Adsorption of L-Alanine on Cu(111) Studied by Scanning Tunnelling Microscopy

The adsorption of L-alanine on Cu(111) surface is studied by means of scanning tunnelling microscopy under ultra-high vacuum conditions. The results show that the adsorbates are chemisorbed on the surface, and can form a two-dimensional gas phase, chain phase and solid phase, depending on deposition rate and amount. The adsorbed molecules can be imaged as individual protrusions and parallel chains in gas and chain phases respectively. It is also found that alanine can form (2×2) superstructure on Cu(111) and copper step facet to <110> directions in solid phase. On the basis of our scanning tunnelling microscopic images, a model is proposed for the Cu(111)(2×2)-alanine superstructure. In the model, we point out the close link between \langle 110\rangle-direction hydrogen bond chains with the same direction copper step faceting.