Raman Spectroscopy of nanomaterials: How spectra relate to disorder, particle size and mechanical properties

Abstract

The purpose of this review is to provide non-specialists with a basic understanding of the information micro-Raman Spectroscopy (mRS) may yield when this characterization tool is applied to nanomaterials, a generic term for describing nano-sized crystals and bulk homogeneous materials with a structural disorder at the nanoscale e typically nanoceramics, nanocomposites, glassy materials and relaxor ferroelectrics. The selected materials include advanced and ancient ceramics, semiconductors and polymers developed in the form of dots, wires, films, fibres or composites for applications in the energy, electronic and aeronauticseaerospace industries. The text is divided into five sections:

Characterisation, phase stability and surface chemical properties of photocatalytic active Zr and Y co-doped anatase TiO2 nanoparticles

“…Except for the shoulder at 650 cm -1 , these bands disappear after annealing (see below). The Raman spectrum of sample TiZrY5 exhibits a broad background and less distinct bands, again signalling an amorphous content with a characteristic Bose-Einstein background [27,46], in good agreement with the XRD observations. The results from the XRD and Raman analysis are consistent with Y and Zr replacement of Ti atoms in the anatase lattice up to a total doping concentration of about 3 at% Zr and 3 at% Y as determined by XPS.…”

Potential and Drawbacks of Raman (Micro)spectrometry for the Understanding of Iron and Steel Corrosion

“…The recording of the Raman signatures will depend on the phase colour -i.e. their electronic band structure -that determines the light penetration and the intensity of the scattered signal as well as on the phase structure : the higher the symmetry, the lower number of Raman peaks (Lewis & Edwards, 2001;Gouadec & Colomban, 2007a). Fig.…”

“…The Raman signature of any compound that structure is built with one or many strong covalent-bonded vibrational units, can be separated in four groups (Gouadec & Colomban, 2007a): i. (symmetric) stretching modes, for instance Fe II -O and/or Fe III -O modes peaking in the 400-700 cm -1 region for oxides, 300-600 cm -1 for chlorides , 200-400 cm -1 for sulphides.…”

“…5). The numerical aperture is a key parameter because it sets the resolution R of the microscope, defined as the shortest spacing for two points on a sample surface to be resolved with λ wavelength observation (see references in Gouadec & Colomban, 2007a;Gouadec et al, 2010):…”

“…The former is called Rayleigh scattering and the latter, which occurs only if vibrations change polarizability (∂α ij /∂Q≠0), is Raman scattering. Other terms correspond to Hyper and higher orders Raman scattering (Long, 1977: Gouadec & Colomban, 2007a Table 1. Raman fingerprint of main corrosion products.…”