Study on the design of ZnO/PANI composites and the mechanism of enhanced humidity sensing properties

ZnO/PANI composite humidity sensor was prepared by hydrothermal method. The first principles of density functional theory study the sensing mechanism. The calculation shows that the oxygen vacancy on ZnO surface is beneficial to the adsorption of water molecules. The {0 0 0‾1} crystal plane with the largest lattice oxygen number in ZnO has a strong adsorption capacity for water molecules, which is also conducive to improving the humidity sensitivity. PANI is easy to be combined on {0 1‾1 0} plane of ZnO, and it indirectly promotes the growth of {0 0 0‾1} plane, increasing the adsorption of water molecules and the proportion of H⁺ and H₃O⁺ ions. In addition, the N–H group in ZnO/PANI enhances the H⁺ conduction, which further improves the performance of the sensor. The results concluded that the proportion of lattice oxygen in humidity sensor is an important factor of humidity sensor sensitive detection.     

Ferromagnetism in Eu-doped ZnO films deposited by radio-frequency magnetic sputtering

This paper reports that Eu-doped ZnO films were successfully deposited on silicon (100) by radio-frequency magnetic sputtering. The x-ray diffraction patterns indicate that Eu substitutes for Zn in the lattice. Ferromagnetic loops were obtained by using superconducting quantum interference device at 10 K and room temperature. No discontinuous change was found in both of the zero-field-cooled and field-cooled curves. The observed ferromagnetism in Eu-doped ZnO can be attributed to a single magnetic phase. The saturation magnetisation decreased remarkably for the Eu-doped ZnO prepared by introducing 5% of oxygen in the sputtering gas or by the post annealing in O2, suggesting that the defects play key roles in the development of ferromagnetism in Eu-doped ZnO films.     

Fast synthesize ZnO quantum dots via ultrasonic method

Green emission ZnO quantum dots were synthesized by an ultrasonic sol–gel method. The ZnO quantum dots were synthesized in various ultrasonic temperature and time. Photoluminescence properties of these ZnO quantum dots were measured. Time-resolved photoluminescence decay spectra were also taken to discover the change of defects amount during the reaction. Both ultrasonic temperature and time could affect the type and amount of defects in ZnO quantum dots. Total defects of ZnO quantum dots decreased with the increasing of ultrasonic temperature and time. The dangling bonds defects disappeared faster than the optical defects. Types of optical defects first changed from oxygen interstitial defects to oxygen vacancy and zinc interstitial defects. Then transformed back to oxygen interstitial defects again. The sizes of ZnO quantum dots would be controlled by both ultrasonic temperature and time as well. That is, with the increasing of ultrasonic temperature and time, the sizes of ZnO quantum dots first decreased then increased. Moreover, concentrated raw materials solution brought larger sizes and more optical defects of ZnO quantum dots.     

Effect of defect content on the unipolar resistive switching characteristics of ZnO thin film memory devices

In this study, unipolar resistive switching (URS) characteristics in ZnO thin film memory devices were systematically investigated with variable defect content. ZnO films displayed typically URS behavior while oxygen-deficient ZnO_1?x films did not show resistive switching effects. The devices with two intentional Ohmic interfaces still show URS. These results show that appearance of URS behavior can be dominated by initial oxygen vacancy content in ZnO thin films. Modest increase in oxygen vacancy content in ZnO films will lead to forming-free and narrower distributions of switching parameters (set and reset voltage, high and low resistance states). It indicates that controlling the initial oxygen vacancy content was an effective method to enhance the URS performance.     

Interplay of native defect-related photoluminescence response of ZnO nanosticks subjected to 80 keV Ar ion irradiation

We report on the effect of 80 keV Ar⁺ ion irradiation on the luminescence response of zinc oxide (ZnO) nanosticks synthesized using a simple microemulsion route. The formation of nanoscale rods was confirmed from the transmission electron microscopy, whereas the hexagonal wurtzite phase of the nanorods was detected in an X-ray diffraction pattern. The photoluminescence pattern of the nanorods was dominated by various native defect states of ZnO, which are responsible for the quenching of the typical band edge emission of ZnO. Under Ar⁺ ion irradiation at a fluence of 1×10¹³ ions/cm², the band edge emission was recovered owing to the suppression of oxygen vacancy defects. In addition, the formation of new zinc vacancy and ionized zinc interstitial defects were also evident. Conversely, the band edge emission was found to be quenched as a result of the creation of more oxygen vacancy (V_O) defects due to ion irradiation (fluence: 1×10¹⁵ ions/cm²). The nuclear energy loss of the Ar⁺ ions in ZnO is responsible for the formation of point (vacancy-related) defects, while relatively small amount of electronic energy loss of the Ar⁺ ion results in the ionization of the neutral zinc interstitial (Zn_i) defects. The energy deposition scheme of the energetic ions has been elaborated with the help of theoretical modeling that explains the observed features quite satisfactorily.     

Investigation of Cu Doping,Morphology and Annealing Effects on Structural and Optical Properties of ZnO:Dy Nanostructures

Dysprosium (Dy) doped ZnO nanosheets and nanorods were synthesized by hydrothermal method. Effects of Cu doping, morphology and annealing in Oxygen ambient on structural and optical properties of ZnO nanostructures were investigated using X–ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectra (DRS) and photoluminescence (PL) spectroscopy. This study recommends that both of intrinsic and extrinsic defects facilitate energy transfer (ET) from the ZnO host to Dy³⁺ ions and consequently have an effective role on producing intense Dy emissions at indirect excitation. The results also revealed that annealing process improved the crystal structure of ZnO nanorods due to decrease of surface; however decreased ET and Dy emissions because of diminishing in oxygen vacancy. In addition, as a result of increasing of surface area in nanorods compared to nanosheets, the oxygen vacancies and ET were enhanced. Moreover the results exhibited that electrical and optical properties of ZnO:Dy can be tuned by various amount of Dy concentrations and also Cu doping.     

Effects of temperature and atmosphere on the magnetic properties of Co-doped ZnO rods

Co-doped ZnO (Zn_0.95Co_0.05O) rods are fabricated by co-precipitation method at different temperatures and atmospheres. X-ray diffraction, Energy dispersive X-ray spectroscopy and Raman results indicate that the samples were crystalline with wurtzite structure and no metallic Co or other secondary phases were found. Raman results indicate that the Co-doped ZnO powders annealed at different temperatures have different oxygen vacancy concentrations. The oxygen vacancies play an important role in the magnetic origin for diluted magnetic semiconductors. At low oxygen vacancy concentration, room temperature ferromagnetism is presented in Co-doped ZnO rods, and the ferromagnetism increases with the increment of oxygen vacancy concentration. But at very high oxygen vacancy concentration, large paramagnetic or antiferromagnetic effects are observed in Co-doped ZnO rods due to the ferromagnetic-antiferromagnetic competition. In addition, the sample annealed in Ar gas has better magnetic properties than that annealed in air, which indicates that O₂ plays an important role. Therefore, the ferromagnetism is affected by the amounts of structural defects, which depend sensitively on atmosphere and annealing temperature.     

沉淀剂对ZnO压敏陶瓷缺陷结构和电气性能的影响

研究了不同沉淀剂(NH₄HCO₃和NaOH)对共沉淀法制备的ZnO压敏陶瓷性能的影响. 结果表明: 不同的沉淀剂对ZnO压敏陶瓷的微观结构及电气性能有明显的影响. 其中陶瓷微观结构的变化主要由沉淀剂本身的性质引起; 而电气性能的改变除了与微观结构相关外, 主要受不同沉淀剂对陶瓷晶界势垒参数的影响; 此外, 沉淀剂NaOH引入的Na⁺作为施主杂质离子掺杂ZnO压敏陶瓷, 增加晶粒中的自由电子浓度, 因此本征缺陷(锌填隙和氧空位)浓度受到抑制, 而锌填隙浓度相对于氧空位而言对施主离子掺杂更为敏感. 由此, 采用共沉淀法制备ZnO压敏陶瓷粉体时, 沉淀剂种类的选择很重要, 即使微量的杂质也会引起压敏陶瓷性能的较大改变, 应尽可能避免杂质离子的引入. 关键词： ZnO压敏陶瓷 缺陷结构 沉淀剂 介电性能     

外电场极化对纳米氧化锌拉曼活性及气敏性能的影响

采用沉淀法制备了纳米氧化锌粒子,着重对其进行了不同条件(电场强度、极化温度)下的外电场极化处理.以X射线衍射仪和拉曼光谱仪对产物的结构、拉曼位移等进行了表征.测试了氧化锌极化产物在乙醇、丙酮气体中的气敏性能,研究了外电场效应对纳米氧化锌拉曼光谱和气敏性能的影响机制.结果表明,纳米氧化锌样品在外电场中存在着极化电场强度和温度的阈值,当电场强度和温度分别大于9375 V·cm~(-1)和150℃时,纳米氧化锌试片出现明显的漏电现象,极化效应显著降低并消失.在电场强度和温度阈值范围内,外电场极化作用能够导致氧化锌437 cm~(-1)处的拉曼特征峰强度明显降低.随外电场强度和极化温度增加,纳米氧化锌元件在丙酮气体中的灵敏度逐渐升高,在乙醇气体中的灵敏度逐渐降低,即外电场极化可以有效调控纳米氧化锌的气敏选择性.     

过渡金属元素X(X=Mn,Fe,Co,Ni)掺杂对ZnO基阻变存储器性能的影响

实验表明掺杂是一种改善阻变存储器性能的有效手段,但其物理机理鲜有研究.本文采用第一性原理方法系统研究了过渡金属元素X(X=Mn,Fe,Co,Ni)掺杂对ZnO基阻变存储器中氧空位迁移势垒和形成能的影响.计算结果表明Ni掺杂可同时有效降低+1和+2价氧空位在掺杂原子附近的迁移势垒,X掺杂均减小了氧空位的形成能,特别是掺杂Ni时氧空位的形成能减小最为显著(比未掺杂时减少了64%).基于该结果制备了未掺杂和Ni掺杂ZnO阻变存储器,研究表明通过掺杂控制体系中氧空位的迁移势垒和形成能,可以有效改善器件的初始化过程、操作电压、保持性等阻变性能.研究结果有助于理解探究影响阻变的微观机制,并可为掺杂提高阻变存储器性能提供一定的理论指导.     

Ga掺杂对ZnO纳米结构可见光发射的抑制效应

采用碳热还原反应和原位掺杂的方法制备了不同Ga掺杂浓度的ZnO纳米结构. X射线衍射 显示掺杂纳米结构中为单一的氧化锌纤锌矿结构. 扫描电子显微镜 观测发现随掺杂浓度的增大, 纳米结构的形貌逐渐从纳米六棱柱变为纳米锥.光致发光 和X射线光电子能谱 测量分别发现随着掺杂浓度升高, 纳米结构的可见发光强度和其中空位 氧峰相对强度逐渐减小直至消失, 两者存在很强的相关性. 上述结果为ZnO可见光发射的氧空位机理提供了新的实验证据. 对Ga掺杂抑制纳米结构中氧空位的原因进行了分析.     

Defect-mediated ferromagnetism in ZnO:Mn nanorods

In this work, the structural, chemical and magnetic properties of ZnO:Mn nanorods were investigated. Firstly, well-aligned ZnO nanorods with their long axis parallel to the crystalline c-axis were successfully grown by the vapor phase transport technique on Si substrates coated with a ZnO buffer layer. Mn metal was then diffused into these nanorods at different temperatures in vacuum. From SEM results, ZnO:Mn nanorods were observed to have diameters of ～100 nm and lengths of 4 μm. XPS analysis showed that the Mn dopant substituted into the ZnO matrix with a valence state of +2. Magnetic measurements performed at room temperature revealed that undoped ZnO nanorods exhibit ferromagnetic behavior which may be related to oxygen vacancy defect-mediated d ⁰ ferromagnetism. ZnO:Mn samples were seen to show an excess room temperature ferromagnetism that is attributed to the presence of oxygen vacancy defects forming bound magnetic polarons involving Mn.     

Effect of surface oxygen vacancy defects on the performance of ZnO quantum dots ultraviolet photodetector

The slower response speed is the main problem in the application of ZnO quantum dots (QDs) photodetector, which has been commonly attributed to the presence of excess oxygen vacancy defects and oxygen adsorption/desorption processes. However, the detailed mechanism is still not very clear. Herein, the properties of ZnO QDs and their photodetectors with different amounts of oxygen vacancy (V_O) defects controlled by hydrogen peroxide (H₂O₂) solution treatment have been investigated. After H₂O₂ solution treatment, V_O concentration of ZnO QDs decreased. The H₂O₂ solution-treated device has a higher photocurrent and a lower dark current. Meanwhile, with the increase in V_O concentration of ZnO QDs, the response speed of the device has been improved due to the increase of oxygen adsorption/desorption rate. More interestingly, the response speed of the device became less sensitive to temperature and oxygen concentration with the increase of V_O defects. The findings in this work clarify that the surface V_O defects of ZnO QDs could enhance the photoresponse speed, which is helpful for sensor designing.     

Influence of hydrostatic pressure on the native point defects in wurtzite ZnO: Ab initio calculation

The formation energies and transition energy levels of native point defects in wurtzite ZnO under applied hydrostatic pressure are calculated using the first-principle band-structure methods. We find that the pressure coefficient of the (2+/0) level for oxygen vacancy is larger than that of the (2+/1+) level for zinc interstitial, which demonstrates that the donor level of oxygen vacancy is deeper than that of zinc interstitial, therefore the latter is the more probable electron resource in native n-type ZnO. And the significantly different pressure dependence of the transition levels between them can be used to determine the origin of the green luminescence center in ZnO. Zinc octahedral interstitial and oxygen tetrahedral interstitial configurations became the dominant defects under 5 GPa at their favorable growth conditions, respectively. The formation of defects under applied pressure is the result of fine interplay between internal strains, charges on the defects and applied external pressures.     

TEMPOS devices as humidity sensors

An impedance spectroscopy technique has been employed to study the humidity sensing property of a novel ion-track-based device called ‘TEMPOS’ (tunable electronic materials with pores in oxide on silicon). Polymer electrolytes (PEs) and semiconductor-dispersed PE have been used as sensing elements. The sensing behaviour depends on the material inserted in the tracks and on the frequency and magnitude of the applied signal. Cole–Cole plots have been obtained at a constant humidity (30%, 43%, 54%, 65% and 82% relative humidity) and at a constant voltage (1–5 V), for frequencies ranging from 1 Hz to 100 kHz. A decrease in the impedance of the sensor is observed with an increase in the humidity and frequency of the applied signal. The width of the sensitive region increases with a decrease in the frequency. At a constant humidity, the influence of voltage on the impedance is small and PEs are found to be better sensing materials. Tracks act as pores for chemisorption and physiosorption to take place at the dielectric surface. Chemisorption probably leads to charge transfer between material inserted in tracks and the moisture.     

掺铕纳米氧化锌的制备及其发光性质

以尿素为沉淀剂，与可溶性硝酸锌、硝酸铕反应制备纳米晶ZnO:Eu3+³⁺，通 过x射线粉末衍射、透射电子显微镜对纳米粒子的组成、结构、形貌及尺寸进行了分析和测定.研究 结果表明，制得的纳米粒子粒度均匀，粒径分布窄，最小粒径为8nm.详细研究了不同制备 方法、不同掺杂浓度及不同粒度等对ZnO:Eu3+³⁺发光性质的影响.为探讨纳米 掺杂材料的制备技术及发光方面的应用提供了可行的方法. 关键词： 光致发光 3+')" href="#">纳米晶ZnO:Eu3+³⁺ 均匀沉淀法     

Humidity sensing properties of Pd-doped ZnO nanotetrapods

Pd²⁺-doped ZnO nanotetrapods were prepared and studied for the humidity detection application. The humidity sensors developed were featured by combination of a quartz crystal microbalance (QCM) as a transducer and Pd²⁺-doped ZnO nanotetrapods as a sensing element. The ZnO nanotetrapods were synthesized by evaporating highly pure zinc pellets (99.999%) at 900 °C in air and PdCl₂ was doped on by traditional solution mixing process. Then the mixed solution distributed onto the electrode surfaces of the quartz crystal at room temperature. Pd²⁺-doped ZnO nanotetrapods were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results indicated that the response of the sensors varied with the different dosage PdCl₂. Linear regression algorithm was used for evincing the highly linear behavior of the Pd²⁺-doped ZnO nanotetrapods sensor. In this humidity sensing system, the Pd²⁺-doped ZnO nanotetrapods sensing material coated on the gold electrode of QCM showed good sensitivity (∼74.24324 Hz/%RH (relative humidity)), reproducibility, linearity (R² = −0.98834), short response and recovery time (less than 5 s).     

Fe掺杂对溶胶凝胶法制备的ZnO: Ni薄膜结构及发光特性的影响

采用溶胶凝胶法在玻璃基片上制备了ZnO及Ni, Fe共掺杂的Zn_0.95-xNi_0.05Fe_xO (x=0, 0.005, 0.01, 0.03, 0.05) 薄膜. 通过扫描电镜(SEM) 和X射线衍射(XRD) 研究了薄膜样品的表面形貌和晶体结构. 结果表明所有样品都具有(002) 择优取向, Fe掺杂导致ZnO: Ni薄膜的晶体质量变差, 晶粒尺寸减小, 但适当的Fe掺杂有利于获得致密、 均匀的薄膜. XPS测试结果表明样品中Ni离子的价态为+2价, Fe离子的价态为+2价和+3价.室温光致发光(PL) 测量表明, 所有样品均观察到较强的紫外发光峰, 蓝光双峰和绿光发光峰. ZnO: Ni薄膜的发光强度可以通过Fe掺杂进行有效调节. 进而我们讨论了Ni, Fe共掺杂ZnO样品的发光机理.     

Effect of irradiating ion fluence on optical properties of ZnO1−x:Nx thin films

Swift heavy ion (SHI) irradiation is an effective technique to modify the optical properties of the materials. In the present investigation, the effect of 100?MeV?Ag⁷⁺ SHI irradiation fluence on the optical properties of ZnO_1?x:N_x thin films was studied. The post irradiation spectroscopic characterizations such as UV–VIS reflectance spectroscopy, Raman spectroscopy and photoluminescence (PL) spectroscopy analysis were carried out. The studies imply that when the SHI passes through the solid, the higher electronic stopping power of ions can weaken oxygen bonds in ZnO, resulting in the formation of donor defects such as oxygen vacancies and zinc interstitials. The formation of donor defects has been acknowledged through the increase in bandgap with irradiating ion fluence. The blue shift observed from the Raman spectra for the 3?×?10¹³ ions/cm² fluence-irradiated films implies the existence of compressive stress in the films. The PL analysis acknowledges the formation of donor defects upon irradiation. Furthermore, it conveys that the presence of N atoms in ZnO lattice leads to the formation of a less number of defects as compared with undoped ZnO while irradiation.     

Study on the defects of ZnO nanowire

The room-temperature photoluminescence property of ZnO nanowires was studied. It showed an ultraviolet peak and a visible light band in the PL spectrum. Through Gaussian fitting, it was found that the visible light band can be divided into two peaks at 2.37 eV and 2.53 eV, which was originated from oxygen antisite and oxygen vacancy defects, respectively. After being exposed to air or post-annealed in oxygen ambience, aging effect was observed and the peak at 2.53 eV disappeared due to the removal of oxygen vacancy defects. Therefore, it is suggested that oxygen antisite and oxygen vacancy coexist in ZnO and induce visible light emission.