Atomic Layer Deposition of Electroluminescent ZnS, SrS, and BaS Thin Films

The light emitted by flat panel displays (FPD) can be generated in many different ways, such as for example alternating current thin film electroluminescence (ACTFEL), liquid crystal display (LCD), light emitting diode (LED), or plasma display panel (PDP) technologies. In this work, the focus was on ACTFEL devices and the goal was to develop new thin film processes for light emitting materials in ACTFEL devices. The films were deposited with the atomic layer deposition (ALD) method, which has been utilized in the manufacturing of ACTFEL displays since the mid-1980s. The ALD method is based on surface-controlled self-terminated reactions and a maximum of one layer of the desired material can be prepared during one deposition cycle. Therefore, the film thickness can be controlled simply by adjusting the number of deposition cycles. In addition, both large areas and deep trench structures can be covered uniformly. During this work, new ALD processes were developed for the following thin film materials: BaS, CuxS, MnS, PbS, SrS, SrSe, SrTe, SrS1-xSex, ZnS, and ZnS1-xSex. In addition, several ACTFEL devices were prepared where the light emitting material was BaS, SrS, SrS1-xSex, ZnS, or ZnS1-xSex thin film that was doped with Ce, Cu, Eu, Mn, or Pb. The sulfoselenide films were made by substituting the elemental selenium for sulfur on the substrate surface during film deposition. In this way, it was possible to replace a maximum of 90% of the sulfur with selenium, and the XRD analyses indicated that the films were solid solutions. The polycrystalline BaS, SrS, and ZnS thin films were deposited at 180-400, 120-460, and 280-500 °C, respectively, and the processes had a wide temperature range where the growth rate of the films was independent of the deposition temperature. The electroluminescence studies showed that the doped sulfoselenide films resulted in low emission intensity. However, the emission intensities and emission colors of the doped SrS, BaS, and ZnS films were comparable with those found in earlier studies. It was also shown that the electro-optical properties of the different ZnS:Mn devices were different as a consequence of different ZnS:Mn processes. Finally, it was concluded that because the higher deposition temperature seemed to result in a higher emission intensity, the thermal stability of the reactants has a significant role when the light emitting materials of ACTFEL devices are deposited with the ALD method.

Properties of Ammonium Nitrate based fertilisers

The text is divided into three parts; Properties, Application and Safety of Ammonium Nitrate (AN) based fertilisers. In Properties, the structures and phase transitions of ammonium and potassium nitrate are reviewed. The consequences of phase transitions affect the proper use of fertilisers. Therefore the products must be stabilised against the volume changes and consequent loss of bulk density and hardness, formation of dust and finally caking of fertilisers. The effect of different stabilisers is discussed. Magnesium nitrate, ammonium sulphate and potassium nitrate are presented as a good compromise. In the Application part, the solid solutions in the systems (K+,NH4+)NO3- and (NH4+,K+)(Cl-,NO3-) are presented based on studies made with DSC and XRD. As there are clear limits for solute content in the solvent lattice, a number of disproportionation transitions exist in these process phases, e.g., N3 (solid solution isomorphous to NH4NO3-III) disproportionates to phases K3 (solid solution isomorphous to KNO3-III) and K2 (solid solution isomorphous to KNO3-II). In the crystallisation experiments, the formation of K3 depends upon temperature and the ratio K/(K+NH4). The formation of phases K3, N3, and K2 was modelled as a function of temperature and the mole ratios. In introducing chlorides, two distinct maxima for K3 were found. Confirmed with commercial potash samples, the variables affecting the reaction of potassium chloride with AN are the particle size, time, temperature, moisture content and amount of organic coating. The phase diagrams obtained by crystallisation studies were compared with a number of commercial fertilisers and, with regard to phase composition, the temperature and moisture content are critical when the formation and stability of solid solutions are considered. The temperature where the AN-based fertiliser is solidified affects the amount of compounds crystallised at that point. In addition, the temperature where the final moisture is evaporated affects the amount and type of solid solution formed at this temperature. The amount of remaining moisture affects the stability of the K3 phase. The K3 phase is dissolved by the moisture and recrystallised into the quantities of K3, which is stable at the temperature where the sample is kept. The remaining moisture should not be free; it should be bound as water in the final product. The temperatures during storage also affect the quantity of K3 phase. As presented in the figures, K3 phase is not stable at temperatu¬res below 30 °C. If the temperature is about 40 °C, the K3 phase can be formed due to the remaining moisture. In the Safety part, self-sustaining decomposition (SSD), oxidising and energetic properties of fertilisers are discussed. Based on the consequence analysis of SSD, early detection of decomposition in warehouses and proper temperature control in the manufacturing process is important. SSD and oxidising properties were found in compositions where K3 exists. It is assumed that potassium nitrate forms a solid matrix in which AN can decompose. The oxidising properties can be affected by the form of the product. Granular products are inherently less oxidising. Finally energetic properties are reviewed. The composition of the fertiliser has an importance based on theoretical calculations supported by experimental studies. Materials such as carbonates and sulphates act as diluents. An excess of ammonium ions acts as a fuel although this is debatable. Based on the experimental work, the physical properties have a major importance over the composition. A high bulk density is of key importance for detonation resistance.

Structural transitions in (La,Ln)2CuO4 and La2(Cu,Ni)O4 systems

Solid solutions of the formula La2−xLnxCuO4 (Ln = Pr, Nd) possess the orthorhombic structure of La2CuO4 for small values of x and transform to the tetragonal Nd2CuO4 structure at a critical value of x. At the critical composition, there is an abrupt change in specific volume as well as the Image ratio. The material exhibits temperature-independent electrical resistivity below the critical value x and semiconducting behaviour above it. The specific volume and Image ratio smoothly decrease with increase in x in the La2Cu1−xNixO4 system, although the solid solution possess the tetragonal K2NiF4 structure when x>0.1. Compositions with x>0.1 exhibit a gradual semiconductor metal transition similar to that of La2NiO4, the transition temperature decreasing with increasing

In situ pump probe optical absorption studies on Sb/As2S3 nanomultilayered film

We report the in situ optical transmission change in the complete visible region of the electromagnetic spectrum to asses the kinetics of photo induced interdiffusion in Sb/As2S3 nanomultilayered film. The interdiffusion of Sb into As2S3 matrix results in the formation of Sb-As2S3 ternary solid solutions which is explained by the change in optical band gap, absorption coefficients and Tauc parameter (B-1/2) with evolution of time. The wavelength dependence of the time constants provides a better description of photo induced effects. The time evolution of the absorption coefficients and optical band gap are significantly faster in this process. (C) 2009 Elsevier B.V. All rights reserved.

Compatibility of RuO2 electrodes with PZT ceramics

Because of its high electrical conductivity and good diffusion barrier properties ruthenium dioxide (RuO2) is a good electrode material for use with ferroelectric lead zirconate-titanate (PZT) solid solutions. Under certain conditions, RuO2 can react with PZT to form lead ruthenate (Pb2Ru2O6.5) during processing at elevated temperatures resulting in lead depletion from PZT. The standard Gibbs energies of formation of RuO2 and Pb2Ru2O6.5 and activities of components of the PZT solid solution have been determined recently. Using this data along with older thermodynamic information on PbZrO3 and PbTiO3, the stability domain of Pb2Ru2O6.5 is computed as a function of PZT composition, temperature and oxygen partial pressure in the gas phase. The results show PbZrO3-rich compositions are more prone to react with RuO2 at all temperatures. Increasing temperature and decreasing oxygen partial pressure suppress the reaction. Graphically displayed are the reaction zones as a function of oxygen partial pressure and PZT composition at temperatures 973, 1173 and 1373 K.

Phase diagram of the system Ca-Ti-O at 1200 K

Phase relations in the system Ca-Ti-O have been established by equilibration of several samples at 1200 K for prolonged periods and identification of phases in quenched samples by optical and scanning electron microscopy, XRD and EDS. Samples representing 20 compositions in the ternary system were analyzed. There was negligible solid solubility of Ca in the phases along the binary Ti-O, and of Ti in CaO. Four ternary oxides were identified: CaTiO3, Ca4Ti3O10 and Ca3Ti2O7 containing tetravalent titanium, and CaTi2O4 containing trivalent titanium. Tie-lines link calcium titanite (CaTi2O4) with the three calcium titanates (CaTiO3, Ca4Ti3O10 and Ca3Ti2O7), CaO, oxygen excess TiO1+delta and stoichiometric TiO. Tie-lines connect CaTiO3 with TiO2-x, Magneli phases TinO2n-1 (28 >= n >= 4), Ti3O5, Ti2O3 and TiO1+delta. CaO was found to coexist with TiO, and Ti-O solid solutions alpha and beta. The phase diagram is useful for understanding the mechanisms and kinetics of direct calciothermic reduction of TiO2 to metal and electrochemical reduction of TiO2 using graphite anode and molten CaCl2 electrolyte.

Phase Diagram for the System RuO2-TiO2 in Air

There are conflicting reports in the literature regarding solid solubility in the system RuO2-TiO2. To resolve this issue a few experiments were conducted in air at 1673, 1723, and 1773 K. The results show limited terminal solid solubility. There is an extended solid-state miscibility gap that intersects the decomposition curve for the RuO2-rich solid solution generating a peritectoid reaction at 1698 K. The measured equilibrium compositions of the solid solutions are used to develop a thermodynamic description of the oxide solid solution with rutile structure. Using the subregular solution model, the enthalpy of mixing can be represented by the expression, Delta H-M/J center dot mol(-1) = XTiO2XRuO2 ( 34,100X(TiO2) + 30,750X(RuO2)). The binodal and spinodal curves and T-X phase diagram in air are computed using this datum and Gibbs energy of formation of RuO2 available in the literature. The computed results suggest that equilibrium was not attained during solubility measurements at lower temperatures reported in the literature.

Random existence of charge ordered stripes and its influence on the magnetotransport properties of La0.6Sr0.4MnO3 perovskite substituted with diamagnetic ions at Mn sublattice

Phase-singular solid solutions of La0.6Sr0.4Mn1-yMeyO3 (0 <= y <= 0.3) [Me=Li1+, Mg2+, Al3+, Ti4+, Nb5+, Mo6+ or W6+] [LSMey] perovskite of rhombohedral symmetry (space group: R (3) over barc) have been prepared wherein the valence of the diamagnetic substituent at Mn site ranged from 1 to 6. With increasing y-content in LSMey, the metal-insulator (TM-I) transition in resistivity-temperature rho(T) curves shifted to low temperatures. The magnetization studies M(H) as well as the M(T) indicated two groups for LSMey. (1) Group A with Me=Mg, Al, Ti, or Nb which are paramagnetic insulators (PIs) at room temperature with low values of M (< 0.5 mu(B)/Mn); the magnetic transition [ferromagnetic insulator (FMI)-PI] temperature (T-C) shifts to low temperatures and nearly coincides with that of TM-I and the maximum magnetoresistance (MR) of similar to 50% prevails near T-C (approximate to TM-I). (2) Group-B samples with Me=Li, Mo, or W which are FMIs with M-s=3.3-3.58 mu(B)/Mn and marginal reduction in T-C similar to 350 K as compared to the undoped LSMO (T-C similar to 378 K). The latter samples show large temperature differences Delta T=T-c-TM-I, reaching up to similar to 288 K. The maximum MR (similar to 60%) prevails at low temperatures corresponding to the M-I transition TM-I rather than around T-C. High resolution lattice images as well as microscopy analysis revealed the prevalence of inhomogeneous phase mixtures of randomly distributed charge ordered-insulating (COI) bistripes (similar to 3-5 nm width) within FMI charge-disordered regions, yet maintaining crystallographically single phase with no secondary precipitate formation. The averaged ionic radius < r(B)>, valency, or charge/radius ratio < CRR > cannot be correlated with that of large Delta T; hence cannot be used to parametrize the discrepancy between T-C and TM-I. The M-I transition is controlled by the charge conduction within the electronically heterogeneous mixtures (COI bistripes+FMI charge disordered); large MR at TM-I suggests that the spin-ordered FM-insulating regions assist the charge transport, whereas the T-C is associated with the bulk spin ordered regions corresponding to the FMI phase of higher volume fraction of which anchors the T-C to higher temperatures. The present analysis showed that the double-exchange model alone cannot account for the wide bifurcation of the magnetic and electric transitions, contributions from the charge as well as lattice degrees of freedom to be separated from spin/orbital ordering. The heterogeneous phase mixtures (COI+FMI) cannot be treated as of granular composite behavior. (c) 2008 American Institute of Physics.

Thermodynamic Properties and Phase Diagram for the System MoO2–TiO2

The activity of molybdenum dioxide (MoO2) in the MoO2–TiO2 solid solutions was measured at 1600 K using a solid-state cell incorporating yttria-doped thoria as the electrolyte. For two compositions, the emf was also measured as a function of temperature. The cell was designed such that the emf is directly related to the activity of MoO2 in the solid solution. The results show monotonic variation of activity with composition, suggesting a complete range of solid solutions between the end members and the occurrence of MoO2 with a tetragonal structure at 1600 K. A large positive deviation from Raoult's law was found. Excess Gibbs energy of mixing is an asymmetric function of composition and can be represented by the subregular solution model of Hardy as follows.The temperature dependence of the emf for two compositions is reasonably consistent with ideal entropy of mixing. A miscibility gap is indicated at a lower temperature with the critical point characterized by Tc (K)=1560 and . Recent studies indicate that MoO2 undergoes a transition from a monoclinic to tetragonal structure at 1533 K with a transition entropy of 9.91 J·(mol·K)−1. The solid solubility of TiO2 with rutile structure in MoO2 with a monoclinic structure is negligible. These features give rise to a eutectoid reaction at 1412 K. The topology of the computed phase diagram differs significantly from that suggested by Pejryd.

Metal-spinel-corundum three phase equilibria in the system Ni-Cr-Al-O at 1373 K

The tie-lines representing the inter-crystalline ion exchange equilibria between the NiCr2O4-NiAl2O4 spinet solid solution and Cr2O3-Al2O3 corundum solid solution are determined by electron microprobe andEDAX pointcountanalysis of the oxide phases equilibrated with metallic Ni at 1373 K. The component activities in the spinet solid solution are derived from the tie-lines and thermodynamic data for Cr2O3-Al2O3 solid solution available in the literature. The Gibbs energy of mixing of the spinet solid solution calculated from the experimental data is discussed in relation to the values derived from the cation distribution models which assume random mixing of cations on both tetrahedral and octahedral sites. Positive deviation from the models is observed indicating significant positive enthalpy contribution arising form the size mismatch between Al+3 and Ni+2 ions on the tetrahedral site and Al+3, Ni+2 and Cr+3 on the octahedral site. Variation of the oxygen potential for threephase equilibrium involving metallic nickel, spinet solid solution and corundum solid solution is computed as a function of composition of the solid solutions at 1373 K. The oxygen potential exhibits a minimum at aluminum cationic fraction eta(Al)/(eta(Al) + eta(Cr)) = 0.524 in the oxide solid solutions.

Pd and Pt ions as highly active sites for the water-gas shift reaction over combustion synthesized zirconia and zirconia-modified ceria

Noble metal substituted ionic catalysts were synthesized by solution combustion technique. The compounds were characterized by X-ray diffraction, FT-Raman spectroscopy, and X-ray photoelectron spectroscopy. Zirconia supported compounds crystallized in tetragonal phase. The solid solutions of ceria with zirconia crystallized in fluorite structure. The noble metals were substituted in ionic form.The water-gas shift reaction was carried out over the catalysts.Negligible conversions were observed with unsubstituted compounds. The substitution of a noble metal ion was found to enhance the reaction rate. Equilibrium conversion was obtained below 250 degrees C in the presence of Pt ion substituted compounds. The formation of Bronsted acid-Bronsted base pairs was proposed to explain the activity of zirconia catalysts. The effect of oxide ion vacancies on the reactions over substituted ceria-zirconia solid solutions was established. (c)2010 Elsevier B.V. All rights reserved.

Structure of Ce1-xSnxO2 and its relation to oxygen storage property from first-principles analysis

CeO2-SnO2 solid solution has been reported to possess high oxygen storage/release property which possibly originates from local structural distortion. We have performed first-principles based density functional calculations of Ce1-xSnxO2 structure (x=0, 0.25, 0.5, 1) to understand its structural stability in fluorite in comparison to rutile structure of the other end-member SnO2, and studied the local structural distortion induced by the dopant Sn ion. Analysis of relative energies of fluorite and rutile phases of CeO2, SnO2, and Ce1-xSnxO2 indicates that fluorite structure is the most stable for Ce1-xSnxO2 solid solution. An analysis of local structural distortions reflected in phonon dispersion show that SnO2 in fluorite structure is highly unstable while CeO2 in rutile structure is only weakly unstable. Thus, Sn in Ce1-xSnxO2-fluorite structure is associated with high local structural distortion whereas Ce in Ce1-xSnxO2-rutile structure, if formed, will show only marginal local distortion. Determination of M-O (M=Ce or Sn) bond lengths and analysis of Born effective charges for the optimized structure of Ce1-xSnxO2 show that local coordination of these cations changes from ideal eightfold coordination expected of fluorite lattice to 4+4 coordination, leading to generation of long and short Ce-O and Sn-O bonds in the doped structure. Bond valence analyses for all ions show the presence of oxygen with bond valence similar to 1.84. These weakly bonded oxygen ions are relevant for enhanced oxygen storage/release properties observed in Ce1-xSnxO2 solid solution. (C) 2010 American Institute of Physics.

Evolution of magnetic order in the system LaNi1-xMnxO3 (x < 0.10)

Magnetic susceptibility measurements on dilute solid-solutions LaNi1-xMnxO3 (x < 0.1) have been carried out. With increasing x the magnetic susceptibility behaviour changes from Pauli paramagnetic to Curie-Weiss type. The temperature coefficient of resistance (TCR) changes sign around x = 0.03 but the system seems to be metallic in terms of showing a finite extrapolated conductivity at 0 K even when x = 0.10. The x = 0.10 system shows indications of spin-glass like behaviour.

Ba3ZnTa2-xNbxO9 and Ba3MgT2-xNbxO9: synthesis, structural and dielectric studies

Oxides of the families Ba3ZnTa2-xNbxO9 and Ba3MgTa2-xNbxO9 were obtained by the solid state reaction route at 1573 K and were found to crystallize in the disordered (cubic) perovskite structure. In Ba3ZnTa2-xNbXO9 and Ba3MgTa2-xNbxO9 the entire range (0 less than or equal to x less than or equal to 1) of solid solutions could be synthesized. The dielectric constant decreases with increase in frequency for all compositions in the range 40 Hz to 100 kHz (epsilon (r) varies from 16 to 22). The dielectric loss (D) shows a broad maximum for both Ba3ZnTa2-xNbxO9 and Ba3MgTa2-xNbxO9. The maxima is centered around 2 kHz in the former and near 10 kHz in the latter. (C) 2001 Elsevier Science Ltd. All sights reserved.

Photo induced optical changes in Sb/As2S3 multilayered film and (As2S3)(0.93)Sb-0.07 film of equal thickness

The increase in optical band gap (photo bleaching) due to light illumination was studied at room temperature as well as at low (4.2 K) temperature for Sb/As2S3 multilayered film of 640 nm thickness by Fourier Transform Infrared Technique. The interdiffusion of Sb into As2S3 matrix results the formation of Sb-As2S3 ternary solid solutions which is explained by the change in optical band gap (E-g), absorption coefficient (alpha), Tauc parameter (B-1/2), Urbach edge (E-e). At the same time, photo darkening phenomena was observed in (As2S3)(0.93)Sb-0.07 film of same thickness both at low and room temperatures. From our X-ray Photoelectron Spectroscopy measurements,we are able to show that some of the As-As, S-S and Sb-Sb bonds are converted into As-S and S-Sb bonds in case of multilayers. We found that the energetically favoured heteropolar bond formation take place by a phonon-assisted mechanism using the lone pair pi electrons of S-2(0). But in case of (As2S3)(0.93)Sb-0.02 film, the homopolar bonds are playing a major role. (C) 2010 Elsevier B.V. All rights reserved.