In this work, we study the surface energy of monolayer, bilayer and multilayer graphene coatings, produced through exfoliation of natural graphite flakes and chemical vapor deposition.
Atomically
thin, two-dimensional (2D) indium selenide (InSe) has attracted considerable
attention because of the dependence of its bandgap on sample thickness,
making it suitable for small-scale optoelectronic device applications.
In this work, by the use of Raman spectroscopy with three different
laser wavelengths, including 488, 532, and 633 nm, representing resonant,
near-resonant, and conventional nonresonant conditions, a conclusive
understanding of the thickness dependence of lattice vibrations and
electronic band structure of InSe and InSe/graphene heterostructures
is presented. Combining our experimental measurements with first-principles
quantum mechanical modeling of the InSe systems, we identified the
crystal structure as ε-phase InSe and demonstrated that its
measured intensity ratio of Raman peaks in the resonant Raman spectrum
evolves with the number of layers. Moreover, graphene coating enhances
Raman scattering of few-layered InSe and also makes its photoluminescence
stable under higher intensity laser illumination. The optically induced
charge transfer between van der Waals graphene/InSe heterostructures
is observed under excitation of the E′ transition in InSe,
where the observed mechanism may potentially be a route for future
integrated electronic and optoelectronic devices.
The synthesis of TiO2 thin films by the chemical spray pyrolysis method at different titanium isopropoxide (TTIP) to acetylacetone (AcacH) ratios has been shown to lead to the highest photodegradation at 1 (TTIP):8 (AcacH). These films hold promise in the field of indoor pollution treatment. Carbon incorporation into the surface and into the TiO2 lattice could be responsible for the observed performance, but the mechanism is still to be elucidated. Here, we report the correlation of contact potential difference (CPD) contrast maps as produced using Kelvin Probe Force Microscopy, and the observed functionality dependence on the TTIP to AcacH ratio. Since the CPD contrast locally provides information about the sample's Fermi level, this correlation provides a means to interpret enhanced photocatalytic activity in terms of the presence of acceptors that make possible a faster transfer of charge carriers to the surface.
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