摘要:

SUMMARYThe scanning tunnelling microscope (STM) has proved to be an extraordinary method to investigate surfaces in vacuum, air and liquid environments. Several issues regarding the use of the STM for atomic resolution studies are discussed. These include electronic contributions to STM images, the role of the tip in resolution and spectroscopy, as well as the need for complementary information about chemical composition or sub‐surface structur

ISSN:2047-1491    

DOI:10.1111/j.1365-2818.1870.tb06051.x

出版商:Blackwell Publishing Ltd    

年代:1870

数据来源: WILEY

摘要:

SUMMARYWe present a theoretical analysis of the contact resistance in the Scanning Tunnelling Microscope. Under the assumption of a single contact atom on the tip's apex, we find that the resistance saturates at close contact, its value beingh/2e2. Our analysis of the recent experimental results of Gimzewski&Möller (1987), shows that the mechanical instability predicted by Pethica&Sutton (1988), appears for a distance 1·5 Å larger than the close contact distance between the tip and the samp

ISSN:2047-1491    

DOI:10.1111/j.1365-2818.1870.tb06052.x

出版商:Blackwell Publishing Ltd    

年代:1870

数据来源: WILEY

摘要:

SUMMARYWe have detected the light emitted from an STM at both ultraviolet (9·5 eV) and optical (1–4 eV) energies. We show that this light contains spectroscopic information on the sample surface comparable to conventional inverse photoelectric spectroscopy, but with nearly atomic spatial resolution. At optical energies we found sufficiently high intensities to allow spatial imaging of the emission probability. We propose that the high quantum efficiency is due to resonance phenomena, and present fluorescence spectra of the emitted light that support this view. We believe that atomic resolution inverse photoemission microscopy and spectroscopy will provide an important new dimension to surface studi

ISSN:2047-1491    

DOI:10.1111/j.1365-2818.1870.tb06053.x

出版商:Blackwell Publishing Ltd    

年代:1870

数据来源: WILEY

摘要:

SUMMARYA clean Si(111) flat surface was irradiated by pulsed Nd‐YAG laser beams. STM observation of the irradiated surfaces indicates that the laser irradiation generates two kinds of corrugations: rounded hills 100 Å high and 600 Å wide and small spikes 20 Å high and 35 Å wide. The corrugations grew and spread with repeated irradiation and increased laser power. The heating of the irradiated surface at 1200°C for 5 s smoothed the surface atomically, but no ordered structure was observed, possibly due to the covering contaminants released from the surfaces surrounding the specimen by laser irradiation and h

ISSN:2047-1491    

DOI:10.1111/j.1365-2818.1870.tb06054.x

出版商:Blackwell Publishing Ltd    

年代:1870

数据来源: WILEY

摘要:

SUMMARYScanning tunnelling microscopes operable in both ultrahigh vacuum (UHV) and aqueous conditions are described with emphasis on a tip geometry. An atomically resolved STM image was obtained for the Si(111)‐Mo√3 surface in UHV condition and changes of a diffraction grating surface in aqueous condition due to an electrochemical reaction were monito

ISSN:2047-1491    

DOI:10.1111/j.1365-2818.1870.tb06055.x

出版商:Blackwell Publishing Ltd    

年代:1870

数据来源: WILEY

摘要:

SUMMARYProgress in STM, in particular for the interpretation of the tunnel signals of corrugated surfaces, is related to the possibility of sharpening and regeneratingin situreproducible tips for use as the probe. We proposed two techniques for the production of tips with controlled geometry at the atomic level. These two techniques are based on the production of tips with equilibrium profiles obtained under heat treatments in vacuum and in the presence of an electric field. Based on the pseudo‐stationary profile principle, the microtips can be sharpenedin situand in a reproducible manner, either from initial cylindrical (111)‐W wire, or from breakdown tips; in both cases without the need for heavy control devices (like FIM for examp

ISSN:2047-1491    

DOI:10.1111/j.1365-2818.1870.tb06056.x

出版商:Blackwell Publishing Ltd    

年代:1870

数据来源: WILEY

摘要:

SUMMARYFrictional forces are usually measured by detecting spring displacement. To obtain high‐resolution measurements of frictional force distributions, a sharp tip and a light load are required. In measuring frictional force on relatively rough surfaces, using very sharp tips (submicron radii), significant stick‐slip motions are observed, and continuously varying dynamic frictional forces can not be measured.To measure continuous friction distributions between sharp tips and surfaces with light loads, a new frictional force microscope (FFM) is developed. This FFM has an electromagnet to maintain the tip suspension spring in a non‐deflected position. The frictional force is then measured from the magnet current. Using this FFM, continuous friction distributions between 0·1 μm radius diamond tips and magnetic disk surfaces with light loads (less than 10 μN) are

ISSN:2047-1491    

DOI:10.1111/j.1365-2818.1870.tb06057.x

出版商:Blackwell Publishing Ltd    

年代:1870

数据来源: WILEY

摘要:

SUMMARYA new variable temperature STM has been developed which utilizes two concentric piezoelectric tubes; an inner scanning tube, and an outer thermal compensation tube which also provides for inertial translation of the sample into tunnelling range. With this design, continuously variable temperature operation is demonstrated for the first time in an STM. Also, by eliminating all mechanical components such as springs, levers and gears, which normally couple directly to the tunnelling gap in other designs, atomic resolution operation is demonstrated in which no vibration isolation is necessary. During operation, the inside of the scanning tube is maintained at ground potential while the feedback signal is electronically summed to the scanning voltages applied to the outer quadrants. In addition to shielding the sensitive tunnelling circuit, this mode of operation enables one to electronically balance out mechanical imperfections of the scanning tube. To date, this new STM has been operated over the 77–400 K temperature range with the observed thermal drift as low as 1 Å/h and 10 Å/K. Another useful feature of this new design is the ability to reposition a sample to within 200 Å of the same location after it has been translated macroscopic distances (several mm) out of tunnelling r

ISSN:2047-1491    

DOI:10.1111/j.1365-2818.1870.tb06058.x

出版商:Blackwell Publishing Ltd    

年代:1870

数据来源: WILEY

摘要:

SUMMARYThis article is a presentation of the results of a finite element method analysis of piezoelectric tube scanners of the type presently in wide use in scanning tunnelling microscopes. The tube scanner moves a tunnelling tip by bending sideways when unsymmetrical voltages are applied to longitudinal stripes of metallization on its walls. It also can be extended and contracted in length by application of symmetrical voltages. One wishes to know the characteristics and magnitudes of the resulting three‐dimensional motion. We divided a model tube into radially polarized elements, and constructed a computer program to perform electromechanical stress calculations. The results show the dependence of motion upon applied voltage, tube material, and tube dimension

ISSN:2047-1491    

DOI:10.1111/j.1365-2818.1870.tb06059.x

出版商:Blackwell Publishing Ltd    

年代:1870

数据来源: WILEY

摘要:

SUMMARYThe scanning speed and quality of images obtained with a scanning tunnelling microscope can be increased by replacing the tunnelling tip holder with an active, high resonance frequency piezoelectric positioner. The combination tip holder and positioner has a resonance frequency near 100 kHz, allowing fast closed‐loop feedback control of the STM. With appropriate electronic shielding, the active tip holder can also be used to modulate the tip to surface distance at high frequencies for work function mapping.The high speed positioner is complemented by a ‘tip‐saver’ circuit which senses imminent tip‐surface contact, preventing tip crashes. The circuit, when driving the fast positioner, has a response time of under 20 μs and is not subject to the oscillation problems normally associated with closed‐loop feedback systems operated at high gains and large signal bandwidths.With computer control, the resulting design enables rapid changes in magnification and resolution over the present range of 10−3to 1·0 μm, facilitating SEM‐type examinations of surface topography.The high speed positioner and drive circuitry can be easily incorporated into existing STM. The design of the active tip holder and tip‐saver circuitry, and the details of application to existing S

ISSN:2047-1491    

DOI:10.1111/j.1365-2818.1870.tb06060.x

出版商:Blackwell Publishing Ltd    

年代:1870

数据来源: WILEY