We report on measurements of the thermal conductivity of atomic layer deposited polycrystalline zinc oxide (ZnO) films between 30 and 300 K. The room temperature thermal conductivity of the films is found to be twofold less than that of single-crystal ZnO. The maximum thermal conductivities of the polycrystalline samples occur at about 60 K and their values are almost an order of magnitude lower than bulk ZnO. The effect of the grain size and the transparency of the intergrain boundary on the thermal conductivity are analyzed within the framework of the phonon-hopping transport model.

TiO 2 supported Ag nanoparticles with metal loading ranging from 2.0 to 12.0 wt.% have been prepared by reduction of a silver precursor with formic acid under mild conditions. XPS showed that silver remains in a reduced state and TEM has demonstrated that the procedure was effective to produce silver nanoparticles. Only small changes in the metal particle size from 2.0-3.4 nm occurs when the Ag content increases from 2.0 to 12.0 wt.%. O 2 TPD has revealed the presence of different types of adsorbed oxygen species being the one assigned to the active specie called O b which one displayed the highest proportion in the catalysts with higher metal loading. Catalytic activity in the conversion of methanol to formaldehyde showed that those samples with metal loading higher than 7.0 wt% displays higher yields compared to the unsupported silver catalyst.

Electronic doping of transition-metal oxides (TMOs) is typically accomplished through the synthesis of nonstoichiometric oxide compositions and the subsequent ionization of intrinsic lattice defects. As a result, ambipolar doping of wide-band-gap TMOs is difficult to achieve because the formation energies and stabilities of vacancy and interstitial defects vary widely as a function of the oxide composition and crystal structure. The facile formation of lattice defects for one carrier type is frequently paired with the high-energy and unstable generation of defects required for the opposite carrier polarity. Previous work from our group showed that the brucite (β-phase) layered metal hydroxides of Co and Ni, intrinsically p-type materials in their anhydrous three-dimensional forms, could be n-doped using a strong chemical reductant. In this work, we extend the electron-doping study to the α polymorph of Co­(OH)2 and elucidate the defects responsible for n-type doping in these two-dimensional materials. Through structural and electronic comparisons between the α, β, and rock-salt structures within the cobalt (hydr)­oxide family of materials, we show that both layered structures exhibit facile formation of anion vacancies, the necessary defect for n-type doping, that are not accessible in the cubic CoO structure. However, the brucite polymorph is much more stable to reductive decomposition in the presence of doped electrons because of its tighter layer-to-layer stacking and octahedral coordination geometry, which results in a maximum conductivity of 10–4 S/cm, 2 orders of magnitude higher than the maximum value attainable on the α-Co­(OH)2 structure.

No abstract

Ambipolar doping of metal oxides is critical toward broadening the functionality of semiconducting oxides in electronic devices. Most metal oxides, however, show a strong preference for a single doping polarity due to the intrinsic stability of particular defects in an oxide lattice. In this work, we demonstrate that layered metal hydroxide nanomaterials of Co and Ni, which are intrinsically p-doped in their anhydrous rock salt form, can be n-doped using n-BuLi as a strong electron donor. A combination of X-ray characterization techniques reveal that hydroxide vacancy formation, Li + adsorption, and varying degrees of electron delocalization are responsible for the stability of injected electrons. The doped electrons induce conductivity increases of 4−6 orders of magnitude relative to the undoped M(OH) 2 . We anticipate that chemical electron doping of layered metal hydroxides may be a general strategy to increase carrier concentration and stability for n-doping of intrinsically p-type metal oxides.