Depth profiles of transition-metal atoms implanted in a titanium dioxide matrix at medium energies

The depth profiles of 40-keV cobalt, chromium, and copper ions implanted into a titanium dioxide matrix at doses of 10¹⁶–10¹⁷ ions/cm² are simulated with the DYNA software package. Its algorithm is based on the effects of pair collisions of introduced ions with substrate atoms, which result in a dynamic change in the elemental composition of the near-surface layer in the irradiated material, and takes into account surface sputtering. The results obtained are compared with the standard statistical distribution calculated by the TRIM algorithm.     

Ionic conduction in Li<Subscript>2</Subscript>Ge<Subscript>7</Subscript>O<Subscript>15</Subscript> crystals doped with Cr and Mn ions

The electrical conductivity σ of crystals of lithium heptagermanate Li₂Ge₇O₁₅ doped with Cr and Mn is measured in an alternating-current field with a frequency of 1 kHz in the temperature range 300–700 K. It is found that doping strongly affects the electrical conductivity. It is established that the addition of 0.1 wt % Cr leads to an increase in the electrical conductivity σ by almost one order of magnitude, whereas the introduction of 0.03 wt % Mn substantially reduces the electrical conductivity along particular crystallographic directions. Data available on the incorporation of Cr and Mn impurity atoms into the lattice suggests that the electrical conductivity is determined by lithium ions hopping over interstitial positions along the structural channels.     

Magnetic Resonance Study of Fe-Implanted TiO<Subscript>2</Subscript> Rutile

Single-crystal (100) and (001) TiO₂ rutile substrates have been implanted with 40 keV Fe⁺ at room temperature with high doses in the range of (0.5–1.5) × 10¹⁷ ions/cm². A ferromagnetic resonance (FMR) signal has been observed for all samples with the intensity and the out-of-plane anisotropy increasing with the implantation dose. The FMR signal has been related to the formation of a percolated metal layer consisting of close-packed iron nanoparticles in the implanted region of TiO₂ substrate. Electron spin resonance (ESR) signal of paramagnetic Fe³⁺ ions substituting Ti⁴⁺ positions in the TiO₂ rutile structure has been also observed. The dependences of FMR resonance fields on the DC magnetic field orientation reveal a strong in-plane anisotropy for both (100) and (001) substrate planes. An origin of the in-plane anisotropy of FMR signal is attributed to the textured growth of the iron nanoparticles. As result of the nanoparticle growth aligned with respect to the structure of the rutile host, the in-plane magnetic anisotropy of the samples reflects the symmetry of the crystal structure of the TiO₂ substrates. Crystallographic directions of the preferential growth of iron nanoparticles have been determined by computer modeling of anisotropic ESR signal of substitutional Fe³⁺ ions.     

First-principles calculations on implanted TiO<Subscript>2</Subscript> by 3d transition metal ions

3d transition metal (V, Cr and Fe) ions are implanted into TiO₂ by the method of metal ion implantation. The electronic band structures of TiO₂ films doped 3d transition metal ions have been analyzed by ab initio band calculations based on a self-consistent full-potential linearized augmented plane-wave method within the first-principle formalism. Influence of implantation on TiO₂ films is examined by the method of UV-visible spectrometry. The results of experiment and calculation show that the optical band gap of TiO₂ films is narrowed by ion implantation. The calculation shows that the 3d state of V, Cr and Fe ions plays a significant role in red shift of UV-Vis absorbance spectrum.     

Ion beam sputter deposition of TiO<Subscript>2</Subscript> films using oxygen ions

TiO₂ thin films were grown by ion beam sputter deposition (IBSD) using oxygen ions, with the ion energy and geometrical parameters (ion incidence angle, polar emission angle, and scattering angle) being varied systematically. Metallic Ti and ceramic TiO₂ served as target materials. The thin films were characterized concerning thickness, growth rate, surface topography, structural properties, mass density, and optical properties. It was found that the scattering geometry has the main impact on the film properties. Target material, ion energy, and ion incidence angle have only a marginal influence. Former studies on reactive IBSD of TiO₂ using Ar and Xe ions reported equivalent patterns. Nevertheless, the respective ion species distinctively affects the film properties. For instance, mass density and the refractive index of the TiO₂ thin films are remarkably lower for sputtering with oxygen ions than for sputtering with Ar or Xe ions. The variations in the thin film properties are tentatively attributed to the angular and the energy distribution of the film-forming particles, especially, to those of the backscattered primary particles.     

Electron transfer in the structure of a photorefractive doped Bi<Subscript>12</Subscript>TiO<Subscript>20</Subscript>: Ru crystal

The ac conductivity of Bi₁₂TiO₂₀: Ru crystals has been studied in the frequency range 10²–10⁶ Hz and at temperatures 293–773 K. The experimental data have been analyzed in the framework of the model of correlated barrier hops. In this material, the potential barriers are due to the existence of a block structure, crystal lattice defects, and also the presence of a ruthenium impurity. The microparameters characterizing the charge transfer in doped bismuth titanate single crystals have been determined.     

Structural and magnetic properties of layered Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> thin films

Layered cobalt oxides Ca₃Co₄O₉ thin films have been grown directly on c-cut sapphire substrates using pulsed laser deposition. X-ray diffraction and transmission electron microscopy characterizations show that the deposited films present the expected monoclinic structure and a texture along the direction perpendicular to the Al₂O₃(001) plane. The Ca₃Co₄O₉ structure presents six variants in the film plane. Rutherford backscattering spectroscopy shows that the films are stoichiometric and that the film thickness agrees with the nominal value. The susceptibility χ of the films, recorded along the c-axis of the substrate, after field cooling and zero field cooling in an applied field of 1 kOe shows two magnetic transitions at 19 and 370 K which agree well with previous findings on single crystal samples. In turn, at low temperature (5 K), the magnetization curve along the c-axis exhibits coercive field and remanent magnetization much smaller than those reported for bulk samples, which can be related to the influence of structural variants and structural defects.     

FMR and TEM Studies of Co and Ni Nanoparticles Implanted in the SiO<Subscript>2</Subscript> Matrix

Fused silica plates have been implanted with 40 keV Co⁺ or Ni⁺ ions to high doses in the range of (0.25–1.0) × 10¹⁷ ions/cm², and magnetic properties of the implanted samples have been studied with ferromagnetic resonance (FMR) technique supplemented by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. The high-dose implantation with 3d-ions results in the formation of cobalt and nickel metal nanoparticles in the irradiated subsurface layer of the SiO₂ matrix. Co and Ni nanocrystals with hexagonal close packing and face-centered cubic structures have a spherical shape and the sizes of 4–5 nm (for cobalt) and 6–14 nm (for nickel) in diameter. Room-temperature FMR signals from ensembles of Co and Ni nanoparticles implanted in the SiO₂ matrix exhibit an out-of-plane uniaxial magnetic anisotropy that is typical for thin magnetic films. The dose and temperature dependences of FMR spectra have been analyzed using the Kittel formalism, and the effective magnetization and g-factor values have been obtained for Co- and Ni-implanted samples. Nonsymmetric FMR line shapes have been fitted by a sum of two symmetrical curves. The dependences of the magnetic parameters of each curve on the implantation dose and temperature are presented.     

Co离子注入TiO2薄膜的显微结构和磁性研究

利用直流磁控溅射技术在玻璃衬底上沉积了TiO₂薄膜,并对其进行了Co离子注入,最后在真空中500 ℃退火50 min,得到系列薄膜样品. 利用剥离-分散方法制备了薄膜的透射电镜样品,并用扫描电镜(SEM)、X射线能量散射谱(EDX)和高分辨透射电镜(HRTEM)对样品做了近似原位观察,研究了薄膜样品中不同Co离子注入深度的成分分布和显微结构. 结果表明,薄膜呈锐钛矿结构,Co元素主要分布在薄膜表层,Co离子的注入使TiO₂薄膜的晶粒被部分破坏,并形成CoO,而5 关键词： 2薄膜')" href="#">Co注入TiO₂薄膜 电镜原位观察 室温铁磁性     

Sensitizing of Sm<Superscript>3+</Superscript> fluorescence by silver dopant in the TiO<Subscript>2</Subscript> films

Composite material based on a TiO₂ matrix doped with Sm³⁺ ions and co-doped with silver was investigated. Samarium ions together with nano- and micro-aggregates of silver were incorporated into the titanium alkoxide during the sol-gel process. Samarium ions were excited either directly (λ _exc = 488 nm) or through the TiO₂ host (λ _exc = 355 nm). It was revealed that samarium fluorescence (λ _exc = 488 nm) in gelled TiO₂ films is enhanced by up to 20 times in the vicinity of silver inclusions. Sensitizing and plasmonic mechanisms of enhancement in Sm³⁺ fluorescence are discussed.     

Microwave surface resistance of pristine and neutron-irradiated MgB<Subscript>2</Subscript> samples in magnetic field

We report on the microwave surface resistance of two polycrystalline Mg¹¹ B₂ samples; one consists of pristine material, the other has been irradiated at very high neutron fluence. It has already been reported that in the strongly irradiated sample the two gaps merge into a single value. The mw surface resistance has been measured in the linear regime as a function of the temperature and the DC magnetic field, at increasing and decreasing fields. The results obtained in the strongly irradiated sample are quite well justified in the framework of a generalized Coffey and Clem model, in which we take into account the field distribution inside the sample due to the critical state. The results obtained in the pristine sample show several anomalies, especially at low temperatures, which cannot be justified in the framework of standard models for the fluxon dynamics. Only at temperatures near T_c and for magnetic fields greater than 0.5H_c2(T) the experimental data can quantitatively be accounted for by the Coffey and Clem model, provided that the upper-critical-field anisotropy is taken into due account.     

Nonlinear dielectric response of epitaxial Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript> TiO<Subscript> 3</Subscript> thin films

Based on Landau-Devonshire (LD)-type phenomenological thermodynamic theory, the electric field dependence of the dielectric properties of tetragonal single-domain barium strontium titanate(Ba_1-xSr_xTiO₃) films on cubic substrates is theoretically investigated by taking into account the high order terms of the polarization. At room temperature, the nonlinear dielectric responses of epitaxial Ba_0.6Sr_0.4TiO₃ films are provided by adjusting the film thickness and growth temperature. The strong nonlinearity of relative dielectric constant and pyroelectric coefficient are attained around critical film thickness on MgO (69 nm) and LaAlO₃ (132 nm) substrates or critical growth temperature on MgO (337 °C) substrate with respect to epitaxy-induced lattice misfit and thermal stresses during deposition. This can be explained that small compressive stresses are effective to support high nonlinearity of dielectric constant and pyroelectric coefficient for Ba_0.6Sr_0.4TiO₃ films irrespective of whether they are on compressive substrate or tensile substrate. It is also predicted that a large tunability may be achieved by altering processing conditions, such as the film thickness and growth temperature for different substrates. Our theoretical results are in good agreement with the experimental data reported in literature.     

Dielectric and conduction mechanism studies of Ni doped LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> synthesized by solution combustion method

In the present work, structural, morphological, dielectrical, and electrochemical properties of LiNi_xMn_(2-x)O₄ (where x?=?0, 0.1,0.3, 0.5 mol%) prepared by solution combustion method were reported. X-ray diffraction studies confirmed the formation of cubic spinel structure without any impurity phases. Scanning electron micrographs revealed grains of micrometer range with a spherical like morphology and narrow size distribution. Dielectric parameters such as dielectric constant, dielectric loss, impedance, and electrical modulus were found to depend on temperature, frequency, and dopant concentration. AC conductivity was found to increase with increase in temperature exhibiting negative temperature co-efficient of resistance (NTCR) property in the material. Complex impedance and electrical modulus studies revealed the existence of temperature-dependent electrical relaxation in the material. The Correlated Barrier Hopping (CBH) model of conduction mechanism was confirmed by the decrease in s parameter with increase in temperature. Charge-discharge studies revealed the stabilization of spinel lattice by Ni ions, contributing to better capacity retention.     

Depth profiles of metal ions implanted in dielectrics at low energies

The depth profiles of Cu⁺, Ag⁺, and Au⁺ ions implanted into amorphous dielectric SiO₂, Al₂O₃, and soda-lime silicate glass (SLSG) are simulated by the DYNA program. The algorithm follows projectile-ion-substrate-atom pair collisions giving rise to a dynamic variation in the phase composition in the surface layer of the irradiated material and takes into account surface sputtering. Ion implantation up to doses of ≤10¹⁶ ion/cm² at low ion energies of 30, 60, and 100 keV is considered. The measured dynamic variation of the depth profiles of implanted ions as a function of the dose is compared with the standard statistical distribution calculated by the TRIM algorithm.     

Two-dimensional electron gas at the interface of Ba<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>TiO<Subscript>3</Subscript> ferroelectric and LaMnO<Subscript>3</Subscript> antiferomagnet

The temperature dependence of the electrical resistance has been studied for heterostructures formed by antiferromagnetic LaMnO₃ single crystals of different orientations with epitaxial films of ferroelectric Ba_0.8Sr_0.2TiO₃ deposited onto them. The measured electrical resistance is compared to that exhibited by LaMnO₃ single crystals without the films. It is found that, in the samples with the film, for which the axis of polarization in the ferroelectric is directed along the perpendicular to the surface of the single crystal, the electrical resistance decreases significantly with temperature, exhibiting metallic behavior below 160 K. The numerical simulations of the structural and electronic characteristics of the BaTiO₃/LaMnO₃ ferroelectric?antiferromagnet heterostructure has been performed. The transition to the state with two-dimensional electron gas at the interface is demonstrated.     

An experimental and theoretical study of Ni impurity centers in Ba<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>TiO<Subscript>3</Subscript>

The local environment and the charge state of a nickel impurity in cubic Ba_0.8Sr_0.2TiO₃ are studied by XAFS spectroscopy. According to the XANES data, the mean Ni charge state is ~2.5+. An analysis of the EXAFS spectra and their comparison with the results of first-principle calculations of the defect geometry suggest that Ni²⁺ ions are in a high-spin state at the B sites of the perovskite structure and the difference of charges of Ni²⁺ and Ti⁴⁺ is mainly compensated by distant oxygen vacancies. In addition, a considerable amount of nickel in the sample is in a second phase BaNiO_{3 ? δ}. The measurements of the lattice parameter show a decrease in the unit cell volume upon doping, which can indicate the existence of a small amount of Ni⁴⁺ ions at the B site.     

Structural and optical properties of novel surfactant-coated Yb@TiO<Subscript>2</Subscript> nanoparticles

In this paper a novel hybrid approach to synthesise composite nanoparticles is presented. It is based on the laser ablation of a bulk target (Yb) immersed in a reversed micellar solution which contains nanoparticles of a different host material (TiO₂ nanoparticles) previously synthesised by chemical method. This approach thus exploits the advantages of the chemical synthesis through reversed micellar solution (size control, nanoparticle stabilisation), and of the laser ablation (“clean” synthesis, no side reactions). Central role is played by the microscopic processes controlling the deposition of the ablated Yb atoms onto the surface of TiO₂ nanoparticles which actually behave as nucleation seeds. The structural features of the resulting Yb@TiO₂ composite nanoparticles have been studied by Transmission Electron Microscopy, whereas their peculiar optical properties have been explored by UV–Vis spectroscopy and steady-state fluorescence. Results consistently show the formation of Yb and TiO₂ glued nanodomains to form nearly spherical and non-interacting nanoparticles with enhanced photophysical properties.     

Investigation of the SiO<Subscript>2</Subscript>(Co)/GaAs heterostructures using the surface scattering of synchrotron radiation

The giant injection magnetoresistive effect has been observed in a granulated Co/SiO₂ film on a semiconductor GaAs substrate in a narrow temperature range near T = 300 K. According to the existing theory, the nature of the effect is due to the structure and physical problems of the interface layer. The spatial distribution of cobalt nanoparticles in the bulk of the Co/SiO₂ granular film and at the granular film/semiconductor substrate (GF/SS) interface has been investigated by the reflectometry and small-angle scattering of synchrotron radiation in the grazing geometry. It has been shown that the characteristic average distance between the cobalt granules in the bulk of the film is 7.3 nm. At the same time, the average distance between the granules with a vertical size of about 7.5 nm at the GF/SS interface is 32 nm. The experimental data indicate the low concentration of cobalt at the interface and the point character of the contact of the main bulk of the Co/SiO₂ film with the GaAs substrate through a relatively diluted layer of ferromagnetic cobalt granules.     

Effect of structural defects on the magnetic properties of the EuBaCo<Subscript>1.90</Subscript>O<Subscript>5.36</Subscript> single crystal

The effect of structural defects in cobalt and oxygen sublattices with the constant average oxidation level 3+ of all cobalt ions on the magnetic properties of the EuBaCo_1.90O_5.36 single crystal has been studied. The magnetic properties of the single crystal and the polycrystalline sample of the corresponding composition are compared in the range T = 200–650 K. The results show that the cobalt-deficient EuBaCo_2–xO_5.5–δ samples demonstrate a three-dimensional XY ferromagnetic ordering of magnetic sublattices. The values of the effective magnetic moment at T > 480 K indicate the existence of the IS and HS states of Co³⁺ ions. The large difference of values of μ_eff of the EuBaCo_1.90O_5.36 single crystal and polycrystal can be due to that the magnetic ion spins lie in plane ab. The magnetic field directed along plane ab substantially influences the magnetic ordering at T < 300 K.     

Cobalt Modification of Thin Rutile Films Magnetron-Sputtered in Vacuum

Using X-ray phase analysis, atomic force microscopy, and secondary ion mass-spectrometry, the phase formation and component distribution in a Co–TiO₂ film system have been investigated during magnetron sputtering of the metal on the oxide and subsequent vacuum annealing. It has been found that cobalt diffuses deep into titanium oxide to form complex oxides CoTi₂O₅ and CoTiO₃. A mechanism behind their formation at grain boundaries throughout the thickness of the TiO₂ film is suggested. It assumes the reactive diffusion of cobalt along grain boundaries in the oxide. A quantitative model of reactive interdiffusion in a bilayer polycrystalline metal–oxide film system with limited solubility of components has been developed. The individual diffusion coefficients of cobalt and titanium have been determined in the temperature interval 923–1073 K.