Elastic constants and cross-sectional dimensions of imprinted nanolines of poly(methyl methacrylate) (PMMA) on silicon are determined nondestructively from finite-element inversion analysis of dispersion curves of hypersonic acoustic modes of these nanolines measured with Brillouin light scattering (BLS). The results for the cross-sectional dimensions, under the simplifying assumption of vertical sides and a semicircular top, are found to be consistent with dimensions determined from critical-dimension small-angle xray scattering (CD-SAXS) measurements. The elastic constants C_11 and C_44 are found to be, respectively, 11.6 % and 3.1 % lower than their corresponding values in bulk PMMA. This result is consistent with thickness-dependent changes in Young's modulus determined from quasi-static buckling measurements on PMMA films with lower molecular weights. This study provides the first evidence of size-dependent effects on hypersonic elastic properties of polymers.
Pub Type: Journals
BLS, Brillouin light scattering, elastic constants, finite element analysis, nanoimprint lithography, nanolines, PMMA