Liang Haihe, Tian Hong, McCreery Richard L
Department of Chemistry, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, USA.
Appl Spectrosc. 2007 Jun;61(6):613-20. doi: 10.1366/000370207781269765.
Raman and ultraviolet-visible (UV-Vis) absorption spectra were obtained for nitroazobenzene (NAB) chemisorbed on smooth and rough silver, and they were compared to published spectra for NAB on sp(2) hybridized pyrolyzed photoresist film (PPF) surfaces. High signal-to-noise ratio Raman spectra were obtained for 4.5 nm thick NAB films on PPF and smooth Ag due to significant enhancement of the NAB scattering relative to that observed in solution. The UV-Vis spectra of chemisorbed NAB exhibited a significant shift toward longer wavelength, thus bringing the NAB absorption closer to the 514.5 nm laser wavelength. The red shift was larger for PPF than for smooth Ag, consistent with the approximately 5x stronger Raman signal obtained on PPF. Deposition of Ag onto quartz without a chromium adhesion layer produced a rough Ag surface that enhanced the Raman spectrum of chemisorbed NAB by a factor of approximately 1000, as expected for roughened Ag due to electromagnetic field enhancement. The strong Raman signal permitted observation of NAB at low coverage and revealed changes in the NAB spectrum as the film progressed from submonolayer to multilayer thicknesses. Finally, deposition of Ag onto PPF/NAB samples through a metal grid produced Ag squares on top of the NAB, which enhanced the Raman scattering of the NAB layer by a factor of approximately 100. Deposition of a final conducting film on the Ag squares should permit in situ observation of a wide range of molecules in operating molecular electronic junctions.
我们获得了吸附在光滑和粗糙银表面的硝基偶氮苯（NAB）的拉曼光谱和紫外可见（UV-Vis）吸收光谱，并将它们与已发表的NAB在sp(2)杂化热解光刻胶膜（PPF）表面的光谱进行了比较。由于相对于溶液中观察到的情况，NAB散射有显著增强，因此在PPF和光滑银表面上4.5 nm厚的NAB薄膜获得了高信噪比的拉曼光谱。化学吸附的NAB的UV-Vis光谱向更长波长有显著位移，从而使NAB吸收更接近514.5 nm激光波长。PPF上的红移比光滑银上的更大，这与在PPF上获得的约5倍更强的拉曼信号一致。在没有铬粘附层的情况下将银沉积到石英上会产生粗糙的银表面，如预期的那样，由于电磁场增强，粗糙的银使化学吸附的NAB的拉曼光谱增强了约1000倍。强拉曼信号允许在低覆盖率下观察NAB，并揭示了随着薄膜从亚单层到多层厚度的变化，NAB光谱的变化。最后，通过金属网格将银沉积到PPF/NAB样品上，在NAB顶部产生了银方块，这使NAB层的拉曼散射增强了约100倍。在银方块上沉积最终的导电膜应该能够原位观察操作中的分子电子结中的各种分子。
