Using a top-down approach, we report a theoretical investigation of the melting temperature at the nanoscale, T m , 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 R shape is defined. Considering this parameter, we argue why smaller size effects are observed in high bulk melting temperature materials. Using T m , 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.

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 resistive phonon-point-defects and phonon-boundary scattering expressions. The phonon-boundary scattering mechanism is taken as a function of the phonon frequency, incidence angles, and surface roughness. The importance of all the mechanisms we have involved in the model is demonstrated clearly with reference to reported data regarding the isotopic composition effect in bulk Si and Si NW samples. Namely, our model accounts for previously unexplained experimental results regarding (i) the isotope composition effect on the thermal conductivity of bulk silicon reported by Ruf et al. [Solid State Commun. 115, 243 (2000)], (ii) the size effect on κ(T) of individual Si NWs reported by Li et al. [Appl. Phys. Lett. 83, 2934 (2003)], and (iii) the dramatic decrease in the thermal conductivity for rough Si NWs reported by Hochbaum et al. [Nature (London) 451, 163 (2008)].

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.