Characterization of ordered Cu2O nanowire arrays prepared by heat treated Cu/PAM composite

Cu nanowire arrays were synthesized via a porous alumina membrane (PAM) template with a high aspect ratio, uniform pore size (120–140 nm), and ordered pore arrangement. The Cu₂O nanowire arrays were prepared from the oxidization of Cu metal nanowire arrays. The electrochemical deposition potential of Cu metal nanowires (?180 mV vs. SCE) was determined from X-ray diffraction (XRD) patterns. The microstructure and chemical composition of Cu nanowire arrays were characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). Results indicate that the Cu/Cu₂O nanowire arrays assembled into the nanochannel of the porous alumina template with diameters of 120–140 nm. The valence of copper was controlled by the porous alumina template during the annealing process. Copper nanowires transformed to the Cu₂O phase with the space limitation of the PAM template. Single-crystal Cu₂O nanowire arrays were also obtained under the template embedded.     

The characteristic of the ZnO nanowire morphology grown by the hydrothermal method on various surface-treated seed layers

ZnO nanowires with various density and diameters were obtained by altering the wetting properties of aluminum doped ZnO (AZO) seed layers. AZO seed layers deposited on glass substrates were treated by inductor coupled plasmas (ICP) or atmospheric pressure plasma (APP) systems in order to control wettability before ZnO nanowire growth. Morphology of ZnO nanowires grown by the hydrothermal method was influenced by wettability of AZO seed layers. Our investigation shows that the diameter of ZnO nanowire increases and the length of ZnO nanowire decreases when the contact angle on the AZO seed layer is decreased. As a result, we confirmed that the morphology of ZnO nanowires could be easily controlled by surface treatment of seed layers with the plasma system.     

Layer-by-layer assembly synthesis of ZnO/SnO2 composite nanowire arrays as high-performance anode for lithium-ion batteries

A layer-by-layer approach has been developed to synthesize ZnO/SnO₂ composite nanowire arrays on copper substrate. ZnO nanowire arrays have been first prepared on copper substrate through seed-assisted method, and then, the surface of ZnO nanowires have been modified by the polyelectrolyte. After oxidation-reduction reaction, SnO₂ layer has been deposited onto the surface of ZnO nanowires. The as-synthesized ZnO/SnO₂ composite nanowire arrays have been applied as anode for lithium-ion batteries, which show high reversible capacity and good cycling stability compared to pure ZnO nanowire arrays and SnO₂ nanoparticles. It is believed that the improved performance may be attributed to the high capacity of SnO₂ and the good cycling stability of the array structure on current collector.     

ZnO sputter coating on SnO2 nanowires: Effects of thin coating and subsequent thermal annealing

The structural and optical properties of SnO₂–ZnO core–shell nanowires were studied and the effects of thermal annealing were investigated. As-prepared SnO₂–ZnO core–shell nanowires exhibited a smooth and continuous shell layer along the nanowire, with a thickness in the range of 5–10 nm. While the thin ZnO shell layer disappeared after annealing at 800 °C, this did not occur after annealing at 600 °C. The as-fabricated SnO₂–ZnO core–shell nanowires exhibited yellow emission, presumably from the core SnO₂ nanowires. The UV emission from ZnO shell layer was obtained by annealing at 600 °C, whereas it was removed by annealing at 800 °C.     

Electrochemical template synthesis of large-scale uniform copper selenides nanowire arrays

Ordered Cu₃Se₂ nanowire arrays have been prepared by electrochemical template synthesis based on anodic alumina membranes at room temperature. After annealing in argon ambient at 300 °C for 1 h, Cu₂Se nanowire arrays were obtained by structural change. Field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED) results show that single crystal copper selenides nanowires with a high filling rate are dense, smooth, and uniform in large area. The effects of several electrodeposition parameters on high-filling, stoichiometric and single crystal copper selenides were discussed.     

ZnO纳米线阵列修饰对材料表面浸润性调控

采用溶胶-凝胶法制备了ZnO薄膜,利用溶剂热沉积法获得大面积均匀ZnO纳米线阵列。通过对水在ZnO材料表面的浸润性研究,发现薄膜材料表面的粗糙度对ZnO膜亲水性有增强作用,而周期性ZnO阵列微结构表面可以实现其疏水性质增强效果。同时从理论上分析了这两种现象的物理机制,讨论了空气填隙对ZnO纳米线阵列表面的浸润性质的敏感性。制备出ZnO纳米线阵列的表观接触角约为103°,具有较强的疏水性质,可为进一步的ZnO光流控研究提供实验基础。     

Rapid thermal-plasma annealing of ZnO:Al films for silicon thin-film solar cells

Rapid thermal annealing of sputter-deposited ZnO and Al-doped ZnO (AZO) films with and without an amorphous silicon (a-Si) capping layer was investigated using a radio-frequency (rf) argon thermal plasma jet at atmospheric pressure. The resistivity of bare ZnO films on glass decreased drastically from 10⁶ to 10³ Ω·cm at maximum surface temperatures T_max above 650 °C, whereas the resistivity increased from 10^− 4 to 10^− 3-10^− 2 Ω·cm for bare AZO films. On the other hand, the resistivity of AZO films with a 30-nm-thick a-Si capping layer remained below 10^− 4 Ω·cm, even after TPJ annealing at a T_max of 825 °C. X-ray diffraction and X-ray photoemission electron studies revealed that the film crystallization of both AZO and a-Si layers was promoted without the formation of an intermixing layer. Additionally, the crystallization of phosphorous- and boron-doped a-Si layers at the sample surface was promoted, compared to that of intrinsic a-Si under identical plasma annealing conditions. The role of the a-Si capping layer on sputter-deposited AZO and ZnO films during TPJ annealing is demonstrated. The effects of the mixing of phosphorous and boron impurities in a-Si:H during TPJ annealing of flat and textured AZOs are also discussed.     

Influence of seed layers on the vertical growth of ZnO nanowires

We synthesized vertically aligned ZnO nanowires on SiO₂ wafer <100> using the Au, ZnO and Au/ZnO seed layers through the physical vapor deposition process. The growth direction of ZnO nanowire was controlled by using the three different seed layers. From the XRD results, we observed the highest intensity of the (002) peak on the Au/ZnO seed layer among the three seed layers. The SEM images show that all of the ZnO nanowires have an average diameter of about 100 ~ 200 nm and a length of about 5 μm, and the nanowires grown on the Au/ZnO seed layer are oriented the most perpendicularly to the substrate surface. From the PL analysis, we observed that the intensity of broad emissions at 400-600 nm relating the green emission for the ZnO nanowires on the Au/ZnO seed layer was much weaker than that for the ZnO nanowires on the ZnO seed layer. The experiment results indicate that the selection of seed layers is important to grow nanowires vertically for the application of nanoscale devices.     

Water repellent ZnO nanowire arrays synthesized by simple solvothermal technique

The authors report on the water repellent properties of quasialigned zinc oxide (ZnO) nanowire arrays grown by low-temperature solvothermal technique. The uniform and dense ZnO nanowires of average diameter ∼ 75 nm have been found to have hexagonal wurtzite type structure. The as synthesized ZnO nanowire surfaces have hydrophilic nature with a water contact angle of 73° ± 3°. The superhydrophobic behavior with a water contact angle of 145° ± 3° of the nanowire arrays has been realized due to the reduction of surface free energy after being coated with an octadecyltrichlorosilane (OTS) monolayer. This work may be of huge importance from the viewpoint of both the understanding of the mechanisms involved and industrial applications.     

Study on the structures and magnetic properties of Ni, Co-Al2O3 electrodeposited nanowire arrays

We report on the direct electrodeposition of nickel and cobalt nanowire arrays within the nanopores of ordered porous alumina films prepared by a two-step anodization. SEM and TEM images reveal that the pore arrays are regularly arranged throughout the alumina film. X-ray diffraction and TEM analysis show that the nickel and cobalt nanowires are single crystalline with highly preferential orientation. The aspect ratio of nanowires is over 300. M-H hysteresis loops determined by VSM indicate that the nanowire arrays obtained possess obvious magnetic anisotropy. Because of proper square ratio and coercivity the nanowire arrays of nickel seem to be more suitable candidates for perpendicular magnetic recording medium than those of cobalt.     

The use of aluminium doped ZnO as transparent conductive oxide for CdS/CdTe solar cells

CdTe/CdS and CdTe/ZnO thin film solar cells were grown with a high vacuum evaporation based low temperature process (≤ 420 °C). Aluminium doped zinc oxide (AZO) was used as transparent conducting oxide (TCO) material. AZO exhibited excellent stability during the solar cell processing, and no significant change in electrical conductivity or transparency was observed. The current density loss due to absorption in the 1 μm thick AZO layer with 5 Ω per square sheet resistance was found to be 1.2 mA/cm². We investigated the influence of an intrinsic ZnO layer (i:ZnO) in combination with various CdS thicknesses. The i:ZnO layer was found to significantly increase the open circuit voltage of the solar cells with very thin CdS layer. Increasing thickness of the i:ZnO layer leads to UV absorption losses, narrowing of the depletion layer width and hence reduced collection efficiency in the long wavelength (685-830 nm) part. With AZO/i:ZnO bi-layer TCO we could achieve cell efficiencies of 15.6% on glass and 12.4% on the flexible polyimide film.     

Towards Perfectly Ordered Novel ZnO/Si Nano‐Heterojunction Arrays

The fabrication of a highly ordered novel ZnO/Si nano‐heterojuntion array is introduced. ZnO seed layer is first deposited on the Si (P<111>) surface. The nucleation sites are then defined by patterning the surface through focused ion beam (FIB) system. The ZnO nanorods are grown on the nucleation sites through hydrothermal process. The whole fabrication process is simple, facile and offers direct control of the space, length and aspect ratio of the array. It is found that ZnO/Si nanojunctions show an improved interface when subjected to heat treatment. The recrystallization of ZnO and the tensile lattice strain of Si developed during the heating process contribute the enhancement of their photoresponses to white light. The photoluminescence (PL) measurement result of nano‐heterojunction arrays with different parameters is discussed.     

Optical properties of ZnO nanowire arrays electrodeposited on n- and p-type Si(1 1 1): Effects of thermal annealing

Electrodeposition is a low temperature and low cost growth method of high quality nanostructured active materials for optoelectronic devices. We report the electrochemical preparation of ZnO nanorod/nanowire arrays on n-Si(1 1 1) and p-Si(1 1 1). The effects of thermal annealing and type of substrates on the optical properties of ZnO nanowires electroplated on silicon (1 1 1) substrate are reported. We fabricated ZnO nanowires/p-Si structure that exhibits a strong UV photoluminescence emission and a negligible visible emission. This UV photoluminescence emission proves to be strongly influenced by the thermal annealing at 150-800 °C. Photo-detectors have been fabricated based on the ZnO nanowires/p-Si heterojunction.     

Ultra-fast microwave-assisted hydrothermal synthesis of long vertically aligned ZnO nanowires for dye-sensitized solar cell application

Long vertically aligned ZnO nanowire arrays were synthesized using an ultra-fast microwave-assisted hydrothermal process. Using this method, we were able to grow ZnO nanowire arrays at an average growth rate as high as 200?nm?min(-1) for maximum microwave power level. This method does not suffer from the growth stoppage problem at long growth times that, according to our investigations, a normal microwave-assisted hydrothermal method suffers from. Longitudinal growth of the nanowire arrays was investigated as a function of microwave power level and growth time using cross-sectional FESEM images of the grown arrays. Effect of seed layer on the alignment of nanowires was also studied. X-ray diffraction analysis confirmed c-axis orientation and single-phase wurtzite structure of the nanowires. J-V curves of the fabricated ZnO nanowire-based mercurochrome-sensitized solar cells indicated that the short-circuit current density is increased with increasing the length of the nanowire array. According to the UV-vis spectra of the dyes detached from the cells, these increments were mainly attributed to the enlarged internal surface area and therefore dye loading enhancement in the lengthened nanowire arrays.     

Effects of thermal annealing on the performance of Al/ZnO nanorods/Pt structure ultraviolet photodetector

ZnO nanorod arrays were fabricated on ZnO coated glass substrate by hydrothermal method. Schottky barrier ultraviolet photodetectors (PDs) were obtained by sputtering Pt electrode and evaporating Al electrode on the top of ZnO nanorod arrays with thermal treatment. It is illustrated that Schottky contacts at the electrode/ZnO NRs interface were formed at the annealing temperature of 300 °C and above. When annealing temperature was up to 300 °C, the performance of the PDs was improved with the great decrease of response and recovery times. At the forward bias of 2 V, the Schottky contact PDs showed the biggest responsivity and the best detectivity at the annealing temperature of 300 °C. For annealing temperature at 300 °C and above, the responsivity decreases with increasing annealing temperature and the ratio of detectivity (D₂₅₄^* to D₅₄₆^*) was calculated as high as 10³ for all PDs annealed at 300 °C and above.     

Selective growth of ZnO nanorods for gas sensors using ink-jet printing and hydrothermal processes

Selective growth of ZnO nanorod arrays with well-defined areas was developed to fabricate the NO₂ gas sensor. The seed solution was ink-jet printed on the interdigitated electrodes. Then, vertically aligned ZnO nanorods were grown on the patterned seed layer by the hydrothermal approach. The influences of seed-solution properties and the ink-jet printing parameters on the printing performance and the morphology of the nanorods were studied. Round micropattern (diameter: 650 μm) of ZnO nanorod arrays is demonstrated. The dimensions and positions of the nanorod arrays can be controlled by changing the printed seed pattern. The effects of nanorod structure and nanorod size on the gas-sensing capability of ZnO nanorod gas sensors were demonstrated. Due to the high surface-to-volume ratios of the nanorod-array structure, the ZnO nanorod gas sensor can respond to 750 ppb NO₂ at 100 °C. The sensors without baking treatment exhibit the typical response of a p-type semiconductor. However, only the response of n-type semiconductor oxides was observed after the annealing treatment at 150 °C for 2 h.     

Boosting ZnO nanowire dye-sensitized solar cell efficiency by coating a porous ZnO layer on the nanowires

Novel ZnO core/shell nanostructures were constructed by depositing a porous ZnO layer directly on the surfaces of pre-fabricated ZnO nanowires through a facile chemical method. The morphology and structure of the obtained products have been investigated by field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction analysis. In these unique nanostructures, the porous overlayer exhibits a large surface area for sufficient dye loading to enhance light harvesting and the ZnO nanowire cores provide direct conduction pathways for the photogenerated electron transport to diminish the chance of electron recombination. The obtained ZnO nanostructures were used as photoanode material in dye-sensitized solar cell which showed an increase in performance of 141 % compared with an equivalent solar cell employing ZnO nanowire arrays as photoanode. This result was achieved mainly due to an increase in photogenerated current density directly resulting from improved light harvesting of the porous layer.     

非晶Co及CoP纳米阵列的制备及研究

采用交流电化学沉积法,在多孔阳极氧化铝(AAO)模板孔洞中成功制备出直径50nm的Co纳米线阵列.采用透射电子显微镜(TEM)和选区电子衍射(SAED)观察了样品的微观形貌结构.结果显示,阵列中纳米线均匀有序,形状各向异性较大,其晶体结构为非晶.在沉积Co纳米线阵列的电解液中添加一定的还原剂(NaH2PO2·H2O),制备出非晶CoP纳米阵列,由TEM观察可知,阵列形貌发生变化,沉积产物为离散的纳米粒子而非纳米线.探讨了交流电沉积纳米阵列的生长机理.     

Performance of ethanol electro-oxidation on Ni-Cu alloy nanowires through composition modulation

To reduce the cost of the catalyst for direct ethanol fuel cells and improve its catalytic activity, highly ordered Ni-Cu alloy nanowire arrays have been fabricated successfully by differential pulse current electro-deposition into the pores of a porous anodic alumina membrane (AAMs). The energy dispersion spectrum, scanning and transmission electron microscopy were utilized to characterize the composition and morphology of the Ni-Cu alloy nanowire arrays. The results reveal that the nanowires in the array are uniform, well isolated and parallel to each other. The catalytic activity of the nanowire electrode arrays for ethanol oxidation was tested and the binary alloy nanowire array possesses good catalytic activity for the electro-oxidation of ethanol. The performance of ethanol electro-oxidation was controlled by varying the Cu content in the Ni-Cu alloy and the Ni-Cu alloy nanowire electrode shows much better stability than the pure Ni one.     

Low-temperature growth of well-aligned ZnO nanowire arrays by chemical bath deposition for hybrid solar cell application

Well-aligned ZnO nanowire arrays were grown on indium tin oxide coated glass substrates by a facile chemical bath deposition technique. Morphologies, crystalline structure and optical transmission were investigated by field-emission scanning electron microscope, X-ray diffraction and UV–visible transmission spectrum, respectively. The results showed that ZnO nanowires were aligned in a dense array approximately perpendicular to substrate surface, they were wurtzite-structured (hexagonal) ZnO. In addition, the nanowire arrays exhibited high optical transmission (>85 %) in the visible region. Furthermore, an inverted inorganic/polymer hybrid solar cell was built using as-grown well-aligned ZnO nanowire arrays as inorganic layer, under the AM 1.5 illumination with a light intensity of 80 mW/cm², the device showed an open circuit voltage (V_oc) of 0.44 V, a short circuit current (J_sc) of 3.23 mA/cm², a fill-factor of 38 %, and a power conversion efficiency of 0.68 %.