Small Semiconductor Particles Research Articles

Fine tuning of quantum particle plasmon

It is of recent interest to study plasmonics of metallic and semiconductor particles that are so small that carriers in the conduction band are separated at discrete subbands due to quantum confinement. These small metallic and semiconductor particles are referred as quantum particles in the present work. The modifications of plasmons of quantum particles are studied in the framework of an electron-in-a-box model with an every-electron-count computational scheme. The quantum size effects are incorporated into the classic description of small particle plasmons with the emphasis on intra-subband fluctuations caused by the quantum confinement. The carrier redistribution at subbands is related to the environmental temperature via Fermi-Dirac distribution. Numerical results have shown that the frequency, the strength, and the shape of the plasmons are modified as a function of both particle size and temperature. The discovery suggests potential applications to tune the plasmonics of quantum particles externally and to calibrate the particle properties accounting to plasmonics. It is proposed that the environmental temperature can be conveniently controlled by evanescent light concentration, such as, laser beams in a slot waveguide.

Microwave absorption by small dielectric and semi-conductor coated metal particles

The presence of the oxide coatings on conducting metal particles is often ignored in the calculations of microwave absorption. However, we find that the optical properties of the coatings play a significant role in enhancing or suppressing the absorption of electromagnetic energy. Here, we solve the Mie scattering equations numerically to separate and quantify the role of electric and magnetic field absorption from microwaves at 2.45 GHz by small metal spheres coated with dielectric or semi-conducting materials. The range of size and conductivities of the metal particles and the optical properties of the coatings are chosen for their practical importance. We also provide simple approximate expressions for the absorption per unit volume by coated spheres in the small particle limit which agrees very well with the exact Mie solution. We have demonstrated that for highly conducting particles coated with a material of low conductivity, the electric field absorption depends only on the optical properties, and the volume fraction of the coating. In contrast, the magnetic field absorption depends only on the properties of the core which is the same as the bare metal. We find that the power absorbed by coated particles via the electric field is maximized when loss tangent, tanδ~1. A key result of this study is that a thin layer of lossy coating (~15% of the particle size) on highly conductive particles will significantly enhance (up to a factor of 105) both the power absorbed from the E-field and the total power absorbed.

Photocatalytic activity and charge carrier dynamics of TiO2 powders with a binary particle size distribution.

The effects of the particle size distribution on the charge carrier dynamics and the photocatalytic activity of mixed titanium dioxide (TiO2) powder samples were investigated in this work. Instead of the synthesis of the small semiconductor particles, the binary particle size distributions of the powders were obtained by mixing commercially available TiO2 powders with different particle sizes. The pure anatase samples (average diameters: 7, 20, and 125 nm, respectively) were created via ultrasound treatment and discreet drying. The photocatalytic activity of the powder samples was assessed by the degradation of nitric oxide (NO) and acetaldehyde in the gas phase. Furthermore, the charge carrier kinetics was determined using transient absorption spectroscopy following pulsed laser excitation. Importantly, a recently published model based on fractal dimensions was used to fit the transient signals of the photo generated charge carriers in the TiO2 powder samples. The effects of the particle size on the acetaldehyde degradation could be explained by the formation of agglomerates, which reduce the available surface area of smaller particles. The fast oxidation of acetaldehyde on the surface of TiO2 by direct hole transfer was further independent of the observed charge carrier lifetimes on the microsecond time scale. The photocatalytic NO degradation, on the other hand, increased for samples containing larger amounts of small particles. The corresponding photonic efficiencies correlated well with the charge carrier lifetimes determined by the time-resolved studies. Hence, it was concluded that a long charge carrier lifetime generally leads to higher fractional conversions of NO. The employed fractal fit function was proved to be beneficial for the kinetic analysis of charge carrier recombination in TiO2, in direct comparison with a second order fit function.

The influence of the polymer-stabilizer molecular weight on the spectral luminescence properties of composite sols and coatings containing PbS quantum dots

The influence of the polyvinylpyrrolidone (PVP) molecular weight on the stability and spectral luminescence properties of sols of lead sulfide nanocrystals and the related composite coatings has been studied. It is shown that the spectral properties of PbS sols stabilized with low-molecular (PVP) and the related coatings are determined to a great extent by the formation of large particle aggregates in these materials and, accordingly, high level of light scattering. It is effective to use low-molecular PVP for preparing powder materials containing PbS quantum dots (QDs), because it allows one to perform fast powder precipitation and form small semiconductor particles. High-molecular PVP provides high aggregative and sedimentation stabilities of semiconductor nanocrystal sols. This polymer is effective for use in preparing stable QD sols and homogeneous coatings transparent in the visible spectral range.

Edge contribution to the electronic energy of cut microcrystals

The surface part of electronic energy in small metal or semiconductor particles contains a contribution due to the presence of crystallite edges and vertices. In the approximation of quadratic electron spectrum, the edge contribution is calculated as a function of the dihedral angle of the edge and its orientation to the axes of the effective mass tensor.

Formation and Properties of Sol-Gel Films and Glasses with Ultrafine Metal and Semiconductor Particles

A novel method of fabrication of silica-based sol-gel films and glasses containing small semiconductor particles was developed. A series of films and glasses with nanoparticles of copper chalcogenides (CuS, Cu2Se, CuInS2) and metal particles (Cu) were fabricated through the chemical transformation of precursors incorporated into a sol-gel derived matrix. The properties of the nanoparticles studied by means of XRD, XPS, TEM and optical spectroscopy are provided both by size effects and the chemical nature of surface states and can be controlled at different steps of chemical treatment.

The role of nanosized particles. A frontier in modern materials science, from nanoelectronics to environmental problems

Small metal and semiconductor particles with a size of a few nanometers are one of the important systems in modern materials science. Nanoparticles have found applications in many fields, ranging from catalysis to magnetic storage. In the present work, we discuss some of the methods to characterize the structure of nanoparticles using electron microscopy. We also discuss some of the exciting novel applications of nanoparticles in nanoelectronics and nanophotonics. Finally, we show that nanoparticles play an important role in producing atmospheric pollutants.

Analysis of colloids: VII. Wide-bore hydrodynamic chromatography, a simple method for the determination of particle size in the nanometer size regime

Wide-bore hydrodynamic chromatography in a polyether ether ketone (PEEK) capillary (I.D. 0.7 mm, length 20 m) was used to determine the weight average diameter d w of colloidal particles. The method was applied to cadmium sulphide and gold sols in the diameter range between 3 nm and 27 nm. The method is based on the radial distribution of the analyte in the capillary due to the hydrodynamic flow profile in the capillary and due to the diffusion coefficient of the particles, which is dependent on their diameter. The diameter was calculated from the ratio of the heights of convection peak and diffusion peak. The size-quantization effect of small semiconductor particles made it possible to visualise the separation inside of the capillary. One important advantage of the applied method is the very much reduced adsorption, which often causes serious problems in the HPLC especially of inorganic colloids. The results of wide-bore hydrodynamic chromatography, size exclusion chromatography and transmission electron microscopy were compared.

Electronic Coherence and Nonlinear Susceptibilities of Conjugated Polyenes

A dynamic theory that connects electronic motions and the nonlinear optical response of conjugated polyenes is developed by introducing the concept of electronic normal modes. A useful picture for the mechanism of optical nonlinearities is obtained by identifying the few dominant modes. This quasi-particle electron-hole representation establishes a close analogy with small semiconductor particles (quantum dots) and is very different from the traditional approach based on electronic eigenstates. The effective conjugation length (coherence size), which controls the scaling and saturation of the static third-order susceptibility X((3)) with the number of double bonds, is related to the coherence of the relative motion of electron-hole pairs created upon optical excitation.

Analysis of Colloids. VI. Semiconductor Colloids of High Monodispersity by Preparative Size Exclusion Chromatography

Abstract The recently described method of size exclusion chromatography (SEC) of very small colloidal semiconductor particles was transferred from the analytical scale to the preparative one. The particular difficulties dealing just with SEC and the special situation when working with inorganic colloids are described. The influence of flow rate, sample volume, sample concentration and fraction volume were studied using CdS-sols with particle diameters ranging from 2nm to 8nm. Up to 200mg samples were separated in less than one hour. The fractions were generally characterized by analytical SEC and in two instances by transmission electron microscopy showing excellent consistency and standard deviations down to 11%.

Size dependence of the carrier ground state of small semiconductor particles

By calculating the carrier density distribution and the effective one-particle potential self-consistently, we investigate the size dependence of the carrier ground state of small spherical semiconductor particles with the doping level fixed. The particles are assumed to be in an insulating medium or in the vacuum. The prominent peak just inside the carrier-deficient surface layer in the carrier density profile persists regardless of the particle size, while, with increasing size, the oscillatory density-profile feature inside the prominent peak becomes less and less conspicuous and reduces to nearly constant density to achieve charge neutrality. The remarkable variation of the potential bending with increase of the size depends upon where the newly occupied carrier states have their probability density concentrated. This variation of the potential bending often involves the energy intersection of two close energy levels with different angular momenta l.

Photoelectrochemical catalysis of the oxidation of organic molecules by oxygen on small semiconductor particles with TiO 2 as an example

The kinetics of the photocatalytic oxidation of organic molecules at TiO 2 particles are analyzed with the aim of determining the conditions required to obtain high quantum yields. With the assumption that holes react at the interface faster than electrons, the particles contain, in the steady state, an excess of electrons under illumination. It is shown that the rate of electron capture by oxygen is a decisive parameter for the yield. It also transpires that only very small particles can reach a high yield.

Redox properties of small semiconductor particles

The size dependence of electrical and thermodynamic quantities of intermediate-sized semiconductor particles in an electrolyte solution with a given redox pair are studied. The equilibrium constant for this system is then derived based on the relationship of the electrolytic redox components to the size, charges, and concentration of the semiconductor particles. 25 refs., 9 figs., 1 tab.

Below-band-gap third-order optical nonlinearity of nanometer-size semiconductor crystallites.

We find evidence that quantum confinement of electrons in small semiconductor particles causes the nonlinear optical properties in the transparency region to differ markedly from those of bulk semiconductors. The optical Stark effect makes the dominant contribution to the third-order refractive nonlinearity.

Local field effect in small semiconductor clusters and particles

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLocal field effect in small semiconductor clusters and particlesYing WangCite this: J. Phys. Chem. 1991, 95, 3, 1119–1124Publication Date (Print):February 1, 1991Publication History Published online1 May 2002Published inissue 1 February 1991https://doi.org/10.1021/j100156a019RIGHTS & PERMISSIONSArticle Views191Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Linear and nonlinear optical properties of semiconductor particles

Abstract The field of nonlinear optics is briefly introduced, followed by a review of quantum size effects in small semiconductor particles, with special reference to the linear and nonlinear optical properties. Experimental methods, especially the “laser induced grating” technique are described. Semiconductor (CdS x Se1−x ) doped glasses are examined, both the commercially available niters and a specially made experimental CdSe doped glass. Both linear and nonlinear optical properties are discussed. Colloidal and polymers systems are also briefly discussed.

Small-particle research: physicochemical properties of extremely small colloidal metal and semiconductor particles

Small-particle research: physicochemical properties of extremely small colloidal metal and semiconductor particles

Optical and photoredox properties of small colloidal semiconductor particles in the presence of trivalent lanthanide ions

Size quantization effects upon the optical properties of small size semi-conductor particles ( d < 50 A ̊ ) have been documented in several systems. As the particle size decreases the band gap energy increases accompanied by a blue-shifted emission, and consequently the photoredox activity should increase. We are studying the correlation between the recombination luminescence of CdS particles and the redox potential of the conduction band probed in terms of oxidative luminescence quenching via electron transfer to Ln 3+ Ln 2+ and Ln 3+ Ln redox couples associated with different redox potentials. The electron transfer process from the conduction band of small CdS particles to electron acceptors ( ΔG ° el. tr < 0) is size dependent.

Effect of excess charge on band energetics (optical absorption edge and carrier redox potentials) in small semiconductor particles

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffect of excess charge on band energetics (optical absorption edge and carrier redox potentials) in small semiconductor particlesChong Yang Liu and Allen J. BardCite this: J. Phys. Chem. 1989, 93, 8, 3232–3237Publication Date (Print):April 1, 1989Publication History Published online1 May 2002Published inissue 1 April 1989https://doi.org/10.1021/j100345a069RIGHTS & PERMISSIONSArticle Views307Altmetric-Citations71LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (775 KB) Get e-Alerts

Structural study of silicate glasses by luminescence probing: The nature of small semiconductor particles formed in glasses

Three types of sol-gel processes for the production of silicate glasses have been studied by analysing the luminescence decay profiles of ruthenium tris-(2,2′-bipyridine) in the presence of methylviologen. Two of the types were based on a low- and a high- pH catalyst while the third contained formamide as drying-control agent. Cadmium sulfide and lead sulfide particles have been produced in these glasses and their nature depends on the structure of the glasses.