Zur Spinordnung von paramagnetischen Zusätzen in abschreckend kondensierten Schichten aus Supraleitern

The susceptibility of the dilute alloys Pb-Mn, Cu-Mn, Sn-Mn, and La-Gd is measured in the temperature range from 2 to 300 °K. The dilute alloys are produced by simultaneous evaporating of both components on a substrate at 14 °K. In this way one gets a statistic distribution of the paramagnetic impurities in the solvent. The Mn atoms, dissolved in Pb, obeyCurie's law. The paramagnetic Curie temperature equals zero at every chosen concentration for the mentioned systems. Mn in Pb shows an effective magnetic moment of 3.9 Bohr magnetons in the concentration range from 2 to 10 at% Mn. At low temperature there exists a quasi-antiferromagnetic ordering among the spins of the Mn atoms. The temperature at which this ordering appears, linearly increases with the concentration of Mn. With regard to the systems of Cu-Mn, Sn-Mn, and La-Gd we also find an antiferromagnetic spin ordering. The transition temperature of superconductivity is depressed by adding Mn to Pb. The decrease disappears when the Pb-Mn films are annealed to 290 °K. This agrees with the fact that Mn loses its magnetic moment after annealing the films to room temperature.     

Zum Einsatz metallischer Leitfähigkeit während der Kondensation von Metallschichten

Ag-, Cd-, Tl-, Pb- and Bi-films are condensed at constant deposition rates onto crystalline quartz. Film conductance is measured as a function of the mass condensed. During the growth of the film metallic conductivity appears at a “critical” thickness. This critical thickness is constant at low temperatures and begins to rise exponentially at a certain temperature which depends on the condensation energy of the metal. For metals with low thermal conductivity a large critical thickness is found at low temperatures. If the substrate is pre-sensitized with silver the critical thickness of lead films is reduced considerably while amorphous bismuth films show just the opposite behaviour.     

Zur Widerstandsanomalie von Legierungen bei tiefen Temperaturen

Dilute alloys of Cu-Fe, Au-Fe, Zn-Mn, and Ag with V, Cr, Mn, Fe, Co are produced by simultaneous evaporation of both components on a substrate at 77 °K. By this method one succeeds in solving all systems, especially Cu alloys with high Fe concentration, which alloys normally show precipitations after cooling from the molten state. For these alloys we observe resistance minima up to 150 °K. Besides this, Cu-Fe shows a resistance maximum which depends on concentration. For Au-Fe and Ag-Mn we measure resistance anomalies which are even bigger for quenched films than for annealed films and bulk material. Apparently the lattice defects have an influence on the resistance anomaly. The increase of the resistance with decreasing temperature can be described by the functionρ _s /ρ _s0 =f(T/T _k ) for all systems. The result does not agree with the theories basing on Kondo's model. Here is tried an explanation by means of spin-orbit interaction. This interaction results in a temperature dependent cross-section for a molecule consisting of a magnetic impurity and a lattice defect.     

Electrical resistivity of amorphous alloys

Amorphous alloys of Ga, Sn, Pb and Bi with Cu, Ag and Au are produced by evaporation on a cold substrate. The residual resistivity, the temperature dependence of the resistivity, the transition temperature of superconductivity and the temperature of the amorphous-crystalline transformation are measured. We observe e.g. that the residual resistivity increases with the noble metal concentration, and that the temperature coefficient of the resistivity of the Au alloys is always negative. In these two respects amorphous alloys differ in behaviour from the corresponding liquid alloys. These observations can be correlated with the atomic energy levels of the free atoms.     

Stark effect on donor transitions in high-purity GaAs

A quantitative study of line narrowing of the 1s?2p_- transitions in hydrogenic GaAs donors with increasing magnetic field shows that the observed widths are due to Stark-effect inhomogeneous broadening. From the parameters involved we conclude that internal electric fields should very often play a dominant role in determining lineshapes of shallow impurity optical transitions in high purity partly compensated semiconductors at low temperatures.     

Near infrared emission spectroscopy induced by ultrasonic irradiation

Near infrared emission caused by ultrasonic excitation is demonstrated for the first time in this work. The instrument is constituted of an acousto-optical tunable filter-based spectrometer, an ultrasonic processor connected to a titanium alloy ultrasonic probe and a cylindrical borosilicate flask containing the sample to be excited. The radiation emitted by the sample is collected by a concave mirror and sent to the spectrometer. The effects of the position of the probe extremity in relation to a lateral entrance of the borosilicate flask and of the ultrasonic power on the emission signal were studied. The best results were obtained by positioning the probe extremity up to 2mm from the reflexive body (lateral entrance) using 30% of the full ultrasonic incident power and acquiring spectra after 5 min of sonication. The NIR emission spectra resulting from the ultrasonic excitation were in agreement with that obtained by thermal excitation. The proposed technique was utilized to study different poly(dimethylsiloxane) samples having different viscosities.     

Sample Preparation for the Determination of Metals in Food Samples Using Spectroanalytical Methods—A Review

Abstract

The present article gives an overview of recent publications and modern techniques of sample preparation for food analysis employing atomic and inorganic mass spectrometric techniques, such as flame atomic absorption spectrometry, chemical vapor generation atomic absorption and atomic fluorescence spectrometry, graphite furnace atomic absorption spectrometry, inductively coupled plasma optical emission spectrometry, and inductively coupled plasma mass spectrometry. Among the most frequently applied sample preparation techniques for food analysis are dry ashing, usually with the addition of an ashing aid, and acid digestion, preferably with the assistance of microwave energy. Slurry preparation, particularly with the assistance of ultrasound, is increasingly used to reduce acid consumption and sample preparation time. Direct analysis of solid samples is gaining importance in the field of food analysis as it offers the highest sensitivity, avoids the use of acids and other aggressive reagents, makes possible the analysis of micro‐samples, and can be applied for fast screening analysis, e.g., of fresh meat.     

Ultrasound‐Assisted Synthesis of Hybrid Vanadium Oxide/Polyaniline Nanowires

A single‐step sonochemical procedure to synthesize hybrid vanadium oxide/polyaniline nanowires starting from crystalline V₂O₅ and aniline in aqueous medium is presented. The synthesis explores the effect of high power ultrasounds on heterogeneous solid–aqueous phases, which leads to 30 nm width wires of 5 to 10 µm in length. Monomer intercalation and oxidative polymerization within the inorganic matrix proceed simultaneously with morphological changes. The electronic conductivity of hybrid nanowires reaches 0.8 S · cm⁻¹ at room temperature.

     

Determination of phenols and chlorophenols as trimethylsilyl derivatives using gas chromatography-mass spectrometry

A rapid and simple method is described for the simultaneous determination of 6 phenols (phenol, o-, m-, p-cresol, catechol and resorcinol) and 19 chlorophenols (all mono-, di-, tri-, and tetrachlorophenol isomers and pentachlorophenol) present in aqueous samples. The method is based on derivatization with trimethylsilyl-N,N-dimethylcarbamate (TMSDMC). In contrast to other derivatization agents, TMSDMC instantaneously reacts with the phenolic compounds at room temperature and no further sample processing is necessary prior to instrumental analysis. The determination of the derivatives was performed by capillary gas chromatography-mass spectrometry (GC-MS). The stability of the most instable trimethylsilyl derivative (pentachlorophenol) was studied using different excess levels of the derivatization reagent. The derivatization method was tested on spiked water samples preconcentrated by solid phase extraction on Isolute ENV+ cartridge. The overall method gave detection limits of 0.01-0.25 microg/L for all compounds and < 0.05 microg/L for 17 of them.