Comparison of Structure and Properties among Various PAN Fibers for Carbon Fibers

To find out the high-quality polyacrylonitrile (PAN) fibers, some differences are sought by comparing domestic PAN fibers with the foreign ones. X-ray diffractometer (XRD), transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectrometer, elemental analyzer, tensile-testing machine and high-temperature differential scanning calorimeter (DSC) are used to characterize the individual microstructure, chemical structure, elemental content, mechanical properties and thermal properties. It is found that high-quality PAN fibers have high density, lower titre, higher or adequate tensile strength, and they also have better conglomeration structure, smaller crystal dimension with dispersive distribution, less microvoids and flaws.     

Poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate): Correlation between colloidal particles and thin films

We deal with correlation between sizes of colloidal particles and minimum thickness of spin-coated thin films of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) studied by a dynamic light scattering (DLS), a scanning transmission electron microscopy coupled with an energy dispersive X-ray spectroscopy (STEM-EDX), C₆₀-sputtering X-ray photoelectron spectroscopy (XPS), and an atomic force microscopy. Based on the various measurements, it was pointed out that, PEDOT/PSS colloidal dispersion contained majority of primary nanoparticles with mean diameter of 41 nm and 16 nm for BAYTRON P AG (denote P grade) or BAYTRON PH500 (denote PH grade) solutions, respectively, and small amount of clusters aggregated by the primary particles, based on the DLS measurement and STEM observation. On the other hand, PEDOT/PSS thin films with thickness of 44 nm and 16 nm were easily prepared by spin-coating on silicon wafers from the P and PH grade solutions, respectively. Results of STEM-EDX, DLS, and XPS measurements suggested that the PEDOT/PSS thin films consist of the randomly packed primary nanoparticle-“monolayer”.     

Nanosecond pulsed laser deposition of TiO2: nanostructure and morphology of deposits and plasma diagnosis

Nanostructured TiO₂ films on Si (100) substrates have been grown by nanosecond pulsed laser deposition at the wavelengths of 266, 355 and 532 nm using a Q-switched Nd:YAG laser and TiO₂ sintered rutile targets. The effect of laser irradiation wavelength, the temperature of the substrate and the presence of O₂ as background gas on the crystallinity and surface structure of deposits were determined, together with the composition, expansion dynamics and thermodynamic parameters of the ablation plume. Deposits were analyzed by X-ray photoelectron spectroscopy, X-ray diffraction, environmental scanning electron microscopy and atomic force microscopy, while in situ monitoring of the plume was carried out and characterized with spectral, temporal and spatial resolution by optical emission spectroscopy. Stoichiometric, crystalline deposits, with nanostructured morphology were obtained at substrate temperatures above 600 °C. Microscopic particulates were found overimposed on the nanostructured films but their size and density were significantly reduced by operating at short wavelength (266 nm) and upon addition of a low pressure of oxygen (0.05 Pa). The dominant crystalline phase is rutile at 355 and 532 nm. At the short irradiation wavelength, 266 nm, the preferred phase in the presence of oxygen is rutile, while anatase is preferably observed under vacuum. The narrowest size distribution and smallest nanoparticle diameters, of around 25 nm, were found by deposition at 266 nm under 0.05 Pa of oxygen.     

Nitrogen incorporation into titanium diboride films deposited by dc magnetron sputtering: Structural modifications

This work reports a study of titanium boron nitride (Ti-B-N) films deposited at room temperature by dc magnetron sputtering using a TiB₂ target in different Ar-N₂ gas mixture atmospheres. The influence of the nitrogen partial pressure on the structural, mechanical and tribological properties of these films has been studied. The films were analyzed by Rutherford backscattering spectrometry in order to determine their chemical composition and atomic density. X-ray diffraction (XRD) was used to probe the film microstructure and X-ray photoelectron spectroscopy (XPS) for the chemical characterization of the film surface. An atomic force microscope (AFM) was used to analyze the surface topography and, when operating in the lateral force mode, for the friction characterization of the films. The XPS results showed that the surface of the films deposited in pure argon atmosphere was composed essentially by Ti and B oxides, while TiB₂, TiB, TiN and BN phases were present in the sputtered Ti-B-N films. Characterization by XRD determined the nanocrystalline nature of the films structure. While internal stress and friction increase upon the nitrogen incorporation, AFM measurements reveal a strong reduction of the surface roughness.     

Studies of the chemical and electrical properties of fullerene and 3-aminopropyltrimethoxysilane based low-k materials

Among an extremely large number of possible fullerene applications in the field of electronics, optics and photovoltaics, C₆₀-cages are also considered as a promising dopant for low dielectric constant (low-k) materials. In this study, we incorporated C₆₀ species into a 3-aminopropyltrimethoxysilane (APTMS) based material. We prepared thin films by spin coating. Using X-ray photoelectron spectroscopy we analyzed the time-related interactions between the components of the prepared samples and the influence of the C₆₀ replacement by its better soluble derivative [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) on the chemical properties of the material. We applied atomic force microscopy to investigate the surface texture and thicknesses of the obtained films. In order to obtain information concerning the electrical properties of the material we performed capacitance-voltage characterization. We have proven that the increase of C₆₀ species realized by PCBM incorporation within the APTMS-based matrix reduces the dielectric constant of the examined films while preserving its homogeneity.     

NO2 gas sorption studies of Ge33Se67 films using quartz crystal microbalance

A study on the NO₂ gas sorption ability of amorphous Ge₃₃Se₆₇ coated quartz crystal microbalance (QCM) is presented. The thin films have been characterized before and after sorption/desorption processes of NO₂ by energy-dispersive X-ray spectroscopy (EDS), grazing angle X-ray diffraction (GAXRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and atom force microscopy (AFM) measurements. These studies indicated that physisorption occurs when NO₂ gas molecules are introduced into the chalcogenide film and the thin film composition or structure do not change. The mass loading due to NO₂ gas sorption was calculated by the resonator’s frequency shift. At the conditions of our experiment, up to 6.8 ng of the gas was sorbed into 200 nm thick Ge₃₃Se₆₇ film at 5000 ppm NO₂ concentration. It has been established that the process of gas molecules sorption is reversible.     

Influence of Sputtering Gas on Morphological and Optical Properties of Magnesium Films

The influence of sputtering gas(He & Ar) on the structural properties of Mg thin films has been investigated.The optical property(reflectance) that results from the growth of films at varying substrate temperatures(Tsub) was also studied.The deposited films were characterized by using X-ray diffraction(XRD),field emission scaning electron microscopy(FE-SEM),atomic force microscopy(AFM) and UV-Vis-NIR spectrophotometer.The smaller crystallite size and lower deposition rate were observed in the presence of Helium atmosphere compared to Argon.Morphology of the films shows 2D hexagonal geometry of grains in the deposition temperature range(Tsub≈50-150℃) in both the sputtering gases.The surface roughness of the polycrystalline films were found to increase with increase in the deposition temperature of both ambient gases.Optical reflectance of Mg films was measured in near infrared region and larger reflectance was observed from Mg films sputtered in He atmosphere compared to that in argon.     

Growth of thin Ag films produced by radio frequency magnetron sputtering

Thin Ag films in the thickness range D = 14–320 nm were deposited by radio frequency magnetron sputtering on glass substrates at room temperature inside a vacuum chamber with base pressure of about 5 × 10^− 6 Pa. The growth of the films was studied via X-ray diffraction and atomic force microscopy experiments. The two techniques are complementary and give us the opportunity to study the surface roughness, the statistical distribution and the average value of the grain size, as well as the texture of the samples. It is shown that the film roughness increases negligibly within the first 60 atomic layers of growth. The thicker films (D 300 nm) develop a nanocrystalline structure with a root mean square roughness of about 2.5 nm. The grain size evolves linearly with the thickness from 9.4 nm at D = 54 nm to 31.6 nm at D = 320 nm.     

Size distribution-controlled preparation of graphene oxide nanosheets with different C/O ratios

A convenient and efficient preparation method for separation graphene oxide with well-defined size distribution is developed using a centrifugation technique. The graded profile of graphene oxide nanosheets with narrow size distribution is effectively controlled by varying the centrifugation speed. The results show that the oxygen content of graphene oxide is highly dependent on their size distribution. Graphene oxide nanosheet with large size shows a red-shift in UV–vis absorption spectra, compared to graphene oxide with small size. This phenomenon is interpretation by a density functional theory calculation. The present work will provide a simple method to prepare graphene oxide nanosheets with controllable size distribution and C/O ratio, which will be valuable for the functionalization of graphene-based hybrids and the fabrication of graphene nano-devices.     

Microscopic investigations of chemo-mechanical polishing of tungsten

The influence of aqueous solutions of KNO₃, KClO₃, and KIO₃ on tungsten surfaces has been investigated in terms of the degree of surface oxidation, metal dissolution and interfacial friction. The surface properties of tungsten films have been measured ex-situ with X-ray photoelectron spectroscopy and in situ with atomic force microscopy. Measurements of the surface composition reveal a greater degree of oxidation for surfaces treated in solutions of KIO₃ in comparison to the other solutions. This increase in surface oxidation is correlated to a greater rate of localized film dissolution that occurs under the action of the scanning probe tip. In turn, the process of material removal is the predominant origin of the higher interfacial friction measured at tungsten surfaces immersed in KIO₃ solutions, as compared to KClO₃ and KNO₃ solutions. Collectively, these measurements portray a fundamental pathway of material removal at tungsten surfaces in the presence of oxidizing species and highlight complementary roles of chemical and mechanical action.     

Study of the effect of process parameters for n-heptylamine plasma polymerization on final layer properties

Plasma polymerization processes are widely used to chemically functionalize surfaces, which properties can be tuned by different operating variables. In this study, thin amine-containing polymer layers were produced on solid substrates in a custom-made cylindrical plasma polymerization reactor by radio frequency glow discharges of n-heptylamine vapours. Carefully planned experiments were conducted to evaluate the importance of four different process parameters on the chemical composition and thickness of the resulting films. The parameters investigated were: 1) deposition time, 2) power of the glow discharge, 3) distance between the electrodes, and 4) monomer pressure. Possible interactions between these variables were investigated through the use of statistical analyses (i.e., factorial design). This study reveals that n-heptylamine plasma polymer (HApp) layer thickness is influenced by the power of the glow discharge and the deposition time, as assessed by surface plasmon resonance and atomic force microscopy step height measurements. Also, the atomic ratio of nitrogen to carbon atoms on the treated surfaces is mainly influenced by the power of the glow discharge, as revealed by X-ray photoelectron spectroscopy. Quartz crystal microbalance analysis also confirmed that HApp layers are stable when immersed in aqueous solution.     

Electrochemical responses to degradation of the surface layer nano-mechanical properties of stainless steels under cavitation

Nano-indentation technology was used to measure quantitatively the surface layer nano-mechanical properties (the nano-hardness, H_nano, and the nano-elastic modulus, E_nano) for stainless steels before and after cavitation corrosion testing. The nano-mechanical properties of the surface layers were comprehensively defined as (H/E)_nano, which is a dimensionless function. The relationship of the cumulative mass loss to the surface layer nano-mechanical property (H/E)_nano and the corresponding AFM images of the corroded surfaces were studied. The electrochemical responses to the degradation of the surface layer nano-mechanical properties of stainless steels without cavitation and under cavitation were also investigated. It was found that degradation of the surface layer nano-mechanical properties had a significant influence on the cavitation corrosion of stainless steels and that there was an (H/E)_nano threshold, above which the cumulative mass loss decreased slowly. This threshold was found to be independent of the stainless steel type. The electrochemical corrosion processes were varied, resulting in accelerated electrochemical corrosion as a result of degradation of the surface layer nano-mechanical properties. A significant peak in the low frequency regime was observed in the Bode figure. When degradation of the surface layer nano-mechanical properties was below the (H/E)_nano threshold, the phase angle in the Bode figure was approximately constant. The presence of the specific peak in the Bode figure was used as a marker for the occurrence of significant cavitation corrosion as a result of degradation in the surface layer nano-mechanical properties.     

溅射靶功率对氮化碳薄膜结构的影响

利用双放电腔微波ECR等离子体增强非平衡磁控溅射技术,在Si(100)上制备氮化碳薄膜,并对薄膜进行了拉曼(Raman)、原子力显微镜(AFM)、X射线光电子谱(XPS)等结构的表征.发现溅射靶功率对制膜工艺、薄膜的结构和表面形貌产生很大影响.随着溅射靶功率的增大,薄膜的沉积速率减小,表面粗糙度增大,薄膜结构中的sp2含量增加.     

纳米SiC表面接枝修饰的XPS研究

聚合物在纳米粒子表面接枝后,可在其表面建立起空间位阻稳定层,提高纳米粒子的分散稳定性及其与树脂基体的相容性.本文采用缩聚法在纳米SiC表面接枝了聚缩醛,X射线光电子能谱(XPS)的分析结果表明,经过聚缩醛接枝改性的纳米SiC表面Si2p峰明显降低,而C1s峰和O1s峰明显地增长,对C1s、Si2p峰精细扫描及分峰拟合表明,纳米SiC表面碳元素中有38.4%属于接枝物聚缩醛的有机碳,而79.8%的Si元素结合能增加了2.5eV,由此表明,纳米SiC表面形成了良好的表面修饰层,接枝物聚缩醛以化学键结合于纳米SiC表面;对比XPS和热失重分析(TG)的数据结果,可以推测,聚缩醛主要分布在纳米SiC的表面,而在体相中独立存在的几率较小.     

Initial stages of WO3 growth on silicon substrates

Ultrathin films (5 nm, 10 nm and 20 nm effective thickness) of WO₃ have been deposited in high vacuum (10^− 6 Torr) onto single crystal Si(100) substrates and studied with X-ray diffraction, atomic force microscopy, scanning tunneling microscopy and spectroscopy. The experiments have been carried out on “as-deposited” thin films or after 1 h post-deposition annealing at various temperatures (ranging from 300 °C to 500 °C). A size induced increase of the amorphous to crystalline (monoclinic) phase transition has been observed for the 5 nm and 10 nm films, with a critical crystallite size of 25 ± 5 nm and a critical temperature of 345 ± 5 °C. All the experimental evidences show that, upon annealing, there is a diffusion limited aggregation growth of WO₃ that forms large flat two-dimensional islands composed by aggregates of individual crystallites approximately uniform in size and shape. These islands are isolated in the 5 nm thin films, are connected in the 10 nm case and form a uniform patchwork in the 20 nm thin films. Scanning tunneling spectroscopy shows the opening of a large surface band gap (2.7 eV) in the 500 °C annealed films and the significant presence of in gap states for thin films prepared with a lower (below 400 °C) annealing temperature. These findings are discussed in view of the optimization of the best morphological, structural and electronic parameters to fabricate WO₃ gas sensing devices at the sub-micrometer length scale.     

热氧化对钛合金表面氧化层的影响

对钛合金Ti6Al7Nb(以下简称TAN)和Ti6Al4V(以下简称TAV)通过热氧化处理获得表面氧化层,用金相显微镜、维氏硬度计、XRD和XPS等手段对氧化层的性能进行表征。结果表明:相同氧化温度和氧化时间,TAN合金较TAV合金表面形成的氧化层更薄、致密度更好;合金表面硬度随热氧化温度的升高和氧化时间的延长而增加,但温度过高(TAN:1000℃;TAV:900℃)会使氧化层疏松多孔,硬度反而会下降;通过XPS对不同温度短时间氧化样品进行表面分析发现,氧化温度对合金中Nb添加元素的氧化行为影响较小,对V添加元素的氧化行为影响剧烈。两种合金元素对氧化过程有着显著的影响。     

Green synthesis of zinc oxide nanoparticles using tomato (Lycopersicon esculentum) extract and its photovoltaic application

With an increasing awareness of green and clean energy, zinc oxide-based solar cells were found to be suitable candidates for cost-effective and environmentally friendly energy conversion devices. In this paper, we have reported the green synthesis of zinc oxide nanoparticles (ZnONPs) by thermal method and under microwave irradiation using the aqueous extract of tomatoes as non-toxic and ecofriendly reducing material. The synthesised ZnONPs were characterised by UV–visible spectroscopy (UV–vis), infra-red spectroscopy, particle size analyser, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction study (XRD). A series of ZnO nanocomposites with titanium dioxide nanoparticles (TiO₂) and graphene oxide (GO) were prepared for photovoltaic application. Structural and morphological studies of these nanocomposites were carried out using UV–vis, SEM, XRD and AFM. The current–voltage measurements of the nanocomposites demonstrated enhanced power conversion efficiency of 6.18% in case of ZnO/GO/ TiO₂ nanocomposite.     

Direct imaging by atomic force microscopy of surface-localized self-assembled monolayers on a cuprate superconductor and surface X-ray scattering analysis of analogous monolayers on the surface of water

A self-assembled monolayer of CF₃(CF₂)₃(CH₂)₁₁NH₂ atop the (001) surface of the high-temperature superconductor YBa₂Cu₃O_7-x was imaged by atomic force microscopy (AFM). The AFM images provide direct 2D-structural evidence for the epitaxial 5.5 Å square √2 × √2R45° unit cell previously predicted for alkyl amines by molecular modeling [J.E. Ritchie, C.A. Wells, J.-P. Zhou, J. Zhao, J.T. McDevitt, C.R. Ankrum, L. Jean, D.R. Kanis, J. Am. Chem. Soc. 120 (1998) 2733]. Additionally, the 3D structure of an analogous Langmuir monolayer of CF₃(CF₂)₉(CH₂)₁₁NH₂ on water was studied by grazing-incidence X-ray diffraction and specular X-ray reflectivity. Structural differences and similarities between the water-supported and superconductor-localized monolayers are discussed.     

Grafting of gold nanoparticles on polyethyleneterephthalate using dithiol interlayer

Two different procedures of grafting of polyethyleneterephthalate (PET), modified by plasma treatment, with gold nanoparticles (nanospheres) are studied. In the first procedure the PET foil was grafted with biphenyl-4,4′-dithiol and subsequently with gold nanoparticles. In the second one the PET foil was grafted with gold nanoparticles previously coated by the same dithiol. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and electrokinetic analysis were used for characterization of the polymer surface at different modification steps. Gold nanoparticles were characterized by ultraviolet–visible spectroscopy. The first procedure was found to be more effective. It was proved that the dithiol was chemically bonded to the surface of the plasma activated PET and it mediates subsequent grafting of the gold nanoparticles.     

Short-time Oxidation of Alloy 690 in High-temperature and High-pressure Steam and Water

The oxidation behavior of alloy 690 exposed to high-temperature and high-pressure steam and water at 280 ℃ for 1 h was investigated by scanning electron microscopy(SEM),atomic force microscopy(AFM) and X-ray photoelectron spectroscopy(XPS).In high-temperature and high-pressure steam,the oxide film is composed of an outermost Ni-rich hydroxides layer,an intermediate layer of hydroxides and oxides enriched in Cr,an inner oxide layer.The film formed in high-temperature water is similar to that in steam,except for missing the Ni-rich hydroxides layer.Samples with different surface finishes(electropolished,mechanically polished,ground,and as-received) were prepared for comparison.A general increase of the oxide thickness with the degree of surface roughness is observed.The equivalent oxide thicknesses lie in the range of 100-200 nm for the as-received samples,150-250 nm for the samples ground to 400# and 10-20 nm for the samples ground to 1500#,mechanically polished,and electropolished.