Chemistry Reference
In-Depth Information
Fig. 10.1 Schematic of 1-D
surface modulated
distribution OH ? H
2
O/H
2
O/
OH ? H
2
O on Pt(111). The
width of H
2
O region d was
400 lm. Reprinted with
permission from Ref. [
7
].
Copyright 2008, American
Physical Society
switching and desorption, as well as to initiate chemical reactions such as disso-
ciation, bond formation, dehydrogenation and cis-trans conversion. STM has also
been used to study sequential bond dissociation/formation reactions propagating
along self-assembled molecular chains [
1
]. Here I show a new class of single-
molecule chemistry with STM involving H bonds. By engineering a platform of H-
bonded one-dimensional chains on a Cu(110) surface we are able to transfer an H-
atom from one end of the chain to the other.
H-transfer reactions play a crucial role in many chemical and biological processes
[
2
], yet still imperfectly understood, which is also related to many functional
materials such as proton conductors [
3
], organic ferroelectric compounds [
4
], and
confined liquids mimicking protein channels [
5
]. H-bond between water molecules is
the path of H-transfer and hydronium ion is structurally-transferred from one
location to the other through the sequential exchange of H- and covalent bond in
condensed phase. This process is well-known as Grotthuss mechanism [
6
] and
(H
+
) in aqueous solutions compared to other cations. The elementary processes of
H-transfer have been simulated by ab initio calculations, providing the detailed
picture of the transportation mechanism. However the Grotthuss mechanism has
never been directly observed in experiment. This is because it is extremely difficult
to eliminate complex environmental effects in conventional spectroscopic methods
that rely on ensemble from many species.
In surface chemistry, H-atom/proton transfer is of fundamental importance in
the elementary processes of electrode chemistry, heterogeneous catalysis and
energy productions. The experimental characterization is still extremely limited.
Recently, H-atom migration on a metal surface via the relay mechanism was
investigated using a combination of the laser-induced thermal desorption (LITD)
and the micro-meter scale x-ray photoelectron spectroscopy (micro-XPS) [
7
]. The
unique approach to observe the H-transfer is illustrated in Fig.
10.1
. First 2-D
H-bonding network composed of H
2
O and OH is formed on Pt(111) and then the
H
2
O-OH layer is patterned by the LITD using a pulsed laser beam focused into
small spot, yielding the narrow bare area on the Pt surface. Then the patterned
