AVS 60th International Symposium and Exhibition
    Surface Science Wednesday Sessions
       Session SS+EM-WeA

Paper SS+EM-WeA1
Monte Carlo Simulation Studies of Ge(100)-2 × 1 Surface Chemistry

Wednesday, October 30, 2013, 2:00 pm, Room 201 A

Session: Semiconductor Surfaces and Interfaces
Presenter: B. Shong, Stanford University
Authors: B. Shong, Stanford University
S.F. Bent, Stanford University
Correspondent: Click to Email
Organic functionalization of semiconductor surfaces is of interest due to its possibilities for forming tailorable organic-inorganic interfaces. The (100) surface of Si or Ge reconstructs to a highly ordered 2 × 1 pattern under proper vacuum preparation. On these surfaces, only a few possible two-dimer configurations exist [1], and such a simple geometry allows facile introduction of stochastic simulations. However, to date, such methods have not been well utilized in organic functionalization studies. In this talk, we will introduce recent results in the integration of Monte Carlo (MC) simulations with other widely used techniques, and will show that the addition of MC simulations leads to deeper understanding of many coverage-dependent behaviors.

In the first example, self-assembly of two small organic building block molecules, ethylene and methanol, on the Ge(100) surface is explained through MC simulations based on density functional theory (DFT) calculations [2]. Characteristic one-dimensional adsorbate patterns along the rows of Ge(100) were observed in previous scanning tunneling microscope (STM) studies, where the dimers linearly aligned within the same rows are the nearest neighbor sites on Ge(100). Our DFT calculations show that the adsorption of ethylene is hindered next to another ethylene, whereas adsorption of methanol is facilitated by the presence of an adjacent methanol. Kinetic MC simulations based on the DFT-calculated adsorption probabilities predict adsorbate patterns that agree well with the experimental observations.

In another example, the adsorption of a bifunctional molecule, 1,3-benzenediol, is explored by a similar MC approach. Whether dual or single reaction occurs during attachment of bifunctional molecules is critical, since dual binding adsorbates terminate the reaction site. Fourier transform infrared (FTIR) spectroscopy experiments as well as DFT calculations show that 1,3-benzenediol adsorbed on Ge(100) assumes only one type of dual binding configuration. This limitation simplifies the geometrical dimension of the adsorption phenomena. The fraction of singly bound adsorbates increases nonlinearly with increasing coverage according to X-ray photoelectron spectroscopy (XPS) measurements. This behavior is explained through MC simulations showing that unreacted functionalities appear on the reactive surface due to limitations in available adjacent sites. In conclusion, we demonstrate the potential of combining MC simulations with other techniques in studies of semiconductor surface chemistry.

1. B. Shong, K.T. Wong, S.F. Bent, J. Phys. Chem. C 116, 4705 (2012).

2. B. Shong, S.F. Bent, J. Phys. Chem. C 117, 949 (2013).