ZnO Nanotips Research Articles

A comparison of optical properties of ZnO nanorods and ZnO nanotips for improving light absorption in rGO/ZnO nanostrctures

In this study, two types of ZnO nanostructures (ZnO nanotips and ZnO nanorods) were synthesized through a chemical bath deposition (CBD) method. These two structures were then compared by optical and structural analyses. The result showed the significant effect of ammonia concentration and the preferential etchings along the c axis on the formation of ZnO nanotips (NTs). To improve the absorption, nanostructures were optimized by reflectance analysis. To enhance the optical properties of the optimized sample, reduced graphene oxide (rGO) layers were transferred on the ZnO NTs surface by the electrophoretic deposition (EPD) method. The deposition of rGO layers on ZnO NTs can increment the optical absorption over a wide range of frequencies. The reflectance results showed enhanced adsorption capacity in the case of rGO/ZnO NTs.

Zinc oxide nanotips growth by controlling vapor deposition on substrates

ZnO nanotips structure fabrication was undertaken through controlled growth by chemical vapor deposition (CVD) method. Substrate position and deposition time role was investigated systematically by controlling the parameters such as temperature, flow rate, and growth pressure. The obtained result showed that ZnO nanorods undergo a sharp regrowth process with increase in ZnO vapor availability in the CVD reactor. The surface morphology and structural properties were investigated by using field-emission scanning electron microscopy and X-ray diffraction (XRD) techniques. The grown nanostructures were used for gas sensor fabrication to detect and to study the sensitivity effects of H2 and CO.

Photocatalysis of zinc oxide nanotip array/titanium oxide film heterojunction prepared by aqueous solution deposition

A TiO2 film was prepared on indium tin oxide (ITO)/glass by aqueous solution deposition (ASD) with precursors of ammonium hexafluoro-titanate and boric acid at 40 °C. The photocatalysis of annealed TiO2 film increases with increasing growth time and decreases with increasing growth times longer than 60 min. A ZnO nanotip array was prepared on ZnO seed layer/TiO2 film/glass by aqueous solution deposition with precursors of zinc nitrate and ammonium hydroxide at 70 °C. The photocatalysis of ASD-ZnO/ASD-TiO2 film/ITO glass can be better than that of P25.

Integrated ZnO Nano-Electron-Emitter with Self-Modulated Parasitic Tunneling Field Effect Transistor at the Surface of the p-Si/ZnO Junction.

The development of high performance nano-electron-emitter arrays with well reliability still proves challenging. Here, we report a featured integrated nano-electron-emitter. The vertically aligned nano-emitter consists of two segments. The top segment is an intrinsically lightly n-type doped ZnO nano-tip, while the bottom segment is a heavily p-type doped Si nano-pillar (denoted as p-Si/ZnO nano-emitter). The anode voltage not only extracted the electron emission from the emitter apex but also induced the inter-band electron tunneling at the surface of the p-Si/ZnO nano-junction. The designed p-Si/ZnO emitter is equivalent to a ZnO nano-tip individually ballasted by a p-Si/ZnO diode and a parasitic tunneling field effect transistor (TFET) at the surface of the p-Si/ZnO junction. The parasitic TFET provides a channel for the supply of emitting electron, while the p-Si/ZnO diode is benefit for impeding the current overloading and prevent the emitters from a catastrophic breakdown. Well repeatable and stable field emission current were obtained from the p-Si/ZnO nano-emitters. High performance nano-emitters was developed using diamond-like-carbon coated p-Si/ZnO tip array (500 × 500), i.e., 178 μA (4.48 mA/cm2) at 75.7 MV/m.

Efficiency of pyramid textured silicon solar cell with aqueous solution deposited ZnO nanotip array

The efficiency of pyramid textured silicon solar cell with ZnO nanotip array was investigated. ZnO seed layer was first prepared on the top side of solar cell by radio frequency sputtering. Zinc nitrate and ammonium were used as precursors for the growth of ZnO nanotip array on ZnO seed layer by aqueous solution deposition at 70 °C. The efficiency of solar cell with ZnO nanotip array increases with the ZnO nanotip length, and the efficiency can be enhanced from 11.74% to 14.38%.

Characterization of annealed zinc oxide nanotip array prepared by chemical bath deposition

We investigate the characteristics of thermally annealed ZnO nanotip in various ambient. AZO seed layer was first prepared on glass substrate by RF sputtering. A vertically oriented ZnO nanotip array was grown on AZO seed layer/glass by chemical bath deposition with precursors of zinc nitrate and ammonia at 70 °C. By thermal annealing in N2O ambient at 300 °C for 1 hour, the characteristics of ZnO nanotip array were improved and the ultraviolet sensor shows the best rise time of 50 s, decay time of 70 s and on/off current ratio of 26.04.

Efficiency Enhancement of DSSC With Aqueous Solution Deposited ZnO Nanotip Array

The efficiency of dye-sensitized solar cell with ZnO nanotip array was investigated. The ZnO seed layer was first prepared on the glass side of glass/ TiO2 electrode by RF sputtering. Zinc nitrate and ammonium hydroxide were used as precursors for the growth of ZnO nanotip array with the density of 8.2×108 cm-2 on ZnO seed layer by aqueous solution deposition at 85 °C. There is about 16% efficiency enhancement for DSSC with ZnO nanotip array.

Vertically aligned nanostructures based on Na-doped ZnO nanorods for wide band gap semiconductor memory applications

Vertically aligned undoped ZnO nanotips, nanotubes and nanorods were synthesized on the top facets of Na-doped ZnO nanorods without catalytic assistance under different growth times in a chemical vapor deposition system. The growth mechanism is discussed. The Na-doped nanorods were grown on a ZnO seed layer on Si. The p-type conductivity of the Na-doped nanorods was studied by temperature-dependent photoluminescence and nanorod back-gated field effect transistor measurements. The undoped nanorods, Na-doped nanorods and undoped seed layer form an n–p–n memory structure. The programming and retention characteristics have been demonstrated.

Super rapid response of humidity sensor based on MOCVD grown ZnO nanotips array

This work deals with the fabrication of a-plane ZnO nanotip based humidity sensor on r-plane sapphire substrate by metal organic chemical vapor deposition (MOCVD). The humidity sensing property has been studied for this sensor by impedance measurements. The impedance of the humidity sensor decreases by about six orders of magnitude (from 2.8×108Ω to 4.3×102Ω at 1V, 100Hz) with increase in relative humidity (RH) (from 19% to 95%). The response and recovery times were found to be 3 and 12s, respectively. It shows super fast response and recovery time with good selectivity to humidity. Considering different sensor parameters investigated in the present study, it is observed that MOCVD grown ZnO nanotips respond promptly to the changes in RH due to quantum size effect as is evident from the blue shift of its band gap; and high atomic density on the a-plane of ZnO. The response has been explained on the basis of the adsorption of water molecules on a-plane ZnO and proton transport mechanism.

Preparation and characterization of epitaxial growth of ZnO nanotip arrays by hydrothermal method

Preparation and characterization of epitaxial growth of ZnO nanotip arrays are essential for field emission applications due to its high emission rate of electron and fast electron-transfer rate. At first, nanocrystalline ITO thin films were prepared on glass substrates by ion-beam sputter deposition (IBSD) method. ZnO seed layer was prepared on the ITO coated glass substrates by IBSD at room temperature, and then, ZnO nanotip arrays were epitaxially grown on the as-prepared ZnO seed layer coated ITO/Glass substrates by hydrothermal method. The surface morphology study confirmed that the ZnO nanotip array films were epitaxially grown on ITO/Glass substrates, and it clearly showed the formation of well-aligned ZnO nanotip arrays on ITO/Glass substrate. The as-prepared samples were annealed at different temperatures (100, 150 and 270°C). After annealing, the surface morphology of ZnO nanotip arrays did not show any remarkable change. X-ray diffraction pattern of ZnO nanotip array films prepared on ITO/Glass showed a main peak at 2θ=34.3°, which corresponds to (002) plane. The photoluminescence spectra showed the strong intensity of UV emission and weak intensity of green emission. The J–V characteristic of Ag/NPB/PMMA/ZnO/ITO showed good rectification behavior.

Density of ZnO Nanotip Array Controlled by ZnO Seed Layer

ZnO nanotips were synthesized on a sputtered ZnO buffer layer/ITO/glass by aqueous solution deposition with precursors of zinc nitrate and ammonia. The density of ZnO nanotips can be controlled by the thickness of sputtered ZnO buffer layer. The average height of 13 μm was obtained at 70°C for 24 hr and the diameter of ZnO nanotips was ranged from 60 nm to 100 nm. By thermal annealing at 300 oC in N2, the ZnO quality can be much improved and strong Micro-PL UV emission (380 nm) and lower defect emission (520 nm) of visible region are obtained. After thermal annealing at 300 °C in O2, both emissions are much improved.

Structural and optical properties of ultrathin ZnO nanoneedles grown on GaN substrate by hybrid approach

Ultrathin ZnO nanoneedles were grown on GaN substrate by the low temperature aqueous solution method. FESEM results demonstrated that the ZnO nanoneedles stem and a tip have a diameter of 100–200nm and 10–30nm and length (stem) 300–500nm and (tip) 200–600nm respectively. Structural analysis showed that ZnO nanoneedles are single crystalline with wurtzite hexagonal phase and grown along the c-axis direction. Room temperature photoluminescence spectrum of ZnO nanoneedles showed a strong ultra-violet emission at 381nm and weak green emission at 580nm. The ZnO nanotip can be explored for heterojunction formation.

Field Emission Properties and Reliability of ZnO Nanorod, Nanopagoda, and Nanotip Current Emitters

Fabrication, optical, and field emission properties of ZnO nanorod, nanopagoda, and nanotip emitters were studied. The ZnO nanotip emitters are prepared by using combination of solution method and oxygen plasma treatment. All the emitters exhibit a highly c-axis preferred orientation crystalline structure. The nanopagoda and nanotip emitters have turn-on fields of 1.43 and 1.07 V/μm, respectively, under 1 μA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and field enhancement factors of 3681 and 4735 at 25 °C, respectively. The nanotip emitters with tip angle of 20° and number density of 10 emitters/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> have very stable emission at 25 °C over 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s and successive operation between the 25°C and 100 °C over 5000 s. Our finding provides an effective route for practical applications in flat panel display and light-emitting device in the future.

Multifunctional Biosensor Based on Zno Nanostructures

The present invention provides the multifunctional biological and biochemical sensor technology based on ZnO nanostructures. The ZnO nanotips serve as strong DNA or protein molecule binding sites to enhance the immobilization. Patterned ZnO nanotips are used to provide conductivity-based biosensors. Patterned ZnO nanotips are also used as the gate for field-effect transistor (FET) type sensors. Patterned ZnO nanotips are integrated with SAW or BAW based biosensors. These ZnO nanotip based devices operate in multimodal operation combining electrical, acoustic and optical sensing mechanisms. The multifunctional biosensors can be arrayed and combined into one biochip, which will enhance the sensitivity and accuracy of biological and biochemical detection due to strong immobilization and multimodal operation capability. Such biological and biochemical sensor technology are useful in detection of RNA-DNA, DNA-DNA, protein-protein, protein-DNA and protein-small molecules interaction. It can be further applied for drug discovery, and for environmental monitoring and protection.

Carbon nanotube mat as substrate for ZnO nanotip field emitters

We have reported the synthesis of ZnO nanotips on a multi walled carbon nanotube (MWCNT) mat by a vapour transport process. This combination of ZnO nanotips and a MWCNT mat exhibit ideal field emission behaviour. The turn on field and threshold field is found to be 0.34 and 1.5 V μm−1, respectively. The low threshold field is due to the good adherence of the ZnO nanotips on the MWCNT mat. The field enhancement factor is found to be 5 × 102 which is in agreement with the intrinsic field emission factor of ZnO nanotips. The emission current is found to be highly stable even at moderate vacuum.

Efficiency Improvement of Solar Cell with ZnO Nanotip Array Prepared by Aqueous Solution Deposition

ZnO nanotips were synthesized on a sputtered ZnO buffer layer/ITO/glass by aqueous solution deposition with precursors of zinc nitrate and ammonia. Growth direction of ZnO nanotips can be controlled by the thickness of sputtered ZnO buffer layer. The average height of 13 μm was obtained at 70 °C for 24 hr and the diameter of ZnO nanotips was ranged from 60 nm to 100 nm.

Integrated nanophotonic hubs based on ZnO-Tb(OH)3/SiO2 nanocomposites

Optical integration is essential for practical application, but it remains unexplored for nanoscale devices. A newly designed nanocomposite based on ZnO semiconductor nanowires and Tb(OH)3/SiO2 core/shell nanospheres has been synthesized and studied. The unique sea urchin-type morphology, bright and sharply visible emission bands of lanthanide, and large aspect ratio of ZnO crystalline nanotips make this novel composite an excellent signal receiver, waveguide, and emitter. The multifunctional composite of ZnO nanotips and Tb(OH)3/SiO2 nanoparticles therefore can serve as an integrated nanophotonics hub. Moreover, the composite of ZnO nanotips deposited on a Tb(OH)3/SiO2 photonic crystal can act as a directional light fountain, in which the confined radiation from Tb ions inside the photonic crystal can be well guided and escape through the ZnO nanotips. Therefore, the output emission arising from Tb ions is truly directional, and its intensity can be greatly enhanced. With highly enhanced lasing emissions in ZnO-Tb(OH)3/SiO2 as well as SnO2-Tb(OH)3/SiO2 nanocomposites, we demonstrate that our approach is extremely beneficial for the creation of low threshold and high-power nanolaser.

Light Extraction Efficiency Enhancement of GaN Blue LED with ZnO Nanotips Prepared by Aqueous Solution Deposition

We investigate the light extraction efficiency of GaN blue LED with ZnO nanotips prepared by aqueous solution deposition at near-room temperature. Zinc nitrate (Zn(NO3)2) and ammonium hydroxide (NH4OH) were used as precursors for the growth of ZnO nanotips on GaN blue LED with sputtered ZnO as the seed layer. The quality of ZnO nanotips were much improved by thermal annealing in N2O ambient. The optical power output of GaN LED with ZnO nanotips shows about 1.32 times enhancement compared with that without ZnO nanotips.

A facile shape-selective growth of ZnO nanotips and graded nanowires from its orientednanorods in a saturated ZnS solution

A facile solution-based route is developed for the preparation of distinctive ZnO nanostructures viaa dissolution-growth of ZnO nanorods in a saturated ZnS solution at a water-bath temperature of95 °C. In the dissolution-growth process, a series of novel morphologies including nanotips,tapered and graded nanowires can be conveniently achieved by simply changing the heatingtime. The pointed ends of the nanotips have a diameter of several nanometers, and thegraded nanowires have a gradient change in diameter from a few to tens of nanometersalong the longitudinal direction with the size of the thin end matching the Bohr excitonradius of ZnO. Furthermore, the formation mechanism from the ZnO nanorods to thenanotips, to the tapered and graded nanowires is discussed based on shape-evolutionobservations.

Decisive role of Au layer on the oriented growth of ZnO nanorod arrays via a simple aqueous solution method

Vertically aligned arrays of ZnO nanorod were synthesized on the Au/SiO 2/Si(1 0 0) substrate by a simple aqueous solution growth process, without pre-prepared ZnO seed layer. For comparison, glass and SiO 2/Si were also used as substrates, and the results show that the Au layer plays a decisive role in orienting the growth of the ZnO nanorod. The effects of other growth parameters, including Zn 2+ concentration and growth time, on morphology, density, and orientation of the ZnO nanostructure were also studied and with longer reaction time, a new structure namely ZnO nanotip was obtained. Moreover, the growth mechanism of ZnO nanorod arrays grown on the Au/SiO 2/Si substrate was proposed.