ZnO Nanowire Arrays Research Articles

Optical and Electrical Investigation of ZnO Nano-Wire Array to Micro-Flower from Hierarchical Nano-Rose Structures.

We have demonstrated a simple solvo-chemical and solvo-thermal route to design various nano-structures growth of zinc oxide (ZnO). The shapes and morphologies can be easily controlled by using different ambient conditions. We successfully fabricated ZnO nano-wires array on ITO substrate. Those nano-wire array center gradually formed micro-flower like structure evolved in this solvo-chemical route. This novel synthesis happened under cationic surfactant CTAB in the solution helps to form hierarchical structures of ZnO. The length of nano-wire is around 2.0 µm, which formed micro-flower diameter 5.0 µm. Micro-flowers were scratched out from ITO substrate thin film and annealed at 650 °C in electric oven for 1 hour, eventually this micro-flower transformed to novel nano-rose structure confirmed by electron microscopic study. Synthesized nano-rose diameter was around 730 nm. Moreover, we found a drastic change of dielectric behavior and DC conductivity of ZnO nanostructures depending on geometry regulated by the duration of preparation. Interestingly enough, optical and electrical properties also changed due to different crystalline structure formation. The dielectric constant is higher at 7.5 also high threshold voltages at 4 V, corresponds to nano-wires array with micro-flower system. A detail dielectric analysis of one step behavior of broad single relaxation peak was obtained only shows the normal dispersion in this system from 1000 kHz to 10 MHz. While less dielectric constant 1.7 and low threshold voltage 1 V, investigated nano-wires with micro-flower, then nano-rose transition appeared in two step behaviors of double relaxations phenomenon appeared one at low frequency and other at higher frequency region. Besides, I~V response characteristics is new idea about different breakdown voltages and bi-stable DC switching capability. Our work demonstrates the possibility of a fast novel synthesis route using a Solvo-chemical process for this type of nanomaterials transition. This special structural character was able to tune band gap which has potential applications in semiconductor electronic devices.

Continuous formation of a seed layer and vertical ZnO nanowire arrays enabled by tailored reaction kinetics in a microreactor

ZnO nanowires (NWs) are gaining widespread popularity due to their many unique physical and chemical properties. The hydrothermal process is the most commonly used approach to prepare vertical ZnO NW arrays. Its fundamental issues are the rather slow deposition rate and the variation of reactant concentrations as a function of time. In this study, we employed a continuous flow microreactor and deposition system to prepare both a ZnO seed layer and vertical ZnO NW arrays continuously by simply tuning the flow rate of reactant solutions. The change in flow rate allows reaction kinetics to be selectively tuned, resulting in the generation of molecular zinc species and colloidal ZnO nanocrystals at a high and low flow rate, respectively. The molecular zinc species constitute the seed layer at the high flow rate, and subsequently the colloidal ZnO nanocrystals contribute to the growth of ZnO NWs at the low flow rate. Since the direct delivery of the controlled building blocks on the substrate prevents the formation of homogeneously induced ZnO particles, we were able to obtain highly uniform ZnO NW arrays, with a growth rate as fast as 240 nm min−1, which is significantly higher than typical growth rates from gas-phase or batch hydrothermal processes. Based on the growth mechanism study, the dimensions of the vertical ZnO NW arrays were varied, leading to an aspect ratio of the NWs up to 23. The advantages of our system were highlighted by preparing a high-quality heterogeneous surface having both hydrophilic and hydrophobic nature on one substrate. These results demonstrate the capability of the continuous flow microreactor and deposition system in efficiently preparing functional vertical ZnO NW arrays.

Suppression of nanowire clustering in hybrid energy harvesters

The performance of hybrid energy harvesters based on ZnO nanowire arrays has been effectively enhanced by the introduction of PMMA.

The large response current of a vacuum pressure sensor based on a vertically-aligned ZnO nanowires array

A vertically-aligned ZnO nanowires (VA-ZnO-NWs) array was prepared via chemical vapor deposition, which was used to fabricate a vacuum pressure sensor and its sensitive characteristics were measured using a semiconductor parameter tester.

Effect of growth time and annealing on the structural defect concentration of hydrothermally grown ZnO nanowires

As a low temperature and low cost synthesis method, the hydrothermal deposition is widely used to grow ZnO nanowire arrays. Their optical properties are closely related to concentration of the structural defects in the ZnO nanowires. In this work we report on investigation on the evolution of the structural defects of ZnO nanowire arrays for different growth time, before and after post-annealing. The photo-emission properties of the ZnO nanowire arrays have been investigated in detail by using photoluminescence (PL) spectroscopy both on the as-grown nanowires and on the annealed ones. The PL analysis results showed an increasing intensity in the visible emission band with the growth time which is closely related to the change of the concentration of the structural defects in the ZnO nanowires regarding to the UV near-edge emission. The visible PL emission band can be deconvoluted into three Gaussians components, which correspond to the green, yellow-orange and red emissions, respectively. It is further revealed that the intensity of the orange and red emission bands increase with the increase of the growth time, which are ascribed to the interstitial oxygen and/or hydroxide groups and adsorbed oxygen, respectively. The correlation between energy-dispersive X-ray spectroscopy (EDS) analysis and PL measurements revealed that the excess zinc can be formed in the nanowires during the hydrothermal process.

Efficiency enhance the photoluminescence of ZnO nanowires array by the surface plasmonic effect of Au nanoparticles

Attaching Au nanoparticles to nanowires is an important approach to enhance the properties of photoelectric nano-devices based on ZnO nanowires array. We carry out a systematic investigation on affection of the Au nanoparticles size to the photoluminescence of ZnO nanowire array. Different sizes of Au nanoparticles range from 8 nm to 20 nm distinguished by 2 nm are synthesised by a method combining spurting and annealing. The green emission is quenched effectively and the UV emission of ZnO nanowires array is enhanced drastically, which is consistent with the wavelength-dependent generation of surface plasmon. We also find that 10 nm is the optimise size of Au nanoparticles to furthest enhance the UV emission of the ZnO nanowires array. This method can improve the photoelectric properties of ZnO based nano-devices conveniently and economically.

A general and rapid approach to hybrid metal nanoparticle–ZnO nanowire arrays and their use as active substrates for surface-enhanced Raman scattering detection

Rapid SERS substrate preparation: an aqueous phase reaction of metal precursors with ZnO@Zn has been exploited for synthesizing SERS-active metal–ZnO nanowire arrays.

Finite Element Analysis of Polymer-encapsulated ZnO Nanowire-based Sensor Array Intended for Pressure Sensing in Biometric Applications

This work presents results of finite element analysis of an array of ZnO nanowires with bottom-bottom electrode configuration, which are integrated onto a multi-layer chip stack and encapsulated within a polymer. The dynamically-deformed array constitutes a representative part of a high-resolution pressure sensor intended for reliable identification of the smallest fingerprint features such as shape of the ridges and pores. Parametric study was performed in order to predict the most rational values of the Young's modulus and thickness of the encapsulation layer in terms of magnitude and variability of the piezoelectric signals. The results also demonstrate the impact of nanowire aspect ratio and load orientation on the generated electrical signals.

Fabrication of ZnO nanowires array with nanodiamond as reductant

The availability of well-aligned high quality ZnO nanowires will extend the potential applications of such materials.

Enhanced field emission properties of ZnO-Ag2S core-shell heterojunction nanowires.

A simple approach to Ag2S quantum dot (QD) modification was used to tune the field emission (FE) properties of ZnO nanowire arrays (NWAs). By a simple and facile successive ionic layer adsorption and reaction (SILAR) approach, Ag2S QDs were uniformly and densely packed on ZnO nanowires (NWs) to form ZnO-Ag2S core-shell heterojunction structures. The FE properties of ZnO NWAs were effectively tuned by controlling the amount of Ag2S QDs. The turn-on field first reduces and then increases as the amount of Ag2S QDs increases, while the trend of the field-enhancement factor is inverse. This is attributed to the clustering of Ag2S QDs into nanoparticles (NPs) which cover the nanowire tips, as SILAR cycles increase.

In situ formation of zinc ferrite modified Al-doped ZnO nanowire arrays for solar water splitting

A simple wet-chemical treating method is introduced to in situ fabricate ZnFe2O4 onto conductive Al:ZnO nanowire arrays for solar-driven water splitting.

On-chip fabrication of lateral growth ZnO nanowire array UV sensor

In this paper, we integrate nano technology into traditional microelectronic processing, and develop an on-chip UV sensor based on lateral growth ZnO nanowire arrays. Traditional procedures are used to fabricate the interdigital electrodes, and ZnO nanowires are self-organized and grown between electrodes laterally by hydrothermal method. Additional inclined nanowires are removed during the post-processing procedures, such as ultrasound cleansing and electrode reinforcement. Two kinds of electrode structures are applied, i.e., Cr and Au. For the Cr electrode device structure, because Cr will restrain nanowires from growing vertically on its top, the laterally grown nanowire is long enough to reach the other side of the electrode. The corresponding photoelectric response mechanism is photoconduction controlled by surface oxide ion adsorption. Although the photocurrent is large, the gain is low, and the response speed is slow. Under the UV radiations of 20 mW/cm2 and of 365 nm in wavelength, the dark current is 2.210-4 A with 1 V bias voltage, the gain is up to 64, the photocurrent cannot reach saturation after 25 s, and the recovery time is 51.9 s. A secondary electrode can be fabricated after growing the nanowire arrays to reinforce the connection between the electrode and the ends of the nanowires. However, the direct contact between metal and semiconductor will form a Schottky contact. The photoelectric response mechanism is then changed to photovoltaic effect, which can greatly improve the gain and response speed. Under UV radiations of 20 mW/cm2 and of 365 nm in wavelength, the dark current is 4.310-8 A with 1 V bias voltage, the gain is up to 1300, the respond time is 3.8 s, and the recovery time is 5.7 s. For the Au electrode device structure, because Au is catalysis for ZnO nanowire growth, nanowires grown in lateral direction will compete with those grown in vertical direction, and hence the laterally grown nanowires are not long enough to reach the other side of the electrode. Nanowires grown from two sides of the electrodes will meet each other and form a bridging junction, however, this will turn the photoconduction mechanism from surface ion controlled into a bridging junction controlled, which yields the best device performance. Before removing the inclined nanowires by ultrasound cleansing, under UV radiations of 20 mW/cm2 and of 365 nm in wavelength, the dark current is 8.310-3 A with 1 V bias voltage, the gain is up to 1350, the respond time is 3.3 s, and the recovery time is 3.4 s. After removing the inclined nanowires, under UV radiations of 20 mW/cm2 and of 365 nm in wavelength, the dark current is 10-9 A with 1 V bias voltage, the gain is up to 8105, the respond time is 1.1 s, and the recovery time is 1.3 s.

ZnO nanowire array growth on precisely controlled patterns of inkjet-printed zinc acetate at low-temperatures.

ZnO nanowires have been fabricated through the hydrothermal method on inkjet-printed patterns of zinc acetate dihydrate. The silicon substrate used was heated accordingly during the printing period in order to maintain good spatial uniformity of the zinc acetate nanoparticles, responsible for the pattern morphology. Printing more than one pass of precursor ink leads to an increase in seed layer thickness that subsequently alters the density and dimensions of nanowires. It has been demonstrated that with the right inkjet-printing parameters and substrate temperature, ZnO nanowires can be effortlessly fabricated in accordance with the desired pattern variations under low temperature and mild conditions that ensures promising applications in optoelectronic devices.

Dimensional Tailoring of Hydrothermally Grown Zinc Oxide Nanowire Arrays.

Hydrothermally synthesized ZnO nanowire arrays are critical components in a range of nanostructured semiconductor devices. The device performance is governed by relevant nanowire morphological parameters that cannot be fully controlled during bulk hydrothermal synthesis due to its transient nature. Here, we maintain homeostatic zinc concentration, pH, and temperature by employing continuous flow synthesis and demonstrate independent tailoring of nanowire array dimensions including areal density, length, and diameter on device-relevant length scales. By applying diffusion/reaction-limited analysis, we separate the effect of local diffusive transport from the c-plane surface reaction rate and identify direct incorporation as the c-plane growth mechanism. Our analysis defines guidelines for precise and independent control of the nanowire length and diameter by operating in rate-limiting regimes. We validate its utility by using surface adsorbents that limit reaction rate to obtain spatially uniform vertical growth rates across a patterned substrate.

Strain-Gated Field Effect Transistor of a MoS2-ZnO 2D-1D Hybrid Structure.

Two-dimensional (2D) molybdenum disulfide (MoS2) is an exciting material due to its unique electrical, optical, and piezoelectric properties. Owing to an intrinsic band gap of 1.2-1.9 eV, monolayer or a-few-layer MoS2 is used for fabricating field effect transistors (FETs) with high electron mobility and on/off ratio. However, the traditional FETs are controlled by an externally supplied gate voltage, which may not be sensitive enough to directly interface with a mechanical stimulus for applications in electronic skin. Here we report a type of top-pressure/force-gated field effect transistors (PGFETs) based on a hybrid structure of a 2D MoS2 flake and 1D ZnO nanowire (NW) array. Once an external pressure is applied, the piezoelectric polarization charges created at the tips of ZnO NWs grown on MoS2 act as a gate voltage to tune/control the source-drain transport property in MoS2. At a 6.25 MPa applied stimulus on a packaged device, the source-drain current can be tuned for ∼25%, equivalent to the results of applying an extra -5 V back gate voltage. Another type of PGFET with a dielectric layer (Al2O3) sandwiched between MoS2 and ZnO also shows consistent results. A theoretical model is proposed to interpret the received data. This study sets the foundation for applying the 2D material-based FETs in the field of artificial intelligence.

Nanostructured zinc oxide systems with gold nanoparticle pattern for efficient light trapping

In this work we describe the design of a system consisting of a zinc oxide nanowire array and ITO glass nanostructured with gold NPs. Our goal was to create a more efficient system that could be used in various optical applications, such as photovoltaics or photodetectors. The impact of gold NPs of different shapes, single as well as arranged in a pattern, on the optical properties of the system was studied by using a finite integration technique. The absorptance and transmittance spectra of individual components of the system were calculated. Finally, the integrated spectral enhancement factors of the photons absorbed and transmitted by the electrode were estimated using the different geometrical parameters of the electrode. The results suggested that the most effective absorber of light should include zinc oxide nanowires (NWs), with smaller diameters and cylindrical shapes of single gold NPs, as well as in a pattern, while the highest transmittance is obtained for greater diameter of NWs and conical shapes of gold NPs in a pattern. Based on these results, the absorption current density (derived from the generation and collection of light-generated charge carriers) was calculated for the ZnO-CdTe core-shell NWs nanostructured with gold NPs arranged into a pattern. The results suggest that the most efficient electrode contains ZnO NWs with gold NPs in a conical shaped pattern. Our results confirm the importance of computational simulation in the design of the photonic and photovoltaic devices, making it possible to predict the most efficient systems. These results could be useful to further optimize photonic or photovoltaic devices based on plasmonic NPs and semiconductor nanostructures.

Photosensitization of ZnO nanowire-based electrodes using one-step hydrothermally synthesized CdSe/CdS (core/shell) sensitizer

One-step assembled CdSe/CdS (core/shell) quantum dots (QDs) were deposited onto ZnO nanowires (NWs) and characterized for their structure, morphology and optical analyses. As deposited ZnO NWs array were wurtzite in structure. During a single hydrothermal cycle a layer of ∼4nm CdSe/CdS QDs was formed onto ZnO NWs and overgrowth evidenced with an additional 2–5 layers due to which, (a) absorbance density, and (b) Raman Shift of 1LO mode (from 286cm−1 to 296cm−1) increased and (c) the photoluminescence intensity of the near band-edge emission peak at ∼379nm decreased. Due to more accumulation of CdSe/CdS, photoelectrochemical cells of ZnO-based photoelectrodes designed for 1–4 cycles of CdSe/CdS onto indium-tin-oxide substrate demonstrated increasing power conversion efficiency trend from 0.18% to 1.29% whereas, for 5th cycle power conversion efficiency, due to an increased series resistance, decreased to 1.12% on account of an accumulation of several QDs.

Study on Dye-sensitized Solar Cells based on ZnO Nanorods and Graphene Enhanced P3HT as HTM

A quasi solid state dye-sensitized solar cells (DSSC) is fabricated using 1-propyl-3methylimidazolium iodide andPoly (3-Hexail Thiophene) P3HT, and P3HT-loading graphene (G) as the composite electrolyte. The electrolyte without added iodine is sandwiched between ZnO NW photo electrode both pristine and graphene enhanced P3HT (G-P3HT, 5% wt graphene) were used in solid state dye as Hole transport material draw a lot of attention due to easy fabrication, using P3HT-Graphene (P3HTI-graphene) nanocomposites were synthesized on FTO glass by solution process and employed as HTM to replace the conventionally used expensive Pt electrode, The solar cells based on vertical ZnO nanowire arrays by utilizing a mixture paste of LiI, PMII and solid iodine as electrolyte. The initial results showed the power conversion efficiency of 2.1%. The cells with pristine and G-P3HT showed different performance. The power conversion efficiency was improved from 0.16 to 2.1 mA for G-P3HT solar cells. It exhibited increased power conversion efficiency from 0.87 to 2.1%

3D‐Branched ZnO/CdS Nanowire Arrays for Solar Water Splitting and the Service Safety Research

Modulation of broadband light trapping through assembly of 3D structures and modification with narrow band‐gap semiconductors provide an effective way to improve the photoelectrochemical (PEC) performance. Here, 3D‐branched ZnO nanowire arrays (NWAs) modified with cadmium sulfide (CdS) nanoparticles are designed and synthesized via solution chemical routes. The 3D‐branched ZnO NWA–CdS nanoparticle photoanodes show an excellent PEC performance in UV and visible region and the maximum photo‐to‐hydrogen conversion efficiency reaches to 3.1%. The high performance of 3D‐branched ZnO NWA–CdS composites is mainly attributed to the excellent carrier collection capability and high light‐trapping ability of 3D‐branched ZnO NWAs as well as the excellent photocatalytic activity of CdS nanoparticles in the visible region. In addition, the photocorrosion mechanism of 3D‐branched ZnO NWA–CdS photoanodes is systematically investigated, and a protective TiO2 layer is deposited onto the photoanodes to elevate the PEC stability. The results benefit a deeper understanding of the role of 3D‐branched structures decorated with narrow band‐gap semiconductors in solar water splitting.

Synthesis of ZnO nanowire array film on Mg doped gallium nitride substrate

ZnO nanowire array films, composed of well aligned ZnO nanowires ∼200 nm in diameter and 1 μm in length, were successfully synthesised on Mg doped gallium nitride by hydrothermal method. In addition, the films possess quite flatten surface. In the synthesised process, there was no catalyst that had been used. Growth conditions were comprehensively discussed in the process of aqueous solution method. It was found that the length of ZnO nanowires and the thickness of the film could be tunable by altering solution concentration and growth time. Such ZnO film assembled with vertically aligned nanowire may have potential applications as UV light emitting diodes.