Microstructural, mechanical and magnetic properties of shape memory alloy Ni55Mn23Ga22 thin films deposited by radio-frequency magnetron sputtering

The near-stoichiometric Ni₂MnGa ferromagnetic alloys are one of the smart materials, that are of a great interest when they are deposited as a thin film by r.f. sputtering. These thin films of shape memory alloys are prospective materials for micro and nanosystem applications. However, the properties of the shape memory polycrystalline thin films depend strongly on their structure and internal stress, which develop during the sputtering process as well as during the post-deposition annealing treatment. In this study, about 1 μm Ni₅₅Mn₂₃Ga₂₂ thin films were deposited in the range 0,45 to 1,2 Pa of Ar pressure and P = 40 to 120 W. Their composition, crystallographic structure, internal stress and stress gradient, indentation modulus, hardness, deflection induced by magnetic field and magnetic properties were systematically studied as a function of the temperature of the silicon substrate ranging from 298 to 873 K and the vacuum annealing treatment at 873 K for 21,6 ks and 36 ks. A silicon wafer having a native amorphous thin SiO_x buffer layer was used as a substrate. This substrate influences the microstructure of the films and blocks the diffusion process during the heat treatment.The crystal structure of the martensitic phase in each film was changed systematically from bct or 10 M or 14 M. In addition, the evolution of the mechanical properties such as mean stress, stress gradient, roughness, hardness and indentation modulus with the temperature (of substrate or of heat treatment) were measured and correlated to crystal structure and morphology changes.Moreover, it has been shown that it is necessary to associate a high temperature (873 K) annealing during a long time (21 ks and 36 ks) to obtain good ferromagnetic properties. Thus, for the well annealed films (36 ks at 873 K) the magnetostrain is about - 170 ppm for a magnetic field of 1 MA m^- 1 applied along the beams.As a conclusion, the response of free-standing magnetic shape memory films to a magnetic field of 0,2 MA m^- 1 depends strongly on the martensitic structure, internal mechanical stress (mean and gradient) and magnetic properties. The free-standing annealed film at 873 K for 36 ks points out a considerable magnetic actuation associated with bct or 10 M or 14 M martensitic structures.     

Electrochemical performance of potentio-dynamically deposited Co<Subscript>3</Subscript>O<Subscript>4</Subscript> electrodes: influence of annealing temperature

Co₃O₄ thin films were deposited potentiodynamically on to the stainless steel substrate. Prepared samples were annealed within the temperature range 473 K to 873 K by the interval of 100 K. XRD study reveals cubic crystal structure of Co₃O₄. FE-SEM showed compact agglomerated granular type morphology. Electrochemical characterization of electrodes showed pseudo capacitive behavior. Maximum value of specific capacitance (441.17 F/g) was achieved at the scan rate 2 mV/s in 1 M KOH with 87.88% stability. Charge–discharge curves showed nonlinear behavior and used to calculate the specific energy, specific power and columbic efficiency which were 20.98 W/kg, 15.96 kW/kg and 86.63% respectively. EIS of complex impedance spectra showed internal resistance ~0.9435 Ω.     

Rietveld analysis of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin films obtained by RF-sputtering

Calcium copper titanate, CaCu₃Ti₄O₁₂, CCTO, thin films with polycrystalline nature have been deposited by RF sputtering on Pt/Ti/SiO₂/Si (100) substrates at a room temperature followed by annealing at 600 °C for 2 h in a conventional furnace. The crystalline structure and the surface morphology of the films were markedly affected by the growth conditions. Rietveld analysis reveal a CCTO film with 100 % pure perovskite belonging to a space group Im3 and pseudo-cubic structure. The XPS spectroscopy reveal that the in a reducing N₂ atmosphere a lower Cu/Ca and Ti/Ca ratio were detected, while the O₂ treatment led to an excess of Cu, due to Cu segregation of the surface forming copper oxide crystals. The film present frequency -independent dielectric properties in the temperature range evaluated, which is similar to those properties obtained in single-crystal or epitaxial thin films. The room temperature dielectric constant of the 600-nm-thick CCTO films annealed at 600 °C at 1 kHz was found to be 70. The leakage current of the MFS capacitor structure was governed by the Schottky barrier conduction mechanism and the leakage current density was lower than 10^?7 A/cm² at a 1.0 V. The current–voltage measurements on MFS capacitors established good switching characteristics.     

Effect of PbO<Subscript>2</Subscript> on the Formation of YBCO Films Fabricated Via Sedimentation Deposition and Partial Melting Technique

PbO₂ addition in sedimentation deposition prepared films was investigated by SEM, EDX, and RT measurements to determine its effect on the formation of YBCO films. YBCO films on SrTiO₃ (STO) (100) substrates of varying amounts of PbO₂ were partially melted at 980 ^°C, annealed, and oxygenated in flowing oxygen atmosphere. In addition, a YBCO sample partially melted at higher temperature was also done for comparison. From the SEM, EDX, and RT analyses, it was found that the film having 8 wt% PbO₂ produces a film with the highest superconducting transition temperature comparable to that of a YBCO sample partially melted at peritectic point. Moreover, it was observed that addition of PbO₂ enhances matter transport between Y123 particles and lowers the processing temperature for the fabrication of YBCO films via the sedimentation deposition method.     

Effect of particle size on the conductive and electrochemical properties of Li<Subscript>2</Subscript>ZnTi<Subscript>3</Subscript>O<Subscript>8</Subscript>

We have studied the effect of final annealing temperature on the formation of lithium zinc titanate, its electrical conductivity, and its electrochemical performance. Li₂ZnTi₃O₈ has been shown to form in a wide range of annealing temperatures, from 673 to 1073 K. Its particle size increases systematically with increasing annealing temperature, whereas its conductivity decreases. The highest electrochemical capacity at low currents is offered by the materials annealed at 773 and 873 K, and the highest cycling stability is offered by the material prepared at 873 K.     

Structural and optical properties of nanocrystalline WO<Subscript>3</Subscript> thin films

The nanocrystalline WO₃ thin films were deposited by r.f. magnetron sputtering on quartz and p- type Si (100) substrates at a constant power of 25 W and at three different sputtering pressures (0.05, 0.01 and 0.5 mbar) and post annealed at different temperatures. The deposited films were characterized by XRD, UV–VIS spectrophotometry, ellipsometry and atomic force microscopy (AFM). The structural studies from XRD spectra reveals that the films deposited at 0.05 mbar and post annealed at 573 and 673 K have the predominant orthorhombic phase, whereas at 0.1 mbar and 573, 673 K triclinic phase is predominant. When sputtering pressure is at 0.5 mbar the predominant phase is monoclinic when annealed at 473 K and triclinic at 673 K. The optical energy gap is influenced significantly by sputtering pressure and post annealing temperatures. The optical energy gap of the films deposited at higher sputtering pressures and post annealed at lower temperatures is high due to smaller crystallite sizes. The thickness of all deposited films at different conditions is around 200 nm.     

Effects of post-deposition annealing temperature and ambient on RF magnetron sputtered Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> gate on n-type silicon substrate

Samarium oxide (Sm₂O₃) thin films with thicknesses in the range of 15–30 nm are deposited on n-type silicon (100) substrate via radio frequency magnetron sputtering. Effects of post-deposition annealing ambient [argon and forming gas (FG) (90% N₂ + 10% H₂)] and temperatures (500, 600, 700, and 800 °C) on the structural and electrical properties of deposited films are investigated and reported. X-ray diffraction revealed that all of the annealed samples possessed polycrystalline structure with C-type cubic phase. Atomic force microscope results indicated root-mean-square surface roughness of the oxide film being annealed in argon ambient are lower than that of FG annealed samples, but they are comparable at the annealing temperature of 700 °C (Argon—0.378 nm, FG—0.395 nm). High frequency capacitance–voltage measurements are carried out to determine effective oxide charge, dielectric constant and semiconductor-oxide interface trap density of the annealed oxide films. Sm₂O₃ thin films annealed in FG have smaller amount of effective oxide charge and semiconductor-oxide interface trap density than those oxide films annealed in argon. Current–voltage measurements are conducted to obtain barrier heights of the annealed oxide films during Fowler–Nordheim tunneling.     

Strain-Induced First-Order Magnetic Phase Transition in Epitaxial Sm<Subscript>0.35</Subscript>Pr<Subscript>0.15</Subscript>Sr<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> Thin Film

Epitaxial Sm_0.35Pr_0.15Sr_0.5MnO₃ thin films were deposited on LaAlO₃ (LAO, (001)), SrTiO₃ (STO, (001)), and (La_0.18Sr_0.82)(Al_0.59Ta_0.41)O₃ (LSAT, (001)) single-crystalline substrates by using pulsed laser deposition technique. In order to examine the strain effect on electronic and magnetic properties, films were studied by X-ray diffraction, electrical resistivity, and dc magnetization measurements. The film grown on LAO substrate is under compressive strain, and it undergoes ferromagnetic → paramagnetic transition at Curie temperature (T _C) of ～ 165 K and metal → insulator transition at ～ 107 K. The films grown on STO and LSAT substrates are under tensile strain and have T _C of ～ 120 and 130 K, respectively, and show metal → insulator transition at ～ 145 and 137 K, respectively. At T < T _C, the zerofield and fieldcooled magnetization curves of all the films show a huge bifurcation. In the case of films on STO and LSAT substrates, hysteresis is also observed in fieldcooled cooling and warming magnetization vs. temperature measurement protocols at low magnetic field. All the signatures of the firstorder magnetic phase transition are absent in the case of film on LAO substrate. The occurrence and absence of firstorder magnetic phase transition in films on LAO, STO, and LSAT substrates, respectively, have been well explained through the substrateinduced film lattice strain.     

Phase Composition and Dielectric Properties of Thin Films Produced by Annealing Sn/Pb/Ti/Si and Pb/Sn/Ti/Si Heterostructures

Sn/Pb/Ti/Si and Pb/Sn/Ti/Si heterostructures were deposited by magnetron sputtering using Ti and Sn solid targets and liquid-phase Pb self-sputtering in the former case and three solid targets in the latter. The heterostructures were then annealed in flowing oxygen at 470–970 K. The major phase in the film produced from the Sn/Pb/Ti/Si heterostructure at 970 K was the Pb(Sn_0.55Ti_0.45)O₃ solid solution with ferroelectric properties. The film prepared from the Pb/Sn/Ti/Si heterostructure consisted of Pb(Sn_0.55Ti_0.45)O₃ and PbTiO₃ and exhibited nonlinear dielectric properties. The coercive field and remanent polarization of the films were determined.     

Optical and structural properties of ZnO + Zn<Subscript>2</Subscript>TiO<Subscript>4</Subscript> thin films prepared by the sol–gel method

ZnO + Zn₂TiO₄ thin films were obtained by the sol–gel method using precursor solutions with different Ti/Zn ratios in the 0.18–2.13 range. The films were deposited on glass substrates and annealed in an open atmosphere at 550 °C. The oxide was characterized by X-ray diffraction and photoacoustic (PA) spectroscopy. The films were constituted of polycrystalline ZnO for the lowest Ti/Zn ratio (0.18), polycrystalline Zn₂TiO₄ for the 0.70 and 1.0 ratios, and mixes of both oxides for the intermediate ratios (0.32 and 0.50). For the highest ratios studied (1.44 and 2.13), the films were amorphous. The energy band gap (E_g) values were determined from optical absorption spectra, measured by means of the PA technique spectra. E_g varied in the 3.15 eV (ZnO) to 3.70 eV (Zn₂TiO₄) range.     

Effect of substrate temperature and deposited thickness on the formation of iron silicide prepared by ion beam sputter deposition

Ion beam sputter deposition (IBSD) method was employed to find optimum conditions for the formation of epitaxial β-FeSi₂ films on Si(100) substrate. It was found that crystal structure of the films as determined by X-ray diffraction (XRD) analysis is dependent on the substrate temperature as well as on the deposited thickness of sputtered Fe. The film with best crystal properties was obtained either at 873 K with the deposited Fe thickness of 15 nm, or at 973 K with the deposited Fe thickness of 30 nm. The obtained results indicate the importance of Fe and/or Si diffusion in determining the crystal properties of β-FeSi₂ film.     

Formation behavior of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> from CaTiO<Subscript>3</Subscript>, CuO and TiO<Subscript>2</Subscript>

The formation behavior of CaCu₃Ti₄O₁₂ (CCTO) had been investigated via solid state reaction from CaTiO₃, CuO and TiO₂ powders. In the temperature range from 750 to 1,200 °C, the reaction sequence was traced by XRD, and the microstructure evolution of calcined powders was also investigated by SEM. CCTO began to form owing to the reaction between CaTiO₃, CuO and TiO₂ at around 850 °C, and became the major phase at 1,000 °C. Finally, the single phase CCTO was obtained at 1,150 °C. However, CCTO was decomposed at CaTiO₃, CuO and TiO₂ when the temperature increased to 1,200 °C. In addition, no other intermediate phases occurred in the synthesized process. The formation behaviors indicated that CaTiO₃ prevented the formation and growth of CCTO.     

Synthesis and characterization of photosensitive TiO<Subscript>2</Subscript> nanorods by controlled precipitation route

Nanocrystalline TiO₂ thin films have been successfully synthesized by controlled precipitation route. These films are further annealed at 623 K for 2 h. The change in structural, morphological, optical, and wettability properties are studied by means of X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), scanning electron microscopy (SEM), optical absorption, and contact angle measurement. From the XRD pattern it is clear that the as-grown TiO₂ films are amorphous in nature which becomes polycrystalline after annealing. The FTIR study reveals the formation of TiO₂ compound. Scanning electron micrographs shows that the as-grown TiO₂ film consists of agglomerated nanograins well covered to the substrate surface which gets converted into vertical nanorods after annealing. As-deposited and annealed TiO₂ films showed hydrophilic behavior as water contact angles were 24° and 32°, respectively. The optical absorption study reveals the small red shift due to annealing and attributed to grain size. The annealed TiO₂ film showed conversion efficiency of 0.037% in photoelectrochemical cell with 1 M NaOH electrolyte.     

Chemical solution deposition of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin film

CaCu₃Ti₄O₁₂ (CCTO) thin film was successfully deposited on boron doped silica substrate by chemical solution deposition and rapid thermal processing. The phase and microstructure of the deposited films were studied as a function of sintering temperature, employing X-ray diffractometry and scanning electron microscopy. Dielectric properties of the films were measured at room temperature using impedance spectroscopy. Polycrystalline pure phase CCTO thin films with (220) preferential orientation was obtained at a sintering temperature of 750°C. There was a bimodal size distribution of grains. The dielectric constant and loss factor at 1 kHz obtained for a film sintered at 750°C was k ∼ 2000 and tan δ ∼ 0.05.     

Chemical–hydrothermal combined surface modification of titanium for improvement of osteointegration

The chemical–hydrothermal combined synthesis of TiO₂ and CaTiO₃ films on pure Ti substrates was examined with a focus on crystallinity and surface morphology of the films. Pure Ti disks were chemically treated with H₂O₂/HNO₃ solutions at 353 K for 5–60 min in order to introduce a TiO₂ layer with low crystallinity on the surface. The samples were then hydrothermally treated in an autoclave at 453 K for 12 h. Anatase-type TiO₂ and perovskite-type CaTiO₃ films with high crystallinity were obtained upon treatment with distilled water and an aqueous solution of Ca(OH)₂, respectively. Cracks in the TiO₂ precursor films disappeared after hydrothermal treatment. Uniform and crack-free films could be obtained by the present process. In addition, in vitro formation of hydroxyapatite (HAp) on the films was investigated. Obtained samples were immersed in SBF (Simulated Body Fluid), adjusted to 310 K. A light HAp precipitate could be observed on non-surface modified Ti after 6 days of immersion. In contrast, precipitate formed after only 2 days on the present oxide films. The present surface modification was confirmed to drastically promote deposition of HAp on the surface of Ti.     

General aspects of the growth of In-In<Subscript>2</Subscript>O<Subscript>3</Subscript> films

Transformations in indium nanolayers have been studied by optical spectroscopy, microscopy, and gravimetry in relation to the thickness of the layers (2–147 nm) and heat treatment temperature (473–873 K) and time (0–120 min). The kinetic curves for the degree of conversion are adequately described by a linear, inverse logarithmic, parabolic, or logarithmic law, depending on the thickness of the indium film and heat treatment temperature. We have measured the contact potential difference across the In and In₂O₃ films and the photovoltage in the In-In₂O₃ system. The results have been used to derive the energy band diagram of the In-In₂O₃ system. A model has been proposed for the thermal transformation of indium films, which involves oxygen adsorption steps, charge carrier redistribution in the In-In₂O₃ interfacial field (positive on the In₂O₃ side), and In₂O₃ formation.     

Effect of annealing on leakage current characteristics of Pt/Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript>/Pt thin-film capacitors

The effect of annealing on leakage current characteristics of Pt/Ba_0.6Sr_0.4TiO₃/Pt ferroelectric thin-film capacitors was investigated at the temperature range from 273 K to 393 K. The results show that the depletion layer width of the as-deposited BST film is about 3–5 times greater than that of the annealed film. For as-deposited samples, the Schottky barrier height increases with increasing temperature and voltage. However, for annealed samples, the Schottky barrier height linearly decreases with increasing voltage and is almost independent upon temperature.     

Oxygen treatment effects on properties of MgO thin films grown on single-crystalline diamond (1 0 0)

Oxygen post-treatment effects on the electronic structure and electrical properties of MgO films grown on homoepitaxial single-crystalline (1 0 0) diamond have been studied. MgO films examined were deposited at room temperature (RT) using an electron beam evaporator and were subsequently either annealed at 573-773 K for 12 h in oxygen ambient or treated by O₂ plasma for 10-40 min. RT resistivities remarkably increased after the O₂ annealing and plasma treatment, indicating that the post treatments play an essential part on the formation and positioning of bandgap states. Cathodoluminescence (CL) spectra had a broad band feature in a wavelength region from 360 to 530 nm, which were decomposed to several peaks originating mainly from the oxygen-vacancy-related F and F⁺ centers and the interstitial vacancies of MgO film. A prominent rectifying behavior of I-V property was observed for a Au/MgO/p-diamond layered structure. Based on temperature dependences of the electrical properties in a temperature region from RT to 600 K, the electrical conduction mechanism in the MgO films is discussed in relation to polaron-related conduction as well as the ionic conduction.     

Mixed Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>:MoO<Subscript>3</Subscript> (95:5 and 85:15) thin films and their properties for electrochromic device applications

Nb₂O₅:MoO₃ (95:5 and 85:15) thin films were deposited onto glass and fluorine doped tin oxide coated glass substrates at 100 and 300 °C by RF magnetron sputtering technique. The physical and electrochromic properties of the films were studied. XRD result reveals that deposited films were amorphous. The XPS study confirms the compositional purity and the presence of Nb⁵⁺ and Mo⁶⁺ in the deposited film. Surface morphological study shows platelet like features of deposited film. The average transmittance of the film is varied between 91 and 85 %. Photoluminescence study exhibits three characteristic emission peaks and confirms the better optical quality of deposited film. Raman spectra show the LO–TO splitting of Nb–O stretching of the deposited film. Electrochromic behavior of the deposited films characterized by cyclic voltammetry using 0.5 M LiClO₄·PC and 0.5 M H₂SO₄ electrolyte solutions show all the films are having better reversibility and reproducibility in their electrochemical analysis.     

Influence of film thickness and annealing atmosphere on the structural, optical and luminescence properties of nanocrystalline TiO2 thin films prepared by RF magnetron sputtering

TiO₂ thin films were deposited onto quartz substrates by RF magnetron sputtering. Inorder to investigate the effect of film thickness on the structural and optical properties, films were deposited for different time durations, and post-annealed at 873 K. The influence of annealing atmosphere (air/oxygen) on the film properties was also investigated. The films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectroscopy and photoluminescence (PL) spectroscopy. Films deposited at different time durations are amorphous-like in nature. From XRD patterns it can be inferred that deposition for longer duration is essential for achieving crystallisation in TiO₂ thin films prepared by RF magnetron sputtering. The films exhibited good adherence to the substrate and are crack free as revealed by SEM images. Film thickness was found to increase with increase in sputtering time. The optical band gap of the films was found to decrease with increase in film thickness, which is consistant with XRD observations. Film thickness did not show any significant variation when annealed in both air and oxygen. Defect related PL emission in the visible region (blue) was observed in all the investigated films, which suggests the application of these films in optoelectronic display devices.