Capacitive Humidity Sensors With High Sensitivity and Subsecond Response Times

Capacitive-based humidity sensors were fabricated using coplanar interdigitated electrodes coated with nanostructured TiO₂ thin films produced by glancing angle deposition. In this letter, we show that increased sensitivity (nF/%RH) is obtained by decreasing the electrode periodicity or by increasing the planar area of the electrodes, or both. The devices were sensitive over a wide range of relative humidity levels (<1% to >92%) and exhibited extremely fast, subsecond response times. Typical adsorption and desorption response times were measured to be <220 and >400 ms, respectively     

Impact of morphology on high-speed humidity sensor performance

Capacitive-based humidity sensors were fabricated using unique nanostructured aluminum-oxide thin films. These sensors exhibited extremely fast desorption response times as short as 42 ms. In this paper, we present the effects of varying the thin-film porosity on sensor performance. Specifically, we look at the capacitive response and the desorption response time of the sensors. It was found that increased porosity tends to decrease the desorption response time and increase the relative humidity where the devices become sensitive.     

Comparative study on chemical stability of dielectric oxide films under HF wet and vapor etching for radiofrequency microelectromechanical system application

HF wet and vapor etching of dielectric oxide films, which were prepared by thermal atomic layer deposition (ALD) and plasma-enhanced ALD (PEALD), are examined for radiofrequency microelectromechanical system (RF MEMS) application. The chemical stability of oxide films was increased in the order of ALD–Al₂O₃ < PEALD–ZrO₂ < PEALD–TiO₂ ≈ ALD–Ta₂O₅ under wet etching in 6:1 buffered HF aqueous solution, but in a different order of Ta₂O₅ < ZrO₂ < TiO₂ ≈ Al₂O₃ under anhydrous HF/CH₃OH vapor etching at 4 kPa. The unstable films were uniformly and completely etched under the wet etching, while transformed to have increased thickness or non-uniformly etched with thicker residue under the vapor etching. Al₂O₃ and TiO₂ (Ta₂O₅ and TiO₂) can be used for RF MEMS capacitive switch fabricated by using HF vapor (wet) etching of sacrificial SiO₂.     

Characterization and properties of r.f.-sputtered thin films of the alumina–titania system

Thin films of the aluminum oxide (Al₂O₃)–titanium oxide (TiO₂) system including Al₂O₃, TiO₂, and Al₂O₃/TiO₂ were prepared by radio-frequency (r.f.) magnetron sputtering using ceramic targets of Al₂O₃, TiO₂, and Al₂O₃/TiO₂ composites with different Al₂O₃/TiO₂ ratio. These films were studied at different substrate temperatures, r.f. powers, and annealing temperatures. Composition, microstructure, thermomechanical property of internal stress, and mechanical property of scratch adhesion, were evaluated. A thin film with a dielectric constant of 62 and a loss tangent of 0.012 was obtained at 500 °C from a 10/90 target. This thin film remained the high dielectric constant of TiO₂, but had an improvement in the dielectric loss tangent. Al₂O₃-containing films had a higher resistivity and breakdown field, which was improved further by annealing. Optical properties, such as refractive index and optical transmittance, were also investigated.     

Comparison of the electrochemical behavior of CeO2–SnO2 and CeO2–TiO2 electrodes produced by the Pechini method

CeO₂–SnO₂ and CeO₂–TiO₂ thin films were prepared by the Pechini method and their characteristics were compared, using a fractional factorial design to quantify the effect of five preparation variables. It was observed that CeO₂–SnO₂ electrodes show a greater electrochemical response than the CeO₂–TiO₂ films. The best intercalation charge densities were 18.11 and 9.91 mC/cm² for CeO₂–SnO₂ and CeO₂–TiO₂, respectively. Both films were optically inactive with transparencies, in most cases, higher than 90%.     

玻璃固载TiO2/纳米纤维素复合薄膜的制备及其光催化性能

将微晶纤维素溶解于NaOH-尿素的低温溶液中形成纤维素溶液, 在水浴中再生形成纳米纤维素溶液。然后将纳米纤维素溶液与TiO₂(P25)混合, 并添加少量的钛酸正丁酯作为交联剂形成复合溶液。将制备得到的复合溶液通过流延法固载到玻璃片表面形成玻璃固载的TiO₂/纳米纤维素复合膜。通过SEM、XRD表征了复合膜的形貌与结构。将玻璃固载的TiO₂/纳米纤维素复合膜在紫外光下进行光催化降解甲基橙(MO)以评估复合膜的光催化性能, 研究了纳米TiO₂含量对复合膜光催化性能的影响, 复合膜的重复使用性能以及光降解的动力学过程。结果表明: 复合膜对MO的光催化降解能力可达90%以上, 与纯TiO₂粉末相当, 并重复使用3次光催化性能基本保持不变。复合膜对甲基橙的降解动力学符合一级动力学特征。当纳米TiO₂相对于纤维素的质量分数为33.3%时, 光催化活性最高, 动力学速率常数为0.035 min^-1。     

Effect of Nb, Cr, Sn additions on gas sensing properties of TiO2 thin films

The effect of Nb and Cr dopants as well as Sn⁴⁺ additions on the electronic structure of rf-sputtered TiO₂ thin films and its subsequent influence on gas sensor performance is reported. The changes in the electrical conductivities of TiO₂ thin films doped with up to 10 at.% Nb, 4 at.% Cr and TiO₂-SnO₂ in the full range of compositions upon exposure to hydrogen and oxygen are demonstrated. The spectral dependence of the absorption coefficient in the vicinity of the band gap transition of TiO₂ is shown to be affected by doping.     

WO3/TiO2复合薄膜的制备及其电致变色性能

使用水热法在掺氟SnO₂涂覆的导电玻璃（FTO）基板上生长TiO₂纳米线,随后在TiO₂纳米线上采用水热法生长WO₃纳米线,制备出WO₃/TiO₂复合薄膜。通过循环伏安法（CV）、计时电流法（CA）、计时电量法（CC）等电化学测试技术研究了WO₃/TiO₂复合薄膜的电致变色性能;采用紫外分光光度计对薄膜的着色﹑漂白状态的响应时间进行测试。通过以上测试,计算得到了薄膜的循环稳定性﹑光调制﹑着色效率和切换时间（Y和X）等参数。结果显示WO₃/TiO₂复合薄膜的电致变色性明显提高,其中WO₃/TiO₂复合薄膜可逆性增加了6%,着色效率提高了40.96 cm2/C。      

Behaviors of different dispersers on morphologies of porous TiO2 films

TiO₂ films with nanoparticles dispersed by using three different additives such as acetylacetone, Emulsifier OP-10, and polyethylene glycol, respectively. It is found that for the TiO₂ films produced with appropriate amount of Emulsifier OP-10, there are no reaggregation of TiO₂ nanoparticles with pores of about 5–20 nm. By adding polyethylene glycol, the pore size of the TiO₂ films could be in the range from about 50 to 200 nm. However, by using acetylacetone, aggregations of TiO₂ nanoparticles always exist in the TiO₂ films. The related mechanism on the aggregation of nanoparticles in the TiO₂ slurries is discussed.     

聚酰亚胺/二氧化钛纳米复合薄膜制备与耐电晕性

采用原位聚合法制备不同TiO₂组分聚酰亚胺(PI)/纳米TiO₂复合薄膜, 薄膜厚度50μm。 测试结果表明, TiO₂呈球状颗粒, 直径约为100 nm, 聚酰亚胺呈片状, 尺寸约为2μm×1μm。随着TiO₂含量的增加, 复合薄膜介电常数和介电损耗增大, 击穿场强先增加后降低; 在40 kV/mm电场强度下, 复合薄膜耐电晕老化寿命增加, 纯PI薄膜寿命为3 h, 20wt%TiO₂含量薄膜寿命达到25 h; TiO₂颗粒耐电晕能力强, 与聚合物形成界面相, 改变材料陷阱能级, 有利于空间电荷的扩散和热量的传输, 在薄膜表面形成放电阻挡层, 降低局部放电对薄膜内部的侵蚀, 显著提高薄膜耐电晕老化寿命。     

Indium Tin Oxide Thin-Film Sensor for Detection of Volatile Organic Compounds (VOCs)

Indium tin oxide (ITO) (In₂O₃ + 17% SnO₂) thin films were grown on glass substrate by direct evaporation method. Two thick gold pads were deposited to take out contacts. The response of these films at different operating temperatures, when exposed to various volatile organic compounds (VOCs) such as methanol, ethanol, butanol, and acetone in the concentration range 200-2500 ppm was evaluated. Additionally, the effect of film thickness on the response charateristics of methanol and acetone was studied. The linearity and sensitivity of the sensors were measured. The ITO thin-film sensors showed a sensitivity of 0.256 ohms/ppm to acetone vapors, which was almost linear in the range 200-2500 ppm. In order to improve sensitivity and selectivity, a thin layer of various metal and metal oxides such as Cu and PbO was deposited on the sensor surface to work as catalytic layer and the effect on the performance of the sensor was studied. The response and recovery times of the sensor were determined for acetone vapors and were found to be 155 sec and 110 sec, respectively.     

TiO_2-海藻酸钙复合膜的表征、对染料的光催化降解及TiO_2回收

为了解决TiO2纳米粒子难分离,负载的催化剂难回收等问题,首先,将TiO2与海藻酸钠充分混合制成铸膜液,在玻璃板上刮膜,经钙离子交联制备了TiO2-海藻酸钙(T-CA)复合膜。然后,对T-CA复合膜进行了SEM和XRD表征,并研究了T-CA复合膜对染料的光催化降解性能。最后,将T-CA复合膜从染料降解液中取出,浸泡在柠檬酸钠水溶液中,柠檬酸根对钙离子的结合力较强,可使海藻酸盐水凝胶溶解,离心分离TiO2纳米粒子并清洗干燥后,得到了回收TiO2;利用SEM、TEM、FTIR和XRD对回收TiO2进行了表征。结果表明:T-CA复合膜对甲基橙的光催化降解率可达82.37%。回收TiO2与初始的TiO2几乎完全一样,可重新使用且催化能力不变。该方法是一种绿色环保、方便快速的从载体中回收TiO2纳米粒子的方法。     

TiO2对琼胶-κ-卡拉胶膜性能的影响

采用热铸法,制备了琼胶膜、κ-卡拉胶膜及其两者的共混膜,并在共混膜中添加质量分数为0.8%的TiO₂粉末,制得TiO₂/琼胶-κ-卡拉胶复合膜。对这4种膜的SEM、XRD、力学性能、透光率、不透明度和对水的阻抗性进行测试。结果表明：琼胶-κ-卡拉胶膜的力学性能、透光率、不透明度和对水的阻抗性均介于琼胶膜和κ-卡拉胶膜之间,琼胶和κ-卡拉胶之间有良好的共混性,并且在共混膜中形成了分子间作用力。TiO₂/琼胶-κ-卡拉胶复合膜的拉伸强度（45.44 MPa）比其他3种膜的拉伸强度都大,其中比琼胶-κ-卡拉胶膜的拉伸强度（31.06 MPa）提高46.30%,但断裂伸长率（15.73%）却比其他3种膜的都低,TiO₂与复合膜基质分子间形成强相互作用力,增强复合膜的拉伸强度;在相同波长下,TiO₂/琼胶-κ-卡拉胶复合膜的透光率比其他3种膜都低,在200~400 nm的紫外光区,TiO₂/琼胶-κ-卡拉胶复合膜的透光率明显低于其他3种膜,添加TiO₂的复合膜对紫外光有显著的屏蔽作用,但在600 nm波长处,不透明度（0.96）比其他3种膜都高;TiO₂/琼胶-κ-卡拉胶复合膜对水的阻抗性高于琼胶-κ-卡拉胶膜。     

Synthesis of nanocrystalline photocatalytic TiO2 thin films and particles using sol–gel method modified with nonionic surfactants

A simple sol–gel route has been developed for the preparation of nanocrystalline photocatalytic TiO₂ thin films and particles at 500 °C. The synthesis involved a novel chemistry method employing nonionic surfactant molecules as a pore directing agent along with acetic acid-based sol–gel route without direct addition of water molecules. This study investigated the effect of surfactant type and concentration on the homogeneity, morphology, light absorption, dye adsorption and degradation, and hydrophilicity of TiO₂ films as well as on the structural properties of the corresponding TiO₂ particles. The method resulted in the synthesis of mesoporous TiO₂ material with enhanced structural and catalytic properties including high surface area, large pore volume, pore size controllability, small crystallite size, enhanced crystallinity, and active anatase crystal phase. The prepared TiO₂ thin films were super-hydrophilic and possessed thermally stable spherical bicontinuous mesopore structure with highly interconnected network. Highly porous TiO₂ films prepared with polyethylene glycol sorbitan monooleate surfactant exhibited four times higher photocatalytic activity for the decoloration of methylene blue dye than the nonporous control TiO₂ films prepared without the surfactant. This sol–gel method modified with surfactant templates is useful in the preparation of nanostructured anatase TiO₂ thin films with high photocatalytic activity and desired pore structure.     

Preparation and antibacterial behavior of Fe-doped nanostructured TiO2 thin films

Fe³⁺-doped nanostructured TiO₂ thin films with antibacterial activity were prepared on soda–lime–silica glass slides by using sol–gel technology. Water containing Escherichia coli K-12 with TiO₂ thin films in was exposed to low intensity fluorescent light and antibacterial efficiency was evaluated with spread plate techniques. The films are porous and have anatase phase. Iron ions increased luminous energy utilization as the absorption edge of the Fe³⁺-doped film has a red shift compared to that of the pure TiO₂ film in the UV–VIS absorption spectrum. The bacterial removal efficiency reached 95% at the optimum concentration of iron ion (about 0.5% (mol)) after 120 min irradiation. The antibacterial behavior of the doped TiO₂ films was explicitly observed using scanning electron microscopy and cell wall damage was found.     

硅片上集成高介电调谐率的柱状纳米晶BaTiO3铁电薄膜

钛酸钡(BaTiO₃)具有优异的介电、铁电、压电和热释电等性能, 在微电子机械系统和集成电路领域具有广泛的应用。降低BaTiO₃薄膜的制备温度使其与现有的CMOS-Si工艺兼容, 已成为应用研究和技术开发中亟需解决的问题。本研究引入与BaTiO₃晶格常数相匹配的LaNiO₃作为缓冲层, 以调控其薄膜结晶取向, 在单晶Si(100)基底上450 ℃溅射制备了结构致密的柱状纳米晶BaTiO₃薄膜。研究表明：450 ℃溅射温度在保持连续柱状晶结构和(001)择优取向的前提下, 能获得相对较大的柱状晶粒(平均晶粒直径27 nm), 一定残余应变也有助于其获得了较好的铁电和介电性能。剩余极化强度和最大极化强度分别达到了7和43 μC·cm^-2。该薄膜具有良好的绝缘性, 在 0.8 MV·cm^-1电场下, 漏电流密度仅为10^-5 A·cm^-2。其相对介电常数ε_r展现了优异的频率稳定性：在1 kHz时ε_r为155, 当测试频率升至1 MHz, ε_r仅轻微降低至145。薄膜的介电损耗较小, 约为0.01~0.03 (1 kHz ~ 1 MHz)。通过电容-电压测试, 该薄膜材料展示出高达51%的介电调谐率, 品质因子亦达到17(@1 MHz)。本研究所获得的BaTiO₃薄膜在介电调谐器件中有着良好的应用前景。     

疏水耐环境型SiO2/TiO2/SiO2-TiO2太阳能宽光谱增透膜的制备及性能研究

利用TFCcal设计软件构建膜系结构, 采用溶胶-凝胶工艺和提拉法在超白玻璃上制备出厚度精确可控的宽光谱、高增透型SiO₂/TiO₂/SiO₂-TiO₂减反膜, 同时结合甲基三乙氧基硅烷(MTES)改性碱催化的SiO₂溶胶, 通过提拉法一次制备出高透过率疏水型薄膜。研究表明, 高增透型三层宽光谱减反膜的理论膜层厚度依次为: 80.9 nm(内层SiO₂-TiO₂)、125.0 nm(中间层TiO₂)、95.5 nm(外层SiO₂), 其在400~700 nm可见光范围内平均透过率实际可高达97.03%以上。多层膜经过退火处理后, 膜面的水接触角高达131.5°, 同时陈化两个月以后的多层膜透过率仅下降0.143%, 表明制备的SiO₂/TiO₂/ SiO₂-TiO₂多层减反膜具有优良的疏水和耐环境性能。     

Mg掺杂TiO2纳米晶光氧化还原染料的可逆颜色转变研究

由于非直接接触、远程控制、高效及快捷的优点, 光可逆颜色转换材料在信息存储、显示器件、传感器等领域有着重要应用。复合无机材料和有机材料, 实现协同增效, 是新型光驱动可逆颜色转换材料的研究热点之一。本研究采用一步液相合成法制备粒径约为5 nm的锐钛矿型Mg²⁺掺杂TiO₂纳米晶, 通过X射线衍射、透射电子显微镜、X射线光电子能谱、红外光谱和拉曼光谱等表征手段确认材料的组成结构, 并对比研究了Mg²⁺掺杂TiO₂对亚甲基蓝(MB)光可逆颜色转换性能的增强效应。结果表明, 掺杂Mg²⁺在TiO₂晶格中能产生杂质能级, 有效抑制了光生载流子的复合, 提高了TiO₂光氧化还原MB的活性; 另一方面, 掺杂Mg²⁺降低了TiO₂纳米晶的吸收波长, 在可见光照射下能够有效地抑制MB向还原态LMB的转变, 提高系统着色速率。这种基于碱金属掺杂TiO₂纳米晶的光可逆颜色转换材料在许多光电子器件领域具有潜在的应用价值。     

Successive deposition of layered titanium oxide/indium tin oxide films on unheated substrates by twin direct current magnetron sputtering

Layered titanium oxide/indium tin oxide (TiO₂/ITO) films were successively deposited on unheated glass substrates in situ using a twin direct current magnetron sputtering system. The layered TiO₂/ITO films exhibited a strongly polycrystalline structure that comprises anatase and rutile phases, as revealed by X-ray diffraction and Raman spectra. The X-ray photoelectron spectrum of Ti2p also verified the stoichiometric state of titanium oxide near the surface. The photo-induced hydrophilic properties of the films were determined from changes in the water contact angles under ultra-violet (UV) irradiation. The results revealed that the layered TiO₂/ITO films possessed a dissipated rate of 30% when they were stored in the dark for 12 h. This result shows that the layered TiO₂/ITO films acted as “electron pools” with an inherent energy storage capability. This unique property is attributable to the rougher surface and nearly porosity-free columnar structure, which is responsible for increased UV energy absorption and loss-free hole or electron transportation.     

钴掺杂TiO2纳米管阵列薄膜的制备及其光催化还原性能

用磁控溅射法在ITO玻璃基底上制备Ti-Co合金薄膜,对其阳极氧化处理制备出钴掺杂TiO₂纳米管阵列薄膜,研究了钴掺杂对纳米管阵列薄膜的形貌、结构、吸收光谱以及光催化还原性能的影响。结果表明：钴掺杂TiO₂纳米管阵列薄膜为锐钛矿相,管状阵列的管径均一、排列规整。钴掺杂使薄膜形成(001)择优取向。随着钴掺杂量的提高,薄膜吸收可见光的能力提高。钴含量(原子分数)为0.19%的薄膜光催化性能最优,可见光照150 min后对Cr(VI)的还原率可达98.4%。