| dc.description.abstract | Hexagonal boron nitride (h-BN) is an ultra-wide band gap van der Waals semiconducting material. It has been extensively studied for electronic applications such as tunnel and gate di-electric, and as a substrate for two-dimensional (2D) materials. Large area (mm2) h-BN films are typically grown using chemical vapor deposition (CVD) on various transition metal foils, including copper (Cu) and nickel (Ni) foils. The growth on Cu is monolayer limited and controlled large area n-layer h-BN remains a challenge. Alternatively, h-BN growth on Ni yields multilayer h-BN films, but results in submicron domain sizes and substrate grain-dependent growth. h-BN films with large crystal sizes and thicknesses are needed for electronic applications, to demonstrate tunnel junction and field effect devices using 2D materials.
In this work, we demonstrate h-BN growth using atmospheric pressure chemical vapor de-position (APCVD) on polycrystalline Cu and Cu-Ni binary alloys. The h-BN growth morphology on Cu was studied using scanning probe microscopy, which revealed a ≈1-2 µm crystal size, corrugated nature of h-BN growth, and poor coalescence of h-BN domains. A two-step thermal annealing and electropolishing technique was used to improve the Cu foil surface, which in-creased the h-BN crystal size from ≈1 µm to ≈4 µm and reduced secondary nucleation on h-BN films. While these are incremental improvements, the need for n-layer h-BN growth still persists. Thus, we utilized Cu-Ni binary alloys as substrates. The Cu-Ni binary alloys were prepared using electroplating Cu on Ni and Ni on Cu to create Cu-rich and Ni-rich alloys, respectively, and sub-sequent thermal annealing at 1030°C for >5 hours. This resulted in the growth of well-coalesced monolayered h-BN on Cu-rich alloys with ≈15 µm crystal size and multilayered h-BN with ≈20 µm crystal size on Ni-rich alloys. Characterization techniques such as atomic force microscopy, electron microscopy techniques, X-ray photoelectron spectroscopy and Fourier transform infrared reflection absorption spectroscopy were used to analyze the alloy substrate morphology, h-BN crystal and film morphology. This work demonstrates the use of alloy composition along with CVD growth parameters to achieve controlled large area n-layer h-BN. | |
