Browsing by Author "Liu, Li-Hong"
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Item Morphology and Chemical Termination of HF-Etched Si₃N₄ Surfaces(American Institute of Physics Inc.) Liu, Li-Hong; Debenedetti, William J. I.; Peixoto, Tatiana; Gokalp, Sumeyra; Shafiq, Natis; Veyan, Jean-François; Michalak, D. J.; Hourani, R.; Chabal, Yves J.Several reports on the chemical termination of silicon nitride films after HF etching, an important process in the microelectronics industry, are inconsistent claiming N-Hx, Si-H, or fluorine termination. An investigation combining infrared and x-ray photoelectron spectroscopies with atomic force and scanning electron microscopy imaging reveals that under some processing conditions, salt microcrystals are formed and stabilized on the surface, resulting from products of Si₃N₄ etching. Rinsing in deionized water immediately after HF etching for at least 30s avoids such deposition and yields a smooth surface without evidence of Si-H termination. Instead, fluorine and oxygen are found to terminate a sizeable fraction of the surface in the form of Si-F and possibly Si-OH bonds. The fluorine termination is remarkably stable in air and water vapor in ambient conditions, with clear implications on further surface chemical functionalization.Item Structural Band-Gap Tuning in g-C₃N₄(Royal Society of Chemistry) Zuluaga, S.; Liu, Li-Hong; Shafiq, Natis; Rupich, Sara M.; Veyan, Jean-François; Chabal, Yves J.; Thonhauser, T.g-C3N4 is a promising material for hydrogen production from water via photo-catalysis, if we can tune its band gap to desirable levels. Using a combined experimental and ab initio approach, we uncover an almost perfectly linear relationship between the band gap and structural aspects of g-C3N4, which we show to originate in a changing overlap of wave functions associated with the lattice constants. This changing overlap, in turn, causes the unoccupied pz states to experience a significantly larger energy shift than any other occupied state (s, px, or py), resulting in this peculiar relationship. Our results explain and demonstrate the possibility to tune the band gap by structural means, and thus the frequency at which g-C3N4 absorbs light.Item Structural Band-Gap Tuning in g-C₃N₄(The Royal Society of Chemistry) Zuluaga, S.; Liu, Li-Hong; Shafiq, Natis; Rupich, Sara M.; Veyan, Jean-François; Chabal, Yves J.; Thonhauser, T.g-C₃N₄ is a promising material for hydrogen production from water via photo-catalysis, if we can tune its band gap to desirable levels. Using a combined experimental and ab initio approach, we uncover an almost perfectly linear relationship between the band gap and structural aspects of g-C₃N₄, which we show to originate in a changing overlap of wave functions associated with the lattice constants. This changing overlap, in turn, causes the unoccupied pz states to experience a significantly larger energy shift than any other occupied state (s, p(x), or p(y)), resulting in this peculiar relationship. Our results explain and demonstrate the possibility to tune the band gap by structural means, and thus the frequency at which g-C₃N₄ absorbs light.