Polarized Raman study on the lattice structure of BiFeO3 films prepared by pulsed laser deposition

Polarized Raman spectroscopy was used to study the lattice structure of BiFeO₃ films on different substrates prepared by pulsed laser deposition. Interestingly, the Raman spectra of BiFeO₃ films exhibit distinct polarization dependences. The symmetries of the fundamental Raman modes in 50–700 cm⁻¹ were identified based on group theory. The symmetries of the high order Raman modes in 900–1500 cm⁻¹ of BiFeO₃ are determined for the first time, which can provide strong clarifications to the symmetry of the fundamental peaks in 400–700 cm⁻¹ in return. Moreover, the lattice structures of BiFeO₃ films are identified consequently on the basis of Raman spectroscopy. BiFeO₃ films on SrRuO₃ coated SrTiO₃ (0 0 1) substrate, CaRuO₃ coated SrTiO₃ (0 0 1) substrate and tin-doped indium oxide substrate are found to be in the rhombohedral structure, while BiFeO₃ film on SrRuO₃ coated Nb: SrTiO₃ (0 0 1) substrate is in the monoclinic structure. Our results suggest that polarized Raman spectroscopy would be a feasible tool to study the lattice structure of BiFeO₃ films.     

Unexpected formation by pulsed laser deposition of nanostructured Fe/olivine thin films on MgO substrates

Olivine-type LiFePO₄ thin films were grown on MgO (1 0 0) substrates by pulsed laser deposition (PLD). The formation of an original nanostructure is evidenced by transmission electron microscopy measurements. Indeed, on focused ion beam prepared cross sections of the thin film, we observe, the amazing formation of metallic iron/olivine nanostructures. The appearance of such a structure is explained owing to a topotactic relation between the two phases as well as a strong Mg diffusion from the substrate to the film surface. Magnesium migration is thus concomitant with the creation of metallic iron domains that grow from the core of the film to the surface leading to large protuberances. To the best of our knowledge, this is the first report on iron extrusion from the olivine-type LiFePO₄.     

Epitaxial growth of high purity cubic InN films on MgO substrates using HfN buffer layers by pulsed laser deposition

Cubic InN films have been grown on MgO substrates with HfN buffer layers by pulsed laser deposition (PLD). It has been found that the use of HfN (100) buffer layers allows us to grow cubic InN (100) films with an in-plane epitaxial relationship of [001]_InN//[001]_HfN//[001]_MgO. X-ray diffraction and electron back-scattered diffraction measurements have revealed that the phase purity of the cubic InN films was as high as 99%, which can be attributed to the use of HfN buffer layers and the enhanced surface migration of the film precursors by the use of PLD.     

High-resolution transmission electron microscopy investigation of nanostructures in SnO2 thin films prepared by pulsed laser deposition

Pulsed laser deposition (PLD) was used to grow nanocrystalline SnO₂ thin films onto glass substrates. The nanocrystallites and microstructures in SnO₂ thin films grown by PLD techniques have been investigated in detail by using X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The PLD process was carried out at room temperature under a working pressure of about 2×10⁻⁶ mbar. Experimental results indicate that thin films are composed of a polycrystalline SnO₂ and an amorphous SnO phase. In particular, the presence of such an amorphous SnO phase in the thin films greatly limits their practical use as gas-sensing devices. HRTEM observations revealed that SnO₂ nanocrystallites with tetragonal rutile structure embed in an amorphous SnO matrix, which are approximatively equiaxed. These approximatively equiaxed SnO₂ nanocrystallites contain a high density of defects, such as twin boundaries and edge dislocations. The grain growth of SnO₂ thin films may be discussed in terms of the coalescent particle growth mechanism.     

Epitaxial oxide thin films by pulsed laser deposition: Retrospect and prospect

Pulsed laser deposition (PLD) is a unique method to obtain epitaxial multi-component oxide films. Highly stoichiometric, nearly single crystal-like materials in the form of films can be made by PLD. Oxides which are synthesized at high oxygen pressure can be made into films at low oxygen partial pressure. Epitaxial thin films of highT _c cuprates, metallic, ferroelectric, ferromagnetic, dielectric oxides, superconductor-metal-superconductor Josephson junctions and oxide superlattices have been made by PLD. In this article, an overview of preparation, characterization and properties of epitaxial oxide films and their applications are presented. Future prospects of the method for fabricating epitaxial films of transition metal nitrides, chalcogenides, carbides and borides are discussed.     

XPS analysis of aluminum nitride films deposited by plasma source molecular beam epitaxy

Ten samples of crystalline aluminum nitride (AlN) film were deposited on sapphire and silicon substrates by a plasma source molecular beam method. The samples were analyzed using X‐ray photoelectron spectroscopy (XPS) depth profiling and high‐resolution X‐ray diffraction. Oxygen levels were observed to decrease exponentially from the surface into the bulk film. Aluminum, nitrogen and oxygen peaks were fitted with subpeaks in a consistent manner and the subpeaks were assigned to chemical states. AlN subpeaks were observed at 73.5 eV for Al2p and 396.4 eV for N1s. An N1s subpeak at 395.0 eV was assigned to N? N defects. No direct N? O bonds are assigned; rather it is proposed that an N? Al? O bond sequence is the source of higher binding energy N1s subpeaks. The observations in this study support a model in which oxygen is bound only to aluminum in the form of Al? O octahedral complexes dispersed or clustered throughout the main AlN matrix or as Al? O bonds on the crystal grain boundaries. The data also suggest that the AlN lattice parameters are related to oxygen content, since the c‐axis is observed to increase with increasing oxygen content. Copyright © 2008 John Wiley & Sons, Ltd.     

Removal of La(III) by amino-phosphonic acid functionalized polystyrene microspheres prepared via electron beam irradiation

A new aminophosphonic acid chelating resin was successfully prepared via electron beam irradiation grafting combined with chemical modification and used for the efficient removal of La(III). Firstly, glycidyl methacrylate (GMA) was grafted to polystyrene microspheres (PS) via electron beam co-radiation to obtain PS-PGMA microspheres, then followed by the amination with diethylenetriamine (DETA) to formed PS-PGMA-DETA (PGD) microspheres through nucleophilic substitution between amino and epoxy group, and finally PS-PGMA-DETA-PA (PGDP) microspheres was obtained by phosphorylation with phosphorous acid (PA). The obtained chelating resin absorbent was characterized by Fourier-transform infrared (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), which demonstrated that the millimetric aminophosphonic acid chelating resin were successfully prepared with well-defined morphology and enhanced thermal stability. The X-ray photoelectron spectroscopy (XPS) characterization results confirmed a possible adsorption mechanism, which is mainly based on the chelation and coordination of N and O in PDGP with La(III) in the solution. A series of parameters were taken into account in the adsorption experiment, such as absorbed dose, GMA concentration, dosage of PGDP, pH, contact time, temperature, and the initial concentrations of La(III). The maximum adsorption capacity obtained from the research can be achieved 288.69 mg/g at 298.15 K, pH = 6. The kinetic sorption for for La(III) fitted the type 1 pseudo-second-order (R² = 0.9981), which revealed that the La(III) are chemisorbed on the surface of the PGDP. It was concluded that the La(III) adsorption conformed to the Freundlich equation, indicating a multilayer adsorption process. Thermodynamic data indicated that the La(III) uptake process was a spontaneous and endothermic. In addition, this research provided a new irradiation grafting method for rare earth ions removal.     

Electrochemical properties of diamond-like carbon electrodes prepared by the pulsed laser deposition method

Diamond-like carbon electrodes (DLCEs) have been synthesized by the pulsed laser deposition method. The surface structure of the DLCEs has been studied by atomic force microscopy and the root-mean-square roughness has been established as R _ms≥81 ?. Electrochemical impedance spectroscopy and cyclic voltammetry data show that DLCEs are nearly ideally polarizable in the potential region –0.4<E<1.1 V (vs. Ag|AgCl|sat. KCl in H₂O) in 0.1 M NaF+H₂O solution. Various equivalent circuits have been used for fitting the complex plane and Bode plots. A very good agreement between experimental and calculated Nyquist curves has been established if the charge transfer and double layer charging at the surface, intercalation of the H⁺ and (or) Na⁺ ions and solid phase diffusion inside the nanoparticle, as well as the effect of an insulating film at the surface (i.e. surrounding the nanoparticles), are taken into account.     

Optimizing coverage of metal oxide nanoparticle prepared by pulsed laser deposition on nonenzymatic glucose detection

Metal oxide nanoparticles prepared by pulsed laser deposition (PLD) were applied to nonenzymatic glucose detection. NiO nanoparticles with size of 3 nm were deposited on glassy carbon (GC) and silicon substrates at room temperature in an oxygen atmosphere. Transmission electron microscope (TEM) image showed nanoparticles with the size of 3 nm uniformly scattered on the Si(0 0 1) substrate. Unlike co-sputtering nanoparticle and carbon simultaneously, the PLD method can easily control the surface coverage of nanoparticles on the surface of substrate by deposition time. Cyclic voltammetry was performed on the samples deposited on the GC substrates for electrochemical detection of glucose. The differences between peak currents with and without glucose was used to optimize the coverage of nanoparticles on carbon electrode. The results indicated that optimal coverage of nanoparticles on carbon electrode.     

Growth feature of PTFE coatings on rubber substrate by low‐energy electron beam dispersion

Polytetrafluoroethylene (PTFE) coatings were prepared on Si and acrylonitrile‐butadiene rubber substrates by low‐energy electron beam dispersion. The effects of substrate nature, distance of target to substrate (d_ts) and coatings thickness on the surface morphology, structure, and tribological properties of the coatings were investigated. The results showed that substrate nature affects the shape and size distribution of surface conglomerations of PTFE coatings due to the interaction process of active dispersion particles with underlying polymer layer. Surface energy of PTFE coatings decreases first with the coatings thickness increases to 1.25 µm and then slowly increases with the thickness. Structure defects (pore, interstice, and so on) in the coatings increase with the thickness increases but reduce significantly with the d_ts increases. PTFE coating prepared at the d_ts of 20 cm had a higher intensity of the amorphous absorption bands. Friction experiment indicated that the destroyed area of the coatings in the friction region decreases with increases the coatings thickness but increases with the d_ts. The rubber modified by PTFE coatings with spherical structure possesses a higher stability in the friction process and a lower coefficient of friction. Copyright © 2015 John Wiley & Sons, Ltd.     

Innovative energy efficient low-voltage electron beam emitters

Advanced electron beams (AEB) has developed a modular, low voltage (80–125 keV), high beam current (up to 40 ma), electron emitter with typically 25 cm of beam width, that is housed in an evacuated, returnable chamber that is easy to plug in and connect. The latest in nanofabrication enables AEB to use an ultra-thin beam window. The power supply for AEB's emitter is based on solid-state electronics. This combination of features results in a remarkable electrical efficiency. AEB's electron emitter relies on a touch screen, computer control system. With 80 μm of unit density beam penetration, AEB's electron emitter has gained market acceptance in the curing of opaque, pigmented inks and coatings used on flexible substrates, metals and fiber composites and in the curing of adhesives in foil based laminates.     

Selective synthesis of boron nitride nanotubes by self-propagation high-temperature synthesis and annealing process

Four types of BN nanotubes are selectively synthesized by annealing porous precursor in flowing NH₃ and NH₃/H₂ atmosphere at temperature ranging from 1000 to 1200 °C in a vertical furnace. The as-synthesized BN nanotubes, including cylinder, wave-like, bamboo-like and bubble-chain, are characterized by XRD, FTIR, Raman, SEM, TEM and HRTEM. Three phenomenological growth models are proposed to interpret growth scenario and structure features of the four types of BN nanotubes. Selectivity of nanotubes formation is estimated as approximately 80-95%. The precursor containing B, Mg, Fe and O prepared by self-propagation high-temperature synthesis (SHS) method plays a key role in selective synthesis of the as-synthesized BN nanotubes. Chemical reactions are also discussed.     

Improvement of municipal wastewaters by electron beam accelerator in Brazil

Radiation processing of municipal sewage and sludge has been considered not only for disinfection but also for solids and organic matter removal in Brazil. The improvement of irradiated systems were demonstrated by the elimination of indicator bacteria and by the reduction on the total bacteria count, on the chemical and biochemical oxygen demand from raw sewage and biologically treated effluents. The selected doses of radiation to be applied to sewage and sewage sludge are in the range of 3.0 to 4.0 kGy to sewage and 4.0 to 6.0 kGy to sewage sludge.     

In situ spectroelectrochemical behaviour of nanocrystalline TiO_2 thin films electrode fabricated by pulsed laser deposition

Nanocrystalline titanium oxide thin films have been successfully deposited on ITO coated glass by pulsed laser ablation of metallic Ti target in O_3/O_2 ambient gases. The intercalation of Li ions in the anatase TiO_2 film electrode is examined by cyclic vohammetry. The electrochromic behaviour of TiO_2 electrode is investigated by in-situ visible transmittance measurement, and two absorption bands at 420 and 650 nm are observed. The absorption falling and rising in color changing with excellent revisibility is relative to the insertion and deintercalation processes of Li ion. These resuits suggest that nanocrystalline titanium oxide films fabricated by pulsed laser deposition exhibit excellent spectroelectrochemical property.     

Growth of c‐axis‐oriented aluminum nitride thin films onto different substrates and buffer layers

The growth of aluminum nitride thin films onto various substrates (glass, flexible polyimide, or silicon) and onto different buffer layers (Au, Nb, Cu, Ag, Co, Fe, NiFe, or IrMn) is reported. Samples grown on IrMn, Co, NiFe, Nb, or Au show smooth surfaces. This same smooth quality is observed in samples grown at a lower 200 °C temperature directly on glass, Si, or flexible polyimide. In applications where thin and smooth piezoelectric films are necessary, c‐axis‐oriented AlN can be grown onto a wide range of different surfaces: conducting, insulating, ferromagnetic, antiferromagnetic, or flexible. Copyright © 2014 John Wiley & Sons, Ltd.     

Quantification of the electron beam damage of thin films

Owing to diverse possible mechanisms of the e-beam damage, some changes either in the crystalline structure, chemical composition or film thickness occur as the proper damage of the virgin state. Changes in the chemical bonds are often connected with some change in thickness or structure so that the other two are the most important items to be detected, preferably in real time of the electron-microscopical or electron-spectroscopical examination. We propose to measure the film thickness on the basis of the most probable energy loss due to the electron pass through the film and back, i.e. on the basis of the position of the broad background maximum in the electron spectra of stratified specimens. A change in crystallinity can be sensed through the elastic peak intensity. Placing a measurement window between these features in the energy scale and measuring the energy filtered background during the irradiation, we get a pronounced dependence of the signal on the dose which unambiguously reveals the damage limit in the form of a curve knee. In some cases, two stages of damage are detectable.     

Solid-State polymerization of the binary mixture of methacrylate and liquid-crystalline compound by electron beam

Solid-state polymerization of a binary mixture of nonliquid-crystalline monomer and liquidcrystalline compound was carried out using electron beam. The monomers were benzoic acid containing 4-[ω-(meth)acryloyloxyalkyloxy] benzoic acids, in which the alkylene spacer was ethylene, hexamethylene, or undecamethylene. The conversion yield of monomer to polymer to a large extent increased with increasing content of a liquid-crystalline compound with a terminal carboxylic group, such as 4-n-alkyloxybenzoic acid, while the addition of a liquid-crystalline compound without terminal carboxylic group did not affect polymerization of the monomer. Phase diagrams of the mixture of monomer and liquid-crystalline compound were examined using cross-polarizing microscopy and differential scanning calorimetry (DSC). All mixtures of monomer and 4-n-alkyloxybenzoic acid or liquid-crystalline compound without terminal carboxylic group showed liquid-crystallinity in a broad composition range. It was concluded that liquid-crystalline compounds with terminal carboxylic acid may form hydrogen bondings with methacrylate or acrylate monomer having terminal carboxylic acid which enhance polymerizability of the mixture. The stereoregularity of polymers determined by NMR depended on increasing irradiation dose and temperature rather than the content of the added liquid-crystalline 4-n-decanoxybenzoic acid.     

Tin colloids and metal-metal oxide films prepared by chemical liquid deposition. III

Colloids and thin metal-metal oxide films have been prepared by a method we call Chemical Liquid Deposition (CLD). The metal is evaporated to yield atoms which are solvated at liquid nitrogen temperature, and upon warming stable liquid colloidal solutions are formed. In the case of tin, the particle size of these colloids ranges between 200–500 Å. Zeta potentials were calculated by a Hückel approximation for most of these negatively charged particles. Upon solvent removal, colloidal particles coalesce to form films, which contain some residual solvent. The synthesis of colloids and films from Sn with acetone, 2-butanone, THF, ethanol, 2-propanol, DMF and DMSO is reported. FTIR, High Resolution Mass Spectrometry, Thermogravimetric Analyses (TGA) and Scanning Electron Microscopy (SEM) film characterization has been carried out. These studies indicate that solvents are incorporated into the films. The resistivity studies showed that they more behave as semiconductors than pure metals. TGA studies reveal that loss of weight occurs within 200–500°C. The films are very stable with 5–10% weight loss at 550°C. SEM reveals their surface morphology. Mössbauer gives information about oxidation states of some tin films.