Nanocrystalline ruthenium oxide and ruthenium in sensing applications – an experimental and theoretical study

In this project, we have explored RuO₂ and Ru nanoparticles (∼ ∼10 and ∼ ∼5 nm, respectively, estimated from XRD data) to be used as gate material in field effect sensor devices. The particles were synthesized by wet chemical procedure. The capacitance versus voltage characteristics of the studied capacitance shifts to a lower voltage while exposed to reducing gases. The main objectives are to improve the selectivity of the FET sensors by tailoring the dimension and surface chemistry of the nanoparticles and to improve the high temperature stability. The sensors were characterized using capacitance versus voltage measurements, at different frequencies, 500 Hz to 1 MHz, and temperatures at 100–400°C. The sensor response patterns have been found to depend on operating temperature. X-ray photoelectron spectroscopy (XPS) analyses were performed to investigate the oxidation state due to gas exposure. Quantum-chemical computations suggest that heterolytic dissociative adsorption is favored and preliminary computations regarding water formation from adsorbed hydrogen and oxygen was also performed.     

First-principle study on the structural and electronic properties of H2S and SO2 adsorption on Pd-doped MoS2 monolayer

The partial discharge in SF₆-insulated equipment produces characteristic decomposition products: SO₂ and H₂S. The characteristic decomposition products vastly speed up the process of discharge faults. Based on density functional theory (DFT) calculation, single layer Pd-doped MoS₂ (Pd-MoS₂) is adopted as the adsorbent to adsorb SO₂ and H₂S to ensure the operational stability of SF₆-insulated equipment. The adsorption energy, charge transfer and structure parameters of SF₆, H₂S, and SO₂ adsorption on the Pd-MoS₂ monolayer are analysed to find the most stable adsorption structure. The molecular orbital theory, total density of states and partial density of states are studied to analyse the adsorption mechanism. The results show that Pd-MoS₂ adsorbent possesses high catalytic activity and excellent adsorption performance to H₂S and SO₂ by strong chemical adsorption. This study is of great significance to ensure the operational stability of SF6-insulated equipment by removing these characteristic decomposition products.     

ZnO thin film on side polished optical fiber for gas sensing applications

In this work, thin ZnO films have been produced by pulsed laser deposition on side-polished fiber for optical gas sensor applications. The influence was investigated of the processing parameters, such as substrate temperature and oxygen pressure applied during deposition, on the sensitivity to ammonia of the sensing element. A shift of the spectral position of the resonance minimum to the longer wavelengths was observed at room temperature for the sample prepared at 150 °C substrate temperature and 20 Pa oxygen pressure. Spectral changes in the range 0.16-1.13 nm for NH₃ concentrations between 500 and 5000 ppm were also observed.     

Theoretical study of molecular properties of low-lying electronic excited states of H2O and H2S

Geometries, excitation energies, dipole moments and dipole polarisability tensor components of the ground and four lowest excited states ³ B ₁, ¹ B ₁, ³ A ₂, ¹ A ₂ of the H₂O and H₂S molecules were calculated at the CASSCF, CASPT2, CCSD and CCSD(T) level of approximation. Vertical excitation and equilibrium transition energies of these states, having the Rydberg character, are reported too. Properties of both molecules in the ground and in low lying excited states are compared and discussed from the point of view of their molecular electronic structure. Upon excitation we observe dramatic changes of dipole moments and polarisabilities with respect to the ground state. We stress the change of the polarity of H₂O in all excited states accompanied by the enhancement of the dipole polarisability by an order of magnitude. Large, even if less pronounced, are changes of electric properties of H₂S in its excited states. Dipole moments and dipole polarisabilities of ³ B ₁, ¹ B ₁ states of H₂S and H₂O behave quite analogously in comparison to their respective ground state. The general pattern of properties for both molecules in their ³ A ₂ and ¹ A ₂ excited states is more different due to a pronounced participation of the sulphur d-orbitals in these states of the H₂S molecule.     

C27H28O5Br2S薄膜在氨蒸汽中的气敏透过光谱特性的研究

分析了溴百里酚蓝的气敏作用机理 ,介绍用涂膜法和喷膜法制备溴百里酚蓝气敏薄膜 ,并用单色仪测量溴百里酚蓝薄膜在氨蒸汽中气敏前后的光谱透过特性。     

Effect of crystallographic orientation on the anodic formation of nanoscale pores/tubes in TiO2 films

Self-organized nanopores and nanotubes have been produced in thin films of titanium (Ti) prepared using filtered cathodic vacuum arc (FCVA), DC- and RF-sputter deposition systems. The anodization process was performed using a neutral electrolyte containing fluoride ions with an applied potential between 2 and 20 V (for clarity the results are only presented for 5 V). Scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques were used to characterise the films. It was found that the crystallographic orientation of the Ti films played a significant role in determining whether pores or tubes were formed during the anodic etching process.     

ESR of Gamma Irradiated C2H204.2H2O Single Crystal

The gamma-irradiated samples of vacuumed powder and single crystal of C₂H₂O₄.2H₂O have been investigated by ESR method. the spectra of these single crystal and unvacuumed powder are attributed to R C HOH radical, but the peaks belonging to this radical in the gamma irradiated powder sample are not observed in the spectrum after having been vacuumed. After a and g tensor values of this radical have been calculated, it was observed to be anisotropic. At low temperature, a considerable change in the spectrum has not been observed.     

The location of excess electrons on H2O/TiO2(110) surface and its role in the surface reactions

Excess electrons play a key role in many of the properties of Titanium dioxide (TiO₂). Understanding their behaviour is important for improving the performance of TiO₂ in energy-related applications. Here, we describe a DFT + U study of the locations of the unpaired electron (UPE) on rutile TiO₂(110) (R-TiO₂(110)) surface and H₂O/R-TiO₂(110) surface. Our results show that the subsurface are preferred with R-TiO₂(110) surface. In contrast to previous studies, we find that the UPE tends to migrate to the surface H₂O-Ti_5c (the five-coordinated titanium (Ti_5c) at surface with H₂O adsorption) with the increasing of H₂O coverage and UPE concentration. In addition, we have shown that the UPE plays an important role in the O-H bond dissociation and other important elementary reactions in photo-catalytic H₂O dissociation on R-TiO₂(110) such as H, OH and H₂ desorption. Specifically, it enhances the O-H bond dissociation, as well as H and H₂ desorption from bridging hydroxyl and Ti_5c-OH (the Ti_5c with OH adsorption), but hinders the OH and H desorption from Ti_5c. We believe our results afford a further understanding of the adsorbent dependent UPE migration, and the role of UPE in the surface reactions.     

Substrate effects on the oxygen gas sensing properties of SnO2/TiO2 thin films

In this study, SnO₂/TiO₂ thin films are fabricated on SiO₂/Si and Corning glass 1737 substrates using a R.F. magnetron sputtering process. The gas sensing properties of these films under an oxygen atmosphere with and without UV irradiation are carefully examined. The surface structure, morphology, optical transmission characteristics, and chemical compositions of the films are analyzed by atomic force microscopy, scanning electron microscopy and PL spectrometry. It is found that the oxygen sensitivity of the films deposited on Corning glass 1737 substrates is significantly lower than that of the films grown on SiO₂/Si substrates. Therefore, the results suggest that SiO₂/Si is an appropriate substrate material for oxygen gas sensors fabricated using thin SnO₂/TiO₂ films.     

Investigations on Pd:SnO2/porous silicon structures for sensing LPG and NO2 gas

P-type porous silicon (PS) structure has been prepared by anodic electrochemical etching process under optimized conditions. Photoluminescence studies of the PS structure show emission at longer wavelengths (red) for the excitation at 365 nm. Scanning electron microscope investigations of the PS surface confirm the formation of uniform porous structure, and the pore diameter have been estimated as 25 μm. Pd:SnO₂/PS/p-Si heterojunction with top gold ohmic contact developed by conventional methods has been used as the sensor device. Sensing properties of the device towards liquefied petroleum gas (LPG) and NO₂ gas have been investigated in an indigenously developed sensor test rig. The response and recovery characteristics of the sensor device at different operating temperatures show short response time for LPG. From the studies, maximum sensitivity and optimum operating temperature of the device towards LPG and NO₂ gas sensing has been estimated as 69% at 180 °C and 52% at 220 °C, respectively. The developed sensor device shows a short response time of 25 and 57 s for sensing LPG and NO₂ gases, respectively. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Structure and optical anisotropy of pulsed-laser deposited TiO2 films for optical applications

The evolution of the crystal, the microstructural and the optical properties of pulsed-laser deposited TiO₂ films, investigated by X-ray diffraction, atomic force microscopy, scanning electron microscopy, optical transmittance and m-line spectroscopy measurements are reported. The samples were grown on (0 0 1) SiO₂ substrates at temperatures from 250 to 600 °C and oxygen pressures from 1 to 15 Pa. Crystalline films consisting of single anatase or anatase and rutile phases, were obtained at temperatures higher than 400 °C. A tendency toward columnar-like growth morphology was observed in the samples. Strong dependence of the optical properties on the surface roughness and the microstructure was determined. All films revealed single-mode waveguiding and optically anisotropic properties.     

TiO2 nanoparticle thin film deposition by matrix assisted pulsed laser evaporation for sensing applications

The MAPLE technique has been used for the deposition of nanostructured titania (TiO₂) nanoparticles thin films to be used for gas sensors applications. An aqueous solution of TiO₂ nanoparticles, synthesised by a novel chemical route, was frozen at liquid nitrogen temperature and irradiated with a pulsed ArF excimer laser in a vacuum chamber. A uniform distribution of TiO₂ nanoparticles with an average size of about 10 nm was deposited on Si and interdigitated Al₂O₃ substrates as demonstrated by high resolution scanning electron microscopy-field emission gun inspection (SEM-FEG). Energy dispersive X-ray (EDX) analysis revealed the presence of only the titanium and oxygen signals and FTIR (Fourier transform infra-red) revealed the TiO₂ characteristic composition and bond. A comparison with a spin coated thin film obtained from the same solution of TiO₂ nanoparticles is reported. The sensing properties of the films deposited on interdigitated substrates were investigated, too.     

CdTe太阳电池前电极SnO2:F/SnO2复合薄膜性能分析

减薄CdS窗口层是提高CdS/CdTe太阳电池转换效率的有效途径之一,减薄窗口层会对器件造成不利的影响,因此在减薄了的窗口层与前电极之间引入过渡层非常必要.利用反应磁控溅射法在前电极SnO₂:F薄膜衬底上制备未掺杂的SnO₂薄膜形成过渡层,并将其在N₂/O₂=4 ∶1,550 ℃环境进行了30 min热处理,利用原子力显微镜、X射线衍射仪、紫外分光光度计对复合薄膜热处理前后的形貌、结构、光学性能进行了表征,同时分析了复     

AgSbSe2 and AgSb(S,Se)2 thin films for photovoltaic applications

Silver antimony selenide (AgSbSe₂) thin films were prepared by heating sequentially deposited multilayers of antimony sulphide (Sb₂S₃), silver selenide (Ag₂Se), selenium (Se) and silver (Ag). Sb₂S₃ thin film was prepared from a chemical bath containing SbCl₃ and Na₂S₂O₃, Ag₂Se from a solution containing AgNO₃ and Na₂SeSO₃ and Se thin films from an acidified solution of Na₂SeSO₃, at room temperature on glass substrates. Ag thin film was deposited by thermal evaporation. The annealing temperature was 350 °C in vacuum (10⁻³ Torr) for 1 h. X-ray diffraction analysis showed that the thin films formed were polycrystalline AgSbSe₂ or AgSb(S,Se)₂ depending on selenium content in the precursor films. Morphology and elemental analysis of these films were done using scanning electron microscopy and energy dispersive X-ray spectroscopy. Optical band gap was evaluated from the UV-visible absorption spectra of these films. Electrical characterizations were done using Hall effect and photocurrent measurements. A photovoltaic structure: glass/ITO/CdS/AgSbSe₂/Al was formed, in which CdS was deposited by chemical bath deposition. J-V characteristics of this structure showed V_oc = 435 mV and J_sc = 0.08 mA/cm² under illumination using a tungsten halogen lamp. Preparation of a photovoltaic structure using AgSbSe₂ as an absorber material by a non-toxic selenization process is achieved.     

Nb/SnO2复合薄膜的制备、结构及光电性能

用溶胶-凝胶旋涂法在玻璃基底上制备出Nb/SnO₂复合透明导电薄膜,利用XRD,SEM,紫外—可见分光光度计,四探针电阻仪等测试方法对Nb/SnO₂复合薄膜的结构和物性进行了研究.结果表明: 当Nb含量小于0.99at%时,Nb/SnO₂复合薄膜为较纯的四方金红石结构;复合薄膜中晶粒分布均匀,平均尺寸在5—7 nm.当Nb含量小于0.99at%时,Nb/SnO₂复合薄膜的电阻率先减小后增大,当Nb含量为0.37at%时 关键词： 溶胶-凝胶法 2复合薄膜')" href="#">Nb/SnO₂复合薄膜 结构表征 光电性能     

Grain Size Effects in Sensor Response of Nanostructured SnO2- and In2O3-Based Conductometric Thin Film Gas Sensor

Based on the experimental results, obtained by studying both structural and gas-sensing properties of the SnO₂ and In₂O₃ films deposited by the spray pyrolysis method, we analyzed the influence of crystallite size on the parameters of the SnO₂- and In₂O₃-based thin film solid-state gas sensors. For comparison, the behavior of ceramic-type gas sensors was considered as well. In particular, we examined the correlation between the grain size and parameters of conductometric-type gas sensors such as the magnitude of sensor signal, the rate of sensor response, thermal stability, and the sensitivity of sensor signal to air humidity. Findings confirmed that that grain size is one of the most important parameters of metal oxides, controlling almost all operating characteristics of the solid state gas sensors fabricated using both the ceramic and thin film technologies. However, it was shown that there is no single universal requirement for the grain size, because changes in grain size could either improve, or worsen of operating characteristics of gas sensors. Therefore, the choice of optimal grain size should be based on the detailed consideration of all possible consequences of their influence on the parameters of sensors designed.     

Molecular Structures of H2X and D2X(X=0, S,Se, Te)

There are two possible configurations for H₂O, linear(D_∞h) or bent(C_2v). For a C_2v′, the three bands ν_1′ ν₂ and ν₃ should appear in both Raman and infrared. For a D_∞h. however, the ν₁, band should appear in only Raman and the ν₂ and ν₃ bands, in only infrared, that is, a principle of mutual exclusion of Raman and infrared should hold. The present author concludes that H₂X and D₂X(X=O, S, Se, Te) have a linear D_∞h. structure, since the obtained spectra show mutual exclusion of Raman and infrared.     

Application of gaseous sphere injection method for modeling under-expanded H2 injection

A methodology for modeling gaseous injection has been refined and applied to recent experimental data from the literature. This approach uses a discrete phase analogy to handle gaseous injection, allowing for addition of gaseous injection to a CFD grid without needing to resolve the injector nozzle. This paper focuses on model testing to provide the basis for simulation of hydrogen direct injected internal combustion engines. The model has been updated to be more applicable to full engine simulations, and shows good agreement with experiments for jet penetration and time-dependent axial mass fraction, while available – radial mass fraction data is less well predicted.