THz frequency-domain ellipsometer
In the heart of THeMAC is the in-house developed THz frequency-domain spectroscopic ellipsometer - the only one in Europe and only the third in the world. The instrument design employs elements of the stealth technology in order to minimize parasitic signals, which are particularly strong in the THz spectral range. The ellipsometer is controlled and the measurements are performed with software developed by J. W. Woollam Co., the leading producer of ellipsometry equipment. The ellipsometer features:
- Backward wave oscillator THz source (97-178 GHz)
- Output power up to 26 mW
- Schottky diode frequency multipliers: x2, x3, x6
- Achievable spectral range 0.1 – 1 THz
- Golay cell and Bolometer detector
- Free standing wire grid polarizers
- Anti-standing wave design
- Rotating analyzer configuration
- Measure the upper (3x3) block of the full (4x4) Mueller matrix
- Reflection and transmission measurements
- Variable angles of incidence (30°-75°)
Current THz ellipsometer configuration
Superconducting magnet for OHE measurements
THeMAC has purchased a closed-cycle cryostat superconducting magnet with variable temperature insert (VTI) from Cryogenis Ltd. The magnet features:
- variable magnetic field from -8T to +8T
- variable sample temperature from 1.5K to 400K
- large 17mm diameter optical ports to minimize diffraction effects
- diamond windows for minimal signal losses
- reflection measurements at 45° fixed angle of incidence
- transmission measurements
The magnet expends our capabilities to perform OHE measurements at variable magnetic field and temperature. The magnet has been installed at the instrument and is in its final acceptance test phase.
Superconducting magnet for OHE measurements
Room temperature THz optical Hall effect
The THz ellipsometer is specifically designed to allow measurement of samples in external magnetic field, dubbed optical Hall effect (OHE). Current instrument configuration allows OHE measurements only at room temperature and using a permanent low-magnetic field magnet (B=0.55T). This configuration implements the so-called Cavity Enhanced Optical Hall effect (CE-OHE), where the reflective surface of the magnet serves as a mirror and the distance between the sample and the magnet can be varied. This approach greatly enhances the OHE signal and compensates for the low magnetic field provided by the permanent magnet.
CE-OHE setup with computer controled air gap
Extension to far infrared wavelengths
Vertext 70 far-infrared (FIR) Fourier transform spectromenter has been purchesed from Bruker. It has been integrated into the system and is in a testing phase. The spectrometer expands the range of the ellipsometer and the OHE measurements up to 20 THz.
Gas-cell for in-situ measurements
A gas-cell, which allows measurement of samples under different environments at room temperature is also available. The cell can be flushed with dry and humidified air, nitrogen, helium or other non-reactive gases. The cell can be equipped with a permanent magnet allowing in-situ CE-OHE measurements at 45° angle of incidence.
Gas-cell for in-situ CE-OHE measurements
Data storage and analysis lab
The data storage and analysis lab features a server with 1 CPU (with a possibility add one more) with 12 physical cores (24 virtual). It allows to access the data analysis software remotely. A data bank with materials’ THz model dielectric functions, model approaches and structural models is being developed and will be made available to the users. We are developing a web-based portal, where THeMAC internal and external users can learn about the THeMAC instrumentation, receive online training. Furthermore, we will offer our users training courses on spectroscopic ellipsometry data analysis.
To connet from Windows use Remote Desktop
To connect from Linux you need to use Remmina. It is also necessary to install freerdp - a free implementation of Windows Remote Desktop Protocol
We plan to upgrade the THe ellipsoment to dual-rotating configuration. This will allow to measure the full (4x4) Mueller maxrix.
Cell for measuring of liquids
We will develop a cell to allow performing ellipsometry on liquids. The goal is to extend the scope of THeMAC toward mesuring bio-melecules in solutions.
Gas cell with sample temperature control
A gas cell for in-situ ellipsometry and CE-OHE measurements in different environments at high temperatures (20°C to 400°C) will be developed. This will allow:
- to study the temperature dependence of material properties
- establish the material properties and device characteristics at the devices operational temperatures