Paper 2D-ThP15
Controlled Growth of Multilayered Hexagonal Boron Nitride on Ni-Cu Alloys

Thursday, November 2, 2017, 6:30 pm, Room Central Hall

Hexagonal boron nitride (h-BN) has been frequently studied as a potential substrate and a tunnel dielectric for two-dimensional materials such as graphene and transition metal dichalcogenides. Large area (>1 cm²) single and multilayered h-BN films have been successfully grown using chemical vapor deposition (CVD) on various single crystal and polycrystalline transition metal substrates such as Cu, Ni, Pt, and Ag. Of these substrates, polycrystalline Cu followed by polycrystalline Ni are by far the most commonly used substrates for CVD growth. Despite the popularity of polycrystalline Cu and Ni for the growth of h-BN, controlled uniform growth of multilayered (>3 layers) and few-layered (<3 layers) h-BN still remains a challenge.

We propose a method to grow few and multilayered h-BN on nickel-copper (NiCu) alloys, and control the thickness of h-BN by varying the concentration of Cu in NiCu alloy samples. These NiCu alloys are prepared by electroplating Cu onto high purity (99.8%) Ni foils (25 µm) and thermally annealing them at 1030°C for > 3 hours in H₂ environment. The Cu concentration in the alloy can be controlled by the electroplating current density and time to give desired weight percent of Cu deposited on Ni foils. NiCu alloys with four different Cu weight percentages (10%, 20%, 30%, 40%) are prepared using electroplating and thermal annealing procedure. The alloyed foils are subsequently cut into smaller pieces (~1 cm²) and are further annealed before h-BN growth. h-BN films are grown on these alloyed samples at 1030°C using borazane as the precursor, with H₂ and N₂ as the carrier gases, and high purity Cu (99.98%) and Ni (99.8%) are used as control samples. We use energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) to quantify the Ni and Cu concentration in the alloy. Scanning electron microscopy (SEM) is used to assess the surface morphology of the alloys, and ascertain the crystal size of h-BN films. We use Fourier transform grazing-incidence infrared reflection absorption spectroscopy (FT-IRRAS) to assess the h-BN film growth. Our preliminary results show that there is an immediate increase in the amount (thickness) of h-BN with the introduction of Cu in the NiCu alloy. We observe a subsequent decrease of h-BN thereafter with increasing Cu concentration in the NiCu alloy samples. We consistently observe that the thickest h-BN films, as calculated by FT-IRRAS peak area, grow on Ni₉₀Cu₁₀ while the thinnest grow on Ni₆₀Cu₄₀. We also observe that the alloy grain size decreases with increasing Cu concentration. The role of alloy surface morphology and the h-BN growth kinetics will also be discussed.