The electronic structure of a single Na monolayer on the surface of single-crystal HfSe2 is investigated using angle-resolved photoemission spectroscopy. We find that this system exhibits an almost perfect "nearly-free-electron" behavior with an extracted effective mass of ∼ 1me, in contrast to heavier masses found previously for alkali metal monolayers on other substrates. Our densityfunctional-theory calculations indicate that this is due to the large lattice constant, causing both exchange and correlation interactions to be suppressed, and to the weak hybridization between the overlayer and the substrate. This is therefore an ideal model system for understanding the properties of two-dimensional materials.

Conductive glass was coated with multiwall carbon nanotubes (MWCNTs) by a hydrothermal method. MWCNTs films were subsequently used as dye-sensitized solar cell (DSSC) counter electrodes. The performance of hydrothermal MWCNT DSSC was ∼2.37%. After film annealing in an Ar atmosphere, annealed-hydrothermal MWCNT (AHT-CNT) DSSC efficiency was significantly increased to ∼7.66%, in comparison to ∼8.01% for sputtered-Pt DSSC. Improvement of AHT-CNT DSSC performance is attributed to a decrease in charge-transfer resistance from 1500 Ω to 30 Ω as observed by electrochemical impedance spectroscopy.

By using angle-resolved photoemission spectroscopy (ARPES), the variation of the electronic structure of HfSe2 has been studied as a function of sodium intercalation. We observe how this drives a band splitting of the p-orbital valence bands and a simultaneous reduction of the indirect band gap by values of up to 400 and 280 meV respectively. Our calculations indicate that such behaviour is driven by the band deformation potential, which is a result of our observed anisotropic strain induced by sodium intercalation. The applied uniaxial strain calculations based on density functional theory (DFT) agree strongly with the experimental ARPES data. These findings should assist in studying the physical relationship between doping and strain, as well as for large-scale two-dimensional straintronics.

Light-sensitive capacitance variation of Bi 0.95 La 0.05 feo 3 (BLfo) ceramics has been studied under violet to UV irradiation. The reversible capacitance enhancement up to 21% under 405 nm violet laser irradiation has been observed, suggesting a possible degree of freedom to dynamically control this in high dielectric materials for light-sensitive capacitance applications. By using ultraviolet photoemission spectroscopy (UpS), we show here that exposure of BLfo surfaces to UV light induces a counterintuitive shift of the o 2p valence state to lower binding energy of up to 243 meV which is a direct signature of negative electronic compressibility (NEC). A decrease of BLFO electrical resistance agrees strongly with the UpS data suggesting the creation of a thin conductive layer on its insulating bulk under light irradiation. By exploiting the quantum capacitance model, we find that the negative quantum capacitance due to this NEC effect plays an important role in this capacitance enhancement

In this work, room-temperature ferromagnetism, which is not caused by conventional magnetic elements (e.g., Fe, Co, and Ni), is observed in carbon films prepared by using adamantane (C10H16): the smallest member of the so called diamondoid series (nano-diamond structures). These chemical-vapor-deposition films exhibit a moderately strong ferromagnetism which can be further enhanced by mechanically exfoliating the top layers of the films off; the saturated magnetization can be as large as 4.4 emu/cm3 at room temperature. Magnetic force microscopy measurements show a clear contrast in magnetization between the original and exfoliated regions, indicating that the magnetic origin likely comes from the broken “dangling” bonds at the exfoliated surface. This work suggests an inexpensive method for creating carbon films whose magnetization can be activated from mechanical exfoliation.