Brief Instrument Overview
	We have two versions of the Microscope, a Room temperature and Low temperature Scanning Hall Probe Microscopes. Both microscopes can also be used as STM, AFM, and other Scanning Probes. In the standard configuration a sub-micron Hall probe microfabricated into a GaAs/GaAlAs heterostructure 2DEG is scanned over the sample to measure the surface magnetic fields using conventional scanning tunneling microscopy-positioning techniques as shown in Fig. 1. A closer look at the microscope head is given at Fig. 2.
	Fig. 1 - Schematics of the Scanning Hall Probe
	Fig. 2.1 - Low Temperature SHPM head with sensors (STM tip, Quartz tuning fork, head)    Fig. 2.2 - Details of the SHPM head
	It is expected that we should be able to reach the highest magnetic measurement sensitivity currently available only with the use of SQUIDs (~500µB) at helium temperatures. Our overall objective, is to reach, in collaboration with Nanomagnetics, the sensitivity of several Bohr magnetons (µB) and ultimately 1µB. This will be instrumental in fabricating novel nanostructures, with potential application in intelligent characterization of molecules and manipulation of single charges and spins. The single spin detection capability will bring further advances for nanoelectronics, nanomagnetics, spintronics, and quantum information technology.
	In order to approach the single spin sensitivity we are planning to: Reduce the sample-probe separation to 50 nm (see estimates below). Decrease the minimum temperature from 4.2 to at least 1.2 K to reduce noise and improve the mobility of the 2D gas.
	The minimum detectable magnetic field obtained with the SHPM, Bmin is given by the following formula: Bmin(T/√(Hz))=√(4kBTRs)/RHallIHall , where Rs, RHall and IHall are the series resistance, Hall resistance and the Hall current passing through the Hall probe, respectively. The Hall current cannot be increased indefinitely; there is a maximum current, IHall max , which can be passed through the probe without increasing the noise.
	While the field sensitivity is naturally the highest at the lowest operating temperature (see the Table below), the scan size significantly decreases with temperature. Another trade off is the requirement that the surface should be conductive, as an STM feedback is presently used to scan immediately next to the sample surface. Magnetic field distribution of the sample is obtained simultaneously with the STM topography of the surface.

Examples of Low Temperature-SHPM scans of Garnet at variable temperatures (5-300 K)

A) Contact mode scan with Low Temperature Hall Probe over 16x16µm2. Hall Probe current is 3 µA. Scan speed is 3µm/s. Resolution is 128x128 pix. Left panel: 3D image; Middle panel: 2D image with cross-section along x-coordinate; Right panel: Cross-sectional magnetic field (Hall voltage). T = 300K; Noise-to-signal ratio shown in the right panel is fairly high.

B) Contact mode scan with Low Temperature Hall Probe over 10x10µm2. Hall Probe current is 3 µA. Scan speed is 2µm/s. Resolution is 128x128 pix. Left panel: 3D image; Middle panel: 2D image with cross-section along x-coordinate; Right panel: Cross-sectional magnetic field (Hall voltage). T = 120K; Noise-to-signal ratio shown in the right panel has improved.

C) Contact mode scan with Low Temperature Hall Probe over 14x14µm2. Hall Probe current is 3 µA. Scan speed is 1µm/s. Resolution is 384x384 pix. Left panel: 3D image; Middle panel: 2D image with cross-section along x-coordinate; Right panel: Cross-sectional magnetic field (Hall voltage). T = 120K; Noise-to-signal ratio has further improved.

	D) Contact mode scan with Low Temperature Hall Probe over 15x15µm2. Hall Probe current is 10 µA. Scan speed is 1.5µm/s. T = 5K - High Resolution Image. Resolution is 384x384 pix. Below – sample topography.

SHPM operating parameters and sensitivity at various temperatures

300K 77K 4.2K RHall (Ω/Gauss) 0.3 0.3 0.3 IHall Max (µA) 3 60 >60 Rs (kΩ) 60 3 1.5 VJohnson Noise (nV/√(Hz)) 32 3.6 0.6 Bmin(nT√(Hz)) 3560 20 3.3