(a) Schematic diagram of the chemical vapour deposition approach for h-BN synthesis. Borazine is used as a precursor. A multilayer h-BN film is grown on a Fe foil in a quarts tube. (b,c) Photographs of as-grown h-BN film on a Fe foil and the transferred h-BN film onto a SiO2/Si substrate. (d,e) SEM images of an h-BN film on a Fe foil. (f) Cathodoluminescence spectra of multilayer h-BN film. (g) Optical image of multilayer h-BN film. (h) Raman mapping image of the E2g peak near 1,366 cm−1 corresponding to the area of g. (i) Raman spectra of each spot for the corresponding blue triangle, red circle and black square in h. (j) X-ray diffraction pattern of multilayer h-BN film on a SiO2/Si substrate. (k) Contact angles of bare Fe (top) and as-grown h-BN on a Fe foil (bottom). (l,m) AFM images of multilayer h-BN film (l) and exfoliated h-BN flake (m) on a SiO2/Si substrate. The surface roughness of the multilayer h-BN film, except for the wrinkled region and exfoliated h-BN film, is found to be ~0.2 nm indicating that these CVD-grown multilayer h-BN films are highly flat. Scale bars, 10 μm (d); 5 μm (e); 20 μm (g,h).
Researchers have assiduously studied the relationship between insulators and conductors. The international team has tested layered hexagonal boron nitride (h-BN), an insulating 2D material of remarkable properties. All the atoms in 2-D layer materials are exposed to the surface, the related physical and chemical properties are strongly influenced by adjoining materials and sometimes surface corrugation. Thus, special care is required to deal with atomically thin layered materials. There are several unique physical and chemical properties of h-BN, which have potential applications as a dry-lubricant, passivation layer and deep UV emitter.
h-BN layer is superior to its competing insulator, silicon dioxide (SiO2), as it “has demonstrated to be an ideal substrate {supporting material} for 2-D materials due to its atomic flatness, large band gap, superb mechanical strength, absence of dangling bonds and low dielectric screening.” The compound is highly desired for numerous real device applications in keyboards and power cabling manufacturing.
The team reports large-area h-BN films grown by chemical vapor deposition (CVD) using copper foil (Fe foil). CVD is a method employed to produce high quality, high performance solid materials. The thickness of the h-BN (5-15 nm) is controlled by the cooling rate, i.e., the segregated boron and nitrogen atoms that are precipitated in an iron substrate at a high temperature.
Field effect transistors (FETs) with CVD-grown monolayer graphene, monolayer molybdenum disulfide (MoS2), and monolayer tungsten diselenide (WSe2) — both semiconducting materials- are fabricated on the grown multi-layer h-BN substrates, achieving carrier mobilities as high as ~ 24,000, 40, and ~ 9 cm2 V-1s-1 at room temperature, respectively. The reported graphene mobility is the highest value among those of the previous reports with CVD-grown graphene samples on CVD-grown h-BN substrates.
Hexagonal boron nitride is an ideal substrate for 2-D materials including graphene and transition metal dichalcogenides monolayers family (TMdC). While exfoliated h-BN resulted in a very high performance, integration is not possible with a limited area. Large-area CVD-grown h-BN can be easily integrated with various 2-D materials. To demonstrate h-BN film as a potential substrate, graphene, MoS2, and WSe2 devices were fabricated on-top of our large-area CVD-grown h-BN. The large-area and high-quality h-BN substrate in this work not only advances the high performance of 2-D nanoelectronics for the future, but also provides a new synthesis technique for potential multi-layer 2-D materials. http://www.nature.com/ncomms/2015/151028/ncomms9662/full/ncomms9662.html http://www.ibs.re.kr/cop/bbs/BBSMSTR_000000000738/selectBoardArticle.do?nttId=12275&pageIndex=1&searchCnd=&searchWrd=
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