Laser implantation of sodium nitrite into artificial opal pores upon exposure of artificial opal samples to pulsed radiation of the ultraviolet laser

We present experimental results on the introduction (laser implantation) of ferroelectric NaNO₂ into artificial opal pores upon exposure of a thin powder layer of sodium nitrite applied on the artificial opal surface to radiation of the ultraviolet excimer laser. Reflection spectra of broadband radiation from the laser-implanted sample surface are compared with the reflection spectra of pure initial opals, artificial opals impregnated with a saturated aqueous solution of sodium nitrite and evaporated from solvent, and samples in which NaNO₂ was directly introduced in the form of a melt.     

Optical and dielectric properties of nanostructured photonic crystals loaded by ferroelectrics and metals

The properties of new materials produced by loading artificial opals with different ferroelectrics (sodium nitrite, barium titanate, lithium niobate. etc.) are analyzed. The possibility of modifying the ferroelectric properties of materials by introducing them into pores of artificial opals is reported. The physical properties of artificial opals with pores loaded by conducting media (mercury, amorphous carbon, silver, gold, etc.) are studied. An analysis is made of the transmission and reflection spectra of broad-band radiation, which permit one to establish the characteristics of the stop bands as a function of the globule diameter, the type of ferroelectric or metal inserted into the opal pores, thermal annealing conditions, etc. The conditions favoring emission of slow electromagnetic waves in artificial opals are specified, and their characteristic properties are reported. The possibilities for increasing the efficiency of Raman and nonlinear optical processes in photonic crystals loaded by ferroelectrics and metals are analyzed.     

Thermal conductivity of opal filled with a LiIO<Subscript>3</Subscript> ionic conductor

The temperature dependences of the thermal conductivity of a synthetic opal and opal-based nano-composites prepared by introducing a LiIO₃ superionic conductor into pores of the opal matrix from an aqueous solution or melt are measured by the hot-wire technique in the temperature range 290–420 K. It is demonstrated that the thermal conductivity of pure opal increases with an increase in the diameter of the SiO₂ spheres forming a face-centered cubic lattice of an opal and is determined by the total thermal resistance of interfaces between the spheres. Filling of opal pores with the ionic conductor leads to an increase in the thermal conductivity. The behavior of the thermal conductivity and its magnitude in opal-based nanocomposites depend to a large extent on the method of filling the matrix pores.     

Impact of nanoconfinement on the diisopropylammonium chloride (C6H16ClN) organic ferroelectric

The dielectric studies of diisopropylammonium chloride (DIPAC) nanoparticles embedded into opal and MCM-41 silica matrices are presented. It is shown that the ferroelectric phase transition shifts to low temperatures and broadens for DIPAC within the opal pores compared to bulk. The thermal hysteresis of the transition increases under opal nanoconfinement. No anomalies of the permittivity relevant to the ferroelectric transition are observed for DIPAC within the MCM-41 molecular sieves likely due to formation of the amorphous phase.     

Linear and nonlinear dielectric properties of nanocomposites based on the organic ferroelectric of diisopropylammonium bromide

ABSTRACT

The present work aims at investigating linear and nonlinear dielectric properties of nanocomposites based on diisopropylammonium bromide (C₆H₁₆NBr, DIPAB) embedded into Al₂O₃ films having honeycomb structure with pores of 100?nm in diameter, and into opal matrices with three-dimensional structure containing pores of 100 and 60?nm. The obtained results indicated the shift of Curie point toward lower temperatures for DIPAB in porous aluminum oxide and the appearance of two phase transitions, detected upon heating and cooling for DIPAB in opal matrices. In addition, a ferroelectric phase was found to form between these two phase transitions without significant change of Curie temperature.     

Unusual behavior of thermal conductivity of a crystalline-NaCl-opal nanocomposite

An opal-based nanocomposite has been prepared with NaCl incorporated in its pores. The nanocomposite was produced by impregnating the opal with a NaCl solution at room temperature. Thermal conductivity of the nanocomposite has been measured in the temperature range 4.2–300 K. The effective heat conductivity of the nanocomposite was found to be equal to that of pure opal. The observed phenomenon can be explained by assuming that NaCl resides in opal pores in the form of noncontacting needles, thus precluding heat propagation through it. Fiz. Tverd. Tela (St. Petersburg) 40, 379–380 (February 1998)     

Photoluminescence properties of bare and ZnO infilled artificial opal

Photoluminescence of bare and ZnO infilled artificial opals was investigated. A presence of a photonic band gap results in distortion of the photoluminescence spectra of both the bare and ZnO infilled opal nanocomposite. Filling of the opal with ZnO resulted in a shift of the Bragg diffraction peak from 430 to 460 nm. The emission from ZnO infilled opal contains no UV photoluminescence from ZnO nanocrystals, while the ZnO nanocrystals deposited on substrate by the same method exhibit strong excitonic UV emission. Although a high temperature treatment in ambient air results in an increase in the photoluminescence intensity of the ZnO nanocrystals, the quenched behavior of the excitonic emission from ZnO nanocrystals embedded in the opal matrix remains. A domination of the artificial opal matrix intrinsic emission in the photoluminescence spectra from the untreated as well as heat treated ZnO filled opal nanocomposites is observed.     

Properties of three-dimensional composites based on opal matrices and magnetic nanoparticles

Three-dimensional nanocomposites consisting of an opal matrix and a metal have been prepared by the interaction of salts and oxides of different elements (Ni, Co, Fe, etc.) embedded in an opal matrix with isopropanol in the range of supercritical state parameters of the alcohol. According to X-ray powder diffraction analysis and transmission electron microscopy data, the composites consist of an X-ray amorphous opal matrix with pores filled by nanoparticles of Co (or CoO _x ), metallic Ni, or Fe₃O₄ with a magnetite structure of various morphology. The sizes of the nanoparticles do not exceed the diameter of the pores in the opal matrix. A complex investigation of the nanocomposites has been performed using the electron magnetic resonance and vibrating magnetometry methods. All the studied samples at room temperature exhibit a ferromagnetic behavior. The coercive force of the samples lies in the range from 150 Oe for iron-containing nanocomposites to 565 Oe for cobalt-containing nanocomposites.     

Structural, photonic band-gap, and luminescence properties of the opal-erbium composite

Erbium oxide and silicates were embedded in the pores of synthetic opal by using the chemical bath deposition technique. Electron-microscopic images showed the synthesized compounds to be deposited predominantly in a thin uniform layer on the inner surface of the pores. An analysis of the transmittance spectra suggested that the opal-erbium composite thus obtained retained the photonic band-gap properties of the original ordered opal matrix. The Er³⁺ ions in the composite emitted light at several wavelengths in the visible and near-IR regions (550, 860, 980, 1240, 1530 nm) at 80 K.     

Photonic band structure of 3D ordered silica matrices

The symmetry and orientation of a photonic lattice of 3D ordered porous silica matrices (synthetic opals) are determined by analysis of transmission electron micrographs. By optical transmission measurements the photonic band edges are mapped out at pointsLandKof the Brillouin zone. It is shown that modulating the refractive index of opal pores by filling them with liquids results in variation of the light attenuation length within the forbidden gap. To increase the refractive index contrast of the lattice, the pores of opals were filled with CdS. A dramatic decrease in attenuation length is observed for opal/CdS. The parameters of a photonic lattice with a ‘pseudo-gap’, that is, with a prominent depletion of the photonic density of states, are estimated.     

Laser implantation of KTiPO4 ferroelectric nanoparticles into pores of synthetic opal placed into water

We present the results of experiments on the implantation of KTP (KTiPO₄) ferroelectric nanoparticles into pores of synthetic opal along with the data on spectral analysis of the reflection coefficients of specimens obtained. KTP powder was irradiated by an ultraviolet KrF laser in water, which increased the pore filling efficiency.     

生长周期对有机金属化学气相沉积法制备SiO2-InP光子晶体的影响

有机金属化学气相沉积(MOCVD)方法在人工蛋白石空隙中填充了磷化铟(InP)晶体以改变这类材料的光学行为,在选择了InP的生长条件的基础上进行了周期生长试验。利用扫描电子显微镜(SEM)和紫外可见光谱(UV-Vis)对人工蛋白石晶体及其填充InP后的形貌和反射谱特性进行了分析。结果发现,采用周期生长方式有利于InP在模板空隙中的填充,且在反应时间相同的条件下,反应周期数越多,InP在空隙中的填充率越高,填充率增加反过来增大了二氧化硅球和空隙之间的折射率差,从而可控地对所制备光子晶体光子带隙进行调制。实验表明InP具有较好的生长质量,此项研究为制备三维InP光子晶体打下了基础。     

Cu_2O particles with ordered pores via electrochemical deposition method

Cu2O particles cube with ordered pores are electrodeposited by using colloidal crystal template method. The shape of Cu2O cube particle is partly determined by its growing habit. Therefore, Cu2O cube particles with ordered pores are fabricated instead of three dimensional inverse opal structures.     

UV irradiation-induced modification of photonic band gap and birefringence in artificial opal nanocomposite

A red shift of the photonic band gap and stress-induced birefringence have been observed in the bare and ZnO infilled artificial opal samples under UV laser irradiation. The stress-induced birefringence appeared between the irradiated and non-irradiated parts of the opal. These effects were related to the irradiation-stimulated increase in the density and the refractive index of the opal. Using the obtained results, the UV illumination-induced changes in the degree of polarization, volume and refractive index of the opal were estimated.     

Stimulated globular scattering of laser radiation in photonic crystals: Temperature dependences

The characteristics of stimulated globular scattering such as the frequency shift, threshold, and conversion efficiency are studied in photonic crystals (synthetic opal matrices and opal nanocomposites) at different temperatures. The results are compared with the study of stimulated Raman scattering in calcite single crystals. In both cases, a decrease in temperature from +20° C to −196° C resulted in an increase in the energy of stimulated scattering energy and its redistribution into the higher-order components.     

Secondary emission of globular photonic crystals based on the opal-POPOP composite

The spectra of secondary emission of a globular photonic crystal such as the opal matrix filled with the POPOP aromatic compound (a known luminophore) and initial materials excited by semiconductor light-emitting diodes were studied. It was found that the luminescence spectrum of opal filled with POPOP significantly differs from luminescence spectra of POPOP itself and initial opal. It was shown that the observed luminescence in the visible region is mostly caused by three-photon parametric light scattering. In this case, the spectral shape is controlled by the photon density of states, differing from the photon density of states of pure opal. The shape of the secondary emission spectrum of artificial opal filled with POPOP was calculated. The effect of the photonic bandgap position on the intensity distribution of spontaneous emission of used luminophore was established.     

Atomic mobility in a ternary liquid Ga–In–Sn alloy of the eutectic composition

The nuclear spin–lattice relaxation and Knight shift of ⁷¹Ga, ⁶⁹Ga, and ¹¹⁵In nuclei in a ternary liquid gallium–indium–tin alloy of the eutectic composition, which was introduced into pores of an opal matrix and porous glasses with pore sizes of 18 and 7 nm, have been investigated and compared with those for the bulk melt. It has been found that longitudinal relaxation is accelerated and the Knight shift is decreased, depending on the size of pores. The correlation time of the atomic motion has been calculated for the nanostructured melt in porous matrices. It has been shown that the atomic mobility in the melt decreases with decreasing size of pores in the glasses.

     

Thermal conductivity of the opal-epoxy resin nanocomposite

The effective thermal conductivity κ_eff of seven opal + epoxy resin nanocomposite samples with 100% filling of first-order pores by epoxy resin was measured in the 100-to 300-K temperature interval. In the nanocomposite studied, the thermal conductivity of the matrix (amorphous SiO₂ spheres) is larger than that of the filler material (epoxy resin). κ_eff(T) of the opal + epoxy resin nanocomposite at intermediate temperatures (100–300 K) is shown to behave similar to pure opal. An explanation of the observed effect is proposed.     

Synthesis of a periodic SiC/C nanostructure

Highly porous periodic structures consisting of a three-dimensional replica of pores in the initial opal lattice have been synthesized by high-temperature thermochemical treatment of opal matrices filled with carbon compounds, followed by dissolution of silicon dioxide. It has been shown that the main phases of the composite are carbon and silicon carbide. Based on the X-ray diffraction, Raman, and IR spectroscopy data, it has been assumed that the composite contains fragments of hexagonal diamond. The photoluminescence and optical reflection spectra of the composites have been measured.     

Laser implantation of sodium nitrite ferroelectric into pores of synthetic opal

We present the experimental results on implantation of NaNO₂ ferroelectric into pores of synthetic opal by illuminating with focused ultraviolet excimer-laser radiation of a sodium nitrite film located on the synthetic-opal surface. The reflection spectra of broadband radiation from the surface of implanted specimens are compared with the reflection spectra of initial (without any treatment) opals, synthetic opals filled with a saturated aqueous solution of sodium nitrite with subsequently evaporated solvent, and specimens with NaNO₂ embedded as a melt. The possible mechanisms of shifts of reflected- and transmitted-radiation peaks are analyzed. Methods of implanting materials with high melting points into pores of 3D photonic crystals are proposed.