A nanosheet is a two-dimensional nanostructure with thickness in a scale ranging from 1 to 100 nm.[1][2][3]
A typical example of a nanosheet is graphene, the thinnest two-dimensional material (0.34 nm) in the world.[4] It consists of a single layer of carbon atoms with hexagonal lattices.
Examples and applications
As of 2017[update], silicon nanosheets are being used to prototype future generations of small (5 nm) transistors.[5]
3D AFM topography image of multilayered palladium nanosheet on silicon wafer.[7]
The most commonly used nanosheet synthesis methods use a bottom-up approach, e.g., pre-organization and polymerization at interfaces like Langmuir–Blodgett films,[8] solution phase synthesis and chemical vapor deposition (CVD).[9] For example, CdTe (cadmiumtelluride) nanosheets could be synthesized by precipitating and aging CdTe nanoparticles in deionized water.[10] The formation of free-floating CdTe nanosheets was due to directional hydrophobic attraction and anisotropicelectrostatic interactions caused by dipole moment and small positive charges. Molecular simulations through a coarse-grained model with parameters from semi-empirical quantum mechanics calculations can be used to prove the experimental process.
Ultrathin single-crystal PbS (leadsulfur) sheets with micro scale in x-, y- dimensions can be obtained using a hot colloidal synthesis method.[11] Compounds with linear chloroalkanes like 1,2-dichloroethane containing chlorine were used during the formation of PbS sheets. PbS ultrathin sheets probably resulted from the oriented attachment of the PbS nanoparticles in a two-dimensional fashion. The highly reactive facets were preferentially consumed in the growth process that led to the sheet-like PbS crystal growth.
Nanosheets can also be prepared at room temperature. For instance, hexagonal PbO (lead oxide)) nanosheets were synthesized using gold nanoparticles as seeds under room temperature.[3] The size of the PbO nanosheet can be tuned by gold NPs and Pb2+ concentration in the growth solution. No organic surfactants were employed in the synthesis process. Oriented attachment, in which the sheets form by aggregation of small nanoparticles that each has a net dipole moment,[12][13] and ostwald ripening[14] are the two main reasons for the formation of the PbO nanosheets. The same process was observed for iron sulfide nanoparticles.[15]
Carbon nanosheets have been produced using industrial hempbast fibres with a technique that involves heating the fibres at over 350F (180C) for 24 hours. The result is then subjected to intense heat causing the fibers to exfoliate into a carbon nanosheet. This has been used to create an electrode for a supercapacitor with electrochemical qualities ‘on a par with’ devices made using graphene.[6]
Metal nanosheets have also been synthesized from solution-based method by reducing metal precursors, including palladium,[16] rhodium,[17] and gold.[18]
^Coleman, J. N.; Lotya, M.; O'Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; et al. (2011). "Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials". Science. 331 (6017): 568–571. Bibcode:2011Sci...331..568C. doi:10.1126/science.1194975. hdl:2262/66458. PMID21292974.
^Guo, Shaojun; Dong, Shaojun (2011). "Graphene nanosheet: synthesis, molecular engineering, thin film, hybrids, and energy and analytical applications". Chemical Society Reviews. 40 (5): 2644–2672. doi:10.1039/C0CS00079E. PMID21283849.
^Bai, Yongxiao; Yeom, Jihyeon; Yang, Ming; Cha, Sang-Ho; Sun, Kai; Kotov, Nicholas A. (2013-02-14). "Universal Synthesis of Single-Phase Pyrite FeS2 Nanoparticles, Nanowires, and Nanosheets". The Journal of Physical Chemistry C. 117 (6): 2567–2573. doi:10.1021/jp3111106. ISSN1932-7447.
^Li, Zhonghao; Liu, Zhimin; Zhang, Jianling; Han, Buxing; Du, Jimin; Gao, Yanan; Jiang, Tao (2005). "Synthesis of Single-Crystal Gold Nanosheets of Large Size in Ionic Liquids". The Journal of Physical Chemistry B. 109 (30): 14445–14448. doi:10.1021/jp0520998. PMID16852818.
