Elastic constants of CdSe at low temperature

Bonello, Bernard; Fernández, Braulio

doi:10.1016/0022-3697(93)90310-n

Cited by 47 publications

(17 citation statements)

References 12 publications

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“…For the investigation of the effects of an epitaxial ZnS shell a Zn and S atom can initially be placed on the Cd and Se sites, respectively. [62]. The lattice parameters for wurtzite CdSe a = 4.34Åand c = 7.09Å are also in good agreement with experimental values [28].…”

Section: Cdse Nanorodssupporting

confidence: 78%

Optical phonons in colloidal CdSe nanorods

Lange

Mohr

Artemyev

et al. 2010

Physica Status Solidi (b)

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Colloidal CdSe nanorods are nanoparticles synthesized in solution. The synthesis allows the growth of CdSe nanorods with well defined diameters and aspect ratios. They have many potential applications in the field of optoelectronics and biotechnology. The nanorods can be epitaxially covered with a graded CdS/ZnS shell of a few monolayers in thickness. The shell leads to an increased quantum efficiency and improved photostability of the nanorods. However, the lattice mismatch between the nanorod core material and the shell material introduces strain into the core lattice. In this work Raman spectroscopy, accompanied by ab-initio calculations, is used to determine the amount of this strain, the exciton-phonon coupling strength in the nanorods and to investigate confinement effects. The longitudinal optical phonons in a nanorod are confined to the nanorod volume. The confinement of a phonon wavefunction leads to a neutralization of the q = 0 rule and the phonon frequency is found to depend on the nanorod diameter. The coupling strength between longitudinal optical phonons and excitons is investigated. It also depends on the nanorod diameter. The total coupling strength is much lower than in bulk material due to a decrease of the influence of the Coulomb interaction in nanoparticles. However, the coupling strength is found to rise for decreasing diameters. This is due to the increasing contributions of higher frequency phonons for smaller nanoparticle sizes. A radial breathing mode with a diameter dependent frequency is deduced from ab-initio calculations and its existence in nanorods is verified experimentally. The diameter-dependence of the modes' frequency can be used to estimate the nanorod diameter from a Raman measurement. In core-shell structures, the coverage of a CdSe nanorod with a ZnS shell leads to a compressive strain of the CdSe core due to the smaller lattice parameter of ZnS compared to CdSe. Ab-initio calculations show that all bonds of the CdSe core are shortened. The bonds in the lateral direction are much more strongly compressed than the bonds parallel to the c-axis. The amount of strain is estimated from the Raman spectra. The compressive nature of the shell decreases for thicker nanorods. The exciton wave function changes with the modified boundary from air to ZnS. This is reflected in a altered exciton-phonon coupling strength and can be monitored in the Raman spectra. ZusammenfassungCdSe Nanorods sind Nanopartikel, die in einer kolloidalen Lösung synthetisiert werden. Für diese existieren viele mögliche Anwendungen im Bereich der Optoelektronik und der Biotechnologie. Der Durchmesser und die Länge der Nanorods lässt sich durch die Syntheseparameter festlegen. Die Nanorods können in eine epitaktische Hülle aus einem Halbleitermaterial mit einer größeren Bandlücke, ZnS, eingebettet werden. Diese Hülle verbessert die optischen Eigenschaften und ermöglicht eine weitere Funktionalisierung der Oberfläche. Der Unterschied der Gitterparameter zwischen ZnS und CdSe führt jedoch zu Verspannung...

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Section: Cdse Nanorodssupporting

confidence: 78%

Optical phonons in colloidal CdSe nanorods

Lange

Mohr

Artemyev

et al. 2010

Physica Status Solidi (b)

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“…The deviations from the bulk lattice constants were found to be small (<1 %) for wurtzite CdSe and ZnS. Another test for the validity of our calculations is the bulk modulus and values of 55.5 and 80.2 GPa were obtained for CdSe and ZnS, respectively, in good agreement with the experimental values of 53.4 and 76.0 GPa [13,14].…”

Section: Calculationsupporting

confidence: 59%

Effects of a ZnS‐shell on the structural and electronic properties of CdSe‐nanorods

Mohr

Thomsen

2008

Physica Status Solidi (b)

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CdSe nanorods were studied via density functional theory calculations. The influence of a ZnS shell on the structural and electronic propertieswas investigated. The ZnS shell leads to a shortening of the CdSe bond length, the magnitude depending on the bond length orientation with respect to the axis. The electronic band gap is reduced by the presence of the ZnS shell. In the present study, the CdSe/ZnS multistructure forms a type II heterojunction, in contrast to plane CdSe/ZnS superlattices. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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“…In the cubic zinc-blende (ZB) and hexagonal wurzite (WZ) phases, the calculated zero-pressure equilibrium lattice constants, equilibrium cell volume V 0 , bulk modulus B 0 and its pressure derivative B′ 0 together with the available experimental (Madelung et al 1982;Bonello and Fernandez 1993) and theoretical data (Rabani 2002;Deligoz et al 2006;Zhuravlev 2007) are summarized in table 1. It is seen that the obtained equilibrium lattice constants and cell volumes with CASTEP code (GGA-PBE) are a little bigger than the experimental data so that the drawn bulk modulus are underestimated.…”

Section: Ground State Structure and Thermal Equation Of Statementioning

confidence: 99%

High pressure phase transitions for CdSe

et al. 2014

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The structure and pressure-induced phase transitions for CdSe are investigated using firstprinciples calculations. The pressure-induced phase transition sequence WZ/ZB → Rs → Cmcm → CsCl for CdSe is drawn reasonably for the fist time, the corresponding transition pressures are 3.8, 29 and 107 GPa, respectively and the intermediate states between the Cmcm structure and the CsCl structure should exist.

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Elastic constants of CdSe at low temperature

Cited by 47 publications

References 12 publications

Optical phonons in colloidal CdSe nanorods

Optical phonons in colloidal CdSe nanorods

Effects of a ZnS‐shell on the structural and electronic properties of CdSe‐nanorods

High pressure phase transitions for CdSe

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