Structural and magnetic properties of Mn-doped ZnO nanorod arrays grown via a simple hydrothermal reaction

High density Mn-doped ZnO nanorod arrays were vertically grown on ITO substrate via hydrothermal reaction at relatively low temperature of 95 °C. The microstructure and magnetism of the arrays have been examined. Field emission scanning electron microscopy shows that the nanorods of 100 nm diameter and 1 μm length grow along the [001] direction. X-ray photoemission spectroscopy demonstrates that Mn is successfully doped into the nanorods. Meanwhile, all the Mn-doped ZnO nanorod arrays are ferromagnetic at room temperature. It is also found that the value of the saturation magnetization (M_s) of the ZnO nanorod arrays firstly increases with increasing the Mn concentration and then decreases. The higher M_s value is 0.11emu/g, which is obtained in the 5 at.% Mn-doped ZnO nanorod arrays. The ferromagnetism comes from the ferromagnetic interaction between the Mn ions, which partly replace Zn ions.     

ZnO纳米棒阵列膜的制备及其光电化学性能研究

采用化学溶液沉积法,在ZnO纳米颗粒膜修饰的FTO导电玻璃基底上,制备了ZnO纳米棒阵列。用X射线衍射仪（XRD）、场发射扫描电子显微镜（FESEM）、透射电子显微镜（TEM）对样品进行表征。研究结果表明所制备的ZnO纳米棒为六方纤锌矿相单晶结构,沿c轴择优取向生长,平均直径约为40nm,长度约为900nm;ZnO纳米棒阵列生长致密,取向性较一致。以曙红Y敏化的ZnO纳米棒阵列膜为光阳极制作了染料敏化太阳能电池原型器件,在光照强度为100mW/cm2下,其开路电压为0.418V,短路电流为0.889mA/cm2,总的光电转换效率为0.133%。     

Growth of well-aligned ZnO nanorod arrays on Si substrates by thermal evaporation of Cu-Zn alloy powders

Well-aligned ZnO nanorod arrays with uniform diameters and lengths have been fabricated on a Si substrate by simple thermal evaporation of Cu-Zn alloy powders in the presence of oxygen without using a template, catalyst, or pre-deposited ZnO seed layer. The ZnO nanorods are characterized by X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy and the growth mechanism is suggested. The nanorods have a single-crystal hexagonal structure and grow along the (0001) direction. Their diameters range from 200 to 400 nm and the lengths are up to several micrometers. The photoluminescence (PL) and Raman spectra disclose the optical properties of the products. The PL spectra show intense near-band ultraviolet emission at 378 nm from the nanorod arrays. The well-aligned ZnO nanorod arrays have a low turn-on field of 6.1 V/microm, suggesting good field emission properties. The simple synthesis methodology in conjunction with the good field emission and optical properties make the study both scientifically and technologically interesting.     

CdS-sensitized ZnO nanorod arrays coated with TiO2 layer for visible light photoelectrocatalysis

A novel ZnO/CdS/TiO₂ nanorod array composite structure was fabricated by depositing CdS-sensitized layer onto ZnO nanorod arrays via chemical bathing deposition and subsequently coated by TiO₂ protection layer via a vacuum dip-coating process. The films were characterized by x-ray diffraction, field emission scanning electron microscopy, energy dispersive spectrum, and UV–Vis diffuse reflectance spectroscopy. For the films severed as the photoanodes, linear sweep voltammetry and transient photocurrent (i _ph) were investigated in a three-electrode system. The photoelectrocatalytic activity was evaluated by the degradation of methylene blue (MB) under visible light irradiation. The results show that the oriented ZnO nanorods are adhered by relatively uniform CdS-sensitized layer and coated with TiO₂ layer. Both the coated and uncoated CdS-sensitized ZnO nanorod arrays exhibit the visible light response and the photoelectrocatalytic activity on the degradation of MB under visible light irradiation. The ZnO/CdS/TiO₂ nanorod array film possesses stable and superior photoelectrocatalytic performance owing to the TiO₂ thin layer protecting the CdS from photocorrosion.     

Preparation N-F-codoped TiO2 nanorod array by liquid phase deposition as visible light photocatalyst

An efficient method for the preparation of N-F-codoped visible light active TiO₂ nanorod arrays is reported. In the process, simultaneous nitrogen and fluorine doped TiO₂ nanorod arrays on the glass substrates were achieved by liquid phase deposition method using ZnO nanorod arrays as templates with different calcination temperature. The as-prepared samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectra measurements. It was found that calcination temperature is an important factor influencing the microstructure and the amount of N and F in TiO₂ nanorod arrays samples. The visible light photocatalytic properties were investigated using methylene blue (MB) dye as a model system. The results showed that N-F-codoped TiO₂ nanorod arrays sample calcined at 450 °C demonstrated the best visible light activity in all samples, much higher than that of TiO₂ nanoparticles and P25 particles films.     

Synthesis and photoluminescence properties of the ZnO@SnO<Subscript>2</Subscript> core–shell nanorod arrays

The ZnO@SnO₂ core–shell nanorod arrays have been synthesized. As the cores, ZnO nanorod arrays were first prepared by aqueous chemical growth method. Then using a simple liquid-phase deposition method, SnO₂ was deposited on the ZnO nanorod arrays. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction were used to characterize the morphologies and structures of the products. Photoluminescence properties were also investigated. It was found that the ZnO@SnO₂ core–shell nanorod arrays showed enhanced UV and green emissions when compared with the bare ZnO nanorod arrays.     

Activating ZnO nanorod photoanodes in visible light by Cu ion implantation

Utilization of visible light is of crucial importance for exploiting efficient semiconductor catalysts for solar water splitting. In this study, an advanced ion implantation method was utilized to dope Cu ions into ZnO nanorod arrays for photoelectrochemical water splitting in visible light. X-ray diffraction （XRD） and X-ray photo-electron spectroscopy （XPS） results revealed that Cu^＋ together with a small amount of Cu^2＋ were highly dispersed within the ZnO nanorod arrays. The Cu ion doped ZnO nanorod arrays displayed extended optical absorption and enhanced photoelectrochemical performance under visible light illumination （A 〉 420 nm）. A considerable photocurrent density of 18 μA/cm^2 at 0.8 V （vs. a saturated calomel electrode） was achieved, which was about 11 times higher than that of undoped ZnO nanorod arrays. This study proposes that ion implantation could be an effective approach for developing novel visible-light-driven photocatalytic materials for water splitting.     

Fabrication and photocatalytic property of ZnO nanorod arrays on Cu2O thin film

ZnO nanorod arrays were fabricated on Cu₂O thin film by a simple low-temperature liquid-phase-deposition method. The samples were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM). The UV-Vis spectroscopy showed that the obtained sample was able to absorb a large part of visible light (up to 650 nm). Their photocatalytic activities were investigated by degradation of dye methylene blue (MB) under UV-Vis and visible light irradiation. It was found that the photocatalytic activity of the ZnO/Cu₂O NRs was higher than the ZnO/ZnO NRs under UV-Vis light. In a word, Cu₂O played an important role in enhancing the photocatalytic activity of the ZnO/Cu₂O NRs.     

可见光诱导TiO2光催化及其机理研究进展

简述了二氧化钛的光催化机理。针对其禁带宽度较大,只能被小于387nm的紫外光所激发的缺点,综述了近年来国内外针对纳米TiO2可见光催化的改性方法和改性机理研究进展,包括离子掺杂、半导体复合、表面光敏化等方法。最后展望了提高纳米TiO2可见光光催化活性研究的前景。     

Effect of Cu additions on morphology and optical properties of ZnO nanorod arrays by two-step method

ZnO, Zn_0.9Cu_0.1O, Zn_0.8Cu_0.2O and Zn_0.7Cu_0.3O nanorod arrays are produced via a two-step process including an initial sol–gel method followed by hydrothermal growth. Effects of the Cu on microstructure, surface topography and optical properties of the nanorod arrays were studied and discussed. The results indicate that the nanorod arrays with a highly preferred orientation along the c axis were obtained on glass substrate. The Zn_0.7Cu_0.3O possesses the maximum density of nanorod arrays of 6.0 × 10⁹ cm^?2. The optical band-gap energy E _g decreases first and then increases with Cu additions increase. The broadening of the optical band-gap can be explained by Moss–Burstein effect. The Cu additions will effective enhance the violet emission and suppress the green emission. The violet and green emissions are likely due to the electron transition from the localized level below conduction band and oxygen vacancy to the valance band.     

The effect of growth conditions on the properties of ZnO nanorod dye-sensitized solar cells

In this article, we report ZnO nanorod samples grown on transparent conductive SnO₂:F (FTO) glass substrates by two different growth routes through hydrothermal method in a closed autoclave. One route is one-step continuous growth for 10 h. The other route is discrete multi-step growth for total 48 h. In this process, fresh solution was repeatedly introduced in every step. The structural, photoluminescence (PL) and photovoltaic properties of the as-prepared nanorod arrays were investigated. The nanorod arrays obtained through multi-step growth show longer rods, higher aspect ratio, larger spacing, better crystalline quality. The PL spectrum of nanorod arrays obtained through multi-step growth shows a strong and sharp near-band-gap emission (UV) peak and a weak green-yellow emission (GY) peak (I_UV/I_GY = 7.7), which also implies its good crystallinity and high optical quality. Dye-sensitized solar cells based on ZnO nanorod arrays were fabricated, and those grown with discrete multi-step procedure present better photovoltaic properties duo to its special morphology and better crystal quality.     

Study on the electron emission properties of ZnO nanorod arrays on different substrates

Large area well-aligned ZnO nanorod arrays on different substrates were synthesized by hydrothermal methods. The electron emission properties of the ZnO nanorod arrays on different substrates were investigated under both direct current (DC) and pulse electric fields. Owing to the excellent conductivity of substrates, the array on stainless steel substrate had better electron emission properties than that on silicon substrate. Under the DC and pulse electric fields, the electron emission of arrays had different production mechanisms which were pure field emission and plasma-induced emission respectively. During the plasma-induced emission, the plasma formed on the array surface, and the maximum emission current density of arrays on stainless steel was 118.87 A/cm2. The plasma-induced emission of ZnO nanorod arrays were always distributed uniformly. In this work, the results show that the ZnO nanorod arrays are expected to be applied to different electronic devices as electron beam sources under different electric fields.     

Fe dopants enhancing ethanol sensitivity of ZnO thin film deposited by RF magnetron sputtering

Pure and 5 % Fe-doped ZnO thin films (TFs) have been successfully deposited on Al₂O₃ substrate from pre-doped target material by RF magnetron sputtering technique. X-ray diffraction (XRD) patterns confirm the formation of both films in single phase wurtzite structure without any extra impurity peak. The calculated average crystallite sizes are found to be 22 and 17 nm for pure and Fe-doped ZnO TFs, respectively. The broadening in XRD peaks of Fe-doped ZnO TF occurs due to decrease in crystallite size and increase in lattice strain. Field emission scanning electron microscopy images exhibit that the particles growth in Fe-doped ZnO TF is more uniform and smaller than pure ZnO. Energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy results confirm the existence of Fe dopants into ZnO matrix. The doping effect enhances the sensitivity of ZnO sensor almost three times for ethanol gas sensing, the improvement in the response time and recovery time is noticeable as the size reduction effect increases the surface to volume ratio, and resulting more numbers of ethanol gas molecules are adsorbed to produce a higher concentration of oxygen ions which leads a larger deviation in capacitance.     

Growth specificity of vertical ZnO nanorods on patterned seeded substrates through integrated chemical process

A simple and cost effective method has been employed for the random growth and oriented ZnO nanorod arrays over as-prepared and patterned seeded glass substrates by low temperature two step growth process and growth specificity by direct laser writing (DLW) process. Scanning electron microscopy (SEM) images and X-ray diffraction analysis confirm the growth of vertical ZnO nanorods with perfect (0 0 2) orientation along c-axis which is in conjunction with optimizing the parameters at different reaction times and temperatures. Transmission electron microscopy (TEM) images show the formation of vertical ZnO nanorods with diameter and length of ∼120 nm and ∼400 nm respectively. Photoluminescence (PL) spectroscopic studies show a narrow emission at ∼385 nm and a broad visible emission from 450 to 600 nm. Further, site-selective ZnO nanorod growth is demonstrated for its high degree of control over size, orientation, uniformity, and periodicity on a positive photoresist ZnO seed layer by simple geometrical (line, circle and ring) patterns of 10 μm and 5 μm dimensions. The demonstrated control over size, orientation and periodicity of ZnO nanorods process opens up an opportunity to develop multifunctional properties which promises their potential applications in sensor, piezoelectric, and optoelectronic devices.     

Low-temperature hydrothermal synthesis of flower-like ZnO microstructure and nanorod array on nanoporous TiO2 film

A novel ZnO architecture, with flower-like microstructure on the top layer and nanorod arrays on the bottom layer, was hydrothermally synthesized on the Fluorine-doped SnO₂ (FTO) conducting glass pre-coated with nanoporous TiO₂ film. The as-prepared architecture was characterized with Field-emission scanning electron microscopy (FE-SEM) and X-ray diffractometer (XRD). Dye-sensitized solar cell studies showed that the power conversion efficiency (η) was 1.26% for this novel ZnO architecture-covered TiO₂ electrode.     

Low-temperature growth and optical properties of Ce-doped ZnO nanorods

Ce-doped ZnO nanorod arrays were grown on zinc foils by a hydrothermal method at 180°C. The effects of Ce-doping on the structure and optical properties of ZnO nanorods were investigated in detail. The characterisation of the rod array with X-ray diffraction and X-ray photoelectron spectroscopy indicated that Ce³⁺ ions were incorporated into the ZnO lattices. There were no diffraction peaks of Ce or cerium oxide in the pattern. From UV-Vis spectra, we observed a red shift in the wavelength of absorption and decreased band gap due to the Ce ion incorporation in ZnO. The photoluminescence integrated intensity ratio of the UV emission to the deep-level green emission (I _UV/I _DLE) was 1.25 and 2.87, for ZnO and Ce-doped ZnO nanorods, respectively, which shows a great promise for the Ce-doped ZnO nanorods with applications in optoelectronic devices.     

A novel, substrate independent three-step process for the growth of uniform ZnO nanorod arrays

We report a three-step deposition process for uniform arrays of ZnO nanorods, involving chemical bath deposition of aligned seed layers followed by nanorod nucleation sites and subsequent vapour phase transport growth of nanorods. This combines chemical bath deposition techniques, which enable substrate independent seeding and nucleation site generation with vapour phase transport growth of high crystalline and optical quality ZnO nanorod arrays. Our data indicate that the three-step process produces uniform nanorod arrays with narrow and rather monodisperse rod diameters (∼ 70 nm) across substrates of centimetre dimensions. X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction were used to study the growth mechanism and characterise the nanostructures.     

Microstructural and optical characteristics of solution-grown Ga-doped ZnO nanorod arrays

Highly oriented Ga-doped zinc oxide (ZnO) nanorod arrays have been prepared on a ZnO-buffered silicon substrate in an aqueous solution, which is a mixture of methenamine (C(6)H(12)N(4)), zinc nitrate hexahydrate (Zn(NO(3))(2)·6H(2)O), and gallium nitrate hydrate (Ga(NO(3))(3)·xH(2)O). The microstructure characteristics and optical properties of the nanorod arrays were analyzed using different characterization techniques including field-emission scanning electron microscopy (FESEM), x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL). The experimental results show that the morphology, density, and surface compositions of ZnO nanorod arrays are sensitive to the concentration of gallium nitrate hydrate. The PL spectra of all ZnO nanorod arrays show three different emissions, including UV (ultraviolet), yellow, and NIR (near infrared) emissions. With the increase in the Ga doping level, the luminescence quality of ZnO nanorods has been improved. The peak of UV emission has a small redshift, which can be ascribed to the combined effect of size and Ga doping. Furthermore, Ga doping has caused defects that respond to NIR emission.     

Preparation of Fe-doped TiO2 nanotube arrays and their photocatalytic activities under visible light

Fe-doped TiO₂ nanotube arrays have been prepared by the template-based liquid phase deposition method. Their morphologies, structures and optical properties were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and UV-vis absorption spectroscopy. Their photocatalytic activities were evaluated by the degradation of methylene blue under visible light. The UV-vis absorption spectra of the Fe-doped TiO₂ nanotube arrays showed a red shift and an enhancement of the absorption in the visible region compared to the undoped sample. The Fe-doped TiO₂ nanotube arrays exhibited good photocatalytic activities under visible light irradiation, and the optimum dopant amount was found to be 5.9 at% in our experiments.     

Controlled hydrothermal growth and optical characterization of wide band gap Be x Zn1−x O nanorod arrays

Wide band gap Be _x Zn_1?x O nanorod arrays on Zn foil substrates have been successfully prepared for the first time by a facile hydrothermal method at 80 °C for 24 h. The structure, morphology, and optical properties of the nanorod arrays were studied by X-ray diffraction (XRD), field emission scanning electron microscopy, and photoluminescence (PL). The composition x and band gap energy of the Be _x Zn_1?x O nanorod arrays were calculated from XRD and PL results, respectively. The results show that the PL emission peak energy increased with increasing x, as expected, and these materials should be suitable for developing UV-based optoelectronics.