应用

Why TERS? to give a fundamental insight into the optical and electronic properties of 1D materials.

The synthesis of carbon nanotubes (CNTs) results in bundles that often contain a variety of tubes with different structural properties. Conventional Raman is widely used to characterize quasi-one dimensional structures such as CNTs, however the optical imaging of their nanoscale properties is severely restricted to the optical diffraction limit. A good illustration of how TERS can be used to gain information that would not have been accessible with conventional Raman can be seen in the following TERS map.

Why TERS? to characterize graphene in terms of size, shape, electronic properties, distribution of defects and contaminants.

The discovery of graphene in 2004 has given rise to a surge in research activities on 2D materials with novel properties and the need to characterize them at the nanoscale. As for 1D materials, TERS gives localized information down to 10 nm through the Raman signature and allows identification of defects (point defects, vacancies or dopants). More than identification, thanks to TERS imaging, the local distribution of the defects concentration in graphene and graphene oxide is possible.

Monitoring the defects of the graphene flakes and their concentration (via the distribution of the ratio of G to D band intensities) is of great interest to study the impact on the design of devices made with such materials.

Graphene, but also any functionalized and decorated 2D materials, molybdenum disulfide MoS2, tungsten diselenide WSe and others 2D TMDCs (two-dimensional transition metal dichalcogenide materials) are good candidates for a TERS study.

Why TERS? the chemical characterization of molecules on a surface is crucial for understanding the reactivity and function of molecules.

In surface chemistry, catalysis or biology, the chemical characterization of molecules on a surface is crucial for understanding their reactivity and function. However, the small quantity of molecules present renders their spectroscopic characterization challenging and most of the time impossible by confoncal Raman.

Why TERS? Monitoring the local stress/strain in semiconducting nanostructures and the impact on the electronic properties.

Characterization of the strain present in semiconductor nanostructures such as strained Si (sSi) on insulator (sSOI) or epitaxially grown Si_xGe_1-x on Si (SiGe/Si) is of special interest for the microelectronics industry.

The stress state in crystal materials can be determined by using techniques such as X-ray diffraction, transmission electron microscopy and Raman spectroscopy. The main advantages of the Raman technique over the first two are its non-destructive nature and no need for sample preparation. The presence of strain breaks the crystal symmetry and shifts the frequencies of the Raman modes with respect to the unstrained ones thus making possible the determination of the stress state. Anyway Raman spectroscopy only gives an average value of the strain, and the optical resolution is not suited to current problems of the microelectronics industry.

Because it has the capability to provide nanoscale chemical composition and morphology in a label-free manner, TERS has been used to study a number of biomaterials such as amino acid and nucleobase monolayers, proteins, macromolecular protein assemblies, nucleic acids, cell surfaces, and cell surface interactions.

Some of the earliest TERS studies on biomaterials focused on pure components, like nucleobases and amino acids. It was shown that the normal nucleobases A, T, G, C adsorbed separately on a surface in picomole quantities could be differentiated based on their TER spectra. Later, they were also identified in nucleic acids with TERS, which makes TERS a novel method of label-free sequencing.