Electronic structure of carbon nitride thin films studied by X-ray spectroscopy techniques

Magnetron-sputtered carbon nitride thin films with different structures and compositions were analyzed by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), as well as X-ray emission spectroscopy (XES). In all techniques, the carbon spectra are broad and featureless with little variation depending on growth conditions. The nitrogen spectra, on the other hand, show more distinct features, providing a powerful tool for structural characterization. By comparing the experimental spectra with calculations on different model systems, we are able to identify three major bonding structures of the nitrogen—N1: nitrile (CN) bonds; N2: Pyridine-like N, i.e., N bonded to two C atoms; and N3: graphite-like N, i.e., N bonded to three C atoms as if substituted in a graphitic network, however, possibly positioned in a pentagon and/or with sp³ carbon neighbors. The presence of N2 and N3 are best detected by XPS, while N1 is better detected by NEXAFS. The calculated XES spectra also give good indications how valence band spectra should be interpreted. Films grown at the higher temperatures (≥350 °C) show a pronounced angular dependence of the incoming photon beam in NEXAFS measurements, which suggests a textured microstructure with standing graphitic basal planes, while amorphous films grown at low temperatures show isotropic properties.     

硅溶胶添加对氧化铝多孔陶瓷烧结性能的影响

以煅烧α-Al2 O3粉末为原料,硅溶胶为高温结合剂,羧甲基纤维素钠为成型黏结剂,通过混料、困料、模压成型、高温烧结等工序制备氧化铝多孔陶瓷,利用SEM和XRD对多孔陶瓷微观形貌和晶体结构进行测试,并对多孔陶瓷的线收缩率、体积密度、显气孔率和抗弯强度进行表征,系统地研究硅溶胶添加对氧化铝多孔陶瓷高温烧结特性的影响.结果表明:低温下硅溶胶的热解产物石英型SiO2将氧化铝颗粒黏结起来,形成物理黏结,能提高多孔陶瓷的力学性能;烧结温度达1500℃时,SiO2开始与氧化铝反应形成莫来石,莫来石结合相的生成使得氧化铝多孔陶瓷趋于致密,力学性能优异,抗弯强度可达(105.5±8.0)MPa;随烧结温度的升高莫来石生成量增多,导致氧化铝多孔陶瓷的体积膨胀,进而使得孔隙率增大,力学性能降低.烧结温度介于1400～1500℃之间时,可以得到微观结构合理、力学性能优异、孔隙率适中的氧化铝多孔陶瓷.     

Optical properties of CdTe thin films studied by photothermal deflection spectroscopy

Photothermal deflection spectroscopy (PDS) was used to analyze CdTe thin films which are to be used to construct solar cells. It was found that CdTe thin films grown on a conducting SnO₂ layer deposited on glass show deviations from a stoichiometric composition due to an excess of tellurium. This non-stoichiometry modifies the absorption spectrum obtained from the PDS measurements.     

Dielectric properties of KDP filled porous alumina nanocomposite thin films

A new concept of a composite dielectric thin film fabrication is presented. The fabrication process consists of two stages. The first stage is anodizing a thin aluminum film to produce a porous alumina film that contains an array of nanometer sized parallel pores. The second stage is filling the pores with a saturated KDP (KH2PO4) liquid solution due to capillary forces. After drying KDP nanocrystals are formed inside the pores. This process results in a formation of a composite dielectric thin film composed of the alumina pores walls as one dielectric material and the KDP nanocrystals inside the pores as another dielectric material. The dielectric permittivity of this composite film is higher than that of the porous alumina film at all applied frequencies. The dielectric enhancement is more pronounced at low frequencies due to an interface polarization mechanism. This fabrication process enables controlling the size, composition, and microstructure of the composite dielectric film constituents and thus changing its dielectric properties over a wide range of values.     

X射线反射(XRR)对薄膜样品厚度的研究

X射线的反射(XRR)测量法可精确地确定平行层及其薄膜结构,如测定光滑基体上聚合物膜的特性,包括层的厚度、密度和界面粗糙度.使用X'Pert X射线粉晶衍射仪对单晶硅片上的有机薄膜镀层进行了其厚度的精确测定,测定结果为该单晶硅片上的有机薄膜有3层,其厚度分别为5.0、60.2和245.3nm.并用倒易向量方法计算和验证了测量结果的正确性.还讨论了用X射线反射测定薄膜结构的一些影响因素.     

Interface properties in granular compound films studied by Mössbauer spectroscopy

The nature of iron atoms in granular iron compounds (FeSiO₂, FeAl₂O₃, FeZrO₂) was studied by the Mössbauer effect. Granular compounds with a low concentration of iron are almost amorphous and exhibit a large distribution of hyperfine parameters. Superparamagnetism occurs, the transition temperature depending on the diameter of the grains. The behaviour of iron in granular samples depends on the nature of the insulating matrix.     

X-ray optic characteristics of microchannel plates studied by X-ray absorption spectroscopy

The X-ray absorption spectra of white and black microchannel plates (MCPs) have been studied in the energy range from 80 to 250 eV. Data on the fine X-ray absorption near edge structure are presented. A new approach is described, which allows the effect of various treatments on the X-ray optic characteristics of MCPs to be studied. In particular, it is established that the thermal reduction of MCPs in hydrogen increases the critical reflection angle for long-wavelength X-rays in the channels.     

Effect of substrate temperature and film thickness on the surface structure of some thin amorphous films of MoO3 studied by X-ray photoelectron spectroscopy (ESCA)

X-ray photoelectron spectroscopy (XPS) core level spectra of MoO₃ substoichiometric amorphous thin films in the thickness range 100 to 670 nm were studied as a function of thickness. Some samples 500 nm thick were studied for different substrate temperatures in the range 293 to 543 K. It was observed that with the increase of thickness of the samples no change in the electron spectrum was observed in the material. Under vacuum conditions, MoO₃ turned blue when the substrate temperature was higher than 373 K. XPS spectra supported the formation of the Mo⁵⁺ oxidation state in the blue samples. Blue coloration was observed after heating in vacuum and this was attributed to an internal electron transfer from oxygen to metallic orbitals by thermal ionization creating an Mo⁵⁺ oxidation state.     

多孔阳极氧化铝膜的结构修饰研究

以5%草酸为电解液,温度控制在5℃左右,采用两步阳极氧化工艺制备出多孔氧化铝膜,在1 μm范围内获得了孔径为10～60nm的多孔结构.通过原子力显微技术分析氧化时间及热处理条件对多孔氧化铝膜结构的影响,阳极氧化3h后,在0.3μm2范围内获得了有序的纳米孔阵列,当氧化时间延长至24h,有序孔阵列范围增加至～1μm2.将在聚乙烯中经过超声振荡过的样品在600～700℃中热处理3h.研究结构表明,经过适当的热处理能有效改善多孔氧化铝膜的结构特性,X射线衍射分析结果证实经过结构修饰后的样品呈非晶态结构.     

Ag衬底层对FePt薄膜结构和性能的影响

采用磁控溅射方法在自然氧化的单晶Si(100)衬底上制备了双层结构的FePt-X/Ag(X=Ag或Pt)薄膜.以20nm厚的Ag做衬底,可以制备出易磁化轴垂直基片的FePt合金薄膜;Ag在FePt薄膜中优先团聚,不利于控制FePt晶粒的长大,调整Pt的含量可以控制热处理过程中FePt薄膜的晶粒尺度;通过XRD、TEM、VSM对薄膜样品的结构、晶粒尺寸的观察和磁性检测,我们认为FePt合金薄膜有序化转变的最佳热处理温度在400℃;经过500℃热处理,薄膜软硬磁耦合较好,晶粒尺寸约为100nm,有最大的矫顽力1.04×106A/m.     

Formation of complex anodic films on porous alumina matrices

The kinetics of growth of complex anodic alumina films was investigated. These films were formed by filling porous oxide films (matrices) having deep pores. The porous films (matrices) were obtained voltastatically in (COOH)₂ aqueous solution under various voltages. The filling was done by reanodization in an electrolyte solution not dissolving the film. Data about the kinetics of reanodization depending on the porosity of the matrices were obtained. On the other hand, the slopes of the kinetic curves during re-anodization were calculated by two equations expressing the dependence of these slopes on the ionic current density. A discrepancy was ascertained between the values of the calculated slopes and those experimentally found. For this discrepancy a possible explanation is proposed, related to the temperature increase in the film, because of that the real current density significantly increases during re-anodization.     

Structure of amorphous alumina tubes studied by positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PALS) is used to investigate the detailed structure of amorphous alumina tubes prepared via thermohydrolysis of anhydrous AlCl₃ . The results demonstrate that PALS is a sensitive probe of the structure of amorphous materials, capable of distinguishing between the structures of amorphous alumina tubes and amorphous alumina prepared by a standard procedure, which are shown to differ slightly in the concentration and size of free-volume elements. The observed distinctions can be understood in terms of the anisotropic aggregation of primary alumina particles during hydrolysis in aqueous media or thermohydrolysis in water vapor.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 314–320.Original Russian Text Copyright © 2005 by Shantarovich, Kevdina, Miron, Baronova, Berdonosov, Baronov, Melikhov.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Structural properties of low-temperature grown ZnO thin films determined by X-ray diffraction and X-ray absorption spectroscopy

The epitaxial growth of ZnO thin films on Al₂O₃ (0001) substrates have been achieved at a low-substrate temperature of 150 °C using a dc reactive sputtering technique. The structures and crystallographic orientations of ZnO films varying thicknesses on sapphire (0001) were investigated using X-ray diffraction (XRD). We used angle-dependent X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to examine the variation of local structure. The XRD data showed that the crystallinity of the film is improved as the film thickness increases and the strain is fully released as the film thickness reached about 800 Å. The Zn K-edge XANES spectra of the ZnO films have a strong angle-dependent spectral feature resulting from the preferred c-axis orientation. The wurtzite structure of the ZnO films was explicitly shown by the XRD and EXAFS analysis. The carrier concentration, Hall mobility and resistivity of the 800 Å-thick ZnO film were 1.84 × 10¹⁹ cm^− 3, 24.62 cm²V^− 1s^− 1, and 1.38 × 10^− 2 Ω cm, respectively.     

The influence of substrate temperature on the properties of aluminum-doped zinc oxide thin films deposited by DC magnetron sputtering

Transparent, conducting, aluminum-doped zinc oxide (AZO) thin films were deposited on Corning 1737 glass by a DC magnetron sputter. The structural, electrical, and optical properties of the films, deposited using various substrate temperatures, were investigated. The AZO thin films were fabricated with an AZO ceramic target (Al₂O₃:2 wt%). The obtained films were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The lowest resistivity was 6.0 × 10⁻⁴Ω cm, with a carrier concentration of 2.7 × 10²⁰ cm⁻³ and a Hall mobility of 20.4 cm²/Vs. The average transmittance in the visible range was above 90%.     

The influence of the substrate and the substrate temperature on the crystallinity of tin films

Thin films of tin were prepared on various substrates (NaCl, KCl, KBr and KI) and at various substrate temperatures (28–90°C) and were studied using transmission electron microscopy and selected area electron diffraction techniques. To determine the dependence on cleanness, tin was deposited on single-crystal surfaces prepared by vacuum cleaving. Films were prepared on substrate surfaces to which a parallel d.c. electric field (0–1000 V cm⁻¹) was applied. It was observed that the crystallites of tin films deposited on KBr were more preferentially oriented than those deposited on NaCl, KCl or KI. The effects of vacuum cleaving and of d.c. electric fields are discussed.     

Characterization of complex anodic alumina films by electrochemical impedance spectroscopy

Complex anodic alumina films are formed by pore-filling (reanodization) of porous anodic films (matrices). These films are characterized by electrochemical impedance spectroscopy. It is determined that the recorded impedance spectra are well described by an equivalent circuit, containing a Constant Phase Element. The fitted parameters of the complex films are calculated, and information about certain dielectric characteristics of these films in contact with an electrolyte is obtained. The paper also discusses changes in the surface non-homogeneity of the complex films in comparison with those of the porous matrix.     

低温烧结氧化铝基体材料性能的研究

以目前最常用的LTCC材料为基础,选择Al2O3为片式熔断器基体材料.系统研究在不同烧结温度下的Al2O3-Bi2O3陶瓷基体,通过X射线衍射和扫描电镜分析了不同温度下样品的相组成及密度变化,指出形成这种相结构的可能影响因素;测试了不同频率下样品的介电性能.结果表明,Bi2O3的掺杂可以提高Al2O3陶瓷的烧结活性,进而大大降低了陶瓷的烧结温度,密度在900℃达到最大值3.7g/cm3,陶瓷样品的主晶相为α-Al2O3,没有杂相存在,且断口形貌分布均匀没有明显的气孔存在,同时总结出了介电常数和介质损耗的变化规律.     

Adsorption of diborane and hydrogen selenide on porous alumina and silica

Adsorption of diborane (B2H6) and hydrogen selenide (H2Se) on porous -alumina and amorphous silica at room temperature were investigated. Both physical and chemical adsorption of H2Se on alumina were observed, while amorphous silica did not adsorb H2Se. Chemical adsorption of H2Se on alumina was accompanied by dissociation chemically on alumina and silica. The adsorption capacity of silica for B2H6 dramatically decreased after elimination of water molecules adsorbed on the surface by drying at about 100 °C in an N2 atmosphere, although that of alumina was not changed by drying. Although B2H6 reacts with adsorbed water on alumina and silica surface, B2H6 is deduced to react with hydroxyl groups on alumina but not with those on silica. These observations are compatible with adsorption of various metal hydrides such as SiH4, AsH3 and PH3 on alumina and silica. The difference in the reactivity on metal hydride gases to -alumina and silica can be related to the basicity of oxides and the proton affinity of hydrides. © 1998 Chapman & Hall     

The substrate influence on the magnetization of nickel electrodeposited thin films

The effects of diffusion of substrate copper atoms into the film as well as substrate stresses on both saturation magnetization and coercive force of annealed electrodeposited Ni films have been investigated.