Tip-enhanced Raman spectroscopy (TERS) is based on the optical excitation of localized surface plasmons in the tip-substrate cavity, which provides a large but local field enhancement near the tip apex. We report on TERS with smooth single crystalline surfaces as substrates. The adsorbates were CN ÿ ions at Au(111) and malachite green isothiocyanate (MGITC) molecules at Au(111) and Pt(110) using either Au or Ir tips. The data analysis yields Raman enhancements of about 4 10 5 for CN ÿ and up to 10 6 for MGITC at Au(111) with a Au tip, probing an area of less than 100 nm radius.

Our recently developed approach of UHV-tip-enhanced Raman spectroscopy permits us to acquire Raman spectra of a few single brilliant cresyl blue (BCB) molecules and even a single one adsorbed on a Au(111) surface. This is substantiated by simultaneously recorded STM images. Furthermore, because of the reduced photobleaching in UHV, the time frame for spectral acquisition is sufficiently extended to allow tip-enhanced Raman imaging of a single BCB molecule with a lateral resolution of 15 nm.

We describe a method of preparing gold scanning tunneling microscopy (STM) tips by direct current electrochemical etching in concentrated HCl and ethanol solution. Gold tips with tip apex radius lower than 30 nm can be reproducibly prepared by this method. The influence of the solution composition, etching voltage on the surface structure, and sharpness has been investigated. These tips can be efficiently used for STM imaging, tip-enhanced Raman spectroscopy, and light emission investigations on the same sample

Tip-enhanced Raman spectroscopy (TERS) is a very powerful variant of surface-enhanced Raman spectroscopy (SERS). In a sense, TERS overcomes most of the drawbacks of SERS but keeps its advantages, such as its high sensitivity. TERS offers the additional advantages of high spatial resolution, much beyond the Abbe limit, and the possibility to correlate TER and other scanning probe microscope images, i.e., to correlate topographic and chemical data. TERS finds application in a number of fields, such as surface science, material science, and biology. Single-molecule TERS has been observed even for TERS enhancements of “only” 106–107. In this review, TERS enhancements are discussed in some detail, including a condensed overview of measured contrasts and estimated total enhancements. Finally, recent developments for TERS under ultrahigh vacuum conditions are presented, including TERS on a C60 island with a diameter of a few tens of nanometers, deposited on a smooth Au(111) surface.

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By application of 20 fs laser pulses, vibrational wave packets of low-energy modes (mainly 357 and 421 cm-1) were generated in the perylene chromophore that gave rise to periodic beats that lasted longer than 1 ps in transient absorption signals. Electron transfer from the excited singlet state of the perylene chromophore, attached as molecule DTB−Pe via the −CH2−phosphonic acid group to anatase TiO2, was measured in ultrahigh vacuum with a time constant of 75 fs. The vibrational wave packet that was generated in the donor state continued its motion for several hundred femtoseconds in the product state of the reaction, i.e., in the ionized chromophore. This is direct proof for electron transfer occurring from a nonrelaxed vibrational population that was created by the short laser pulse in the donor molecule. The rise of the product state showed a staircase-like time dependence. The steps are attributed to electron transfer that occurs preferentially each time the vibrational wave packet (frequency 480 cm-1) reaches a crossing point for the potential curves of reactant and product state. Such wave-packet modulation of heterogeneous electron transfer can arise if the density of electronic acceptor states in the electrode is changing strongly over an energy range on the order of the reorganization energy below the excited molecular donor orbital.