Natural and persistent superhydrophilicity of SiO2/TiO2 and TiO2/SiO2 bi-layer films

Sol-gel SiO₂/TiO₂ and TiO₂/SiO₂ bi-layer films have been deposited from a polymeric SiO₂ solution and either a polymeric TiO₂ mother solution (MS) or a derived TiO₂ crystalline suspension (CS). The chemical and structural properties of MS and CS bi-layer films heat-treated at 500 °C have been investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscospy. Water contact angle measurements show that MS SiO₂/TiO₂ and CS TiO₂/SiO₂ bi-layer films exhibit a natural superhydrophilicity, but cannot maintain a zero contact angle for a long time over film aging. In contrast, CS SiO₂/TiO₂ bi-layer films exhibit a natural, persistent, and regenerable superhydrophilicity without the need of UV light. Superhydrophilic properties of bi-layer films are discussed with respect to the nature of the TiO₂ single-layer component and arrangement of the bi-layer structure, i.e. TiO₂ underlayer or overlayer.     

Flat epitaxial ferromagnetic CoFe2O4 films on buffered Si(001)

Ferromagnetic films of spinel CoFe₂O₄ have been grown epitaxially on Si(001) using CeO₂/YSZ double buffer layers. The heterostructures were built in a single process by pulsed laser deposition with real-time control by reflection high-energy electron diffraction. YSZ and CeO₂ grow cube-on-cube on Si(001) and CoFe₂O₄ grows with (111) out-of-plane orientation, presenting four in-plane crystal domains. The interface with the buffer layers is smooth and the CoFe₂O₄ surface is atomically flat, with roughness below 0.3 nm. The films are ferromagnetic with saturation magnetization around 300 emu/cm³. The properties signal that CoFe₂O₄ is a good candidate for monolithic devices based on ferromagnetic insulating spinels.     

SiO2/TiO2 multilayer films grown on cotton fibers surface at low temperature by a novel two-step process

A novel two-step process was developed to synthesize and deposit SiO₂/TiO₂ multilayer films onto the cotton fibers. In the first step, SiO₂ particles on cotton fiber surface were synthesized via tetraethoxysilane hydrolysis in the presence of cotton fibers, in order to protect the fibers against photo-catalytic decomposition by TiO₂ nanoparticles. In the second step, the growth of TiO₂ nanoparticles into the modified cotton fiber surface was carried out via a sol-gel method at the temperature as low as 100 °C. The as-obtained SiO₂/TiO₂ multilayer films coated on cotton fibers were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy and X-ray diffraction, respectively.     

Growth and structure characterization of epitaxial Bi2Sr2Co2Oy thermoelectric thin films on LaAlO3 (001)

Epitaxial Bi₂Sr₂Co₂O_y thin films with excellent c-axis and ab-plane alignments have been grown on (001) LaAlO₃ substrates by chemical solution deposition using metal acetates as starting materials. Microstructure studies show that the resulting Bi₂Sr₂Co₂O_y films have a well-ordered layer structure with a flat and clear interface with the substrate. Scanning electron microscopy of the films reveals a step-terrace surface structure without any microcracks and pores. At room temperature, the epitaxial Bi₂Sr₂Co₂O_y films exhibit a resistivity of about 2 mΩ cm and a seebeck coefficient of about 115 μV/K comparable to those of single crystals.     

A study of textured non-stoichiometric MoTe2 thin films used as substrates for textured stoichiometric MoS2 thin films

Textured MoTe₂ films have been prepared by sequential evaporation of the constituents followed by annealing under a tellurium pressure. The films are systematically textured with the c-axis of the crystallites perpendicular to the plane of substrate, however, the film composition is difficult to control and even after process optimization the films are tellurium deficient. This is thought to be caused by the electro negativity difference of the constituents.The textured MoTe₂ films have been used as substrates on which to grow MoS₂ films by annealing under a pressure of sulfur that allows textured MoS₂ films to be grown with good crystalline properties. The presence of sulfur at the surface and annealing under dynamic vacuum is important for this process and moreover, suppresses the superficial oxidation of the Mo and Te constituents.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

Study of the growth of CuAlS2 thin films on oriented silicon (111)

Within the chalcopyrite family the sulphur based compounds CuMS₂ (M = In, Ga, Al) have attracted much interest in recent years because they show a direct wide band-gap covering from E_gap = 1.53 eV (CuInS₂) over E_gap = 2.43 eV (CuGaS₂) to E_gap = 3.49 eV (CuAlS₂). Therefore they are particularly suitable for optoelectronic as well as photovoltaic applications. The CuAlS₂ semiconductor is one of these compounds and has good luminescent properties and a wide direct gap of 3.5 eV making it suitable for the use as material for light-emitting devices in the blue region of the spectrum. To dig up fully its potential a better understanding of the fundamental properties of the CuAlS₂ film itself is essential, which could be achieved from high-quality single-crystalline materials. So, the aim of this work has been to study the growth of multilayer CuAlS₂ thin films on Si(111) substrates at a substrate temperature of 723 K. One, two and three layers with 60, 120 and 180 nm thicknesses, respectively, were deposited on Si(111) substrate. The effect of the CuAlS₂ layer numbers on the structure, morphology and optical properties of the samples was investigated. The X-ray diffraction studies revealed that all the samples are polycrystalline in nature, single CuAlS₂ phase and exhibiting chalcopyrite structure with a preferred orientation along the (112) direction. However, the sample with three CuAlS₂ layers exhibit the highly oriented (112) plane with grain sizes of 80 nm. So we show that this experimental process affects significantly the structural properties of the CuAlS₂ films. Raman spectroscopic measurements indicated five prominent peaks at 193, 205, 325, 335 and 370 cm^− 1. The possible origin of the 370 cm^− 1 peak was investigated and was found to be some local vibration in the structure. The peaks at 193-205 and 335 cm^− 1 were ascribed to A₁ and B₂ modes, respectively.     

Single-step sputtered Cu2SnSe3 films using the targets composed of Cu2Se and SnSe2

Cu₂SnSe₃ thin films were prepared by single-step D.C. sputtering at 100-400 °C for 3 h using targets composed of Cu₂Se and SnSe₂ in three different ratios of 2/1 (target A), 1.8/1 (target B), and 1.6/1 (target C). The advantages of self-synthesized SnSe₂ instead of commercially available SnSe for depositing Cu₂SnSe₃ thin films were demonstrated. Effects of target composition and substrate temperature on the properties of Cu₂SnSe₃ thin films were investigated. Structure, surface morphology, composition, electrical and optical properties at different process conditions were measured. The 400 °C-sputtered films obtained from target B display with direct band gap of 0.76 eV, electrical resistivity of 0.12 Ω cm, absorption coefficient of 10⁴-10⁵ cm^− 1, carrier concentration of ∼ 1.8 × 10¹⁹ cm^− 3, and electrical mobility of 2.9 cm²/V s.     

N2 adsorption curve of mesoporous SiO2: A neglected characterization technique

Mesoporous SiO₂ sieve and SiO₂ nanoparticles were synthesized by a traditional method in the presence and absence of tri-block copolymer surfactant P123 as structure directed agent respectively. The characterization results show that the mesoporous SiO₂ sieve has larger specific area (789 m²/g) than SiO₂ nanoparticles (373 m²/g), and there exists a substantial difference in the N₂ adsorption curves between the two samples. A speculative scheme shows that the formation of bottleneck during the N₂ adsorption process of mesoporous SiO₂ sieve should be responsible for the phenomenon.     

纳米-Al2O3/SiO2加入量对MgO-Al2O3-SiO2复相陶瓷烧结机理的影响

为了探究纳米-Al₂O₃/SiO₂加入量对MgO-Al₂O₃-SiO₂复相陶瓷烧结行为的作用机理。以微米级MgO、纳米级Al₂O₃和SiO₂为主要原料制备陶瓷基复合材料。通过XRD和 SEM等检测手段对烧后试样的物相组成和微观结构进行测试与表征,重点研究Al₂O₃/SiO₂的加入对复相陶瓷物相组成、微观结构及烧结性能的影响。结果表明:随着Al₂O₃/SiO₂加入量的增大,试样烧后相对密度和烧后线变化率呈先增大后减小再增大的趋势,加入15%Al₂O₃/SiO₂(质量分数)的试样经1 500 ℃烧结后,其相对密度可以达到94%。引入的Al₂O₃/SiO₂与基体中的MgO生成镁铝尖晶石与镁橄榄石相,原位反应伴随的体积膨胀,抵消部分烧结过程中的体积收缩。Al₂O₃/SiO₂加入量为75%(质量分数)的试样经1 400 ℃烧结后,基体中有大量堇青石相生成,随着煅烧温度提高到1 500 ℃,堇青石分解所产生的高温液相促进了试样的烧结收缩。     

Preparation of CuAlO2 and CuCrO2 thin films by sol-gel processing

CuAlO₂ and CuCrO₂ thin films were prepared by sol-gel processing and subsequent thermal treatment in air and inert gas atmosphere. Resistivities of 700 Ω cm and 60 Ω cm with optical transmissions of 65% and 32% were achieved respectively. The crystallization temperature of 700 °C allows the preparation of CuCrO₂ on borosilicate glass. P-type conductivity was verified by Seebeck measurements and a transparent heterostructure including p-CuCrO₂ showed rectifying behavior.     

Organic/inorganic nanocomposite films based on poly(3-methoxythiophene) and WO3

Organic/inorganic nanocomposite films based on poly(3-methoxythiophene) (PMOT) and WO₃ were prepared by a consecutive two-step electrochemical method. The products were characterized in detail by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDS) and Fourier-transform infrared spectroscopies (FTIR). The results show that the PMOT/WO₃ nanocomposite films consist of two layers, the substrate WO₃ with 30 nm grains and superstratum PMOT, which average grain size is 60 nm. The obtained PMOT/WO₃ nanocomposite films were also characterized by cyclic voltammetry to investigate their electrochemistry properties which display significant enhancement of electrochemical activity than that of pure PMOT and WO₃ films.     

Characterization of stepwise flash-evaporated CuInSe2 films

CuInSe₂ (CIS) films were deposited by stepwise flash evaporation from polycrystalline powder source onto glass substrates held at various temperatures ranging from 100 to 560 K. The phase purity and microstructure were analyzed by transmission electron microscopy. The investigations show that films grown at 300 K and below were amorphous, whereas those grown at 370 K and above were polycrystalline in nature. The grain size in polycrystalline films were found to improve with increase in substrate temperature and during post-deposition annealing. The films had near stoichiometric composition as revealed by Rutherford backscattering spectrometry. Analysis of the optical transmittance spectra of CIS films deposited at 520 K yielded a value of ∼0.97 eV for the fundamental band gap.     

Cr-doped TiO2 thin films deposited by RF-sputtering

Cr-doped TiO₂ thin films with different band gaps were prepared. Higher Cr doping was beneficial to the formation of the rutile-TiO₂ phase over the anatase-TiO₂ phase. A 4.8% Cr-doped thin film indicated a band gap of 2.95 eV, which was lower than the band gap of the rutile-TiO₂. Cr doping was accompanied by the formation of not only the rutile-TiO₂ phase but also the Cr₂O₃ phase, lead to the degradation of the hydrophilicity. The TiO₂ thin films with the mixed phase were not desirable to improve the hydrophilicity.     

聚四氟乙烯/二氧化硅杂化材料的性能研究

为解决纳米粒子在聚四氟乙烯(PTFE)树脂中难分散均匀的问题,使用PTFE乳液通过原位溶胶-凝胶法(Sol-Gel)制备了聚四氟乙烯/二氧化硅(SiO2)杂化材料,并对其性能进行了表征与研究.研究表明:杂化材料的拉伸强度在SiO2含量为1.05%(记为FS-2)时达到最大值20.96 MPa,为纯PTFE的两倍;断裂伸长率随着SiO2含量的增加而降低,硬度逐渐升高,接触角由121°降至79°.由SEM结果发现,试样FS-2中SiO2的粒径仅为100 nm左右,但随着SiO2含量的增加,粒径变大.杂化材料的耐热性较PTFE有一定提高,当杂化材料中SiO2含量达到5.00%时,热分解温度由纯PTFE的503℃上升至528℃.     

Simulation of Si and SiO2 etching in CF4 plasma

The reactive ion etching (RIE) of Si and SiO₂ in CF₄ plasma is considered. The dependences of RIE rates of Si and SiO₂ on pressure have maxima due to the presence of single-atom vacancies. The RIE rates approach the maximum values at different pressures but at the same concentration of SiF and SiOF molecules in the adsorbed layer. Using the obtained results Si/SiO₂ etching selectivity is investigated.     

Oxide and interface charges in thin SiO2 films thermally grown on RF plasma hydrogenated silicon

A study of the defect centres, related to oxide charge and interface traps, induced in thin SiO₂ layer by technological procedures has been made. Thermal oxidation of Si was performed in dry O₂ at a temperature of 850°C. The Si cleaning procedures included dry hydrogen plasma treatment at different substrate temperatures and standard RCA wet cleaning. Characterization of defects was performed by analyzing the frequency dispersion of the capacitance-voltage characteristics. The origin of the defects was assessed by analysis of the IR spectra through computer simulation of the oxide structure and AFM images.     

Fe3Si nanodots epitaxially grown on Si(111) substrates using ultrathin SiO2 film technique

Ultrahigh density (> 10¹² cm⁻²) Fe₃Si nanodots (NDs) are epitaxially grown on Si(111) substrates by codeposition of Fe and Si on the ultrathin SiO₂ films with ultrahigh density nanovoids. We used two kinds of methods for epitaxial growth: molecular beam epitaxy (MBE) and solid phase epitaxy. For MBE, low temperature (< 300 °C) growth of the Fe₃Si NDs is needed to suppress the interdiffusion between Fe atoms deposited on the surfaces and Si atoms in the substrate. These epitaxial NDs exhibited the ferromagnetism at low temperatures, which were expected in terms of the application to the magnetic memory device materials.     

A model of the passivation of ultrathin SiO2 layer/Si substrate interfaces by atomic hydrogen from a thermalised plasma source

A theoretical model is developed to account for the kinetics of the decrease of the density of recombination active centres at the interface of SiO₂ layers with Si(111) substrates as a result of treatment by thermalised hydrogen plasma. The recombination active centres at the SiO₂/Si interface are ascribed to be the P_b centres. The model developed takes into account the kinetics of the incorporation of hydrogen atoms into the SiO₂ layer from the plasma source and their interaction with both passivated and unpassivated P_b centres. A special attention is given to ultrathin (∼2 nm) SiO₂ layers. A simplification of the general model to this important case allows one to obtain analytical solution for the density of unpassivated recombination active P_b centres as a function of the flow of hydrogen atoms from plasma, the initial density of P_b centres, and the treatment time. The model applicability is verified comparing the results of calculations with the experimentally measured values of the relative density of recombination active centres at the ultrathin SiO₂/Si(111) substrate interface upon passivation by atomic hydrogen from thermalised plasma source. A conformity of the model predictions to the experimental results is demonstrated.     

Preparation and characterization of NaSm9(SiO4)6O2 powders with infrared absorptive properties

NaSm₉(SiO₄)₆O₂ powders were synthesized by mild hydrothermal method at 180 °C for 24 h. The infrared optical properties and structure of the obtained powders were characterized. There existed two narrow and sharp absorptive bands near 943 cm^− 1 (10.6 μm). The band at 938 cm^− 1 was assigned to the stretching vibrations of SiOSm groups connecting to Q¹ species and the band at 989 cm^− 1 was attributed to the stretching vibrations of SiOSm groups linking with Q⁰ species. The reflectivity was lower than 1% from 900 to 1200 nm and reached the minimum of 0.46% at 1073 nm. The prepared powders exhibit potential to act as a new kind of absorptive material for the infrared light of 10.6 μm and 1.06 μm.