Self-Phase-Matched Second-Harmonic and White-Light Generation in a Biaxial Zinc Tungstate Single Crystal

Second-order nonlinear optical materials are used to generate new frequencies by exploiting second-harmonic generation (SHG), a phenomenon where a nonlinear material generates light at double the optical frequency of the input beam. Maximum SHG is achieved when the pump and the generated waves are in phase, for example through birefringence in uniaxial crystals. However, applying these materials usually requires a complicated cutting procedure to yield a crystal with a particular orientation. Here we demonstrate the first example of phase matching under the normal incidence of SHG in a biaxial monoclinic single crystal of zinc tungstate. The crystal was grown by the micro-pulling-down method with the (102) plane perpendicular to the growth direction. Additionally, at the same time white light was generated as a result of stimulated Raman scattering and multiphoton luminescence induced by higher-order effects such as three-photon luminescence enhanced by cascaded third-harmonic generation. The annealed crystal offers SHG intensities approximately four times larger than the as grown one; optimized growth and annealing conditions may lead to much higher SHG intensities

The use of small angle neutron scattering with contrast matching and variable adsorbate partial pressures in the study of porosity in activated carbons

The porosity of a typical activated carbon is investigated with small angle neutron scattering (SANS), using the contrast matching technique, by changing the hydrogen/deuterium content of the absorbed liquid (toluene) to extract the carbon density at different scattering vector (Q) values and by measuring the p/p0 dependence of the SANS, using fully deuterated toluene. The contrast matching data shows that the apparent density is Q-dependent, either because of pores opening near the carbon surface during the activation processor or changes in D-toluene density in nanoscale pores. For each p/p0 value, evaluation of the Porod Invariant yields the fraction of empty pores. Hence, comparison with the adsorption isotherm shows that the fully dry powder undergoes densification when liquid is added. An algebraic function is developed to fit the SANS signal at each p/p0 value hence yielding the effective Kelvin radii of the liquid surfaces as a function of p/p0. These values, when compared with the Kelvin Equation, show that the resultant surface tension value is accurate for the larger pores but tends to increase for small (nanoscale) pores. The resultant pore size distribution is less model-dependent than for the traditional methods of analyzing the adsorption isotherms

Growth conditions, structure, and superconductivity of pure and metal-doped FeTe1-xSex single crystals

Superconducting single crystals of pure FeTe1 xSex and FeTe0.65Se0.35 doped with Co, Ni, Cu, Mn, Zn, Mo, Cd, In, Pb, Hg, V, Ga, Mg, Al, Ti, Cr, Sr or Nd into Fe ions site have been grown applying Bridgman's method. It has been found that the sharpness of transition to the superconducting state in FeTe1 xSex is evidently inversely correlated with crystallographic quality of the crystals. Among all of the studied dopants only Co, Ni and Cu substitute Fe ions in FeTe0.65Se0.35 crystals. The remaining examined ions do not incorporate into the crystal structure. Nevertheless, they form inclusions together with selenium, tellurium and/or iron, what changes the chemical composition of host matrix and therefore influences Tc value. Small disorder introduced into magnetic sublattice, by partial replacement of Fe ions by slight amount of nonmagnetic ions of Cu (~ 1.5 at%) or by magnetic ions of Ni (~ 2 at%) and Co (~5 at%) with spin value different than that of Fe ion, completely suppresses superconductivity in FeTe1 xSex system. This indicates that even if superconductivity is observed in the system containing magnetic ions it can not survive when the disorder in magnetic ions sublattice is introduced, most likely because of magnetic scattering of Cooper pairs.Comment: 18 pages, 12 figures, 3 table

Surface Fractal Dimension of Single-walled Carbon Nanotubes

Isolated single-walled carbon nanotubes (SWNTs), SWNT bundles, and ropes (or strands) show a structural self-similar characteristic. By calculating the Hausdorff dimension, it was found that their self-similar organization leads to surface fractality and the value of the surface dimension (Ds) depends on self-similar patterns. Experimentally, Ds obtained by nitrogen adsorption measurements at 77.3 K and by the small-angle x-ray scattering technique in our study proved our calculation that the surface dimension of SWNTs is nonintegral,

The K-X-ray intensity ratios as a tool of examination and thickness measurements of coating layers

The ED-XRF (Energy-Dispersive X-ray Fluorescence) measurements and the FLUKA simulations have been made to discuss the possibility of recognition of coating layer as well as to its thickness measurement. In this work the $I_{K\alpha}$(Cu)/$I_{K\alpha}$(Ag) intensity ratios as well as $I_{K\beta}$(Ag)/$I_{K\alpha}$(Ag) and $I_{K\beta}$(Cu)/$I_{K\alpha}$(Cu) for copper samples coated with various thickness of sputtered silver have been analyzed. The results show strong dependence of these factors with coating silver layer thickness. The measurements show the performance of this method in archaeometry. Since the use of non-destructive methods during tests on ancient silver artifacts may not supply to obtain reliable bulk results and should be considered applicable for only surface analyses, the measured intensity ratios can be applied as a tool to estimation of surface silver enrichment thickness.Comment: Accepted to publication to the Measurement journa

New records of Mexican Tardigrada

In 9 moss samples collected from Mexico, 6 tardigrade species, including 4 new records for the country, were found. The new records raise the number of known Mexican water bear species to forty-one. We provide a full list of the known Mexican tardigrade species and discuss some biogeographical and taxonomic issues

The K-X-ray intensity ratios as a tool of examination and thickness measurements of coating layers

The ED-XRF (Energy-Dispersive X-ray Fluorescence) measurements and the FLUKA simulations have been made to discuss the possibility of recognition of coating layer as well as to its thickness measurement. In this work the IKα(Cu)/IKα(Ag) intensity ratios as well as IKβ(Ag)/IKα(Ag) and IKβ(Cu)/IKα(Cu) for copper samples coated with various thickness of sputtered silver have been analyzed. The results show strong dependence of these factors with coating silver layer thickness. The measurements show the performance of this method in archaeometry. Since the use of non-destructive methods during tests on ancient silver artifacts may not supply to obtain reliable bulk results and should be considered applicable for only surface analyse

Priprema i karakterizacija C60/C70 + Ni polikristalnih tankih slojeva naraslih na raznim podlogama

C60/C70 + Ni films were obtained by thermal evaporation method in a wide range of Ni concentration (from 1.5 to 10 wt. %). The polycrystalline structure was detected in layers with Ni concentration of 1.5 wt. %. For this Ni concentration, growth of grains in columnar form was observed by SEM. TEM examination showed existence of crystalline grains of a size of a few micrometers and 10 - 200 nm thick. The electron and X-ray diffraction exhibited Bragg distances of approx. 0.87, 0.83, 0.50 and 0.32 nm, and in electron diffraction 1.0, 0.76 and 0.65 nm interplanar distances were found. In Raman spectra, typical fullerenes and two other bands placed at 580 and 1100 cm-1 were observed. The intensity of the latter bands depends on Ni concentration. For Ni concentration higher then 1.5 wt. %, the degradation of fullerene structure was observed by HRTEM, electron and X-ray diffraction.Tanki slojevi C60/C70 + Ni dobiveni su toplinskim isparavanjem s koncentracijom Ni od 1.5 do 10 tež. %. Polikristalna struktura je opažena u slojevima s 1.5 tež. % Ni. Pomoću SEM je u takvim slojevima opažen stupčast rast zrna. Pomoću TEM ustanovljena su zrna duljine nekoliko µm i debljine 10-200 nm. Ispitivanja su načinjena također elektronskom i rendgenskom difrakcijom. U Ramanovim spektrima opažene su tipične vrpce fulerena pri 580 i 1100 cm−1 . Za koncentracije Ni iznad 1.5 tež. % opažena je degradacija strukture fulerena