| dc.description.abstract | Under near ambient oxygen pressure condition, there are two kinds of
copper oxide having been confirmed. The interaction between initial state of
copper oxide and substrate and the structure evolution with pressure increase
will influence the catalytic capability. With regulating the oxygen pressure
from high vacuum to near ambient pressure and controlling at moderate
growth temperature (550 K), we observe the changes of crystal structure
and electronic state on Cu(110) surface by reflective high energy electron
diffraction (RHEED), scanning tunneling microscopy (STM) and ambient
pressure X-ray photoelectron spectroscopy (AP-XPS).
When the oxygen pressure is below 10?5 Torr, the result from electron
diffraction demonstrates the surface is composed of the co-existence state of
c(6 × 2) and (2 × 1). As the oxygen pressure is regulated in the interval
between 10?5 Torr and 10?2 Torr and the oxygen exposure is greater than
1.8 × 104 L, only the structure c(6 × 2) appears on the surface from the
diffraction result and only the signal of bulk copper is captured in the Cu
2p spectrum which denotes that there is not the formation of copper oxide.
However, the oxygen 1s spectrum shows that the amount of oxygen does
increase. In addition, we found there was a significant undulation in the
terrace in the STM images, which led to the inference that this phenomenon
was caused by the formation of bonds between oxygen and copper under
the surface. When the oxygen pressure is in the interval between 10?2 Torr
and 10?1 Torr, Cu2O gradually occupies the surface. In the initial stage,
Cu2O is double phase when it coexists with c(6×2) and also prefers to grow
downward. Finally, at a pressure of 10?1 Torr, the thickness of Cu2O is about
3.5 nm and the structure changes to the amorphous state, accompanied by
thin film state of CuO. As the oxygen pressure is increased to greater than 1
Torr, from the spectrum we can see that the CuO thickness exceeds 3.41 nm
and the strongly chemisorbed oxygen increases significantly. However, no
diffraction structure can be observed at this pressure, which indicates that
the growth mode of CuO transfers to the amorphous state. The oxygen
pressure was further adjusted to 5 Torr, no new copper compounds appear.
The thickness of CuO has not changed significantly, only the amount of
strongly chemisorbed oxygen has increased. | en_US |