Surface enhanced Raman scattering of organic sample powders spread over vacuum-evaporated silver thin film

Surface enhanced Raman scattering (SERS) from samples prepared by spreading para-nitrobenzoic acid (PNBA) and adenosine powders over silver thin films was achieved. The SERS intensities of the ionized PNBA on the silver film increase with increased applied pressure through a cover-glass and reach a maximum at 0.6 MPa. In contrast, the signals caused by adenosine remain nearly unchanged under applied pressures of 0-0.6 MPa. Beyond 0.6 MPa, the signals attributable to samples decrease in intensity. Atomic force microprobe images reveal that nanometer-scale surface morphology is changed by 0.8 MPa pressure, suggesting that the decrease in SERS intensity is related to pressure-induced morphological changes. Results obtained in this study indicate that SERS spectra are obtainable easily, without solvents, under ambient conditions using dispersion of the sample powder.