In this talk I will present the changes in optical properties of InSe from bulk until the single monolayers: Band structure and absorption calculations, vibrational modes and photoluminescence at low and high temperatures. First of all, the optical contrast between thin InSe flakes on SiO2/Si substrates can be used to detect and estimate the thickness of few layer InSe nanoflakes using standard white illumination and color CCD imaging, even if these simple measurements points towards a change in the dielectric constant of InSe when reducing the size down to the nanometer scale. In contrast, Raman active modes in these nanoflakes are not very sensitive to its reduction in thickness, other than a decrease in intensity of the Raman signal.

Photoluminescence of InSe nanoflakes has been measured by micro-photoluminescence at low and high temperatures. At 4 K, a blue-shift up to 0.2 eV is found for the thinnest InSe nanoflake, but carrier recombination is limited by impurities. At room temperature we are able to observe free exciton recombination and quantum-size effects make this InSe to exhibit one of the largest band gap tunability ranges observed until now in a two-dimensional semiconductor: from infrared, in bulk material, to visible wavelengths at the single layer, i.e., ≈ 1 eV. Furthermore, we have introduced morphological manipulation strategies, such as nanotexturing, to enhance light absorption and the luminescent response of atomically thin Indium Selenide nanosheets, in order to compensate the reduction of absorption when the electric field is parallel to the plane of InSe nanosheets. These results are relevant for the design of new optoelectronic devices, particularly based on heterostructures of two-dimensional materials with optimized band gap functionalities, as well as in-plane heterojunctions with minimal junction defect density.


Seminar, May 30, 2016, 15:00. ICFO's Seminar Room

Hosted by Prof. Valerio Pruneri