Experiments - Visualization of Hydrogen-Bond Dynamics - page 36

Fig. 3.5 a STM-IETS spectra for an isolated C 2 H 2 molecule on Cu(110) (red solid curve) and
clean surface (black dashed curve). The tip was fixed vertically to give I t = 50 pA at V s = 0.1 V.
b The differential spectra show peaks at 350 and 258 mV for C 2 H 2 (red solid curve) and C 2 D 2
(blue dashed curve), respectively, which are assigned to the C-H(D) stretch mode of *sp 3
rehybridized acetylene molecule

ð DV Þ 2
2

dV DV sin ð xt Þþ d 2 I

I ½ V 0 þ DV sin ð xt Þ ¼ I ð V 0 Þþ dI sin 2 ð xt Þ

dV 2

ð DV Þ 2
4 dV DV sin ð xt Þþ d 2 I

¼ I ð V 0 Þþ dI ð 1 cos ð 2xt ÞÞ

dV 2

thus dI/dV and d 2 I/dV 2 signals can be extracted from x and 2x components,
respectively. In order to verify our setup and stability, I measured the STM-IETS
of an acetylene molecule on Cu(110). Since it was first studied on Cu(100) and the
C-H(D) stretch mode was clearly observed [ 12 ], acetylene can be considered as a
good referable molecule. Figure 3.5 shows the d 2 I/dV 2 (IET) spectra of acetylene
molecules adsorbed on Cu(110), where the C-H(D) stretch mode is also observed
[ 13 ].