Effect of the number of iron oxide nanoparticle layers on the magnetic properties of nanocomposite LbL assemblies

Aqueous colloidal suspension of iron oxide nanoparticles has been synthesized. Z-potential of iron oxide nanoparticles stabilized by citric acid was −35±3 mV. Iron oxide nanoparticles have been characterized by the light scattering method and transmission electron microscopy. The polyelectrolyte/iron oxide nanoparticle thin films with different numbers of iron oxide nanoparticle layers have been prepared on the surface of silicon substrates via the layer-by-layer assembly technique. The physical properties and chemical composition of nanocomposite thin films have been studied by atomic force microscopy, magnetic force microscopy, magnetization measurements, Raman spectroscopy. Using the analysis of experimental data it was established, that the magnetic properties of nanocomposite films depended on the number of iron oxide nanoparticle layers, the size of iron oxide nanoparticle aggregates, the distance between aggregates, and the chemical composition of iron oxide nanoparticles embedded into the nanocomposite films. The magnetic permeability of nanocomposite coatings has been calculated. The magnetic permeability values depend on the number of iron oxide nanoparticle layers in nanocomposite film.     

Monte Carlo simulation of magnetic nanostructured thin films

Using Monte Carlo simulation, we have compared the magnetic properties between nanostructured thin films and two-dimensional crystalline solids. The dependence of nanostructured properties on the interaction between particles that constitute the nanostructured thin films is also studied. The result shows that the parameters in the interaction potential have an important effect on the properties of nanostructured thin films at the transition temperatures.     

Application of spectroscopic ellipsometry to the investigation of the optical properties of cobalt-nanostructured silica thin layers

Spectroscopic ellipsometry is used to investigate optical properties of cobalt-implanted silica thin films. The films under investigation are 250 nm thick thermal SiO₂ layers on Si substrates implanted with Co⁺ ions at energy of 160 keV and at fluences of 10¹⁷ ions/cm² for different temperatures of substrate during implantation (77 and 295 K). Changes due to Co⁺ implantation are clearly observed in the optical response of the films. Optical behaviours are furthermore different for the three implantation temperatures. To understand the optical responses of these layers, the ellipsometric experimental data are compared to different models including interference effects and metal inclusions effects into the dielectric layer. The simulated ellipsometric data are obtained by calculating the interferences of an inhomogeneous layer on a Si substrate. The material within this layer is considered as an effective medium which dielectric function is calculated using the Maxwell-Garnett effective medium approximation. We show that although the structures of these layers are very complicated because of ion-implantation mechanisms, quite simple models can provide relatively good agreement. The possibilities of ellipsometry for the study of the optical properties of such clusters-embedded films are discussed. We especially provide the evidence that ellipsometry can give interesting information about the optical properties of nanostructured layers. This is of special interest in the field of nanostructured layered systems where ellipsometry appears to be a suitable optical characterization technique.     

Self-Assembled TiO2/PSS Multilayer Films Studied by Slow Positron Spectroscopy

TiO2/PSS nano-structured multilayer films are fabricated by a layer-by-layer self-assembly method, and the deposition process and interface structure of films are studied in detail by slow positron spectroscopy. The results indicate that injection energy of positron at the interface between the substrate and the film shows a linear dependence on the number of bilayer, which suggests that the repeatability of the depositing process is good, and the thickness of films shows a linear increase with the number of bilayers adding. The calculated result of the film thickness shows that there is an overlay between the adjacent TiO2 nanoparticle layers.     

Studies of thin FeAlN films prepared by different techniques

The microstructure, morphology, and magnetic properties of FeAlN films deposited by reactive rf magnetron sputtering with subsequent treatment by three techniques, namely, in situ, ex situ (with the sputtering and annealing processes separated), and thermal crystallization of amorphous alloys, have been studied. FeAlN films prepared by the ex situ technique exhibit the best soft magnetic characteristics. Thermal crystallization of amorphous alloys produced films with properties having the highest thermal stability. Films 800-to 1000-nm thick were found to have the best soft magnetic properties. The dependences of the properties of FeAlN films on nitrogen content and annealing temperature were established. The conditions favoring the preparation of thin nanostructured FeAlN films featuring the best soft magnetic characteristics (saturation induction B _S = 1.8 T, coercivity H _C = 1.2 Oe, magnetic susceptibility μ₁ (1 MHz) = 3400) were determined.     

Magnetic properties of Co films and Co/Pt multilayers deposited on PDMS nanostructures

The magnetic properties of magnetron sputtered Co films (with in-plane anisotropy) and Co/Pt multilayers (with perpendicular anisotropy) deposited on elastomeric poly-dimethylsiloxane (PDMS) films and nanostructured templates are presented. Apart from the etched nanosize features, maze-like submicron features develop after the sputter deposition as a result of film buckling due to thermal contraction of the underlying PDMS layer. The nanostructured templates can physically isolate the magnetic entities but magnetic correlations within the range of the buckling features remain. By using oblique deposition geometries in-plane anisotropy develops and it is transferred to the PDMS buckling patterns. In the case of Co/Pt multilayers deposition on PDMS nanostructured templates results in a loss of the perpendicular anisotropy, attributed to the acuteness of the PDMS nanostructures.     

Facile synthesis of group-I elements (K,Li and Na)-doped nanostructured CdO films

In this study, we report an application of facile and low-cost successive ionic layer adsorption and reaction method to investigate nanostructured CdO films. We have tried to enhance some physical properties of nanostructured CdO films by group-I (K, Li and Na) elements doping. The crystal structures, morphology, absorption, transmittance, reflectance behaviour and optical band gap values of CdO films were characterized by using X-ray diffraction (XRD), scanning electron microscopy and ultraviolet–visible spectroscopy techniques. XRD analysis reveals formation of CdO cubic crystalline structure. From these characterizations, it was seen that there are important distinctions in the structural, morphological and optical properties of undoped and K-, Li- and Na-doped nanostructured CdO films.     

Optical properties of antimicrobial barrier layers based on polyethylene terephthalate with a nanostructured surface

The optical properties of nanostructured barrier layers based on polyethylene terephthalate formed by ion technology and their resistance to biodegradation are discussed. The influence of the surface energy and relief parameters on the antimicrobial activity of nanostructured barrier layers is established. The study of reflection spectra demonstrates the fine structure of spectral lines apparently connected with the scattering of electromagnetic radiation by charged centers. These centers are formed on a nanostructured polymer surface after ion-plasma treatment as well as upon the deposition of α-C:H films which are known as electrets with a large number of broken bonds.     

A novel approach to enhancement of surface properties of CdO films by using surfactant: dextrin

We studied the effect of an organic surfactant, dextrin, concentration on structural, morphological and optical properties of nanostructured CdO films deposited on glass substrates by using an easy and low-cost SILAR method. Microstructures of the nanostructured CdO films were optimized by adjusting dextrin concentration. XRD, SEM and UV–Vis Spectroscopy were used to study phase structure, surface morphology and optical properties of CdO films. Furthermore, effects of dextrin concentration on the surface roughness characteristics of CdO samples were reported. The results showed that the presence of organic surfactant highly affected the physical properties of CdO nanomaterials.     

Hetero-Colloidal Metal Particle Multilayer Films Grown Using Electrostatic Interactions at the Air–water Interface

The formation of nanoparticle multilayer films by electrostatic immobilization of surface-modified colloidal particles at the air–water interface has been recently demonstrated by us. In this paper, we extend our study to show that multilayer assemblies consisting of metal particles of different chemical nature (hetero-colloidal particle superlattices) and size can be deposited by the versatile Langmuir–Blodgett technique. Multilayer films consisting of a different number of bilayers of gold and silver colloidal particles have been deposited and characterized using quartz crystal microgravimetry and UV–visible spectroscopy measurements. It is observed that while layer-by-layer deposition of the different colloidal particle assemblies is possible by this technique without a detectable variation in the cluster density in the different layers, a degree of post-deposition reorganization of the clusters occurs in the film. In addition to this aging behavior, the effect of different organic solvents on the reorganization process has also been studied.     

Effects of post-thermal treatments on morphological and optical properties of NiO/Ni(OH)2 thin films synthesized by solution growth

Room temperature deposition of PVP capped nanostructured NiO/Ni(OH)₂ thin film, the morphological and optical characterizations by solution growth technique are reported. The nanostructured thin films which were deposited on optical glass substrates were annealed at different temperatures and then subjected to structural, morphological and optical characterizations. X-ray diffraction measurements of the films revealed that higher temperatures during the thermal treatment enhanced the crystallinity of the thin films. The SEM surface micrographs show non-interconnected uniformly deposited fibre-like structures with approximate lengths between 400 and 1200 nm. The optical band gap energy roughly decreased from about 2.7 eV to about 2.2 eV with thermal treatment. The absorbance of the thin films annealed at 300 and 400 °C was as high as 90% in the visible region of the electromagnetic spectrum. These materials could be useful in solar thermal conversion processes.     

Magnetotransport properties of La0.67Ca0.33MnO3//La0.67Sr0.33MnO3 bilayers

The perovskite bilayers La0.67Ca0.33MnO3 （LCMO） （100 nm） / La0.67Sr0.33MnO3（LSMO） （100 nm） and LSMO （100 nm） / LCMO （100 nm） are fabricated by a facing-target sputtering technique. Their transport and magnetic properties are investigated. It is found that the transport properties between them are different obviously due to distinguishable structures, and the different lattice strains in both films result in the difference of metal-to-insulator transition. Only single-step magnetization loop appears in our bilayers from 5K to 320K, and the coercive force of LSMO/LCMO varies irregularly with a minimum ～ 2387A/m which is lower than that of LCMO and LSMO single layer films. The behaviour is explained by some magnetic coupling.     

NANO-CRYSTALLINE SILICON FILMS PRODUCED BY LAYER-BY-LAYER DEPOSITION TECHNIQUE AND THEIR NOVEL PROPERTIES

We have applied the layer-by-layer deposition technique to the growth of nano-crystalline silicon films by varying the hydrogen plasma exposure time. The tailoring effect of hydrogen plasma has been studied, The novel optical and electronic proper-ties of these films have also been reported.     

NANO-CRYSTALLINE SILICON FILMS PRODUCED BY LAYER-BY-LAYER DEPOSITION TECHNIQUE AND THEIR NOVEL PROPERTIES

We have applied the layer-by-layer deposition technique to the growth of nano-crystalline silicon films by varying the hydrogen plasma exposure time. The tailoring effect of hydrogen plasma has been studied, The novel optical and electronic proper-ties of these films have also been reported.     

Effect of Terraces at the Interface on the Structural and Physical Properties of La_(0.8)Sr_(0.2)MnO_3 Thin Films

Employing atomic force microscopy,transmission electron microscopy and the second harmonic generation technique,we carefully explore the structural properties of 6-unit-cell-thick La_(0.8)Sr_(0.2)MnO_3 films grown on SrTiO_3 with atomically flat TiO_2-terminated terraces on the surface.The results clearly demonstrate that the terraces on the surface of TiO_2-terminated SrTiO_3 can improve the layer-by-layer epitaxial growth of the manganite films,which results in uniform film coverage at the beginning of growth and thus reduces the substrate-induced disorder at or near the interface.Comparing the magnetic and transport properties of La_(0.8)Sr_(0.2)MnO_3 films with the thicknesses varying from 6 unit cells to 80 unit cells grown respectively on as-received SrTiO_3 and TiO_2-terminated SrTiO_3,it is found that these atomically flat terraces on the surface of TiO_2-terminated SrTiO_3 can greatly enhance the Curie temperature and conductivities of the ultrathin La_(0.8)Sr_(0.2)MnO_3 films with thickness less than 50 unit cells,while no obvious difference is detected in the magnetic and transport properties of the 80unit-cell thick films.     

磁控溅射法制备钴掺杂氧化锌薄膜室温磁学性质

钴掺杂氧化锌是室温稀磁半导体的重要候选材料,其磁学特性和钴掺杂浓度、显微结构及光学性质密切相关。磁控溅射具有成本低、易于大面积沉积高质量薄膜等特点,是广受关注的稀磁半导体薄膜制备方法。利用磁控溅射方法制备了不同浓度的钴掺杂氧化锌薄膜,并对其显微结构、光学性质和磁学特性进行了系统分析。结果表明:当掺杂原子分数在8%以内时,钴掺杂氧化锌薄膜保持单一的铅锌矿晶体结构,钴元素完全溶解在氧化锌晶格之中;薄膜在可见光区域有很高的透射率,但在567, 615和659 nm处有明显吸收峰,这些吸收峰源于Co2+处于O2-形成的四面体晶体场中的特征d-d跃迁。磁学特性测试结果表明钴掺杂氧化锌薄膜具有室温铁磁性,且钴的掺杂浓度对薄膜的磁学特性有重要影响。结合薄膜结构、光学和电学性质分析,实验中观察到的室温铁磁性应源于钴掺杂氧化锌薄膜的本征属性,其铁磁耦合机理可由束缚磁极化子模型进行解释。     

各向同性纳米结构Fe-Pt薄膜的结构和磁性

采用直流溅射和热处理技术制备了两个各向同性的纳米结构Fe-Pt永磁合金薄膜系列,并研究了它们的结构和磁性.研究表明,在富Fe双相纳米结构Fe-Pt永磁合金薄膜中,仅由硬磁的FePt相与软磁的Fe₃Pt相组成;在同一系列中,随Fe层厚度的增加,饱和磁极化强度和剩磁明显增大.由Kelly-Henkel图研究指出,在上述Fe-Pt纳米结构永磁合金薄膜中,磁相互作用主要由近邻纳米晶粒间的铁磁交换相互作用控制. 关键词： 磁性薄膜 纳米结构 矫顽力     

Miniature plasma focus as a novel device for synthesis of soft magnetic FeCo thin films

The Letter reports the first ever application of low energy miniature plasma focus device as a deposition facility for nanostructured thin films. We demonstrate successful utilization of a 120 J fast miniature plasma focus device as a novel facility for the deposition of magnetically soft FeCo thin films. Different gas types and the substrate materials were used to investigate their effects on magnetic properties of the films. The FeCo films deposited on Si₍₁₀₀₎ with hydrogen as the filling gas were found to have an average grain size of 10.8±1.2 nm with narrow size distribution and soft magnetic properties with coercivity of about 6.3 Oe. The experimental coercivity value matched reasonably well with the theoretical calculation done using ripple theory.     

Aggregation-induced emission of an aminated silole: A fluorescence probe for monitoring layer-by-layer self-assembling processes of polyelectrolytes

A new fluorescence technique for monitoring layer-by-layer self-assembling processes of polycations and polyanions is developed in this work. The fluorescent probe is a fluorogenic dye named 1,1-bis[p-(diethylaminomethyl)phenyl]-2,3,4,5-tetraphenylsilole (A₂HPS). Whereas fluorescence of a “normal” fluorophore is often quenched by aggregate formation, the protonated salt of A₂HPS, i.e., [H₂A₂HPS]²⁺, emits strong light in the suspensions of its nanoaggregates and in the solid films of its blends with poly(diallyldimethylammonium chloride) (PDDAC), thanks to its novel aggregation-induced emission (AIE) characteristics. When ([H₂A₂HPS]²⁺+PDDAC) cations and poly(styrenesulfonate) (PSS) anions were used to fabricate thin films via layer-by-layer deposition processes on quartz and glass substrates, the emission intensity of [H₂A₂HPS]²⁺ showed linear relationship with the number of ([H₂A₂HPS]²⁺+PDDAC)/PSS bilayers, due to the uniform co-deposition of [H₂A₂HPS]²⁺ cations into the PDDAC/PSS bilayers. This proves that the AIE fluorophore is an excellent probe for monitoring the layer-by-layer self-assembling processes of the polyelectrolytes on various substrates.     

Isotropic ferromagnetic resonance field shift in as-prepared permalloy/FeMn bilayers

Exchange-coupled wedged-permalloy (Py)/FeMn bilayers are studied by ferromagnetic resonance (FMR) technique at room temperature. In comparison, Py single layer films were also made. For Py single layer films and Py/FeMn bilayers, only one uniform resonance peak was observed at high magnetic fields, indicating no interfacial diffusion at the Py/FeMn and Py/Cu interfaces. Negative isotropic in-plane resonance field does exist in Py/FeMn bilayers and its magnitude increases with decreasing Py layer thickness. In order to explain above phenomena, interfacial perpendicular anisotropy must be considered simultaneously, in addition to irreversible rotation of spins in FeMn layers. This is because the perpendicular resonance field of the bilayers is larger than that of Py single layer films.