Phonon Spectra and Thermodynamic Properties Of Crystalline Nanowires
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1017-DD08-50
Phonon Spectra and Thermodynamic Properties of Crystalline Nanowires Duöan Ilic1, Siniöa Vucenovic2, Stevo Jacimovski3, Vojkan Zoric3, and Jovan äetrajcic3 1 Faculty of Technical Sciences, University of Novi Sad, Novi Sad, 21000, Yugoslavia 2 Faculty of Medicine, University of Banja Luka, Banja Luka, Republic of Srpska, Bosnia and Herzegovina 3 Department of Physics, Faculty of Sciences, University of Novi Sad, Novi Sad, 21000, Yugoslavia 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. 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. INTRODUCTION Nanowires are confined crystalline structures [1-3] in which conditions on boundary surfaces differ from those inside the wires, i.e. translational symmetry is broken along directions perpendicular to the wire (z and y directions, Figure 1). Z
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Figure 1. Cross section (along X-plane) of the nanowire model
Providing that there is no disturbance of the crystalline structure inside the wire (between its boundary surfaces), we assume that nanowire is ideal. On the contrary, if there are impurities, vacancies and the like in the crystalline lattice, nanowire is deformed. The scope of our study in this paper is the ideal nanowire of simple
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