Computational simulation of the effects of oxygen on the electronic states of hydrogenated 3C-porous SiC

Abstract

A computational study of the dependence of the electronic band structure and density of states on the chemical surface passivation of cubic porous silicon carbide (pSiC) was performed using ab initio density functional theory and the supercell method. The effects of the porosity and the surface chemistry composition on the energetic stability of pSiC were also investigated. The porous structures were modeled by removing atoms in the [001] direction to produce two different surface chemistries: one fully composed of silicon atoms and one composed of only carbon atoms. The changes in the electronic states of the porous structures as a function of the oxygen (O) content at the surface were studied. Specifically, the oxygen content was increased by replacing pairs of hydrogen (H) atoms on the pore surface with O atoms attached to the surface via either a double bond (X = O) or a bridge bond (X-O-X, X = Si or C). The calculations show that for the fully H-passivated surfaces, the forbidden energy band is larger for the C-rich phase than for the Si-rich phase. For the partially oxygenated Si-rich surfaces, the band gap behavior depends on the O bond type. The energy gap increases as the number of O atoms increases in the supercell if the O atoms are bridge-bonded, whereas the band gap energy does not exhibit a clear trend if O is double-bonded to the surface. In all cases, the gradual oxygenation decreases the band gap of the C-rich surface due to the presence of trap-like states.

Cross‐Linked g‐C3N4/rGO Nanocomposites with Tunable Band Structure and Enhanced Visible Light Photocatalytic Activity

“…As shown in Figure 4, except for −OH group, almost all of other oxygen‐containing functional groups on the GO surface were removed at 550 °C (see the rGO curve in Figure 4), which means that the non‐removed –OH groups could act as cross‐linkers to connect rGO and g‐C 3 N 4 by forming C−O−C bonds in the nanocomposites during thermal conversion. Obviously, the C−O−C peak at ∼1231 cm −1 can be observed for all investigated CN/rGO nanocomposites (Figure 4), further indicating that the non‐removed –OH groups on the rGO surface can be used as cross‐linkers to link rGO and g‐C 3 N 4 , resulting in bandgap narrowing of the nanocomposite 27…”

“…The formation of C−O−C covalent bonding results in a red shift in the absorption band edge of the resulting material 26. Further, theoretical calculations illustrated that oxygen near the conduction and valence bands originated from the C−O−C covalent bonding which introduces extra p states can also decrease the bandgap of a semiconductor 27. It can be also seen from Figure 2a that the rGO modification in g‐C 3 N 4 can not only narrow the bandgap of the nanocomposite, but also improve visible light utilization (stronger absorption intensity of the CN/rGO nanocomposites than that of the pure g‐C 3 N 4 ), which can be advantageous to enhancing the visible light photocatalytic activity of the nanocomposite.…”

“…Obviously, the C − O − C peak at ∼ 1231 cm − 1 can be observed for all investigated CN/ rGO nanocomposites (Figure 4 ), further indicating that the non-removed -OH groups on the rGO surface can be used as cross-linkers to link rGO and g-C 3 N 4 , resulting in bandgap narrowing of the nanocomposite. [ 27 ] X-ray photoelectron spectroscopy (XPS) technique was further employed to characterize the elemental composition and oxygen bonding confi gurations in CN/rGO nanocomposites. As shown in Figure 5 a, the XPS survey spectra of pure g-C 3 N 4 shows only carbon and nitrogen elements.…”

Gold as an intruder in ZnO nanowires

“…37,38 Electronic calculations were undertaken by applying the minimal basis set using effective core pseudopotential to describe the inner electrons of Zn and Au. The ZnO NWs were modelled using a supercell scheme described elsewhere 40 , from a bulk ZnO with hexagonal wurtzite structure. It is noteworthy to point out that different basis sets (double zeta and effective core potential model) have been tested in order to find the optimal basis set for describing electronic properties and energetic stability in ZnO nanowires.…”

“…The calculation of the formation energy in semiconductors has been well established by Zhang and Northrup previously 44,45. Due to the absence of experimental thermochemical data required in the model of Zhang and Northrup, other models are used recently for29,40 . In this work we used the chemical potential for the reagents (Zn, O, Au in the most stable state) calculated with the same model used in the NWs as a reference in the formation of NWs.…”