Predicted Raman spectra of Si[111] nanowires

Thonhauser, Timo; Mahan, G. D.

doi:10.1103/physrevb.71.081307

Cited by 36 publications

(44 citation statements)

References 19 publications

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“…Its frequency was found to be highly dependent on the nanotubes diameter (Alvarez et al, 2000;Jorio et al, 2003;Maultzsch et al, 2005). The same mode has been observed even in semiconductor nanowires (Thonhauser & Mahan, 2005;Lange et al, 2008), and in both cases the inverse dependence on the nanowire diameter has been found. Assuming the nanowire as an infinitely long isotropic cylinder, the linear elasticity theory furnishes an expression of the RBM:…”

Section: Appearance Of New Modes: Surface and Breathing Modessupporting

confidence: 50%

Raman Spectroscopy on Semiconductor Nanowires

Zardo¹,

Abstreiter²,

Morral³

2010

Nanowires

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Section: Appearance Of New Modes: Surface and Breathing Modessupporting

confidence: 50%

Raman Spectroscopy on Semiconductor Nanowires

Zardo¹,

Abstreiter²,

Morral³

2010

Nanowires

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“…Thonhauser and Mahan find a similar dependence for Si[111] nanowires treated with a Stillinger-Weber-type model for isotropic elasticity theory [91]. There, the radial breathing mode frequency is 9) with r = µ λ + 2µ , the longitudinal speed of sound ν l and the elastic constants (λ, µ).…”

Section: Linear Elasticity Theorymentioning

confidence: 82%

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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“…[67] Yang and coworkers demonstrate the high density arrays of GaN nanowires with distinct geometric and physical properties by using MOCVD and appropriate substrate selection. The epitaxial orientation of wurtzite gallium nitride on (110) γ -LiAlO 2 single-crystal substrates is preferable in the orthogonal [1][2][3][4][5][6][7][8][9][10] and [001] directions, exhibiting triangular and hexagonal cross sections and drastically different optical emission (Figure 7.6). [68] …”

Section: Nitrides Nanowiresmentioning

confidence: 99%

“…[121] Thonhauser and Mahan also predicted the RBMs in Si nanowires based on the elastic theory. [8,133] They found that a low frequency Raman mode much lower than the first-order TO mode at ∼520 cm −1 became significant and blueshifted as the diameter of SiNWs decreased to a few nanometer regimes. This behavior is totally different with the redshift behavior of the high frequency mode because of phonon confinement effect.…”

Section: Radial Breathing Modesmentioning

confidence: 99%

“…Phonon confinement has been systematically studied in Si nanowires. [7] Another confinement effect in SNWs is a new vibration mode, known as the radial breathing mode (RBMs), [8] the energy of which increases as the diameter of nanowires decreases. Besides, the nanowire shape is also important to determine the phonon properties in nanowires, which is elaborated in this chapter by examples of surface optical phonons, antenna effect, and stimulated Raman scattering in SNWs.…”

mentioning

confidence: 99%

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