Eu-activated heavy scintillating glasses

Eu³⁺-activated scintillating glasses with molar compositions of 35SiO₂–15B₂O₃–30Ln₂O₃–20AlF₃ (Ln = Y, La, Gd, Lu) have been prepared. The effects of Ln³⁺ ions on the density, transmission, photoluminescence and radioluminescence have been studied. The glasses have high density, ranging from 4.0 to 6.1 g/cm³ in the order of Y < La < Gd < Lu. Gd-containing glass exhibits a much higher light yield than the other glasses. The effect of complete substitution of fluorine by oxygen on the scintillation properties is also investigated.     

Design,fabrication and optical characterization of cerium oxide-magnesium fluoride double layer antireflection coatings on monocrystalline silicon substrates

Theoretical and experimental studies of a double layer antireflection coating deposited onto silicon wafers have been carried out. Magnesium oxide and cerium oxide fabricated by physical vapor deposition method have been applied as low- and high-refractive index materials. MgF₂–CeO₂–Si structures exhibited the reflectivity below 3% in the wavelength window from 0.5 μm to 1.2 μm. Theoretical simulations of spectral characteristics of the reflectivity of these coatings have been performed. A good correlation between experimental data and theoretical curves has been observed with the assumption that a thin SiO₂ layer of a thickness of 16 nm is formed onto Si substrates.     

Ion formation by high velocity impacts on porous metal targets

In impact ionization studies the target normally consists of a metal surface of compact solid density. In the present experiments, we investigate the use of a layer of a highly porous structure of nanometre-sized grains, sometimes also called “metal black”, as an alternative target. In our comparative experiments, spherical iron particles (0.1<d_p<1.5 μm) were shot with velocities 2–30 km/s onto both a compact solid silver plate and a silver metal black layer of about 7 μm thickness (grain size 20–40 nm, mean density ≈1 g/cm³), deposited on a compact solid gold plate. Impact generated ions were analysed by means of time-of-flight mass spectrometry. The results reveal important advantages of the porous black layer, such as better mass resolution and a larger amount of ions from the impacting particle. Therefore metal blacks may be very suitable targets for the purposes of identification and characterisation of the impacting particle's composition. An attempt is made to give a physical explanation of the results in the frame of existing empirical ionization models. The study is part of a programme to improve devices for in-situ analysis of fast moving cosmic dust particles.     

Microstructures, densification and mechanical properties of TiC–Al2O3–Al composite by field-activated combustion synthesis

Dense TiC–Al₂O₃–Al composite was prepared with Al, C and TiO₂ powders by means of electric field-activated combustion synthesis and infiltration of the molten metal (here Al) into the synthesized TiC–Al₂O₃ ceramic. An external electric field can effectively improve the adiabatic combustion temperature of the reactive system and overcome the thermodynamic limitation of reaction with x < 10 mol. Thereby, it can induce a self-sustaining combustion synthesis process. During the formation of Al₂O₃–TiC–Al composite, Al is molten first, and reacted with TiO₂ to form Al₂O₃, followed by the formation of TiC through the reaction between the displaced Ti and C. Highly dense TiC–Al₂O₃–Al with relative density of up to 92.5% was directly fabricated with the application of a 14 mol excess Al content and a 25 V cm⁻¹ field strength, in which TiC and Al₂O₃ particles possess fine-structured sizes of 0.2–1.0 μm, with uniform distribution in metal Al. The hardness, bending strength and fracture toughness of the synthesized TiC–Al₂O₃–Al composite are 56.5 GPa, 531 MPa and 10.96 MPa m^1/2, respectively.     

Formation and control of zinc nitride in a molten LiCl–KCl–Li3N system

We investigated a possibility of electrochemical formation and control of zinc nitride in a molten LiCl–KCl–Li₃N system at 673 K. Zinc nitride films were obtained by means of potentiostatic electrolysis of zinc electrodes in the melt. From XRD analysis, it was confirmed that obtained films consisted of Zn₃N₂ and LiZnN and that the composition of each film was effected by the applied potential value. In the potential range from 0.75 to 1.6 V (versus Li⁺/Li), the ratio of Zn₃N₂ increased as the applied potential was more positive. Based on the result, we achieved the formation of Zn₃N₂ film (3–5 μm) in anti-scandium oxide structure (a = 0.977 nm) by means of potentiostatic electrolysis at 1.6 V for 3 h.     

Photoluminescence and field emission properties of ZnS:Mn nanoparticles synthesized by rf-magnetron sputtering technique

Nanoparticles of ZnS:Mn have been grown by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction patterns and selected area electron diffraction patterns confirmed the nanocrystalline cubic ZnS phase formation. TEM micrographs of the films revealed the manifestation of ZnS:Mn nanoparticles with an average size 6 nm. UV–Vis–NIR spectrophotometric measurement showed that the films are highly transparent (90%) in the wavelength range 400–2600 nm. From the measurements of transmittance spectra of the films the direct allowed bandgap values have been calculated and they lie in the range 3.89–4.12 eV. The bandgap decreased with the increase of Mn concentration in the films. The Mn concentrations in the films have been varied from 0% to 8.9% and was measured by energy dispersive X-ray analysis. The photoluminescence of the Mn doped ZnS nanoparticles was measured. The intensity of the PL peaks at first increased with the increase of Mn concentration in the films up to 3.8% of Mn doping and at a Mn concentration higher than this, the intensity of PL peak decreased. Nanocrystalline ZnS:Mn showed good field emission property with a turn on field lying in the range 5.26–6.78 V/μm for a variation of anode to sample distance from 60 μm to 100 μm.     

Photoinduced nonlinear optics in Sb2Se3–BaCl2–PbCl2 glasses

Photoinduced structural transformations in amorphous Sb₂Se₃–BaCl₂–PbCl₂ glasses were studied using a differential IR spectroscopy Fourier technique in the spectral region between 100 and 300 cm⁻¹. A stage of the reversible photodarkening is realized in the Sb₂Se₃ fragments after the first cycle of photoexposure and thermoannealing. The whole scheme of the photo- and thermoinduced transformations in the amorphous system may be explained as a coordination of formation and annihilation of defects. The vibrational density of states calculated using quantum chemical solid state methods confirms our experimental results and their interpretation. Photoinduced photodarkening changes using a CO₂ pulse laser (λ=10.6 μm) in new synthesized Sb₂Se₃–BaCl₂–PbCl₂ glasses were investigated. At the same time we have studied photoinduced second harmonic generation (SHG) and two-photon absorption (TPA). The possibility of using this glass as perspective materials for IR optoelectronics and nonlinear optics was shown.     

Preparation of Sm-doped ceria (SDC) nanowires and tubes by gas–liquid co-precipitation at room temperature

Sm-doped cerium dioxide (SDC) with fcc structure was formed using a gas–liquid chemical co-precipitation process at room temperature. Morphology and structure of the as-prepared samples were characterized using TG, XRD, TEM, HRTEM and SAED techniques. Under our specific experimental conditions, two kinds of 1D nano-structures SDC have been mainly obtained. SDC nanowires are 0.3–1.2 μm in lengths and 5–20 nm in diameters. SDC nanotubes have outer diameters in 10–40 nm with lengths up to 2 μm. The as-prepared SDC shows very strong UV absorption ability and the maximum absorption peak redshifts compared with that of SDC nanoparticles.     

Infrared optical properties of Bi2Ti2O7 thin films by spectroscopic ellipsometry

Bi₂Ti₂O₇ thin films have been grown directly on n-type GaAs (1 0 0) by the chemical solution decomposition technique. X-ray diffraction analysis shows that the Bi₂Ti₂O₇ thin films are polycrystalline. The optical properties of the thin films are investigated using infrared spectroscopic ellipsometry (3.0–12.5 μm). By fitting the measured ellipsometric parameter (Ψ and Δ) data with a three-phase model (air/Bi₂Ti₂O₇/GaAs), and Lorentz–Drude dispersion relation, the optical constants and thickness of the thin films have been obtained simultaneously. The refractive index and extinction coefficient increase with increasing wavelength. The fitted plasma frequency ω_p is 1.64×10¹⁴ Hz, and the electron collision frequency γ is 1.05×10¹⁴ Hz, and it states that the electron average scattering time is 0.95×10⁻¹⁴ s. The absorption coefficient variation with respect to increasing wavelength has been obtained.     

Preparation of gold nanosheets using poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymers via photoreduction

Gold nanosheets having single crystalline structure were successfully synthesized using the bulk phase mixture of HAuCl₄ and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymers through the irradiation of a glow lamp for 5 days. When the molar ratio of propylene oxide to ethylene oxide block units in the block copolymer is about 1.75, mostly gold nanosheets were obtained. Gold nanosheets with an average width of 8 and 5 μm were obtained from the when the molar ratio of gold salt to the ethylene oxide units in the block copolymer were 1/80 and 1/160, respectively.     

Fabrication of β-Si3N4 whiskers by combustion synthesis with MgSiN2 as additives

β-Si₃N₄ whiskers with diameter of 0.5–2 μm and aspect ratio of 10–15 have been successfully prepared by combustion synthesis under 30–50 atm nitrogen pressure. The addition of MgSiN₂ powder plays a significant role in the growth of β-Si₃N₄ whiskers. The as-prepared products were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).     

Synthesis and characterization of aromatic self-assembled monolayers containing methylene and ethyleneglycol entities by means of sum-frequency generation spectroscopy

We use infrared-visible sum-frequency generation (SFG) spectroscopy in order to investigate the adsorption properties on Pt(111) of molecules having CH₃–C₆H₄–(O–CH₂–CH₂)_n–O–(CH₂)_m–SH as general chemical formula. We synthesized three molecules defined by the values m = 5 n = 4, m = 11 n = 4, m = 11 n = 8 and characterized them by Nuclear Magnetic Resonance spectroscopy. Thanks to spectroscopic measurements, we show that these molecules build self-assembled monolayers on Pt(111). First, the weak SFG signals arising from the ad-layer indicate low order and surface coverage of the substrate by these molecules. Next, the vibrational fingerprints of the aforementioned molecules are determined between 2825 and 3125 cm^− 1 and the observed SFG spectral features are ascribed on the basis of the analysis of shorter and simpler molecules (1-dodecanethiol, 4-methylbenzenethiol and CH₃–C₆H₄–O–(CH₂)₁₁–SH) also adsorbed on Pt(111). The occurrence of methylene vibration modes indicates a significant amount of chain defects whatever the n and m numbers are. Finally, the identification of a particular vibration mode, characteristic of the aromatic ring, enables us to qualitatively discuss the effect of the number of methylene and ethylene glycol entities on its orientation. More precisely, higher these numbers, more tilted (with respect to the substrate normal) the aromatic ring plane is.     

Effects of ZnO on piezoelectric properties of 0.01PMW–0.41PNN–0.35PT–0.23PZ ceramics

The microstructure and piezoelectric properties of the 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃ + 0.1 and 0.3 wt.% Y₂O₃ + x ZnO ceramics were investigated. The crystal structure changed from psudocubic to tetragonal when ZnO added. The average grain size increased from 4 μm to 8 μm with the addition of ZnO by oxygen diffusion, even if the growth rate was low. When ZnO added until 0.5 wt.%, the , k_p and d₃₃ values of specimens were slightly increased regardless Y₂O₃ contents. The curie point of PMW–PNN–PT–PZ ceramics were increased from 162 °C to 232 °C, as increasing the ZnO contents. When ZnO added, the k_p of specimens slightly was increased regardless Y₂O₃ contents. The mechanical quality factors were abruptly decreased regardless Y₂O₃ contents, when ZnO added until 0.75 wt.%. The optimized piezoelectric properties were obtained; d₃₃ = 730 (pC/N), k_p = 60, Q_m = 50, and  = 4750, when PMW–PNN–PT–PZ + 0.3 wt.% Y₂O₃ + 0.5 wt.% ZnO sintered at 1200 °C for 1 h.     

High electrical properties of W-additive Mn-modified PZT–PMS–PZN ceramics for high power piezoelectric transformers

The ceramics were prepared successfully by the addition of WO₃ to the Mn-modified Pb(Zr_0.52Ti_0.48)O₃–Pb(Mn_1/3Sb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃ (PZT–PMS–PZN) for high power piezoelectric transformers application. XRD analysis indicated that the ceramics were mainly composed of a tetragonal phase in the range of 0–1.0 wt.% WO₃ addition. The grain size of the ceramics significantly decreased from 10.0 to 2.9 μm by addition of WO₃. Moreover, the addition of WO₃ promoted densification of the ceramics and increased mechanical quality factor (Q_m), planar coupling factor (K_p) and piezoelectric constant (d₃₃) kept high values, whereas, dielectric loss (tan δ) was low. Δf (=f_a − f_r) slightly changed when WO₃ addition was above 0.5 wt.%. The ceramics with 0.6 wt.% WO₃ addition, sintered at 1150 °C showed the optimized piezoelectric and dielectric properties with Q_m of 1852, K_p of 0.58, d₃₃ of 243 pC/N and tan δ of 0.0050. The ceramics are promising candidates for high power piezoelectric transformers application.     

Corrosion of magnesia–chrome brick in molten MgO–Al2O3–SiO2–CaO–FetO slag

The corrosion of magnesia–chrome (MgO–Cr₂O₃) brick in molten MgO–Al₂O₃–SiO₂–CaO–Fe_tO slag has been characterized using a dynamic rotary slag corrosion testing for various test cycles at 1650 °C. The open porosity decreases from 15.3 to 4.0% for three cycles, then it gradually increases from 4.0 to 4.8% when the test is extended to nine cycles, in which the permeating depth of the slag maintains at about 20 mm. The XRD pattern of the permeated layer shows the presence of the MgO, MgCr₂O₄ and CaMgSiO₄ phases. In the interior of the permeating layer cracks are formed and corrosion starts at the pores and cracks of MgO and decreases gradually. However, at 20–40 mm beneath the permeated layer edge, different shapes of MgO particles are found.     

Field-emission characteristics of chemical vapor deposition-diamond films

Discontinuous and continuous diamond films with different morphologies and qualities were deposited on n²⁺-type Si(100) substrates, using the hot-filament chemical vapor deposition (CVD) technique from CH₄–H₂ gas mixtures. The field-emission characteristics of these diamond films were investigated. The turn-on fields at a 0.01mA/cm² current density were recorded for all the tested CVD-diamond films. It was found that discontinuous diamond films showed a much lower turn-on field (1.2 V/μm) than continuous ones (20 V/μm). The effective working function of continuous diamond films was around 0.1 eV, while that for discontinuous diamond films is about 0.03 eV. O₂ plasma post-deposition sharpening of thick diamond films indicated that the geometrical-field enhancement, caused by the surface topographic changes, has no significant influence on the turn-on field.     

Synthesis of hydroxyapatite on titanium coated with organic self-assembled monolayers

The work focuses the formation of hydroxyapatite (HA) layers from simulated body fluids (SBF) onto titanium coated with NH₂-, SH-, and SO₃H-SAMs, respectively, at room temperature and 37 °C as well as pH values of SBF of 7.4, 8, and 8.4. At an upside up arrangement of the samples in the SBF, the formation of sufficient thick HA layers with a pillow like structure onto all SAMs were observed, which is believed to be caused by combined homogeneous and heterogeneous precipitation of HA from the SBF. These layers do not show sufficient adhesive strength. An upside down arrangement of the samples result in the formation of up to 5–10 μm thick flat HA layers with a much higher adhesive strength, which is believed to be due to formation of HA from the SBF only by heterogeneous precipitation. Also HA layers were obtained onto all studied SAMs, SH-SAM appears to favour the formation of HA resulting in a layer with a thickness of about 10 μm and an almost stoichiometric Ca/P-ratio of the layer of 1.72. All other layers exhibit much lower ratios.     

A simple and an effective method for the fabrication of densified glass-ceramics of low temperature co-fired ceramics

This study reports a new, simple and effective pre-calcined method for fabrication BaO–TiO₂–B₂O₃–SiO₂ low temperature co-fired ceramics (LTCC) at a sintering temperature below 900 °C, and with dielectric losses (tan δ) lower than 2 × 10⁻³. The research results have shown that the addition of 2–5 wt% Al₂O₃ could easily eliminate the porosity of the glass-ceramics because of the excellent wetting behavior between alumina and the BaO–B₂O₃–SiO₂ glass liquid phase in the low temperature co-fired ceramic system.     

Enhanced ferroelectric properties of multilayer SrBi2Ta2O9/SrBi2Nb2O9 thin films for NVRAM applications

Ferroelectric SrBi₂Ta₂O₉/SrBi₂Nb₂O₉ (SBT/SBN) multilayer thin films with various stacking periodicity were deposited on Pt/TiO₂/SiO₂/Si substrate by pulsed laser deposition technique. The X-ray diffraction patterns indicated that the perovskite phase was fully formed with polycrystalline structure in all the films. The Raman spectra showed the frequency of the O–Ta–O stretching mode for multilayer and single layer SrBi₂(Ta_0.5Nb_0.5)₂O₉ (SBNT) samples was 827–829 cm⁻¹, which was in between the stretching mode frequency in SBT (813 cm⁻¹) and SBN (834 cm⁻¹) thin films. The dielectric constant was increased from 300 (SBT) to 373 at 100 kHz in the double layer SBT/SBN sample with thickness of each layer being 200 nm. The remanent polarization (2P_r) for this film was obtained 41.7 μC/cm², which is much higher, compared to pure SBT film (19.2 μC/cm²). The coercive field of this double layer film (67 kV/cm) was found to be lower than SBN film (98 kV/cm).     

Characterization of Cat-CVD grown Si–C and Si–C–O dielectric films for ULSI applications

Si–C films with the Si compositions ranging from 40 to 70% have been grown by Cat-CVD using dimethylsilane [DMSi, Si(CH₃)₂H₂] compounds. Tetraethoxysilane [TEOS, Si(OC₂H₅)₄] and dimethyldimethoxysilane [DMDMOS, Si(CH₃)₂(OCH₃)₂] gas source gave us Si–C–O (C-doped SiO_x) films with wide ternary alloy compositions. The dielectric constant of a Si–C film has been evaluated by C–V measurements (at 1 MHz) using Al/Si–C/n-Si(001)/Cu MIS structure. The relative dielectric constant value of a Si–C film was estimated to be 3.0. The resistivity of the Si–C layer with 1 mm diameter and 0.24 μm thickness was estimated to be more than 24.5 Gohm·cm. These results gave us promising characteristics of Si–C and Si–C–O films grown by alkylsilane- and alcoxysilane-based Cat-CVD.