Scanning Tunneling Microscopy

A scanning tunneling microscope (STM) provides a way to examine surfaces with atomic resolution. The STM operates by scanning a sharp probe - usually the tip of a sharpened wire - over the surface to be studied. The tip's height above the surface is controlled to be about 1 nm or less. (1 nm = 10^-9m or about 40 billionths of an inch, for the metrically challenged.)

Even though the tip and sample are not touching, they can exchange electrons by quantum mechanical tunneling. A net exchange of electrons can be sustained by applying a small bias voltage between the tip and sample. This resulting tunneling current is very sensitive to changes in tip/sample separation. By rastering the tip over the surface and recording the variations in the tunneling current due to variations in the surface height, a map of the surface can be produced. Alternatively, a feedback system can raise and lower the tip to maintain a constant current as the tip is scanned. The feedback signal, applied to a piezoelectric element, then provides a measure of the surface topography. A few of these images are available here.

• 1 nm x 1nm Image of graphite - line scan.
• 1 nm x 1 nm Image of graphite - surface plot.
• 1 nm x 1 nm Image of graphite - filled contour view.
• 2 nm x 2 nm Image of graphite - surface plot.
• Large area (100 nm x 100 nm) scan of an evaporated silver film

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This page is maintained by Jon Maps who is solely responsible for its content.

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