Sensitivity enhancement for H2 gas detection using a SnO2–Ag2O–PdOx nanocrystalline system

Thick film H₂ sensors were fabricated using SnO₂ loaded with Ag₂O and PdO_x. The composition that gave highest sensitivity for H₂ was in the wt.% ratio of SnO₂:Ag₂O:PdO_x as 93:5:2. The nano-crystalline powders of SnO₂–Ag₂O–PdO_x composites synthesized by sol–gel method were screen printed on alumina substrates. Fabricated sensors were tested against gases like H₂, CH₄, C₃H₈, C₂H₅OH and SO₂. The composite material was found sensitive against H₂ at the working temperature 125 °C, with minor interference of other gases. H₂ gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on SnO₂–Ag₂O–PdO_x nanocrystalline system exhibited high performance, high selectivity and very short response time to H₂ at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of H₂.     

Structural, electrical and optical characteristics of SnO2:Sb thin films by ultrasonic spray pyrolysis

Antimony-doped tin oxide (SnO₂:Sb) thin films were fabricated by an ultrasonic spray pyrolysis method. The effect of antimony doping on the structural, electrical and optical properties of tin oxide thin films were investigated. Tin(II) chloride dehydrate (SnCl₂·2H₂O) and antimony(III) chloride (SbCl₃) were used as a host and a dopant precursor. X-ray diffraction analysis showed that the non-doped SnO₂ thin film had a preferred (211) orientation, but as the Sb-doping concentration increased, a preferred (200) orientation was observed. Scanning electron microscopy studies indicated that the polyhedron-like grains observed for the non-doped SnO₂ thin films became rounder and decreased in size with the Sb-doping concentration. The lowest resistivity (about 8.4 × 10^− 4 Ω·cm) was obtained for the 3 at.% Sb-doped films. Antimony-doping led to an increase in the carrier concentration and a decrease in Hall mobility. The transmittance level in the near infrared region was lowered with the Sb-doping concentration.     

一步法制备纳米SnO-SnO2复合材料及其光催化性能增强机制的光生载流子动力学

半导体复合材料中的光生载流子动力学过程是影响其光催化性能的重要因素之一。该工作以二水合氯化亚锡（SnCl₂·2H₂O）为原料,NaOH为沉淀剂,采用一步溶剂热法制备了Sn的氧化物纳米SnO-SnO₂复合材料,并利用SEM、XRD、TEM和Uv-Vis光谱等对产物进行了表征。结果表明,通过控制反应条件可以获得粒径约为10~20 nm的SnO-SnO₂复合材料和粒径约为10 nm的四方相SnO₂颗粒,分散性较好。光催化性能研究表明,纳米SnO-SnO₂复合材料完全催化降解罗丹明B（RhB）的时间比纳米SnO₂颗粒减少50%。针对这一结果,利用瞬态表面光电压（TSPV）技术分别对上述纳米材料的光生载流子动力学过程进行了讨论。结果表明,纳米SnO-SnO₂复合结构的构建可以有效地促进光生载流子的分离,抑制SnO₂表面光生载流子的复合及提高材料表面的光生载流子的寿命,进而显著增强其光催化性能。     

Effect of SnO2 on the photocatalytical properties of TiO2 films

TiO₂/SnO₂ thin films with different tin atomic percentages were successfully prepared on glass substrates by the spray pyrolysis method from an alcoholic solution of TiO[C₅H₇O₂]₂ with different concentrations of SnCl₄. The TiO₂/SnO₂ thin films prepared at 450 °C presented the anatase phase in polycrystalline configuration from %Sn = 0 in the starting solution up to %Sn = 20, at higher tin content the films present an amorphous configuration. The resulting thin films have a homogeneous surface structure with some porosity. The photocatalytical properties of the films were evaluated with the degradation of methylene blue. The products of the degradation reaction were identified by ¹H nuclear magnetic resonance and the film properties were studied by atomic force microscopy, scanning electron microscopy, UV–Vis spectroscopy, and X-ray diffraction.     

Au修饰SnO2复合纳米材料的制备和气敏性能

以氯金酸和乙酰丙酮氯化锡为主要材料,通过一步水热法制备了SnO₂和Au修饰的SnO₂（Au/SnO₂）纳米粒子.使用TEM、EDS、XRD和XPS等手段对样品的形貌、组成及结构进行表征,研究了两种材料对乙醇的气敏性能.结果表明,两种纳米颗粒的尺寸都比较均一,平均直径约为9-12 nm;SnO₂为四方金红石结构,Au为面心立方结构;在Au/SnO₂样品中,Au与SnO₂的重量比为2.6%,Au元素主要以Au⁰的价态存在并含有少量的Au³⁺价态;与纯SnO₂纳米粒子相比,Au修饰可显著提高气敏元件对乙醇响应的灵敏度和选择性。     

SnO2修饰石墨毡电极的制备及其性能表征

采用H₂O₂对石墨毡（GF）进行预处理,然后在其表面电沉积Sn,最后在120℃烘箱氧化24 h制备出SnO₂修饰的石墨毡电极。通过扫描电镜（SEM）对SnO₂修饰前后的石墨毡表面形貌进行表征,采用循环伏安法研究了SnO₂修饰后石墨毡电极的电化学性能。结果表明：SnO₂能够均匀地包覆在石墨毡表面;SnO₂修饰石墨毡后V⁴⁺/V⁵⁺电对的氧化峰的峰电流由0.0538 A增加到0.0708 A,与未处理石墨毡相比增加了31.5%,反应峰出峰持续时间提高,说明SnO₂对V⁴⁺/V⁵⁺电对电极过程具有一定的催化作用。析氧电位由1.382 V增加到了1.517 V,使电极在VOSO₄溶液中的电化学窗口变宽。     

FeVO4/Cu3(BTC)2(H2O)3异质结制备及光催化性能

以Cu片和1, 3, 5-苯三甲酸为原料,电化学法制备经典Cu-MOF材料Cu₃(BTC)₂(H₂O)₃,即HKUST-1,作为基底金属有机框架材料(MOFs),采用室温沉积法制备FeVO₄/HKUST-1异质结复合材料,通过XRD、SEM、BET、UV-Vis DRS等对其晶体结构、形貌、比表面积、光吸收性能等进行了表征。结果表明:FeVO₄与HKUST-1复合形成异质结后,有利于光生电子-空穴的产生和转移,对目标染料污染物罗丹明B(RhB)的降解性能显著增强。可见光照射120 min后,异质结体系中RhB的降解率可达93%,而单一FeVO₄或HKUST-1体系中仅为12%和5%。此外,对材料的组成比例进行了优化,当FeVO₄与HKUST-1摩尔比为1∶1时,制备的FeVO₄/HKUST-1复合材料具有最佳的光催化性能。进一步,考察了其循环使用的稳定性,循环5次后对RhB的降解效率仍保持在90%以上,稳定性良好。      

Flame spray synthesis of ZrO2 nano-particles using liquid precursors

This paper studies the feasibility of using flame spray to produce ZrO₂ nano-particles using a liquid precursor. The effects of varying precursor concentrations and ratio of diluting medium on the phase composition, size and morphology of ZrO₂ nano-particles are discussed. The morphology and size of the ZrO₂ nano-particles was very much dependent on the precursor concentration. The solvent ratio of H₂O:ethanol also played a part in determining the characteristics of the ZrO₂ nano-particles. The nano-particles had the best characteristics when the precursor concentration was low and ethanol (added as solvent) content was high. In particular, the best characteristics were obtained using precursor concentration of 0.25 M, H₂O:ethanol ratio of 0:1. The nano-particles had very small particle size (50 nm), relatively high specific surface area (28.6 m²/g) and high degree of crystallinity. However, particles synthesized tend to be agglomerated.     

Effect of N2O/SiH4 ratio on the properties of low-temperature silicon oxide films from remote plasma chemical vapour deposition

Silicon oxide films have been deposited with remote plasma chemical vapour deposition (RPCVD) at low temperatures (<300 °C) from SiH₄---N₂O. The effect of a gas-phase reaction on the SiO₂ film properties and Si/SiO₂ interface was investigated. As the partial pressure ratio was increased above N₂O/SiH₄ = 4, a gas-phase reaction with powder formation was observed, which degraded film properties, increased surface roughness, and decreased deposition rate. When N₂O/SiH₄ <4, there was no detectable IR absorption in the film associated with hydrogen-related bonds (Si---OH and Si---H) but when N₂O/SiH₄ >4, the incorporation of Si---OH bond became significant and Si¹⁺, intermediate state silicon at the interface, was more abundant. The oxide fixed charge, interface trap density, surface roughness and leakage current were increased when there was powder formation in the gas phase. High plasma power also favoured the powder formation in the gas phase. C---V and I---V characteristics were measured and it was shown that these electrical properties were directly related to the process condition and material properties of the oxide and the Si/SiO₂ interface.     

Effect of preparation conditions on properties of atomic layer deposited TiO2 films in Mo–TiO2–Al stacks

TiO₂ films were grown by atomic layer deposition on Mo electrodes in order to elucidate the dominating conductance mechanism and its dependence on the growth chemistry. TiCl₄ and Ti(OC₂H₅)₄ served as titanium precursors, and H₂O or H₂O₂ as oxygen precursors. The films grown at lower temperatures were amorphous. With increasing growth temperatures the crystallization first started in the TiCl₄–H₂O process. The films grown in this process were clearly leakier compared to the films grown from Ti(OC₂H₅)₄ and H₂O and from Ti(OC₂H₅)₄ and H₂O₂. In the Ti(OC₂H₅)₄-based processes, the application of H₂O₂ instead of H₂O resulted in the films with considerably lowered conductivity, although structural differences in these films were insignificant. Space–charge-limited currents were prevailing in all our amorphous Mo–TiO₂–Al packages. Measurements at different temperatures suggested quite high trap densities likely due to the presence of impurities and structural disorder, while the strong differences in conductivity seemed to be due to different densities of gap states.     

模板剂F127对介孔SnO2的孔结构及电化学性能的影响

以SnCl₄·5H₂O和尿素为原料, 嵌段聚醚F127(EO₁₀₆-PO₇₀-EO₁₀₆)为模板剂, 通过水热法制备了介孔SnO₂材料。XRD、TEM和BET等分析结果表明, 模板剂F127添加量对介孔SnO₂的孔结构有重要影响。F127添加量增加, SnO₂比表面积增大, 孔容增大, 孔径分布变宽。电化学测试结果表明, 介孔的存在不仅能为锂离子脱嵌提供通道, 而且可以缓冲SnO₂的体积膨胀, 从而提高介孔SnO₂负极材料的电化学性能; 当F127添加量为6.0 g时, 所制备SnO₂具有124 m²/g的比表面积, 平均孔径为4.94 nm, 表现出最佳的循环性能和倍率性能, 在60 mA/g的电流密度下经30次循环后, 其可逆容量仍保持在434 mAh/g; 循环伏安测试表明部分高活性Li₂O的可逆还原提供了附加的可逆容量。     

Atmospheric plasma discharge chemical vapor deposition of SnOx thin films using various tin precursors

A series of 0.2–0.6 μm thick SnO_x films were deposited onto borosilicate and sodalime silica glass substrates by atmospheric plasma discharge chemical vapor deposition at 80 °C. SnO_x films deposited from monobutyltin trichloride contained a large percentage of SnCl₂:2H₂O, and therefore were partially soluble in water. SnO_x coatings deposited from tetrabutyltin were not soluble in water or organic solvents, had good adhesion even at growth rates as high as 2.3 nm/s, had high transparency of  90% and electrical resistivity of 10⁷ Ω cm. As-grown tin oxide coatings were amorphous with a small concentration of SnO₂, SnO and Sn crystalline phases as determined by grazing angle X-ray diffraction and X-ray photoelectron spectroscopy measurements. Upon annealing in air at 600 °C the resistivity of SnO_x films decreased to 5–7 Ω cm. Furthermore, optical and X-ray measurements indicated that SnO_x was converted into SnO₂ (cassiterite) with a direct band gap of 3.66 eV. Annealing of as-grown SnO_x films in vacuum at 340 °C led to formation of the p-type conductor SnO/SnO_x. The indirect band gap of SnO was calculated from the optical spectra to be 0.3 eV.     

Hydrogen-radical durability of TiO2 thin films for protecting transparent conducting oxide for Si thin film solar cells

Hydrogen-radical durability of TiO₂ thin films has been investigated under conditions for preparing Si thin film solar cells by catalytic chemical vapor deposition method. It is found that the composition and the optical transmittance of TiO₂ films are almost the same before and after hydrogen-radical exposures with a filament temperature at approximately 1700 °C and a H₂ pressure of approximately 133 Pa. The durability of TiO₂ film has also been observed even under the condition with higher hydrogen-radical density under a filament temperature at approximately 1900 °C, in which SnO₂ and ZnO are easily deoxidized. The application of TiO₂ film as a protecting material of transparent conducting oxide film for Si thin film solar cells are discussed by the hydrogen-radical durability and fundamental properties of TiO₂ thin film.     

Corrosion resistant coatings (Al2O3) produced by metal organic chemical vapour deposition using aluminium-tri-sec-butoxide

The metal organic chemical vapour deposition (MOCVD) of amorphous alumina films on steel was performed in nitrogen at atmospheric pressure. This MOCVD process is based on the thermal decomposition of aluminium-tri-sec-butoxide (ATSB). The effect of the deposition temperature (within the range 290–420 °C), the precursor vapour pressure (5.33×10^-3−2.67×10^-2 kPa), and the gas flow (6.5−12.5 1 min^-1) of the MOCVD process have been studied in relation to corrosion properties at high temperatures. The corrosion experiments were performed at 450 °C in a gas atmosphere containing 1% H₂S, 1% H₂O, 19% H₂, and balanced Ar.

It was found that the amount of corrosion products on an alumina film (0.20±0.05 mg cm^-2)-AISI 304 combination decreased with increasing deposition temperature of the coating. This was more pronounced for the products formed through the coating owing to a certain porosity. The crack density, where products were also formed, was almost unaffected.     

Porous SnO2 sputtered films with high H2 sensitivity at low operation temperature

Undoped and Pd-doped SnO₂ films were deposited at various substrate temperatures and discharge gas pressures using reactive magnetron sputtering. Structural factors of the films, such as crystallite size, grain size, and film density, were systematically investigated. The main objectives of this study are to clarify the operation temperature dependence of the H₂ sensitivity of these films as well as to clarify the dominant structural factor in the determination of the sensitivity. The operation temperature at which the sensitivity defined by (R_a−R_g)/R_g, where R_a and R_g are the resistances before and after exposure to H₂, showed a maximum decreased with decreasing film density. The highest sensitivity of 4470 was obtained for a Pd-doped film with the lowest density of 3.1 g/cm³ at 100 °C. It was found that the sensitivity correlated with film density rather than with crystallite size and grain size. The high sensitivity of a Pd-doped porous film at a low temperature was discussed in relation to the Schottky-barrier-limited transport as well as the chemical and electronic effects of Pd.     

Properties of thin In2O3 and SnO2 films prepared by corona spray pyrolysis, and a discussion of the spray pyrolysis process

Thin films of doped In₂O₃ and SnO₂ were prepared by the “corona spray pyrolysis” technique with a deposition efficiency of 80%. The electrical and optical properties of the films were determined. A transmission of 88% in the visible region and an IR reflection of more than 90% were the maximum values obtainable for a doped In₂O₃ film.

A detailed discussion of the physical and chemical processes that occur during spray pyrolysis is presented to aid the understanding of this coating technique.

A minimum temperature of about 350°C for the formation of In₂O₃ was empirically confirmed.

Furthermore the powdery precipitate obtained during deposition of In₂O₃ was clearly identified as polycrystalline In₂O₃ formed by a homogeneous reaction.     

MgCl2对锌在干湿交替环境中腐蚀行为的影响

使用腐蚀失重、X射线衍射(XRD)、扫描电子显微镜与能谱(SEM-EDS)等手段研究了干湿交替环境中MgCl₂对锌腐蚀行为的影响。结果表明,MgCl₂对锌的腐蚀有显著的抑制作用;在沉积NaCl条件下锌表面的腐蚀产物为Zn₅(OH)₈Cl₂·H₂O、Zn₄CO₃(OH)₆·H₂O和Zn(OH)₂,而在沉积MgCl₂条件下锌表面的腐蚀产物只有Zn₅(OH)₈Cl₂·H₂O。在干湿交替环境中MgCl₂对锌腐蚀行为的影响主要是Mg²⁺与氧还原反应产生的OH^-结合使阴极区的pH值降低造成的。     

Lithographic patterning of benzoylacetone modified SnO2 and SnO2:Sb thin films

The synthesis of directly UV-photopatternable pure and antimony-doped organo-tin materials is presented. UV-photopatternability has been achieved by using the synthesized benzoylacetone modified tin and antimony 2-isopropoxyethoxides. Photopatterned pure and antimony-doped organo-tin films are crystallized by thermal annealing in order to obtain conductive SnO₂ and Sb:SnO₂ thin films. The molar ratio between benzoylacetone and metal alkoxides has to be 2 in order to obtain crack-free, good-quality structures. The effects of UV-irradiation, increasing antimony doping level and benzoylacetone concentration on the electrical properties of the single-layered films are analyzed. The highest obtained conductivity was 20 S/cm. Benzoylacetone concentration and UV-irradiation has only a negligible effect on the film electrical conductivities.     

Preparation of SiO2 thin films using the Cat-CVD method

Using the catalytic chemical vapor deposition (Cat-CVD) method, a-Si and SiN_x films have been the main focus of studies. SiO₂ films have not been studied because of the limited life of catalysts such as tungsten or molybdenum in an oxidative atmosphere. In this report, we describe oxide film preparation using an iridium catalyst. We determined the most appropriate catalyst material for the oxide film process by exposing heated materials in tetraethoxysilane (TEOS) or O₂ gas. As the result, it was confirmed that the Ir catalyst works in a slow oxidative atmosphere. Using the Ir catalyst, SiO₂ films were deposited in two gas combinations: TEOS and N₂O, and SiH₄ and N₂O. Although the SiO₂ film processed with the combination of TEOS and N₂O was stoichiometric, its breakdown voltage is not sufficient. The SiO₂ film processed with the combination of SiH₄ and N₂O showed good electrical property.     

Effect of CH4 and H2 on CVD of SiC and TiC for possible fabrication of SiC/TiC/C FGM

SiC and TiC coatings were deposited by CVD on graphite substrates and the effect of the variation of the methane (CH₄) and hydrogen (H₂) ratio on deposition was investigated. SiCl₄, TiCl₄ and CH₄ were used as sources of Si, Ti and C. In case of the SiC coatings, stoichiometric SiC was obtained when the ratios of CH₄/(SiCl₄ + CH₄)andH₂/(SiCl₄ + CH₄) are 0.4 and 10, respectively. Stoichiometric TiC was also obtained under similar conditions. In order to obtain non-stoichiometric materials for possible fabrication of functionally gradient materials (FGM), a change of microstructure and composition was observed with changes of the CH₄ and H₂ ratio. As a result, SiC, TiC and C contents were more easily controlled by a change of the H₂ ratio compared to the CH₄ ratio for SiC and TiC deposition. It has been verified that the change of the H₂ ratio is more desirable for possible manufacturing of SiC/TiC/C FGM.