Spectroscopic Ellipsometry (SE) is a contact-free, nondestructive method for characterization of the dielectric and optical properties (refractive index, absorption and thickness) of layered nanostructures in the size range of < 1 nm to several μm.
Ellipsometry is an accurate technique of calculating materials’ parameters, including complex refractive index or dielectric function. The samples are usually measured in reflection and the information is given on the basis of the change of polarization of the reflected light. Standard SE methods measure the Fresnel reflection coefficients as a function of wavelength only. While, variable angle SE (VASE) measures the sample’s coefficients in s- and p-polarized light as a function of wavelength and angle of incidence.
Ellipsometry can be used to characterize thickness (depth), roughness, composition, electrical conductivity, doping concentration and other material properties. Depending on the spectral coverage of a VASE instrument, dielectrics, semiconductors, and metals can be characterized. Typical applications are the characterization of manufactured devices (semiconductors, nanoelectronics, thin films) and surface characterization, including film growth, roughness and adsorption processes.
Operando SE is an optical technique that allows accurate measurement of the optical properties and the thickness of thin-films and multi-layer systems while applying an electrochemical impulse (i.e. in operation). The equipment offered at IREC is capable to measure the changes of such variables in-situ/operando conditions. Samples can be embedded in a controlled environment such as different gases or liquid electrolytes, and can be accessed with electrical contacts. A range of operando chambers is accessible, including electrochemical chambers (tight liquid chamber with reference electrodes) and high temperature stages.
In TEM/Scanning TEM (STEM) high energy electrons incident on ultra-thin samples, allow imaging, diffraction, electron energy loss spectroscopy and chemical analysis of solid materials with a spatial resolution on the order of 1-2 Å. Samples must have a thickness of a few tens of nanometres and are prepared in sample preparation laboratory.
IR spectroscopy is based on the absorption of infrared radiation by matter. This leads to energetic transitions in the vibrational state of concrete chemical bonds. Since the frequencies that are absorbed by the molecules are characteristic of their structure, this technique is a powerful tool for qualitative and quantitative molecular analysis.
XRD provides non-destructive information on the structural order of a material. At large scattering angles XRD permits to identify different crystal phases and to quantify lattice distances and crystalline volume fractions. At low angles of incidence the surface roughness of a single crystal and the thickness of a deposition layer can be obtained.
Laser patterning is a technique for the controlled patterning of materials at micro- and nano-scales. It offers the ability to directly write patterns on the surface and complex 3D channels into the bulk of solid materials, also biomaterials. Applications can range from microfluidic systems and sensors to tissue engineering scaffolds.
Raman spectroscopy (RS) investigates the vibrational properties of a sample and provides chemical as well as structural information. RS does not require any specific sample preparation, size or condition and may be combined with micron/nano spatial resolution when operated using a confocal microscope/TERS or SNOM configuration.
