We describe a low-noise scanning Hall probe microscope having unpreced
ented magnetic field sensitivity (similar to 2.9x10(-8) T/root Hz at 7
7 K), high spatial resolution, (similar to 0.85 mu m),nd operating in
real-time (similar to 1 frame/s) for studying flux profiles at surface
s. A submicron Hall probe manufactured in a GaAs/A1GaAs two-dimensiona
l electron gas (2DEG) is scanned over the sample to measure the surfac
e magnetic fields using conventional scanning tunneling microscopy pos
itioning techniques. Flux penetration into a high T-c YBa2Cu3O7-delta
thin film has been observed in real time at 85 K with single vortex re
solution. Flux is seen to enter the film in the form of vortex bundles
as well as single flux quanta, Phi(0). (C) 1996 American Institute of
Physics.