We report the synthesis of two-dimensional
porous ZnO nanosheets,
CuSCN nanocoins, and ZnO/CuSCN nano-heterostructure thin films grown
on fluorine-doped tin oxide substrates via two simple and low-cost
solution chemical routes, i.e., chemical bath deposition and successive
ionic layer adsorption and reaction methods. Detail characterizations
regarding the structural, optoelectronic, and morphological properties
have been carried out, which reveal high-quality and crystalline synthesized
materials. Field emission (FE) investigations performed at room temperature
with a base pressure of 1 × 10–8 mbar demonstrate
superior FE performance of the ZnO/CuSCN nano-heterostructure compared
to the isolated porous ZnO nanosheets and CuSCN nanocoins. For instance,
the turn-on field required to draw a current density of 10 μA/cm2 is found to be 2.2, 1.1, and 0.7 V/μm for the ZnO,
CuSCN, and ZnO/CuSCN nano-heterostructure, respectively. The observed
significant improvement in the FE characteristics (ultralow turn-on
field of 0.7 V/μm for an emission current density of 10 μA/cm2 and the achieved high current density of 2.2 mA/cm2 at a relatively low applied electric field of 1.8 V/μm) for
the ZnO/CuSCN nano-heterostructure is superior to the isolated porous
ZnO nanosheets, CuSCN nanocoins, and other reported semiconducting
nano-heterostructures. Complementary first-principles density functional
theory calculations predict a lower work function for the ZnO/CuSCN
nano-heterostructure (4.58 eV), compared to the isolated ZnO (5.24
eV) and CuSCN (4.91 eV), validating the superior FE characteristics
of the ZnO/CuSCN nano-heterostructure. The ZnO/CuSCN nanocomposite
could provide a promising class of FE cathodes, flat panel displays,
microwave tubes, and electron sources.
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