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High crystalline ZnO nanorods (NRs) on Zn pre-deposited graphene/Cu sheet without graphene transfer process have been fabricated by self-catalyzed vapor-phase transport synthesis. Here, the pre-deposited Zn metal on graphene not only serves as a seed to grow the ZnO NRs, but also passivates the graphene underneath. The temperature-dependent photoluminescence spectra of the fabricated ZnO NRs reveal a dominant peak of 3.88 eV at 10 K associated with the neutral-donor bound exciton, while the redshifted peak by bandgap shrinkage with temperature and electron-lattice interactions leads a strong emission at 382 nm at room temperature. The optical absorption of the ZnO NRs/graphene hetero-nanostructure at this ultraviolet (UV) emission is then theoretically analyzed to quantify the absorption amount depending on the ZnO NR distribution. By simply covering the ZnO NR/graphene/Cu structure with the graphene/glass as a top electrode, it is observed that the current-voltage characteristic of the ZnO NR/graphene hetero-nanojunction device exhibits a photocurrent of 1.03 mA at 3 V under a light illumination of 100 μW/cm2. In particular, the suggested graphene/ZnO NRs/graphene hybrid-nanostructure-based devices reveal comparable photocurrents at a bidirectional bias, which can be a promising platform to integrate 1D and 2D nanomaterials without complex patterning process for UV device applications.

Highlights • ZnO nanorods could be enlarged by incorporating graphene. • ZnO nanorods/graphene/porous silicon structures were formed. • Defect concentrations might be increased by incorporating graphene. • Multiple material analyses investigate graphene-incorporated ZnO. Abstract In this research, graphene was incorporated into the ZnO nanorods (NRs) growth in two different ways to enlarge the rod diameter of ZnO NRs on porous silicon (PS) substrates. We etched the P-type Si (1 0 0) wafer to form the PS layer in solution with HF and C 2 H 5 OH and H 2 O 2 for appropriate time. Then, ZnO NRs with and without incorporating graphene were grown with solgel/hydrothermal methods on top of the PS substrates, respectively. To characterize the graphene incorporated ZnO NRs on PS substrates, multiple material analyses including field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, photoluminescence, IV curves were used to study the graphene-incorporated ZnO NRs. Results indicate that ZnO NRs with larger diameters could be viewed with graphene included into the ZnO NR growth in two different ways. Furthermore, higher defect concentrations could be observed for the graphene-contained NRs. In addition, the ZnO/PS contact exhibited rectifying electrical behaviors without graphene addition but non-rectifying electrical behaviors with graphene incorporation. Tuning ZnO NRs growth on PS substrates with graphene is promising for future ZnO NRs/Si-based device applications. [ABSTRACT FROM AUTHOR]

In this study, ZnO nanorods (NRs) were grown using solgel/hydrothermal methods on SiO 2 , carbon nanotube (CNT)/SiO 2 , and graphene/SiO 2 substrates to form hydrogen gas sensing chips. Results indicate that ZnO NRs/CNT/SiO 2 structures exhibited better H 2 sensing performance than the other two types of ZnO NRs-based structures. Furthermore, multiple electrical and material characterizations show that ZnO NRs/CNT/SiO 2 structures had a stronger (002) crystalline phase, with nanorod fusion near the bottom, and more oxygen-related defects. Owing to their small size, simple fabrication, and low cost, the ZnO NRs/CNT/SiO 2 based H 2 gas sensors are promising for future industrial H 2 sensing applications. [ABSTRACT FROM AUTHOR]

In this study, graphene was added into the ZnO seed layer and spread on the substrate to tune the aspect ratio of ZnO nanorods (NRs) on SiO2 substrates, respectively. Compared with ZnO NRs with sol gel/hydrothermal growth in a normal condition, the aspect ratio of ZnO NRs could be enhanced by incorporating graphene into the seed layer. Furthermore, the c-axis crystallinity and hydrophobic properties could be strengthened, too. On the other hand, ZnO NRs grown on graphene/SiO2 substrate exhibited lower aspect ratio but stronger antibacterial capability. These graphene-incorporated ZnO NRs growth shows promise for future ZnO nanostructure-based applications. [ABSTRACT FROM AUTHOR]

Here, we demonstrated the transparency of graphene to the atomic arrangement of a substrate surface, i.e., the "lattice transparency" of graphene, by using hydrothermally grown ZnO nanorods as a model system. The growth behaviors of ZnO nanocrystals on graphene-coated and uncoated substrates with various crystal structures were investigated. The atomic arrangements of the nucleating ZnO nanocrystals exhibited a close match with those of the respective substrates despite the substrates being bound to the other side of the graphene. By using first-principles calculations based on density functional theory, we confirmed the energetic favorability of the nucleating phase following the atomic arrangement of the substrate even with the graphene layer present in between. In addition to transmitting information about the atomic lattice of the substrate, graphene also protected its surface. This dual role enabled the hydrothermal growth of ZnO nanorods on a Cu substrate, which otherwise dissolved in the reaction conditions when graphene was absent. [ABSTRACT FROM AUTHOR]

A counter electrode based on graphene, ZnO nanoparticles and ZnO nanorods was designed for dye-sensitized solar cells (DSSCs). In this counter electrode, a 200 nm thick composite film of graphene with ZnO nanoparticles served as the scaffolds while vertically aligned ZnO nanorods with the lengths of about 730 nm and the diameters of about 50 nm were employed to decorate these scaffolds. The surface morphology, crystal structure, photoluminescence of the graphene/ZnO composite counter electrodes were analysed by means of field-emission scanning electron microscope, X-ray diffractometer and photoluminescence spectroscopy, respectively. Under 1-Sun illumination (100 mW cm− 2, AM 1.5), J- V measurements were performed to characterise the photovoltaic performance of the DSSCs with the graphene/ZnO composite counter electrode. The power conversion efficiency of the DSSCs with the graphene/ZnO composite counter electrode was 0.17%, which was slightly higher than that of the DSSC with the Pt counter electrode (0.15%). The reasonable photovoltaic performance of the DSSCs can be attributed to the large surface area for the reduction of and direct pathway for electron transport from counter electrode to electrolyte. Our results have demonstrated that graphene/ZnO composite may be used as the low-cost counter electrodes for highly efficient DSSCs. [ABSTRACT FROM AUTHOR]

SUMMARY Fabrication and performance study of dye-sensitized solar cells using different counter electrodes and photoanodes is reported. Spin coated, E-beam coated platinum, and graphene electrodes were used as counter electrodes. Different combinations of TiO2 nanoparticle and ZnO nanorods (NRs) with CdSe quantum dots were prepared and used as photoanodes. The photoanodes comprising of both ZnO NRs and TiO2 nanoparticles have shown improved performances in short-circuit current density and open-circuit voltage comparing the devices fabricated using only ZnO NR or TiO2 nanoparticles. The inclusion of CdSe quantum dots has been found to increase the performance of dye-sensitized solar cell for all the photoanodes. In case of counter electrodes, the cells fabricated with graphene showed improved performance. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highlights: [•] The ZNRs are synthesized on glass substrates using the hydrothermal process. [•] The graphene films are grown on Cu foils by the thermal chemical vapor deposition technique. [•] The graphene films are transferred onto the ZNRs with various cycles to form the GS/ZNR hybrids by wet transfer process. [•] All GS/ZNR hybrids exhibit higher levels of FE properties than the pristine ZNRs. [Copyright &y& Elsevier]

Abstract: We present the fabrication and characterization of new type of flexible gas sensors, composed mainly of a bottom ZnO conductive layer on metal foil, vertically aligned ZnO nanorod channel, and graphene-based top conductive electrode. Multiple cycling tests demonstrated the ZnO nanorods (NRs) and graphene (Gr) hybrid architectures accommodated the flexural deformation without mechanical or electrical failure for bending radius below 0.8cm under the repeated bending and releasing up to 100 times. In addition, the hybrid architectures fabricated on glass substrate showed good optical transmittance larger than ∼70% for visible light, indicating potential application in transparent devices. Furthermore, our gas sensors demonstrated the ppm level detection of ethanol gas vapor with the sensitivity (resistance in air/resistance in target gas) as high as ∼9 for 10ppm ethanol. [Copyright &y& Elsevier]

• A 3D Graphene/ZnO macroporous substrate was constructed for CTCs adhesion. • The resistance change shows high detection sensitivity and excellent specificity. • The EIS also revealed the regular impedance changes during the adhesion process. • The sensing process was analyzed by equivalent circuit model. A three-dimensional (3D) graphene macroporous foam substrate with ZnO nanorod array was developed for specific and non-invasive detection of circulating tumor cells (CTCs). With the help of the epithelial cell adhesion molecule antibody (anti-EpCAM) and the array structure, the EpCAM-positive CTCs can adhere on the detection substrate (rGO-ZnO-antiEpCAM foam). Moreover, the resistance and the electrochemical impedance spectroscopy (EIS) of the rGO-ZnO-antiEpCAM foam was changing during the CTCs adhering process with high sensitivity. Compared to the EpCAM-negative cancer cell, the resistance of the substrate is rising with the amount of the EpCAM-positive CTCs. The possible reason is that the negative charges of CTCs affected the conductivity of the p -type reduced graphene oxide (rGO), and when CTCs were adhering to the rGO-ZnO-antiEpCAM foam, the resistance of the rGO-ZnO-antiEpCAM foam increased. In addition, the EIS measurement also shows the regular changes during the adhering process. From the equivalent circuit modeling of EIS, the charge transfer resistance (R ct) on the surface of the rGO-ZnO-antiEpCAM foam electrode had a linear growth. This may be due to the fixation of negatively charged Breast cancer cells (MCF-7) on the substrate, the charge transfer process was hindered, which caused the semicircle domain of the EIS curve to expand significantly with time. These results reveal that CTCs can not only be specifically adhered on the rGO-ZnO-antiEpCAM foam, but also the electrical microenvironment of the detection substrate was changed during CTCs adhering process. The construction of the detection substrate, the measurement and analysis methods of the electrical signals are of great significance in CTCs acquisition and sensing, which will provide an effective strategy for the real-time monitoring of CTCs at the clinic. The CTCs adhered on the 3D graphene/ZnO macroporous structure, and the electrical properties of this substrate changed dramatically during the adhesion of CTCs. [Display omitted] [ABSTRACT FROM AUTHOR]

Herein, we report an innovative and facile approach to prepare graphene quantum dot (GQD)-wrapped vertically aligned zinc oxide (ZnO) nanorod (NR) arrays. The ZnO NR/GQD heterostructure was prepared as a core/shell structure on an indium tin oxide (ITO) substrate using spin-coating, electron-beam evaporation, and a rapid thermal process combined in a novel way. Spin-coated poly(methyl methacrylate) (PMMA) was converted to GQDs on ZnO NRs by high temperature thermal treatment. A metal-capping layer was used to convert PMMA into GOD by avoiding the thermal evaporation of PMMA. Two different metals Ni and In were used as capping layers and studied their effect in the thermal conversion of PMMA into GQDs and in the properties of the fabricated devices. Structural, morphological, compositional and optical properties of the as-prepared ZnO NR/GQD heterostructures were characterized. The devices consisting of 50–70 nm ZnO NRs covered with GQDs as a core-shell structure demonstrated efficient UV photosensing with excellent photoresponse due to the GQDs showing high carrier transport and photoabsorption. The fabricated ITO/ZnO NR/GQD/In device showed better photosensing responsivity than the ITO/ZnO NR/GQD/Ni one. This is an entirely new technique for growing GQDs directly on previously prepared ZnO NRs. Image 1 • A novel approach for the preparation of graphene quantum dot-wrapped vertically aligned zinc oxide nanorod (NR) arrays is reported in first time. • PMMA spin-coated onto ZnO NRs is thermally converted as graphene quantum dots directly on ZnO NRs. • The top metal coated on the ZnO NRs/GOD heterostructure has significant role in deciding the applicability of the structure. • Indium top metal showed efficient photosensor property, whereas, nickle metal showed catalytic and memristive properties. • Sandwich type parallel plate conductor showed good response in charge collecting efficiency compared to metal tip-based probe contacts. [ABSTRACT FROM AUTHOR]

High crystalline ZnO nanorods (NRs) on Zn pre-deposited graphene/Cu sheet without graphene transfer process have been fabricated by self-catalyzed vapor-phase transport synthesis. Here, the pre-deposited Zn metal on graphene not only serves as a seed to grow the ZnO NRs, but also passivates the graphene underneath. The temperature-dependent photoluminescence spectra of the fabricated ZnO NRs reveal a dominant peak of 3.88 eV at 10 K associated with the neutral-donor bound exciton, while the redshifted peak by bandgap shrinkage with temperature and electron-lattice interactions leads a strong emission at 382 nm at room temperature. The optical absorption of the ZnO NRs/graphene hetero-nanostructure at this ultraviolet (UV) emission is then theoretically analyzed to quantify the absorption amount depending on the ZnO NR distribution. By simply covering the ZnO NR/graphene/Cu structure with the graphene/glass as a top electrode, it is observed that the current-voltage characteristic of the ZnO NR/graphene hetero-nanojunction device exhibits a photocurrent of 1.03 mA at 3 V under a light illumination of 100 μW/cm2. In particular, the suggested graphene/ZnO NRs/graphene hybrid-nanostructure-based devices reveal comparable photocurrents at a bidirectional bias, which can be a promising platform to integrate 1D and 2D nanomaterials without complex patterning process for UV device applications. [ABSTRACT FROM AUTHOR]

Well-arranged ZnO nanorods were hydrothermally grown on reduced graphene oxide coated indium tin oxide electrode, and subsequently gold nanoparticles (AuNPs) were electrodeposited on these nanorods. Glucose sensors were constructed with glucose oxidase (GOx) loaded on the AuNPs decorated ZnO nanorods via electrostatic interaction, and during the electrochemical measurements were stimulated with UV irradiation. The results indicate that the AuNPs simultaneously increase the yield and transfer rate of electrons. On the one hand, the AuNPs accelerate the electrons to transfer from the redox centers of GOx to the ZnO nanorods and hence, the transfer rate of the electrons is obviously increased. On the other hand, together with UV irradiation, the AuNPs effectively facilitate the separation of the photoinduced charges within the ZnO nanorods, and further enable more quantity of holes to participate in the oxidation of GOx(FADH 2) to GOx(FAD) during the redox reaction. Therefore, the yield of the electrons is also raised. In comparison to the glucose sensor without the AuNPs, the sensitivity of the glucose sensor with the AuNPs is increased 4.8 times and the low detection limit (signal-to-noise of 3) is decreased 5 times. Besides, the other performance of the glucose sensor with the AuNPs, such as the detection range, selectivity, stability, and the detection accuracy to serum glucose concentration, is also improved accordingly. Therefore, it is an effective method to functionalize ZnO nanorods with AuNPs to enhance the electrochemical and photoelectrochemical performance of enzymatic glucose sensors. [ABSTRACT FROM AUTHOR]