Self-Assembled and Field-Induced 2D Structures of Glutaric Acid on Cu(110)

We have investigated the adsorption structures of glutaric acid (HOOC–(CH₂)₃–COOH) on the Cu(110) surface as a function of coverage by using scanning tunneling microscopy (STM) and reflection–absorption IR spectroscopy (RAIRS). Above a critical coverage, the molecules self-assemble on Cu(110) into three kinds of well-organized structures at room temperature. In contrast, glutaric acid molecules diffuse freely on Cu(110) below a critical coverage, and so cannot form ordered structures. Interestingly, we were able with STM to fabricate novel ordered structures of glutaric acid that cannot naturally occur at room temperature. We conclude that this new structure is created through field-induced assembly

Functional Group-Selective Adsorption Using Scanning Tunneling Microscopy

In this study, we selectively enhanced two types of adsorption of 3-mercaptoisobutyric acid on a Ge(100) surface by using the tunneling electrons from an STM and the catalytic effect of an STM tip. 3-Mercaptoisobutyric acid has two functional groups: a carboxylic acid group at one end of the molecule and a thiol group at the other end. It was found that the adsorption occurring through the carboxylic acid group was selectively enhanced by the application of electrons tunneling between an STM tip and the surface. Using this enhancement, it was possible to make thiol group-terminated surfaces at any desired location. In addition, <i>via</i> the use of a tungsten STM tip coated with a tungsten oxide (WO₃) layer, we selectively catalyzed the adsorption through the thiol group. Using this catalysis, it was possible to generate carboxylic acid group-terminated surfaces at any desired location. This functional group-selective adsorption using STM could be applied in positive lithographic methods to produce semiconductor substrates terminated by desired functional groups

Comparison and Contrast Analysis of Adsorption Geometries of Phenylalanine versus Tyrosine on Ge(100): Effect of Nucleophilic Group on the Surface

The discrepancy of geometric configuration between phenylalanine and tyrosine adsorbed on Ge(100) surfaces was investigated using scanning tunneling microscopy (STM) in conjunction with density functional theory (DFT) calculations and core-level photoemission spectroscopy (CLPES). The study focused on the role of nucleophilic group (hydroxyl group) on phenyl ring of tyrosine, and we elucidated the difference of the adsorption geometry between phenylalanine and tyrosine on Ge(100) surfaces. We first confirmed that the “O–H dissociated–N dative bonded structure” was the most favorable structure in both molecules at low coverage by results of CLPES and DFT calculations. Geometric differences for the adsorption configurations between phenylalanine and tyrosine were observed: the phenyl ring of phenylalanine was aligned axially with respect to the Ge(100) surface, whereas that of tyrosine was tilted, as determined by DFT calculations. In sequence, we found out the results of STM images to confirm DFT results. We determined the different geometric configurations are attributed to the nucleophilic hydroxyl group of tyrosine, which creates an uneven charge distribution