Study of Silicon-metal Interaction in Adsorption Process: An Ab-initio Approach
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Study of Silicon-metal Interaction in Adsorption Process: An Ab-initio Approach Sudip Chakraborty1,2 S. V. Ghaisas,1,a) and Chiranjib Majumder2 1
Department of Electronic Science, University of Pune, Pune 411007 , India
2
Chemistry Division, Bhabha Atomic Research Center, Trombay, Mumbai 400085, India
Abstract: The formation of metal silicide plays important role in deciding the nature of the contact on silicon.Due to their chemically neautral nature,Au and Ag are used as contact metals in various devices.In particular the role of silicides is known to be crucial in defining the behavior of the electrical contact. The interaction of these metals with silicon at cluster level is still under the study.For naoscale devices, the nature at such interaction carries lot more inportance. Bulk Gold silicide(Cohesive energy ~ 3.81eV/atom) shows higher stability compared to silver silicide(Cohesive enrgy ~ 2.95 eV/atom). In the present work we show computational results based on Density Functional Theory(DFT) of Si cluster adsorption on Ag(111) surface and compare with the results of Si adsorption on Au(111). These results bring out the difference in Si cluster-metal surface interactions at the nanoscale. In particular the Si island-metal surface interaction shows island size dependence. We have presented results for most stable orientations only.
a)corresponding author: [email protected] Keywords: Metal surface; silicon cluster; adsorption; projected density of states; binding energy; charge transfer.
I. Introduction: Metal-silicon interaction has been an important subject of study due to their use as inevitable external conducting contacts required in various devices [1-3]. Gold has been used as the contact material[4] due to its chemical neutrality[5] and electrical suitability[6] as ohmic contact on silicon. Recent experiments on Si nanowires with SiO2 coating also indicate the device favorable coating properties of gold nanoparticles [7] on nanowires. Silver has similar chemical properties as gold, however, it is not used as a contact material for silicon, at least in most of the small scale devices. The formation of metal silicides plays important role in deciding the nature of the contact on silicon. Both
Au and Ag are known to form silicides [8]. Gold silicide shows [9] higher thermodynamic stability(cohesive energy 3.81eV/atom) compared to silver(cohesive energy 2.95eV/atom). Experiments on ion beam mixing [10] of Au-Si and Ag-Si interfaces show that at room temperature Au can form a silicide on mixing, but Ag does not [8]. It’s only at higher (400oc) temperatures, that Ag silicide can be formed.[8] This implies that kinetic reaction barrier of Au-Si is smaller compared to Ag-Si interface reaction. Computational studies performed on Si clusters on Au(111) surface[11] show that at 0K the Si cluster adsorption on Au surface leads to Au surface distortion indicating the tendency of Au and Si to interact strongly. In the present work we show computational results based on Density Functional Theory(DFT)
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