21 Davey Lab
Penn State UniversityContacts:
Paul S. Weiss: stm@psu.edu
Tomo Takami: tut3@psu.edu
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This STM is a half home built. The STM controller is RHK SPM100, the first stage preamp is RHK IVP-300, two microwave frequency generators are HP 83623B, lock-in amplifier is SRS SR850, and the rests are home built.
The instrument is a custom-built alternating current scanning tunneling microscope (ACSTM), tunable over a wide frequency range of 0-20 GHz, and capable of detecting transmitted and reflected, fundamental and nonlinear alternating current signals. This instrument was adapted in several ways to facilitate dopant profiling, and will be applied to measure and control a single molecular rotors.
The instrument is a beetle-style ACSTM for the ability to position the sample in three dimention with sub-micron resolution is required locate devices on or beneath a surface. Data acquisition was acomplished using a difference frequency mixing strategy. In addition to the conventional DC bias applied to the tunnel junction, two frequencies are introduced from tunable waveform generators. The frequencies are offset by a small amount (e.g., 3.5 kHz) that becomes the detected frequency. The mixing product occurs at low frequency, so that it is conveniently extracted and detected using a lock-in amplifier. A reference signal for the lock-in is created by splitting off a portion of the applied AC signals prior to the tunnel junction in a directional coupler, and sending them through a diode to generate the desired difference frequency.
Electronics Schematic:
