Synthesis, modeling of the structure and kinetic study of the thermal decomposition of La(III) and Nd(III) complexes with 3-hydroxypicolinic acid

Synthesis, spectroscopic studies, prediction of the structure and thermal decomposition of the La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O (3-OHpic = 3-hydroxypicolinic acid) complexes are described. Elemental analysis and the IR vibrational data are consistent with the complex formulae. The absorption spectra in ethanol of the La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O show maximum absorptions at 214 and 211 nm, respectively, which are shifted to 225 nm in the free ligand. The ab initio method RHF/STO-3G/ECP(MWB52) was used to optimize the geometry and the INDO/S-CI model for calculating the electronic spectra of these complexes. A good agreement between theoretical and experimental UV absorption spectra has been obtained. The thermal decomposition was studied by non-isothermal thermogravimetry. Thermal decomposition reactions of the complexes La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O are best described by R2 and R3 kinetic models.     

The discrete variable method for the solution of the time-dependent Schrödinger equation

A solution of the time-dependent Schrödinger equation (TDSE) is required in a variety of problems in physics and chemistry. These include atoms and molecules in time dependent electromagnetic fields, a variety of atomic collision problems and in describing the behavior of materials subjected to internal and external forces. In many situations, especially at the nanoscale level, the evolution of the physical system occurs over multiple length and time scales and a computationally efficient approach is a necessity to make progress. Here we explore and compare, for both accuracy and efficiency, a number of methods to discretize and to propagate solutions to the Schrödinger equation.     

Characterization of ALCVD-Al2O3 and ZrO2 layer using X-ray photoelectron spectroscopy

The atomic layer chemical vapor deposition (ALCVD) deposited Al₂O₃ and ZrO₂ films were investigated by ex situ X-ray photoelectron spectroscopy. The thickness dependence of band gap and valence band alignment was determined for these two dielectric layers. For layers thicker than 0.9 nm (Al₂O₃) or 0.6 nm (ZrO₂), the band gaps of the Al₂O₃ and ZrO₂ films deposited by ALCVD are 6.7±0.2 and 5.6±0.2 eV, respectively. The valence band offsets at the Al₂O₃/Si and ZrO₂/Si interface are determined to be 2.9±0.2 and 2.5±0.2 eV, respectively. Finally, the escape depths of Al 2p in Al₂O₃ and Zr 3p3 in ZrO₂ are 2.7 and 2.0 nm, respectively.     

Why model high-k dielectrics?

New dielectrics need more than a high dielectric constant. They need to satisfy various constraints concerning band offsets, limits on charge traps, processability, reproducibility, and stability against degradation and breakdown. It seems unlikely that purely empirical approaches will produce a dielectric which justifies major investment. I discuss some of the atomistic modelling which can aid selection, and which might indicate routes around some of the interface-related and defect-related problems. These include diffusion during processing or in operation, the use of interface engineering to adjust band offsets, and the issues of crystallinity and of stoichiometry.     

The role of surface and volume defects in the fracture of glass under quasi-static and dynamic loadings

In this paper, the role of surface and volume defects on fracture in soda-lime glass is analyzed when samples are submitted to quasi-static or dynamic loadings. To investigate fracture, different experiments are carried out, namely, quasi-static compression of glass spheres and edge-on-impacts. The first test series aims at studying crack initiation. Different surface treatments are performed to study their influence on the failure load, from which it is concluded that initiation of cracks occurs in the vicinity of the contact surface. The second series is concerned with the examination of crack patterns under dynamic loadings with two different strikers (i.e., soft/flat and hard/perforating projectiles). Crack initiation under dynamic load histories is investigated near and far from the impact zone and it is concluded that it cannot take place within the volume, except in a very small zone close to the impact point. Conversely, initiation of damage from the surface, at a location far from the impact point, is possible and clearly present with a soft projectile.     

Insulator-like electrical transport in structurally ordered Al65Cu20+xRu15−x (x = 1.5, 1.0, 0.5, 0.0 and −0.5) icosahedral quasicrystals

Low-temperature resistivities, in zero-field and 8 T field, and magnetoresistance have been measured down to 1.4-300 K for stable icosahedral quasicrystals Al₆₅Cu_20+xRu_15−x (x = 1.5, 1.0, 0.5, 0.0 and −0.5). The analysis of the magnetoresistance data shows an overwhelming presence of anti weak-localization effect (τ_so ∼ 10⁻¹² s). But the sample with x = −0.5 shows anomalous magnetoresistance and the anti weak-localization effect breaks down (τ_so to be 10⁻¹⁵ s). The in-field σ-T between 5 K and 20 K, for x = 1.0, 0.5, 0.0 and −0.5 samples, and between 1.4 K and 40 K for x = 1.5 sample, follow a power-law behavior with an exponent of 0.5 and above ∼30 K the exponent ranges from 1.17 to 1.58. The observed power-laws basically characterize the presence of critical regime of the metal-insulator (MI) transition, dominated by electron-electron and electron-phonon inelastic scattering events respectively. In samples with x = 1.0, 0.5, 0.0 and −0.5 the in field σ-T has been found to follow ln σ-vs-T^1/4 below 5 K, which indicates the presence of variable range hopping. The observed transport features indicate the occurrence of proximity of metal-insulator transition in these Al-Cu-Ru quasicrystal samples.     

Spectroscopic and magnetic behavior of xNd2O3(1−x)(3Bi2O3 · PbO) glasses

Glasses of the xNd₂O₃(1−x)(3Bi₂O₃ · PbO) system with 0?x?0.30 were obtained and studied by IR spectroscopy, X-ray photoelectron spectroscopy (XPS), density and magnetic susceptibility measurements. IR and density measurements show that the addition of neodymium ions produces structural changes and the neodymium ions play a network modifier role in the host glass matrix. XPS investigation permitted following the evolution of the structural disorder, of the degree of polymerization of bismuthate chains and of the fraction of bridging oxygens with respect to the neodymium ion concentration of the studied glasses. Magnetic susceptibility data show that the Nd³⁺ ions are present as isolated species for x?0.05 and as both isolated and exchange coupled species for higher x values.     

Microstructure and optical properties of (Pb,Ca)TiO3 films grown on Si(1 0 0) substrates by a simple sol-gel process

Amorphous and polycrystalline (Pb_0.76Ca_0.24)TiO₃ (PCT) thin films deposited on an Si(1 0 0) substrate have been prepared by a simple sol-gel process. The microstructure and surface morphologies of the thin films have been studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The polycrystalline PCT film on the Si(1 0 0) substrate has a tetragonal perovskite structure with grain size from 60 to 110 nm. AFM reveals smooth surfaces and root mean square (rms) roughness of 0.17 and 4.4 nm for amorphous and polycrystalline films, respectively. The refractive index n and extinction coefficient k of the amorphous and polycrystalline thin films was obtained by spectroscopic ellipsometry as a function of the photon energy in the range from 2.0 to 5.4 eV. The maximum n and direct bandgap energies of amorphous and polycrystalline thin films were 2.66 and 4.11 eV, 2.64 and 3.84 eV, respectively.     

Chemical annealing of oxygen hole centers in bulk glasses

Chemical annealing of the oxygen hole centers in bulk glasses by using hydrogen (or deuterium) has been extensively reported in the literature. Hydrogen chemically anneals these defect centers by reacting with them to form hydroxyl species. We have here presented a reaction-diffusion model to predict the chemical annealing rates of these defect centers in bulk glasses. The model considers diffusion of hydrogen (or its isotopes, e.g., deuterium) through the glass and its simultaneous reaction with the oxygen hole defect centers, resulting in the formation of the hydroxyl species in the glass. The predictions from the model are in excellent agreement with the experimental data presented in [J. Appl. Phys. 60 (12) (1986) 4325]. The model also establishes the precise connection between the dependence of effective hydrogen diffusivity on its intrinsic diffusivity, temperature, hydrogen and defect concentration. We also discuss methods for understanding chemical annealing behavior at high temperatures, where hydrogen not only reacts with the oxygen hole centers, but also with the silica matrix. For the case where hydrogen interaction with the silica matrix is the dominant reaction, a reaction-diffusion model is presented and the equilibrium constant (between 500 and 900 °C) for the reaction is estimated by comparing the predictions from the model with the hydroxyl profiles reported in [Appl. Phys. Lett. 47 (3) (1985) 328; J. Appl. Phys. 61 (12) (1987) 5447].     

Effect of barium contamination on gate oxide integrity in high-k dram

Barium impact on the gate oxide breakdown was studied using E-ramp and constant current stress (CCS) charge to breakdown. Wafers were contaminated with Ba after a 7.5 nm gate oxide growth and 300 nm poly-silicon deposition. The measurements were done on capacitors having areas of 0.1, 1, 4, and 16 mm². Up to a contamination level of 4×10¹⁴ atoms/cm² no degradation in oxide integrity was observed either by E-ramp or CCS. Time of flight (ToF)-SIMS measurement of Ba diffusion profile at 800 °C shows a diffusion of Ba over distances of some tens of nanometers, thus Ba does not reach the gate oxide region. The effect on the gate oxide breakdown can be correlated with the slow diffusion of Ba in poly-Si. Therefore, no major concern of yield and reliability due to Ba contamination is seen for the integration of Ba containing dielectrics into memories.     

Precipitation of icosahedral quasicrystalline and crystalline approximant phases in Zr-Cu-(Co, Rh or Ir) metallic glasses

Zr₇₀Cu₃₀, Zr₇₀Cu₂₀Co₁₀, Zr₇₀Cu₂₀Rh₁₀ and Zr₇₀Cu₂₀Ir₁₀ glassy alloys were prepared by the single roller melt-spinning method and the crystallization process was studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy, with an emphasis on the initial stage. The Zr₇₀Cu₃₀ metallic glass crystallizes through the direct precipitation of the stable crystalline phase from the matrix. The addition of Co, Rh and Ir to the Zr₇₀Cu₃₀ metallic glass induces the precipitation of metastable phases prior to the formation of the stable ones. The metastable phases are a Ti₂Ni-type compound for Zr₇₀Cu₂₀Co₁₀, a mixture of the Ti₂Ni-type compound and an icosahedral quasicrystalline phase (I-phase) for Zr₇₀Cu₂₀Rh₁₀, and the I-phase for Zr₇₀Cu₂₀Ir₁₀ metallic glasses. The different effects of Co, Rh and Ir addition are explained based on their difference in atomic radius.     

The structure of nanovolumes of amorphous materials

In this paper we demonstrate reduced density function (G(r)) analysis from amorphous volumes as small as 2 nm in width. Obtaining the G(r) from a diffraction pattern is a common starting point in the characterisation of amorphous materials. The use of electrons to form the diffraction pattern allows very small volumes of amorphous material to be investigated.     

Nanosized gold clusters formation in selected areas of soda-lime silicate glass

Nanosized gold clusters were developed in a gold-doped soda-lime silicate glass after X-ray irradiation followed by annealing, which provided an alternative way of forming metallic nanoclusters in glass to ion implantation. The formation of gold nanoclusters can be controlled by irradiation time or annealing time.     

Characterization of ultrathin gate dielectrics by grazing X-ray reflectance and VUV spectroscopic ellipsometry on the same instrument

Precise characterization of high k gate dielectrics becomes a challenging task due to the very thin thickness (<3-4 nm), which will be needed in the next generation of integrated circuits. Conventional techniques such as spectroscopic ellipsometry (SE) in the UV-visible range becomes difficult to use alone because of the great correlation between thickness and optical indices. To overcome this problem a new versatile instrument integrating SE in the VUV spectral range and grazing X-ray reflectance (GXR) has been developed recently by SOPRA. Both kinds of measurements can be made at the same location on the sample and at the same time. The analysis is made with a common optical model adjusting the layer thickness and the surface and interface roughness on the GXR data and the optical indices and other parameters like surface or interface roughness or inter-diffusion on the SE data. The paper describes some experimental results obtained with this system on ZrO₂, HfO₂ and La₂O₃ films. Results are correlated with other experimental techniques in some cases.     

Structural properties of liquid Fe-Si alloys

The atomic structure of liquid Fe-Si alloys within the whole concentration range (including pure components) was investigated at the temperature of 1550 °C by means of X-ray diffraction. Analysis of the reported data on physical properties of Fe-Si melts has been carried out. Interrelation between liquid-state structure and solid-state properties was considered. Fe-Si alloys in the liquid state are shown to be micro-inhomogeneous and they contain atomic micro-formations (clusters) that differ by atomic composition and packing. There are five types of clusters: two of them consist of atoms of one kind (Fe or Al); the composition of the other clusters depends on the stoichiometry of solid Fe₃Si, FeSi and Fe₂Si₅ phases. The entire concentration range of the Fe-Si system consists of four concentration intervals. Within each interval melts are constituted of the clusters of two kinds. The variation of the component concentrations in Fe-Si alloys results in changing of volume fraction of each type clusters, whereas the atomic composition and arrangement inside the clusters remains constant.     

Atomic layer deposition of ZrO2 thin films using a new alkoxide precursor

Zirconium oxide thin films were grown by atomic layer deposition using a new type of Zr alkoxide: [Zr(O^tBu)₂(dmae)₂]₂ (dmae is dimethylaminoethoxide). Water was used as the oxygen source. The films grown at 190-240 °C were amorphous, and the films grown at 290-340 °C were nanocrystalline. The highest refractive index of the films was 2.08 at a wavelength of 580 nm. The permittivity of a film grown at 240 °C was 25.     

Formation of nanocrystalline Fe-N-B-Cu soft magnetic ribbons

The potential of iron nitride alloys as nanocrystalline materials for soft magnetic ribbons was explored. Nanocrystalline Fe_83.4N_8.4B_7.3Cu_0.9 soft magnetic ribbons with a principal constituent of α^′′-Fe₁₆N₂ are formed after the nitriding and tempering of amorphous Fe₉₁B₈Cu₁ ribbons. The formation mechanism of α^′′-Fe₁₆N₂ is the transformation of austensite by its quenching to α^′-Fe (N) martensite and subsequent tempering to α^′′-Fe₁₆N₂. The good soft magnetic properties show that Fe nitride alloys are good candidate materials for nanocrystalline soft magnetic ribbons.     

Crystalline and non-crystalline growth of two-dimensional square-triangle lattices

We have studied the possible structures of two-dimensional lattices composed of squares and equilateral triangles obtained by a coherent way of growing them. The model of growth uses the Stochastic Matrix Method, which is based on the concept of statistical agglomeration of elementary units. The studied lattices satisfy two conditions, they are free of voids and defects and they conserve the relative concentration of elementary units before and after the growth process. In order to compare our results with some specific tilings, we also define an algorithm to construct crystalline families of a given symmetry.     

X-ray scattering studies of polymeric zirconium species in aqueous xerogels

X-ray scattering in the small angle range was used to investigate the structure and size of the polymeric species present in zirconium acetate (ZrAc)-based gel powders (GP) and thin films (TF). The formation of amorphous zirconia aggregates/linear polymers was studied by measuring their gyration radii and their correlation and hydrodynamic lengths via Guinier, `longrods', Zimm and Porod plots. Scattering data obtained in this investigation suggest that both amorphous ZrAc-based GP and TF contain `tetrameric' units, arranged in a cylindrical fashion, that polymerize upon thermal treatment. Housdorff fractal dimensionality, D, of amorphous zirconia GP (D∼2.25) and TF (D∼2.5) indicates a diffusion-limited aggregation mechanism. Tricyclic cluster aggregates (Porod D∼1.85) with a M_w∼12 000 were found within amorphous ZrAc-based GP. This structure is preserved over the entire curing range. In contrast, a linear polymeric chain (Porod D∼1.52), with a M_w∼20 000 below 165 °C and ∼13 000 at higher temperatures, was suggested for amorphous ZrAc-based TF.