In Situ Observations during Chemical Vapor Deposition of Hexagonal Boron Nitride on Polycrystalline Copper

Abstract

Using a combination of complementary in situ X-ray photoelectron spectroscopy and X-ray diffraction, we study the fundamental mechanisms underlying the chemical vapor deposition (CVD) of hexagonal boron nitride (h-BN) on polycrystalline Cu. The nucleation and growth of h-BN layers is found to occur isothermally, i.e., at constant elevated temperature, on the Cu surface during exposure to borazine. A Cu lattice expansion during borazine exposure and B precipitation from Cu upon cooling highlight that B is incorporated into the Cu bulk, i.e., that growth is not just surface-mediated. On this basis we suggest that B is taken up in the Cu catalyst while N is not (by relative amounts), indicating element-specific feeding mechanisms including the bulk of the catalyst. We further show that oxygen intercalation readily occurs under as-grown h-BN during ambient air exposure, as is common in further processing, and that this negatively affects the stability of h-BN on the catalyst. For extended air exposure Cu oxidation is observed, and upon re-heating in vacuum an oxygen-mediated disintegration of the h-BN film via volatile boron oxides occurs. Importantly, this disintegration is catalyst mediated, i.e., occurs at the catalyst/h-BN interface and depends on the level of oxygen fed to this interface. In turn, however, deliberate feeding of oxygen during h-BN deposition can positively affect control over film morphology. We discuss the implications of these observations in the context of corrosion protection and relate them to challenges in process integration and heterostructure CVD.

Chemical vapour deposition of freestanding sub-60 nm graphene gyroids

“…The template stabilisation for h-BN CVD is more complex to rationalise as the supply, solubility and chemical behaviour of both B and N with respect to the catalyst template have to be considered. This connects to our previous detailed h-BN growth studies, 51,52 but an in-depth discussion of this goes beyond the scope of this paper. Similarly, without discussing the specific growth mechanisms involved, our approach can be extended to transition metal dichalcogenides, for instance by using Au gyroids for WS2 CVD.…”

On the use of two dimensional hexagonal boron nitride as dielectric

“…As expected, the thickness of the h-BN film on the Ni and Cu foils was 2 nm and 2-15 nm Furthermore, after the thermal pre-annealing process for increasing the Cu or Ni grain size, the grooves in the Ni foil are normally much deeper than the ones in the Cu foil, resulting in a bad quality of the h-BN grown on the grain boundaries. As a result, many authors preferred to use h-BN film yielded on Cu substrate for the application of the electronic devices [70,[83][84][85][86][87][88][89][90][91][92].…”

Mechanical characterization and cleaning of CVD single-layer h-BN resonators

“…7 Among all the 2D materials, few studies on single-layer h-BN exist 8,9 despite the early attempts to exfoliate it 10 and the welldeveloped synthesis techniques. [11][12][13][14][15][16][17] The reason for its difficult exfoliation to a monolayer thickness is unclear, possibly being its AA′ stacking, its slightly-ionic bonds or flatness that causes adhesion between h-BN layers and other surfaces stronger than other 2D materials. [18][19][20][21] Moreover, h-BN surfaces are hydrophillic in nature, but after being exposed to air they get covered by an hydrophobic layer of hydrocarbons as reported in h-BN nanotubes 22 and graphene.…”