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Intercalation of lithium ions in amorphous tungsten oxide films and in monoclinic polycrystalline tungsten oxide films has been studied using electrochemical analyses and Raman spectroscopy. We present direct evidence for W5+ 5d-electron localization in amorphous tungsten oxide films upon lithium ion and electron intercalation by comparing the Raman spectra of amorphous and crystalline tungsten oxide films. We observe that when lithium ions and electrons are inserted into the crystalline tungsten oxide films, the monoclinic structure of the material proceeds to progressively increased symmetry. On the other hand, when lithium ions and electrons are inserted into amorphous tungsten oxide films, the inserted electrons are localized in W5+ sites and polarize their surrounding lattice to form small polarons. The extra Raman peaks due to the W5+&z.sbnd;O single bonds and W5+&z.dbnd6;O double bonds appear at 330 and 450 cm−1, respectively. [Copyright &y& Elsevier]

We report the effects of electrochromic coloration on the Raman spectra of sputtered a-MoO3 films. The Raman spectra of as-deposited films show two strong peaks at 828 and 951 cm−1 due to vibrations of the O&z.sbnd;Mo6+&z.sbnd;O and Mo6+&z.dbnd6;O bonds, respectively. A shoulder on the right side of the Raman peak at 951 cm−1 is observed, and we attribute it to the Mo6+&z.dbnd6;O bonds which originate from the singly coordinated oxygen atoms in α phase layered MoO3. When lithium (or hydrogen) ions and electrons are intercalated into a-MoO3, the overall Raman intensity decreases due to electrochromic coloration and an extra Raman peak due to the bonds between Mo5+ and oxygen atoms appears at ∼400 cm−1. In addition, the force constant for the O&z.sbnd;Mo6+&z.sbnd;O bonds increases due to the compressive stress induced by lithium (or hydrogen) ion insertion. We conclude the Mo5+ states are generated as a result of the reduction of the Mo6+ states with ion/electron insertion and the optical absorption in the colored state is caused by transitions between the Mo6+ and Mo5+. [Copyright &y& Elsevier]

Atomically thin two-dimensional (2D) transition-metal dichalcogenide (TMDC) films have emerged as promising semiconducting materials for use in thermoelectric (TE) applications. However, the utilization of such materials remains challenging owing to the relatively high intrinsic resistance as the size of the TMDC thin films increases to the centimeter scale. These 2D TMDC films can also form vertically stacked homo- or heterostructures at large interfaces with other 2D TMDC films, resulting in unique TE properties at room temperature. This article reports on the in-plane TE properties when the interfaces formed within a PtSe 2 /PtSe 2 (3 nm/3 nm) homostructure are modulated as a function of O 2 plasma treatment time. The results show enhanced Seebeck coefficients compared with that of the single-layer PtSe 2 with the same thickness. The independent enhancement in the Seebeck coefficient while keeping the electrical conductivity leads to a substantial increase in the power factor. Such extra Seebeck voltage in 2D PtSe 2 /PtSe 2 homostructures is mainly as a result of momentum exchange by charge carriers caused by the temperature gradient in the vertical direction, which occurs in-plane Seebeck coefficient measurements, at the interface between the PtSe 2 layers in the in-plane temperature gradient along the samples. These results resemble the characteristics of the phonon drag effect at low temperatures, which can independently increase the Seebeck coefficient at room temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

We investigated alternating current driven inorganic electroluminescence (EL) devices, in which chlorobenzene (CB) treated carbon nanotubes (CNTs) were incorporated within the dielectric layer. The devices having CB-treated CNTs exhibited better performance than the reference device without CNTs. Especially, 0.01 wt% of CB-treated CNTs yielded the best results—an enhancement of up to 50% in the luminance, along with a 30% reduction in the current density compared with the reference one. The improvement in EL performance was attributed to the enhanced dielectric constant of the dielectric layer by inclusion of CB-treated CNTs. This is considered to arise from the combined effect of the micro-capacitors from numerous CNTs in the dielectric layer and the interfacial polarization from the C Cl bonds originating from the CB treatment. In addition, it is essential to control the concentration of CNTs low enough to prevent leakage current paths by percolation, here, 0.01 wt% sufficed this condition. Thus, incorporating CB-treated CNTs into the dielectric layer improved the characteristics of the EL devices, which would be considered as a candidate for future display applications. Image 100768 [ABSTRACT FROM AUTHOR]