Phonon Spectra and Thermodynamic Properties Of Crystalline Nanowires

Abstract

Phonon spectra and allowed phonon states, as well as thermodynamic characteristics of nanowires of simple cubic crystalline structure, are analyzed using the method of two-time dependent Green's functions, adjusted to bounded crystalline structures. Poles of Green's functions, defining phonon spectra, can be found by solving of the secular equation. For different boundary parameters, this problem is presented graphically. The presence of boundaries as well as the change of boundary parameters leads to appearance of new properties of low dimensional structures (thin film and nanowire). The most important feature is that beside allowed energy zones (which are continuous as in the bulk structure), zones of forbidden states appear. Different values of boundary parameters lead to appearance of lower and upper energy gaps, or dispersion branches spreading out of bulk energy zone. The correlation with spectra of phonons in corresponding unbounded structures is maintained in the work. Determination of phonon spectra and allowed phonon energies has great importance for kinetic and thermodynamic properties of semiconductive nanostructures and devices. The temperature behavior of nanowire thermal capacitance is compared to that of bulk structures. It is shown that at extremely low temperature nanowire thermal capacitance is considerably lower than the thermal capacitance of bulk sample. It was discussed what are the consequences of this fact to the thermal, conducting and superconducting properties of materials.

Phonon Contribution in Thermodynamics οf Nano-Crystalline Films and Wires

“…Starting point of our theoretical approach is the standard Hamiltonian of the phonon subsystem for bulk structures [5][6][7][8], written in the harmonic as well as in the nearest neighbor approximations, which is adapted to the model-structure of quantum wire presented in Fig. 1b:…”

Phonon Participation in Thermodynamics and Superconductive Properties of Thin Ceramic Films

“…Phonon participation in thermodynamic properties (or heat capacitance temperature behavior, i.e. generallyin heat transferring) in thin film was found in our previous paper (Lazarev et al, 2000;Jaćimovski et al, 2004;Šetrajčić et al, 2007;Ilić et al, 2007;Šetrajčić et al, 2009). Getting that, when k → 0 (in long-wave approximation: 4 sin 2 (ak x /2) + sin 2 ak y /2 ≈ a 2 k 2 , k 2 = k 2 x + k 2 y ), energies of all three phonon branches have non-zero values, it can be utilized dispersion relations 22, 49 and 64, in somewhat simplified form:…”

Shell-Nanostructured Materials for Biopharmacy and Biomedicine

“…The most significant results that we have achieved in our previous researches [32][33][34][35], concerning the formation and the analysis of the core-shell crystalline nanomodel and its potential application in nanomedicine, can be briefly defined in the following way: on bordering surfaces of the nanofilm (here it is a nanoshell), due to extreme localization of elementary excitations, all the physical properties of the material change, therefore: − Small, thermally or mechanically stimulated disturbances can become surface waves of great amplitude, i.e. energies that can imply the braking up of crystallographic connections between the atoms of bordering planes and the decomposition of the bordering layer, and then of all the other atoms; − Heat can be more easily absorbed and surface conducted, which allows the nanolayer to be supplied with additional energy which is necessary to melt the material on bordering layers first, and the other layers afterwards;…”