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Defect formation of CuI-doped by group-IIB elements
摘要： First-principles calculations have been performed to investigate the doping defects in CuI with group-IIB elements such as Zn, Cd and Hg. The calculated transition energies for substitutional Zn, Cd and Hg are 1.32, 1.28 and 0.60 eV, respectively. These group-IIB elements at the substitutional sites complex with a copper vacancy (VCu) have the lower formation energies as compared to dopants located at the substitutional sites or interstitial sites, respectively. Among all the complex defects considered, [HgCu + VCu] has the lowest formation energy and it induces the acceptor level ε(0/?) = 0.18 eV above the valence-band maximum (VBM), which is close to the acceptor level ε(0/?) = 0.1 eV of VCu, suggesting that Hg may be a good dopant for CuI to improve its p-type conductivity.
关键词： group-IIB elements,defects formation,first-principles calculation,Semiconductor
更新于2025-09-23 15:23:52
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A Green and Facile Synthesis for rGO/Ag Nanocomposites Using One-step Chemical Co-reduction Route at Ambient Temperature and Combined First Principles Theoretical Analyze
摘要： Recently, graphene decorated with various inorganic nanoparticles, such as Pt, Au, Ag, TiO2 and Fe3O4, among which Ag nanocomposites are good candidates for electronics, optics, electrochemistry and catalysis. However, preparation techniques for Ag nanoparticles/carbon matrix hybrids require tedious multi-step processes often involving toxic reducing agents / high temperatures which is not viable for scalable production. Here, a facile, one step and eco-friendly chemical co-reduction route was utilized to synthesis of a new nanocomposites by Ag nanoparticle anchored on reduced graphene oxide (rGO) at ambient temperature and combined first principles theoretical analyze their interfacial adsorption behavior, is reported. In this way, graphene oxide (GO) and Ag+ simultaneously reduced by thiourea dioxide (TD) without using any additional reduced reactants. Results indicated that GO was successfully reduced to rGO and well-dispersed Ag nanoparticles with sizes of 6~7 nm, anchored on the surface of rGO sheets. Reduction mechanism was attributed to the synergistic effect of its hydrolysis products in aqueous media. The experiment and theoretical calculation results obtained demonstrate this method to be applicable to the synthesis of other metals on rGO sheets in order to improve wettability and interfacial bonding between rGO and metal and may possibly find various forthcoming medicinal, industrial and technological applications.
关键词： In-stiu co-reduction,Green reduce graphene/Ag nanocomposites,Interfacial behavior,First principles,Thiourea dioxide
更新于2025-09-23 15:23:52
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Shining light on growth-dependent surface chemistry of organic crystals: a polarised Raman spectroscopic and computational study of aspirin
摘要： Understanding and controlling crystal surfaces is a critical problem in contemporary materials science. Organic crystal surfaces present the additional complexity of multiple terminations with different functional groups. These alternate terminations influence the surface chemistry and exert control on many material properties. While established tools for surface characterization exist, few provide the chemical information required to unambiguously identify functional groups. Polarized Raman spectroscopy is a versatile tool that can provide detailed chemical information on molecular materials, and, when used in a microscope configuration, can be used to map substrates on a micron scale. In this work, we demonstrate the use of polarized Raman to study the surface chemistry of aspirin. By analyzing crystals grown under a variety of conditions, we relate the growth solvent to the surface termination and reconcile the conflicting results in the literature on the nature of the <100> surface. Our results are supported by detailed first-principles modelling of the surfaces and their vibrational spectra. This study establishes the potential of polarized Raman microscopy as a tool for organic surface science that, when combined with predictive modelling, provides a powerful means to understand and ultimately control surface chemistry.
关键词： aspirin,first-principles modelling,crystal growth,polarized Raman spectroscopy,surface termination,lattice dynamics
更新于2025-09-23 15:23:52
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Roles of Carrier Doping, Band Gap, and Electron Relaxation Time in the Boltzmann Transport Calculations of a Semiconductor’s Thermoelectric Properties
摘要： Although there is a growing demand for first-principles predictions of the thermoelectric properties of materials, the contribution of various errors in Boltzmann transport calculations is not negligible. We conducted a typical first-principles calculation and a Boltzmann transport analysis on a typical semiconductor (Si) at various temperatures T while varying the band gap ?g, electron relaxation time ?el, and phonon thermal conductivity ?ph to demonstrate how the calculated thermoelectric properties, which are functions of the carrier doping level, are affected by these parameters. Bipolar conduction drastically decreased zT via a degradation of the Seebeck coefficient S and an increase in the effective Lorenz factor Leff, indicating the importance of a wide enough ?g (several multiples of kBT or higher) for high zT. Thus, the underestimation of ?g, which frequently happens in first-principles calculations, could induce large errors in calculations for narrow-gap semiconductors. The calculation of the electron thermal conductivity without Peltier thermal conductivity was found to limit the zT of typical semiconductors to below 1. A small value of ?ph/?el, where ?ph/?el is the degree to which a material is a phonon-glass electron-crystal, was necessary to achieve a high zT. Fitting the calculations with experimental thermoelectric properties showed that ?el can vary by an order of magnitude from 10115 to 10114 s, depending on both T and the samples. This indicates that the use of a fixed relaxation time is inappropriate for thermoelectric materials.
关键词： Boltzmann transport calculation,first-principles calculation,thermoelectric properties
更新于2025-09-23 15:23:52
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Electronic structure, mechanical and optical properties of ternary semiconductors Si <sub/>1-x</sub> Ge <sub/>x</sub> C (X?=?0, 0.25, 0.50, 0.75, 1)
摘要： The electronic structure of silicon carbide with increasing germanium content have been examined using first principles calculations based on density functional theory. The structural stability is analysed between two different phases, namely, cubic zinc blende and hexagonal phases. The zinc blende structure is found to be the stable one for all the Si1-xGexC semiconducting carbides at normal pressure. Effect of substitution of Ge for Si in SiC on electronic and mechanical properties is studied. It is observed that cubic SiC is a semiconductor with the band gap value 1.243 eV. The band gap value of SiC is increased due to the substitution of Ge and the band gap values of Si 0.75 Ge 0.25 C, Si 0.50 Ge 0.50 C, Si 0.25 Ge 0.75 C and GeC are 1.322 eV, 1.413 eV, 1.574 eV and 1.657 eV respectively. As the pressure is increased, it is found that the energy gap gets decreased for Si1-x GexC (X = 0, 0.25, 0.50, 0.75, 1). The elastic constants satisfy the Born – Huang elastic stability criteria. The bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are also calculated and compared with the other available results.
关键词： mechanical properties,electronic structure,optical properties,First principles study
更新于2025-09-23 15:23:52
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Electrowetting on 2D dielectrics: a quantum molecular dynamics investigation
摘要： Electrowetting on dielectrics (EWOD) is widely used to manipulate the spreading of a conductive liquid on a dielectric surface by applying an electric field. 2D hydrophobic dielectrics are promising candidates for EWOD applications. In this study, extensive quantum molecular dynamics (MD) simulations are performed to investigate the electrowetting behavior of salty water on hexagonal boron nitride (h-BN) monolayer. The proximal adsorption of salt ions and the associated realignment of the dipole moments of interfacial water with the applied electric field are found to be the physical origin of the electrowetting behavior. At low salt concentration and low electric fields, the proximal adsorption and the realignment follow the applied electric field, and the cosine of the water contact angle (WCA) follows a quadratic dependence on the applied electric field. At high salt concentration and high electric fields, the proximal adsorption saturates, which restricts further realignment and causes a saturation of the WCA. This case study provides physical insights into the much debated mechanism that underlies the contact angle saturation (CAS) found in macroscopic electrowetting phenomena and also provides an avenue for further studies of electrowetting at the atomic scale.
关键词： hexagonal boron nitride monolayer,contact angle saturation,electrowetting on dielectrics,first-principles
更新于2025-09-23 15:23:52
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Air-stable N-doped black phosphorus transistor by thermal deposition of metal adatoms
摘要： In this work, a simple and effective thermal deposition method is described to enhance the stability and achieve n-doping of two-dimensional black phosphorus (BP), resulting the successful fabrication of logic devices. By doping with Al adatoms, the stability of BP against oxidation is enhanced and the transfer characteristics are maintained for several days under ambient conditions. Furthermore, the resulting BP is n-doping showing a negative-shifted threshold voltage and enhanced electron mobility. The mechanism of Al doping is investigated by first-principles calculation and Al induces a downward shift of the conduction band minimum and increases the Femi level. In addition, integration of bare BP and Al-doped BP enables the fabrication of various logic devices such as inverters and p?n diodes. This work reveals a facile strategy to simultaneously enhance the stability and regulate the conductivity of BP by doping with metal adatoms boding well for device applications.
关键词： n-doping,stability,black phosphorus,thermal deposition,first-principles calculation
更新于2025-09-23 15:23:52
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Adsorption of hazardous gases in nuclear islands on monolayer MoS2 sheet
摘要： Monitoring and removing the hazardous gases (such as radioactive gases and hydrogen) in the nuclear islands are full with enormous challenges, although the two methods can improve the safety level of the nuclear power plant. Due to its excellent electronic and chemical properties, two dimensional materials are considered as the candidate for monitoring and removing the hazardous gases in the nuclear islands. In this paper, the adsorption of the hazardous gases on monolayer MoS2 sheet was investigated by using the first principles calculation method. The adsorption energy, total charge transfer, and density of states (DOS) were calculated to understand the adsorption mechanism and sensing performance of the monolayer MoS2 sheet to the hazardous gases. The results show that an attractive interaction exists between the hazardous gases and the monolayer MoS2 sheet. The magnitude of the adsorption energy demonstrates that physisorption dominates the adsorption of the hazardous gas molecules on the monolayer MoS2 sheet, but the adsorption of the dissociated H/I atom belongs to chemisorption. The DOS shows that the orbitals, H 1s and I 5p, play a crucial role in the adsorption, and the change of the electronic structure indicates that the monolayer MoS2 sheet might be a promising material which is used for monitoring the gaseous radioactive iodine in the nuclear islands.
关键词： Hydrogen,Hazardous gases,Radioactive gases,First principles calculation,Monolayer MoS2 sheet
更新于2025-09-23 15:23:52
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Investigation on electronic structure and luminescence mechanism of CaF2:Eu3+ from first principles calculations
摘要： In this work, we present the results of theoretical calculations based on the density functional theory (DFT) of structural, electronic and optical properties of CaF2 crystal doped with Eu3+ ion. This study covers both ground and excited states of considered material by ?xing spin magnetic moment 6μB and 4μB, respectively. The Eu3+ doping induces slight displacement of its nearest neighbors. The presence of Eu3+ ion is con?rmed by the calculated charge density and magnetic moment. Some electronic states belonging to 4f orbital are found in the forbidden energy region of CaF2 and the spin ?ipping of one 4f electron of Eu3+ caused by the excitation is demonstrated by means of the computed electronic properties. The absorption spectra of CaF2:Eu3+ is calculated and compared with that of pure CaF2. Finally, the possible mechanism of luminescence is proposed based on the obtained electronic and optical properties.
关键词： CaF2:Eu3+,First principles study,Electronic structure,Luminescence
更新于2025-09-23 15:22:29
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First-principles study of the surface reparation of ultrathin InSe with Se-atom vacancies by thiol chemistry
摘要： Utilizing first-principles calculations, the surface reparation of monolayer InSe with Se-atom vacancies by thiol chemistry was studied. The geometrical structures and electronic properties of monolayer InSe with Se-atom vacancies were evaluated before and after reparation by S atoms, benchmarked against defect-free case. The parameters of bond lengths, band gaps and carrier mobilities can be recovered to the standard of pristinely defect-free structure. Moreover, the interaction of S atom with complete part of monolayer InSe was also investigated. S atom cannot adsorb on the surface without Se-atom vacancies, while it can substitute Se atom or insert into the interior of monolayer InSe. And the insertion was able to induce a decrease by one order of magnitude. It was demonstrated that thiol chemistry was an effective method to repair Se-atom vacancies and maintain its oxidation resistance, while the insertion of S atom into the interior of monolayer InSe should be avoided.
关键词： Indium selenides,Carrier mobility,Se-atom vacancies,Band gap,First-principles
更新于2025-09-23 15:22:29