Single Molecule Tip-Enhanced Raman Spectroscopy with Silver Tips
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- 作者：Weihua Zhang ; Boon Siang Yeo ; Thomas Schmid ; Renato Zenobi
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：February 1, 2007
- 年：2007
- 卷：111
- 期：4
- 页码：1733 - 1738
- 全文大小：397K
- 年卷期：v.111,no.4(February 1, 2007)
- ISSN：1932-7455
文摘
We present single molecule tip-enhanced resonance Raman spectra from brilliant cresyl blue (BCB)submonolayers adsorbed on a planar Au surface with Ag tips. A gap of 1 nm between a Ag tip and the Ausubstrate was employed to create a highly enhanced electric field and to generate Raman scattering from anarea of ~100 nm2. Three lines of evidence are presented to prove the single molecule sensitivity of ourexperiments: (1) Extremely diluted samples were used. Estimations show that at most a few molecules wereexcited by the Ag tip. (2) Spectroscopic fluctuations, including intensity fluctuations, frequency shifts, andline shape changes were observed. A histogram analysis of the intensity fluctuations of two different BCBcoverages was carried out. The results clearly show the features of single molecule behavior. (3) Discretesignal losses also were observed. This is because of photochemical processes involving single molecules.Besides BCB, which shows a strong resonant absorption at 633 nm (the wavelength of the excitation laser),a self-assembled monolayer of benzenethiol, which does not strongly absorb at 633 nm, was studied. Goodquality spectra were recorded with a short exposure time (10 s) and time-dependent spectral changes werealso observed.