Lattice dynamics of silicon nanostructures

Hepplestone, Steven P.; Srivastava, G. P.

doi:10.1088/0957-4484/17/13/035

Cited by 29 publications

(33 citation statements)

References 34 publications

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“…The embedding technique employed by Hepplestone and Srivastava [85] for nanowires almost mimics the clamped boundary conditions employed by Thonhauser and Mahan [86] and has the advantage that the resulting phonon dispersion curves represent those of a nanostructure on a substrate. However, the disadvantage of this technique is that, as the rotational freedom is not available, it would not allow for the fourth acoustic branch obtained for a free standing nanowire [87].…”

Section: Si Nanowiresmentioning

confidence: 99%

“…The phonon dispersion curves and density of states obtained by Hepplestone and Srivastava [85] for an ultrathin Si nanowire (NW) of cross-section 0.543 nm × 0.543 nm and growth direction [001], obtained from BCM calculations [85], are shown in Fig. 5.…”

Section: Si Nanowiresmentioning

confidence: 99%

“…The DOS curves for the wire and bulk are shown with bold and dashed lines, respectively. Taken with permission from [85].…”

Section: Si Nanowiresmentioning

confidence: 99%

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Tuning phonon properties in thermoelectric materials

Srivastava

2015

Rep. Prog. Phys.

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Abstract.This review article presents a discussion of theoretical progress made over the past several decades towards our understanding of thermoelectric properties of materials. Particular emphasis is paid towards describing recent progress in 'tuning' phonon properties of nano-composite materials for gaining enhancement of the thermoelectric figure of merit. Tuning phonon properties in thermoelectric materials2

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Section: Si Nanowiresmentioning

confidence: 99%

Section: Si Nanowiresmentioning

confidence: 99%

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Tuning phonon properties in thermoelectric materials

Srivastava

2015

Rep. Prog. Phys.

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“…The concept of an atomic supercell has been studied by Hepplestone et al 46 where they considered different reduced-dimension configurations of silicon. In their supercell lattice dynamics calculations they modeled bulk unit cells with a special treatment for the outer atoms to extract the configuration of the reduced dimension structure of interest.…”

Section: A Supercells: Structure and Lattice Dynamicsmentioning

confidence: 99%

Thermal characterization of nanoscale phononic crystals using supercell lattice dynamics

Davis

Hussein

2011

AIP Advances

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The concept of a phononic crystal can in principle be realized at the nanoscale whenever the conditions for coherent phonon transport exist. Under such conditions, the dispersion characteristics of both the constitutive material lattice (defined by a primitive cell) and the phononic crystal lattice (defined by a supercell) contribute to the value of the thermal conductivity. It is therefore necessary in this emerging class of phononic materials to treat the lattice dynamics at both periodicity levels. Here we demonstrate the utility of using supercell lattice dynamics to investigate the thermal transport behavior of three-dimensional nanoscale phononic crystals formed from silicon and cubic voids of vacuum. The periodicity of the voids follows a simple cubic arrangement with a lattice constant that is around an order of magnitude larger than that of the bulk crystalline silicon primitive cell. We consider an atomic-scale supercell which incorporates all the details of the silicon atomic locations and the void geometry. For this supercell, we compute the phonon band structure and subsequently predict the thermal conductivity following the Callaway-Holland model. Our findings dictate that for an analysis based on supercell lattice dynamics to be representative of the properties of the underlying lattice model, a minimum supercell size is needed along with a minimum wave vector sampling resolution. Below these minimum values, a thermal conductivity prediction of a bulk material based on a supercell will not adequately recover the value obtained based on a primitive cell. Furthermore, our results show that for the relatively small voids and void spacings we consider (where boundary scattering is dominant), dispersion at the phononic crystal unit cell level plays a noticeable role in determining the thermal conductivity

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“…The failure of such models arises in accurately obtaining bulk phonon eigensolutions, where several parameters (over 20) are required and physical meaning is lost. The adiabatic bond-charge model [9] has successfully been applied to study the lattice dynamics of tetrahedrally bonded semiconductors and their nanostructures. In this work, we have applied an enhanced version of the bond-charge model (EBCM) to tetrahedrally bonded PCs Si=Sn and Si=Ge by considering the parameters required to calculate the matrix elements for interface bonds as appropriately weighted average values of the bulk materials.…”

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confidence: 99%

Hypersonic Modes in Nanophononic Semiconductors

Hepplestone

Srivastava

2008

Phys. Rev. Lett.

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Frequency gaps and negative group velocities of hypersonic phonon modes in periodically arranged composite semiconductors are presented. Trends and criteria for phononic gaps are discussed using a variety of atomic-level theoretical approaches. From our calculations, the possibility of achieving semiconductor-based one-dimensional phononic structures is established. We present results of the location and size of gaps, as well as negative group velocities of phonon modes in such structures. In addition to reproducing the results of recent measurements of the locations of the band gaps in the nanosized Si=Si 0:4 Ge 0:6 superlattice, we show that such a system is a true one-dimensional hypersonic phononic crystal. DOI: 10.1103/PhysRevLett.101.105502 PACS numbers: 63.22.Np, 43.35.+d, 63.20.Àe, 68.35.Iv Phononic crystals (PCs) are the vibrational analogues of photonic crystals and offer the possibility of novel applications for phonon engineering including noise-proof devices and sound filters [1,2]. A PC is created by arranging two or more different materials with contrasting vibrational properties periodically. The acoustic mismatch between the constituent materials can be considered to arise either from difference in interatomic force constants and masses (atomic-scale theory) or in density and elastic modulii (continuum-scale theory). The novel physical properties of such structures arise from the possibility of two important features: creation of phononic band gaps (frequency ranges in which acoustic crystal vibrations cannot propagate) and negative refraction (phonon branches with negative group velocity). These features have been predicted by various theories [3] and have been confirmed by experiments [2,4]. Most currently realizable phononic structures rely on solid or fluid composites [2] on the scale of m-mm, which are poor candidates for electronic and optical applications. Recent technological advances have led to the fabrication of nanophononic materials [5,6], which are potential hypersonic systems. However, from an application point of view, relatively little progress has been made on Si based structures, with most relying on Si-air interfaces [7].In this Letter, we investigate, by employing at different levels of sophistication and examining available experimental evidence, the criteria to produce nanophononic semiconductor structures. We first apply an easy-tounderstand periodic ball-and-spring model to establish criteria for phononic band gaps. Within the framework of these criteria, we apply an enhanced adiabatic bond-charge model (EBCM) to explore the possibility of semiconducting PCs. Various structures possessing one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) periodicities are investigated, including the Si=SiGe superlattice fabricated by Ezzahri et al. [6]. We produce full phonon dispersion relations and reveal the phononic nature of these systems. In particular, we compare our results with the measurements of Ezzahri et al. and reveal important features previously n...

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Lattice dynamics of silicon nanostructures

Cited by 29 publications

References 34 publications

Tuning phonon properties in thermoelectric materials

Tuning phonon properties in thermoelectric materials

Thermal characterization of nanoscale phononic crystals using supercell lattice dynamics

Hypersonic Modes in Nanophononic Semiconductors

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