Apertureless near-field Raman spectroscopy

Exploring the Nanoscale: Fifteen Years of Tip-Enhanced Raman Spectroscopy

Spectroscopic methods with high spatial resolution are essential to understand the physical and chemical properties of nanoscale materials including biological and chemical materials. Tip-enhanced Raman spectroscopy (TERS) is a combination of surface-enhanced Raman spectroscopy (SERS) and scanning probe microscopy (SPM), which can provide high-resolution topographic and spectral information simultaneously below the diffraction limit of light. Even examples of sub-nanometer resolution have been demonstrated. This review intends to give an introduction to TERS, focusing on its basic principle and the experimental setup, the strengths followed by recent applications, developments, and perspectives in this field.

Developments in and practical guidelines for tip-enhanced Raman spectroscopy

This feature review provides an overview of the state-of the art and recent developments in tip-enhanced Raman spectroscopy (TERS), in-depth information about the different available types of instruments including their (dis-)advantages and capabilities as well as a short glance at a number of samples that have recently been investigated using TERS. Issues concerning the progression of TERS from point spectroscopy to an imaging technique are discussed, as well as problems arising from background and contamination signals. This review is concluded with a short TERS 'user guideline', trying to aid researchers new in the field to properly align and test their own TERS setups. Finally, a short outlook is given and some critical issues are raised that need to be solved by the community sooner or later, in order to promote TERS towards a 'push-button' operation.

Sequential electrochemical oxidation and site-selective growth of nanoparticles onto AFM probes

In this work, we reported an approach for the site-selective growth of nanoparticle onto the tip apex of an atomic force microscopy (AFM) probe. The silicon AFM probe was first coated with a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) through a chemical vapor deposition (CVD) method. Subsequently, COOH groups were selectively generated at the tip apex of silicon AFM probes by applying an appropriate bias voltage between the tip and a flat gold electrode. The transformation of methyl to carboxylic groups at the tip apex of the AFM probe was investigated through measuring the capillary force before and after electrochemical oxidation. To prepare the nanoparticle terminated AFM probe, the oxidized AFM probe was then immersed in an aqueous solution containing positive metal ions, for example, Ag+, to bind positive metal ions to the oxidized area (COOH terminated area), followed by chemical reduction with aqueous NaBH 4 and further development (if desired) to give a metal nanoparticle-modified AFM probe. The formation of a metal nanoparticle at the tip apex of the AFM probe was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA).

Stress characterization of Si by near-field Raman microscope using resonant scattering

We have developed a tapping-mode scanning near-field optical Raman microscope (SNORM) with a caved and pyramidical probe, using resonant Raman scattering, and have measured the stress distribution of Si. The peak frequency shifts to a lower frequency by 0-0.5 cm(-1) in the area covered by silicon dioxide, whereas it shifts to a higher frequency by 0-0.3 cm(-1) in the area uncovered by silicon dioxide, showing that the areas covered and uncovered by silicon dioxide are under tensile and compressive stresses, respectively. It has been found that compressive stresses of about 0.69 GPa/cm2 are concentrated on the corner of the area uncovered by silicon dioxide. The comparison of stress distributions measured with and without the cantilever shows that the SNORM we developed has a spatial resolution of at least less than 250 nm.

Nanoscale imaging of carbon nanotubes using tip enhanced Raman spectroscopy in reflection mode

An apertureless tip enhanced Raman spectrometer in reflection mode geometry is demonstrated. A spatial resolution as small as 30 nm was achieved. This was implemented by placing a sharp gold tip near the single wall carbon nanotubes using an atomic force microscope (AFM). The tip was illuminated from the same side of the sample which eliminated the need for a transparent substrate. The tip was maintained at a distance of a few nanometers using a quartz tuning fork. The Raman signal was collected from the G peak of the single wall carbon nanotubes using a single photon detecting module and topography image was acquired by the AFM.