Phosphorus diffusion processes in SiO2 films

During the diffusion of dopants into silicon, two primary mechanisms of masking by silicon dioxide are known. The most prevalent reactive diffusion-limited type has been explored for phosphorus in SiO₂ in this work. Doped oxide diffusion conditions were used to diffuse ³²P radioisotope into 1100°C thermal SiO₂. Two phosphorus-containing diffusing species were identified. Their diffusion characteristics were used with the literature data on the kinetics of phosphosilicate glass formation to construct a multiple-zone model of P₂O₅ diffusion into thermal SiO₂. This physical model was quantitatively verified by several types of masking experiments.     

The photoluminescence and optical constant of ZnSe/SiO2 thin films prepared by sol–gel process

In this paper, ZnSe/SiO₂ thin films were prepared by sol–gel process. X-ray diffraction results indicate that the phase structure of ZnSe particles embedded in SiO₂ thin films is sphalerite (cubic ZnS). The dependence of ellipsometric angle ψ on wavelength λ of ZnSe/SiO₂ thin films was investigated by spectroscopic ellipsometers. The optical constant, thickness, porosity and the concentration of ZnSe/SiO₂ composite thin films were fitted according to Maxwell–Garnett effective medium theory. The thickness of ZnSe/SiO₂ thin films was also measured by surface profile. The photoluminescence properties of ZnSe/SiO₂ thin films were investigated by fluorescence spectrometer. The photoluminescence results reveal that the emission peak at 487 nm (2.5 eV) excited by 395 nm corresponds to the band-to-band emission of sphalerite ZnSe crystal (2.58 eV). Strong free exciton emission and other emission peaks corresponding to ZnSe lattice defects are also observed.     

Holographic scattering in SiO2 nanoparticle-dispersed photopolymer films

We describe an experimental study of holographic (coherent) scattering due to parasitic noise gratings recorded in SiO2 nanoparticle-dispersed photopolymer films. Dependences of film thickness and nanoparticle concentration on holographic scattering losses are evaluated. It is shown that the geometric feature of the holographic scattering pattern in the two-beam recording setup can be explained by the Ewald sphere construction. It is found that holographic scattering becomes noticeable when a film with nanoparticle concentrations higher than 10 vol.% is thicker than 100 microm. The significance of holographic scattering in the characterization of a volume grating recorded in a thick (>100 microm) nanoparticle-dispersed photopolymer film is also discussed.     

Dielectric constant and mixing model of BaTiO3 composite thick films

BaTiO₃ (BT) composite thick films of X7R BT particles with different BT gel fractions were prepared by using an aqueous BT sol. The dielectric constant versus different BT gel volume fractions showed a sigmoidal behavior as the BT gel phase filled the interstitials of the X7R BT particle compact. To explain and predict the effect of the BT gel as a second phase based on the experimental results, various models such as series, parallel, cubic, Lichtenecker’s model, and Hashin-Shtrikman bounds were considered. None of the existing theoretical models fit the experimental results. An empirical sigmoidal fitting function was proposed to fit the experimental data.     

Dielectric engineering of Ge nanocrystal/SiO2 nanocomposite thin films with Ge ion implantation: Modeling and measurement

Ge nanocrystal (nc-Ge) embedded SiO₂ nanocomposite thin films have been synthesized with the ion implantation technique. The distribution profile of nc-Ge in the SiO₂ matrix can be tailored by varying the implantation energy and dose in the Ge ion implantation process; thus the effective dielectric constant of the nc-Ge/SiO₂ nanocomposite thin films can be engineered. The effective metal–oxide-semiconductor (MOS) capacitance of the nanocomposite thin films has been calculated using the sub-layer model and the Maxwell–Garnett effective medium approximation, taking the reduced dielectric constant corresponding to the nanometer size of nc-Ge into account. On the other hand, capacitance–voltage measurements on the MOS structures based on the nc-Ge/SiO₂ thin films have been conducted to extract the capacitance experimentally. The modeling and measurement results have shown good agreement, suggesting that the nanocomposite dielectric engineering can be easily realized through the energy- and dose-controlled Ge⁺ implantation technique.     

Elastic and plastic relaxation of densified SiO2 films

Ion- and plasma-assisted deposition has been extensively used for the fabrication of high-performance optical films with dense and smooth microstructures that are essential for applications such as low-loss and environmentally stable optics. SiO(2) is a well-known amorphous material suitable for energetic deposition. SiO(2) single layers and SiO(2)-based single-cavity narrow-bandpass filters were prepared by plasma-ion-assisted deposition. The refractive index and film thickness were determined by variable-angle spectroscopic ellipsometry. The high compressive stress of the densified film was correlated to increased packing density. The center wavelength shift of the narrow-bandpass filters as a function of sample-temperature as well as high-temperature annealing was determined via spectral transmission measurement. Structural relaxation of the densified SiO(2) films was observed from the variation of the refractive index and physical thickness for the single layers and the center wavelength shift for the narrow-bandpass filters, suggesting elastic and plastic deformation of the densified films corresponding to a reversible and an irreversible center wavelength shift, respectively.     

Catalysts and the structure of SiO2 sol-gel films

In the fabrication of silica films by sol-gel synthesis, the role of various catalysts is systematically examined. The precursor solutions were made by mixing tetraethylorthosilicate (TEOS), ethanol and water in the molar ratio of 1 : 2 : 2. The spin coated films were thermally treated at various temperatures, and characterised using ellipsometry, molecular probe ellipsometry (MPE), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and optical scattering. By employing different catalysts with the same concentration (0.1 M in water), it was found that dramatic effects on the porosity, optical quality, shrinkage, thickness, structural evolution during thermal treatment, and film stress can be observed.     

SiO2-TiO2光催化薄膜的制备及其晶化过程的研究

利用溶胶-凝胶法在石英玻璃表面制备出一层折射率可调的SiO2-TiO2光催化薄膜.采用X射线衍射分析、扫描电镜及氮气吸附实验等测试手段,研究了利用溶胶-凝胶法制备SiO2掺杂的TiO2薄膜的相变行为.提出了通过加入SiO2的比例超过10%时,在TiO2内部形成高度分散的SiO2网络,抑制TiO2晶粒的生长以及晶型转变,增加薄膜材料的热稳定性的方法.通过甲基橙水溶液的光催化降解实验表明:当SiO2的掺杂比例为10%,经过500℃以上的热处理后,所获得的SiO2-TiO2复合薄膜具有最大的光催化活性.     

Synthesis and Microwave Dielectric Properties of MgO–TiO2–SiO2 Ceramics

The dielectric properties of MgO–TiO₂–SiO₂ ceramics were studied. The results demonstrate that the presence of MgTi₂O₅ increases dielectric losses in the ceramics. The synthesized materials offer low microwave losses and temperature-stable permittivity in the range 10–20.     

低介电常数介孔氧化硅薄膜的结构与介电性能研究

利用溶胶-凝胶技术制备了介孔氧化硅薄膜.采用MIM结构,通过平行板电容器法测量了介孔氧化硅薄膜的介电常数,结果表明采用表面修饰的方法可以在保持较低介电常数(k=2.25)的前提下极大地降低薄膜的漏电流,提高薄膜的环境稳定性能.通过对富氏红外光谱的分析,讨论了薄膜的键结构与介电性能之间的关系,结果表明去除介孔氧化硅薄膜中的OH基团是提高薄膜介电性能的关键.     

Optical properties of SiO2-TiO2 sol-gel thin films

The optical properties of thin SiO₂-TiO₂ sol-gel composite films were investigated using exact optical models and the Forouhi-Bloomer model, (Phys. Rev. B34, 7018 (1986)), which describes the optical dispersion of amorphous dielectrics. Films deposited on glass and silicon substrates, were characterized by optical transmission and reflection measurements. Theoretical spectra have been generated and fitted to the experimental ones via standard regression analysis techniques. The (five) adjustable Forouhi-Bloomer parameters describing the dispersion of the complex refractive index, as well as the film thickness were determined. The refractive index and absorption coefficient of the films were found to depend on the molar contents of the component oxides.     

Selective deposition of SiO2 thin films in acid baths

We report observation of deposition of SiO₂ thin films on a variety of surfaces in nitric acid and hydrochloric acid solutions. Scanning electron microscopy shows that the films are composed of closely packed spheres 1000 Å in diameter. Chemical identification is made with Auger electron spectroscopy. The films are generally between 1000 and 2000 Å thick and are possibly hydrated. Deposition occurs in either acid for molarities in the 1–8 M range and at temperatures between 80 and 100 °C. The effects for molarities greater than 8 M and temperatures greater than 100 °C have not been investigated.Materials on which the films form in nitric acid are tantalum, gold, silicon, niobium and Al₂O₃; in hydrochloric acid, films will form on tantalum, gold, silicon and Al₂O₃. Materials which are insoluble in the acids but upon which films have not been observed to form are graphite, platinum, chromium (nitric acid) and niobium (hydrochloric acid).Deposition occurs inside a sealed vessel made entirely of Pyrex-type glass. Vessels are partially filled with acid and are heated so that the upper glass surfaces (not in contact with the acid reservoir) are about 10–30 °C cooler than the reservoir. Acid vapors condense on the cooler glass surfaces forming droplets that run down the vessel walls to the reservoir. This process of acid flow on the walls leaches SiO₂ from the glass and increases the SiO₂ concentration in the reservoir until the SiO₂ films form. It is believed that a supersaturated condition is present during SiO₂ deposition. Experiments show that cessation of acid condensation halts film formation. Attack of the vessel provides the sole source of SiO₂.Preliminary kinetic measurements indicate that vessels must be heated for periods longer than 150 h before deposition occurs. Iron can be incorporated into the SiO₂ films by the dissolution of iron metal in the acid before sealing of the vessel.     

Quantum confinement effect in SiO2 films containing Ge microcrystallites

SiO₂ thin films embedded with Ge microcrystallites (Ge-SiO₂ films) were prepared by RF-magnetron co-sputtering method from a composite target of Ge and SiO₂. The average size of Ge crystallites can be modulated by the experiment parameters. The optical absorption and non-linear optical properties of Ge-SiO₂ films were measured. The blue shift of the optical absorption edge, the saturated absorption and two-photon absorption under the condition of resonant absorption have been observed, and are discussed according to the quantum confinement effect.     

Sm3+ photoluminescence in co-sputtered SiO2 thin films

Thin films of SiO₂ containing Sm were deposited by magnetron co-sputtering. The concentration of Sm in the films was varied by changing the amount of Sm placed on the fused silica target. The samarium content in the films was established by Rutherford back-scattering measurements. Photoluminescence (PL) was excited with the 488-nm line of an Ar ion laser. It consists of several lines in the visible, which are assigned to transitions between multiplets of Sm³⁺. The concentration dependence of the PL intensity was studied. It passes through a maximum and decreases at higher Sm content. The films were annealed in vacuum at temperatures between 300 and 1000 °C. There was a strong increase in the PL intensity after annealing at 600 °C, and then it fell again after annealing at 1000 °C. The data are compared to spectra of Sm³⁺ in other matrices. The mechanisms of PL excitation and quenching are discussed.     

Synthesis of TiO2-doped SiO2 composite films and its applications

The TiO₂-doped SiO₂ composite films were prepared by two-step sol-gel method and then it was applied in the degradation of methylene red (MR) as photocatalysts. In XRD, FT-IR, and TEM investigations of these TiO₂-doped SiO₂ composite films, the titanium oxide species are highly dispersed in the SiO₂ matrixes and exist in a tetrahedral form. And special attention has been focused on the relationship between the local structure of the titanium oxide species in the TiO₂-doped SiO₂ composite films and the photocatalytic reactivity in order to provide vital information for the design and application of such highly efficient photocatalytic systems in the degradation of toxic compounds diluted in a liquid phase.     

Dielectric properties of R2O−SiO2 glasses prepared via sol-gel

Gels from R₂O−SiO₂ (R=potassium, sodium and lithium) systems with a maximum alkaline content of 5 mol % were prepared. The conductivity and the alkaline ion incorporation degree as a function of temperature were studied by a.c. impedance spectroscopy and dielectric relaxation measurements. At low temperature (20 to 200°C) the major contribution to the total electric conductivity is due to water conducting species (mainly protons) which are adsorbed inside the gels. From 450°C gels start to behave as conventional glasses. The total electric conductivity and activation energy values for conduction at those high temperatures are of the same order as those for glasses prepared by direct melting.