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

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

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

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

Physico-Chemical Changes Occurring in Gamma Irradiated Flours Studied by Small-Angle X-ray Scattering

Commercial samples of wheat, rye and potato flour and flaked oats, as well as ground flaked oats and fresh potatoes were gamma-irradiated (20 or 30 kGy dose). The products and appropriate control samples were inves tigated by small-angle X-ray scattering (SAXS) in the range of 28 from 0.357 to 6.46 degree (CuKa radiation). The results were compared with those obta ined for pure potato starch. Effects of grinding and heating at 100° Con SAXS results were also examined. Different scattering curves were obtained for various unirradiated products. Refl ect ions derived from starch were de tected for some uni rradiated :ls well as irradiated products. A reflection connected with long-range ordering in sta rch (co rresponding to the distance d =: 10 nm)was observed for potato, wheat, rye flour and potato powde r. A reflection corresponding to the distanced = 1.6 nm (due to short-range ordering) was observed in the cases of potato flour and potato powder. Comparison of diffractograms of gamma- irradiated and unirradiated products, have revea led changes of the reflection corresponding to d = 10 nm intensity and elevation of scattering curves, connected with changes of long-range ordering in starch gra nules. The effect of gamma-irradiation on long-range ordering in starch was also observed aft er heating of starch at 100°C. Heating at 100°C as well as grinding, cause diminution of long-range ordering m starch granules

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

High-pressure synthesis and the enhancement of the superconducting properties of FeSe0.5Te0.5

A series of FeSe0.5Te0.5 bulk samples have been prepared through the high gas pressure and high-temperature synthesis (HP-HTS) method to optimize the growth conditions, for the first time and investigated for their superconducting properties using structural, microstructure, transport, and magnetic measurements to reach the final conclusions. Ex-situ and in-situ processes are used to prepare bulk samples under a range of growth pressures using Ta-tube and without Tatube. The parent compound synthesized by convenient synthesis method at ambient pressure (CSP) exhibits a superconducting transition temperature of 14.8 K. Our data demonstrate that the prepared FeSe0.5Te0.5 sealed in a Ta-tube is of better quality than the samples without a Ta-tube, and the optimum growth conditions (500 MPa, 600{\deg}C for 1 h) are favourable for the development of the tetragonal FeSe0.5Te0.5 phase. The optimum bulk FeSe0.5Te0.5 depicts a higher transition temperature of 17.3 K and a high critical current density of the order of >10^4 A/cm^2 at 0 T, which is improved over the entire magnetic field range and almost twice higher than the parent compound prepared through CSP. Our studies confirm that the high-pressure synthesis method is a highly efficient way to improve the superconducting transition, grain connectivity, sample density, and also pinning properties of a superconductor

Comparison of Gd addition effect on the superconducting properties of FeSe0.5Te0.5 bulks under ambient and high-pressure conditions

We have prepared a series of (FeSe0.5Te0.5 + xGd) bulk samples, with x = 0, 0.03, 0.05, 0.07, 0.1 and 0.2, through the convenient solid-state reaction method at ambient pressure (CSP). High gas pressure and high-temperature synthesis methods (HP-HTS) are also applied to grow the parent compound (x = 0) and 5-wt% of Gd-added bulks. Structural, microstructural, transport and magnetic characterizations have been performed on these samples in order to draw the final conclusion. Our analysis results that the HP-HTS applied for the parent compound enhances the transition temperature (Tc) and the critical current density (Jc) with the improved sample density and intergrain connections. The lattice parameter c is increased with Gd additions, suggesting a small amount of Gd enters the tetragonal lattice of FeSe0.5Te0.5 and the Gd interstitial sites are along the c-axis. A systematic decrease of the onset transition temperature Tc is observed with Gd additions, however, the calculated Jc of these Gd-added samples is almost the same as that of the parent compound prepared by CSP. It specifies that there is no improvement of the grain connections or pinning properties due to these rare earth additions. However, Gd-added FeSe0.5Te0.5 bulks prepared by HP-HTS have revealed a slightly improved critical current density due to improved grain connections and sample density but have a lower transition temperature than that of the parent compounds.Comment: 33 pages, 9 figures, 3 table

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