Nanostructured Vanadium Oxide Electrodes for Enhanced Lithium‐Ion Intercalation

This article summarizes our most recent studies on improved Li⁺‐intercalation properties in vanadium oxides by engineering the nanostructure and interlayer structure. The intercalation capacity and rate are enhanced by almost two orders of magnitude with appropriately fabricated nanostructures. Processing methods for single‐crystal V₂O₅ nanorod arrays, V₂O₅·n H₂O nanotube arrays, and Ni/V₂O₅·n H₂O core/shell nanocable arrays are presented; the morphologies, structures, and growth mechanisms of these nanostructures are discussed. Electrochemical analysis demonstrates that the intercalation properties of all three types of nanostructure exhibit significantly enhanced storage capacity and rate performance compared to the film electrode of vanadium pentoxide. Addition of TiO₂ to orthorhombic V₂O₅ is found to affect the crystallinity, microstructure, and possible interaction force between adjacent layers in V₂O₅, and subsequently leads to enhanced Li⁺‐intercalation properties in V₂O₅. The amount of water intercalated in V₂O₅ is found to have a significant influence on the interlayer spacing and electrochemical performance of V₂O₅·n H₂O. A systematic electrochemical study has demonstrated that the V₂O₅·0.3 H₂O film has the optimal water content and exhibits the best Li⁺‐intercalation performance.     

氧化钒薄膜的性能和制备

为制备低相变温度、高相变特性的氧化钒薄膜,分析了氧化钒的结构,及其结构决定的特有相变,相变前后独特的光电性能及其应用。比较研究了各种制备方法,得到最低相变温度、最高的电阻变化率和电阻温度系数分别达24℃、105-、5.2%K-1,研究表明,掺杂改性及新的成膜工艺的研究是氧化钒薄膜的发展方向。     

射频磁控溅射氧化钒薄膜的结构与性能研究

以非制冷微测辐射热计型红外探测器应用为需求背景,采用射频磁控溅射技术在300℃低温条件下制备了氧化钒薄膜.采用X射线衍射(XRD)、原子力显微镜(AFM)、能量色散谱(EDS)及X射线光电子能谱(XPS)技术表征了薄膜的结晶状态、微观结构与化学组成.采用四探针技术研究了薄膜的电学性能.结果表明该薄膜主要为非晶态的二氧化钒( VO2),并具有光滑的表面形貌.这种非晶VO2薄膜在22～100℃温度范围内不存在半导体-金属相变.100 nm厚的非晶VO2薄膜室温下的面电阻为600 kΩ/,同时表现出-2.1％/℃的较高电阻温度系数(TCR),这表明该薄膜有希望用于非制冷微测辐射热计型红外探测器.     

热处理时间对氧化钒薄膜相变性能的影响

采用直流磁控溅射的方法在普通玻璃上制备了低价的氧化钒薄膜,在氧气和氩气混合气氛中,对所制备的薄膜进行不同时间的热处理,得到具有相变特性的VO2薄膜。分别利用X射线衍射(XRD)和场发射扫描电镜(SEM)分析了薄膜的组分、结晶结构和表面形貌,利用四探针法测试了薄膜的电阻。结果表明:热处理前的氧化钒薄膜主要成分为V2O3,经过热氧化处理后,低价的氧化钒被氧化,薄膜中VO2含量增加,薄膜发生金属-半导体相变,其中450℃、2h为最佳处理参数,其电阻相变幅度超过2个数量级,薄膜的相变温度仅为30℃。     

溅射时间对氧化钒薄膜性能的影响

采用直流磁控溅射法在普通玻璃上制备了氧化钒薄膜,并对薄膜采取了450 ℃真空退火处理,分别测量了退火前后薄膜XRD图谱及电阻,比较了不同溅射时间（120 min、100 min、60 min）对薄膜性能的影响。结果表明,溅射时间增长,薄膜的结晶度也增强,经过退火处理,薄膜的电阻明显减小,且溅射时间越长,薄膜的阻值越小,3块薄膜的电阻分别达到16.0 MΩ、65.0 MΩ、71.5 MΩ,其随温度变化的幅度也越小。     

膜厚对氧化钒薄膜结构和光学性质的影响

利用真空热蒸发在石英基片上制备了不同厚度的氧化钒薄膜, 研究厚度对薄膜的结构、形貌和光学特性的影响。薄膜的结构由X射线衍射(XRD)仪和拉曼(Raman)光谱仪测得, 表面形貌用原子力显微镜(AFM)观测。利用分光光度计测量薄膜的光学透射率, 并且采用Forouhi-Bloomer模型与修正的德鲁德(Drude)自由电子模型相结合的方法拟合透射率来确定薄膜的折射率、消光系数和带隙。结果表明, 热蒸发的氧化钒薄膜呈非晶态, 薄膜的主要成分为五氧化二钒, 且含有少量的二氧化钒。薄膜表面的颗粒粘结在一起, 随着薄膜厚度的增加, 薄膜表面粗糙度以及颗粒尺寸变小, 膜层表面平整度越来越好, 颗粒之间的空隙变小, 导致折射率随膜厚的增加而增大, 消光系数减小。另外, 随着薄膜厚度从200 nm增加到450 nm, 光学带隙从2.67 eV减小到2.45 eV。     

Designing the Width and Texture of Vanadium Oxide Macroscopic Fibers: Towards Tuning Mechanical Properties and Alcohol‐Sensing Performance

Macroscopic vanadium oxide fibers have been fabricated by an extrusion process. By varying the shear rate associated with the gel extrusion process we have been able to tune the diameter and transversal geometry of the fibers at macroscopic length scales. At the mesoscopic length scale, small‐angle X‐ray scattering (SAXS) analysis provides evidence for the possibility of fine tuning the degree of alignment of the V₂O₅ ribbons inside the fibers; this alignment is clearly improved upon increasing the shear rate. Nitrogen physisorption measurements (Brunauer–Emmett–Teller (BET)) indicate that the as‐synthesized fibers exhibit poor mesoporosity, largely due to the presence of remaining poly(vinyl alcohol) (PVA) entities. Microscopically, from XRD measurements, the fiber structure appears to be semi‐crystalline. ⁵¹V magic angle spinning NMR (MAS NMR) spectroscopy reveals that the local environment of ⁵¹V is typical of the structure of a V₂O₅·1.8 H₂O xerogel. We demonstrate here that the alignment of the nanoribbon subunits can be tuned via the shear rate applied during the extrusion process, which provides a good handle for tuning the mechanical and sensing properties of the as‐synthesized fibers.     

掺杂氧化钒薄膜的制备及其热光特性

以石英片为基底材料,采用直流/射频磁控共溅射方法制备了掺Al和掺Ti的氧化钒薄膜,重点探索了用这种方法制备掺杂氧化钒薄膜的工艺条件,对所制备的氧化钒薄膜进行了热光性能测试,并利用能带理论对测试结果进行分析.实验及测试结果表明,在氧化钒薄膜中掺入Ti杂质与掺入Al杂质相比,对薄膜的热光性质的改变所起的作用更为明显.增大Ti杂质的含量对薄膜的电阻-温度特性、相变温度,以及相变滞豫区的改善比较明显,但提高了薄膜的相变温度,而掺Al引起的变化规律与此相反.     

氧分压对溅射氧化钒薄膜结构和透光性能的影响

采用射频磁控溅射法,在K9抛光玻璃基底上沉积氧化钒(VOx)薄膜,研究在其他参数保持不变时氧分压参量对薄膜的结构、表面质量及透光性能的影响。利用表面轮廓仪、X射线衍射仪、原子力显微镜及分光光度计分别对样品的沉积速率、物相结构、表面形貌和紫外-近红外光透射率进行分析。结果表明,制备的VOx薄膜的晶相随氧分压不同发生改变,调整氧分压在可见-近红外光区域可获得弱吸收的光学膜,但氧分压过高只能获得低的薄膜沉积速率,氧分压对薄膜表面粗糙度及晶体生长模式也有不同程度的影响。本文对实验结果进行了分析和讨论。     

Semiconducting and Piezoelectric Oxide Nanostructures Induced by Polar Surfaces

Zinc oxide, an important semiconducting and piezoelectric material, has three key characteristics. First, it is a semiconductor, with a direct bandgap of 3.37 eV and a large excitation binding energy (60 meV), and exhibits near‐UV emission and transparent conductivity. Secondly, due to its non‐centrosymmetric symmetry, it is piezoelectric, which is a key phenomenon in building electro‐mechanical coupled sensors and transducers. Finally, ZnO is bio‐safe and bio‐compatible, and can be used for biomedical applications without coating. With these unique advantages, ZnO is one of the most important nanomaterials for integration with microsystems and biotechnology. Structurally, due to the three types of fastest growth directions—<0001>, <01 0>, and <2 0>—as well as the ±(0001) polar surfaces, a diverse group of ZnO nanostructures have been grown in our laboratory. These include nanocombs, nanosaws, nanosprings, nanorings, nanobows, and nanopropellers. This article reviews our recent progress in the synthesis and characterization of polar‐surface‐induced ZnO nanostructures, their growth mechanisms, and possible applications as sensors, transducers, and resonators. It is suggested that ZnO could be the next most important nanomaterial after carbon nanotubes.     

微测辐射热计用氧化钒薄膜制备及特性

热敏薄膜电阻制备是非致冷微测辐射热计红外焦平面的一项关键技术。对目前在非致冷微测辐射热计研制中得到成功应用的氧化钒薄膜的特性、制备及表征技术进行综述。氧化钒存在多种物相和结构 (VOx:0 相似文献   

退火对IBED氧化钒薄膜结构和性能的影响

对离子束增强沉积(IBED)氧化钒薄膜作不同条件的退火，用X射线衍射分析薄膜的晶体结构；用电阻．温度测试分析了薄膜的热电阻温度系数。实验发现，沉积薄膜存在一个形成二氧化钒结构的临界结晶温度，该温度随薄膜制备时离子束增强沉积条件的不同而改变。退火温度低于临界结晶温度时，很难使薄膜结晶成二氧化钒结构；高于临界温度较多的退火或形成VO2结构后再长时间退火，都会使VO2多晶薄膜中的钒分解降价，使薄膜的结构退化、性能变差。IBED多晶VO2薄膜在室温附近的电阻温度系数可达到4％／K以上。     

From Layered Basic Zinc Acetate Nanobelts to Hierarchical Zinc Oxide Nanostructures and Porous Zinc Oxide Nanobelts

Novel hierarchical ZnO nanostructures, porous ZnO nanobelts, and nanoparticle chains are prepared from a precursor of synthetic bilayered basic zinc acetate (BLBZA) nanobelts. BLBZA nanobelts are obtained by a simple synthetic route under mild conditions. X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, and thermal analysis are used to characterize the BLBZA nanobelts and ZnO nanostructures. The obtained BLBZA precursor consists of a lamellar structure with two interlayer distances of 1.33 and 2.03 nm, exhibits a beltlike morphology, and has widths of 200 to 600 nm, thicknesses of 10 to 50 nm, and lengths of up to 50 μm. Refluxing an aqueous dispersion of BLBZA nanobelts at 120 °C for 12 h leads to the formation of well‐defined hierarchical ZnO nanostructures. The time‐dependent shape‐evolution process suggests that spindlelike ZnO particles form first, and then the ringlike nanosheets grow heterogeneously on the backbone of these spindles. In addition, calcination in air can remove ligand molecules and intercalated water molecules from BLBZA nanobelts, resulting in the formation of porous ZnO nanobelts and nanoparticle chains. The BLBZA nanobelts serve as templates during the transformation to form ZnO beltlike nanoparticle chains without morphological deformation. Photoluminescence results show that both the as‐synthesized hierarchical ZnO nanostructures and porous ZnO nanobelts show a narrow and sharp UV emission at 390 nm and a broad blue–green emission at above 466 nm when excited by UV light.     

The Capturing of Ionized Oxygen in Sodium Vanadium Oxide Nanorods Cathodes under Operando Conditions

The control of voltage window has been considered as a universal strategy in improving the cycling stability of cathode materials, which is supposed and explained by avoiding side reactions. To address the conjecture, the detailed structure evolution of Na_0.76V₆O₁₅ nanorods is investigated with different electrochemical reaction voltage windows. High time resolution in situ X‐ray diffraction, ex situ X‐ray photoelectron spectroscopy, ex situ Raman spectroscopy, and transmission electron microscopy demonstrate the amorphization of Na_0.76V₆O₁₅ nanorods and formation of ionized oxygen in nanorods, leading to the increased polarization voltage and fast capacity fading. The amorphization and diffusion of ionized oxygen in nanorods is controlled by optimizing the voltage window, resulting in the great increase of capacity retention from 26% to 80%. It is demonstrated that controlling the voltage window and corresponding ionized oxygen diffusion can mitigate the fast capacity fading to achieve long lasting lithium ion batteries.     

氧化钒薄膜光伏效应机理分析

氧化钒薄膜是非致冷红外焦平面探测器的重要组成部分,光电特性一直是国内外的研究热点.用反应磁控溅射方法在K9玻璃衬底上制备了氧化钒薄膜,并在特定条件下对其进行了退火处理.结果发现,在300℃下退火180 s的氧化钒薄膜在可见光照射情况下呈现出了光伏效应,这说明光生载流子在氧化钒薄膜表层形成后得到了有效分离.该光伏特性为氧...     

On‐Demand Nanoscale Manipulations of Correlated Oxide Phases

Controlling material properties at the nanoscale is a critical enabler of high performance electronic and photonic devices. A prototypical material example is VO₂, where a structural phase transition in correlation with dramatic changes in resistivity, optical response, and thermal properties demonstrates particular technological importance. While the phase transition in VO₂ can be controlled at macroscopic scales, reliable and reversible nanoscale control of the material phases has remained elusive. Here, reconfigurable nanoscale manipulations of VO₂ from the pristine monoclinic semiconducting phase to either a stable monoclinic metallic phase, a metastable rutile metallic phase, or a layered insulating phase using an atomic force microscope is demonstrated at room temperature. The capability to directly write and erase arbitrary 2D patterns of different material phases with distinct optical and electrical properties builds a solid foundation for future reprogrammable multifunctional device engineering.     

Nanoscale Effects on the Ionic Conductivity of Highly Doped Bulk Nanometric Cerium Oxide

Nanometric ceria powders doped with 30 mol % samaria are consolidated by a high‐pressure spark plasma sintering (HP‐SPS) method to form > 99 % dense samples with a crystallite size as small as 16.5 nm. A conductivity dependence on grain size was noted: when the grain size was less than 20 nm, only one semicircle in the AC impedance spectra was observed and was attributed to bulk conductivity. In contrast to previous observations on pure ceria, the disappearance of the grain‐boundary blocking effect is not associated with mixed conductivity. With annealing and concomitant grain growth, the samples show the presence of a grain‐boundary effect.     

一种制备氧化钒薄膜的新工艺

采用两步法工艺,即先在衬底上溅射一层金属钒膜,再对其进行氧化的方法,在硅和氮化硅衬底上制备了高电阻温度系数的混合相VOx多晶薄膜。电学测试结果表明:厚度为50nm的氧化钒薄膜的方块电阻和电阻温度系数(TCR)在室温时分别达到50kΩ和0.021K-1。     

电化学还原法制备氧化铅纳米棒

用电化学还原法制备出氧化铅纳米棒，用SEM、TEM、EDS和XRD研究其微观形貌和晶体结构。实验过程中发现电流密度是影响氧化铅纳米棒生成质量的主要因素。研究结果表明，用电化学还原法制备氧化铅纳米棒的最佳电流密度是30mA/cm^2，所制备的氧化铅纳米棒是单晶结构。     

Cu掺杂对ZnO氧化物电子结构与电输运性能的影响

采用平面波超软赝势密度泛函理论计算的方法研究了p型Cu掺杂的纤锌矿结构氧化物ZnO的电子结构,在此基础上分析了其电输运性能。计算结果表明,Cu掺杂ZnO氧化物具有0.6eV的直接带隙,且为p型半导体,在导带和价带中都出现了由Cu电子能级形成的能带,体系费米能级附近的能带主要由Cup态、Cud态和Op态电子构成,且他们之间存在着强相互作用。电输运性能分析结果表明,Cu掺杂的ZnO氧化物价带中的载流子有效质量较大,导带中的载流子有效质量较小;其载流子输运主要由Cup态、Cud态、Op态电子完成,且需要载流子（空穴和电子）跃迁的能隙宽度较未掺杂的ZnO氧化物减小。