SiO2 Ta2O5 Research Articles

Effect of Ta2O5 addition on the structure, crystallization mechanism, and properties of CaO–B2O3–SiO2 glasses for LTCC applications

CaO–B2O3–SiO2–Ta2O5 (CBST) glass-ceramics, with different Ta2O5 content, (up to 6 mol%), have been prepared by using glass melt quenching followed by heat treatment between 800 and 880 °C. The Fourier Transform Infrared (FTIR) results showed that the stronger the attraction of Ta5+ to the oxygens in the BO33− and SiO32− structures, the more easily the B–O and Si–O bonds will be destroyed. The underlying reason is most probably the high field strength of Ta5+, which results in a weakening of the vibration intensities of the [BO3] and [SiO4] units. Moreover, the Differential Scanning Calorimetry (DSC) results showed that the softening point (Tg), crystallization starting temperature (Tc1), and exothermic crystallization peak temperature (Tp1), of the CaSiO3 phase, shifted to higher values with the addition of Ta2O5. Also, the crystallization activation energy (Ea) and the glass stability factor (ΔT) of the CaSiO3 phase increased, which indicated that the CaSiO3 phase of the glass became inhibited by the addition of Ta2O5. It was, thus, obvious that there was a need of glass characterization. The results of the crystallization kinetics showed that the critical cooling rate decreased with the addition of Ta2O5, which indicated that the viscosity of the system had increased. The CBST glass-ceramics, containing 1 mol% Ta2O5, that were sintered at 875 °C for 15 min showed excellent dielectric properties: εr = 6.22 and tanδ = 1.19 × 10−3 (1 MHz). To sum up, CaO–B2O3–SiO2–Ta2O5 glass-ceramics are potential low temperature co-fired ceramic substrate materials.

Effect of different stacking orders of Ta2O5 and SiO2 films on the reflective properties of a blue distributed Bragg reflector

The Ta2O5 and SiO2 single-layer films were deposited on the glass substrates to measure their refractive properties under different optical wavelengths. After that, the Ta2O5 and SiO2 films were used as high and low refractive index materials to design the blue distributed Bragg reflectors (DBRs) with different periods. The approximate formula proposed by Sheppard was used to calculate the maximum reflectance ratio of the bi-layer SiO–Ta2O5 DBRs with two, four, six, and eight periods. The COMSOL Multiphysics software was used to simulate the reflective spectra of the SiO2–Ta2O5 DBRs with different stacking orders and periods by incorporating the refractive indexes of the Ta2O5 and SiO2 films at a wavelength of 550 nm. The SiO2–Ta2O5 DBRs with different periods were fabricated by depositing the Ta2O5 and SiO2 films on glass substrates, and their reflective properties were measured. We compared the measured reflective spectra of the fabricated SiO2–Ta2O5 DBRs with the simulated reflective spectra to show the effect of the different stacking orders.

Miniaturized pH‐Sensitive Field‐Effect Capacitors with Ultrathin Ta2O5 Films Prepared by Atomic Layer Deposition

Miniaturized electrolyte–insulator–semiconductor capacitors (EISCAPs) with ultrathin gate insulators have been studied in terms of their pH‐sensitive sensor characteristics: three different EISCAP systems consisting of Al–p‐Si–Ta2O5(5 nm), Al–p‐Si–Si3N4(1 or 2 nm)–Ta2O5 (5 nm), and Al–p‐Si–SiO2(3.6 nm)–Ta2O5(5 nm) layer structures are characterized in buffer solution with different pH values by means of capacitance–voltage and constant capacitance method. The SiO2 and Si3N4 gate insulators are deposited by rapid thermal oxidation and rapid thermal nitridation, respectively, whereas the Ta2O5 film is prepared by atomic layer deposition. All EISCAP systems have a clear pH response, favoring the stacked gate insulators SiO2–Ta2O5 when considering the overall sensor characteristics, while the Si3N4(1 nm)–Ta2O5 stack delivers the largest accumulation capacitance (due to the lower equivalent oxide thickness) and a higher steepness in the slope of the capacitance–voltage curve among the studied stacked gate insulator systems.

Effects of Ta2O5 on the microstructure and electrical properties of ZnO linear resistance ceramics

ZnO linear resistance ceramics were synthesized from ZnO–Al2O3–MgO–TiO2–SiO2–Ta2O5 by a conventional ceramics method. Effects of Ta2O5 on the phase composition, microstructures, and electrical properties of ZnO linear resistive ceramics were investigated. The results show that doping with appropriate amount of Ta2O5 can refine the grains of the main crystalline phase ZnO and the secondary crystalline phase ZnAl2O4 in terms of microstructure, and also can reduce the grain boundary barrier and optimize the I–V characteristics in terms of electrical properties. In addition, the doping of Ta2O5 can improve the stability of the resistivity , and the impedance frequency indicates that the doping of Ta2O5 makes the sample suitable for high-frequency electric fields. The resistivity of the sample doped with 0.2 mol% Ta2O5 is 56.2 Ω·cm, and this sample has the best grain boundary barrier height, nonlinear coefficient and temperature coefficient of resistance of 0.054 eV, 1.04 and −3.48 × 10−3 °C−1, respectively.

Refractive Indexes and Spectroscopic Properties to Design Er3+-Doped SiO2-Ta2O5 Films as Multifunctional Planar Waveguide Platforms for Optical Sensors and Amplifiers.

This paper reports on the news about refractive index measurements and spectroscopic features of thin films, which can be applied as optical planar waveguides, focusing on their manufacturing processes, designs, and possible applications as optical amplifiers and sensors. Er3+-doped SiO2–Ta2O5 planar waveguides, with Si/Ta ratios of 90:10, 80:20, 70:30, 60:40, and 50:50, were prepared by a soft sol–gel process. Multilayer films were deposited by the dip-coating technique onto 10 μm SiO2–Si (100) p-type silicon and Si (100) silicon easily and successfully. The mechanisms of the densification process, porosity, and hydroxy group or water molecule occurrence have been accompanied by m-line and vibrational spectroscopy analyses. The thickness and refractive index values were used to understand better the influence of temperature and annealing time on the densification of the bulk films and the reduction of the pore volume as the tantalum oxide concentration increases. The refractive index shows the density of the films, and by the atomic force microscopy (AFM) technique, the films showed low surface roughness, achieving relatively high light confinement within the waveguide structure, and negligible optical loss due to surface scattering. Nanoparticle crystallization of Ta2O5 with size distribution ranging from 2.0 to 15.0 nm embedded in SiO2 was observed with size depending on annealing time and tantalum concentration. Intense and broadband emission positioned at 1550 nm, which is attributed to the 4I13/2 → 4I15/2 transition of Er3+ ions, was observed for all planar waveguides under excitation at 271, 272, and 278 nm. Depending on the porosity degree, the adsorption of H2O molecules occurs, changing the refractive index and contributing to the deactivation of excited states of Er3+ ions, making them an optical platform for use as an optical sensor for different species. Besides, the densified waveguides containing 20 or 30 mol % Ta exhibit high potential for applications as broadband optical amplifiers for wavelength division multiplexing (WDM), optical sensing, or augmented reality.

Electroluminescence of Ta2O5 Films Formed by Molecular Layer Deposition

The possibility of using electroluminescence to study Si–Ta2O5 and Si–SiO2–Ta2O5 structures and obtain information on the electronic structure of the Ta2O5 layer and on the properties of the SiO2–Ta2O5 interface is shows. A model of the electronic structure of the Ta2O5 layer formed by molecular layer deposition is proposed, which explains the spectral distribution of luminescence independently of the method of its excitation. It is shown that the formation of a Ta2O5 layer on the surface of thermally oxidized silicon is accompanied by transformation in the near-surface SiO2 layer and by quenching of the luminescence band in the spectral region of 650 nm.

A tantalum(v) oxide impregnated silica gel surface: application as a promising adsorbent for simultaneous heavy metal preconcentration

This article reports on an investigation into the ability of SiO2–Ta2O5 as a new sorbent for simultaneous preconcentration of Cd(ii), Co(ii), Cr(iii), Cu(ii), Fe(iii), Mn(ii), Ni(ii) and Pb(ii) ions from water by the column method and the parameters involved in this process.

Blue and NIR emission from nanostructured Tm3+/ Yb3+ co-doped SiO2–Ta2O5 for photonic applications

This paper reports on the synthesis of Tm3+/Yb3+ co-doped SiO2–Ta2O5 nanocomposites prepared by a sol–gel route. XRD analysis revealed initial crystallization of the L-Ta2O5 structure dispersed in the silica host, which depended on lanthanide concentration. Vibrational spectroscopy showed low OH groups content, SiO2–Ta2O5 nanocomposite formation, and controlled phase separation characterized by the presence of Ta2O5 nanoparticles. Emission in the near infrared was evident and also depended on lanthanide concentration and excitation wavelength. Direct excitation on the host promoted NIR luminescence; higher intensity emerged at 980 nm, attributed to Yb3+ ions. Excitation of the Tm3+ excited levels elicited energy transfer between Tm3+ and Yb3+ ions. Excitation of the Tm3+ levels (visible range) and the host (UV) promoted emission in the S telecom band for all the samples. Excitation at 980 nm gave rise to upconversion emissions at 476 nm (blue) and 793 nm (NIR). At higher lanthanide concentration, the presence of a dominant cross-relaxation process reduced the blue emission with respect to the NIR emission. The color coordinates were similar to the coordinates of standard blue. All these luminescent properties make the synthesized materials potential candidates for photonic applications like energy converting devices, solar concentrators, and blue emitters.

Enhancement of photocatalytic efficiency using heterostructured SiO2–Ta2O5 thin films

Fabrication of controlled layered structured thin films with tunable physical properties is an important area of research as thin film technology holds potential for a variety of industrial applications. In the present work, we have demonstrated the process for fabrication of multilayer films of silica and tantalum oxide by Langmuir–Blodgett film fabrication technique and investigated their photocatalytic degradation efficiency for organic dye (Rhodamine B) under UV radiation. The photocatalytic degradation of RhB in presence of SiO2–Ta2O5 exhibited remarkably enhanced photocatalytic activity than pure Ta2O5. This is because of the high separation efficiency of photo-generated electron–hole pair due to the Lewis acidity of silica and the greater contact area between these two layers. The SiO2–Ta2O5 system was optimized for the number of self-assembled layers of silica and tantalum oxide, and it has been found that 10S–15T–10S–15T–10S–15T (where S and T represents SiO2 and Ta2O5 respectively) pattern has been found to have maximum photocatalytic degradation efficiency of 71% (with 18% degradation per unit area of the film) which is 3.5 fold higher than pure Ta2O5 under identical experimental condition. Also, the photocatalytic activity of these films was also proved to be sensitive to the sequence of silica and tantalum oxide layers when the film area of all the samples was kept constant (3.75 cm2). Further analysis confirms that the degradation of dye molecules has been largely promoted by the photo generated holes, rather than the super oxide radical anions.

Low-Loss Silica-Based SiO2-Ta2O5Waveguides With Extremely High Δ Fabricated Using Sputtered Thin Films

Low-loss silica-based SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> waveguides with an extremely high refractive index difference (Δ) are realized, while avoiding Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> crystallization. First, we determined in detail the thermal conditions needed for thermal treatment in a film-refinement process after the deposition of extremely high-Δ SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> thin films to suppress Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> crystallization. Moreover, we confirmed that the crystallization of Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> was prompted mainly by the diffusion of boron (B) and phosphorus (P) dopants from the overcladding layer into the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> core region of the waveguide during the embedding process. By suppressing the diffusion of the B and P dopants from the overcladding layer using the double-layer cladding technique, we successfully fabricated extremely high-Δ waveguides and achieved a propagation loss of as low as 0.06 dB/cm. Extremely high-Δ waveguides appear to be a promising technology with which to realize high-density optically integrated and low-cost optical devices.

An application of field-effect sensors for in-situ monitoring of degradation of biopolymers

The characterization of the degradation kinetics of biodegradable polymers is mandatory with regard to their proper application. In the present work, polymer-modified electrolyte–insulator–semiconductor (PMEIS) field-effect sensors have been applied for in-situ monitoring of the pH-dependent degradation kinetics of the commercially available biopolymer poly(d,l-lactic acid) (PDLLA) in buffer solutions from pH 3 to pH 13. PDLLA films of 500nm thickness were deposited on the surface of an Al–p-Si–SiO2–Ta2O5 structure from a polymer solution by means of spin-coating method. The PMEIS sensor is, in principle, capable to detect any changes in bulk, surface and interface properties of the polymer induced by degradation processes. A faster degradation has been observed for PDLLA films exposed to alkaline solutions (pH 9, pH 11 and pH 13).

Color tunability of intense upconversion emission from Er3+–Yb3+ co-doped SiO2–Ta2O5 glass ceramic planar waveguides

This work reports on the infrared-to-visible CW frequency upconversion from planar waveguides based on Er3+–Yb3+-doped 100–xSiO2–xTa2O5 obtained by a sol–gel process and deposited onto a SiO2–Si substrate by dip-coating. Surface morphology and optical parameters of the planar waveguides were analyzed by atomic force microscopy and the m-line technique. The influence of the composition on the electronic properties of the glass-ceramic films was followed by the band gap ranging from 4.35 to 4.51 eV upon modification of the Ta2O5 content. Intense green and red emissions were detected from the upconversion process for all the samples after excitation at 980 nm. The relative intensities of the emission bands around 550 nm and 665 nm, assigned to the 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 transitions, depended on the tantalum oxide content and the power of the laser source at 980 nm. The upconversion dynamics were investigated as a function of the Ta2O5 content and the number of photons involved in each emission process. Based on the upconversion emission spectra and 1931CIE chromaticity diagram, it is shown that color can be tailored by composition and pump power. The glass ceramic films are attractive materials for application in upconversion lasers and near infrared-to-visible upconverters in solar cells.

Structural and Spectroscopic Properties of Luminescent Er3+-Doped SiO2-Ta2O5 Nanocomposites

This paper reports on the preparation and structural, morphological, and luminescence properties of Er3+-doped nanocomposites based on SiO2–Ta2O5 prepared by the sol–gel method. The influence of the tantalum oxide content on the structural and spectroscopic properties was analyzed for Si/Ta molar ratios of 90:10, 80:20, 70:30, 60:40, and 50:50. The sols were kept at 60°C for formation of the xerogel, followed by annealing at 900°, 1000°, and 1100°C for 2 h for production of the nanocomposites. The densification, phase separation, and crystallization processes were monitored through vibrational spectroscopy (FTIR), X-ray diffraction, and high-resolution transmission electron microscopy. Er3+ emission in the infrared region, assigned to the 4I13/2→4I15/2 transition, was observed for all the nanocomposites. Evolution from a vitreous-like environment to a crystalline one was identified upon increasing the annealing temperature and tantalum content. According to the results obtained, the Er3+ ions are preferentially localized close to the region rich in Ta2O5 nanoparticles. The localization of Er3+ ions was shown to be dependent on the amount of tantalum. Moreover, the fact that the Er3+ ions are located close to Ta2O5 nanoparticles promotes a broadband emission with full-width at half-maximum of 90 nm around 1550 nm.

Structural characterization of amorphous Ta2O5 and SiO2–Ta2O5 used as solid electrolyte for nonvolatile switches

Diffusivity of Cu in amorphous (a-) Ta2O5 is increased by low temperature annealing above 350 °C but the increase is suppressed by adding SiO2 to Ta2O5. To clarify the reasons, we investigated the structural difference between a-Ta2O5 and a-SiO2–Ta2O5. The results show that the low temperature annealing does not cause polycrystallization of Ta2O5 but purges weakly bonded oxygen atoms from the bulk and decreases the film density. Adding SiO2 to Ta2O5 is shown to increase the coordination number of Ta–O, which results in the improved thermal stability.

Charge Properties of a Condenser System Based on the Two‐Layer Dielectric SiO2–Ta2O5

A variant of a combined dielectric for the condensers of very large‐scale integrated circuits (VLSICs) has been proposed. Its electrophysical and mechanical properties have been analyzed. The influence of the thickness of each of the dielectrics on the effective built‐in charge, the permittivity, and the threshold voltage has been considered. Special emphasis has been placed on the residual mechanical stresses in a three‐layer dielectric system, namely, the influence of the thickness of a Ta2O5 film on the radius of curvature of the Si–SiO2–Ta2O5 system has been analyzed and the dependence of the change in the effective built‐in charge in the Ta2O5 film on the radius of curvature of the plate has been determined.

Synthesis and Characterization of Ta2O5–SiO2 Mixed Oxides

Abstract Mixed oxides, especially silica containing multicomponent oxides, have recently found many applications in the production of glasses, ceramics and catalysts. This paper reports for the first time the synthesis of SiO2–Ta2O5 mixed oxide by the sol–gel method. The advantage of the sol–gel method is that a relatively large concentration of tantalum can be incorporated in the mixed oxide structure. Physicochemical characterization shows that tantalum atoms are incorporated into the silica matrix producing Si–O–Ta bonds.

Refractive index and attenuation characteristics of SiO_2–Ta_2O_5 optical waveguide film

The refractive index and optical attenuation of sputtered SiO2–Ta2O5 waveguide film were measured in the 0.633–1.32-μm wavelength region. The waveguide film had a large refractive-index range of 1.46–2.08, which can be adjusted by suitable selection of the composition ratio of the SiO2–Ta2O5 target. Substrate heating, up to 270°C, during the sputtering process was effective for obtaining low attenuation. The waveguide films showed low attenuations, <0.41 dB/cm for the TE0 mode. The best fits of the form λγ to the measured attenuation have γ between 0 and −1, where λ is the wavelength. This wavelength dependence of the attenuation can be interpreted based on mode conversions due to the film surface roughness.

Total reflection optical waveguide switching through dielectric chip motion

An optical waveguide switch has been realized utilizing the total reflection critical angle controlled by the motion of a dielectric chip set on a waveguide surface. By the contact-noncontact of a GGG chip with the SiO(2)-Ta(2)O(5) waveguide film having a built-in low refractive-index channel, a switching angle of 22.5x and extincion ratio of 12-16 dB were obtained for the TE(0) mode at 0.633-microm wavelength. A 1 x 3 switch that includes two switching positions driven by 6-V electromagnets is demonstrated.

Refractive index decrease phenomena in SiO2–Ta2O5 waveguide films by CO2 laser irradiation

SiO2-Ta2O5 waveguide film exhibits a refractive index decrease up to 2% and a simultaneous film thickness increase proportional to the index decrease by CO2 laser irradiation. A partial restoration to the pre-irradiated state is observed by annealing in air at temperatures between 700 and 780 °C. The origin of the index decrease may be due to the density change with Ta2O5 crystallization. For application to the optical circuit design, the effective refractive indices of the index-decreased area are estimated, and a TE0-TE1 mode separation experiment by a 20°angle is done successfully, in order to examine the usefulness of the effective index.