Epitaxial growth and exchange coupling of spinel ferrimagnet Ni0.3Zn0.7Fe2O4 on multiferroic BiFeO3

Thin films of the zinc nickel ferrite, Zn_0.7Ni_0.3Fe₂O₄ (ZNFO), were deposited by the RF magnetron sputtering on a number of substrates, including (001) oriented single crystals of LaAlO₃ (LAO) and SrTiO₃ (STO), polycrystalline Pt/Si, and epitaxial films of BiFeO₃ (BFO) and LaNiO₃ (LNO). Except for the films on Pt/Si, the ZNFO films grown on other substrates were epitaxial and their magnetic properties were affected by the heteroepitaxy induced strains. Typically, the coercivity (H_c) was increased with the strain, i.e. H_c varied from 31 Oe for the 150 nm thick polycrystalline films grown on Pt/Si, to 55 Oe and 155 Oe for the 20 nm thick epitaxial films grown on BFO and LAO, respectively. The saturation magnetization of the epitaxial films was reduced accordingly to about 470 emu/cm³ from 986 emu/cm³ in the polycrystalline films. The all-oxide architecture allowed field-annealing to perform at the temperature above the Neel temperature of BFO (~ 370 °C), after which clear exchange bias was observed.     

Photocatalytic properties of BiFeO3 nanoparticles with different sizes

BiFeO₃ nanoparticles with different average grain sizes have been prepared through a polyacrylamide gel route. In the present synthesis route, the grain size is tailored by varying the ratio of bis-acrylamide to acrylamide. The photocatalytic activity of the as-prepared BiFeO₃ nanoparticles has been investigated by the degradation of methyl orange (MO), a typical azo dye. It is revealed that the products exhibit a pronounced photocatalytic activity under ultraviolet as well as visible-light irradiation. With decrease in particle size, the photocatalytic activity exhibits a rising trend. The influences of catalyst dosage and initial dye concentration on the photocatalytic efficiency have been also investigated. In the present experiments, the optimum loading of BiFeO₃ nanoparticles and initial concentration of MO are obtained to be ~ 2.5 g L⁻¹ and ~ 10 mg L⁻¹, respectively.     

Synthesis of (Na2O,PbO)-Nb2O5, (Na2O,BaO)-Nb2O5, and (K2O,SrO)-Nb2O5 thin films using sol-gel method

Homogeneous pore-free Ba₂NaNb₅O₁₅, KSr₂Nb₅O₁₅, and 2·Na₂O-PbO-6·Nb₂O₅ thin films were fabricated on sapphire substrates using the sol-gel technique. By controlling the gelation and coating process, thickness of thin films fabricated was controllable from ~ 40 nm to ~ 10 μm. Synthesized thin films possessed highly preferred orientated microstructure. Another advantage of this method is the subsequent heat treatment temperature dramatically decreased compared with other methods. This increases stoichiometry control and makes the large scale fabrication more feasible and efficient.     

Surface characterization of poly(methylmethacrylate) based nanocomposite thin films containing Al2O3 and TiO2 nanoparticles

Poly(methylmethacrylate) (PMMA) based nanocomposite electron beam resists have been demonstrated by spin coating techniques. When TiO₂ and Al₂O₃ nanoparticles were directly dispersed into the PMMA polymer matrix, the resulting nanocomposites produced poor quality films with surface roughnesses of 322 and 402 nm respectively. To improve the surface of the resists, the oxide nanoparticles were encapsulated in toluene and methanol. Using the zeta potential parameter, it was found that the stabilities of the toluene/oxide nanoparticle suspensions were 7.7 mV and 19.4 mV respectively, meaning that the suspension was not stable. However, when the TiO₂ and Al₂O₃ nanoparticles were encapsulated in methanol the zeta potential parameter was 31.9 mV and 39.2 mV respectively. Therefore, the nanoparticle suspension was stable. This method improved the surface roughness of PMMA based nanocomposite thin films by a factor of 6.6 and 6.4, when TiO₂ and Al₂O₃ were suspended in methanol before being dispersed into the PMMA polymer.     

Superhydrophilicity of TiO2 thin films using TiCl4 as a precursor

TiO₂ thin films on soda lime glass were prepared by the sol-gel method and spin coating process using TiCl₄ as a precursor. The AFM images indicate that the surface morphology of the films is granular with 72 nm particle size. The roughness and thickness of the films are about 3 nm and 140 nm, respectively. The XRD spectrum shows polycrystalline anatase phase without any considerable impurity phase. The UV-vis spectroscopy of the films show 80-90% transmission in the visible region. The absorption edge is at 370 nm, which corresponds to 3.3 eV energy band gap. The films have a high superhydrophilicity character after being exposed to UV illumination for about 10 min. The surfaces, which were synthesized by this method, can retain their superhydrophilicity property for at least 24 h. Our results are consistent with the idea that UV-induced wetting of TiO₂ surface is caused by the removal of hydrophobic layers of hydrocarbons by TiO₂-mediated photooxidation, which leads to the attractive interaction of water with clean TiO₂ surface. TiO₂ thin films on Si(1 1 1), Si(1 0 0), and quartz substrates need less time than glass and polycrystalline Si substrates to be converted to superhydrophilic surface.     

An investigation of super-hydrophilic properties of TiO2/SnO2 nano composite thin films

A sol-gel dip coating technique was used to fabricate TiO₂/SnO₂ nano composite thin films on soda-lime glass. The solutions of SnO₂ and TiO₂ were mixed with different molar ratios of SnO₂:TiO₂ as 0, 3, 4, 6, 8, 9, 10.5, 13, 15, 19.5, 25 and 28 mol.% then the films were prepared by dip coating of the glasses. The effects of SnO₂ concentration, number of coating cycles and annealing temperature on the hydrophilicity of films were studied using contact angle measurement. The films were characterized by means of scanning electron microscopy, X-ray diffraction and atomic force microscopy measurements. The nano composite thin films fabricated with 8 mol.% of SnO₂, four dip coating cycles and annealing temperature of 500 °C showed super-hydrophilicity.     

Structural and electrical properties of BiFeO3 thin films by solution deposition and microwave annealing

Lead-free polycrystalline BiFeO₃ (BFO) thin films were developed using a chemical solution deposition method to deposit the films and the multi-mode 2.45 GHz microwave furnace to optimize the annealing condition of the films. Phase-pure BFO films were obtained at 500 °C-600 °C for 1-5 min with a heating rate of 10 °C/min. The film by microwave annealing (MW) at 550 °C for 5 min exhibited a (012)-preferred orientation with a dense morphology of grain size ~ 294 nm. Its dielectric constant of 96.2, low leakage current density of 2.466 × 10^− 6 A/cm², polarization (2P_r) and coercive field (2E_c) of 0.931 μC/cm² and 57.37 kV/cm, respectively, were improved compared to those by conventional annealing (CA) at the same annealing conditions.     

One-step synthesis of Fe-phthalocyanine/Fe3O4 hybrid microspheres

Fe-phthalocyanine/Fe₃O₄ hybrid microspheres were synthesized from bis-phthalonitrile and FeCl₃·6H₂O through a simple and effective solvent-thermal route. The hybrids were monodispersed solid microspheres with diameter of ~ 400 nm. The ferromagnetic signature emerged with the saturated magnetization of ~ 55.7 emu g⁻¹, and the coercive force of ~ 93.7 Oe at 300 k. The addition of bis-phthalonitrile oligomer brought Fe₃O₄ nanoparticles novel dielectric property: a new dielectric loss peak appeared at ~ 8 GHz. Considering the microwave magnetic loss properties, two microwave magnetic loss peaks were presented at ~ 1.5 GHz and ~ 10 GHz, the former peak was attributed to the natural properties of the Fe₃O₄, and the latter originated from the interface effects between the bis-phthalonitrile oligomer and Fe₃O₄.     

Low-temperature synthesis of BiFeO3 nanoparticles by ethylenediaminetetraacetic acid complexing sol-gel process

This paper reported a novel approach to synthesize pure BiFeO₃ nanoparticles through an ethylenediaminetetraacetic acid complexing sol-gel process at low temperature. The pure BiFeO₃ nanoparticles were attained at much lower temperature as 600 °C by this process, in contrast to above 800 °C for the traditional solid-state sintering process. The SEM results showed that the prepared BiFeO₃ nanoparticles had a better homogeneity and fine grain morphology. The BiFeO₃ nanoparticles show a weak ferromagnetic order at room temperature, which is quite different from the linear M-H relationship in bulk BiFeO₃. The origin of the weak magnetic property in our samples should be attributed to the size-confinement effects of the BiFeO₃ nanostructures.     

Atomic layer deposition of Ru thin film using N2/H2 plasma as a reactant

Ruthenium (Ru) thin films were grown by atomic layer deposition using IMBCHRu [(η6-1-Isopropyl-4-MethylBenzene)(η4-CycloHexa-1,3-diene)Ruthenium(0)] as a precursor and a nitrogen-hydrogen mixture (N₂/H₂) plasma as a reactant, at the substrate temperature of 270 °C. In the wide range of the ratios of N₂ and total gas flow rates (fN₂/N₂ + H₂) from 0.12 to 0.70, pure Ru films with negligible nitrogen incorporation of 0.5 at.% were obtained, with resistivities ranging from ~ 20 to ~ 30 μΩ cm. A growth rate of 0.057 nm/cycle and negligible incubation cycle for the growth on SiO₂ was observed, indicating the fast nucleation of Ru. The Ru films formed polycrystalline and columnar grain structures with a hexagonal-close-packed phase. Its resistivity was dependent on the crystallinity, which could be controlled by varying the deposition parameters such as plasma power and pulsing time. Cu was electroplated on a 10-nm-thick Ru film. Interestingly, it was found that the nitrogen could be incorporated into Ru at a higher reactant gas ratio of 0.86. The N-incorporated Ru film (~ 20 at.% of N) formed a nanocrystalline and non-columnar grain structure with the resistivity of ~ 340 μΩ cm.     

NH4Cl-assisted low temperature synthesis of anatase TiO2 nanostructures from Ti powder

A simple, low temperature and low cost method, which was based on heating the mixture of Ti and NH₄Cl powders in air at 300 °C, has been developed for the controlled synthesis of anatase TiO₂ nanostructures including irregular nanoparticle aggregates, curved nanowires built up by the oriented attachment of nanoparticles, and nanoplates constructed with nanoparticles. The characterization results from X-ray diffraction and Raman spectra indicated that the as-obtained products were anatase TiO₂. Field emission scanning electron microscope images revealed that the products obtained for 3, 10 and 16 h comprised, in turn, irregular nanoparticle aggregates (8-55 nm), curved nanowires built up by the oriented attachment of nanoparticles (~ 9 nm), and nanoplates constructed with nanoparticles (~ 8 nm).     

Surface planarization and masked ion-beam structuring of YBa2Cu3O7 thin films

Surface planarization and masked ion-beam structuring (MIBS) of high-T_c superconducting (HTS) YBa₂Cu₃O_7-δ (YBCO) thin films grown by pulsed-laser deposition (PLD) method is reported. Chemical-mechanical polishing, plasma etching, and oxygen annealing of YBCO films strongly reduce the particulate density (~ 10^-2 ×) and surface roughness (~ 10^-1 ×) of as-grown PLD layers. The resistivity, critical temperature T_c ≈ 90 K and critical current density J_c (77 K) > 1 MA/cm² of films are not deteriorated by the planarization procedure. The YBCO films are modified and patterned by irradiation with He⁺ ions of 75 keV energy. Superconducting tracks patterned by MIBS without removal of HTS material and, for comparison, by wet-chemical etching show same T_c and J_c(T) values. Different micro- and nano-patterns are produced in parallel on planarized films. The size of irradiated pattern depends on the mask employed for beam shaping and features smaller than 70 nm are achieved.     

BaTiO3-SrTiO3 layered dielectrics for energy storage

BaTiO₃-SrTiO₃ (BST) thick films (~ 250-390 μm) with layered structures were fabricated by tape-casting and lamination process. Layered composites with various Ba/Sr ratios were obtained by lamination of BaTiO₃ (BT) and SrTiO₃ (ST) tapes in different spatial configurations (2-2). As-prepared BST ceramics showed much improved sinterability over the laminates of pure BT or pure ST tapes. Dielectric properties of materials were measured in the temperature range of 25 °C to 200 °C. The method of utilizing of layered structures offered flexibility to maximize the energy storage capability at specific operating conditions: (temperature and electric field) by tailoring the dielectric properties through varying the spatial configurations of BT and ST films.     

Catalyst-free growth of Sb2Te3 nanowires

In this study, a catalyst-free growth method was discovered to prepare the high-quality single crystal Sb₂Te₃ nanowires from the Al:Ge:Sb:Te thin films. The diameters of Sb₂Te₃ nanowires were found to be ~ 100 nm and their lengths were as great as tens of micrometers. The Al content and the annealing temperature play an important role in the growth of Sb₂Te₃ nanowires. When the Al content (> 12.4 at.%) was sufficiently contained in Al:Ge:Sb:Te film, Sb₂Te₃ nanowires were extruded spontaneously on the surface of thin film with increase in annealing temperatures. Compared with the vapor-liquid-solid method, our method has advantages of low temperature (~ 300 °C) and no impurities, such as a metal catalyst.     

Synthesis, crystal structure and thermal decomposition of [La2(CH3CH2COO)6·(H2O)3]·3.5H2O precursor for high-k La2O3 thin films deposition

Lanthanum acetylacetonate La(C₅H₇O₂)₃·xH₂O has been used in the preparation of the precursor solution for the deposition of polycrystalline La₂O₃ thin films on Si(1 1 1) single crystalline substrates. The precursor chemistry of the as-prepared coating solution, precursor powder and precursor single crystal have been investigated by Fourier Transformed Infrared Spectroscopy (FTIR), differential thermal analysis coupled with quadrupole mass spectrometry (TG-DTA-QMS) and X-ray diffraction. The FTIR and X-ray diffraction analyses have revealed the complex nature of the coating solution due to the formation of a lanthanum propionate complex. The La₂O₃ thin films deposited by spin coating on Si(1 1 1) substrate exhibit good morphological and structural properties. The films heat treated at 800 °C crystallize in a hexagonal phase with the lattice parameters a = 3,89 Å and c = 6.33 Å, while at 900 °C the films contain both the hexagonal and cubic La₂O₃ phase.     

Optical properties of nanocrystalline SnS2 thin films

Thin films of nanocrystalline SnS₂ on glass substrates were prepared from solution by dip coating and then sulfurized in H₂S (H₂S:Ar = 1:10) atmosphere. The films had an average thickness of 60 nm and were characterized by X-ray diffraction studies, scanning electron microscopy, EDAX, transmission electron microscopy, UV-vis spectroscopy, and Raman spectroscopy. The influence of annealing temperature (150-300 °C) on the crystallinity and particle size was studied. The effect of CTAB as a capping agent has been tested. X-ray diffraction analysis revealed the polycrystalline nature of the films with a preferential orientation along the c-axis. Optical transmission spectra indicated a marked blue shift of the absorption edge due to quantum confinement and optical band gap was found to vary from 3.5 to 3.0 eV with annealing temperature. Raman studies indicated a prominent broad peak at ∼314 cm⁻¹, which confirmed the presence of nanocrystalline SnS₂ phase.     

Self-patterned Nano Structures in Structurally Gradient Epitaxial La0.5Ba0.5CoO3 Films

Highly epitaxial La_0.5Ba_0.5CoO₃ (LBCO) thin films with sharp interface and a thickness of 200 nm were epitaxially grown on (001) SrTiO₃ substrates using pulsed laser deposition. High-resolution transmission electron microscopy and electron diffraction analysis revealed that the films have a triple-layered structure. The first layer, close to the film/substrate interface, has a thickness of ~ 6 nm and is a defect free single crystal disordered cubic structure (a = 3.882 Å) which has a lattice mismatch of − 0.59% with respect to the substrate. The second layer which dominates the film structure has a single crystal disordered cubic structure (a = 3.854 Å) which has a lattice mismatch of − 1.31% with respect to the substrate. The third layer located on the top of the film has a thickness of several nanometers and consists of 112-type ordered tetragonal structure. The cubic structures in the first and second layer have an orientation relationship of (001)_LBCO//(001)_STO and < 100 > _LBCO//< 100 > _STO with respect to the substrate. Self-patterned 3-dimensional nano structures with a dimension range from 2 to 10 nm were formed in the second and third layers. These nano structures were formed by the enclosure of anti-phase boundary planes which are parallel to the {100} of the cubic structure. Epitaxial LBCO thin films with such nano structures are hard ferromagnetic with a large coercive field value and magnetoresistance effect value (~ 24%), and exhibit semiconductor behavior at temperatures < 300 K.     

MoO3 nanoparticles distributed uniformly in carbon matrix for supercapacitor applications

A highly uniform nanocomposite of MoO₃ and carbon with a weight ratio of 1:1 is prepared by employing a simple procedure of ball milling. Such composite as electrochemical pseudocapacitor materials for potential energy storage applications exhibits a high specific capacitance of ~ 179 F/g at a charge and discharge current density of 50 mA/g with excellent cycling ability over 1000 cycles. Compared with the capacitance of pure milled graphite (~ 22 F/g) and MoO₃ (< 10 F/g), an enhanced electrochemical performance of the composite with a weight ratio of 1:1 is attributed to its unique structure, in which MoO₃ nanoparticles (with a size range of 1-180 nm) are uniformly dispersed in an electrically conductive carbon host.     

Synthesis and thermodynamic stability of multiferroic BiFeO3

Ceramic BiFeO₃ samples were prepared by the sol gel combustion method using urea as fuel. The obtain powders were thermal treated at different temperatures (300-840  °C) and times (1-64  h) to investigate the best synthesis conditions of the material. The resulting materials were analysed by TGA, FTIR, SEM/EDS and XRD. Rietveld analysis was applied to the diffraction data. The temperature and time of the heat treatment are critical for a high BiFeO₃ phase content. Thermal treatment of 1  h at 600  °C yielded 99% molar of the BiFeO₃ phase with a mean particle size of 120  nm. Upper or lower calcinations temperatures yielded higher content of the secondary phases Bi₂Fe₄O₉ and Bi₂₅FeO₃₉. Further heat treatment in air or in argon, up to 64  h, induces a decomposition of the BiFeO₃ phase according to the reaction 49 BiFeO₃ BiFeO₃ → 12 Bi₂Fe₄O₉ + Bi₂₅FeO₃₉ pointing out that BiFeO₃ is not thermodynamically stable at 600  °C. The BiFeO₃ decomposition follows Avrami-Erofeev law with a slope of 1 indicating a one-dimensional kinetics.     

Epitaxial growth and rectification characteristics of double perovskite oxide La2NiMnO6 films on Nb-SrTiO3 single crystal substrates

High-quality thin films of double perovskite La₂NiMnO₆ (LNMO) were epitaxially grown on Nb-doped SrTiO₃ (NSTO) substrates by pulsed laser deposition. The films were found to undergo a ferromagnetic-to-paramagnetic transition at ~ 280 K, which is consistent with the literature report. In the electrical measurements, typical rectifying behavior was observed in the LNMO/NSTO heterojunction. The diffusion voltage (V_D) increases linearly with temperature (T) during cooling until T = 170 K. At T < 170 K, V_D increases at a higher rate and the V_D-T relationship becomes non-linear. A disordered phase related spin polarization was used to understand such behaviors in the heterojunctions.