Decomposition Of Thin Films Research Articles

A numerical exploration of the comparative analysis on water and kerosene oil-based Cu–CuO/hybrid nanofluid flows over a convectively heated surface

The fluid flow over an extending sheet has many applications in different fields which include, manufacturing processes, coating, thin film decomposition, heat and mass transfer, biomedical applications, aerospace engineering, environmental science, energy production. Keeping in mind these applications, the non-Newtonian hybrid nanofluid flow comprising of Cu and CuO nanoparticles over an extending sheet is analyzed in this work. Two different base fluids called kerosene oil and water have been incorporated. The sheet is considered to be thermally convective along with zero mass flux condition. The main equations of modeled problem have been transformed to dimensionless form by using similarity variables. The designed problem is evaluated computationally by using bvp4c Matlab function. Validation of the present results is also performed. The impacts of magnetic, Brownian motion, chemical reaction, suction and thermophoresis factors are analyzed and discussed in details. The outcomes of the present investigation declare that the kerosene oil-based hybrid nanofluid flow has greater velocity and concentration profiles than that of the water-based hybrid nanofluid flow. The water-based hybrid nanofluid has greater temperature distribution than that of kerosene oil-based hybrid nanofluid flow. The streamlines of the kerosene oil-based Newtonian and non-Newtonian hybrid nanofluid flows are more stretched than water-based Newtonian and non-Newtonian hybrid nanofluid flows.

Cation and anion immobilization through chemical bonding enhancement with fluorides for stable halide perovskite solar cells

Defects play an important role in the degradation processes of hybrid halide perovskite absorbers, impeding their application for solar cells. Among all defects, halide anion and organic cation vacancies are ubiquitous, promoting ion diffusion and leading to thin-film decomposition at surfaces and grain boundaries. Here, we employ fluoride to simultaneously passivate both anion and cation vacancies, by taking advantage of the extremely high electronegativity of fluoride. We obtain a power conversion efficiency of 21.46% (and a certified 21.3%-efficient cell) in a device based on the caesium, methylammonium (MA) and formamidinium (FA) triple-cation perovskite (Cs0.05FA0.54MA0.41)Pb(I0.98Br0.02)3 treated with sodium fluoride. The device retains 90% of its original power conversion efficiency after 1,000 h of operation at the maximum power point. With the help of first-principles density functional theory calculations, we argue that the fluoride ions suppress the formation of halide anion and organic cation vacancies, through a unique strengthening of the chemical bonds with the surrounding lead and organic cations. Defects and defect migration are detrimental for perovskite solar cell efficiency and long-term stability. Li et al. show that fluoride is able to suppress the formation of halide anion and organic cation vacancy defects by restraining the relative ions via ionic and hydrogen bonds.

Two-dimensional bicontinuous structures from symmetric surface-directed spinodal decomposition in thin films.

We present numerical simulations of symmetric surface-directed spinodal decomposition in thin films with varying film thickness and film composition. The simulations utilize a Cahn-Hilliard model to describe phase separation kinetics in confined film geometries. The systems consist of two phases: a wetting phase that completely wets the top and bottom surfaces, and a nonwetting phase. Three distinct morphologies emerge including a discrete nonwetting morphology, a discrete wetting morphology, as well as a unique two-dimensional bicontinuous morphology that forms for specific values of film thickness and composition. The morphologies are analyzed with a Hoshen-Kopelman algorithm to quantify the degree of continuity of the nonwetting phase, and a morphology map is presented to guide future work.

As-grown enhancement of spinodal decomposition in spinel cobalt ferrite thin films by Dynamic Aurora pulsed laser deposition

Cobalt ferrite CoxFe3−xO4 thin films with composition within the miscibility gap were grown using Dynamic Aurora pulsed laser deposition. X-ray diffraction patterns reveal as-grown phase separation to Fe-rich and Co-rich phases with no post-deposition annealing. The interconnected surface microstructure of thin film shows that this phase separation occurs through spinodal decomposition enhanced by magnetic-field-induced ion-impingement. The lattice parameter variation of the thin films with the magnetic field indicates that the composition fluctuations can be enhanced further by increasing the magnetic field. Results show that spinodal decomposition enhancement by magnetic-field-induced ion-impingement is independent of the lattice-mismatch-induced strain. This approach can promote spinodal decomposition in any thin film with no post-deposition annealing process.

Phonon spectroscopy near phase transition temperatures in multiferroicBiFeO3epitaxial thin films

We report a Raman-scattering investigation of multiferroic bismuth ferrite $({\text{BiFeO}}_{3})$ epitaxial ($c$-axis-oriented) thin films from $\ensuremath{-}192$ to $1000\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$. Phonon anomalies have been observed in three temperature regions: in the $\ensuremath{\gamma}$ phase from 930 to $950\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$; at $\ensuremath{\sim}370\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$, N\'eel temperature $({T}_{\text{N}})$, and at $\ensuremath{\sim}\ensuremath{-}123\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$, due to a phase transition of unknown type (magnetic or structural). An attempt has been made to understand the origin of the weak phonon-magnon coupling and the dynamics of the phase sequence. The disappearance of several Raman modes at $\ensuremath{\sim}820\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ $({T}_{\text{c}})$ is compatible with the known structural phase transition and the $Pbnm$ orthoferrite space group assigned by Arnold et al. [Phys. Rev. Lett. 102, 027602 (2009)]. The spectra also revealed a noncubic $\ensuremath{\beta}$ phase from $820--930\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and the same noncubic phase extends through the $\ensuremath{\gamma}$ phase between $930--950\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$, in agreement with Arnold et al. [Phys. Rev. B (to be published)], and an evidence of a cubic $\ensuremath{\delta}$ phase around $1000\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ in thin films that is not stable in powder and bulk. Such a cubic phase has been theoretically predicted by and Gonzalez-Vazquez and Iniguez [Phys. Rev. B 79, 064102 (2009)]. Micro-Raman scattering and x-ray diffraction showed no structural decomposition in thin films during the thermal cycling from $22--1000\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$.

Analysis of multitone holographic interference filters by use of a sparse Hill matrix method.

A theory is presented for the application of Hill's matrix method to the calculation of the reflection and transmission spectra of multitone holographic interference filters in which the permittivity is modulated by a sum of repeating functions of arbitrary period. Such filters are important because they may have two or more independent reflection bands. Guidelines are presented for accurately truncating the Hill matrix, and numerical methods are described for finding the exponential coefficient and the coefficients of the Floquet-Bloch waves within the filter. The latter calculation is performed by use of a computational technique known as inverse iteration. The Hill matrix for such problems is sparse, and thus, even though the matrix can be quite large, it may be efficiently stored and processed by a desktop computer. It is shown that the results of using Hill's matrix method are in close agreement with numerical calculations based on thin-film decomposition, a transfer-matrix technique. An important result of this research is the demonstration that Hill's matrix method may, in principle, be used to analyze any multiperiodic problem, so long as the periods are known to finite precision.

Holographic interference filters for infrared communications

We demonstrate that high-quality interference filters for the wavelength range 1300-1600 nm can be holographically fabricated in DuPont HRF-800X001 photopolymer material by use of visible laser illumination. We also summarize a chain-matrix technique, which we call thin-film decomposition, that is useful for modeling multilayer films with an arbitrary index profile n(z). We use the thin-film-decomposition technique to create design curves that allow one to choose the proper exposure angle and film thickness with which to fabricate a holographic interference filter with a desired transmission efficiency and bandwidth at a particular wavelength. These curves are of general utility and are not confined to any particular holographic recording medium. Excellent agreement between theory and experiment is found.

Effect of interfacial segregation on phase decomposition of a thin film on a patterned substrate

Numerical simulations of phase decomposition in thin films on patterned substrates are presented for a binary alloy in order to study the influence of substrate composition on microstructural evolution. For systems with a substrate composition less than the film composition, a preferential segregation ofA to the interface was observed and no phase decomposition occurred within the film. For patterned systems with a substrate composition exceeding the film composition, theB-rich phase was able to grow by a barrierless transformation for a range of film compositions outside the chemical spinodal. The number of precipitates which formed on the mesa, the dihedral angles at the three-phase trijunctions, and the resulting microstructure within the film were shown to be sensitive to the substrate composition.

Mass spectrometric study of combustion and thermal decomposition of GAP

Glycidyl azide polymer (GAP) is an active energetic binder in rocket propellants. The main objective of this research was to study the decomposition and combustion chemistry of thoroughly characterized GAP samples to develop a model for the combustion of GAP and propellants based on GAP. The combustion characteristics (burning rates, temperature profiles) and kinetic parameters (order of reaction, activation energy, pre-exponential factor of rate constants) for the thermal decomposition of GAP together with the composition of the products of both the combustion and decomposition of uncrosslinked GAP (with a molecular weight of 350 or 2000) and cured GAP were studied. The flame and thermal decomposition of GAP, as well as the composition of the products were studied using molecular-beam mass-spectrometry (MBMS). The final temperature of a flame of GAP was measured as 1000 to 1100 K. About half of the mass of the combustion products involves large fragments of a polymer without its azide groups. For this reason the mass spectrum obtained on direct MBMS sampling of a flame burning GAP could not be completely interpreted. However, ∼47% of the mass of the combustion products was found to be the volatile gases N2, H2, CO, CO2, CH4, C2H4, C2H6, NH3, H2O, acetonitrile, acrylonitrile, and furane, as obtained by mass-spectrometry using freezing/thawing in a liquid nitrogen trap.The thermal decomposition of thin films of GAP at 1 bar was done in a flow reactor with Ar flowing through it. A tungsten plate was used as a sample heater; its temperature was controlled using a chromel-copel (copel is an alloy of 56.5% Cu, 43.0% Ni and 0.5% Mn) or Pt-PtRh (10%) thermocouples. The thermal decomposition of GAP was studied at a high heating rate over a wide temperature range in three ways: (1) the heating rate was changed from the maximal to the minimal one in the course of decomposition (400–100 K/s); (2) at the linear heating rate (50–400 K/s); (3) fast heating (∼400 K/s) to the given temperature and subsequently maintained isothermal. Three stages of thermal decomposition were found. The first stage (yield of nitrogen is ∼15%) is a first order reaction. The second stage (yield of N2 is ∼25%) is an autocatalytic one; the third stage is first order and is a weakly exothermic one, with a yield of nitrogen of ∼60%. Kinetic parameters (activation energy and pre-exponential factor of rate constants) were found for each stage. The results for both the combustion and thermal decomposition of GAP were compared with literature data and it was concluded that the results strongly depend on the conditions of the experiment and on the source of the GAP.

Percolation inversion in spinodal decomposition of mixtures with strong kinetic asymmetry

It is shown that spinodal decomposition in thin films of mixtures of liquids of very different viscosity may exhibit an inversion of percolation of the low- or the high-mobility portions of the liquid. The condition is that the initial single phase lies in the low-mobility region. This result is derived from the non-linear Cahn-Hilliard equation with a stongly concentration-dependent mobility. Viscoelastic effects are neglected.

Quantitative Compositional Mapping of Phase Separation in Thin Polymer Films

Abstract Experiments and theoretical work on spinodal decomposition of thin films of binary polymer blends indicate large changes in phase behavior and dynamics relative to the bulk behavior due to the complex interactions of the polymer-polymer, polymer-air, and polymer-substrate interfaces. Currently used techniques are able to sense growing domain sizes but are not always able to sense local two and three dimensional variations within domains. We are using a new characterization approach to these thin films utilizing the Scanning Transmission X-ray Microscope (STXM) at beamline XIA at the National Synchrotron Light Source (NSLS)2. We extract component thickness maps of each polymer in a sample region. This allows for quantitative investigation of the dynamics of polymer phase separation and should allow the determination of important parameters affecting the domain formation in these thin films.

Fabrication of on-chip barium strontium titanate capacitors by metallo-organic decomposition

Metallo-organic thin film decomposition (MOD) was used in forming barium strontium titanate (BST) thin film capacitors on phosphorus doped polysilicon films deposited on 4 in. silicon wafers. A single step deposition process yielded highly uniform, crack-free BST films ranging up to 0.25 εm in thickness and having various step heights and dimensional area. Scanning electron microscopy (SEM) showed very good step coverage and planarization of the BST. The capacitors had capacitance densities above 200 nF/cm2, leakage current densities less than 1.55 εA/cm2 at a bias voltage of 10 V, and a dielectric breakdown field above 1 MVycm. Small temperature coefficients of capacitance and dissipation (tan δ) were also observed. Frequency response measurements were made using the BST capacitors and on-chip resistors in low pass and high pass circuit configurations. A plot of relative gain and phase angle versus frequency showed excellent agreement with predicted results.

Spinodal decomposition in thin polymer films

AbstractWe have studied the influence of the boundary surfaces on spinodal decomposition in thin films of a critical polymer mixture. The wetting layer formed during spinodal decomposition is found to grow as t1/3 and the corresponding composition vs. depth profiles exhibit dynamic scaling behavior. For sufficiently thin films, the effects of the two boundary surfaces interfere and the overall domain structure is found to be strongly thickness dependent.

Thermal Reactions of Thin Film of Trilinoleoylglycerol on Plate of Iron and Silica under Nitrogen

The thermal polymerization and degradation of thin films of trilinoleoylglycerol (TLG) (thickness 85 μm) on a iron cell plate (Fe cell) and silica cell plate (SiO2 cell) under nitrogen were investigated by vacuum thermal gravimetric analysis (VTGA) using dynamic thermal programs.The results obtained are as follows.1) The thermal polymerization of thin films of TLG in the Fe and SiO2 cell was started at 160 °C and the rates of the reactions were quite rapid at 230°C and 250°C under nitrogen respectively.2) The rate constants and apparent activation energy of the thermal polymerization of TLG in the Fe cell were 1.23 × 10-3 -2.40 × 10-3 wt %/s and 11 kcal/mol in temperature ranges of 200°C to 230°C, and 2.40 × 10-3 -8.75 × 10-3 wt %/s and 33 kcal/mol of 230°C to 250°C, respectively. For TLG on the SiO2 cell, these parameters were 2.22 × 10-4 -6.94 ×10-4 wt %/s and 53 kcal/mol from 160 °C to 250°C, and 6.94 ×10-4 -24.1 × 10-4 wt %/s and 126 kcal/mol of 250°C to 270°C, respectively.3) The thermal decomposition of thin films of TLG on the Fe and SiO2 cells were initiated at 220°C and 240°C, respectively. The reaction rates were very fast at 240°C and 270°C under nitrogen, respectively.

Spinodal decomposition in thin films of a polymer blend.

Spinodal decomposition in thin films of a blend of deuterated polystyrene and poly(styrene-co-4-bromostyrene) was studied with time-of-flight--elastic-recoil detection and light microscopy. We found different demixing behavior, depending on whether the films were prepared on the oxide layer of a silicon wafer or on a chromium-plated one. On the latter surface a bilayer of the two bulk phases is formed, whereas on the oxide layer a domain structure remains. The formation of the bilayer is ascribed to the complete wetting of each surface by the corresponding, preferentially adsorbed component.

Laser-initiated microchemistry: Dynamic probes of metallopolymer thin-film decomposition

Transient absorption has been used as a probe of the reaction kinetics in the laser-initiated thermal decomposition of Au metallopolymers. Feature sizes are considerably larger than the dimensions of the laser spot due to the propagation of a reaction front driven by the heat release from the highly exothermic reaction. Front velocities in the range of 30–50 cm/s are measured using spatially separated generating and probe lasers. These effects should be generalizable to any laser-driven thermal reaction in the condensed phase with sufficient heat release, and, as such, constitute a major limitation on feature size obtainable in these systems.

The preparation and properties of chemically deposited thin films of amorphous and crystalline zinc oxide

The semiconducting properties of zinc oxide that was obtained by the decomposition of thin films of zinc hydroxide formed by a wet chemical method were studied. For amorphous zinc oxide films the log R versus 1/ T curves are straight lines. For crystalline films, however, the log R versus 1/ T curves show a complex behaviour, with both a maximum and minimum. This property depends on the history of the sample. A possible mechanism to explain the results is suggested.

The Decomposition of Thin Films on Bombardment with Slow Electrons

The thresholds are determined for the incidence of electron absorption, decomposition and secondary emission for several types of thin film bombarded with slow electrons. With crystalline barium oxide, electron absorption and decomposition both set in at a bombarding energy near 4 eV, and are intensified at 7 eV. Secondary emission is initiated at 5 eV and increases at 7 eV and 10 eV. The optical absorption threshold is at 3.8 eV, and is attributed to exciton formation; it seems likely that the electron absorption and the decomposition are also due to exciton formation. With oxidized films of barium, crystalline barium oxide is not formed; the absorption and decomposition thresholds are at 7 eV, and the main secondary emission threshold at 10 eV. Decomposition of barium chloride sets in at 5 eV, and of barium sulphate at 7 eV. With films of the alkali halides, the decomposition is intensified at an energy corresponding with the first optical absorption band, having been initiated at a lower energy. A tentative explanation of this is proposed.