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Thickness-dependent bandgap of transition metal dichalcogenides dominated by interlayer van der Waals interaction
摘要： Based on a bandgap thermodynamic approach, the thickness-dependent bandgap of two-dimensional transition metal dichalcogenides is modeled without any adjustable parameter. An efficient expansion in bandgap upon lowering the thickness is predicted. The thickness-dependence of bandgap is believed originated from the interlayer van der Waals (vdW) interaction, while the surface effect is characterized by the difference in atomic thermal vibration between the surface and the interior. Due to the suppression role of the interlayer vdW interaction on the thermal vibration of interior chalcogen atoms, the surface effect is variable, which changes from monotonic increase for sulfides to decrease for tellurides. The role of the interlayer vdW interaction depends on the polarity of metal-chalcogen bonds. The model predictions agree with available experiment and simulation results.
关键词： Surface effect,Thickness-dependence,Bandgap,Interlayer van der Waals interaction,Thermodynamics
更新于2025-09-23 15:23:52
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Real-time profiling Anti-EpCAM Based Immune capture, from Molecules to Cells using MP-SPR
摘要： Antibodies of epithelial cell-adhesion-molecule (anti-EpCAM)-based interfaces have proven to be highly efficient at capturing circulating tumor cells (CTCs). To achieve the bonding of anti-EpCAM to the interface, biotin and streptavidin are used to modify the surface. These processes are critical to subsequent cell-capture efficiencies. However, quantitative research on the interactions between biotin, streptavidin and biotinylated anti-EpCAM on the interface is lacking. In this work, the thermodynamics and kinetics of biomolecular interactions were determined by using surface plasmon resonance. The equilibrium binding affinities for biotinylated anti-EpCAM to streptavidin and streptavidin to biotin (illustrated by biotin-PEG400-thiol) were found to be 2.75×10^6 M^-1 and 8.82×10^6 M^-1, respectively. Each streptavidin can bind up to 2.30 biotinylated anti-EpCAM under thermodynamic equilibrium. The findings provide useful information to optimize the modification of anti-EpCAM and improve the capture efficiency of CTCs.
关键词： surface plasmon resonance,antibodies of epithelial cell-adhesion-molecule,cell capture,biotin–streptavidin interaction,thermodynamics,kinetics
更新于2025-09-23 15:23:52
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Thermodynamic Simulation of Polysilicon Production in Si-H-Cl System by Modified Siemens Process
摘要： A study on thermodynamics of the various steps involved in the polysilicon manufacture in the Siemens process is presented in this paper. The synthesis of SiHCl3 (TCS), silicon deposition from SiHCl3 and hydrogenation of by-production SiCl4 (STC) for recycle are the main processes studied in this paper. Based on the thermodynamic data for related pure substances, the relation of (nCl/nH)Eq (i.e. the mole ratio of Si to Cl at equilibrium) and the feeding mole ratio of Cl to H (nCl/nH) was plotted in the Si-Cl-H system. Then, the effects of temperature, pressure and feed fraction on TCS selectivity in the synthesis of SiHCl3 process, polysilicon yield in the silicon deposition process and SiCl4 conversion ratio in the SiCl4 hydrogenation process have been studied. Useful conclusions for improving these processes have been drawn. Finally, the optimum conditions have been obtained and compared with limited published data in the literature. The results show that comparison with the limited reported values in the literature indicates that the operating conditions are close to those predicted by the thermodynamics for all three reactions. However, the reported conversion or yield is lower. It is hoped that this paper makes a contribution as future polysilicon plants move to higher capacity and seek a reduction in the cost of production.
关键词： Siemens Process,Silicon Deposition,Thermodynamics,Hydrogenation
更新于2025-09-23 15:22:29
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Thermal Imaging Experiments as an Inspiration for Problem-based Learning
摘要： In the last decade, a powerful tool has been given to physics teachers to visualize thermodynamic phenomena. Thermal imaging cameras are fascinating devices opening the world of (even small) temperature changes and being able to uncover hidden manifestations of many processes around us. This paper describes a few qualitative thermal imaging experiments prepared primarily for problem-based lessons and repeatedly used with high school or even university students in the Interactive Physics Laboratory at Charles University. These experiments are focused on thermal processes, which often run in unexpected ways (at least for the students), and their explanations typically require a complex insight into physics, so they can be used as a starting point for discussions and activities designed for some level of inquiry.
关键词： thermodynamics,physics education,problem-based learning,thermal imaging
更新于2025-09-23 15:21:21
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Thermodynamic consistency of the optomechanical master equation
摘要： We investigate the thermodynamic consistency of the master equation description of heat transport through an optomechanical system attached to two heat baths, one optical and one mechanical. We employ three different master equations to describe this scenario: (i) The standard master equation used in optomechanics, where each bath acts only on the resonator that it is physically connected to; (ii) the so-called dressed-state master equation, where the mechanical bath acts on the global system; and (iii) what we call the global master equation, where both baths are treated nonlocally and affect both the optical and mechanical subsystems. Our main contribution is to demonstrate that, under certain conditions including when the optomechanical coupling strength is weak, the second law of thermodynamics is violated by the first two of these pictures. In order to have a thermodynamically consistent description of an optomechanical system, therefore, one has to employ a global description of the effect of the baths on the system.
关键词： heat transport,thermodynamics,second law of thermodynamics,optomechanics,master equation
更新于2025-09-23 15:21:01
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Preparation of porous graphene/carbon nanotube composite and adsorption mechanism of methylene blue
摘要： The graphene oxide (GO) and modified carbon nanotubes (MCNTs) were dispersed in water and mixed with toluene to form homogeneous emulsion, then the porous graphene–carbon nanotubes composites (MCG) were prepared through hydrothermal reaction. The adsorption mechanism of MCG was investigated by adsorption methylene blue. The morphology of MCG was analyzed by scanning electron microscope and transmission electron microscopy. It was found that MCG had rich micropore structures and MCNTs were interlaced on graphene sheets. The pore size of MCG can be effectively controlled by changing the volume ratio of toluene to the GO/MCNTs solution in the emulsion. MCG was characterized by X-ray diffractometer, Raman spectrometer, X ray photoelectric instrument and other analytical instruments. It was found that MCG had more oxygen functional groups. The experimental results show that kinetics can be well-described by pseudo-second-order model. The smaller the pore size, the higher the equilibrium adsorption capacity and the slower the adsorption rate. The adsorption thermodynamic parameters show that the adsorption process is spontaneous and belongs to physical adsorption, and high temperature is beneficial to adsorption. The fitting results of MCG-5 equilibrium adsorption data are matched with the Langmuir model and the saturated adsorption capacity is 232 mg g?1. After five cycles of adsorption–desorption operation, the adsorption capacity of MCG-5 decreases slightly.
关键词： Thermodynamics,Graphene,Methylene blue,Carbon nanotubes,Kinetics
更新于2025-09-23 15:21:01
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Double quantum-dot engine fueled by entanglement between electron spins
摘要： The laws of thermodynamics allow work extraction from a single heat bath provided that the entropy decrease of the bath is compensated for by another part of the system. We propose a thermodynamic quantum engine that exploits this principle and consists of two electrons on a double quantum dot (QD). The engine is fueled by providing it with singlet spin states, where the electron spins on different QDs are maximally entangled, and its operation involves only changing the tunnel coupling between the QDs. Work can be extracted since the entropy of an entangled singlet is lower than that of a thermal (mixed) state, although they look identical when measuring on a single QD. We show that the engine is an optimal thermodynamic engine in the long-time limit. In addition, we include a microscopic description of the bath and analyze the engine’s finite-time performance using experimentally relevant parameters.
关键词： quantum dots,quantum engine,entanglement,quantum thermodynamics
更新于2025-09-23 15:19:57
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Thermodynamics of Multicomponent Perovskites: A Guide to Highly Efficient and Stable Solar Cell Materials
摘要： With their dramatic improvement of photoconversion efficiency, metal-halide perovskite (MHP) solar cells are receiving great attention. For successful deployment of these materials as next-generation solar cells, many research efforts are being undertaken to develop highly efficient and stable perovskite solar cells. Because compositional engineering in particular has provided a powerful route to optimize the material properties, MHPs with high efficiency and stability often include a number of different components. In this study, using ab-initio thermodynamics for ternary mixtures at the A-site (FA, MA, and Cs) and varying Br/I content at the X-site, we provide thermodynamic modeling on how mixtures of different cations and halides at A- and X-sites can modify the stability of MHPs. Our in-depth calculation reveals that Br mixing is inevitable to stabilize the corner-shared perovskite structure of highly efficient FAPbI3 with low bandgap. To maintain the minimal content of Br, which widens the bandgap, MA co-mixing is required, while Cs mixing contributes to prevent the decomposition of MHPs into precursors. We anticipate that the present study will provide thermodynamic insight into the distinctive roles of different components of MHPs and offer a design guideline for future compositional engineering of MHPs.
关键词： efficiency,thermodynamics,metal-halide perovskite,compositional engineering,stability,solar cells
更新于2025-09-23 15:19:57
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Mesoscopic study of thermal behavior, fluid dynamics and surface morphology during selective laser melting of Ti-based composites
摘要： A mesoscopic simulation based on the randomly packed powder bed model was developed to study the thermal behaviors during selective laser melting (SLM) of Ti-based composites. Effects of processing parameters on the thermal behavior, fluid dynamics and surface morphology evolution within the molten pool were investigated. The obtained results revealed that the operating temperature, cooling rate and melt lifetime were highly enhanced as the laser power was increased. Meanwhile, the increased molten pool dimensions, the turbulent fluid flows, the improved escaping rate of the entrapped gas and the efficient rearrangement of reinforcing particles within the molten pool appeared at the application of the high laser power. At the optimized processing parameters, the peak of the operating temperature profile located in the laser and powder interaction area was apparently disappeared with the formation of the maximum temperature of 3300 K and, the mean operating temperature of the platform caused by the heat accumulation was as high as 1300 K. Moreover, the surface morphology of the molten pool predicted by the simulation showed a variation from continuous pores to fragments, then to the typical and regular liquid front, and finally to the turbulent liquid front and spatter and balling phenomenon as the laser power increased. At the laser power of 200 W and laser energy density of 140 J/m, the maximum velocity was located in the front and rear region and, the velocity vector located in the melt advanced front pointed to the rear region of the molten pool, indicating that the melt from the irradiation region would complete the efficient melt supplement and avoid the formation of residual pores and therefore, a good and flat surface with few spatters was obtained with the clear liquid front. The simulated surface morphology was found to be consistent with the experimental measurements.
关键词： Surface morphology,Thermodynamics,Mesoscopic simulation,Selective laser melting,Titanium matrix composite
更新于2025-09-23 15:19:57
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Theoretical investigation on the kinetics and mechanism of the synthesis of fluorescent 3,8-disubstituted-3H-imidazo[4,5-a]acridine-11-carbonitriles
摘要： 3,8-Disubstituted-3H-imidazo[4,5-a]acridine-11-carbonitriles show very interesting optical properties. In some cases, they have higher quantum yields compared to well-known fluorescent dyes such as fluorescein. Hitherto, no detailed theoretical study has been reported on the mechanism of the synthesis of the titled compounds, hence an accurate and detailed theoretical investigation on the synthesis of these dyes is desirable. In this paper, density functional theory (DFT) methods have been employed to investigate the most reasonable mechanism in formation of these fluorophores. All species and related transition states were optimised and the relative energies of all species and the activation energies for all proposed mechanisms were obtained. Comparing the Ea values of all pathways reveals that intramolecular electrophilic aromatic substitution is the most plausible mechanism for the cyclisation reaction in the preparation of these dyes. Also, the effects of substituents in positions 3 and 8 were investigated and the results show that electron-donor substituents can reduce the activation energy for formation of the σ complex in the electrophilic aromatic substitution.
关键词： kinetics,intramolecular electrophilic aromatic substitution,thermodynamics,5-a]acridine,DFT calculations,imidazo[4,substituent effects
更新于2025-09-19 17:15:36