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Automatic Approach System in an Atomic Force Microscope for Bringing the Tip Very Close to the Sample

IP.com Disclosure Number: IPCOM000114004D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Nonnenmacher, M: AUTHOR [+2]

Abstract

In order to utilize scanning probe techniques in real world environments, it is important to automate the approach of the tip to the sample. Optical methods can be used in the initial approach, but they cannot take into account the various tip geometries that exists in the scanned probe applications. This is because the tip is shielded optically by the cantilever assembly, resulting in an ambiguity as to how far the tip is away from the sample.

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Automatic Approach System in an Atomic Force Microscope for Bringing
the Tip Very Close to the Sample

      In order to utilize scanning probe techniques in real world
environments, it is important to automate the approach of the tip to
the sample.  Optical methods can be used in the initial approach, but
they cannot take into account the various tip  geometries  that
exists  in the scanned probe applications.  This is because the tip
is shielded optically by the cantilever assembly, resulting in an
ambiguity as to how far the tip is away from the sample.

      The best way to approach the tip to the sample is to use the
end of the tip as a reference.  Optical and acoustic techniques use
the cantilever as the reference thereby resulting in an uncertainty
which is dependant on the length of the tip.

      By applying an electrical signal to the probe, a capacitive
force will exist between the tip and sample.  The amplitude of this
force is dependant on the distance between the tip and sample.  The
closer the tip is to the sample, the stronger the force.  The force
is easily monitored by applying an AC signal which may be at a
resonance of the cantilever and monitoring the induced vibration of
the cantilever.  This technique  allows one to approach the tip to
within 10 um of the sample.

      For further refinement, to get the tip even closer in a
controllable manner, a feedback loop is used that nulls the force
between the tip and sample.  This...