The antimony thin films were synthesized in ultra-high vacuum (base pressure: 4 î 10 À11 mbar) by evaporation of Sb 4 molecules from a resistance-heated effusive oven (temperature: 330 8C; deposition rate: 0.1 nm s À1 ; Sb: 99.9999 %, Johnson-Matthey). The layer thickness is given in monolayers of Sb atoms. The MoS 2 substrates were prepared by cleavage according to the procedure given in reference [13]. The AuSb 2 surface alloy was prepared starting from Au(111). [14] On this substrate the surface alloy AuSb 2 with the (100) orientation forms spontaneously, if less than one monolayer of antimony is deposited at room temperature. [15] The beetle-type STM [16] is located in an analysis chamber directly attached to the preparation chamber. [17] To increase image contrast, the STM data were electronically differentiated directly during acquisition. Therefore the STM images appear as if they are illuminated from the side.

The synthesis of diastereo- and enantiomerically pure beta-aminocyclopropanecarboxylic acids (beta-ACCs) is described. Starting from pyrrole, (rac)-4 is readily obtained, which was kinetically resolved by enzymatic hydrolysis. Subsequent oxidation of (-)-4 and deformylation gives rise to the cis-beta-ACC derivative (ent)-9, while (+)-10 was converted to the trans-beta-ACC derivative 8. Both 8 and (ent)-9 and their benzyl esters 13 and 16, being conformationally restricted beta-alanine or gamma-aminobutyric acid (GABA) derivatives, represent useful building blocks for peptides containing unnatural amino acids.

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