Tunneling Phenomena as a Probe to Investigate Atomic Scale Fluctuations in Metal/Oxide/Metal Magnetic Tunnel Junctions

Local transport properties of ${\mathrm{Al}}_2{\mathrm{O}}_3$ tunnel barriers have been investigated at a nanometric spatial scale with an unconventional near field microscope. Using the tunneling effect, which is extremely sensitive to fluctuations of the barrier parameters (less than 1 to $2Å$), a unique method is introduced to investigate the tunnel barrier quality. This technique provides atomic scale information on the barrier characteristics which cannot be obtained by conventional surface analysis techniques since they are all subject to averaging over surface and depth.