Search

Employing the graphene sheets (GSs), the electron scattering constants are measured in the high-angle annular dark-field (HAADF) imaging by the scanning transmission electron microscopy. Single scattering is found to be dominant until the layer number of 200, complying with a simple relation of I = Io(1 - e(-tau/lambda)). The discrete layer counting of the GSs enables precise determination of incident depths. This work results values of lambda = 48.2, 61.4, 97.9 and 115.6 nm for 80, 120, 160 and 200 keV electrons, respectively. The uncertainties with the mean free paths and the cross sections are confined to 10 percent. The dependences on the electron beam energy and the collection angle are discussed based on a multislice simulation.

Thin Bi2Te3 flakes, with as few as 3 quintuple layers, are optically visualized on the SiO2-capped Si substrates. Their optical contrasts vary with the illumination wavelength, flake thickness and capping layers. The maximum contrast appears at the optimized light with the 570 nm wavelength. The contrast turns reversed when the flake is reduced to less than 20 quintuple layers. A calculation based on the Fresnel law describes the above observation with the constructions of the layer number-wave length-contrast three-dimensional (3D) diagram and the cap thickness-wavelength-contrast 3D diagram, applicative in the current studies of topological insulating flakes.

Thin Bi2Te3 flakes, with as few as 3 quintuple layers, are optically visualized on the SiO2-capped Si substrates. Their optical contrasts vary with the illumination wavelength, flake thickness and capping layers. The maximum contrast appears at the optimized light with the 570 nm wavelength. The contrast turns reversed when the flake is reduced to less than 20 quintuple layers. A calculation based on the Fresnel law describes the above observation with the constructions of the layer number-wave length-contrast three-dimensional (3D) diagram and the cap thickness-wavelength-contrast 3D diagram, applicative in the current studies of topological insulating flakes.