System design considerations for precision measurement of high magnetic fields by Faraday effect

Practical and technical considerations for an instrument designed to measure high magnetic fields by Faraday effect are given. Magnetic fields up to 2 Tesla were measured and the results compared to those of Nuclear Magnetic Resonance technique. Results of measurements at low temperatures are also reported.     

Surface plasmon resonance and surface-enhanced Raman scattering activity of SiO2–Au core-cap nanostructure arrays

SiO₂–Au core-cap nanostructure arrays were prepared by dip-coating technique combined with wet chemical reduction method. The surface morphologies, structures, and optical properties of the obtained samples were characterized by scanning electron microscopy, X-ray diffraction, and ultraviolet–visible spectrophotometer, respectively. The surface-enhanced Raman scattering (SERS) activity of SiO₂–Au core-cap nanostructure arrays substrates was investigated using leucine as probe molecule. And the relationship between the SERS effect and the surface plasmon resonance (SPR) peaks was discussed. High-quality, stable, and reproducible SERS spectra of leucine were successfully obtained. When the maximum SPR peak matched with the excitation wavelength, the substrate gave rise to the highest SERS enhancement. Furthermore, six different fluorescent dyes were also chosen as probe molecules. It was found that the substrate showed good Raman enhancement and highly efficient fluorescence quenching characteristic on these fluorescent dyes.     

The KLL Auger spectrum of fluorine

The KLL Auger spectrum of fluorine (Z=9) has been studied in three different fluoride salts. Five Auger lines are observed in each compound in accordance with extreme LS coupling theory. A cation dependence of the Auger transition energies and line-widths is observed. The energy shifts are in agreement with a theoretical model.     

Synthesis of fluorescent carbon dots from one-step pyrolysis of frontal-polymerized poly(acrylamide-co-4-vinylpyridine)

We report herein the synthesis of carbon dots (CDs) by a one-step pyrolysis from poly(acrylamide-co-4-vinylpyridine) [poly(AAM-co-4-VP)]. The poly(AAM-co-4-VP) was fabricated using frontal polymerization within 5 min in an easy and rapid way and then was pyrolyzed to afford CDs. The as-prepared CDs show crystalline structure and excellent dispersibility with particle sizes in the range of 2–4 nm. The optical properties were throughly investigated, and we found the CDs exhibit strong blue fluorescence with quantum yield of ~18 % and excellent photoluminescent stability, which is rarely influenced by the external conditions. This process can be exploited as an effective path for synthesis CDs with polymers by a facile and rapid way.     

Radiative lifetimes of some energy levels of doubly ionized Xenon

Using 1–5 MeV Xenon ions we have studied the beam-foil spectrum of Xenon between 105 nm and 500 nm. Radiative lifetimes were measured for levels of Xenon III. For those lifetimes which have been measured previously (Andersen et al. [l]) good agreement is obtained. The interpretation of the decay curves and the assignment of a measured value, were done with the help of theoretical lifetimes obtained by Coulomb-approximation calculations [2].     

Plasma-assisted hot filament chemical vapor deposition of AlN thin films on ZnO buffer layer: toward highly c-axis-oriented,uniform, insulative films

c-Axis-oriented aluminum nitride (AlN) thin film with improved quality was deposited on Si(111) substrate using ZnO buffer layer by plasma-assisted hot filament chemical vapor deposition. The optical and electrical properties and surface morphology as well as elemental composition of the AlN films deposited with and without ZnO buffer layer were investigated using a host of measurement techniques: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and current–voltage (I–V) characteristic measurement. The XRD and XPS results reveal that the AlN/ZnO/Si films are free of metallic Al particles. Also, cross-sectional FESEM observations suggest formation of a well-aligned, uniform, continuous, and highly (002) oriented structure for a bi-layered AlN film when Si(111) is covered with ZnO buffer. Moreover, a decrease in full width at half maximum of the E₂ (high)-mode peak in Raman spectrum indicates a better crystallinity for the AlN films formed on ZnO/Si substrate. Finally, I–V curves obtained indicate that the electrical behavior of the AlN thin films switches from conductive to insulative when film is grown on a ZnO-buffered Si substrate.     

The secondary-electron background problem in electron excited auger electron spectroscopy

Dynamic background subtraction is used to demonstrate that the recently suggested spline-polynomial scheme for characterizing the secondary electron background neglects an important aspect of the Auger feature. As a consequence of this neglect, area measurements using the spline approximation are difficult to relate to the true Auger current.     

Beam-foil lifetime measurements on energy levels of singly ionized Xenon

Radiative lifetimes were measured for levels of Xenon II by use of the beam-foil technique. Results are compared with other experimental and theoretical data. The coulomb approximation [1] was used to calculate lifetimes of the higher levels of Xenon II to facilitate an unambiguous assignment of the measured lifetime to a level.     

Double-walled core-shell structured Si@SiO2@C nanocomposite as anode for lithium-ion batteries

Double-walled core-shell structured Si@SiO₂@C nanocomposite has been prepared by calcination of silicon nanoparticles in air and subsequent carbon coating. The obtained Si@SiO₂@C nanocomposite demonstrates a reversible specific capacity of about 786 mAh g^?1 after 100 cycles at a current density of 100 mA g^?1 with a capacity fading of 0.13 % per cycle. The enhanced electrochemical performance can be due to that the double walls of carbon and SiO₂ improve the electronic conductivity and enhance the compatibility of electrode materials and electrolyte as a result of accommodating the significant volumetric change during cycles. The interlayer SiO₂ may release the mechanical strain and enhance the interfacial adhesion between carbon shell and silicon core.     

Luminescent properties of Eu2+ ions in AlN at low and high intensity of excitation

Luminescent properties of powder AlN∶Eu²⁺ phosphors were studied by excitation of 2-nd harmonic of ruby laser (hv=3·56 eV). It was shown that emission spectra of AlN∶Eu²⁺ phosphors consist of five or two overlapping bands according to the concentration of europium and the intensity of excitation. Decay times of luminescence of Eu²⁺ centres in different peaks lie between 0·9 and 1·5 μsec which is in agreement with the value of decay time of 4f⁶ 5d→47⁷ transition of Eu²⁺ ions. It is evident from the decomposition of emission spectra of Eu²⁺ centres that there exist several types of Eu²⁺ centres in AlN as was already demonstrated in the case of oxygen centres in AlN.     

Methods of IR spectroscopy in monitoring of chemotherapy of oncological pathologies using palladium complexes

FTIR spectroscopy is used to study mammary-gland tissues of mice with a sarcoma tumor (strain 180). Spectral features that are typical of malignant tumors are revealed in the FTIR spectra in the sarcoma-tumor tissues. Tumor tissues are studied after treatment using coordination compounds based on palladium complexes with 3-amino-1-hydroxypropylidene-1,1-diphosphonic acid and zoledronic acid. A therapeutic effect is not revealed after treatment using palladium complex with 3-amino-1-hydroxypropylidene-1,1-diphosphonic acid. The suppression of tumor growth amounts to 59% when palladium complexes with zoledronic acid are used. Suppression of tumor growth is accompanied by variations in spectral characteristics. With respect to diagnostic features, the FTIR spectra of tumor tissues after treatment with the palladium complexes with zoledronic acid are similar to the FTIR spectra of tissues that are free of malignant tumors. Specific spectroscopic characteristics that make it possible to control the chemotherapy of oncological pathologies are determined.     

Synthesis at the nanoscale of ZnO into poly(methyl methacrylate) and its characterization

In this paper, PMMA/ZnO nanocomposites have been prepared by a very simple, facile and versatile chemical approach. The prepared PMMA/ZnO nanocomposites possess no color, high transparency, good thermal stability, UV-shielding capability, luminescence and homogeneity. The chemical process involved solution mixing of ZnO nanoparticles dispersed in DMAc with the Polymethylmethacrylate (PMMA) matrix dissolved in the same solvent. The effect of ZnO content on the physical properties of the PMMA matrix is investigated by X-ray diffraction, field emission scanning electron microscopy, thermogravimetric analysis, UV–Vis absorption and photoluminescence spectroscopy. It was found that pure hexagonal ZnO nanoparticles with an average particle size of 4–8 nm were homogeneously dispersed in the PMMA matrix. A significant improvement in thermal properties was observed with the incorporation of 1.0 wt% ZnO nanoparticles. The prepared nanocomposite films are highly transparent and a clear excitonic peak is observed in their absorption spectra. Measurement of room temperature photoluminescence spectra shows intensive near-band edge emission peak at 3.28 eV without any structural defects for a nanocomposite film with a filler content of 1.0 wt%.     

Beam-foil-excited Auger transitions in neon

Energy spectra of electrons ejected from collisions between a carbon foil and Ne projectiles with energies between 1.4 and 20 MeV have been measured. Continuous and discrete electron energy distributions are observed. Auger transitions of foil-excited Ne have been studied. Using relativistic Dirac-Fock multiconfiguration calculations, most of the measured Auger transitions have been identified.     

Superoxide- and NO-Dependent Mechanisms of the Reprogramming of Bone Marrow Cells by Tumor Cells

Electron paramagnetic resonance (EPR) experiments in vitro; spin trapping of the reactive oxygen/nitrogen species (superoxide radicals and nitric oxide, NO); gel zymography measurements in the tumor tissues, in the healthy and tumor-affected bone marrow (BM) samples of rats are carried out. The superoxide and NO generation rates are derived; matrix metalloproteinases (MMP-2 and MMP-9) concentrations are measured. Their changes after the incubation of BM samples with Guérin carcinoma cells at 37 °C are defined. It is shown that the impact of tumor cells on BM manifests in the metabolic disorder, increased concentrations of active forms of MMP-2 and MMP-9, increased production of superoxide and NO radicals. Correlation between the appearance and intensity of the broad EPR signal at g = 2.2–2.4 with the concentrations of active forms of MMP-2 and MMP-9, NO and superoxide radicals’ rates is observed. The obtained spatial and temporal changes of the measured parameters demonstrate the usefulness of the potential application of EPR imaging to study the mechanisms of tumor invasion. The EPR signal may indicate the presence of distant metastases, may become a part of diagnostics and used for the estimation of the therapeutic treatments in the pre-clinical studies. It is proposed that labile iron pool is responsible for the appearance of the EPR signal in tumor and BM samples.     

On the theory of electron diffusion under a temperature gradient in degenerate semiconductors having non-parabolic energy bands

The theory of electron diffusion under a temperature gradient (Soret effect) in degenerate semiconductors having non-parabolic energy bands and spherical constant-energy surfaces is worked out for the first time. An expression is given for the Soret coefficient which may be determined from the knowledge of the energy dependence of the relaxation time and can be related to the thermoelectric power.     

Beam-foil level lifetimes in Krypton III

The radiative lifetimes of levels in doubly-ionized Krypton have been measured after foil excitation of a beam of Krypton particles in the wavelength range 120nm–500nm. The results are compared with the experimental values obtained by Fink et al. [1], as well as theoretical values resulting from Coulomb approximation (C.A.) and single configuration Hartree-Fock (H.F.) calculations.     

Determination of cesium distributions in oxides of MOS structures by photoinjection studies

The photoinjection technique of Berglund and Powell has been used for the determination of cesium profiles in the oxide films of MOS-structures. Measurements of photocurrent as a function of the applied voltage provide information on the distribution of charges in the vicinity (10–200 Å) of both the interfaces of the insulating layer. The charge profiles to be measured were introduced into SiO₂ by ion implantation. Cesium ions, which cause positive surface charge and show great stability under temperature-bias stress, have been implanted before and after oxidation. In the first case, cesium ions were implanted into the silicon surface, which was subsequently oxidized. After oxidation, the cesium ions were found mainly at both the interfaces and only a few of them in bulk SiO₂. In the second case, cesium ions were implanted into SiO₂ at an energy of 5 keV. The cesium distribution measured by the photoinjection technique agrees within 5 Å with that predicted by implantation theory.     

A comparative study of the dopant profiles in diffused planar optical waveguides by SIMS and guided wave probe

A technique has been developed for dopant concentration depth profiling using static Secondary Ion Mass Spectrometry (SIMS), and an ex-situ ion milling facility to produce “tapers” through the region of interest of an optical waveguide sample. Results have been obtained for titanium-diffused optical waveguides in lithium niobate and for potassium and caesium ion-exchanged glass waveguides. The SIMS profiles have been compared with refractive index profiles in multimode structures. The refractive index profiles have been obtained from the waveguide mode spectra by a piecewise linear Wentzel-Kramers-Brillouin (WKB) method. The two profiles are in close agreement. Use of the SIMS technique for single mode Ti∶LiNbO₃ waveguides has revealed significant changes in the forms of the profiles, compared with deeper structures, and we suggest a mechanism to account for these changes.     

Conductivities and ion association constants of ferric chloride and chromic chloride in DMF and DMSO as a function of temperature

The equivalent conductivities of anhydrous ferric chloride (FeCl₃) and anhydrous chromic chloride (CrCl₃) were measured in nonaqueous aprotic solvents such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) at temperatures between 278.15 and 318.15 K. In both DMF and DMSO, conductivity values for FeCl₃ were found to be higher than those for CrCl₃. In addition, the conductivity values for both FeCl₃ and CrCl₃ in DMF were higher than those in DMSO at all temperatures. The conductivity data were analyzed by the Robinson–Stokes equations. The limiting equivalent ionic conductivities for ferric ion (Fe³⁺) and chromic ion (Cr³⁺) and the ion association constants (K _A ) for FeCl₃ and CrCl₃ were determined in DMF and DMSO. The K _A values calculated for both FeCl₃ and CrCl₃ in DMF were higher than those in DMSO. This can be ascribed to an increase of the ion association constants with a decrease of the relative permittivity of solvents used in this study. The K _A values increased with the increase in temperature in the studied solvents. Thermodynamic functions (Gibbs’ free energy, entropy, and enthalpy of ion association) were estimated from the temperature dependence of the ion association constant. The positive values of entropy and enthalpy found for FeCl₃ and CrCl₃ at all temperatures indicate that the association process in DMF and DMSO is endothermic.