Combination Of Thermal Annealing Research Articles

Synthesis of g-C3N4@ZnIn2S4 Heterostructures with Extremely High Photocatalytic Hydrogen Production and Reusability

The g-C3N4@ZnIn2S4 heterostructures were successfully synthesized through a combination of thermal annealing and hydrothermal methods. To enhance the photocatalytic hydrogen production performance and explore the interface between charge carriers, heterostructures of g-C3N4@ZnIn2S4 were fabricated using varying weights of g-C3N4 nanostructures under visible light irradiation. Remarkably, the photocatalytic hydrogen production efficiency of g-C3N4@ZnIn2S4 heterostructures with 0.01 g g-C3N4 nanostructures was significantly improved, showing approximately 228.6 and 2.58 times higher than that of g-C3N4 nanostructures and ZnIn2S4 nanostructures, respectively. This enhancement in photocatalytic performance is attributed to the effective utilization of visible light and the efficient separation of photogenerated electron-hole pairs facilitated by the heterojunction structures. Moreover, the reusability test validated the outstanding performance of g-C3N4@ZnIn2S4 heterostructures, as they maintained high photocatalytic hydrogen production even after undergoing eight cycles without any noticeable decrease in efficiency. This study offers a promising strategy for designing and synthesizing an environmentally friendly g-C3N4@ZnIn2S4 heterojunction with potential applications in photocatalytic hydrogen evolution.

X-Ray Detector Based on All-Inorganic Lead-Free Cs2AgBiBr6 Perovskite Single Crystal

In this paper, single crystals (SCs) of the Cs2AgBiBr6 double perovskite were grown using the method of crystallization from a supersaturated solution. It was shown that the natural crystal growth surface of the perovskite with perfect crystal quality is along the (111) plane by X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) analyses. The fabricated high-sensitivity X-ray detector based on the Cs2AgBiBr6 SCs with vertical structure achieved detection sensitivity up to $316~\mu $ CGyair−1 cm−2 under bias voltage of 18 V. Furthermore, the frequency noise characteristics of the device under different posttreatment processes were systematically analyzed, which indicated that the combination of thermal annealing and isopropanol rinsing can suppress field-driven ion migration and surface conduction channel, thereby increasing the resistivity of the perovskite material and reducing the noise current of the device. Our results revealed that the Cs2AgBiBr6 SCs-based X-ray detector with high sensitivity and low cost has a great potential for application in manufacturing lead-free and stable radiation detection electronics in the future.

Electrochemically Prepared Polycrystalline Copper Surface for the Growth of Hexagonal Boron Nitride

The controlled and reproducible growth of hexagonal boron nitride (h-BN) by chemical vapor deposition on polycrystalline copper foil substrates remains a challenge as typical growth surfaces contain microscopic ridges (height ≈ 100 μm) arising from the foil manufacturing process. In this work, we report a method to prepare commercially cold-rolled polycrystalline copper substrates for greatly improved growth of h-BN by a combination of thermal annealing in a reducing environment and electrochemical polishing to create an excellent surface that enables control of BN nucleation sites. We report a root mean square roughness of ∼1.2 nm for the Cu substrate after electropolishing and a reduction of nucleation sites along with enlargement of h-BN crystals with this combined approach. We also assess the potential role of surface features that exist on the Cu surface as nucleation sites. The development of an electrochemical process to prepare two-dimensional (2D) material growth substrates and demonstration of g...

Vinazene end-capped acceptor-donor-acceptor type small molecule for solution-processed organic solar cells

An acceptor-donor-acceptor (A-D-A) type molecule based on dioctyltertthiophene-benzo[1,2-b:4,5-b′]dithiophene-dioctyltertthiophene central donor and vinazene terminal acceptor was designed and synthesized for solution-processed small molecule bulk-heterojunction (BHJ) solar cells. The thermal and optochemical properties, BHJ morphology and solar cell performance were investigated. The BHJ morphology was systematically optimized by thermal annealing, solvent vapor annealing, and the use of solvent additives. Processed by a combination of thermal annealing and solvent vapor annealing treatments, V-BDT:PC71BM device showed an optimized PCE of 3.73% with a VOC of 0.89 V, an JSC of 6.88 mA cm−2 and a FF of 0.61.

The effect of acceptor end groups on the physical and photovoltaic properties of A–π–D–π–A type oligomers with same S, N-heteropentacene central electron donor unit for solution processed organic solar cells

Synthesis and characterization of novel acceptor–donor–acceptor small molecules with different end group acceptors such as dicyanovinyl, cyanoacetate and indenedione, denoted as SM1, SM2 and SM3, respectively, linked with same central S, N-heteropentacene donor is described. These small molecules are used as electron donor along with the PC71BM as an electron acceptor for the fabrication of solution processed bulk heterojunction organic solar cells. The optimized devices based on as cast SM1:PC71BM, SM2:PC71BM and SM2:PC71BM showed power conversion efficiency about 2.01%, 1.60% and 2.65%, respectively and improved to 5.64%, 4.24% and 6.64%, respectively, using active layer processed with two steps annealing, i.e. combination of thermal annealing and subsequent solvent vapor annealing. This increase in the power conversion efficiency was due to the enhancement in Jsc and FF attributed to the enhancement of the light harvesting ability of the active layer, which is reflected by favorable nanoscale morphology.

Highly Branched RuO2 Nanoneedles on Electrospun TiO2 Nanofibers as an Efficient Electrocatalytic Platform

Highly single-crystalline ruthenium dioxide (RuO2) nanoneedles were successfully grown on polycrystalline electrospun titanium dioxide (TiO2) nanofibers for the first time by a combination of thermal annealing and electrospinning from RuO2 and TiO2 precursors. Single-crystalline RuO2 nanoneedles with relatively small dimensions and a high density on electrospun TiO2 nanofibers are the key feature. The general electrochemical activities of RuO2 nanoneedles-TiO2 nanofibers and Ru(OH)3-TiO2 nanofibers toward the reduction of [Fe(CN)6](3-) were carefully examined by cyclic voltammetry carried out at various scan rates; the results indicated favorable charge-transfer kinetics of [Fe(CN)6](3-) reduction via a diffusion-controlled process. Additionally, a test of the analytical performance of the RuO2 nanoneedles-TiO2 nanofibers for the detection of a biologically important molecule, hydrogen peroxide (H2O2), indicated a high sensitivity (390.1 ± 14.9 μA mM(-1) cm(-2) for H2O2 oxidation and 53.8 ± 1.07 μA mM(-1) cm(-2) for the reduction), a low detection limit (1 μM), and a wide linear range (1-1000 μM), indicating H2O2 detection performance better than or comparable to that of other sensing systems.

Two-dimensional materials under electron irradiation

Abstract

Modification of the structural and optical properties of tin oxide nanoparticles by Co doping and thermal annealing

Enhancement of the UV photoluminescence emission of sol–gel synthesized tin oxide nanoparticles is achieved by a combination of thermal annealing and Co doping. The UV as well as the defect-related visible photoluminescence are correlated to the structural characteristics and surface Sn(OH)2 content. The nanoparticle structure, size, crystallinity, and Sn(OH)2 content are monitored by a combination of X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. In the undoped powders, a suitable annealing leads to a significant UV luminescence at around 365 nm. After doping with Co and annealing, the UV emission is further enhanced. The improvement in the UV emission intensity following annealing and Co doping of SnO2 is demonstrated to be due to a reduction in the hydroxyl content. The defect-related broad visible photoluminescence (∼400–650 nm) can be deconvoluted into three bands at around 440 nm (blue), 510 nm (green), and 600 nm (orange). The green emission is related to Sn(OH)2 determined by Raman spectroscopy. The blue and orange emissions are attributed to oxygen vacancies.

Rapid and reversible morphology control in thin films of poly(ethylene oxide)-block-POSS-containing poly(methacrylate)

Here we report rapid control of the morphology of a polyhedral oligomeric silsesquioxane (POSS)-containing block copolymer (PEO143-b-PMAPOSS12), which is composed of poly(ethylene oxide) (PEO) and POSS-containing poly(methacrylate), (PMAPOSS), between ordered arrays of dots and lines for several tens of seconds by a combination of thermal annealing and solvent annealing. The PEO143-b-PMAPOSS12 was synthesized by atom transfer radical polymerization of POSS methacrylate by using a macroinitiator of PEO. An ordered array of dots was obtained by thermal annealing for the as-spun cast thin film at 90 °C for 60 s. The resultant ordered dots were quickly converted to lines by solvent annealing with chloroform vapor at room temperature for 120 s. The lines were converted back to dots by thermal annealing under the same conditions (90 °C, 60 s) without any changes to the initial diameter, d-spacing or thickness. We also demonstrated the simple and rapid formation of a hexagonally packed array of dots by spin casting onto a trench-patterned silicon wafer under chloroform vapor. Under thermal and solvent annealing conditions, reversibility and a high degree of ordering in the phase morphology of PEO143-b-PMAPOSS12 are distinctive properties that can be attributed to highly mobile polymer chains.

Morphological transformation during cross-linking of a highly sulfonated poly(phenylene sulfide nitrile) random copolymer

We present a new approach of morphological transformation for effective proton transport within ionomers, even at partially hydrated states. Highly sulfonated poly(phenylene sulfide nitrile) (XESPSN) random network copolymers were synthesized as alternatives to state-of-the-art perfluorinated polymers such as Nafion®. A combination of thermal annealing and cross-linking, which was conducted at 250 °C by simple trimerisation of ethynyl groups at the chain termini, results in a morphological transformation. The resulting nanophase separation between the hydrophilic and hydrophobic domains forms well-connected hydrophilic nanochannels for dramatically enhanced proton conduction, even at partially hydrated conditions. For instance, the proton conductivity of XESPSN60 was 160% higher than that of Nafion® 212 at 80 °C and 50% relative humidity. The water uptake and dimensional swelling were also reduced and mechanical properties and oxidative stability were improved after three-dimensional network formation. The fuel cell performance of XESPSN membranes exhibited a significantly higher maximum power density than that of Nafion® 212 under partially hydrated environments.

Purification, Cutting, and Sidewall Functionalization of Multiwalled Carbon Nanotubes Using Potassium Permanganate Solutions

In this work multiwalled carbon nanotubes were examined using a combination of thermal annealing followed by chemical treatments with potassium permanganate solution. Functionalization with carboxylic acid moieties through this newly devised process simultaneously purified and cut the nanotubes. A cutting procedure using potassium permanganate that could keep or remove the MnO2 has not been previously reported, making this study a stepping stone to further functionalization/application opportunities. One such further functionalization was explored here with alkyl groups, through the generation of an amide linkage. A very detailed standard suspension test was performed on this material. What was found was an increased suspension stability toward polar solvents for the nanotubes with high concentrations of MnO2 deposits, and in nonpolar solvents the nanotubes with large alkyl chains attached were observed, thus proving it to be a versatile treatment.

Restoration of coercivity in crushed Nd–Fe–B magnetic powder

An attempt has been made to prepare a high coercivity Nd–Fe–B powder from a sintered Nd 14Fe 80B 6 magnet. The combination of thermal annealing and chemical modification of particle surface using the DyF 3 salt was found to be an effective processing technique for preparing a high-coercivity powder from the crushed sintered Nd–Fe–B magnets.

Photodefinable Metal Oxide Dielectrics II: Direct Fabrication of Patterned High-k Dielectrics for Low Cost RF Capacitive MEMS Switches

ABSTRACTIn this paper, recent advancements related to a novel approach for fabricating low cost capacitive radio frequency microelectromechanical (RF MEMS) switches using directly photodefinable high dielectric constant metal oxides are discussed. In this approach, a radiation sensitive metal-organic precursor is deposited via spin coating and converted patternwise to a metal oxide using exposure to ultraviolet light. The feasibility of this approach has previously been demonstrated by fabricating bridge-type and cantilever-type RF MEMS switches. These early experiments showed that the photopatterned oxides displayed dielectric breakdown strengths that were insufficient for reliable operation of MEMS switches which required actuation voltages on the order of 20 V to 30 V. Recent work has focused on developing advanced processes based on the photodefinable metal-organic approach that can produce oxides with higher dielectric breakdown strengths and higher dielectric constants. A variety of post-patterning processes, including thermal baking and oxygen plasma annealing, were investigated and the impact of such processing on the resulting dielectric properties are discussed in this paper. It is shown that a combination of thermal annealing and oxygen plasma treatment can substantially improve the dielectric breakdown strength of the metal oxides produced using the photosensitive metal-organic process.

Quantitative secondary ion mass spectrometry analysis of SiO 2 desorption during in situ heat cleaning

Analysis of silicon oxide (SiO 2) desorption was performed by a combination of thermal annealing in an ultra high vacuum (UHV), consecutive growth of a thin silicon (Si) layer by molecular beam epitaxy (MBE) and ex situ secondary ion mass spectrometry (SIMS). Together with the Si substrate the Si-MBE layer creates a uniform Si matrix which allows quantitative analysis by SIMS. The protective oxide on as-received wafers stored for a few months turned out to be 0.8–1.6 nm thick. Desorption in a vacuum takes place in a narrow temperature window below 875°C. The main residual contaminations were carbon (C) with a surface concentration of about 10 12 cm −2 and boron (B) with a concentration of 6×10 10–6×10 11 cm −2. Metallic impurities were below the SIMS detection limit.