Verlag des Forschungszentrums Jülich
JUEL-3529 This thesis deals with the investigation of diffusion processes and surface reactions
on metal surfaces by means of scanning tunneling micoroscopy (STM) and electron energy
loss spectroscopy (EELS). A new combined STM/EELS ultra high vacuum apparatus has been set up which allows
surface imaging and surface vibrational spectroscopy without sample transfer. The
tunneling microscope is integrated in the scattering chamber of the electron spectrometer
so that the tunneling tip is able to scan the sample surface while the electron beam is
scattered at the latter simultaneously. The sample can be cooled down below 30 K and
heated to 1300 K. First measurements show that the vibrational isolation of the sample and
the performance of the STM (``beetle type'') have to be improved in the future. The Ostwald ripening of two dimensional Cu adatom islands on the Cu(100) surface has
been followed with STM between 333 and 413 K. By considering the time dependence of the
sizes of individual islands the mechanism for the ripening is characterized. The result is
unexpected for a simple metal surface: The flow of atoms from one island to another is
limited by attachment-detachment kinetics at the island edges. To explain this result, it
is proposed that the transport of atoms between the islands occurs by vacancy rather than
by adatom diffusion. From the temparature dependence of the island decay the activation
energy is found to be Eact=0.80±0.03eV. EELS and STM have been used to characterize the adsorption of potassium on Pt(111)
surfaces at room temparature. The STM results indicate an incorporation of potassium at
the platinum surface, especially at steps. The EELS data show no definite evidence for
potassium bound in a subsurface site. The vibrational frequency of adsorbed potassium
adatoms shifts from 135 cm-1 at low coverages to 175 cm-1 at a
coverage of [Theta]K=0.16. This frequency shift can be explained by lateral
dipole-dipole interactions between the adsorbed alkali metal atoms. For potassium
coverages up to [Theta]K=0.33, the frequency decreases to 155 cm-1
and the loss intensity nearly vanishes which is attributed to the metallization of the
alkali metal layer. Above potassium coverages of about [Theta]K=0.10 the
adsorbed potassium reacts with residual water molecules to form potassium hydroxide, with
the potassium atom bonding to the platinum.
Klünker, Christian
Aufbau eines hochauflösenden Elektronenenergieverlustspektrometers mit integriertem Rastertunnelmikroskopie
120 S., 1998
Neuerscheinungen
Schriften des Forschungszentrums Jülich
Ihre Ansprechperson
Heike Lexis
+49 2461 61-5367
zb-publikation@fz-juelich.de