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Lateral Forces and Topography Using the Scanning Tunneling Microscope and Optical Sensing of the Tip Position

IP.com Disclosure Number: IPCOM000035783D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

Taubenblatt, MA: AUTHOR

Abstract

A technique is disclosed for measurement of the lateral forces on a Scanning Tunneling Microscope (STM) tip simultaneously with a measurement of surface topography, by using optical sensing of the STM tip vibration.

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Lateral Forces and Topography Using the Scanning Tunneling Microscope and Optical Sensing of the Tip Position

A technique is disclosed for measurement of the lateral forces on a Scanning Tunneling Microscope (STM) tip simultaneously with a measurement of surface topography, by using optical sensing of the STM tip vibration.

Scanning Tunneling Microscopy and Force Microscopy have provided the means to observe surface topography and near surface forces on a scale of atomic dimensions. Observation of vertical forces on an STM tip, at the same time that topography was measured with the STM, has also been reported. This was accomplished by observing the deflection of a sample, that was itself a vibrating cantilevered beam. In this disclosure, a technique is demonstrated which allows observation of forces in the lateral direction (with respect to the average surface normal) at the same time that topography data is taken using the STM.

The STM tip is caused to vibrate near a resonant mode in the lateral direction, using the capacitive forces between the tip and the surface under study. Topography is monitored using the z-displacement feed-back voltage, in a low frequency loop, while optical sensing of the high frequency tip vibration amplitude monitors lateral forces acting on the tip. Changes in resonance frequency due to lateral forces result in a change in the tip vibration amplitude.

The optical method for detecting lateral tip motion is shown in the figure. The STM tip vibration is observed by monitoring the reflected light from a HeNe laser beam 13 focused onto the end of the STM tip 4. This is accomplished by directing the laser beam through the back of the sample 5, which consists of a glass slide with a thin (100- 400 Ao) Au layer sputter deposited on it. A portion of the HeNe beam 13 (linearly polarized) is first split off by a beam splitter 9 and directed at the reference photodetector 11. The remaining portion of the beam passes t...