166
S. Majidi et al.
microscopy was used to measure the thickness, which presented about 1.44 nm for the
thinnest obtained BNNS, relating to two layers of h-BN. In addition to the mentioned
advantages of this method, the procedure indicated that not only high temperatures,
vacuum, or high pressures are not essential but also simple scale up of the method is
possible via wet chemical processing [22].
2.3 Liquid Exfoliation
The exfoliation of layered compounds in liquids is another possible solution to obtain
a great amount of dispersed nanosheets, which involves oxidation, ion intercalation/exchange, or surface passivation by solvents. This allows the methods to give a
substantial amount of 2D materials which can be processed by available industrial
procedures.
Liquid exfoliation results in the synthesis of thin composites with scalable potential and facile processes using standard technologies. Fabrication of mono- and fewatomic-layer nanosheets from polycrystalline h-BN through liquid exfoliation was
firstly reported by Han et al. [39], where 0.2 mg of h-BN was put into 5 mL of 1,2dicloroethane solution of poly (m-phenyl-enevinylene-co-2,5-dictoxy-p phenylene
vinylene) in a 1.2 mg/10 mL ratio and then to breaking up and dispersing the hBN powder into few layered h-BN upon sonication for an hour. Subsequently, many
other solvents have been verified to extend the nanosheet formation. One of the highly
polar solvents is N, N-dimethylformamide (DMF), which was used to interact with
the surface of h-BN and produced only milligram levels of pure nanosheets with
thicknesses at the ranging of 2–10 nm [34]. The solvent selection can be also more
optimized so that the energy of surface shall match with that of h-BN to overcome
the vdW forces between layers [4].
2.4 Chemical Vapor Deposition (CVD)
The methods based on epitaxy could synthesis monolayer h-BN with high crystallinity structure, but they were highly sensitive to the substrates so that most of
them with special orientations required very limited pretreatments, which resulted
in long-term and complicated procedures. Consequently, the development of new
simple processes seems necessary to produce 2D materials, especially h-BN, on
the usual substrates with a large area and high quality. The process should adapt to
silicon-based procedures and must meet the common demands. The chemical vapor
deposition (CVD) method is a bottom-up process applied to fabricate high-quality
nanoscale films. In reality, a substrate that acts as a catalyst or new catalysts could be
deposited on a silica wafer for synthesizing h-BN film on top of it during the CVD
method. The CVD of h-BN nanosheets is possible through several substrates and
S. Majidi et al.
microscopy was used to measure the thickness, which presented about 1.44 nm for the
thinnest obtained BNNS, relating to two layers of h-BN. In addition to the mentioned
advantages of this method, the procedure indicated that not only high temperatures,
vacuum, or high pressures are not essential but also simple scale up of the method is
possible via wet chemical processing [22].
2.3 Liquid Exfoliation
The exfoliation of layered compounds in liquids is another possible solution to obtain
a great amount of dispersed nanosheets, which involves oxidation, ion intercalation/exchange, or surface passivation by solvents. This allows the methods to give a
substantial amount of 2D materials which can be processed by available industrial
procedures.
Liquid exfoliation results in the synthesis of thin composites with scalable potential and facile processes using standard technologies. Fabrication of mono- and fewatomic-layer nanosheets from polycrystalline h-BN through liquid exfoliation was
firstly reported by Han et al. [39], where 0.2 mg of h-BN was put into 5 mL of 1,2dicloroethane solution of poly (m-phenyl-enevinylene-co-2,5-dictoxy-p phenylene
vinylene) in a 1.2 mg/10 mL ratio and then to breaking up and dispersing the hBN powder into few layered h-BN upon sonication for an hour. Subsequently, many
other solvents have been verified to extend the nanosheet formation. One of the highly
polar solvents is N, N-dimethylformamide (DMF), which was used to interact with
the surface of h-BN and produced only milligram levels of pure nanosheets with
thicknesses at the ranging of 2–10 nm [34]. The solvent selection can be also more
optimized so that the energy of surface shall match with that of h-BN to overcome
the vdW forces between layers [4].
2.4 Chemical Vapor Deposition (CVD)
The methods based on epitaxy could synthesis monolayer h-BN with high crystallinity structure, but they were highly sensitive to the substrates so that most of
them with special orientations required very limited pretreatments, which resulted
in long-term and complicated procedures. Consequently, the development of new
simple processes seems necessary to produce 2D materials, especially h-BN, on
the usual substrates with a large area and high quality. The process should adapt to
silicon-based procedures and must meet the common demands. The chemical vapor
deposition (CVD) method is a bottom-up process applied to fabricate high-quality
nanoscale films. In reality, a substrate that acts as a catalyst or new catalysts could be
deposited on a silica wafer for synthesizing h-BN film on top of it during the CVD
method. The CVD of h-BN nanosheets is possible through several substrates and