Epitaxial growth of titanium oxycarbide on MgO (0 0 1) substrates by pulsed laser deposition

Epitaxial TiC_xO_y thin films were grown on MgO (0 0 1) substrates by using pulsed laser deposition method. High-resolution X-ray diffraction and transmission electron microscopy were used to examine crystallinity and microstructure of epitaxial TiC_xO_y film on MgO. The chemical composition of the film is determined to be x ∼ 0.47 and y ∼ 0.69 by X-ray photoelectron spectroscopy. Atomic force microscopy revealed that the surface of TiC_xO_y film is very smooth with roughness of 0.18 nm. The resistivity of the TiC_xO_y film measured by four-point-probe method was about 137 μ Ω cm.     

Mn-doped Bi<Subscript>26</Subscript>Mo<Subscript>10</Subscript>O<Subscript>69-d</Subscript>: synthesis and characterization

In this work, we research two series of Mn-substituted bismuth molybdates: Bi_26-2xMn_2xMo₁₀O_69-d and Bi₂₆Mo_10-2yMn_2yO_69-d. The synthesis of powder samples is performed by the conventional solid state technology. Samples are characterized by X-ray diffraction, scanning electron microscopy, and chemical analysis methods, and it is shown that single phase Bi_26-2xMn_2xMo₁₀O_69-d and Bi₂₆Mo_10-2yMn_2yO_69-d complex oxides form up to x = 0.8 and y = 0. We use densitometry, grain size measurements and scanning electron microscopy to study the morphology of ceramic pellets and powders. This issue reveals formation of dense ceramic samples with low porosity (≤3%). High-temperature X-ray diffraction is used to define small deviation of unit cell parameters from their linear dependence on temperature. Measurement of electrical conductivity is made using a.c. impedance spectroscopy method. We observe the decrease of electrical conductivity in Bi_26-2xMn_2xMo₁₀O_69-d series depending on dopant concentration.     

Al<Subscript>2</Subscript>O<Subscript>3</Subscript> plasma production during pulsed laser deposition

A Nd:YAG laser operating in second harmonic (532 nm), 3 ns pulse duration, 150 mJ pulse energy, and 10 Hz repetition rate, is employed to irradiate Al₂O₃ target placed in high vacuum. The produced plasma is investigated by an ion collector used in time-of-flight configuration and by a mass quadrupole spectrometer, in order to determine the equivalent plasma temperature and the atomic and molecular composition. Pulsed laser deposition technique has been used to produce thin films on different substrates placed close to the target. Different surface analyses, such as energy dispersive X-ray fluorescence (EDXRF), X-ray photoelectron spectroscopy (XPS) and surface profilometry are employed to characterize the produced films. Measurements of ablation yield, plasma equivalent temperature, acceleration voltage and characterization of grown thin films are presented and discussed.     

An investigation into ultra-thin pseudobinary oxide (TiO<Subscript>2</Subscript>)<Subscript>x</Subscript>(Al<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>1-x</Subscript> films as high-<Emphasis Type="Italic">k</Emphasis> gate dielectrics

As potential gate dielectric materials, pseudobinary oxide (TiO₂)_x(Al₂O₃)_1-x (0.1≤x≤0.6) films (TAO) were deposited on Si (100) substrates by pulsed-laser deposition method and studied systematically via various measurements. By a special deposition process, including two separate steps, the TAO films were deposited in the form of two layers. The first layer was deposited at room temperature and the second layer was completed at the substrate temperature of 400 °C. Detailed data show that the properties of the TAO films are closely related to the ratio between TiO₂ and Al₂O₃. The existence of the first layer deposited at room temperature can effectively restrain the formation of the interfacial layer. And according to the results of X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy performed on the films, no other information belonging to the silicon oxide could be observed. For the (TiO₂)_0.4(Al₂O₃)_0.6 film, the best result has been achieved among all samples and its dielectric constant is evaluated to be about 38. It is valuable for the amorphous TAO film as one of the promising dielectric materials for high-k gate dielectric applications. PACS 77.55.+f; 73.40.Qv; 81.15.Fg     

X-Ray Spectral Studies of the Interface Interaction in CuO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/MWCNTs Nanocomposite

Results of a comprehensive study of the interface interaction of a nanostructured CuO_x and multiwalled carbon nanotubes (MWCNTs) in CuO_x/MWCNT nanocomposite by X-ray absorption spectroscopy (XANES, NEXAFS) and X-ray photoelectron spectroscopy (XPS) methods using a synchrotron radiation are presented. It is established that a nanostructured CuO_x in CuO_x/MWCNT nanocomposite is predominantly formed by CuO and has the form of flakelike particles 200–500 nm in size uniformly dispersed over an array of nanotubes. A chemical interaction of CuO_x and nanotubes with formation of covalent carbon–oxygen bonds, which does not lead to a significant destruction of the outer layers of carbon nanotubes, is observed at the interfaces of the nanocomposite.     

Raman scattering spectroscopy of inclusions of carbon in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films and its solid solutions with HfO<Subscript>2</Subscript>

We apply Raman scattering spectroscopy to study the nature of carbon inclusions in Al₂O₃ and (HfO₂) _x (Al₂O₃)_{1 ? x} films deposited using volatile complex compounds. Raman spectra of the films under investigation contain D and G vibrational modes, which indicate that carbon clusters of the sp ² configuration tend to form in the films. We estimate the size of clusters from the integrated intensity ratio I _D /I _G and find it to be in the range of 14–20 Å. The content of hydrogen in carbon clusters is calculated from the height of the photoluminescence pedestal and is found to vary from 14 to 30 at % depending on the regime of the film’s synthesis.     

Effect of thermal annealing on the structure of ZnSe/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite films

The ZnSe/Al₂O₃ nanocomposite films synthesized by laser evaporation followed by heat treatment are studied. X-ray diffraction and electron-microscopic investigations of the as-deposited films demonstrate the presence of ZnSe crystallites in an Al₂O₃ amorphous matrix. Annealing changes the structures of ZnSe and Al₂O₃, increases the ZnSe crystallite size, and causes the appearance of the ZnSeO₄ phase. The presence of aluminum oxide layers decreases the phase transformation temperature of zinc selenide.     

Electric and magnetic properties of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Pb(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript> bilayer thin films prepared by pulsed-laser deposition

CoFe₂O₄ (CFO) thin film with highly (111)-preferential orientation was first deposited on the silicon substrate by a pulsed-laser deposition, and then Pb(Zr_0.52Ti_0.48)O₃ (PZT) layers were deposited with different oxygen pressures to form the bilayer CFO/PZT nanocomposite thin films. X-ray diffraction showed that the PZT preferential orientation was strongly dependant on the oxygen pressure. The smooth film surface was obtained after depositing the CFO and PZT layers. The bilayer thin films exhibit good ferromagnetic and ferroelectric properties, and a low leakage current density of 0.004 μA/cm² at 50 kV/cm. The leakage current density curves show loops for the electric polarized field when the electric field reverses. PACS 77.84.Lf; 75.80+q; 81.05.Zx; 81.15.Fg     

DO<Subscript>3</Subscript>-type cubic structure of nonstoichiometric vanadium monoxide

An X-ray diffraction study indicates that nonstoichiometric vanadium monoxide VO _y ≡ V _x O _z (y = z/x) has a cubic structure of the DO₃ type (space group Fm $ \bar 3 $ \bar 3 m), where vanadium atoms are not only at the 4(a) sites of the metal fcc sublattice, but also at the tetrahedral 8(c) sites. This circumstance fundamentally distinguishes monoxide VO _y from strongly nonstoichiometric MX _y compounds with the B1 structure and the same space group, where atoms M and X and structural vacancies ▪ and ▭ of the metal and nonmetal sublattices, respectively, are distributed over the 4(a) and 4(b) sites. The dependence of the filling factor q of the tetrahedral interstices by vanadium atoms on the relative content y of oxygen in VO _y has been obtained. It has been shown that the composition of cubic vanadium monoxide should be represented as VO _y ≡ V _x O _z ≡ V _{x − 2q} V_2q ^(t)▪_{1 − x + 2q} O _z ▭_{1 − z} , taking into account the structure.     

Influence of electromagnetic radiation on the phase composition of clustered CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films

The effect of white and UV radiation on the phase composition of amorphous CN _x films are studied by X-ray diffraction analysis and visible-range spectroscopy. The films have variable-range atomic order and consist of amorphous graphite clusters (30 Å) crystalline clusters (50–100 Å) of graphite, diamond, and carbon nitride phases; and intercluster medium with long-range (1–2 Å) atomic order. It is shown that irradiation of the films by white light facilitates the growth of fine graphite clusters. Irradiation by UV light suppresses the growth of the graphite and carbon nitride phases, favoring the growth of the diamond phase (1.5%). It is demonstrated that a change in the mesoscopic phase composition of the CN _x films causes a change in the energy gap width in the visible range from E _g = 0.75 eV for the films irradiated by white light to E _g = 1.75 eV for those exposed to UV radiation.     

The Nernst-Ettingshausen coefficient in the normal phase of doped HTSCs of the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>y</Subscript> system

The temperature dependence of the Nernst-Ettingshausen coefficient Q(T) in the normal phase of doped HTSCs of the yttrium system was studied. The main features characterizing the behavior of this coefficient were revealed, and the character and mechanism of the effect that various nonisovalent substituents exert on the Q(T) dependence were analyzed. It is shown that the narrow-band model permits one not only to describe all the specific features observed in the Q(T) curves but also to perform a simultaneous quantitative analysis of the temperature dependences of four kinetic coefficients (the electrical resistivity and the Seebeck, Hall, and Nernst-Ettingshausen coefficients) with the use of a common set of model parameters characterizing the band structure and carrier system in the normal phase of an HTSC. This approach was employed to determine the carrier mobilities and the asymmetry of the dispersion curve in the systems studied (YBa₂Cu₃O_y, y = 6.37–6.91; YBa₂Cu_3?xCo_xO_y, x = 0–0.3; Y_1?xCa_xBa₂Cu₃O_y, x = 0–0.25; Y_1?xCa_xBa_2?xLa_xCu₃O_y, x = 0–0.5) and to analyze the effect of the substitutions involved on the variation of these parameters.     

Effect of Al-Mo codoping on the structure and ionic conductivity of sol-gel derived Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript> ceramics

Al-Mo codoped Li₇La₃Zr₂O₁₂ ceramics with fine grain were prepared by sol-gel method. The influences of Al-Mo codoping on the structure, microstructure, and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and impedance spectroscopy. The cubic phase Li₇La₃Zr₂O₁₂ has been stabilized by partial substitution of Al for Li and Mo for Zr. Li_6.6-3yAl_yLa₃Zr_1.8Mo_0.2O₁₂ (0?≤?y?≤?0.1) has been sintered at 1040–1060 °C for 3 h. The liquid sintering facilitated its densification. The relative density of the composition with x?=?0.075 was approximately 96.4%. Results indicated that the Al-Mo codoped LLZO synthesized by sol-gel method effectively lowered its sintering temperature, accelerated densification, and improved the ionic conductivity.     

The effects of copper and titanium co-substitution on LiNi<Subscript>0.6</Subscript>Co<Subscript>0.15</Subscript>Mn<Subscript>0.25</Subscript>O<Subscript>2</Subscript> for lithium ion batteries

The Li(Ni_0.6Co_0.15Mn_0.25)_1?x (CuTi) _x O₂ (x = 0.00, 0.01, 0.02, 0.03) cathode materials were synthesized via a hydroxide co-precipitation method followed by a solid-state reaction. The elementary composition, crystal structure features, morphology, and electrochemical performances of the powders were investigated in detail by inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), galvanostatic charge/discharge test, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), respectively. The results of XRD and Rietveld refinements demonstrate that Cu and Ti co-substitution does not destroy the crystal structure, but can decrease cation ordering level and improve structural integrity. Electrochemical results show that Cu and Ti addition also results in an improved rate and cycling performances compared to pristine LiNi_0.6Co_0.15Mn_0.25O₂. An increase in rate performance and cycle stability upon copper and titanium co-substitution is related to the better hexagonal structure and enhanced kinetics of the intercalation process. Especially, Li(Ni_0.6Co_0.15Mn_0.25)_0.99(CuTi)_0.01O₂ exhibits the best rate performance and cycle stability among all samples with discharge specific capacity of 178.8 mAh/g and capacity retention of 90.6% after 30 cycles at 0.2C, which are higher than those of other materials.     

Specific features of praseodymium-doping induced changes in the critical temperature and energy spectrum parameters of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> in the presence of calcium ions in the lattice

The results of the experimental study of the specific features of changes in the temperature and concentration dependences of the thermopower coefficient and the critical temperature in the Y_{0.85 − x} Ca_0.15Pr _x Ba₂Cu₃O _y system as the praseodymium content increases are presented. The results obtained have been analyzed based on the narrow band model, the energy spectrum and charge carrier system parameters have been determined, and their behavior with an increase in the doping level has been analyzed. It has been found that both superconducting properties and parameters of the normal state of Y_{0.85 − x} Ca_0.15Pr _x Ba₂Cu₃O _y vary differently in various doping ranges. Based on a comparison of the results obtained with the available data for the case of single doping of YBa₂Cu₃O _y with praseodymium, conclusions have been drawn regarding the mechanism of the energy spectrum modification in the studied compound. The Fermi-level pinning effect has been revealed in the region of a local peak of the density-of-states function, and the energy position of this peak has been determined. It has been shown that the consideration of the Fermi level dynamics caused by the specific features of the structure and transformation of the Y_{0.85 − x} Ca_0.15Pr _x Ba₂Cu₃O _y energy spectrum upon doping makes it possible to explain the observed dependence of the critical temperature on the praseodymium content.     

High-temperature complex impedance and modulus spectroscopic studies of doped Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> ferroelectric ceramics

Lead-free Na_0.5Bi_0.5TiO₃ (NBT) and (1 ? x)Na_0.5Bi_0.5TiO₃ + xBaTiO₃ with x = 0.1 and 0.2 (where x = 0.1 and 0.2 are named as NBT1 and NBT2, respectively), (1 ? y)Na_0.5Bi_0.5TiO₃ + yBa_0.925Nd_0.05TiO₃ with y = 0.1 and 0.2 (where y = 0.1 and 0.2 are named as NBT3 and NBT4, respectively)-based relaxor ferroelectric ceramics were prepared using the sol-gel method. The crystal structure was investigated by X-ray diffraction (XRD) at room temperature (RT). The XRD patterns confirmed the presence of the rhombohedral phase in all the samples. The electrical properties of the present NBT-based samples were investigated by complex impedance and the modulus spectroscopy technique in the temperature range of RT–600 °C. The AC conductivity was found to increase with the substitution of Ba²⁺ ions to the NBT sample whereas it significantly decreased with the addition of Nd³⁺ ions. The more anion vacancies in Ba-added samples and the lower anion vacancies in Nd-added samples were found to be responsible for higher and lower conductivities, respectively.     

Interfacial structures of LaAlO<Subscript>3</Subscript> films on Si(100) substrates

This paper investigates the interfacial characteristics of LaAlO₃ (LAO) and LaAlO_xN_y (LAON) films deposited directly on silicon substrates by the pulsed-laser deposition technique. High-resolution transmission electron microscopy (HRTEM) pictures indicate that an interfacial reaction between LAO and Si often exists. The interfacial layer thickness of LAO films deposited in a nitrogen ambient atmosphere is smaller than that of LAO films deposited in an oxygen ambient atmosphere. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to study the composition of the interfacial layer. The shift of the La 3d photoelectron peak to a higher binding energy compared to LaAlO₃, the shift of the Al 2p peak to a higher binding energy compared to LaAlO₃, the shift of the Si 2p peak to a lower binding energy compared to SiO₂ and the intermediate location of the O 1s peak compared to LaAlO₃ and SiO₂ indicate the existence of a La–Al–Si–O bonding structure, which was also proved by the AES depth profile of LAO films. It can be concluded that the interfacial layer is not simply SiO₂ but a compound of La–Al–Si–O. PACS 77.84.Bw; 77.84.-s; 77.55.+f     

Gas release in the process of thermal treatment of sputtered Pb(Ti<Subscript>0.48</Subscript>Zr<Subscript>0.52</Subscript>)O<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript> films

The conditions (regimes of deposition and thermal treatment) for gas bubble formation in ferroelectric Pb(Ti_1–yZr_y)O₃ films have been determined by thermal desorption and electron and optical micros-copy. A mechanism of bubble formation has been proposed. This mechanism rests upon the notion that lead can form oxides of the PbO₂ type with a high oxygen content at relatively low temperatures and that these oxides break down with the release of oxygen to lower oxides of the PbO type upon subsequent heating. These ideas have been taken as the basis of a technique for the fabrication of Pb(Ti_1–yZr_y)O₃ films with a reduced (by an order of magnitude) density of through defects.     

Effect of N content on phase configuration, nanostructure and mechanical behaviors in Ti-Cx-Ny thin films

Ti-C_x-N_y thin films with different nitrogen contents were deposited by way of incorporation of different amounts of nitrogen into TiC_1.02 using unbalanced reactive unbalanced dc magnetron sputtering method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and microindentation methods were used to investigate their phase configurations, nanostructures and mechanical behaviors in order to investigate their dependences on nitrogen content. The result indicated that the nitrogen content had a significant effect on phase configuration, nanostructure and mechanical behaviors of Ti-C_x-N_y thin films. The nitrogen-free TiC_1.02 films exhibited a polycrystallite with nano-grains. On one hand, incorporated nitrogen substituted C in TiC_1.02, producing Ti(C,N), and subsequently linked to the substituted C, forming C-N. On the other hand, the substituted C lined to each other, forming C-C. As a result, nanocomposite thin films consisting of nanocrystalline Ti(C,N) and amorphous (C, C-N) were produced. With further incorporation of nitrogen more C was substituted, accompanying with formation of more amorphous matrices and decrease of size of nanocrystalline Ti(C,N). The trend was enhanced with further increase of nitrogen content. A microhardness maximum of ∼58 GPa was obtained in nitrogen-free TiC_1.02 thin films. This value was linearly decreased with incorporation of N or increase of N content, and finally a hardness value of about 28 GPa was followed at a N content of ∼25 at.%. Both elastic modulus and residual compressive stress values exhibited similar trends.     

Relations between physical properties of the biferroic Pb(Fe<Subscript>1-x</Subscript>Nb<Subscript>x</Subscript>)O<Subscript>3</Subscript>ceramics and their composition change

The work shows basic features of ferromagnetic ceramics Pb(Fe_{1 - x}Nb_x)O₃ with various contents of Fe/Nb (x=1/3, 1/2, 2/3). The synthesis were carried out by powders sintering and calcination whereas densification by hot uniaxial pressing and conventional sintering methods. Optimum conditions of PFN obtention with various contents were based on X-ray, microstructural, dielectrical and conductivity tests together with increase of iron contents in Pb(Fe_{1 - x}Nb_x)O₃ usage parameters of those ceramics worsen. Optimum parameters are shown by the ceramics with contents Pb(Fe_{1 / 2}Nb_{1 / 2})O₃ synthetized using calcination method and densified by hot uniaxial pressing method.     

Magnetic resonance in Pb<Subscript>x</Subscript>Nb<Subscript>y</Subscript>O<Subscript>z</Subscript> ceramics as a system containing chemical fluctuation regions

Simulation of the chemical fluctuation regions in PMN-like relaxors through growth of the Pb_xNb_yO_z eramics was performed. Different Pb_xNb_yO_z clusters (chemically and structurally) coexist in such ceramics. Hole polaron and bipolaron (Cr³⁺-two polaronic-hole) paramagnetic complexes were considered for explanation of the EPR spectra in Pb_xNb_yO_z ceramics. Dynamical averaging, light-induced effects, and significant effects of reduction treatment giving the coexistence of Nb⁵⁺ and Nb³⁺ ions, as well as of a strong internal magnetic field, were discovered in this ceramics. The latter could be related to antiferromagnetic phase realization in Pb_xNb_yO_z clusters containing a sufficiently high concentration of magnetic Nb³⁺ host lattice ions. Such a situation leads to antiferromagnetic resonance on Nb³⁺ ions, as well as to EPR of Cr³⁺-related paramagnetic complexes in a Nb³⁺-induced internal magnetic field. Charge transfer vibronic excitons (CTVE) in free and in CTVE phase states were detected in Pb_xNb_yO_z ceramics by photoluminescence studies.