First-principles time-dependent simulation of laser assisted desorption of hydrogen atoms from H–Si(111) surface

Abstract

The dynamics of hydrogen desorption from H-terminated silicon surface clusters has been simulated in the framework of real space time-dependent density functional theory complemented with molecular dynamics for ions. It has been demonstrated that by choosing an appropriate frequency and intensity of the laser it is possible to remove the hydrogen layer from the surface without destroying the structure of underlying silicon. At the laser field intensities used in the current study ͑0.5-2.0 V/Å͒ the desorption process is notably nonlinear. © 2011 American Institute of Physics. ͓doi:10.1063/1.3580563͔Bond scission by laser pulses is an ideal way to induce and control chemical reactions. [1][2][3][4] Selective control of surface reactions 4 is especially desired as it allows patterning of reaction areas by creating dangling bonds and fabricating functionalized structures by active manipulation of chemical bonds. 5 Among the many surfaces explored by experiments, the hydrogen terminated Si surface is the most studied system. [6][7][8][9] Desorption of atoms from surfaces can be induced by electronic excitations directly by coupling between the laser field and the bond electrons or by indirect mechanisms, where the excitation of the substrate transferred to the desorption coordinates. [10][11][12] Desorption of atoms can also be initiated by other forms of energy transfer to the system, e.g., by moving a scanning tunneling microscope ͑STM͒ tip close to the surface. 10,13 The hydrogen-terminated Si͑111͒ surface is one of the simplest and basic examples of a semiconductor interface. Hydrogen atoms chemisorbed onto dangling bonds of the silicon substrate form a protection layer that prevents oxidation and adsorption of impurities. In spite of its apparent simplicity, the hydrogenation of H-Si͑111͒ surface is important for both industrial applications and understanding of fundamental processes and mechanisms, including those that occur in more complicated systems.In this letter, we will carry out first-principles timedependent simulations of laser assisted hydrogen desorption from a Si͑111͒ surface. The physical mechanisms behind the laser induced desorption are not fully understood and computer simulations are indispensable to gain physical insights of the problem. The real space real time density functional calculation complemented with Ehrenfest molecular dynamics simulation presented in this letter shows that the hydrogen layer can be removed from a silicon surface with a proper choice of laser parameters. This process, which does not destroy the underlying silicon surface, is highly nonequilibrium and nonlinear. The results of the study enhance our understanding of the dynamics of electrons and atoms in and on surfaces.Hydrogen desorption from silicon has been subject to various theoretical studies 14-18 including first-principles time-dependent simulations. 19 The latter work simulated the STM induced desorption: The Si-H bond of the hydrogenated S͑111͒ surface was subjected an excitation by promoting electrons from...

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