Thermal Treatment In Nitrogen Research Articles

Novel SnSb2S4 Thin Films Obtained by Chemical Bath Deposition using Tartaric Acid as Complexing Agent for Their Application as Absorber in Solar Cells

Ternary Sn-Sb-S thin films with remarkable optical, electrical and structural properties were developed by chemical bath deposition. Tin and antimony chlorides and thioacetamide were used as tin, antimony, and sulfur ion sources, respectively, while tartaric acid was used as a complexing agent. XRD analysis of as-deposited films showed a combination of binary phases of SnS, Sn2S3, and Sb2S3, while after thermal treatment in nitrogen at 400 °C, the films became crystalline showing well-defined reflections of the ternary SnSb2S4. The heating also influenced the morphology, compactness, and thickness of the films. On the other hand, all the films showed an absorption coefficient higher than 104 cm-1, while the optical band gap of the as-deposited film decreased from 1.49 to 1.37 eV after heating at 400 °C. In addition, the photoconductivity of the films prior to heating was of 10-9 Ω-1 cm-1, while after that at 400 °C was of 10-7 Ω-1 cm-1. The evaluation of the ternary film in solar cells gave an open-circuit voltage Voc of 448 mV and short-circuit current density of Jsc of 2.4 mA/cm2.

Enhancing the performance of nanostructured ZnO as an anode material for lithium-ion batteries by polydopamine-derived carbon coating and confined crystallization

Transition metal oxides (TMOs) generally suffer severe capacity degradation as the potential anode materials for lithium-ion batteries, since the large volume changes of TMO anodes during conversion reactions result in the collapse of electrode structures. Fabricating specific nanostructures of TMOs has been demonstrated as a successful approach to partially solve this issue. Besides the concern of capacity retention, our previous work has demonstrated that the specific capacities of TMOs can be improved by enhancing their degrees of crystallinity. Therefore, the TMO nanostructures with high degrees of crystallinity are highly desired to achieve both high specific capacity and good capacity retention. However, the high crystallinity and desired nanostructure are usually contradictory in nanofabrication since the thermal treatment will lead to the collapse of a nanostructure. To overcome the obstacle, herein, the polydopamine coating followed by a thermal treatment in nitrogen is first introduced as a confined crystallization strategy to enhance the degree of crystallinity and simultaneously maintain the nanostructure of ZnO microspheres. Electrochemical performance tests demonstrate that the appropriate coating thickness and heat treatment can enhance the specific capacity from 288.0 mAh g−1 of pristine ZnO to 527.0 mAh g−1 of carbon coated ZnO after 100 cycles. The present work provides a good opportunity to develop TMO anodes with high capacities and superior cycling performances by the polydopamine-derived carbon coating and confined crystallization.

Insights into the effects of surface/bulk defects on photocatalytic hydrogen evolution over TiO2 with exposed {001} facets

This paper describes the effects of defect distribution on energy band structure and the subsequent photocatalytic activity over TiO2 with exposed {001} facets as the model catalyst. Our results show that only surface oxygen vacancies (Vo’s) and Ti3+ centers in TiO2 can be induced by hydrogenation treatment, whereas the generation of bulk Vo’s and Ti3+ species depends on the thermal treatment in nitrogen. Both the surface and bulk defects in TiO2 can promote the separation of electron-hole pairs, enhance the light absorption, and increase the donor density. The presence of surface and bulk defects in TiO2 can not change the valence band maximum, but determine the conduction band minimum. Surface defects in TiO2 induce a tail of conduction band located above the H+/H2 redox potential, which benefits the photocatalytic performance. However, bulk defects in TiO2 generate a band tail below the H+/H2 potential, which inhibits hydrogen production. Thus, the change of band gap structure by defects is the major factor to determine the photocatalytic activity of TiO2 for hydrogen evolution. It is a new insight into the rational design and controllable synthesis of defect-engineered materials for various catalytic processes.

Improved resistance of chemically-modified nanocellulose against thermally-induced depolymerization

The study demonstrated the improvement in the resistance of nanocellulose against thermally-induced depolymerization by esterification with benzoyl (BNZ) and pivaloyl (PIV). The change in the degree of polymerization (DP) and molecular weight distribution (MWD) after thermal treatment in nitrogen and in air was investigated using viscometry and gel permeation chromatography. BNZ and PIV nanocellulose esters without α-hydrogens gave higher DP and narrower MWD than pure bacterial cellulose; and the acetyl and myristoyl esters, which possess α-hydrogens. Results also showed that when depolymerization is suppressed, thermal discoloration is also reduced. Resistance against depolymerization inhibits the formation of reducing ends which can be active sites for thermal discoloration. Finally, the findings suggest that benzoylation and pivaloylation can be an excellent modification technique to improve the thermal stability of nanocellulose.

Highly uniform Co9S8 nanoparticles grown on graphene nanosheets as advanced anode materials for improved Li-storage performance

A Co9S8/GNS (graphene nanosheets) nanocomposites has been synthesized via a facile solvothermal approach followed by thermal treatment in nitrogen at 500°C using graphite oxide sheets, CoCl2·6H2O and thiourea as the starting materials. Highly uniform Co9S8 nanoparticles with a size of about 80–90nm are evenly grafted on the surface of GNS, forming a unique Co9S8/GNS hybrid nanostructure. When evaluated as anode materials for lithium ion batteries, impressive electrochemical performances of the as-prepared nanocomposites are achieved compared to that of pure bulk Co9S8, with an high reversible capacity of 1480mAhg−1. Moreover, the as-synthesized nanocomposites present excellent cycling durability and high-rate capability. The improvement in the electrochemical properties could be attributed to the well-designed structure of the Co9S8/GNS nanocomposite which possesses large number of accessible active sites for lithium-ion insertion, fast ion diffusion rate and good electronic conductivity.

Substrate and atmosphere influence on oxygen p-doped graphene

The mechanisms responsible for p-type doping of substrate supported monolayer graphene (Gr) by thermal treatments in oxygen ambient have been investigated by micro-Raman spectroscopy, atomic force microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS), considering commonly employed dielectric substrates, such as SiO2 and Al2O3 thin films grown on Si. While a high p-type doping (∼1013 cm−2) is observed for Gr on SiO2, no significant doping is found for Gr samples on the Al2O3 substrate, suggesting a key role of the Gr/SiO2 interface states in the trapping of oxygen responsible for the Gr p-type doping. Furthermore, we investigated the doping stability of Gr on SiO2 during subsequent thermal treatments in nitrogen (N2), carbon dioxide (CO2), water (H2O) or in vacuum controlled atmospheres. These processes induce only minor effects on the doping of Gr but for H2O and principally affect its defectiveness, suggesting that the literature reported air influence on the doping depends on water present in the atmosphere.

Ultrahigh surface area carbon from carbonated beverages: Combining self-templating process and in situ activation

Ultrahigh surface area carbons (USACs, e.g., >2000m2/g) are attracting tremendous attention due to their outstanding performance in energy-related applications. The state-of-art approaches to USACs involve templating or activation methods and all these techniques show certain drawbacks. In this work, a series of USACs with specific surface areas up to 3633m2/g were prepared in two steps: hydrothermal carbonization (200°C) of carbonated beverages (CBs) and further thermal treatment in nitrogen (600–1000°C). The rich inner porosity is formed by a self-templated process during which acids and polyelectrolyte sodium salts in the beverage formulas make some contribution. This strategy covers various CBs such as Coca Cola®, Pepsi Cola®, Dr. Pepper®, and Fanta® and it enables an acceptable product yield (based on sugars), for example: 21wt% for carbon (2940m2/g) from Coca Cola®. Being potential electrode materials for supercapacitors, those carbon materials possessed a good specific capacitance (57.2–185.7Fg−1) even at a scan rate of 1000mVs−1. Thus, a simple and efficient strategy to USACs has been presented.

Physical and electrical characterization of TiO2 particles after high temperature processing and before and after ultraviolet irradiation

In this work, rutile-phase TiO2 particles (r-TiO2, about 360 nm in size) are embedded within a silicon oxide matrix using different concentration ratios of r-TiO2 with respect to SiO2:H2O, so that suspensions of mixed TiO2:SiO2 oxides were obtained and analyzed. These TiO2:SiO2 suspensions were deposited on previously-cleaned crystalline silicon and quartz substrates so that thin films of TiO2:SiO2 were obtained. All films were then exposed to relatively high-temperature thermal treatments in nitrogen and different characterization techniques were used to determine their physical and electrical properties before and after ultraviolet (UV) irradiation. Before high thermal treatment, X-ray diffraction patterns show that the main diffraction peaks for the obtained TiO2:SiO2 films correspond to the crystalline phase of rutile-TiO2. Infrared analyses before and after thermal treatment show significant changes in the chemical bonding of the final films relative to the temperatures used during annealing. Also, UV–visible spectra provide a constant optical band gap for the films, independent of different TiO2 concentrations as expected. On the other hand, atomic-force microscopy measurements before and after UV irradiation show an appreciable difference in the grain size and surface morphology of the resulting TiO2:SiO2 oxides annealed at 1000 °C. Finally, photoelectrical I–V properties were obtained for all TiO2:SiO2 films by depositing ultrathin titanium stripes on top of the photoactive material and then, measuring the total current flowing through the metal electrode before and after UV irradiation. From these last measurements, a detectable increase in the I–V slope (lower resistance of the titanium stripe) is found for all samples during UV exposure, thus making this device to act as a simple photoresistor based on r-TiO2 particles.

Mesoporous isocyanurate-containing organosilica–alumina composites and their thermal treatment in nitrogen for carbon dioxide sorption at elevated temperatures

Composite mesostructures consisting of organosilica with isocyanurate bridging groups and alumina have been synthesized using evaporation-induced self-assembly (EISA) in the presence of a triblock copolymer, Pluronic P123, in absolute ethanol solution. These mesostructures were prepared using aluminum isopropoxide and aluminum nitrate nonahydrate as alumina precursors and tris[3-(trimethoxysilyl)propyl]isocyanurate (ICS). The triblock copolymer was removed by extraction with 95% ethanol solution followed by additional thermal treatment of the extracted sample at 300 °C in flowing nitrogen; this process assured a complete removal of the polymeric template without degradation of the ICS bridging groups. The use of aluminum nitrate nonahydrate and a N-containing ICS precursor with a small amount of 3-aminopropyltriethoxysilane (AP) led to the hybrid materials with well-developed porosity and high specific surface area (200–450 m2 g−1). A controlled heating of these materials in nitrogen resulted in N-doped alumina–silica mesostructures showing high affinity towards CO2 at elevated temperatures. The use of inexpensive aluminum nitrate instead of aluminum alkoxides in the EISA synthesis had a significant impact on the pore structure, surface area and adsorption properties of the resulting composite materials.

Gold nanoparticles on ceria supports for the oxidation of carbon monoxide

Ultrafine cubic CeO 2 particles were prepared by a solvothermal method, using methanol and different conditions of synthesis, and compared with a commercial CeO 2, used as received and after a thermal treatment in nitrogen. The solvothermally prepared materials showed higher specific surface areas (from ∼124 to ∼157 m 2/g) than the commercial sample (∼20 m 2/g). Au was loaded onto the obtained ceria supports by a double impregnation (DIM) method. Samples were characterised by high-resolution transmission electron microscopy (HTREM), selected area electron diffraction (SAED), energy-dispersive X-ray spectrometry (EDXS), high-angle annular dark-field imaging (HAADF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and temperature programmed desorption (TPD). Activities for CO oxidation were compared and results were discussed. A gold reference catalyst from the World Gold Council (Type C—Au/Fe 2O 3) was also used for comparison purposes. Considering the ceria supports alone, the solvothermally prepared samples clearly showed better performance for CO oxidation than the commercial ceria. This can be due to their large amounts of surface oxygen groups, as seen by TPR and TPD, since XRD showed that the same phase was present in all ceria samples. When gold was loaded, full CO conversion was obtained at much lower temperatures. The best results were obtained with the commercial as received sample, which can be explained by the small size of the Au particles (2–5 nm). Other samples (solvothermal) yielded larger Au particle sizes (∼10–30 nm). Although the gold particle size of these solvothermal materials is far from the “ideal” range (below 5 nm), and their activity is consequently lower than that of the commercial ceria, these samples still show better catalytic behaviour in comparison to the reference catalyst. It was shown that Au was in its metallic state when supported in the commercial ceria sample, while a larger contribution from oxidic Au was found in the solvothermal samples.

Nanocasting Synthesis of Iron-Doped Mesoporous Al−Ti Mixed Oxides Using Ordered Mesoporous Carbon Templates

Mesoporous Al−Ti mixed oxides have been prepared by employing pyrrole-based nitrogen-doped mesoporous carbon templates with p6mm and Im3m symmetries. These oxides were obtained using isopropanol solutions of aluminum and titanium isopropoxides, Al(PriO)3 and Ti(PriO)4, respectively, by a combined nanocasting and sol−gel synthesis, involving hydrolysis of the aforementioned precursors in the pores of the carbon templates, followed by controlled thermal treatment of the resulting composites in nitrogen and oxidative removal of the templates in flowing air at 700 °C. The resulting mixed oxides and corresponding oxide−carbon nanocomposites were characterized by thermogravimetry, CHNS elemental analysis, nitrogen adsorption at −196 °C, small and wide angle X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy (HR TEM), energy-dispersive X-ray spectrometry (EDX), and elemental mapping. Nitrogen adsorption revealed that the ordered mesopores of the carbon templates were almost completely filled in a single nanocasting step, and the oxide inverse replicas possessed a specific surface area of about 200 m2/g, large pore volume, and uniform mesopores. The corresponding pore size distributions are narrow and centered at ∼7 nm; the latter value showed a tendency to increase with increasing temperature of the thermal treatment preceding the oxidative removal of the carbon template. In addition, HR TEM analysis confirmed ordered porosity of some oxide samples. The mixed oxide samples were found to be amorphous, if the temperatures of the thermal treatments in nitrogen and air did not exceed 700 °C. At higher temperatures, crystalline phases were gradually formed. The wide angle XRD analysis of the mixed oxides treated at 1000 °C revealed the presence of α-Al2O3 and rutile TiO2 phases. For some nanocomposites, the Magnéli phase Ti6O11 was also detected. Because the carbon templates used possessed iron phases due to employing iron chloride to catalyze polymerization of pyrrole during carbon synthesis, this residual iron was oxidized during carbon removal and transferred to the resulting oxide replicas. Elemental mapping and EDX analysis revealed a homogeneous distribution of Al, Ti, and Fe for all amorphous samples of mixed oxides with the Al/Ti atomic ratios close to those used in the synthesis.

Thermal decomposition study of selected isopolymolybdates

The thermal decomposition of ammonium trimolybdate (NH4)2Mo3O10·H2O, anilinium trimolybdate (C6NH8)2Mo3O10·4H2O and anilinium pentamolybdate (C6NH8)2Mo5O16 in air and nitrogen has been investigated. The decomposition of molybdates was studied in situ by powder X-ray diffraction. Moreover, results of TG, as well as scanning microscopy studies, are presented. It was found that during thermal treatment in air phases of MoOx type are obtained, while thermal treatment in nitrogen leads to obtaining a mixture of MoyCz and MopNq. It is worth noting that even though chemical decomposition and formation of new compounds took place, in some cases needle-like or plate-like shapes of crystallites were preserved during thermal treatment.

Characterization of Mg-Doped AlInN Annealed in Nitrogen and Oxygen Ambients

Mg-doped AlInN grown by metalorganic chemical vapor deposition (MOCVD) was demonstrated using the postgrowth thermal treatment in nitrogen and oxygen ambients. High-resolution x-ray diffraction (HRXRD) measurements showed that the crystalline quality of AlInN depends on the indium content, which is attributed to the effect of the lattice mismatch between AlInN and GaN. Interestingly, the formation of rod-shaped AlInN, which possibly resulted from the oxidation process, was observed after the postgrowth thermal treatment in the oxygen ambient. Furthermore, an InGaN/GaN multiple-quantum-well (MQW) light-emitting diode (LED) with an AlInN cladding layer was also fabricated. We believe that Mg-doped AlInN, nearly lattice matched to GaN, could play an important role for the further development of lattice-matched AlInN/GaN device applications.

Growth of crystalline/amorphous biphase Sm–Fe–Ta–N magnetic nanodroplets

Thin films of biphase (amorphous/crystalline) magnetic Sm–Fe–Ta–N nanodroplets were fabricated at room temperature with 157 nm pulse laser deposition in nitrogen from a Sm 13.8Fe 82.2Ta 4.0 target. The 50–100 nm biphase spherical nanodroplets consist of a 5–10 nm internal crystal portion surrounded by the external amorphous phase. Nitrogen fixation in the nanodroplets occurred in the plume. The films exhibit a ferromagnetic response of 2.5 kOe coercivity at room temperature. With further annealing and thermal treatment in nitrogen, the coercivity was increased to 5.0 kOe. The surrounding amorphous layer prevents post-ablation oxidization of the crystalline magnetic nucleus of the nanodroplet.

Influence of the implantation and annealing parameters on the photoluminescence produced by Si hot implantation

We report an investigation on the effect of the fluence and annealing time on the photoluminescence (PL) from Si nanocrystals produced by hot implantation of Si into a SiO2 matrix followed by thermal treatment in nitrogen. We have varied the implantation fluence in a wide range, from 0.35×1017 to 4×1017Si/cm2. In addition, the PL evolution with the annealing time (1 up to 15h) was studied for the samples implanted with fluences between 1×1017 and 4×1017Si/cm2. After annealing the spectra present two PL bands: one centered at 780nm and a second one around 1000nm. The influence of the studied parameters on the PL behavior of both bands suggests different origins for their emission. The results are discussed in terms of current models.

Cobalt ferrite nanoparticles: Achieving the superparamagnetic limit by chemical reduction

An unanticipated superparamagnetic response has been observed in cobalt ferrite materials after thermal treatment under inert atmosphere. Cobalt ferrite particles were prepared via normal micelle precipitation that typically yields CoxFe3−xO4 nanoparticles (x=0.6−1.0). While samples thermally treated under oxygen show majority spinel phase formation, annealing in nitrogen gas yields materials consisting of Co-Fe alloy, FeS, and CoFe2O4 spinel. After thermal treatment, thermomagnetic studies reveal composition-insensitive, but highly treatment-sensitive, saturation magnetization, coercivity, blocking temperature, and Verwey transition temperature dependence. Extremely high saturation magnetization (159 emu/g) with low coercivity (31 Oe) was observed for one of the treated compositions, which drastically deviates from prototypical cobalt ferrite with large magnetocrystalline anisotropy. We attribute such unique magnetic response to Co-Fe alloy coexisting with FeS and CoFe2O4 spinel where the diameter of the metallic phase is below the superparamagnetic limit. While thermal treatment in nitrogen was not anticipated to yield Co-Fe alloy, chemisorbed surfactant molecules (i.e., sodium dodecylsulfate) are postulated to act as reducing agents in the present scenario.

Propane dehydrogenation over supported platinum silicon nitride catalysts

Amorphous silicon nitrides were prepared by gas phase ammonolysis of tetrachlorosilane followed by thermal treatment in nitrogen or ammonia atmosphere. After deposition of platinum on the materials the obtained catalysts proved to be catalytically active and selective for propane dehydrogenation. Incorporation of boron, carbon and titanium in the supports influences significantly the catalytic properties. It is suggested that the comparable high catalytic activity, propene selectivity and stability of the catalysts are due to the basic properties of the catalyst surface.

Pregate Oxidation Treatment using Radio Frequency Activated Nitrogen in a Rapid Thermal Reactor

A rapid thermal treatment in nitrogen could be inserted immediately before the gate oxidation step in a typical process flow for making metal‐oxide‐semiconductor field effect transistors. The treatment, performed in a radio frequency induction heated single‐wafer rapid thermal reactor, is used to reduce the subsequent oxidation rate and to incorporate nitrogen in the resulting gate dielectrics. It is believed that activated molecular or atomic nitrogen is generated in the rapid thermal reactor and is responsible for the slight nitridation of the exposed silicon area during the rapid thermal treatment. Potential radiation damage to the silicon area is minimized by activating the nitrogen remotely from the wafer chamber. The effects of the nitrogen flow rate and the temperature during the treatment process on the kinetics of the subsequent oxidation in a regular furnace and the chemical composition of the resulting gate dielectrics are studied. Potential use of the proposed treatment in making scaled devices is discussed. © 1999 The Electrochemical Society. All rights reserved.

Surface Chemistry of Porous Silicon

AbstractAs-prepared porous silicon comes out covered with covalently bonded hydrogen. This hydrogen coating provides a good electronic passivation of the surface, but it exhibits limited stability, being removed by thermal desorption or converted into an oxide upon prolonged storage in air. Starting from the hydrogenated surface, an oxide layer with good electronic properties is also obtained by anodic oxidation or rapid thermal oxidation.The hydrogenated surface may be nitridized using thermal treatments in nitrogen or ammonia. Fast halogenation of the surface may be obtained at room temperature, but the resulting coating is rapidly converted to an oxide in the presence of moisture. Many metals have been incorporated into the pores, using chemical or vacuum techniques, or even direct incorporation during porous silicon formation.More interestingly, organic derivatization may increase surface stability or provide chemical functionalities. The poor reactivity of the hydrogenated surface can be remedied by using various methods: thermal desorption of hydrogen, hydroxylation or halogenation of the surface, thermal or UV assisted reaction. However, most promising results have been obtained through either Lewis-acid catalyzed grafting or electrochemical activation of the surface. The latter method has been used for grafting formate, alkoxy, and recently methyl groups. In most of these methods, oxidation is present as a parallel path, and care must be taken if it is not desired. Also, 100% substitution of the hydrogens by organic groups has never been attained, due to steric hindrance problems. The electrochemical method appears especially fast, and has led to 80% substitution of the hydrogens by methyl groups, with no photoluminescence loss and a chemical stability increased by one order of magnitude.

Texture evolution of nickel and cobalt activated-charcoal-supported catalysts during thermal treatments at increasing temperatures

The effect of thermal treatment in an inert atmosphere up to 723 K on the textural properties of Ni and Co activated-charcoal-supported catalysts has been studied by means of nitrogen adsorption at 77 K. Various approaches have been followed in order to analyse the adsorption data (Langmuir, t-method, Dubinin-Radushkevich, Horvath-Kawazoe and density functional theory). The combination of these methods has allowed us to perform a full characterization of the samples in the micropore and mesopore ranges. The density functional approach has been especially useful, since it provides information for both the micropore and mesopore ranges simultaneously. Impregnation of the activated-charcoal-support with Ni or Co nitrates produces the expected loss of specific surface area and specific pore volume. Thermal treatment in nitrogen at 573 K gives a relatively surprising high recovery of textural properties, particularly in the micropore range, which has been related to the poor dispersion of the supported NiO and CoO particles. Treatment of the samples at 723 K gives an additional low increase in external surface area and micropore volume with respect to the 573 K treated samples. This behaviour has been discussed in terms of both a volume reduction of the supported particles and the creation of new microporosity, which may be produced during the carbon-promoted reduction of NiO and CoO to the metallic state that takes place under treatment in nitrogen at 723 K.