Figure 1.

3D AFM images of scratch tracks formed in GaN films on sapphire substrates: a 2,000 μN ramped force, c-axis sapphire; b 4,000 μN, c-axis sapphire; c 2,000 μN, a-axis sapphire; d 4,000 μN, a-axis sapphire

Lin et al. Nanoscale Research Letters 2010 5:1812-1816   doi:10.1007/s11671-010-9717-8