Michel Kazan

Bio: Michel Kazan is an academic researcher from American University of Beirut. The author has contributed to research in topics: Phonon & Thermal conductivity. The author has an hindex of 17, co-authored 66 publications receiving 896 citations. Previous affiliations of Michel Kazan include American University & Aristotle University of Thessaloniki.

Mechanical and Thermal Properties of Metallic and Semiconductive Nanostructures

Abstract: Using a top-down approach, we report a theoretical investigation of the melting temperature at the nanoscale, Tm, for different shapes of “free-standing” nanostructures. To easily calculate the nanoscale melting temperature for a wide range of metals and semiconductors, a convenient shape parameter called αshape is defined. Considering this parameter, we argue why smaller size effects are observed in high bulk melting temperature materials. Using Tm, a phase transition stress model is proposed to evaluate the intrinsic strain and stress during the first steps of solidification. Then, the size effect on the Thornton & Hoffman's criterion at the nanoscale is discussed and the intrinsic residual stress determination in nanostructures is found to be essential for sizes below 100 nm. Furthermore, the inverse Hall-Petch effect, for sizes below ∼15 nm, can be understood by this model. Finally, the residual strain in hexagonal zinc oxide nanowires is calculated as a function of the wire dimensions.

Thermal conductivity of silicon bulk and nanowires: Effects of isotopic composition, phonon confinement, and surface roughness

Abstract: We present a rigorous analysis of the thermal conductivity of bulk silicon (Si) and Si nanowires (Si NWs) which takes into account the exact physical nature of the various acoustic and optical phonon mechanisms. Following the Callaway solution for the Boltzmann equation, where resistive and nonresistive phonon mechanisms are discriminated, we derived formalism for the lattice thermal conductivity that takes into account the phonon incidence angles. The phonon scattering processes are represented by frequency-dependent relaxation time. In addition to the commonly considered acoustic three-phonon processes, a detailed analysis of the role of the optical phonon decay into acoustic phonons is performed. This optical phonon decay mechanism is considered to act as acoustic phonon generation rate partially counteracting the acoustic phonon scattering rates. We have derived the analytical expression describing this physical mechanism which should be included in the general formalism as a correction to the resisti...

Elastic constants of aluminum nitride

Abstract: We report on the application of Brillouin spectroscopy as an approach to non-destructive optical characterization of the elastic constants of semiconductors with the wurtzite symmetry. Three different configurations were used to achieve a complete determination of the elastic stiffness constants of bulk AlN substrates grown by the Physical Vapor Transport (PVT) method. The scattering diagrams of these three configurations are presented showing the geometrical arrangements necessary to observe all the elastic stiffness constants for the partially nontransparent wurtzite type of the crystal structure. Because aluminum nitride (AlN) is a suitable material for the fabrication of light emitting devices, the characterization of its elastic constants was carried out very precisely to provide a reliable data which can be used for the determination of residual stress arising during the growth of AlN thin films or wide band gap semiconductor thin films on substrates of AlN. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Plasmonic mode interferences and Fano resonances in Metal-Insulator- Metal nanostructured interface

Abstract: Metal-insulator-metal systems exhibit a rich underlying physics leading to a high degree of tunability of their spectral properties. We performed a systematic study on a metal-insulator-nanostructured metal system with a thin 6 nm dielectric spacer and showed how the nanoparticle sizes and excitation conditions lead to the tunability and coupling/decoupling of localized and delocalized plasmonic modes. We also experimentally evidenced a tunable Fano resonance in a broad spectral window 600 to 800 nm resulting from the interference of gap modes with white light broad band transmitted waves at the interface playing the role of the continuum. By varying the incident illumination angle shifts in the resonances give the possibility to couple or decouple the localized and delocalized modes and to induce a strong change of the asymmetric Fano profile. All these results were confirmed with a crossed comparison between experimental and theoretical measurements, confirming the nature of different modes. The high degree of control and tunability of this plasmonically rich system paves the way for designing and engineering of similar systems with numerous applications. In particular, sensing measurements were performed and a figure of merit of 3.8 was recorded ranking this sensor among the highest sensitive in this wavelength range.

Oxygen behavior in aluminum nitride

Abstract: The infrared lattice-vibration spectra of three polycrystalline samples of wurtzite AlN differing in their oxygen contamination have been studied by measuring the room-temperature reflectivity at near-normal incidence in the 400-3000cm−1 frequency range using unpolarized light. A type of highly-contaminated-material reflectivity spectrum has been observed. Two-mode behavior has been observed at low oxygen concentration, one-mode behavior tends to be dominant when the oxygen concentration increases and only one-mode behavior has been observed at high oxygen concentration. Otherwise, a careful analysis of the data using the Kramers-Kronig technique and classical dispersion theory gives, in addition to the transverse and longitudinal mode frequencies, two in-band resonance modes attributed to oxygen point defects in AlN. Changes in the frequencies of these modes with oxygen concentration are interpreted as a transition in the oxygen accommodation defect as the concentration of oxygen increases. A model for t...

Highly confined low-loss plasmons in graphene-boron nitride heterostructures

Abstract: Graphene plasmons were predicted to possess ultra-strong field confinement and very low damping at the same time, enabling new classes of devices for deep subwavelength metamaterials, single-photon nonlinearities, extraordinarily strong light-matter interactions and nano-optoelectronic switches. While all of these great prospects require low damping, thus far strong plasmon damping was observed, with both impurity scattering and many-body effects in graphene proposed as possible explanations. With the advent of van der Waals heterostructures, new methods have been developed to integrate graphene with other atomically flat materials. In this letter we exploit near-field microscopy to image propagating plasmons in high quality graphene encapsulated between two films of hexagonal boron nitride (h-BN). We determine dispersion and particularly plasmon damping in real space. We find unprecedented low plasmon damping combined with strong field confinement, and identify the main damping channels as intrinsic thermal phonons in the graphene and dielectric losses in the h-BN. The observation and in-depth understanding of low plasmon damping is the key for the development of graphene nano-photonic and nano-optoelectronic devices.

Low-loss, infrared and terahertz nanophotonics using surface phonon polaritons

Abstract: The excitation of surface-phonon-polariton (SPhP) modes in polar dielectric crystals and the associ- ated new developments in the field of SPhPs are reviewed. The emphasis of this work is on providing an understand- ing of the general phenomenon, including the origin of the Reststrahlen band, the role that optical phonons in polar dielectric lattices play in supporting sub-diffrac- tion-limited modes and how the relatively long opti- cal phonon lifetimes can lead to the low optical losses observed within these materials. Based on this overview, the achievements attained to date and the potential tech- nological advantages of these materials are discussed for localized modes in nanostructures, propagating modes on surfaces and in waveguides and novel metamaterial designs, with the goal of realizing low-loss nanophoton- ics and metamaterials in the mid-infrared to terahertz spectral ranges.

Group III nitride and SiC based MEMS and NEMS: materials properties, technology and applications

Abstract: With the increasing requirements for microelectromechanical systems (MEMS) regarding stability, miniaturization and integration, novel materials such as wide band gap semiconductors are attracting more attention. Polycrystalline SiC has first been implemented into Si micromachining techniques, mainly as etch stop and protective layers. However, the outstanding properties of wide band gap semiconductors offer many more possibilities for the implementation of new functionalities. Now, a variety of technologies for SiC and group III nitrides exist to fabricate fully wide band gap semiconductor based MEMS. In this paper we first review the basic technology (deposition and etching) for group III nitrides and SiC with a special focus on the fabrication of three-dimensional microstructures relevant for MEMS. The basic operation principle for MEMS with wide band gap semiconductors is described. Finally, the first applications of SiC based MEMS are demonstrated, and innovative MEMS and NEMS devices are reviewed.

Manipulation of Phonon Transport in Thermoelectrics.

Abstract: For several decades, thermoelectric advancements have largely relied on the reduction of lattice thermal conductivity (κL ). According to the Boltzmann transport theory of phonons, κL mainly depends on the specific heat, the velocity, and the scattering of phonons. Intensifying the scattering rate of phonons is the focus for reducing the lattice thermal conductivity. Effective scattering sources include 0D point defects, 1D dislocations, and 2D interfaces, each of which has a particular range of frequencies where phonon scattering is most effective. Because acoustic phonons are generally the main contributors to κL due to their much higher velocities compared to optical phonons, many low-κL thermoelectrics rely on crystal structure complexity leading to a small fraction of acoustic phonons and/or weak chemical bonds enabling an overall low phonon propagation velocity. While these thermal strategies are successful for advancing thermoelectrics, the principles used can be integrated with approaches such as band engineering to improve the electronic properties, which can promote this energy technology from niche applications into the mainstream.