B位Co掺杂对Sr14Cu24O41的结构和电输运的影响

采用固相反应法制备了系列Sr14(Cu1-xCox)24O41(x=0,0.02,0.06,0.1,0.14,0.18)的样品,X-射线衍射结果显示所有样品均为单相,且Co的掺杂几乎不改变样品的晶格常数,电子衍射和X-射线光电子能谱的测量结果证实Co替代的是链上的Cu原子;电输运的测量显示,Co掺杂样品表现为半导体行为,且渡越温度T 随掺杂量的增加逐渐减小.     

Photon interaction studies using 241Am γ-rays

We have carried out some photon interaction measurements using 59.54 keV γ-rays from a ²⁴¹Am source. These include γ attenuation studies as well as photoelectric absorption studies in various samples. The attenuation studies have been made using leaf and wood samples, samples like sand, sugar etc., which contain particles of varying sizes as well as pellets and aqueous solutions of rare earth compounds. In the case of the leaf and wood samples, we have used the γ-ray attenuation technique for the determination of the water content in fresh and dried samples. The variation of the attenuation coefficient with particle size has been investigated for sand and sugar samples. The attenuation studies as well as the photoelectric studies in the case of rare earth elements have been carried out on samples containing such elements whose K-absorption edge energies lie below and close to the γ-energy used. Suitable compounds of the rare earth elements have been chosen as mixture absorbers in these investigations. A narrow beam good geometry set-up was used for the attenuation measurements. A well-shielded scattering geometry was used for the photoelectric measurements. The mixture rule was invoked to extract the values of the mass attenuation coefficients for the elements from those of the corresponding compounds. The results are consistent with theoretical values derived from the XCOM package.     

Two-step numerical procedure for complex permittivity retrieval of dielectric materials from reflection measurements

A two-step measurement procedure has been proposed for measurement of complex permittivity of dielectric materials using one-port reflection measurements. In the procedure, as a first step, a graphical method is applied to analyze on the complex reflection-coefficient plane the general pattern of dielectric behavior of the sample. Then, as a second step, optimization algorithms are utilized for retrieving electrical properties of samples. The procedure requires measurement of complex reflection scattering parameters of at least two samples with different lengths. It has been validated by X-band measurements of three polyvinyl chloride samples with lengths 5, 10, and 20 mm.     

Influence of a Cr seed layer on the magnetic anisotropy of epitaxial Fe/Ag films on MgO(001)

The magnetic anisotropy of epitaxial 300 Å thick Fe films on Ag and Ag/Cr buffer layers on MgO(001) has been studied by ferromagnetic resonance and magneto-optic Kerr effect measurements. The samples were grown by molecular beam epitaxy at ambient temperature. A reduction of the effective magnetization for the samples with a Ag buffer layer is attributed to strain and dislocation formation as seen from X-ray diffraction measurements at low and high angles. In the samples with a Cr seed layer, a higher magnetic anisotropy is found which correlates with a reduced roughness.     

Simultaneous recording of two- and four-probe resistive transitions in laser-processed Sr-Ru-O

To confirm previously reported evidence of high-temperature superconductivity in laser processed Sr-Ru-O, we performed simultaneous two-probe and four-probe resistive measurements, using bar-geometry samples. A superconducting-type transition with an onset at about 250K was recorded in one of the samples, consistent with our previously reported measurements in the X-bridge geometry. Some new data on samples preparation are also presented.     

The importance of fabric structure in the construction of 2D textile radiation dosimeters

A range of fabrics was selected for examination as material for construction of 2D radiation dosimeters as a consequence of previously obtained results confirming the possibility of radiation dose measurement with the modified polyamide textiles. These fabrics were surface finished with either 2,3,5-triphenyltetrazolium chloride (TTC) or nitrotetrazolium blue chloride (NBT). Under UV light irradiation the fabrics change colour to reddish (TTC) or bluish (NBT). The tinge intensity depends on the absorbed dose, which was analysed through the reflectance of light measurements. Some parameters of the samples are discussed in this work, such as dose sensitivity, quasi-linear and dynamic dose response, which allowed the samples that were potentially attractive for 2D dosimetry to be selected. The textile samples were assessed in terms of 2D measurements with the application of a computer operated scanner. The accuracy of 2D measurements was found to depend on the type and structure of fabric and tinge distribution after irradiation as well as additional polymer finishing of the textiles.     

The annealing of damage in ion implanted gallium arsenide

Photoluminescence measurements at 77°K and Rutherford scattering of 450 keV protons were used to study radiation damage and annealing in ion implanted GaAs. The characteristic band edge luminescence (8225 Å) in GaAs is completely quenched by ion implantation. Photoluminescence measurements on samples which were isochronally annealed show a single annealing stage at 600°C. A luminescence peak at 9140 Å is introduced into the spectra of all implanted and annealed samples. This peak is attributed to an acceptor level created by As vacancies. The intensity of the peak is greatly reduced by protecting the surface of implanted layers with SiO₂ during annealing. Rutherford scattering measurements on isochronally annealed samples reveal two annealing stages. A 300°C annealing stage is observed on samples which have an initial aligned yield less than random while a 650°C stage is observed on samples which have an initial aligned yield equal to random.     

Precision of the material parameter measurements in the acoustic low-frequency pipe

The effect of errors in the technique implementation on the precision of measurements using the Acoustic Low-Frequency Pipe system that is based on the principle of unidirectional sound reception is considered. Errors in determination of the complex reflection and transmission coefficients of sound for samples tested are calculated theoretically. A numerical analysis of these errors is performed using standard samples as examples.     

Determination of absorption correction by the ‘two masses’ method for XRF analysis of intermediate samples

A simple method for the determination of the absorption correction for intermediate samples is presented. This method consists in measurements of the intensity of radiation of an analyte element in two samples with different masses per unit area and with identical composition. The absorption correction can be determined for samples loaded on the thin or thick substrate or without substrate in the same way. The results obtained are compared with those given by an emission–transmission method with the use, as an example, of synthetic samples pressed into pellets. The absorption correction was also determined for geological samples collected on a filter mounted on a thick substrate. A simple apparatus for collecting powder material on the filter is presented. Copyright © 2003 John Wiley & Sons, Ltd.     

Integrated cavity output spectroscopy measurements of NO levels in breath with a pulsed room-temperature QCL

A cavity-enhanced spectrometer is developed for detection of exhaled nitric oxide in human breath. A thermoelectrically cooled, pulsed, quantum cascade laser, coupled to a high-finesse cavity, is used for trace-gas measurements. The trace-gas analyzer operates at 5.2 microns and utilizes integrated cavity output spectroscopy. Effective optical path lengths of 1.5 km are achieved in a 50-cm-length cell with a sample volume of 60 mL. The instrument is also capable of simultaneously measuringCO2 concentration in exhaled breath. Measurements were performed on human breath samples as well as simulated breath samples. Here we report a detection limit of ≤ 1 ppbv in 4 s for NO in human breath samples.     

Synthesis,characterization and radiation damage studies of high-k dielectric (HfO2) films for MOS device applications

The current trend in miniaturization of metal oxide semiconductor devices needs high-k dielectric materials as gate dielectrics. Among all the high-k dielectric materials, HfO₂ enticed the most attention, and it has already been introduced as a new gate dielectric by the semiconductor industry. High dielectric constant (HfO₂) films (10?nm) were deposited on Si substrates using the e-beam evaporation technique. These samples were characterized by various structural and electrical characterization techniques. Rutherford backscattering spectrometry, X-ray reflectivity, and energy-dispersive X-ray analysis measurements were performed to determine the thickness and stoichiometry of these films. The results obtained from various measurements are found to be consistent with each other. These samples were further characterized by I–V (leakage current) and C–V measurements after depositing suitable metal contacts. A significant decrease in the leakage current and the corresponding increase in device capacitance are observed when these samples were annealed in oxygen atmosphere. Furthermore, we have studied the influence of gamma irradiation on the electrical properties of these films as a function of the irradiation dose. The observed increase in the leakage current accompanied by changes in various other parameters, such as accumulation capacitance, inversion capacitance, flat band voltage, mid-gap voltage, etc., indicates the presence of various types of defects in irradiated samples.     

The dispersion of platinum on silica-correlation of esca and gas adsorption data

For five catalyst samples (Pt supported on silica) prepared by an ion exchange method, a correlation plot of chemisorption data against ESCA Pt/Si signal area ratio was a smooth curve essentially linear at low surface Pt levels but curving at high Pt values. Two samples prepared by an impregnation method were also studied. A line connecting points on the correlation plot for these samples was approximately parallel to but not coincident with the correlation curve obtained for samples prepared by ion exchange. The data strongly support the use of ESCA for measurements of metal particle size (dispersion) in catalyst systems such as these.     

Local eddy current measurements in pulsed fields

This work presents new eddy current measurements in pulsed fields. A commercial point pick-up coil is used to detect the induction signal along the radius of Cu and Al samples with cylindrical shape and diameters between 5 and 35 mm. Local eddy current measurements were performed on the surface of conducting materials due to the small dimensions of the coil. A simple electrical circuit, used as a model, is proposed to describe the local eddy current effect in pulsed fields. The proposed model allows to calculate the phase shift angle between the signal proportional to eddy currents and the applied external field in a pulsed field magnetometer.     

Temperature dependence of magnetic properties in Fe/Fe-O nanoparticles dispersed in water

Commercial water dispersions of Fe/Fe-O nanoparticles (∼50-80 nm diameter) were prepared bare and treated with a biodegradable polymer to stabilize the suspension. Hysteresis loops and FC-ZFC curves of samples in liquid and dried form were measured by means of a vibrating sample magnetometer from 77 to 300 K. A marked dependence on the conditioning field is observed in all samples that display the Verwey transition at about 120 K. The role of magnetic interactions on dried samples was also investigated by means of magnetoresistance measurements as a function of temperature.     

Luminescence study of Si/Ge quantum dots

We present a photoluminescence (PL) study of Ge quantum dots embedded in Si. Two different types of recombination processes related to the Ge quantum dots are observed in temperature-dependent PL measurements. The Ge dot-related luminescence peak near 0.80 eV is ascribed to the spatially indirect recombination in the type-II band lineup, while a high-energy peak near 0.85 eV has its origin in the spatially direct recombination. A transition from the spatially indirect to the spatially direct recombination is observed as the temperature is increased. The PL dependence of the excitation power shows an upshift of the Ge quantum dot emission energy with increasing excitation power density. The blueshift is ascribed to band bending at the type-II Si/Ge interface at high carrier densities. Comparison is made with results derived from measurements on uncapped samples. For these uncapped samples, no energy shifts due to excitation power or temperatures are observed in contrast to the capped samples.     

The role of carbon in the precipitation of oxygen in silicon

Oxygen precipitates were formed in Czochralski-grown silicon samples at different temperatures and for different lenghts of times of heat treatment. Precipitation was evident from infrared(IR) analysis of so treated samples. These samples were irradiated with 2 MeV electrons at near room temperature (310 K). Deep level transient spectroscopy measurements and IR measurements were performed on these samples. The results show directly that a single carbon atom or a carbon-oxygen complex can serve as nucleation centers for the oxygen precipitation.     

Determination of the fundamental optical characteristics of absorbing films

A new method is proposed for the determination of the principal optical characteristics of absorbing films deposited on substrates for all cases when it is impossible to neglect the effect of the substrate. The method is based on measurements of transmission and absorption of unpolarized light.In conclusion, the author thanks F. A. Koroleva for her interest in the work and valuable advice and R. P. Fialkovskaya for kindly supplying the titanium oxide film samples for the measurements.     

Raman spectroscopy and chemometrics for quantitative analysis of complex flows in an industrial transesterification process

A method based on Raman spectroscopy has been used for determination of ester acrylate mixture composition from an industrial production of acrylic monomers. Five molecules of the industrial mixture have been studied: main components and an impurity. Experiments were carried out with an immersion probe on the spectral range of 100–3425 cm⁻¹. Usually, monitoring a complex industrial flow by spectroscopic analysis requires a lot of samples in order to have a representative prediction model. Here only 60 samples from the process were necessary to build the model. The statistics was then artificially increased by synthetically increasing the number of samples. A qualitative study by principal component analysis was at first done, and then a partial least squares method was performed to assess the feasibility of quantitative measurements in such transesterification process. Internal and external validations methods have been used and their results show a RMSEP below 1% of samples predicted concentration ranges. The repeatability and reproducibility of Raman measurements are also discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Radiographic method for measuring the continuum hard X-ray output spectrum of a Plasma Focus device

A radiographic method is proposed and then applied to infer the continuum part of the hard X-ray spectrum of a 4.7 kJ Plasma Focus from differential absorption measurements on metals. Copper, nickel, titanium and silver samples with thicknesses spanning between 0.1 and 10 mm were employed as filters. The X-ray radiation was detected using a standard radiographic screen-film system. The results show the presence of a dominant peak around 75 keV with significant spectral components in the range of 40 to 200 keV. The method is easy to follow, inexpensive, and allows for calibrated, single shot, spectral measurements.     

A new method for ESCA studies of liquid-phase samples

A new technique is described for obtaining ESCA spectra from liquid-phase samples. It combines temperature regulation of the liquid samples, which are continuously created as thin films on a metal backing, with the use of monochromatized A1 Kα radiation for excitation. The technique is simple to implement and can be used routinely over essentially unlimited periods of recording time in the spectrometer. The results show substantially increased quality with respect to earlier measurements in terms of signal-to-background ratio and resolution. The technique also implies a vast increase in the number of solvents usable for future liquid-phase ESCA work.