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Electron surface scattering and quantum finite-size effect on dielectric and optical properties of thin gold films
摘要： With the size of metal nanostructures entering into the nanoscale region, electron surface scattering and quantum finite-size effect gradually dominate the physical properties of surface plasmon resonances. In this context, we investigate both the quantum corrected dielectric functions and the absorption spectra of thin gold films for different thickness by excluding and including electron surface scattering. Our results show that when don't taking into account electron surface scattering, the multiple peaks appear for both the quantum-corrected dielectric functions and the absorption spectra of thin gold films, which features the discretization of electronic states in small quantum-sized system. When including electron surface scattering, however, the multipeak structures are masked and even disappear due to a large broadening of themselves. The transition from the quantum results to the classical ones for increasing thickness is also clearly demonstrated for the two cases. Although we only discuss the dielectric function and optical absorption of gold films with quantum sizes, the phenomena are expected to be exhibited in other metal nanostructures. Our findings enrich our understanding of both electron surface scattering and quantum finite-size effect in small metal nanostructures, and pave the way for the designs of quantum plasmonic devices.
关键词： Quantum finite-size effect,Electron surface scattering
更新于2025-09-23 15:23:52
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Inverse size-dependence of piezoelectricity in single BaTiO3 nanoparticles
摘要： The piezoelectric charge coefficients d33 of single BaTiO3 (BT) nanoparticles (NPs) were characterized using a transmission electron microscope (TEM) that is equipped with a precise charge meter and an in-situ TEM indentation holder that enables controlled compression experiments. An exceptionally high d33 of 1775 pC/N was obtained in NPs that are smaller than the critical diameter (D; typically known as < 100 nm) that has been regarded as the lower limit to permit for ferroelectricity in BT. The mechanical conversion efficiency of piezoelectric BT nanogenerators enhanced as D of BT NPs was decreased; this result corresponds with the single-NP compression measurements of d33. This quantification of the effect of D in ferroelectric materials may guide development of efficient and high-powered nanostructured piezoelectric energy devices such as piezoelectric nanogenerators.
关键词： in-situ TEM,size effect,STEM,Ferroelectric,piezoelectric,nanogenerator
更新于2025-09-23 15:23:52
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Néel transition in the multiferroic BiFeO <sub/>3</sub> -0.25PbTiO <sub/>3</sub> nanoparticles with anomalous size effect
摘要： The role of size reduction on the structural parameters, antiferromagnetic transition temperature (TN), and spin reorientation transition temperature of BiFeO3-0.25PbTiO3 (BF-0.25PT) has been studied. Rietveld analysis using high resolution synchrotron x-ray powder diffraction data confirms that the space group of BF-0.25PT solid solutions is monoclinic Cc and not rhombohedral R3c for both bulk and nanocrystalline powders. This settles a longstanding controversy about the structure of these solid solutions toward the BiFeO3 rich end of the morphotropic phase boundary in the BiFeO3-xPbTiO3 system. Using magnetization and neutron powder diffraction data, we show that the Néel transition temperature (TN) of BF-0.25PT increases from 445 K for bulk to 480 K for 150 nm particle size. This is in marked contrast to the scaling theories of phase transitions in finite size systems. We also show that the spin reorientation transition occurring below TN in bulk monoclinic compositions like BF-0.25PT is suppressed in the nanocrystalline samples of ～150 nm particle size. Based on Rietveld refined structural parameters, we show that the asymmetry and non-linearity of the Fe-O-Fe superexchange pathways grow with decreasing particle size and that they exhibit a strong correlation with TN. We believe that the substantially enhanced Dzyaloshinskii-Moriya interaction with decreasing particle size as a result of asymmetric and non-collinear Fe-O-Fe superexchange pathways may be the key factor in raising the TN on decreasing the particle size. These observations present a new facet of type-I multiferroic materials, where superexchange pathways are intimately dependent on the ferroelectric distortion.
关键词： multiferroic,antiferromagnetic transition,BiFeO3-PbTiO3,size effect,Dzyaloshinskii-Moriya interaction,Néel transition,nanoparticles
更新于2025-09-23 15:23:52
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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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The Size Effect of Exfoliated MoS <sub/>2</sub> Based Thin Film Humidity Sensor
摘要： Layered two-dimensional nanomaterials such as MoS2 show great potential for sensor application owing to their distinct nature that most atoms are surface atoms. The difficult in mass production of exfoliated MoS2 hinders its practical application. In this study, we investigate the ultrasound assisted liquid method to efficiently exfoliate MoS2 into nanosheets and nanoparticles. The dependence of ultrasonic dosing, e.g., ultrasonic time, on the morphology and yield of final products are studied. The exfoliated MoS2 nanomaterials are fabricated into thin film sensors and examined with humidity gas. The sensors exhibit excellent and quick response toward humidity gas. We find the sensor prepared with longer ultrasonic treatment presents higher response owing to that the longer ultrasonic irradiation exposes more active edge sites.
关键词： Exfoliation,Humidity Sensor,MoS2,Size Effect,Thin Film
更新于2025-09-23 15:22:29
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Surface plasmon-enhanced solution-processed phosphorescent organic light-emitting diodes by incorporating gold nanoparticles
摘要： Organic light-emitting diodes (OLEDs) have attracted increasing attention due to their superiority as high quality displays and energy-saving lighting. However, improving the efficiency of solution-processed devices especially based on blue emitter remains a challenge. Excitation of surface plasmons on metallic nanoparticles has potential for increasing the absorption and emission from optoelectronic devices. We demonstrate here that the incorporation of gold nano particles (GNPs) in the hole injection layer of poly(3,4-ethylene dioxythiophene):polystyrene sulfonic acid with an appropriate size and doping concentration can greatly enhance the efficiency OLED device especially at higher voltage. Apparently, the spectral of the multiple plasmon resonances of the GNPs and the luminescence of the emitting materials significantly overlap with each other. At 1000?cd/m2 for example, the power efficiency of a studied green device is increased from 29.0 to 36.2 lm/W1, an increment of 24.8%, and the maximum brightness improved from 21,550 to 27,810?cd/m2, an increment of 29.1%, as 2 wt% of a 12 nm GNP is incorporated. Remarkably, designed blue OLED also exhibited an increment of 50% and 35% in power efficacy at 100 and 1,000 cd/m2, respectively, for same device structure. The reason why the enhancement is marked may be attributed to a strong absorption of the short-wavelength emission from the device by the gold nano particles, which in turn initiates a strong surface plasmon resonance effect, leading to a high device efficiency.
关键词： OLED,surface plasmon resonance effect,efficiency,gold nano particle,size effect
更新于2025-09-23 15:19:57
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Calculations of defect states in various sizes of InN nanowires
摘要： InN has received considerable attentions due to its small band-gap and unique properties in the III-nitride family. Understanding the effects of defects on optoelectronic properties of InN nanowire is essential for exploring its applications in future nanodevices. In this work, we have systematically calculated defect states in InN nanowires based on density-functional theory. Hydrogen passivation and several potential intrinsic point defects are considered in various sizes of nanowires, as well as charged defect states. For small-sized hexagonal nanowires, VN at N-poor condition or NIn at N-rich condition is the most stable defect. Whereas for larger-sized nanowires, VN and InN defects are competing when the N chemical potential changes, showing obvious size effect of the defect stability on the nanowire surface. Those defect states change the electronic structure of the nanowires drastically by introducing empty bands or deep level and provide possibility to tailor the optical properties in terms of forming different stable defects.
关键词： InN,nanowires,size effect,first-principals calculations,electronic structure,defects
更新于2025-09-19 17:15:36
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Size effect-enhanced thermoelectric properties of nanoscale Cu2-xSe
摘要： As a promising thermoelectric material, copper selenides have attracted the interest of researchers owing to their low cost, abundance in earth, environmental friendliness, and low thermal conductivity. In this study, copper selenide (Cu2-xSe) powders with controllable sizes from nanoscale to mesoscale were obtained by a facile one-pot solvothermal method. After treatment with spark plasma sintering, the nanoscale Cu2-xSe pellets exhibited excellent thermoelectric properties such as sharply reduced thermal conductivity and enhanced Seebeck coefficient as well as a suppressed electrical conductivity. The figure of merit (ZT) of the nanoscale Cu2-xSe reached up to ~1.51 at 873 K, which is about 2.67 times higher than that of the meso-Cu2-xSe. This study confirms that thermoelectric properties can be enhanced by the size effect.
关键词： size effect,solvothermal method,thermoelectric property,Copper selenide,nanoscale
更新于2025-09-19 17:15:36
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Electronic Structure and Optical Gain of InNBiAs/InP Pyramidal Quantum Dots
摘要： Dilute bismide alloys and dilute nitride alloys have garnered increasing research interest over the past few years, as it promises increased engineering flexibility in the design of advanced compound semiconductor heterostructure devices. Key device parameters such as lattice constant, bandgap and band offsets can be controlled with greater precision, and this leads to better performance for a wide range of electronic and optoelectronic devices. For dilute nitride alloys, band anticrossing effects are produced due to the coupling of their resonant states with the conduction band states. This lowers the conduction band edge energy. Likewise, the coupling of the resonant states of dilute bismide with the valence band states results in the valence band anticrossing and the valence band edge energy rises. Additionally, the effective bandgap may fall below the spin-orbital-splitting energy, thus inhibiting Auger recombination. This makes them excellent candidates for optoelectronic device applications. In this work, the electronic bandstructure and optical gain of InNBiAs/InP pyramidal quantum dots are investigated using the 16-band k·p model with constant strain. The effective bandgap falls as we increase the composition of nitrogen and bismuth. With an appropriate choice of composition of doped atoms, we can tune the emission wavelength in the range of 2–5μm suitable for mid-infrared device applications. Additionally, we observe the size effect by tuning the size of quantum dot.
关键词： Optical gain,Quantum dot,Dilute bismuth,Dilute nitrogen,Band anticrossing,Size effect
更新于2025-09-16 10:30:52
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The size dependence of optical properties in colloidal ZnxCd1-xS:Mn quantum dots in gelatin
摘要： Size-selected colloidal ZnxCd1-xS quantum dots were successfully prepared by aqueous synthesis in gelatin. Quantum dots with an average size of a few nanometers were obtained by changing the synthesis conditions such as the amount of precursors and temperature. Variation of the composition and size of particles leads to a change in the optical, in particular, luminescent characteristics of quantum dots. Estimation of particle sizes were performed by several methods based on X-Ray diffraction and optical data. The mechanisms of trap state photoluminescence in ZnxCd1-xS quantum dots are proposed. Models of increasing / decreasing the photoluminescence intensity depending on the composition and particle size are presented.
关键词： zinc sulfide,quantum dots,luminescence,quantum size effect,aqueous synthesis,cadmium sulfide
更新于2025-09-12 10:27:22