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.
Highlights
Nanoscale engineering of silicon carbide (SiC) allows for considerable modification of its basic physicochemical properties
To study the stability of the porous silicon carbide (pSiC) structures with different porosities and varying amounts of oxygenation, we calculated the formation energies Ef according to the expression [19]: X
Where EpSiC is the ground-state energy of the passivated pSiC, ni indicates the number of the atomic species per supercell, and μi is the chemical potential of the atomic species
Summary
Nanoscale engineering of silicon carbide (SiC) allows for considerable modification of its basic physicochemical properties. SiC nanostructures have shown greater elasticity and strength than bulk SiC [1], and SiC nanowires have stable emission properties and an electron field emission threshold comparable to those of carbon nanotube-based materials. Various SiC nanostructures, such as nanospheres, nanowires, nanorods, nanopowders, and even nanoflowers, have been developed [2,3,4,5] with interesting technological applications. Among the multiple SiC nanostructures, porous silicon carbide (pSiC) is. SiC is a material with multiple polytypes, and porous structures, such as 6H and 4H porous SiC, have been developed in these polytypes. Porous structures have not received as much attention because of the special conditions required to grow crystals of this polytype [10]; cubic pSiC exhibits promising properties for use in fast-response hydrogen (H) sensors [11]. This research could be fundamental to understanding the properties of these materials to enhance their possible applications
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