Figure 2.

Typical profiles of the coefficient of friction (μ) plotted with respect to the scratch duration at ramped loads of 2,000 and 4,000 μN for GaN films on a c-axis and b a-axis sapphire substrates

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