Thermal transport in two- and three-dimensional nanowire networks

Abstract

We report on thermal transport properties in 2 and 3 dimensions interconnected nanowire networks (strings and nodes). The thermal conductivity of these nanostructures decreases in increasing the distance of the nodes, reaching ultra-low values. This effect is much more pronounced in 3D networks due to increased porosity, surface to volume ratio and the enhanced backscattering at 3D nodes compared to 2D nodes. We propose a model to estimate the thermal resistance related to the 2D and 3D interconnections in order to provide an analytic description of thermal conductivity of such nanowire networks; the latter is in good agreement with Molecular Dynamic results.New innovating and hightly sophisticated architectured nanostructures are now feasible with the rapid evolution of the elaboration methods [1][2][3][4]. Among them 2D and 3D networks of nanowires are a new class of nanostructured materials with interesting mechanical, optical, electronic and thermal properties. 2D networks are proposed as optoelectronic or biological devices and sensors due to their mechanical strength and flexibility [4]. Furthermore, 2D or 3D ordered or disordered networks could be useful for complex integrated nanoelectronic circuits [5]. Independently of their application, their main characteristics are the extremely low mass density, the high surface to volume ratio as well as high porosity and their remarkable mechanical properties. In the literature, 3D networks have been elaborated during the last decade at the nanoscale with several different materials (silver [6], manganese dioxide [7] or silicon [8,9]).There are three main fields of applications for silicon nanowire (NW) networks and nanomeshes. (i) Thermoelectricity (TE): The huge porosity and surface-tovolume ratio of such nanostructures reduce strongly their lattice thermal conductivity (TC), making Si NW networks promising candidate for TE applications [10][11][12][13].(ii) Transistors: These systems can be easily integrated in nanoelectronic devices (Si compatible) and could be the next generation of transistors thanks to their high density of nanowire interconnections [14][15][16]. (iii) Catalysis: Nanowire networks are interesting for catalysis applications because of their large surface-to-volume ratio that allows improved efficiency of chemical reactions. Furthermore, their strong mechanical robustness as compared to isolated nanowires or nanoparticles make them interesting candidates to practically achieved all these innovative applications [1,17].Concerning the thermal properties of nanostructures, they have attracted high attention for various applications in the fields of microelectronics, optoelectronics and energy harvesting. Nanoscale heat transfer is known to diverge from classical physics [18], especially in semi- * Konstantinos.Termentzidis@insa-lyon.fr conductors where heat is mostly carried by lattice vibrations (phonons). Interestingly, nano-structuration usually reduces the TC due to boundary scattering while the electrical properties could be preserved [19]....

Ballistic Heat Transport in Nanocomposite: The Role of the Shape and Interconnection of Nanoinclusions

“…It has even been shown recently for argon NWs that this specularity parameter has a stronger effect on the thermal conductivity than the confinement effect [ 71 ]. Moreover, due to the geometry, the impact of boundary scattering might be even more important, especially in the case of the NW-M, where back scattering at intersections is expected to play an important role [ 28 ], whereas no impact of the intersection of the NW is visible in Table 3 .…”

“…More generally, Car et al showed that it is possible to obtain single crystalline nanowire meshes (NW-M) [ 26 ]. These NW-M, in 2D or 3D, are also known to have a low thermal conductivity compared to bulk material [ 27 , 28 ]. Finally, a crystalline/amorphous nanocomposite is comparable to nanocrystalline materials.…”

Hierarchically nanostructured thermoelectric materials: challenges and opportunities for improved power factors

“…The phonon NEGF with anharmonic effects, however, although developed by some groups but primarily for ultra-narrow channels [266][267][268], has not yet been expanded to treat large nanostructured TE materials. To-date, the most important method to compute the thermal conductivity in nanostructures remains molecular dynamics, which has been used extensively (mostly for Si/Ge materials) [207,[269][270][271][272][273][274][275][276][277][278][279][280][281][282][283][284]. Molecular dynamics, on the other hand, require accurate interatomic potentials which are only available for a limited range of materials.…”

Effects of Size Reduction on the Electrical Transport Properties of 3D Bi Nanowire Networks

“…[ 14,29,30 ] In the case of 3D nanowire networks, carrier transport can be at the same time influenced by additional scattering effects at the intersections between adjacent nanowires, which number can be systematically adjusted by varying nanowire density and/or size. [ 31,32 ] In this way, the morphology of the sample can be customized from a network of interconnected individual nanowires whose transport is dominated by the individual nanowire properties to a porous film with bulk‐like transport properties. Due to the experimental difficulty to fabricate NWNWs with controlled hierarchical assembly and geometry, experimental data on the influence of wire interconnects on the transport properties are still scarce.…”