l-Cysteine Adsorption Structures on Au(111) Investigated by Scanning Tunneling Microscopy under Ultrahigh Vacuum Conditions

Abstract

Adsorption structures formed upon vapor deposition of the natural amino acid L-cysteine onto the (111) surface of gold have been investigated by scanning tunneling microscopy under ultrahigh vacuum conditions. Following deposition at room temperature and at cysteine coverages well below saturation of the first monolayer, we found coexistence of unordered molecular islands and extended domains of a highly ordered molecular overlayer of quadratic symmetry. As the coverage was increased, a number of other structures with local hexagonal order emerged and became dominant. Neither of the room temperature, as-deposited, ordered structures showed any fixed rotational relationship to the underlying gold substrate, suggesting a comparatively weak and nonspecific molecule-substrate interaction. Annealing of the cysteine-covered substrate to 380 K lead to marked changes in the observed adsorption structures. At low coverages, the unordered islands developed internal order and their presence started to perturb the appearance of the surrounding Au(111) herringbone reconstruction. At coverages beyond saturation of the first monolayer, annealing led to development of a ( radical3 x radical3)R30 degrees superstructure accompanied by the formation of characteristic monatomically deep etch pits, i.e., the behavior typically observed for alkanethiol self-assembled monolayers on Au(111). The data thus show that as-deposited and thermally annealed cysteine adsorption structures are quite different and suggest that thermal activation is required before vacuum deposited cysteine becomes covalently bound to single crystalline Au(111).

Molecular Tips for Scanning Tunneling Microscopy: Intermolecular Electron Tunneling for Single-molecule Recognition and Electronics

“…The images exhibit closely packed arrays of cysteine molecules adsorbed on the surface. This adlayer structure agrees well with that observed with a metal STM tip, 29 demonstrating that chiral molecular tips can reveal the adsorbed structures at the molecular level. The most important observation is the extent of electron tunneling between the chiral molecular tips and the cysteine enantiomers.…”

Electrochemically controlled self-assembled monolayers characterized with molecular and sub-molecular resolution

“…75 4.2.3 Thiol and disulfide groups: cysteine and cystine/ Au(111) give the same surface structure. As an important amino acid and the only -SH containing natural amino acid, assembling of cysteine monolayers on various substrates in different environments 72,118,[127][128][129][130][131][132] has attracted significant attention ever since their introduction. A variety of L-cysteine and cystine assembling conditions will be addressed in Sections 4.3 and 4.4.…”

“…This is in contrast to the observations in UHV, where both cysteine adlayer and herringbone reconstruction lines from Au(111) are visible by UHV-STM. 130,131 Cluster structures are found on Au(111) in both UHV 130 and liquid environment 72 but the unit cell and the cluster size are different, with six and four cysteine molecules assigned to each SAM cluster in liquid and UHV, respectively. This is in contrast to cysteine SAMs on Au (110).…”

Interface Electronic Structures of the L-Cysteine on Noble Metal Surfaces Studied by Ultraviolet Photoelectron Spectroscopy

“…Therefore, an understanding of the interaction of L-cysteine with metal surfaces is necessary. There have been experimental and theoretical research studies that examined the behavior of L-cysteine adsorbed on different faces of gold [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], silver [20][21][22][23], and copper [24][25][26] metallic single crystals as model systems for understanding the interaction of L-cysteine with metal surfaces and also L-cysteine adsorbed on some other surfaces considering technological interests [27][28][29][30][31][32][33][34][35]. In the experimental studies, the L-cysteine sample for investigation was formed using either the self-assembly or evaporation method.…”