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Effects of Microsphere Size on the Mechanical Properties of Photonic Crystals
摘要： Photonic crystal (PC) thin films that are self-assembled from different-sized silica microspheres were prepared for studying mechanical properties via nanoindentation at the submicron scale. We found that the silica photonic crystals (PCs) possessed a face-centered cubic (FCC) microstructure and their elastic modulus and hardness were in the range of ~1.81–4.92 GPa and 0.008–0.033 GPa, respectively. The calculated results proved that there were size-dependent properties in the silica PCs, in that the elastic modulus and hardness increased as the diameter decreased from 538 nm to 326 nm. After studying the total work and plastic work in the progressive deformation of silica PCs during the nanoindentation tests, we developed a two-stage deformation model to explain how the microsphere size affects the mechanical properties of PC thin films. The phenomenon of 'smaller is stronger' is mainly due to the energy consumption, which combines the effects of microstructure collapse, microsphere slide, and reduced porosity during the whole loading and unloading process. In addition, the results of numerical simulation matched the experimental data and reflected the energy change rules of PCs during the indentation process. Furthermore, the study affords useful guidance for constructing high-performance films with proper design and potential application in next-generation PC materials.
关键词： photonic crystals,deformation mechanism,nanoindentation,size-dependent
更新于2025-09-23 15:22:29
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Effect of Size, Coverage, and Dispersity on the Potential-Controlled Ostwald Ripening of Metal Nanoparticles
摘要： Here we describe the size-dependent, electrochemically-controlled Ostwald ripening of 1.6, 4 and 15 nm diameter Au nanoparticles (NPs) attached to (3-aminopropyl)triethoxysilane (APTES)-modified glass/Indium tin oxide (glass/ITO) electrodes. Holding the Au NP-coated electrodes at a constant potential negative of the dissolution potential in bromide-containing electrolyte led to electrochemical Ostwald ripening of the different-sized Au NPs. The relative increase in the diameter of the NPs (Dfinal/Dinitial) during electrochemical Ostwald ripening increases with decreasing NP size, increasing applied potential, increasing NP population size dispersity, and increasing NP coverage on the electrodes. Monitoring the average size of the Au NPs as a function of time at a controlled potential allows the measurement of the Ostwald ripening rate. Anodic stripping voltammetry (ASV) and electrochemical determination of the surface area-to-volume ratio (SA/V) provides fast and convenient size analysis for the many different samples and conditions, with consistent sizes from scanning electron microscopy (SEM) images for some samples. It is important to better understand electrochemical Ostwald ripening, especially under potential control, since it is a major process that occurs during the synthesis of metal NPs and leads to detrimental size instability during electrochemical applications.
关键词： electrochemical control,surface area-to-volume ratio,anodic stripping voltammetry,size-dependent,metal nanoparticles,Ostwald ripening
更新于2025-09-23 15:19:57
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Comparison of size-dependent characteristics of blue and green InGaN microLEDs down to 1a?? <b> <i>??</i> </b> m in diameter
摘要： There is growing interest in microLED devices with lateral dimensions between 1 and 10 lm. However, reductions in external quantum ef?ciency (EQE) due to increased nonradiative recombination at the surface become an issue at these sizes. Previous attempts to study size-dependent EQE trends have been limited to dimensions above 5 lm, partly due to fabrication challenges. Here, we present size-dependent EQE data for InGaN microLEDs down to 1 lm in diameter fabricated using a process that only utilizes standard semiconductor processing techniques (i.e., lithography and etching). Furthermore, differences in EQE trends for blue and green InGaN microLEDs are compared. Green wavelength devices prove to be less susceptible to reductions in ef?ciency with the decreasing size; consequently, green devices attain higher EQEs than blue devices below 10 lm despite lower internal quantum ef?ciencies in the bulk material. This is explained by smaller sur- face recombination velocities with the increasing indium content due to enhanced carrier localization.
关键词： InGaN,microLEDs,size-dependent characteristics,external quantum efficiency,blue and green wavelengths
更新于2025-09-23 15:19:57
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Dynamic growth of rhombic dodecahedral Cu <sub/>2</sub> O crystals controlled by reaction temperature and their size-dependent photocatalytic performance
摘要： Compared with low-index {100} or {111} planes of Cu2O crystals, rhombic dodecahedra (RD) Cu2O crystals exposing 12 {110} facets exhibit the most superior photodegradation of organic pollutants. Herein, a series of RD Cu2O crystals with different sizes were successfully synthesized by precisely adjusting the reaction temperature ranging from 40 °C to 100 °C. The results revealed that truncated rhombic dodecahedra (TRD) Cu2O crystals were fabricated when the temperatures was 40 °C. More importantly, on raising the temperature to above 40 °C, Cu2O architectures dynamically evolved from TRD to RD. Meanwhile, the sizes gradually decreased with elevation of the temperature, while the RD morphology of Cu2O crystals remained, demonstrating the importance of temperature for determining the morphology and size of Cu2O crystals. In addition, we also carefully investigated the visible-light photodegradation performance of Cu2O crystals for methyl orange (MO). RD Cu2O crystals exhibited superior photocatalytic activity compared with TRD, and showed size-dependent photocatalytic activity for MO. The photocatalytic activity of RD Cu2O crystals can be greatly improved by decreasing the size. In particular, RD-60 with the minimum size achieved the best photocatalytic properties compared to the other RD and TRD Cu2O crystals, and still displayed high photocatalytic efficiency even after three cycles. Such results advance the understanding that temperature modulation serves as an effective means to fabricate RD Cu2O crystals.
关键词： size-dependent photocatalytic performance,photodegradation,reaction temperature,Cu2O crystals,rhombic dodecahedra
更新于2025-09-16 10:30:52
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Two-Dimensional Phosphorene, Arsenene, Antimonene Quantum Dots: Anomalous Size-Dependent Behaviors of Optical Properties
摘要： Employing size effect to tailor photo-absorption and -emission properties of quantum dots (QDs) nanostructures is a widely used method for optoelectronic and biomedical applications. In this work, based on time-dependent density functional theory calculations, we systematically research the size-dependent optical absorption and emission properties of two-dimensional phosphorene, arsenene, antimonene single-element QDs. As expected, the photo-absorption gap presents monotonically decreasing with the increase of QDs diameter which is consistent with the well-accepted quantum confinement effect (QCE). Surprisingly, the emission gap increases with the increase of size within ~3 nm diameter range. It is revealed that the anomalous phenomenon derives from the competition between the QCE and excited state structure rearrangement during the relaxation of excited state. The smaller two-dimensional QDs is more prone to structure deformation at excited state accompanied with the greater change of electronic structure, which prevails over the QCE and reduces the emission gap. The atomic level picture of anomalous emission phenomenon revealed in our research is valuable for the fundamental understanding size effect of QDs as well as for optical utilization in optoelectronics and biomedical field.
关键词： quantum dots,antimonene,optical properties,phosphorene,arsenene,size-dependent behaviors
更新于2025-09-16 10:30:52
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Excitation-wavelength- and size-dependent photo-darkening and photo-brightening of photoluminescence from PbS quantum dots in glasses
摘要： PbS quantum dots (QDs) with mean radii of 3.7 nm to 9.0 nm are precipitated in silicate glasses. Upon above-band-gap excitation, photoluminescence from QDs is strongly dependent on their size and excitation wavelength, exhibiting photo-darkening (PD) or photo-brightening (PB). Photoluminescence of PbS QDs exhibits strong darkening by short excitation wavelength but the darkening gradually mitigated as the excitation wavelength increased and even turns to be photo-brightening at room temperature. But PD and PB show a much more complicated variation tendency under the same excitation condition when the size of QDs increased. The dependence of PD and PB on the QDs’ size and excitation wavelength indicates that electron/hole trap states of PbS QDs, defect states in surrounding glass matrix as well as on the interface between the glass matrix and PbS QDs all have strong effects on the photoluminescence properties of PbS QDs. These findings are important to modulate the photoluminescence and promote the potential applications of PbS QDs embedded glasses towards various optoelectronic devices.
关键词： photoluminescence,PbS quantum dots,photo-darkening,excitation wavelength,size-dependent,photo-brightening
更新于2025-09-12 10:27:22
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Size-dependent dielectric function for electron-energy-loss spectra of plasmonic nanoparticles
摘要： A size-dependent complex dielectric function is proposed to describe the impact that size effects have on the dielectric response for electron energy loss spectroscopy (EELS) of plasmonic nanoparticles. Our implementation is based on experimental bulk complex refractive index and the modification of the Lorentz-Drude model. Our theoretical framework is verified and analysed by performing numerical simulation comparisons of EELS for Au spherical nanoparticles of different sizes. The results show that finite-size effects cannot be neglected for a broader size range of up to at least 200 nm for Au spherical nanoparticles. Moreover, the EELS regions in which contributions of surface or bulk energy loss are dominant are confirmed by the optical extinction spectra of Au spherical nanoparticles of different sizes, which takes into account the size-dependent dielectric function. The results provided here provide a suitable and versatile framework for the design of plasmonic elements on the nanometre scale.
关键词： metallic nanoparticles,Plasmonics,size-dependent dielectric function,surface plasmon,electron energy loss spectroscopy (EELS)
更新于2025-09-12 10:27:22
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On the numerical investigation of size and surface effects on nonlinear dynamics of a nanoresonator under electrostatic actuation
摘要： This study aims to investigate the influences of nanostructure parameter and surface elasticity parameters on the nonlinear vibration of a nanoelectromechanical system under double-sided electrostatic actuation. For this, the effects of size dependency and surface energy are modeled through applying the consistent couple-stress theory together with the Gurtin–Murdoch elasticity theory. Taking into account the midplane stretching effect for doubly clamped boundary conditions, the nonlinear strain–displacement relationship is considered based on the Euler–Bernoulli beam assumption. Hamilton’s principle is utilized in order to establish the governing differential motion’s equation, and reduced-order model is obtained through implementing Galerkin’s procedure. Bifurcation diagrams are plotted to capture the steady-state response of the system with varying the nondimensional parameter, the ratio of AC to DC voltage amplitude. The influences of the length-scale parameter, surface elasticity modulus and density, and residual surface stress on the system dynamic response have been explored. The results reveal that the pull-in excitation frequency is highly influenced by these parameters, and also the interval length of the bifurcation parameter corresponding to the periodic and chaotic motions is extremely shifted by the amount of couple-stress and residual surface stress parameters.
关键词： Size-dependent NEMS,Chaos,Bifurcation,Surface effects
更新于2025-09-09 09:28:46
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Size Effects in Vibrating Silicon Crystal Microbeams
摘要： The vibrations of ultrathin silicon cantilever microbeams are studied using consistent couple-stress theory to investigate size-dependent effects. The corresponding Euler-Bernoulli beam theory is used to estimate the couple-stress length scale parameter of single crystal silicon, based on measured experimental data for the resonant frequency of cantilever microbeams. The present work demonstrates that conventional use of classical beam theories, along with rigidly clamped cantilever boundary conditions, can lead to misinterpretation of experimental data, necessitating the introduction of nonphysical size-dependent effective material properties, such as an effective Young’s modulus. Alternatively, proper modeling of the cantilever boundary conditions combined with use of couple-stress theory can account for the observed mechanical scale dependence in silicon micro- and nanostructures from fundamental principles of continuum mechanics. Moreover, the modeling approach presented here can be generalized to other micro- and nanoscale structures and materials. As such, the developed approach may be useful for the rational design of additional novel applications of such structures, ranging from optomechanical transducers to ultrasensitive biochemical sensors.
关键词： Effective material properties,Resonant nano- and microcantilever sensors,Size-dependent silicon material properties,Resonant nano- and microcantilever transducers,Nanotechnology,Resonant nano- and microcantilevers
更新于2025-09-09 09:28:46