Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
Browse
2 results
Search Results
Article Citation - WoS: 21Citation - Scopus: 24Effect of Nano-Film Thickness on Thermal Resistance at Water/Silicon Interface(Elsevier Ltd., 2019) Yenigün, Onur; Barışık, MuratParallel to the developments in micro/nano manufacturing techniques, component sizes in micro/nano electro mechanical systems have been decreasing to nanometer scales. Decrease in lengths in heat transfer direction below the heat carrier phonon length scales reduces thermal conduction in semiconductors. This study shows that such altered phonon spectrums with the decrease of size also reduce the heat transfer at the solid/liquid interfaces and can be correlated with the thermal conductivity of the slab. Using Molecular Dynamics (MD), we measured heat transfer between water and silicon of different thickness between 5 nm and 60 nm. Silicon slabs exhibit a linear temperature profile through the bulk where thermal conductivities measured based on Fourier law decreased by the decreasing slab thickness. We applied a semi-theoretical formulism on variation of conductivity by slab thickness. At the interface of these slabs and water, heat passage is disturbed due to the phonon mismatch of dissimilar materials, which is mostly considered as solid/liquid couple interface properties by the earlier literature. Resistance for phonon passage characterized as Kapitza length (L-K) is measured for different slab thicknesses at different surface wetting conditions varying between hydrophilic to hydrophobic. Increasing surface wetting decreases the L-K while at a certain wetting, decreasing the slab thickness increases the L-K. Once the L-K of different size slabs normalized by its bulk value (assumed to be the L-K of the thickest slab at the corresponding wetting), L-K variation by silicon thickness shows a universal behavior independent of surface wetting. A mathematical model describing the exponential increase of L-K by decreasing thickness was developed and validated by an earlier model. We further developed a correlation between the corresponding changes of L-K and conductivity with respective to their bulk values by analytically combining two models as (L-K/L-K-(Bulk)) = exp (3.94(k(Bulk) - k)/(k x k(Bulk))), using which L-K can be predicted from available thermal conductivities of a certain material. Results are crucial for thermal management of current and future electronics. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 18Citation - Scopus: 17Wetting of Single Crystalline and Amorphous Silicon Surfaces: Effective Range of Intermolecular Forces for Wetting(Taylor and Francis Ltd., 2020) Özçelik, Hüseyin Gökberk; Özdemir, Abdullah Cihan; Kim, Bohung; Barışık, MuratWetting at nanoscale is a property of a three-dimensional region with a finite length into the solid domain from the surface. Understanding the extent of the solid region effective on wetting is important for recent coating applications as well as for both crystalline and amorphous solids of different atomic ordering. For such a case, we studied the wetting behaviour of silicon surfaces at various crystalline and amorphous states. Molecular distributions of amorphous systems were varied by changing the amorphisation conditions of silicon. Semi-cylindrical water droplets were formed on the surfaces to be large enough to remain independent of line tension and Tolman length effects. Contact angles showed up to 38% variation by the change in the atomic orientation of silicon. Instead of a homogeneous solid density definition, we calculated different solid densities for a given surface measured inside different extents from the interface. We correlated the observed wetting variation with each of these different solid densities to determine which extent governs the wetting variation. We observed that the variation of solid density measured inside a 0.13 nm extent from the surface reflected the variation of wetting angle better for both single crystalline and amorphous silicon surfaces.