Effect of lattice contraction on the Raman shifts of CdSe quantum dots in glass matrices

Hwang, Y.N.; Shin, Sei One; Park, Hong Lee; Park, Seung Han; Kim, Ung; Jeong, Hae-Yong; Shin, Eun Joo; Kim, Dongho

doi:10.1103/physrevb.54.15120

Cited by 95 publications

(100 citation statements)

References 19 publications

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“…[15 -18] The observation of a blue shift of LO phonon modes of CdSe NCs in borosilicate (B 2 O 3 -SiO 2 ) and silicate (SiO 2 ) glass matrices is attributed to the lattice contraction effect due to the compressive strain on the surface of the nanoparticles. [19] This compressive strain is caused mainly by the mismatch of the linear thermal-expansion coefficients between microcrystals (α) and their host material (α ), as well as by an increase in the surface tension (σ ), with a decrease in the microcrystal size. [8] Considering the lattice contraction effect of the NCs and the effects of the phonon confinements with negative phonon dispersion, it is possible to show that LO phonon frequency, depending on the average NCs radius (R), is given by Ref [19] …”

Section: Resultsmentioning

confidence: 99%

Confirming the lattice contraction in CdSe nanocrystals grown in a glass matrix by Raman scattering

Neto¹,

Dantas²,

Silva³

et al. 2010

J Raman Spectroscopy

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This work gives the evidence of the lattice contraction in CdSe nanocrystals (NCs) grown in a glass matrix. The CdSe NCs were investigated by atomic force microscopy (AFM), optical absorption (OA), and Raman spectroscopy. The average size of CdSe NCs can be estimated by AFM images. Using the OA spectra and the effective-mass approximation, it was also possible to estimate the average sizes of CdSe NCs, which agree very well with the AFM data. These results showed that the CdSe NCs grow with increasing time of heat treatment. The blue shift of the longitudinal optical (LO) modes and surface optical (SO) phonon modes with an increase in the average radius of the NCs, shown in the Raman spectra, was explained by the lattice contraction in CdSe NCs caused by thermodynamic interactions at the interface with the host glass matrix.

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Section: Resultsmentioning

confidence: 99%

Confirming the lattice contraction in CdSe nanocrystals grown in a glass matrix by Raman scattering

Neto¹,

Dantas²,

Silva³

et al. 2010

J Raman Spectroscopy

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show abstract

“…There are some difficulties, however, to use this equation, as remarked on by Hwang et al [463] since the thermal expansion coefficient within the temperature range T ÿ T g is hardly detectable. The value of B in Eq.…”

Section: Optical Phonon Softeningmentioning

confidence: 97%

Size dependence of nanostructures: Impact of bond order deficiency

Sun

2007

Progress in Solid State Chemistry

817

717

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“…The redshift will follow a K 2 j relation. There are some difficulties however in using this equation, as remarked by Hwang et al 28 The thermal expansion coefficients are hardly detectable within the temperature range T and T g . The value of B in Eqn (3) is given by the difference of the phonon negative dispersion and the size-dependent surface tension.…”

Section: Size-induced Raman Redshiftmentioning

confidence: 95%

“…Hwang et al 28 and Kim and Jang 29 indicated for the first time that the effect of lattice contraction must be considered to explain the observed differences in the redshift of phonon energies for CdSe nanodots embedded in different glass matrices and in ZrTiO 4 nanocrystals. Interface bond contraction has been confirmed recently by Pan et al 30 using fluorescence X-ray absorption fine structure and X-ray diffraction.…”

Section: Size-induced Raman Redshiftmentioning

confidence: 99%

“…27 Using a phenomenological Gaussian envelope function of phonon amplitudes, Tanaka et al 7 showed that the size dependence of the redshift of Raman optical modes originated from the relaxation of the q D 0 selection rule based on the confinement argument with negative phonon dispersion. The phonon energies for all the glasses are reduced, and the values of the phonon energies of CdSe nanosolids are found to be quite different for different host glasses because of interfacial interaction.Hwang et al 28 and Kim and Jang 29 indicated for the first time that the effect of lattice contraction must be considered to explain the observed differences in the redshift of phonon energies for CdSe nanodots embedded in different glass matrices and in ZrTiO 4 nanocrystals. Interface bond contraction has been confirmed recently by Pan et al 30 using fluorescence X-ray absorption fine structure and X-ray diffraction.…”

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confidence: 99%

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Atomistic origin and temperature dependence of Raman optical redshift in nanostructures: a broken bond rule

Pan

Tay

et al. 2007

J Raman Spectroscopy

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Consistent insight is presented into the atomistic origin and temperature (T) dependence of the redshift of Raman optical modes in nanostructures from INTRODUCTIONThe vibration of under-coordinated atoms at a surface and in a nanosolid is of great importance because the behavior of surface phonons influences directly the electrical, optical, and dielectric properties in semiconductor materials and devices, such as electron-phonon coupling, photoabsorption, and photoemission, as well as phonon scattering in the transport dynamics of electrons, phonons, and photons in devices. 1 -5 With miniaturization of a solid down to nanometer scales, the optical Raman modes shift toward lower wavenumbers. 6 On the other hand, when the temperature is increased, the Raman peaks also shift down to low wavenumbers monotonically yet nonlinearly at low temperatures. 7 -9 It is expected that the magnitude of vibration for a surface atom is always greater than that in the bulk. 10,11 However, the underlying mechanisms behind the size-and temperatureinduced Raman redshift of the optical modes remain ambiguous.Ł Correspondence to: Chang Q. Sun, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore. E-mail: ecqsun@ntu.edu.sg Size-induced Raman redshiftThe size-induced redshift of Raman optical modes has usually been suggested to be activated by surface disorder, 12 surface stress, 13 -15 quantum confinement, 16 -19 local heating effects, 20 -22 or surface chemical passivation. The Raman shifts of TiO 2 particles are attributed to the effects of decreasing particle size on the force constants and the amplitudes of vibration of the nearest atomic neighbors. 23 However, the effect of stress can usually be ignored for hydrogenated silicon, 24,25 in which hydrogen atoms terminate the surface dangling bonds, which reduce the bond strains and hence the residual stress. The phonon quantum confinement argument 16 attributes the redshift of the asymmetric Raman line to the relaxation of the q-vector selection rule for the excitation of the Raman active phonons due to their localization. The relaxation of the momentum conservation rule arises from the finite crystalline size and the distribution of the diameters of the nanosolid in the films. When the size is decreased, the rule of momentum conservation will be relaxed and the Raman active modes will not be limited to the center of the Brillouin zone. 13 However, Alim et al. 21,22 who have measured resonant and nonresonant Raman scattering spectra for ZnO nanocrystals with an average diameter of 20 nm, proposed that the observed phonon redshift can be attributed to the local heating effects instead of phonon Atomistic origin and temperature dependence of Raman redshift in nanostructures 781 confinement effects. A Gaussian-type phonon confinement model 17 that has been used to fit the experimental data indicates that strong phonon damping is present, whereas calculations 26 using the correlation functions of the local dielectric constant...

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Effect of lattice contraction on the Raman shifts of CdSe quantum dots in glass matrices

Cited by 95 publications

References 19 publications

Confirming the lattice contraction in CdSe nanocrystals grown in a glass matrix by Raman scattering

Confirming the lattice contraction in CdSe nanocrystals grown in a glass matrix by Raman scattering

Size dependence of nanostructures: Impact of bond order deficiency

Atomistic origin and temperature dependence of Raman optical redshift in nanostructures: a broken bond rule

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