Monolayer tellurium (Te) or tellurene has been suggested by a recent theory as a new two-dimensional (2D) system with great electronic and optoelectronic promises. Here we present an experimental study of epitaxial Te deposited on highly oriented pyrolytic graphite (HOPG) by molecular-beam epitaxy. Scanning tunneling microscopy of ultrathin layers of Te reveals rectangular surface cells with the cell size consistent with the theoretically predicted β-tellurene, whereas for thicker films, the cell size is more consistent with that of the [101[combining macron]0] surface of the bulk Te crystal. Scanning tunneling spectroscopy measurements show that the films are semiconductors with the energy band gaps decreasing with increasing film thickness, and the gap narrowing occurs predominantly at the valence-band maximum (VBM). The latter is understood by strong coupling of states at the VBM but a weak coupling at conduction band minimum (CBM) as revealed by density functional theory calculations.
WO3 nanoparticles doped with Sb, Cd, and Ce were synthesized
by a chemical method to enhance the sensing performance of WO3 for NO2 at room temperature. The doping with Sb
element can significantly enhance the NO2-sensing properties
of WO3. Upon exposure to 10 ppm of NO2, particularly
the 2 wt % Sb-doped WO3 sample exhibits a 6.8-times higher
response and an improved selectivity at room temperature compared
with those of undoped WO3. The enhanced NO2-sensing
mechanism of WO3 by doping is discussed in detail, which
is mainly ascribed to the increase of oxygen vacancies in the doped
WO3 samples as confirmed by Raman, photoluminescence, and
X-ray photoelectron spectroscopy spectra. In addition, the narrower
band gap may also be responsible for the enhancement of response as
observed from the corresponding ultraviolet–visible spectra.
Graphdiyne (GDY) could provide a unique platform for synthesizing uniform single-atom catalysts (SACs) with high catalytic activity toward oxygen reduction (ORR) and oxygen evolution (OER) reactions.
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