Precursor evolution and growth mechanism of BTO/YBCO films by TFA–MOD process

In this study, BaTiO3 （BTO）-doped YBCO films are prepared on LaA103 （100） single-crystal substrates by metal- organic decomposition （MOD） using trifluoroacetate （TFA） precursor solutions. The critical current density （Jc） of BTO/YBCO film is as high as 10 MA/cm2 （77 K, 0 T）. The BTO peak is found in the X-ray diffraction （XRD） pattern of a final YBCO superconductivity film. Moreover, a comprehensive study of the precursor evolution is conducted mainly by X-ray analysis and μ-Raman spectroscopy. It is found that the TFA begins to decompose at the beginning of the thermal process, and then further decomposes as temperature increases, and at 700 ℃ BTO nanoparticles begin to appear. It sug- gests that the YBCO film embedded with BTO nanoparticles, whose critical current density （Jc） is enhanced, is successfully prepared by an easily scalable chemical solution deposition technique.     

Relationship between crystallization process and superconducting properties of YBCO films by TFA–MOD method using starting solution with various compositions

We have investigated the influence of partial pressure of water vapor [P(H₂O)] in the crystallization process on the superconducting properties of YBa₂Cu₃O_7−y (YBCO) films fabricated by a trifluoroacetate–metal organic deposition (TFA–MOD) method. The starting solution with different compositions of Y: Ba:Cu = 1.0:2.0:3.0 and 1.0:1.5:2.0 were studied. The critical current density (J_c) values of YBCO films fabricated from Y:Ba:Cu = 1.0:2.0:3.0 starting solution significantly increase (1.71 → 2.55 MA/cm²) with increasing P(H₂O) from 12.3 to 47.4 kPa. In the YBCO films fabricated from Y:Ba:Cu = 1.0:1.5:2.0 starting solution, high J_c values of over 2.5 MA/cm² were recognized in a wide range of P(H₂O) (12.3–47.4 kPa). One of the reason for J_c improvement is the suppression of coarsening of the secondary phases grains such as Y₂Cu₂O₅ and CuO due to increase in growth rate of YBCO layer in the crystallization process. The J_c values of all YBCO films decreased as P(H₂O) increased up to 70.1 kPa. This degradation of J_c values may be caused by difference of crystal growth mechanism in high growth rate.     

Aqueous polymer–nitrate solution deposition of YBCO films

High critical current density YBa₂Cu₃O_7?x (YBCO) films were prepared by solution deposition of aqueous non-fluorine precursors. Non-fluorine polymer-assisted deposition (PAD) processes utilizing rheology modifiers and chelating agents were used to produce 50 nm films with a critical current density (J_c) over 3 MA/cm² and 400 nm films with J_c > 1 MA/cm²_. T_c measurements indicated that films have T_c values near 90 K. The total heat treatment time to produce these high performance films was less than 4 h. Rheology modifiers such as polyvinyl alcohol (PVA) and hydroxyethyl cellulose (HEC) were used to increase the thickness of deposited films independent of the solution cation concentration. Chelating agents such as polyethylene glycol (PEG) and sucrose increased the barium ion solubility. Nitrate crystallization during deposition was controlled through rapid drying with vacuum and coating with hot solutions.     

Studies on electrical switching behavior and optical band gap of amorphous Ge–Te–Sn thin films

Amorphous thin film Ge₁₅Te_85−x Sn _x (1≤x≤5) and Ge₁₇Te_83−x Sn _x (1≤x≤4) switching devices have been deposited in sandwich geometry using a flash evaporation technique, with aluminum as the top and bottom electrodes. Electrical switching studies indicate that these films exhibit memory type electrical switching behavior. The switching fields for both the series of samples have been found to decrease with increase in Sn concentration, which confirms that the metallicity effect on switching fields/voltages, commonly seen in bulk glassy chalcogenides, is valid in amorphous chalcogenide thin films also. In addition, there is no manifestation of rigidity percolation in the composition dependence of switching fields of Ge₁₅Te_85−x Sn _x and Ge₁₇Te_83−x Sn _x amorphous thin film samples. The observed composition dependence of switching fields of amorphous Ge₁₅Te_85−x Sn _x and Ge₁₇Te_83−x Sn _x thin films has been understood on the basis of Chemically Ordered Network model. The optical band gap for these samples, calculated from the absorption spectra, has been found to exhibit a decreasing trend with increasing Sn concentration, which is consistent with the composition dependence of switching fields.     

Synthesis and performance of Zn–Ni–P thin films

The electroplating of Zn–Ni–P thin film alloys from a sulfate bath containing phosphoric and phosphorous acid was investigated. The bath composition and the deposition parameters were optimized through Hull cell experiments, and the optimum experimental conditions were determined(p H = 2, temperature = 298–313 K, zinc sulfate concentration =30 g·L-1, EDTA concentration = 15 g·L-1, and current density = 1.0–2.0 A·dm-2). The SEM analysis of the coating deposited from the optimum bath revealed fine-grained deposits of the alloy in the presence of EDTA. Optical microscopy analysis indicated an electrodeposited thin film with uniform thickness and good adhesion to the steel substrate. The good adherence of the coatings was also demonstrated by the scratch tests that were performed, with a maximum determined value of 25 N for the critical load. Corrosion resistance tests revealed good protection of the steel substrate by the obtained Zn–Ni–P coatings, with values up to 85.89% for samples with Ni contents higher than 76%. The surface analysis of the thin film samples before and after corrosion was performed by X-ray photoelectron spectroscopy(XPS).     

Fabrication of YBCO／YSZ and YBCO／MgO thick films using electrophoretic deposition with top-seeded melt growth process

Superconducting thick films were grown on single crystals MgO and YSZ by electrophoretic deposition with Y_2BaCuO_5(Y211) addition. YBCO thick films were then accomplished by sintering the precursor films above the peritectic temperature. Single crystals of MgO (3×3×0.5 mm^3) were used as top-seed to control crystal structure of the thick films. As shown by scanning electron microscopy, the morphologies of YBCO/YSZ and YBCO/MgO thick films are spherulitic texture and platelet type. The critical temperature is ～89 K for the YBCO/YSZ thick film; the onset transition temperature is 86.4 K and the transition width is ～3 K for YBCO/MgO thick film. The critical current densities (as determined by Bean model) are, in A/cm^2, 3870 (77 K) for YBCO/YSZ thick films and 2399 (77 K) for YBCO/MgO thick films, which are comparable to the best J_c reported of the thick films prepared by the same method.     

Preparation and characterization of iron–molybdate thin films

Mixed Fe–Mo oxides are used in industrial catalytic processes of selective oxidation of methanol to formaldehyde. For better understanding of the structure-reactivity relationships of these catalysts we aim to prepare well-ordered iron–molybdate thin films as model catalysts. Here we have studied Mo deposition onto Fe₃O₄ (111) thin films produced on Pt(111) as a function of Mo coverage and annealing temperature using LEED, AES, STM and IRAS. At low temperatures, the iron oxide film is covered by Mo = O terminated molybdena nanoparticles. Upon oxidation at elevated temperatures (T > 900 K), Mo species migrate into the film and form new bonds with oxygen in the film. The resulting films maintain the crystal structure of Fe₃O₄, and the surface undergoes a (√3 × √3)R30° reconstruction. The structure is rationalized in terms of Fe substitution by Mo in the surface layers.     

Optical parameters and work function of Zn–In–Sn–O films

The work function behavior of Zn–In–Sn–O (ZITO) films with various Zn and Sn contents were studied. The work function increased with addition of Zn content. With further increase of Zn contents, the work function gradually decreased. The work function behavior can be investigated by (1) Fermi level position relative the carrier concentration, (2) ionization potential by the surface dipole change. The Fermi level position related the carrier concentration was calculated by Drude parameters, and ionization potential measured by UPS. As results, we confirmed that the work function of ZITO may be linked to changes in ionization potential, not carrier concentration.     

Nanotribology of Mo–Se–C films

Transition metal dichalcogenides with a layered structure are well known for their self-lubricating properties, particularly in a vacuum or dry atmosphere. The macrotribological properties of these films have been studied extensively. However, the tribological behaviour of these films in the nanonewton load range has hardly been reported. Study of tribological properties with load in the nanonewton range is required for applications related to microelectromechanical systems or nanoelectromechanical systems. In view of the above, the hardness, surface force, friction force, etc. of Mo–Se–C films were investigated at an applied load in the nanonewton range using a nanoindenter and atomic force microscopy. The effect of carbon content, applied load and scanning speed on the friction coefficient was determined. Data pertaining to topography, lateral force and pull-off force of various surfaces are illustrated. The observed nanotribological behaviour of these films is analysed in the light of their nanohardness. The results indicate that the friction force of all the films is very low and in general dependent on surface force. However, a film having the highest carbon content exhibits the maximum friction force. With increasing carbon content of the films tested, the hardness increases and wear decreases. The above results pertain to investigations under ambient conditions.     

Synthesis and characterization of highly textured Pt–Bi thin films

Pt–Bi films were synthesized on glass and thermally oxidized silicon substrates by e-beam evaporation and annealing. The structures were characterized using X-ray diffraction (XRD) and transmission electron microscopy/selected area electron diffraction (TEM/SAED) techniques. Single-phase PtBi was obtained at an annealing temperature of 300°C, whereas a higher annealing temperature of 400°C was required to obtain the highly textured γ-PtBi₂ phase. TEM/SAED analysis showed that the films annealed at 400°C contain a dominant γ-PtBi₂ phase with a small amount of β-PtBi₂ and α-PtBi₂ phases. Both the PtBi and γ-PtBi₂ phases are highly textured in these two kinds of film: the c-axis of the hexagonal PtBi phase is mostly in the film plane, whereas the c-axis of the trigonal γ-PtBi₂ phase is perpendicular to the film plane. The electrical resistivity of the film with the γ-PtBi₂ phase was smaller by one order of magnitude than that of the film with the PtBi phase.     

Electrical and optical properties of a-SexTe100–x thin films

The dc electrical conductivity of as deposited thin films of a-Se_xTe_100?x (x=3, 6, 9 and 12) is measured as a function of temperature range from 298 to 383 K. It is observed that the dc conductivity increases exponentially with the increase in temperature in this glassy system. The value of activation energy calculated from the slope of ln σ_dc vs. 1000/T plot, is found to decrease on incorporation of dopant (Se) content in the Te system. On the basis of pre-exponetial factor (σ₀), it is suggested that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. The optical absorption measurements show an indirect optical band gap in this system and it decreases on increasing Se concentration. The optical constants (extinction coefficient (k) and refractive index (n)) do change significantly with the photon energy and also with the dopant Se concentration. The decrease in optical band gap may be due to the decrease in activation energy in the present system. It is also found that the real and imaginary parts of dielectric constants show a significant change with the photon energy as well as with the dopant concentration. With large absorption coefficients and compositional dependence of optical band gap and optical constants (n and k), these materials may be suitable for optical disk applications.     

Structure and magnetic properties of co-sputtered Co–C thin films

We studied the structure and magnetic properties of co-sputtered Co_1−xC_x thin films using a transmission electron microscope (TEM) and a SQUID magnetometer. These properties were found to depend critically on deposition temperature, T_S, and composition, x. Generally, phase separation into metallic Co and graphite-like carbon phases proceeds with increasing T_S and decreasing x. Plan view and cross-sectional TEM images of the films prepared showed that Co grains about 10–20 nm in diameter and 30–50 nm in height are three-dimensionally separated by graphite-like carbon layers 1–2 nm thick. Optimum magnetic properties with saturation magnetization of 380 emu/cc and coercivity of 400 Oe were obtained for a film with x=0.5 and T_S=350°C.     

Determination of the thickness and optical constants of amorphous Ge–Se–Bi thin films

The effect of varying bismuth concentration on the optical constants of amorphous Ge₂₀Se_{80? x} Bi _x (where x = 0, 3, 6, 9 and 12 at%) thin films prepared by thermal evaporation has been investigated. The transmission spectra T(λ) of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. An analysis proposed by Swanepoel [J. Phys. E: Sci. Instrum. 16 (1983) p.1214], based on the use of the maxima and minima of the interference fringes, was applied to derive the real and imaginary parts of the complex index of refraction and also the film thickness. Increasing bismuth content was found to affect the refractive index and extinction coefficient of the Ge₂₀Se_{80? x} Bi _x films. Optical absorption measurements show that the fundamental absorption edge is a function of composition. With increasing bismuth content, the refractive index increases while the optical band gap decreases.     

A comparison study between two types of nuclear detectors having (Metal–Organic thin films–Silicon) and (Metal–Silicon) structures

Nuclear detectors having metal–organic thin film–semiconductor structures have been prepared and tested. The organic thin films (50–200 nm) were thermally sublimed and deposited onto silicon slides (n-type 1000 Ω.cm). The prepared detectors show remarkable performance and their energy resolution was highly improved in comparison to metal–semiconductor (Schottky type) detectors manufactured on identical substrates and under similar conditions.     

Microstructures and soft magnetic properties of as-deposited Fe–Sm–O thin films

The influences of O₂ partial pressure on saturation magnetization, coercivity and effective permeability of the as-deposited Fe–Sm–O thin films, which were fabricated by RF magnetron reactive sputtering method, were investigated. The nanocrystalline Fe_83.4Sm_3.4O_13.2 thin film fabricated at O₂ partial pressure of 5% exhibited the best magnetic softness with a saturation magnetization of 1.43 MA/m, coercivity of 65.2 A/m and effective permeability of about 2600 in the frequency range from 0.5 to 100 MHz. The electrical resistivity of Fe_83.4Sm_3.4O_13.2 was 130 μΩ cm. The microstructures and electrical resistivity were investigated in this work.     

Optical and structural analysis of plasma-treated and annealed Al–Sb bilayer thin films

Aluminum–antimony (Al–Sb) seems to be a promising semiconducting material for high-temperature application especially for transistors and P–N junction diodes and is a highly coefficient solar material. No attempt has been made to study the bilayer diffusion properties of Al–Sb thin film by plasma exposure. In this paper, the characterization of plasma-exposed Al–Sb bilayer thin films is presented. Thin films were coated by thermal vapor coating technique, and after coating, the sample was annealed and exposed with plasma. Results were obtained from optical band gap data and X-ray diffraction for treated and untreated Al–Sb thin films, and these results were compared with annealed Al–Sb thin films.