A novel nanotube of composite of calcium carbonate and calcium sulfate

Nanotube-shaped precursor which is composed of layered structured sodium dodecylsulfate (SDS) calcium carbonate were obtained by titration of an aqueous solution of Na₂CO₃ into an aqueous solution containing CaCl₂ and SDS at 333-335 K. A unit of the repetition of the precursor was about 4 nm. Nanotube-shaped composite which is composed of CaCO₃ and CaSO₄ of 100-200 nm in diameter and 0.5-2 µm in length was obtained from nanotube-shaped precursor composed of layers of CaCO₃ and SDS by calcinations at 673 K in air. The precursor sheet composed of CaCO₃ layers on which SDS molecules attached to both side seemed to curl up and form a pipe.     

Synthesis and microstructure of nanostructured Al/Al2O3 (H)-composite

By means of a metal organic chemical vapour deposition, starting from a single precursor compound [tBuOAlH₂]₂, an aluminium/aluminium hydrido-oxide composite has been synthesized in thin layers. Electron micrographs indicate self-similarity. A detailed analysis by small angle neutron scattering directly yields a surface fractal microstructure with a fractal dimension of 2.26; in the framework of a surface fractal model we determine the relevant particle dimensions and their size distribution.     

Preparation and characterization of TiO2 anode film with spinodal phase separation structure in dye-sensitized solar cells

Low electronic transmission efficiency and high charge recombination are the existing problems of photoanode film in traditional dye sensitized solar cells (DSSCs). This paper put forward the photoanode TiO₂ films with spinodal phase separation structure (SPSS) and continuous TiO₂ skeleton which were triggered by the photopolymerization of organic monomers in a photomonomer-inorganic precursor system. The photoanode TiO₂ films fabricated by different precursor solution compositions and different coating layers were characterized mainly by scanning electron microscopy (SEM), photocatalysis and photoelectric performance test. The results indicated that, the as-prepared TiO₂ anode film with seven coating layers and heat treated at 500 °C showed higher photoelectric conversion efficiency at about 2% than that of other samples with less coating layers and lower heat treatment temperature. The film also showed excellent photocatalytic activity by using methylene blue (MB) dye as a model organic substrate under fluorescent lamp irradiation. It is suggested that the film with SPSS structure has the potential to improve the electronic transmission efficiency and reduce the carrier recombination due to its particular structure, higher surface area, and lack of bottleneck in electronic transmission. It is worth noting that the SPSS structure provides new ideas to develop new photoanode films and further improve the photoelectric conversion performance of the DSSC in future.     

Preparation of pure superconductors from polymer chelate YBa2Cu3O7-x precursors using poly[(N, N-dicarboxymethyl)allylamine]

Bulk Yba₂Cu₃O_7-x (YBCO) was prepared by a polymer chelate precursor method using poly[(N,N-dicarboxymethyl)allylamine] (PDAA) as a chelating polymer. An aqueous solution containing PDAA and 1/2 or 1/4 equivalent molar amount of metal nitrates (Y : Ba : Cu=1 : 2 : 3) to the repeating unit of PDAA at pH 8 was poured into ethanol to precipitate the polymer-metal chelate precursor. The precursor containing 1/2 equivalent molar amount of metal ions was calcined at 880°C for 10 h, sintered at 920°C for 2 h, and annealed at 600°C for 5 h. The product exhibited a pure superconducting orthorhombic phase. However, the precursor containing 1/4 equivalent molar amount of metal ions gave a mixture of orthorhombic and tetragonal phases under the same conditions. The influence of a purification process for PDAA on the preparation of YBCO was also examined. The electrical resistance and susceptibility of the YBCO sample prepared by optimum conditions were measured. The sintered sample showed superconductivity with T_c (onset) at 93 K and T_c (end) at 91 K. The narrow superconducting transition demonstrated here is attributed to the high purity and homogeneity of the sample prepared from optimized polymer chelate precursor technique. This revised version was published online in November 2006 with corrections to the Cover Date.     

Control of metal salt ratio and MoS2 layer thickness in a Cu2ZnSnS4 thin film solar cell

Cu₂ZnSnS₄ (CZTS) absorber layers were prepared from copper acetate, zinc acetate, tin chloride, and thiourea in a solution of methanol, ethylenediamine, and ethanolamine using a sol–gel spin-coating method. Sol–gel precursor solutions were prepared with different metal salt ratios, and the effects on film growth, optical properties, and crystal properties of CZTS films were investigated. In addition, the role of sulfurization temperature on grain size of CZTS and formation of the MoS₂ layer at the CZTS and Mo interface were investigated. By changing the metal salt ratio in the precursor solution, a Zn-rich and Cu-poor condition in the CZTS film was obtained. By preparing Zn-rich and Cu-poor CZTS film with a thinner MoS₂ layer at a lower sulfurization temperature, the CZTS cell efficiency was improved, and a conversion efficiency of 1.22 % was obtained.     

Polyol mediated synthesis of sub-micrometer Bi2O3 particles

Bi₂O₃ particles 70 to 90 nm in size were prepared with the polyol method. According to this method a suitable metal precursor (e.g. halogenide, acetate, alcoholate) and a defined amount of water were heated in a high boiling alcohol (e.g. diethylene glycol). Based on temperatures up to 180°C crystalline -Bi₂O₃ particles were formed. The material was isolated by centrifugation and characterized by XRD and SEM. The size of Bi₂O₃ particles in colloidally stable diethylene glycol suspension as well as in diethylene glycol/water mixtures was determined with laser diffraction methods. These suspensions were used to prepare homogeneous thin Bi₂O₃ particle layers on planar glass substrates.     

Polymer-metal chelate precursor reduced its firing temperature and time for preparing yttrium barium cuprate powder

Bulk YBa₂Cu₃O _x was prepared by a polymer chelate precursor method using poly[(N,Ndicarboxymethyl)allylamine] as a chelating polymer of which molecular weights were 3 × 10⁴ (PDAA-L) and 3 × 10⁵ (PDAA-H), respectively. X-ray diffraction (XRD) analysis of the precursor from PDAA-H shows that YBa₂Cu₃O _x (Y123) phase appeared after being calcined at 750 °C for 5 h and the mixture was completely converted to tetragonal Y123 phase after being calcined at 800 °C for 5 h. The phase evolution of the precursor from PDAA-H during isothermal experiment at 800 °C showed that pure tetragonal Y123 was produced even after the polymer chelate precursor was heated for 2 h in air, although a very small amount of BaCO₃ was recognized. This BaCO₃ phase was hardly recognized after 4 h calcination. The precursor prepared from PDAA-L was fully converted to pure tetragonal Y123 after 3 h calcining at 800 °C. On the other hand, the sample prepared from metal nitrate solution without PDAA was not fully transferred to Y123 phase after heating at 800 °C for 10 h. Large amounts of Y₂O₃, BaCO₃ and CuO were observed. These results indicated that the greater homogeneity in the polymer chelate precursor leads to reduced firing times and temperature compared with the metal nitrate precursor.     

Effect of microwaves on synthesis of MoS2 and WS2

The present work was aimed on utilizing the solid state microwave synthetic method for the growth of molybdenum disulphide (MoS₂) and tungsten disulphide (WS₂) in powder as well as in the form of thin films. It was observed that the microwave exposure of simple powder mixture of Mo (or W) and S could not lead to the formation of MoS₂ (or WS₂).Therefore the work was pursued by the study of the possibility to use this technique to grow thin films. Either Mo or W in the form of thin foils or Mo layers deposited by sputtering onto glass substrates was used as metal source. These metal samples were introduced with some sulphur into a Pyrex tube and sealed under vacuum. After microwave oven exposure the formation of polycrystalline 2H-WS₂ with well-defined grains was confirmed by X-ray diffraction and scanning electron microscopy, respectively. Mo foil as well as Mo layers deposited on glass showed formation of MoS₂ under the limit of our experimental conditions that is to say homogeneous thin films can be achieved only as small surface films.     

Synthesis of aluminum borate nanorods by a low-heating-temperature solid-state precursor method

Well-crystalline Al₄B₂O₉ nanorods were synthesized by a low-heating-temperature solid-state precursor method. This process does not involve the use of metal catalyst or protective gas. The products were characterized by thermogravimetry and differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results showed the products to possess a single phase, large surface area, narrow size distribution of 20-30 nm and lengths up to several micrometers. A self-catalytic growth mechanism of the aluminum borate nanorods is proposed.     

R.f. sputtering of high-quality Cu/In precursor layers and conversion to CuInS2 using elemental sulfidization processes

Thin films of CuInS₂ have been produced by a two-stage process, the formation of a Cu/In precursor layer using r.f. magnetron sputtering of alternate layers of the elements followed by the conversion into the compound by either (i) annealing the precursor layers in a closed chamber in the presence of sulfur or (ii) annealing the precursor layers in sulfur that was transported over the layers using argon as a carrier gas. These out-of-line-of-sight methods have potential for large-scale batch processing of the absorber layers. The physical and chemical properties of the precursor layers and the CuInS₂ formed were investigated using a range of methods including energy dispersive X-ray analysis, Rutherford backscattering spectrometry, and synchrotron X-ray diffraction. The data confirms that the uniform layers produced using the former method have potential for use in both substrate and superstrate configuration devices. For the latter method there was significant indium loss during the conversion process and this problem needs to be overcome before the layers can be used in solar-cell devices.     

The preparation of YBCO epitaxial superconducting films by a chemical solution deposition process

The utility of a chemical precursor solution for the production of YBa₂Cu₃O_7-x superconducting films has been investigated. The homogeneous precursor solution made of metal acetates, 1,3-bis(dimethylamino) -2-propanol, and acetic acid was applied to [1 0 0] MgO substrates via spin-coating. Subsequent heating and sintering removed the organic components. The best epitaxial film obtained by this chemical solution deposition method has a T_c of 78 K.     

High performance metal-insulator-metal capacitors with atomic vapor deposited HfO2 dielectrics

Thin HfO₂ films were grown as high-k dielectrics for Metal-Insulator-Metal applications by Atomic Vapor Deposition on 8 inch TiN/Si substrates using pure tetrakis(ethylmethylamido)hafnium precursor. Influence of deposition temperature (320-400 °C) and process pressure (2-10 mbar) on the structural and electrical properties of HfO₂ was investigated. X-ray diffraction analysis showed that HfO₂ layers, grown at 320 °C were amorphous, while at 400 °C the films crystallized in cubic phase. Electrical properties, such as capacitance density, capacitance-voltage linearity, dielectric constant, leakage current density and breakdown voltage are also affected by the deposition temperature. Finally, TiN/HfO₂/TiN stacks, integrated in the Back-End-of-Line process, possess 3 times higher capacitance density compared to standard TiN/Si₃N₄/TiN capacitors. Good step coverage (> 90%) is achieved on structured wafers with aspect ratio of 2 when HfO₂ layers are deposited at 320 °C and 4 mbar.     

Synthesis and characterization of nanocrystalline MgAl2O4 spinel via sucrose process

Nanocrystalline MgAl₂O₄ spinel powder was synthesized using metal nitrates and a polymer matrix precursor composed of sucrose and polyvinyl alcohol (PVA). The precursor and the calcined powders were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to XRD results, the inceptive formation temperature of spinel via this technique was between 600 and 700 °C. The calcined powder at 800 °C for 2 h has faced shaped morphology and its crystallite size is in the range of 8-12 nm. Further studies also showed that the amount of polymeric matrix to metal ions has significant influence on the crystallite size of synthesized magnesium aluminate spinel powder.     

Abscheidung leitender und nichtleitender Hartstoffschichten auf metallischen und keramischen Werkstoffen mittels Hochfrequenz-Plasma-CVD

Deposition of conductive and nonconductive hard coatings on metallic and ceramic materials by RF-PA-CVD Conductive titanium nitride and nonconductive aluminium oxide layers were deposited on conductive and nonconductive substrates by a RF-PA-CVD process. The influence of substrate material, pressure, plasma power and the components of the gas mixture on the layer properties was investigated. TiN coatings with a homogeneous structure could be deposited by using TiCl₄ as precursor. The properties of the layer are strongly influenced by the substrate material. An increasing pressure causes a faster deposition rate and a higher chlorine content. A lower chlorine content and at the same time a faster deposition rate can be achieved by increasing the r.f. power. Aluminium and aluminium oxide layers could be deposited on steel and Si₃N₄ substrates by using AlCl₃ as precursor in dependence on the CO₂ content in gas mixture. Higher CO₂ content facilitates the deposition of aluminium oxide.     

Effects of precursor evaporation temperature on the properties of the yttrium oxide thin films deposited by microwave electron cyclotron resonance plasma assisted metal organic chemical vapor deposition

Yttrium oxide thin films are deposited using indigenously developed metal organic precursor (2,2,6,6-tetra methyl-3,5-hepitane dionate) yttrium, commonly known as Y(thd)₃ (synthesized by ultrasound method). Microwave electron cyclotron resonance plasma assisted metal organic chemical vapor deposition process was used for these depositions. Depositions were carried out at a substrate temperature of 350 °C with argon to oxygen gas flow rates fixed to 1 sccm and 10 sccm respectively throughout the experiments. The precursor evaporation temperature (precursor temperature) was varied over a range of 170-275 °C keeping all other parameters constant. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and infrared spectroscopy. Thickness and refractive index of the coatings are measured by the spectroscopic ellipsometry. Hardness and elastic modulus of the films are measured by load depth sensing nanoindentation technique.C-Y₂O₃ phase is deposited at lower precursor temperature (170 °C). At higher temperature (220 °C) cubic yttrium oxide is deposited with yttrium hydroxide carbonate as a minor phase. When the temperature of the precursor increased (275 °C) further, hexagonal Y₂O₃ with some multiphase structure including body centered cubic yttria and yttrium silicate is observed in the deposited film. The properties of the films drastically change with these structural transitions. These changes in the film properties are correlated here with the precursor evaporation characteristics obtained at low pressures.     

The use of silver(I)-2-[2-(2-methoxyethoxy)ethoxy]acetate as precursor in the deposition of thin silver layers on float glass by the atmospheric pressure combustion chemical vapor deposition process

The innovative use of silver(I)-2-[2-(2-methoxyethoxy)ethoxy]acetate ([AgO₂C(CH₂OCH₂)₃H], 3) as precursor for the deposition of silver on float glass by applying the atmospheric pressure combustion chemical vapor deposition process is described. As nucleation layer tungsten oxide was utilized, conformal, closed and dense silver layers of ca. 70 nm thickness were obtained. They are adhesive and high reflective with a resistivity of 5 ? 10⁻⁸ Ωm.     

Low temperature preparation of nanocrystalline Sr0.5Ba0.5Nb2O6 powders using an aqueous organic gel route

Nano-sized Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramic powders have been synthesized by an aqueous organic gel route. Homogeneous Sr-Ba-Nb precursor gels are prepared with Ba-EDTA, Sr-EDTA, and Nb-citrate complex as source of Sr, Ba, and Nb, respectively. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used as the chelating agents. The structural variation of the SBN powder with annealing temperature was studied by TG-DTA, FT-IR and XRD. The precursor gel on calcination at 800 °C for 2 h produces a pure tungsten bronze SBN phase and the corresponding average particle size is 30-50 nm. The influences of the pH and the molar ratio of citric acid:Nb cation on the formation of homogeneous Sr-Ba-Nb precursor gels were also studied. The results show that a homogeneous Sr-Ba-Nb precursor gel with no precipitate is formed at pH 8 and the optimum molar ratio of citric acid and the metal cations is 3:1.     

Effect of the composition and annealing conditions of precursor films on the structure of thin CuIn1 − x GaxSe2 (0 ≤ x ≤ 0.7) layers

A technique has been developed for the preparation of CuIn _x Ga_{1 ? x} Se₂ layers through closed-space selenization of precursor films containing intermetallic compounds. We also have produced CuIn _x Ga_{1 ? x} Se₂ films by selenizing metallic precursor films. Examination of the CuIn _x Ga_{1 ? x} Se₂ layers by X-ray diffraction, atomic force microscopy, and scanning electron microscopy has shown that the use of inter-metallic precursors offers a number of important advantages: phase purity and homogeneity of CuIn _x Ga_{1 ? x} Se₂ layers, in combination with good adhesion of the layers to substrates (glass or glass/molybdenum).     

PMMA–SiO2 hybrid films as gate dielectric for ZnO based thin-film transistors

In this paper we report a low temperature sol–gel deposition process of PMMA–SiO₂ hybrid films, with variable dielectric properties depending on the composition of the precursor solution, for applications to gate dielectric layers in field-effect thin film transistors (FE-TFT). The hybrid layers were processed by a modified sol–gel route using as precursors Tetraethyl orthosilicate (TEOS) and Methyl methacrylate (MMA), and 3-(Trimethoxysilyl)propyl methacrylate (TMSPM) as the coupling agent. Three types of hybrid films were processed with molar ratios of the precursors in the initial solution 1.0: 0.25, 0.50, 0.75: 1.0 for TEOS: TMSPM: MMA, respectively. The hybrid films were deposited by spin coating of the hybrid precursor solutions onto p-type Si (100) substrates and heat-treated at 90 °C for 24 h. The chemical bonding in the hybrid films was analyzed by Fourier Transform Infrared Spectroscopy to confirm their hybrid nature. The refractive index of the hybrid films as a function of the TMSPM coupling agent concentration, were determined from a simultaneous analysis of optical reflectance and spectroscopic ellipsometry experimental data. The PMMA–SiO₂ hybrid films were studied as dielectric films using metal-insulator-metal structures. Capacitance–Voltage (C–V) and current–voltage (I–V) electrical methods were used to extract the dielectric properties of the different hybrid layers. The three types of hybrid films were tested as gate dielectric layers in thin film transistors with structure ZnO/PMMA–SiO₂/p-Si with a common bottom gate and patterned Al source/drain contacts, with different channel lengths. We analyzed the output electrical responses of the ZnO-based TFTs to determine their performance parameters as a function of channel length and hybrid gate dielectric layer.     

Ultrasonically sprayed indium sulfide buffer layers for Cu(In,Ga)(S,Se)2 thin-film solar cells

Indium sulfide layers were grown by an ultrasonic spray pyrolysis method for application in Cu(In,Ga)(S,Se)₂ solar cells. X-ray diffraction measurements of layers on soda lime glass showed polycrystalline In₂S₃ with preferential orientation along the [103] direction and X-ray photoelectron spectroscopy revealed presence or absence of oxygen and chlorine impurities depending on the composition of the spray solution. For more quantitative chemical composition measurements In₂S₃ layers were sprayed on silicon substrates and analyzed with Rutherford backscattering spectrometry. The structural and chemical information on the In₂S₃ layer sprayed with different sulfur concentrations in the chemical precursor solution are correlated to the photovoltaic performance of solar cells. Best cell efficiency of 12.4% was achieved with an ultrasonically sprayed In₂S₃ buffer layer on a Cu(In,Ga)(S,Se)₂ absorber.