The optoelectronic properties and effect of calcium doping on structural and electrical properties of ZO-Ca aerogel nanoparticles

Calcium-doped ZnO (ZO-Ca) and undoped ZnO nanopowders were synthesized by the sol–gel method. The XRD results indicate that the structural properties of these samples presented hexagonal Wurtzite phase. In addition, the average crystallite size calculated is 37 and 44 nm for an undoped and doped sample, respectively. Further, impedance spectroscopy was investigated to study the calcium doping effect on the electrical behavior of ZnO nanoparticles. The decrease of the exponent s with increasing temperature suggests that the conduction mechanism predominant is the correlated barrier hopping (CBH). The complex impedance analysis of the ZO-Ca samples showed that at low frequency, there is a plateau that get reduced with a temperature which verifies the thermal activation of the conduction mechanism. The obtained results are interesting for understanding the effect of doping on the electronic transport mechanism which is unavoidable to explain the fundamental aspect in various technological applications.

     

Study of carbon fibres and carbon–carbon composites by scanning thermal microscopy

Scanning thermal microscopy (SThM) is a relatively new technique based on atomic force microscopy in which the tip is replaced by an ultra‐miniature temperature probe. This paper reports on a preliminary investigation of the application of SThM in the characterization of the thermal properties of carbon fibres and carbon–carbon (CC) composites. The technique enabled a comparative study to be made of discrete fibre and matrix thermal properties in a series of model unidirectional composites. The thermal images revealed a marked increase in thermal conductivity of the matrix with increasing temperature of treatment and hence confirmed the development of a highly ordered carbon matrix. The results were in qualitative agreement with previously determined values of thermal conductivity from which the separate values of fibre and matrix thermal conductivity had been derived. The technique was also applied to the characterization of samples of unknown processing history, enabling an estimation to be made of the heat treatment and type of the fibres and matrix present in the composite. It was concluded that SThM promises to be a powerful technique for the study of the thermal properties of CC composites and carbon fibres, as it uniquely enables variations in local thermal conductivity to be detected and resolved. Absolute quantification of the technique remains the key to its future widespread acceptance in materials characterization.     

A Transparent,Smooth, Thermally Robust,Conductive Polyimide for Flexible Electronics

In this work, a thermally and mechanically robust, smooth transparent conductor composed of silver nanowires embedded in a colorless polyimide substrate is introduced. The polyimide is exceptionally chemically, mechanically, and thermally stable. While silver nanowire networks tend not to be thermally stable to high temperatures, the addition of a titania coating on the nano­wires dramatically increases their thermal stability. This allows for the polyimide to be thermally imidized at 360 °C with the silver nanowires in place, creating a smooth (<1 nm root mean square roughness), conductive surface. These transparent conducting substrate‐cum‐electrodes exhibit a conductivity ratio figure of merit of 272, significantly outperforming commercially available indium‐tin‐oxide (ITO)‐coated plastics. The conductive polymide is subjected to various mechanical tests and is used as a substrate for a thermally deposited, flexible, organic light‐emitting diode, which shows improved device performance compared to a control device made on ITO coated glass.     

Real-time correction of heart interbeat intervals

Heart rate variability (HRV) is traditionally analyzed while a subject is in a controlled environment, such as at rest in a clinic, where it can be used as a medical indicator. This paper concerns analyzing HRV outside of controlled environments, such as on an actively moving person. We describe automated methods for inter-heartbeat interval (IBI) error detection and correction. We collected 124,998 IBIs from 18 subjects, undergoing a variety of active motions, for use in evaluating our methods. Two human graders manually labeled each IBI, evaluating 10% of the IBIs as having an error, which is a far greater error percentage than has been examined in any previous study. Our automated method had a 96% agreement rate with the two human graders when they themselves agreed, with a 49% rate of matching specific error corrections and a 0.01% false alarm rate.     

Defluorination of Wet-Phosphoric Acid： Equilibrium and Kinetic Studies

This study describes the advantages of using iron-oxide-pillared MF （montmorillonite） and EDTA （ethylenediaminetetraacetic acid）-pillared MD （montmorillonite） for the removal of fluoride in the phosphoric acid. The MF and MD were characterized by using BET （Brunauer-Emmett-Teller） and SEM （scanning electron microscope） for there to appreciate their textural and structural properties and in order to appraise their capacity in the fixation of the fluorine experimental results of fluorine adsorption show a defluoration of the phosphoric acid passing beyond 90% with both clays with a light performance for the MD. The kinetics of fluorine adsorption on MF and on MD has been measured at different temperatures. Indeed, the adsorbed quantity increases more favorably to temperatures more high. This kinetics could be described by two models： pseudo-first-order or pseudo-second-order, which depends on temperature and the nature of adsorbent. At different temperatures used and with various adsorbents （MD and MF, the pseudo second order model was the most reliable to determine the order of kinetics of adsorption of fluorine, which is also reflected a good correlation coefficient （above 0.99）. The fluoride sorption was reasonably explained with Langmuir or Freundlich isotherms. Thermodynamic parameters such as AG~, AH~, AS~ and kinetic one E,, （apparent activation energy） were calculated in order to understand the nature of sorption process. Results indicate that the mechanism of adsorption of the ion of fluoride on the pillared montmorillonite is an exothermic reaction. During equilibrium conditions, both the systems showed negative Gibbs energy, which indicates stability of system. The values of apparent activation energy for the both clays show that the adsorption of F ions is easier on the MF.     

Synthesis,Surface Characterization and Photocatalytic Activity of TiO2 Supported on Almond Shell Activated Carbon

Three types of photocatalysts were synthesized by metal organic chemical vapor deposition and impregnation methods using the almond shell activated carbon as support. These photocatalysts denoted by （TiO2/ASAC （V）, TiO2/ASAC （11） and TiO2/ASAC （12）） were characterized by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FTIR）, diffuse reflectance spectroscopy （DRS） and nitrogen adsorption-desorption isotherms. SEM observation shows that TiO2 was deposited on activated carbon surface. XRD results confirm that TiO2 existed in a mixture of anatase and rutile phases. The DRS spectra show the characteristic absorption edge of TiO2 at approximate 380 nm corresponding to the optical band gap of 3.26 eV. Besides, FTIR spectrum indicated the presence of （Ti-O） groups. The specific surface area of photocatalysts decreased drastically in comparison with the original activated carbon. The catalysts were very efficient for the photodegradation of total organic carbon （TOC） from industrial phosphoric acid solution under UV irradiation. The kinetics of photocatalytic TOC degradation was found to follow a pseudo- first-order model. The prepared TiO2/ASAC showed high photoactivity for the photodegradation of TOC in the following order： TiO2/ASAC （V） 〉 TiO2/ASAC （11） 〉 TiO2/ASAC （12） 〉 ASAC 〉 TiO2 （P25）.     

Quantitative predictions from solid-state physics—What do phase diagram calculators want?

The types of information required for the calculation of phase diagrams are discussed by considering the computation of typical ternary sections from the constituent, binary systems. Such calculations require a knowledge of the Gibbs energy of transformation (lattice stabilities) and Gibbs energies of mixing of wholly metastable, as well as stable, phases in binary systems. Similarly, the stabilities of metastable compounds, such as Fe₇C₃, would be required for computations in the C?Cr?Fe system. These requirements are compared to the information provided by solid-state theoreticians.     

Synthesis and Characterization of Nanostructured BSTO Thin-Films for Microwave Applications

Nanophase synthesis of ferroelectric thin-films of Ba_0.6Sr_0.4TiO₃ (BSTO) was studied systematically for applications in tunable microwave components. Synthesis of nanostructured BSTO was performed using a pulsed-laser deposition system with real-time in-situ process control. The main research goal was to utilize the pulsed laser deposition parameters to control the grain growth for low microwave loss nanostructured BSTO thin-films on crystalline substrates such as LaAlO₃. These parameters include the energy density of the laser pulses, wavelength, oxygen partial pressure, distance between the target and the substrate, and the substrate temperature. The nanostructural characterization was performed using XRD, SEM and AFM. Microwave characterization was done using coplanar waveguide lines to characterize the frequency dependent dielectric properties (?_r and tan δ). BSTO films were grown at the same measured temperature and energy density but in different oxygen ambient pressures from 19 mTorr through 300 mTorr. Using contact mode AFM, the grain size was found to decrease as the oxygen ambient pressure was reduced from 150 mTorr to 38 mTorr. The growth process changed when the pressure was increased above 150 mTorr. Nanocluster structures rather than nanoparticles were found at 225 mTorr. Average grain sizes less than 100 nm were obtained to oxygen pressures below 75 mTorr. The XRD spectra indicate the highly crystalline nature of the film. Microwave measurements, performed between 9–18 GHz, suggest the nano-structured BSTO thin-films on LaAlO₃ (LAO) substrates are highly tunable (up to 25%).     

Concurrently pumped ultrasonic spray coating for donor:acceptor and thickness optimization of organic solar cells

We assess the utility of concurrent spray coating to efficiently screen and optimize solutions for organic solar cells. With this technique two independent solutions are coaxially pumped to the ultrasonic nozzle tip of the spray coater, where a micron-scale mist of droplets, each consisting of one of the two respective solutions with negligible mixing, is ejected toward the substrate. Concurrent spray coating is shown to allow the scanning of two important photoactive layer parameters: thickness, by concurrently diluting concentrated donor:acceptor (D:A) solution with pure solvent, and D:A ratio by concurrently spraying independent solutions of donor and acceptor. The assessment is done using the archetypal poly(3-hexylthiophene) (P3HT):(6,6)-phenyl C61-butyric acid methyl ester (PCBM) system. By allowing the droplets to coalesce on the substrate prior to drying, the resulting film realizes a favorable morphology, confirmed via high-performance OSC devices, with a peak efficiency of 4.1%, 72% fill factor, 9.3 mA/cm² short circuit current density, and a 620 mV open circuit voltage.