Abstract
ZnO-CdS, ZnO-ZnS, and ZnO-Ag2S core-shell heterojunction structures were fabricated using low-temperature, facile and simple aqueous solution approaches. The polycrystalline sulfide shells effectively enhance the field emission (FE) properties of ZnO nanowires arrays (NWAs). This results from the formation of the staggered gap heterointerface (ZnO-sulfide) which could lead to an energy well at the interfaces. Hence, electrons can be collected when an electric field is applied. It is observed that ZnO-ZnS NWAs have the lowest turn-on field (3.0 Vμm−1), compared with ZnO-CdS NWAs (6.3 Vμm−1) and ZnO-Ag2S NWAs (5.0 Vμm−1). This may be associated with the pyramid-like ZnS shell which increases the number of emission nanotips. Moreover, the Fowler-Nordheim (F-N) plot displays a nonlinear relationship in the low and high electric field regions caused by the double well potential effect of the heterojunction structures.
Highlights
The core-shell heterostructures have attracted much attention due to its consisting of two components with distinct functionalities[1,2] that often exhibit enhanced characteristics, such as emission efficiency[3] and high electron mobility[4]
The field emission (FE) properties of ZnO nanowire arrays (NWAs) have been effectively improved by modifying with sulfide shell
CdS and ZnS formed a uniform shell layer on ZnO NWs, while Ag2S were uniformly deposited on ZnO NWAs as quantum dots (QDs)
Summary
From the XRD patterns of the ZnO-sulfide nanocomposites, all the Bragg peaks of ZnO of different samples located at the same degree The peak in O 1s spectrum (Fig. 4b) of ZnO-ZnS weakly moves to higher binding energy (532.2 eV) compared with the ZnO-CdS and ZnO-Ag2S which both locate at 531.8 eV This implies that the chemical states of ZnO core were weakly affected by the sulfide shells. Materials ZnO25 ZnO26 ZnO27 ZnO-ZnS29 ZnO-CdS30 ZnO* ZnO-CdS* ZnO-ZnS* ZnO-Ag2S*
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