(a) Concept of tip-enhanced near-field Raman spectroscopy using a metallized cantilever tip, (b) enhancement of the electric field, and (c) atomic site-selective sensitivity at the very end of the tip.
Optimized geometry of free adenine molecule and adenine-silver isomers; Ad-N1, Ad-N3, Ad-N7, Ad-N10. Potential energy of each isomer plotted as a function of the bond distance between silver atom and nitrogen atom (Ag–N).
Calculated Raman spectra of four isomers at the optimized bond distance of nitrogen and silver atom shown in Fig. 2 in comparison with free adenine molecule. Right column is the expanded spectrum of each spectrum between 600 and , in which the RBM is contained.
Assigned vibration modes shown in Fig. 3. Capitals (A)–(D) correspond to the same bands classified by the same capital alphabets (A)–(D) in Fig. 3 (A) is in-plane ring-deforming mode, (B) is out-of-plane ring-deforming mode, (C) is ring breathing mode, and (D) is out-of-plane ring-bending mode.
(a) Tip-enhanced Raman (with a metallic tip) and (b) micro-Raman (without a metallic tip) spectra of an adenine nanocrystal. (c) Micro-Raman spectrum of bulk adenine sample. (d) Three sets of tip-enhanced Raman spectra of RBM at different positions of the nanocrystal. The excitation wavelength is . The exposure time is for (a)–(c) and for (d), respectively.
Calculated Raman shifts and intensities of five vibrational modes as a function of the bond distance between silver atom and nitrogen atom (Ag–N). (a) RBM, (b) in-plane ring-deforming mode, (c) out-of-plane ring-bending mode, (d) out-of-plane ring-deforming mode, and (e) out-of-plane bending mode. Zoomed features of Raman intensities of (a) and (b) are also plotted as insets.
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