Boron nitride is a synthetic refractory material that exists in several microstructural forms, which are typically characterized as either amorphous or crystalline. The primary form of interest in materials science sectors is hexagonal boron nitride (hBN), often referred to as white graphene.
In powdered form, hexagonal boron nitride has found increasing use as a thermal interface material (TIM) and as a functional filler for cosmetics and personal care products. These are typically synthesized using boron nitride nanoplatelets exfoliated from the macro-material. Single-layer hexagonal boron nitride sheets, by contrast, are currently synthesized via epitaxial-like growth on a suitable substrate using chemical vapor deposition (CVD) in a high-vacuum chamber. These exhibit distinct anisotropic properties with theoretically myriad end-use applications.
This blog post will explore the properties and applications of single-layer hexagonal boron nitride in more detail.
Single-Layer Hexagonal Boron Nitride Explained
Hexagonal boron nitride is a structural analog of graphite with a layered system of hexagonal lattices, each comprising covalently-bound boron (B) and nitrogen (N) atoms. These concurrent layers are bound together by Van der Waals forces, such as the weak attraction between interlaid boron and nitrogen atoms of individual sheets. Conversely, the intralayer B-N bonds are extremely tough. This explains the anisotropic behavior of the material alongside its inherent lubricity and exceptional wear-resistant properties.
Single-layer hexagonal boron nitride is a two-dimensional structure that can be produced through epitaxy or mechanical cleaving. While exfoliating 2D materials from the macro product has proven useful in research and academic environments, it has a limited yield and throughput compared to CVD processes. CVD-growth of single-layer hexagonal boron nitride can generate high-quality sheets of just a few atomic layers with a comparatively large surface area and good topographical uniformity.
One of the most attractive properties of hexagonal boron nitride is the material’s unique thermoelectric properties. It is a strong dielectric material that is transparent to both electromagnetic waves and radio frequencies, with one of the greatest thermal conductivities of electrical insulators on the market. This is partially determined by the wide bandgap of single-layer boron nitride, roughly 5.97 eV.
Why is it Called White Graphene?
Single-layer boron nitride is described as white graphene simply because it is white in appearance and is structurally analogous to graphene. The white coloring arises due to the material’s wide bandgap, yet it will typically appear transparent when deposited in a few atomic layers to a substrate of silicon (Si) or copper (Cu).
Hexagonal Boron Nitride from Grolltex
Grolltex is one of the only suppliers of single-layer boron nitride and graphene sheets, as well as composite heterostructures of the two. These can be transferred onto a number of suitable substrate materials including tailored options specifically requested by our customers. Additionally, Grolltex has begun the design and manufacture of 2D sensing materials using both monolayer graphene and hBN, on plastic substrates as opposed to silicon wafers, creating cost savings of as much as 100X over silicon-based designs.