Herein, enhancements in thermoelectric performance, both power factor and thermal stability, are exhibited by sandwiching HfO 2 and TiO 2 layers onto atomic layer deposited ZnO thin films. High temperature thermoelectric measurements from 300 to 450 K revealed an almost two-fold improvement in electrical conductivity for TiO 2 /ZnO (TZO) samples, primarily owing to increase in carrier concentration by Ti doping. On the other hand, HfO 2 /ZnO (HZO) achieved the highest power factor values owing to maintaining Seebeck coefficients comparable to pure ZnO. HZO also exhibited excellent stability after multiple thermal cycles, which has not been previously observed for pure or doped ZnO thin films. Such improvement in both thermoelectric properties and thermal stability of HZO can be attributed to a shift in crystalline orientation from a-axis to c-axis, as well as the high bond dissociation energy of HfO, stabilizing the ZnO structure. These unique properties exhibited by ALD HZO and TZO thin films pave the way for next generation transparent thermoelectric devices.
This study aims to characterize the Philippine natural bentonite from Mangatarem, Pangasinan for potential topical applications. Six samples were obtained from the mine site. Using the low angle region of their XRD patterns, initial mineralogical analysis of the samples was conducted. The presence of the 6.08° peak, which represents the presence of pure smectite material, was only observed in one sample, D2. The long range XRD pattern of the D2 bentonite sample confirmed montmorillonite as the main component. Other clay minerals such as hectorite and mordenite were also detected in small intensities. In the chemical analysis, Si and Al were the primary elemental components. However, the presence of high amount of Ca revealed that the sample is Ca-bentonite. Also present are other exchangeable cations such as Na+, K+, and Mg2+. To confirm their applicability for topical uses, the CEC, pH and presence of E. coli were determined. The CEC of the sample was 114.32 meq/100g, and the pH value was 7.1. Microbial test also confirmed the absence of E. coli. These tests all validate that the sample is safe and viable for topical applications.
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