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.

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) was investigated with malachite green isothiocyanate adsorbed at an Au(111) surface. TERS is based on the excitation of localized surface plasmons in the tip apex, producing strongly enhanced electromagnetic fields. The key conditions for giant TERS are sideillumination of the tip, well-prepared single-crystalline surfaces and sharp, smooth gold tips. A TERS enhancement of about 6 × 10 6 has been observed for dye molecules adsorbed at the Au(111) substrate in a region of about 50 nm diameter beneath the tip. This corresponds to a 2500-fold increase in the light intensity at the Au(111)/air interface, which in addition causes fast but local bleaching of the dye. This bleaching behavior was analyzed in detail, giving direct insight into the strength and size of the enhanced field. In addition, the bleaching constant was higher for MGITC in an unperturbed environment than for MGITC in an environment that had been substantially bleached. The MGITC spectra were also different for these two cases. Copyright  2005 John Wiley & Sons, Ltd.KEYWORDS: apertureless scanning near-field optical microscopy; gold(111); tip-enhanced Raman spectroscopy; malachite green isothiocyanate; near-field enhancement INTRODUCTIONThe general use of Raman spectroscopy for surface studies is an old dream of surface scientists. However, with differential Raman cross-sections of the order of d /d ³ 10 31 -10 28 cm 2 sr 1 , surface studies were out of reach in general, although a (small) number of attempts were made to apply (normal) Raman scattering for the investigation of well-defined surfaces.Ł Correspondence to: Bruno Pettinger, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany. E-mail: pettinger@fhi-berlin.mpg. Recently, a new approach has been developed, denoted tip-enhanced Raman spectroscopy (TERS), in some cases also called 'apertureless scanning near-field optical microscopy (SNOM)'. 1 With the advent of TERS, the above-mentioned dream is now becoming a reality. 1 -12 TERS is a particular promising variant of SERS, the well-studied field of surface-enhanced Raman scattering spectroscopy. The latter requires roughened surfaces at which two cooperative enhancement mechanisms for Raman scattering are working. Roughened surfaces can support the excitation of localized surface plasmons leading to the so-called 'electromagnetic enhancement' and provide the peculiar adsorption sites at which the so-called 'chemical enhancement' is operative. In the literature, a large range of (total) enhancement factors are given, starting with the 10 6 -fold enhancement found for pyridine on roughened silver electrodes 13 up to the giant 10 12 -10 14 -fold enhancement reported more recently by Nie and Emory 14 and Kneipp et al. 15 for dyes at colloidal particles. In the latter case, the authors claim to have reached single-molecule detection sensitivity. However, in all these cases the general drawback of SERS investigations remains: the surface enhancement (in particular its ...

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A tip for surface scientists: Tip‐enhanced Raman spectroscopy (TERS) was used to record surface Raman spectra of benzenethiol and pyridine‐4‐thiol adsorbed on Au and Pt single‐crystal surfaces (see picture). The benzenethiol spectra on the two surfaces are distinctly different. This result illustrates the power of TERS as a diagnostic tool with high spatial resolution for surface studies.

We report an in-plane solid-liquid-solid (IPSLS) mode for obtaining self-avoiding lateral silicon nanowires (SiNW) in a reacting-gas-free annealing process, where the growth of SiNWs is guided by liquid indium drops that transform the surrounding a-SiratioH matrix into crystalline SiNWs. The SiNWs can be approximately mm long, with the smallest diameter down to approximately 22 nm. A high growth rate of >10(2) nm/s and rich evolution dynamics are revealed in a real-time in situ scanning electron microscopy observation. A qualitative growth model is proposed to account for the major features of this IPSLS SiNW growth mode.

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