Preparation and investigation of VOx thin films of n- and p-types

In this work we present first results on the synthesis of vanadium oxide semi-transparent conducting thin films of p- and n-types. The films were deposited by thermal evaporation method in vacuum, on: silicon, glass, sapphire, and gold substrates. Temperature of substrate during deposition was set around 250 °C. As deposited films were of a p-type of conductivity. Thermal annealing at 420 °C of as-deposited films in air at atmospheric pressure resulted in a change in the conductivity type.Optical, electrical and thermal properties of the deposited films were studied. The topography of the films was studied using AFM microscope. P-N structures were created using VO_x films on silicon and glass substrates. Electrical measurements had shown a non-linear behaviour of the samples.     

Magnetic properties of Nd–Fe–B/FeMn multilayer films

[Nd–Fe–B(x nm)/FeMn(d nm)]_n thin films were deposited by magnetron sputtering on Si (100) substrates heated at 650 °C. The influence of the composition and thickness of FeMn layer on the structure and magnetic properties of Nd–Fe–B films are investigated. The Nd–Fe–B/FeMn multilayer films present an enhanced coercivity and a reduced saturation magnetization, in comparison with those of a Nd–Fe–B single layer. The coercivity of [Nd–Fe–B(x nm)/FeMn(5 nm)]_n films increases with increasing the period number of FeMn layer for the same thickness of magnetic layer, while the coercivity in [Nd–Fe–B(50 nm)/FeMn(5 nm)]_n films increases with decreasing the period number of Nd–Fe–B/FeMn bilayers. The coercivity H_c of about 17.2 kOe is achieved in the Nd–Fe–B(50 nm)/FeMn(5 nm) film.     

Growth and characterization of La5/8Sr3/8MnO3 thin films prepared by pulsed laser deposition on different substrates

Colossal magnetoresistance La_5/8Sr_3/8MnO₃ (LSMO) thin films were directly grown on MgO(100), Si(100) wafer and glass substrates by pulsed laser deposition technique. The films were characterized using X-ray diffraction (XRD), field emission-scanning electron microscope and atomic force microscopy (AFM). The electrical and magnetic properties of the films are studied. From the XRD patterns, the films are found to be polycrystalline single-phases. The surface appears porous and cauliflower-like morphology for all LSMO films. From AFM images, the LSMO films deposited on glass substrate were presented smooth morphologies of the top surfaces as comparing with the films were deposited on Si(100) and MgO(100). The highest magnetoresistance (MR) value obtained was ?17.21 % for LSMO/MgO film followed by ?15.65 % for LSMO/Si and ?14.60 % for LSMO/Cg films at 80 K in a 1T magnetic field. Phase transition temperature (T_P) is 224 K for LSMO/MgO, 200 K for LSMO/Si and above room temperature for films deposited on glass substrates. The films exhibit ferromagnetic transition at a temperature (T_C) around 363 K for LSMO/MgO, 307 K for LSMO/Si and 352 K for LSMO/Cg thin film. T_C such as 363 and 352 K are the high T_C that has ever been reported for LSMO films deposited on MgO substrate with high lattice mismatch parameter and glass substrates with amorphous nature.     

Synthesis of nanocrystalline iron oxide ultrathin films by thermal decomposition of iron nitropruside: Structural and optical properties

Ultrathin films of nanocrystalline α-Fe₂O₃ have been deposited on glass substrates from an inorganic precursor, iron nitropruside. This is a novel route of synthesis for iron oxide thin films on glass substrates, by annealing the precursor thin film in air at 650 °C for 15 min. The films were characterized using TG-DTA analysis, X-ray diffraction, UV-visible, FESEM, AFM and Raman measurements. X-ray diffraction and Raman analyses revealed that the deposited films contain α-phase of Fe₂O₃ (hematite). The synthetic route described here provides a very simple and cost-effective method to deposit α-Fe₂O₃ thin films on glass substrates with band gap energy of about 2.75 eV. The deposited films were found to show catalytic effect for the photo-degradation of phenol.     

Photocatalyst TiO2–Co: the effect of doping depth profile on methylene blue degradation

In this work, we study the effect of doping depth profile on the photocatalytic and surface properties of TiO₂ films. Two thin film layers of TiO₂ (200 nm) and Co (5 nm), respectively, were deposited by physical evaporation on glass substrate. These films were annealed for 1 s at 100 and 400 °C and the Co layer was removed by chemical etching. Atomic force microscopy (AFM) phase images showed changes in the surface in function of thermal treatment. The grazing-incidence X-ray fluorescence (GIXRF) measurements indicated that the thermal treatment caused migration of Co atoms to below the surface, the depths found were between 19 and 29 nm. The contact angle showed distinct values in function of the doped profile or Co surface concentration. The UV–vis spectra presented a red shift with the increasing of thermal treatment. Photocatalytical assays were performed by methylene blue discoloration and the higher activity was found for TiO₂–Co treated at 400 °C, the ESI-MS showed the fragments formed during the methylene blue decomposition.     

Tunable In-Plane Anisotropy in Amorphous Sm–Co Films Grown on (011)-Oriented Single-Crystal Substrates

Amorphous Sm–Co films with uniaxial in-plane anisotropy have great potential for application in information-storage media and spintronic materials. The most effective method to produce uniaxial in-plane anisotropy is to apply an in-plane magnetic field during deposition. However, this method inevitably requires more complex equipment. Here, we report a new way to produce uniaxial in-plane anisotropy by growing amorphous Sm–Co films onto (011)-cut single-crystal substrates in the absence of an external magnetic field. The tunable anisotropy constant, k_A, is demonstrated with variation in the lattice parameter of the substrates. A k_A value as high as about 3.3 × 10⁴ J·m⁻³ was obtained in the amorphous Sm–Co film grown on a LaAlO₃(011) substrate. Detailed analysis indicated that the preferential seeding and growth of ferromagnetic (FM) domains caused by the anisotropic strain of the substrates, along with the formed Sm–Co, Co–Co directional pair ordering, exert a substantial effect. This work provides a new way to obtain in-plane anisotropy in amorphous Sm–Co films.     

Low-temperature processing of thin films based on rutile TiO2 nanoparticles for UV photocatalysis and bacteria inactivation

Using a low-temperature, simple, and economic processing technique, TiO₂ nanoparticles (rutile phase) are immobilized in an inorganic matrix and then deposited on glass for bacteria inactivation in water. Using this low thermal budget method (maximum processing temperature of 220 °C), thin films of immobilized TiO₂ nanoparticles are obtained so that practical water decontamination after UV radiation is possible by avoiding the additional step of catalyst separation from treated water. In order to validate the photocatalytic activities of these TiO₂ nanoparticles (prepared as thin films), they were tested for bacteria inactivation in water under UV–A radiation (λ > 365 nm), while extensive characterizations by dynamic light scattering, X-ray diffraction, ultra violet–visible absorption spectroscopy, fourier-transform infra red spectroscopy, and profilometry were also carried out. Despite previous reports on the low or lack of photocatalytic activity of rutile-phase TiO₂, inactivation of Escherichia coli in water was observed when thin films of this material were used when compared with the application of UV radiation alone. Physical characterization of the films suggests that size and concentration-related effects may allow the existence of photocatalytic activity for rutile-TiO₂ as long as they are exposed under UV–A radiation, whereas no effect on bacteria inactivation was observed for thin films in the absence of TiO₂ or radiation. In brief, a low thermal budget process applied to thin films based on TiO₂ nanoparticles has shown to be useful for bacteria inactivation, while possible application of these films on widely available substrates like polyethylene terephthalate materials is expected.     

Magnetic Perovskite Superlattices Grown by Pulsed Laser Deposition

Magnetic multilayers of (SrRuO₃) _m (SrMnO₃) _n were grown artificially using the pulsed laser deposition technique on (001)-oriented SrTiO₃ substrates. The temperature and magnetic field dependent reisistivity of the superlattices consisting of ferromagnetic (FM) SrRuO₃ and antiferromagnetic (AFM) SrMnO₃ are studied as a function of the SrRuO₃ unit cells. We observed a pinned/biased moment instead of the biased field in the superlattices and we redefine the structure as AFM/FM(Pin)/FM(Free)/FM(Pin) units below a critical field.     

Substrate influence on the morphological and conductive properties of modified iron-phthalocyanine thin films

In this work, molecular thin films prepared with the cyano(phthalocyaninate)iron(III) [PcFeCN] _n macrocycle axially modified with the 1,8-dihydroxyanthraquinone ligand were studied. The films were formed by using electrodeposition and evaporation techniques onto Si(001) and 7059 Corning glass substrates in order to investigate the influence of the substrate and the preparation method on the morphological and conductive properties of the films. In this study, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy and atomic force microscopy (AFM) techniques were employed. From AFM measurements, it was found that the evaporated films exhibited a more regular distribution with low roughness values in contrast with the electrodeposited films. The electrical conductivity results for the evaporated films exhibited semiconductor behaviours with conductivity values at room-temperature of 10⁻⁶ Ω⁻¹cm⁻¹. Better conductivity results were obtained for films onto glass substrates.     

Microstructure, Magnetic and Electronic Transport Properties of Co–TiO2 Nanocomposite Films in Metal Matrix

In this work, Co–TiO₂ metallic composite films with a novel nanostructure have been electrodeposited in potentiostatic regime onto copper substrates, from a solution based on cobalt sulfate containing suspended TiO₂ nanoparticles, with magnetic stirring of the electrolyte. The effect of deposited film thickness on the morphology, microstructure, and composition of the films was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. Functional properties (magnetic and electronic transport) of films with different thicknesses were studied in a view to find out the possibility for some technological applications. Nanocomposite Co–TiO₂ films contain three main phases: hcp Co crystalline grains (9–10 nm average size), TiO₂ nanoparticles (28 nm average diameter) embedded in Co metallic matrix and Co(OH)₂ adsorbed on the crystallite frontiers. The films display hysteresis (coercive field of 7.8÷11.9 kA/m) and significant values of magnetoresistance (with a maximum of ?59 % in the case of 0.07 μm film thickness). These properties can be qualitatively explained both by the elastic spin-dependent scattering of the conduction electrons at the interface between the magnetic Co matrix grains and the nonmagnetic regions, and by occurrence of antiferromagnetic coupling between Co crystallites, favored by inclusion in film of TiO₂ nanoparticles.     

Optical properties of nanostructured ruthenium dioxide thin films via sol–gel approach

High purity ruthenium dioxide (RuO₂) nanoparticles with the average size is about 9 nm in diameter are readily synthesized through a low cost sol–gel method. RuO₂ thin films have been deposited on SiO₂ substrates by sol–gel spin coating techniques at room temperature, followed by annealing at 500 °C for 2 h. The result of X-ray diffraction indicates that the RuO₂ nanoparticles are well crystallized with a rutile tetragonal structure. Morphological of RuO₂ films were characterized using atomic force microscopy (AFM), transmission electron microscopy and high resolution transmission electron microscopy. The AFM images confirmed a spherical-shape nanoparticles with diameter of 9 nm and surface roughness of 12 nm of the films. The optical absorption studies showed the presence of direct band transition with band gap equal to 1.87 eV. Refractive index and dielectric properties of the films were estimated from optical measurements. Room temperature photoluminescence of RuO₂ film showed an emission band at 432 nm.     

Effect of oxygen on the surface morphology of CuGaS2 thin films

Since the effect of oxygen is very significant during the heat treatment of the thin films, we study the effect of this during the annealing of CuGaS₂ thin films by two different types. In this study, CuGaS₂ thin films were deposited by vacuum thermal evaporation of CuGaS₂ powder on heated glass substrates at 200 °C submitted to a thermal gradient. The films are annealed in air and under nitrogen atmosphere at 400 °C for 2 h. In order to improve our understanding of the influence of oxygen during two annealing types on device performance, we have investigated our CuGaS₂ material by X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray analysis (EDX) and spectrophotometry. A correlation was established between the surface roughness, growth morphology and optical properties, of the annealed CuGaS₂ thin films. It was found that annealing of CuGaS₂ film in nitrogen atmosphere leads to a decrease of the mean grain size and to an evolution of a (112) preferred film orientation. Annealing in air results in the growth of oxide phases such as CuO and modifies the films structure and their surface morphology.     

Nano structure formation in vacuum evaporated zinc phthalocyanine (ZnPc) thin films

In this article we have reported the nano structure formation in ZincPhthalocyanine (ZnPc) thin films coated on glass substrates by thermal evaporation method. The structure of the films was analyzed by an X-ray diffractometer (using Cu K_α radiation with λ = 1.5418 Å). It reveals that the vacuum evaporated ZnPc thin films are having nano particles in its structure. It is confirmed by the scanning electron microscopy (SEM), X-ray diffraction (XRD) and optical absorption studies. The results of the XRD, SEM and AFM studies have been discussed in this article. A metastable α to the stable β-phase transformation has been observed when the films are coated at higher substrate temperatures. The core structure of the ZnPc macrocycle is formed by four isoindole units endowing the molecule with a two-dimensional conjugated π electron system.     

Thermal sensor properties of PANI(EB)-CSA<Subscript>x</Subscript> (X = 0.4 ±0.1 mol) polymer thin films

Films of polyaniline(EB) doped with camphor sulfonic acid (CSA) fromm-cresol on glass substrates exhibit considerable metallic properties. Such polymer metallic films have thermal sensitivity superior to ceramic metal (Cermet) films, prepared by metallo organic deposition (MOD) technique on silicon substrates. These PANI(EB)-CSA_x (X = 0.5, 0.4, 0.3 mol) polymer films were developed through controlled temperature atmosphere 60 ±2°C for 60 min, and with the help of temperature dependence of resistivity (ρ) values, high temperature coefficient of resistance (TCR) i.e. a values, and figure of merit (ρα) values of these films, thermal sensitivity were compared from that we observed. Among the three doping ratios the PANI(EB)—CSA_{0.3 mol}i film (4.4 ⧎m thick) on glass substrate resistivity (ρ) values in the range of 838–1699 Ω.⧎m with high TCR i.e. a = 10,291 ppm/°C and figure of merit (ρα) value in range of 8.62-17.48 Ωm/dgC seems to be the best. This paper deals with these superior thermal-sensing properties together with optical studies and surface topography by atomic force microscopy (AFM). These polymer films offer design advantages in developing ‘thin film polymer thermal sensor’.     

Optical Study of the Strain Effects on Pr0.6Ca0.4MnO3 Thin Films

We report a systematic Raman and infrared (IR) study of Pr_0.6Ca_0.4MnO₃ (PCMO) thin films grown on SrTiO₃ (STO) and LaAlO₃ (LAO) substrates (PCMO/STO and PCMO/LAO, respectively). The measurements were performed for a temperature range 78 K<T<295 K. The A_g(2) tilting Raman mode has shown substrate dependence, implying an effect of the lattice mismatch on the tilting angle, as the MnO₆ octahedra are tilted to optimize the structure. The Raman and the IR modes are affected by the different kinds of strain induced by different substrates. In the mid-IR (MIR) region, there are broad bands implying that FM and AFM clusters are formed and competing even at RT.     

Formation of β-FeSi2 thin films on non-silicon substrates

β-FeSi₂ films were prepared on non-silicon substrates by sputtering. The crystalline growth, stress induced cracks and adhesive ability to the substrate were investigated on substrate temperature and thermal expansion coefficient of substrate materials. It was found that crack formation in β-FeSi₂ films was dependent on the thermal expansion coefficients of CaF₂, MgO and quartz glass insulating materials. High-density cracks were observed from β-FeSi₂ films on CaF₂ and quartz glass substrates with large difference of the thermal expansion coefficient between β-FeSi₂ film and substrate materials, and it was crack-free on MgO substrate with a thermal expansion coefficient close to that of β-FeSi₂ films. Polycrystalline β-FeSi₂ films grew on Mo, Ta, W, Fe and stainless steel (SS) substrates at low substrate temperature around 400 °C. There was no α-FeSi₂ phase confirmed in the films. All the films had continuous structures without noticeable cracks even though they have different thermal expansion coefficients. Capacity-voltage measurements showed that β-FeSi₂ films formed on SS substrates has n-type conductivity, with residual carrier concentrations of about 1.3∼6.4 × 10¹⁸ cm^− 3. Auger electron spectroscopy depth profile measurements identified homogeneous distribution of Fe and Si atoms in the film region, but with a large interface region between the film and the substrate.     

In situ probe nanophase transition in nanocomposite using thermal AFM

Nanocomposites made from inorganic nanoparticles and polymers have many applications in optics, electronics and biomaterials. However, the glass transition temperature (T_g) of a nanocomposite is very difficult to measure accurately by conventional thermal analysis such as DSC or TMA when the concentration of the nanoparticle reaches a threshold of the percolation network. At this threshold stage, the phase transition in the nano domains of the matrix is too small to be detected by macroscale thermal analysis. We have developed a methodology basis on thermal atomic force microscope (AFM) to monitor the nanophase transition of the nanocomposite in situ upon heating. This method has demonstrated the capability in determining the T_g of a nanocomposite made by spherical SiO₂ nanoparticles dispersed in polyacrylate. The threshold of the percolation network of this nanocomposite is at 40 wt% of SiO₂ nanoparticles according to the results of refractive index, AFM, nanoindentation, DSC, TMA and TGA.     

Morphological study by XPS and AFM of wide band gap β-ln2S3 thin films synthesized by a dry physical process

Wide band gap -ln₂S₃ thin films have interesting properties to substitute CdS as the buffer layer in thin film solar cells. They have n-type conductivity and their optical band gap is about 2.8 eV. In this paper, -ln₂S₃ thin films deposited on smooth glass and on rough SnO₂-coated glass substrates have been morphologically studied by X-ray photoelectron spectroscopy (XPS) and by atomic force microscopy (AFM). The results obtained show that on each substrate the films are continuous without any pinholes and cracks. Films deposited on glass cover homogenously the whole surface of the substrate. In the case of SnO₂ substrates, the material deposited preferentially fills the hollows of the rough surface inducing a decrease of its roughness value. It is shown that these morphological properties are very promising for buffer layer application.     

Negative-differential-resistance effects in amorphous CuInS2 thin film

The microstructure and the optical properties of amorphous CuInS₂ thin films deposited on glass substrates by a single source thermal evaporation technique, are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission and reflection measurements. Amorphous CuInS₂ thin films sandwiched between gold and copper electrodes, show current-controlled electronic switching. The switching is believed to be associated rather with electronic processes than the thermal ones.     

Preparation of smooth potassium hexatitanate nanofilms by sol–gel method

New nanosmooth potassium hexatitanate films have been prepared on crystalline Si (111) and ITO glass substrates by sol–gel method using Ti(n-OC₄H₉)₄ and CH₃COOK as precursors. Atomic force microscopy (AFM) topographic images were analyzed to select the optimal preparation conditions for the films. It is shown that the films consist of flat particles with the ratio of diameter to height around 11. The root mean square (RMS) roughness of the films based on the measurement of an area of 2,000 nm × 2,000 nm in AFM images is 6.4 nm. The crystal growth process of potassium hexatitanate film was characterized by XRD, Raman spectra, and TEM. The results showed that the crystal growth of potassium hexatitanate nanofilm is a confined growth mechanism. Electrochemical measurements demonstrated that the photocurrent of potassium hexatitanate film electrode is more stable than that of TiO₂ film electrode.