- 标题
- 摘要
- 关键词
- 实验方案
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Preferential Positioning, Stability, and Segregation of Dopants in Hexagonal Si Nanowires
摘要： We studied the physics of common p- and n-type dopants in hexagonal-diamond Si –a Si polymorph that can be synthesized in nanowire geometry without the need of extreme pressure conditions– by means of first-principles electronic structure calculations and compared our results with those for the well-known case of cubic-diamond nanowires. We showed that i) as observed in recent experiments, at larger diameters (beyond the quantum confinement regime) p-type dopants prefer the hexagonal-diamond phase with respect to the cubic one as a consequence of the stronger degree of three-fold coordination of the former, while n-type dopants are at a first approximation indifferent to the polytype of the host lattice; ii) in ultra-thin nanowires, because of the lower symmetry with respect to bulk systems and the greater freedom of structural relaxation, the order is reversed and both types of dopant slightly favor substitution at cubic lattice sites; iii) the difference in formation energies leads, particularly in thicker nanowires, to larger concentration differences in different polytypes, which can be relevant for cubic-hexagonal homojunctions; iv) ultra-small diameters exhibit, regardless of the crystal phase, a pronounced surface segregation tendency for p-type dopants. Overall these findings shed light on the role of crystal phase in the doping mechanism at the nanoscale and could have a great potential in view of the recent experimental works on group IV nanowires polytypes.
关键词： density functional theory,Nanowires,formation energy,dopants,2H-Si,hexagonal diamond silicon
更新于2025-09-23 15:23:52
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - A Doppler Centroid Estimator for Synthetic Aperture Radar Based on Phase Center Point Tracking
摘要： Heterogeneity is an important feature of multiagent systems. This paper addresses the consensus problem of heterogeneous multiagent systems composed of first-integrator and double-integrator agents. The dynamics of each agent switches between continuous-time and discrete-time dynamics. By using the graph theory and nonnegative matrix theory, we derive that the system can achieve consensus if and only if the fixed interaction topology has a directed spanning tree. For switching topologies, we get that the system can reach consensus if each interaction topology has a directed spanning tree. Simulation examples are provided to demonstrate the effectiveness of our theoretical results.
关键词： switching dynamics,nonnegative matrix theory,consensus,heterogeneous multiagent systems,graph theory
更新于2025-09-23 15:22:29
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Diffraction Focal Position and Vector Diffraction Theory for Micro Holographic Storage Systems
摘要： In this study, we proposed a method to determine the optimal focal position for micro-holographic storage systems, using vector diffraction theory; the theory provides exact solutions when the numerical aperture (NA) exceeds 0.6. The best diffraction focus was determined by the position and wavelength corresponding to minimal spherical aberration. The calculated refractive index modulation, polarization illumination, and boundary conditions at the interface of different media were analyzed. From the results of our analysis, we could confirm the size of micrograting as a function of NA and wavelength, based on vector diffraction theory, compared with scalar diffraction theory which defines the micrograting by . To demonstrate our analysis, we adapted an optical alignment method using a Twyman-Green interferometer, and could obtain good agreement between analysis and experimental results.
关键词： microholographic storage system,diffraction focus,vector diffraction theory,scalar diffraction theory,diffraction efficiency,refractive index modulation,interferogram,polarization
更新于2025-09-23 15:22:29
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Indicator-Kriging-Integrated Evidence Theory for Unsupervised Change Detection in Remotely Sensed Imagery
摘要： This study proposes a novel approach based on indicator kriging and Dempster–Shafer (DS) theory for unsupervised change detection (CD) in remote sensing images (DSK). Indicator kriging is integrated to the standard DS theory. A feature set with four difference images (DIs) providing complementary change information is initially generated. Subsequently, the mass functions for each DI are determined automatically using fuzzy logic, the four pieces of DI evidence are combined by DS theory, and a preliminary CD map is achieved. The preliminary CD map is then divided into three parts adaptively—weakly con?icting part of no change, weakly con?icting part of change, and strongly con?icting part—by calculating the evidence con?ict degree for each pixel. Finally, the pixels in the weakly con?icting parts, which have little or no con?ict, are labeled as the current class, and the pixels in the strongly con?icting part that contains misclassi?ed pixels are reclassi?ed based on indicator kriging. DSK combines the advantages of different DI features and solves the con?icting situations to a large extent. The main contributions of this study include the following: 1) introducing indicator kriging into CD to manage con?ict information during DS fusion and 2) presenting a scheme for producing DI set with complementary change information, developing a novel DSK fusion model for information fusion, and de?ning the proposed CD framework. Experimental results verify that the proposed DSK is robust and effective for CD.
关键词： unsupervised change detection (CD),remote sensing,Con?ict management,indicator kriging,Dempster–Shafer (DS) theory
更新于2025-09-23 15:22:29
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[IEEE 2018 International Conference on Radar (RADAR) - Brisbane, Australia (2018.8.27-2018.8.31)] 2018 International Conference on Radar (RADAR) - Radar Cross Section of Modified Target Using Gaussian Beam Methods: Experimental Validation
摘要： The aim of this paper is to study the Radar Cross Section (RCS) of modified radar targets (plate with notch) using Gaussian Beam techniques. The Gaussian methods used in this work are Gaussian Beam Summation (GBS) and Gaussian Beam Launching (GBL). We establish the theoretical formulation of the GBS and GBL techniques and analyze the influence of the main Gaussian beam parameters on the variation of the scattered field. Then, we present the simulations of RCS. The numerical results are compared with PO, MoM methods, and also with experimental measurements performed in the anechoic chamber at Lab-STICC (ENSTA Bretagne).
关键词： Radar Cross Section (RCS),Physical Theory of Diffraction (PTD),Physical Optic (PO),Gaussian Beam Summation (GBS),Gaussian Beam Launching(GBL),Method of Moment (MoM)
更新于2025-09-23 15:22:29
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Size-Dependent Buckling and Vibrations of Piezoelectric Nanobeam with Finite Element Method
摘要： In the present paper, a finite element method is used to study the vibrations and buckling of a piezoelectric nanobeam. The beam theory used here is Bernoulli–Euler model. In order to achieve the goal, first, the governing equations of the piezoelectric nanobeam were obtained via the Hamilton principle, based on the higher-order theory such as modified couple stress. The shape functions were embedded in these equations, and the matrix form of the equations was obtained. In other words, the governing equations were discretized by the finite element method. By calculating the matrix form of equations, mass matrices, mechanical stiffness and electrical stiffness of the beam were obtained. It should be noted that when calculating stiffness matrices, first, the definition of a new element must be added to the effects of the electric field in the elements of the beam, and the effects of the gradient of strain should be added in the form of non-classical matrix to the stiffness matrix. With the aid of these critical load matrices, the buckling force and voltage and the natural frequency of the piezoelectric nanobeam have been calculated. Numerical results show that this method can involve the size effects.
关键词： Size effect,Piezoelectric,Buckling voltage,Couple stress theory,Free vibration,Buckling load
更新于2025-09-23 15:22:29
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[IEEE 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Austin, TX, USA (2018.9.24-2018.9.26)] 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Biaxial Strain based Performance Modulation of Negative-Capacitance FETs
摘要： In this work, we report device simulations conducted to study the performance of biaxially strained ferroelectric-based negative capacitance FETs (NCFETs). We adopted PbZr0.5Ti0.5O3 (PZT) and HfO2 as ferroelectric materials and applied biaxial strain using the first-principles method. It was found that PZT and HfO2 show different trends in the negative capacitance (NC) region under biaxial strain. Biaxial strain strongly affects the NC of PZT, whereas HfO2 is not as susceptible to biaxial strain as PZT. When no strain is applied, HfO2-based NCFETs exhibit a better performance than PZT-based NCFETs. However, the subthreshold slope and ON-state current are improved in the case of PZT-based NCFETs when the compressive biaxial strain is increased, whereas the performance of HfO2-based NCFETs is slightly degraded. In particular, the negative drain-induced barrier lowering and negative differential resistance vary considerably when compressive strain is applied to PZT-based NCFETs.
关键词： strain,negative capacitance FETs,ferroelectrics,density functional theory,HfO2,PZT
更新于2025-09-23 15:22:29
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A hypothesis testing approach for communication over entanglement assisted compound quantum channel
摘要： We study the problem of communication over a compound quantum channel in the presence of entanglement. Classically such a channel is modeled as a collection of conditional probability distributions wherein neither the sender nor the receiver is aware of the channel being used for transmission, except for the fact that it belongs to this collection. We provide near optimal achievability and converse bounds for this problem in the one-shot quantum setting in terms of the quantum hypothesis testing divergence. We also consider the case of informed sender, showing a one-shot achievability result that converges appropriately in the asymptotic and i.i.d. setting. Our achievability proof is similar in spirit to its classical counterpart. To arrive at our result, we use the technique of position-based decoding along with a new approach for constructing a union of two projectors, which might be of independent interest. We give another application of the union of projectors to the problem of testing composite quantum hypotheses.
关键词： quantum hypothesis testing,one-shot information theory,position-based decoding,compound quantum channel,entanglement-assisted communication
更新于2025-09-23 15:22:29
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Circular Corrugated Miter Bend and Gap Losses for Broadband Frequency Applications
摘要： Circular corrugated waveguides are often used in fusion applications at single, multiple, or broadband millimeter frequencies due to their low ohmic loss, expected large frequency bandwidth, and direct coupling to free-space Gaussian modes. For single-frequency corrugated waveguide systems, transmission line components can be optimized to the desired frequency. For broadband or multiple-frequency applications, this is not possible. The goal of this paper is to demonstrate that the frequency bandwidth of circular corrugated waveguides can be compromised by diffraction losses to miter bends and gaps. It is shown that if the corrugation depth differs significantly from λ/4, a theory can substantially underpredict the gap and miter bend losses. The simulations are also shown to compare favorably to experimental measurements. To improve the transmission line performance in large frequency bandwidth systems, such as 33–165 GHz reflectometry, reducing the number of miter bends may, therefore, be necessary. For the improvement of performance in narrower frequency bandwidth or multiple-frequency systems, especially high-powered systems, wavelength-dependent techniques may be applicable. One such application is shown for a Bragg reflection technique to reduce the thermal load to insulating ceramic rings in a dc break component for multiple-frequency ITER electron cyclotron heating transmission lines.
关键词： gap,miter bend,full-wave simulation,waveguide theory,Corrugated waveguide
更新于2025-09-23 15:22:29
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Structural, energetic and spectroscopic studies of new luminescent complexes based on 2-(2′-hydroxyphenyl)imidazo[1,2- <i>a</i> ]pyridines and 1,2-phenylenediboronic acid
摘要： Three new blue-luminescent complexes of selected imidazo[1,2-a]pyridine derivatives and 1,2-phenylenediboronic acid have been synthesized and structurally characterized using single-crystal X-ray diffraction. Additionally, the crystal structures of two of the (N,O)-donor compounds have been evaluated for the first time. The crystal packing and molecular motifs observed in the studied crystals have been thoroughly analysed, including computational studies, and are also discussed within the context of analogous systems reported in the literature. It appears that the new compounds form different crystal networks with regard to the asymmetric unit content and packing, although some similarities can be found. In all cases a typical centrosymmetric dimer bound via boronic acid groups is formed, characterized by an interaction energy of about -80 kJ mol-1, while the 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine complex and its methoxy derivative form solvate structures, somewhat resembling the previously studied 8-oxyquinolinate analogues. As far as the spectroscopic properties are concerned, the lowest energy excitation observed in the studied complexes is based on the highest occupied molecular orbital–lowest unoccupied molecular orbital transition, and both these molecular orbitals are centred predominantly on the (N,O)-donor species according to the results of time-dependent density functional theory. Thus, the charge transfer observed for the 8-oxyquinolinate equivalents does not occur in these cases. Consequently, the spectroscopic behaviour of the series is very much comparable with that of the parent imidazo[1,2-a]pyridine derivatives, if the excited-state intramolecular proton-transfer process does not take place, as shown by the absorption and emission spectra collected in toluene and acetone solutions. Complexation causes a reduction in the Stokes shift compared with the respective (N,O)-donor molecules.
关键词： periodic calculations,TDDFT,UV–Vis spectroscopy,X-ray diffraction,time-dependent density functional theory,spectroscopic properties,luminescent boron complexes,transferred aspherical atom model (TAAM) refinement
更新于2025-09-23 15:22:29