Browsing by Author "Kucukayan-Dogu, G."

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Open Access
Analysis of charge transfer for in situ li intercalated carbon nanotubes
(American Chemical Society, 2012) Rana, K.; Kucukayan-Dogu, G.; Sen, H. S.; Boothroyd, C.; Gulseren, O.; Bengu, E.
Vertically aligned carbon nanotube (VA-CNT) arrays have been synthesized with lithium (Li) intercalation through an alcohol-catalyzed chemical vapor deposition technique by using a Li-containing catalyst. Scanning electron microscopy images display that synthesized carbon nanotubes (CNTs) are dense and vertically aligned. The effect of the Li-containing catalyst on VA-CNTs has been studied by using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS). XPS results show the change in binding energy of Li 1s and C 1s peaks, which indicates that Li is inserted in VA-CNTs during growth. Analysis of Raman spectra reveals that the G-band profile of CNTs synthesized with the Li-containing catalyst is shifted, suggesting an electronic interaction between Li and neighboring C atoms of the CNTs. The EELS spectra of the C K edge and Li K edge from CNTs also confirmed that Li is inserted into CNTs during synthesis. We have performed ab inito calculations based on density functional theory for a further understanding of the structural and electronic properties of Li intercalated CNTs, especially addressing the controversial charge-transfer state between Li and C.
Open Access
Evidence for Nonradiative Energy Transfer in Graphene-Oxide-Based Hybrid Structures
(American Chemical Society, 2013-11-13) Yeltik, A.; Kucukayan-Dogu, G.; Guzelturk, B.; Fardindoost, S.; Kelestemur, Y.; Demir, Hilmi Volkan
Solution processed graphene variants including graphene oxide (GO) and reduced graphene oxide (RGO) are promising materials for potential optoelectronic applications. To date, efficiency of the excitation energy transfer into GO and RGO thin layers has not been investigated in terms of donor-acceptor separation distance. In the present work, we study nonradiative energy transfer (NRET) from CdSe/CdS quantum dots into single and/or double layer GO or RGO using time-resolved fluorescence spectroscopy. We observe shorter lifetimes as the separation distance between the QDs and GO or RGO decreases. In accordance with these lifetimes, the rates reveal the presence of two different mechanisms dominating the NRET. Here we show that excitonic NRET is predominant at longer intervals while both excitonic and nonexcitonic NRET exist at shorter distances. In addition, we find the NRET rate behavior to be strongly dependent on the reduction degree of the GO-based layers. We obtain high NRET efficiency levels of similar to 97 and similar to 89% for the closest separation of the QD-RGO pair and the QD-GO pair, respectively. These results indicate that strong NRET from QDs into thin layer GO and RGO makes these solution-processable thin films promising candidates for light harvesting and detection systems.
Open Access
Growth of vertically aligned carbon nanotubes over self-ordered nano-porous alumina films and their surface properties
(Elsevier, 2012) Rana, K.; Kucukayan-Dogu, G.; Bengu, E.
Nanoporous anodic aluminum oxide (AAO) with self-organized arrays of uniform nanopores have been used for various applications in the fields of sensing, storage, separation and template-based fabrication of metal nanowires, carbon nanotubes, oxides and polymers. The work presented here involves the production and use of AAO templates for growth of aligned multi walled carbon nanotube arrays. AAO templates were formed by electrochemical oxidation of aluminum in different electrolyte solutions containing sulfuric, oxalic and phosphoric acid. SEM was used for the analysis of the surface morphology of the AAO films. The porous structures with pore size in the range of 25–120 nm were observed. Pore sizes were correlated with the type of acidic solutions used as the electrolyte. Finally, AAO surfaces have been used as substrates for the growth of vertically aligned carbon nanotubes through chemical vapor deposition technique, which showed super-hydrophobic behavior as confirmed by contact angle measurements.
Open Access
A new tool for differentiating hepatocellular cancer cells: patterned carbon nanotube arrays
(Elsevier, 2015) Kucukayan-Dogu, G.; Gozen, D.; Bitirim, V.; Akcali, K. C.; Bengu, E.
We aimed to develop a new approach to detect the invasiveness and metastatic degree of hepatocellular carcinoma cells (HCC) based on their epithelial mesenchymal transition (EMT) status by using patterned carbon nanotubes (CNT) without any further surface functionalization. We used well differentiated HUH7 and poorly differentiated SNU182 cells to examine and compare their adhesive features on patterned CNTs. We found that the well differentiated HUH7 cells attached significantly more on the patterned CNTs than the poorly differentiated SNU182 cells due to the difference in epithelial and mesenchymal phenotypes of these cells. Collagen coated patterned CNTs having less roughness resulted in a decrease in the number of attached cells compared to non-coated patterned surfaces indicating that surface topography playing also a vital role on the cell attachment. LDH testing indicated no adverse, or thereof toxic effect of collagen coated or non-coated patterned surfaces on the HCC cells. The results of this study clearly suggest that patterned CNT surfaces can be used as a diagnostic tool to determine the invasiveness and metastatic level of HCCs. Hence, CNTs could be considered as a promising diagnostic tool for the detection of differentiation and invasiveness of the HCC cells. © 2015 Elsevier B.V. All rights reserved.
Open Access
Simultaneous growth of self-patterned carbon nanotube forests with dual height scales
(Royal Society of Chemistry, 2012) Sam, E. D.; Kucukayan-Dogu, G.; Baykal, B.; Dalkilic, Z.; Rana, K.; Bengu, E.
In this study, we report on a unique, one-step fabrication technique enabling the simultaneous synthesis of vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with dual height scales through alcohol catalyzed chemical vapor deposition (ACCVD). Regions of VA-MWCNTs with different heights were well separated from each other leading to a self-patterning on the surface. We devised a unique layer-by-layer process for application of catalyst and inhibitor precursors on oxidized Si (100) surfaces before the ACCVD step to achieve a hierarchical arrangement. Patterning could be controlled by adjusting the molarity and application sequence of precursors. Contact angle measurements on these self-patterned surfaces indicated that manipulation of these hierarchical arrays resulted in a wide range of hydrophobic behavior changing from that of a sticky rose petal to a lotus leaf.