Ablation and compaction of amorphous SiO2 irradiated with ArF excimer laser

The structure of amorphous SiO₂ exposed to ArF excimer laser irradiation was examined. Threshold fluence for causing ablation with a single pulse depended on sample preparation: more specifically, 1 J/cm² for thermally grown SiO₂ films on silicon and 2.5 J/cm² for bulk SiO₂. It was found that the bond angle of Si-O-Si was reduced by irradiation near the interface of thermally grown SiO₂ films. In contrast, evolution of the bond angle by irradiation was absent in both the bulk SiO₂ and SiO₂ film-near the top surface, even though the concentration of puckered four-membered rings deduced from Raman spectra dramatically increased. It is assumed that planar three-membered rings were generated in the SiO₂ thin layer near the interface, and puckered four-membered rings were generated in the bulk SiO₂. The concentration of both the Si³⁺ and Si²⁺ structure was increased at a fluence of 800 mJ/cm² with an increasing number of pulses, although generation of both was absent at higher fluence for a single pulse. The author proposes that the structure of SiO₂ is created by flash heating and quenching by pulse laser irradiation. Structural similarities were found between the irradiated SiO₂ and SiO₂ at high temperatures.     

Thermally oxidized zirconium nanostructured films grown on Si substrates

Zirconium thin films grown on Si substrates by a planar magnetron sputtering system were thermally oxidized at oxygen ambient within 523‐823 K resulting in zirconium oxide films with various stoichiometries. XRD analysis of the ex situ oxidized films revealed the phases at different oxidation temperatures. To achieve a reasonable fit between the experimental and SIMNRA simulated RBS spectra of the prepared samples; it was required to introduce a SiO₂buffer layer in the simulated target between Si substrate and ZrO₂ film. The presence of this intermediate SiO₂ layer was confirmed by observation of SiO₂ phase in the XRD patterns of all the thermally oxidized samples. Using RBS analysis data, the effect of oxidation temperature on the stoichiometry of zirconium oxide films and thickness of ZrO_xand SiO₂ films were investigated. XRD patterns of thermally oxidized Zr films also revealed that crystallization of zirconium oxide films was initiated at about 673 K and was almost completed at 823 K. Diffusion of oxygen atoms through surface layer was investigated and the effective activation energy for oxygen mass transport was estimated to be 1.75 eV using RBS data and Arrhenius relation. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of highly c‐axis textured SrTiO3 thin films directly grown on Si(001) substrates by ion beam sputter deposition

Highly c‐axis textured SrTiO₃ (STO) thin films have been directly grown on Si(001) substrates using ion beam sputter deposition technique without any buffer layer. The substrate temperature was varied, while other parameters were fixed in order to study effect of substrate temperature on morphology and texture evolution of STO films. X‐ray diffraction, pole figure analysis, atomic force microscope, and high‐resolution electron microscopy were used to characterize and confirm quality and texture of the STO films. The experimental results show that optimum substrate temperature to achieve highly c‐axis textured films is at 700 °C. The full width at half maximum (FWHM) of 002_STO was found to be 2° and fraction of (011) orientation was as low as 1%. The surface morphology was Volmer‐Weber growth mode with a small roughness ∼1 nm. The lowest leakage current density (5.8 μA/cm² at 2 V) and the highest dielectric constant (ε_STO ∼ 98) were found for highly c‐axis textured films grown at 700 °C. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature dependence of growth orientation and surface morphology of Li‐doped ZnO thin films on SiO2/Si substrates

ZnO thin films doped with Li (ZnO:Li) were deposited onto SiO₂/Si (100) substrates by direct‐current sputtering technique in the temperature range from room temperature to 500 °C. The crystalline structure, surface morphology and composition, and optical reflectivity of the deposited films were studied by X‐ray diffraction (XRD), Scanning Electron Microscopy (SEM), X‐ray Photoelectron Spectroscopy (XPS) and optical reflection measurements. Rough surface p‐type ZnO thin film deposition was confirmed. The results indicated that the ZnO:Li films growed at low temperatures show c‐axis orientation, while a‐axis growth direction is preferable at high temperatures. Moreover, the optical reflectivity from the surface of the films matched very well with the obtained results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural Characteristics of Er Doped LiNbO3 Thin Films Grown by the Liquid Phase Epitaxy Method

Erbium (Er³⁺) doped LiNbO₃ single crystal thin films have been grown LiNbO₃ (001) substrate by the liquid phase epitaxy method. The crystallinity was determined by high‐resolution X‐ray diffraction. The lattice mismatch between Er³⁺ doped LiNbO₃ films and LiNbO₃ (001) substrate was investigated by X‐ray rocking curve analysis. Also we studied the structural characteristics of Er³⁺ doped LiNbO₃ films and surface morphology dependent on the film thickness.     

Low-K factor of SiO2 layer on Si irradiated by YAG:Nd laser

The change of optical and electrical properties of SiO₂ layer on Si single crystal exposed to YAG:Nd laser radiation has been found experimentally. The second harmonic of YAG:Nd laser was used as a source of light. Before irradiation the SiO₂ layer with thickness 0.75 μm had red color in reflecting light due to the interference. After irradiation with the laser with intensity of more than 3.5 MW/cm² red color changed to yellow. However, samples with thickness 0.21 μm did not change color after irradiation. We explain such peculiarities of optical properties by change of optical path. Capacity (C) measurements of SiO₂ layer with thickness 0.21 μm by the method of capacity–voltage characteristics have shown a decrease of C to more than 40%. It is possible if real part of dielectric permittivity (K) decreases or thickness of the SiO₂ layer increases. Atomic force microscope and profilemeter measurements did not show any change of surface roughness for the SiO₂ layer with thickness 0.21 μm. We suppose that after irradiation of the SiO₂ layer decrease of K takes place due to the formation of nanopores in SiO₂ or/and generation of the charged point defect at the interface of Si–SiO₂. Particularly the first is in agreement with measurements of micro hardness and capillary effect.     

Formation of ultrasmooth thin silver films by pulsed laser deposition

Ultrasmooth thin silver films have been formed on a quartz substrate with a buffer yttrium oxide layer by pulsed laser deposition. The dependence of the surface morphology of the film on the gas (N₂) pressure in the working chamber and laser pulse energy is investigated. It is found that the conditions of film growth are optimal at a gas pressure of 10^?2 Torr and lowest pulse energy. The silver films formed under these conditions on a quartz substrate with an initial surface roughness of 0.3 nm had a surface roughness of 0.36 nm. These films can be used as a basis for various optoelectronics and nanoplasmonics elements.     

Crystalline and electrical properties of pulsed laser deposited BST on platinized silicon substrates

In order to produce thin film capacitors with elevated capacitance and breakdown strength, pulsed laser deposition of the ferroelectric material Ba_0.6Sr_0.4TiO₃ (BST) has been made on (1 1 1)Pt/Ti/SiO₂/Si substrates. The films are in situ crystallized at 700 °C, polycrystalline in nature, and exhibit a single perovskite phase. This paper reports on both the effect of the oxygen pressure during heating and deposition, and the influence of different modes of introduction during the deposition stage, on the crystalline and electrical properties of the BST films. Orientation of films depends on the deposition oxygen pressure, with a (1 1 1) preferential orientation obtained when depositing under vacuum. XRD characterization reveals that the out-of-plane parameter of BST films increases when depositions are made under lower oxygen pressure. This phenomenon is related to a higher concentration of vacancies and defects in the films grown under low-pressure environment. However, a local introduction of oxygen on the substrate improves the annihilation of these defects. The crystalline orientation of the films is also highly dependent on the residual oxygen pressure during heating. A high (1 1 1) preferentially oriented BST film is obtained when heating and depositing under 0.1 mbar oxygen pressure. The heating atmosphere is thought to influence the out-diffusion of titanium on the surface of the Pt layer, thus modifying the nucleation and growth of BST films. Aluminum electrodes have been deposited on top of the BST films by dc sputtering to measure electrical capacitances. The calculated dielectric constant of in situ crystallized films deposited under 0.1 mbar oxygen pressure exceeds 500 at 100 kHz under zero dc bias. This high dielectric constant value obtained without post-deposition treatment appears to be of great technological interest.     

Optical Properties of Er Doped Congruent and Stoichiometric LiNbO3 Single Crystals

Erbium doped LiNbO₃ (Er:LiNbO₃) single crystal fibers were grown free of cracks along c‐axis by the micro‐pulling down (μ‐PD) method. We have investigated the up‐conversion property with the change of doped Er₂O₃ concentration and the starting melt composition. An enhancement of green upconversion according host matrix is also observed the stoichiometric LiNbO₃. And, the dependence of the green emission according to Er³⁺ concentration is analyzed. The possible application of the Er³⁺ doped stoichiometric LiNbO₃ single crystal fiber for up‐conversion based optical devices is discussed.     

在Si(100)上以AlN作过渡层低温外延生长ZnO薄膜

采用脉冲激光沉积(PLD)方法在Si(100)上成功生长了高度c轴取向的AlN薄膜,并以此为衬底,实现了ZnO薄膜的低温准外延生长.通过X射线衍射(XRD)、原子力显微镜(AFM)以及荧光分光光度计表征ZnO薄膜的结构、表面形貌和发光性能.结果表明,ZnO薄膜能在AlN过渡层上沿c轴准外延生长,采用AlN过渡层后,其荧光强度也有大幅提高.     

Preparation and Characterization of MBE-grown Si/CaF2 Heterostructures

Growth and fabrication of silicon-on-insulator structures, based on heteroepitaxial growth of insulating films on Si, is an area of research that has rapidly developed in recent years. Thin CaF₂ films and Si/CaF₂ multilayers were prepared on {111}-oriented Si substrates by molecular beam epitaxy (MBE) and were investigated by RHEED and RBS. For epitaxial growth the Si substrates were cleaned using the ultraviolet/ozone surface cleaning method which is an effective tool to remove contaminants from the surface by low-temperature in-vacuo preheating. The growth of CaF₂ on such Si{111} substrates provides epitaxial layers with a high structural perfection. When this layer system, however, is used as a substrate for epitaxial Si growth the Si layers show always twin formation. Si layers without twins could be obtained only after deposition of thin amorphous Si buffer layers at room temperature, immediately followed by Si growth at 700 °C.     

Growth and characterisation of Zn:LiNbO3/Mg:LiNbO3 multilayer thin films grown by liquid phase epitaxy

1, 3 and 5 mol% ZnO doped LiNbO₃ film and 2 mol% MgO doped LiNbO₃ multilayer films were grown on the LiNbO₃ (001) substrate by liquid phase epitaxy (LPE) method with a Li₂O‐V₂O₅ system. We examined the optical transmission spectra of the Zn:LiNbO₃ by Fourier Transform‐Infrared Spectrophotometer (FT‐IR). The crystallinity and the lattice mismatch between the Zn:LiNbO₃ film and Mg:LiNbO₃ film was confirmed by x‐ray rocking curve (XRC) and observed the ZnO and MgO distribution in the cross‐section of the multilayer thin films by electron probe micro analyzer (EPMA). Furthermore, the surface morphology of the films was observed using atomic force microscopy (AFM). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Substitution effects on ferroelectric,leakage current and anti‐fatigue characteristic of Bi4‐xSbxTi3O12 thin films

Bi_4‐xSb_xTi₃O₁₂ (BSTO) (x = 0, 0.03, 0.04, 0.05, 0.06 and 0.07) thin films have been fabricated on Pt/Ti/SiO₂/Si substrates by sol‐gel method. The effects of various Sb³⁺ content on microstructure and ferroelectric properties of systems are investigated. XRD show that Bi_4‐xSb_xTi₃O₁₂ (x≠0) thin films prefer (117) orientation. The substitution Sb³⁺ for Bi³⁺ reduces the grain size of the film surface. Compared to the BTO (x = 0) film, Bi_4‐xSb_xTi₃O₁₂ films display exciting electric properties. Especially when x = 0.04, the film Bi_3.96Sb_0.04Ti₃O₁₂ has achieved the max 2Pr value of 87μC/cm². This film also has a better anti‐fatigue characteristic, which can be up to 10¹⁰ switching cycles without fatigue. The leakage current density improved with J = 8×10⁻⁸ A/cm².     

Effects of the Substrate Crystals upon the Structure of Thermal Oxide Layers on Si

Comparisons of Bragg reflections from thermal oxide thin films on Si wafers were made for five sets of samples with various kinds of substrates. The intensities of the reflections for the samples with the substrate of better quality were stronger than those of poor one, indicating that the structures of the crystalline SiO₂ in the oxide layer were related with the quality of the Si substrates. It is also shown that no diffraction peaks were observed from the oxide layers grown on Si substrates by chemical vapor deposition.     

Initial growth of Bi4 LaTi3 FeO15 thin films on SrTiO3, MgO and YSZ substrates

The initial growth modes of Bi₄LaTi₃FeO₁₅ thin films on (001) SrTiO₃, (001) MgO and (001) Y:ZrO₂ (YSZ) substrates are studied. Detailed crystal structure, microstructure and surface morphology characterizations substantiate that Bi₄LaTi₃FeO₁₅ films grow on these substrates via three‐dimensional grain growth mode. The synthesized Bi₄LaTi₃FeO₁₅ films on (001) MgO and (001) SrTiO₃ substrates do have c‐axis epitaxial Aurivillius layered structure, and have relative smooth surface roughness. While films grown on (001) YSZ show the polycrystalline quality with large surface roughness. The different crystal quality of films grown on MgO/SrTiO₃ and YSZ substrates is explained qualitatively by considering the different atomic surface structures of these substrates.     

Melting and crystallization of silicon layers on insulator with millisecond lamp heating

Melting and crystallization of silicon layers in a SOI structure (Si SiO₂ Si) at millisecond lamp heating have been studied by model calculations using the solution of conduction equation. Pulse heating conditions that do not lead to silicon substrate melting under SiO₂ have been determined. For pulses of 1 and 4.4 ms duration the silicon melt lifetime on the SiO₂ surface has been estimated. The lengths of the crystal oriented growth from windows in the SiO₂ layer that open the single-crystalline silicon substrate have been measured (25 and 64 μm).     

Strain inhomogeneities in epitaxial BaFe2As2 thin films

Epitaxial BaFe₂As₂ thin films grown by pulsed laser deposition on spinel substrates with a thin iron buffer layer show strain‐induced superconductivity. Using high resolution electron backscatter diffraction in a scanning electron microscope very small orientation changes (≤ 0.2°) of the lattice and strain inhomogeneities on a length scale of few 100 nm or less were measured. Furthermore, partially strain relaxed areas were revealed. It was found, that the quality of the BaFe₂As₂ thin films crucially depends on the iron buffer layer.     

The microstructure and magnetic property of TiO2‐terminated SrTiO3 substrate selected growth cubic phase CaRuO3 film

CaRuO₃ thin films with various thicknesses were synthesized by pulsed laser deposition respectively on SrTiO₃ substrates with SrO‐ and TiO₂‐termination. The microstructure of these films was studied by transmission electron microscopy. The results demonstrate that the CaRuO₃ thin films grown on TiO₂‐terminated substrates show quite uniform morphology, whilst they do the facet morphology when the substrates are SrO‐terminated. In addition, there is a 5∼7 unit‐cell‐thickness cubic CaRuO₃ layer in the films grown on TiO₂‐terminated substrates. The measured ferromagnetic hysteresis loop is attributed to the cubic CaRuO₃ layer, which is supported by a first‐principles calculations. On the contrary, there is free of cubic CaRuO₃ layer in samples grown on SrO‐terminated substrates. The crystallographic domains, the orientation relationship between domains and substrates and crystal defects in these films were studied as well. The different growth mechanism of CaRuO₃ on SrO‐ and TiO₂‐terminated SrTiO₃ substrates may be correlated with the selective nucleation and growth.     

Influence of Mg/Er co‐doping on the principal laser parameters of LiNbO3 crystals

Mg: Er: LiNbO₃ crystals were grown by the Czochralski technique with various concentrations of MgO = 2 mol%, 4 mol%, 6 mol% and the fixed concentration of Er₂O₃= 1 mol% in the melt, and the 8 mol%Mg: 1 mol%Er: LiNbO₃ crystal was fabricated by the Czochralski technique with special technology process. The crystals were treated by polarization, reduction and oxidation. The segregation coefficients of Mg²⁺ and Er³⁺ in Mg: Er: LiNbO₃ crystals were measured by X‐ray fluorescence spectrograph, as well as the crystal's defect structure and optical properties were analyzed by the UV‐Vis, IR and fluorescent spectroscopy. The pump wavelength and the surge wavelength were determined. Using m‐line method tested optical damage resistance of those crystals, the results show that photodamage threshold of Mg: Er: LiNbO₃ crystals are higher than that of Er: LiNbO₃ crystal, and the oxidation treat could enhance the photodamage resistant ability of crystals while the reduction treat could depress the ability. The optical damage resistance of 8 mol%Mg: 1 mol%Er: LiNbO₃ crystal was the strongest among the samples, which was two orders magnitude higher than that of 1 mol%Er: LiNbO₃ crystal. The dependence of the optical properties on defect structure of Mg: Er: LiNbO₃ crystals was discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Decisive role of Au layer on the oriented growth of ZnO nanorod arrays via a simple aqueous solution method

Vertically aligned arrays of ZnO nanorod were synthesized on the Au/SiO₂/Si(1 0 0) substrate by a simple aqueous solution growth process, without pre-prepared ZnO seed layer. For comparison, glass and SiO₂/Si were also used as substrates, and the results show that the Au layer plays a decisive role in orienting the growth of the ZnO nanorod. The effects of other growth parameters, including Zn²⁺ concentration and growth time, on morphology, density, and orientation of the ZnO nanostructure were also studied and with longer reaction time, a new structure namely ZnO nanotip was obtained. Moreover, the growth mechanism of ZnO nanorod arrays grown on the Au/SiO₂/Si substrate was proposed.