Experimental techniques employing Brillouin light scattering (BLS) and analytical techniques employing finite-element (FE) and Farnell-Adler models are being developed for characterizing acoustic modes and determining elastic moduli and dimensions of nanolines on substrates. The model specimen used for this work is an array of parallel nanoimprinted lines of polymethyl methacrylate (PMMA) on silicon with cross-sectional dimensions determined from critical-dimension small-angle x-ray scattering (CD-SAXS) to be approximately 65 nm in width and 140 nm in height. Several acoustic modes localized primarily in the nanolines were observed with BLS in the low-gigahertz frequency range, and the forms of the vibrational displacements were identified through correlation with calculations using measured bulk PMMA moduli and density as input. The acoustic modes include several flexural, Rayleigh-like, and Sezawa-like modes. Fitting of Farnell-Adler calculations to the measured dispersion curves was explored as a means of extracting elastic moduli and nanoline dimensions from the data. The results of this inversion analysis indicate that approximations involved in the Farnell-Adler calculations are too coarse to enable realistic determination of nanoline parameters. In forward calculations, the frequencies determined with the FE method are found to more closely match measured frequencies. This suggests that the FE approach may be more accurate for inversion analysis. Initial estimates of uncertainties in the FE calculations support this conclusion.
Conference Dates: April 17-21, 2006
Conference Location: San Francisco, CA
Conference Title: 2006 Materials Research Society Spring Meeting
Pub Type: Conferences
acoustic, characterization, elastodynamics, finite element, light scattering, nanoimprint, nanolines, PMMA, vibration