Sequential Annealing Research Articles

One-source PVD of n-CuIn5Se8 photoabsorber films for hybrid solar cells

Highly photosensitive CuIn5Se8 photoabsorber layers of n-type were deposited onto glass/ITO substrates from the bulk CuIn5Se8 source polycrystal by using the one-source physical vapour deposition (PVD) technique with following thermal annealing. The parameters of deposition process and thermal annealing were selected with the purpose to prepare photoabsorber layers for the hybrid photovoltaic structures based on inorganic and conductive polymer functional layers. As-deposited structures were annealed at the temperature range from 450 to 500°C in vacuum. Also, thermal annealing in argon and in vacuum in sequence was applied for the part of obtained structures according to conception of the sequential annealing. Obtained results show the chalcopyrite structure of prepared photoabsorber films and dominating presence of the CuIn5Se8 phase in the layers annealed in vacuum. It was found, that the CuIn5Se8 layers deposited at the temperature of substrate of 200°C and annealed at 500°C for 2h in vacuum show maximal photosensitivity under white light illumination with an intensity of 100mW/cm2. On the basis of the electrochemical impedance spectroscopy the order of charge carriers concentration in prepared photoabsorber layers was evaluated and n-type of conductivity confirmed.

Structural reconstruction and defects transition in mediating room temperature ferromagnetism in Co-doped ZnO film

Room temperature (RT) ferromagnetism (FM) was achieved in H2/N2 annealed Co-doped ZnO films on silicon substrates and we got annealing temperature, Tan, dependence of saturation magnetization, Ms, which increased and finally reached a maximum as Tan elevated. The curve of Ms versus Tan seems like three steps. Surprisingly, after sequential oxygen annealing, Ms of each annealed film decreased abruptly at first, and then restored to its original order after the second annealing, which may owe to the formation of zinc-blende ZnO during thermal oxidation. This experiment illustrated that room temperature ferromagnetism in Co-doped ZnO films is associated with multiple factors.

Iron Pyrite Thin Films Synthesized from an Fe(acac)3 Ink

Iron pyrite (cubic FeS2) is a promising candidate absorber material for earth-abundant thin-film solar cells. Here, we report on phase-pure, large-grain, and uniform polycrystalline pyrite films that are fabricated by solution-phase deposition of an iron(III) acetylacetonate molecular ink followed by sequential annealing in air, H2S, and sulfur gas at temperatures up to 550 °C. Phase and elemental compositions of the films are characterized by conventional and synchrotron X-ray diffraction, Raman spectroscopy, Auger electron spectroscopy, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy (XPS). These solution-deposited films have more oxygen and alkalis, less carbon and hydrogen, and smaller optical band gaps (E(g) = 0.87 ± 0.05 eV) than similar films made by chemical vapor deposition. XPS is used to assess the chemical composition of the film surface before and after exposure to air and immersion in water to remove surface contaminants. Optical measurements of films rich in marcasite (orthorhombic FeS2) show that marcasite has a band gap at least as large as pyrite and that the two polymorphs share similar absorptivity spectra, in excellent agreement with density functional theory models. Regardless of the marcasite and elemental impurity contents, all films show p-type, weakly activated transport with curved Arrhenius plots, a room-temperature resistivity of ~1 Ω cm, and a hole mobility that is too small to measure by Hall effect. This universal electrical behavior strongly suggests that a common defect or a hole-rich surface layer governs the electrical properties of most FeS2 thin films.

Atomic retention and near infrared photoluminescence from PbSe nanocrystals fabricated by sequential ion implantation and electron beam annealing

Nanocrystals of PbSe have been fabricated in a silicon dioxide matrix by sequential low energy ion implantation followed by an electron beam annealing step. Transmission electron microscopy reveals PbSe nanocrystals with typical sizes between 3 and 10nm in the sub-surface region. Rutherford Backscattering Spectrometry has been used to study the total atomic retention, as a function of implanted atoms, following annealing. Photoluminescence was observed in various samples, at 4K, as a broad peak between 1.4 and 2.0μm, with observation of a dependence of the peak wavelength on annealing temperature. Room temperature photoluminescence was observed for samples with a high retention of implanted atoms, demonstrating the importance of nanocrystal density for achieving ambient temperature emission in these systems.

Solution-based synthesis of cobalt-doped ZnO thin films

Undoped and cobalt-doped (1–4wt.%) ZnO polycrystalline, thin films have been fabricated on quartz substrates using sequential spin-casting and annealing of simple salt solutions. X-ray diffraction (XRD) reveals a wurzite ZnO crystalline structure with high-resolution transmission electron microscopy showing lattice planes of separation 0.26nm, characteristic of (002) planes. The Co appears to be tetrahedrally co-ordinated in the lattice on the Zn sites (XRD) and has a charge of +2 in a high-spin electronic state (X-ray photoelectron spectroscopy). Co-doping does not alter the wurzite structure and there is no evidence of the precipitation of cobalt oxide phases within the limits of detection of Raman and XRD analysis. Lattice defects and chemisorbed oxygen are probed using photoluminescence and Raman spectroscopy — crucially, however, this transparent semiconductor material retains a bandgap in the ultraviolet (3.30–3.48eV) and high transparency (throughout the visible spectral regime) across the doping range.

Zinc vacancy and oxygen interstitial in ZnO revealed by sequential annealing and electron irradiation

By combining results from positron annihilation and photoluminescence spectroscopy with data from Hall effect measurements, the characteristic deep level emission centered at $\ensuremath{\sim}$1.75 eV and exhibiting an activation energy of thermal quenching of 11.5 meV is associated with the zinc vacancy. Further, a strong indication that oxygen interstitials act as a dominating acceptor is derived from the analysis of charge carrier losses induced by electron irradiation with variable energy below and above the threshold for Zn-atom displacement. We also demonstrate that the commonly observed green emission is related to an extrinsic acceptorlike impurity, which may be readily passivated by oxygen vacancies.

Thermally induced interface chemistry in Mo/B4C/Si/B4C multilayered films

B4C diffusion barrier layers are often introduced into Mo/Si multilayered films for enhancement of thermal stability. We observe that such multilayered films exhibit both period expansion and period compaction upon annealing at temperatures below 300 °C, depending on the annealing temperature and time. Using in-situ grazing incidence x-ray reflection measurements during sequential annealing, we resolved picometer periodicity changes in Mo/B4C/Si/B4C, Si/B4C, and Mo/B4C multilayer films, and show that the two opposite period-change effects are a result of interaction of Si with B4C layers, leading to expansion, and MoxSiy formation, leading to compaction. The study of Si/B and Si/C multilayer sub-systems suggests that the cause of expansion is the formation of relatively low density SixBy compounds at the Si-B4C interface. Although the Mo-B4C interface seems to be stable based on reflectometry data, other techniques such as depth profiling x-ray photoelectron spectroscopy and wide angle x-ray diffraction measurements show that Mo and B4C actually intermix.

Using optimization procedures to minimize machining time while maintaining surface quality

In this study, we present a methodology for minimizing machining time, where the surface roughness is constrained for the problem. The objective of the methodology is to encounter optimized cutting parameters which reduce machining time without reducing the surface quality of the machined workpiece. Three optimization schemes were considered to encounter the minima of a quantity which is a function of machining parameters: (a) sequential quadratic programming, (b) genetic algorithms, and (c) simulated annealing. For the discussion of the methodologies employed, an example of a machined surface is presented. The formalisms are used to obtain the parameters which minimize the machining time while maintaining the surface roughness within acceptable limits.

Formation of a crystalline InSe phase from a quaternary single crystal of the Cu–Ag–In–Se system by massive ion motion

The composition and structural properties of a single crystal of the Cu–Ag–In–Se system are analyzed. Laue diffraction shows a single crystal while XRD diffraction and EDAX composition indicate two crystalline phases and two compositions close to Cu0.97Ag0.03In1.75Se2.84 and Cu0.95Ag0.05In2Se3.5 with lattice parameter, a = 5.770 Å and a = 5.790 Å and c/a ≅ 2.0 respectively. Impedance spectroscopy is carried out at temperatures up to 120 °C in a sequential annealing in order to obtain the electrical properties. A motion of two ions is observed and two ionic resistances and activation energies are computed in the 0.15–0.17 eV range and 0.52 eV, respectively. In the successive annealing, the impedance spectra change, probably due to a non-reversible process in the sample. After the impedance analysis, composition measurements and the structural analysis show a massive motion of Ag + Cu and In ions in the slice. These motions produce different phases with very different compositions in different regions. Due to the high disorder in Cu and In sublattices and to the high number of (2VCu + InCu) defect pairs, these ions are easily moved, leading to the formation of an InSe crystalline phase. Ions are rearranged in the chalcopyrite phase region, along with the transformation of In3+ into In2+ chemical species accompanied by the corresponding electron conduction capture. These changes are responsible of the non-reversibility of the process. These results would allow to understand the highest solar energy conversion efficiencies of up to 20.3% observed in CuIn1−xGaxSe2 (CIGS) thin films obtained using a three-stage co-evaporation process. In these films, the CIGS layer reaches a copper rich composition and a quasi-liquid Cu2−ySe phase is formed which enhances crystallization of the absorber layer and also affects the distribution of the group III elements throughout the layer.

Transparent conductive CuFeO2 thin films prepared by sol–gel processing

In this study, transparent conductive CuFeO2 thin films were deposited onto a quartz substrate using a low-cost sol–gel process and sequential annealing in N2. The sol–gel derived films were annealed at 500°C for 1h in air and then annealed at 700°C in N2 for 2h. The CuO and CuFe2O4 phases appeared as the film annealed in air, and a single CuFeO2 phase (delafossite, R3m) appeared as the film annealed in N2. X-ray photoelectron spectroscopy showed that the chemical composition of the CuFeO2 thin films was similar to the stoichiometry. The optical bandgap of the CuFeO2 thin films was 3.1eV. The p-type characteristics of the films were verified by Hall-effect measurements. The electrical conductivity and carrier concentration of the CuFeO2 thin films were 0.358Scm−1 and 5.34×1018cm−3, respectively. These results show that the proposed low-cost sol–gel process provides a feasible method of depositing transparent CuFeO2 thin films.

Forecasting the effect of seasonal parameters on fouling deposition: a single effect thermal-vapor compression desalination unit as study case

Abstract The aim of this paper is to apply a new approach focus in the context of the desalination process in the Caribbean. A practical procedure based on in the combination of a nonlinear function and sequential annealing (SA) algorithm allowed predicting the fouled deposit thickness. The methodology is based on the fact that values of these parameters are target values along the year rather than fixed real numbers. The results of this paper indicate that the fouling deposition can change up to 0.4 mm according to the season.

Rapid structural reorganization in thin films of block copolymer self-assembly

In the present study, the thin films of a symmetric polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) were prepared on a neutral substrate and subjected to solvent annealing, sequentially coupled with thermal annealing for a short time. For this process, a P(S-r-MMA)-grafted substrate was used for surface neutrality to the PS and PMMA blocks. During solvent annealing with PMMA-selective acetone vapor, the block copolymer (BCP) films show a predominantly parallel orientation of the cylindrical PS microdomains over the underlying perpendicular PS cylinders on the substrate. Sequential thermal annealing of the BCP films for a short time led to efficient structural reorganization to an equilibrium morphology with the perpendicular orientation of the lamellar microdomains. This approach suggests a simple and useful route for directing the orientation of microdomain arrays in the thin films of BCP self-assembly.

Synthesis and Lithium Storage Properties of NiO@TiO2 Nanotube Heterojunction Arrays

Abstract The present work describes using TiO2 nanotube arrays as the building block to form ordered NiO@TiO2 heterojunctions via pulse electrodeposition and sequential annealing, and a key finding in the electrochemical investigation is that the enhanced capacity and rate capability derives from the hybrid nature of the electrodes with improved conductivity and dual lithium storage mechanism.

Structural Characterization of Si1-xCx Nanolayers Synthesized by C Implantation into SiO2/Si

We report the conversion of Si layer in 40 nm SiC by 40 keV carbon (C) implantation into SiO2/Si structure. SiC layer is revealed to the sample surface after final SiO2 etching. Two distinct methods were carried out: a) by sequential C implantations followed by 1250°C annealing after each implantation step (under a flux consisting of a mixture of 99% Ar with 1% O2) and, b) by single-step implantation followed by the same annealing. Rutherford Backscattering Spectrometry was employed to measure layer composition evolution after each sequential implantation step and annealing. Transmission electron microscopy (TEM) has shown that single-step implantation, up to the same minimum fluence, results in better structural quality and granular nature layer in the case of sequential synthesis

Defect-mediated resonance shift of silicon-on-insulator racetrack resonators

We present a study on the effects of inert ion implantation of Silicon-On-Insulator (SOI) racetrack resonators. Selective ion implantation was used to create deep-level defects within a portion of the resonator. The resonant wavelength and round-trip loss were deduced for a range of sequential post-implantation annealing temperatures from 100 to 300 °C. As the devices were annealed there was a concomitant change in the resonance wavelength, consistent with an increase in refractive index following implantation and recovery toward the pre-implanted value. A total shift in resonance wavelength of ~2.9 nm was achieved, equivalent to a 0.02 increase in refractive index. The excess loss upon implantation increased to 301 dB/cm and was reduced to 35 dB/cm following thermal annealing. In addition to providing valuable data for those incorporating defects within resonant structures, we suggest that these results present a method for permanent tuning (or trimming) of ring resonator characteristics.

Simulation of diffusion and phase formation during isothermal annealing of lamellar Fe-Zr systems

Results of the simulation of diffusion and phase formation in lamellar Fe-Zr systems subject to sequential isothermal annealing are presented. The simulation is performed in the framework of a physical model whose basis is Darken’s phenomenological theory and the mechanism of mutual diffusion of components along continuous phase channels in two-phase regions of the system. The results of simulation agree well with the data obtained using Mossbauer spectroscopy and X-ray diffractometry; this indicates that the character of phase transformations in the studied lamellar systems is determined by the change of local component concentration in the course of mutual diffusion and corresponds to the specific features of phase diagram of equilibrium states of the binary system.

Optical and microstructural properties of self-assembled InAs quantum structures in silicon

Abstract The InAs quantum structures were formed in silicon by sequential ion implantation and subsequent thermal annealing. Two kinds of crystalline InAs nanostructures were successfully synthesized: nanodots (NDs) and nanopyramids (NPs). The peaks at 215 and 235 cm−1, corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs single-phonon modes, respectively, are clearly visible in the Raman spectra. Moreover, the PL band at around 1.3 µm, due to light emission from InAs NDs with an average diameter 7±2 nm, was observed. The InAs NPs were found only in samples annealed for 20 ms at temperatures ranging from 1000 up to 1200°C. The crystallinity and pyramidal shape of InAs quantum structures were confirmed by HRTEM and XRD techniques. The average size of the NPs is 50 nm base and 50 nm height, and they are oriented parallel to the Si (001) planes. The lattice parameter of the NPs increases from 6.051 to 6.055 Å with the annealing temperature increasing from 1100 to 1200°C, due to lattice relaxation. Energy dispersive spectroscopy (EDS) shows almost stoichiometric composition of the InAs NPs.

Specific features of the effect of dopants on the phase formation of YBO3 and ScBO3 during synthesis from the amorphous precursor state

The effect of dopants on the structural states of the YBO3 and ScBO3 borates during sequential isothermal annealings of the amorphous precursor state and the batch from a mixture of micropowders of initial rare-earth metal oxides of the same composition has been investigated using X-ray diffraction. It has been demonstrated that, in both cases, the phase sequences of rare-earth metal borates differ substantially from each other. Possible factors responsible for the strong effect of dopants on the structural sequences during the synthesis of the YBO3 and ScBO3 borates from the amorphous precursor state have been analyzed.

Prepassivated AlGaN/GaN HEMTs with improved edge acuity in annealed ohmic contacts

Sharp edge definition of annealed ohmic contacts is of great concern in AlGaN/GaN high electron mobility transistors (HEMTs) because it is strongly associated with breakdown voltage uniformity and reliability. In this reported work, two-step sequential annealing in conjunction with a low-damage SiNx dry etching technique was employed in a prepassivation process in order to improve the edge acuity in annealed ohmic contacts. As a result, uniformity in breakdown voltage was significantly improved in comparison with a conventional process.

Ferromagnetism Driven by Oxygen Vacancies in SnO<SUB>2</SUB> Nanowires

Room temperature ferromagnetism has been observed in SnO2 nanowires synthesized by a chemical vapor deposition using Au layers as catalyst. The nanowires are homogeneous and single-crystalline grown along the [101] direction, with diameters ranging from 25 to 100 nm and length greater than 20 microm. The special magnetization reaches 0.114 emu/g for the nanowires with diameter of approximately 25 nm and reduces with increasing diameters. Branched SnO2 nanowires were prepared via a two-step vapor-liquid-solid approach, and an enhanced magnetization was obtained. To the contrary, the nanowires annealed at 1300 degrees C in air were completely transformed into the particles and exhibit weakened magnetization. These results demonstrate that the ferromagnetic properties of the samples depend on the surface-to-volume ratio of nanowires. With a combined study of photoluminescence, our results reveal that the oxygen vacancies at the surface of nanowires contribute to the ferromagnetism of SnO2 nanowires. This argument is further confirmed by a sequential annealing in a rich-oxygen atmosphere, then in a low vacuum condition.