Akademik Veri Yönetim Sistemi
Tezin Türü: Doktora
Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Bilimleri Enstitüsü, Fen Bilimleri Enstitüsü, Türkiye
Tezin Onay Tarihi: 2017
Öğrenci: TUĞÇE İRFAN AKAY
Eş Danışman: HANDE TOFFOLİ, BURCU AKATA KURÇ
Özet:In the past few decades, nanomaterials have received increasing attention in various applications such as drug delivery, sensors, hydrogen storage and solar cells. This thesis focuses on the theoretical exploration of pristine and defective graphene in order to highlight the functionalization potential with the use of a wide variety of molecules such as benzene (C6H6), toluene (C7H8), fluorobenzene (C6H5F), benzonitrile (C7H5N) , benzoic acid (C7H6O2), and boron (B) atom. The structures as well as electronic properties of these graphene based nano structures are investigated in detail using first-principle calculations using planewave pseudopotential method based on density functional theory (DFT). In order to understand the effect of different van der Waals (vdW) dispersion forces on structural and electronic properties, the adsorption of C6H6 and C7H8 on pristine and defective graphene are investigated with three different exchange-correlation functionals namely vdW-DF, vdW-DF2-C09 and Grimme-D2. This study reveals that the vdW-DF2-C09 exchange-correlation protocol for the vdW interactions produces the closest agreement with literature. Furthermore, the adsorption of C6H6 and C7H8 is investigated on bilayer graphene to understand the effects of number of layers on adsorption characteristics. This study reveals that the presence of the second layer increases the adsorption energy by approximately 70 meV for both molecules. Following the exploration of the interaction of pristine graphene and its derivatives with C6H6 and C7H8, boron (B) is introduced in the graphene network with mono and divacancy defect to controllablly engineer the electronic properties of graphene. A systematic study for the magnetization characteristics is demonstrated where the resulting magnetization of B-doped vacancy-defected graphene (BVG) is 0.9 mB per cell while it is 0 mB per cell for B-doped divacancy-defected graphene (BDG). For the electronic properties, we show the role of B concentration and position on charge transfer and band structure. The band gap opening increases with the increased concentration of B while graphene sheet becomes p-doped with B as a dopant. Finally, we focus on organic adsorbates for additional control of the electronic properties of BVG. C6H6, C7H8, C6H5F, C7H5N, and C7H6O2 are studied with different adsorption geometries. C6H5F and C7H6O2 are found to adsorb through weak vdW interactions, C7H5N molecules are observed to form strong covalent bonds with the atoms surrounding the defect, and in particular the B atoms. Different bond formation characteristics are observed resulting in phenyl (C6H5) and benzaldehyde (C7H6O) formation. The charge transfer analysis indicate the fact that organic adsorbates donate electron resulting in positively charged species at the end of calculations.