| Abstract
| - Tuning of the electronic properties of semiconductors can be achieved by surface modification with organicmolecules. In this work, we study, by periodic density functional theory, the change in work function thatoccurs upon the modification of nominally hydrogen-terminated Si(100)-2 × 1 by chemisorption of substitutedstyrene molecules. Our results show that monolayers derived from 4-X-styrene molecules, with X being electrondonating groups or hydrogen, decrease the work function of the system. Conversely, monolayers derivedfrom 4-X-styrene molecules, with X being electron withdrawing groups, increase the work function of thesystem. For the molecules used in the modeling, the calculations indicate that the work function can besubstantially modified from −1.4 eV (XN(CH3)2) to +1.9 (XNO2) eV relative to H−Si(100)-2 × 1.Because the direction and magnitude of charge transferred upon chemisorption is the same for all molecules,the work function changes are not the result of band bending. The work function modification comes exclusivelyfrom the inherent dipoles of the molecules chemisorbed on the surface. The computed dipoles for the monolayersrange from −1.3 (XN(CH3)2) to +1.4 (XNO2) Debye. We conclude that substantial local control oversome of the electronic properties of silicon can be achieved by the chemisorption of dipole-containing molecules.
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