Application of Ab Initio Theory to the Chemistry of Ultrathin Films

摘要

In this work, we investigate a number of important nanosheets, e.g., graphene, haeckelites, and titanium disulde for the expressed purpose of tuning the electronic ground state properties. We employ condensed matter techniques to interrogate realized and theoretically postulated ultrathin lms to mine ground state properties that may bolster established, or nascent nanotechnologies. In this regard, a number of ultrathin lms are tuned to induce new material properties that are not intrinsic to the original crystal. We show that chemical modication with extrinsic substitutional pnictogen dopants placed within the crystal lattice of graphene can functionalize the basal plane of graphene to obtain potentially catalytic properties. Furthermore, an alternative doping strategy, less intensive than pnictogenic substitutions, including halogen diatomic molecules were introduced as adsorbates on monolayer, bilayer, and multilayer graphenes of dierent polymorphism to in uence the ground state of the graphitic nanosheets. We observed the induction of a band gap of controllable size as a function of halogen and polymorphism. Consequently, the semimetallic graphene systems formed a p-type semiconductor, which enables eld-dependent control of Dirac carriers within the ultrathin lms. Each of these studies take advantage of the orbital and lattice degrees of freedom enabling tunability of this monoelemental nanosheet. Furthermore, the authors postulate theorized ultrathin lms dubbed Archimedean ultrathin lms. These nanosheets form a unique semiregular polygonal (4,8)-tessellated conguration. This conguration was extended to bulk crystals where we show the potential for forming ultrathin lms that contain this unique symmetry. Two groups were studied: the boron pnictides, and the aluminum pnictides. The ground states featured indirect band gap semiconductors, where it was discovered that the boron-pnictides, in particular the planar congurations, possessed a double band gap. Subsequently, the optical response of the boron pnictides were revealed within linear response time-dependent density functional theory, which showed that the planar ultrathin lms displayed strong optical response from the UV to the IR. Finally, the electronic ground state of 1T-TiS2 was mechanically strained to induce phase transitions converting this nanosheet into a direct band gap semiconductor. Hence, we demonstrate the tunability of material properties for a series of ultrathin lms, whose material properties could provide or support existing and nascent nanotechnologies for the 21st-century.