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Surface modification and wetting state transformation of ZnO based nanomaterials have been extensively investigated due to their substantial roles in current industrial applications. In this work, we demonstrated the formation of highly crystalline and ordered Bi/ZnO nanorods arrays (Bi/ZNRs) grown on FTO substrate via a feasible hydrothermal method, as a function of reaction time (t). The lateral diameter of the nanostructures were found increased from 23 nm to 43 nm when the reaction time increased from 30 min to 90 min. An in-depth analysis and incisive mechanism of crystal growth under the function of reaction time were proposed. The crystal defect which originated from different Bi incorporation pathways has been declared as the main factor altering the optical energy, electrical properties and band structure of Bi/ZNRs. The Bi/ZNRs showed a higher localize current of 14.5 pA as compared to pristine ZNRs under an 6V applied bias condition, revealing the nature of Bi as a pentavalent dopant that contributed to a density of free electron. Additionally, the Bi/ZNRs also revealed a red shifted in optical energy band gap and exhibit a wetting transition from hydrophobic to hydrophilic textured surface. The novel nanostructures reported herein exhibit interesting physical and optical properties for the fabrication of high performance optoelectronic devices.

Zinc oxide nanorods (ZnO NRs) have gained considerable research interest due to their robust energy conversion efficiency. In the present work, ZnO NRs arrays were pinpointed to probe their electromechanical response under strain conditions. ZnO seed was sputtered on different substrates by radio frequency magnetron sputtering (RF) technique at 80 W constant power and 3.49 × 10−5 mbar base pressure. The X-ray diffraction patterns exhibit hexagonal wurtzite structure with preferred c-axis crystal directions in the (002) plane. The average thickness of the seed layer for all the samples was estimated at around 214.6 nm. Surface roughness and morphologies of the nanorods have been characterized by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM), respectively. FE-SEM images show homogeneous growth in different directions on substrates. The average diameters of ZnO NRs on silicon, glass and ITO were 51, 58 and 61 nm, respectively. The average length of all the nanorods on the substrates were measured around 1–2 μm. The local piezoresponse measurements conducted on two selected domain regions of the nanorod arrays had been characterized by piezoresponse force microscopy (PFM) to confirm the switching-piezoelectric behavior.

One-dimensional ZnO nanorods (ZnO NRs) have the edge over other nanostructures due to their unique properties. Current work fabricated ZnO NRs on pre-seeded ITO glass substrate through hydrothermal synthesis using customized hydrothermal set-up. The sources of Zn2+ and OH− ions were supplied continuously from zinc nitrate hexahydrate and hexamethylenetetramine (HMTA), respectively whereby the concentration of both precursors and the temperature of growth solution varied from 0.01 M to 0.05 M and from 80 °C to 120 °C, respectively. The impact of concentration and temperature variation on hydrothermal reaction and corresponding PEC cell performance is discussed. Field emission scanning electron microscopy (FESEM) results revealed that the morphology of prepared ZnO NRs arrays is concentration- and temperature-dependent. X-ray diffraction (XRD) reflected strong orientation along (002) direction for the hexagonal wurtzite ZnO NRs, and the film crystallinity greatly improved when the temperature increased. At optimal concentration and hydrothermal temperature, the ZnO NRs photoanode exhibited a bandgap value of 3.22 eV and achieved an impressive photocurrent density of 0.483 mA/cm2 that was attributed to the ordered rods alignment and improved optical properties. In addition, the electrochemical impedance spectroscopy (EIS) demonstrated optimized one-dimensional (1D) NRs sample showed better charge separation and transfer rate, which was two times larger than ZnO nanoparticles. The present work exhibited better photoelectrochemical performance than the other reported literature showing the high quality of ZnO NRs produced.

Crystallinity and band offset alignment of inorganic electron acceptor play a vital role in enhancing the device performance of inverted organic solar cell (IOSC). In this report, homogenous and vertically-aligned chemical treated ZnO nanorods (ZNR) were successfully grown on fluorine-doped tin oxide (FTO) substrate via a fully-solution method. It was found that the morphology of ZnO was fine-tuned from truncated surface to tubular structure under both of the anionic (KOH) and protonic (HCl) treatment. An extraordinary defect quenching phenomenon and hyperchromic energy band edge shift were observed in 0.1 M KOH-treated ZNR proven by the highest (0 0 2) peak detection and the lowest defect density. Compared with the pristine sample, the 0.1 M KOH-treated ZNR device showed a remarkable improvement in power conversion efficiency (PCE) up to 0.32%, signifying the effectiveness of anodic treatment. The robust correlation between the dependency of chemical treated ZNR and the device performance was established. This work elucidates a feasible method towards efficient IOSC devices development.

Charge transport dynamics in ZnO based inverted organic solar cell (IOSC) has been characterized with transient photocurrent spectroscopy and localised photocurrent mapping-atomic force microscopy. The value of maximum exciton generation rate was found to vary from 2.6 × 1027 m−3s−1 (Jsat = 79.7 A m−2) to 2.9 × 1027 m−3s−1 (Jsat = 90.8 A m−2) for devices with power conversion efficiency ranging from 2.03 to 2.51%. These results suggest that nanorods served as an excellent electron transporting layer that provides efficient charge transport and enhances IOSC device performance. The photovoltaic performance of OSCs with various growth times of ZnO nanorods have been analysed for a comparison between AM1.5G spectrum and local solar spectrum. The simulated PCE of all devices operating under local spectrum exhibited extensive improvement with the gain of 13.3–13.7% in which the ZnO nanorods grown at 15 min possess the highest PCE under local solar with the value of 2.82%.

Incorporating cadmium sulfide quantum dots (CdS QDs) onto ZnO nanorod (ZNRs) has been investigated to be an efficient approach to enhance the photovoltaic performance of the inverted organic solar cell (IOSC) devices based on ZNRs/poly (3-hexylthiophene) (P3HT). To synthesize CdS/ZNRs, different durations of deposition per cycle from 1 to 9 min were used to deposit CdS via SILAR technique onto ZNRs surface grown via hydrothermal method at low temperature on FTO substrate. In typical procedures, P3HT as donor polymer were spun-coating onto CdS/ZNRs to fabricate IOSC devices, followed by Ag deposition as anode by magnetron sputtering technique. Incorporation of CdS QDs has modified the morphological, structural, and optical properties of ZNRs. Incorporation of CdS QDs onto ZNRs also led to higher open circuit voltage (Voc) and short circuit current density (Jsc) of optimum ZNRs/CdS QDs devices due to the increased interfacial area between ZNRs and P3HT for more efficient exciton dissociation, reduced interfacial charge carrier recombination as a result of lower number of oxygen defects which act as electron traps in ZnO and prolonged carrier recombination lifetime. Therefore, the ZNRs/CdS QDs/P3HT device exhibited threefold higher PCE (0.55%) at 5 min in comparison to pristine ZNR constructed device (0.16%). Overall, our study highlights the potential of ZNRs/CdS QDs to be excellent electron acceptors for high efficiency hybrid optoelectronic devices.

Metal oxide based optical absorbance gas sensor (MOAGS) exhibits underlying potential to be the most promising energy-saving device with long-term stability and excellent sensing performance. In this work, a self-customized automated MOAGS setup was employed to study the carbon monoxide (CO) gas sensing performance between the hydrothermal synthesized ZnO nanorod (ZNR) and Indium-doped ZnO nanorod (IZNR) operating at room temperature of (25 ± 1)°C. Specifically, it was found that the In 3+ was evenly doped into ZnO lattice which in turn increased the defect density and generated an impurity state within the energy band structure of ZnO. The results showed that 0.04 mol% IZNR exhibited an optimum sensing performance with absolute optical absorbance change (OAC) of 0.067 a.u. under the 10 ppm of CO gas testing environment with fastest respond and recovery time. The dependency of sensing performances to the optical band gap energy alteration and the defect state was evaluated. This work provides a simple and feasible route to develop the room temperate operating MOAGS for hazardous gas detection.

A homogeneous CuO-ZnO nanostructure with tunable morphology and optical band structure is successfully synthesized via a hydrothermal method under the different dopant mole ratios of Cu. The robust correlation between the crystallite size, surface morphology, optical band gap alteration of the synthesized CuO-ZnO and its performance in photoelectrochemical (PEC) activity are investigated and compared to the reference ZnO based photocathode. In this report, it is found that the morphology of hexagonal ZnO nanorod is changed to nanosheet and vertically align CuO-ZnO based nanograss after the Cu incorporation. This result is mainly due to the composition phase change after the excessive incorporation of Cu metal into ZnO lattice. Furthermore, the optical band gap of the sample also presented a bathochromic shifted after the Cu insertion. The measurements on PEC activity of CuO-ZnO nanostructure was performed under the irradiation of a 100 mWcm−2 Xenon light in 0.5M Na2SO4 electrolyte. Among the sample, 0 Zn:1 Cu exhibited a highest photocurrent density which is 5 fold as compared to its reference ZnO samples. This finding could be due to the highest surface active area and lowest optical energy band gap in the 0 Zn:1 Cu nanograss that eventually contributes to a high free electron density that facilitates the charge transport in the photoelectrochemical cells. This novel approach could provide an alternative to the future solar hydrogenation application.

Highly oriented ZnO nanorod was successfully synthesised on Ag nanoseed coated FTO substrate via a microwave hydrolysis approach. It was found that the morphology and the optical properties of the ZnO nanorod are strongly influenced by the power of the microwave irradiation used during the growth process. The aspect ratio of the nanorods changed from high to low with the increasing of microwave power. It was also found that the optical band gap of the ZnO nanorod red shifted with the increasing of the microwave power, reflecting an excellent tune ability of the optical properties of ZnO nanorods. The photocatalytic activity of these unique nanorod was evaluated by a dehydrogenation process of isopropanol to acetone in the presence of ZnO nanorod. It was found that the ZnO nanorod exhibited an excellent catalytic performance by showing an ability to accelerate the production of 0.031 mol L−1 of acetone within only 35 min or 0.9 mmol L−1 min−1 from isopropyl alcohol dehydrogenation. It was almost no conversion from isopropyl alcohol when ZnO nanorods was absence during the reaction. In this report, a detailed mechanism of ZnO nanorod formation and the relationship between morphology and optical energy band gap are described.

Surface modification in nanostructures enables a thorough control on intrinsic properties, surface activity and enhancement of their usefulness in several device applications. The crystal growth and design in a low temperature regime (

The controllable growth of metal sulfide–metal oxide based nanomaterials with a tunable band gap structure is vital in the fabrication of new generation optoelectronic devices. In this paper, two-dimensional hierarchical CdS/ZnO nanorod arrays were successfully grown via a low temperature hydrothermal-SILAR method. A concise mechanism related to the surface and band gap modification on the CdS/ZnO nanorods was investigated under various CdS deposition cycles (N). The diameter and surface roughness properties of the sample were found to be linearly dependent on the value of N. A bathochromic shift in the optical energy band gap revealed the quantum size effects of the CdS/ZnO nanorods, as well as the induced interface band state and energy band split in the ZnO band state. An impressive improvement in the crystallinity of the sample was also observed under the CdS treatment. The correlation between the optical band gap and photovoltaic efficiency was evaluated. The results proved that the ZnO nanorod/CdS devices exhibited a threefold higher power conversion efficiency in comparison to a pristine ZnO nanorod device.

A simple low-temperature solution processed bismuth-doped ZnO nanorods (NRs) and poly(3-hexylthiophene) (P3HT) were used as electron acceptor and donor, respectively, in a hybrid inorganic–organic photovoltaic system. Controlling Bi precursor concentration via solution processing (hydrothermal method) plays an important role in altering the morphology, structure, and intrinsic defects of ZnO NRs. Interstitial doping of Bi–Bi2O3 into ZnO (BiZO) NRs results in simultaneous improvement of the open circuit voltage and short circuit current density primarily due to prolonged charge carrier recombination lifetime, increased donor–acceptor interfacial areas with efficient exciton dissociation, and charge carrier mobility. As a result, the power conversion efficiency of the 2 wt % BiZO NRs-P3HT device was significantly enhanced by 55% compared with that of the pristine device. Overall, our study highlighted the immense potential of BiZO NRs as an excellent electron acceptor for fabrication of hybrid optoelectroni...

One-dimensional ZnO nanorods (ZNRs) synthesized on fluorine-doped tin oxide (FTO) glass by hydrothermal method were modified with cadmium sulfide quantum dots (CdS QDs) as an electron transport layer (ETL) in order to enhance the photovoltaic performance of inverted organic solar cell (IOSC). In present study, CdS QDs were deposited on ZNRs using a Successive Ionic Layer Adsorption and Reaction method (SILAR) method. In typical procedures, IOSCs were fabricated by spin-coating the P3HT:PC61BM photoactive layer onto the as-prepared ZNRs/CdS QDs. The results of current-voltage (I-V) measurement under illumination shows that the FTO/ZNRs/CdS QDs/ P3HT:PC61BM/ PEDOT: PSS/Ag IOSC achieved a higher power conversion efficiency (4.06 %) in comparison to FTO/ZNRs/P3HT:PC61BM/PEDOT: PSS/Ag (3.6 %). Our findings suggest that the improved open circuit voltage (Voc) and short circuit current density (Jsc) of ZNRs/CdS QDs devices could be attributed to enhanced electron selectivity and reduced interfacial charge carrier recombination between ZNRs and P3HT:PC61BM after the deposition of CdS QDs. The CdS QDs sensitized ZNRs reported herein exhibit great potential for advanced optoelectronic application.

One dimensional ZnO nanorod has been extensively studied in sensor application due to its unique properties in direct energy band gap and high binding energy. In this report, ZnO nanorod arrays were synthesized via hydrothermal approach. Highly oriented (002) nanorods array with diameter of (22.42 ± 1.40) nm was successfully grown on the quartz surface. A low cost and room temperature optical based NO sensor was introduced. ZnO nanorods array show a high sensitivity upon the NO gas which is 20.1 % within 3 minutes. This newly established method can be potentially used in detection of other toxicity gas.

In the present work, we have discovered a photoinduced linear electrooptics in ZnO nanorods which were fabricated by simply varying the content of the growth solution. It was established that by varying the growth solution concentration one can vary the surface density of the ZnO nanorod arrays growth on the surface. The lowest ZnO content produces the lowest surface density in the nanorods. The photoinduced linear electrooptics was studied using the He–Ne laser at wavelength 1150 nm and was stimulated by 7 ns nitrogen laser at 371 nm. The nonlinear dependence of the Ag nanoparticle (NP) concentration was found and it was significantly higher than that for the pure ZnO NP. Principal role of the Ag NP on the observed effects was discussed. & 2014 Published by Elsevier B.V.

One-dimensional ZnO semiconductor nanomaterials have been attracting increasing attention due to their outstanding properties, which are different from bulk materials. ZnO has a direct band gap of 3.37 eV and large exciton binding energy hence its nanowires and nanorods have been regarded as one of the most promising materials for nanoscale electronic and optoelectronic devices such as ultraviolet laser diodes, optical detectors and gas sensor. ZnO nanowires and nanorods have been successfully synthesized by various techniques such as evaporation, sputtering and pyrolysis. In this paper we report the preparation of nanorod arrays of ZnO on ITO glass substrates which were pre-coated with ZnO nanoparticles by using low temperature chemical solution method and the result was compared with microwave hydrolysis process. The morphology and structure of ZnO nanorod arrays were investigated using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The ZnO nanorod arrays with a diameter of 40-70 nm were successfully synthesized. In microwave hydrolysis method, the diameter, density and surface roughness was found to depend on the microwave power. The microwave method is far superior in producing ZnO nanostructure growth.

Anion passivation effect on metal-oxide nano-architecture offers a highly controllable platform for improving charge selectivity and extraction, with direct relevance to their implementation in hybrid solar cells. In current work, we demonstrated the incorporation of fluorine (F) as an anion dopant to address the defect-rich nature of ZnO nanorods (ZNR) and improve the feasibility of its role as electron acceptor. The detailed morphology evolution and defect engineering on ZNR were studied as a function of F-doping concentration (x). Specifically, the rod-shaped arrays of ZnO were transformed into taper-shaped arrays at high x. A hypsochromic shift was observed in optical energy band gap due to the Burstein-Moss effect. A substantial suppression on intrinsic defects in ZnO lattice directly epitomized the novel role of fluorine as an oxygen defect quencher. The results show that 10-FZNR/P3HT device exhibited two-fold higher power conversion efficiency than the pristine ZNR/P3HT device, primarily due to the reduced Schottky defects and charge transfer barrier. Essentially, the reported findings yielded insights on the functions of fluorine on (i) surface –OH passivation, (ii) oxygen vacancies (Vo) occupation and (iii) lattice oxygen substitution, thereby enhancing the photo-physical processes, carrier mobility and concentration of FZNR based device.

Band gap energy and surface defect on the nanostructure play an important role especially in determining the performance and properties of the optical based gas sensor. In this report, ZnO nanorods (ZNRs) with various growth concentrations were successfully synthesized using a facile wet chemical approach. The gas sensing performance of the ZNRs samples with different concentrations were tested toward the highly hazardous carbon monoxide (CO) gas at a concentration of 10 ppm operated at room temperature. It was found that the 40 mM ZNRs sample exhibited the highest response coupled with the shortest response time (123.3 ± 1.3 s) and recovery time (7.7 ± 0.3 s). The high response and accelerated sensing reaction were attributed to the band gap narrowing of the 40 mM ZNRs induced by the increase in oxygen vacancy related defect states, and it is directly proportional to the CO gas sensing activity. These defects acted as the oxygen trap sites which will promote the oxygen adsorption on the surface of ZNRs a...

This paper reports a study of the effect of ZnO nanoseed structure on the growth orientation of ZnO nanorods prepared using a seed-mediated hydrothermal process. In this work, we prepared vertical align ZnO nanorods by a two-step process namely seeding and growth process. ZnO nanoseed on a silicon oxide (SiO2) coated silicon (Si) substrate was deposited by rf- sputtering under argon gas atmosphere at room temperature (ca. 25ºC). The samples were annealed in air at 500 °C for both different annealing times namely 1 and 2 h to obtain nanoseed with varies structure and crystallinity. The ZnO nanorods were then grown from the nanoseed via a hydrothermal process in a growth solution that contained equimolar of zinc nitrate hexahydrate and hexamethylenetetramine (HMT) at 70°C for 4 h. It was found that the durations of annealing treatment on the nanoseed indicated an effective modification on the crystal growth orientation of the nanorods, which preferred well-aligned orientation for shorter annealing time and random growth for longer annealing time. These results should find potential use for manipulating the nanostructure growth of ZnO for applied in current existing application.

Hybrid ZnO nanostructure with controlled morphology have been proved to enhance the physical and chemical properties of the material and used as photodiode and sensor. In this paper, hybrid graphene-ZnO nanoflower and nanorods have been successfully synthesized via a seed mediated method with micropatterned ZnO nanoseed treated with multilayer graphene (MLG) in a hydrothermal process. In typical process, the ZnO nanoseeds with and without resists were spin coated with a multilayer graphene prior to the growth process. The treated seed was then used to grow the ZnO nanostructures in the growth solution that contained equimolar (0.04 M) of zinc nitrate hexahydrate and hexamethylenetetramine. The growth process was carried out inside an autoclave at temperature 70 °C. The growth time was 4 h. It was proved that the MLG treatment on micropatterning substrate may induce new morphology formation of ZnO nanostructure. It is expected that the heteroepitaxy reaction occurred between the MLG and ZnO interface. This presence method can be used as an alternative approach to control the morphology of hybrid ZnO nanostructure growth.

One dimensional (1D) zinc oxide, ZnO nanostructures have shown promising results for usage in photodiode and optoelectronic device due to their high surface area. Faster and conventional method for synthesis ZnO nanorods has become an attention for researcher today. In this paper, ZnO nanorods have been successfully synthesized via two-step process, namely alcothermal seeding and seed-mediated microwave hydrolysis process. In typical process, the ZnO nanoseeds were grown in the growth solution that contained equimolar (0.04 M) of zinc nitrate hexahydrate, Zn (NO3).6H2O and hexamethylenetetramine, HMT. The growth process was carried inside the inverted microwave within 5- 20 s. The effect of growth parameters (i.e. concentration, microwave power, time reaction) upon the modification of ZnO morphology was studied. ZnO nanostructures were characterized by Field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). The densities of nanorods were evaluated by the Image J analysis. It was found that the morphology (e.g. shape and size) of nanostructures has changed drastically with the increment of growth solution concentration. The density of ZnO nanorods was proven to increase with the increasing of reaction time and microwave power. We hypothesize that the microwave power might enhance the rate of nucleation and promote the faster nanostructure growth as compared with the normal heating condition due to the superheating phenomenon. This method might promote a new and faster alternative way in nanostructure growth which can be applied in currently existing application.

Fibrous, ultra small nanorod-constructed Pt nanocubes (PtNCs) directly grown on the substrate surface show enhanced heterogeneous catalytic reduction of methyl orange with efficiency 103 times higher compared to those in homogeneous reaction. The PtNCs may find potential application in organic reactions and photoelectrochemical devices.