Adsorption Structures of Acetic Acid on Ge(100) at High Coverage

The adsorption of acetic acid on Ge(100) in the submonolayer and saturation coverages was investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At room temperature, acetic acid formed both monodentate and end-bridged structures on Ge(100) while paired adsorption structures also appeared. Increasing the amount of adsorbed acetic acid resulted in more pairing between adsorbates in straight and diagonal directions relative to the dimer row. The stabilization through pairing was theoretically confirmed for the adsorption structures and was very high for monodentate structures. At saturation coverage, the adsorbates are closely packed in the form of a square, parallelogram, or rectangle. After annealing at 380 K, the successive adsorptions showed 2 × n periodicity. Annealing at 410 K resulted in an ordered array of adsorbate over a long-range along the dimer row, which was identified to be several adsorbed acetic acid with the most stable on-top bidentate structure. Simulated STM images of the relatively stable configuration could explain the experimentally observed images.