Browsing by Subject "Carbon nanotubes"
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Item Open Access Ab-initio electron transport calculations of carbon based string structures(American Physical Society, 2004) Tongay, S.; Senger, R. T.; Dag, S.; Çıracı, SalimThe new stable structures of carbon-based strings and their unusual electronic transport properties were discussed. Total energy and electronic structure calculations using first principles pseudopotential plane wave method within density functional theory (DFT) and supercell geometries were also carried out. It was found that carbon chains were suitable for structural and chemical functionalizations because of their flexibility. These carbon chains also form stable ring, helix, grid and network structures. The results show that the double covalent bonding of carbon atoms underlies their unusual chemical, mechanical and transport properties and carbon chains can form stable string structures with impressive physical properties.Item Open Access Alignment controlled growth of single-walled carbon nanotubes on quartz substrates(American Chemical Society, 2009-09-11) Xiao, J.; Dunham, S.; Liu, P.; Zhang, Y.; Kocabaş, Coşkun; Moh, L.; Huang, Y.; Hwang, K. -C.; Lu, C.; Huang, W.; Rogers, J. A.Single-walled carbon nanotubes (SWNTs) possess extraordinary electrical properties, with many possible applications in electronics. Dense, horizonally aligned arrays of linearly configured SWNTs represent perhaps the most attractive and scalable way to implement this class of nanomaterial in practical systems. Recent work shows that templated growth of tubes on certain crystalline substrates yields arrays with the necessary levels of perfection, as demonstrated by the formation of devices and full systems on quartz. This paper examines advanced implementations of this process on crystalline quartz substrates with different orientations, to yield strategies for forming diverse, but welldefined horizontal configurations of SWNTs. Combined experimental and theoretical studies indicate that angle-dependent van der Waals interactions can account for nearly all aspects of alignment on quartz with X, Y, Z, and ST cuts, as well as quartz with disordered surface layers. These findings provide important insights into methods for guided growth of SWNTs, and possibly other classes of nanomaterials, for applications in electronics, sensing, photodetection, light emission, and other areas.Item Open Access All-fiber Yb-doped laser mode-locked by nanotubes(IEEE, 2013) Zhang, Zewang; Popa, D.; Sun, Z.; Hasan, T.; Ferrari, A.C.; İlday, F. ÖmerSingle-wall carbon nanotubes (SWNTs) and graphene have emerged as promising saturable absorbers (SAs), due to their broad operation bandwidth and fast recovery times [1-3]. However, Yb-doped fiber lasers mode-locked using CNT and graphene SAs have generated relatively long pulses. All-fiber cavity designs are highly favored for their environmental robustness. Here, we demonstrate an all-fiber Yb-doped laser based on a SWNT saturable absorber, which allows generation of 8.7 ps-long pulses, externally compressed to 118 fs. To the best of our knowledge, these are the shortest pulses obtained with SWNT SAs from a Yb-doped fiber laser. © 2013 IEEE.Item Open Access Atomic strings of group IV, III-V, and II-VI elements(American Institute of Physics, 2004) Tongay, S.; Durgun, Engin; Çıracı, SalimA systematic first-principles study of atomic strings made by group IV, III-V, and II-VI elements has revealed interesting mechanical, electronic, and transport properties. The double bond structure underlies their unusual properties. We found that linear chain of C, Si, Ge, SiGe, GaAs, InSb, and CdTe are stable and good conductor, although their parent diamond (zincblende) crystals are covalent (polar) semiconductors but, compounds SiC, BN, AlP, and ZnSe are semiconductors. First row elements do not form zigzag structures.Item Open Access Chemically specific dynamic characterization of photovoltaic and photoconductivity effects of surface nanostructures(American Chemical Society, 2010) Ekiz, O. Ö.; Mizrak, K.; Dâna, A.We report characterization of photovoltaic and photoconductivity effects on nanostructured surfaces through light induced changes in the X-ray photoelectron spectra (XPS). The technique combines the chemical specificity of XPS and the power of surface photovoltage spectroscopy (SPV), with the addition of the ability to characterize photoconductivity under both static and dynamic optical excitation. A theoretical model that quantitatively describes the features of the observed spectra is presented. We demonstrate the applicability of the model on a multitude of sample systems, including homo- and heterojunction solar cells, CdS nanoparticles on metallic or semiconducting substrates, and carbon nanotube films on silicon substrates.Item Open Access Chiral single-wall gold nanotubes(American Physical Society, 2004) Senger, R. T.; Dag, S.; Çıracı, SalimThe formation of freestanding and tip-suspended chiral-wall (n,m) nanotubes, which were composed of helical atomic strands, from gold atoms was investigated using first-principles calculations, where (n,m) notation defines the structure of the tube. The tubes with 3≤n≤5 were found to be stable and exhibited electronic and transport properties investigated. The (5,3) gold tube was energetically the most favourable. It was observed from the quantum ballistic conductance, band structure and charge density analysis that the current on these wires was less chiral, and no direct correlation between the numbers of conduction channels and helical strands was found.Item Open Access DFT studies of CNT-functionalized uracil-acetate hybrids(Elsevier, 2015) Mirzaei, M.; Gulseren, O.Calculations based on density functional theory (DFT) have been performed to investigate the stabilities and properties of hybrid structures consisting of a molecular carbon nanotube (CNT) and uracil acetate (UA) counterparts. The investigated models have been relaxed to minimum energy structures and then various physical properties and nuclear magnetic resonance (NMR) properties have been evaluated. The results indicated the effects of functionalized CNT on the properties of hybrids through comparing the results of hybrids and individual structures. The oxygen atoms of uracil counterparts have been seen as the detection points of properties for the CNT-UA hybrids.Item Open Access Electronic structure of the contact between carbon nanotube and metal electrodes(American Institute of Physics, 2003) Dag, S.; Gülseren, O.; Çıracı, Salim; Yildirim, T.Our first-principles study of the contact between a semiconducting single-walled carbon nanotube ~s-SWNT! and metal electrodes shows that the electronic structure and potential depend strongly on the type of metal. The s-SWNT is weakly side-bonded to the gold surface with minute charge rearrangement and remains semiconducting. A finite potential barrier forms at the contact region. In contrast, the molybdenum surface forms strong bonds, resulting in significant charge transfer and metallicity at the contact. The radial deformation of the tube lowers the potential barrier at the contact and increases the state density at the Fermi level.Item Open Access Energetics and Electronic Structures of Individual Atoms Adsorbed on Carbon Nanotubes(American Chemical Society, 2004) Durgun, Engin; Dag, S.; Çıracı, Salim; Gülseren, O.The adsorption of individual atoms on the semiconducting and metallic single-walled carbon nanotubes (SWNT) has been investigated by using the first principles pseudopotential plane wave method within density functional theory. The stable adsorption geometries and binding energies have been determined for a large number of foreign atoms ranging from alkali and simple metals to the transition metals and group IV elements. We have found that the character of the bonding and associated physical properties strongly depends on the type of adsorbed atoms, in particular, on their valence electron structure. Our results indicate that the properties of SWNTs can be modified by the adsorbed foreign atoms. Although the atoms of good conducting metals, such as Zn, Cu, Ag, and Au, form very weak bonds, transition-metal atoms such as Ti, Sc, Nb, and Ta and group IV elements C and Si are adsorbed with a relatively high binding energy. Owing to the curvature effect, these binding energies are larger than the binding energies of the same atoms on the graphite surface. We have showed that the adatom carbon can form strong and directional bonds between two SWNTs. These connects can be used to produce nanotube networks or grids. Most of the adsorbed transition-metal atoms excluding Ni, Pd, and Pt have a magnetic ground state with a significant magnetic moment. Our results suggest that carbon nanotubes can be functionalized in different ways by their coverage with different atoms, showing interesting applications such as ID nanomagnets or nanoconductors, conducting connects, and so forth.Item Open Access Functionalized carbon nanotubes and device applications(IOP, 2004) Çıracı, Salim; Dağ, Sefa; Yıldırım, T.; Gülseren, Oğuz; Senger, Ramazan TuğrulCarbon nanotubes, in which the two-dimensional hexagonal lattice of graphene is transformed into a quasi-one-dimensional lattice by conserving the local bond arrangement, provide several structural parameters for engineering novel physical properties suitable for ultimate miniaturization. Recent interest in nanoscience and nanotechnology has driven a tremendous research activity in carbon nanotubes, which has dealt with a variety of problems and produced a number of new results. Most of the effort has gone into revealing various physical properties of nanotubes and functionalizing them in different ways. This paper covers a narrow region in this enormous research field and reviews only a limited number of recent studies which fit within its scope. First, we examine selected physical properties of bare carbon nanotubes, and then study how the mechanical and electronic properties of different tubes can be modified by radial strain, structural defects and adsorption of foreign atoms and molecules. Magnetization of carbon nanotubes by foreign atom adsorption has been of particular interest. Finally, we discuss specific device models as well as fabricated devices which exploit various properties of carbon nanotubes.Item Open Access Graphene and carbon nanotubes interfaced electrochemical nanobiosensors for the detection of SARS-CoV-2 (COVID-19) and other respiratory viral infections: A review(Elsevier BV, 2021-10) Özmen, E. N.; Kartal, Enise; Turan, Mehmet Bora; Yazıcıoğlu, A.; Niazi, J. H.; Qureshi, A.Recent COVID-19 pandemic has claimed millions of lives due to lack of a rapid diagnostic tool. Global scientific community is now making joint efforts on developing rapid and accurate diagnostic tools for early detection of viral infections to preventing future outbreaks. Conventional diagnostic methods for virus detection are expensive and time consuming. There is an immediate requirement for a sensitive, reliable, rapid and easy-to-use Point-of-Care (PoC) diagnostic technology. Electrochemical biosensors have the potential to fulfill these requirements, but they are less sensitive for sensing viruses/viral infections. However, sensitivity and performance of these electrochemical platforms can be improved by integrating carbon nanostructure, such as graphene and carbon nanotubes (CNTs). These nanostructures offer excellent electrical property, biocompatibility, chemical stability, mechanical strength and, large surface area that are most desired in developing PoC diagnostic tools for detecting viral infections with speed, sensitivity, and cost-effectiveness. This review summarizes recent advancements made toward integrating graphene/CNTs nanostructures and their surface modifications useful for developing new generation of electrochemical nanobiosensors for detecting viral infections. The review also provides prospects and considerations for extending the graphene/CNTs based electrochemical transducers into portable and wearable PoC tools that can be useful in preventing future outbreaks and pandemics.Item Open Access High-frequency performance of submicrometer transistors that use aligned arrays of single-walled carbon nanotubes(American Chemical Society, 2009-04-08) Kocabaş, Coşkun; Dunham, S.; Cao, Q.; Cimino, K.; Ho, X.; Kim, H.-S.; Dawson, D.; Payne, J.; Stuenkel, M.; Zhang, H.; Banks, T.; Feng, M.; Rotkin, S. V.; Rogers, J. A.The unique electronic properties of single-walled carbon nanotubes (SWNTs) make them promising candidates for next generation electronics, particularly in systems that demand high frequency (e.g., radio frequency, RF) operation. Transistors that incorporate perfectly aligned, parallel arrays of SWNTs avoid the practical limitations of devices that use individual tubes, and they also enable comprehensive experimental and theoretical evaluation of the intrinsic properties. Thus, devices consisting of arrays represent a practical route to use of SWNTs for RF devices and circuits. The results presented here reveal many aspects of device operation in such array layouts, including full compatibility with conventional small signal models of RF response. Submicrometer channel length devices show unity current gain (ft) and unity power gain frequencies (fmax) as high as ∼5 and ∼9 GHz, respectively, with measured scattering parameters (S-parameters) that agree quantitatively with calculation. The small signal models of the devices provide the essential intrinsic parameters: saturation velocities of 1.2 × 107 cm/s and intrinsic values of ft of ∼30 GHz for a gate length of 700 nm, increasing with decreasing length. The results provide clear insights into the challenges and opportunities of SWNT arrays for applications in RF electronics.Item Open Access Intimate relationship between structural deformation and properties of single-walled carbon nanotubes(Cambridge, 2002) Yıldırım, Taner; Gülseren, Oğuz; Çıracı, SalimCarbon nanotubes continue to surprise scientists with their novel properties. Recently we have discovered many intimate relationships between structural deformation and the properties of single-walled nanotubes (SWNT), that could be important in technological applications. From first-principles we show that by using pressure, carbon nanotubes can be covalently joined to form one and two-dimensional networks of interlinked nanotubes. We also find that the band gap of an insulating nanotube can be engineered by elliptical distortion, which is found to be in the elastic range. This could allow the fine-tuning of the properties of SWNTs via reversible deformation and ultimately lead to variable quantum devices. Finally, we have very recently shown that the chemical reactivity of nanotubes can be tuned by elliptical deformation, which may provide a way to attach various atoms such as H and metals to a specific location on a nanotube.Item Open Access Molecular scale buckling mechanics in individual aligned single-wall carbon nanotubes on elastomeric substrates(American Chemical Society, 2008) Khang, D. -Y.; Xiao, J.; Kocabaş, Coşkun; MacLaren, S.; Banks, T.; Jiang, H.; Huang, Y. Y.; Rogers, J. A.We have studied the scaling of controlled nonlinear buckling processes in materials with dimensions in the molecular range (i.e., ∼1 nm) through experimental and theoretical studies of buckling in individual single-wall carbon nanotubes on substrates of poly(dimethylsiloxane). The results show not only the ability to create and manipulate patterns of buckling at these molecular scales, but also, that analytical continuum mechanics theory can explain, quantitatively, all measurable aspects of this system. Inverse calculation applied to measurements of diameterdependent buckling wavelengths yields accurate values of the Young’s moduli of individual SWNTs. As an example of the value of this system beyond its use in this type of molecular scale metrology, we implement parallel arrays of buckled SWNTs as a class of mechanically stretchable conductor.Item Open Access Operation of carbon nanotube thin-film transistors at elevated temperatures(IEEE, 2009-12) Öztürk, Sadi; Doğan, Mustafa; Aktaş, ÖzgürThe authors study the operation of carbon nanotube thin-film transistors (CNT-TFT) at elevated temperatures. Due to the small bandgap of semiconducting carbon nanotubes, CNT-TFTs are not suitable to be developed as high-temperature devices. However, CNT-TFTs will still have to endure elevated temperatures when employed in large-area and flexible electronic applications. The temperature range that can be expected in these applications is well below 100°C. In this work, the authors demonstrate that even at 100°C, CNT-TFT devices are operational but with a reduced ON/OFF ratio. Beyond 100°C, the ON/OFF ratio degrades rapidly.Item Open Access Printed multilayer superstructures of aligned single-walled carbon nanotubes for electronic applications(American Chemical Society, 2007-10) Kang, S. J.; Kocabaş, Coşkun; Kim, H.-S.; Cao, Q.; Meitl, M. A.; Khang, D.-Y.; Rogers, J. A.We developed means to form multilayer superstructures of large collections of single-walled carbon nanotubes (SWNTs) configured in horizontally aligned arrays, random networks, and complex geometries of arrays and networks on a wide range of substrates. The approach involves guided growth of SWNTs on crystalline and amorphous substrates followed by sequential, multiple step transfer of the resulting collections of tubes to target substrates, such as high-k thin dielectrics on silicon wafers, transparent plates of glass, cylindrical tubes and other curved surfaces, and thin, flexible sheets of plastic. Electrical measurements on dense, bilayer superstructures, including crossbars, random networks, and aligned arrays on networks of SWNTs reveal some important characteristics of representative systems. These and other layouts of SWNTs might find applications not only in electronics but also in areas such as optoelectronics, sensors, nanomechanical systems, and microfluidics.Item Open Access Quantum effects in electrical and thermal transport through nanowires(Institute of Physics Publishing, 2001) Çıracı, Salim; Buldum, A.; Batra, I. P.Nanowires, point contacts and metallic single-wall carbon nanotubes are one-dimensional nanostructures which display important size-dependent quantum effects. Quantization due to the transverse confinement and resultant finite level spacing of electronic and phononic states are responsible for some novel effects. Many studies have revealed fundamental and technologically important properties, which are being explored for fabricating future nanodevices. Various simulation studies based on the classical molecular dynamics method and combined force and current measurements have shown the relationship between atomic structure and transport properties. The atomic, electronic and transport properties of these nanostructures have been an area of active research. This brief review presents some quantum effects in the electronic and phononic transport through nanowires.Item Open Access Structural and electronic properties of carbon-based materials(Bilkent University, 2000) Kılıç, ÇetinIn this thesis, some carbon-based materials in nano scale have been investigated by using first-principles methods as well as transferable tight-binding and empirical potential models. The focus of interest has been in the cubane molecule among cage-like structures and in the carbon nanotubes among graphite-related materials. The first-principles calculations predict that cubane-like structures can exist for other group IV elements such as Si and Ge. The energetics and dynamics of such molecules has been studied. By performing quantum molecular dynamics simulations at high temperature a deformation path from cubane to cyclooctatetraene has been established. For solid cubane the structural and electronic properties and doping by alkali metal atoms have been studied. In the study of carbon nanotubes under pressure some new carbon forms due to covalent bonding between the neighboring tubes has been identified. It has been shown that the electronic structure of single wall carbon nanotubes is affected by radial deformations. For example, some zigzag nanotubes have been found to experience semiconductor-to-metal transition as a result of compression. Exploiting this property, it has been shown that variable and reversible quantum structures can be realized on a single carbon nanotube. Finally, other quantum structures which can lead to novel nano-scale molecular devices have been proposed.Item Open Access Titanium-decorated carbon nanotubes as a potential high-capacity hydrogen storage medium(American Physical Society, 2005) Yildirim, T.; Çıracı, SalimWe report a first-principles study, which demonstrates that a single Ti atom coated on a single-walled nanotube (SWNT) binds up to four hydrogen molecules. The first H2 adsorption is dissociative with no energy barrier while the other three adsorptions are molecular with significantly elongated H-H bonds. At high Ti coverage we show that a SWNT can strongly adsorb up to 8 wt% hydrogen. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nanostructures and suggest new routes to better storage and catalyst materials.Item Open Access Ultra-conductive wires with cascaded carbon nanotube/Cu structure(Elsevier Ltd, 2021-12) Özmen, A.; Mobtakeri, S.; Kocak, Yusuf; Akbaba, U.; Ertuğrul, M.; Gül, E.In the present study, ultra-conductive wires were produced by the cascaded Cu/MWCNT wire structure. Cascaded wires were prepared on the industrial 1 mm diameter Cu wire with two steps; Firstly, electrophoretic deposition (EPD) was used to deposit the functionalized MWCNT on the Cu wires. Secondly, a novel inverted cylindrical magnetron sputtering (ICMS) has been built to coat Cu on the MWCNT deposited Cu wire. Different number of cascaded layers up to 13 layers of Cu/MWCNT wires as well as different Cu coating parameter were produced. High deposition rate of MWCNT on Cu wires has been achieved by the EPD method. As can be seen from the cross-sectional SEM images, the intended cascaded structures were successfully formed. The ampacity of the 1 mm industrial Cu wire used in this study has increased by 9.2%. In addition, the temperature of the cascaded wires has shown slow increase compared to that of reference Cu wire. On the other hand, the maximum current able to carry with 1 °C temperature raise has increased by 50%.