Deposition of HfO2 thin films on ZnS substrates

HfO₂ thin films with columnar microstructure were deposited directly on ZnS substrates by electron beam evaporation process. SiO₂ thin films, deposited by reactive magnetron sputtering, were used as buffer layers, HfO₂ thin films of granular microstructure were obtained on SiO₂ interlayer by this process. X-ray diffraction patterns demonstrate that the as-deposited HfO₂ films are in an amorphous-like state with small amount of crystalline phase while the HfO₂ films annealed at 450 °C in O₂ for 30 min and in Ar for 150 min underwent a phase transformation from amorphous-like to monoclinic phase. Antireflection effect in certain infrared wave band, such as 3–6 μm, 4–12 μm, 4–8 μm and 3–10 μm, can be observed, which was dependent on the thickness of thin films. The cross-sectional images of HfO₂ films, obtained by field emission scanning electron microscopy, revealed that there was no distinct morphological change upon annealing.     

残余应力对涂覆Al2O3涂层的ZrO2陶瓷的强度和裂纹扩展阻力的影响

本研究在ZrO₂基体表面涂覆一薄层Al₂O₃涂层, 利用基体与涂层之间热膨胀系数不匹配, 在Al₂O₃-ZrO₂预应力陶瓷(简称A_CZ_S预应力陶瓷)表层引入压应力。采用维氏压痕法评价残余应力对A_CZ_S预应力陶瓷的表层和基体中裂纹扩展阻力的影响。理论分析结合实验结果表明: 表层的压应力使得A_CZ_S预应力陶瓷的裂纹扩展阻力增大, 最终导致强度和损伤容限提高; 且A_CZ_S预应力陶瓷表层的压应力和裂纹扩展阻力随着基体截面积与涂层截面积比值的增加而增大。当ZrO₂基体表层的Al₂O₃涂层厚度为40 μm时, 表层压应力使A_CZ_S预应力陶瓷的弯曲强度达到(1207±20) MPa, 相比于同种工艺下制备的ZrO₂陶瓷强度提高了32%, 同时也是Al₂O₃强度的3倍。此外, A_CZ_S预应力陶瓷也表现出很好的抗热震性能。     

Preparation and properties of radiofrequency sputtered X-ray amorphous films in the system SiO2–ZrO2

Amorphous films in the system SiO₂–ZrO₂ were prepared by radiofrequency sputtering method and their density, refractive index, elastic constants, and thermal expansion coefficient were measured. All of the physical properties had a similar compositional dependence; that is, they increased, but not proportionally, with increasing ZrO₂ content. The coordination states of cations in these amorphous films were estimated by the compositional dependence of volume and molar refractivity. The coordination state of silicon ions in the amorphous films did not change, but the coordination number of zirconium ions changed from 8 to 6, depending on ZrO₂ content. These results indicate that, in amorphous films in the system SiO₂–ZrO₂, the change of the coordination state of zirconium ions in the amorphous films has an important effect on the properties.     

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).     

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).     

Fabrication of robust Bi3.25La0.75Ti3O12 thin film resistant to hydrogen damage

Ferroelectric bismuth lanthanum titanate (Bi_3.25La_0.75Ti₃O₁₂; BLT) thin films were deposited on Pt/TiO₂/SiO₂/Si substrate by chemical solution deposition method. The films were crystallized in the temperature range of 600–700 °C. The spontaneous polarization (P_s) and the switching polarization (2P_r) of BLT film annealed at 700 °C for 30 min were 22.6 μC/cm² and 29.1 μC/cm², respectively. Moreover, the BLT capacitor did not show any significant reduction of hysteresis for 90 min at 300 °C in the forming gas atmosphere.     

Low-temperature growth and orientational control in RuO2 thin films by metal-organic chemical vapor deposition

For growth temperatures in the range of 275°C to 425°C, highly conductive RuO₂ thin films with either (110)- or (101)-textured orientations have been grown by metal-organic chemical vapor deposition (MOCVD) on both SiO₂/Si(001) and Pt/Ti/SiO₂/Si(001) substrates. Both the growth temperature and growth rate were used to control the type and degree of orientational texture of the RuO₂ films. In the upper part of this growth temperature range ( 350°C) and at a low growth rate (< 3.0 nm/min.), the RuO₂ films favored a (110)-textured orientation. In contrast, at the lower part of this growth temperature range ( 300°C) and at a high growth rate (> 3.0 nm/min.), the RuO₂ films favored a (101)-textured orientation. In contrast, higher growth temperatures (> 425°C) always produced randomly-oriented polycrystalline films. For either of these low-temperature growth processes, the films produced were crack-free, well-adhered to the substrates, and had smooth, specular surfaces. Atomic force microscopy showed that the films had a dense microstructure with an average grain size of 50–80 nm and a rms. surface roughness of 3–10 nm. Four-probe electrical transport measurements showed that the films were highly conductive with resistivities of 34–40 μΩ-cm (at 25°C).     

Al2O3/BaZrO3双陶瓷界面微观组织演化及机理

以Al₂O₃为背层(硅溶胶为粘结剂), 电熔BaZrO₃作为面层材料(钇溶胶为粘结剂), 1550℃烧结后制成50 mm×25 mm×5 mm的Al₂O₃/BaZrO₃双陶瓷试样。通过光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和EDS等手段观察了BaZrO₃层和Al₂O₃/BaZrO₃界面的显微结构, 研究了BaZrO₃与Al₂O₃的界面反应。结果表明, 面层由BaZrO₃基体和分布其上的大小10 μm左右的Y稳定的ZrO₂晶粒组成; Al₂O₃/BaZrO₃界面发生反应形成厚约300 μm的过渡层, 界面反应生成物有BaOAl₂O₃、ZrO₂和BaO·Al₂O₃·2SiO₂。界面从单纯的BaZrO₃/Al₂O₃双陶瓷结构演变为BaZrO₃、ZrO₂、BaO·Al₂O₃、BaO·Al₂O₃·2SiO₂和Al₂O₃等多种物相组成的复杂结构。反应过程中Al元素基本不迁移扩散, BaZrO₃中Ba元素向Al₂O₃所在的位置扩散形成BaO·Al₂O₃, 残留物形成一层条状ZrO₂, 而BaO·Al₂O₃·2SiO₂围绕着EC95(Al₂O₃+5%SiO₂)粉体颗粒周围生成。     

Low-temperature ionic conductivity of the solid solution in the system ZrO2–Y2O3–Yb2O3

Compositional dependence of ionic conductivity in the system ZrO₂–Y₂O₃–Yb₂O₃ was investigated in the temperature range 573–873 K using the complex impedance technique. It was shown that the conductivity decreases with increasing concentration of Yb₂O₃ in the system ZrO₂–Y₂O₃–Yb₂O₃. Analyzing the experimental data according to the classic Arrhenius equation showed that such an experimental phenomenon can be attributed to the tighter association between Yb³⁺ and oxygen vacancy, compared with that between Y³⁺ and oxygen vacancy, which hinders the migration of oxygen vacancy in the materials.     

Low temperature plasma-assisted oxidation and thin-film deposition processes for forming device-quality SiO2/Si and composite dielectric-SiO2/Si heterostructures

In the high-temperature thermal oxidation of Si, the SiO₂/Si interface is continuously regenerated as the bulk oxide grows. This paper describes an alternative low temperature, 200–300 °C, plasma-assisted process that optimizes electrical properties of SiO₂/Si interfaces and bulk SiO₂ layers by separately controlling interface formation and bulk oxide deposition. Composite dielectrics, oxide/nitride (ON) and oxide (ONO), have been fabricated by extending the low temperature plasma-assisted processes to include deposition of Si₃N₄ films. The electrical properties of SiO₂/Si structures formed by the two-step, low temperature oxidation-deposition process are essentially the same as those of SiO₂/Si structures formed by high temperature, 850–1050 °C, thermal oxidation. The electrical properties of devices incorporating ON and ONO composite dielectrics are degraded with respect to the SiO₂/Si structures, but are similar to those of composite dielectrics formed by combinations of high temperature processing.     

Magnetic properties of NiSb2O4

The magnetic transition of the antimony oxide NiSb₂O₄ has been studied using heat capacity measurements and magnetic susceptibility data. The Néel temperature previously evaluated from neutron diffraction is confirmed: T_N = 45 ± 1 K. The entropy excess ΔS(20 – 60 K) associated with the transition is calculated and compared with the theoretical value. The susceptibility data are interpreted in terms of a Curie-Weiss law (θ_p = − 98K, M_eff = 3.98 μ_ß). Exchange integrals are evaluated.     

Optical properties of Er-doped SiO2-GeO2-Al2O3 planar waveguide fabricated by sol–gel processes

In this paper, we report silica based planar waveguides doped with Er³⁺, and co-doped with GeO₂ and Al₂O₃. These sol–gel derived planar waveguides were fabricated on SOS (silica on silicon) using multiple spin-coating and rapid thermal processing (RTP). Investigation has been made on their characteristics in terms of their application in optical amplification and lasing, including photoluminescence (PL), fluorescence lifetime, refractive index, propagation loss, surface roughness, Fourier transform infrared (FTIR) spectrum and X-ray diffraction (XRD) analysis. The propagation loss of a 20-layer planar waveguide was measured to be about 1.6 dB/cm for TE₀ and 2.2 dB/cm for TM₀ mode. A strong emission transition (⁴I_13/2→⁴I_15/2) at 1.536 μm with a lifetime of 3.6 ms has been obtained for an optimized molar composition of 90SiO₂: 10GeO₂: 20AlO_1.5: 1ErO_1.5.     

High concentration erbium doping of silicon-rich SiO2 thin films on silicon

In this work, high concentration erbium doping in silicon-rich SiO₂ thin films is demonstrated. Si plus Er dual-implanted thermal SiO₂ thin films on Si substrates have been fabricated by using a new method, the metal vapor vacuum arc ion source implantation with relatively low ion energy, strong flux and very high dose. X-Ray photoelectron spectroscopy measurement shows that very high Er concentrations on the surfaces of the samples, corresponding to 10 at.% or the doping level of 10²¹ atoms cm⁻³, are achieved. This value is much higher than that obtained by using other fabrication methods such as the high-energy ion implantation and molecular beam epitaxy. Reflective high-energy electron diffraction, atomic force microscopy and cross-section high-resolution transmission electron microscopy observations show that the excess Si atoms in SiO₂ matrix accumulate to form Si clusters and then crystallize gradually into Si nanoparticles embedded in SiO₂ films during dual-ion implantation followed by rapid thermal annealing. Er segregation and precipitates are not formed. Photoluminescence at the wavelength of 1.54 μm exhibits very weak temperature dependence due to the introduction of Si nanocrystals into the SiO₂ matrix. The 1.54-μm light emission signals from annealed samples decrease by less than a factor of 2 when the measuring temperature increases from 77 K to room temperature.     

Optical constants of polycrystalline CuGaTe2 films

Thin films of CuGaTe₂ with thicknesses in the range, 0.1–1.0 μm were deposited on Corning 7059 glass substrates by flash evaporation. The substrate temperatures, T_s, were maintained in the range 373–623 K. The transmittance of the films was recorded in the wavelength range 900–2500 nm. The dependence of the optical band gap, E_g, on substrate temperature showed that the value of E_g varied from 1.21 eV to 1.24 eV. The variation of refractive index and extinction coefficient with photon energy was studied from which the material properties such as the limiting value of dielectric constant, ε_∞, plasma frequency, ω_p, and hole effective mass, m_h^*, were evaluated as ε_∞ = 7.59, ω_p = 1.47 × 10¹⁴ and m_h^* = 1.25 m₀.     

On the optical, structural, and morphological properties of ZrO2 and TiO2 dip-coated thin films supported on glass substrates

This article reports the optical and morphological properties of dip-coated TiO₂ and ZrO₂ thin films on soda-lime glass substrates by metal-organic decomposition (MOD) of titanium^IV and zirconium^IV acetylacetonates respectively. Thermogravimetric and differential thermal analysis (DTA–TG) were performed on the precursor powders, indicating pure TiO₂ anatase and tetragonal ZrO₂ phase formation. Phase crystallization processes took place in the range of 300–500 °C for anatase and of 410–500 °C for ZrO₂. Fourier Transform Infrared Spectroscopy (FT-IR) was used to confirm precursor bidentate ligand formation with keno-enolic equilibrium character. Deposited films were heated at different temperatures, and their structural, optical and morphological properties were studied by grazing-incidence X-ray Diffraction (GIXRD) and X-Ray Photoelectron Spectroscopy (XPS), Ultraviolet Visible Spectroscopy (UV-Vis), and Atomic Force Microscopy (AFM) respectively. Film thinning and crystalline phase formation were enhanced with increasing temperature upon chelate decomposition. The optimum annealing temperature for both pure anatase TiO₂ and tetragonal ZrO₂ thin films was found to be 500 °C since solid volume fraction increased with temperature and film refractive index values approached those of pure anatase and tetragonal zirconia. Conditions for clean stoichiometric film formation with an average roughness value of 2 nm are discussed in terms of material binding energies indicated by XPS analyses, refractive index and solid volume fraction obtained indirectly by UV-Vis spectra, and crystalline peak identification provided by GIXRD.     

Luminescence quantum efficiency of F2 and F3 centers in LiF crystals

F^-₂ color center in LiF crystals is a unique specie of color centers concerning its photothermal stability, its broad absorption band, centered at 0.96 μm, and its broad emission band peaking at 1.12 μm, being a tunable laser operating in the range from 1.08 μm to 1.22 μm. The luminescence quantum efficiency of the main transition in the laser optical cycle was determined, at room temperature, and its value is 0.5 ± 0.1. This value was obtained using a method correlating the absorption, excitation and photoacoustic spectra. Besides, the luminescence quantum efficiency of the fundamental transition of the F^-₃ color center was determined. Also was estimated the energy transfer efficiency due to the overlapping of the F^-₃ center emission and the F^-₂ center absorption bands. Possible nonradiative deexcitation mechanisms accounting for the small luminescence quantum efficiency of the F^-₂ color centers in LiF are also discussed.     

Synthesis of MoSi2–Al2O3 nanocomposite by mechanical alloying

MoSi₂–Al₂O₃ nanocomposite was synthesized by mechanical alloying (MA) of MoO₃, SiO₂ and Al powder mixture. The structural evolution of the powders was studied by X-ray diffraction (XRD). Both β-MoSi₂ and -MoSi₂ were obtained after 3 h of milling. The spontaneous formation of β-MoSi₂ during milling proceeded by a mechanically induced self propagating reaction (MSR), analogous to that of the self propagating high temperature synthesis (SHS). After 70 h of milling the β-phase transformed to -phase. The crystallite size of -MoSi₂ and Al₂O₃ after milling for 100 h was 12 and 17 nm, respectively. Residual Mo and Si in the 3 and 70 h milled samples formed β-MoSi₂ and Mo₅Si₃ during heating at 1000 °C, respectively.     

Crystal structure of GeTe and Ge2Sb2Te5 meta-stable phase

Direct X-ray diffraction measurement of the erased state of the Ge–Sb–Te recording layer in a four-layered phase change optical disk, which was produced by an optical disk drive, was performed. It was identified as an fcc crystal structure. In order to carry out the detailed crystal structure analysis by the powder X-ray diffraction method with Rietveld refinements, somewhat larger amount of the fcc crystal powder was prepared from deposited 10 μm thick films. It revealed that Ge₂Sb₂Te₅ belongs to the NaCl type structure (Fm m) with the 4a site including 20% vacancies. The conclusion was supported by the results of the density measurements with Grazing Incidence of X-ray Reflectivity.     

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.     

Study of HfO2 films prepared by ion-assisted deposition using a gridless end-hall ion source

HfO₂ thin films were deposited using e-beam gun evaporation with ion assisted deposition (IAD) of low energy oxygen ions (40–100 eV) from an end-Hall ion source. A comparison was made using Hf and HfO₂ starting materials. The index of refraction was measured as a function of the ion source voltage and compared to results without IAD. Application to high power laser mirrors was verified by measurements of laser damage thresholds at 1.06 μm.