Polar optical vibrational modes in quantum dots

AbstractThe optical, structural, and thermodynamic properties of materials can be changed by reducing their dimensions. We sequentially implanted In and As into fused silica windows in order to investigate the formation and properties of InAs nano-particles. The UV/VIS/NIR, FTIR in mid-IR, and far-IR spectroscopy were mainly used to study the change in electronic transitions and in vibrational modes (phonons) of the nanoparticle InAs. The phonons can be confined to the surface of nanoparticles and have frequencies falling between the transverse and longitudinal optical modes of the bulk material. Thermal annealing developed the formation of InAs quantum dots from as-implanted In+As system. At a certain annealing temperature, we observed a change in UV/VIS transmission spectra and IR reflectance spectra indicating the formation of InAs quantum dots. This is particularly evident from the absorption in the IR, and surface phonon bands are observed confirming the presence of quantum confined InAs.

Download Full-text

Investigation of Vibrational Modes and Phonon Density of States in ZnO Quantum Dots

The Journal of Physical Chemistry C ◽

10.1021/jp300985k ◽

2012 ◽

Vol 116 (12) ◽

pp. 6893-6901 ◽

Cited By ~ 29

Author(s):

David Raymand ◽

T. Jesper Jacobsson ◽

Kersti Hermansson ◽

Tomas Edvinsson

Keyword(s):

Quantum Dots ◽

Density Of States ◽

Phonon Density ◽

Vibrational Modes ◽

Phonon Density Of States ◽

Zno Quantum Dots

Download Full-text

IR-active vibrational modes of CdTe and CdSe colloidal quantum dots and CdTe/CdSe core/shell nanoparticles and coupling effects

Physics of the Solid State ◽

10.1134/s1063783407030304 ◽

2007 ◽

Vol 49 (3) ◽

pp. 547-551 ◽

Cited By ~ 11

Author(s):

R. B. Vasiliev ◽

V. S. Vinogradov ◽

S. G. Dorofeev ◽

S. P. Kozyrev ◽

I. V. Kucherenko ◽

...

Keyword(s):

Quantum Dots ◽

Colloidal Quantum Dots ◽

Core Shell ◽

Vibrational Modes ◽

Coupling Effects ◽

Cdse Core ◽

Shell Nanoparticles ◽

Core Shell Nanoparticles

Download Full-text

Nanostructure of semiconductor quantum dots in a borosilicate glass matrix by complementary use of HREM and AEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100176770 ◽

1990 ◽

Vol 48 (4) ◽

pp. 728-729

Author(s):

M.J. Kim ◽

L.C. Liu ◽

S.H. Risbud ◽

R.W. Carpenter

Keyword(s):

Quantum Dots ◽

Borosilicate Glass ◽

Glass Matrix ◽

Optical Switching ◽

Response Times ◽

Fast Response ◽

Processing Technique ◽

Internal Stresses ◽

Electron Hole ◽

Spatial Dimensions

When the size of a semiconductor is reduced by an appropriate materials processing technique to a dimension less than about twice the radius of an exciton in the bulk crystal, the band like structure of the semiconductor gives way to discrete molecular orbital electronic states. Clusters of semiconductors in a size regime lower than 2R {where R is the exciton Bohr radius; e.g. 3 nm for CdS and 7.3 nm for CdTe) are called Quantum Dots (QD) because they confine optically excited electron- hole pairs (excitons) in all three spatial dimensions. Structures based on QD are of great interest because of fast response times and non-linearity in optical switching applications.In this paper we report the first HREM analysis of the size and structure of CdTe and CdS QD formed by precipitation from a modified borosilicate glass matrix. The glass melts were quenched by pouring on brass plates, and then annealed to relieve internal stresses. QD precipitate particles were formed during subsequent "striking" heat treatments above the glass crystallization temperature, which was determined by differential thermal analysis.

Download Full-text