A first-principles investigation on substitutions in the carbon allotropes glitter and graphene

In the literature, a number of syntheses of carbon materials under extremecondition exhibit the presence of a carbon phase, called n-diamond, whosecrystal structure remains unclear. Several crystallographic arrangementshave been proposed, which are critically assessed in this work with regards todynamical stability. It is shown that tetragonal carbon (glitter) is the onlystructure that satisfies this criterion. Glitter is a metallic 3-, 4-connectedallotrope containing 1,4-cyclohexadieneoid units, giving a high energy meta-stable phase. Applying a fully first principles approach, which couples den-sity functional theory (DFT) calculations and Ising-like parameterisation,the possibility of stabilising the structure with nitrogen, boron and siliconsubstitutions has been investigated, finding that there are arrangements withnegative formation energy. These novel arrangements have been tested forvibrational stability, whereby it has been proven that they are dynamicallystable. Moreover a bandgap opens, leading to semiconductor bulk materialsbased on Si, C, B and N.Graphene, a carbon allotrope having the so-called chicken-net structure,is a zero-bandgap semiconductor, which make it promising for nano-electronicapplications. However tuning and modifying the bandgap would expand therange of possible applications, in particular for post-silicon transistors. Theeffect of B substitutions in the graphene lattice has been studied, in termsof stability and electronic structure. The doping at low B concentrationhas been studied with a direct DFT approach while the effect at higherconcentration has been studied with the above-mentioned coupled approach.Novel arrangements, that have semiconductor behaviour, have been provento be dynamically stable at 0 K. The effect of a second B-C layer has alsobeen investigated, finding that is effective on bandgap tuning