Optical waveguides – Miscellaneous
Patent
1996-02-07
1997-10-14
Lee, John D.
Optical waveguides
Miscellaneous
385 13, 385 43, 385125, G02B 602
Patent
active
056779780
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention is a general purpose device for measuring nanometer scale surface characteristics. The device integrally consists of a very sensitive force sensor for measuring surface topography and forces. The structure of the device also allows for the simultaneous monitoring of a number of other surface characteristics. In addition, the device may also be used for modification and patterning with nanometer scale resolutions.
BACKGROUND OF THE INVENTION
Scanned probe technologies today rely on a microscopically small tip interacting with a surface as the tip is scanned in very close proximity to the surface.. The interaction between the tip and the sample can typically be used both to track the surface topography and/or measure other characteristics. The two most common interactions which are utilized are electron tunneling (scanning tunneling microscopy--STM) and force sensing (scanning force microscopy--SFM). Tunneling requires a conducting probe and a conducting sample and is thus restricted in its application. Force sensing removes this restriction. Force sensing requires a structure which is sensitive enough to detect the small forces (van der walls, columbic, etc.) that are present at an interface between a tip and a surface which are typically of piconewton magnitude. In addition the probe must be flexible enough so as not to deform the surface as it scans over it. This requires a force constant on the order of 1 Newton/meter.
One of the basic requirements of a probe for practical application of scanned force sensing is to have a sharp, finely tapered tip which can accurately track over and into surface corrugations. If the probe has a blunt or quickly tapered tip, scanning the tip at a constant height above the surface will not produce an accurate rendition of the topography but rather a convolution of the tip structure with the surface. This is particularly significant when force imaging is to be used for metrology applications. A great deal, of effort, using sophisticated electron beam deposition techniques, is currently expended in order to produce sharp formed by focussed ion beams, Rev. sci. instrm. 62,2167 (1991); Kado H., Yokoyama K. and Tohda T. A Novel ZnO Whisker Tip for Atomic Force Microscopy, Ultramicroscopy (1992)!.
The deflection of the probe induced by the interaction with the surface force is generally detected by optical means. For the detection of normal forces of the surface on the tip, the probe consists of a cantilever with a tip hanging off one end. The forces on this tip are typically measured by focusing a laser beam onto a small spot on the back side of the probe. When the probe bends the small angular deviation of the beam is detected Today, 43, 23 (1990); K. Wickramasinghe, Sci. Am. 26, 90 (1989)!. Alternatively, the motion of the probe and beam can be monitored K. Wickramasinghe, Sci. Am. 26, 90 (1989)!. Both techniques require for normal force sensing a small, flat reflecting surface on which to direct the beam. Alternately, lateral force sensing does not depend on a cantilevered structure.
STATE OF PRIOR ART
The first normal force cantilevers were fabricated by etching thin wires and mechanically bending them near the tip to produce a cantilevered Wickramasinghe, Sci. Am. 26, 90 (1989)!. Such probes had a number of problems including control over etching and the difficulty in mechanically bending the tip in a reproducible fashion. In addition such probes are not well suited to optical deflection sensing since they contain no flat region which may be used to reflect a laser beam.
Force cantilevers in common use today are typically microfabricated with Today 43, 23 (1990); K. Wickramasinghe, Sci. Am. 26, 90 (1989)!. Such probes consist of a thin silicon membrane or cantilever onto which a small (1990); K. Wickramasinghe, Sci. Am. 26, 90 (1989)!. At the tip of the cone an additional filament is often grown to produce a sharper and finer tapered tip. The mechanical characteristics of such probes are determined by the materials used, tip mass
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Lewis Aaron
Lieberman Klony
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