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An improved 2D–3D model for charge transport based on the maximum entropy principle
摘要： To study the electron transport in a some tens of nanometers long channel of a metal oxide ?eld effect transistor, in order to reduce the computational cost of simulations, it can be convenient to divide the electrons into a 2D and a 3D population. Near the silicon/oxide interface the two populations coexist, while in the remaining part of the device only the 3D component needs to be considered because quantum effects are negligible there. The major issue is the description of the scattering mechanisms between the 2D and the 3D electron populations, due to interactions of electrons with nonpolar optical phonons and interface modes. Here, we propose a rigorous treatment of these collisions based on an approach similar to that used in Fischetti and Laux (Phys Rev B 48:2244–2274, 1993), in the context of a Monte Carlo simulation. We also consider all the other main scatterings, which are those with acoustic phonons, surface roughness, and impurities.
关键词： Semiconductors,2DEG,Quantum con?nement,Maximum entropy principle,Hydrodynamical models
更新于2025-09-23 15:22:29
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Electrochemistry of Atomically Precise Metal Nanoclusters
摘要： Thiolate-protected metal nanoparticles containing a few to few hundred metal atoms are interesting materials exhibiting unique physicochemical properties. They encompass the bulk-to-molecule transition region, where discrete electronic states emerge and electronic band energetics yield to quantum con?nement e?ects. Recent progresses in the synthesis and characterization of ultrasmall gold nanoparticles have opened up new avenues for the isolation of extremely monodispersed nanoparticles with atomically precision. These nanoparticles are also called nanoclusters to distinguish them from other regular metal nanoparticles with core diameter >2 nm. These nanoclusters are typically identi?ed by their actual molecular formulas; prominent among these are Au25(SR)18, Au38(SR)24, and Au102(SR)44, where SR is organothiolate. A number of single crystal structures of these nanoclusters have been disclosed. Researchers have e?ectively utilized density functional theory (DFT) calculations to predict their atomic and electronic structures, as well as their physicochemical properties. The atomically precise metal nanoclusters have been the focus of recent studies owing to their novel size-speci?c electrochemical, optical, and catalytic properties. In this Account, we highlight recent advances in electrochemistry of atomically precise metal nanoclusters and their applications in electrocatalysis and electrochemical sensing. Compared with gold nanoclusters, much less progress has been made in the electrochemical studies of other metal nanoclusters, and thus, we mainly focus on the electrochemistry and electrochemical applications of gold-based nanoclusters. Voltammetry has been extremely powerful in investigating the electronic structure of metal nanoclusters, especially near HOMO and LUMO levels. A sizable opening of HOMO?LUMO gap observed for Au25(SR)18 gradually decreases with increasing nanocluster size, which is in line with the change in the optical gap. Heteroatom-doping has been a powerful strategy to modify the optical and electrochemical properties of metal nanoclusters at the atomic level. While the superatom theory predicts 8-electron con?guration for [Au25(SR)18]? and many doped nanoclusters thereof, Pt- and Pd-doped [PtAu24(SR)18]0 and [PdAu24(SR)18]0 nanoclusters show dramatically di?erent electronic structures, as manifested in their optical spectra and voltammograms, suggesting the occurrence of the Jahn?Teller distortion in these doped nanoclusters. Furthermore, metal-doping may alter their surface binding properties, as well as redox potentials. Metal nanoclusters o?er great potential for attaining high activity and selectivity in their electrocatalytic applications. The well-de?ned core?shell structure of a metal nanocluster is of special advantage because the core and shell can be independently engineered to exhibit suitable binding properties and redox potentials. We discuss recent progress made in electrocatalysis based upon metal nanoclusters tailored for water splitting, CO2 conversion, and electrochemical sensing. A well-de?ned model nanocatalyst is absolutely necessary to reveal the detailed mechanism of electrocatalysis and thereby to lead to the development of a new e?cient electrocatalyst. We envision that atomically controlled metal nanoclusters will enable us to systematically optimize the electrochemical and surface properties suitable for electrocatalysis, thus providing a powerful platform for the discovery of ?nely tuned nanocatalysts.
关键词： quantum con?nement,electrocatalysis,atomically precise metal nanoclusters,electrochemistry,electrochemical sensing
更新于2025-09-23 15:21:21
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Optical and electronic properties of CdTe quantum dots in their freezed solid matrix phase and solution phase
摘要： The present work deals with the comparison of sizes, optical and electronic properties of COOH functionalized CdTe quantum dots (QDs) in freezed solid polymeric (polyvinyl alcohol (PVA) matrix and in solution phase (water). PVA has been chosen as host material for guest CdTe QDs because of its unique properties like hydrophilicity, good thermo stability, and easy process ability. Experimental absorption, emission, X-Ray diffraction spectra and electronic band gap have been studied by UV–Vis absorption, luminescence and X-Ray diffraction spectroscopy. The smaller size of CdTe QDs in solid PVA polymer matrix ((cid:1)6 nm) and larger band gap of (cid:1)9.5 eV validates their quantum con?nement regime in freezed solid phase. The smaller particle size in solid phase compared to that of the particle size in its solution phase (8 nm) validates the non existence of agglomeration in solid phase. Appearance of high intense and wide luminescence emission in solid form proves the strong candidature of CdTe QDs as promising sensors for today’s optoelectronic and biomedical industry.
关键词： Quantum Dot,CdTe/PVA thin ?lm,Quantum con?nement,UV–Visible,Photoluminsence spectroscopy
更新于2025-09-23 15:19:57
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Tailoring Photoluminescence from Si-Based Nanocrystals Prepared by Pulsed Laser Ablation in He-N2 Gas Mixtures
摘要： Using methods of pulsed laser ablation from a silicon target in helium (He)-nitrogen (N2) gas mixtures maintained at reduced pressures (0.5–5 Torr), we fabricated substrate-supported silicon (Si) nanocrystal-based ?lms exhibiting a strong photoluminescence (PL) emission, which depended on the He/N2 ratio. We show that, in the case of ablation in pure He gas, Si nanocrystals exhibit PL bands centered in the “red - near infrared” (maximum at 760 nm) and “green” (centered at 550 nm) spectral regions, which can be attributed to quantum-con?ned excitonic states in small Si nanocrystals and to local electronic states in amorphous silicon suboxide (a-SiOx) coating, respectively, while the addition of N2 leads to the generation of an intense “green-yellow” PL band centered at 580 nm. The origin of the latter band is attributed to a radiative recombination in amorphous oxynitride (a-SiNxOy) coating of Si nanocrystals. PL transients of Si nanocrystals with SiOx and a-SiNxOy coatings demonstrate nonexponential decays in the micro- and submicrosecond time scales with rates depending on nitrogen content in the mixture. After milling by ultrasound and dispersing in water, Si nanocrystals can be used as e?cient non-toxic markers for bioimaging, while the observed spectral tailoring e?ect makes possible an adjustment of the PL emission of such markers to a concrete bioimaging task.
关键词： pulsed laser ablation in gases,pulsed laser deposition,silicon quantum dots,bioimaging,silicon nanoparticles,quantum con?nement,photoluminescence,silicon oxynitride
更新于2025-09-19 17:13:59
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One-step synthesis of strongly confined, defect-free and hydroxy-terminated ZnO quantum dots
摘要： This paper reports the production of strongly con?ned ligand-free, defect-free, hydroxy-terminated ZnO quantum dots with a mean diameter of 1.9 nm, by radio frequency atmospheric pressure microplasma. Systematic characterization is performed to understand the surface chemistry of ZnO quantum dots. Photoluminescence studies show strong con?nement effect on emission with only ultraviolet (UV) emission without any defect-related visible emission. Emission is again tested after eighteen months and con?rms the QDs long-term emission stability. The mechanism responsible for this UV emission is also discussed and originates from OH-related surface terminations.
关键词： band alignment,quantum con?nement,defect-free,photoluminescence,hydroxy-terminated ZnO quantum dots
更新于2025-09-19 17:13:59
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Time controlled growth of CdSe QDs for applications in white light emitting diodes
摘要： Semiconductor nanophosphors have the exceptional resources to demonstrate the quantum phenomenon due to their tailored-size dependent photoluminescence (PL). The work here is focused on the synthesis of highly luminescent Cadmium Selenide (CdSe) Quantum Dots (QDs) by a simple technique. This is a time dependent process where change in the size of CdSe QDs was observed at a reaction temperature of 100 °C without any inert atmosphere. The CdSe QDs were synthesised by using 3-Mercapto propionic acid (MPA) rather than using the typically utilized capping agent. All the samples were characterised for their optical properties. The size of QDs was calculated in a range up to 3 nm by UV–Vis Spectroscopy and con?rmed by High Resolution Transmission Electron Microscopy (HRTEM). It was clear from the UV studies that QDs exhibit size dependent tunable optical absorption. The broad Photoluminescence (PL) emission spectra depicts the presence of surface defects produced along with band edge spectrum. The absorbance and emission spectra were shifted to the red region due to the quantum con?nement e?ect occurred in QDs. The water soluble QDs were economical and easy to fabricate has applications in Light Emitting Diodes (LEDs).
关键词： 3-Mercapto propionic acid,Light Emitting Diodes,Quantum con?nement,Photoluminescence,CdSe Quantum Dots
更新于2025-09-11 14:15:04
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Schottky Nature of Au/SnO <sub/>2</sub> Ultrathin Film Diode Fabricated Using Sol–Gel Process
摘要： In this letter, sol–gel-processed SnO2 ?lms were deposited, with thicknesses varying from 3.5 to 5.0 nm, by controlling the concentration of the precursor solutions. Through electrical and spectroscopic investigations, it was found that the optical energy bandgap and the electron af?nity were affected by the quantum con?nement effect and Burstein–Moss effect. Moreover, the increased barrier height between Au and SnO2 semiconductors was enhanced when thinner SnO2 layers were used, resulting in strong Schottky diode characteristics. This letter allows one to examine the size scaling effects of ultrathin electrical devices with SnO2 channel layers. In addition, a generalized energy band diagram derived from the bandgap broadening in ultrathin SnO2 semiconductors is presented, which will allow the elucidation of the carrier transport mechanism and optical properties of quantum con?ned SnO2 semiconductor-based optical and electrical devices.
关键词： SnO2,Burstein-Moss effect,Sol-gel,quantum con?nement,Schottky diode
更新于2025-09-09 09:28:46