Quantum-confined Cadmium Research Articles

Zeeman Field-Induced Two-Dimensional Weyl Semimetal Phase in Cadmium Arsenide.

We report a topological phase transition in quantum-confined cadmium arsenide (Cd_{3}As_{2}) thin films under an in-plane Zeeman field when the Fermi level is tuned into the topological gap via an electric field. Symmetry considerations in this case predict the appearance of a two-dimensional Weyl semimetal (2D WSM), with a pair of Weyl nodes of opposite chirality at charge neutrality that are protected by space-time inversion (C_{2}T) symmetry. We show that the 2D WSM phase displays unique transport signatures, including saturated resistivities on the order of h/e^{2} that persist over a range of in-plane magnetic fields. Moreover, applying a small out-of-plane magnetic field, while keeping the in-plane field within the stability range of the 2D WSM phase, gives rise to a well-developed odd integer quantum Hall effect, characteristic of degenerate, massive Weyl fermions. A minimal four-band k·p model of Cd_{3}As_{2}, which incorporates first-principles effective g factors, qualitatively explains our findings.

Anisotropy of Structure and Optical Properties of Self-Assembled and Oriented Colloidal CdSe Nanoplatelets

Abstract Atomically flat colloidal nanoplatelets with strong one-dimensional confinement represent the most recently discovered type of quantum-confined cadmium chalcogenide nanocrystals. In almost a decade a great progress has been achieved in the colloidal synthesis of nanoplatelets and understanding of their basic optical and electronic properties. However, up until recently methods of their controlled spatial orientation were quite scarce, what in turn hindered obtaining reliable information on their anisotropic structural and optical properties arising from their shape. In this paper we provide a mini-review of recent advances in this field of study.

Luminescence in quantum-confined cadmium selenide nanocrystals and nanorods in external electric fields

It is found that the absorption and luminescence spectra of CdSe nanocrystals and nanorods depend on the external electric field. It is shown that the external electric field quenches the P-polarized photoluminescence of CdSe nanorods to a degree higher than the degree of field-induced quenching of the S-polarized photoluminescence. It is established that the nanocrystals are more sensitive to the external electric field than the nanorods. The effect of the external electric field on the luminescence properties of the semiconductor nanorods is discussed.

Conjugated Chromophore Near the Quantum-Confined Cadmium Sulfide Cluster: Quenched Photoluminescence and Enhanced Two-Photon Absorption

Quenching effect of the photoluminescence of 1,2,4,5-tetrakis(4-pyridylvinyl)benzene in the presence of CdS colloids stabilized by inverse micelles was observed. The observed regularities of luminescence quenching by the quenchers of different size were studied. An increase in the two-photon absorption cross section (6.5 times higher) and in the two-photon-induced fluorescence intensity was observed for the composite solution when pumped by 740-nm laser irradiation. The results are in accord with theoretical prediction of enhancement of third-order optical nonlinearity of quantum-confined semiconductor.

Thermochemical Passivation of DNA-Stabilized Q-Cadmium Sulfide Nanoparticles

In this work, the conditions required to transform quantum-confined cadmium sulfide (Q-CdS) nanoparticles stabilized by calf thymus deoxyribonucleic acid from deep trap photoluminescent states to “band edge”-type luminescence are probed. The presence of fivefold excess sulfide relative to cadmium concentration during cluster synthesis, followed by mild heating at 80°C, results in the desired transformation of the Q-CdS emission spectrum. We also indirectly analyze the accompanying structural changes in the polymeric stabilizer, accomplished in this case by use of well-known spectrofluorometric methods with the dyes ethidium bromide and trisphenanthroline ruthenium(II).

Effect of Pressure on the Photoluminescence of Polynucleotide-Stabilized Cadmium Sulfide Nanocrystals

This work describes the effects of pressure on the photoluminescence of Q-CdS (quantum-confined cadmium sulfide) nanoparticles stabilized by hexametaphosphate, calf thymus DNA, polyadenylic acid, polyuridylic acid, and polyadenylic−uridylic acid in the pressure range from atmospheric pressure to 4 kbar. A marked difference is observed between Q-CdS/polyadenylic acid and that of Q-CdS/polyuridylic acid in terms of pressure-induced changes in the luminescence; coating the surface of each type of Q-CdS with cadmium hydroxide results in a leveling effect whereby only a steady diminution of emission intensity is observed in each case. A model involving pressure-induced perturbation of anionic sulfide hole traps at the semiconductor nanocrystal surface is proposed to explain these observations.

The influence of adenine content on the properties of Q-CdS clusters stabilized by polynucleotides

In this work the nature of the interaction between quantum-confined cadmium sulfide (Q-CdS) clusters and either single or double-stranded polynucleotide stabilizers of varying nucleic acid base composition is investigated. We specifically focus here on the influence of adenine content on cluster size, photoluminescence behavior, and the relative ability of these small particles to increase in average diameter upon conditions of mild heating. Thermolysis of Q-CdS/polynucleotide samples affects the interfacial interaction between cluster and stabilizer giving rise to a shift in the emission maximum, a change in luminescence quantum yield, and in some cases an increase in average size. For a fixed set of reactant concentrations, Q-CdS stabilized by polyadenylic acid (Poly[A]) and other adenine-rich polynucleotides are unique in stabilizing the formation of smaller clusters with an average diameter near 38 Å under ambient conditions, but Poly[A]-stabilized Q-CdS clusters readily fuse to larger (about 60 Å) clusters upon mild heating. In contrast, Q-CdS stabilized by other types of single-stranded hompolymers (Poly[U], [G], and [C]) as well as double-stranded calf thymus and Escherichia coli deoxyribonucleic acids form somewhat larger clusters during intitial synthesis and typically exhibit greater protection against radical changes in size upon thermolysis.

Stabilizer-mediated photoluminescence quenching in quantum-confined cadmium sulfide clusters

In this account the influence of charge possessed by the stabilizing medium on the steady-state quenching behavior of quantum confined cadmium sulfide (Q-CdS) semiconductor clusters is reported. Q-cluster stabilizers such as the inverse micelle/hexametaphosphate (HMP) system and thiophenol caps, which afford an anionic solution/stabilizer interface, permit quenching of the integrated trap photoluminescence (PL) intensity (λ max between 550 and 650 nm) up to ∼45% (HMP) or 54% (thiophenol) by the cation methyl viologen (MV 2+ ), However, minimal quenching is observed upon addition of the anion iodide (I - ), and virtually no quenching is observed following the addition of neutral molecules (amines and ketones)

An examination of the interfacial interactions between quantum-confined cadmium sulfide clusters and aminocalixarene stabilizer molecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAn examination of the interfacial interactions between quantum-confined cadmium sulfide clusters and aminocalixarene stabilizer moleculesJeffery L. Coffer, Robin R. Chandler, C. David Gutsche, Iftikhar Alam, Russell F. Pinizzoto, and Hong YangCite this: J. Phys. Chem. 1993, 97, 3, 696–702Publication Date (Print):January 1, 1993Publication History Published online1 May 2002Published inissue 1 January 1993https://doi.org/10.1021/j100105a027RIGHTS & PERMISSIONSArticle Views128Altmetric-Citations20LEARN 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 (4 MB) Get e-Alerts

Addition of ferrocene derivatives to the surface of quantum-confined cadmium sulfide clusters: steady-state and time-resolved photophysical effects

The effect of substituted ferrocene complexes on the surface of quantum-confined (Q) cadmium sulfide clusters in inverse micelles was examined by steady-state and time-resolved photoluminescence (PL) spectroscopy. Addition of (dimethylamino)methylferrocene (DMAMF) to Q-CdS enhanced cluster PL peak areas by 120%, in contrast to the carboxylic acid derivatives ferrocenecarboxylic acid (FCA) and ferrocenedicarboxylic acid (FDCA), which quenched PL by 60% and 80%, respectively

Porous silica glasses doped with quantum-confined cadmium selenide

The formation of stable cadmium selenide-doped silica glasses, via semiconductor diffusion into a porous glass obtained using a sol-gel process, is described. Exposure of quantum-confined (‘Q-state’) CdSe clusters, of average diameter 30 A and dissolved in an ethylpyridine solution, to a colorless sol-gel disk possessing an average pore diameter of 35 A yields an intense red-green glass within hours. Subsequent drying and heat treatment up to 200°C does not degrade the samples. These CdSe-doped glasses are characterized by both absorption and emission (photoluminescence) spectroscopy as well as surface area measurements. The effect of different functional groups present in the gel pores, Cl − versus OH − , on the properties of the diffused CdSe is also reported.

Use of Calixarene Host Molecules to Stabilize Quantum-confined Cadmium Sulfide Formation

ABSTRACTWe describe here the use of calixarenes, methylene (-CH2-) linked phenolic macrocyclic molecules, to stabilize the formation of quantum-confined (Q-) CdS clusters. Specifically, we focus on the use of an amino-derivatized calixarene, para-[(dimethylamino)- methyl]calix[6]arene, to stabilize Q-CdS clusters which have been characterized by High Resolution TEM (HREM), as well as absorption and emission spectroscopies. Under typical preparative conditions, an average particle diameter of 36 Å is obtained. HREM, in combination with Selected Area Diffraction (SAD), confirms the structure of the clusters as zinc blende CdS. Spectroscopic studies using absorption and emission methods indicate that both particle size and cluster photophysics are sensitive to the ratio of CdS to calixarene.

Antiquenching effect of lanthanide .beta.-diketonate complexes on the photoluminescence of quantum-confined cadmium sulfide clusters

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAntiquenching effect of lanthanide .beta.-diketonate complexes on the photoluminescence of quantum-confined cadmium sulfide clustersRobin R. Chandler and Jeffery L. CofferCite this: J. Phys. Chem. 1991, 95, 1, 4–6Publication Date (Print):January 1, 1991Publication History Published online1 May 2002Published inissue 1 January 1991https://doi.org/10.1021/j100154a002RIGHTS & PERMISSIONSArticle Views120Altmetric-Citations23LEARN 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 (375 KB) Get e-Alerts

A picosecond bleaching study of quantum-confined cadmium sulfide microcrystallites in a polymer film

We report a picosecond pump–probe study of 55 Å cadmium sulfide microcrystallites embedded in polymer films. Large negative absorbance changes at wavelengths corresponding to energies near the band gap are observed. This absorption bleaching and the associated changes in refractive index are mainly responsible for the large nonlinearity observed in degenerate four-wave mixing experiments. Based on photoluminescence data, the known electron-trapping cross section of defects, and these pump–probe experiments, we show that the conventional carrier density-dependent band-filling mechanism cannot account for the data, and the absorption bleaching is due to the saturation of the excitonic transition. We further show that the phase-space filling and exchange effects from exciton–exciton and exciton-free carrier interactions fail to account for the observed data. Instead, we propose that the exciton-trapped carrier interaction is mainly responsible for the observed bleaching of the excitonic absorption. This interaction is unique for small semiconductor clusters since the presence of a high density of defects (most likely on the surfaces) causes the extremely rapid trapping of free carriers. According to this model, the recovery time of the absorption bleaching is determined by the trapped-carrier relaxation time, which is sensitive to the fabrication methods and can be controlled by surface chemistry. Our study also demonstrates that one needs to understand the effects of surfaces and control the surface chemistry before the important question of size effects on the nonlinear optical properties can be addressed.