| dc.description.abstract | Abstract
This thesis is divided into three parts. First, we employed cyclic
voltammetry (CV) and in situ scanning tunneling microscopy (STM)
to study the spatial structures of aniline on the reconstructed and
unreconstructed Au(111) in 0.1 mM aniline + 0.1 M H2SO4.
Depending on the electrode potential, three highly ordered
adlattices are identified as the coverage increased with potential.
Real-time STM imaging revealed the kinetics of two-dimensional
phase transitions in the aniline adlayer. Order structures,(?21 × ?43) and (2?13 × ?19) of aniline are identified for the potential regions between 0.7 and 0.72 V respectively. Another structure of (4 × ?3) was observed between 0.9 and 0.95 V. The surface coverage of aniline increased from 0.088 to 0.11, then to 0.125 near saturation. In situ STM imaging revealed that these phase transitions were reversible with respect to potential. When [aniline] > 10 mM, STM discerned an ordered array, (4 × 2?3). This adlayer has a coverage of 0.25 , much higher than those formed at lower concentration.
Second, high-resolution scanning tunneling microscopy (STM) has been used to examine the real-space structures of
1,6-hexanedithiol (HDT) on well-ordered Au(111) electrode in 0.1
M HClO4. The concentrations of HDT in the aqueous dosing
solutions, together with electrochemical potential, determine the
coverage and spatial arrangements of HDT ad-molecules. Low
dosages result in two order structures, (2 × ?7), θ = 0.167 and (4 ×
?3), θ = 0.25. The former is assigned as a monolayer of dithiols
adsorbed via two sulfur headgroups. The latter is assigned as
dithiols adsorbed via only one thiol group. High dosages
respectively resulted in (4 × ?3), θ = 0.25 and some more densely
packed structures at 0.3 ~ 0.5 V, which suggested a stand-up configuration of the ad-molecules.
Third, We have employed in situ STM to study the structures of
benzenethiol and the reconstruction of well-ordered Au(100)-(hex)
electrodes in 0.1 M HClO4. When dosage is low at 0 V, ordered
Au(100)-(hex) surface was transformed into Au(100)-(1 × 1) structure with monoatomic high mesas. STM molecular resolution
revealed the formation of a highly ordered adlattice of (?2 × ?2) , θ
= 0.5, between 0 ~ 0.5 V on Au(100) - (1 × 1). The adlayer consisted of stand-up benzenethiol molecules bonded to gold surface through the Au-S coordination. Intermolecular interaction of benzenethiol molecules is attributed to π-π stacking of phenyl groups. The interaction of Au-S and lateral π-stacking produced island features on terraces, a phenomenon associated with severe etching of Au(100) surface, and aggregations of more benzenethiol ad-molecules at 0.6 ~ 0.7 V. | en_US |