Specific Annealing Conditions Research Articles

Encapsulation of FePt and FePt3 alloys inside carbon-foam materials

We demonstrate an advanced chemical vapour deposition (CVD) approach in which the addition of Pt-containing hydrocarbons to ferrocene allows the nucleation of a novel carbon-foam material completely filled with elemental Fe and Pt crystal-phases. These phases are then found to alloy into tetragonal FePt and cubic FePt3 in specific annealing conditions. A dependence of the FePt nucleation on the Ar/H2 flow rate is reported. In addition, high pressure (5 GPa) experiments are found to favor the formation of a single FePt3 encapsulated phase together with the nucleation of C–O rich carbon layers in the foam surface.

Influence of annealing on the optical properties, structure, photosensitivity and chemical stability of As30S70 spin-coated thin films

Chalcogenide glass (ChG) thin films prepared by solution based deposition technique offer important advantages over vacuum deposited films, which are useful for many applications especially in infrared optics. Their fabrication, which comprises dissolving the ChG in volatile organic solvent and then depositing thin film by spin coating the solution, is simpler and significantly cheaper. However, contaminants from the solvent are incorporated. The residual organic content in the films is significantly reduced by appropriate thermal treatment. This work reports the influence of specific annealing conditions and UV light exposure on the structure, opto-physical and chemical properties of As30S70 spin-coated ChG films. The results show increase in refractive index with increasing annealing temperature, whereas the thickness and optical bandgap decrease. The UV exposed regions of the samples exhibit positive etching in amine based solvents. The HS-LEIS spectroscopy is used to determine the elemental concentration profile of annealed thin film, which shows almost stable As/S ratio with composition close to that of the source bulk glass. Thus UV light induced structural changes and the mechanism of selective etching are proposed.

Optimization of Annealing Catalyst Powder for High Temperature PEMWE

1. IntroductionRenewable energy is an alternative choice to solve the universal problem of energy depletion and environmental pollution. Among various energy carriers, hydrogen is a most competitive one, because it is friendly to environment and can be produced from renewable energy through water electrolysis. Among types of water electrolysis, polymer electrolyte membrane water electrolysis (PEMWE) attracts most attention for its advantages because of simple structure and high energy conversion efficiency.Usually, water electrolysis needs higher voltage supply than theoretical value, due to high overvoltage in oxygen evolution reaction at anode. To minimize the anodic overvoltage, it is recently suggested that annealing catalyst powder at certain temperature and time can decrease both the HFR and activation overvoltage, and the annealing effects are proven in the conventional PEMWE, where operation temperature is around 80℃ [1-4]. The current mechanisms about how annealing impacts electrolysis performance are as followings: (i) annealing can largely decrease electrolysis voltage by reducing HFR [1]; (ii) annealing will enlarge the specific surface area [2]; (iii) annealing increases the catalyst activity by changing the structure of catalyst particle [3~4]. In order to examine the above three mechanisms, we evaluated I-V and I-HFR characteristics of IrO2 samples which have different specific surface area and were annealed under different temperatures and time. This study also challenges to find the optimum condition of annealing time and temperature, to minimize electrolysis voltage under rather high temperature operation of 100℃. 2. ExperimentPEMWE cell used in this study consists of a homemade CCM (with electro-catalyst area of 4cm2), porous current collectors, and separators with flow channels. For the CCM fabrication, anode and cathode catalytic electrodes are hot pressed to a membrane (Nafion117). Iridium oxide powder (IrO2 powder, type IV, Tokuriki Co., Japan) as for anode catalyst is annealed in air at different time and temperatures shown in table 1. Rasten et al [1] suggests that annealing at 490℃ and 8hrs results in the lowest electrolysis voltage. Siracusano et al [3~4] shows that the optimum annealing condition should be 350℃ and 1hr. Based on these, Annealing condition of the powder is at 350℃ and 490℃ from 1 to 8 hrs. To examine the effect of enlarging specific surface area, IrO2 samples with two different specific surface area were selected: sample 1 and sample 2 originally has the specific surface area of 42m2/g and 84m2/g respectively. A commercial 46% Pt/C (Tanaka Kikinzoku Japan) catalyst is used for cathode electrode. Ti mesh (Nikko Techno Co., Japan, fiber diameter 20μm) is used for anode current collector. As for cathode current corrector, carbon paper (hydrophobic, SGL Co., Germany, 34BC) is chosen for comparing with each other. Water at room temperature is fed into only anode channel at a flow rate of 1mL/min, which corresponds to the water utilization of 2% at 1A/cm2. All the experiments are conducted at atmospheric pressure and 100℃.3. Result and discussionFig. 1 (a) and (b) shows how specific surface area and annealing conditions impact on I-V characteristics and high frequency resistance at 10 kHz. The IV and I-HFR characteristics revealed that: (i) enlarging specific surface area to two times has little impact on electrolysis performance; (ii) annealing catalyst powder at 350℃ and 1hr introduced the best electrolysis performance and annealing at 490℃ and 8hrs introduced the highest electrolysis voltage. When annealing temperature is 350℃, long annealing time will raise the electrolysis voltage. But when annealing temperature is 490℃, annealing time makes a limited impact on electrolysis voltage. It also should be noticed that the OCV changes with annealing temperature, annealing catalyst annealed at 490℃ generates much higher OCV (about 80mV) than that annealed at 350℃. Such phenomenon means annealing at 490℃ will decrease the catalyst activity. Annealing catalyst at certain temperature can decrease the HFR, but the decreased ohmic overvoltage can’t explain the total electrolysis voltage difference. Therefore, among the above three main mechanisms, annealing method should impact the electrolysis performance by increasing the catalyst activity via changing the structure of catalyst particle.

Formation of axial metal–semiconductor junctions in GaAs nanowires by thermal annealing

We demonstrate the formation of nanoscale axial Schottky contacts in GaAs nanowires by thermal annealing of NiGeAu multilayers. Energy dispersive x-ray spectroscopy indicates that in specific annealing conditions a sharply-defined Au-rich phase can be obtained in the vicinity of the metallic contacts. Charge transport characteristics are analyzed for different degrees of diffusion of the Au-rich phase in the wire and indicate that it has a metallic nature. The mechanism behind this local post-growth modification of the nanowire composition and its potential impact on device applications are discussed.

Atomic structure and formation mechanism of identically sized Au clusters grown on Si(111)-(7×7) surface

Identically sized Au clusters are grown on the Si(111)-(7×7) surface by room temperature deposition of Au atoms and subsequent annealing at low-temperature. The topographical images investigated by in situ scanning tunneling microscopy show a bias-dependent feature. The current-voltage properties measured by scanning tunneling spectroscopy indicate some semiconducting characteristics of the Au adsorbed surface, which is attributable to the saturation of Si dangling bonds. These experimental results, combined with the simulated scanning tunneling microscopy images and the first-principles adsorption energy calculations, show that the Au cluster is most likely to have a Au(6)Si(3) structure. In the Au(6)Si(3) cluster, three adsorbed Au atoms replace the three Si center adatoms, forming a hollow triangle, while the replaced Si atoms and other three Au atoms connect into a hexagon locating within the triangle. The formation mechanism of this atomic configuration is intimately associated with the complicated chemical valences of Au and the specific annealing conditions.

Ultrafine Grained High Strength Low Alloy Steel with High Strength and High Ductility

In this study a C-Mn High Strength Low Alloy steel (HSLAs) was processed by quenching and austenite reverted transformation during annealing (ART-annealing), which results in an ultrafine grained duplex microstructure characterized by scanning electron microscopy equipped with electron back scattered diffraction, transmission electron microscopy and x-rays diffraction (SEM/EBSD, TEM and XRD). Microstructural observation revealed that the full hard martensitic microstucture gradually transformed into ultrafine grained duplex structure with austenite volume fraction up to 30% at specific annealing conditions. Mechanical properties of this processed steel measured by uniaxial tensile testing demonstrated that an excellent combination of strength (Rm~1GPa) and total elongation (A5~40%) at 30% metastable austenite condition in studied C-Mn-HSLAs. This substantially improved strength and ductility were attributed to the strain induced phase transformation of retained austenite dispersed throughout the ultrafine grained microstructure. At last it is proposed that ART-annealing is a promising way to produce high strength and high ductility steel products.

Helium behaviour and vacancy defect distribution in helium implanted tungsten

The distribution and the nature of 3He implantation-induced defects in polycrystalline tungsten samples were studied by Positron Annihilation Spectroscopy as a function of implantation fluence. The implanted helium profile was determined by Nuclear Reaction Analysis, and its evolution under different thermal annealings was investigated. Results show that vacancy-like defects are generated along the path of the ions and that their concentration varies directly as the implantation fluence. No helium desorption was observed under any thermal treatments. However, a change in 3He depth profile under specific annealing conditions suggests the formation of nanometric-size He bubbles.

Nonconservative Ostwald ripening of a dislocation loop layer under inert nitrogen-rich SiO2∕Si interfaces

In this work we perform a systematic study of the dissolution of a dislocation loop layer under the influence of inert SiO2∕Si and nitrogen-rich SiO2∕Si interfaces. The composition of the dislocation loop layer was just after its formation 10%–20% Frank dislocation loops and 90%–80% perfect prismatic loops. During subsequent inert (N2) ambient annealing the differences of the kinetics between the two loop populations have been studied as a function of the interface type. It has been shown that during the nonconservative Ostwald ripening process the defect band loses interstitials mainly due to the dissolution of perfect prismatic loops, while Frank loops remain almost unaffected by the presence of both interfaces. In parallel a competition between the interface and the population of Frank loops in absorbing the interstitials released by the prismatic loops took place. The nitrogen-rich SiO2∕Si interface has been proved in general a less effective interstitial sink than the common one and under specific annealing conditions less effective even than the small Frank loops population.

Influence of the Ge Dose in Ion-implanted SiO2 Layers on the Related Nanocrystal-memory Properties

ABSTRACTThin silicon dioxide (SiO2) on Si layers with embedded germanium nanocrystals (Ge-ncs) were fabricated using 74Ge+-implantation at 15 keV and subsequent annealing. Transmission electron microscopy and Rutherford backscattering spectrometry have been used to study the Ge redistribution in the SiO2 films as a function of implantation dose under specific annealing conditions. At low implantation doses, Germanium is found to segregate at the Si/SiO2 interface leading to poor electrical properties. At higher doses and when the disorder limit of one displacement per atom is reached at the interface, transmission electron microscopy revealed the formation of a Ge-nc layer array located close to the Si/SiO2 interface and an another one inside the SiO2 host material. This near-interface high density (>1012 ncs/cm2) nc-layer is found to act as a floating gate embedded within the silicon dioxide. Capacitance-voltage measurements performed on metal-oxide-semiconductor structures containing such implanted SiO2 layers show significant memory properties (few volts hysteresis) at low programming voltages (<|10V|) due to the presence of Ge-ncs near the Si/SiO2 interface

High-efficiency photovoltaic devices based on annealed poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1- phenyl-(6,6)C61 blends

The effects of annealing and fullerene loading in regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) based bulk heterojunction photovoltaics have been investigated. Under specific loading and annealing conditions, a combination of morphological and electronic factors can be brought to play to achieve optimal filling factors, open-circuit voltage (Voc), and short-circuit current density (Jsc). We demonstrate that this occurs at surprisingly low loadings of PCBM and annealing temperatures nearing the melting point of the polymer. Further, we report power conversion efficiencies approaching 5% in the P3HT:PCBM system.

Epitaxial growth of NiSi2 on (001)Si inside nanoscale contact holes prepared by atomic force microscope tip-induced local oxidation of the thin Si3N4 layer

Epitaxial NiSi2 has been grown on (001)Si inside 50–200 nm Si3N4 openings prepared by atomic force microscope tip-induced local oxidation. The morphology of epitaxial NiSi2 was found to be significantly influenced by the opening size. For specific annealing conditions, there exists a transitional opening size below which a pyramidal faceted structure of epitaxial NiSi2 is preferred. The opening size effect is attributed to a limited supply of Ni atoms, the increased interface∕volume ratio of silicides with decreasing size of openings, and the considerable stress level inside miniature openings.

Specific features of the physical properties of a modified CdTe surface

Specific features of the optoelectronic properties of CdTe substrates with a modified layer and surface-barrier diodes based on them are revealed and explained by quantum confinement effects in the nanocrystalline structure of the modified layer. The formation of the modified layer is confirmed by study of its surface using atomic-force microscopy and is attributed to the processes of self-organization, which is dominant under specific annealing conditions.

Structural and electrical properties of Ge nanocrystals embedded in SiO2 by ion implantation and annealing

Silicon dioxide (SiO2) on Si layers with embedded germanium nanocrystals (Ge-ncs) were fabricated using Ge+ implantation and subsequent annealing. Transmission electron microscopy and Rutherford backscattering spectrometry have been used to study the Ge redistribution in the SiO2 films as a function of annealing temperature. A monolayer of Ge-ncs near the Si∕SiO2 interface was formed under specific annealing conditions. This layer, with a nc density and mean size measured to be, respectively, 1.1×1012∕cm2 and 5nm, is located at approximately 4nm from the Si∕SiO2 interface. Capacitance–voltage measurements were performed on metal-oxide-semiconductor structures containing such implanted SiO2 layers in order to study their electrical properties. The results indicate a strong memory effect at relatively low programming voltages (<5V) due to the presence of Ge-ncs near the Si∕SiO2 interface.

Thermal annealing effect on 1.3-μm GaInNAs/GaAs quantum well structures capped with dielectric films

Two kinds of dielectric films, Si3N4 and SiO2, deposited onto the surface of 1.3-μm GaInNAs/GaAs quantum well (QW) structures were studied upon post-growth thermal annealing. The blue-shift in photoluminescence (PL) as a function of annealing time showed distinct dependence on the selection of the dielectric films. It was found that a Si3N4 cap layer inhibits the blue-shift under specific annealing conditions and the blue-shift inhibition effect increases with the thickness of the Si3N4 cap; while a SiO2 cap layer enhances the PL blue-shift. X-ray diffraction (XRD) and secondary-ion-mass-spectrometry (SIMS) indicated that the enhanced blue-shift in PL from the SiO2-capped sample was caused by two factors: interdiffusion of Ga and In atoms across the QW interfaces and the decrease of N–Ga ion density (and hence N) in the QW material. Compared with the SiO2 caps, Si3N4 cap layers can inhibit both of these factors. Time-resolved PL decay measurements at room temperature were performed to study the optical properties of the uncovered and Si3N4-capped samples.

Quantification and control of the sulfur c(2 × 2) superstructure on {100}〈100〉 Ni for optimization of YSZ, CeO2, and SrTiO3 seed layer texture

We investigated the influence of a chemisorbed S template with c(2 × 2) structure on the epitaxial growth of different oxide buffer layers on {100}〈100〉 Ni. The sulfur superstructure spontaneously forms on the Ni surface during the texturing anneal as a consequence of segregation. However, depending on the initial S bulk concentration and/or specific annealing conditions, the S layer can cover less than the entire substrate's surface. We show that an incomplete c(2 × 2) coverage causes degradation of the seed buffer layer texture as compared to the substrate texture. A simple step consisting of an H2S predeposition anneal can be used to control the superstructure coverage and optimize the seed layer texture.

Annealing studies of Al-implanted 6H-SiC in an induction furnace

6H-SiC samples were amorphised by multiple Al implantations at room temperature, in order to study the annealing process. The paper deals with the influence of specific annealing conditions, such as furnace atmosphere and heating rate, on SiC reordering and Al profile. Below a certain deposited nuclear energy, solid phase epitaxy is possible and leads to recrystallisation under precise conditions (high heating rate, silicon partial pressure prescribed). Above it, material etching and dopant losses are observed, even though annealing has proven to be efficient for avoiding surface impairment (due to a specific cleaning process).

Interface Quality and Electrical Performance of Low-Temperature Metal Organic Chemical Vapor Deposition Aluminum Oxide Thin Films for Advanced CMOS Gate Dielectric Applications

ABSTRACTIn this work, the electrical performance and interfacial characteristics of MOCVD-grown Al2O3 films are evaluated. Electrical characteristics (dielectric constant, leakage current) of as-deposited and annealed capacitor metal-oxide-semiconductor (MOS) stacks were determined using capacitance-voltage (C-V) and current-voltage (I-V) measurements. It was observed that the electrical properties were dependent upon specific annealing conditions, with an anneal in O2 followed by forming gas being superior with respect to leakage current, resulting in leakage characteristics superior to those of SiO2. All annealing conditions evaluated led to an increase in dielectric constant from 6.5 to 9.0–9.8. Also, Al2O3 growth and interfacial oxide growth characteristics on oxynitride/Si and Si substrates were evaluated and compared using spectroscopic ellipsometry. A parasitic oxide layer was observed to form on silicon during the initial stages of MOCVD Al2O3 growth, while a thin oxynitride layer deposited on Si prevented the growth of interfacial oxide.

Analysis of gene expression following oxidative stress.

Abstract The modulation of gene expression by cellular stress is a universal phenomena that has been described in organisms ranging from bacteria to animals to plants, and in response to a wide range of stress agents including heat shock, glucose deprivation, oxidants, radiation, and heavy metals (1). For oxidative stress alone, many genes have been identified whose steady-state mRNA product levels are modulated by a multitude of oxidant stress agents (1). These genes were identified using various techniques that are still popular, such as two-dimensional gel electrophoresis, subtractive hybridization, differential display (DD), restriction fragment differential display (RFDD), serial analysis of gene expression (SAGE), and gene arrays; as well as other techniques that have lost their popularity, including one-dimensional protein gel electrophoresis and differential hybridization (1). Differential display (DD) is a polymerase chain reaction (PCR)-based technique that requires only small amounts of sample, is relatively sensitive, and able to identify both induced and reduced species (2–3). Its main drawbacks are a high number of false-positives and products that are strongly biased for the ’3’ untranslated region of the mRNA. These drawbacks have been addessed by a more recent technique called restriction fragment differential display (RFDD), which uses restriction enzyme-generated cDNA fragments as PCR templates (1). This modification allows for the use of much higher temperature and more specific annealing conditions as well as the ability to generate products that include the coding region and ’5’ untranslated region.KeywordsDifferential DisplayPolymerase Chain Reaction TemplateReverse Northern BlotOxidant Stress AgentPolymerase Chain Reaction ThermocyclerThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Investigation of Al-implanted 6H– and 4H–SiC layers after fast heating rate annealings

6H– and 4H–SiC n-type layers were amorphised by multiple Al implantations at room temperature, in order to study the annealing process. This paper deals with the influence of specific annealing conditions, such as furnace atmosphere and heating rate, on SiC reordering and Al profile. Below a certain deposited nuclear energy, solid phase epitaxy (SPE) is possible and leads to recrystallisation under precise conditions (high heating rate, silicon partial pressure prescribed). Above that, partial reordering is only observed for 4H–SiC layers, and leads to some increasing roughness, even though annealing has proven to be efficient for avoiding surface impairment (due to a specific cleaning process). Some Al oscillations have been observed near the junction in case of SPE, whereas a flat homogeneous profile is formed in amorphised layers.

Atomic force microscopy studies of self-assembled Si1−xGex islands produced by controlled relaxation of strained films

Self-assembled Si1−xGex islands were studied in detail using atomic force microscopy. The self-assembled Si1−xGex islands were formed by a novel two-step process. First, highly strained Si1−xGex thin films (with x∼0.4) were selectively grown on a silicon wafer by chemical vapor deposition at 650 °C. The growth was followed by an annealing step performed in hydrogen at 750 °C at reduced pressure conditions for specific times. The size and distribution of the islands was found to be a function of the annealing conditions and an ordered pattern could be achieved with specific annealing conditions. This growth process shows a new way of creating device islands, which are confined within oxide regions and could be ordered, for applications in optical and electronic devices on silicon.