Laboratory for the Fourier transform Infrared (FTIR) spectroscopy and ellipsometry is equipped with two FTIR systems: a Bomem DA-8, and a SPECAC spectrometers. The former system allows for the measurements in the wide frequency range (30-25000 cm-1) at temperatures between 4 and 300 K. The latter set-up provides the excellent conditions for the measurements to be conducted in the low-frequency region (1-250 cm-1) within the 77-300 K temperature range.
The High Resolution Variable Angle Spectroscopic Ellipsometer (SOPRA GES5E - IRSE) can measure the dielectric functions of different materials and thin films in the wide spectral range from 190 nm to 28 µm at temperatures between 10 K and 400 K using ARS Inc. low vibration closed cycle cryostat, Model CS204SE-X20(OM).
Bomem DA8 Fourier-transform
IR-PLAN analytical microscope
IR-PLAN analytical microscope is a visible light microscope equipped with a high performance infrared sampling accessory designed for operation with FT-IR spectrometer. The microscope performance is directly related to the detection system because usually the analyzing samples are small so it is necessary to use MCT (mercury cadmium telluride) detector. IR-PLAN enables viewing of the exact sample area that will be analyzed and offers the best resolution available in FT-IR microscopy in order to obtain the highest possible quality spectra with the least stray light. IR-PLAN can be mounted, depending on the type of the spectrometer, in the primary compartment or in an external sample compartment or alongside of the spectrometer (Fig.1). IR-PLAN analytical microscope is equipped with a standard 1"x2" manual stage with a stage clip which provides the movement of the sample along the x, y and z-axis (focus adjustment). Usage of two circular, rotatable masking apertures above and below the sample reduces the stray light and other unwanted spectral contributions. The upper aperture is located in the infrared path between the infrared source and the sample whereas the lower aperture is located in the infrared path between the sample and the infrared detector. IR-PLAN analytical microscope can operate in transmission and reflectance mode.
Standard 15X Reflachromat IR/VIS objective of the Cassegrainian type
design for 150X viewing and 10X D-plan achromat glass objective for 100X
viewing and visual identification of the sample area with a larger field
Polarising Fourier Transform Spectrometer SPECAC 40000 for FAR IR
The instrument is designed for operation in the spectral range between 3 and 250 cm-1 (90 GHz to 7.5 THz). It is configured as a polarisation interferometer using a single pair of wire grid polarisers acting as a beamsplitter and operates with either a phase or an amplitude modulation in a step-scan mode.
The interferometer is based upon the polarising wire grid configuration developed by Martin and Puplett. The wire grids that are made from 5 mm diameter Tungsten wire spaced 12.5 (25) mm centre-to-centre. The first grid acts as a polariser to the collimated beam from the quartz-encapsulated mercury vapour arc lamp, producing two orthogonally plane polarised beams. The wires of the second grid are oriented at an angle of 45o relative to the first one, acting effectively as a beamsplitter.
The moving mirror has a mechanical path of 50 mm which in the case of a two-sided interferogram, gives the best resolution of 0.4 cm-1. The instrument is assembled with either a transmission or a reflection module for measurements on solid state specimens.
An advantage of this spectrometer is a phase modulation which has a better signal-to-noise ratio comparing to amplitude modulation. In the case of the phase modulation the fixed mirror vibrates with the frequencies between 10 and 20 Hz. As a consequence we have an asymmetric interferogram with the zero-leveled background as it is shown in the inset in figure down. For both modulations a lock-in amplifier must be used. The instrument works under the vacuum and is equipped with a LN2 cryostat.
The GES5E-IRSE Spectroscopic Ellipsometer is a combined system consisting of: DUV-Visible-NIR Spectroscopic ellipsometer (SE) and Fourier Transform Infra-Red Spectroscopic Ellipsometer (FTIR-SE). The polarizer and analyzer arms of both ellipsometers are mounted on a high resolution goniometric bench, made of double hollow crown. Both these crowns are driven by computer controlled stepper motors. The incidence angle can vary from 7 to 90° in DUV-Visible-NIR range, and from 20 to 90° in MIR range, with a theoretical resolution of 0.0005°.
The DUV-Visible-NIR Spectroscopic ellipsometer (SE) is working in a rotating polarizer configuration. It operates on the principle of mechanical modulation of the incidence light polarization by rotation of the polarizer at a constant angular frequency of 9 Hz. The analyzer remains in a fixed position, preparing the signal for the detector, insensitive to polarization. The precision of the ellipsometer for both weak and strong absorbing materials characterization is significantly enhanced with an automatically adjustable compensator. The light source is one 75 W Xe arc lamp, directly adapted to the polarizer arm. It emits a continuous spectrum of light, ranging from ultraviolet, trough visible to infrared (185-2000 nm). The light spot on the sample in parallel beam configuration is 1-10 mm2, depending on the aperture. There is also an additional miscrospot option for focusing the beam with a spot size of 365 x 270 μm, for an incidence angle of 75°. The light is introduced from the analyzer arm to the spectrometer using optical fiber making the light beam more stable. By combining the spectrometer with the photomultiplier tube (PMT) detector in UV-VIS range (190-900 nm), and InGaAs detector in NIR range (750-2000 nm), a high resolution spectrum is obtained by scanning the ellipsometric image at many discrete wavelengths. The spectrometer contains two dispersive elements (grating and prism) in collaboration with each other, separated by an intermediate fixed slit. The grating is blazed at optimum wavelength in order to obtain a maximum efficiency and the prism refracts the incoming wavelengths to act as a filter for higher order of diffraction produced by the grating.
The Fourier Transform Infra-Red Spectroscopic Ellipsometer (FTIR-SE) is a combination of a rotating analyzer configuration and a Fourier transform spectrometer. The basis of the FTIR spectrometer is a Michelson interferometer, which modulates each wavelength by a different frequency. The light leaving the Michelson interferometer enters the ellipsometer and successively passes the polarizer, the sample, the analyzer and finally hits the detector.
The light source for this IR ellipsometer is a silicon carbide (SiC) globar. Our system uses two different detectors: MCT in a range 580 cm-1 to 7000 cm-1, and DTGS in a range 385 cm-1 to 6500 cm-1. There is also an optional compensator in order to improve the accuracy of the measurements.
The spectroscopic ellipsometry can provide information about very thin layers, even down to a single atomic layer, or less. The measurements of the complex refractive index or dielectric function tensor give access to fundamental physical parameters that are related to a variety of sample properties, that include morphology, crystal quality, chemical composition, or electrical conductivity. It is commonly used to characterize single layer thin films or complex multilayer stacks ranging from a few parts of nanometers to several micrometers with an excellent accuracy.