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Anodizing of valve metals under oscillating conditions is one of versatile and reproducible methods of the preparation of one-dimensional photonic crystals. Here, an effect of anodizing voltage profile on morphology and optical properties of anodic titanium oxide photonic crystals is investigated. Samples are obtained by cyclic anodizing of titanium in ethylene glycol based electrolyte using sine, triangle, and square wave voltage versus charge density modulation. The optimization of anodizing parameters allowed us to prepare anodic titanium oxide photonic crystals with reflectance within the photonic band gap of up to 85%.

Anodic titanium oxide is a promising material for the formation of photonic crystal structures due to its high refractive index, stability in acidic media, and semiconductor conductivity. One-dimensional photonic crystals are obtained by the anodization of titanium with triangle wave modulation of the voltage versus the charge density. The dependence of the position of the photonic band gap on the charge density per anodizing cycle is studied. The reflection coefficient within the photonic band gap of the obtained samples reaches 70%. Taking into account chemical dissolution of the pore walls during anodic oxidation and gradual reduction of the structure period along the film thickness make it possible to obtain photonic crystals based on titanium oxide with a record value of the Q factor of 9.6.

Geometrical frustration arised in spin ices leads to fascinating emergent physical properties. Nowadays there is a wide diversity of the artificial structures, mimicking spin ice at the nanoscale and demonstrating some new effects. Most of the nanoscaled spin ices are two dimensional. Ferromagnetic inverse opal-like structures (IOLS) are among inspiring examples of the three-dimensional system exhibiting spin ice behaviour. However, a detailed examination of its properties is not straightforward. An experimental technique which is able to unambiguously recover magnetization distribution in 3D mesoscaled structures is lacking. In this work, we used an approach based on complementary exploiting of small-angle neutron diffraction technique and micromagnetic simulations. An external magnetic field was applied along three main directions of the IOLS mesostructure. Comparison of the calculated and measured data allowed us to determine IOLS magnetic state. The results are in good agreement with the spin ice model. Moreover influence of the demagnetizing field and vortex states on the magnetizing process were revealed. Additionally, we speculate that this approach can be also applied to other 3D magnetic mesostructures.

The self-ordered anodic aluminium oxide (AAO) structure consists of micron-scale domains—defect-free areas with a hexagonal arrangement of pores. A substantial increase in domain size is possible solely by pre-patterning the aluminium surface in the form of a defect-free hexagonal array of concaves, which guide the pore growth during subsequent anodization. Among the numerous pre-patterning techniques, direct etching by focused gallium ion beam (Ga FIB) allows the preparation of AAO with a custom-made geometry through precise control of the irradiation positions, beam energy, and ion dosage. The main drawback of the FIB approach includes gallium contamination of the aluminium surface. Here, we propose a multi-step anodizing procedure to prevent gallium incorporation into the aluminium substrate. The suggested approach successfully covers a wide range of AAO interpore distances from 100 to 500 nm. In particular, anodization of FIB pre-patterned aluminium in 0.1 M phosphoric acid at 195 V to prepare AAO with the interpore distance of about 500 nm was demonstrated for the first time. The quantification of the degree of pore ordering reveals the fraction of pores in hexagonal coordination above 96% and the in-plane mosaicity below 3° over an area of about 1000 μm2. Large-scale defect-free AAO structures are promising for creating photonic crystals and hyperbolic metamaterials with distinct functional properties.

Anodic titanium oxide (ATO) photonic crystals (PhCs) are promising for photonics, photocatalysis, and solar cells. A refractive index modulation in ATO PhCs is caused by the modulation of porosity and, thus, the pore diameter should be controlled precisely. The ATO cell walls etching in electrolyte solution during anodizing increases the porosity of the PhC structure and shifts the photonic band gap (PBG) position to shorter wavelengths. Until now, the ATO cell walls etching in organic based electrolytes has been associated solely with the chemical dissolution of ATO in fluoride-containing solutions. Here, a significant enhancement of cell walls etching is observed when electric current flows under anodic polarization. This effect leads to the blue shift of the PBG position with the number of periods of ATO PhC structure. Therefore, it is essential for the synthesis of ATO PhCs with a precise PBG position.

The structure of surface layers of thin metal inverse opals has been studied first by the grazing-incidence small-angle X-ray scattering technique. Contributions of the form factor and structure factor to the small-angle diffraction pattern have been separated using a numerical model of the scattering process. The complementary use of the small-angle X-ray scattering and grazing-incidence small-angle X-ray scattering techniques has provided independent information about the bulk and surface properties of the samples and allowed a type of defect in the investigated structures to be determined. The measurement results have been verified by atomic force microscopy.

We perform micromagnetic simulations of the magnetization distribution in inverse opal-like structures (IOLS) made from ferromagnetic materials (nickel and cobalt). It is shown that the unit cell of these complex structures, whose characteristic length is approximately 700 nm, can be divided into a set of structural elements some of which behave like Ising-like objects. A spin-ice behavior of IOLS is observed in a broad range of external magnetic fields. Numerical results describe successfully the experimental hysteresis curves of the magnetization in Ni- and Co-based IOLS. We conclude that ferromagnetic IOLS can be considered as the first realization of three-dimensional artificial spin ice. The problem is discussed of optimal geometrical properties and material characteristics of IOLS for the spin-ice rule fulfillment.

Photonic crystals based on titanium oxide are promising for optoelectronic applications, for example as components of solar cells and photodetectors. These materials attract great research attention because of the high refractive index of TiO2. One of the promising routes to prepare photonic crystals based on titanium oxide is titanium anodizing at periodically changing voltage or current. However, precise control of the photonic band gap position in anodic titania films is a challenge. To solve this problem, systematic data on the effective refractive index of the porous anodic titanium oxide are required. In this research, we determine quantitatively the dependence of the effective refractive index of porous anodic titanium oxide on the anodizing regime and develop a model which allows one to predict and, therefore, control photonic band gap position in the visible spectrum range with an accuracy better than 98.5%. The prospects of anodic titania photonic crystals implementation as refractive index sensors are demonstrated.

M-Zn (M = Sb, V, Nb) substituted M-type strontium hexaferrites were prepared by a ceramic method. The phase composition, morphology and magnetic properties were studied by x-ray diffractometry, scanning electron microscopy and vibrating sample magnetometry. Saturation magnetization increases with a substitution up to 75.0 emu/g (2.5 % higher compared to unsubstituted hexaferrite) and then decreases with a further substitution. A coercive field of substituted hexaferrite powders with highest saturation magnetization is more than 3 kOe. Substituted strontium hexaferrite powders prepared in this work are a rare example of high M S compositions without doping rare-earth elements and would be a promising candidate for a permanent magnet application.

A new simple and versatile technique for the phase transfer of nanoparticles from water to water-immiscible organic solvents is presented. The proposed method is based on using charged colloids as carriers for the transfer of nanoparticles with opposite surface charge. The method has been successfully applied for the transfer of SrFe12O19 nanoplatelets and CdTe nanoparticles.

M-type strontium hexaferrite powders were synthesized by the modified sol–gel method with calcination in NaCl matrix in a temperature range 790–850 °C for 1 h. X-ray diffraction analysis shows the formation of pure M-type strontium hexaferrite phase. The SrFe12O19 particles have a plate-like shape with a mean diameter 130–185 nm and a thickness 45–55 nm. The prepared powders show a saturation magnetization 70–72 emu/g and a coercive force 6.0–6.4 kOe. The suggested synthesis method combines simplicity, using of low calcination temperatures and allows to synthesize pure strontium hexaferrite powders with excellent hard magnetic properties.

Formation of artificial opal films by a vertical deposition method was in situ studied using the grazing incidence X-ray diffraction technique. Monodisperse spherical polymethyl methacrylate particles (200 nm in diameter) were deposited on the polished Si substrate from an aqueous suspension. The ordering of particles on a fixed area of the substrate located in turn in the bulk suspension under the meniscus and in the air was continuously monitored by the X-ray scattering upon moving the meniscus down owing to evaporation of the solvent. The triple air-liquid-solid phase boundary, i.e. the top line of the meniscus, is identified as the most probable location of the crystallization process. The analysis of observed Bragg reflections and the particle form-factor indicates that the obtained artificial opal-like structures are composed of the spheres arranged in a close-packed hexagonal layers parallel to the substrate. The characteristic correlation length along the normal to the substrate of 550 ± 100 nm is obtained from the half full width of Bragg peaks.

The type and degree of imperfection for opal-like photonic crystals on conducting substrates have been investigated using synchrotron small-angle X-ray scattering with a microradian resolution. It has been demonstrated that self-assembly of poly(styrene) spheres by the vertical deposition method leads to the formation of a face-centered cubic structure on a mica/Au substrate and a random hexagonal close packing on a glass substrate with the In2O3(SnO2) conducting coating.

The distribution of the scattering intensity in the reciprocal space for natural and artificial opals has been reconstructed from a set of small-angle X-ray diffraction patterns. The resulting three-dimensional intensity maps are used to analyze the defect structure of opals. The structure of artificial opals can be satisfactorily described in the Wilson probability model with the prevalence of layers in the fcc environment. The diffraction patterns observed for a natural opal confirm the presence of sufficiently long unequally occupied fcc domains.

Magnetic γ-Fe2O3/SiO2 nanocomposites have been synthesized by impregnating a mesoporous silica matrix with a hexane solution of γ-ferric oxide nanoparticles. The subsequent heat treatment of samples in the course of synthesis influences the optical properties of the final nanostructural material. It is established that an increase in the temperature of annealing (crystallization) leads to a decrease in the energies of both direct and indirect allowed electron transitions to the conduction band.

Magnetic γ-Fe2O3/SiO2 nanocomposites are synthesized by impregnating mesoporous silica with a hexane solution of γ-iron oxide nanoparticles. Materials with various structural and magnetic properties can be obtained using a subsequent thermal treatment of the synthesized samples (annealing for three hours in an air flow).

Europium fluoride based systems are promising luminescent materials due to the possibility of realizing photon splitting effect, allowing emission of two photons in visible part of spectra after the excitation of one photon in vacuum ultraviolet. The EuF3 nanoparticles are of special interest due to an opportunity of sensitizing fluoride particles with an light absorbing shell. In the present work the synthesis of monodisperse trioctylphosphine oxide-capped europium fluoride nanostructures is described. The diameter of obtained particles can be controlled in the range of 3–10 nm. The formation of fluoride nanoparticles was confirmed by TEM, electron diffraction, X-ray diffraction and luminescence spectroscopy.

Here we report the synthesis and investigation of cobalt nanowire arrays using mesoporous silica as a host material. In the present work, a novel variant of synthesis of ordered magnetic nanowires in the mesoporous silica matrix was suggested. The method is based on incorporation of a hydrophobic metal compound Co2(CO)8 into the hydrophobic part of the silica-surfactant composite. The amount of cobalt intercalated into the mesoporous matrix was measured by chemical analysis (~5 wt %). Additional thermal modification was performed in order to provide a crystallization process of the cobalt nanowires. The prepared nanocomposites were characterized by X-ray diffraction (XRD), small-angle X-ray spectroscopy (SAXS), transmission electron microscopy (TEM), nitrogen capillary adsorption method (BET and BJH), and magnetic measurements. The anisotropy parameters of nanowires were determined using temperature dependence of magnetic susceptibility. For cobalt-containing sample annealed at 300 °C (form factor of nanowire higher than 16), the coercive force at room temperature was found to be 42.2 kA/m at saturation magnetization of 0.5 A.m2/kg, which is nearly sufficient for modern information recording media. According to TEM studies, cobalt particles are uniform and well ordered in the silica matrix. Thus, the suggested method leads to one-dimensional anisotropic nanostructures, which could find an application in high-density data storage devices.

The structure of inverse opal crystals based on nickel was probed on the mesoscopic and atomic levels by a set of complementary techniques such as scanning electron microscopy and synchrotron microradian and wide-angle diffraction. The microradian diffraction revealed the mesoscopic-scale face-centered-cubic (fcc) ordering of spherical voids in the inverse opal-like structure with unit cell dimension of 750±10nm. The diffuse scattering data were used to map defects in the fcc structure as a function of the number of layers in the Ni inverse opal-like structure. The average lateral size of mesoscopic domains is found to be independent of the number of layers. 3D reconstruction of the reciprocal space for the inverse opal crystals with different thickness provided an indirect study of original opal templates in a depth-resolved way. The microstructure and thermal response of the framework of the porous inverse opal crystal was examined using wide-angle powder x-ray diffraction. This artificial porous structure is built from nickel crystallites possessing stacking faults and dislocations peculiar for the nickel thin films.

The evolution of the magnetic structure for an inverse opal-like structure under an applied magnetic field is studied by small-angle neutron scattering. The samples were produced by filling the voids of an artificial opal film with Co. It is shown that the local configuration of magnetization is inhomogeneous over the basic element of the inverse opal-like lattice structure (IOLS) but follows its periodicity. Applying the “ice-rule” concept to the structure, we describe the local magnetization of this ferromagnetic three-dimensional lattice. We have developed a model of the remagnetization process predicting the occurrence of an unusual perpendicular component of the magnetization in the IOLS which is defined only by the direction and strength of the applied magnetic field.

Investigations of microwave properties of Ni-based inverse ferromagnetic opal-like film with the [111] axis of the fcc structure along the normal direction to the film have been carried out in the 2--18 GHz frequency band. We observed multiple spin wave resonances for the magnetic field applied perpendicular to the film, i.e., along the [111] axis of this artificial crystal. For the field applied in the film plane, a broad band of microwave absorption is observed, which does not contain a fine structure. The field ranges of the responses observed are quite different for these two magnetization directions. This suggests a collective magnetic ground state or shape anisotropy and collective microwave dynamics for this foam-like material. This result is in agreement with SQUID measurements of hysteresis loops for the material. Two different models for this collective behavior are suggested that satisfactorily explain the major experimental results.

Recent progress in information technologies has made microand nanolithography key processes in modern industry. Today these methods are among the most rapidly developing areas in both science and engineering. In the last two decades, wellknown and widespread methods of photoand electron-beam lithography have been complemented by a number of novel approaches that include direct writing processes, such as scanning probe lithography and dip-pen nanolithography, mask-based techniques including soft-lithography, nanoimprint, nanostencil and nanosphere lithography, and unconventional wet lithographies. Progress in the development of these methods has allowed high throughput to be attained at an ultimate resolution of less than 10 nm and enabled massproduction of microelectronic components. Further improvements in this method were introduced by the addition of chemical transformations, which can be applied through the integration of lithography with chemical or electrochemical processes. Electrochemical processing possesses a number of important advantages, including room-temperature synthesis (thereby avoiding thermal expansion problems), ability to control deposition rates, increased deposition density, and enhanced versatility. Moreover, electrochemical processes are easy to control through manipulation of charge values and current transient shapes. Several electrochemical lithography methods have been reported that achieve resolution down to 10 nm. However, all of these methods require contact lithography processing, as electrochemical photolithographic pattern-transfer techniques have yet to be developed. Nevertheless, numerous papers have been published on light-induced electrochemical effects, which have the potential to be further utilized for the development of non-contact electrochemical lithography techniques. One drawback to this approach however, is that the wavelengths of visible and UV light restrict the resolution level. A possible solution to this problem is the use of X-rays, which have long been known to trigger surface charging and radiolysis in matter. It could be expected that these effects would provide the conditions necessary for the electrochemical equilibrium shift required for electrochemical etching or deposition. Despite this, there have been only a few reports on X-rayassisted electrochemical processing. While some chemical X-ray lithography methods use X-rays for induced chemical transformations, they are restricted to reactions where radiolysis products are formed within the solution volume. Some work discusses reactions driven by photoelectrons ejected from the substrate surface, but do not complete the electrochemical circuit to control Helmholtz layer. Lastly, we also failed to find any studies concerning direct electrochemical lithography under X-ray irradiation. Thus in the present study we have focused our attention on the development of an electrochemical X-ray photolithography approach for direct pattern transfer to a liquid– solid interface by coherent X-ray irradiation. The concept is based upon variation in electrochemical deposition/etching rates provided by local photoionization effects. Local reduction of electrolyte components by photoelectrons generated on the working electrode surface under X-rays was chosen to test the concept. The electrochemical X-ray photolithography method was investigated by pattern transfer onto electrochemically deposited nickel, which plays a pivotal role in industry, particularly in microelectronics. The experiment is shown in Figure 1. A parallel X-ray beam collimated by slits was passed through a 4 mm pitch silicon grating and guided to the

Inverse photonic nickel-based crystal films formed by electrocrystallization of metal inside the voids of polymer artificial opal have been studied using the microradian X-ray diffraction. Analysis of the diffraction images agrees with an face-centred cubic (FCC) structure with the lattice constant a0 650 10 nm and indicates two types of stacking sequences coexisting in the crystal (twins of ABCABC... and ACBACB... ordering motifs), the ratio between them being 4:5 The transverse structural correlation length Ltran is 2.4 0.1 μm, which corresponds to a sample thickness of 6 layers. The in-plane structural correlation length L long is 3.4 0.2 μm, and the structure mosaic is of order of 10°.

Using microradian X-ray diffraction, we investigated the crystal structure of convectively assembled colloidal photonic crystals over macroscopic (0.5 mm) distances. Through adaptation of Wilson's theory for X-ray diffraction, we show that certain types of line defects that are often observed in scanning electron microscopy images of the surface of these crystals are actually planar defects at 70.5 degrees angles with the substrate. The defects consist of two parallel hexagonal close-packed planes in otherwise face-centered cubic crystals. Our measurements indicate that these stacking faults cause at least 10% of stacking disorder, which has to be reduced to fabricate high-quality colloidal photonic crystals.

Nickel inverse opals were fabricated by templating a colloidal crystal. Perfect fcc ordering was confirmed by scanning electron microscopy. Several kinds of magneto-optical effects were studied: linear longitudinal and transversal Kerr effects, nonlinear longitudinal Kerr effect (magnetization-induced second harmonic generation), which were all consistent with the photonic band structure studied by reflectivity spectroscopy.

Nanostructured nickel surfaces representing periodically arranged spherical voids in a nickel film are obtained by electrochemical deposition through a self-assembled opaline template. Excitation of surface plasmon-polaritons (SPPs) on the surface of the sample is experimentally observed as the Wood’s anomaly in the reflectance spectra. Transversal magneto-optical Kerr effect (TMOKE) spectra are measured at the different angles of incidence and azimuthal angles. The two- to-threefold enhancement of TMOKE caused by the excitation of mixed plasmons in two selected azimuthal configurations is observed.

The kinetics of nickel electrodeposition through a template of ordered polystyrene spheres is addressed experimentally and applied to prepare a series of metallic inverse opals with a non-integer number of layers. The observed layer-by-layer growth is discussed in terms of subsequently increasing disorder of the growth front. Reflection and transmission spectra of the samples demonstrate that the key optical features of these photonic crystals are most pronounced when the thickness does not essentially exceed two layers. The intensities and band positions can be additionally tuned by varying the height of the metal coating continuously, not discretely. These findings are confirmed semi-quantitatively by means of computational modeling of the spectra. Specific deposition current transients for in situ control of geometric parameters are discussed.