High quality TbMnO3 films deposited on YAlO3

High quality thin films of TbMnO₃ were grown by pulsed laser deposition on orthorhombicYAlO₃ (1 0 0). The interface and surface roughness of a 55 nm thick film were probed by X-ray reflectometry and atomic force microscopy, yielding a roughness of 1 nm. X-ray diffraction revealed untwinned films and a small mosaic spread of 0.04° and 0.2° for out-of-plane and in-plane reflections, respectively. This high degree of epitaxy was also confirmed by Rutherford backscattering spectrometry. Using polarized neutron diffraction we could identify a magnetic structure with the propagation vector (0 0.27 0), identical to the bulk magnetic structure of TbMnO₃.     

Microstructure and high-temperature strength in MoSi2/NbSi2 duplex silicides

Pseudo-binary (Mo_0.90Nb_0.10)Si₂ and (Mo_0.85Nb_0.15)Si₂ containing duplex C11_b and C40 phases were prepared in a slow solidification process using the floating zone method to obtain basic knowledge regarding control of their microstructure. In (Mo_0.90Nb_0.10)Si₂ a thick band-like C40 phase was formed along grain boundaries in the C11_b matrix, while peculiar fine lamellar colonies composed of the C11_b and C40 phases appeared in (Mo_0.85Nb_0.15)Si₂ accompanied by constituent large C11_b and C40 grains. The orientation relationship between the two phases at the lamellar boundary was determined to be (0001)_C40(110)_C11b and [110]_C40[11]_C11b. Although the atomic stacking sequence changed from three-fold periodical layers on (0001) planes in the C40 phase to two-fold layers on (110) planes in the C11_b phase at the lamellar boundary, the lattice mismatch at the interface was very small (within 3%), resulting in good thermal stability of this microstructure and high strength at high temperatures. The phase transformation must proceed by the motion of all four 1/612-type partial dislocations on two layers of every three (0001) layers in the C40 phase to avoid large lattice distortion.     

Low temperature oxidation of Cr-alloyed MoSi2

Cr-alloyed MoSi2 was compared with monolithic MoSi2 with respect to oxidation at 450℃ for 456 h. Phases formed on Cr-alloygd MoSi2 after exposure are Cr2（MoO4）3, MOO3, and cristobalite （SiO2） according to X-ray diffraction results. Monolithic MoSi2 forms MoO3 and mainly amorphous SiO2. X-ray photoelectron spectroscopy indicates that the main oxidation product on the outermost surface is SiO2 for all studied samples. The samples form a relatively loose oxide but the oxide adherence improves with increasing Cr content. It is indicated that Cr addition can benefit pesting control in MoSi2.     

Annealing driven performance and optical effects in nanocrystalline SnO2 thin films induced by pulsed delivery

Tin dioxide thin films were prepared successfully by pulsed laser deposition techniques on glass substrates. The thin films were then annealed for 30 min from 50 °C to 550 °C at 50 °C intervals. The influence of the annealing temperature on the microstructure and optical properties of SnO₂ thin films was investigated using X-ray diffraction, optical transmittance and reflectance measurements. Various optical parameters, such as optical band gas energy, refractive index and optical conductivity were calculated from the optical transmittance and reflectance data recorded in the wavelength range 300-2500 nm. We found that the SnO₂ thin film annealed at temperatures up to 400 °C is a good window material for solar cell application. Our experimental results indicated that SnO₂ thin films with the high optical quality could be synthesized by pulsed laser deposition techniques.     

Microstructure and grain growth kinetics of nanocrystalline SnO2 thin films prepared by pulsed laser deposition

The isothermal grain growth of SnO₂ thin films prepared by pulsed laser deposition techniques was investigated at Si (100) substrate temperatures between 300 and 450 °C with 50 °C intervals for different annealing times. X-ray diffraction patterns proved that the average grain sizes are in the range of 2.4–27.8 nm. The grain growth data were analyzed using two different models. The first model, assuming normal grain growth as that in conventional polycrystalline materials, yields large grain growth exponent (n) and extremely low activation energy (Q). Although it can describe the evolution of grain sizes, it fails to give satisfactory physical interpretation of n and Q, both beyond the theoretical predictions. The second model is based on the structural relaxation of the interface component in nanocrystalline materials. In this case, the ordering of distorted interfaces by structural relaxation proceeds with grain growth. This structure relaxation model not only describes the evolutions of grain growth well, but also makes reasonable attribution of the low activation energy to the short-range rearrangement of atoms in the interface region as well.     

Preparation of delafossite-type CuCrO2 films by sol-gel method

High-quality c-axis oriented delafossite-type CuCrO₂ films were successfully prepared by a simple sol-gel method. The microstructure, optical properties as well as room temperature resistivity were studied. It was found that the grain sizes of CuCrO₂ films pretreated with different temperatures are different; the films were smooth and consisted of fine particles. The maximal transmittance of CuCrO₂ films can reach 70% in the visible region. Optical transmission data of CuCrO₂ films indicate a direct band gap and an indirect-gap of about 3.15 eV and 2.66 eV, respectively. The carrier mobility of the films pretreated at 300 °C is smaller than that of the films pretreated at a higher temperature, because of the stronger carrier scattering.     

Structural and electrical properties of SrBi2(Ta0.5Nb0.5)2O9 thin films

SrBi₂(Ta_0.5Nb_0.5)₂O₉ (SBTN) thin films were obtained by polymeric precursor method on Pt/Ti/SiO₂/Si(1 0 0) substrates. The film is dense and crack-free after annealing at 700 °C for 2 h in static air. Crystallinity and morphological characteristic were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). The films displayed rounded grains with a superficial roughness of 3.5 nm. The dielectric permittivity was 122 with loss tangent of 0.040. The remanent polarization (P_r) and coercive field (E_c) were 5.1 μC/cm² and 96 kV/cm, respectively.     

Room-temperature synthesis of crystallized LiCoO2 thin films by electrochemical technique

LiCoO₂ thin films have been directly synthesized on cobalt substrate in LiOH solution at room temperature by electrochemical method. The obtained LiCoO₂ thin films were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The influence of electrochemical reaction time, current density and concentration of LiOH solution on the crystal structure and morphology of the obtained LiCoO₂ thin films was discussed emphatically. Our results show that the as-synthesized LiCoO₂ films all are pure hexagonal structure. The crystallinity, densification and uniformity of the films increase with increasing electrochemical reaction time, current density as well as concentration of LiOH solution and then decrease. The preferable electrochemical reaction conditions were optimized as: electrochemical reaction time is 50 h, current density is 1 mA cm⁻² and concentration of LiOH solution is 3 mol dm⁻³.     

Phase transformations after long-time annealing in metastable Fe–Cr alloy films prepared by pulsed laser deposition

Metastable Fe–Cr alloy films of various composition prepared by cross-beam pulsed laser deposition using two different procedures are investigated by wide-angle X-ray scattering. Depending on the Fe–Cr composition of the samples in an extended range, a body-centered cubic (bcc) phase or metastable phases with body-centered tetragonal (bct), face-centered orthorhombic (fco) or primitive orthorhombic (po) and primitive cubic (pc) lattices are formed in the films prepared by simultaneous co-deposition of Fe and Cr. In the films produced by layer-by-layer deposition of thin separate Fe and Cr layers (thickness of about 1 nm), only bcc and bct Fe–Cr phases were observed. A long-time annealing (50 h) at a temperature of 425 °C near the low-temperature existence limit of the σ-phase under equilibrium conditions followed by slow cooling (rate 0.5 °C/min) has been performed and various phase transformations were observed. In addition to known equilibrium and metastable Fe–Cr crystalline phases (mainly bcc and bct phases in the films prepared by layer-by-layer technique and bcc, bct and σ-FeCr phases in co-deposited films), a new metastable Fe–Cr superstructure characterised by a primitive tetragonal lattice with parameters a and c of about 0.57 and 0.63 nm, respectively, has been identified. It is shown that the formation of ″-crystallites with preferred orientation in the metastable Fe–Cr alloy films during dedicated long-time annealing gives rise to a spatially periodic modulation of chemical composition resulting in the formation of multilayers with periods of one or a few atomic monolayers of individual Fe and Cr components.     

Synthesis of MoSi2/WSi2 nanocrystalline powder by mechanical-assistant combustion synthesis method

MoSi₂/WSi₂ nanocrystalline powder has been successfully synthesized by the mechanical-assistant combustion synthesis method. This method includes a ball-milling process followed by combustion synthesis. The composition and microstructure of the as-milled powder mixture were detected by X-ray diffraction and scanning electron microscopy analyses. Their results show that the Mo(W) solid solution and Si nanocrystals could be obtained during the ball-milling process. Compared with normal powder mixture (Mo + Si + W), it could be easily ignited and high maximum combustion temperature was achieved. It was also confirmed that MoSi₂/WSi₂ solid solution powder with nanometric structure could be prepared through combustion synthesis method from the mechanical activated powder mixture.     

Multiferroic properties of Bi3.15Nd0.85Ti3O12-CoFe2O4 bilayer films derived by a sol-gel processing

Multiferroic Bi_3.15Nd_0.85Ti₃O₁₂ (BNT)-CoFe₂O₄ (CFO) bilayer films with different preferential orientations and thickness fractions for the BNT layer were prepared on Pt/Ti/SiO₂/Si substrate by a sol-gel processing. The experimental results showed that the bilayer films with preferentially a-axis oriented and thicker BNT layer have better ferroelectric properties. The magnetoelectric coupling response is weak when the degree of a-axis orientation of the BNT layer is low or the leakage current is high, while it is mainly controlled by the thickness fraction in other cases.     

Nano-wear, nano-hardness and corrosion-resistance of electroplated nickel surfaces after co-implantation of Cr and N2 ions

In this work, a successful sequential co-implantation treatment of Cr⁺ and N₂⁺ ions into electrodeposited nickel plates is presented. The goal of this treatment is the simultaneous enhancement of the wear resistance, mechanical stability and corrosion-protection properties of the Ni surfaces. The ion-implanted surfaces have been characterized by glow-discharge optical-emission spectroscopy, X-ray diffraction, nano-hardness, roughness, nano-wear and potentio-dynamic corrosion tests. It has been observed that the implantation of Cr⁺ or N₂⁺ alone is not sufficient to achieve simultaneously the enhancement of both the wear-resistance and the corrosion-protection properties. Conversely, the sequential implantation of Cr⁺ and N₂⁺ at 140 keV and fluencies of 3 × 10¹⁷ and 1.5 × 10¹⁷ ions/cm² respectively, permits the formation of a functional surface capable of reducing both the corrosion rate and the wear rates, with respect to those exhibited by the un-implanted Ni surfaces.This treatment can be used to protect the surfaces of micro-embossing/stamping dies based on electroformed Nickel, as an alternative to other coating strategies. Furthermore, the ion implantation assures the non-modification of the net-shape and surface finish of these types of dies, which is of crucial importance when they are used for high-precision micro-texturing/imprinting applications.     

Optical properties of thermally evaporated Bi2Se3 thin films treated with AgNO3 solution

Bismuth selenide (Bi₂Se₃) thin films have been prepared onto clean glass substrates by the thermal evaporation technique. The deposited films were then immersed in silver nitrate solution for different periods of time, followed by annealing in Argon atmosphere at 473 K for 1 h, to obtain Ag/Bi₂Se₃ samples. The prepared films have been examined by X-ray and transmission electron microscopy for structural determination. The optical transmission and reflection spectra of the deposited films have been recorded within the wavelength range 400-2500 nm. The variation of the optical parameters of the prepared films, such as refractive index, n, and the optical band gap, E_g as a function of the immersion duration times has been determined. The refractive index dispersion in the transmission and low absorption region is adequately described by the well-known Sellmeier dispersion relation, whereby the values of the oscillator strength, oscillator position, the high-frequency dielectric constant, ε_∞ as well as the carrier concentration to the effective mass ratio, N/m* were calculated as a function of the immersion duration time.     

Surface roughness and dispersion parameters of indium doped amorphous As2Se3 thin films

Both a binary amorphous system of composition As₂Se₃ and a ternary amorphous system of composition amorphous (As₂Se₃)_0.99In_0.01 with thickness in the range 150–250 nm have been prepared by thermal evaporation technique. Indium doping and thickness effects on the features of As₂Se₃ thin films have investigated. The optical transmission spectra of these films have been measured in the range 200–1200 nm where the absorption coefficient and the optical energy gap Eg are evaluated. The refractive index and surface roughness of the prepared films are found to be highly dependent on film thickness and indium doping, using Swanepoel method.The single oscillator energy (E_o) and the energy dispersion parameter (E_d) have been calculated and discussed in terms of the Wemple and DiDomenico model. The results reveal that, they are thickness dependent—both E_o and E_d being higher for the undoped samples than that for the doped films.     

The molybdenum diphosphate Mo1.3O(P2O7), containing Mo2 and Mo3 clusters

A novel molybdenum diphosphate, Mo_1.3O(P₂O₇), was obtained by electrochemical lithium deintercalation. The diphosphate crystallises in space group I2/a with the lattice parameters a=22.88(1), b=22.94(2), c=4.832(1) Å, γ=90.36°, Z=8. Its original framework is built up from MoO₆ octahedra, P₂O₇ groups and also from MoO₄, Mo₂O₄ and Mo₃O₈ units containing Mo₂ and Mo₃ clusters. These polyhedra delimit large octagonal and z-shaped tunnels running along c, in which the inserted cations may be located.     

Deposition and characterization of CuInSe2 films for solar cells using an optimized chemical route

CuInSe₂ (CISe) thin films have been deposited on glass using successive ionic layer adsorption and reaction (SILAR). The as-deposited films are treated at 400 °C in argon atmosphere and etched in KCN solution to remove detrimental secondary phases. The preparation and temperature of the precursor solutions, the duration of the reaction cycles and the duration of the annealing stage have been optimized. The films have been characterized employing grazing incident X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive scanning spectroscopy. Relevant semiconductor parameters have been calculated. Photoelectrochemical tests confirm p-type conduction. The films are crystalline and the stoichiometry can be improved by renewing the precursor solution after completing half of the cycles, annealing for 90 min and later etching in KCN. The quality of the material seems to be promising for application in solar cell devices.     

Surfactant assisted electrodeposition of MnO2 thin films: Improved supercapacitive properties

In order to obtain a high specific capacitance, MnO₂ thin films have been electrodeposited in the presence of a neutral surfactant (Triton X-100). These films were further characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and contact angle measurement. The XRD studies revealed that the electrodeposited MnO₂ films are amorphous and addition of Triton X-100 does not change its amorphous nature. The electrodeposited films of MnO₂ in the presence of the Triton X-100 possess greater porosity and hence greater surface area in relation to the films prepared in the absence of the surfactant. Wettability test showed that the MnO₂ film becomes superhydrophilic from hydrophilic due to Triton X-100. Supercapacitance properties of MnO₂ thin films studied by cyclic voltammetry, galvanostatic charge-discharge cycling and impedance spectroscopy showed maximum supercapacitance for MnO₂ films deposited in presence of Triton X-100 is 345 F g⁻¹.     

New Zr6CoAs2-type compounds: Y6CoBi2, Ho6CoBi2 and Tm6CoBi2

Results of a powder X-ray diffraction investigation of new ternary compounds are reported. The compounds Y₆CoBi₂ [a=0.8312(1) nm, c=0.4144(1) nm], Ho₆CoBi₂ [a=0.8246(2) nm, c=0.4095(1) nm], and Tm₆CoBi₂ [a=0.8155(2) nm, c=0.4066(1) nm] crystallize in the hexagonal Zr₆CoAs₂-type structure (space group P6b2m No. 189). The Zr₆CoAs₂-type structure is a superstructure of the Fe₂P-type structure.     

Structural characteristics and resistive switching properties of thermally prepared TiO2 thin films

Polycrystalline TiO₂ thin films were formed on Pt(1 1 1)/Ti/SiO₂/Si by thermal oxidation of Ti films with temperatures ranging from 600 °C to 800 °C. Results of Raman spectra testing indicate that the structure of the oxidized TiO₂ films is rutile phase. The resistance switching behaviors (RSB) have been confirmed in Pt/TiO₂/Pt structures. A stable RSB with a narrow dispersion of the resistance states and switching voltages was observed in the sample fabricated with the oxidation temperature of 600 °C. The resistance ratios of high resistance states to low resistance states are larger than 10³ with the set and reset voltage as low as 2.5 V and 0.6 V, respectively.