- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Opto-mechanics driven fast martensitic transition in two-dimensional materials
摘要： Diffusional phase-change materials, such as Ge-Sb-Te alloys, are used in rewritable non-volatile memory devices. But the continuous pursuit of readout/write speed and reduced energy consumption in miniaturized devices calls for optically driven, diffusionless phase change scheme in ultra-thin materials. Inspired by optical tweezers, in this work, we illustrate theoretically and computationally that a linearly polarized laser pulse with selected frequency can drive an ultrafast diffusionless martensitic phase transition of two-dimensional ferroelastic materials such as SnO and SnSe monolayers, where the unit-cell strain is tweezed as a generalized coordinate that affects the anisotropic dielectric function and electromagnetic energy density. At laser power of 2.0×1010 and 7.7×109 W/cm2, the transition potential energy barrier vanishes between two 90°-orientation variants of ferroelastic SnO and SnSe monolayer, respectively, so displacive domain switching can occur within picoseconds. The estimated adiabatic thermal limit of energy input in such optomechanical martensitic transition (OMT) is at least two orders of magnitude lower than that in Ge-Sb-Te alloy.
关键词： martensitic phase transition,ferroelasticity/ferroelectricity,two-dimensional materials,dielectric function,density functional theory,opto-mechanics
更新于2025-09-23 15:21:01
-
Structural and electronic properties of III-nitride nanoribbons
摘要： The structural and electronic properties of group III-nitride nanoribbons have been systematically investigated using density functional theory calculations. We computed the edge stresses and edge moduli for III-nitride nanoribbons with a variety of widths and edge terminations, including bare, fully as well as partially hydrogen-passivated edges. In addition, fluorine-passivated zigzag-terminated nanoribbons were also investigated. Our results show that all edges of III-nitride nanoribbons are subjected to compressive stresses. The magnitude of edge stresses strongly depends on the edge terminations. Compressive stress states of nanoribbon edges result in drastically different edge distortions and edge elastic moduli, depending again on the edge configurations. Finally, the electronic band structures are calculated for all zigzag-terminated nanoribbons. We found only fully-passivated nanoribbons are semiconductors with indirect bandgaps. These results suggest that edge terminations significantly affect the edge elastic properties as well as the electronic properties of group III-nitride nanoribbons and their applications.
关键词： edge stresses,III-nitride nanoribbons,edge moduli,electronic band structures,density functional theory
更新于2025-09-23 15:21:01
-
Structural properties of silicon–germanium and germanium–silicon core–shell nanowires
摘要： Core–shell nanowires made of Si and Ge can be grown experimentally with excellent control for different sizes of both core and shell. We have studied the structural properties of Si/Ge and Ge/Si core–shell nanowires aligned along the [1 1 0] direction, with diameters up to 10.2 nm and varying core to shell ratios, using linear scaling density functional theory. We show that Vegard’s law, which is often used to predict the axial lattice constant, can lead to an error of up to 1%, underlining the need for a detailed ab initio atomistic treatment of the nanowire structure. We analyse the character of the intrinsic strain distribution and show that, regardless of the composition or bond direction, the Si core or shell always expands. In contrast, the strain patterns in the Ge shell or core are highly sensitive to the location, composition and bond direction. The highest strains are found at heterojunction interfaces and the surfaces of the nanowires. This detailed understanding of the atomistic structure and strain paves the way for studies of the electronic properties of core–shell nanowires and investigations of doping and structure defects.
关键词： Vegard’s law,nanowire,linear scaling density functional theory,core–shell
更新于2025-09-23 15:21:01
-
Non-flipping <sup>13</sup> C spins near an NV center in diamond: hyperfine and spatial characteristics by density functional theory simulation of the C <sub/>510</sub> [NV]H <sub/>252</sub> cluster
摘要： Single NV centers in diamond coupled by hyperfine interaction (hfi) to neighboring 13C nuclear spins are now widely used in emerging quantum technologies as elements of quantum memory adjusted to a nitrogen-vacancy (NV) center electron spin qubit. For nuclear spins with low flip-flop rate, single shot readout was demonstrated under ambient conditions. Here we report on a systematic search for such stable NV?13C systems using density functional theory to simulate the hfi and spatial characteristics of all possible NV?13C complexes in the H-terminated cluster C510[NV]-H252 hosting the NV center. Along with the expected stable ‘NV-axial?13C’ systems wherein the 13C nuclear spin is located on the NV axis, we found for the first time new families of positions for the 13C nuclear spin exhibiting negligible hfi-induced flipping rates due to near-symmetric local spin density distribution. Spatially, these positions are located in the diamond bilayer passing through the vacancy of the NV center and being perpendicular to the NV axis. Analysis of available publications showed that, apparently, some of the predicted non-axial near-stable NV?13C systems have already been observed experimentally. A special experiment performed on one of these systems confirmed the prediction made.
关键词： density functional theory,diamond,NV centers
更新于2025-09-23 15:21:01
-
Interfacial structure of SrZr <sub/><i>x</i> </sub> Ti <sub/>1?</sub><sub/><i>x</i> </sub> O <sub/>3</sub> films on Ge
摘要： The interfacial structure of SrZrxTi1?xO3 films grown on semiconducting Ge substrates is investigated by synchrotron X-ray diffraction and first-principles density functional theory. By systematically tuning the Zr content x, the effects of bonding at the interface and epitaxial strain on the physical structure of the film can be distinguished. The interfacial perovskite layers are found to be polarized as a result of cation-anion ionic displacements perpendicular to the perovskite/semiconductor interface. We find a correlation between the observed buckling and valence band offsets at the SrZrxTi1?xO3/Ge interface. The trends in the theoretical valence band offsets as a function of Zr content for the polar structures are in agreement with reported X-ray photoelectron spectroscopy measurements. These results have important implications for the integration of functional oxide materials with established semiconductor based technologies.
关键词： synchrotron X-ray diffraction,density functional theory,valence band offsets,SrZrxTi1?xO3 films,Ge substrates,interfacial structure
更新于2025-09-23 15:21:01
-
First theoretical probe for efficient enhancement of nonlinear optical properties of quinacridone based compounds through various modifications
摘要： In this study, first attempt has been made for theoretical designing of quinacridone (QA) dye and new QA-based compounds (QA-1 to QA-9) were proposed by installing auxiliary donors (dimethylvinyl, methoxy, and N,N-dimethylamine), donor (diphenylamine) and acceptors (cyanoacrylic acid, CN and NO2) segments into fixed π-bridge QA. DFT and TDDFT calculations with B3LYP/6-31G(d,p) and CAM-B3LYP/6-31G(d,p) functional were used to shed light on the promising structure, charge transport and NLO properties. Introduction of auxiliary donors/donor and acceptor successfully modified the structure which led to superior NLO properties. An eye-catching NLO response was observed in all designed compounds. Interestingly, QA-9 exhibits appealingly large enhancement in NLO properties through ICT process with < α > and βtot computed to be 716.02 (a.u) and 128082.15 (a.u) respectively. UV–Vis results indicates the QA-9 most red shifted among all studied compounds with λmax = 489.02 nm. QA-1 to QA-9 showed narrow HOMO-LUMO energy gap as compared to QA which results in enhanced NLO response. NBO analysis confirms the formation of charge separation state in QA-1 to QA-9 due to successful migration of electrons from auxiliary donors/donor to acceptors via π-bridge. The present research evokes the scientific interest regarding the development of QA based tempting NLO compounds that can be beneficial in modern hi-tech applications.
关键词： Density functional theory,Molecular modeling,Quinacridone-based dyes,Donor and acceptor units,NLO properties,Two-state model
更新于2025-09-23 15:21:01
-
DFT calculations of energy dependent XPS valence band spectra
摘要： In the past few years it became regularly possible to measure valence band X-ray photoelectron spectra (XPS) using variable excitation energies. This ranges from UV-light to conventional X-ray sources (like Al Kα) all the way to synchrotron radiation with energies of several keV. In order to explain the observed variations in intensity with respect to the excitation energy, we performed XPS calculations using the WIEN2k code. The new PES module computes the XPS spectra using a combination of partial density of states times excitation-energy-dependent atomic-orbital cross sections. It considers as additional correction the charge fraction of the corresponding orbital located inside the atomic spheres. The resulting XPS spectra are compared with experimental data for SiO2, PbO2, CeVO4, In2O3 and ZnO at different excitation energies and in general good agreement between the simulated and experimental spectra has been achieved. In some cases significant unexpected contributions like Pb-6d in PbO2 or Zn-4p in ZnO appear and explain some features in the experimental spectra which previously have not been identified.
关键词： Valence bands,XPS,Density functional theory,APW,Orbital cross sections
更新于2025-09-23 15:21:01
-
Stability, spontaneous and induced polarization in monolayer MoC, WC, WS, and WSe
摘要： Using density functional theory based calculations, we design buckled honeycomb binary monolayer MoC, WC, WS, and WSe. The feasibility of their experimental synthesis is evident from their low formation energies, stable lattice vibrations, and high elastic stiffnesses. The difference in electronegativity of the building atoms and lack of inversion symmetry results in high spontaneous out-of-plane polarization whereas all the in-plane components cancel out. The existence of the mirror plane along the armchair direction vanishes the in-plane piezoelectric stress effects for a strain applied along the zigzag direction. However, a strain along the armchair direction on MoC and WC results in a high piezoelectric coefficient up to 10×10?10 C/m, about three times larger than that reported for monolayer MoS2. The polarization switching barriers for the out-of-plane components range from 0.55 to 2.70 eV per formula unit.
关键词： ferroelectricity,monolayer,density functional theory,polarization,piezoelectricity
更新于2025-09-23 15:21:01
-
Deformation of Charged Graphene Membrane
摘要： Geometrical capacitors with memory (memcapacitors) are of interest because of potential applications in future computing machines. When employing a buckled membrane as one of the capacitor plates, two possible buckled positions serve as the states of low and high capacitance. Using the hybrid B3LYP/6-31G approximation, we investigate the snap-through transition of neutral and negatively charged buckled graphene membranes under the transverse load and external electrostatic field created by a point charge. Estimations show that the chosen calculation method reproduces the elastic properties of graphene within the limits of experimental error. The obtained results testify to the fact that the membrane charge and external electrostatic field affect notably the threshold snap-through switching force in nanosized membranes and, therefore, should be taken into account in the design and development of such nanodevices.
关键词： capacitor,density functional theory,graphene,membrane
更新于2025-09-23 15:21:01
-
Persistence of the R3m Phase in Powder GeTe at High Pressure and High Temperature
摘要： As a phase-change material, rhombohedral GeTe (space group R3m) was believed to transform to the cubic rock-salt phase (B1) at 3–4 GPa, associated with the disappearance of a Peierls distortion. However, using a combination of synchrotron X-ray diffraction and theoretical calculations, we found that the R3m phase persists from ambient pressure up to pressures of about 15.8 GPa, in contrast to previous reports. Neither was the B1 phase observed in a heating X-ray powder diffraction experiment. The spurious transformation from R3m to B1 is caused by changes to the compression ratio of lattice parameters in the R3m phase under high pressure/temperature. These findings provide insight into transitions of phase-change materials, relevant to other materials undergoing displacive transitions under high pressure/temperature.
关键词： structural phase transitions,density-functional theory,high pressure,phase-change materials,high temperature,GeTe,synchrotron X-ray diffraction
更新于2025-09-23 15:21:01