3 research outputs found
Self-Assembled and Field-Induced 2D Structures of Glutaric Acid on Cu(110)
We
have investigated the adsorption structures of glutaric acid
(HOOC–(CH<sub>2</sub>)<sub>3</sub>–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 (WO<sub>3</sub>) 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