Ellipsometry

Spectroscopic Ellipsometry (SE) is a contact-free, nondestructive method for the characterization of the dielectric and optical properties (refractive index, absorption coefficient, anisotropy) and structural properties (roughness, thickness and intermix of layers) in the thickness range of < 1 nm to few µm.

Ellipsometry is an accurate technique for calculating materials’ parameters, including complex refractive index or dielectric function. The samples are measured in reflection and the information is given based on the change of the 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. In addition, thanks to the vertical configuration it can be measured also the sample transmittance to be coupled with the ellipsometric data during fitting. All measurements can be done with a motor stage on a 4x4cm area.

Depending on the spectral coverage of a VASE instrument, dielectrics, semiconductors, and metals can be characterized. Typical applications are the characterization of manufactured thin films used in devices. Sample size can vary from 1x1cm up to a 6” wafer.

Finally, the measurements, thanks to a closed cell, can be performed in an N₂ environment in the case of air-sensitive samples and or by varying the temperature in the range -90°C up to 600°C to identify phase changes.

Available instruments

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Lab's Facility

Catania

CNR-IMM@CT

Instruments' description and comparison

Also consider

Ultrafast spectroscopy (or Pump-probe spectroscopy) is a technique used to study the dynamics of excited states in various materials, such as molecules, semiconductors, and solids.

It involves the use of two laser pulses. The first laser pulse, the "pump," excites the sample, elevating electrons from the ground state to an excited state. This initiation creates a non-equilibrium condition in the sample. After a controlled delay, a second laser pulse, the "probe," is sent through the sample. The probe pulse interrogates the sample to gather information about the transient states and the evolution of the excited states over time.

By varying the delay time between the pump and probe pulses, researchers can create a time-resolved picture of the dynamic processes occurring in the material. This time resolution can be on the order of femtoseconds (10^-15 seconds), allowing scientists to observe ultrafast phenomena.

These techniques provide insights into ultrafast processes, such as electronic transitions, high-order harmonics generation, molecular vibrations, and energy transfer mechanisms, that occur on very short time scales. It helps in understanding the fundamental properties of materials, such as the relaxation times of excited states, carrier dynamics in semiconductors, topological effects and the mechanisms of photochemical reactions.

Other possible studies can cover the world of solar cells, light-emitting devices, and photocatalysts, where understanding the dynamics of excited states is essential for improving efficiency and performance. Moreover, in biophysics and biochemistry, pump-probe spectroscopy can be used to investigate the dynamics of biomolecules, such as the folding and unfolding of proteins, photosynthesis mechanisms, and the behavior of molecular motors.

Ultrafast-Spectroscopy

Advanced Characterization and Fine Analysis