Development of NiO-based thin film structures as efficient H2 gas sensors operating at room temperatures

P-type NiO thin films have been developed on high resistivity Si and SiO₂ substrates by a pulsed laser deposition technique using an ArF^? 193 nm excimer laser at deposition temperature of 300 °C and in 40 Pa partial oxygen pressure. Structures based on such NiO films as host material in the form of Au-NiO Schottky diodes have been subsequently developed under vacuum. In a different procedure, an n-SnO₂ layer has been deposited by a CVD technique on a NiO film to produce a p/n heterojunction. The sensing properties of all above structures have been tested upon exposure to a H₂ flow in air ambient gas at various operating temperature ranging from 30 to 180 °C. For the NiO films, the optimum temperature was about 150 °C exhibiting a sensitivity of 94%. After surface sensitization of NiO by Au the NiO films showed an H₂ response at operating temperature of 30 °C. The sensitivity of p-NiO/n-SnO₂ heterojunction devices was extracted from I-V measurements in air and under H₂ flow mixed in air. In this case a dramatic increase of the sensitivity was achieved at operating temperature of 30 °C for a forward bias of 0,2 V.     

Frictional properties of an immobilized fluorinated polymer nanosheet

The frictional properties of an immobilized fluorinated polymer nanosheet were investigated to develop an ultrathin solid lubrication film with an excellent wear-resistant. N-(1H,1H-Pentadecafluorooctylmethacrylamide) copolymers containing carboxyl group as a reactive moiety form a stable monolayer on the water surface and a highly ordered reactive fluorinated polymer nanosheet can be fabricated by the Langmuir-Blodgett technique. The reactive fluorinated polymer nanosheet was immobilized onto solid substrates through chemical binding with an aminosilane coupling agent, and the film showed smooth surface even after the reaction. The immobilized fluorinated polymer nanosheet had a low friction coefficient and strong wear-resistant.     

Influence of doping concentration on the properties of ZnO:Mn thin films by sol-gel method

Thin films of Mn-doped ZnO with different doping concentration (0.8, 1, 3, 5 at%) were prepared on Pt/Ti/SiO₂/Si substrates by using sol-gel method. The effects of the doping concentration on the structural properties, electrical characteristics and element binding energy in films were investigated. X-ray diffraction (XRD) results showed that the c-axis orientation of ZnO films was affected by Mn²⁺ content. Current-voltage (I-V) measurements indicated that resistivities of ZnO films were observably enhanced by dopant of Mn²⁺ and the resistivities value increased with a doping level up to 5 at% Mn. X-ray photoelectron spectroscopy (XPS) patterns suggested that the binding energies of O1s and ZnL₃M₄₅M₄₅ were affected by the content of Mn²⁺.     

Thermal stability of advanced gate stacks consisting of a Ru electrode and Hf-based gate dielectrics for CMOS technology

Metallic Ru and Hf-based dielectrics such as HfO₂, HfSiO_x and HfSiON, are promising materials for the gate electrode and gate dielectrics, respectively. This paper reports on the thermal stability of gate stack systems comprised of Ru/Hf-based dielectrics. Layers of both types of material were prepared on Si substrate by metal-organic chemical vapour deposition (MOCVD). The stacks underwent exposure by rapid thermal annealing (RTA) in pure nitrogen ambience at temperatures 800, 900, and 1000 °C for 10 s. The samples were analysed using Rutherford backscattering spectrometry (RBS). Small changes were found in the stacks treated at 800 and 900 °C. The most stable stack was found to be one with a HfSiON dielectric layer, which was resistant also at temperature 900 °C. However, the annealing at 1000 °C induced massive diffusion at both interfaces for all types of stack. The results imply a limited thermal stability of the Ru/Hf-based dielectric gate stacks during the source/drain activation step.     

镁合金表面Ti—TiN复合镀层的阴极多弧离子制备与表征

表面强化、耐蚀处理对镁及其合金的应用至关重要。采用阴极多弧离子镀膜技术，在AZ91C镁合金基底上首次成功镀制了强结合力的以Ti为过渡层的TiN复合膜层，并利用高分辨扫描电子显微镜（SEM）、X射线能谱仪（EDS）、CSM显微划痕测试等技术对复合膜层的形貌、组织结构及性能进行分析研究。结果表明，采用适当的多弧离子镀膜工艺，能在经恰当预处理方法处理的镁舍金基底上制备性能良好的TiN膜。膜层均匀、致密，膜基结合力达130mN以上，复合硬度达500HV左右（AZ91镁合金基底125HV）。此外中性盐雾强化实验表明，经该方法处理后的镁合金在ASTM-B117标准测试条件下，腐蚀速度明显降低，经过200h后，表面无明显腐蚀现象。真空多弧离子镀膜技术有望在镁合金表面防护领域得到应用。     

Electrochemical investigation and characterization of thin-film porosity

In thin-film applications it is necessary to control film properties such as homogeneity and porosity to obtain high-quality coatings. Electrochemistry can be a very helpful tool since it can provide information about processes taking place at the interface between substrate and coating. Different thin carbon-based coatings were deposited via physical vapour deposition methods and vapour phase polymerization on pure iron substrates: fullerene films, which were modified by an ion bombardment and thin films of poly(p-xylylene), which is a very good insulating polymer. The film porosity and stability of the film/substrate system against aqueous corrosion were investigated and compared using cyclic voltammetry. The dependence of porosity and film stability on various deposition process parameters such as film thickness and plasma conditions was measured via the dissolution current density and the open circuit potential shift of the substrate material. It could be shown that the two measurements, current density I_crit. and open circuit potential E_ocp. can provide useful complementary information about film porosity that can lead to a better understanding of the coatings properties and the deposition process as well.     

Dependence of target-substrate distance on crystallographic and optical properties of WO3 films prepared by reactive radio frequency magnetron sputtering

WO₃ films were deposited on glass substrates using radio frequency magnetron sputtering in a mixed gas of 80%Ar-20%O₂. From the X-ray diffraction patterns, the WO₃ films deposited at source to substrate distance (D_T-S) of 40 mm were polycrystalline, crystallizing in the monoclinic crystal structure, with highly preferred c-axis orientation perpendicular to the film plane. On the other hand, amorphous films were observed in the WO₃ films deposited at 70 mm. The crystallite sizes of the WO₃ films deposited at D_T-S of 40 mm were larger for films deposited at lower working gas pressures (P_W). The optical absorption edge of the films shifted to shorter wavelength region with increase in P_W irrespective of the D_T-S. The oxygen deficient films are obtained when the films are deposited at D_T-S of 40 mm and P_W of 0.3 Pa and stoichiometric films are formed at higher P_W. The photocatalytic oxidation of methanol proceeds via CO and formaldehyde as the intermediate species on WO₃/TiO₂ bilayer films and CO₂ is identified as the final product.     

Effects of periodicity and oxygen partial pressure on the crystallinity and dielectric property of artificial SrTiO3/BaTiO3 superlattices integrated on Si substrates by pulsed laser deposition method

Epitaxial SrTiO₃(STO)/BaTiO₃(BTO) artificial superlattices have been grown on TiN buffered Si (001) substrates by pulsed laser deposition method and the effects of stacking periodicity and processing oxygen partial pressure on their crystallinity and dielectric properties were studied. The crystal orientation, epitaxy nature, and microstructure of STO/BTO superlattices were investigated using X-ray diffraction and transmission electron microscopy. The TiN buffer layer and superlattice thin films were grown with cube-on-cube epitaxial orientation relationship of [110](001)_films∣∣[110](001)_TiN∣∣[110](001)_Si. The c-axis lattice parameter of the STO/BTO superlattice decreased from 0.412 nm to 0.406 nm with increasing oxygen partial pressure and the dielectric constants, measured at the frequency of 100 kHz at room temperature, of the superlattices with 2 nm/2 nm periodicity increased from 312 at 1 × 10^− 5 Torr to 596 at 1 × 10^− 3 Torr. The dielectric constants of superlattices grown at oxygen partial pressure of 1 × 10^− 3 Torr increased from 264 to 678 with decreasing periodicity of the superlattices from 10 nm/10 nm to 1 nm/1 nm.     

Effect of lattice-mismatch strain on the structural and dielectric properties of (Pb,Sr)TiO3 thin films grown by pulsed laser deposition

Pb_0.35Sr_0.65TiO₃ (PST) thin films have been fabricated on LaAlO₃ (LAO) and MgO substrates using the pulsed laser deposition technique. The microstructure characteristics of the films were examined by means of X-ray diffraction, atomic force microscopy, scanning electron microscopy and Raman spectroscopy, and the results indicate that the films are epitaxially grown and show good crystallinity. The dielectric constant dependence on DC bias voltage and temperature were measured in a planar capacitor configuration for these films. Compared to the PST thin film grown on LAO, the film grown on MgO showed a higher temperature of the capacitance maximum and a higher dielectric constant at zero bias. We explain the results by taking into account the lattice-mismatch strain between the substrate and the film. In contrast to the in-plane compressive strain induced by the LAO substrate, the in-plane tensile strain induced by the MgO substrate enlarges the unit cell of PST and enhances the magnitude of dipole moments, which increases the dielectric constant. These results indicate that a reasonable in-plane tensile strain could improve the dielectric properties of PST thin films.     

P型透明导电氧化物LaCuOS的研究进展

透明导电氧化物半导体的出现开拓了光电子器件研究的新领域，但是缺少性能良好的P型材料就限制了透明导电氧化物的利用空间。LaCuOS由于其结构、电学和光学等方面具有许多的优点，成为近年来P型半导体的研究热点。介绍了P型LaCuOS薄膜的基本性质，综述了不同的制备工艺并对其光电学与应用方面进行了研究总结。