on the electrical and thermomechanical properties of Al/Si3N4 deposited silica composites was investigated using the Taguchi method and analysis of variance (ANOVA): infiltration temperature and time, atmosphere, effect of Si3N4 coating, porosity content in the preforms, and magnesium content in the alloy. The contributions of each of the parameters to modulus of elasticity, electrical resistivity, coefficient of thermal expansion (CTE), and thermal diffusivity of the resulting composites were determined. The maximum modulus of elasticity and electrical resistivity of obtained composites were 265 GPa, and 1.37 × 10−3 Ω m, respectively. …
Performance evaluation and stability of silicide-based thermoelectric modules
2020
Abstract Long-term studies on thermoelectric generators based on N-type magnesium silicide (Mg2.01Si0.49Sn0.5Sb0.01) and P-type higher manganese silicide (Mn0.98Mo0.02Si1.73Ge0.02) materials are presented, in the operating temperature range of 200 °C–400 °C. Emphasis is put on the performance and reliability of the current collector configuration, especially on the hot side of the module, and on the thermomechanical stresses that are created during operation and lifetime testing as a result of large temperature gradients experienced across the thermoelectric legs. With silver (Ag) paste as contact material, the long term-stability of the uni-couples was carried out on non-metalized legs and…
How Gettering Affects the Temperature Sensitivity of the Implied Open Circuit Voltage of Multicrystalline Silicon Wafers
2019
The temperature sensitivity of the open circuit voltage of a solar cell is mainly driven by changes in the intrinsic carrier concentration, but also by the temperature dependence of the limiting recombination mechanisms in the cell. This paper investigates the influence of recombination through metallic impurities on the temperature sensitivity of multicrystalline silicon wafers. Spatially resolved temperature dependent analysis is performed to evaluate the temperature sensitivity of wafers from different brick positions before and after being subjected to phosphorus diffusion gettering. Local spatial analysis is performed on intra-grain areas, dislocation clusters and grain boundaries. Lar…
Fabrication and characterization of low cost Cu 2 O/ZnO:Al solar cells for sustainable photovoltaics with earth abundant materials
2016
Abstract The low cost electrodeposition method was used to grow Cu2O thin films and experimentally determine the optimal absorber layer thickness. Raman scattering studies indicate the presence of solely crystalline Cu2O and SEM images show that the thin films consist of grains with a pyramidal shape. The influence of the thickness of the light absorbing Cu2O layer on the basic characteristic of the heterojunction and their properties have been investigated using reflectivity, current–voltage (J–V), capacitance–voltage (C–V) and the external quantum efficiency (EQE) measurements. The depletion layer, the charge collection length of the minority carrier, and reflectivity are the main factors…
SiC MOSFET vs SiC/Si Cascode short circuit robustness benchmark
2019
Abstract Nowadays, MOSFET SiC semiconductors short circuit capability is a key issue. SiC/Si Cascodes are compound semiconductors that, in some aspects, show a similar MOSFET behaviour. No interlayer dielectric insulation suggests, in theory, Cascode JFETs as more robust devices. The purpose of this paper is to compare the drift and degradation of two commercial devices static parameters by exposing them to different levels of repetitive 1.5 μs short-circuit campaigns at 85% of its breakdown voltage. Short-circuit time has been set experimentally, and longer times result in catastrophic failure of MOSFET devices due to over self-heating. For this purpose, pre- and post-test short circuit ch…
Partial discharge of gel insulated high voltage power modules subjected to unconventional voltage waveforms
2016
Performances and duration of the new generation of high voltage power electronic components are dependent on dielectric materials aim to insulating their internal terminals. The presence of defects, some due to faults generated during the manufacturing process, but also due to the internal design of layers and connections, can cause local enhancements of electric field and consequently possible activity of partial discharges phenomena or other effects (aging, tracking) that may result in reduction of device reliability. Furthermore, the usage of unconventional voltage waveforms, like square waves or pulse width modulated waves, additionally increases the electrical aging of the insulation s…
Partial discharge detection and localization along medium voltage cables
2017
In the last years different partial discharge (PD) measuring techniques have been developed because PD diagnostic is the most widely tool to evaluate the insulation condition of a power cable. Recently non-conventional methods and sensors have been used in order to reach improved results in PD measurements. The purpose of this work is to perform measurements that allow to study the variation of pulses when they travel along a MV cable and to locate the pulse source through the time arrival difference of the pulses obtained from two sensors installed separately.
Deformation of bubbles in silicon gel insulation under an alternating electric field
2019
The behavior of silicone gel under electrical stress plays a significant role in the reliability and durability of high voltage electronic power devices due to its widespread use for the insulation of IGBT modules and other components. The charges accumulation at the bubble boundaries leads to significant displacements due to the establishment of Coulombic forces and the high deformability of colloidal system. The main purpose of this work is to validate a numerical approach useful to investigate, for a given silicone gel, the non-linear relation between the applied HVDC stress and the electric field over an air bubble within the insulation bulk. The analysis has been carried out by means o…