Surface modification of SiO2 glass by laser processing

Various oxide films on SiO₂ glass substrates were irradiated by a laser beam. A continuous CO₂ laser source (wavelength 10.6 μm) was used for this purpose; the composition change at the surface layer was determined by Rutherford backscattering spectrometry (RBS). All the alkaline-earth oxides as well as those of lanthanum and yttrium, entered the glass after treatment. ZrO₂ and CeO₂, however, did not enter the SiO₂ glass due to laser irradiation. It is interesting, however, that a film of ZrO₂ + Al₂O mixture easily entered into the SiO₂ glass by laser processing. The conditions and mechanism of laser-enhanced interaction of ZrO₂ or other oxide films with SiO₂ glass surfaces are discussed especially in view of their structural behaviour in glass.     

Correlation between interfacial structure and c-axis-orientation of LiNbO3 films grown on Si and SiO2 by electron cyclotron resonance plasma sputtering

Thin films of crystalline lithium niobate (LN) grown on Si(1 0 0) and SiO₂ substrates by electron cyclotron resonance plasma sputtering exhibit distinct interfacial structures that strongly affect the orientation of respective films. Growth at 460–600 °C on the Si(1 0 0) surface produced columnar domains of LiNbO₃ with well-oriented c-axes, i.e., normal to the surface. When the SiO₂ substrate was similarly exposed to plasma at temperatures above 500 °C, however, increased diffusion of Li and Nb atoms into the SiO₂ film was seen and this led to an LN–SiO₂ alloy interface in which crystal-axis orientations were randomized. This problem was solved by solid-phase crystallization of the deposited film of amorphous LN; the degree of c-axis orientation was then immune to the choice of substrate material.     

TOPCon太阳电池发射极Al2O3/SiNx与SiO2/Al2O3/SiNx叠层膜钝化性能的比较

本文对TOPCon电池发射结的叠层钝化膜进行了研究,对比了3种不同叠层钝化膜(SiO₂/SiN_x、Al₂O₃(1.5 nm)/SiN_x、SiO₂/Al₂O₃(1.5 nm)/SiN_x)的钝化性能。结果表明:Al₂O₃(1.5 nm)/SiN_x的钝化性能优于SiO₂/SiN_x,SiO₂/Al₂O₃(1.5 nm)/SiN_x的钝化水平最佳,隐开路电压均值可达到705 mV。基于Al₂O₃/SiN_x叠层膜研究了Al₂O₃厚度(1.5 nm、3 nm和5 nm)对钝化性能和电池转换效率的影响。当Al₂O₃厚度由1.5 nm增加到3 nm时,钝化性能得到明显提升,隐开路电压均值提高了20 mV,达到707 mV,对应电池的光电转换效率升高了0.23个百分点,与SiO₂/Al₂O₃(1.5 nm)/SiN_x叠层膜电池的转换效率持平。然而,当Al₂O₃厚度继续增加至5 nm时,隐开路电压均值保持不变。因此可以使用Al₂O₃(3 nm)/SiN_x叠层膜代替SiO₂/Al₂O₃(1.5 nm)/SiN_x叠层膜,不仅简化了电池的工艺步骤,而且降低了生产成本。     

Structural transformation of the TiO2---SiO2 system gel during heat-treatment

The gel formation of the (100-x)TiO₂·xSiO₂ (x = 0–10 mol%) system has been studied. The progressive elimination of residues was followed by DTA and TGA curves. DTA curves showed that the formation of anatase during heat treatment could be sensibly slowed down with the increase of SiO₂. The relationship between the gel composition and crystallization temperature of anatase has been systematically investigated. The X-ray diffraction spectra demonstrated that the crystallization temperature of anatase is 400°C for TiO₂ gel and 430°C for 90TiO₂ - 10SiO₂ gel. The infrared absorption spectra were used to follow the structural transformation of gels heat-treated at different temperatures. With the help of EPR it is evident that titanium ions exist only in tetravalence.     

Some characteristics of glass in the Al2O3---B2O3---SiO2 system from the gel

The colorless and transparent glasses in the Al₂O₃---B₂O₃---SiO₃ system with high B₂O₃ and SiO₂ content were prepared from gels at low temperature. Their IR spectra not only revealed the evolution of the gel to glass conversion, but also showed that the formation of mixed bonds in the glasses obtained did not show any effect due to the B₂O₃ content. The accuracy of the glass composition is dependent upon the SiO₂/B₂O₃ molar ratio. The higher the ratio, the less the deviation of the analyzed compositions of the resulting glasses from their original calculated values. It is obvious that the higher the ratio, the lower the thermal expansion coefficient and the higher the transformation temperature of the glass, and the temperature at which the thermal contraction reaches an equilibrium is higher.     

Solidification of superalloy in a SiO2–ZrO2–B2O3 coating mould

The preparation of glass-lined coating mould from gels in the ternary system of SiO₂–ZrO₂–B₂O₃ has been investigated. The crystallization characterization and high temperature structure stability of this coating mould are demonstrated. We can find that the crystallization of t-ZrO₂ as well as the tetragonal to monoclinic phase transformation are, respectively, retarded and impeded owing to the encasement of SiO₂ matrix. While the inhibitive effect of B₂O₃ on crystallization of the SiO₂–ZrO₂–B₂O₃ coating mould is explained. Finally, DD3 single crystal superalloy melt can realize highly undercooled rapid solidification by adopting this coating mould, which further evinces that SiO₂–ZrO₂–B₂O₃ coating mould has an ideal nucleation inhibition for superalloy.     

Photoluminescence from E band centers in amorphous and crystalline SiO2

Photoluminescence (PL) originating from intrinsic defects in neutron-irradiated crystalline (x-) SiO₂ is observed and compared with that from amorphous (a-) SiO₂. The PL and photoluminescence excitation (PLE) spectra of x-SiO₂ are qualitatively similar to those of a-SiO₂. This suggests that PL centers, similar to those found in amorphous systems, are present in ordered systems. In addition, the PL and PLE spectra a-SiO₂ and a-As₂S₃ scale with energy band gap, suggesting that the radiative processes in a-SiO₂ and semiconducting chalcogenide glasses are alike. The similarity of the PL from x-SiO₂ to that from a-SiO₂ and the scaling of the PL from a-SiO₂ and a-As₂S₃ with energy band gap strongly suggest that PL centers are unique bonding configurations which primarily depend on the chemistry of the system rather than on the degree of long range order.     

Epitaxial growth of the CoFe2O4 film on SrTiO3 and its characterization

Cobalt ferrite (CoFe₂O₄) thin film is epitaxially grown on (0 0 1) SrTiO₃ (STO) by laser molecular beam epitaxy (LMBE). The growth modes of CoFe₂O₄ (CFO) film are found to be sensitive to laser repetition, the transitions from layer-by-layer mode to Stranski–Krastanov (SK) mode and then to island mode occur at the laser repetition of 3 and 5 Hz at 700 °C, respectively. The X-ray diffraction (XRD) results show that the CFO film on (0 0 1) SrTiO₃ is compressively strained by the underlying substrate and exhibits high crystallinity with a full-width at half-maximum of 0.86°. Microstructural studies indicate that the as-deposited CFO film is c-oriented island structure with rough surface morphology and the magnetic measurements reveal that the compressive strained CoFe₂O₄ film exhibits an enhanced out-of-plane magnetization (190 emu/cm³) with a large coercivity (3.8 kOe).     

Vibrational spectroscopy of LaBSiO5 glass and glass–crystal composites

Infrared (IR) reflectivity and Raman scattering spectra of LaBSiO₅ glass and glass–crystal composites were studied in the temperature range 25–260 °C. Using an analogy with the LaBGeO₅ crystal it was possible to assign the main spectral features of the LaBSiO₅ glass and glass–crystal composites. The BO₄ chain arrangement and the bending vibrations of SiO₄ are influenced by the loss of the long-range order in the glass whereas the stretching vibrations of the SiO₄ groups are practically unaffected. The structural disorder in LaBSiO₅ crystallites is caused by rotation of BO₄ tetrahedra.     

Mössbauer studies on some glasses and crystals in the Na2O---Fe2O3---SiO2 system

Mössbauer absorption measurements have been made at room temperature on ⁵⁷Fe in iron sodium silicate glasses containing 3–15 mol% Fe₂O₃ and various iron alkali silicate crystals in order to study the state of iron in these glasses. The spectra of all the glasses gave one doublet with a quadrupole splitting varying from 0.73–0.78 mm s⁻¹, while those of Na₂O · Fe₂O₃ · 4 SiO₂ and 5 Na₂O · Fe₂O₃ · 8 SiO₂ crystals showed much smaller quadrupole splitting, 0.28 mm s⁻¹ and 0.10 mm s⁻¹, respectively, and an asymmetrical doublet of much narrower linewidth. When sodium was replaced by other alkali metals of larger size, such as K and Cs, in MFeSi₂O₆ and MFeSi₃O₈ crystals, the quadrupole splitting became wider and approached to 0.73 mm s⁻¹. Such a variation was not observed for glasses. These results suggest that a larger number of non-identical sites exist in iron sodium silicate glasses than in the corresponding crystals.     

Cation site occupation by Ag/Na ion-exchange in R2O–Al2O3–SiO2 glasses

Ag⁺/Na⁺ ion-exchanged R₂O–Al₂O₃–SiO₂ glasses with uniform concentration profile of Ag⁺ and Na⁺ were prepared by heat treatment in molten silver salt followed by holding at the same temperature in an ambient atmosphere. Their glass transition temperature (T_g) and thermal expansion coefficient (TEC) were measured and structures were investigated using ²⁹Si-MAS NMR, ²⁷Al-MAS NMR, IR and Raman spectroscopies. Both T_g and TEC decreased with increase of the exchange ratio, but T_g was still above the ion-exchange temperature of 400°C even for the fully exchanged sample. The ²⁹Si- and ²⁷Al-MAS NMR spectra were mostly unchanged and no sign of the structural alteration of the glass network was observed. On the other hand, the vibrational spectra showed remarkable peak shifts depending on the exchange ratio. From these structural results, it was found that when the exchange ratio was low, the introduced Ag⁺ ions were stabilized at the non-bridging oxygen (NBO) site, and then Na⁺ ions in AlØ₄ site were exchanged by Ag⁺ ions after full replacement of NBO sites, where Ø represents the bridging oxygen.     

Effects of SiO2 overlayer at initial growth stage of epitaxial Y2O3 film growth

We investigated the dependence of the Y₂O₃ film growth on Si surface at initial growth stage. The reflection high-energy electron diffraction, X-ray scattering, and atomic force microscopy showed that the film crystallinity and morphology strongly depended on whether Si surface contained O or not. In particular, the films grown on oxidized surfaces revealed significant improvement in crystallinity and surface smoothness. A well-ordered atomic structure of Y₂O₃ film was formed on 1.5 nm thick SiO₂ layer with the surface and interfacial roughness markedly enhanced, compared with the film grown on the clean Si surfaces. The epitaxial film on the oxidized Si surface exhibited extremely small mosaic structures at interface, while the film on the clean Si surface displayed an island-like growth with large mosaic structures. The nucleation sites for Y₂O₃ were provided by the reaction between SiO₂ and Y at the initial growth stage. The SiO₂ layer known to hinder crystal growth is found to enhance the nucleation of Y₂O₃, and provides a stable buffer layer against the silicide formation. Thus, the formation of the initial SiO₂ layer is the key to the high-quality epitaxial growth of Y₂O₃ on Si.     

Structure and thermal stability of MOCVD ZrO2 films on Si (1 0 0)

The structure and thermal stability of ZrO₂ films grown on Si (1 0 0) substrates by metalorganic chemical vapor deposition have been studied by high-resolution transmission electron microscopy, selected area electron diffraction and X-ray energy dispersive spectroscopy. As-deposited films consist of tetragonal ZrO₂ nanocrystallites and an amorphous Zr silicate interfacial layer. After annealing at 850°C, some monoclinic phase is formed, and the grain size is increased. Annealing a 6 nm thick film at 850°C in O₂ revealed that the growth of the interfacial layer is at the expense of the ZrO₂ layer. In a 3.0 nm thick Zr silicate interfacial layer, there is a 0.9 nm Zr-free SiO₂ region right above the Si substrate. These observations suggest that oxygen reacted with the Si substrate to grow SiO₂, and SiO₂ reacted with ZrO₂ to form a Zr silicate interfacial layer during the deposition and annealing. Oxygen diffusion through the tetragonal ZrO₂ phase was found to be relatively easier than through the monoclinic phase.     

Nuclear magnetic resonance studies of alkaline earth phosphosilicate and aluminoborosilicate glasses

The ¹¹B, ²⁷Al, ²⁹Si and ³¹P magic angle spinning (MAS) NMR spectra of MO–P₂O₅, MO–SiO₂–P₂O₅ and MO(M^′₂O)–SiO₂–Al₂O₃–B₂O₃ (M=Mg, Ca, Sr and Ba, M^′=Na) glasses were examined. In binary MO–P₂O₅ (M=Ca and Mg) glasses, the distributions of the phosphate sites, P(Q_n), can be expressed by a theoretical prediction that P₂O₅ reacts quantitatively with MO. In the ternary 0.30MO–0.05SiO₂–0.65P₂O₅ glasses, the 6-coordinated silicon sites were detected, whose population increases in the order of MgOxCaO–0.05SiO₂–(0.95−x)P₂O₅ glasses, its population increases with an increase in f (=([P₂O₅]−[MO]−[B₂O₃]−[Na₂O])/[SiO₂]) and has maximum at f=9. The signal due to the 5-coordinated silicon atoms is also observed when x is smaller than 0.45. When three network-forming oxides such as SiO₂, Al₂O₃ and B₂O₃ coexist, Al₂O₃ reacts preferably with MO. The populations of 4-coordinated boron atoms, N₄, are expressed well with r/(1−r), where r=([Na₂O]−[Al₂O₃])/([Na₂O]−[Al₂O₃]+[B₂O₃]). The correlation of the Raman signal at 1210 and 1350 cm⁻¹ with the NMR signal of Si(Q₆) at −215 ppm is also seen.     

Electronic traps in mixed Si1−xGexO2 films

Thermally stimulated luminescence (TSL) and infrared (IR) spectroscopy were measured in plasma grown Si_1−xGe_xO₂ (x=0, 0.08, 0.15, 0.25, 0.5) with different thicknesses (12–40 nm). A comparison with the TSL properties of thermally grown SiO₂ and GeO₂ was also performed. A main IR absorption structure was detected, due to the superposition of the peaks related to the asymmetric O stretching modes of (i) Si–O–Si (at ≈1060 cm⁻¹) and (ii) Si–O–Ge (at 1001 cm⁻¹). Another peak at ≈860 cm⁻¹ was observed only for Ge concentrations, x>0.15, corresponding to the asymmetric O stretching mode in Ge–O–Ge bonds. A TSL peak was observed at 70°C, and a smaller structure at around 200°C. The 70°C peak was more intense in all Ge rich layers than in plasma grown SiO₂. Based on the thickness dependence of the signal intensity we propose that at Ge concentrations 0.25x0.5 TSL active defects are localised at interfacial regions (oxide/semiconductor, Ge poor/Ge rich internal interface, oxide external surface/atmosphere). Based on similarities between TSL glow curves in plasma grown Si_1−xGe_xO₂, thermally grown GeO₂ and SiO₂ we propose that oxygen vacancy related defects are trapping states in Si_1−xGe_xO₂ and GeO₂.     

Multilayer SiO2 and TiO2 coatings on glasses by the sol-gel process

Glass films of pure SiO₂ and TiO₂ have been prepared on sodalime silica flat slide glasses by the sol-gel process using the dip-coating technique from TEOS and Ti(OC₃H₇)₄ solutions. The various parameters such as chemicals concentrations, viscosity, type of catalyst, withdrawal speed and temperature of densification leading to the obtention of good and adherent coatings with definite film thicknesses are reported. The same technique has been used for the depositon of layers of colored films SiO₂---M_xO_y (M = Co, Mn, Nd and Cr). Brilliant yellow coatings have been obtained with TiO₂---CeO₂.     

Feasibility of the electrical characterization of single SiO2 breakdown spots using C-AFM

Due to the progressive scaling down of MOS devices, new methods are required to study the failure mechanisms of the gate oxide in a nanometer range. In this work, an atomic force microscope equipped with a conductive tip and a sensitive preamplifier has been used to study the electrical properties and degradation dynamics of single breakdown spots of 3–6 nm SiO₂ films on a nanometer scale. With this purpose, voltage ramps over areas of 30–50 nm² (of the order of the breakdown spot area) have been repeatedly applied to induce the degradation of the SiO₂ films. Similar results to those observed with conventional tests (such as the switching between two states of well-defined conductivity) have been measured with this technique. As a conclusion, our results point out the conductive atomic force microscope as a tool for the analysis of the electrical properties and degradation of single breakdown spots.     

Effect of CaO on the surface morphology and strength of water soaked Na2O–B2O3–Al2O3–SiO2 vitrified bond

The surface morphology of Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond with and without calcium oxide was studied by soaking vitrified bonded microcrystalline alumina composites in water. The content of water introduced to the vitrified bond was determined by thermal gravity analysis, and the effects of water and calcium on the phase separation and nucleation of the vitrified bond were investigated using scanning electron microscope and energy-dispersive X-ray spectrometer. Soaked in water for 72 h, the Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond presented a porous surface, and its bending strength declined with increasing sintering temperature. However, the Na₂O–CaO–B₂O₃–Al₂O₃–SiO₂ vitrified bond was more durable against aqueous coolant even needle-shape crystals were found clustered on the surface of the vitrified bond. The crystals were enriched with aluminosilicate tested by energy-dispersive X-ray spectrums. The appearance of crystals lessened the dissolution of the vitrified bond and made the bending strength increase in the sintering temperature region between 870 °C and 930 °C.     

Electrical conductivities of mixed cation glasses

The electrical conductivities of (1−x) Li₂O · x BaO · 2 SiO₂, (1−x) Na₂O · x MgO ·2 SiO₂, (1−x) Na₂O · x CaO · SiO₂ and (1−x) Na₂O · x BaO · 2SiO₂ glasses were measured at temperature ranging from room temperature to 450°C. The transport numbers for Na⁺ ion in (1−x) Na₂O · x BaO · 2 SiO₂ glasses were measured. It was found that the alkali ion carried a significant part of the current in these glasses except one that had no alkali ions, and the conductivity decreased markedly as the alkali oxide was substituted by an alkaline earth oxide. The results of conductivity measurements combined with the data hitherto reported on mixed alkali glasses led to the proposal that the so-called mixed alkali effect could be explained on the basis of the independent path model in which it is assumed that cations can move only through vacant sites left by those of the same type.     

Crystallization behavior and hydrophilic performances of V2O5–TiO2 films prepared by sol–gel dip-coating

Homogeneous and transparent V₂O₅–TiO₂ composite nanometer thin films were prepared on glass substrates by sol–gel processing and dip-coating technique. The films as well as the dried powder of bulk gel were characterized by different techniques like X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), atomic force microscope (AFM) and thermogravimetry–differential thermal analysis (TG–DTA). The hydrophilicity of the films was determined by measuring the water contact angles on the films. The results showed that the dopant of V₂O₅ on TiO₂ thin films could produce a visible-light response to the films, and the introduction of V₂O₅ could suppress the structural phase transition and crystal growth of TiO₂ crystal. Finally, the relationship between crystalline size and hydrophilicity under sunlight was investigated in this article.