Vacancy filling effect of graphene on photoluminescence behavior of ZnO/graphene nanocomposite

We report on the aerosol synthesis and optical characterization of ZnO/unoxidized graphene (UG) platelets nanocomposite films with high optical transparency (>85% at visible wavelengths). The ZnO/UG composite films, in which UG nanoplatelets are embedded in nano‐grained ZnO, were fabricated from colloidal suspensions of UG platelets with an aqueous zinc precursor. From photoluminescence (PL) spectra of the UG composite films, it was found that PL intensity decreases with the addition of UG platelets. The features of PL intensity in the UG composites are in contrast to that of ZnO/graphene oxide (G‐O) platelets composites, and can be explained by the absence of an oxygen vacancy filling effect, due to the unoxidized nature of UG and an increase in defect sites in its composites. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Colloid electrostatic self-assembly synthesis of SnO2/graphene nanocomposite for supercapacitors

Journal of Nanoparticle Research - Most anticancer drugs cannot kill cancer stem cells (CSCs) effectively, which lead to the failure of anticancer chemotherapy, such as relapse and metastasis. In...     

基于收缩高密度碳纳米管阵列的柔性固态超级电容器

柔性超级电容器因其加工方式灵活,具有高的能量密度和可剪裁可弯曲的特性,近年来受到广泛的关注.碳纳米管阵列凭借其自身良好的电化学性能、高效的电荷转移率和良好的循环寿命被视为理想的能量储存材料.然而原始碳纳米管阵列密度较小,且因管间较弱的相互作用力使得其在加工和转移过程中容易倒塌散落,从而限制了碳纳米管阵列直接用于组装柔性电子器件.本文应用无水乙醇对阵列进行收缩处理,在保持阵列高度取向优势的前提下大大增加了阵列的密度和机械强度,同时使用生物相容性好的聚乙烯醇(PVA)导电凝胶包埋碳纳米管阵列来制备柔性固态超级电容器件.PVA包埋的阵列复合体在折叠、弯曲过程中既能保持良好的机械稳定性和柔性,又能保持碳纳米管的高度取向性.使用原位电氧化对碳纳米管阵列外壁进行简单的电化学修饰,可以进一步提高该复合器件的性能.该方法为未来研发可穿戴电子器件以及可植入医学器件提供了新思路.     

Flexible resistance memory devices based on Cu/ZnO:Mg/ITO structure

Resistance memory devices based on a Cu/Mg‐doped ZnO/indium‐tin‐oxide structure on a PET (polyethylene terephthalate) flexible substrate were fabricated. The devices showed stable bipolar resistance switching property and good flexibility. The high to low resistance ratio was larger than 30 times, the endurance was more than 10² cycles, and the resistance retention was longer than 10⁴ s. The resistance values of both high and low resistance states were not significantly changed by bending in a radius (≥20 mm) for more than 10³ times. This resistance switching phenomenon of our devices can be explained by creation/rupture of metal conductive channels induced by electrochemical migration of Cu ions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical behaviors of ZnO/graphene/Si and ZnO/graphene/PS composite structures obtained by spraying different volumes of graphene solution

In this paper, a novel ZnO/graphene/porous silicon hybrid device is fabricated and its electrical behaviors are studied along with a ZnO/graphene/silicon device. Graphene (G) is prepared by exfoliation of graphite foil in aqueous solution of inorganic salt. Porous silicon (PS) is fabricated by electrochemical etching of p-type silicon (Si). Graphene is deposited on the surface of Si and PS substrates by thermal spray pyrolysis method. ZnO rods are grown on the samples by using catalyst-free chemical vapor transport and condensation method. The current–voltage relationships of ZnO/G/Si and ZnO/G/PS devices are studied under different volumes of graphene solution. The results reveal the distinctive features of the I–V characteristics of the two devices for different volumes of graphene solution under room light as well as UV illumination.     

Flexible piezoelectric harvesting based on epitaxial growth of ZnO

A flexible piezoelectric harvester based on the epitaxial growth of an array ZnO nanorods with zigzag layers to enhance bending and compression deformation is investigated. The effects of the growth temperature, growth time, and growth concentration for ZnO epitaxial growth are determined on the flexible substrate. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the nanostructures and crystalline characteristics of the nanorods, respectively. Nanorod piezoelectric harvesting with screen printing technology was integrated on the polyimide substrate. The results show that epitaxial ZnO nanorods at a concentration ratio of (1:4), a growth time of 4 hours, and a growth temperature of 90°C have perfect crystal morphology for piezoelectric harvesting. The current-voltage characteristics exhibit Schottky-like behavior. During the harvesting process, the current output was highly reproducible and repeatable when the ultrasonic wave equipment was turned on and off. The current output after bending increases with increasing curvature radius due to a compression force during the bending process.     

Multi-objective optimization of laser-scribed micro grooves on AZO conductive thin film using Data Envelopment Analysis

Laser scribing process has been considered as an effective approach for surface texturization on thin film solar cell. In this study, a systematic method for optimizing multi-objective process parameters of fiber laser system was proposed to achieve excellent quality characteristics, such as the minimum scribing line width, the flattest trough bottom, and the least processing edge surface bumps for increasing incident light absorption of thin film solar cell. First, the Taguchi method (TM) obtained useful statistical information through the orthogonal array with relatively fewer experiments. However, TM is only appropriate to optimize single-objective problems and has to rely on engineering judgment for solving multi-objective problems that can cause uncertainty to some degree. The back-propagation neural network (BPNN) and data envelopment analysis (DEA) were utilized to estimate the incomplete data and derive the optimal process parameters of laser scribing system. In addition, analysis of variance (ANOVA) method was also applied to identify the significant factors which have the greatest effects on the quality of scribing process; in other words, by putting more emphasis on these controllable and profound factors, the quality characteristics of the scribed thin film could be effectively enhanced. The experiments were carried out on ZnO:Al (AZO) transparent conductive thin film with a thickness of 500 nm and the results proved that the proposed approach yields better anticipated improvements than that of the TM which is only superior in improving one quality while sacrificing the other qualities. The results of confirmation experiments have showed the reliability of the proposed method.     

Effect of gamma irradiation on HPMC/ZnO nanocomposite films

The present work looks into the structural, chemical, mechanical, optical and thermal modification in ZnO nanoparticle incorporated hydroxypropyl methylcellulose (HPMC) polymer films, induced by gamma irradiation. The irradiation process was performed in a gamma chamber at room temperature using Cobalt-60 source (average energy of 1.25?MeV) at different doses: 0, 50, 100, 150 and 200?kGy. The modifications in structural, chemical, mechanical, optical and thermal properties, due to gamma irradiation in HPMC/ZnO nanocomposite films, have been studied using wide angle X-ray scattering (XRD), Fourier transform infrared spectroscopy, universal testing machine, ultraviolet–visible spectrophotometry and thermogravimetric analysis. It is found that gamma irradiation improves the mechanical and thermal properties of nanocomposite films.     

Temperature dependent photoluminescence study on ZnO/Graphene nanocomposite films

We report observation of both free and defect-mediated excitonic emissions from temperature-dependent PL study on ZnO/graphene oxide (G-O) nanocomposite grown by ultrasonic assisted spray pyrolysis (UASP). From the temperature-dependent photoluminescence (PL) spectra of the ZnO/G-O nanocomposite, new graphene-related peak was observed at 372 nm along with the exciton transition bound to neutral acceptors or deep donors. The PL intensity of new graphene-related peaks (3.33 eV) become more prominent with increasing G-O concentration, and it was saturated or decreased with the addition of >7.0 wt% of G-O. This feature indicates that new graphene-related states were created below conduction band of ZnO, which supports the excitonic PL enhancement by graphene-embedding is contributed not by charge transfer, but by vacancy filling effect of G-O.     

Growth of hierarchical based ZnO micro/nanostructured films and their tunable wettability behavior

Hierarchical zinc oxide (ZnO) micro/nanostructured thin films were grown onto as-prepared and different annealed ZnO seed layer films by a simple two step chemical process. A cost effective successive ionic layer adsorption and reaction (SILAR) method was employed to grow the seed layer films at optimal temperature (80 °C) and secondly, different hierarchical based ZnO structured thin films were deposited over the seed layered films by chemical bath deposition (CBD). The influence of seed layer on the structural, surface morphological, optical and wettability behavior of the ZnO thin films were systematically investigated. The XRD analysis confirms the high crystalline nature of both the seed layer and corresponding ZnO micro/nanostructured films with a perfect hexagonal structure oriented along (0 0 2) direction. The surface morphology revels a complex and orientated hierarchical based ZnO structured films with diverse shapes from plates to hexagonal rod-like crystal to tube-like structure and even much more complex needle-like shapes during secondary nucleation, by changing the seed layer conditions. The water contact angle (WCA) measurements on hierarchical ZnO structured films are completely examined to study its surface wettability behavior for its suitability in future self-cleaning application. Photoluminescence (PL) spectra of the ZnO structured film exhibit UV and visible emissions in the range of 420-500 nm. The present approach demonstrates its potential for low-temperature, large-scale, controlled synthesis of crystalline hierarchical ZnO nanostructures films.     

Flexible electrically pumped random lasing from ZnO nanowires based on metal–insulator–semiconductor structure

Flexible electrically pumped random laser(RL) based on ZnO nanowires is demonstrated for the first time to our knowledge. The ZnO nanowires each with a length of 5 μm and an average diameter of 180 nm are synthesized on flexible substrate(ITO/PET) by a simple hydrothermal method. No obvious visible defect-related-emission band is observed in the photoluminescence(PL) spectrum, indicating that the ZnO nanowires grown on the flexible ITO/PET substrate have few defects. In order to achieve electrically pumped random lasing with a lower threshold, the metal–insulator–semiconductor(MIS) structure of Au/SiO_2/ZnO on ITO/PET substrate is fabricated by low temperature process. With sufficient forward bias, the as-fabricated flexible device exhibits random lasing, and a low threshold current of ～ 11.5 m A and high luminous intensity are obtained from the ZnO-based random laser. It is believed that this work offers a case study for developing the flexible electrically pumped random lasing from ZnO nanowires.     

Self-breathing ternary nanocomposite based on nitrogen-doped graphene aerogel/polyaniline/sulfur as a cathode material for lithium-sulfur (Li-S) batteries

Li-S batteries are one of exciting new technologies in high energy density storage devices. But, their widespread commercialization has been limited by several obstacles. Elemental sulfur is not conductive electrically and electrochemical conversion during cycles causes intense change in volume. In this work, a sulfur/polyaniline/nitrogen-doped graphene aerogel (S@PANi-NGA) nanocomposite synthesized through a facile chemical procedure. Nitrogen-doped amino functionalized graphene aerogel (NGA) used as cross-linker for polyaniline to improve the stability of the entire cathode framework. Also, NGA possesses porous structure, high surface area, and enhances electronic conductance due to the nitrogen atoms doped into graphene sheets. As a result, S@PANi-NGA delivered an initial discharge capacity of 1332 mAh g^?1 at a scan rate of 0.2 C and 872 mAh g^?1 of the capacity retained after 100 cycles. The performance was clearly superior to the sulfur/PANi binary composite, in which pure polyaniline used as accommodator.     

Solvothermal synthesis and characterization of sandwich-like graphene/ZnO nanocomposites

Graphene-based nanocomposites are emerging as a new class of materials that hold promise for many applications. In this paper, we present a general approach for the preparation of sandwich-like graphene/ZnO nanocomposites in ethylene glycol (EG) medium using graphene oxide as a precursor of graphene and zinc acetylacetonate as a single-source precursor of zinc oxide. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy and thermogravimetry analysis. It was shown that the as-formed ZnO nanoparticles with a diameter of about 5 nm were densely and uniformly deposited on both surfaces of the graphene sheets to form a sandwich-like composite structure and as a result, the restacking of the as-reduced graphene sheets was effectively prevented. The ZnO-coated graphene nanocomposites can be expected to effectively improve the photocatalysis and sensing properties of ZnO and would be promising for practical applications in future nanotechnology.     

Microstructure and optical properties of ZnO/porous silicon nanocomposite films

In this study, porous silicon (PS) templates were formed by electrochemical anodization on p-type (100) silicon wafer and ZnO films were deposited on PS substrates using radio frequency (RF) reactive magnetron sputtering technique. The effects of oxygen partial pressures of growth ZnO films and annealing ambience on the microstructure and photoluminescence (PL) of the ZnO/PS nanocomposite films were systematically investigated by X-ray diffraction and fluorescence spectrophotometry. The results indicated that all ZnO/PS nanocomposite films were polycrystalline in nature with a hexagonal wurtzite structure and the (002) oriented ZnO films had the best crystal quality under O₂:Ar ratio of 10:10 sccm and annealing in vacuum. PL measurements at room temperature revealed that ZnO/PS nanocomposite systems formed a broad PL band including the blue and green emissions from ZnO and red-orange emission from the PS. The mechanism and interpretation of broadband PL of the nanocomposites were discussed in detail using an oxygen-bonding model in PS and a native defects model in ZnO.     

Effect of graphene/ZnO hybrid transparent electrode on characteristics of GaN light-emitting diodes

In order to reduce the Schottky barrier height and sheet resistance between graphene(Gr) and the p-GaN layers in GaN-based light-emitting diodes(LEDs), conductive transparent thin films with large work function are required to be inserted between Gr and p-GaN layers. In the present work, three kinds of transparent conductive oxide(TCO) zinc oxide(ZnO) films, Al-, Ga-, and In-doped ZnO(AZO, GZO, and IZO), are introduced as a bridge layer between Gr and p-GaN,respectively. The influence of different combinations of Gr/ZnO hybrid transparent conducting layers(TCLs) on the optical and thermal characteristics of the GaN-LED was investigated by the finite element method through COMSOL software. It is found that both the TCL transmittance and the surface temperature of the LED chip reduce with the increase in Gr and ZnO thickness. In order to get the transmittance of the Gr/ZnO hybrid TCL higher than 80%, the appropriate combination of Gr/ZnO compound electrode should be a single layer of Gr with ZnO no thicker than 400 nm(1 L Gr/400-nm ZnO),2 L Gr/300-nm ZnO, 3 L Gr/200-nm ZnO, or 4 L Gr/100-nm ZnO. The LEDs with hybrid TCLs consisting of 1 L Gr/300-nm AZO, 2 L Gr/300-nm GZO, and 2 L Gr/300-nm IZO have good performance, among which the one with 1 L Gr/300-nm GZO has the best thermal property. Typically, the temperature of LEDs with 1 L Gr/300-nm GZO hybrid TCLs will drop by about 7 K compared with that of the LEDs with a TCL without ZnO film.     

Effect of swift heavy ion irradiation on photoluminescence properties of ZnO/PMMA nanocomposite films

We report a study on the SHI induced modifications on structural and optical properties of ZnO/PMMA nanocomposite films. The ZnO nanoparticles were synthesized by the chemical route using 2-mercaptoethanol as a capping agent. The structure of ZnO nanoparticles was confirmed by XRD, SEM and TEM. These ZnO nanoparticles were dispersed in the PMMA matrix to form ZnO/PMMA nanocomposite films by the solution cast method. These ZnO/PMMA nanocomposite films were then irradiated by swift heavy ion irradiation (Ni⁸⁺ ion beam, 100 MeV) at a fluence of 1×10¹¹ ions/cm². The nanocomposite films were then characterized by XRD, UV-vis absorption spectroscopy and photoluminescence spectroscopy. As revealed from the absorption spectra, absorption edge is not changed by the irradiation but the optical absorption is increased. Enhanced green luminescence at about 527 nm and a less intense blue emission peak around 460 nm were observed after irradiation with respect to the pristine ZnO/PMMA nanocomposite film.     

PPV/PVA/ZnO nanocomposite prepared by complex precursor method and its photovoltaic application

In this article, we describe a new method to prepare a ZnO and conjugated polymer nanocomposite and its application in bulk-heterojunction solar cells. The composite was composed of zinc oxide (ZnO) and poly(phenylene vinylene)/poly(vinyl alcohol) (PPV/PVA). For the preparation, the composite was prepared first through the complex reaction between Zn²⁺ ion and –OH of the PVA–PPV precursor by simply mixing zinc salts and a PVA–PPV precursor aqueous solution at 70 °C. By addition of a concentrated aqueous ammonia into the system, highly regular Zn(OH)₂ nanodots were formed and dispersed in the PVA/PPV precusor mixed solution. The PVA/PPV precursor can well bind Zn²⁺ ion through complex interaction, so act as a template to direct the distribution of ZnO in the process. The nanocomposite films were finally obtained by solution casting and subsequently treated by heating samples at 160 °C for 6 h. TEM observations showed that ZnO nanodots uniformly dispersed in PVA–PPV mixtures. The resulting nanocomposite films possess a large interfacial area between the electron donor and acceptor of the bulk-heterojunction. Improved charge seperation and collection are evidenced by the large photoluminescence intensity difference between pure PPV and composites films, which result in the increase in both open circuit voltage and short circuit current of the hybrid solar cells.     

Rod-like polyaniline supported on three-dimensional boron and nitrogen-co-doped graphene frameworks for high-performance supercapacitors

In this work, novel three-dimensional (3D) boron and nitrogen-co-doped three-dimensional (3D) graphene frameworks (BN-GFs) supporting rod-like polyaniline (PANI) are facilely prepared and used as electrodes for high-performance supercapacitors. The results demonstrated that BN-GFs with tuned electronic structure can not only provide a large surface area for rod-like PANI to anchor but also effectively facilitate the ion transfer and charge storage in the electrode. The PANI/BN-GF composite with wrinkled boron and nitrogen-co-doped graphene sheets interconnected by rod-like PANI exhibits excellent capacitive properties with a maximum specific capacitance of 596 F/g at a current density of 0.5 A/g. Notably, they also show excellent cycling stability with more than 81% capacitance retention after 5000 charge-discharge cycles.     

基于银纳米线电极-rGO敏感材料的柔性NO2气体传感器

使用银纳米线作为材料制备柔性叉指电极,用还原氧化石墨烯(reduced graphene oxide, rGO)作为气体敏感材料制备出柔性气体传感器,并研究其对二氧化氮气体的响应特性以及柔韧性能.实验结果表明,制备的以银纳米线作为电极的r GO气体传感器可以实现室温下对浓度为5-50 ppm (1 ppm=10^–6)的NO2气体的检测,对50 ppm的NO2的响应能够达到1.19,传感器的重复性较好,恢复率能够保持在76%以上,传感器的灵敏度是0.00281 ppm^-1,对浓度为5 ppm的NO2气体的响应时间是990 s,恢复时间是1566 s.此外,传感器在0°-45°的弯曲角度下仍表现出优异的电学特性与气体传感性能,所制备的器件具有相对稳定的导电性和较好的弯曲耐受性.