Chemistry Reference
In-Depth Information
Fig. 4.20
Temperature-dependent photoemission spectra of Pb films for
(a)
23ML and
(b)
24ML
collected within a temperature range of 75-270 K. The
vertical dashed lines
reveal the variation of
the QWS binding energy as the film temperature is changed [
58
]
24ML films is shown in Fig.
4.20
a and b. These results show that, with increasing
substrate temperature, the peak position of the QWS shifts toward higher binding
energies while the peak widths broaden. To find out the exact relation between the
line width (
E
) of the QWS and the temperature, a curve fitting by Voigt line shape
was made. The fitting results are plotted in Fig.
4.21
a for the films of 22 and 23ML,
where
E
increases linearly with increasing temperature and exhibits prominent
different slopes for the adjacent layers. The relation between this slope and the
electron-phonon coupling strength,
λ
,is
1
d
E
d
T
λ
=
(4.11)
2
π
k
B
values derived from the QWS peaks for different thicknesses are shown
in Fig.
4.21
b (triangles), where only the values for stable layers (15, 17, 19, 21, 22,
23, and 24ML) are plotted. Besides an overall gradual increase of
The
λ
λ
toward the bulk
λ
value (1.55), an oscillation of
with a period of 2ML is clearly noted from 21 to
24ML.
Theoretically, Yndurain and Jigato [
59
] recently do the DFT calculations to
investigate the surface phonons and electron-phonon interaction. Zero parallel
momentum phonon modes for Pb(111) freestanding slabs of widths ranging from
