The use of instrumented indentation to characterize the mechanical response of polymeric materials was studied. A model based on contact between a rigid probe and a linear viscoelastic material was used to calculate values for the creep compliance and stress relaxation modulus for two glassy polymeric materials, epoxy and poly(methyl methacrylate), and two poly(dimethyl siloxane) (PDMS) elastomers. Results from bulk rheometry studies were used for comparison with the indentation stress relaxation results. For the two glassy polymers, the use of sharp pyramidal tips produced responses that were considerably more compliant (less stiff) than the rheometry values. Additional study of the deformation remaining in epoxy after indentation creep testing as a function of the creep hold time revealed that a large portion of the creep displacement measured was due to postyield flow. Indentation creep measurements of the epoxy with a rounded conical tip also produced nonlinear responses, but the creep compliance values appeared to approach linear viscoelastic values with decreasing creep force. Responses measured for the unfilled PDMS were mainly linear elastic, with the filled PDMS exhibiting some time-dependent and slight nonlinear responses in both rheometry and indentation measurements.

Dynamic nanoindentation was performed on a cured epoxy, a poly(methyl methacrylate) (PMMA), and two poly(dimethyl siloxane) (PDMS) samples of different crosslink densities. These samples were used to compare dynamic nanoindentation with classical rheological measurements on polymeric samples in the glassy and rubbery plateau regions. Excellent agreement between bulk rheological data and dynamic nanoindentation data was observed for the two glassy materials (epoxy and PMMA) and the less compliant PDMS sample. More divergent results were observed for the more compliant PDMS sample. The theoretical foundation and historical development of the working equations for these two types of instrumentation are presented and discussed. The major difference between nanoindentation and the more classical rheological results is in the treatment of the instrument-sample interface.

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Raman shifts are investigated on silicon and germanium substrates under the uniaxial tensile strain on various substrate orientations. The strain splits the triply degenerate optical (LO, TO) phonons at the zone center (k approximate to 0). The redshifts of Si Raman peaks induced by the tensile strain on all substrate orientations are observed. With the specific polarization of the incident light, however, the unusual blueshifts of Ge Raman peaks induced by the tensile strain are observed on (110) and (111) Ge substrates. By using the suitable phenomenological constants and taking the Raman selection rules into consideration, the experimental results are in reasonable agreement with the lattice dynamical theory