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Title: Electronic transport properties of carbon nanotubes: the impact of atomic charged impurities.
Creator: Tsuchikawa, Ryuichi, Ishigami, Masa, Mucciolo, Eduardo, Peale, Robert, Masunov, Artem, University of Central Florida
Abstract / Description: Even changing one atom in nanoscale materials is expected to alter their properties due to their small physical sizes. Such sensitivity can be utilized to modify materials' properties from bottom up and is essential for the utility of nanoscale materials. As such, the impact of extrinsic atomic adsorbates was measured on pristine graphene and a network of carbon nanotubes using atomic hydrogen, cesium atoms, and dye molecules. In order to further quantify such an atomic influence, the...
Show moreEven changing one atom in nanoscale materials is expected to alter their properties due to their small physical sizes. Such sensitivity can be utilized to modify materials' properties from bottom up and is essential for the utility of nanoscale materials. As such, the impact of extrinsic atomic adsorbates was measured on pristine graphene and a network of carbon nanotubes using atomic hydrogen, cesium atoms, and dye molecules. In order to further quantify such an atomic influence, the resistance induced by a single potassium atom on metallic and semiconducting carbon nanotubes was measured for the first time. Carbon nanotubes are sensitive to adsorbates due to their high surface-to-volume ratio. The resistance arising from the presence of extrinsic impurity atoms depends on the types of nanotubes. Metallic carbon nanotubes are resilient to a long-ranged, Coulomb-like potential, whereas semiconducting carbon nanotubes are susceptible to these impurities. The difference in the scattering strength originates from the chirality of carbon nanotubes, which defines their unique electronic properties. This difference had not directly measured experimentally because of the issue of contact resistance, the difficulty of chirality identification, and the uncertainty in the number of impurity atoms introduced on carbon nanotubes.We synthesized atomically clean, long ((>)100 ?m) carbon nanotubes, and their chirality was identified by Rayleigh scattering spectroscopy. We introduced potassium atoms on the nanotubes to impose a long-range, Coulomb potential and measured the change in resistivity, excluding the contact resistance, by plotting the resistance as a function of the carbon nanotube length. The flux of potassium atoms coming onto the nanotubes was monitored by quartz crystal microbalance, and the scattering strength of a single potassium atom was deduced from the change in resistivity and the density of potassium atoms on the nanotubes. We found that the scattering strength of potassium atoms on semiconducting nanotubes depends on the charge carrier type (holes or electrons). Metallic nanotubes were found to be less affected by the presence of potassium atoms than semiconducting nanotubes, but the scattering strength showed a large dependence on Fermi energy. These experimental results were compared to theoretical simulations, and we found a good agreement with the experiments. Our findings provide crucial information for the application of carbon nanotubes for electronic devices, such as transistors and sensors.
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Date Issued: 2015
Identifier: CFE0005729, ucf:50078
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005729

Title: First Principle Studies of Cu-Carbon Nanotube Hybrid Structures with Emphasis on the Electronic Structures and the Transport Properties.
Creator: Yang, Chengyu, Chen, Quanfang, Leuenberger, Michael, Coffey, Kevin, Ishigami, Marsahir, Fang, Jiyu, University of Central Florida
Abstract / Description: Carbon nanotubes have been regarded as ideal building blocks for nanoelectronics and multifunctional nanocomposites due to their exceptional strength, stiffness, flexibility, as well as their excellent electrical properties. However, carbon nanotube itself has limitations to fulfill the practical application needs: 1) an individual carbon nanotube has a low density of states at the Fermi level, and thus its conductivity is only comparable to moderate metals but lower than that of copper. 2)...
Show moreCarbon nanotubes have been regarded as ideal building blocks for nanoelectronics and multifunctional nanocomposites due to their exceptional strength, stiffness, flexibility, as well as their excellent electrical properties. However, carbon nanotube itself has limitations to fulfill the practical application needs: 1) an individual carbon nanotube has a low density of states at the Fermi level, and thus its conductivity is only comparable to moderate metals but lower than that of copper. 2) Metallic and semiconducting nanotubes are inherently mixed together from the synthesis, and the selection/separation is very difficult with very low efficiency. 3) Carbon nanotubes alone cannot be used in practical application and a bonding material is normally needed as the join material for actual devices. In this work, we fundamentally explored the possibility that metals (Cu, Al) could tailor carbon nanotube's electronic structure and even transit it from semiconducting to metallic, thus skipping the selection between the metallic and the semiconducting CNTs. We also found out a novel way to enhance a semiconducting CNT system's conductance even better than that of a metallic CNT system. All these researches are done under density functional theory (DFT) frame in conjunction with non-equilibrium Green functions (NEGF).At first we studied the adsorbed copper's influence on the electronic properties of CNT (10, 0) and CNT (5, 5). Results indicate that both the Density of States (DOS) and the transmission coefficients of CNT (5,5) /Cu have been increased. For CNT (10,0)/Cu, the band gap has been shrank, which means the improved conducting properties by the incorporation of copper . As a further case, semiconductor SWCNT (10, 0) with more adsorbed copper chains outside has been studied. 1, 4, 5 and 6 Cu chains have been added onto the carbon nanotube (10,0), and the adsorption of 6 Cu chains finally lead to the transform of the system from semiconducting to metallic. Considering the confining effect, the case that Cu filled into CNT (10, 0) is also studied. It is found that the filled copper chains could modify the system to be metallic more efficiently than the adsorbed Cu chain. Similarly, Al adsorbed on CNT (10, 0) is also studied, and it is found that Al has a better efficiency than copper in tuning the semiconducting CNT to metallic. The existing chemical bonds between the CNT and Al atoms may account for this higher efficiency. In addition, the resultant conductivity of the Al/CNT system is better than that of Cu/CNT system. The Cu/CNT (5,5)+Cu/Cu junction, as another realistic device setup, has been studied in terms of the conductance. The results show that the incorporation of Cu would enhance the conductance of the Cu/CNT/Cu system due to the interaction between Cu and the CNT.
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Date Issued: 2013
Identifier: CFE0005280, ucf:50561
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005280

Title: Electrostatic control over temperature-dependent tunneling across single-molecule junctions.
Creator: Rodriguez Garrigues, Alvar, Del Barco, Enrique, Flitsiyan, Elena, Ishigami, Masa, Hernandez, Eloy, University of Central Florida
Abstract / Description: The aim of the present dissertation is to improve the understanding and methodology of temperature-dependent tunnel conduction through individual molecules by single-electron transport spectroscopy. New advances in electrochemistry present individual molecular diodes as a realistic option for the implementation on molecular circuits thanks to their high current rectification ratios. Therefore, a major requisite in this field is to understand and control the conduction behaviors for a large...
Show moreThe aim of the present dissertation is to improve the understanding and methodology of temperature-dependent tunnel conduction through individual molecules by single-electron transport spectroscopy. New advances in electrochemistry present individual molecular diodes as a realistic option for the implementation on molecular circuits thanks to their high current rectification ratios. Therefore, a major requisite in this field is to understand and control the conduction behaviors for a large variety of conditions. This work focuses on the electric conduction through ferrocene-based molecules as a function of temperatures within a wide range of bias and gate voltages by means of three-terminal electromigrated-broken single-electron transistors (SETs).The results show that the temperature dependence of the current (from 80 to 260 K) depends strongly on the bias and gate voltages, with areas in where the current increases exponentially with temperature (at the Coulomb blockade regimes), and others where the increase of the temperature makes the current only to vary slightly (at resonance) or to decrease monotonically (at the charge degeneracy points). These different observed behaviors of the tunneling current with increasing temperatures can be well explained by a formal single-level coherent tunneling model where the temperature dependence relies on the thermal broadening of the Fermi distributions of the electrons in the leads. The model portraits the molecule as a localized electrostatic level capacitively coupled to the transistor leads, and the electrical conduction through the junction as coherent sequential tunneling.
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Date Issued: 2016
Identifier: CFE0006171, ucf:51132
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006171

Title: Spin and Charge Transport in Graphene Based Devices.
Creator: Anguera Antonana, Marta, Del Barco, Enrique, Peale, Robert, Bhattacharya, Aniket, Schoenfeld, Winston, University of Central Florida
Abstract / Description: The present dissertation is comprehended in two main parts. The first part is focused on understanding the mechanisms behind spin current to charge current interconversion (i.e. the spin Hall angle), where the spin current is generated by means of spin pumping. The measurement of a positive spin Hall angle of magnitude 0.004 in Uranium is reported in Chapter 2. These results support the idea that the electronic configuration may be at least as important as the atomic number in governing spin...
Show moreThe present dissertation is comprehended in two main parts. The first part is focused on understanding the mechanisms behind spin current to charge current interconversion (i.e. the spin Hall angle), where the spin current is generated by means of spin pumping. The measurement of a positive spin Hall angle of magnitude 0.004 in Uranium is reported in Chapter 2. These results support the idea that the electronic configuration may be at least as important as the atomic number in governing spin Hall effects. In Chapter 3, the design of a spintronics device designed to interconvert charge and spin currents in CVD graphene is presented. The second part of the thesis is centered in the study of transport through single molecules with the use of three-terminal devices. The first evidence of a molecular double quantum dot is detailed in Chapter 5. The conclusions are supported by self-assembled monolayers (SAMs) and single-electron transistors (SETs) measurements. Using gold electrodes for SETs measurements has its disadvantages, two of the main ones being: the junctions are not stable at room temperature and it does not allow for transport measurements in the presence of light. Graphene electrodes, on the other hand, have been reported to be stable at temperatures above room temperature and have no absorption in the visible range. Along those lines, the development of a multilayer graphene-based SET is reported in Chapter 6. Finally, a new technique, based on CVD graphene transistors, that will allow three-terminal measurements on an STM is described in Chapter 7.
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Date Issued: 2017
Identifier: CFE0006715, ucf:51897
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006715

Title: Investigation of Optical and Electronic Properties of Au Decorated MoS2.
Creator: Bhanu, Udai, Khondaker, Saiful, Leuenberger, Michael, Zhai, Lei, University of Central Florida
Abstract / Description: Achieving tunability of two dimensional (2D) transition metal dichalcogenides (TMDs) functions calls for the introduction of hybrid 2D materials by means of localized interactions with zero dimensional (0D) materials. A metal-semiconductor interface, as in gold (Au) - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science as it constitutes an outstanding platform to investigate optical and electronic properties due to charge transfer. The applied aspects...
Show moreAchieving tunability of two dimensional (2D) transition metal dichalcogenides (TMDs) functions calls for the introduction of hybrid 2D materials by means of localized interactions with zero dimensional (0D) materials. A metal-semiconductor interface, as in gold (Au) - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science as it constitutes an outstanding platform to investigate optical and electronic properties due to charge transfer. The applied aspects of such systems introduce new options for electronics, photovoltaics, detectors, catalysis, and biosensing. Here in this dissertation, we study the charge transfer interaction between Au nanoparticals and MoS2 flakes and its effect on Photoluminescence and electronic transport properties. The MoS2 was mechanically exfoliated from bulk single crystal. Number of layers in the flake was identified with the help of AFM and Raman Spectra. Au was deposited by physical vapor deposition method (PVD) in multiple steps to decorate MoS2 flakes.We first study the photoluminescence of pristine and Au decorated MoS2 and shows that in the presence of Au, the photoluminescence of MoS2 quenches significantly. We infer that the PL quenching can be attributed to a change in the electronic structure of the MoS2-Au system. The difference in Fermi level of a of MoS2 and Au results in a 0.4 eV energy level offset, which causes a band bending in the MoS2-Au hybrid. Upon illumination, the electrons in the excited state of MoS2 transfer to Au, leaving a hole behind, thus cause p-doping in MoS2. As electrons from MoS2 are transferred to Au, they do not decay back to their initial ground state, leading to PL quenching in the hybrid system.ivTo study the effect of Au deposition on electronic properties of ultra-thin and multilayers MoS2 flakes, we have fabricated MoS2 FETs from (1) ultra-thin sample (2-4 MoS2 layers) and (2) multilayers samples (more than 20 layers). After each deposition of Au, we measured the electrical characteristics of FET at room temperature. We show that the threshold voltage shifts towards the positive gate voltage as we increase the thickness of Au. This shift in threshold voltage is indicative of p doping of the MoS2. We further show that the field effect mobility of MoS2 FET decrease with Au thickness. We have quantitatively estimated the charge transferring from MoS2 to Au.
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Date Issued: 2015
Identifier: CFE0006025, ucf:51013
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006025

Title: Electronic Transport Investigation of Chemically Derived Reduced Graphene Oxide Sheets.
Creator: Joung, Daeha, Khondaker, Saiful, Chow, Lee, Leuenberger, Michael, Zhai, Lei, University of Central Florida
Abstract / Description: Reduced graphene oxide (RGO) sheet, a chemically functionalized atomically thin carbon sheet, provides a convenient pathway for producing large quantities of graphene via solution processing. The easy processibility of RGO sheet and its composites offer interesting electronic, chemical and mechanical properties that are currently being explored for advanced electronics and energy based materials. However, a clear understanding of electron transport properties of RGO sheet is lacking which is...
Show moreReduced graphene oxide (RGO) sheet, a chemically functionalized atomically thin carbon sheet, provides a convenient pathway for producing large quantities of graphene via solution processing. The easy processibility of RGO sheet and its composites offer interesting electronic, chemical and mechanical properties that are currently being explored for advanced electronics and energy based materials. However, a clear understanding of electron transport properties of RGO sheet is lacking which is of great significance for determining its potential application. In this dissertation, I demonstrate fabrication of high-yield solution based graphene field effects transistor (FET) using AC dielectrophoresis (DEP) and investigate the detailed electronic transport properties of the fabricated devices. The majority of the devices show ambipolar FET properties at room temperature. However, the mobility values are found to be lower than pristine graphene due to a large amount of residual defects in RGO sheets. I calculate the density of these defects by analyzing the low temperature (295 to 77K) charge transport data using space charge limited conduction (SCLC) with exponential trap distribution. At very low temperature (down to 4.2 K), I observe Coulomb blockade (CB) and Efros-Shklovskii variable range hopping (ES VRH) conduction in RGO implying that RGO can be considered as a graphene quantum dots (GQD) array, where graphene domains act like QDs while oxidized domains behave like tunnel barriers between QDs. This was further confirmed by studying RGO sheets of varying carbon sp2 fraction from 55 (-) 80 % and found that both the localization length and CB can be tuned. From the localization length and using confinement effect, we estimate tunable band gap of RGO sheets with varying carbon sp2 fraction. I then studied one dimensional RGO nanoribbon (RGONR) and found ES VRH and CB models are also applicable to the RGONR. However, in contrast to linear behavior of decrease in threshold voltage (Vt) with increasing temperature (T) in the RGO, sub linear dependence of Vt on T was observed in RGONR due to reduced transport pathways. Finally, I demonstrate synthesis and transport studies of RGO/nanoparticles (CdS and CeO2) composite and show that the properties of RGO can be further tuned by attaching the nanoparticles.
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Date Issued: 2012
Identifier: CFE0004785, ucf:49743
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004785

Title: Electronic transport and correlations in single magnetic molecule devices.
Creator: Romero, Javier, Mucciolo, Eduardo, Del Barco, Enrique, Stolbov, Sergey, Hernandez, Florencio, University of Central Florida
Abstract / Description: In this dissertation, we study the most important microscopic aspects that grant molecules such as Single Molecule Magnets (SMMs) their preferential spin direction. We do so by proposing and solving a model that includes correlations between electrons occupying atomic orbitals. In addition, we study the relation between the non-equilibrium electronic transport signatures in a SMM model weakly coupled to a three-terminal single electron transistor device, and the interference features of the...
Show moreIn this dissertation, we study the most important microscopic aspects that grant molecules such as Single Molecule Magnets (SMMs) their preferential spin direction. We do so by proposing and solving a model that includes correlations between electrons occupying atomic orbitals. In addition, we study the relation between the non-equilibrium electronic transport signatures in a SMM model weakly coupled to a three-terminal single electron transistor device, and the interference features of the SMM model in the presence of a magnetic field. Finally, we investigate the equilibrium transport features in a giant-spin model of a SMM in the Kondo regime. We study how the magnetic field modulation of the energy in a highly anisotropic molecule can affect the conductance of the molecule in the Kondo regime.
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Date Issued: 2014
Identifier: CFE0005407, ucf:50420
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005407

Title: Charge and Spin Transport in Low-Dimensional Materials.
Creator: Ahmadi, Amin, Mucciolo, Eduardo, Del Barco, Enrique, Ishigami, Masa, Guo, Jing, University of Central Florida
Abstract / Description: My research has been focused on two main areas. First, electronic transports in chiral carbonnanotubes in the presence of charged adatoms. To study such systems we employed recursiveGreens function technique to evaluate the conductance using the Landauer formula. Comparingwith the experimental data, we determined the effective amplitude and the range of scatteringpotentials. In addition, using a similar approach we explained qualitatively an unusual conductancefeature in a metallic carbon...
Show moreMy research has been focused on two main areas. First, electronic transports in chiral carbonnanotubes in the presence of charged adatoms. To study such systems we employed recursiveGreens function technique to evaluate the conductance using the Landauer formula. Comparingwith the experimental data, we determined the effective amplitude and the range of scatteringpotentials. In addition, using a similar approach we explained qualitatively an unusual conductancefeature in a metallic carbon nanotube. The second part of my study was concerned to the dynamicalspin injection and spin currents in low-dimensional materials. We have developed an atomisticmodel to express the injected spin current in terms of the systems Greens function. The newformulation provides a framework to study the spin injection and relaxation of a system with anarbitrary structure.
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Date Issued: 2017
Identifier: CFE0006550, ucf:51343
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006550

Title: CONTROLLED ASSEMBLY AND ELECTRONIC TRANSPORT STUDIES OF SOLUTION PROCESSED CARBON NANOTUBE DEVICES.
Creator: Stokes, Paul, Khondaker, Saiful I., University of Central Florida
Abstract / Description: Developing techniques for the parallel fabrication of Complementary Metal Oxide Semiconductor (CMOS) compatible single walled carbon nanotube (SWNT) electronic devices is of great importance for nanoelectronic applications. In this thesis, solution processed SWNTs in combination with AC dielectrophoresis (DEP) were utilized to fabricate CMOS compatible SWNT field effect transistors (FETs) and single electron transistors (SETs) with high yield and their detailed electronic transport properties...
Show moreDeveloping techniques for the parallel fabrication of Complementary Metal Oxide Semiconductor (CMOS) compatible single walled carbon nanotube (SWNT) electronic devices is of great importance for nanoelectronic applications. In this thesis, solution processed SWNTs in combination with AC dielectrophoresis (DEP) were utilized to fabricate CMOS compatible SWNT field effect transistors (FETs) and single electron transistors (SETs) with high yield and their detailed electronic transport properties were studied. Solution processing of SWNTs is attractive not only for the high throughput and parallel manufacturing of SWNT devices but also due to the ease of processing at room temperature, and compatibility with various substrates. However, it is generally believed that solution processing introduces defects and can degrade electronic transport properties. The results presented in this dissertation show that devices assembled from stable solutions of SWNT can give rise to high quality FET devices at room temperature and relatively clean SET behavior at low temperature. This is a strong indication that there are no or few intrinsic defects in the SWNTs. The dissertation will also discuss the controlled fabrication of size tunable SWNT SET devices using a novel mechanical template approach which offers a route towards the parallel fabrication of room temperature SET devices. The approach is based on the formation of two tunnel barriers created in a SWNT a distance L apart by bending the SWNT at the edge of a local Al/Al2O3 bottom gate. The local gate tunes individual electrons one by one in the device and defines the size of the quantum dot though its width. By tuning both the back gate and local gate, it is possible to tune the transparency of tunnel barriers and the size of the quantum dot further. Detailed transport spectroscopy of these devices will be presented.
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Date Issued: 2010
Identifier: CFE0003061, ucf:48310
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003061

Title: SINGLE-ELECTRON TRANSPORT SPECTROSCOPY STUDIES OF MAGNETIC MOLECULES AND NANOPARTICLES.
Creator: Haque, Md. Firoze, del Barco, Enrique, University of Central Florida
Abstract / Description: Magnetic nanoparticles and molecules, in particular ferromagnetic noble metal nanoparticles, molecular magnet and single-molecule magnets (SMM), are perfect examples to investigate the role of quantum mechanics at the nanoscale. For example, SMMs are known to reverse their magnetization by quantum tunneling in the absence of thermal excitation and show a number of fundamental quantum mechanical manifestations, such as quantum interference effects. On the other hand, noble metal nanoparticles...
Show moreMagnetic nanoparticles and molecules, in particular ferromagnetic noble metal nanoparticles, molecular magnet and single-molecule magnets (SMM), are perfect examples to investigate the role of quantum mechanics at the nanoscale. For example, SMMs are known to reverse their magnetization by quantum tunneling in the absence of thermal excitation and show a number of fundamental quantum mechanical manifestations, such as quantum interference effects. On the other hand, noble metal nanoparticles are found to behave ferromagnetically for diameters below a few nanometers. Some of these manifestations are still intriguing, and novel research approaches are necessary to advance towards a more complete understanding of these exciting nanoscale systems. In particular, the ability to study an isolated individual nanoscale system (i.e just one molecule or nanoparticle) is both challenging technologically and fundamentally essential. It is expected that accessing to the energy landscape of an isolated molecule/nanoparticle will allow unprecedented knowledge of the basic properties that are usually masked by collective phenomena when the systems are found in large ensembles or in their crystal form. Several approaches to this problem are currently under development by a number of research groups. For instance, some groups are developing deposition techniques to create patterned thin films of isolated magnetic nanoparticles and molecular magnets by means of optical lithography, low-energy laser ablation, or pulsed-laser evaporation or specific chemical functionalization of metallic surfaces with special molecular ligands. However, it is still a challenge to access the properties of an individual molecule or nanoparticle within a film or substrate. I have studied molecular nanomagnets and ferromagnetic noble metal nanoparticles by means of a novel experimental approach that mixes the chemical functionalization of nano-systems with the use of single-electron transistors (SETs). I have observed the Coulomb-blockade single-electron transport response through magnetic gold nanoparticles and single-molecule magnet. In particular, Coulomb-blockade response of a Mn4-based SET device recorded at 240 mK revealed the appearance of two diamonds (two charge states) with a clear switch between one and the other is indicative of a conformational switching of the molecule between two different states. The excitations inside the diamonds move with magnetic field. The curvature of the excitations and the fact of having them not going down to zero energy for zero magnetic field, indicated the presence of magnetic anisotropy (zero-field splitting) in the molecule. In addition, the high magnetic field slope of the excitations indicates that transitions between charge states differ by a net spin value equal to 9 (dS = 9), as expected from the behavior of Mn4 molecules in their crystalline form. Anticrossings between different excitations are indicative of quantum superpositions of the molecular states, which are observed for the first time in transport measurements through and individual SMM.
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Date Issued: 2011
Identifier: CFE0003718, ucf:48776
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003718

Title: FABRICATION AND TRANSPORT STUDIES OF N-TYPE ORGANIC FIELD EFFECT TRANSISTORS USING ALIGNED ARRAY CARBON NANOTUBES ELECTRODES.
Creator: Jimenez, Edwards, Khondaker, Saiful, University of Central Florida
Abstract / Description: We present fabrication of n-type organic field effect transistors (OFETs) using densely aligned array carbon nanotube (CNT) electrodes. The CNTs were aligned with a high linear density via dielectrophoresis (DEP) from an aqueous solution. In order to fabricate the CNT electrodes, aligned CNTs were cut by using electron beam lithography (EBL) and precise oxygen plasma etching. The n-type OFETs were fabricated in a bottom-contact configuration by depositing a thin film of C60 molecules between...
Show moreWe present fabrication of n-type organic field effect transistors (OFETs) using densely aligned array carbon nanotube (CNT) electrodes. The CNTs were aligned with a high linear density via dielectrophoresis (DEP) from an aqueous solution. In order to fabricate the CNT electrodes, aligned CNTs were cut by using electron beam lithography (EBL) and precise oxygen plasma etching. The n-type OFETs were fabricated in a bottom-contact configuration by depositing a thin film of C60 molecules between the CNT source and drain electrodes, and compared against a controlled C60 OFET with gold electrodes. The electron transport measurements of the OFETs using CNT electrodes show better transistor characteristics compared to OFETs using gold electrodes due to improved charge injection from densely aligned and open-ended nanotube tips.
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Date Issued: 2012
Identifier: CFH0004217, ucf:44941
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004217

Title: Electronic and Optoelectronic Transport Properties of Carbon Nanotube/Organic Semiconductor Devices.
Creator: Sarker, Biddut, Khondaker, Saiful, Schulte, Alfons, Stolbov, Sergey, Gesquiere, Andre, University of Central Florida
Abstract / Description: Organic field effect transistors (OFETs) are of significant research interest due to their promising applications in large area, low-cost electronic devices such as flexible displays, sensor arrays, and radio-frequency identification tags. A major bottleneck in fabricating high-performance OFET is the large interfacial barrier between the metal electrodes and organic semiconductors (OSC) which results in an inefficient charge injection. Carbon nanotubes (CNTs) are considered to be a promising...
Show moreOrganic field effect transistors (OFETs) are of significant research interest due to their promising applications in large area, low-cost electronic devices such as flexible displays, sensor arrays, and radio-frequency identification tags. A major bottleneck in fabricating high-performance OFET is the large interfacial barrier between the metal electrodes and organic semiconductors (OSC) which results in an inefficient charge injection. Carbon nanotubes (CNTs) are considered to be a promising electrode material which can address this challenge.In this dissertation, we demonstrate fabrication of high-performance OFETs using aligned array CNT electrodes and investigate the detailed electronic transport properties of the fabricated devices. The OFETs with CNT electrodes show a remarkable enhancement in the device performance such as high mobility, high current on-off ratio, higher cutoff frequency, absence of short channel effect and better charge carrier injection than those OFETs with metal electrodes. From the low temperature transport measurements, we show that the charge injection barrier at CNT/OSC interface is smaller than that of the metal/OSC interface. A transition from direct tunneling to Fowler-Nordheim tunneling observed in CNT/OSC system shows further evidence of low injection barrier. A lower activation energy measured for the OFETs with CNT electrodes gives evidence of lower interfacial trap states. Finally, OFETs are demonstrated by directly growing crystalline organic nanowires on aligned array CNT electrodes.In addition to investigating the interfacial barrier at CNT/OSC interface, we also studied photoconduction mechanism of the CNT and CNT/OSC nanocomposite thin film devices. We found that the photoconduction is due to the exciton dissociations and charge carrier separation caused by a Schottky barrier at the metallic electrode/CNT interface and diffusion of the charge carrier through percolating CNT networks. In addition, it is found that photoresponse of the CNT/organic semiconductor can be tuned by changing the weight percentage of CNT into the organic semiconductors.
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Date Issued: 2012
Identifier: CFE0004596, ucf:49217
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004596

electron transport (5)	+ -
graphene (3)	+ -
carbon nanotube (2)	+ -
carbon nanotubes (2)	+ -
electronic transport (2)	+ -

molecular electronics (2)	+ -
transport (2)	+ -
Anticrossing (1)	+ -
C60 (1)	+ -
Carbon nanotube (1)	+ -
Charge Transport (1)	+ -
Charge injection (1)	+ -
Electrodes (1)	+ -
Electronic transport (1)	+ -
Ferromagnetic metal nanoparticle (1)	+ -
Kondo effect (1)	+ -
MoS2 (1)	+ -
Molecular nanomagnet (1)	+ -
OFET (1)	+ -
Organic Electronics (1)	+ -
Organic field effect transistors (1)	+ -
Organic semiconductor (1)	+ -
SET (1)	+ -
STM (1)	+ -
Single-electron transistors (1)	+ -
Single-electron transport (1)	+ -
Single-molecule magnet (1)	+ -
adsorption (1)	+ -
assembly (1)	+ -
charge injection (1)	+ -

ETD Collection (11)	+ -
Honors Collection (1)	+ -

University of Central Florida (12)	+ -
Del Barco, Enrique (4)	+ -
Khondaker, Saiful (4)	+ -
Ishigami, Masa (3)	+ -
Leuenberger, Michael (3)	+ -

Mucciolo, Eduardo (3)	+ -
Peale, Robert (2)	+ -
Stolbov, Sergey (2)	+ -
Zhai, Lei (2)	+ -
Ahmadi, Amin (1)	+ -
Anguera Antonana, Marta (1)	+ -
Bhanu, Udai (1)	+ -
Bhattacharya, Aniket (1)	+ -
Chen, Quanfang (1)	+ -
Chow, Lee (1)	+ -
Coffey, Kevin (1)	+ -
Fang, Jiyu (1)	+ -
Flitsiyan, Elena (1)	+ -
Gesquiere, Andre (1)	+ -
Guo, Jing (1)	+ -
Haque, Md. Firoze (1)	+ -
Hernandez, Eloy (1)	+ -
Hernandez, Florencio (1)	+ -
Ishigami, Marsahir (1)	+ -
Jimenez, Edwards (1)	+ -
Joung, Daeha (1)	+ -
Khondaker, Saiful I. (1)	+ -
Masunov, Artem (1)	+ -
Rodriguez Garrigues, Alvar (1)	+ -
Romero, Javier (1)	+ -

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