Characterization of ZrO2 and SiC ceramic thin films prepared by electrostatic atomization

ZrO₂ and SiC ceramic thin films and their bilayer have been successfully prepared by a newly developed electrostatic atomization technique. This technique can generate fine spray of ceramic suspensions in a micrometer sized range with a narrow size distribution which is crucial for preparation of uniform thin films of these ceramic materials. Compared to some other thin film deposition techniques, such as Chemical vapour deposition (CVD), physical vapour deposition (PVD) and plasma spray (PS) etc. the thin film deposition process using electrostatic atomization is not only cheap but also controllable. The prepared ZrO₂ and SiC thin films were investigated using scanning electron microscopy (SEM) and energy dispersion analysis (EDA) techniques. These thin films were observed to be homogenous with a particle size less than 10 m. The ZrO₂-SiC bilayer was found to have an abrupt interface, implying that the deposition process is controllable and also that functionally graded ceramic/ceramic materials can be prepared in this way if the thickness of each layer is accurately controlled.     

Chemical solution method for fabrication of nanocrystalline iron(III) oxide thin films

A chemical solution technique for preparation of nanocrystalline iron(III) oxide thin films is developed. The deposition process is essentially based on the thermal decomposition of urea. The as-deposited and post-deposition heat-treated materials were characterized by X-ray analysis and Fourier transform infrared (FTIR) spectroscopy. Basic optical and electrical investigations were also performed. X-ray analysis confirmed that post-deposition heat-treated material is nontextured -iron(III) oxide, with an average crystal size of 22 nm. The optical investigations show that the absorption of films (as-deposited and post-deposition treated) gradually decreases with an increase of the wavelength in the 390–820 nm region. The optical band gap for the as-deposited and post-deposition heat-treated films was determined to be 3.2 eV and 2.0 eV, respectively. The obtained -Fe₂O₃ thin films exhibit a rather high resistivity at room temperature. However, our preliminary qualitative investigations have shown that the room temperature resistivity of -Fe₂O₃ thin films is highly sensitive to moisture, indicating their potential applicability in moisture sensing systems.     

Thermal Diffusivity by Modified ac Calorimetry Using a Modulated Laser Beam Energy Source

Modified ac calorimetry, a variation of the Angstrom method, has been shown to be a precise tool for measuring the in-plane thermal diffusivity of thin films (thickness less than 300 m) of a wide variety of materials and layered composites. The property is determined from an analysis of the decay curve of the ac temperature waves generated by irradiation of a specimen using uniform chopped light (at frequencies from 1 to 20 Hz) from a halogen lamp source. To address certain limiting factors, especially to improve the signal-to-noise ratio and to eliminate heat losses, an improved form of measurement instrument has been developed. It is based on the use of a modulated laser beam heating to provide a higher intensity energy source plus a special optical system to ensure that one-dimensional ac temperature wave propagation is obtained. Measurements can now be made using frequencies in the range of 0.01 to 10 Hz, i.e., 10 times lower than in the traditional method. The performance of the improved measurement instrument will be illustrated by results on various materials of known thermal properties such as nickel and stainless steel, proposed reference materials such as a glassy carbon and alumina, plus a comparison of results obtained on CVD diamond films used in an international round-robin series with those obtained by the traditional technique.     

Eco-friendly method to synthesize and characterize 2D nanostructured (1,2-bis(diphenyl-phosphino)ethyl) tungsten tetracarbonyl methyl red/copper oxide di-layer thin films

Three-layer thicknesses (\({T}_{1 }= 50\), \({T}_{2 }= 75\) and \({T}_{3 }= 100\) nm) of 1,2-bis(diphenylphosphino)ethyl tungsten tetracarbonyl methyl red (DPE-W-MR) were deposited onto the CuO thin film (50 nm) to produce DPE-W-MR/CuO di-layer thin films by sol–gel spin-coating technique. The composition and the chemical structure of the as-prepared thin films were characterized using various techniques including elemental analysis, Fourier transform infrared spectroscopy, \(^{1}\hbox {H}\)-NMR and X-ray diffraction (XRD). Scanning electron microscopy was used to investigate the size and shape of the CuO nanoparticles and the fabricated thin films. The films are crystalline as evidenced by the XRD pattern and DPE-W-MR has an orthorhombic crystal system. The crystallite size was calculated from an analysis of the line broadening features using the Scherrer formula; the average crystallite sizes of DPE-W-MR/CuO di-layer thin films are 52.92, 56.24 and 72.26 nm for \({T}_{1}\), \({T}_{2}\) and \({T}_{3}\), respectively. Thermogravimetric analysis and the thermal curve of DPE-W-MR complex were studied. Optical properties of DPE-W-MR/CuO di-layer thin films are discussed. The optical band gap energies of DPE-W-MR di-layer thin films/CuO decreased (2.25, 2.1 and 1.88 eV) as the film thickness increased (from \({T}_{1}\) to \({T}_{3})\). Based on the optical results and the quantum confinement effects, the DPE-W-MR/CuO di-layer thin films may be candidates as semiconductor materials for optoelectronic devices.     

Strain and carrier-induced coexistence of topologically insulating and superconducting phase in iodized Si(111) films

The importance of silicon in modern electronic devices has led to considerable interest in exploring the unconventional electronic properties of Si-based materials for future applications in spintronics and quantum computing. Here, using density functional theory, we present the results of a systematic study of the effect of strain on Si(111) thin films whose surfaces are functionalized with iodine. Films with an odd number of layers under biaxial strain are found to undergo a phase transition from a normal insulator to a topological insulator and ultimately to a metal. The spin-orbit coupling-induced topologically nontrivial band gap at the Γ point is found to be as large as 0.50 eV, which not only surpasses that of other Si-based topological materials, it is also large enough for practical realization of quantum spin Hall states at room temperature. No such nontrivial states are found in films with an even number of layers. Mechanisms for such a strain-induced transition are illustrated by a tight-binding model composed of s, p_x, and p_y orbitals. Equally important, we predict that iodized silicene, when stretched and hole-doped, would be a phonon-mediated superconductor with a critical temperature of 9.2 K. This coexistence of a topological insulator and a superconducting phase in a single material is unusual; it has the potential for applications in electronic circuits and for the realization of Majorana fermions in quantum computations.

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Effect of $$\hbox {Ar}^{+}$$ ion implantation on the properties of electrodeposited CdTe thin films

Semiconducting nanomaterials of II–VI groups are the key elements of continued technological approaches made in the field of optoelectronic, magnetic and photonic devices due to their size-dependent properties. Ion beams create changes in the material along their track; this not only exhibits excellent properties but also tailors new materials. This article reports the effect of \(\hbox {Ar}^{+}\) ion implantation on the properties of cadmium telluride thin films of about 80 nm thickness. The implantation parameters were adjusted based on computer-aided learning using SRIM (stopping and range of ions in matter) software. The CdTe thin films were deposited by electrodeposition method on ITO substrate. Thin films of CdTe are exposed to \(\hbox {Ar}^{+}\) ions with different fluencies of \(1 \times 10^{15}\), \(5 \times 10^{15}\) and \(1 \times 10^{16} \, \hbox {ions cm}^{-2}\) at Ion Beam Centre, Kurukshetra University, Kurukshetra, India. After implantation, the films were characterized using UV–visible spectroscopy, photoluminescence (PL) and a four-probe set-up with a programmable current–voltage (I–V) source metre. The scanning electron microscopy of pristine film showed smooth and uniform growth of sphere-shaped grains on substrate surface. From optical studies, the values of optical band gap for as-deposited and argon-ion-implanted thin films were calculated. It was found that values of optical band gap decreased with the increase in fluence of ion beam. From PL studies it was found that the intensity got increased with ion fluence. A considerable increase in current was noticed from I–V measurements with ion fluence after implantation. Different properties of pre- and post-implanted thin films are studied.     

Microwave properties of highly oriented YBa2Cu3O7-δ superconducting thin films

We have performed millimeter-wave frequency (94 GHz) measurements on high-quality YBa₂Cu₃O₇- superconducting films on yttrium-stabilized (100) ZrO₂ and MgO substrates. The 0.2m thin films fabricated by magnetron sputteringin situ with the YBa₂Cu₃O₇- powders as target exhibit superconducting transition temperatures up to 88 K. The critical current density of 6×10⁵ A/cm² at 77 K and the X-ray diffraction spectrum as well as scanning electron microscope photographs indicate these thin films are fullyc-axis oriented, extremely high in density, and universally homogeneous. Millimeter-wave surface resistances have been measured on a hemisphere open resonator in the temperature range of 20 K toT _c and beyond. The surface resistance at 94 GHz and 77 K for these films is found to be about 30 m, nearly 1/4 that for copper, and a drop of two orders in the surface resistance within 4 K is observed, which indicates that these films are good materials for applications in the millimeter-wave range, especially for fabricating microwave devices. We observed such low surface resistance in these thin films due to the near absence of grain and phase boundaries coupled with a high degree of crystalline orientation.     

Co-electrodeposition and Characterization of Cu (In, Ga)Se2 thin films

Cu (In, Ga)Se₂(CIGS) thin films were electrodeposited on Mo-coated soda lime glass substrate by the electrodeposition technique. The chemical bath for co-electrodeposition was prepared from copper chloride, indium chloride, gallium chloride and selenous acid. The effect of different chemical bath concentration of the CIGS films on the microstructure and electric properties has been investigated. The microstructure and morphology of the selenized CIGS thin films were investigated by X-ray diffraction and scanning electron microscopy. The composition of the selenized CIGS thin films were characterized by energy dispersive spectroscopy. Hall coefficient, Conductivity and Mobility of the selenized CIGS thin films were measured by ACCENT HL5500 Hall System. The results indicate CIGS thin films deviate little from the ideal stoichiometric one and single chalcopyrite structure. At room temperature, electrical conductivity, Hall mobility and charge-carrier concentration of the films vary from 49.63 to 64.56 ( cm)^‒1,271 to 386 cm²V^‒1 s^‒1, 8.026 × 10¹⁷ to 1.4 87×10¹⁸ cm^‒3, respectively, and are dependent on the composition of the films.     

Preparation of highly oriented thin film exhibiting transparent conduction by the sol-gel process

Highly oriented thin films exhibiting transparent conduction aluminium-doped ZnO (AZO), were prepared by a spin-coating method. The effects of the solvents on the preparation and electrical properties of the thin films were examined. The thin films were formed on quartz glass substrates by spin-coating into a selected solution and calcining at 700 °C for 5 h. The thin films had a resistivity of ( cm)=1.5 after heat treatment in an air atmosphere, and 1.5 × 10^–3 cm in a reducing atmosphere, and a transmission of about 85% in the visible light region. The differences in the high orientation and the conductivities were attributed to a chelate formation in the aluminium-doped ZnO due to the solvent effect.     

Preparation and optical properties of organic/inorganic nanocomposite materials by UV curing process

In this study, photo-polymerized poly(acrylic)/silica hybrid thin films were prepared from various acrylic monomers and monodispersed colloidal silica with the coupling agent, 3-(trimethoxysilyl)propyl methacrylate (MSMA). The silica content in the hybrid thin films varied from 0 to 50 wt.%. The experimental results show that the particle size of silica in hybrid films could be effectively controlled at 15–20 nm as the weight ratio of MSMA to colloidal silica is higher than 0.68 and 0.60 for the poly(methyl methacrylate)/silica (US) and poly(ethylene glycol dimethacrylate-trimethylolpropane trimethacrylate)/silica (UDT) hybrid materials, respectively. The polymerization conversion for US and UDT hybrid materials could reach to 100% and 94.5%, respectively. The comparison of surface roughness with the film thickness is less than 0.10%, indicating the excellent surface planarity of the prepared hybrid thin films. Besides, the prepared hybrid films from the crosslinked acrylic polymer moiety show much better film uniformity, thermal stability and mechanical properties than those obtained from poly(methyl methacrylate). The refractive index decreases with increasing the silica content in the hybrid films. Excellent optical transparency is obtained in the prepared hybrid films. These results show that the prepared hybrid thin films have potential applications as passive films for optical devices.     

Improved electrochemical performance of nitrocarburised stainless steel by hydrogenated amorphous carbon thin films for bone tissue engineering

In this study, hydrogenated amorphous carbon thin films, structurally similar to diamond‐like carbon (DLC), were deposited on the surface of untreated and plasma nitrocarburised (Nitrocarburizing‐treated) stainless steel medical implants using a plasma‐enhanced chemical vapour deposition method. The deposited DLC thin films on the nitrocarburising‐treated implants (CN+DLC) exhibited an appropriate adhesion to the substrates. The results clearly indicated that the applied DLC thin films showed excellent pitting and corrosion resistance with no considerable damage on the surface in comparison with the other samples. The CN+DLC thin films could be considered as an efficient approach for improving the biocompatibility and chemical inertness of metallic implants.Inspec keywords: tissue engineering, bone, biomedical materials, electrochemistry, amorphous state, carbon, hydrogen, thin films, plasma CVD, adhesion, corrosion resistance, surface hardeningOther keywords: electrochemical performance, plasma nitrocarburised stainless steel medical implants, hydrogenated amorphous carbon thin films, bone tissue engineering, plasma‐enhanced chemical vapour deposition method, adhesion, corrosion resistance, biocompatibility, chemical inertness, metallic implants, C:H     

Penetration depth variation in high quality YBaCuO thin films

We report results obtained on state-of-the-art YBCO thin films prepared by pulsed laser deposition on LaAlO ₃ substrates, using samples as similar as possible in two different experimental set-ups: a surface impedance measurement on 4000 Å thick films using a parallel plate resonator (10 GHz), and a far infrared transmission (100-400 GHz) measurement which requires thinner (1000 Å) samples. The measurements show a reduction of the penetration depth slope dMdT with improving quality of the thin films, which exhibit a low temperature scattering rate and residual surface resistance, comparable to single crystals. A linear fitting to the (T) experimental results yields d/dT=2 Å/K in both experiments in the low frequency limit.     

Buffer layers for high-Tc thin films on sapphire

Buffer layers of various oxides including CeO₂ and yttrium-stabilized zirconia (YSZ) have been deposited onR-plane sapphire. The orientation and crystallinity of the layers were optimized to promote epitaxial growth of YBa₂Cu₃O_7– (YBCO) thin films. An ion beam channeling minimum yield of 3% was obtained in the CeO₂ layer on sapphire, indicating excellent crystallinity of the buffer layer. Among the buffer materials used, CeO₂ was found to be the best one for YBCO thin films onR-plane sapphire. HighT _c andJ _c were obtained in YBCO thin films on sapphire with buffer layers. Surface resistances of the YBCO films were 4 m at 77 K and 25 GHz.     

Growth and Characterization of TlBaCaCuO Thin Films

We discuss two methods tor the ex-situ furnace growth of pure TIBaCaCuO superconducting thin films on LaAlO₃(100) substrates. The traditional approach of crucible processing is used to grow high-quality films of several of the TIBaCaCuO phases. Two-zone processing promises greater thermodynamic control, yet film properties from optimized films are not as good as those grown from crucibles. The transport kinetics of Tl-oxide vapor from a source to the film surface appears to be a dominant factor. The best results are from single-phase Tl-1212 and Tl-2212 thin films. T_c's are high and sharp, J_c's > 1 × 10⁷ A/cm² at 5 K, and surface morphologies are relatively smooth.     

Intermediate state of thin superconductors

The purpose of this study was to examine the state of a thin type-I superconductor in a magnetic field to determine its dependence on the specimen thickness and on the value of the Ginzburg-Landau parameter . Three materials (aluminum, indium, and In_0.99Pb_0.01) with values of the Ginzburg-Landau parameter ranging from 0.19 to 0.34 were studied. Specimen thicknesses ranged from 200 to 200,000 Å. All of the materials studied were type-I or nonlocal superconductors in the bulk. Yet, it has been predicted that they would behave in ways characteristic of type-II or local superconductors if the specimen were sufficiently thin. For intermediate thicknesses the specimens were expected to be in one of many possible states. We have inferred from critical field studies that the structure of the intermediate state in thin type-I superconductors is equivalent to the type-II vortex state for very thin films (d ₀), and to the type-I macroscopic domain state for very thick films d 2(t). For thicknesses between these limits the intermediate-state structure takes on many forms as the area of each normal domain and the amount of flux threading it increases with increasing thickness.Work supported in part by the Army Research Office (Durham) under Grant No. DAHC04-70-G-0009 and also a grant from the Research Foundation, State University of New York.     

Epitaxial growth and magnetic properties of <Emphasis Type="Italic">h</Emphasis>-LuFeO<Subscript>3</Subscript> thin films

In this paper, the epitaxial hexagonal LuFeO₃ (h-LuFeO₃) thin films with c-axis-oriented single phase, smooth surface were grown on YSZ (111) substrates by pulsed laser deposition method. Furthermore, a structural distortion of increased lattice constant of c is found in the epitaxial h-LuFeO₃ thin films. Moreover, the epitaxial h-LuFeO₃ thin films show room-temperature ferromagnetism. The coercive field and remnant magnetization of the epitaxial h-LuFeO₃ thin film decrease with the increase in the test temperature from 50 to 300 K. The study would be of benefit to the room-temperature single-phase multiferroic materials.     

Crystalline characterization by Rutherford backscattering spectrometry and electron channelling of in situ grown YBa2Cu3O7 thin films deposited on (1 0 0) MgO by d.c. sputtering or laser ablation

YBa₂Cu₃O₇ (YBCO) superconducting thin films have been grown in situ on single-crystal (1 0 0) MgO substrates by single target d.c. sputtering or laser ablation. The films were highly textured, with full c-axis orientation, as shown by standard –2 X-ray diffractometry. The inplane structure of the films was characterized by reflection high energy electron diffraction (RHEED), oscillating single-crystal photographs, Rutherford backscattering spectrometry (RBS) and by electron channelling patterns (ECP). According to the results obtained from all these methods the films were found to be single-crystal-like. Channelling RBS experiments were carried out in order to provide additional information on the crystal quality, quantitatively evaluated from the _min values:for samples deposited in optimized conditions, we have found these values on sputtered films as well as on laser ablated films deposited on (1 0 0) MgO substrates to be close to that of the virgin substrate. These values strongly depend on the deposition temperature, in good agreement with ECP data. On the other hand, RBS analysis gives access to the composition of the thin films and in addition the in-depth homogeneity in composition was checked by secondary ion mass spectrometry (SIMS).     

Effect of excess Bi content on electrical properties of BiFe<Subscript>0.95</Subscript>Cr<Subscript>0.05</Subscript>O<Subscript>3</Subscript> thin films

The Bi_1?+?xFe_0.95Cr_0.05O₃ (BFCO) (x?=?0, 5, 10, 15 and 20%) thin films are fabricated on FTO/glass substrate using a chemical solution deposition method and sequential-layer annealing process. The effects of the excess Bi content on crystalline structure, morphology, and electrical performance of BFCO thin films are investigated. All the BFCO thin films are crystallized into polycrystalline perovskite structure and belonging to the space group of R3c. The BFCO thin films with 5 and 10% excess Bi contents possess no impurity phase. Especially, a dense surface morphology and columnar crystal structure can be obtained for the film with 5% excess Bi content. Especially, the one possesses superior ferroelectricity with a relative high remnant polarization (P _r) of 69.8 µC/cm² and low coercive electric field (E _c) of 291 kV/cm at 1 kHz due to the relatively low leakage current density of 3.04?×?10^??5 A/cm² at 200 kV/cm.     

Preparation and characterization of radio-frequency-sputtered Ba2Si2TiO8 thin films

Radio-frequency-sputtered barium titanium silicate (BST, Ba₂Si₂TiO₈) thin films were grown on crystalline Si (100) substrates and were characterized using wavelength-dispersive spectrometry (WDS), X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM), and diagonal techniques for dielectric properties. The chemical compositions of the films increasingly deviated from stoichiometry with film thickness. At the initial stage of deposition the grain configuration is dependent on the Si substrate texture. XRD analysis indicates that the BST films deposited at an optimum substrate temperature of 845 °C were strongly c-axis oriented, and that the film orientation is manipulated by substrate temperature and supersaturation. The corresponding film-growth rate in the direction normal to the film surface at 845 °C was 1.95 nm min^–1 at the initial stage, and decreased with sputtering time. The as-deposited films have a room-temperature bulk resistivity of 1.8 ×10⁷ m in the direction of thickness and an isotropic surface resistivity of 1.5×10³ m. The high-frequency relative dielectric constant, 0.05 at frequencies higher than 9 MHz, is lower than that of many typical piezoelectric materials. The high-frequency impedance character is typical of piezoelectric materials, giving a minimum impedance frequency of 9.0 MHz and a serial resonant frequency at about 9.5 MHz.     

A Novel Method for Determination of the Thermal Diffusivity of Thin Films Using a Modulated CO<Subscript>2</Subscript> Laser

The thermal diffusivity of thin metal films has been measured by combining a fast infrared radiation thermometer with a mercury cadmium telluride (MCT) detector and a CO₂ laser modulated at a radio frequency up to 2 MHz. The laser output beam modulated by an acousto-optic modulator (AOM) is directed to the front surface of the blackened copper thin film (10m thick, 9.5 mm in diameter). The thermal radiation from the back surface of the sample is detected. From the observed phase delay in the detected signal of 0.68 radian to the input laser beam, the thermal diffusivity is determined to be 1.11 × 10^-4m²·s^-1, which agrees well with the value of 0.99 × 10^-4m²·s^-1 calculated from literature results. The method is generally applicable for measurements of thermal properties of nano/micro materials.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.