Experimental Control and Statistical Analysis of Thermal Conductivity in ZnO–Benzene Multilayer Thin Films

Abstract

We have fabricated a model system of precisely layer-engineered inorganic–organic thin-film structures using atomic/molecular-layer deposition (ALD/MLD). The samples consist of nanoscale polycrystalline ZnO layers and intervening benzene layers, covering a broad range of layer sequences. The samples characterized in this study combined with previous publications provide an excellent sample set to examine thermal transport properties in inorganic–organic thin films. The cross-plane thermal conductivity is found to depend on multiple factors, with the inorganic–organic interface density being the dominating factor. Our work highlights the remarkable capability of interface engineering in suppressing the thermal conductivity of hybrid inorganic–organic materials, e.g., for thermoelectric applications.

Atomic/Molecular Layer Deposition for Designer's Functional Metal–Organic Materials

“…Diethylzinc is the most common precursor for zinc in the ALD/MLD processes; it is often combined with HQ, [54,55,66,107,133,230,[244][245][246][247]250,361,366,[370][371][372][373][374][375][376][377][378] but also with many other organic components. [46,48,115,134,211,212,226,228,233,238,239,241,265,272,278,324,345,349,[379][380][381][382][383][384][385][386][387][388]…”

“…Through smart design of the organic component itself and the frequency pattern, it is introduced within the ZnO film, the thermal conductivity of ZnO films has been suppressed by the factor of 50 without compromising the electrical transport properties. [64,245,375] Another unique feature of the ALD-/MLD-grown ZnO:organic SL films is the fact that they can be deposited in a conformal manner on textile fibers so that the entire textile piece becomes an active part of the device; this is highly promising considering the potential wearable thermoelectric devices. [55] An attractive new organic component for the multifunctional SL structures is the photoresponsive azobenzene moiety which undergoes reversible trans-cis-trans photoisomerization reactions upon successive UV and visible light illuminations.…”

“…Diethylzinc is the most common precursor for zinc in the ALD/MLD processes; it is often combined with HQ, [ 54,55,66,107,133,230,244–247,250,361,366,370–378 ] but also with many other organic components. [ 46,48,115,134,211,212,226,228,233,238, 239,241,265,272,278,324,345,349,379–390 ] The DEZ + HQ process has been widely utilized for the growth of different superlattice structures in which the Zn–HQ layers are combined with thicker ZnO layers grown with ALD cycles from DEZ plus H 2 O.…”

Sn-Doped In2O3Nanoparticles as Thermal Insulating Materials for Solar–Thermal Shielding in the Infrared Range

“…Recent works on thermal transport research have been devoted to controlling thermal conductivity in disordered materials. For example, grain boundaries (GBs) are among the most commonly observed imperfections in solids, and phonon and electron scattering at GBs plays a critical role in thermal conduction in polycrystalline materials. , These scattering processes dominate the thermal transport in polycrystalline ZnO/Al and ITO films. − These boundary scatterings have been further investigated in detail using two-dimensional (2D) superlattices with atomic interfaces. , Moreover, silica aerosols have attracted much attention because of their low thermal conductivity at room temperature (RT) . These silica-based mesoporous structures have been suggested to control thermal conductivity as a consequence of their nanoscale architecture .…”

Robust and Electrically Conductive ZnO Thin Films and Nanostructures: Their Applications in Thermally and Chemically Harsh Environments

“…“Harsh electronics”, which are electronic devices designed to operate in harsh environments, have garnered significant attention owing to increasing demands for chemical imaging, energy harvesting, and conventional electrical applications in extreme conditions. − In these harsh electronics, such as bio- and chemical sensors, stable electronic materials in harsh environments (e.g., high temperature, high humidity, chemically active medium) are necessitated. The intrinsic stability of electronic materials under harsh conditions is difficult to secure in harsh electronics because conventional encapsulation packaging cannot be used in bio- and chemical sensors, which must be exposed to the surroundings. − The thermal stability of the electrical properties is one of the most important requirements for materials used in harsh electronics because chemical sensor, chemical industry, and aerospace applications are typically operated at temperatures exceeding 200 °C. − Wide bandgap semiconductors are suitable for electron devices operated at high temperatures because the intrinsic carrier density increases significantly with temperature in conventional narrow bandgap semiconductors (Si, III–V). Morphological changes such as crystallization and phase transition can cause the electrical degradation of electronic materials at high temperatures. , Furthermore, in open-top applications such as chemical sensors, chemical reactions with chemically active species in atmospheric air (e.g., O 2 , H 2 O, and CO 2 ) must be suppressed at high operating temperatures. − Chemical stability is another essential challenge for materials used in harsh electronics.…”