Semiconductor strained layer superlattices are an ideal model material to
study the effects of coherency strain in plasticity, due to the fine control
of nanolayer thickness and internal strain afforded by MBE deposition.
Previously, nanoindentation of bulk InGaAs at 300K gave a yield pressure of
6GPa (Jayawera et al Proc. Roy Soc, A459, 2049, 2003) while bending at 500
centigrade gave a yield value of 30MPa (Pp’ ng et al Phil. Mag. 85, 4429,
2005). In contrast, coherently strained InGaAs superlattices gave
nanoindentation values of 3GPa at room temperature and bending at 500oC gave
a yield value also around 3GPa. It appears that the coherency strain can
impart an athermal strengthening to the superlattice. It is clearly
necessary to do mechanical testing over the range 300-800K that will be able
to link the room temperature nanoindentation with the results from the high
temperature bending experiment and to determine the relationship between
strength, coherency strain and temperature. Preliminary experiments on these
samples at elevated temperatures using a hot stage and the UMIS
nanoindentation system is difficult but feasible with the help of AFM to
verify the contact area.