CO-DEPOSITION OF FULLERENES AND SULFUR FROM DILUTED SOLUTION

A new method to synthesize fullerene and sulfur compounds has been developed. Using this method, C₆₀S₁₆ and C₇₀S₁₆ compounds were grown from dilute fullerene and sulfur toluene solution. Their atomic structures were analyzed by x-ray diffraction with the single crystal. The C₆₀S₁₆ crystal is C-centered monoclinic structure of a=2.0874 nm, b=2.1139 nm, c=1.05690 nm and β=111.93°, and the C₇₀S₁₆ has a primitive monoclinic, P2₁/c, with lattice parameters of a=1.5271 nm, b=1.49971 nm, c=2.18024 nm and β=109.791°. In this compound, the structure of fullerenes is maintained and sulfur atoms form S₈ rings placed around the fullerenes.     

Phase formation process of IrxSi1−x thin films Structure and electrical properties

Experimental data on the phase formation process of amorphous Ir_xSi_1−x thin films with 0.30 ≤ x ≤ 0.41 are presented and discussed in relation to electric transport properties. The structure formation process at temperatures from 300 K up to 1223 K was investigated by means of X-ray diffraction. Distinct phases were observed in the final stage in dependence on the initial composition: Ir₃Si₄, Ir₃Si₅, and IrSi₃. An unknown metastable phase was found in films with a silicon concentration of 61 at.% to 64 at.% after annealing above the crystallization temperature T = 970 K. The crystal structure of this phase was determined by the combined use of X-ray diffraction and electron diffraction. It was found to be monoclinic, basic-face centred with lattice constants a = 1.027 nm, b = 0.796 nm, c = 0.609 nm, and γ = 113.7°. Additionally, microstructure and morphology of the films were investigated by transmission electron microscopy (TEM). The annealing process was studied by means of mechanical stress investigations as well as by electrical resistivity and thermopower measurements. Correlations between the structure, the phase formation and the electrical transport behaviour are discussed on the basis of conduction mechanism.     

Electro-optic properties of c-axis oriented LiNbO3 films grown on Si(1 0 0) substrate

We developed a spectroscopic–ellipsometric approach to evaluate the electro-optic coefficient of highly c-axis oriented LiNbO₃ films on an Si(1 0 0) substrate grown by electron cyclotron resonance plasma sputtering. Applying an electric field between the TiN transparent top electrode and Si substrate, the interference fringe appearing in the tan Ψ spectrum was slightly modulated by phase retardation in the wavelength domain. The change in effective wavelength was converted to refractive index change, yielding dispersion in the Pockels coefficient (r₃₃) between 0.3 and 0.8 μm. At 633 nm, we obtained an r₃₃ that was 57% of the bulk LN crystal value.     

Electrochemical deposition of PbSe and CdTe nanoparticles onto p-Si(100) wafers and into nanopores in SiO2/Si(100) structure

Electrochemical deposition of PbSe and CdTe nanoparticles onto p-Si(100) wafers and into nanopores in SiO₂ layer grown thermally on p-Si(100) substrates (SiO₂/Si(100) structure) under illumination was studied. To produce nanopores we used SiO₂ layer with tracks developed by irradiation of 350 MeV Au ions. Pores structure was formed by chemical etching of the irradiated SiO₂ layer in dilute HF. The pores were shaped like truncated cones with a base diameter of 200 and 250 nm and height of 200 nm. Photoelectrochemical deposition of PbSe and CdTe was carried out with constant cathodic potentials from the water solutions containing Pb²⁺, Cd²⁺ cations and H₂SeO₃, H₂TeO₃ acids. The potentials applied were more positive than the equilibrium E_{Meⁿ⁺/Me⁰} redox potential. The underpotential deposition of Pb (or Cd) occurs only onto the co-deposited Se (or Te) atoms due to electrons photogenerated in Si substrate. The average sizes of PbSe and CdTe particles electrodeposited onto Si(100) wafers were dependent on the duration of electrodeposition, changing from 50 to 200 nm for PbSe and 30–80 nm for CdTe. According to XRD data, PbSe particles formed at ambient conditions had the crystalline structure. To deposit CdTe nanoparticles we used an electrolyte heated up to 80 °C. Variations in the electrodeposition time enabled one to form either separate chalcogenide particles or a polycrystalline film-like layer in case of electrodeposition onto p-Si(100) wafers and to control the degree of pore filling in case of electrodeposition into the nanopores of SiO₂/Si(100) structure.     

Preparation of highly c-axis-oriented Bi4Ti3O12 thin films and their crystallographic, dielectric and optical properties

Bismuth titanate (Bi₄Ti₃O₁₂) thin films with a high c-axis orientation up to 99% were prepared on (100)-oriented silicon wafers by r.f. planar magnetron sputtering using a Bi₂TiO₅ ceramic target at a substrate temperature of 600 °C. From the Auger electron spectroscopy depth profile of the film, there is no evidence of interdiffusion of a specific element between the film and the substrate. Relative dielectric constant of these films depends on film thickness. The behavior was explained assuming a low-dielectric-constant interface layer. Using this assumption, the relative dielectric constant of Bi₄Ti₃O₁₂ film was estimated to be approximately 140. This value is close to that along the c axis in a bulk form. The remanent polarization and the coercive field were 0.8 μC cm⁻² and 20 kV cm⁻¹, respectively.     

Structure, magnetic and thermal properties of Gd2MnTiO6

A new perovskite compound Gd₂MnTiO₆ was synthesized and its crystal structure, magnetic and thermal properties have been investigated. The XRD patterns were refined by the Rietveld method and the refined lattice parameters with the monoclinic space group P2₁/n (No. 14) were a=0.5398 (2), b=0.5704 (2), c=0.7767 (2) nm and β=89.68 (2)°. The antiferromagnetic behavior was observed below 16.0 K and λ-type heat capacity was measured near this temperature.     

Morphological changes induced by thermal anneals in NiFe/Ag multilayers; their relation to the resistive and magnetoresistive properties

(Ti, Al)N films have drawn much attention as alternatives for TiN coatings, which are oxidized easily in air above 500 °C. We have investigated the effect of Al content on the oxidation resistance of (Ti_{1 − x}Al_x)N films prepared by r.f. reactive sputtering.

(Ti_{1 − x}Al_xN films (O ≤ x ≤ 0.55) were deposited onto fused quartz substrates by r.f. reactive sputtering. Composite targets with five kinds of Al-to-Ti area ratio were used. The sputtering gas was Ar (purity, 5 N) and N₂ (5 N). The flow rate of Ar and N₂ gas was kept constant at 0.8 and 1.2 sccm, respectively, resulting in a sputtering pressure of 0.4 Pa. The r.f. power was 300 W for all experiments. Substrates were not intentionally heated during deposition. The deposited films (thickness, 300 nm) were annealed in air at 600 900 °C and then subjected to X-ray diffractometer and Auger depth profiling.

The as-deposited (Ti_{1 − x}Al_x)N films had the same crystal structure as TiN (NaCl type). Al atoms seemed to substitute for Ti in lattice sites. The preferential orientation of the films changed with the Al content of the film, x. Oxide layers of the films grew during annealing and became thicker as the annealing temperature increased. The thickness of the oxide layer grown on the film surface decreased with increasing Al content in the film. For high Al content films an Al-rich oxide layer was grown on the surface, which seemed to prevent further oxidation. All of the films, however, were oxidized by 900 °C annealing, even if the Al content was increased up to 0.55.     

Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3

An all alkoxide based sol–gel route was investigated for preparation of epitaxial La_0.5Sr_0.5CoO₃ (LSCO) films on 100 SrTiO₃ (STO) substrates. Films with 20–30 to 80–100 nm thickness were prepared by spin-coating 0.2–0.6 M (metal) solutions on the STO substrates and heat treatment to 800 °C at 2 °C min^− 1, 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 Å closely; a and b = 3.894 Å and 3.897 Å for the 20–30 and 80–100 nm films, respectively. The c-axis was compressed to 3.789 Å and 3.782 Å for the 20–30 and 80–100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an -Al₂O₃ substrate was dense and polycrystalline with crystallite sizes in the range 10–50 nm and gave cubic cell dimensions of a_c = 3.825 Å. The conductivity of the ca 30–40 nm thick polycrystalline film was 1.7 mΩcm, while the epitaxial 80–100 nm film had a conductivity of around 1.9 mΩcm.     

Effect of hydrogen radical on growth of μc-Si in hetero-structured SiCx alloy films

The changes of the crystallinity of μc-Si phase are studied in samples deposited with hydrogen dilution ratio, H₂/SiH₄, from 9.0 to 19.0 by hot-wire CVD (Cat-CVD). In the samples deposited at filament temperature, T_f, of 1850 °C, the crystalline fraction and the crystallite size of μc-Si phase increased with increasing the H₂/SiH₄. The carbon content, C/(Si+C), was almost constant. In the XRD patterns, the intensity of Si(1 1 1) peak decreased and that of Si(2 2 0) peak increased with increasing the H₂/SiH₄. In the samples deposited at T_f of 2100 °C with H₂/SiH₄ over 11.4, the μc-Si phase was not formed and the C/(Si+C) increased. The growth mechanism of μc-Si in hetero-structured SiC_x alloy films is discussed.     

Effect of GeF4 addition on the growth of hydrogenated microcrystalline silicon film by plasma-enhanced chemical vapor deposition

The effects of the addition of germanium tetrafluoride, GeF₄, are demonstrated on the growth of films of hydrogenated microcrystalline silicon, μc-Si:H, from SiH₄ and H₂ by r.f. plasma-enhanced chemical vapor deposition (r.f. PECVD). The structural and optoelectrical properties of the μc-Si(Ge):H(F) film are examined as a function of the flow rates of GeF₄ and H₂. The addition of GeF₄ enhances the deposition rate and the crystallinity of the Si network, when the flow rate ratio, r=Fr(GeF₄)/Fr(SiH₄) is below 10%. On the other hand, under conditions, r>0.1, the formation of a SiGe_x crystalline phase is promoted. The combination of the flow rates of GeF₄ and H₂ greatly affects the enhancement of crystallinity along with an increase in surface roughness.     

Preparation of SiO2 films with embedded Si nanocrystals by reactive r.f. magnetron sputtering

SiO_x films with a nominal x-value (1≤x≤2) were deposited on flat-surface silicon substrates by reactive r.f. magnetron sputtering at substrate temperatures of 20 and 500°C, respectively. X-ray diffraction and high resolution TEM investigations of SiO_x films with x=1.45 and x=1 show that as-deposited films have an amorphous structure. After annealing, a nucleation of Si nanocrystals was found with increasing size at increasing initial Si concentration and annealing temperature. The weak photoluminescence in the visible region of as-deposited SiO_x films increases remarkably by annealing with dependence on x.     

Molecular beam epitaxial growth of SmBa2Cu3O7−δ thin films and effect of substrate temperature on the surface roughness

Stoichiometrically optimized, epitaxial SmBa₂Cu₃O_7-δ thin films with high T_{c, R = 0} and high critical current densities j_c have been prepared for the first time in a tightly controlled molecular beam epitaxy process in non-reactive molecular oxygen, followed by an in situ loading process with molecular oxygen. The surface roughness (on a submicrometre scale) of single-crystal films with their c axes perpendicular to the surface depends markedly on the surface temperature of the substrate during the deposition of the epitaxial films, within a range of only a few degrees centigrade. The calibrated optimal temperature for the preparation of epitaxial films 200 nm thick of this single orientation is found to be 680 ± 5 °C. In scanning tunnelling microscopy investigations, they show a surface roughness of less than 6 nm (five SmBa₂Cu₃O_7−δ unit cells) on a 2 μm × 2 μm scale. At deposition temperatures below this optimal deposition temperature, the well-known a-axis growth increases rapidly, whereas higher temperatures give a significantly higher surface roughness, which can be observed by scanning electron microscopy.     

Influence of thickness and growth temperature on the properties of zirconium oxide films grown by atomic layer deposition on silicon

ZrO₂ films of thicknesses varied in the range of 3–30 nm were atomic layer deposited from ZrI₄ and H₂O–H₂O₂ on p-Si(100) substrates. The effects of film thickness and deposition temperature on the structure and dielectric properties of ZrO₂ were investigated. At 272 and 325 °C, the growth of ZrO₂ started with the formation of the cubic polymorph and continued with the formation of the tetragonal polymorph. The ratio between the lattice parameters increased with the film thickness and growth temperature. The effective permittivity, determined from the accumulation capacitance of Hg/ZrO₂/Si capacitors, increased with the film thickness, reaching 15–17 in 25-nm-thick films. The permittivity decreased with the increasing growth temperature. The hysteresis of the capacitance–voltage curves was the narrowest for the films deposited at 325 °C, and increased towards both lower and higher deposition temperatures.     

Single crystal structure of a layered intercalating phosphate with features of two dimensions and H-bonds

A new organic phosphate of (8-HQDH)(H₂PO₄)·H₂O has been obtained by hydrothermal reaction. The crystal structure was determined with data: triclinic, space group P , a=6.541(1) Å, b=8.5909(8) Å, c=10.769(1) Å, =98.734(7)°, β=91.20(1)°, γ=97.91(1)°, V=591.9(1) ų, and Z=2. The (H₂PO₄)⁻ groups and H₂O molecules stack into sheets and 8-HQ cations fixed parallelly with each other to form an intercalating compound by H-bonds.     

Thickness measurement of SiO2 films thinner than 1 nm by X-ray photoelectron spectroscopy

The thickness measurement of ultra-thin SiO₂ films thinner than 1 nm was studied by X-ray photoelectron spectroscopy (XPS). Amorphous SiO₂ thin films were grown on amorphous Si films to avoid the thickness difference due to the crystalline structure of a substrate. SiO₂ thin films were grown by ion beam sputter deposition under oxygen gas flow and the thickness was measured by in situ XPS. The attenuation length was determined experimentally by a SiO₂ film with a known thickness. The straight line fit between the measured thickness using XPS and the nominal thickness showed a good linear relation with a gradient of 0.969 and a small offset of 0.126 nm. The gradient measured at the range of 3.4–0.28 nm was very close to that measured at sub-nanometer range of 1.13–0.28 nm. This result means that the reliable measurement of SiO₂ film thickness below 1 nm is possible by XPS.     

Preparation and characterization of YBa2Cu3O7−x high Tc superconducting thin films deposited by S-gun sputtering

We have prepared YBa₂Cu₃O_7−x high T_c superconducting (HTS) thin films on (100) yttria-stabilized zirconia (YSZ) and LaAlO₃ (LAO) substrates, using a 2 kW S-gun in an off-axis mode. By varying the temperature of the substrates, films with a axis and c axis orientations were readily obtained. The X-ray diffraction pattern and Laue pattern confirmed that films with a axis orientation exhibited a single-crystal texture. All films had a good mirror-like surface. For films grown on YSZ substrates, scanning electron microscopy (SEM) revealed a clear distinction between the surfaces of the films grown at various temperatures (520–780°C). Films grown on LAO substrates exhibited even smoother and flatter surfaces. The SEM changes will be discussed in correlation with J_c. The best HTS thin films were obtained on LAO substrates at a temperature of 820°C, with T_c=89 K and J_c=1×10⁶ A cm^-2 (77 K).     

Diffusion barrier properties of sputtered TaNx between Cu and Si using TaN as the target

TaN_x films sputtered from a TaN target were used as diffusion barriers between Cu thin films and Si substrates. Material characteristics of TaN_x films and metallurgical reactions of Cu/TaN_x/Si systems annealed in the temperature range 400–900 °C for 60 min were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, cross-sectional transmission electron microscopy, and sheet resistance measurements. We found that the deposition rate decreased with increasing bias. TaN, β-Ta, and Ta₂N phases appeared and/or coexisted in the films at specific biases. A step change in N/Ta ratio was observed whenever a bias was applied to the substrate. After depositing a copper overlayer, we observed that the variation percentage of sheet resistance for Cu (70 nm)/TaN_x (25 nm, x=0.37 and 0.81)/Si systems stayed at a constant value after annealing up to 700 °C for 60 min; however, the sheet resistance increased dramatically after annealing above 700 and 800 °C for Cu/TaN_0.37/Si and Cu/TaN_0.81/Si systems, respectively. At that point, the interface was seriously deteriorated and formation of Cu₃Si was also observed.     

Growth mechanism of stress corrosion cracking in high strength steel

Stress corrosion crack growth rates are measured at sveral stress intensity levels for low-tempered 4340 steel in 0.1N H₂SO₄ solution. The characteristics of the growth rates are divided into three regions of stress intensity factors: Region I near K_1SCC; Region III near unstable fracture toughness, K_1SC; and Region II, which lies between the two. K_1SCC is the value of K at which no crack growth can be detected after 240 hr.

In order to explain these experimental results, the crack initiation analysis reported in a previous paper is extended to the growth rates. A detached crack initiates and grows at the tip of an already existing crack. When the detached crack reaches the tip of the main crack, the process repeats as a new existing crack.

A relationship between crack growth rate, v, and stress intensity factor, K, is obtained as a function of b/a and a = b + d, where b is the distance from the tip of the main crack to the detached crack, and d is the ydrogen atom saturated domain.

The experimental data are in good agreement with the theoretical values in Region II when a = 0.02 mm, b/a = 0.8, c₁/c₀ = 2.8 for 200°C tempered specimens and a = 0.015 mm, b/a = 0.7, c₁/c₀ = 3.0, ρ_b = 0.055 mm for 400°C tempered specimens, where ρ_b is a fictitious notch radius. The plateau part in Region II for 400°C tempered specimens is also successfully explained by the present theory. For Region III, the value of b/a will be almost equal to 1 because v → ∞ for b/a → 1. On the other hand, for Region I, b/a will be zero, since the value of v becomes negligibly small and no crack growth is observable.     

Dislocation, annealing and quenching effects on the microindentation hardness of Bi2Te3 and Bi2Te2.9Se.1 single crystals

Stoichiometric crystals of Bi₂Te₃ and Bi₂Te_2.9Se_.1 have been grown from the melt by the horizontal zone melting (HZM) technique. X-ray powder diffraction and energy dispersive X-ray analysis could prove that the grown crystals are stoichiometric with lattice constants a=0.4374 nm, c=3.044 nm for Bi₂Te₃ and a=0.4374 nm, c=3.038 nm for Bi₂Te_2.9Se_.1. Dislocation density measurements are carried out by etch pit technique and are observed by scanning electron and optical micrograph. The mechanical strength of the as-grown, quenched and annealed crystals is assessed by the Vickers hardness measurements.     

Growth, selectivity and adhesion of CVD-deposited copper from Cu (hexafluoroacetylacetonate trimethylvinylsilane) and dichlorodimethylsilane

Copper films have been deposited by low-pressure (1–20 mTorr) chemical vapour deposition using Cu¹⁺ (hexafluoroacetylacetonate) trimethylvinylsilane onto SiO₂ patterned substrates having seed layers of W, TiN and Al. Blanket deposition is observed for all growth temperatures in the range 140 °C ≤ T_g ≤ 240 °C. However, depending on the initial substrate seed layer and pre-treatment, the relative strength of the copper-oxide and copper-seed layer bond can be dramatically altered particularly when growth is carried out in the presence of dichloromethylsilane (DCDMS). The degree of selectivity as well as film morphology is also found to be sensitive to the initial pre-treatment, growth temperature and flow rate of DCDMS.