Quantum Material Spectroscopy
Prof. Alexander Tartakovskii
DEPARTMENT OF PHYSICS AND ASTRONOMY, THE UNIVERSITY OF SHEFFIELD, UK
Background
Alexander Tartakovskii is a Professor of Solid State Physics at the School of Mathematical and Physical Sciences at the University of Sheffield, where his research group studies atomically thin two-dimensional (2D) materials focusing on a large family of 2D semiconductors. These materials are layered crystals from where thin films are extracted by exfoliation, similar to how graphene is produced from graphite. The original bulk layered crystals feature strong in-plane bonds and weak van der Waals-like interlayer bonds. This allows exfoliation of atomically thin films that can be stacked to produce complex heterostructures. These quantum materials and their heterostructures exhibit a range of quantum effects that can be studied using optical micro-spectroscopy techniques.
Prof. Tartakovskii further explains his research, “Every technique we use is ‘micro’, as these materials are a few microns across and a few atoms thick. We use micro-spectroscopy setups with a range of techniques like micro-photoluminescence, micro-Raman, micro-reflectance contrast, dark-field spectroscopy, and transmission spectroscopy, all often at cryogenic temperatures or high magnetic fields.”
“These materials exhibit quantum confinement effects due to being only a few atoms thick. An exciting recent development is moiré physics observed when two atomically thin films are assembled in a heterostructure and are slightly twisted with their atoms forming periodic super-structures called moiré superlattices. For more subtle effects we cool our samples to cryogenic temperatures, but the measurement tools are still the same, spectrometers and CCDs.”
Figure 1:Image from the lab of Prof. Tartakovskii showing a range of equipment from Teledyne Princeton Instruments, including two SpectraPro HRS 500 spectrometers, one connected to a PyLoN-IR InGaAs camera and one connected to a BLAZE CCD camera.
Challenge
The quantum materials studied by Prof. Tartakovskii are very small, requiring advanced spectroscopy and imaging techniques in order to characterise their behaviour including various quantum effects.
Prof. Tartakovskii outlined some more challenges, “The signal level for techniques like micro photoluminescence spectroscopy is not very high, this is why low-noise cameras are particularly useful and important. Also, when doing micro-Raman, measuring close to the laser line can be extremely difficult.”
“We are also moving to develop tip-enhanced nano-spectroscopy techniques for additional characterisation on the nano-scale. This will require synchronisation of the tip oscillations in kHz range and the read-out from the camera chip.”
We have enjoyed our collaboration with Teledyne Princeton Instruments for the last 15-20 years… the sensitivity and low noise levels of the sensors is quite amazing.
Prof. Alexander Tartakovskii
Solution
Prof. Tartakovskii is a long-time user of Teledyne Princeton Instruments spectroscopy and imaging equipment, making the most of the efficiency, sensitivity and ease of use of these systems.
Prof. Tartakovskii described his experience with his equipment, “We do a lot of different kinds of optical spectroscopy, with very few exceptions we always use Teledyne Princeton Instruments equipment, it’s our equipment of choice. We have enjoyed our collaboration with Teledyne Princeton Instruments. Our labs are full of your equipment including spectrometers and various cameras, which we’ve been buying in the last 15-20 years.”
“For our research we use spectrometers such as the SpectraPro HRS 750, we use the turret to change the gratings so we can easily switch between micro-Raman, micro photoluminescence, or other spectroscopy techniques, as well as being able to work in a wide range of wavelength and extremely close to the laser line.”
“We also have a new model of the BLAZE camera which can image very quickly. I’m excited to see how this can be used with optical nano-spectroscopy, where we will use a tip similar to atomic force microscopy. We plan to attempt synchronisation of the tip oscillations with the readout on the BLAZE, operating at several kilohertz. The sensitivity of the sensor is quite amazing, from the UV towards 1 μm in the NIR. So this powerful system will find many uses across several material types.”
Reference
Alexeev, E.M., Ruiz-Tijerina, D.A., Danovich, M. et al. (2019) Resonantly hybridized excitons in moiré superlattices in van der Waals heterostructures. Nature 567, 81–86 https://doi.org/10.1038/s41586-019-0986-9
