Recent Progress in Synthesis of Plate-like ZnO and its Applications: A Review

Abstract

ZnO is a wide band-gap semiconductor with piezoelectric properties suitable for opto-electronics, sensors, and as an electrode material. Controlling the shape and crystallography of any semiconducting nanomaterial is a key step towards extending their use in applications. Whilst anisotropic ZnO wires have been routinely fabricated, precise control over the specific surface facets and tailoring of polar and non-polar growth directions still requires significant refinement. Manipulating the surface energy of crystal facets is a generic approach for the rational design and growth of one-dimensional (1D) building blocks [1][2][3][4] . Although the surface energy is one basic factor for governing crystal nucleation and growth of anisotropic 1D structures, structural control based on surface energy minimization has not been yet demonstrated [5][6][7][8][9] . Here, we report an electronic configuration scheme to rationally modulate surface electrostatic energies for crystallographic-selective growth of ZnO wires. The facets and orientations of ZnO wires are transformed between hexagonal and rectangular/diamond cross-sections with polar and non-polar growth directions, exhibiting different optical and piezoelectrical properties. Our novel synthetic route for ZnO wire fabrication provides new opportunities for future opto-electronics, piezoelectronics, and electronics, with new topological properties.I norganic compound semiconductors with the inherent structural anisotropy continue to be of considerable interest for both fundamental science and potential technology applications due to their diverse functionalities and unique features combined with the dynamic electro-mechanical coupling and the static polarization [10][11][12][13][14] . In particular, the strong electrical polarization of wurtzite semiconductors such as ZnO and GaN, arising from non-central symmetry and crystallographic polarity, has a profound effect on carrier concentration, energy band structure, photon emission energy, and excitonic behavior [1][2][3][4] . Thus, the nature of the terminating surface on wurtzite crystal, which is intimately associated with the growth direction and the bonding state, can play a crucial role in its electrical, optical, and photophysical features. Furthermore, such anisotropic phenomena are particularly striking and relevant for one-dimensional (1D) structure due to its geometric crystal structure with the highly uniaxial anisotropy as well as the highly confined strain and polarization field, compared to bulk and film structures. Hence, tailoring facets and crystal shapes of 1D wurtzite materials through control of crystal preferred growth orientation is an effective way for achieving not only designed physical properties, but also the ability to manipulate the polarization between parallel to and perpendicular to their length. This in turn allows for creating a new concept of topological architecture and unique function pertinent to potential device applications. However, because of chemically active polar surfaces wi...

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