Electrochemical characterization of diamond like carbon thin films

Diamond-like carbon (DLC) thin films were deposited from pure graphite target by DC magnetron sputtering method. Experimental parameters, i.e., substrate temperature and negative bias voltage, have been changed to finely tune the chemical bonding property (sp²/sp³) of the as-deposited DLC films. The as-deposited DLC films were characterized as anode materials for Li–ion batteries and special attentions were paid to the effects of sp²/sp³ ratio on the electrochemical properties of the DLC films. The results indicated that a high fraction of sp² bonding in the DLC films is preferred for high lithium storage capacity, flat and low charge voltage plateau, and long cycling retention.     

Synthesis and characterization of polyimide/oligomeric methylsilsesquioxane hybrid films

In this study, polyimide/silsesquioxane hybrid materials were synthesized from aminoalkoxysilane‐capped poly(pyromellitic dianhydride‐co‐4,4′‐oxydianiline) (PMDA‐ODA) and oligomeric methylsilsesquioxane (O‐MSSQ) precursors. The O‐MSSQ moiety was used to obtain well characterized nano‐inorganic cage and network structures in the hybrid materials. The effects of molecular structures and composition on the morphologies and properties of the prepared hybrid materials were studied. The phase separation of the prepared hybrid materials could be controlled by varying the molecular weight of the polyimide moiety, the Si? OH end group content of the O‐MSSQ or the coupling agent. Homogeneous and transparent hybrid thin films were obtained from the low molecular weight polyimide moiety with a coupling agent, 3‐aminopropyltrimethoxysilane (APrTMS). However, microphase separation occurred if the molecular weight of the polyimide moiety was enhanced or was prepared without a coupling agent, as evidenced by atomic force microscopy (AFM), field emission scanning electron microscopy (FE‐SEM), and electron spectroscopy for chemical analysis (ESCA). The high Si? OH content of the O‐MSSQ could enhance the bonding density between the organic and inorganic moiety and thus retard phase separation. The thermal and mechanical properties of the prepared hybrid materials were largely improved compared with the parent polyimide, PMDA‐ODA, and were demonstrated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and thermal‐stress analysis. The hybrid materials showed adjustable refractive index and dielectric constant by varying the O‐MSSQ content. The birefringence of the PMDA‐ODA was reduced by incorporating the O‐MSSQ moiety. This work revealed that the polyimide/O‐MSSQ hybrid materials could have potential applications as optical films or low dielectric constant materials. Copyright © 2004 Society of Chemical Industry     

Preparation and characteristics of ZnO films on freestanding diamond substrates

In this paper, preferred and fine grained polycrystalline ZnO films were deposited on smooth nucleation surfaces of freestanding thick diamond films (FTDF) by plasma-assisted metal organic chemical vapor deposition. The properties of the ZnO films were characterized by scanning electron microscopy, X-ray diffraction, glancing angle X-ray diffraction, room temperature photoluminescence spectra, and electron probe microanalysis. The results indicate that the morphological, structural, and optical properties of ZnO films are strongly dependent on the deposition procedures, especially the deposition temperature. The Zn/O atomic ratio plays an important role in the optical properties of ZnO films. The experimental results can help us improve our understanding of how to obtain ZnO films with excellent properties deposited on FTDF. The most significant improvements in morphological, structural, and optical properties of ZnO films are obtained by using the proper deposition temperature of 500 °C.     

Sand erosion of freestanding diamond films prepared by DC arcjet

Sand erosion behavior of freestanding diamond films prepared by high power dc arcjet operating at gas recycling mode was investigated by a laboratory designed blast type apparatus. Four different erodent: glass bids, SiO₂, Al₂O₃, and SiC were used. The speed of the erodent particles was measured by the double disk method. It was found that the erosion behavior for the as-grown and the polished diamond films was quite different. At the initial stage, the erosion rate was rather high for the as-grown diamond film, which rapidly decreased with the increase in erosion time, and eventually reached the steady state erosion stage on prolonged erosion. Whilst for the polished diamond film, the erosion rate was quite low at the initial stage, which rapidly increased with the increase in erosion time, and finally reached the steady state erosion stage after a long erosion time. Surface damage was investigated by SEM observations and Raman spectroscopy. Possible mechanism responsible for the difference in erosion behavior was briefly explained. Comparison of the erosion behavior of freestanding diamond films was also made with the other commonly used IR window materials (Ge, MgF₂, MgAl₂O₄, ZnS and quartz glass). Detailed results were discussed.     

High performance, freestanding and superthin carbon nanotube/epoxy nanocomposite films

We develop a facile, effective and filter free infiltration method to fabricate high performance, freestanding and superthin epoxy nanocomposite films with directly synthesized Sing-Walled Carbon Nanotubes (SWNTs) film as reinforcement skeleton. It is found that the thicknesses of the nanocomposite films can be easily controlled in the range of 0.5-3 μm by dripping target amount of acetone diluted epoxy through the skeleton film. The consequent measurements reveal that the mechanical and electrical properties of SWNTs/epoxy nanocomposite films could be tailored in a quite wide range. For examples, the Young's modulus of nanocomposite films can be tuned from 10 to 30 GPa, and the electrical conductivity can be ranged from 1000 S·cm(-1) to be insulated. Moreover, high load transfer efficiency in the nanocomposite films is demonstrated by the measured ultrahigh Raman bands shift rate (-30 ± 5 cm(-1)/% strain) under strain. The high effective modulus is derived as 774 ± 70 GPa for SWNTs inside this nanocomposite film.     

Synthesis and characterization of continuous freestanding silicon carbide films with polycarbosilane (PCS)

A technique based on melt spinning of precursor was introduced to produce continuous freestanding SiC films. An equipment including spinneret, mandril, tank and seal groove was designed and manufactured for melt spinning. The polycarbosilane (PCS) precursors were deaerated, melt spun, crosslinked (by oxidation or irradiation), and pyrolyzed at high temperature in order to convert the initial PCS into freestanding SiC films. Our results revealed that the continuous freestanding SiC films, approximately 8 μm to 190 μm in thickness depended on setting, were uniform and dense. Their microstructure consisted of amorphous SiOxCy, β-SiC nano-crystals and free carbon. The photoluminescence (PL) spectrum showed two blue emissions at 416 nm and 435 nm. The continuous freestanding SiC films with high modulus, high density, high surface hardness and optoelectronic properties may have potential applications in microelectromechanical systems (MEMS), advanced optoelectronic devices and such complex-shaped materials.     

Bioproperties of nanocrystalline diamond/amorphous carbon composite films

Nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films have been deposited by microwave plasma chemical vapour deposition (MWCVD) from CH₄/N₂ mixtures. The films have been thoroughly characterized by a variety of methods with respect to their composition, morphology, structure and bonding environment. Thereafter, the bioproperties of these films have been investigated. Tests with osteoblast-like cells and pneumocytes proved that the NCD/a-C films are not cytotoxic. In addition, exposure of the films to a simulated body fluid revealed that they are bioinert. Further experiments addressed the question whether biomolecules such as RNA or proteins bind unspecifically on the surfaces of NCD/a-C films. By means of atomic force microscopy (AFM) and scanning force spectroscopy measurements it was established that, in contrast to control experiments with mica and glass, no interaction between the nanocrystalline diamond and either RNA or protein molecules took place. The results of these experiments concerning the biologically relevant properties of NCD/a-C films are discussed in view of possible future applications, e.g. as a material for the immobilization of biomolecules and their characterization by AFM measurements and related techniques.     

Reinforcing randomly oriented transparent freestanding single-walled carbon nanotube films

We report an improvement of the mechanical properties of transparent randomly oriented freestanding single-walled carbon nanotube (SWCNT) films by deposition of polymers using a drop casting method and aluminum oxide utilizing an atomic layer deposition (ALD) technique. Due to the thickness increase, the polymer coating resulted in an increase in toughness, however, simultaneously decreasing the ultimate tensile strength. The 100 nm thick SWCNT films ALD-coated with Al₂O₃ layer revealed significant increase in the ultimate tensile strength from 46 ± 5 to 213 ± 17 and 80 ± 4 to 318 ± 16 MPa depending on the network density, preserving the high level of porosity of the structure.     

改性纳米SiO2/聚氨酯-含氟丙烯酸酯无皂乳液合成及其胶膜性能表征

引言水性聚氨酯相对溶剂型聚氨酯具有不燃、气味小、不污染环境等优点[1-2],从而广泛用于涂料[3]、胶黏剂[4]、油墨[5]等领域。目前,常用于软包装领域的薄膜主要是表面能很低的非极性膜,而水性聚氨酯胶黏剂具有较高的表面自由能,对非极性膜的润湿性差,因此需要降低水性聚氨酯的表面张力,达到润湿非极性膜的目的。     

Surface modification of nanocrystalline diamond/amorphous carbon composite films

The surfaces of nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films deposited from a 17% CH₄/N₂ mixture have been subjected to a variety of plasma and chemical treatments, namely H₂ and O₂ microwave plasmas, a CHF₃ 13.56 MHz plasma, and a chemical treatment with aqua regia (HCl:HNO₃ 3:1). The resulting surfaces have been studied with respect to their chemical nature by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS), concerning their morphology with atomic force microscopy, and by contact angle measurements to study their hydrophobicity and their stability. As-grown surfaces are hydrogen terminated, but the number of C–H bonds can slightly be increased by a H₂ microwave plasma, while treatment with aqua regia considerably lowers the number of C–H bonds at the surface. O₂ and CHF₃ plasmas, on the other hand, lead to a replacement of the terminating C–H bonds by C–O or C–OH and C–F_x groups, respectively. Finally, by contact angle measurements over a period of 150 days it could be shown that the H-terminated surface is very stable whereas the contact angle of the O-treated surface changed considerably with time, probably due to the adsorption of contaminants.     

Electrical properties of ultrananocrystalline diamond/amorphous carbon nanocomposite films

The electrical surface properties of ultrananocrystalline diamond/amorphous carbon composite films have been investigated by four-point probe I/V and Hall measurements, whereas impedance spectroscopy has been used to establish the electrical bulk properties of the films. It turned out that the surface is p-type conductive with a resistivity of 0.14 Ω cm and a sheet carrier concentration of 7.6 × 10¹³ cm^?2. The bulk resistivity is higher by almost seven orders of magnitude (1.3 × 10⁶ Ω cm). The bulk conduction is thermally activated with an apparent activation energy of 0.17 eV. From Cole–Cole plots of the impedance spectra it can be concluded that there are three different contributions to the bulk conductivity. In order to try to identify these three components contributing to the electrical bulk conduction, Raman spectra have been recorded at five different wavelengths from the IR to UV region. These measurements showed that the UNCD/a-C films consist of at least three components: diamond nanocrystallites, an amorphous carbon matrix, and trans-polyacetylene-like structures probably at the interface between these two.     

Structural investigation of nanocrystalline diamond/amorphous carbon composite films

Nanocrystalline diamond/amorphous carbon (NCD/a-C) composite films have been prepared by microwave plasma chemical vapor deposition (MWCVD) from methane/nitrogen mixtures. The complex nature of the coatings required the application of a variety of complementary analytical techniques in order to elucidate their structure. The crystallinity of the samples was studied by selected-area electron diffraction (SAED). The diffraction patterns revealed the presence of diamond crystallites within the films. From the images taken by transmission electron microscopy (TEM) the crystallite size was determined to be on the order of 3–5 nm. The results were confirmed by X-ray diffraction (XRD) measurements exhibiting broad (111) and (220) peaks of diamond from which the average size of the crystallites was calculated. The grain boundary width is 1–1.5 nm as observed by TEM images which corresponds to a matrix volume fraction of about 40–50%. This correlates very well with the crystalline phase content of about 50% in the films estimated from their density (2.75 g/cm³ as determined by X-ray reflectivity). The bonding structure of the composite films was studied by electron energy loss spectroscopy (EELS) in the region of carbon core level. The spectra were dominated by a peak at 292 eV indicating the diamond nature of the investigated films. In addition, the spectra of NCD/a-C films possessed a shoulder at 284 eV due to the presence of a small sp² bonded fraction. This phase was identified also by X-ray photoelectron spectroscopy (XPS). The sp²/sp³ ratio was on the order of 10% as determined by deconvolution of the C1s XPS peak.     

Synthesis and characterization of hybrid composites based on carbon nanotubes

Multi-wall carbon nanotubes (CNTs) were coated with protonated polyaniline (PAni) in situ during the chemical polymerization of aniline. Uniform coating of CNT with PAni was observed by scanning electronic microscopy. An improvement in the covering of CNT composites was found by the association of poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT). The conductivity of composites has been compared with the conductivity of the PAni and CNT. A maximum conductivity of 96.8 S cm⁻¹ has been found for a PAni/PDMcT/CNT composite. High capacitance value (289.4 F g⁻¹) was also determined for this composite, indicating that all materials, PAni, PDMcT and CNT, remain active during the charge–discharge cycling. The reduction in the capacitance after 100 cycles was found to be less than 25%. The capacitive behavior of all materials was confirmed by impedance analysis.     

Synthesis and characterization of hybrid nano-crystallites inside self-ordered mesoporous carbon

The design and construction of nano-crystallites inside ordered mesoporous carbon is of great interest for potential applications in many fields. One of the main challenges is how to control hybrid nano-crystallites formed inside the pores. We describe a synthesis strategy of impregnation/hydrothermal method for incorporation of hybrid nano-crystallites Ru_0.3Cr_0.7O₂ inside CMK-3 with the average size of the nano-crystallites around 2.8–3.05 nm. The texture/structures of the resultant materials have been characterized by X-ray diffraction, transmission electron microscope, and nitrogen adsorption/desorption measurements. No nano-crystallites are observed to be generated on the external surface of CMK-3. The resultant material exhibits a high specific capacitance of approximately 226 F g⁻¹. This approach is expected to be applied to other hybrid metals oxides synthesized inside CMK-3 with specific structures and properties. Furthermore, it provides a versatile route for expanding the application of ordered mesoporous carbon with diverse pore arrangements.     

Optical characterization of ultrananocrystalline diamond films

Optical properties of the ultrananocrystalline diamond films were studied by multi-sample method based on the combination of variable angle spectroscopic ellipsometry and spectroscopic reflectometry applied in the range 0.6–6.5 eV. The films were deposited by PECVD in a conventional bell jar (ASTeX type) reactor using dual frequency discharge, microwave cavity plasma and radio frequency plasma inducing dc self-bias at a substrate holder. The optical model of the samples included a surface roughness described by the Rayleigh–Rice theory and a refractive index profile in which Drude approximation was used. The results conformed with the present understanding of the polycrystalline diamond growth on the silicon substrate because the existence of silicon carbide and amorphous hydrogenated carbon film between the silicon substrate and nucleation layer was proved.     

Construction of NiCo2O4 nanoflake arrays on cellulose-derived carbon nanofibers as a freestanding electrode for high-performance supercapacitors

Cellulose has a wide range of applications in many fields due to their naturally degradable and low-cost characteristics, but few studies can achieve cellulose-nanofibers by conventional electrospinning. Herein, we demonstrate that the freestanding cellulose-based carbon nanofibers are successfully obtained by a special design of electrospinning firstly, pre-oxidation and high-temperature carbonization (1600 °C), which display a superior electrical conductivity of 31.2 S·cm^–1 and larger specific surface area of 35.61 m²·g^–1 than that of the polyacrylonitrile-based carbon nanofibers (electrical conductivity of 18.5 S·cm^–1, specific surface area of 12 m²·g^–1). The NiCo₂O₄ nanoflake arrays are grown uniformly on the cellulose-based carbon nanofibers successfully by a facile one-step solvothermal and calcination method. The as-prepared cellulose-based carbon nanofibers/NiCo₂O₄ nanoflake arrays are directly used as electrodes to achieve a high specific capacitance of 1010 F·g^–1 at 1 A·g^–1 and a good cycling stability with 90.84% capacitance retention after 3000 times at 10 A·g^–1. Furthermore, the all-solid-state symmetric supercapacitors assembled from the cellulose-based carbon nanofibers/NiCo₂O₄ deliver a high energy density of 62 W·h·kg^–1 at a power density of 1200 W·kg^–1. Six all-solid-state symmetric supercapacitors in series can also power a ‘DHU’ logo consisted of 36 light emitting diodes, confirming that the cellulose-based carbon nanofiber is a promising carbon matrix material for energy storage devices.     

Preparation and characterization of polynorbornene/sepiolite hybrid nanocomposite films

Polynorbornene/sepiolite hybrid nanocomposite films were prepared using polynorbornene dicarboximide and modified sepiolite with 3‐ aminopropyltriethoxysilane (3‐APTES). Exo‐N‐(3,5‐dichlorophenylnorbornene)‐5,6‐dicarboxyimide (monomer) and their copolymers were synthesized via ring‐opening polymerization using ruthenium catalysts. Subsequently, the surface‐modified sepiolite by 3‐APTES was mixed with the polynorbornene copolymers to prepare hybrid nanocomposite films. The modified sepiolite particles were well dispersed in N,N‐dimethylacetamide and distributed randomly throughout the polynorbornene matrix in the hybrid films, which enhanced the dimensional stability and mechanical and oxygen barrier properties of the polynorbornene/sepiolite hybrid nanocomposite films. © 2014 Society of Chemical Industry     

Microfabrication issues in constructing freestanding membranes of near-frictionless carbon and diamond-like films

The near-frictionless carbon (NFC) film developed at Argonne National Laboratory has excellent mechanical and tribological properties, such as the super low friction coefficient of 0.001 and the wear rates of 10^− 11–10^− 10 mm³/N m. In this study, microfabrication procedures are developed to fashion the NFC thin films into freestanding structures which are necessary for many MEMS sensor devices. The entire microfabrication process is outlined in detail for use by other researchers. The NFC membranes were characterized with optical, scanning electron, and atomic force microscopy and Raman spectroscopy both before and after the fabrication process to observe any structural changes. Several surface and bulk micromachining issues, such as reactive ion notching effect and NFC film releasing, were studied and mitigated.