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Combined Scanning Tunneling And Capacitance Microscope

IP.com Disclosure Number: IPCOM000099439D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-14
Document File: 2 page(s) / 81K

Publishing Venue

IBM

Related People

Duerig, UT: AUTHOR [+2]

Abstract

Rough sample positioning in scanning tunneling microscopy (STM) is typically surveyed by optical means. However, there is an enormous resolution gap between optical and tunneling microscopy which must be overcome by some other means. Scanning capacitance microscopy (SCM) [1,2,3] is ideally suited to fill this gap in particular since SCM and STM are conceptually similar.

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Combined Scanning Tunneling And Capacitance Microscope

       Rough sample positioning in scanning tunneling microscopy
(STM) is typically surveyed by optical means.  However, there is an
enormous resolution gap between optical and tunneling microscopy
which must be overcome by some other means.  Scanning capacitance
microscopy (SCM) [1,2,3] is ideally suited to fill this gap in
particular since SCM and STM are conceptually similar.

      An embodiment of a combined SCM and STM is sketched in Fig. 1.
The tunnel tip 1, mounted on an xyz piezo actuator 2 simultaneously
serves as a stylus for capacitance sensing. Detection of the
tip/sample capacitance CT is accomplished by monitoring the resonance
frequency of an oscillator comprising a resonator (CT and inductance
L) and a driving circuit, comprising, e.g., a tunnel diode (TD)
inductively or capacitively coupled to the resonator, as shown in
Figs. 1 and 2, respectively.  The oscillator signal is picked up by a
small loop inductor L1 and guided to the frequency detection
electronics 3. For tunnel current detection, the resonator (L,CT) is
connected to a current-voltage converter 4.

      Two modes of operation are conceivable for capacitance
microscopy.  In a first mode (static mode), the resonance frequency
is measured which, to first order, is proportional to the tip/sample
capacitance CT In a second mode (dynamic mode), the gap width between
tip and sample is modulated giving rise to a modulation of the
oscillation frequency proportional to dCT/dz.  The oscillator
frequency is most conveniently measured by means of a phase-locked
loop (PLL) frequency detector 5.  The output signal of the oscillator
is amplified and converted to a lower frequency to facilitate
detection. In the static operation mode, t...