Controlling Catalyst Bulk Reservoir Effects for Monolayer Hexagonal Boron Nitride CVD

Abstract

Highly controlled Fe-catalyzed growth of monolayer hexagonal boron nitride (h-BN) films is demonstrated by the dissolution of nitrogen into the catalyst bulk via NH3 exposure prior to the actual growth step. This “pre-filling” of the catalyst bulk reservoir allows us to control and limit the uptake of B and N species during borazine exposure and thereby to control the incubation time and h-BN growth kinetics while also limiting the contribution of uncontrolled precipitation-driven h-BN growth during cooling. Using in situ X-ray diffraction and in situ X-ray photoelectron spectroscopy combined with systematic growth calibrations, we develop an understanding and framework for engineering the catalyst bulk reservoir to optimize the growth process, which is also relevant to other 2D materials and their heterostructures.

2D-MTJs: introducing 2D materials in magnetic tunnel junctions

“…In parallel, following the path developed in section 4, the mechanisms of the CVD growth of large-scale h-BN layers directly onto the FM have been studied, in particular in the case of the Fe catalyst [36,37]. Monolayer h-BN films of high quality (grains of hundreds of microns) were grown by the catalysed decomposition of borazine on the Fe surface.…”

“…Monolayer h-BN films of high quality (grains of hundreds of microns) were grown by the catalysed decomposition of borazine on the Fe surface. This achievement required an understanding of the careful balance of B and N feeding the catalyst for optimal growth [36,37]. Owing to the knowledge gained through these studies, the integration of h-BN as an ultimately thin tunnel barrier in efficient spin valves has been enabled (see figure 13).…”

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

“…Then, the h-BN/PMMA stack is delaminated from the foil by means of bubbling 17 (ii, iii). The h-BN is transferred to a Si/PVA substrate, and the PMMA is removed with acetone (iv-vi).…”

“…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.…”

“…A continuous layer of CVD h-BN is grown on iron foils and characterized by transmission electron microscopy (TEM) to be single layer as previously reported. 17 Due to the stronger adhesion of h-BN to surfaces, it has to be transported from the growth substrate to the final substrate by using sacrificial layers. Poly (methyl methacrylate) (PMMA) is spin coated on top of the h-BN, and the stack is delaminated with the bubbling technique:…”