Electron Beam Reduction Method for Preparing the Catalyst Layer in the Growth of Carbon Nanotubes

In this paper, electron beam (e-beam) reduction method is applied for the catalyst layer preparation in the growth of carbon nanotubes (CNTs). A hot cathodic electron beam facility was employed to electron bombarding of catalyst layer before stage of CNTs growth. This new method leads to reducing the diameter of particles via sputtering and evaporating the surface of catalyst. The growth of CNTs was performed on the Fe catalyst layer with SiO₂ substrate in an environment of different mixed gases (H₂, NH₃ and C₂H₂) by thermal chemical vapor deposition (TCVD) system. The morphology of the electron beam reduced catalyst particles were probed by atomic force microscopy (AFM). All samples were analyzed by scanning electron microscopy (SEM) before and after growth of CNTs. SEM analyses clarified that the catalyst grains have been smaller under effect of electron beam bombardment.     

Spray pyrolysis deposition and characterization of highly (100) oriented magnesium oxide thin films

Transparent dielectric thin films of MgO has been deposited on quartz substrates at different temperatures between 400 and 600°C by a pneumatic spray pyrolysis technique using Mg(CH₃COO)₂·4H₂O as a single molecular precursor. The thermal behavior of the precursor magnesium acetate is described in the results of thermogravimetry analysis (TGA) and differential thermal analysis (DTA). The prepared films are reproducible, adherent to the substrate, pinhole free and uniform. Amongst the different spray process parameters, the substrate temperature effect has been optimized for obtaining single crystalline and transparent MgO thin films. The films crystallize in a cubic structure and X‐ray diffraction measurements have shown that the polycrystalline MgO films prepared at 500°C with (100) and (110) orientations are changed to (100) preferred orientation at 600°C. The MgO phase formation was also confirmed with the recorded Fourier Transform Infrared (FTIR) results. The films deposited at 600°C exhibited highest optical transmittivity (>80%) and the direct band gap energy was found to vary from 4.50 to 5.25 eV with a rise in substrate temperature from 500 to 600°C. The measured sheet resistance and the resistivity of the film prepared at 600°C were respectively 10¹³Ω/□ and 2.06x10⁷Ω cm. The surface morphology of the prepared MgO thin films was examined by atomic force microscopy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Epitaxial growth of α-SiC layers by chemical vapor deposition technique

Single crystals of α-SiC were grown on α-SiC substrates at a temperature between 1570 and 1630°C with the standard gas flow rate: H₂ ～ 1 liter/min, SiCl₄ ～ 1.7 ml/min and C₃H₈ ～ 0.1 ml/min. The grown layers were transparent greenish-blue, and surfaces were mirror-like. By an X-ray back-reflection Laue pattern and a reflection electron diffraction method, the grown layer was identified as 6H-SiC, one polytype of α-SiC. Crystal growth was influenced by substrate temperature, flow rates of reaction gases and the surface polarity of the substrate. The growth rate decreased with increase of the substrate temperature in the above temperature region. A lamellar structure was observed on the (0001) Si surface and a mosaic structure was observed on the (000$\text{1}$)C surface. The mole ratios of both SiCl₄ and C₃H₈ to H₂ and that of Si to C had some influence on crystal growth. Undoped layers were n-type due to nitrogen. P-type SiC was grown by doping Al during crystal growth. Doping effects were studied by photoluminescence and electrical measurements.     

Microstructural,thermal, and electrical properties of Bi1.7V0.3Sr2Ca2Cu3Ox glass‐ceramic superconductor

A glass‐ceramic Bi_1.7V_0.3Sr₂Ca₂Cu₃O_x superconductor was prepared by the melt‐quenching method. The compound was characterized by scanning electron microscopy, x‐ray diffraction, differential thermal analysis, current‐voltage characteristics, transport resistance measurements, and Hall effect measurements. Two main phases (BSCCO 2212 and 2223) were observed in the x‐ray data and the values of the lattice parameters quite agree with the known values for 2212 and 2223 phases. The glass transition temperature was found to be 426 °C while the activation energy for crystallization of glass has been found to be E_a = 370.5 kJ / mol. This result indicates that the substitution of vanadium increased the activation energy for the BSCCO system. An offset T_c of 80 K was measured and the onset T_c was 100 K. The Hall resistivity ρ_H was found to be almost field‐independent at the normal state. A negative Hall coefficient was observed and no sign reversal of ρ_H or R_H could be noticed. The mobility and carrier density at different temperatures in the range 140‐300 K under different applied magnetic fields up to 1.4 T were also measured and the results are discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and properties of titanium silicide coating glass by CVD

Titanium silicide thin films were prepared on glass substrates by chemical vapor deposition using SiH₄ and TiCl₄ as the precursors. The phase structure of the thin films was identified by XRD. The surface morphology of the thin films was observed by FESEM. The sheet resistance and optical behaviors of the thin films were measured by the four point resistivity test system and FTIR spectrometer, respectively. Titanium disilicide (TiSi₂) thin films with the face-centered orthorhombic structure are formed. The suitable formation temperature of the TiSi₂ crystalline phase is about 710 °C. The formation of TiSi₂ crystalline phase is dependent on the thickness of thin films and a quantity of the crystalline phase of TiSi₂ in the thin film is directly related to mole ratio of SiH₄/TiCl₄. The sheet resistance of the TiSi₂ thin films is dependent on the formation of the TiSi₂ crystalline phase. With the mole ratio of SiH₄/TiCl₄ of 3, the lowest sheet resistance (0.7 Ω/□) of titanium silicide thin film is formed at 710 °C. The maximum reflectance of the TiSi₂ thin films is about 0.95 on the broad IR heat radiation. A related reaction mechanism was proposed.     

Dynamics of low temperature PECVD growth of microcrystalline silicon thin films: Impact of substrate surface treatments

Microcrystalline silicon (μc-Si) films have been deposited on polyimide, Corning glass and c-Si(0 0 1) by rf plasma-enhanced chemical vapour deposition (PECVD) using both SiF₄–H₂ and SiH₄–H₂ plasmas. The effect of substrate pre-treatment using SiF₄–He and H₂ plasmas on the nucleation of crystallites is investigated. Real-time laser reflectance interferometry monitoring (LRI) revealed the existence of a ‘crystalline seeding time’ that strongly impacts on the crystallite nucleation, on the structural quality of the substrate/μc-Si interface and on film microstructure. It is found that SiF₄–He pre-treatment of substrates is effective in suppressing porous and amorphous interface layer at the early nucleation stage of crystallites, resulting in direct deposition of μc-Si films also on polyimide at the temperature of 120 °C.     

The effect of oxidation temperature on the nano crystalline structure of ZrO2 films deposited on silicon and glass substrates

Zirconium oxide (ZrO₂) films have been prepared by using ex situ thermal oxidation of sputtered Zr films on glass and silicon substrates. XRD patterns show that a highly monoclinic (111) preferential orientation of ZrO₂ phase can be formed with increasing the oxidation temperature. According to XRD patterns in all thermal oxidized samples silicon oxide phase is present as interfacial layer at the Zr (ZrO₂) / Si (glass) interface. In the case of silicon substrates, crystallite sizes obtained from ZrO₂ peak with higher intensity reveal an increase with substrate temperature. AFM measurement shows on the whole a decrease of average surface roughness with oxidation temperature. The electrical property of the prepared films is investigated by means of four point probe measurement. An abrupt increase of sheet resistivity occurs when the crystallinity of ZrO₂ phase enhances at higher temperature. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of substrate temperature on the structure of ZnO:Al thin films

ZnO: Al films were prepared using low cost spray pyrolysis technique. The dependence of the physical properties on the substrate temperature was studied. The best films obtained at 500°C substrate temperature with preferred [002] orientation. The sheet resistance decreases with increased substrate temperature, and values as low as R_sh = 207 Ω/cm² are reached for substrate temperature of 500°C. The optical transmittance of films increased by increasing the substrate temperature and received to 75% at 500°C. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

AES study of the low temperature growth of Cu2−xS on CdS

The growth mechnism of Cu_2?xS on CdS substrates was studied by Auger electron spectroscopy, when a CuCl(film)-CdS- (substrate) specimen was heat treated at ∽200°C. It was found that the reaction to form Cu_2?xS would occur before heat treatment (at ∽50°C). Depth-profile measurement of a Cu_2?xS-CdS specimen heat treated for ∽40 min at ∽200°C showed that the junction had a diffuse interface composed of Cu, Cd, and S with a thickness of ∽500 Å, and also that Cu and Cd atoms diffused into CdS substrate and Cu_2?xS layer, respectively, to a depth of 300–600 Å.     

Heteroepitaxial growth of β-SiC on silicon substrate using SiCl4-C3H8-H2 system

Single crystals of β-SiC were prepared on Si substrates at a temperature around 1390°C with the standard conditions: H₂ ≈ 1 1/min, SiCl₄≈3 ml/min, C₃H₈≈1 ml/min, deposition period≈10 min. The dependences of the growth rate and the crystallinity on the substrate temperature were studied. By detailed reflection electron diffraction analyses, the crystallinity of β-SiC with 1 μm thickness was found to be better for the layer on the (100) and (110)Si substrates than for that on the (111)Si substrate. An activation energy of 25kcal/mole was obtained for the formation of β-SiC. Optimum conditions to obtain thicker β-SiC films are discussed.     

Synthesis and self‐assembled mechanism of CuO peony‐flowers by a composite hydroxide‐mediated approach at low temperature

A composite‐hydroxide mediated (CHM) method was utilized for the synthesis of CuO peony‐flower nanostructures under temperatures ranging between 25 and 160 °C. The CHM mechanism was confirmed through X‐ray Powder Diffraction (XRD) and a Thermo‐Gravimetric Differential Scanning Calorimeter (TG‐DSC). Cu(NO₃)₂ was shown to transform into Cu(OH)₂ in the mixed alkalis (NaOH/KOH); the reaction was facilitated by the solvent properties of the mixed alkalis. Cu(OH)₂ subsequently consumed H₂O in the adsorption of the mixed alkalis at 25∼65 °C. At higher reaction temperatures (>65 °C), the Cu(OH)₂ was seen to decompose at an accelerated rate. Therefore, crystalline CuO could be obtained not only above 65 °C but also at 25 °C. The crystal morphology and structure of CuO were examined through Filed Emission Scanning Electron Microscopy (FE‐SEM) and Transmission Electron Microscopy (TEM). It was determined that the CuO peony‐flower had a polycrystalline structure composed of single crystalline CuO petals. Using the Selected Area Electron Diffraction (SAED) results, the rings were indexed as (002), (111), (112), (202) and (−113), which was in agreement with the XRD results. With increasing temperature, the CuO flower petals self‐assembled through random aggregation and gathered CuO nanorod parts, which led to incomplete CuO flower petals through orientated aggregation. Prolonged reaction time led to the growth of CuO flower petals in the direction of [001]. An ideal CuO flower structure was observed through TEM observation.     

Glass formation and crystallization in highly undercooled Te-Cu alloys

The large undercoolings required for glass formation have been achieved by the slow cooling (10-20°C/min) of liquid Te-Cu alloys in the form of a fine droplet emulsion. Within the region of glass formation, between 19 and 39 at.% Cu, DTA measurements indicate that the glass (T_g) and crystallization (T_c) temperatures during heating exhibit a broad maximum at the eutectic. During slow cooling of Te-rich alloy droplets, the maximum undercooling for nucleation increases from 213°C for pure Te to 264°C for Te-12.5 at.% Cu. An enhanced depression of the nucleation (T_n) temperature compared with the change of the liquidus develops in Te-rich alloys upon approaching the glass forming composition range and can be a useful feature in assessing the glass forming tendency. Thermal cycling experiments indicate that even at an undercooling of 181°C crystallization in an eutectic Te-29 at.% Cu alloy is limited by an inadequate nucleation rate in clean droplet samples. For a eutectic alloy, at undercoolings in excess of 200°C crystal nucleation does develop in the droplet samples, but complete crystallization is hindered by a rapidly rising liquid viscosity with increased undercooling.     

Growth behavior of CuPc films by physical vapor deposition

Various Cu‐phthalocyanine (CuPc) films were grown from physical vapor deposition on top of indium‐tin‐oxide glass substrates by controlling substrate temperature (T_sub), source temperature (T_sou), and growth time. From side‐view SEM pictures, the growth rates for these CuPc films are estimated and can be categorized into three regions. From the Arrhenius plot of growth rate versus 1/T_sub, the activation energy E_A can be obtained. As T_sou = 390 °C, for region (A) with T_sub < 140 °C, the growth of CuPc films is dominated by the adhesion process with E_A = 810 meV. For region (B) with 140 °C < T_sub < 320 °C, the growth is then limited by the steric character associated with the organic molecular solids with E_A = 740 meV. For region (C) with T_sub > 320 °C, the re‐evaporation of the CuPc adhered molecules from the interface becomes dominant. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemical durability of Na2OCaOSiO2 glasses in acid solutions

The resistance of Na₂OCaOSiO₂ glasses to acid solutions has been studied. The compositions studied were Na₂O · 4SiO₂, Na₂O · x CaO · (4?x) SiO₂ and a common electrode glass containing 22.63Na₂O and 5.58 CaO, mol%. The reaction was made at 40°C for about 3 h in 1N solutions of HCl, HNO₃ and H₂SO₄. Powdered glass samples were used and the reaction was followed by analyzing the solution for soda, lime and silica.The extraction rates of each constituent were measured. The effect of acid concentration was also studied for each glass using 10^?3–10N solutions of the three acids for a fixed time. The quantity of calcium extracted increased slowly at first with increasing calcium content in the glass, but rapidly when the lime content exceeded ≈10 mol%. Above this concentration, both calcium and sodium appears to pass into solution in the same proportion in which they are present in the glass. The extraction rate was found to depend on the type and concentration of the acid used, being least in H₂SO₄ and much higher and almost equal in both HCl and HNO₃.An attempt was made to correlate the results of decomposition of the soda-lime-silica glasses to their membrane potentials in acidic solutions.     

Obtaining ZnO/CIS heterostructures

ZnO/CuInSe₂ heterostructures were obtained by sequential evaporation of elements. Firstly, a layer of Zn was deposited on the glass substrate by the magnetron sputtering method in vacuum. Needle-shaped nanostructures of ZnO were grown from the prepared Zn films by thermal annealing in the air. Secondly, Se, In and Cu layers were sequentially deposited onto these structures. The obtained samples were then annealed at 400 °C to form the CuInSe₂ (CIS) compound. The morphology, composition and phase identification were obtained using the scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis methods.     

Glass formation through hydrolysis of Si(OC2H5)4 with NH4OH and HCl solution

Monolithic silica glass was obtained by heating the gels prepared by hydrolyzing Si(OC₂H₅)₄ with NH₄OH and HCl solution. The effect of the condition of hydrolysis of Si(OC₂H₅)₄ on glass formation was examined by measuring the bulk density, the infrared spectra and the thermal shrinkage of the gel on heating. The gel prepared by hydrolysis with NH₄OH solution consisted of numerous spherical particles, the bulk density being about 0.8. This gel abruptly shrank at about 1050°C, being converted to the pore free material similar to fused silica. The conversion of the gel to glass followed the sintering model in which the viscous flow controlled the sintering process. The viscosity and the activation energy for viscous flow were calculated on the basis of the Frenkel equation. On the other hand, the spherical particles were not observed in the gel prepared by hydrolysis with HCl solution. The bulk density of the gel was about 1.8. This gel was converted to glass at about 700°C, which was lower than the temperature of glass formation for the gel obtained by hydrolysis with NH₄OH solution.     

Synthesis and growth mechanism of ZnO rod‐like nanostructures by a microwave‐assisted low‐temperature aqueous solution route

A zinc oxide (ZnO) nanoarray (rod‐like nanostructure) was successfully synthesized through a low‐temperature aqueous solution and microwave‐assisted synthesis using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine (HMTA) as raw materials, and using FTO glass as substrate. The effects of parameters in the preparation process, such as solution concentration, reaction temperature and microwave power, on the morphology and microstructure of ZnO nanoarray were studied. Phase structure and morphology of the products were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that hexagonal wurtzite structure ZnO nanoarray with good crystallization could be prepared through a low‐temperature solution method. When the concentration of the mixed solution was 0.05 M, the reaction temperature was 95 °C, and the reaction time was 4 h, high‐density ZnO regular nanorods of 200 nm diameter were obtained. A possible mechanism with different synthesis methods and the influence of microwave processing are also proposed in this paper.     

Kinetics of crystal growth of mirabilite in aqueous supersaturated solutions

The crystallization of sodium sulfate decahydrate (Na₂SO₄·10H₂O, mirabilite) from supersaturated solutions was investigated using stable supersaturated solutions seeded with mirabilite seed crystals. The experiments were done in batch, stirred reactors in which the supersaturated solutions were prepared either by dissolution of sodium sulfate anhydrous at 32 °C followed by cooling to 18 or 20 °C or by mixing equal volumes of equimolar ammonium sulfate and sodium hydroxide solutions at 20 °C. Inoculation of the solutions supersaturated only with respect to mirabilite with seed crystals was accompanied with temperature increase of the thermostated solution. Despite the fact that crystal growth was initiated with seed crystals, the process started past the lapse of induction times inversely proportional to the solution supersaturation. The rates of crystal growth were measured both from the temperature rise and from the concentration–time profiles, which were linearly correlated. The measured crystal growth rates showed a parabolic dependence on supersaturation at low supersaturations. For higher values this dependence changed to linear, a behavior consistent with the BCF spiral crystal growth model. The morphology of the crystals growing at 20 °C showed typical prismatic habit, while at 18 °C when crystallized from cooled sodium sulfate solutions changes in the crystal habit to a leaf like morphology were observed.     

Study on K(DxH1‐x)2PO4 Crystals: Growth Habit,Optical Properties and their Improvement by Thermal‐Conditioning

Phosphite, which often exists in growth solutions obtained directly from commercial P₂O₅ , was found to have significant inhibiting effects on the growth of pyramidal face of KDP crystals. K(D_xH_1‐x)₂PO₄ (referred to as DKDP) crystals with different deuterium fraction x were grown and the optical performances were investigated. The absorption coefficients at 1.05 μm decreases monotonically with the increase of x. The transmission threshold shift from 1.65μm at x=0 to 2.10 μm at x=0.96. The high temperature phase transition temperature and latent heat were measured using the method of differential scanning calorimetry (DSC). Thermal conditioning experiments were carried out at 180°C and 140°C for KDP and DKDP, respectively. After conditioning, a different degree of improvement was observed in the optical homogeneity of the samples, while the laser damage threshold and light absorption coefficient showed no significant change.