液态金属汞在硅片表面的润湿行为研究

针对常温下的液体在固体表面的润湿行为研究。以液态金属汞为研究对象,采用真空等离子体刻蚀工艺制备不同表面形貌的硅片,研究不同硅片的润湿行为,并探究了液滴体积对润湿性的影响。利用金相电子显微镜、白光干涉三维形貌仪以及接触角测量仪分别对不同硅片的表面形貌、表面粗糙度以及润湿行为进行了测量与表征。结果表明:当液滴体积相同时,随硅片表面粗糙度Sa增大,接触角增大;当液滴体积为1μL,表面粗糙度为257.01μm时,测得静态接触角达到最大,为158.3°;而在同一形貌的硅片表面,当液滴体积由1增加到4μL时,硅片表面的接触角呈现逐渐减小的趋势,在致密的网状结构硅片表面,接触角减小的幅度最大,达到11.6°。为今后研究汞在不用材料表面的润湿行为具有一定的参考意义。     

The surface free energy of pyrite films prepared by sulfurizing the precursive electrodeposited films

The pyrite films were prepared by sulfurizing the precursive films at different temperatures. The microstructure, chemical compositions and surface free energy have been investigated. The results indicate that pyrite films are obtained after the sulfuration process of precursive films. The sulfuration temperature remarkably influences the contact angle. Using Owens and Wendt geometric mean approach, the surface free energy, the dispersive surface free energy and polar surface free energy can be evaluated based on the value of contact angles. It has been found that the surface free energy is significantly dependent on the sulfuration temperature and chemical compositions of films. With the increase of the sulfuration temperature, the dispersive surface free energy decreases but the polar surface free energy keeps basically invariable. A possible relationship between the surface free energy and film quality has been discussed.     

A novel cylindrical punch method to characterize interfacial adhesion and residual stress of a thin polymer film

Adhesion of a pre-stressed silicone rubber film to a planar graphite surface was investigated by a new cylindrical punch method. A homemade apparatus was constructed to meet force and displacement resolutions of 0.1 μN and 10 nm. When the punch approached the intersurface force range across the punch-film gap, the film jumped into contact at “pull-in”. Upon unloading, once the tensile load reached a threshold, a spontaneous delamination occurred at “pull-off” with a non-zero contact circle. A theoretical model was constructed based a simple energy balance. The new method can be used to characterize an adhesion interface between a pre-stressed free-hanging film and a rigid substrate.     

A new experiment for investigating evaporation and condensation of cryogenic propellants

Passive and active technologies have been used to control propellant boil-off, but the current state of understanding of cryogenic evaporation and condensation in microgravity is insufficient for designing large cryogenic depots critical to the long-term space exploration missions. One of the key factors limiting the ability to design such systems is the uncertainty in the accommodation coefficients (evaporation and condensation), which are inputs for kinetic modeling of phase change.A novel, combined experimental and computational approach is being used to determine the accommodation coefficients for liquid hydrogen and liquid methane. The experimental effort utilizes the Neutron Imaging Facility located at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland to image evaporation and condensation of hydrogenated propellants inside of metallic containers. The computational effort includes numerical solution of a model for phase change in the contact line and thin film regions as well as an CFD effort for determining the appropriate thermal boundary conditions for the numerical solution of the evaporating and condensing liquid. Using all three methods, there is the possibility of extracting the accommodation coefficients from the experimental observations. The experiments are the first known observation of a liquid hydrogen menisci condensing and evaporating inside aluminum and stainless steel cylinders. The experimental technique, complimentary computational thermal model and meniscus shape determination are reported. The computational thermal model has been shown to accurately track the transient thermal response of the test cells. The meniscus shape determination suggests the presence of a finite contact angle, albeit very small, between liquid hydrogen and aluminum oxide.     

Combinatorial approach to the edge delamination test for thin film reliability—adaptability and variability

We have demonstrated the adaptability and variability of a newly developed combinatorial edge delamination test. This was accomplished through studying the effect of substrate surface energy on the adhesion of thin films. In this combinatorial approach, a library (a single specimen) was fabricated with a polymethyl methacrylate (PMMA) film on a silicon substrate. The film has thickness gradient in one direction and the substrate has an orthogonal surface energy gradient. The thickness gradient was produced with a flow coating technique, and the surface energy gradient was controlled by partial oxidation of an alkylsilane layer on a silicon wafer. Applying a constant temperature to the specimen, interfacial debonding events were observed and a distribution of failure was constructed. Our results demonstrate the proposed combinatorial methodology for rapidly and efficiently evaluating the adhesion of general film/substrate systems as a function of many controllable parameters. In addition, this methodology can be used to predict the reliability distributions of the adhesion for practical parameters.     

Surface characterisation and functionalisation of indium tin oxide anodes for improvement of charge injection in organic light emitting diodes

Wettability studies have been performed to probe the surface properties of ITO substrates, aimed to be used as hole injecting electrode in OLEDs. The elimination of organic contaminants upon the cleaning treatment (ultrasonic bath in organic solvents) leads to an increase of the free energy of the ITO surface becoming hydrophilic. The surface energy components calculated from the Van Oss model show the appearance of a basic component upon the cleaning treatment. A thermal treatment at 100 °C for 3 h leads to a decrease of the surface free energy due to surface dehydration. These properties are attributed to the hydroxides formed at the ITO surface inducing improved adhesion at the ITO/polymer interface. The ITO surfaces have been functionalised with a chloroethylphosphonic acid mono-layer to increase their stability. The appearance of an acid-base component leads to a dipolar character of the ITO surface. The formation of a compact layer of a spin coated poly(phenylenevinylene) derivative induces the shielding of the ITO basic character. The weakening of the near infrared absorption associated to ITO free carriers confirms the formation of a dipole layer at the interface with the molecular layer in contact with ITO. Improved injection properties, shown by the current/voltage characteristics, result from the interface modifications.     

Preparation of defined bulk densities for using the capillary rise method in the case of fine powders

The wetting properties of powders are important in many technological processes. Contact angles can be characterized by an effective contact angle of the particle arrangement relative to the wetting liquid, but their quantification is problematic. An exact determination depends on an accurate preparation of the test samples. A defined pre-consolidation by vertical shocks is introduced in this paper.     

Effects of the co-addition of Zn and sodium dodecylbenzenesulfonate on photocatalytic activity and wetting performance of anatase TiO2 nanoparticle films

In this paper, doped and undoped anatase TiO₂ nanoparticle films on indium tin oxide glasses have been fabricated by spin coating sols containing Zn²⁺ or Zn²⁺ and sodium dodecylbenzenesulfonate (DBS), respectively. The effects of the co-addition of Zn²⁺ and DBS on the photocatalysis performance and wetting properties of the resulting TiO₂ nanoparticle films were investigated. The results showed that the addition of Zn²⁺ improved both the photocatalytic activity and the hydrophilicity, which was attributed to surface oxygen vacancies. The co-addition of Zn²⁺ and DBS resulted in an important increase of the surface roughness, resulting in films showing a superhydrophilic behavior. However, the photocatalytic activity was slightly decreased by co-adding Zn²⁺ and DBS. The DBS addition resulted in changes in the surface microstructure of the TiO₂ films, changing the photocatalytic activity and wetting performance.     

Characterization of sputtered SmCo thin films for light element contamination using RBS and HIERDA techniques

Samarium cobalt films were prepared on silicon substrates with and without a chromium buffer layer at room temperature and 600°C using direct current unbalanced magnetron sputtering. For obtaining ideal magnetic properties, the films should be free from impurities, such as O, Al and others. Rutherford backscattering spectrometry and heavy ion elastic recoil detection analysis were used to determine the composition and film thickness and to monitor the light element contamination across film thickness. X-ray diffractometer and superconducting quantum interference device were employed to characterize the structure and magnetic properties of the films, respectively. The results obtained led to an improved design of the ground shield and the use of a sorption pump to effectively minimize aluminium and oxygen concentration in the films, respectively.     

Electron microscopic tomography: A tool for probing the structure and function of subcellular components

Tomography is a powerful tool for obtaining three-dimensional information from transmission electron microscopy, but its application faces unique challenges. A single-axis tilt geometry for data collection results in anisotropic resolution because full angular coverage is not feasible for most specimen preparations. This effect can be minimized by combining two single-axis tilt series that have been collected orthogonal to each other. Rapid freezing has been successfully used to preserve the native structure of biological specimens in a form that can be visualized in the high-vacuum environment required for electron microscopy; however, these preparations are extremely labile to electron exposure. As a result, application of tomography to frozen-hydrated specimens has only recently become feasible with the development of automatic data collection, and with a renewed appreciation for the principle of dose fractionation. Even with the limitations of traditional specimen preparations and conventional methods of data collection, electron microscopic tomography has been successfully employed to probe the structure and function of several important cellular components. Current efforts include combining electron microscopic tomography and video-enhanced light microscopy to correlate ultrastructural variation with the direction of chromosome motion during mitosis. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 175–187, 1997     

A facile solution-immersion process for the fabrication of superhydrophobic surfaces with high water adhesion

The present work reports a simple and effective way to produce copper compound films on zinc substrate via solution-immersion process. The surfaces were characterized by field-emission scanning electron microscopy, Fourier transform IR, X-ray photoelectron spectrum and X-ray powder diffraction. The wettability of the surfaces is also investigated. The as-prepared superhydrophobic surfaces exhibit high adhesion to water and scratches on the surfaces could be repaired by immersing the damaged samples into the solution again.     

A study of the structure and surface properties of nanostructured biocompatible coatings on Ti alloys

This paper presents a study of the stability of biocompatible nanostructured TiO₂ surfaces prepared on a Ti6Al4V alloy by anodic oxidation, and it considers changes in the contact angles of ethylene glycol and distilled water. In the first stage, we measured the changes in the contact angles of the TiO₂ surfaces before and after sterilization. Then we examined the changes in the temporal contact angles of TiO₂ surfaces in different environments. The surface energy was calculated from the measured contact angles according to the Owens - Wendt model. Stability is significant for providing and innovating biocompatible coatings.The morphology of the deposited layers was observed using a scanning electron microscope (SEM).     

A simple reactor for growth of HgCdTe films using LPE technique

A reactor for growth of Hg_1−x Cd _x Te epilayers by liquid phase epitaxy has been designed and developed. The layers have been successfully grown using this liquid phase epitaxy (LPE) reactor.     

Effect of heating on the residual stresses in TiN films investigated using synchrotron radiation

The structure and residual stresses of TiN films deposited by arc ion plating (AIP) on a steel substrate were investigated using a synchrotron radiation system that emits ultra-intense X-rays. In a previous study, the crystal structures of TiN films deposited by AIP were found to be strongly influenced by the bias voltage. When high bias voltages were used, TiN films that were approximately 200 nm thickness had a preferred orientation of {110}, whereas TiN films that were approximately 600 nm thickness has a multilayer film orientation of {111}/{110}. In this present study, the two-tilt method was used to evaluate the residual stresses in TiN films by measuring lattice strains in two directions determined by the crystal orientation. Residual stresses in 600-nm-thick as-deposited TiN films were found to be −10.0 GPa and −8.0 GPa for {111}- and {110}-textured layers, respectively, while they were −8.0 GPa for {110}-textured layers in 200-nm-thick as-deposited TiN films. Residual stresses of both films relaxed to thermal stress levels upon annealing.     

Large area ZnO:Al films with tailored light scattering properties for photovoltaic applications

Aluminum-doped zinc oxide films on glass are promising substrates for use in thin film solar cells based on amorphous and amorphous/microcrystalline silicon absorber material. The films can be produced by magnetron sputtering on large scale at relative low cost. Especially reactive sputtering of metallic Zn/Al compound targets is a cheap way to produce films at high deposition rate. One drawback of amorphous silicon is the low absorption in the near infrared spectral range. Wet chemical etching has been used to produce a rough TCO surface that enables light trapping in the absorber. The etching behaviour of ZnO:Al films can be tuned by changing oxygen partial pressure during deposition. The etching behaviour is compared to ZnO structure and discussed regarding the performance of solar cells deposited onto the etched films.     

Enhanced Washburn Method (EWM): A comparative study for the contact angle measurement of powders

Washburn Method (WM) as a typical contact angle measurement (θ) method can be used for assessment of powder wettability (especially representative particle size range for flotation separation). However, as an indirect method, WM has several limitations. This investigation is going to introduce an Enhanced Washburn Method (EWM), which fills the gap of those WM obstacles, and can be applied for the meaningful indirect θ measurement of powders. For such a purpose, the wettability of quartz powders (d₈₀: 62 μm) was measured in the absence and in the presence of the cationic surfactant Flotigam®EDA at pH 10. EWM by using pre-conditioning of hydrophobized particles via unblock capillaries measured the θ of powders in different conditions. Statistical evaluations indicated that EWM could quite accurately measure θ of the hydrophobized powders, where there is a significant coefficient of determination (R² above 0.96) between EWM outcomes and other examined direct θ measurement methods (the captive bubble and sessile drop methods).     

Etching process optimization using NH4Cl aqueous solution to texture ZnO:Al films for efficient light trapping in flexible thin film solar cells

0.5 μm-thick aluminum-doped zinc oxide (ZnO:Al) films were deposited at 100 °C on polyethylene terephthalate substrates by Radio Frequency magnetron sputtering. The as-deposited films were compact and dense, showing grain sizes of 32.0 ± 6.4 nm and resistivities of (8.5 ± 0.7) × 10^− 4 Ω cm. The average transmittance in the visible wavelength range of the structure ZnO:Al/PET was around 77%. The capability of a novel two-step chemical etching using diluted NH₄Cl aqueous solution to achieve efficient textured surfaces for light trapping was analyzed. The results indicated that both the aqueous solution and the etching method resulted appropriated to obtain etched surfaces with a surface roughness of 32 ± 5 nm, haze factors at 500 nm of 9% and light scattering at angles up to 50°. To validate all these results, a commercially ITO coated PET substrate was used for comparison.     

Passivation properties of nitric/phosphoric etching on CdTe films: Influence of the etching time and nitric acid concentration

The chemical etch of CdTe surfaces with a mixture of phosphoric and nitric acids is used in research labs in order to enhance the back-contact formation in CdS/CdTe solar cells. However, the possible passivation effect of this approach has not been studied. In this work we report an investigation about the etching effect of nitric/phosphoric acid mixtures with different etching times (0, 30, 40 and 50 s) and variable concentrations of the nitric acid upon the surface recombination velocity of CdTe films deposited by close space vapor transport. Surface recombination velocities with values as low as 93 cm/s were achieved.     

A study on the plasma polymer thin film surface modification for DNA alignment by using high energy electron beam irradiation

The plasma polymer thin films were deposited on Si(100) substrate by PECVD (plasma enhanced chemical vapor deposition) method. Liquid cyclohexene was used as single organic precursor. It was heated up to 60 °C and bubbled up by hydrogen gas, which flow rate was 50 sccm (standard cubic centimeters per min). Deposition temperature was room temperature. Plasma was ignited by a radio frequency (RF; 13.56 MHz) of 10 W.As-deposited plasma polymer thin films were treated by e-beam of 300 keV with various adsorption radiation doses. The plasma polymer films, which were treated by high energy e-beam (HEEB), were investigated by FT-IR (Fourier Transform Infrared), XPS (X-ray Photoelectron Spectroscopy), AFM (Atomic Force Microscopy), and the water contact angles.From IR spectra, the intensity of OH functional group is increased by increasing electron dose rate. XPS results also show that the intensity of O_1s peak is increased by increasing electron dose rate. C_1s peak shows that oxygen bonded at carbon site. The water contact angles are decreased by increasing electron dose rate. From the AFM analysis, we observed the formation of λ-DNA (deoxyribonucleic acid) array on plasma polymer film, which was treated by HEEB with 14 kGy of adsorption radiation dose.