Photoinduced paramagnetic defects and negative charge in SiCN dielectrics for copper diffusion barriers

We investigated defect generation in silicon carbon nitride (SiCN) dielectric films subjected to ultraviolet (UV) lights with two different photon energies at room temperature using electron spin resonance (ESR) and electrical measurements. A buildup of negative charge occurred and paramagnetic defects were generated by exposing the SiCN films to 4.9-eV UV illumination. However, a photon energy of 3.4 eV was insufficient to generate the negative charge and paramagnetic defects. The characteristics of the UV-induced ESR signals suggest that the generated paramagnetic defects are neutral silicon dangling bond centers. On the other hand, in the SiCN-SiO₂ stacked film subjected to 4.9-eV UV illumination, no net negative charge accumulated although a large number of paramagnetic defects were generated. This indicates that the generation of paramagnetic defects and the buildup of negative charge are based on different mechanisms. We discussed a consistent picture to explain these phenomena.     

Chemical deposition of silver shells on the surface of hollow glass microspheres

This article reports the chemical deposition of silver shells on the surface of hollow glass microspheres. This was accomplished by using titanium dioxide, derived from titanium (IV) tetra-n-butoxide, as the surface modifier. Two routes of formation of thin titanium dioxide layers on the substrate were compared in terms of composition and properties: photochemical approach and atmospheric hydrolysis. The structure and composition of the samples were characterized by atomic force microscopy, scanning electron microscopy, IR spectroscopy, electron paramagnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The resulting thickness of uniform silver shells on the surface of microspheres averaged out at 1.0–1.25 μm.     

Nitrogen doping of CVD multiwalled carbon nanotubes: Observation of a large g-factor shift

Nitrogen doped multi-walled carbon nanotubes (N-CNTs) and undoped multi-walled carbon nanotubes (MWCNTs) were synthesized by a chemical vapour deposition (CVD) floating catalyst method. The N-CNTs were synthesized by the decomposition of a ferrocene/N-source/toluene (N-source = triethylamine, dimethylamine, acetonitrile) mixture at 900 °C. The undoped MWCNTs were synthesized using a ferrocene–toluene mixture without a nitrogen source under similar reaction conditions. The structure of the N-CNTs and MWCNTs was ascertained using HRTEM, SEM and Raman spectroscopy. Systematic ESR measurements of the carbon products produced, in the temperature range of 293–400 K showed line widths that were in general very large ∼ kOe. Most importantly, a large g-factor shift in samples of N-CNTs from that of the free electron g-factor was observed. Further, the shift increased with increasing temperature. The large g shift has been analysed in terms of Elliott-Wagoner and Bottleneck models. The temperature dependence of the g shift in the N-CNT samples rules out the Elliott-Wagoner type spin–orbit coupling scenario. The large g shift and temperature dependence can be qualitatively explained in terms of the Bottleneck model.     

Preparation of Fe3+-doped TiO2 catalysts by controlled hydrolysis of titanium alkoxide and study on their photocatalytic activity for methyl orange degradation

Fe3+-doped TiO2 (Fe-TiO2) porous microspheres were prepared by controlled hydrolysis of Ti(OC4H9)4 with water generated "in situ" via an esterification reaction between acetic acid and ethanol, followed by hydrothermal treatment. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), electron paramagnetic resonance (EPR) spectrum, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), and nitrogen adsorption-desorption methods. All of the undoped TiO2 and Fe-TiO2 samples exclusively consist of primary anatase crystallites, which further form porous microspheres with diameters ranging from 150 to 500 nm. The photocatalytic activity of Fe-TiO2 catalysts was evaluated from the photodegradation of methyl orange (MO) aqueous solution both under UV and visible light irradiation. Fe3+ doping effectively improves the photocatalytic activity under both UV light irradiation and visible light irradiation with an optimal doping concentration of 0.1 and 0.2%, respectively. The photocatalytic mechanisms of Fe-TiO2 catalysts were tentatively discussed.     

Nitrogen doping in carbon nanotubes

Nitrogen doping of single and multi-walled carbon nanotubes is of great interest both fundamentally, to explore the effect of dopants on quasi-1D electrical conductors, and for applications such as field emission tips, lithium storage, composites and nanoelectronic devices. We present an extensive review of the current state of the art in nitrogen doping of carbon nanotubes, including synthesis techniques, and comparison with nitrogen doped carbon thin films and azofullerenes. Nitrogen doping significantly alters nanotube morphology, leading to compartmentalised 'bamboo' nanotube structures. We review spectroscopic studies of nitrogen dopants using techniques such as X-ray photoemission spectroscopy, electron energy loss spectroscopy and Raman studies, and associated theoretical models. We discuss the role of nanotube curvature and chirality (notably whether the nanotubes are metallic or semiconducting), and the effect of doping on nanotube surface chemistry. Finally we review the effect of nitrogen on the transport properties of carbon nanotubes, notably its ability to induce negative differential resistance in semiconducting tubes.     

Pr6O11 micro-spherical nano-assemblies: Microwave-assisted synthesis,characterization and optical properties

We report the synthesis of Pr₆O₁₁ microspheres self-assembled from ultra-small nanocrystals formed by the microwave irradiation of a solution of a salt of Pr in ethylene glycol (EG). The as-prepared product consists of microspheres measuring 200 to 500 nm in diameter and made of <5 nm nano-crystallites. The surface of these microspheres/nanocrystals is covered/capped with an organic layer of ethylene glycol as shown by TEM analysis and confirmed by IR spectroscopy measurements. The as-prepared product shows blue-green emission under excitation, which changes to orange-red when the product is annealed in air at 600 °C for 2 h. This change in luminescence behaviour can be attributed to presence of ethylene glycol layer in the as-prepared product. The samples were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), IR Spectroscopy (IR), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA).     

Electrical resistivity and thermoelectric power of polycrystalline and amorphous Se-Te-Cu system

The dark electrical resistivity and thermoelectric power have been measured for the bulk ternary alloy Se-Te-Cu. The samples were both polycrystalline and amorphous in structure. The measurements were carried out below room temperature. Depending on Cu addition, crystallographic structure, and amorphous or polycrystalline state, the samples manifested semiconducting or metallic behaviour. The maximum difference in electrical resistivity magnitude was of 14 orders. The activation energy ΔE of charge carriers determined for all semiconducting samples ranged from 0.07 to 0.25 eV. An increase in thermoelectric power resulting from the electron–phonon mass enhancement was estimated.     

Synthesis of a low-bandgap polymer bearing side groups containing phenoxy radicals

Poly(isothianaphthene methine) bearing di-tert-butylphenoxide in the side chain was prepared by reacting isothianaphthene and 3,5-di-tert-butyl-4-hydroxybenzaldehyde in the presence of POCl₃. A reference polymer with no hydroxy group in the side chain was also synthesized. Both polymers are characterized by a low-bandgap with value of ca. 1.3 eV obtained by optical absorption spectroscopy, and ca. 1.7 eV estimated from an electrochemical method. After treatment with PbO₂ as an oxidizer, phenoxy radicals were generated by oxidation in the polymer side groups. Optical absorption measurements and electron spin resonance (ESR) showed a characteristic signal due to phenoxy radicals. Magnetic properties of the polymer were examined with ESR and superconducting quantum interference device (SQUID) measurements. The results suggested that the polymer shows paramagnetic behavior.     

Towards an ultrasensitive method for the determination of metal impurities in carbon nanotubes

Residual catalyst metal nanoparticles remain one of the major obstructions in the utilization of carbon nanotubes (CNTs) in many areas owing to their ability to participate in redox chemistry of biomarkers. Presented here is a comparative study of several techniques for quality control of carbon nanotubes in terms of metallic impurities, namely magnetic susceptibility, electron paramagnetic resonance, energy-dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, and thermogravimetric analysis. It is found that the dc magnetic susceptibility is the most sensitive method such that the difference between two CNT samples that underwent slightly different treatments can be detected, whereas the two samples are indistinguishable by other techniques. Therefore, it is suggested that the most accurate statistical method for quality control of carbon nanotubes is dc magnetic susceptibility, which allows the detection of traces of magnetic metal impurities embedded in purified carbon nanotubes, whereas other methods may provide false "impurity-free" information.     

Influence of nitrogen flow rates on materials properties of CrN x films grown by reactive magnetron sputtering

Chromium nitride (CrN) hard thin films were deposited on different substrates by reactive direct current (d.c.) magnetron sputtering with different nitrogen flow rates. The X-ray diffraction patterns showed mixed Cr₂N and CrN phases. The variations in structural parameters are discussed. The grain size increased with increasing nitrogen flow rates. Scanning electron microscopy image showed columnar and dense microstructure with varying nitrogen flow rates. An elemental analysis of the samples was realized by means of energy dispersive spectroscopy. The electrical studies indicated the semiconducting behaviour of the films at the nitrogen flow rate of 15?sccm.     

An attempt to prepare carbon nanotubes by carbonizing polyphosphazene nanotubes with high carbon content

Polyphosphazene nanotubes with about 20 nm in inner diameter and 100-200 nm in outer diameter were fabricated easily and then carbonized at 800 °C in a nitrogen atmosphere. Scanning electron microscopy and transmission electron microscope results showed that the bulk morphology of polyphosphazene nanotubes was retained after carbonization. The carbon content of the carbonized samples reached 93.28%. X-ray diffraction and Raman spectrum showed that the carbonized samples had low graphitization state. The present method can be used for a mass production of carbon nanotubes.     

A novel report on Eosin Y functionalized MWCNT as an initiator for ring opening polymerization of ɛ-caprolactone

This research conducted ring opening polymerization (ROP) of ?-caprolactone (C.L.) with a novel initiator, namely; Eosin Y functionalized multiwalled carbon nanotube (MWCNT) at 140 °C with nitrogen sparge under different concentrations. ROP of C.L. carried out at two different experimental conditions similar to variations in [M₀/I₀] and [C.L.]. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy confirmed the structure of MWCNT-Eosin Y initiated ROP of C.L. Gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy (UV–vis), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) further characterized the structure. UV–visible spectroscopy determined the binding constant (K), for samples prepared under different [C.L.].     

Covalent functionalization of single-walled carbon nanotubes with anthracene by green chemical approach and their temperature dependent magnetic and electrical conductivity studies

Single-walled carbon nanotubes (SWCNTs) were covalently functionalized with anthracene in molten urea by a green chemical approach. The anthracene functionalized single-walled carbon nanotubes (Ant-f-SWCNTs) were examined along with SWCNTs, using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, powder X-Ray diffraction (XRD), and scanning, and transmission electron microscopy. The observations revealed the functionalization of SWCNTs by anthracene. The temperature dependent magnetization (300–5 K) and electrical resistivity were also measured for both SWCNTs and Ant-f-SWCNTs. The electrical resistivity of Ant-f-SWCNTs at 300 K was found to be 1.27 KΩm, which is much lower than 388.55 KΩm for pristine. This indicated a 300 fold increase in conductivity at room temperature for Ant-f-SWCNTs when compared to SWCNTs. The temperature dependence of the conductivity provided an indication of the semiconducting behaviour.     

Thermal stability of the phases formed in the near surface layers of unalloyed steels by nitrogen pulsed plasma treatment

Modification of the near surface layer of carbon steels using intense nitrogen plasma pulses leads to improvement of the hardness and wear resistance of the material surfaces, the main reason being the presence of the nitrogen expanded austenite formed during the process. A key factor influencing surface properties is the thermal stability of the identified phases, predominantly, the expanded austenite phases formed under the heat loading.Samples were characterized by nuclear reaction analysis (NRA), conversion electron Mössbauer spectroscopy (CEMS) and wear resistance measurements. The thermal stability of the modified samples has been investigated by annealing samples at increasing temperature in an argon atmosphere which showed phase transformation occurring at a characteristic temperature. The changes of the surface nitrogen concentration and wear resistance of the modified layer were investigated and discussed.     

Effect of heat treatment on the structure and stability of multiwalled carbon nanotubes produced by catalytic chemical vapor deposition technique

The multiwalled carbon nanotubes (MWCNTs) produced by catalytic chemical vapor deposition (CCVD) route were heat treated to 2500 °C to improve the structure, morphology and purity level. The process has lead to substantial reduction in the catalytic impurity along with an improved thermal stability and degree of graphitization of these tubes that can possibly lead to its better utilization in various applications. The structural changes following heat treatment have been correlated using various characterization techniques such as Raman spectroscopy, X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, thermo gravimetric analysis and electron paramagnetic resonance spectroscopy. The electrical and mechanical properties of the polymer composites prepared with heat treated MWCNT show improved properties over the one prepared by as produced MWCNT.     

Structural and gas-sensing properties of nanometre tin oxide prepared by PECVD

A low-temperature plasma-enhanced chemical vapour deposition (PECVD) technique has been employed to produce ultrafine tin oxide powders. The structural features and phase transition of this material have been characterized using differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction, infrared spectroscopy (IR) and transmission electron microscopy (TEM). The oxygen absorption behaviour and gassensing properties have been investigated by electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and electrical measurements. Thick film gas sensors made from such ultrafine SnO₂ powders yield better sensitivities than those of normal undoped SnO₂ gas sensors. A gas-sensing reaction mechanism is also proposed.     

Corrosion behaviour and galvanic coupling with steel of Al-based coating alternatives to electroplated cadmium

The galvanic corrosion behaviour of bare steel coupled to steel with an Al–Zn flake inorganic spin coating, an Al-based slurry sprayed coating, an arc sprayed Al coating and electroplated cadmium has been investigated. The sacrificial and galvanic behaviour of the coatings was studied in 3.5 wt. % NaCl solution using open-circuit potential, potentiodynamic polarisation and electrochemical noise measurements. The coatings were characterised by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Experimental results showed that the Al-based slurry sprayed coating exhibited an open-circuit potential closer to the steel substrate than other coatings, as well as a low corrosion current density and a more positive corrosion potential. In terms of the galvanic suitability of the investigated coatings for the steel substrate, both the Al–Zn flake inorganic spin coating and the Al-based slurry sprayed coating show low galvanic current, in comparison with the arc sprayed Al coating and electroplated cadmium. This behaviour confirms their superior cathodic protection capability and galvanic compatibility over other coatings tested. Electrochemical noise measurements provide accurate information on the coatings' galvanic behaviour, which can be complimented by the data obtained from superposition of potentiodynamic corrosion scans of the coating and bare steel, provided that the corrosion potential difference between the two materials does not exceed 300 mV.     

Effect of calcination temperatures on microstructures and photocatalytic activity of tungsten trioxide hollow microspheres

Tungsten trioxide hollow microspheres were prepared by immersing SrWO₄ microspheres in a concentrated HNO₃ solution, and then calcined at different temperatures. The prepared tungsten oxide samples were characterized by X–ray diffraction, X–ray photoelectron spectroscopy, Fourier transform infrared spectra, differential thermal analysis–thermogravimetry, UV–visible spectrophotometry, scanning electron microscopy, N₂ adsorption/desorption measurements. The photocatalytic activity of the samples was evaluated by photocatalytic decolorization of rhodamine B aqueous solution under visible-light irradiation. It was found that with increasing calcination temperatures, the average crystallite size and average pore size increased, on the contrary, Brunauer–Emmett–Teller-specific surface areas decreased. However, pore volume and porosity increased firstly, and then decreased. Increasing calcination temperatures resulted in the changes of surface morphology of hollow microspheres. The un-calcined and 300 °C-calcined samples showed higher photocatalytic activity than other samples. At 400 °C, the photocatalytic activity decreased greatly due to the decrease of specific surface areas. At 500 °C, the photocatalytic activity of the samples increased again due to the junction effect of two phases.     

Growth and microstructures of carbon nanotube films prepared by microwave plasma enhanced chemical vapor deposition process

Well-aligned carbon nanotubes (CNTs) were grown on iron coated silicon substrates by microwave plasma enhanced chemical vapor deposition. Effect of plasma composition on the growth and microstructures of CNTs were investigated by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and optical emission spectroscopy. Morphology and microstructure of nanotubes were found to be strongly dependent on the plasma composition. Aligned bamboo-shaped nanotubes consisting of regular cone shaped compartments were observed for C₂H₂/NH₃/N₂ and C₂H₂/NH₃/H₂ gas mixtures. Randomly oriented or no nanotubes growth were observed in C₂H₂/H₂ and C₂H₂/N₂ gas mixtures respectively. CNTs grown in nitrogen rich plasma had more frequent short compartments while compartment length increased with decreasing nitrogen concentration in the plasma. Raman spectroscopy of CNTs samples revealed that CNTs prepared in nitrogen rich plasma had higher degree of disorder than those in low nitrogen or nitrogen free plasma. In-situ optical emission spectroscopy investigations showed that CN and H radicals play very important role in both the growth and microstructure of CNTs. Microstructure of CNTs has been correlated as a function of CN radical concentration in the plasma. It is suggested that presence of nitrogen in the plasma enhances the bulk diffusion of carbon through the iron catalyst particles which causes compartment formation. Based on our experimental observations, growth model of nanotubes under different plasma composition has been suggested using base growth mechanism.     

Magnetically responsive,sorafenib loaded alginate microspheres for hepatocellular carcinoma treatment

This study aimed to develop sorafenib loaded magnetic microspheres for the treatment of hepatocellular carcinoma. To achieve this goal, superparamagnetic iron oxide nanoparticles (SPIONs) were synthesised and encapsulated in alginate microspheres together with an antineoplastic agent, sorafenib. In the study, firstly SPIONs were synthesised and characterised by dynamic light scattering, energy‐dispersive X‐ray spectroscopy, and scanning electron microscopy. Then, alginate‐SPIONs microspheres were developed, and further characterised by electron spin resonance spectrometer and vibrating sample magnetometer. Besides the magnetic properties of SPIONs, alginate microspheres with SPIONs were also found to have magnetic properties. The potential use of microspheres in hyperthermia treatment was then investigated and an increase of about 4°C in the environment was found out. Drug release studies and cytotoxicity tests were performed after sorafenib was encapsulated into the magnetic microspheres. According to release studies, sorafenib has been released from microspheres for 8 h. Cytotoxicity tests showed that alginate‐SPION‐sorafenib microspheres were highly effective against cancerous cells and promising for cancer therapy.Inspec keywords: drug delivery systems, drugs, nanofabrication, magnetic particles, iron compounds, scanning electron microscopy, hyperthermia, biomedical materials, encapsulation, nanoparticles, light scattering, nanomagnetics, cellular biophysics, toxicology, cancer, nanomedicine, superparamagnetism, nanocomposites, magnetometry, paramagnetic resonance, X‐ray chemical analysisOther keywords: sorafenib loaded alginate microspheres, hepatocellular carcinoma treatment, sorafenib loaded magnetic microspheres, superparamagnetic iron oxide nanoparticles, dynamic light scattering, energy‐dispersive X‐ray spectroscopy, scanning electron microscopy, electron spin resonance spectrometer, vibrating sample magnetometer, hyperthermia treatment, drug release, alginate‐SPION‐sorafenib microspheres, antineoplastic agent, cytotoxicity tests, cancerous cells, time 8.0 hour, Fe₃ O₄