Thermal Etching Method Research Articles

Polyethyleneimine-induced in-situ chemical epitaxial growth ultrathin 2D/2D graphene carbon nitride intralayer heterojunction with elevating photocatalytic activity: Performances and mechanism insight

Integrating 2D carbon nitride (CN) photocatalyst with 2D graphene into a lateral heterojunction can decrease energy loss within interlayer space, which is an intriguing strategy for tailoring photocatalyst for energy and environmental applications. Herein, a polyethyleneimine (PEI) induced in-situ chemical epitaxial growth strategy was adopted to tailor graphene-oxide CN (GO-CN) intralayer heterostructure photocatalyst, where PEI was served as chemical inducer and crosslinker to construct polymerization precursor, and a one-pot self-assembly followed in-situ thermal-polymerization and thermal-etching method was conducted. Series characterizations manifest the successful construction of ultrathin 2D-2D GO-CN intralayer heterostructure, which possesses ameliorated specific surface area, visible-light harvest and charge behaviors. Quench tests, ESR and LC-MS explored photodegradation active species, intermediate and route, while online FTIR real-time and in-situ monitor the variation of functional groups. In the end, DFT theoretical analysis further affirm the charge transfer between GO and CN, and unveil conceivable elevated mechanism.

Annealing modification and defect analysis of Hg2Br2 crystal

With the urgent demand for wavelength extension of acousto-optic devices in military and civil fields, long wavelength infrared acousto-optic crystals with high performance have become indispensable. In this context, Hg2Br2 crystals with dimensions of Ф 50 × 40 mm3 were successfully obtained by a self-designed physical vapor transport furnace. The transmittance spectra reflect that the Hg2Br2 crystal has a wide spectral transmission range, and the maximum transmittance in the UV–vis IR range exceeds 80%. Annealing is proven to be an effective measure to optimize crystal properties, and the optimal annealing temperature of the Hg2Br2 crystal is defined. The crystal quality and transmittance of the Hg2Br2 crystal are improved, and the stress is reduced after annealing at the optimal temperature. In addition, the dislocation defects of the Hg2Br2 (110) and (001) wafers were characterized via the thermal etching method. The average defect density was assessed on the order of magnitude of ∼105 cm−2, which indicates the high quality of the as-grown Hg2Br2 crystal.

Induced abundant oxygen vacancies in Sc2VO5-δ /g-C3N4 heterojunctions for enhanced photocatalytic degradation of levofloxacin.

Sc2VO5-δ /g-C3N4 heterojunctions (SVCs) with abundant oxygen vacancies (OVs) were synthesized by ultrasonic exfoliation combined with the thermal etching method. The structures, OVs and spatial separation of the photogenerated carriers were systematically characterized. The results manifested that the SVCs were successfully constructed via the strong interaction between g-C3N4 (CN) and Sc2VO5-δ (SV). The SVCs possessed a higher concentration of OVs than that of pristine CN and SV. The formation of the SVC heterostructures and the optimization of the OVs were the two major factors to accelerate the separation of the charge carriers and finally to improve the photocatalysis performance. The as-prepared 10%SVC (containing 10 wt% of SV) catalyst exhibited the highest OV concentration and the best photocatalytic performance. The levofloxacin (LVX) photodegradation activity showed a positive correlation with the OV concentration. The photocatalytic degradation efficiencies were 89.1, 98.8 and 99.0% on 10%SVC for LVX, methylene blue (MB) and rhodamine B (RhB), respectively. These photodegradation processes followed the pseudo first order kinetic equation. The apparent rate constant (k app) of LVX degradation on 10%SVC was 11.0 and 7.5 times that of CN and SV. The h+, ˙OH and ˙O2 - were the major reactive species in the photodegradation process.

Significant photovoltaic enhancement in La-doped BiFeO3 achieved by engineering crystallographic facet arrays

Engineering regular surface crystallographic facet arrays on a large scale is useful for tuning and optimizing photophysical properties of optoelectronic materials. Herein, we achieve textured Bi0.5La0.5FeO3 (BLFO) film surfaces displaying nanosquare arrays composed of {001} and {110} crystallographic facets, via an effective and controllable thermal etching method. Substantially enhanced photocurrent signals from these faceted samples were confirmed via laser-assisted conductive atomic force microscopy at the nanometer scale, where tens of times increment in photo-generated electric field and short circuit current density were further identified. The electronic structures of the {001} and {110} surfaces were compared by ab-initio calculations, and the conduction band minimum of the latter one shows highly dispersive character thus prompted carrier transport can be anticipated. This thermal etching method provides an efficient strategy for fabricating patterned perovskite films with highly active crystallographic facet arrays and thus will inspire new technological possibilities for high-performance photovoltaic devices.

Oriented thermal etching of hollow carbon spheres with delicate heat management for efficient solar steam generation

Hollow carbon spheres (HCSs) with controllable morphology and structure have received considerable attention in the field of energy conversion and storage. Herein, monodispersed HCSs with cavity sizes tuned from 100 nm to 800 nm and shell thickness from 450 nm to 50 nm were successfully synthesized through a unique template-free thermal-etching method. It was evidenced that the dynamically controllable synthesis of HCSs was attributed to the “inside-out” oriented thermal oxidation etching of carbon spheres (CSs) induced by the differentiated “core-shell” chemical structures. Comparing to CSs, the obtained HCSs exhibited much increased efficiency for solar-driven interfacial steam generation (SISG), reaching as high as 88.9%, which outperforms most of the previously reported carbon-based materials. It was then demonstrated that the rational heat management for both photothermal and thermal-evaporation conversion is essential to achieve satisfying SISG efficiency. Depending on the increasing cavity sizes, HCSs presented gradual increases in both photothermal conversion and thermal-evaporation performances, mainly attributed to the improved light absorption and the delicate heat management, respectively. However, the further increase in cavity size resulted in excessive heat loss and presented decreased thermal-evaporation performance. This work provides an alternative and promising approach to the reasonable design of hollow nanostructures with delicate heat management for efficient SISG as well as other solar energy conversion applications.

Coupled porosity and heterojunction engineering: MOF-derived porous Co3O4 embedded on TiO2 nanotube arrays for water remediation

Strive to develop the interaction and efficient co-catalysts is one of the vital projects in realizing hybrid photocatalytic systems for water remediation. In this work, p-type porous Co3O4 was embedded onto n-type vertical TiO2 nanotube via an in-situ thermal etching method. ZIF-67 was employed as the structural template for Co3O4, which then augmented the light harvesting ability of the resultant photocatalyst. Such improvement was prompted by the light reflecting and directing attributes of porous Co3O4. Therefore, a remarkable MB removal rate was attained under sunlight irradiation, with superoxide radical being identified as the major reactive species. Photoelectric properties evaluation also verified that the p-n heterojunction developed herein exhibits outstanding charges separation ability with low impedance, particularly under light irradiation. This work highlights the idea on coupling both porous and p-n heterojunction engineering in augmenting photoactivity of catalyst, while offering insights in such structure-mediating approach.

Synthesis of α-Fe2O3/g-C3N4 photocatalyst for high-efficiency water splitting under full light

Designing efficient photocatalysts for water splitting hydrogen evolution with low cost is a hot topic. In the present work, a α-Fe2O3/g-C3N4 photocatalyst with core-shell structure is successfully synthesized by an modified thermal etching method. Due to the synergy of Z-scheme and electron tunneling, the α-Fe2O3/g-C3N4 photocatalyst exhibits efficient water splitting propertiy under visible light, even red-light irradiation (about 700 nm). In-situ generated α-Fe2O3 nanoparticles facilitate the formation of 2D g-C3N4. The prepared α-Fe2O3/g-C3N4 photocatalyst shows an efficient photocatalytic activity between 500 nm and 700 nm due to the electron tunneling effect. The highest hydrogen evolution rate of α-Fe2O3/g-C3N4 photolyst is 5 mmol g−1 h−1 at λ > 420 nm. The present research provides the guidance for designing red-light-responsive photocatalysts for solar applications

Effect of the Microsegregation on Martensitic and Bainitic Reactions in a High Carbon-High Silicon Cast Steel

Casting processes show some weaknesses. A particular problem is presented when the workpiece needs to be subjected to heat treatments to achieve a desired microstructure. This problem arises from the microsegregation phenomena typically present in cast parts. The effect of the microsegregation on the martensitic and bainitic transformations has been investigated in a high carbon-high silicon cast steel, with the approximate composition Fe-0.8C-2Si-1Mn-1Cr (in wt. %), which was poured into 25 mm keel block-shaped sand molds. The microsegregation maps of Cr, Si, and Mn characterized by electron probe microanalysis (EPMA) show that interdendritic regions are enriched while dendrites are impoverished in these elements, implying that their partition coefficients are lower that the unity (k < 1). As-quenched martensitic and austempered bainitic microstructures (at 230 °C) were obtained and analyzed after applying an austenitization heat treatment at 920 °C (holding for 60 min). The thermal etching method used to reveal the prior austenite grain size showed a bimodal grain size distribution, with larger grains in the dendritic regions (≈22.4 µm) than in the interdendritic ones (≈6.4 µm). This is likely due to both the microsegregation and the presence of small undissolved cementite precipitates. Electron Backscatter Diffraction (EBSD) analysis carried out on the martensitic microstructure do not unveil any differences in misorientation distribution frequency and block size between the dendritic and interdendritic zones related to the microsegregation and bimodality of the austenite grain size. On the contrary, the bainitic transformation starts earlier (incubation time of 80 min), proceeds faster and bainitic ferrite plates are longer in the dendritic zones, were prior austenite grains are larger and impoverish in solute. The presence of these microsegregation pattern leads to the non-uniform development of the bainitic reaction in cast parts, modifying its kinetics and the resulting microstructures, which would probably have a major impact on the mechanical properties.

Влияние повторного цикла нитроцементации зубчатых колес вертолетной трансмиссии на склонность к трещинообразованию

Objective. Estimation of the influence degree of carbonitriding recycle of helicopter transmission gear wheel from 14XHCH2MA steel on the inclination to the crack formation.Methods of research. Microstructure of helicopter transmission gear wheel models from 14XHCH2MA steel was investigated on the optical metallurgical microscope “Axio Observer. Dlm” (firm “Karl Zeis”, producer Germany), equipped by ARTCAM-300MI camera (3M pixels progressive USB 2/0 COLOR CMOS CAMERA); surveying of models was made in reflected light with the help of light background.Received results. In the work, on the basis of experimental research results, influence of carbonitriding recycle on the microstructure, hardness, microhardness and effective depth of carbonitrided layer of helicopter transmission gear wheel from 14XHCH2MA steel was shown.Material quality of gear wheel is similar after carbonitriding as well as after carbonitriding recycle.Scientific novelty. It was experimentally established the influence carbonitriding recycle of helicopter transmission gear wheel from 14XHCH2MA steel on the inclination to the crack formation. When using the thermal etching method, stress cracks were not detected after carbonitriding and after carbonitriding recycle.The results of determining microhardness over the cross section of carbonitrided layer from the side of the tooth profiles and from the side of the gear wheel cavities after the first cycle and after the carbonitriding recycle showed that performances over the cross section of carbonitrided layer after carbonitriding recycle are higher than after one cycle of carbonitriding.Practical value. On the basis of the received results of this experiment it is possible to develop the rational manufacturing process of helicopter transmission gear wheel production from 14XHCH2MA steel, provided high operational characteristics.Microstructural analysis showed, that structure of carbonitrided layer both on the sample No.1 (after one cycle of carbonitriding) and on the sample No.2 (after carbonitriding recycle) is similar. The structure consists of martensite and dispersed carbonitrides. The structure is satisfactory for carbonitrided 14XHCH2MA steel in normal heat-treated condition. Large excess carbonitrides as well as microcracks were not detected in the surface layer. The microstructure of the core is low-carbon martensite. To reveal tensile stresses, fragment of the gear wheel after one cycle of carbonitriding and the fragment, that underwent carbonitriding recycle, were etched in concentrated (50%) hydrochloric acid, that was heated to90 °C. As a result of subsequent inspection under binocular microscope, the formation of surface cracks on the etched fragments was not detected that indicated the absence of tensile stresses.

Realizing Long-Term Stability and Thickness Control of Black Phosphorus by Ambient Thermal Treatment.

Few-layer black phosphorus (BP) has shown great potential for next-generation electronics with tunable band gap and high carrier mobility. For the electronic applications, the thickness modulation of a BP flake is essential due to its thickness-dependent electronic properties. However, controlling the precise thickness of few-layer BP is a challenge for the high-performance device applications. In this study, we demonstrate that thermal treatment under ambient condition precisely controls the thickness of BP flake. The thermal etching method utilizes the chemical reactivity of BP surface with oxygen and water molecules by the repeated formation and evaporation of phosphoric acid during thermal annealing. Field-effect transistor of the thickness-modulated BP sheet by thermal etching method shows a high hole mobility of ∼576 cm2 V-1 s-1 and a high on-off ratio of ∼105. The stability of the BP devices remained for 1 month under ambient condition without an additional protecting layer, resulting from the preservation of active BP layers below native surface phosphorus oxide.

Sloped Sidewalls in 4H-SiC Mesa Structure Formed by a Cl<sub>2</sub>-O<sub>2</sub> Thermal Etching

Sloped sidewalls in 4H-SiC mesa structures on the (000-1) C face were formed by a Cl2-O2 thermal etching method. The etching rate of 4H-SiC (000-1) C face was 10 times faster than that of (0001) Si face, and the etching rate at 910oC was about 18μm/h. The etched surface was rather smooth, and the sidewall of the mesa was inclined to the off-axis substrate. Taking into account the off angle of about 8o toward [11-20] off direction, the angles of the sidewalls were 52-56o for the <1-100> and 55-57o for the <11-20> directions from the crystallographically accurate (000-1) C face. Epitaxial pn junction diodes with the sloped sidewalls structure were fabricated, which had good electrical properties.

Properties of Thermally Etched 4H-SiC by Chlorine-Oxygen System

By the use of Cl2-O2 thermal etching method, the etching rates of 4H-SiC were reached to about 1μm/h for Si and 40μm/h for C face at 950oC. Etch pits only appeared over 0.25-μm-etched depth on the 4H-SiC (0001) Si face. The shapes and density of etch pits are similar tendencies in the case of molten KOH etched surface. To study the relationship between thermally etched surface features and crystal defects, the planar mapping electron-beam-induced current (EBIC) technique was carried out. Almost dark areas in the EBIC image correspond to the etch pits. From the EBIC image, a shell-like pit formed by the Cl2-O2 etching on the (0001) Si face is a basal plane dislocation.

Austenite Grain Coarsening Behaviour in a Medium Carbon Si-Cr Spring Steel with and without Vanadium

The austenite grain coarsening behaviour in a medium carbon Si-Cr spring steel with and without vanadium was investigated by the thermal etching method. This method is efficient when the austenitization temperature is not lower than 900 °C. The average grain sizes on the surfaces of the samples determined by thermal etching vary little from those in the bulk as revealed by chemical etching. The austenite grain coarsening behaviour of the steel with vanadium can be classified in three temperature regimes. Below a critical temperature the vanadium addition is effective to impede grain growth and fine grains are observed. The austenite grain size was significantly smaller than in the steel without vanadium. In a medium temperature regime the steel with vanadium exhibits a bimodal grain size distribution. Above the dissolution temperature of vanadium carbides normal grain growth is observed. An equation was set up to predict the grain coarsening behaviour in the steel without vanadium. The results show how the austenite grain size, which is very important for the toughness and ductility of the spring steels, can be controlled by microalloying with vanadium.

Kinetics of Austenite Grain Growth during a Continuous Heating of a Niobium Microalloyed Steel

Grain growth is a thermally activated process in which the average grain size increases as temperature and time increases. The driving force for grain growth results from the decrease in the free energy associated with the reduction in total grain boundary energy. There are several known factors that influence the migration of grain boundaries such as second phase particles precipitated in the matrix and the solute elements segregated at grain boundaries. The austenite grain boundaries are revealed using the thermal etching method. Carbon extraction replicas were prepared to determine the composition and size of precipitates present in the matrix. In this work, the evolution of the average prior austenite grain size (PAGS) of a low carbon steel microalloyed with niobium is studied as a function of temperature and heating rate. Austenite grains show a two-stage growth. It has been found that as heating rate increases, the grain coarsening temperature (TGC) increases and the grain size at that temperature decreases. TGC temperature lies around 40-60°C below the temperature for complete dissolution of carbonitrides (TDISS).

Thermal Etching of 6H–SiC Substrate Surface

Thermal etching was investigated as one of the methods of obtaining atomically flat surfaces of SiC substrates. The formation of a graphite layer on substrate surface was suppressed by reducing the C/Si ratio in the vapor phase. Although (1120) substrates etched in argon atmosphere had round pits on their surface, such pits were not observed and an atomically flat surface with an RMS roughness of approximately 0.3 nm was obtained in nitrogen atmosphere even at the high etching rate of 250 µm/h. The substrates with higher nitrogen concentrations had both higher surface flatness and higher etching rate. The thermal etching method was found to be an effective technique for obtaining the flat surface of SiC substrates that is suitable for crystal growth and/or device fabrication. The etching mechanisms of (0001) and (1120) surfaces were compared, and the result was discussed by taking into consideration the bond configuration on the surface.

Effect of surface treatment of Si substrate on the crystal structure of FeSi 2 thin film formed by ion beam sputter deposition method

Ion beam sputter deposition method under ultra-high vacuum conditions was employed to form β-FeSi 2 thin films on Si(1 0 0) substrate. We investigated the effect of three different kinds of surface treatment of Si on the crystal structure of FeSi 2 film, which was characterized by means of X-ray diffraction analysis and transmission electron microscopy (TEM) observation. The films formed on a substrate treated by thermal etching (TE) consisted of β-FeSi 2 with various crystal orientations. The films formed with sputter etching (SE) and wet etching methods also consisted of β-FeSi 2, but with comparatively strong (1 0 0) preferential orientation. From TEM observations, the films formed with TE method were composed of coalesced β-FeSi 2 islands, whereas those formed with SE method were almost continuous.

β‐ＦｅＳｉ２薄膜の結晶構造におけるＳｉ基板処理効果

β-FeSi2 thin films on Si (100) substrate were prepared by ion beam sputter deposition (IBSD) method under ultra-high vacuum condition. We investigated the effect of surface treatments of Si on the crystal structure of β-FeSi2 film formed by IBSD method. Three kinds of conventional surface treatment methods were employed; namely, thermal etching (TE), sputter etching (SE) and wet etching (WE). After each etching, Fe was sputtered and deposited on heated Si in the temperature range between 873 K and 1073 K. In order to characterize the crystal structure of the formed films, X-ray diffraction (XRD) analysis was performed. From the XRD results, it was concluded that TE method is not appropriate to obtain an epitaxial β-FeSi2 on Si because the surface distortion is induced in Si. Little difference of the crystal structure was observed between SE and WE methods. These results suggest that a moderate disorder of the substrate surface may well enhance the mixing of Fe and Si atoms to form highly (100) -oriented β-FeSi2.

鋼の結晶粒度におよぼすニオブならびにタンタルの影響

The effects of niobium and tantalum on austenitic grain size and ferritic grain size of pure iron, Fe-C (C=0.1%) and Fe-N (N=0.02%) alloys have been studied and compared with each other. The austenitic grain size were revealed by thermal etching method. The effects of small addition of each element on the grain coarsening temperature of these alloys were also studied. The main results obtained are as follows;(1) Small addition of niobium or tantalum to Fe-C alloys is effective for austenitic grain size refining and this may be due to the precipitation of δ-niobium-carbide or δ-tantalum-carbide. Tantalum is required two times as much amounts (in wt%) as niobium is, to obtain the same fine grain size number such as No 7·5.(2) The addition of niobium or tantalum to pure iron and Fe-N alloys is also effective for austenitic grain size but the finer grain size than No 6 cannot be obtained in these cases.(3) An approximately linear relationship is observed between ferritic and austentic grain size in the series of niobium-added steels as well as of tantalum added steels.(4) Small addition of niobium or tantalum to Fe-C alloys is effective in retarding the austenitic grain coarsening.

On the Mechanism of Grain Growth in Metals, with Special Reference to Steel

The rate of grain growth in the initial stages of isothermal austenitizing has been studied by a thermal etching method in plain, eutectoid, carbon steel in the range 840-970°c. An equation relating the mean initial and instantaneous grain diameters, D0 and D, to the austenitizing time t, of the form D2-D02=Kt exp (-H/kT) is developed on the assumption that the growth rate is controlled by interfacial tension at grain boundaries. An estimate of the constant K is made, and by the use of experimentally obtained values of D, D0 and t the value of H is calculated to be 30 kcal/g atom, close to the activation energy estimated for grain-boundary self-diffusion and to that determined for the damping of low amplitude torsional oscillations.

Study on Polygonization and Recrystallization of Aluminium by Means of Thermal Etching Method (1st Report). Microscopic Observation (Part A)

Study on Polygonization and Recrystallization of Aluminium by Means of Thermal Etching Method (1st Report). Microscopic Observation (Part A)