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Enhancing the Performance of Commercial Infrared Detectors by Surface Plasmons
摘要： The feasibility to improve the response of quantum type (photonic) infrared (IR) detectors by applying surface plasmons is investigated. The HgCdTe material system is used as the detector platform of interest for which selected plasmonic structures and materials are applied and the influence studied by full-fielded electromagnetic simulations. It is shown that even for the several-micrometers-thick detector structures, similar to the commercial ones, broadband absorption enhancements of 30–40% can be achieved. The results suggest that improved, or new, pixel-level functionalities can be created for commercial IR detectors by relatively simple means. Additionally, high potential for cost reduction in high-performance IR imaging systems with multicolour capabilities is foreseen.
关键词： plasmonics,finite element method,computational simulations,infrared detectors
更新于2025-09-23 15:23:52
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Wetting Transition from the Cassie–Baxter State to the Wenzel State on Regularly Nanostructured Surfaces Induced by an Electric Field
摘要： When droplets are placed on hydrophobic textured surfaces, different wetting state Cassie-Baxter (CB) state or Wenzel (W) state may occur depending on materials and structures of surfaces, types and sizes of droplets, thermal fluctuations, and external stimuli. The wetting transition from the CB to the W state and the opposite process have attracted a great deal of attention due to their primary importance for designing and fabricating textured surfaces. In this work, molecular dynamics (MD) simulations are employed to understand the mechanism behind the CB-to-W transition for a nanoscale water film placed on a surface decorated with a single nanogroove when an external electric field is applied. The free energy variation during the transition process is computed on the basis of the restrained MD simulations. Water intrusion into the groove is observed by simulation snapshots, which provides a direct evidence for the electric-field-induced CB-to-W transition. In the previous experiments, however, only a sharp reduction in the apparent contact angle is employed to judge whether the transition takes place. The free energy curves reveal that there are two energy barriers separating the CB and W states (?E1) as well as separating the W and CB states (?E2). Owing to the presence of ?E1, although the CB state has a higher free energy than the W state, it cannot spontaneously convert to the W state. When the external energy input exceeds ?E1, the CB-to-W transition can be triggered, otherwise the transition will stop, and the water film will return to the CB state. Moreover, it is found that the maximum of free energy always occurs after the film touches the groove bottom. Thus, the requirement of the film touching the groove bottom is responsible for the presence of the energy barrier ?E1. Finally, the dependences of the two energy barriers on the electric field strength, groove aspect ratio, and intrinsic contact angle of the groove are also discussed.
关键词： Cassie-Baxter state,wetting transition,Wenzel state,energy barrier,free energy,molecular dynamics simulations.
更新于2025-09-23 15:23:52
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Development of a Visual Field Simulation Model of Longitudinal Point-Wise Sensitivity Changes From a Clinical Glaucoma Cohort
摘要： Purpose: To develop a new visual field simulation model that can recreate real-world longitudinal results at a point-wise level from a clinical glaucoma cohort. Methods: A cohort of 367 glaucoma eyes from 265 participants seen over 10.1 ± 2.5 years were included to obtain estimates of "true" longitudinal visual field point-wise sensitivity and estimates of measurement variability. These two components were then combined to reconstruct visual field results in a manner that accounted for correlated measurement error. To determine how accurately the simulated results reflected the clinical cohort, longitudinal variability estimates of mean deviation (MD) were determined by calculating the SD of the residuals from linear regression models fitted to the MD values over time for each eye in the simulated and clinical cohorts. The new model was compared to a previous model that does not account for spatially correlated errors. Results: The SD of all the residuals for the clinical and simulated cohorts was 1.1 dB (95% confidence interval [CI]: 1.1–1.2 dB) and 1.1 dB (95% CI: 1.1–1.1 dB), respectively, whereas it was 0.4 dB (95% CI: 0.4–0.4 dB) using the previous simulation model that did not account for correlated errors. Conclusions: A new simulation model accounting for correlated measurement errors between visual field locations performed better than a previous model in estimating visual field variability in glaucoma. Translational Relevance: This model can provide a powerful framework to better understand use of visual field testing in clinical practice and trials and to evaluate new methods for detecting progression.
关键词： visual field,glaucoma,simulations,longitudinal
更新于2025-09-23 15:22:29
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Revisiting the structures and energies of silicon ?110? symmetric tilt grain boundaries
摘要： Atomistic simulations of 18 silicon ?110? symmetric tilt grain boundaries are performed using Stillinger Weber, Tersoff, and the optimized Modified Embedded Atom Method potentials. We define a novel structural unit classification through dislocation core analysis to characterize the relaxed GB structures. GBs with the misorientation angle h ranging from 13.44° to 70.53° are solely composed of Lomer dislocation cores. For GBs with h less than but close to 70.53°, GB 'step' appears and the equilibrated states with lowest GB energies can be attained only when such GB 'step' is located in the middle of each single periodic GB structure. For the misorientation angles in the range of 93.37° ￡ h ￡ 148.41°, GB structures become complicated since they contain multiple types of dislocation cores. This work not only facilitates the structural characterization of silicon ?110? STGBs, but also may provide new insights into mirco-structure design in multicrystalline silicon.
关键词： silicon,structural units,energies,grain boundaries,atomistic simulations,dislocation cores
更新于2025-09-23 15:22:29
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Structure/Function/Dynamics of Photosystem II Plastoquinone Binding Sites
摘要： Photosystem II (PSII) continuously attracts the attention of researchers aiming to unravel the riddle of its functioning and efficiency fundamental for all life on Earth. Besides, an increasing number of biotechnological applications have been envisaged exploiting and mimicking the unique properties of this macromolecular pigment-protein complex. The PSII organization and working principles have inspired the design of electrochemical water splitting schemes and charge separating triads in energy storage systems as well as biochips and sensors for environmental, agricultural and industrial screening of toxic compounds. An intriguing opportunity is the development of sensor devices, exploiting native or manipulated PSII complexes or ad hoc synthesized polypeptides mimicking the PSII reaction centre proteins as biosensing elements. This review offers a concise overview of the recent improvements in the understanding of structure and function of PSII donor side, with focus on the interactions of the plastoquinone cofactors with the surrounding environment and operational features. Furthermore, studies focused on photosynthetic proteins structure/function/dynamics and computational analyses aimed at rational design of high-quality bio-recognition elements in biosensor devices are discussed.
关键词： plastoquinone binding site,molecular dynamics simulations,plastoquinone,Molecular docking,protein dynamics,Photosystem II
更新于2025-09-23 15:22:29
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Design and performance evaluation of high resolution small animal PET scanner based on monolithic crystal: a simulation study
摘要： Dedicated small-animal PET scanners functionality can be optimized by improving the sensitivity and spatial resolution of the scanner. Approximately most of the developed and commercially available small-animal PET scanners are equipped with pixelated scintillators; therefore, their spatial resolution is limited to the crystal pixel size. Complex fabrication, low-sensitivity, and disability in depth of interaction calculation (DOI) are the major disadvantages of pixelated crystals. However, monolithic scintillator crystals are known as one of the most commonly used substitutions, as they have higher sensitivity, DOI recognition, and lower cost. We already designed and implemented a dedicated small-animal PET scanner based on pixelated scintillator crystals and silicon photomultiplier (SiPM). In this study, we plan to present a new optimized design based on the monolithic crystal, with similar performance by the previous scanner. Then we would optimize the thickness of the monolithic crystals for animal PET scanners as a function of sensitivity and spatial resolution. All simulations were performed based on GEANT4, a validated Monte Carlo toolkit. We simulated a recently fabricated scanner with pixelated crystals and compared it with a simulated scanner based on an optimized monolithic crystal. The experimental setup used for comparison and validation is a small Animal PET consisting of ten pixelated modules. This study anticipates that by replacing a pixelated crystal (consist of 24 × 24 LYSO elements, and 2 × 2 × 10 mm3 crystal size) with a monolithic crystal (with 8 mm thickness and 50.2 × 50.2 entrance area), the average spatial resolution stays the same and sensitivity grows ～ 17% in the center of AFOV and also the fabrication cost dives remarkably. Simulation reveals that although the depth of interaction DOI was not taken into consideration, the crystals with 6 mm thickness have acceptable spatial resolution (～ 1.3 mm FWHM at the centre of the AFOV) and relatively good absolute sensitivity (～ 1.6%).
关键词： SPECT,coronary CT angiography (CTA),PET PET/CT,Gamma camera,Models and simulations
更新于2025-09-23 15:22:29
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Numerical analysis of single-point spectroscopy curves used in photo-carrier dynamics measurements by Kelvin probe force microscopy under frequency-modulated excitation
摘要： In recent years, the investigation of the complex interplay between the nanostructure and photo-transport mechanisms has become of crucial importance for the development of many emerging photovoltaic technologies. In this context, Kelvin probe force microscopy under frequency-modulated excitation has emerged as a useful technique for probing photo-carrier dynamics and gaining access to carrier lifetime at the nanoscale in a wide range of photovoltaic materials. However, some aspects about the data interpretation of techniques based on this approach are still the subject of debate, for example, the plausible presence of capacitance artifacts. Special attention shall also be given to the mathematical model used in the data-fitting process as it constitutes a determining aspect in the calculation of time constants. Here, we propose and demonstrate an automatic numerical simulation routine that enables to predict the behavior of spectroscopy curves of the average surface photovoltage as a function of a frequency-modulated excitation source in photovoltaic materials, enabling to compare simulations and experimental results. We describe the general aspects of this simulation routine and we compare it against experimental results previously obtained using single-point Kelvin probe force microscopy under frequency-modulated excitation over a silicon nanocrystal solar cell, as well as against results obtained by intensity-modulated scanning Kelvin probe microscopy over a polymer/fullerene bulk heterojunction device. Moreover, we show how this simulation routine can complement experimental results as additional information about the photo-carrier dynamics of the sample can be gained via the numerical analysis.
关键词： Kelvin probe force microscopy,nanostructured photovoltaics,numerical simulations,photo-carrier dynamics,carrier dynamics,carrier recombination,carrier lifetime
更新于2025-09-23 15:22:29
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Research of the substituent effect on non-linear optical properties of bis(difluoroboron)-1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine (BOPHY) derivatives: Molecular simulation analyses
摘要： Modelling studies of bis(difluoroboron)-1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine (BOPHY) derivatives were completed at M06-2X/6-31+G(d) level in vacuo. Structural properties (geometric structure, bond lengths and angles), spectral electronic properties and non-linear optical properties (NLO) of related boron complexes were investigated. Geometric parameters of mentioned boron complexes and electronic structures of them were reported. IR spectrum of boron complexes are calculated in vacuo and potential energy distribution (PED) analyses of frequencies were done. UV-VIS spectrum were calculated in gas phase (ε=1), toluene (ε=2.3741), chloroform (ε=4.7113), methanol (ε=32.613), water (ε=78.3553) and n-methylformamide-mixture (ε=181.56) at M06-2X/6-31+G(d), wB97X-D/6-31+G(d) and CAM-B3LYP/6-31+G(d) levels. Wavelength of observed bands in UV-VIS spectrum were used in the interpretation of optical activity. Molecular orbital energy diagram (MOED), contour diagrams of certain molecular orbitals, density of state (DOS) spectrum and molecular electrostatic potential (MEP) maps are calculated to determination of electronic properties and NLO activity. Finally, some quantum chemical descriptors were calculated and analyzed in determination of NLO properties. It is found that compound 5 and 6 are found as the good materials for NLO applications.
关键词： Hydrazine,Molecular Simulations,BOPHY,Bipyrrole,Optical Properties
更新于2025-09-23 15:22:29
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Multi-fidelity EM simulations and constrained surrogate modelling for low-cost multi-objective design optimisation of antennas
摘要： In this study, a technique for low-cost multi-objective design optimisation of antenna structures has been proposed. The proposed approach is an enhancement of a recently reported surrogate-assisted technique exploiting variable-fidelity electromagnetic (EM) simulations and auxiliary kriging interpolation surrogate, the latter utilised to produce the initial approximation of the Pareto set. A bottleneck of the procedure for higher-dimensional design spaces is a large number of training data samples necessary to construct the surrogate. Here, the authors propose a procedure that allows us to confine the model domain to the subset spanned by the reference points, including the extreme Pareto-optimal designs obtained by optimising the individual objectives as well as an additional design that determines the Pareto front curvature. Setting up the surrogate in the constrained domain leads to a dramatic reduction of the required number of data samples, which results in lowering the overall cost of the optimisation process. Furthermore, the model domain confinement is generic, i.e. applicable for any number of design goals considered. The proposed technique is demonstrated using an ultra-wideband monopole antenna optimised with respect to three objectives. Significant reduction of the design cost is obtained as compared to the reference surrogate-assisted algorithm.
关键词： Pareto set,antenna structures,variable-fidelity EM simulations,kriging interpolation surrogate,multi-objective design optimisation,ultra-wideband monopole antenna
更新于2025-09-23 15:21:21
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Density, Structure, and Stability of Citrate <sup>3–</sup> and H <sub/>2</sub> Citrate <sup>–</sup> on Bare and Coated Gold Nanoparticles
摘要： We simulate the packing of citrate3– and H2citrate– onto gold nanoparticles (AuNPs) to understand how citrate anions cap and stabilize AuNPs. We determine the molecular configurations of citrate on 4, 6, and 8 nm AuNP surfaces as a function of charge state and packing density and find that both the distribution of configurations and maximum packing density are independent of AuNP size. A combination of molecular dynamics simulations and in situ Fourier transform infrared spectroscopy (FTIR) is employed to compare the molecular configurations, stability, and density of citrate on 4 nm citrate-coated (cit-AuNPs) and within polycation-wrapped 4 nm cit-AuNPs. FTIR experiments indicate the presence of H2citrate– within polycation-wrapped cit-AuNPs with coordination between the H2citrate– layer and polycation layer in agreement with simulations. Intermolecular hydrogen bonding between terminal carboxylic-acid groups of H2citrate– stabilizes the anionic layer at the interface between cit-AuNPs and adsorbing charged molecules. The calculated total density of H2citrate– on AuNPs decreases from 3.3 × 10-10 mol/cm2 to 3.0 × 10-10 mol/cm2 upon adsorption of a polycation due to some displacement of dangling H2citrate– hydrogen bonded to the surface-bound layer. The density of the surface-bound layer is consistently 2.8 × 10-10 mol/cm2 with and without polycation adsorption. We provide all-atom level insight into the distribution and organization of experimentally derived binding modes of citrate on bare and coated cit-AuNPs. The citrate density and surface charge density are determined for all-atom and coarse-grained modeling of cit-AuNPs, their functionalization, and transformations in complex environments.
关键词： polycation adsorption,gold nanoparticles,FTIR spectroscopy,citrate,molecular dynamics simulations
更新于2025-09-23 15:21:21