Growth Mechanism and Interfacial Electronic Properties of Graphene and Silicene Two Dimensional Semiconductor Materials

This thesis attempts to paint a clear picture about the growth mechanism of graphene from Polycyclic aromatic hydrocarbons (PAHs) on Cu(111) surface and interfacial electronic properties of graphene and silicene to promote application of Two Dimensional Group IV Semiconductor and shed light on rational design of functional devices.;Firstly, in order to obtain insights into the reaction mechanism, the bottom-up growth of graphene from PAHs on Cu(111) surface has been systematically analyzed by means of large-scale ab initio simulation in a density functional theory (DFT) framework. Theoretical calculation shows that the underlying growth mechanism, which mainly involves surface-mediated nucleation process of dehydrogenated PAHs rather than segregation or precipitation process of small carbon clusters decomposed from the precursors. The quality of the synthesized graphene sheets and minimum growth temperature strongly depends on the structures of PAHs as well as the molecular activities. Increasing the growth temperature will augment the activity of carbon clusters, so as to increase the probability in formation of prefect graphene sheets. Coronene, having 6-fold rotational symmetry and the same lattice as graphene, has the highest probability in forming high quality graphene, especially at relatively low growth temperature.;Secondly, the electronic properties of graphene supported by (0001) SiO 2 surface are theoretically studied using the density functional theory. It is found that the electronic attributes of graphene on (0001) SiO 2 strongly depend on the underlying SiO2 surface properties and the percentage of hydrogen-passivation. By applying methyl to passivate oxygen-terminated (0001) SiO2 surface one can further reduce the interaction between the graphene sheet and oxygen-terminated surface. This can improve the charge carrier mobility of graphene supported by SiO 2 substrate and reduce the influence by residual interfacial molecules. In addition, the external electric field modulates the charge transfer between graphene and the SiO2 surface, when graphene layers are physisorbed on the oxide surface. This phenomenon will enhance the built-in electric field of bilayer graphene so as to effectively modify its band structure. Our results shed light on a better atomistic understanding of the recent experiments on graphene supported by SiO2.;Based on the above two conclusions, the graphene/substrate interface properties and engineering of bottom-gated, large-scale triphenylene-derived graphene transistors by applying octadecyltrimethoxysilane (OTMS) self-assembled monolayers (SAM) onto the gate dielectric surface are studied. To meet the challenge that the isolated carbon monomers are likely to form defective carbon clusters with pentagons, at the initial stage of CVD graphene growth, triphenylene (C18H12) (pentagon-free with only C and H) was used as the solid precursor for high-quality and large-scale graphene synthesis. Transport measurements performed on back-gated graphene field-effect transistors (GFETs) with large channel lengths (~25 microm) show a carrier mobility up to ~ 5090 cm2V-1s-1 on SiO 2/Si substrate at room temperature under vacuum. Furthermore we show that in virtue of the ultrasmooth SAM surface and reduced interfacial impurity scattering as well as attenuated surface polar phonon scattering, the GFET carrier mobility on octadecyltrimethoxysilane (OTMS) passiviated SiO 2 surface is consistently improved up to ~ 9080 cm2V -1s-1, whose graphene active layer has been grown with triphenylene precursor.;Finally, by exploiting first-principles calculations, we show that the band gap and electron effective mass (EEM) of various confined graphene and silicene (D-X/G/H-D, Si-X/S/H-Si and D-X/S/H-D) can be effectively modulated by tuning the pressure (interlayer spacing) and stacking arrangement. Using the confined technique and pressure, the integrity of the honeycomb structure of graphene and silicene will be preserved, so the small effective masses and high mobility of graphene and silicene will remain during compression. The tunable band gap and high carrier mobility of the sandwich structures are promising for building high-performance nanodevices. (Abstract shortened by UMI.).