The Study of the Wrinkles of Hexagonal Boron-Nitride Flake after the Annealing

Hexagonal boron nitride (h-BN) flakes have been widely used due to their excellent physical and chemical properties. Here, thermal-induced wrinkles of thin h-BN flakes deposited on silicon dioxide substrate were investigated through a combination of atomic force microscopy (AFM) and Raman spectroscopy. The experimental results indicated that the wrinkles did not occur at relatively low annealing temperatures and were detected at temperatures as high as 500 °C or even 600 °C. When repeatedly annealed at high temperatures, the number and positions of the wrinkles also changed. From the Raman spectra, the wrinkles were caused by the fact that the h-BN contraction rate was faster than that of the substrate at the cooling stage due to the interfacial sliding between the flake and the substrate and the h-BN flake of 7 nm thickness recovered to the original length at 150 °C. Further cooling introduced the compressive stress and then the wrinkles appeared. Moreover, it was found that if there was a crack in the h-BN flake, the wrinkle always appeared at the crack. Our findings appeal the mechanism of thermal-induced wrinkles of h-BN flakes and help us to research their applications as substrate materials in electronic devices in a high-temperature environment.