A new regime for high rate growth of nanocrystalline diamond films using high power and CH4/H2/N2/O2 plasma

In this work, we report high growth rate of nanocrystalline diamond (NCD) films on silicon wafers of 2 inches in diameter using a new growth regime, which employs high power and CH₄/H₂/N₂/O₂ plasma using a 5 kW MPCVD system. This is distinct from the commonly used hydrogen-poor Ar/CH₄ chemistries for NCD growth. Upon rising microwave power from 2000 W to 3200 W, the growth rate of the NCD films increases from 0.3 to 3.4 μm/h, namely one order of magnitude enhancement on the growth rate was achieved at high microwave power. The morphology, grain size, microstructure, orientation or texture, and crystalline quality of the NCD samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction, and micro-Raman spectroscopy. The combined effect of nitrogen addition, microwave power, and temperature on NCD growth is discussed from the point view of gas phase chemistry and surface reactions.     

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.     

Preparation and characterization of plasma-sprayed yttria stabilized zirconia as a potential substrate for NOx sensor

Fully stabilized zirconia containing 8 mol% of yttria was synthesized by solid state reaction method and deposited as a thick film by plasma spray coating. The crystal structure and phases developed were characterized by X-ray diffraction (XRD). The surface structure, surface morphology and microstructure developed were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The actual doping content was measured by electron probe micro-analyzer(EPMA). The plasma sprayed YSZ was characterized for its electrolytic properties by ac and dc conductivity measurements. The maximum conductivity for plasma sprayed YSZ was found to be −1.62 Scm⁻¹, which was lesser than the conductivity of standard 8YSZ of −1.03 Scm⁻¹ at pO₂=0.21 atm. However; conductivity trends in the arrhenius plot was observed to be similar for entire YSZ's, suggesting that the conductivity mechanism is same and dominated by oxygen ion conductivity independent of oxygen partial pressure. These promising electrolytic properties of thermal sprayed YSZ suggest that the thermal spray coating method may lead to be used as a potential method for the fabrication of NOx sensor.     

Nanocrystalline-diamond thin films with high pH and penicillin sensitivity prepared on a capacitive Si-SiO2 structure

A capacitive field-effect EDIS (electrolyte-diamond-insulator-semiconductor) sensor with improved pH and penicillin sensitivity has been realised using a nanocrystalline-diamond (NCD) film as sensitive gate material. The NCD growth process on SiO₂ as well as an additional surface treatment in oxidising medium have been optimised to provide high pH-sensitive, non-porous O-terminated films without damage of the underlying SiO₂ layer. The surface morphology of O-terminated NCD thin films and the layer structure of EDIS sensors have been studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. To establish the relative coverage of the surface functional groups generated by the oxidation of NCD surfaces, X-ray photoelectron spectroscopy analysis was carried out. The hydrophilicity of NCD thin films has been studied by water contact-angle measurements. A nearly Nernstian pH sensitivity of 54-57 mV/pH has been observed for O-terminated NCD films treated in an oxidising boiling mixture for 80 min and in oxygen plasma. The high pH-sensitive properties of O-terminated NCD have been used to develop an EDIS-based penicillin biosensor. A freshly prepared penicillin biosensor possesses a high sensitivity of 85 mV/decade in the concentration range of 0.1-2.5 mM penicillin G. The lower detection limit is 5 μM.     

Effect of the thicknesses of the Al2SiO5 ion conductor on the opto-electrical properties for all-solid electrochromic devices

In this study, an all-solid-state electrochromic device (ECD) with the structure of ITO/WO₃/Al₂SiO₅/NiO_x/ITO was prepared, and the effect of the Al₂SiO₅ solid electrolyte thicknesses on the opto-electrical performance was investigated. The microstructure and surface morphology were characterized using XRD, SEM and AFM, and the surface morphology and degree of surface looseness demonstrate a significant influence on the opto-electrical properties of ECDs. The charge transfer dynamics at the solid-solid interface were characterized using EIS to obtain an ionic conductivity of 4.637 × 10^-8 S/cm. CV, CA and UV–Visible spectra were employed to record the in situ electrochemical and optical properties. The results revealed that the highest optical modulation was 44.58%, the coloring and bleaching times were 14.8 s and 3.7 s, and the highest coloring efficiency was 98.17 cm²/C, which indicates that excellent opto-electrical properties were obtained. When the thickness increases, the degree of surface dense morphology transforms, and the loose morphology is more favorable for ion conductivity, which improves the opto-electrical properties. The results in this study provide insights into the understanding of Al³⁺-based all-solid-state ECDs, which promote the exploration of new types of Al³⁺ ionic conductors for all-solid-state ECDs.     

PLA-TiO2 nanocomposites: Thermal,morphological, structural,and humidity sensing properties

In this paper, the effect of TiO₂ ceramic nanoparticles on the thermal stability, morphology, molecular mass, structure and electrical properties of the polylactic acid-Titanium dioxide (PLA-TiO₂) composites, aimed for relative humidity (RH) sensing have been reported. PLA-TiO₂ nanocomposites films were developed through a spin coating process. The developed films were characterized by X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and electrochemical impedance spectroscopy analysis (EIS). To investigate the RH-dependent characteristics, the devices were prepared on pre-patterned ITO substrates. The capacitive and resistive response of the nanocomposite films were studied under RH levels ranging from 20–90%. The PLA-TiO₂ nano-sensing films, having modified surface by acetone etching, exhibited superior morphological and electrical performance when compared to PLA-TiO₂ pristine samples.     

Immobilization of horseradish peroxidase via an amino silane on oxidized ultrananocrystalline diamond

We discuss the complete functionalization of nitrogen-doped ultrananocrystalline diamond (UNCD) films, starting from an oxidized surface. First, the presence of hydroxyl groups on oxidized nanocrystalline diamond (NCD) was confirmed by fluorescence microscopy. Next, the grafting of a linker molecule such as 3-aminopropylmethyldiethoxysilane on oxidized NCD was confirmed by fluorescence microscopy and X-ray photoelectron spectroscopy (XPS). Then the horseradish peroxidase (HRP) enzyme was immobilized on silane-modified initially oxidized UNCD. The HRP-modified UNCD was characterized by electrochemical techniques, such as faradaic cyclic voltammetry and the amperometric response to H₂O₂. This response to H₂O₂ is discussed in terms of the layer-by-layer configuration used and the electronic properties of conducting UNCD.     

Surface modification of polyester nonwoven fabrics by Al2O3 sol–gel coating

Nonwoven polyester (PET) fabrics have been extensively studied for various applications. However, the nonwoven PET fabrics have poor wettability. In this work, nonwoven PET fabrics were impregnated in a stable and transparent alumina sol that was prepared by the hydrolysis of aluminium isopropoxide using the sol–gel technique. The Al₂O₃ particles were coated on nonwoven PET fabrics after the rolling-drying process. The surface morphology of modified nonwoven PET fabrics was characterized by scanning electronic microscopy (SEM) and atomic force microscopy (AFM). The SEM and AFM observations revealed the formation of the Al₂O₃ particles on the fiber surface. The Al₂O₃ coating was also confirmed by Fourier transform infrared (FTIR). The mechanical properties of the coated nonwoven PET fabrics were investigated using a tensile strength test, and the results showed that the mechanical properties were improved after surface sol–gel coating. The effect of Al₂O₃ on the wetting behavior of the fabric was also significantly improved.     

Ion beam induced evolution of surface morphology and optical properties of SnO2–ZnO nanocomposite thin films

SnO₂–ZnO nanocomposite thin films, prepared by a simple carbothermal reduction based vapor deposition method, were irradiated with 8 MeV Si³⁺ ions for engineering the morphological and optical properties. The surface morphology of the nanocomposites was studied by atomic force microscopy (AFM), while the optical properties were investigated by photoluminescence spectroscopy (PL) and Raman spectroscopy. AFM studies on the irradiated samples revealed growth of nanoparticles at lower fluence and a significant change in surface morphology leading to the formation of nanosheets and their aggregates at higher fluences. A tentative mechanism underlying the observed ion induced evolution of surface morphology of SnO₂–ZnO nanocomposite is proposed. PL studies revealed strong enhancement in the UV emissions from the nanocomposite thin film at lower fluence, while a drastic decrease in the UV emissions along with a significant enhancement in the defect emissions has been observed at higher fluences.     

Synthesis of Fe2O3 nanoparticles for nitrogen dioxide gas sensing applications

Iron (III) oxide, Fe₂O₃, nanoparticles of approximately 40 nm diameter were synthesized by sol–gel method and their nitrogen dioxide adsorption and desorption kinetics were investigated by custom fabricated gas sensor unit. The morphology and crystal structure of Fe₂O₃ nanoparticles were studied by scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) respectively. The roughness of film surface was investigated by atomic force microscopy (AFM). Relative sensitivity of Fe₂O₃ nanoparticles for NO₂ sensor was determined by electrical resistance measurements. Our reproducible experimental results show that Fe₂O₃ nanoparticles have a great potential for nitrogen dioxide sensing applications operating at a temperature of 200 °C.     

Commercial developments of nano-crystalline diamond — Two prototypes as case studies

Novel technologies for synthesis of nano-crystalline diamond (NCD) enable industrial production allowing large area deposition on a variety of substrate materials – at reasonable price. New perspectives for future innovative products emerge demonstrated by two case studies in the field of micro electro-mechanical systems (MEMS) sensors (case a) and medical implant devices (case b).a) This study comes as a preliminary step towards the integration of NCD thin film membranes in gravimetric sensors with low detection limits. We investigate theoretically and experimentally the mass sensing characteristics of composite thin Film Bulk Acoustic Resonator (FBAR) as a function of the side exposed to a mass perturbation.b) The aim of this study was to demonstrate the influence of different surface terminations of NCD on surface potentials and subsequently its influence on in vivo connective tissue healing. NCD-coated implants were evaluated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM)-surface potential measurements. After in vivo integration of the NCD-membranes into the subdermal layer of Wistar rats and subsequent histological evaluation it was demonstrated that the number of cells increased significantly at the O-terminated NCD and the scar tissue formed was less tight. Thus, a promising technique for controlling connective tissue adhesion in vivo is presented.     

Preparation and electrical properties of Sm-doped Bi2Ti2O7 thin films prepared on Pt (111) substrates

Crack-free Sm-doped Bi₂Ti₂O₇ (Sm:BTO) thin films with strong (111) orientation have been prepared on Pt (111) substrates using a chemical solution deposition (CSD) method. The structural properties and crystallizations were studied by X-ray diffraction. The surface morphology and quality were examined using atomic force microscopy (AFM). The insulating and dielectric properties were also evaluated at room temperature. The results demonstrate that the Sm:BTO films exhibit improved electrical performances as compared to the pure Bi₂Ti₂O₇ thin films and suggest a strong potential for utilization in microelectronics devices.     

Characterization of PVAc/TiO2 hybrid nanofibers: From fibrous morphologies to molecular structures

Polyvinyl acetate (PVAc)/titanium dioxide (TiO₂) hybrid nanofibers were fabricated by combining sol–gel process with electrospinning technology, which consisted of PVAc as organic segment and TiO₂ as inorganic part. The surface structures of the PVAc/TiO₂ hybrid nanofibrous mats were examined using scanning electron microscopy (SEM). The surface morphology and bulk structures of single nanofiber were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Fourier transform infrared spectroscopy (FTIR) was employed to analyze the chemical structures of the PVAc/TiO₂ hybrid nanofibers. SEM scanning revealed that the fibrous structure was formed. AFM observations presented a significant difference in the morphology of the nanofibers before and after hybridization. It was observed from TEM images that some black streaks with various lengths distributed in a nanofiber. The FTIR analysis indicated the newly formed associated hydrogen bond because of the hybrid effect between PVAc and TiO₂ sol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Passive behavior of magnesium alloys (Mg-Zr) containing rare-earth elements in alkaline media

The passive behavior of magnesium alloys ZK31, EZ33 and WE54 was studied in alkaline media (NaOH - pH 13) in the presence and absence of chloride ions. The electrochemical properties were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and capacitance measurements.X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed for the study of the chemical composition and surface morphology of the surface films, respectively.The electrochemical impedance results revealed that the film formed on the surface of the three alloys is characterized by an increasing resistance, which stabilized with time. In the absence of chloride the film resistance was identical for all the three alloys. However, in the presence of chloride, the resistance of the film formed on the EZ33 alloy dropped nearly one order of magnitude comparatively to the other alloys. Generally, in the presence of chloride there was a decrease of the conductive character of the film.The films are homogeneous and, according to the XPS results, the outer layer seemed mainly composed of Mg(OH)₂ and the internal layer composed of MgO, independently of the presence of chloride. The AFM study revealed that the presence of chloride affected film morphology, namely nano-crystallites dimensions and aggregates size that increased.     

Microscopic study of electrical properties of CrSi<Subscript>2</Subscript> nanocrystals in silicon

Semiconducting CrSi₂ nanocrystallites (NCs) were grown by reactive deposition epitaxy of Cr onto n -type silicon and covered with a 50-nm epitaxial silicon cap. Two types of samples were investigated: in one of them, the NCs were localized near the deposition depth, and in the other they migrated near the surface. The electrical characteristics were investigated in Schottky junctions by current-voltage and capacitance-voltage measurements. Atomic force microscopy (AFM), conductive AFM and scanning probe capacitance microscopy (SCM) were applied to reveal morphology and local electrical properties. The scanning probe methods yielded specific information, and tapping-mode AFM has shown up to 13-nm-high large-area protrusions not seen in the contact-mode AFM. The electrical interaction of the vibrating scanning tip results in virtual deformation of the surface. SCM has revealed NCs deep below the surface not seen by AFM. The electrically active probe yielded significantly better spatial resolution than AFM. The conductive AFM measurements have shown that the Cr-related point defects near the surface are responsible for the leakage of the macroscopic Schottky junctions, and also that NCs near the surface are sensitive to the mechanical and electrical stress induced by the scanning probe.     

Morphologies and properties of poly(phthalazinone ether sulfone ketone) matrix ultrafiltration membranes with entrapped TiO2 nanoparticles

Poly(phthalazine ether sulfone ketone) (PPESK) is a newly developed membrane material with superior thermal stability and comprehensive properties. Titanium dioxide (TiO₂)‐entrapped PPESK ultrafiltration (UF) membranes were formed by dispersing uniformly nanosized TiO₂ particles in the casting solutions. Initially, the inorganic nanoparticles were organically modified with silane couple reagent to overcome the aggregation and to improve the dispersibility in organic solvent. The membranes were prepared through the traditional phase inversion method. The effects of inorganic TiO₂ nanoparticles on the membrane surface morphology and cross section structure were investigated using scanning electronic microscopy (SEM) and atomic force microscopy (AFM). Water contact angle (CA) measurement was conducted to investigate the hydrophilicity and surface wettability of the membranes. The influence of TiO₂ on the permeability, antifouling, and tensile mechanical properties of the PPESK membranes were evaluated by UF experiments and tensile tests. The experimental results showed that the obtained TiO₂‐entrapped PPESK UF membranes exhibit remarkable improvement in the antifouling and mechanical properties because of the introduction of TiO₂ nanoparticles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3623–3629, 2007     

Tribological properties of NCD coated cemented carbides in contact with wood

Cemented carbides coated with diamond layers are promising materials for mills in the wood industry. Therefore, a study of the tribological properties of the contact between this material and wood is interesting and important. Wood is a specific material with a highly anisotropic structure, which causes roughness of its surface. For example, the friction coefficient (μ) of wood in contact with polished steel coated with a smooth DLC layer, has a relatively high value of μ=0.2–0.5. Cemented carbides, as manufactured for tools for wood milling purposes with roughness R_z=0.66 μm, have been modified with a nanocrystalline diamond film (NCD) using the RF PACVD method. The surface of the NCD coating showed ‘sharp hills’ morphology, but the surface roughness of cemented carbide decreased slightly after coating. The friction was very high (μ=0.7–0.8 at v=1 m/s; F_N=60 N) and it depended on the species of wood. When examining oak and poplar using carbides coated with the thickest NCD layer and a DLC film on top, this value decreased by 30% with respect to that of uncoated carbides. For fibreboard against NCD, the value was increased. Comparing the friction of NCD against wood to its friction against steel, titanium and aluminium alloys, we could see that the roughness of wood was the main factor which determined its tribological behaviour. Prime novelty: the tribological properties of a NCD layer deposited on cemented carbides with wood.     

Fabrication of conducting polypyrrole film with microlens arrays by combination of breath figures and replica molding methods

Novel conducting polypyrrole (PPy) films with microlens arrays (MLAs) were successfully fabricated by combination of breath figures (BFs) and replica molding methods. Polycarbonate (PC) molds prepared by BFs method contain concave cavities with a diameter of about 3–4 μm and a depth of about 2.5 μm in the center of the cavity as were revealed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). PPy MLAs were achieved by the chemically oxidative polymerization of pyrrole on the surface of PC molds initiated by FeCl₃ and subsequent removal of PC molds with CHCl₃. The PPy MLAs possess well-ordered convex with a height of about 2.1 μm in the center of the microlens as revealed by SEM and AFM, which is highly related to the morphology of PC molds. In addition, the effect of the polymerization time of pyrrole on the electrical conductivity of the resulting patterned PPy films was investigated by standard four probe technique.     

Wear behavior of graded Cr-CrN-Cr(1−x)Al(x)N coatings synthesized by closed-field unbalanced magnetron sputtering for advanced machining operations

Graded Cr-CrN-Cr_(1?x)Al_(x)N coatings were synthesized onto M42 HSS substrates used in advanced machining operations by closed-field unbalanced magnetron sputtering (CFUBMS). The tribological behavior of these graded coatings was explored in detail by advanced electron microscopy, confocal laser scanning microscopy, nanoindentation and dry sliding wear tests. The presence and magnitude of residual stresses in these coatings were determined by the XRD – sin²ψ method, which revealed increasing compressive stresses with increasing Al content. The coating surface morphology, mechanical properties were determined prior to dry sliding wear by atomic force microscopy (AFM) and nanoindentation methods, which yielded decreasing surface roughness (R_a) as well as enhancement of hardness and modulus along with increase in H/E and H³/E² ratios with increasing Al content. Tribological investigation was performed with a pin-on-disc arrangement by keeping the sliding velocity (0.2?ms^?1) and normal axial load (10?N) constant and varying the sliding distance. Specific wear rates of the order ~ 10^–17 m³ N^?1 m^?1 were encountered for all coatings with the wear rates increasing as the Al content increased implying a decrease of wear resistance of the coatings. Abrasive wear has been found to be the dominant wear mechanism during dry sliding wear. Increasing modulus mismatch between coating and substrate can be mainly attributed to a decrease in wear resistance of the coatings.     

Tribological investigation of nanocrystalline diamond films at low load under different tribosystems

The mechanical and frictional properties of hydrogen- and oxygen-terminated nanocrystalline diamond films (NCD) grown by hot-filament chemical vapor deposition (HFCVD) have been investigated in the present work.The structure and morphology of the NCD films have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman-effect spectroscopy. In addition, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) have been used to investigate the surface chemical groups on the NCD surface. Mechanical and frictional properties are determined using atomic force microscopy (AFM), nano-indentation, nano-scratching and micro-tribometer. The friction behavior of these films in the load range of 25 to 200 mN under reciprocating sliding conditions, using steel counter-body material has been thoroughly studied.It is noted that these films are highly crystalline with nanometer size grains and contain a very high fraction of sp³ carbon bonds. They exhibit high hardness and high elastic modulus. The friction coefficient of the film is lower under unidirectional scratch with diamond indenter than the friction coefficient under low load reciprocating sliding against steel ball. Transfer of the film from the counter-body, oxidation of transfer film and mixing of transfer film with carbonaceous layer on the worn surfaces are responsible for such behavior. Although, the friction responses of H-terminated and O-terminated films are similar under unidirectional scratch with diamond indenter, the friction coefficient of O-terminated film is always higher than the friction coefficient of H-terminated film under reciprocating sliding condition against steel counter-body material.