We describe a method of preparing gold scanning tunneling microscopy STM tips by direct currentelectrochemical etching in concentrated HCl and ethanol solution. Gold tips with tip apex radiuslower than 30nm can be reproducibly prepared by this method. The influence of the solutioncomposition, etching voltage on the surface structure, and sharpness has been investigated. Thesetips can be efficiently used for STM imaging, tip-enhanced Raman spectroscopy, and light emissioninvestigations on the same sample.

Layered core-shell bimetallic silver-gold nanoparticles were prepared by coating Au layers over Ag seedsby a seed-growth method. The composition of Ag100-xAux particles can vary from x) 0 to 30. TEM andSEM images clearly show that the bimetallic nanoparticles are of core-shell structure with some pinholes onthe surface. Strong surface-enhanced Raman (SER) signals of thiophenol and p-aminothiophenol have beenobtained with these colloids. It was found that the SERS activity of aggregated colloids critically depends onthe molar ratio of Ag to Au. With the increase of the Au molar fraction, the SERS activity enhances first andthen weakens, with the maximal intensity being 10 times stronger than that of Ag colloids. The AgcoreAushellnanoparticles were then labeled with monoclonal antibodies and SERS probes and used for immunoassayanalysis. In the proposed system, antibodies immobilized on a solid substrate can interact with the correspondingantigens to form a composite substrate, which can capture reporter-labeled AgcoreAushell nanoparticles modifiedwith the same antibodies. The immunoreaction between the antibodies and antigens was demonstrated by thedetection of characteristic Raman bands of the probe molecules. AgcoreAushell bimetallic nanoparticles, as anew SERS active and biocompatible substrate, will be expected to improve the detection sensitivity ofimmunoassay.

Tip-enhanced Raman spectroscopy (TERS) is based on the optical excitation of localized surfaceplasmons in the tip-substrate cavity, which provides a large but local field enhancement near the tipapex. We report on TERS with smooth single crystalline surfaces as substrates. The adsorbates wereCN 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 4105 for CN andup to 106 for MGITC at Au(111) with a Au tip, probing an area of less than 100nm radius.

Investigation of benzene adsorption on different metal surfaces closer to a practical system appears to be avery important intermediate stage to utilize the conclusion obtained on single-crystal surfaces. In this paper, we studied the electrochemical adsorption behaviors of benzene on roughened Pt group electrodes usingsurface enhanced Raman spectroscopy (SERS). The effects of potential, surface roughness, and benzeneconcentration were investigated. Significant difference in surface Raman spectra of benzene on Ru, Rh, Pd,and Pt surfaces were found. On Pt surfaces, the parallel-chemisorbed benzene, the vertical dissociated chemisorbedbenzene, and the physisorbed benzene were observed, evidenced by the ring vibration mode appearingat 872, 1012, and 991cm-1, respectively. On Pd, only parallel-chemisorbed benzene and physisorbed benzenewere found. On Rh and Ru, the SERS signals were mainly from the parallel-chemisorbed benzene, with anextremely weak signal from the physisorbed benzene. The potential dependent study reveals that the parallelchemisorbedspecies interacts strongest with the substrate, while the physisorbed species can be easily removedat positive potentials. The models for the adsorbed benzene were given to account for the different types ofbenzene on these Pt group metals. The difference in the atomization heat of the four metals was used tointerpret the different interaction strength of benzene with Pt group metals.