two-dimensional materials

The AFM-IR is an innovative technique which couples the tip of an atomic force microscope (AFM) to a quantum cascade lasers which emits in the mid-IR regime (900-1800 cm-1) [1]. Exploiting the photothermal expansion of the sample using the nanometric tip of the AFM one can acquire mid-IR spectra or absorption maps beyond the diffraction limit. Due to the limited dimension of the 2D materials, InfraRed spectroscopy is usually impossible on these materials using common spectroscopic techniques. In this contest we aim to exploit the experience acquired with the AFM-IR technique by our group on biological or plasmonic samples [2,3] and move to the near-field study of 2D semiconductors beyond the diffraction limit!

Ref.

[1] Dazzi, Alexandre, and Craig B. Prater. "AFM-IR: Technology and applications in nanoscale infrared spectroscopy and chemical imaging." Chemical reviews 117.7 (2017): 5146-5173.

[2] Giliberti, Valeria, et al. "Tip-enhanced infrared difference-nanospectroscopy of the proton pump activity of bacteriorhodopsin in single purple membrane patches." Nano letters 19.5 (2019): 3104-3114.

[3] Calandrini, Eugenio, et al. "Mapping the electromagnetic field confinement in the gap of germanium nanoantennas with plasma wavelength of 4.5 micrometers." Applied Physics Letters 109.12 (2016): 121104.

Raman Spectroscopy is a useful technique to probe the vibrational and electronic excitation of matter, but also their interplay. It relies on inelastically scattered light from a sample. It is well known that the Raman process cross section (which is anyway very low) is proportional to the fourth power of the energy of the incoming radiation. For that reason Raman scattering studies on solid state materials are usually performed using visible light. Anyway, when the incoming radiation matches a real electronic transition of the system, in a so called resonance condition, a huge enhancement of the Raman signal is observed, which can lead to the visibility of otherwise hidden features [1]. We thus aim to exploit Raman scattering using Infrared Radiation using both commercial and homemade set-up in order to perform resonant raman scattering on materials presenting low energy bandgap which resonance raman spectra are unexplored.

Ref.

[1] Sotgiu, Simone, et al. "Raman scattering with infrared excitation resonant with the MoSe 2 indirect band gap." Physical Review B 106.8 (2022): 085204.