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| 2. |
- Cortes-Escobedo, Claudia A., et al.
(författare)
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Mechanically activated Pt-Ni and Pt-Co alloys as electrocatalysts in the oxygen reduction reaction
- 2014
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 1879-3487 .- 0360-3199. ; 39:29, s. 16722-16730
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of powders of platinum with nickel or cobalt to obtain Ni0.75Pt0.25 or Co0.75Pt0.25 were mechanical alloyed by high energy ball milling. The results of crystal structure, morphology and electrocatalytic performance are presented for mechanically activated powders after 3 and 9 h of ball milling. Total solid solutions of Ni and Co with platinum were analyzed by X-ray diffraction after 3 h of ball milling. After 9 h of ball milling, in both cases, the total solid solution was accompanied by the appearance of NiO or CoO and ZrO associated with a redox reaction with the milling media. The presence of zirconium monoxide was confirmed by energy dispersive spectroscopy analysis. In both cases, an amorphization was detected. X ray absorption spectroscopy measurements showed changes in atomic and electronic environment of platinum, a reduction of the distance to the first coordination sphere and increased d-band vacancy vs pure Pt and Pt nanoparticles were observed for both studied systems. The electrocatalytic activity was determined using cyclic and linear voltammetry. The Co0.75Pt0.25 alloy milled for 9 h showed a higher electrochemical activity for the oxygen reduction reaction (ORR) compared with the other samples, including Pt-Etek. The degree of the ORR electrochemical activity was correlated with the presence of ZrO, which could affect the oxygen adsorption and improve the catalytic activity for the oxygen reduction reaction. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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| 3. |
- Fjer, M., et al.
(författare)
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Low frequency noise in strained Si heterojunction bipolar transistors
- 2011
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Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 58:12, s. 4196-4203
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Tidskriftsartikel (refereegranskat)abstract
- The low frequency noise performance of strained Si heterojunction bipolar transistors (sSi HBTs) is presented for the first time. Conventional SiGe HBTs and Si bipolar junction transistors (BJTs), processed with strained Si devices, were also measured as a reference. It is found that a lower noise level is obtained in sSi HBTs for a given collector current, which is important for circuit applications, compared with either SiGe HBTs or Si BJTs. However, sSi HBTs exhibit greater low frequency noise compared with other devices at fixed base current. This is due to the presence of defects that are caused by the integration of the strain-relaxed buffer in the fabrication of sSi HBTs. The relationship between low frequency noise and defects is supported by material characterization. © 2011 IEEE.
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| 4. |
- Persson, Stefan, et al.
(författare)
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Strained-Silicon Heterojunction Bipolar Transistor
- 2010
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Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 57:6, s. 1243-1252
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Tidskriftsartikel (refereegranskat)abstract
- Experimental and modeling results are reported for high-performance strained-silicon heterojunction bipolar transistors (HBTs), comprising a tensile strained-Si emitter and a compressively strained Si0.7Ge0.3 base on top of a relaxed Si0.85Ge0.15 collector. By using a Si0.85Ge0.15 virtual substrate strain platform, it is possible to utilize a greater difference in energy band gaps between the base and the emitter without strain relaxation of the base layer. This leads to much higher gain, which can be traded off against lower base resistance. There is an improvement in the current gain beta of 27x over a conventional silicon bipolar transistor and 11x over a conventional SiGe HBT, which were processed as reference devices. The gain improvement is largely attributed to the difference in energy band gap between the emitter and the base, but the conduction band offset between the base and the collector is also important for the collector current level.
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