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Tunneling current through localized surface states
A84 55
Surface Science 181 (1987) 55-68 North-Holland, Amsterdam SCANNING
TUNNELING
MICROSCOPY
STUDY OF
METALS:
SPECTROSCOPY AND TOPOGRAPHY W.J. KAISER and R.C. JAKLEVIC Research Staff, Ford Motor Co., Dearborn, MI 48121, USA Received 15 July 1986; accepted for publication 30 July 1986 We will describe experiments on metal surfaces using the scanning tunneling microscope. Our scanning tunneling microscope was designed to operate in ultra-high vacuum together with sample cleaning and characterization. The major component for vibration damping is an external isolation table. The tip positioning mechanism is a quartz lever arm combined with coarse and fine adjusting screws. The STM and feedback control system are designed to obtain both topographic and spectroscopic information. Topographic images of Au(111) have been obtained which show very smooth planes containing only single atomic steps. Other surfaces show monatomic step structure in the form of an ordered array whose period corresponds to a previously studied reconstruction on Au(111). Further, on the same surface we find steeper sloped regions with multiple steps of equal height with wide facets. Spectroscopic data for Au and Pd show the presence of surface and bulk electronic states with good signal to noise. The energy values of these states are compared directly with the results of other experimental methods.
Surface Science 181 (1987) 69-77 North-Holland, Amsterdam TUNNELING R. G A R C i A ,
CURRENT
69 THROUGH
LOCALIZED
SURFACE
STATES
J.J. S~kENZ, J . M . S O L E R a n d N . G A R C I A
Departamento de Fisica Fundamental, Facultad de Ciencias, Universidad Aut6noma de Madrid, Cantoblanco, 28049 Madrid, Spain Received 14 July 1986; accepted for publication 15 September 1986 Tunneling spectroscopy performed with the scanning tunneling microscope (STM) has been used to study unoccupied surface states. The experiments show an oscillatory behavior in the curves d I / d Va versus the applied voltage Va in the constant current mode. Such oscillations have been observed in two different situations: either Va coincides with allowed band energies, as in Au(ll0), or it lies within a gap, as in Ni(100). We have calculated the current for a tunnel barrier between two plane electrodes in these two different cases. We have also included an optical potential which takes into account the existence of inelastic processes. Our results show that the oscillatory behavior of tunnel spectra measured with the STM reflects the existence of localized surface states at the crystal-vacuum interface.
Surface Science 181 (1987) 55-68 North-Holland, Amsterdam SCANNING
TUNNELING
MICROSCOPY
STUDY OF
METALS:
SPECTROSCOPY AND TOPOGRAPHY W.J. KAISER and R.C. JAKLEVIC Research Staff, Ford Motor Co., Dearborn, MI 48121, USA Received 15 July 1986; accepted for publication 30 July 1986 We will describe experiments on metal surfaces using the scanning tunneling microscope. Our scanning tunneling microscope was designed to operate in ultra-high vacuum together with sample cleaning and characterization. The major component for vibration damping is an external isolation table. The tip positioning mechanism is a quartz lever arm combined with coarse and fine adjusting screws. The STM and feedback control system are designed to obtain both topographic and spectroscopic information. Topographic images of Au(111) have been obtained which show very smooth planes containing only single atomic steps. Other surfaces show monatomic step structure in the form of an ordered array whose period corresponds to a previously studied reconstruction on Au(111). Further, on the same surface we find steeper sloped regions with multiple steps of equal height with wide facets. Spectroscopic data for Au and Pd show the presence of surface and bulk electronic states with good signal to noise. The energy values of these states are compared directly with the results of other experimental methods.
Surface Science 181 (1987) 69-77 North-Holland, Amsterdam TUNNELING R. G A R C i A ,
CURRENT
69 THROUGH
LOCALIZED
SURFACE
STATES
J.J. S~kENZ, J . M . S O L E R a n d N . G A R C I A
Departamento de Fisica Fundamental, Facultad de Ciencias, Universidad Aut6noma de Madrid, Cantoblanco, 28049 Madrid, Spain Received 14 July 1986; accepted for publication 15 September 1986 Tunneling spectroscopy performed with the scanning tunneling microscope (STM) has been used to study unoccupied surface states. The experiments show an oscillatory behavior in the curves d I / d Va versus the applied voltage Va in the constant current mode. Such oscillations have been observed in two different situations: either Va coincides with allowed band energies, as in Au(ll0), or it lies within a gap, as in Ni(100). We have calculated the current for a tunnel barrier between two plane electrodes in these two different cases. We have also included an optical potential which takes into account the existence of inelastic processes. Our results show that the oscillatory behavior of tunnel spectra measured with the STM reflects the existence of localized surface states at the crystal-vacuum interface.