Scanning Hall Probe Microscopy

High-resolution Scanning Hall probe microscopy (SHM) is a recently-devloped technique to image local magnetic fields near the surface of a sample. It is characterized by both high magnetic field sensitivity and high spatial resolution. The technique involves scanning a micron-sized Hall probe in raster fashion just above the surface of the sample. We have begun to apply this technique to several problems in the area of superconductivity.

Shown is a Hall probe fabricated in a GaAs heterojunction. A measuring current passes through two opposite arms of the "cross"; the other two arms are used to measure the resulting Hall voltage. The width of the arms of the cross is less than 1 µm. Typical field sensitivities are 3 µV/G at a measuring current of 50 µV. The field noise is on order of a few mG/sqrt(Hz). The Hall probe is then raster scanned over the sample; the resulting Hall voltage is read by a lockin amplifier, digitized, and recorded in the computer. The probe is typically scanned over the surface with no feedback. At cryogenic temperatures, it is possible to scan some 0.5 µm above the surface for many hours.

(Above) The Hall microscope as seen from the bottom end, with the sample stage removed. The most visible part is the red LED, used to induce a persistant photconductivity in the 2DEG. Just below the LED the Hall probe is visible as a small square rotated at 45 degrees.

(Right) The complete microscope attached to the 1.2 K pot. The sample stage is now attached at the bottom.


Shown is a Hall probe fabricated in a GaAs heterojunction. A measuring current passes through two opposite arms of the "cross"; the other two arms are used to measure the resulting Hall voltage. The width of the arms of the cross is less than 1 µm. Typical field sensitivities are 3 µV/G at a measuring current of 50 µV. The field noise is on order of a few mG/sqrt(Hz).	The Hall probe is then raster scanned over the sample; the resulting Hall voltage is read by a lockin amplifier, digitized, and recorded in the computer. The probe is typically scanned over the surface with no feedback. At cryogenic temperatures, it is possible to scan some 0.5 µm above the surface for many hours.