Annealing In Different Atmospheres Research Articles

From non-stoichiometric CTSe to single phase and stoichiometric CZTSe films by annealing under Sn+Se atmosphere

One of the new materials for next-generation thin film solar cells is Cu2ZnSnSe4 (CZTSe). However, achieving a single-phase CZTSe compound remains a challenge. This study describes the development of Cu2ZnSnSe4 thin films through the sequential deposition of stacked films of non-stoichiometric Cu2SnSe3 (CTSe) and ZnSe by magnetron sputtering. The structural, morphological, and electrical properties as well as the surface chemistry of the films were investigated and compared depending on the growth sequence of the thin films. By using Raman spectroscopy and grazing incidence X-ray diffraction, the tetragonal CZTSe structure was confirmed. Scanning electron microscopy and energy-dispersive spectroscopy measurements of the morphological and compositional properties indicated large grains and dense surfaces with an elemental composition close to the desired stoichiometry in SLG\\SnSe2\\Cu\\ZnSe and SLG\\SnSe2\\Cu2Se\\ZnSe stacks. To ascertain the surface chemistry and unique characteristics of the produced films, additional X-ray photoemission spectroscopy experiments were carried out. The optimal band gap values for the absorber layers were found using conventional spectroscopy, and they ranged from 0.88 to 1.47 eV. According to the electrical measurements, all the films were p-type and have high carrier concentrations between 1016 and 1020 cm−3. Our findings demonstrate that employing a sequential deposition approach and annealing in different atmospheres can yield CZTSe absorber layers with desirable properties, overcoming the challenge of non-stoichiometric CTSe precursors.

Mechanoluminescence, thermoluminescence, optically stimulated luminescence and photoluminescence in SrAl2O4:Eu micro- and nanophosphors: effect of particle size and annealing in different atmospheres.

SrAl2O4:Eu in microcrystalline form was prepared by a combustion method. The formation of the material in a single phase was confirmed by XRD analysis. The material was crushed and sieved to get particles with different particle size ranges. It was further ball milled for 1-7 days to get particles in the nanosize ranges. The broadening of the XRD peaks of the phosphor material in nanocrystalline form was used to determine average particle sizes. The shapes and sizes of these particles could also be seen in FESEM images. The materials thus obtained were annealed in reducing (10% H2 in Ar) and oxidizing (in air) atmospheres at different temperatures for 1.0 h. The increase in the mechanoluminescence (ML) intensity on annealing in a reducing atmosphere at different temperatures and decrease on annealing in an oxidizing atmosphere could be attributed to redox reactions. This was further confirmed by PL measurements. Mechanoluminescence (ML), thermoluminescence (TL), and optically stimulated luminescence (OSL) of the materials were studied. In all three cases (i.e., ML, TL, and OSL), the intensities are found to decrease with the particle size. A large shift of approximately 20 °C in the main peak of TL glow curves of micro- and nanocrystalline materials shows a widening of the band gap due to the particle size effect. A decrease in piezoelectric constant (d33) and field (F V m-1) with particle size was also observed. The present systematic study of particle size effect (over a wide range of particle sizes) on ML has great importance from a technological and application point of view for developing stress sensors.

Effects of annealing atmosphere on microstructure and photoelectric properties of titanium-doped ZnO nanofilms

In this research, four titanium-doped zinc oxide (TZO) thin films were deposited on quartz glass substrates by radio frequency (RF) magnetron sputtering. Three of the samples were annealed at [Formula: see text]C for 40 mins in N2, Ar and vacuum, respectively. The microstructure and photoelectric properties of the films were characterized. The results showed that annealing in different atmospheres has a significant effect on the microstructure and photoelectric properties. The structure of all the annealed films remained polycrystalline, with a [Formula: see text]-axis preferred orientation, and the crystallization quality was improved. In addition, the photoelectric properties were also significantly improved by annealing with the average transmittance in the visible region exceeding 90%, the resistivity reaching [Formula: see text]. The conductivity enhancement was mainly attributed to the increased mobility of carriers. Annealing in argon had the best effect. Finally, the resistivity of all the samples experienced an initial negligible change followed by an increase as the temperature was raised from 10 to 350 K.

Influence of annealing environments on the conduction behaviour of KNN-based ceramics

The electrical conduction behaviour of the lead-free (1-x)K0·5Na0·5Nb0·95Sb0·05O3-xBi0.5Na0·41K0·09ZrO3 (x = 0.05) ceramics annealed in air, oxygen, and argon environments at various temperatures was investigated. Post-sintering annealing in different atmospheres affected the temperature of dielectric phase transition and electrical conductivity values significantly. The ceramic sample annealed in an oxygen environment showed the lowest conductivity for grain (σg ∼ 1.22 × 10−5 S/m) and grain boundary (σgb ∼ 1.56 × 10−6 S/m) regions at 250 °C which is due to the reduction in oxygen vacancy defects. The activation energy Ea for DC conduction in this sample obeyed the Arrhenius relation and was found to be ∼ 0.99 ± 0.03 eV. An additional anomaly observed at T ∼ 250 °C dielectrics vs. temperature plots for the as-sintered and argon-annealed samples is ascribed to defect relaxation, which was inconspicuous in the samples annealed in air and oxygen. In addition, the in-situ impedance measurement was performed to analyze the impact of argon atmosphere on the electrical conductivity of the O2-annealed samples with high-temperature electrode curing.

Method for the modification of graphite subsurface layer to a solid mixture of SiC and graphite

We studied the interaction of molten Si and graphite surface during annealing in different atmospheres (CO, vacuum, Ar). The studies have shown that during annealing in CO atmosphere a composite material of SiC and graphite in a thick subsurface layer of the graphite is being formed, whereas at vacuum and Ar atmosphere the modified layer is either thin or absent. The composition and structure of both the composite material itself and the interface between the composite material and the graphite matrix were investigated using the methods of scanning electron microscopy and Raman spectroscopy. Studies have shown that the composite material obtained by this method has a branched fibrous structure consisting of small tubular layers of silicon carbide interspersed with large monocrystalline grains of silicon carbide of the cubic polytype, which leads to significant strengthening of the material. Thus the proposed method can be used to form a thermal protective, chemically resistant coating on graphite surface.

Influence of Oxygen Defects and Their Evolution on the Ferromagnetic Ordering and Band Gap of Mn-Doped ZnO Films

We performed a comprehensive investigation on the influence of oxygen vacancies (VO) defects and their evolution under Mn substitution and thermal annealing in different atmospheres on the ferromag...

Fe2+ Diffusion in CVD ZnSe during Annealing in Different (Ar, Zn, and Se) Atmospheres

We have studied Fe2+ diffusion in polycrystalline CVD ZnSe during high-temperature (900–1100°C) annealing in different atmospheres, determined effective Fe2+ diffusion coefficients in CVD ZnSe, and evaluated the activation energy for the diffusion process. Distinctive features of the doping process in Zn vapor have been identified that are responsible for the observed order-of-magnitude increase in Fe diffusion rate in comparison with annealing in Ar and Se. The effect of annealing conditions on Fe diffusion mechanisms is discussed.

Metal Nanoparticle-Decorated Silicon Nanowire Arrays on Silicon Substrate and their Applications.

Herein, we report an efficient method to produce silver (Ag) nanoparticle-decorated silicon (Si) nanowire (NW) arrays on a pyramidal Si (P-Si) substrate by using a pure chemical method and rapid thermal annealing in different atmospheres. A metal-assisted chemical etching technique was used to produce vertical Si NW arrays on pyramidal Si. The etching was observed to be heavily dependent on the substrate type. On planar Si (100), the etching was observed to occur in a uniform manner. However, the etching rate was observed to increase from the top to the base of the Si pyramid. The Si NWs produced from P-Si have zig-zag sidewalls as observed from high-resolution transmission electron microscopy images. However, for the same oxidant concentration, Si NWs produced from planar Si (100) consist of straight and amorphous sidewalls. Local variation of oxidant concentration is responsible for the formation of different sidewalls. The substrates are both surface-enhanced Raman scattering (SERS) active and hydrophobic. The hydrophobicity is due to the dual scale of roughness contributed to by both pyramidal and NW structures. Finite-difference time-domain simulation shows that the gap between two Ag spheres and also the gap between Si NWs and Ag spheres contributed to SERS enhancement.

Towards CdZnTe solar cells: An evolution to post-treatment annealing atmosphere

The increasing energy demand and resulting decay in the conventional energy resources indicate to find viable and affordable alternative resources. The cell efficiency and properties of absorber/window layers concerned can be tailored by the different post-treatments and therefore an evolution of post-treatment atmosphere conditions is undertaken in this work to enhance the performance of vapor proceed CdZnTe solar cells. Firstly, the microstructural and optical properties of absorber CdZnTe layer were optimized where films have zinc blende cubic structure with maximum crystallinity for Ar + O2 atmosphere while the energy band gap is influenced by the annealing in different atmospheres. Secondly, CdZnTe solar cells were fabricated using vapor proceed technique with device structure ITO/CdS/CdZnTe/Au and performance analysis is done by varying the atmosphere of post-annealing treatment. The device treated at 400 °C in the Ar + O2 atmosphere has maximum cell efficiency of 8.49% and more trap-states crossed the Fermi level as confirmed by Mott-Schottky plots. The dopant density and built-in potential are also evaluated. The findings of this work reveal that the efficiency of CdZnTe solar cells can be enhanced by the post-annealing treatment in different atmospheres.

Diffusion of Au and its influence on the coercivity of [FePt/Au/FePt]2x thin films during annealing in different atmospheres

Influence of heat treatment atmosphere on magnetic properties of post-annealed [FePt(15 nm)/Au(7.5 nm)/FePt(15 nm)]2x thin films was investigated. Thin films were deposited by dc magnetron sputtering at room temperature onto SiO2(100 nm)/Si(100) substrates and post-annealed in a temperature range of 500 °C–800 °C for 30 s in flowing Ar and Ar + H2 (3 vol%) atmospheres. It was shown that hydrogen addition into annealing atmosphere allows to achieve high value of coercivity ~1671.1 kA/m after annealing at 600 °C. Such coercivity could be reached by heat treatment in pure Ar just after annealing at 700 °C. This effect could be related to acceleration of Au grain boundary diffusion into L10-FePt phase. Such acceleration could be possible due to two reasons: hydrogen incorporation into Au crystal lattice, leading to interatomic bounds break and point defects formation; and hydrogen segregation at most defective areas, leading to cohesive energy decrease and upraise of significant stresses. As a result, nonmagnetic grid in grain boundaries of ferromagnetic material was formed at temperature lower by 100 °C.

Metallic Intermediate Phase Inducing Morphological Transformation in Thermal Nitridation: Ni3FeN-Based Three-Dimensional Hierarchical Electrocatalyst for Water Splitting.

Transition-metal nitrides have attracted a great deal of interest as electrocatalysts for water splitting due to their super metallic performance, high efficiency, and good stability. Herein, we report a novel design of hierarchical electrocatalyst based on Ni3FeN, where the presence of carbon fiber cloth as a scaffold can effectively alleviate the aggregation of Ni3FeN nanostructure and form three-dimensional conducting networks to enlarge the surface area and simultaneously enhance the charge transfer. The composition and morphological variations of NiFe precursors during annealing in different atmospheres were investigated. Such Ni3FeN/CC hierarchical electrocatalyst shows much improved electrochemical properties for water splitting in terms of overpotentials (105 and 190 mV at 10 mA/cm2 for hydrogen evolution reaction and oxygen evolution reaction, respectively) and stability.

Electron Microscopy Study of Metal Sulfide Nanocrystals Formed in Langmuir–Blodgett Films

The morphology and crystal structure of CdS, ZnS, CdZnS, and PbS nanocrystals formed by sulfidation and the subsequent annealing of the films of behenates of the respective metals using the Langmuir–Blodgett method have been investigated by high-resolution electron microscopy. It has been found that the crystal size is independent of the initial behenate film thickness. The average lateral nanocrystal size ranges from 2 to 4 nm at a film thickness of 2–14 monolayers. It has been shown that annealing in different atmospheres leads to an increase in the average nanocrystal size, morphology variation, and oxidation at the characteristic temperatures. It has been established by analyzing the interplanar spacings that the nanocrystals have hexagonal and/or cubic crystal lattices characteristic of each investigated material.

Impact of the annealing atmosphere in the electrical and optical properties of ZnO thin films

ZnO thin films were obtained using sol–gel method at room temperature; these films were deposited over glass substrates using dip-coating technique. ZnO thin films were subjected to post-deposition annealing in different atmospheres (air, nitrogen and forming gas), to study the changes in optical, morphological and electrical properties. ZnO thin films were highly transparent (above 80 %) and have an optical band gap of 3.2 eV. The deposition of contacts (100 nm of Al) over the thin film surface was defined by photolithography process. According to the results, electrical resistivity of ZnO thin films was calculated at 2.85 × 102, 3.51 × 104 and 1.83 × 104 Ω-cm for thin films annealed in nitrogen, air and forming gas atmosphere, respectively. The current–voltage (I–V) characteristics were measured for each film in dark current illuminating with a blue laser (405 nm). The current measured in dark was 10−6 A, and the current measured with the blue laser was 10−5 A independent of annealed atmosphere.

Tuning the surface structure of supported PtNi(x) bimetallic electrocatalysts for the methanol electro-oxidation reaction.

The structures of PtNix nanoalloy particles were modified through thermal annealing in different atmospheres. The evolution of surface structures was uncovered by advanced transmission electron microscopy, and the structure-function correlation in methanol electro-oxidation was probed. It provided new insights into the design and synthesis of highly efficient electrocatalysts.

Electrochemical properties of nanocrystalline TiO2 synthesized via mechanochemical reaction

Nanocrystalline anatase TiO2 is successfully synthesized via a facile and rapid mechanochemical reaction with subsequent annealing in different atmospheres. Transmission electron microscopy observation and X-ray diffraction peak broadening reveal the average crystallite size to be about 11nm. Cyclic voltammetry and galvanostatic discharge–charge tests at various current densities are carried out to explore electrochemical properties of the synthesized materials. The first discharge and charge capacities can reach 325mAhg−1 and 234mAhg−1, respectively. Moreover, nanocrystalline TiO2 also exhibits good rate capability and excellent capacity retention for over 700 cycles.

Interaction of Aluminium Oxide with Germanium upon Annealing in Different Atmospheres

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Atmosphere effects on the formation and evolution of Zn and ZnO nanoparticles in Zn ion implanted SiO 2

Metallic Zn nanoparticles (NPs) have been fabricated in the near surface region of SiO 2 by implantation of Zn ions at energy of 45 keV up to 5.0 × 10 16 ions/cm 2. Such NPs were then subjected to the furnace annealing in different atmospheres. Various techniques, such as ultraviolet–visible spectroscopy (UV–vis), grazing incidence X-ray diffraction spectroscopy (GXRD), photoluminescence spectroscopy (PL), were employed to characterize the formation and evolution of the Zn and ZnO NPs, and also their related optical properties. Our results clearly show that the evolution of Zn NPs depends strongly on the annealing atmosphere. ZnO NPs have been effectively formed with preferred (0 0 2) and (1 0 3) orientations when the samples were annealed in a flow of nitrogen gas or sequentially annealed in nitrogen and oxygen ambient. The PL measurements give the evidence that ZnO NPs with high-quality could be formed when the samples were sequentially annealed in the flows of nitrogen and oxygen gases.

Photoluminescence investigation on the gas sensing property of ZnO nanorods prepared by plasma-enhanced CVD method

Gas sensing property of ZnO nanorods prepared by plasma-enhanced chemical vapor deposition (CVD) method is studied using formaldehyde as the probe gas, and the intrinsic defects are investigated by photoluminescence (PL). The results show that high ratio of visible to ultra-violet luminescence cannot account for high gas response. The PL spectra are Gaussian decomposed to subpeaks according to their origination, which are separated into donor-(DL) and acceptor-related (AL) ones. A conclusion is derived that where the content of DL is high and that of AL is low, the gas response is high. This conclusion is further confirmed by tuning the PL spectra and gas sensing property through annealing in different atmospheres. (C) 2009 Elsevier B.V. All rights reserved.

Effect of thermo-chemical treatments on the luminescence and scintillation properties of CaWO4

In this work, we investigated the influence of thermal annealing in different atmospheres on the luminescence and scintillation properties of CaWO4. Luminescence and luminescence excitation spectra were examined using VUV synchrotron radiation. Thermal treatment causes change of the defect subsystem of the crystal, resulting in the alteration of the spectral dependences. The most obvious effect is the relative change in the intensity of the defect emission band which is excited below the fundamental absorption edge 4.7eV. Studies of the scintillation kinetics and light yield carried out over a temperature range 8–300K showed that former does not change upon the treatment, in contrast to the intensity of scintillations. It is found that ∼50% increase of the scintillation response can be achieved for CaWO4 samples annealed in hydrochloric acid.

The influence of annealing atmosphere on the optical properties of flower‐like ZnO

AbstractThe influence of annealing atmosphere on the optical properties of flower‐like ZnO is investigated. The flower‐like ZnO is composed of nanosheets. Annealing at 500°C results in the increase of the thickness of nanosheets and the enhancement of UV emission. PL spectra results show that the annealing atmosphere affects the visible emission band, which is sensitive to intrinsic and surface defects in the flower‐like ZnO. The vibrational properties of the flower‐like ZnO annealing in different atmospheres are characterized by Raman spectra. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)