Hydrogen adsorption studies in micro-size cobalt dots
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Hydrogen desorption curves were obtained from a sample composed of a square arrangement of Co dots with average diameter of 4.4 μm, separated by a distance of 11.6 μm. A macroscopic sample of Co dots grown on a 2.5 × 2.5 cm Si substrate was made by standard lithographic techniques and used in these experiments. Thermal programmed desorption (TPD) was performed under ultra-high vacuum conditions. Hydrogen TPD curves were obtained from a 1 × 1 cm Co dots samples displaying a maximum of intensity at 425 K. Hydrogen TPD curve was also obtained from 1 cm× 1 cm samples of Co films and Co foils for comparison. The hydrogen TPD curves have decreasing intensity from the Co foils to the Co dots and finally to the Co films. This indicates that there are more sites for hydrogen adsorption on the Co dots than in the Co films. This is a surprising result because there is approximately 8.7 times less Co atoms exposed in the Co dots that in the Co film sample. A desorption energy of 27 kcal/mol was obtained for the Co dots suggesting that hydrogen is adsorbed on an hcp hollow site of the Co dot crystalline structure.
KeywordsAtomic Force Microscopy High Resolution Transmission Electron Microscopy Hydrogen Adsorption Hydrogen Desorption Desorption Energy
This research was partially supported by grants from the Chilean Government (FONDECYT 1030642 and 1060634), Fundacion Andes and MECESUP PUC0006 and UCh0205. We thank M. Moreno for SEM analyses, A. Zuñiga for HR-TEM analyses, M. Pino for XRD analyses, J. P. Staforelli and A. Pernas for helping with the TDS experiments and optical characterization of the Co dots.
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