Adsorption, Assembly, and Oligomerization of Aspartic Acid on Pd(111)

Abstract

The surface chemistry of l-aspartic acid is studied on Pd(111) in ultrahigh vacuum using reflection absorption infrared spectroscopy (RAIRS) and scanning tunneling microscopy (STM) as a function of sample temperature and coverage. Density functional theory (DFT) calculations are carried out to supplement the experimental results. At low temperatures, the dominant surface species was found to be monoaspartate species at all the experimental coverages. The monoaspartate species undergo extensive intermolecular hydrogen-bonding interactions and form extended two-dimensional ordered structures, forming either a honeycomb pattern or linear-row structures. At room temperature, aspartic acid undergoes a self-polymerization reaction to form oligosuccinimide networks, although some individual monoaspartate species are also observed.