Tunneling AFM (TUNA)

The tunneling atomic force microscope (TUNA) extends the surface of the high-resistance sample of the original SPM implementation, and scans the conductive sample with a scanning tunnel microscope. TUNA measures the sub-picoampere tip/sample current through high resistance samples.

The geometry of tip determines the lateral resolution, which is roughly equal to the tip radius. By maintaining a constant force between the needle tip and the sample, the topography map and the current image can be generated at the same time, so that the local topography is directly related to the electrical characteristics.

TUNA and conductive AFM use conductive AFM probe contact mode. The sensor signal is the current between the afm tip used to apply a DC bias and the conductive sample. In feedback mode, the output signal is DC bias, adjusted to maintain the current set value. Applications of this model include experiments on the strength and thickness uniformity of semiconductors, data storage devices, and conductive polymer film media. TUNA is also used to test the integrity of friction films, such as diamond-like carbon (DLC) used in the magnetic recording head/disk interface, and electrical conductivity in small structures such as light-emitting polymers and carbon nanotubes.