Subsequent Temperature Annealing Research Articles

Development and investigation of a porous metal-ceramic substrate for solid oxide fuel cells

The process of creating a porous metal-ceramic material based on Ni-Al alloy and gadolinium-doped cerium oxide (CGO) using the thermal explosion method has been investigated. This study aims to analyze the effect of CGO on the thermal explosion parameters and the architecture of the resulting Ni-Al-CGO materials. In this regard, the influence of adding CGO powder to the Ni-Al system on the synthesis process and structure formation during controlled heat loss thermal explosion has been studied. Dependencies of temperature and time characteristics of the thermal explosion on initial parameters have been measured. It has been demonstrated that the concentration of CGO in the initial mixture and heat dissipation from the sample significantly affect the rate of the exothermic reaction. The phase composition of the obtained porous materials, depending on the CGO content and the temperature of subsequent vacuum annealing, was analyzed using X-ray diffraction. The chemical composition and microstructure of the synthesis products were examined through electron microscopy and energy-dispersive X-ray spectroscopy. The possibility of forming metal-ceramic composites with a porosity of 60–65 % for use as supporting substrates for solid oxide fuel cells with a NiO/CGO anode has been shown. An anodic layer of NiO/CGO was applied to a metal-ceramic base of the composition (Ni+25 %Al)+5 %CGO using screen printing, which was then annealed in an air atmosphere at 1300 °C and reduced at 900 °C in a hydrogen atmosphere. The dilatometric method determined that adding 40 wt.% Cr to a mixture of Ni-Al powders reduces the average coefficient of thermal expansion of the new material.

High thermoelectric performance in polycrystalline Yb3Ge5 thin films

The development of eco-friendly thin-film thermoelectric generators for microenergy harvesting applications is highly desired. Ge-based materials have recently attracted significant research interest because of their superior performance at room temperature as human-compatible thermoelectric constituents. We examined the synthesis of Yb3Ge5 thin films and assessed their thermoelectric properties, considering the exceptional ability of Yb as a heavy metal to scatter phonons. The components of the resulting thin film were strongly dependent on the Yb/Ge deposition ratio and the subsequent annealing temperature. An increase in the Yb content augmented the formation of Yb2O3, whereas an increase in the Ge content facilitated the formation of Ge crystals. These trends were more evident at higher annealing temperatures. By controlling the YbGe composition, a power factor of 1470 µW m−1 K−2 was obtained at an annealing temperature of 700 °C, along with a low thermal conductivity of 3.1 W m−1 K−1. Machine-learning-facilitated data analysis revealed that the high power factor originated from Yb3Ge5. Notably, the power factor reached 1370 µW m−1 K−2 even at a temperature of 500 °C, causing the expansion of heat-resistant plastic films. Thus, we established the impressive potential of Yb3Ge5 as a suitable material for eco-friendly thin-film thermoelectric generators.

Green chemistry synthesis and structural and optical study of Dy2(CO3)3→ Dy2O3 transition

This paper presents preliminary results of Dy2(CO3)3→Dy2O3 transition have been successfully obtained by Chemical Bath Deposition technical and subsequent thermal annealing temperature at ~600 °C. Two different temperatures of ~20°C and ~90 °C ± 2 °C are chosen to carry out the nanocrystalline growth. The crystalline phase is investigated by applying X-Ray Diffraction (XRD) and some optical properties; Transmittance, Reflectivity, Normalized Absorbance, real (n) and imaginary (k) parts refractive index. The crystalline phase of these inorganic nanomaterials for Dy2(CO3)3 is orthorhombic phase, while for Dy2O3 it is cubic. Grain size average values located at ranged ~2.8-3.4 nm for Dy2(CO3)3 and ~6.5-9.6 nm for Dy2O3. Vibrational modes are identified by Raman spectroscopy, modes at ~150-1800 cm-1 frequency range assigned to internal vibrations of ion: v1-symmetric stretching (~1098 cm-1) v3-asymmetric -C-O stretching situated at ∼1063 cm-1, were observed corresponding to orthorhombic crystalline phase. The Fg+ Ag and A1g modes, corresponding to cubic phase Dy2O3. Multiple absorption bands with different relative intensities are observed at UV-Vis-NIR region, assigned to 4fs→4fs intra-electronic transitions and band gap energy. Absorption measurement were assigned to the transitions from ground state (6H15/2) to different excited states such as 4I13/2→4F7/2, 4I15/2, 6F3/2, 6F5/2, 6F7/2→6H5/2, 6F9/2→6H7/2, 6F11/2→6H9/2 and 6H11/2 of Dy3+ cation. Tauc’s plot reveals band gap situated at range ~4.66-5.17 eV for Dy2(CO3)3 and ~4.26-4.80 eV for Dy2O3 respectively.

Microstructure evolution maps of AZ31 and AZ91–Ca–Y–MM alloys under precompression and subsequent annealing conditions

This study establishes the microstructure evolution maps of a commercial AZ31 alloy and a recently developed Mg–9Al–0.8Zn–0.9Ca–0.6Y–0.5MM (AZXWMM91100) alloy on the basis of their microstructural variations with precompression amount and subsequent annealing temperature. The fully twinned microstructure of precompressed samples of the AZ31 alloy remains unchanged after annealing at 200 °C. At annealing temperatures above 225 °C, the area fraction of twin-free grains gradually increases with increasing precompression amount and annealing temperature. The microstructure evolution map of the AZ31 alloy consists of three regions: those with a fully twinned grain structure, partially twinned grain structure, and completely twin-free grain structure. The twinned microstructure of precompressed samples of the AZXWMM91100 alloy remains unchanged after annealing even at 250 and 300 °C. At annealing temperatures above 350 °C, the microstructure drastically changes from a fully twinned microstructure to a completely twin-free microstructure irrespective of the precompression amount. Consequently, the microstructure evolution map of the AZXWMM91100 alloy does not include the region with the partially twinned grain structure. The large amount of Al solute atoms and numerous second-phase particles in the AZXWMM91100 alloy inhibit grain-boundary movement during annealing, which results in the different microstructural evolution behavior with the AZ31 alloy.

High Temperature Accelerated Stone-Wales Transformation and the Threshold Temperature of IPR-C60 Formation.

The Stone-Wales bond rotation isomerization of nonicosahedral C60 (C2v-C60) into isolated-pentagon rule following icosahedral C60 (Ih-C60 or IPR-C60) is a limiting step in the synthesis of Ih-C60. However, extensive previous studies indicate that the potential energy barrier of the Stone-Wales bond rotation is between 6 and 8 eV, extremely high to allow for bond rotation at the temperatures used to produce fullerenes conventionally. This is also despite data indicating a possible fullerene road mechanism that necessitates low-temperature annealing. However, these previous investigations often have limiting factors, such as using the harmonic approximation to determine free energies at high temperatures or considering only the reverse Ih-C60 to C2v-C60 transition as a basis. Indeed, when the difference in energy between Ih-C60 and C2v-C60 is accounted for, this barrier is generally reduced by ∼1.5 eV. Thus, utilizing the recently developed density functional tight binding metadynamics (DFTB-MTD) interface, the effects of temperature on the bond rotation in the conversion of C2v-C60 to Ih-C60 have been investigated. We found that Stone-Wales bond rotations are complex processes with both in-plane and out-of-plane transition states, and which transition path dominates depends on temperature. Our results clearly show that at temperatures of 2000 K, the free energy for a C2v-C60 to Ih-C60 transition is only ∼4.21 eV and further reduces to ∼3.77 eV at 3000 K. This translates to transition times of ∼971 μs at 2000 K and ∼34 ns at 3000 K, indicating that defect healing is a fast process at temperatures typical of arc jet or laser ablation experiments. Conversely, below ∼2000 K, bond rotation becomes prohibitively slow, putting a lower threshold limit on the temperature of fullerene formation and subsequent annealing.

Diffusion and Interaction of In and As Implanted into SiO2 Films

By means of Rutherford backscattering spectrometry, electron microscopy, and energy-dispersive X-ray spectroscopy, the distribution and interaction of In and As atoms implanted into thermally grown SiO2 films to concentrations of about 1.5 at % are studied in relation to the temperature of subsequent annealing in nitrogen vapors in the range of T = 800–1100°C. It is found that annealing at T = 800–900°C results in the segregation of As atoms at a depth corresponding to the As+-ion range and in the formation of As nanoclusters that serve as sinks for In atoms. An increase in the annealing temperature to 1100°C yields the segregation of In atoms at the surface of SiO2 with the simultaneous enhanced diffusion of As atoms. The corresponding diffusion coefficient is DAs = 3.2 × 10–14 cm2 s–1.

Anodic Oxidation of Hydrogen-Transferred Silicon-on-Insulator Layers

The anodic oxidation rate of silicon-on-insulator films fabricated by hydrogen transfer is studied as a function of the temperature of subsequent annealing. It is established that the oxidation rate of transferred silicon-on-insulator films is five times lower compared to the oxidation rate of bulk single-crystal silicon samples. The oxidation rate increases, as the annealing temperature is elevated in the range 700–1100°C and as the depth of gradually removed anode-oxidized layers is increased. The results obtained in the study are attributed to an increase in the efficiencies of the anodic current and oxygen–silicon interatomic interaction due to the annealing of defects and due to release of hydrogen from the bound state, respectively. The formation of hydrogen bubbles in the surface region of silicon due to the diffusion of hydrogen, released in the process of the oxidation reaction, towards micropores in the silicon-on-insulator layer is detected.

Анодное окисление слоев кремний-на-изоляторе, созданных методом водородного переноса

AbstractThe anodic oxidation rate of silicon-on-insulator films fabricated by hydrogen transfer is studied as a function of the temperature of subsequent annealing. It is established that the oxidation rate of transferred silicon-on-insulator films is five times lower compared to the oxidation rate of bulk single-crystal silicon samples. The oxidation rate increases, as the annealing temperature is elevated in the range 700–1100°C and as the depth of gradually removed anode-oxidized layers is increased. The results obtained in the study are attributed to an increase in the efficiencies of the anodic current and oxygen–silicon interatomic interaction due to the annealing of defects and due to release of hydrogen from the bound state, respectively. The formation of hydrogen bubbles in the surface region of silicon due to the diffusion of hydrogen, released in the process of the oxidation reaction, towards micropores in the silicon-on-insulator layer is detected.

Диффузия и взаимодействие In и As, имплантированных в пленки SiO-=SUB=-2-=/SUB=-

AbstractBy means of Rutherford backscattering spectrometry, electron microscopy, and energy-dispersive X-ray spectroscopy, the distribution and interaction of In and As atoms implanted into thermally grown SiO_2 films to concentrations of about 1.5 at % are studied in relation to the temperature of subsequent annealing in nitrogen vapors in the range of T = 800–1100°C. It is found that annealing at T = 800–900°C results in the segregation of As atoms at a depth corresponding to the As^+-ion range and in the formation of As nanoclusters that serve as sinks for In atoms. An increase in the annealing temperature to 1100°C yields the segregation of In atoms at the surface of SiO_2 with the simultaneous enhanced diffusion of As atoms. The corresponding diffusion coefficient is D _As = 3.2 × 10^–14 cm^2 s^–1.

Effect of preliminary heterogenization on the structure and hardness of cryorolled aluminum alloy D16

The effect of preliminary heat treatment on transformations of the grain structure of the aluminum alloy D16 under isothermal rolling at the temperature of liquid nitrogen and subsequent annealing was investigated. It was found that heterogenization by intensifying the nucleation of new grains facilitates the nanostructuring of the alloy during cryorolling, as well as the formation of a fine-grained structure upon static recrystallization at post-deformation annealing.

Optimization of Cold Rolling and Subsequent Annealing Treatment on Mechanical Properties of TWIP Steel

This research work studied the effect of cold rolling reduction and subsequent annealing temperature on the microstructural evolution and the mechanical properties of Fe-32Mn-4Si-2Al twinning-induced plasticity steel plates. For this, uniaxial tensile tests were carried out for three cold rolling reductions (50, 65 and 80%) and subsequent annealing treatment at 550-750 °C for 1.8 ks. The results were discussed in terms of the yield strength, ultimate tensile strength and total elongation and its dependence on the introduced microstructure. Regression analysis was used to develop the mathematical models of the mechanical properties. Moreover, analysis of variance was employed to verify the precision of the mathematical models. Finally, desirability function was used as an effective optimization approach for multi-objective optimization of the cold rolling reduction and annealing temperature. It is considerable that there is no research attempting to find optimum mechanical properties of the steels using this approach. The results indicated that applying large cold rolling reduction (upper than 75%) and subsequent annealing treatment in the recovery region and also the application of large cold rolling reduction and the subsequent annealing treatment in the lower limit of partial recrystallization region were effective methods to obtain an excellent combination of mechanical properties.

Random Si nanopillars for broadband antireflection in crystalline silicon solar cells

We demonstrate the fabrication of shallow Si nanopillar structures at a submicron scale which provides broadband antireflection for crystalline Si (c-Si) solar cells in the wavelength range of 350 nm–1100 nm. The Si random nanopillars were made by reactive ion etch (RIE) processing with thermally dewetted Sn metals as an etch mask. The diameters and coverages of the Si nanopillars were adjusted in a wide range of the nanoscale to microscale by varying the nominal thickness of the Sn metals and subsequent annealing temperatures. The height of the nanopillars was controlled by the RIE process time. The optimal size of the nanopillars, which are 340 nm in diameter and 150 nm in height, leads to the lowest average reflectance of 3.6%. We showed that the power conversion efficiency of the c-Si solar cells could be enhanced with the incorporation of optimally designed Si random nanopillars from 13.3% to 14.0%. The fabrication scheme of the Si nanostructures we propose in this study would be a cost-effective and promising light trapping technique for efficient c-Si solar cells.

Structure and magnetic properties of melt-spun Tb0.2Nd0.8(Fe0.8Co0.2)1.9 compound

High-Nd content Tb0.2Nd0.8(Fe0.8Co0.2)1.9 cubic Laves compound which could not be prepared by annealing its as-cast ingot was successfully fabricated by melt-spinning and subsequent low-temperature annealing. The effects of wheel speed and annealing temperature on the structure and magnetic properties of Tb0.2Nd0.8(Fe0.8Co0.2)1.9 ribbons are investigated. The ribbons with single cubic Laves phase were obtained at a wheel speed of 40 m/s and subsequent annealing temperature of 773 K. The average grain size decreases with the increase of the wheel speed from 10 m/s to 40 m/s. The easy magnetic direction of Tb0.2Nd0.8(Fe0.8Co0.2)1.9 Laves phase lies along [111] at room temperature, which was confirmed by Mössbaure spectra. Meanwhile, the resin-bonded ribbons obtained at a wheel speed of 40 m/s have a magnetostriction of 321 ppm at room temperature. This work demonstrates an alternate way to synthesize the metastable high-Nd content cubic Laves phase magnetostrictive compounds under ambient pressure other than high-pressure annealing.

Size dependent compressibility of nano-ceria: Minimum near 33 nm

We report the crystallite-size-dependency of the compressibility of nanoceria under hydrostatic pressure for a wide variety of crystallite diameters and comment on the size-based trends indicating an extremum near 33 nm. Uniform nano-crystals of ceria were synthesized by basic precipitation from cerium (III) nitrate. Size-control was achieved by adjusting mixing time and, for larger particles, a subsequent annealing temperature. The nano-crystals were characterized by transmission electron microscopy and standard ambient x-ray diffraction (XRD). Compressibility, or its reciprocal, bulk modulus, was measured with high-pressure XRD at LBL-ALS, using helium, neon, or argon as the pressure-transmitting medium for all samples. As crystallite size decreased below 100 nm, the bulk modulus first increased, and then decreased, achieving a maximum near a crystallite diameter of 33 nm. We review earlier work and examine several possible explanations for the peaking of bulk modulus at an intermediate crystallite size.

Transparent Conductive Films of Copper Nanofiber Network Fabricated by Electrospinning

Cu nanofiber networks can be a good alternative of the Ag nanowire of high electrical conductivity while having the advantage of low price. An electrospinning method was developed to fabricate copper nanofiber network for use as a transparent conductive film on glass substrate. The effects of liquid diluents for electrospinning processability were examined in relation to the subsequent Cu nanofiber formation processes. Electrospinning solutions of copper acetate/polyvinyl alcohol (PVA) and copper nitrate trihydrate/polyvinyl butyral (PVB) were investigated. The polymer mixing solutions influenced the subsequent annealing temperatures for removal of the polymers and reduction of the formed CuO nanofibers to Cu metal nanofibers. The morphology and structures of the formed nanofiber networks were examined by scanning electron microscopy, energy dispersive spectroscopy, X‐ray diffraction, and so forth. The mixture with PVB provided lower annealing temperatures suitable for application to flexible substrates.

Effect of high-power milling and subsequent annealing on the phase composition and magnetic properties of alloy Nd9.5Fe84B6Cu0.5

Regular features of variation of structure and magnetic properties of cast alloy Nd9.5Fe84B6Cu0.5 are studied as a function of the duration of milling in a high-power ball mill and of the temperature of subsequent annealing. The structure and the phase composition of the alloy are determined by the method of x-ray diffraction. The microstructure is studied with the help of a scanning electron microscope. The magnetic properties are measured with the help of a hysteresigraph with maximum magnetization field 2000 kA/m.

(Electronics & Photonics Division Award Presentation) Si-SiO2 Interface to High-K-Ge/III-V Interface: Passivation and Reliability

The Si-SiO2 interface is one of the most important semiconductor-dielectric interfaces that has been studied extensively over many decades. The understanding and control of structural and electronic properties of Si-SiO2 interfaces has provided many clues for technological advancement. The article discusses how the Si-SiO2 interface migrated through the technological landscape like plasma processing damage, hot carrier effects and negative bias temperature instability (NBTI) and subsequent passivation techniques using hydrogen to nitrogen. Introduction of high-k gate dielectrics brought significant attention to the interface between silicon and high-k dielectrics but Si-SiO2 interface continued to be important because of the presence of a SiO2-based interfacial layer. With deposition of high-k gate dielectrics high carrier mobility substrates (Ge/III-V) are currently being considered as the channel materials. To obtain a high quality interface between the high-k dielectrics and the high mobility substrates some issues like deposition process, precise selection of deposition parameters, predeposition surface treatments, appropriate passivation techniques and subsequent annealing temperatures are also outlined.

Effect of CdCl2 treatment on structural and electronic property of CdTe thin films deposited by magnetron sputtering

The structural and electrical properties of the magnetron sputtered CdTe thin films with subsequent CdCl2 solution treatment have been studied with a major focus on the influence of CdCl2 treatment to achieve high quality thin films. In this study, CdTe films with a thickness of 1.5 to 2μm have been grown using the magnetron sputtering technique on top of glass substrate at an optimized substrate temperature of 250°C. Aqueous CdCl2 concentration varied from 0.3mol to 1.2mol with the annealing temperature from 360°C to 450°C. The surface roughness of the films increases with the increase of solution concentration, while it fluctuates with the increase of annealing temperature. The density of nucleation centers and the strain increases for the films treated at 360°C with 0.3M to1.2M while the grain growth of the films reduces. However, these strains are released at higher annealing temperatures, resulting in reduced dislocation densities, structural defects as well as increased crystalline property and grain size. The carrier concentration increases with the increase of treated CdCl2 concentration and subsequent annealing temperature. The highest carrier concentration of 1.05×1014/cm3 was found for the CdTe thin films treated with 0.3M CdCl2 solution followed by an annealing treatment at 420°C for 20min.

Grain boundary versus particle stimulated nucleation in hot deformed Al–4·5Zn–1Mg alloy

In the present research, an analytical model of recrystallisation combining grain boundary (GB) and particle stimulated nucleation (PSN) in hot deformed Al–4·5Zn–1Mg alloy was developed. The effects of evolving subgrain sizes and associated stored energy in addition to the Zener drag pressure on recrystallisation were incorporated into the model. A number of constants, fitting parameters and activation energies for recrystallisation nucleation were determined for the Al–4·5Zn–1Mg alloy by investigating recrystallisation after axisymmetric hot compression testing. It was found that with increasing temperature and decreasing strain rate, the number density of the nuclei decreased. Both GB and PSN played roles in the recrystallisation of this alloy. The temperature of subsequent annealing was found to be not strongly influential on the mode of recrystallisation, i.e. recrystallisation originated by GB nucleation or PSN. However, deformation conditions (strain, strain rate and temperature) clearly affected the mode of recrystallisation. Nucleation by the GB mechanism was especially marked. However, PSN played a dominant role in recrystallisation after deformation to large strains. In addition, when strain was <1, nucleation by the GB mechanism was only dominant if the strain rate was smaller than 1 s−1 and the deformation temperature was higher than 450°C.

Stranski–Krastanov Shell Growth in ZnTe/CdSe Core/Shell Nanocrystals

ZnTe/CdSe core/shell nanoparticles are synthesized in noncoordinating solvents at different temperatures. The experimental results show that CdSe shell deposition at 215 °C on spherical ZnTe core particles is analogous to Stranski-Kranstanov growth of 2D epitaxial films. The shell thickness inhomogeneity is determined by measuring the inhomogeneity in interfacial hole transfer rates to an adsorbed hole acceptor, phenothiazine. We find that the first approximately three layers of CdSe are deposited uniformly and that subsequent layers produce a rough shell surface. The origin of the shell thickness inhomogeneity is investigated. ZnTe and CdSe have very close to the same lattice constants, and the interface therefore has very little lattice strain. However, cation interdiffusion changes the radial composition profile of the ZnTe-CdSe interface, leading to a large amount of lattice strain. The extent of cation interdiffusion and hence the surface morphology can be controlled by varying the deposition temperature and the subsequent annealing time and temperature. The particle spectroscopy and the shell thickness inhomogeneity are consistent with calculations based on an elastic continuum model with a cation interdiffusion constant of 1.3 × 10–2 nm2 min–1 in the ZnTe/CdSe particles at 250 °C. The comparison of the energetics involved in S–K growth of thin films and nanocrystal shells is discussed.