Presence Of Surface Defects Research Articles

FCSNet: A quantitative explanation method for surface scratch defects during belt grinding based on deep learning

The presence of surface defects during abrasive belt grinding has a significant impact on the service performance of the parts, and the precise extraction of surface defect feature information helps to enhance grinding quality. However, in the face of abrasive belt grinding surfaces with complex texture features, it is a challenging task to effectively extract defect features and quantify the characterization. Therefore, this research suggests a quantitative explanation approach for surface scratch defects in abrasive belt grinding based on the deep learning theory. Facing challenging issues like complex texture background, defect size, area, and depth of grinding surface, the automatic segmentation model (FCSNet) concentrating on the multiscale channel and spatial attention information is proposed. To concentrate on the multiscale channel and spatial information and accurately detect the defect features, the residual atrous convolutional pyramid module with channel and spatial dual attention module (RAPCS) is constructed. To capture the global, long-range context characteristics and emphasize target regions, the convolutional block attention module (CBAM) concatenate block is included in the skip connections between the encoder path and the decoder path. To address the issue of foreground-background data imbalance caused by too small segmented target regions, the Focal Tversky hybrid loss function was adopted to guide the model to learn the difficult region of interest (ROI). At the end of the network structure, Grad-CAM is adopted and statistical knowledge is incorporated for a qualitative and quantitative visual explanation of the segmentation results. Finally, the dataset of surface scratch defects in abrasive belt grinding was established and numerous experiments were carried out based on this dataset. The results demonstrate that the proposed model has an excellent segmentation performance and defect quantitative explanation ability, achieving 98.80% in Accuracy, 81.72% in Recall, 81.81% in Precision, 81.42% in F1-score, and 81.87% in mIoU, respectively.

Understanding and Improving the Oil and Water Barrier Performance of a Waterborne Coating on Paperboard.

Using paperboard as packaging material is more sustainable than using plastic. To be a viable replacement, however, the barrier properties of paperboard need to be improved. Applying a waterborne barrier coating for both oil and water is an attractive method to improve the barrier performance of paperboard food packaging. However, not much is known about the oil and water barrier properties and penetration pathways of such coatings. Here, an alkali-soluble resin (ASR)-stabilized waterborne emulsion polymer was prepared and applied on untreated paperboard. Its performance as oil and water barrier coating was investigated, and the penetration pathways for both oil and water through the coating are discussed. The presence of surface defects in the coating applied on the paperboard strongly affects both the oil and water barrier properties, but the coating’s morphology and chemical nature only play a major role in the water barrier performance. The optimal barrier performance for oil and water was achieved when adding 5 wt % isopropanol (IPA) to the dispersion and applying two coating layers on paperboard. The IPA improves film formation and reduces the number of surface defects, which is explained by a more favorable spreading coefficient of the coating over the paperboard substrate. These insights will help to improve the oil and water barrier properties of polymer-coated paperboard for more sustainable packaging applications.

Experimental verification of the potential of superhydrophobic surfaces in reducing audible noise on HVAC overhead line conductors

Overhead line conductors can generate audible noise across a wide frequency spectrum as a result of elevated electric fields at the conductor surface. Such fields are enhanced by the presence of surface defects, insects, water drops and pollution. Within this paper, the impact of a superhydrophobic coating on the audible noise produced by an overhead line conductor is examined. Noise levels from a conductor coated with a superhydrophobic coating were compared to those from a bare conductor in a semi-anechoic chamber. The conductors were energised at voltages to provide surface electric fields ranging from 6 kV/cm to 21 kV/cm (rms). With a continuous water spray system depositing droplets on the conductor surface, the frequency domain sound pressure level, overall sound pressure levels and corona discharge magnitude were measured. It is demonstrated that the use of a superhydrophobic coating reduced audible noise levels and corona discharge magnitude, especially at electric fields above 14 kV/cm. The image analysis suggests that the water drop size distribution and the position of surface droplets on the conductor circumference play an important role in the magnitude of audible noise.

Correlation between microstructure and cyclic behavior of 316L stainless steel obtained by Laser Powder Bed Fusion

AbstractIn this work, stainless steel 316L obtained by Laser Powder Bed Fusion (L‐PBF) has been produced and characterized. The experimental campaign focuses on the samples in the as‐built state under cyclic tension‐compression loadings. Low cycle fatigue (LCF) and high cycle fatigue (HCF) tests are carried out. Microstructure observations are performed before and after the loadings. As‐built L‐PBF 316L has a good LCF performance despite the presence of surface defects but a low fatigue limit in the HCF regime. Removing the surface roughness has a beneficial effect but does not improve the fatigue strength to that of machined wrought 316L. Observations on the microstructure of fatigue samples indicate that LCF is dominated by the local plastic deformation, which is mostly achieved by the slip in the studied material and is not sensitive to the defect. The lack‐of‐fusion defect impairs the fatigue resistance in the HCF regime.

Fatigue Behavior of Super Duplex Stainless Steel Exposed in Natural Seawater Under Cathodic Protection

Under operating conditions, alternated loading and fatigue are encountered, controlling the durability and safety of components and structures made of super duplex stainless steel (SDSS). In particular, the use of a cathodic protection (CP) system to protect the structure against corrosion can induce hydrogen charging of the SDSS. Thus, the aim of this study was to investigate the sensitivity of some industrial products made of SDSS 2507 (UNS S32750), without artificial thermal aging, under test conditions as close as possible to real environments. In situ fatigue tests under alternated 4-point bending conditions were conducted in natural seawater with and without CP. The fatigue behavior was evaluated as a function of environmental parameters, such as temperature, and material parameters, particularly the austenite spacing and microstructure around orbital welds by Tungsten Inert Gas (TIG) welding and stress concentrations, through the presence of surface defects. The fatigue life obtained in air or in seawater at the open circuit potential (OCP) was rather similar. Fatigue life enhancement was systematically observed under CP particularly in the range of low applied load, despite evidence of brittle failure on the fracture surfaces of samples tested under CP. The data suggest immunity of the SDSS to hydrogen embrittlement under the present experimental conditions of fatigue testing.

Aging due to successive reuse of polyamide 12 powder during laser sintering: extrinsic powder properties and quality of sintered parts

The effects of cumulative build time during the reuse of polyamide 12 (PA 12) for laser sintering (LS) on the morphology, size and shape distribution of the feedstock powder and quality of printed parts were investigated in this study. Both the virgin and reused powders contain potato-shaped, elongated, and relatively few near-spherical particles. In agreement with the scanning electron microscope images, the circularity-roundness plots also indicate presence of near-spherical, potato-shape, and elongated particles in the virgin and reused powders. Particle size distributions of the powders revealed an increase in the proportion of fine particles at higher reuse cycles, which is due to cracking and fragmenting during repeated exposure to the high processing temperature during LS. Mild orange peel was observed at a cumulative build time of 36.4 h, which becomes more evident with increase of the build time. Moreover, the presence of surface defects could be observed at cumulative build times greater than 36.4 h, and all the parts exhibit deviation in average thickness and width from the desired values.

How Does the Step on Graphite Surface Impact Ice Nucleation?

Heterogeneous ice nucleation has always been a hot research topic because of its fundamental importance to a variety of research areas, from climate to biology and from aviation to the energy industry. The formation of ice in the earth’s atmosphere depends on aerosols of various sources. As the main component of atmospheric aerosols, carbon particles composed of graphite have attracted much attention in heterogeneous ice nucleation. There is great variability in the freezing efficiency of ice induced by surface nanostructures, and the presence of surface defects, such as steps, can lead to the complex behavior of ice nucleation. In this work, molecular dynamics (MD) simulation was employed to investigate ice nucleation on graphite surfaces with the step structure. It was found that the graphite step with a real atomic structure reduced the freezing efficiency of surfaces, which was attributed to the large interfacial free energy between ice and the side face of the graphite steps. It was demonstrated by further investigations that the effect of nanogrooves consisting of step edges on ice nucleation was not only determined by the matching of groove width and ice lattice constant but also by the atomic structure of nanogrooves, shedding light on the study of control strategy of ice nucleation by surface nanostructures.

Forward and reverse current transport mechanisms in tungsten carbide Schottky contacts on AlGaN/GaN heterostructures

In this paper, the forward and reverse current transport mechanisms in as-deposited and 400 °C annealed tungsten carbide (WC) Schottky contacts on AlGaN/GaN heterostructures have been studied. In particular, under forward bias, the WC/AlGaN Schottky contacts exhibited a deviation from the ideal thermionic emission model due to the occurrence of a tunneling component of the current. From the temperature dependence of the ideality factor, a characteristic tunneling energy E00 in the range of 33–36 meV has been estimated. On the other hand, two different transport mechanisms have been identified under reverse bias. At low reverse bias (VR < 2 V), Poole–Frenkel emission rules the current transport, with an emission barrier ϕt = 0.68 eV in the as-deposited contact, which increases up to ϕt = 0.79 eV upon annealing at 400 °C. This behavior has been correlated with the improvement of the metal/AlGaN electronic properties. At higher reverse bias (VR > 2 V), the leakage current is dominated by a thermally activated process with an activation energy (0.27 eV) that is independent of the Schottky contact fabrication process. In this case, the temperature dependence of the leakage could be well described by a two-dimensional variable range hopping conduction associated with the presence of surface defects in the material.

Вплив стану поверхні деталей шасі з високоміцного титанового сплаву ВТ-22 в процесі випробувань на втому

The research focuses on the influence of the surface condition on the resource of high-strength titanium alloy VT-22 landing gear details during fatigue tests. The tests were performed on special facilities that simulate the workload on a rod detail at the stage of extending and retraction of the landing gear. Fatigue tests were performed on four rods. Rods № 1-3 were destroyed at the lugs level, rod №4 withstood the entire cycle of loads, and was examined in an undamaged state. It was found that the cause of the failure of the rod №1 was axial play formation as a result of bracket lug deformation, which led to shock loads on the lug of the rod №1 during the tests. The destruction of the rod №2 could be caused by the shock axial loads due to changes in the characteristics and load values of the facility on the rod №2. The priority factor influencing the premature failure of the rod №3 was the high risks from surface machining in the most loaded part of the rod №3, namely at the R-junction of the cylindrical part to the lug. The presence of surface defects formed during the manufacturing stage, as well as the presence of deep scratches in the area with high load reduce the life of rod № 3 fivefold compared to the undamaged rod № 4, which had no visible surface defects. Surface damage detected in the non-chromized area of the rods can be eliminated by blasting with subsequent surface polishing, which will provide the required resource of the detail (rod № 4). Keywords: high-strength titanium alloy VT-22, rod, fatigue tests, surface defects, structure of the surface layer.

Repair and rehabilitation of corroded HDPE100 pipe using a new hybrid composite

The good management of drinking water begins with a supply network, with a low rate of leakage. Currently, the pipes used in the water transport system are mainly made of polymeric materials, such as HDPE. The corrosion degradation of this type of pipe has received a lot of attention from the drinking water supply companies. It is therefore important to understand the effect of pressure on an HDPE pipe with a surface defect. To answer this problem, we will first study the mechanical behavior at failure of HDPE pipes in the presence of a surface defect using a finite element method. For the rehabilitation of pipe in presence of surface defect, we try to use a new composite. This new laminated composite is reinforced with a natural organic load. It is obtained from a laminated composite woven by incorporating a natural non-polluting organic load (granulates of date cores) which becomes hybrid composite. The new economical hybrid composite material is made of an organic matrix containing methyl methacrylate, a woven reinforcement including a reinforcing glass fiber and a fabric perlon having an absorbing role. The textile reinforcement made up of several folds reinforcing laid out according to the orientations (90, 452, and 0). A numerical simulation with the ANSYS Workbench software is carry out to study the behavior of the HDPE pipe with surface defect and with defect repaired by the new hybrid composite material in the form of rings to consolidate the cracked area of ​​the tube. The numerical results will allow us to decide on a real practical use of the new hybrid composite.

Preliminary Evaluation of the Influence of Surface and Tooth Root Damage on the Stress and Strain State of a Planetary Gearbox: An Innovative Hybrid Numerical–Analytical Approach for Further Development of Structural Health Monitoring Models

Wind turbine gearboxes are known to be among the weakest components in the system and the possibility to study and understand the behavior of geared transmissions when subject to several types of faults might be useful to plan maintenance and eventually reduce the costs by preventing further damage. The aim of this work is to develop a high-fidelity numerical model of a single-stage planetary gearbox selected as representative and to evaluate its behavior in the presence of surface fatigue and tooth-root bending damage, i.e., pits and cracks. The planetary gearbox is almost entirely modelled, including shafts, gears as well as bearings with all the rolling elements. Stresses and strains in the most critical areas are analyzed to better evaluate if the presence of such damage can be somehow detected using strain gauges and where to place them to maximize the sensitivity of the measures to the damage. Several simulations with different levels, types and positions of the damage were performed to better understand the mutual relations between the damaged and the stress state. The ability to introduce the effect of the damage in the model of a gearbox represents the first indispensable step of a Structural Health Monitoring (SHM) strategy. The numerical activity was performed taking advantage of an innovative hybrid numerical–analytical approach that ensures a significant reduction of the computational effort. The developed model shows good sensitivity to the presence, type and position of the defects. For the studied configuration, the numerical results show clearly show a relation between the averaged rim stress and the presence of root cracks. Moreover, the presence of surface defects seems to produce local stress peaks (when the defects pass through the contact) in the instantaneous rim stress.

Effect of vacuum annealing on structural, optical and magnetic properties of Sn doped ZnS thin films

Abstract Tin doped Zinc Sulphide (Zn1-xSnxS) thin films at x = 0.00, 0.02, 0.05, 0.08 were prepared onto Corning 7059 glass substrates using electron beam evaporation technique and then subjected to vacuum annealing at 300 °C for 2 h. The effect of vacuum annealing on structural, optical and magnetic properties of the thin films were studied in detail. From XRD studies, it was found that the vacuum annealed thin films were in cubic structure and have finer crystallite size compared to the unannealed thin films. All the films exhibited high transmittance (85%) in the visible region. The vacuum annealing led to narrowing of band gap compared to the unannealed thin films. The presence of surface defects in vacuum annealed thin films were confirmed by the observation of two broad emission photoluminescence peaks at 420 nm and 440 nm. But the reduction in the intensity of photoluminescence emission peaks correlate to the decrease in the concentration of sulphur vacancies. Also, the vacuum annealed Sn doped ZnS thin films were found to exhibit paramagnetic behaviour with lesser maximum magnetization value compared to that of the unannealed Sn doped ZnS thin films.

Cadmium Telluride Nanocomposite Films Formation from Thermal Decomposition of Cadmium Carboxylate Precursor and Their Photoluminescence Shift from Green to Red

This study focuses on the investigation of a CdTe quantum dots (QDs) formation from a cadmium-carboxylate precursor, such as cadmium isostearate (Cd(ISA)2), to produce CdTe QDs with tunable photoluminescent (PL) properties. The CdTe QDs are obtained by the thermal decomposition of precursors directly in the polymer matrix (in situ method) or in solution and then encapsulated in the polymer matrix (ex situ method). In both approaches, the time course of the CdTe QDs formation is followed by means of optical absorption and PL spectroscopies focusing on viable emission in the spectral interval between 520 and 630 nm. In the polymeric matrix, the QDs formation is slower than in solution and the PL bands have a higher full width at half maximum (FWHM). These results can be explained on the basis of the limited mobility of atoms and QDs in a solid matrix with respect to the solution, inducing an inhomogeneous growth and the presence of surface defects. These achievements open the way to the exploitation of Cd(ISA)2 as suitable precursor for direct laser patterning (DPL) for the manufacturing of optoelectronic devices.

Structural and optical behavior of SnS2/NiFe2O4 NCs prepared via novel two-step synthesis approach for MB and RhB dye degradation under sun light irradiation

The present investigation focuses on facile two-step synthesis approach fabrication of tin sulfide (SnS2)/ nickel ferrite (NiFe2O4) nanocomposites (NCs) for the first time. The crystallinity and phase purity of the prepared material was investigated in powder X-ray diffraction (PXRD) studies. The presence of functional groups (stretching and bending vibration) was primarily determined by the Fourier Transform Infrared Spectroscopy (FT-IR) analysis. As well as, optical behavior of the synthesized samples was determined in UV–Vis absorption spectroscopic studies, and the presence of surface defects was established by PL spectroscopic studies. From the FESEM analysis, sponge-like structure was attained and Ni, Fe, Sn, S and O elemental component was determined by the EDAX spectrum analysis. The as-prepared SnS2/NiFe2O4 NCs exhibit superior photocatalytic performance and high stability toward the reduction of methylene blue (MB) and rhodamine B (RhB) dyes under irradiation of direct sunlight. The synthesized nanocomposites showed an efficient photocatalytic activity with a high reaction kinetic rate.

Crystalline Sb2Te3: Side Surfaces and Disappearance of Dirac Cones

Sb2Te3 is an end point of quasibinary GeTe–Sb2Te3 phase‐change alloys and also a prototypical topological insulator (TI). TIs are materials that behave like insulators in their interior but whose surfaces are characterized by metallic states with linear dispersion, the so‐called Dirac cones. Such surface states are symmetry protected, robust, and are maintained even in the presence of surface defects. It has been tacitly implied that any surfaces of a TI possess this property. Herein, using ab initio simulations, it is demonstrated that cleaving Sb2Te3 along certain side surfaces may lead to the disappearance of Dirac surface states. In particular, it is shown that the (110) surface of the typical TI Sb2Te3 is slightly gapped, whereas the () surface is metallic. The significance and potential benefits of the obtained results for practical applications in planar devices and memory cells are discussed.

Oxi-Redox Selective Breast Cancer Treatment: An In Vitro Study of Theranostic In-Based Oxide Nanoparticles for Controlled Generation or Prevention of Oxidative Stress.

In this article, we demonstrate that specifically engineered oxide nanoparticles (NPs) have the potential to act as theranostic materials that are able to generate or prevent oxidative stress through their oxi-redox activity in various types of malignant and nonmalignant cells. The oxi-redox activity is related to the type and presence of surface defects, which is modified with appropriate synthesis conditions. In the present work, we used MDA-MB-231 and MCF-7 human breast cancer cells and nonmalignant MCF-10A human breast cells to demonstrate how controlled oxidative stress mediated by specifically nanoengineered indium tin oxide (ITO) NPs can selectively induce cell death in the cancer cells while reducing the oxidative stress in the normal cells and supporting their proliferation. The ITO NPs are also promising nanotheranostic materials for cancer therapy and contrast agents because of their multimodal imaging capabilities. We demonstrate that the synthesized ITO NPs can selectively increase the generation of reactive oxygen species (ROS) in both breast tumor cell lines, resulting in activation of apoptosis, and can also greatly suppress the cellular proliferation in both types of tumor cells. In contrast, the ITO NPs exhibit ROS scavenging-like behavior, significantly decreasing the ROS levels in MCF-10A cells exposed to the additional ROS, hydrogen peroxide (H2O2), so that they protect the proliferation of nonmalignant MCF-10A cells from ROS damage. In addition, fluorescent microscopy images revealed that the ITO NPs emit strong fluorescence that could be used to reveal their location. Moreover, computed tomography imaging demonstrated that the ITO NPs exhibited a comparable capability toward anatomical contrast enhancement. These results suggest that the synthesized ITO NPs have the potential to be a novel selective therapeutic agent with a multimodal imaging property for anticancer treatment.

Alkali Ion Storage and Migration in Carbonaceous Anode Materials – an Atomic Scale Study

Lithium-ion and post-lithium ion battery technologies are receiving increasing attention due to the need for a transition to a more sustainable energy economy. Apart from lithium ion batteries (LIBs), sodium ion batteries (NIBs) and potassium ion batteries (KIBs) are currently being investigated. Due to their low cost, natural abundance, and suitability for LIBs, NIBs, and KIBs, carbon-based anode materials, especially hard carbons, have gained scientific interest. The molecular structure of hard carbons is complex, and the atomistic understanding of metal ion storage and intercalation/de-intercalation during charge and discharge is limited. In this work we aim to shed light on these mechanisms through systematic computational modelling of LIB, NIB, and KIB carbon-based anode materials. Experimental studies have postulated that surface defects, planar, and curved pores can have a marked effect on metal storage in hard carbon.1–4 Density functional theory simulations of Li, Na, and K on different carbon motifs (defective graphene basal planes, planar graphitic layers, and curved pores) found in hard carbon anode materials were conducted to investigate their effect on the metal incorporation mechanism. Our calculations show that oxygen-, and nitrogen-containing defects are energetically favorable to form on single layer carbon fragment surfaces,5 and on curved morphologies. These defects were found to be highly beneficial for the initial metal storage, with Li, Na, and K adsorption energies greatly improved as compared to the non-defective carbon surface. Hence, it was deduced, as also suggested by experiment, that the presence of surface defects could indeed lead to increased metal storage. The effect of these defects on metal migration, which would influence the anode materials cycling properties, was investigated through nudged elastic band calculations, and showed that metal adsorption on surface defects can lead to capacity loss and irreversible metal storage. From defect formation energy calculations, it was seen that the defect expected to be present in the highest concentration on the carbon surface under equilibrium conditions is the 2OCNC defect, where three adjacent carbon have been substituted by two oxygen, and one nitrogen, respectively. This defect further has metal migration energy barriers many times higher than the corresponding ones at pristine surfaces, and would be highly detrimental for metal diffusion.5,6 We have also made efforts to model a more complex, disordered hard carbon structure. Metal intercalation energy as a function of carbon interlayer distance, and charge transfer of Na, Li, and K were calculated, based on nanoporous structures (expanded planar graphitic pores and cylindrical pores) identified by experimental analysis.1,2 Our simulations showed that metal incorporation and diffusion will be directly influenced by the pore shape and size, regardless of metal type. Planar graphitic pores were shown to play an important role in metal storage, with a direct impact observed on pore expansion, whereas curved morphologies contribute to rapid metal diffusion.2 In summary, the experimentally proposed metal charge/discharge mechanism of initial simultaneous metal storage on defects and intercalation in expanded pores, followed by pore filling was confirmed from atomic scale studies, showing the direct impact of carbon structure on the intercalation and storage properties of these metal ion battery anode materials.AcknowledgmentThe financial support from EPSRC (Engineering and Physical Sciences Council) under the grant number EP/M027066/1, and EP/R021554/2, is acknowledged.References 1 A.C.S. Jensen, E. Olsson, H. Au, H. Alptekin, Z. Yang, S. Cottrell, K. Yokoyama, Q. Cai, M.-M. Titirici, and A.J. Drew, J. Mater. Chem. A 8, 743 (2020). 2 E. Olsson, J. Cottom, H. Au, Z. Guo, A.C.S. Jensen, H. Alptekin, A.J. Drew, M.-M. Titirici, and Q. Cai, Adv. Funct. Mater. 1908209 (2020). 3 C. Matei Ghimbeu, J. Górka, V. Simone, L. Simonin, S. Martinet, and C. Vix-Guterl, Nano Energy 44, 327 (2018). 4 B. Zhang, C.M. Ghimbeu, C. Laberty, C. Vix-Guterl, and J.M. Tarascon, Adv. Energy Mater. 6, 1501588 (2016). 5 E. Olsson, G. Chai, M. Dove, and Q. Cai, Nanoscale 11, 5274 (2019). 6 E. Olsson, T. Hussain, A. Karton, and Q. Cai, Carbon N. Y. 163, 276 (2020).

Light-assisted scanning probe microscopy characterization of the electrical properties of AlGaN/GaN/Si heterostructures

The article proposes a new methodology that combined light-assisted Scanning Surface Potential Microscopy (SSPM), Scanning Spreading Resistance Microscopy (SSRM) and Scanning Capacitance Microscopy (SCM) techniques for the extended nanoscale characterization of the electrical properties of AlGaN/GaN/Si heterostructures. Two measurement regimes were used to investigate the influence of surface defects on local electrical properties of samples: surface mapping with additional light excitation and one-point spectroscopy which enabled the accurate investigation of energetic transitions associated with a specific surface structure. The influence of two types of surface defects existing in the AlGaN/GaN/Si samples grown by metalorganic chemical vapour deposition epitaxy on the two-dimensional electron gas (2DEG) formation process on the AlGaN/GaN interface was explained. In the case of the sample with the SiN nanomasking layer added to the growth scheme, the areas of negative charge associated with defects created the localised, isolated islands that did not influence the process of electric field formation in the AlGaN/GaN system and had no significantly detrimental impact on the electron transport. The presence of surface defects in the sample without the SiN layer caused the disturbance of the 2DEG electrical properties not only in the place of the defect’s presence but also at some distance away from it. In that case, the photovoltage and photoconductivity spectra indicated the existence of a disordered structure of the AlGaN layer, near and away from the defects. Additionally, it was clarified that the characteristic electronic transition at 3.0 eV related to a deep trap state existing in the AlGaN barrier was localised solely at the surface site of the defects. It was observed during the SSRM measurements that both types of defects created a leakage current paths with prolonged conductivity (up to several seconds), which effect was not reported earlier, that provide an original insight into the origins of the long relaxation time effects existing in the AlGaN/GaN heterostructures.

Ab initio molecular dynamics study of wet H2S adsorption and dissociation on Fe(100) surface

Oil and gas pipeline transportation media often contain acidic media, such as H2S and CO2. The corrosion behavior of oil and gas equipment in wet H2S environment affects its service life. In this paper, ab initio molecular dynamics (AIMD) is used to study the dynamic behavior of wet H2S on Fe(100) surface in 300 K, including adsorption, dissociation and diffusion. Besides, the influences of surface defects and H2S coverage are also considered. The calculation results show the primary dissociation and secondary dissociation of H2S occur successively in perfect and defective Fe(100) surface. The presence of surface defects will reduce the dissociation energy of H2S, making it more prone to dissociation to generate H and S atoms, while the increase of H2S coverage will promote the primary dissociation of H2S but inhibit the secondary dissociation. The entire simulation process suggests that the SH, H and S generated from the dissociation of H2S adsorbed preferentially in the hollow site. The adsorption of S atoms is more stable than H atoms since H could diffuse between adjacent hollow site. In addition, no H atoms diffusion into subsurface region was observed during the whole simulation process.

Photo-Induced Black Phase Stabilization of CsPbI3 QDs Films.

α-CsPbI3 quantum dots (QDs) show outstanding photoelectrical properties that had been harnessed in the fabrication of perovskite QDs solar cells. Nevertheless, the stabilization of the CsPbI3 perovskite cubic phase remains a challenge due to its own thermodynamic and the presence of surface defects. Herein, we report the optimization of the CsPbI3 QDs solar cells, by monitoring the structure, the morphology and the optoelectronic properties after a precise treatment, consisting of the conventional solvent washing with a time limited ultraviolet (UV) exposure combination, during the layer-by-layer deposition. The UV treatment compensates the defects coming from the essential but deleterious washing treatment. The material is stable for 200 h and the PCE improved by the 25% compared with that of the device without UV treatment. The photo-enhanced ion mobility mechanism is discussed as the main process for the CsPbI3 QDs and solar cell stability.