Apparent Colors of 2D Materials

Abstract

Finding 2D and thin‐film layered materials have become essential to develop not only in scientific‐related fields, but also in a wide industry, which is constantly feeding from this progress. For electronic devices, thin‐film materials are supposed to be a step forward to overcome Moore's law. In many other technologic areas, the development of tools based on flakes of materials has found new physics, becoming a rising field. Although, destructive techniques are commonly used to characterize the thickness of these materials. Herein, a list of materials is presented, whose thicknesses are characterized by their apparent colors in several substrates, a harmless, fast, and reliable technique that has been already used to determine the number of layers in several works. This list is also enlarged with other materials and substrates.

Self-Hybridized Exciton-Polaritons in Sub-10-nm-Thick WS2 Flakes: Roles of Optical Phase Shifts at WS2/Au Interfaces

“…Incident light undergoes reflection and transmission at the interface of two neighboring media in WS 2 /SiO 2 /Si and WS 2 /Au. The amplitude and phase of light at each medium are determined by the Fresnel equations [ 13 , 26 ]. The superposition of all the reflected waves at the boundaries, i.e., the multiple-beam interference, determines the reflectance spectra and colors of the WS 2 flakes [ 26 ].…”

“…The additional dips in the measured spectra (Figure 6b) agree well with those in the calculations (Figure 6c) These experimental and calculated results suggest that the contribution of the large optica phase shifts at the Au/WS2 interface is crucial for the formation of EPs in WS2 flakes with dWS2 < λ/4nWS2. Many TMDs possess large real and imaginary parts of refractive indices [11][12][13][14][15]30], and hence the EP modes are expected in other kinds of very thin TMD layers Furthermore, strong electronic interactions [31] as well as remarkable plasmonic effects [7,10] at TMD/metal interfaces can give rise to emergent physical phenomena of TMD/metal systems.…”

“…Transition metal dichalcogenides (TMDs) have long attracted the attention of researchers due to their fascinating physical properties for optoelectronic device applications, including sizable bandgap energies, large absorption coefficients, high electron mobility, and superior mechanical flexibility [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. In particular, it has been noted that the exciton–photon interactions dominate the optical responses of TMDs even at room temperature.…”

“…Consequently, a variation in the thickness significantly alters the apparent color of the TMD flakes due to the absorption and interference effects. Such unique optical characteristics enable the rapid and reliable determination of the TMD thicknesses using optical microscopy (OM) [ 13 ]. Moreover, coupling of excitons and the cavity photons in TMDs results in the formation of self-hybridized EPs [ 8 , 9 , 10 , 11 , 12 ].…”

Exploring the structural and optoelectronic properties of natural insulating phlogopite in van der Waals heterostructures

“…shows the optical image of several phlogopite (hBN) flakes obtained by direct exfoliation of a bulk-crystal onto SiO2/Si. The apparent color of the flake under the optical microscope depends on its thickness [72]. The lateral flakesize depends directly on the exfoliation process (scotch tape repetition), then, it may vary from sample to sample.…”