PSI - Issue 23

Sergiy Kotrechko et al. / Procedia Structural Integrity 23 (2019) 310–315 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Rapid development of nanotechnologies and beginning of the utilisation of nanoelements and nanodevices necessitated the problem of predicting their reliability and lifetime. The solution of this task requires fundamentally new approaches, which should take into account the specific features of structure and mechanisms for reaching the limiting state (failure) of nanoelements, namely:  Extremely small sizes of nanoelements, which creates enormous difficulties for experimental investigations, especially - tests for durability; on the other hand, the limited number of atoms in such systems enables to use widely numerical methods (molecular dynamics method, first-principle (DFT) calculations, etc.).  Reaching the limiting state of nanoelements (loss of integrity or functional properties) is associated with the individual atomic bonds break or with atomic rearrangements. In most cases, these are fluctuation-induced processes, accounting for which requires application of the statistical methods.  The specific feature of structure and functioning of the most nanoelements is that the atomic bonds break induced by thermal vibrations occurs under the action of a force field. This creates significant difficulties for the use of classical models based on the Arrhenius theory of reactions [Marinica et al. (2005); Smith (2008)], which are unproductive to account for the effect of stresses on the probability of fluctuation-induced atomic bonds break in nanoelements . This is due to essentially non-linear effects at the atomic scale. Under certain conditions, this is manifested in a synergy of the effect of temperature and stresses on the value of lifetime of nanoelements [Kotrechko et al. (2017)]  The need to take into account quantum-mechanical effects that may influence the probability of failure of nanoelements. The above features of nanosystems are most pronounced in carbyne-graphene nanoelements (CGNs). Therefore, at present, this type of nanoelements are used as a model object both to analyse the atomic mechanisms of fluctuation-induced break of atomic bonds and to predict the lifetime of nanoobjects [Lin et al. (2011)]. The CGNs consists of two graphene sheets connected with a chain of carbon atoms (Fig. 1). From the application point of view, such a nanoelement is considered as a key element of an all-carbon based nanodevice, moreover, it can be used as the element of nanoscale lasers and other optoelectronic devices with tunable wavelengths [Cahangirov et al. (2010)] Lin et al. (2011) have made an attempt to predict the effect of temperature on the lifetime of a carbyne CGN without a force field . It was shown that use of the Meyer-Neldel compensation rule enables to obtain more accurate results in comparison with the classical versions of the Arrhenius theory of reactions. In this paper, by the example of a CGN, key mechanisms are analysed that govern the lifetime of nanoelements within a wide range of both temperatures and mechanical loads. 1. Theory As noted above, prediction of the lifetime of nanoelements requires a description of the fluctuation-induced break of atomic bonds under the conditions of a force field. In classical models, an effect of the force field is accounted via a linear dependence of the height of an energy barrier on the stress level. For nanoobjects this results in large errors. As Slutsker (2004) has shown, even in the simplest case of a monatomic chain, this dependence is essentially nonlinear. Therefore, a fluctuation model was proposed by Kotrechko et al. (2017) to overcome this drawback. According to this model, the probability C P of the atomic bond break is defined as: C C P P   ) ( (1) where C  is the critical value of interatomic distance fluctuation. Fig. 1 . Schematic representation of carbyne-graphene nanoelement