Browsing by Subject "Termination"
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Item Open Access Ab initio study of Ru-terminated and Ru-doped armchair graphene nanoribbons(Taylor and Francis, 2012) Sarikavak-Lisesivdin, B.; Lisesivdin, S. B.; Özbay, EkmelWe investigate the effects of ruthenium (Ru) termination and Ru doping on the electronic properties of armchair graphene nanoribbons (AGNRs) using first-principles methods. The electronic band structures, geometries, density of states, binding energies, band gap information, and formation energies of related structures are calculated. It is well founded that the electronic properties of the investigated AGNRs are highly influenced by Ru termination and Ru doping. With Ru termination, metallic band structures with quasi-zero-dimensional, one-dimensional and quasi-one-dimensional density of states (DOS) behavior are obtained in addition to dominant one-dimensional behavior. In contrast to Ru termination, Ru doping introduces small but measurable (12.4 to 89.6meV) direct or indirect band gaps. These results may present an additional way to produce tunable band gaps in AGNRs.Item Open Access Accurate and process-tolerant resistive load(IEEE, 2020) Sütbaş, Batuhan; Özbay, Ekmel; Atalar, AbdullahResistive terminations cannot preserve high-quality matching at high frequencies due to the parasitic effects of the nonideal resistor. Moreover, resistance values of the termination resistors in integrated circuits are subject to process variations. Therefore, it is difficult to obtain accurate and process-tolerant terminations that are crucial for high performance in microwave circuits. We propose a new resistive network that compensates for the high-frequency parasitic effects of the resistors to improve the bandwidth of the termination. In addition to maintaining accuracy, the presented network provides tolerance to variation in the resistor values. The accuracy and tolerance of the proposed structure is analytically shown and experimentally verified by three test structures at the X-band fabricated on a GaN technology. The experimental results show that a small size and wideband 50-Ω load with a return loss better than 25 dB can be obtained, while the resistor value changes ±30%.Item Open Access Construction of trigger and dependency graphs using event and rule declarations of an active object-oriented database management system(Bilkent University, 1997-07) Tosun, Ali ŞamanTraditional database systems are passive, meaning that they only react to explicit requests by users or applications. An active database S3^stem on the other hand, executes operations automatically when certain events occur and certain conditions are met. A database management system becomes cictive through the addition of rules. The main difficulties in the development of rule applications is the lack of design methods and suitable design tools. Confluence and termination are two important properties to be able to implement rule applications correctly. In this thesis, the construction of trigger and dependency graphs using class and rule declarations of an active object-oriented dcitabase system is described. The construction of these graphs provides that termination can be checked and a confluent rule execution can be achieved. Implementcition of a preprocessor that constructs trigger and dependency graphs is cilso provided.Item Open Access First-principles calculations of Pd-terminated symmetrical armchair graphene nanoribbons(Elsevier, 2013) Kuloglu, A. F.; Sarikavak-Lisesivdin, B.; Lisesivdin, S. B.; Özbay, EkmelThe effects of Palladium (Pd) termination on the electronic properties of armchair graphene nanoribbons (AGNRs) were calculated by using ab initio calculations. After a geometric optimization process, the electronic band structures, density of states, and binding energies of AGNRs with Na = 5-15 were calculated. Pd-termination was found to significantly influence the electronic properties of AGNRs. In DOS, many Q0D and Q1D type states were observed. Binding energy (BE) for single-side or both-side Pd-terminated structures represents characteristic drops with the increasing GNR width. With the increasing GNR width, the BEs of these structures become similar to hydrogenated structures. Because of the GNR width, dependent BE also gave information on the possible stiffness information, in which all of this information can be used in studies where controlled binding to graphene is required.