Radiative properties characterization of ZrB2–SiC-based ultrahigh temperature ceramic at high temperature

Experimental investigations of radiative property on pre-oxidized ZrB₂–SiC–15 vol.%–C ultrahigh temperature ceramic (ZSC UHTC) at high temperature range of 1100–1800 °C were performed. By Fourier transform infrared radiant (FT-IR) spectrometer, spectral emissivity was measured in the wavelength region between 3 and 18 μm. Total normal emissivity was calculated using spectral emissivity data via theoretical formula. It has been found that high emissivity for all the testing specimens was presented, and the total normal emissivity is between 0.65 and 0.92 with temperature range from 1100 to 1800 °C. Moreover, the total normal emissivity of pre-oxidized ZSC ceramic decreased non-monotonously as the temperature increased. The total normal emissivity decreased as the testing temperature increased from 1100 to 1800 °C, whereas the total normal emissivity at the testing temperature of 1600 °C was higher than that of 1400 and 1800 °C. Macroscopical surface morphology and microstructure were carried out before and after the testing.     

VO2 thin films deposited on silicon substrates from V2O5 target: Limits in optical switching properties and modeling

Thermochromic VO₂ thin films presenting a phase change at T_c = 68 °C and having variable thickness were deposited on silicon substrates (Si-001) by radio-frequency sputtering. These thin films were obtained from optimized reduction of low cost V₂O₅ targets. Depending on deposition conditions, a non-thermochromic metastable VO₂ phase might also be obtained. The thermochromic thin films were characterized by X-ray diffraction, atomic force microscopy, ellipsometry techniques, Fourier transform infrared spectrometry and optical emissivity analyses. In the wavelength range 0.3 to 25 μm, the optical transmittance of the thermochromic films exhibited a large variation between 25 and 100 °C due to the phase transition at T_c: the contrast in transmittance (difference between the transmittance values to 25 °C and 100 °C) first increased with film thickness, then reached a maximum value. A model taking into account the optical properties of both types of VO₂ film fully justified such a maximum value. The n and k optical indexes were calculated from transmittance and reflectance spectra. A significant contrast in emissivity due to the phase transition was also observed between 25 and 100 °C.     

Suspended core tellurite glass optical fibers for infrared supercontinuum generation

We report the fabrication and characterization of tellurite TeO₂-ZnO-Na₂O (TZN) microstructured suspended core optical fibers (MOFs). These fibers are designed for infrared supercontinuum generation with zero dispersion wavelength (ZDW) at 1.45 μm. The measured losses at this wavelength are approximately 6 dB/m for a MOF with a 2.2 μm diameter core. The effective area of a particular fiber is 3.5 μm² and the nonlinear coefficient is calculated to be 437 W⁻¹km⁻¹. By pumping a 20 cm long fiber at 1.56 μm with a sub-nJ femtosecond laser source, we generate a supercontinuum (SC) spanning over 800 nm in the 1-2 μm wavelength range.     

Enhanced light absorption of Ag films deposited onto femtosecond laser microstructured silicon

Absorptive properties of silver (Ag) films with the thickness varied from 160 nm to 340 nm deposited onto the surface of femtosecond laser microstructured silicon by vacuum thermal evaporation were measured in a wavelength range of 0.3-16.7 μm. Greatly enhanced light absorption of Ag films has been observed in the whole measured wavelength range. For the same Ag film thickness (268 nm), the light absorption was strongly depended on the height and spacing of the spikes, especially in the region of 1-16.7 μm. The relation between light absorption and thickness of Ag films has also been investigated, it was shown that the light absorption decreases with the increasing thickness of Ag films. The strongly enhanced light absorption in such a wide wavelength range is mainly ascribed to the multiple reflection of light between spikes and surface plasmon excitation of noble metal nano-particles on the spikes surface.     

Study of alumosilicate porcelains: Sol-gel preparation, characterization and erosion evaluated by gravimetric method

In this paper, the sol-gel synthesis and characteristic properties of kalsilite-type alumosilicates (KAlSiO₄ and K_0.5Na_0.5AlSiO₄) are reported. The polycrystalline powders were characterized by thermal analysis (TG/DTA), powder X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Single-phase kalsilite oxides have been obtained after annealing precursor gels for 5 h in the temperature range of 750-850 °C. It was demonstrated that crystallinity of the samples slightly depends on the temperature of annealing. From the results obtained, it could be concluded that the KAlSiO₄ solids are composed of the volumetric plate-like grains with no regular size (from 5 μm to 30 μm at 750 °C and around 5-50 μm at 850 °C). Larger crystallites for mixed potassium-sodium kalsilite have formed (from 10 μm to 80 μm at 750 °C and >100 μm at 850 °C) in comparison with potassium kalsilite samples). The erosion of obtained dental porcelain samples stored in saliva, beer and Coca-Cola was compared.     

Sol-gel derived aluminum doped zinc oxide for application as anti-reflection coating in terrestrial silicon solar cells

Sol-gel grown polycrystalline Al doped zinc oxide (AZO) thin films have been deposited on Si wafers, microscopy slide glass and fluorine doped tin oxide coated glass substrates using the spin coating technique. The atomic ratio of Al:Zn in the films is 0.2. From the X-ray diffraction investigations it is found that the preferential growth of (100) reflection peak has taken place in the 450, 550 and 600 °C annealed films. Scanning electron microscopic study has shown that the films contain well-defined grains arranged in a closely packed array. The resistivity of the 500 °C annealed film is measured to be 5 × 10^− 1 Ω cm. The films have exhibited excellent optical transmittance (~ 90%) in the 400-1100 nm wavelength range. Refractive indices (n = 1.9-1.95) of the films on Si wafer are independent of the annealing temperature. Thickness of the films produced at 4000 rpm is in the range of 58-62 nm. The refractive index and thickness of these films are nearly appropriate to cause destructive interference after reflection from front emitters of solar cells. These films have demonstrated a reflectivity value of about 3% at a wavelength of 700 nm. The AZO coated silicon solar cells possess V_oc and I_sc values of 573 mV and 237 mA, respectively.     

Low temperature amorphous growth of semiconducting Y-Ba-Cu-O oxide thin films in view of infrared bolometric detection

YBa₂Cu₃O_6 + x (YBCO) compounds are well known to exhibit superconducting properties for x > 0.5 and semiconducting properties for lower oxygen content. In this work, YBCO oxide thin films of the semiconducting phase were deposited by direct-current (DC) hollow cathode sputtering at low temperature in the 100 to 400 °C range. Structural, electrical and optical properties are investigated and discussed in relation with the envisaged bolometric detection application. Structural characterizations show that films are amorphous, with a granular structure of low roughness (3 nm rms). DC electrical measurements both reveal that films grown at 100 °C exhibit a high temperature coefficient of resistance (TCR ~ − 3% K^− 1 to − 4% K^− 1 at 300 K) and an optimized low resistivity value of 345 Ω·cm at 300 K. Consequently, this material is suitable for uncooled infrared bolometer application and can be deposited at 100 °C in a complementary metal-oxide-semiconductor compatible technological process for co-integration with readout circuitry. In addition, optical measurements performed in the 0.5 to 2.2 μm wavelength range on films grown at 100 °C highlight optical conductivity values in line with those expected for YBCO material, as well as the presence of two optical band gaps that are discussed with respect to the film nanostructure.     

Synthesis and characterization of beta barium borate thin films obtained from the BaO-B2O3-TiO2 ternary system

This work reports on the synthesis and the structural and optical characterization of beta barium borate (β-BBO) thin films containing 4, 8 and 16 mol% of titanium oxide (TiO₂) deposited on fused silica and silicon (0 0 1) substrates using the polymeric precursor method. The thin films were characterized by X-ray diffraction, Raman spectroscopy, atomic force microscopy and scanning electron microscopy techniques. The optical transmission spectra of the thin films were measured over a wavelength range of 800-200 nm. A decrease was observed in the band gap energy as the TiO₂ content was raised to 16 mol%. Only the β-BBO phase with a preferential orientation in the (0 0 l) direction was obtained in the sample containing 4 mol% of TiO₂ and crystallized at 650 °C for 2 h.     

Molybdenum-silicon aperiodic multilayer broadband polarizer for 13-30 nm wavelength range

Aperiodic molybdenum/silicon (Mo/Si) multilayer designed as a broadband polarizer with reflectivity over a wide wavelength range of 13-30 nm at a fixed incidence angle of 45° was developed by a numerical method. The multilayer was prepared using direct current magnetron sputtering. The reflectivity and polarizing properties were characterized using synchrotron radiation. In 13-30 nm wavelength region, the measured s-reflectivity (R_s) with standard deviation is 13.5%±3.1%, p-reflectivity (R_p) with standard deviation is 1.4%±0.5%. The mean of polarization degree is 81.2%. This broadband multilayer polarizer can be used in extreme ultraviolet polarization measurements, and will greatly simplify experimental arrangements.     

Artificial petal surface based on hierarchical micro- and nanostructures

In this paper, we present an artificial rose petal composed of hierarchical micro- and nanostructures on a polymethyl methacrylate surface. The petal effect implies that the surface has a high adhesion force in spite of being in a super-hydrophobic state, while the lotus effect implies that the surface has a low adhesion force when it is in a super-hydrophobic state. We have fabricated four different types of surfaces, namely, smooth, nanostructured, microstructured, and hierarchically micro-nanostructured surfaces. Microstructures and nanostructures have a quadrangular pyramid shape (one-side length: 15 ± 2 μm, height: 10.6 ± 1 μm) and a circular bump shape (diameter: 130 ± 10 nm, height: 100 ± 10 nm), respectively. The four types of surfaces are also chemically treated with trichlorosilane in order to reduce the surface energy. The contact angles of the smooth, nanostructured, microstructured, and hierarchically micro-nanostructured surfaces are measured to be 104° ± 2°, 112° ± 2°, 138° ± 4°, and 159° ± 2° after the chemical treatment. In the case of the super-hydrophobic micro-nanostructured surfaces, water droplets remain attached to the surface, even when the surface is turned upside down.     

Synthesis of nanocrystalline yttria doped ceria powder by urea-formaldehyde polymer gel auto-combustion process

Nanocrystalline yttria doped ceria powder has been prepared by auto-combustion of a transparent gel formed by heating an aqueous acidic solution containing methylol urea, urea, cerium(III) nitrate and yttrium(III) nitrate. The TGA and DSC studies showed the combustion reaction of the gel initiated at 225 °C and completed within a short period of time. XRD spectrum of the combustion product reveals the formation of phase pure cubic yttria doped ceria during the combustion process. Loose agglomerate of yttria doped ceria particle obtained by the combustion reaction could be easily deagglomerated by planetary ball milling and the powder obtained contains particles in the size range of 0.05-3.3 μm with D₅₀ value of 0.13 μm. The powder particles are aggregate of nanocrystallites with a wide size range of 14-105 nm. Pellets prepared by pressing the yttria doped ceria powder sintered to 95.2% TD at 1400 °C.     

Synthesis and properties of GeS2-Ga2S3-PbI2 chalcohalide glasses

The glass-forming region in the GeS₂-Ga₂S₃-PbI₂ system was determined and the basic parameters of thermal and optical properties (glass transition temperature, density, microhardness and transmission window) for these glasses have been measured. Better thermal stability originated from their larger difference between T_x and T_g in the range of 107-161 °C, higher glass transition temperatures between 252 and 398 °C and wide optical transmission window from 0.5 to 12.7 μm make these glasses the promising candidate materials for rare earth doped fiber amplifiers and nonlinear optical devices.     

Deposition and characterisation of MoSi2 films

Deposition of MoSi₂ films on silicon and tantalum substrates applying pulsed laser deposition technique has been performed. Crystalline, hexagonal symmetry, MoSi₂ films were prepared directly from stoichiometric MoSi₂ tetragonal target on room temperature and heated substrates (500 °C). Textured MoSi₂ films having privileged (110) and (115) orientations and average crystallite size of about 105 nm were grown on Si(111) substrates with a good degree of axial texture (rocking curve full width half maximum of 1.5°). MoSi₂ films grown on Ta(211) substrates, instead, turned out to be polycrystalline, with an average crystallite size of about 100 nm and 50 nm on substrates kept at room temperature and at 500 °C, respectively. Vickers hardness for 1.2 μm thick MoSi₂ films on Si(111) substrates resulted to be 15 GPa both at room temperature and 500 °C, while for 0.4 μm thick MoSi₂ films on Ta(211) substrates — 26 GPa at room temperature and 30 GPa at 500 °C.     

BaTiO3-SrTiO3 layered dielectrics for energy storage

BaTiO₃-SrTiO₃ (BST) thick films (~ 250-390 μm) with layered structures were fabricated by tape-casting and lamination process. Layered composites with various Ba/Sr ratios were obtained by lamination of BaTiO₃ (BT) and SrTiO₃ (ST) tapes in different spatial configurations (2-2). As-prepared BST ceramics showed much improved sinterability over the laminates of pure BT or pure ST tapes. Dielectric properties of materials were measured in the temperature range of 25 °C to 200 °C. The method of utilizing of layered structures offered flexibility to maximize the energy storage capability at specific operating conditions: (temperature and electric field) by tailoring the dielectric properties through varying the spatial configurations of BT and ST films.     

Device characteristics improvement of a-In-Ga-Zn-O TFTs by low-temperature annealing

A low-temperature process to improve performances of a-In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) fabricated at room temperature was examined. Two deposition methods, pulsed laser deposition (PLD) and RF magnetron sputtering were employed to deposit the a-IGZO channels. For the PLD case, the TFT characteristics were improved significantly by wet annealing at dew point (d.p.) of 50 °C at the annealing temperature of 200 °C. For the sputtered TFTs, a wider range of annealing temperature from 100 to 200 °C was examined. It was found that annealing at ≥ 150 °C improved the TFT characteristics when dry annealing was employed. On the other hand, wet annealing also improved μ_sat and S values, but very large negative threshold voltage (V_th) shift was observed. These results indicate that the annealing at 150 °C is enough to obtain mobility (μ_sat) as large as 8 cm² Vs^− 1, but annealing temperature as high as 200 °C provides larger μ_sat comparable to those obtained by 400 °C annealing. It is speculated that the large negative V_th shift originates from compensated donors in as-deposited sputtered films.     

Dielectric properties of sol-gel derived barium strontium titanate thin films

Barium strontium titanate (Ba_xSr_1−xTiO₃) films were deposited by sol-gel technique on platinized silicon substrate for the composition range x = 0.0 to 1.0 in steps of 0.1. The as-deposited films were found to be amorphous. The films crystallize on annealing in air at 700 °C for 1 h. Dielectric constant (ε′) and loss tangent (tanδ) were measured in the temperature range − 180 °C to 150 °C in the frequency range 0.1 to 100 kHz. Both ε′ and tanδ show a small dispersion for all the compositions. This dispersion is more at the peak value than at room temperature. A comparison of the room temperature and peak value of the dielectric constant for various compositions are made with the reported values. Transition temperatures are reported for the entire composition range. All the compositions show a transition from ferroelectric to paraelectric phase except strontium titanate. Transition temperature shows a systematic decrease with increase in strontium content. The variation is at a rate of 3.4 °C/mol% of SrTiO₃. Curie constants are also reported for the entire composition range.     

Broad band optical characterization of sol-gel TiO2 thin film microstructure evolution with temperature

Titanium dioxide (TiO₂) thin films have been produced by spin coating a titanium isopropoxide sol on silicon wafer substrates. The structural evolution of the thin films in terms of decomposition, crystallization and densification has been monitored as a function of annealing temperature from 100 to 700 °C using optical characterization and other techniques. The effect of annealing temperature on the refractive index and extinction coefficient of these TiO₂ thin films was studied in the range of 0.62 to 4.96 eV photon energy (250-2000 nm wavelength) using spectroscopic ellipsometry. Thermal gravimetric analysis and atomic force microscopy support the ellipsometry data and provide information about structural transformations in the titania thin films with respect to different annealing temperatures. These data help construct a coherent picture of the decomposition of the sol-gel precursors and the creation of dense layers of TiO₂. It was observed that the refractive index increased from 2.02 to 2.45 at 2.48 eV (500 nm) in sol-gel spin coated titania films for annealing temperatures from 100 °C to 700 °C.     

Optimization of parameters for silicon planar source of modulated infrared radiation

We report on the performance of planar silicon diodes operating in the double injection mode and emitting modulated infrared radiation at temperature range above 300 K. Results present theoretical analysis and experimental verification of an optimization aimed at maximal difference between emissivity of this structure for cases with and without forward bias applied to p-n junction. Several advantages of the structures were shown: wide emission spectrum (3÷12 μm), short rise-fall time (300 μs), high operating temperature (≈400 K). These planar photonic sources can be used as easily controlled sources of modulated infrared radiation in wide spectral range, image simulators, e.g. dynamic scene simulation devices with frame frequencies well above 200 Hz and for measurements of thermovision camera dynamic parameters.     

Effects of humidity on tin whisker growth — Investigated on Ni and Ag underplated layer construction

The effect of humidity on nickel and silver underlayered tin platings has been observed in relation to whisker formation. Using nickel or silver underlayers between the copper substrate and the tin coating is known to be a useful technique for mitigating the occurrence of whiskers. The underlayer blocks the formation of Cu₆Sn₅ intermetallics which is one of the root causes of whisker growth. Samples with a bronze (94Cu/6Sn) substrate covered with a 1-2 μm underlayer (silver or nickel) and 5-7 μm of tin on the top were tested. The samples were stored in high humidity and at various temperature conditions; 40 °C/95% RH (Relative Humidity), 105 °C/100% RH and 50 °C/25% RH for over 4200 h to demonstrate the importance of humidity in whisker growth. Results have shown differences in whisker growth on the samples depending on the nature of the environmental conditions. The differences originate from the various stress-causing mechanisms. Growth differences have also been found on the two types of underlayer materials.     

Thin gold films on SnO2:In: Temperature-dependent effects on the optical properties

Gold films with thicknesses of 5 ± 0.5 nm were sputter deposited onto SnO₂:In-coated glass kept at different temperatures up to 140 °C, and similar films, deposited onto substrates at 25 °C, were annealing post treated at the same temperatures. Nanostructures and optical properties were recorded by scanning electron microscopy and spectrophotometry in the 0.3 to 2.5 μm wavelength range, respectively. Annealing had a minor influence on the optical transmittance despite significant changes in the scale of the nanostructure, whereas deposition onto substrates heated to 140 °C yielded granular films with strong plasmon absorption of luminous radiation. These results are of considerable interest for optical devices with gold films prepared at elevated temperature or operating at such temperature.