josh@polaris.UUCP (Josh Knight) (09/15/86)
%A G. Binnig %A H. Rohrer %T Scanning Tunneling Microscopy %J IBM J R&D %V 30 %N 4 %P 355-369 %D July 1986 %X Presented here is an overview of the present status and future prospects of scanning tunneling microscopy. Topics covered include the physical basis of the scanning tunneling microscope, its instrumentation aspects, and its use for structural and spectroscopic imaging - on a scale which extends to atomic dimensions. Associated experimental and theoretical studies are reviewed, including several which suggest potential applicability of this new type of microscope to a relatively broad range of biological, chemical and technological areas. %A P.K. Hansma %T Squeezable Tunneling Junctions %J IBM J R&D %V 30 %N 4 %P 370-373 %D July 1986 %X Squeezable tunneling junctions establish the current state of the art for resistance stability of mechanically adjustable tunneling structures at delta R over R approximately equal 0.1%. This is sufficient for use in connection with spectroscopies as subtle as phonon spectroscopy, but it is marginal and cannot at present be maintained to high enough bias voltage to permit molecular vibrational spectroscopy. Squeezable junctions have been used for characterizing bulk samples and for differential capacitance-voltage analyses of semiconductors. %A Norton D. Lang %T Electronic Structure and Tunneling Current for Chemisorbed Atoms %J IBM J R&D %V 30 %N 4 %P 374-379 %D July 1986 %X We discuss the tunneling current density in the vacuum region between two planar metal electrodes, one of which has an atom chemisorbed on its surface. The relation of this current distribution to the electronic structure of the adatom is analyzed. The study of this model problem leads to a better understanding of important aspects of the current flow in the scanning tunneling microscope. The emphasis of this work is not so much on the question of resolution discussed in other theoretical studies as on the characteristic signatures of chemically different atoms. %A A.M. Baro %A R. Miranda %A J.L. Carrascosa %T Application to Biology and Technology of the Scanning Tunneling Microscope Operated in Air at Ambient Pressure %J IBM J R&D %V 30 %N 4 %P 380-386 %D July 1986 %X We have investigated the operation of the scanning tunneling microscope (STM) in air at atmospheric pressure, thus permitting the imaging of samples without the need for subjecting them to a vacuum environment. Clearly, this may be of practical importance for many types of samples having biological and technological interest. Imaging of biological samples has been found to be possible after deposition onto a flat structureless conducting substrate (highly oriented pyrolytic graphite). Three-dimensional profiles of structures derived from the virus designated as bacteriophage phi 29 could thus be obtained. Other profiles have been obtained which indicate applicability to surfaces of technological interest: for example, in the measurement of the surface roughness of industrial components with increased precision, suggesting use of the STM as a new standard instrument for that purpose. %A S.A. Elrod %A A. Bryant %A A.L. de Lozanne %A S. Park %A D. Smith %A C.F. Quate %T Tunneling Microscopy from 300 to 4.2 K %J IBM J R&D %V 30 %N 4 %P 387-395 %D July 1986 %X A scanning tunneling microscope (STM) has been developed for operation over the full temperature range from 300 to 4.2K. At room temperature, the instrument has been used to produce topographic images of grain structure in a copper-titanium alloy foil and of atomic structure on a Pt(100) surface. At low temperatures, the instrument can be used in a new spectroscopic mode, one which combines the high spatial resolution of the STM with the existing technique of electron tunneling spectroscopy. This new capability has been demonstrated by using the microscope to probe spatial variations in the superconducting character of a niobium-tin alloy film. %A J.E. Demuth %A R.J. Hamers %A R.M. Tromp %A M.E. Welland %T A Scanning Tunneling Microscope for Surface Science Studies %J IBM J R&D %V 30 %N 4 %P 396-402 %D July 1986 %X A new design is described for a scanning tunneling microscope intended for surface science studies. The performance of the microscope is evaluated from tunneling images obtained of the Si(111) 7 X 7 surface. Periodic structures, point defects, and grain boundary structures are observed with atomic-scale resolution and are discussed. Illustrations of various types of image processing and data display are presented. %A W. Hosler %A R.J. Behm %A E. Ritter %T Defects on the Pt(100) Surface and their Influence on Surface Reactions - A Scanning Tunneling Microscopy Study %J IBM J R&D %V 30 %N 4 %P 403-410 %D July 1986 %X Structural differences between a clean, reconstructed Pt(100) surface and one exhibiting chemical or structural irregularities have been identified by means of a scanning tunneling microscope. The (temperature-dependent) defect structure of a surface which had undergone a phase transition involving mass transport was characterized and compared to results obtained using other techniques. The catalytic activity of surface step sites was probed by the thermal decomposition of ethylene. The resulting surface roughening and buildup of carbon, which could be resolved in STM images, clearly showed that the decomposition proceeds from terrace edges. %A W.J. Kaiser %A R.C. Jaklevic %T Spectroscopy of Electronic States of Metals with a Scanning Tunneling Microscope %J IBM J R&D %V 30 %N 4 %P 411-416 %D July 1986 %X We have constructed a scanning tunneling microscope (STM) and have obtained current-voltage derivative spectra from metal surfaces. For Au(111) we have observed an electronic surface state 0.4 eV below the Fermi energy. This state has previously been observed with photoemission and oxide tunneling experiments. We have also observed strong peaks in spectra obtained from Pd(111) which we identify with surface states and effects derived from bulk energy bands. In the voltage range investigated here, tunneling takes place through the entire vacuum gap between the metallic tip of the microscope and the surface of the sample being examined. The STM spectroscopy results reported here are compared with previous experimental work and theory. These intrinsic surface states are the first which have been observed with the STM and demonstrate its unique applicability to the investigation of surface electronic structure. %A Dieter W. Pohl %T Some Design Criteria in Scanning Tunneling Microscopy %J IBM J R&D %V 30 %N 4 %P 417-427 %D July 1986 %X Optimum function of a scanning tunneling microscope (STM) requires tip-to-sample position control with picometer precision, a rough and fine positioning capability in three dimensions, a scanning range of at least 100 times the lateral resolution, a scanning speed as high as possible and also, preferably, simplicity of operation. These requirements have to be satisfied in the presence of building vibrations with up to micrometer-size amplitudes, temperature drift, and other perturbations. They result in design rules, presented and discussed here, for the optimization of damping, stiffness, electrical control circuitry, and the performance of the piezolectirc actuators usually employed in STMs. %A Robert Gomer %T Possible Mechanisms of Atom Transfer in Scanning Tunneling Microscopy %J IBM J R&D %V 30 %N 4 %P 428-430 %D July 1986 %X Various mechanisms for the sudden transfer of an atom from or to the tip of a scanning tunneling microscope are considered. it is concluded that thermal desorption could be responsible and also that quasi-contact in which the adsorbed atom is in effect "touching" both surfaces, which would still be separated from each other by 2-4 angstroms, can lead to unactiviated transfer via tunneling. For barrier widths as small as 0.5 angstroms, however, tunneling becomes negligible. -- Josh Knight, IBM T.J. Watson Research josh@ibm.com, josh@yktvmh.bitnet, ...!philabs!polaris!josh