Search

Recently, a technical modification of a Reflectance Anisotropy Spectroscopy (RAS) spectrometer has been proposed to investigate the circular dichroism (CD) of samples instead of the normally studied linear dichroism. CD-RAS measures the anisotropy of the optical properties of a sample under right-handed and left-handed circularly polarized light. Here, we present the application of CD-RAS to measure the circular dichroism of a twisted bilayer of graphene, purposely prepared as a possible substrate for the adsorption of thin molecular layers, in air, in liquid or in a vacuum. This result demonstrates the performance of the apparatus and shows interesting perspectives for the investigation of chiral organic assemblies deposited in solid film. [ABSTRACT FROM AUTHOR]

Reflectance anisotropy spectroscopy (RAS) is applied to investigate GaAsBi samples grown by molecular beam epitaxy on (001)‐oriented GaAs substrates with GaAs or InGaAs buffer layers, resulting in nearly lattice‐matched or compressive strain conditions, with Bi concentration in the alloy in the range 2–5%. These new samples allow to bridge the gap in the Bi concentration values of previous RAS experiments (C. Goletti et al., Appl. Phys. Lett. 2022, 120, 031902), confirming the [110]‐polarized Bi‐related anisotropy in optical spectra below 3 eV and the linear dependence of its amplitude on Bi concentration. The characterization of the grown GaAsBi samples by X‐Ray diffraction and transmission electron microscopy clearly demonstrates the presence of CuPt‐like ordering in the bulk. CuPt structure is the primary origin of the optical anisotropy measured by RAS and by polarized photoluminescence, due to the anisotropic strain produced in the bulk crystal lattice. The lineshape of the RAS spectra above 3 eV, with its overall and characteristic positive convexity, confirms this conclusion. [ABSTRACT FROM AUTHOR]