Negative Sample Bias

The following images were taken with a negative sample bias (tunneling from filled states). The first two images have an X-Y scale of 20 nm. Images 3 thru 7 are 10x10 nm² images taken from the area indicated in figure #2. The bias and tunneling current used is given with the respective images. The directions plotted on the images were determined previously using the c(4x4) reconstruction on the same sample. Since the measurement of the c(4x4) surface, the sample has been transfered from the SPM system to the MBE growth chamber and back to the SPM chamber. Alignment of the sample in the SPM system has only one direction and rotation of the sample in its holder about the surface normal is minimal (< 0.5 degrees).

Model of the asymmetric-(1x3) surface. Originally proposed by Franklin et. al [1] for the GaSb(100)-(1x3) reconstruction.	#1: Vb = -1.0, It = 0.5 nA (20x20 nm). The lattice image is to scale.
#2: Vb = -1.0, It = 0.5 nA (20x20 nm).	#3: Vb = -1.0, It = 0.5 nA (10x10 nm).
#5: Vb = -1.0, It = 0.75 nA (10x10 nm).	#4: Vb = -1.0, It = 0.5 nA (10x10 nm).
#6: Vb = -1.0, It = 0.25 nA (10x10 nm).	#7: Vb = -1.0, It = 0.1 nA (10x10 nm).

Positive Sample Bias

A positive sample bias provides images of empty states.

The following four scans are 10x10 nm with a sample bias of +1.5, +1.5, 1 and +1.5 volts respectively. Tunneling current was held constant at 0.1 nA. Clicking on an image will bring up an image with detail about the scan parameter and height scale.

Vb = +1.5, It = 0.1 nA.	Vb = +1.5, It = 0.1 nA.
Vb = +1.0, It = 0.1 nA.	Vb = +1.5, It = 0.1 nA.

References

1. G. E. Franklin, D. H. Rich, A. Samsavar, E. S. Hirschorn, P. M. Leibsle, T. Miller and T. C. Chiang, Phys. Rev. B 41, 12619 (1990).