Phys Rev B 2007, 76:0143051–0143059. 17. Yang Y, Yang B, Fu Z, Yan H, Zhen W, Dong W, Xia L, Liu W, Jian Z, Li F: Enhanced yellow-green photoluminescence from ZnO-SiO 2 composite opal. J Phys Condens Matter 2004, 16:7277–7286.CrossRef Competing selleck chemical interests The authors declare that they have no competing interests. Authors’ contributions KH and HC carried out the design and the experiment. CH set up the measurement system. MW conceived of the

study and facilitated its coordination. All authors read and approved the final manuscript.”
“Background Thin and ultrathin mica flakes have been recently proposed as a promising dielectric material for graphene- and carbon nanotube-based electronics [1–3]. Among the outstanding properties of thin mica sheets, one finds high dielectric constant, atomically flat surface, chemical and mechanical stability, the possibility to obtain single atomic sheets [2], and excellent adhesion see more to graphene with no ripples [4]. For some applications such as the use of mica sheets as gate dielectric, mica flakes are directly in contact with a metallic surface [3]. It is known that the properties of some ultrathin sheet materials like graphene can be greatly

affected by its contact with a metallic material, and therefore it is fundamental to understand whether this is also the case for ultrathin mica flakes. To develop such investigations, it would be advantageous to have a simple optical technique capable to localize mica flakes directly

on metallic surfaces and determine their thickness in situ similarly as it can be done on Si02/Si substrates [2, 3]. However, the possibility to optically detect mica flakes on metallic substrates has not been reported yet. In this paper, we second precisely address this issue and demonstrate that thin mica flakes can be visualized on semitransparent gold substrates, and their thickness can be estimated by optical microscopy. We show that the optical contrast is largely enhanced using semitransparent metallic substrates, instead of opaque metallic substrates, which enable accurate characterization of ultrathin mica flakes. Theoretical background We consider the mica-gold system schematically shown in the inset of Figure  1a. It consists of a thin mica flake on a metallic layer supported by a glass slab. According to the transfer matrix formalism [5], the reflectance for normal incidence of the mica and gold in the considered structure can be calculated as: Figure 1 Calculated reflectance spectra, optical contrasts, and color evolution of the mica flakes. (a) Calculated reflectance spectra of mica (colored lines) and gold (black lines) in the structure shown in the inset as a function of the wavelength of visible light. Mica thicknesses are 0 nm (black lines, bare gold), 10 nm (red lines), 30 nm (blue lines), and 50 nm (green lines). Gold layer thicknesses are 20 nm (continuous lines) and 300 nm (dashed lines). Inset: schematic representation of the layered structure analyzed.