Theory of the scanning tunneling microscope: Xe on Ni and Al (original) (raw)
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Journal of Molecular Catalysis
A theoretical simulation of STM/STS has been performed for various surface systems, based on the first-principles local density functional (LDA) calculation. Cluster models made of lo-20 atoms are utilized for the tip, and slab models with several atomic layers are adopted for the sample surface. The tunnel current is almost concentrated on a single apex atom, if the other atoms on the top of the tip are not located on the same level. In such a case the STM image is normal, with atomic resolution. However, if the apex of the tip is formed by more than one atom, abnormal images tend to be formed. We verify this feature by numerical results for graphite, Si(loo), and Si (111) /Ag surfaces, and discuss the light emission from STM, based on realistic calculations of the electronic states of the tip/sample systems.
Atomic theory of scanning tunneling microscopy
Physical Review B - PHYS REV B, 1989
We present a quantitative analysis of the modifications of the scanning-tunneling-microscopy images due to the local perturbations of the electronic states induced by the tip in close proximity to the sample surface. Using an empirical tight-binding method, we have calculated the electronic states of a prototype tip-sample system consisting of a single-atom tip and the graphite surface, as a function of the tip-sample distance. We find that as the tip approaches the sample, their states start to interact and become laterally confined in the vicinity of the tip at small tip-sample separation. These states influence the tunneling phenomenon by connecting the tip and sample surface electronically. The effect of the tip-induced localized states is discussed, and the expression for the tunneling current is reformulated by incorporating the tip-induced states. Calculations using this expression show that the corrugation amplitude obtained from scanning tunneling microscopy is enhanced and...
Physical Review B, 1993
A theory of scanning tunneling microscopy (STM) is presented that accounts for a realistic treatment of the electronic structure of the sample surface. The sample is represented by a semi-infinite crystal built from muffin-tin potentials describing the atomic structure and surface electronic wave functions of s, p, d, etc. , electrons. The other electrode carrying the tip atom is a planar free-electron metal surface. The potential of the tip atom is expanded in a localized basis set. Within the single-particle approach, the exact equation for the scattering wave for the combined system (tip plus sample) is derived. It is evaluated using a Green-function technique. From the scattering wave function the spatial distribution of the current density is obtained. The method is applied to study the tunnel current to clean Al(111), Pd(111},and Pd(100) surfaces. At typical tip-sample separations (~3 A) the substrate atoms appear as protrusions. Quite remarkable, the contrast is found to be larger in the Al(ill) images than in the Pd(111) and Pd(100) images. This is a consequence of the tip-sample interaction. As a further consequence of tip-sample interactions we find that at close distances between the tip and the Pd surfaces the interstitial regions appear as maxima in the variation of the tunnel current. The theory covers a broad range of tip-sample separations, including those where perturbation treatments of STM theory (as, e.g. , developed by Tersoff and Hamann) break down. A systematic analysis of the different aspects that may affect the tunnel current is presented.
Le Journal de Physique Colloques
R6sum6.-Nous proposons une theorie utilisant le formalisme des fonctions de Green pour le courant tunnel des experiences de STM. Les fonctions d'onde de la pointe et de la surface y sont traitees de maniere analogue. La decomposition du courant en une some de fonctions de Green de surface multiplihes par le facteur de recouvrrement pointe/surface constitue un outil analytique utile pour Btudier les effects non-lineaires et 5 n-corps. Des resultats numeriques sont donnes pour le systBme mod8le:pointe de tungstGne/surface de silicium (100). 11s r6vBlent l'effet des Btats Blectroniques microscopiques sur le courant tunnel. Abstract .-A systematic Green' s function theory of the tunneling current in STM is proposed, in which the wave functions on the tip and the sample surface are treated on equal footing. The decomposition of the tunneling current into the sum over the surface Green's functions multiplied by the tip/surface overlapping factors provides a useful analytical tool for the study of the non-linear and the many body effect. Some numerical results for the W-tip/Si(100) surface model system are given, which reveal the effect of the microscopic electronic states on the tunneling current. 1.
Theory of Scanning Tunneling Microscopy and Spectroscopy
1990
A method for simulating scanning tunneling microscopy (STM) and spectroscopy (STS) is proposed, 0 which is effective at realistic tip-to-surface distances of 5-10 A, and its application is reported for Si(100) reconstructed surfaces. The vacuum tails of wave functions cannot be accurately described either by linear combination of atomic orbitals or by pure plane-wave expansion. An attempt is made to effectively describe the tail parts by combining this method with realistic calculations of the sample surface electronic states. The method is applied to Si(100) reconstructed surfaces and the features of the STM images and STS spectra of 2X1 dimer structures are clarified. This method confirms that the experimental c(4X2) image of STM is actually obtained from the c (4X2) structure and reveals how the buckling of dimers is rejected on the STM image.
Scanning microscopy, 1993
This communication deals with the applicatio!l of a transfer-matrix strategy for the quantitative evaluation of the tunnel current in a scanning tunneling microscope (STM). The image given by a simple atomic-size object deposited on a metal surface is specifically examined in both modes of STM operation namely the constantheight and the constant-current modes. The two-dimensional corrugation induced at low temperature by Xe atoms physisorbed on an otherwise clean, unreconstructed Ni (110) surface is studied in detail. It is shown that the simple consideration of the elastic scattering of electrons by the three-dimensional potential barrier between the tip and the metal substrates provides a quantitative description of the images produced by the instrument: (1) the Xe atom appears as a conic protrusion, approximately 7 A wide, with a corrugation 1.3 A high; (2) in Xe clusters, each adjoining atom is resolved, with a shape in full agreement with experiment. In order to obtain correct ...
Direct and inverse problems in the theory of scanning tunneling microscopy
Surface Science, 1995
The general expression for tunneling current is derived on the grounds of Lippmann-Schwinger and Green's function technique. This approach naturally includes many particle effects in tunneling an electron and gives the possibility to calculate the electron tunneling transitions with the controlling accuracy. The effective tunneling potential is introduced. It depends on the topology of Fermi surface, the quantum numbers of the tunneling electron and does not coincide with widely used image potential. The procedure for the solution of the reverse STM problem is formulated. A specific example of the extraction of wave function parameters from experimental STM data is discussed for a graphite surface and a W tip.
Multiple-scattering theoretical approach to scanning tunneling microscopy
Physical Review B, 2008
An approach for computing scanning tunneling microscopy from first principles is proposed. Within the framework of Landauer-Büttiker theory, the conductance of a scanning tunneling microscope ͑STM͒ is obtained in terms of real-space Green functions, thereby taking into account incoherent tunneling processes and the tip-sample interaction but avoiding repeated STM tips as in a supercell approach. The approach is formulated within multiple-scattering theory, especially in the Korringa-Kohn-Rostoker method, but can be implemented in any Green-function method for electronic-structure calculations. Extensive tests are presented for planar and STM tunnel junctions involving Au͑111͒ electrodes.