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ZnO/CuO p - n heterojunctions have attracted much attention for device applications, but coherent junctions, which are crucial for controlling electrical properties, still remain a challenge due to different crystal structure. In this work, CuO single-crystalline dots are coherently synthesized on ZnO nanorods by using a proposed two-step process. Transmission electron microscopy images confirm the formation of CuO coherent dots on single-crystalline ZnO nanorods upon annealing the nanorods covered with a poly-crystalline Cu x O layer. The coherent dots exhibit two types of epitaxial orientations: CuO [002] ǀǀ ZnO [ 10 1 ¯ 1 ], CuO [111] ǀǀ ZnO [0002], and CuO [002] ǀǀ ZnO [ 10 1 ¯ 1 ¯ ], CuO [111] ǀǀ ZnO [ 000 2 ¯ ]. As the thickness of the as-deposited Cu x O layer increases from 10 to 30 nm, the aspect ratio of the resulting CuO dots decreases from 0.43 to 0.21, approaching a film-like morphology. This work provides a route to prepare CuO coherent single-crystalline structures on ZnO, which is one step further toward fabricating excellent CuO/ZnO nanodevices. [ABSTRACT FROM AUTHOR]

Cu 2+ - and Cu 1+ -dominant Cu-doped ZnO (CZO) nanowires (NWs) were prepared by annealing Cu x O-coated ZnO NWs synthesized via chemical vapor deposition (CVD) and chemical bath deposition (CBD), denoted as CVD-CZO and CBD-CZO, respectively. Transmission electron microscopy (TEM) analysis showed that Cu doping caused periodic undulations along the surfaces of both the CVD-CZO and CBD-CZO NWs, which are associated with alternating compressive and tensile strain. X-ray diffraction (XRD) patterns showed that the (0002) peak of the CVD-CZO NWs can be deconvoluted to a major peak shifted toward a higher angle, and a minor one toward a lower angle. These findings are consistent with the variation of d (0002) observed from TEM, but CBD-CZO NWs shifted only toward a lower angle. X-ray photoelectron spectra showed that the dominant substitution impurities in the CVD-CZO and CBD-CZO NWs were Cu 2+ and Cu 1+ , respectively, which agrees with the XRD results. Cathodoluminescence spectra of the CVD-CZO NWs exhibited strong blue-green and weak red emissions, while those of the CBD-CZO NWs showed weak blue-green emissions. The distinct luminescences are attributed to different types of defect associated with the valences of dopants, which were caused by the interaction of diffused Cu ions with intrinsic defects within pristine CVD- and CBD-synthesized ZnO NWs. [ABSTRACT FROM AUTHOR]

Abstract: A low-cost noble metal-free substrate comprised of annealed graphene oxide (GO)/ZnO composites is prepared to demonstrate an efficient chemical surface-enhanced Raman scattering effect. A high enhancement factor of about 104, better than those reported for reduced GO (rGO)/Au and GO/Ag composites, is mainly attributed to the unusually abundant oxygen-containing groups generated on surface of rGO by coupling with ZnO nanoparticles at moderate temperature. High-resolution transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy are employed to examine the evolution of ZnO as well as reduction and functionalization of GO after different heat treatments. [Copyright &y& Elsevier]

Nanostructures are the building blocks of future nanodevices and thus methods for fabricating nanostructures of various materials in various forms are fundamentally important. Among those nanostructures ZnO has received much attention over the past few years due to the wide range of research by many different groups focused on different novel nanostructures with different properties. Although ZnO nanowires have been intensively studied, there are only a few methods that showed promising characteristics for practical applications. Without much effort, it can be grown in many different nanostructure forms, thus allowing various novel devices to be achieved. In this study, we intend to review those methods that enable nanostructure growth to be more controllable and feasible for applications. The methods for fabricating ZnO nanostructures are introduced in the first part. In the second part, the application of those nanostructures are mentioned and explained. Finally, the future realization of nanodevices is discussed. [ABSTRACT FROM AUTHOR]

Abstract: A high-performance ZnO/NiO photosensor is fabricated by depositing Ni nanoshells onto the surface of ZnO nanorods (NRs) followed by annealing to transform ZnO/Ni into ZnO/NiO core–shell NR arrays. Photoluminescence spectra show that the ultraviolet (UV) emission of NRs is blue-shifted from 385nm to 374nm after the deposition of Ni nanoshells, and further splits into two peaks, at 360nm and 384nm, respectively, after the oxidation of Ni. Absorption spectra support the shift characteristic, which is ascribed to the doping and de-doping of Ni ions, consistent with the diffraction peak shifts in X-ray diffraction patterns. Photosensing measurements show that the ZnO/NiO NR devices have high sensitivity at a low bias. NiO nanoshells improve the UV sensitivity of ZnO NRs by 70-fold, which is attributed to the extended carrier depletion region near n-ZnO/p-NiO junctions and the enhanced absorption of UV. [Copyright &y& Elsevier]

Abstract: Cu doped ZnO nanoparticle sheets were synthesized via a proposed solution route with mixed Zn(NO3)2 and Cu(NO3)2 precursors at a low temperature of 95°C. Scanning electron microscopy, transmission electron microscopy, and X-ray energy dispersive spectrometry results demonstrate that the nanostructues synthesized by solutions with higher Cu(NO3)2 concentration are nanoparticle sheets comprised of uniform Cu doped ZnO nanoparticles with diameters around 20nm. Room-temperature photoluminescence spectra of the nanoparticle sheets show tunable near band emissions centered at 390–405nm and strong yellow emissions at 585–600nm. Absorbance spectra show gradual redshift in the UV range with the increase of Cu concentrations in the ZnO nanomaterials. The study provides a simple and efficient route to prepare Cu doped ZnO nanomaterials at low temperature. The as-synthesized products with both violet and yellow emissions are promising for white light-emitting diode applications. [Copyright &y& Elsevier]

Abstract: ZnO–Cu2O core–shell nanorod heterostructures were synthesized by a proposed solution process. High-resolution transmission electron microscopy shows the Cu2O nanoshells with a thickness of around 10nm are constructed of single-crystalline nanoparticles with a diameter of around 5nm capped on the surface of ZnO nanorods. Photoluminescence measurements show that the green emission of ZnO nanorods was eliminated by capping with Cu2O nanoshells. An improved photoresponse of ZnO–Cu2O heterojunction nanorods with ultrafast and extended high sensitivity from UV to the visible range is demonstrated. These heterostructures are promising for photosensing and solar energy applications. [ABSTRACT FROM AUTHOR]

ZnO nanoparticles, nanowires, and nanowalls were synthesized rapidly on Si via thermal decomposition of zinc acetate by a modified chemical vapor deposition at a low substrate temperature of 200-250°C for the first time. The diameters of the synthesized nanoparticles and nanowires are around 100 and 30 nm, respectively, and the thickness of nanowalls is around 20 nm. High-resolution transmission electron microscopy shows that the nanowires as well as nanowalls are single-crystalline, and the nanoparticles are highly-textured poly-crystalline structures. Room-temperature photoluminescence spectra of the nanostructures show strong ultraviolet emissions centered at 368-383 nm and weak violet emissions at around 425 nm, indicating good crystal quality. The study provides a simple and efficient route to synthesize ZnO diverse nanostructures at low temperature. [ABSTRACT FROM AUTHOR]

High-performance N-doped carbon quantum dots (NCQDs) were synthesized by a proposed green route based on hydrothermal treatments using waste paper and urea as C and N sources. The single-crystalline NCQDs demonstrated strong blue-green luminescence with the maximum intensity enhancement of 6.5 times when compared with undoped CQDs under UV and visible light excitations. XPS spectra results suggested that the enhanced photoluminescence might be attributed to pyridinic N, which could be controlled by adjusting hydrothermal temperature, time, and urea concentration. The NCQDs having excellent optoelectronic properties were fabricated into broadband photodetectors by incorporating ZnO nanorod arrays. Owing to the NCQDs, the detectors demonstrated broadband photoresponse with significantly enhanced photoresponsivity, faster response, and better sensitivity in visible range. The work provides a low-cost, environment friendly route to fabricate excellent NCQD-based broadband photodetectors for various technological applications. Image 1 • High-performance NCQDs were synthesized by a proposed green route using waste paper and urea. • A broadband photodetector was achieved by incorporating the NCQDs and ZnO nanorod arrays. • The photodetector demonstrated enhanced photoresponsivity and response rate in UV and visible range. • The mechanism for the enhanced performance was investigated. • The work provides a low-cost, environment friendly route to fabricate excellent broadband photodetectors. [ABSTRACT FROM AUTHOR]

Controlled doping into nanomaterials is an enabling technology for functional nanodevices, but still challenging. We report the accomplishment of a facial growth method of controlling Cu doping concentration into ZnO nanorod arrays systematically as an example by faith transfer of Cu content in single hybrid bimetallic organic precursors, zinc copper acetylacetonate, to the end ZnO nanorod arrays using solution method. The incorporation of Cu content is demonstrated to vary from 0 at.% to 10 at.% with a step of 2 at.%, where the control over the accuracy of Cu content can be better. The as-synthesized nanorods of around 150 nm in diameter are characterized by single crystallinity. The systematic Cu incorporation is proved by energy dispersive spectroscopy and X-ray diffraction. Photoelectron spectroscopy shows that the ratio of Cu +2 to Cu +1 varies accordingly, an increasing trend with total Cu doping concentration. The optical and photocatalytic properties of the Cu-doped ZnO nanorods are thus studied. The results reveal that the photodegradation of methyl orange is facilitated with Cu doping and the role of multi-valences of Cu ions on surface is proposed. Several unique features in photoluminescence also accompany with Cu doping, including the UV peak shift toward longer wavelength, the decrease of UV/visible intensity ratio, the increase of visible light emission and the shift of visible light emission from green to orange. [ABSTRACT FROM AUTHOR]

Abstract: In this work, indium (In) doped ZnO nanowires are grown on a Si substrate by chemical vapor deposition (CVD), at a relatively low temperature of 550°C. The effects of In concentration on the morphology, microstructure, luminescence and electrical properties of ZnO nanowires are investigated. The diameters and lengths of these nanowires are in the ranges of 70–311nm and 10–15μm, respectively. These nanowires are single crystals growing in the [0001] direction. The maximum solubility of In in ZnO is estimated to be 3.47at.%. Photoluminescence (PL) spectra reveal a red shift in the ultraviolet emission and intensity enhancement in the green emission with increasing indium doping concentration. Besides, carrier concentration, mobility and resistivity of the nanowires with different doping concentrations are determined based on single-nanowire field effect transistors (FET). [Copyright &y& Elsevier]