Current Search: Khondaker, Saiful (x)
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- 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.
Show less - Date Issued
- 2012
- Identifier
- CFH0004217, ucf:44941
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004217
- Title
- HIGH YIELD ASSEMBLY AND ELECTRON TRANSPORT INVESTIGATION OF SEMICONDUCTING-RICH LOCAL-GATED CARBON NANOTUBE FIELD EFFECT TRANSISTORS.
- Creator
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Kormondy, Kristy, Khondaker, Saiful, University of Central Florida
- Abstract / Description
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Single-walled carbon nanotubes (SWNTs) are ideal for use in nanoelectronic devices because of their high current density, mobility and subthreshold swing. However, assembly methods must be developed to reproducibly align all-semiconducting SWNTs at specific locations with individually addressable gates for future integrated circuits. We show high yield assembly of local-gated semiconducting SWNTs assembled via AC-dielectrophoresis (DEP). Using individual local gates and scaling the gate oxide...
Show moreSingle-walled carbon nanotubes (SWNTs) are ideal for use in nanoelectronic devices because of their high current density, mobility and subthreshold swing. However, assembly methods must be developed to reproducibly align all-semiconducting SWNTs at specific locations with individually addressable gates for future integrated circuits. We show high yield assembly of local-gated semiconducting SWNTs assembled via AC-dielectrophoresis (DEP). Using individual local gates and scaling the gate oxide shows faster switching behavior and lower power consumption. The devices were assembled by DEP between prefabricated Pd source and drain electrodes with a thin Al/Al2O3 gate in the middle, and the electrical characteristics were measured before anneal and after anneal. Detailed electron transport investigations on the devices show that 99% display good FET behavior, with an average threshold voltage of 1V, subthreshold swing as low as 140 mV/dec, and on/off current ratio as high as 8x105. Assembly yield can also be increased to 85% by considering devices where 2-5 SWNT bridge the gap between source and drain electrode. To examine the characteristics of devices bridged by more than one SWNT, similar electron transport measurements were taken for 35 devices with electrodes bridged by 2-3 SWNT and 13 devices connected by 4-5 SWNT. This high yield directed assembly of local-gated SWNT-FETs via DEP may facilitate large scale fabrication of CMOS compatible nanoelectronic devices.
Show less - Date Issued
- 2011
- Identifier
- CFH0003841, ucf:44705
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0003841
- Title
- CONTROLLED ASSEMBLY AND ELECTRONIC TRANSPORT STUDIES OF SOLUTION PROCESSED CARBON NANOTUBE DEVICES.
- Creator
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Stokes, Paul, Khondaker, Saiful I., University of Central Florida
- Abstract / Description
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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.
Show less - Date Issued
- 2010
- Identifier
- CFE0003061, ucf:48310
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003061
- Title
- The effect of carbon nanotube/organic semiconductor interfacial area on the performance of organic transistors.
- Creator
-
Kang, Narae, Khondaker, Saiful, Leuenberger, Michael, Zhai, Lei, University of Central Florida
- Abstract / Description
-
Organic field-effect transistors (OFETs) have attracted tremendous attention due to their flexibility, transparency, easy processiblity and low cost of fabrication. High-performance OFETs are required for their potential applications in the organic electronic devices such as flexible display, integrated circuit, and radiofrequency identification tags. One of the major limiting factors in fabricating high-performance OFET is the large interfacial barrier between metal electrodes and OSC which...
Show moreOrganic field-effect transistors (OFETs) have attracted tremendous attention due to their flexibility, transparency, easy processiblity and low cost of fabrication. High-performance OFETs are required for their potential applications in the organic electronic devices such as flexible display, integrated circuit, and radiofrequency identification tags. One of the major limiting factors in fabricating high-performance OFET is the large interfacial barrier between metal electrodes and OSC which results in low charge injection from the metal electrodes to OSC. In order to overcome the challenge of low charge injection, carbon nanotubes (CNTs) have been suggested as a promising electrode material for organic electronic devices. In this dissertation, we study the effect of carbon nanotube (CNT) density in CNT electrodes on the performance of organic field effect transistor (OFETs). The devices were fabricated by thermal evaporation of pentacene on the Pd/single walled CNT (SWCNT) electrodes where SWCNTs of different density (0-30/um) were aligned on Pd using dielectrophoresis (DEP) and cut via oxygen plasma etching to keep the length of nanotube short compared to the channel length. From the electronic transport measurements of 40 devices, we show that the average saturation mobility of the devices increased from 0.02 for zero SWCNT to 0.06, 0.13 and 0.19 cm2/Vs for low (1-5 /(&)#181;m), medium (10-15 /(&)#181;m) and high (25-30 /(&)#181;m) SWCNT density in the electrodes, respectively. The increase is three, six and nine times for low, medium and high density SWCNTs in the electrode compared to the devices that did not contain any SWCNT. In addition, the current on-off ratio and on-current of the devices are increased up to 40 times and 20 times with increasing SWCNT density in the electrodes. Our study shows that although a few nanotubes in the electrode can improve the OFET device performance, significant improvement can be achieved by maximizing SWCNT/OSC interfacial area. The improved OFET performance can be explained due to a reduced barrier height of SWCNT/pentacene interface compared to metal/pentacene interface which provides more efficient charge injection pathways with increased SWCNT/pentacene interfacial area.
Show less - Date Issued
- 2012
- Identifier
- CFE0004558, ucf:49252
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004558
- Title
- Investigation of Breakdown Power During Electrical Breakdown of Aligned Array of Carbon Nanotubes.
- Creator
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Bhanu, Udai, Khondaker, Saiful, Leuenberger, Michael, Zhai, Lei, University of Central Florida
- Abstract / Description
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Massively parallel arrays of single walled carbon nanotubes (SWNT) have attracted significant research interests because of their ability to (i) average out inhomogeneities of individual SWNTs, (ii) provide larger on currents, and (iii) reduce noise to provide higher cutoff frequency for radio frequency applications. However, the array contains both metallic and semiconducting SWNTs and the presence of metallic nanotube in an aligned array negatively affects the device properties. Therefore,...
Show moreMassively parallel arrays of single walled carbon nanotubes (SWNT) have attracted significant research interests because of their ability to (i) average out inhomogeneities of individual SWNTs, (ii) provide larger on currents, and (iii) reduce noise to provide higher cutoff frequency for radio frequency applications. However, the array contains both metallic and semiconducting SWNTs and the presence of metallic nanotube in an aligned array negatively affects the device properties. Therefore, it is essential to selectively remove metallic nanotubes to obtain better transistor properties. It was recently found that although such a selective removal can be effective for a low density array, it does not work in a high density array and lead to a correlated breakdown of the entire array giving rise to a nanofissure pattern.In order to obtain a deeper understanding of such a correlated SWNT breakdown, we studied the breakdown power in the successive electrical breakdown of both low ( (<) 2 /um) and high density ((>)10 /um) SWNT arrays. We show that the breakdown voltage in successive electrical breakdown increases for low density array while it decreases for high density arrays. The estimated power required for the breakdown remains constant for low density arrays while it decreases for high density arrays in successive electrical breakdowns. We also show that, while a simple model of parallel resistor network can explain the breakdown of low density array, it cannot explain the behavior for the high density array implying that the correlation between the closely spaced parallel nanotubes plays a big role in the successive breakdowns of the high density SWNTs.
Show less - Date Issued
- 2012
- Identifier
- CFE0004518, ucf:49292
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004518
- Title
- Nanoelectronic Devices using Carbon Nanotubes and Graphene Electrodes: Fabrication and Electronic Transport Investigations.
- Creator
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Kang, Narae, Khondaker, Saiful, Leuenberger, Michael, Zhai, Lei, University of Central Florida
- Abstract / Description
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Fabrication of high-performance electronic devices using the novel semiconductors is essential for developing future electronics which can be applicable in large-area, flexible and transparent displays, sensors and solar cells. One of the major bottlenecks in the fabrication of high-performance devices is a large interfacial barrier formation at metal/semiconductor interface originated from Schottky barrier and interfacial dipole barrier which causes inefficient charge injection at the...
Show moreFabrication of high-performance electronic devices using the novel semiconductors is essential for developing future electronics which can be applicable in large-area, flexible and transparent displays, sensors and solar cells. One of the major bottlenecks in the fabrication of high-performance devices is a large interfacial barrier formation at metal/semiconductor interface originated from Schottky barrier and interfacial dipole barrier which causes inefficient charge injection at the interface. Therefore, having a favorable contact at electrode/semiconductor is highly desirable for high-performance devices fabrication.In this dissertation, the fabrication of nanoelectronic devices and investigation of their transport properties using carbon nanotubes (CNTs) and graphene as electrode materials will be shown. I investigated two types of devices using (i) semiconducting CNTs, and (ii) organic semiconductors (OSC). In the first part of this thesis, I will demonstrate the fabrication of high-performance solution-processed highly enriched (99%) semiconducting CNT thin film transistors (s-CNT TFTs) using densely aligned arrays of metallic CNTs (m-CNTs) for source/drain electrodes. From the electronic transport measurements at room temperature, significant improvements of field-effect mobility, on-conductance, transconductance and current on/off ratio for m-CNT/s-CNT devices were found compared to control palladium (Pd contacted s-CNT devices. From the temperature dependent transport investigation, a lower Schottky barrier height for the m-CNT/s-CNT devices was found compared to the devices with control metal electrodes. The enhanced device performance can be attributed to the unique device geometry as well as strong ?- ? interaction at m-CNT/s-CNT interfaces. In addition, I also investigated s-CNT TFTs using reduced graphene oxide (RGO) electrodes.In the second part of my thesis, I will demonstrate high-performance organic field-effect transistors (OFETs) using different types of graphene electrodes. I show that the performance of OFETs with pentacene as OSC and RGO as electrode can be continuously improved by increasing the carbon sp2 fraction of RGO. The carbon sp2 fractions of RGO were varied by controlling the reduction time. When compared to control Pd electrodes, the mobility of the OFETs shows an improvement of ?200% for 61% sp2 fraction RGO, which further improves to ?500% for 80% RGO electrode. Similarly, I show that when the chemical vapor deposition (CVD) graphene film is used as electrodes in fabricating OFET, the better performance is observed in comparison to RGO electrodes. Our study suggests that, in addition to ?-? interaction at graphene/pentacene interface, the tunable electronic properties of graphene as electrode have a significant role in OFETs performance. For a fundamental understanding of the interface, we fabricated short-channel OFETs with sub-100nm channel length using graphene electrode. From the low temperature electronic transport measurements, a lower charge injection barrier was found compared to control metal electrode. The detailed investigations reported in this thesis clearly indicated that the use of CNT and graphene as electrodes can improve the performance of future nanoelectronic devices.
Show less - Date Issued
- 2015
- Identifier
- CFE0006039, ucf:50982
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006039
- Title
- Parallel fabrication and transport properties of carbon nanotube single electron transistors.
- Creator
-
Islam, Muhammad, Khondaker, Saiful, Chow, Lee, Stolbov, Sergey, Zhai, Lei, University of Central Florida
- Abstract / Description
-
Single electron transistors (SET) have attracted significant attention as a potential building block for post CMOS nanoelectronic devices. However, lack of reproducible and parallel fabrication approach and room temperature operation are the two major bottlenecks for practical realization of SET based devices. In this thesis, I demonstrate large scale single electron transistors fabrication techniques using solution processed single wall carbon nanotubes (SWNTs) and studied their electron...
Show moreSingle electron transistors (SET) have attracted significant attention as a potential building block for post CMOS nanoelectronic devices. However, lack of reproducible and parallel fabrication approach and room temperature operation are the two major bottlenecks for practical realization of SET based devices. In this thesis, I demonstrate large scale single electron transistors fabrication techniques using solution processed single wall carbon nanotubes (SWNTs) and studied their electron transport properties. The approach is based on the assembly of individual SWNTs via dielectrophoresis (DEP) at the selected position of the circuit and formation of tunnel barriers on SWNT. Two different techniques: i) metal-SWNT Schottky contact, and ii) mechanical templating of SWNTs were used for tunnel barrier creation.Low temperature (4.2K) transport measurement of 100 nm long metal-SWNT Schottky contact devices show that 93% of the devices with contact resistance (RT) (>) 100 K? show SET behavior. Majority (90%) of the devices with 100 K? (<) RT (<) 1 M?, show periodic, well-de?ned Coulomb diamonds with a charging energy ~ 15 meV, represents single electron tunnelling through a single quantum dot (QD), defined by the top contact. For high RT ((>) 1M?), devices show multiple QDs behaviors, while QD was not formed for low RT ((<) 100 K?) devices. From the transport study of 50 SWNT devices, a total of 38 devices show SET behavior giving an yield of 76%. I also demonstrate room temperature operating SET by using mechanical template technique. In mechanical template method individual SWNT is placed on top of a Al/Al2O3 local gate which bends the SWNT at the edge and tunnel barriers are created. SET devices fabricated with a template width of ~20 nm shows room temperature operation with a charging energy of ~150 meV. I also discussed the detailed transport spectroscopy of the devices.
Show less - Date Issued
- 2015
- Identifier
- CFE0006037, ucf:50987
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006037
- 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
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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.
Show less - Date Issued
- 2015
- Identifier
- CFE0006025, ucf:51013
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006025
- Title
- Vanadium Oxide Microbolometers with Patterned Gold Black or Plasmonic Resonant Absorbers.
- Creator
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Smith, Evan, Peale, Robert, Khondaker, Saiful, Dove, Adrienne, Boreman, Glenn, University of Central Florida
- Abstract / Description
-
High sensitivity uncooled microbolometers are necessary to meet the needs of the next generation of infrared detectors, which seek low power consumption and production cost without sacrificing performance. Presented here is the design, fabrication, and characterization of a microbolometer with responsivity enhanced by novel highly absorptive coatings. The device utilizes a gold-doped vanadium oxide film in a standard air bridge design. Performance estimations are calculated from current...
Show moreHigh sensitivity uncooled microbolometers are necessary to meet the needs of the next generation of infrared detectors, which seek low power consumption and production cost without sacrificing performance. Presented here is the design, fabrication, and characterization of a microbolometer with responsivity enhanced by novel highly absorptive coatings. The device utilizes a gold-doped vanadium oxide film in a standard air bridge design. Performance estimations are calculated from current theory, and efforts to maximize signal to noise ratio are shown and evaluated. Most notably, presented are the experimental results and analysis from the integration of two different absorptive coatings: a patterned gold black film and a plasmonic resonant structure.Infrared-absorbing gold black was selectively patterned onto the active surfaces of the detector. Patterning by metal lift-off relies on protection of the fragile gold black with an evaporated oxide, which preserves gold black's near unity absorptance. This patterned gold black also survives the dry-etch removal of the sacrificial polyimide used to fabricate the air-bridge bolometers. Infrared responsivity is improved 70% for mid-wave IR and 22% for long-wave IR. The increase in the thermal time constant caused by the additional mass of gold black is a modest 15%. However, this film is sensitive to thermal processing; experimental results indicate a decrease in absorptance upon device heating.Sub-wavelength resonant structures designed for long-wave infrared (LWIR) absorption have also been investigated. Dispersion of the dielectric refractive index provides for multiple overlapping resonances that span the 8-12 ?m LWIR wavelength band, a broader range than can be achieved using the usual resonance quarter-wave cavity engineered into the air-bridge structures. Experimental measurements show an increase in responsivity of 96% for mid-wave IR and 48% for long-wave IR, while thermal response time only increases by 16% due to the increased heat capacity. The resonant structures are not as susceptible to thermal processing as are the gold black films. This work suggests that plasmonic resonant structures can be an ideal method to improve detector performance for microbolometers.
Show less - Date Issued
- 2015
- Identifier
- CFE0006004, ucf:51026
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006004
- Title
- Graphene Induced Formation of Nanostructures in Composites.
- Creator
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Shen, Chen, Zhai, Lei, Chen, Quanfang, Thomas, Jayan, Fang, Jiyu, Khondaker, Saiful, University of Central Florida
- Abstract / Description
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Graphene induced nanostructures in graphene-based composites and the performance of these composites have been explored in this study. For the metallic nanoparticles decorated graphene aerogels composites, the fabrication of hierarchically structured, reduced graphene oxide (rGO) aerogels with heavily metallic nanoparticles was realized. Higher loading of palladium nanoparticles in graphene aerogels leads to improved hydrogen gas sensing performance. For polymer derived ceramics (PDCs)...
Show moreGraphene induced nanostructures in graphene-based composites and the performance of these composites have been explored in this study. For the metallic nanoparticles decorated graphene aerogels composites, the fabrication of hierarchically structured, reduced graphene oxide (rGO) aerogels with heavily metallic nanoparticles was realized. Higher loading of palladium nanoparticles in graphene aerogels leads to improved hydrogen gas sensing performance. For polymer derived ceramics (PDCs) composites with anisotropic electrical properties, the fabrication of composites was realized by embedding anisotropic reduced graphene oxide aerogels (rGOAs) into the PDCs matrix. Raman spectroscopy and X-ray diffraction studies of PDCs composites with and without graphene indicate that graphene facilitates the transition from amorphous carbon to graphitic carbon in the PDCs. For composites composed of PDCs and edge functionalized graphene oxide (EFGO), bulk PDCs based composites with embedded graphene networks show high electrical conductivity, high thermal stability, and low thermal conductivity. For the study of poly(3-hexylthiophene) (P3HT) crystallization on graphitic substrates (i.e. carbon nanotubes, carbon fibers and graphene), different types of P3HT nanocrystals (i.e. nanowires, nanoribbons, and nanowalls) were observed. The type of nanocrystals grown from graphitic substrates depends on the curvature of graphitic substrates, the molecular weight of P3HT molecules, and the concentration of P3HT marginal solutions. Besides, both specific surface area and curvature of graphitic substrates have major effects on P3HT crystallization processes.
Show less - Date Issued
- 2018
- Identifier
- CFE0007095, ucf:51961
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007095
- 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.
Show less - Date Issued
- 2012
- Identifier
- CFE0004596, ucf:49217
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004596
- Title
- Detection of Inorganic Phosphate in Environmental Water Samples using a Terbium and Gold Nanoparticle-based FRET Chemosensor.
- Creator
-
Johnson, Madeleine, Campiglia, Andres, Zou, Shengli, Harper, James, Frazer, Andrew, Khondaker, Saiful, University of Central Florida
- Abstract / Description
-
A novel chemosensor for the detection of inorganic phosphate (Pi) in environmental water samples is outlined. The sensing solution is comprised of a luminescent lanthanide, terbium (Tb3+), chelated to ethylenediaminetetraacetic acid (EDTA) acid in solution with cetyltrimethylammonium bromide (CTAB)- capped gold nanoparticles (AuNPs). The Tb-EDTA and AuNPs undergo a Fluorescence resonance energy transfer (FRET) mechanism in which the Tb3+ luminescence is quenched. Upon the addition of...
Show moreA novel chemosensor for the detection of inorganic phosphate (Pi) in environmental water samples is outlined. The sensing solution is comprised of a luminescent lanthanide, terbium (Tb3+), chelated to ethylenediaminetetraacetic acid (EDTA) acid in solution with cetyltrimethylammonium bromide (CTAB)- capped gold nanoparticles (AuNPs). The Tb-EDTA and AuNPs undergo a Fluorescence resonance energy transfer (FRET) mechanism in which the Tb3+ luminescence is quenched. Upon the addition of inorganic phosphate (Pi), the AuNPs begin to aggregate and precipitate out of solution. The aggregation of AuNPs results in the restoration of the Tb-EDTA signal which can then be correlated to Pi concentration in the matrix of analysis. The developed sensor has the potential for on-site monitoring of Pi in environmental waters at the sampling location; this would be advantageous for the prevention and understanding of eutrophication events caused by anthropogenic release of nutrients such as Pi. The limit of detection (LOD) of the luminescence sensor (83 ppb-Pi) is within the range of LODs previously reported for on-site monitoring of Pi. Quantitative analysis carried out via the multiple standard additions method provided accurate determination of Pi concentrations in heavily contaminated environmental waters. Additional studies include the synthesis of an organic antenna for the sensitization of the lanthanide ion and further improvement of detection levels.
Show less - Date Issued
- 2017
- Identifier
- CFE0006747, ucf:51874
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006747
- 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
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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.
Show less - Date Issued
- 2012
- Identifier
- CFE0004785, ucf:49743
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004785
- Title
- Planar Organic Photovoltaic Devices.
- Creator
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Alzubi, Feras, Khondaker, Saiful, Chow, Lee, Schelling, Patrick, Gesquiere, Andre, University of Central Florida
- Abstract / Description
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Organic Photovoltaic devices (OPV) are considered to be attractive candidates for clean and renewable energy source because of their potential for low cost of fabrication, easy processing, and their mechanical flexibility. The device efficiency of OPV cells are limited by several factors. Among them are: (i) donor-acceptor interface, (ii) morphology of the materials, (iii) electrode-organic semiconductor (OSC) interface and (iv) device architecture such as active material thickness and...
Show moreOrganic Photovoltaic devices (OPV) are considered to be attractive candidates for clean and renewable energy source because of their potential for low cost of fabrication, easy processing, and their mechanical flexibility. The device efficiency of OPV cells are limited by several factors. Among them are: (i) donor-acceptor interface, (ii) morphology of the materials, (iii) electrode-organic semiconductor (OSC) interface and (iv) device architecture such as active material thickness and electrode separation. Although, the donor-acceptor interface has been studied in detail, the commonly prevalent vertical OPV device structure does not allow a good understanding of the other key issues as the vertical structure limits one of the electrode to be a transparent electrode as well as introducing inseparable relation between the electrodes separation and the active material thickness. In addition, it is also well known that the charge transport in OSC is anisotropic and the charge mobility is better in lateral direction rather than vertical direction. In order to address some of these issues, we fabricated OPV devices in a planar device structure where cathode and anode of dissimilar metals are in-plane with each other and their photovoltaic behaviors were studied. We used poly(3-hexylthiophene) and [6,6]-pheny1 C61-butyric acid methy1 ester (P3HT:PCBM) blend as an active material. In particular, we present a detailed study about the effects of the structural parameters such as the channel length, the active layer thickness, and the work function of the electrodes on the open circuit voltage (Voc), short circuit current (Isc), fill factor (FF) and the power conversion efficiency (PCE).In order to determine the suitable anode and cathode for the planar organic photovoltaic (P-OPV) structure, we first fabricated and measured organic field effect transistor (OFET) devices with different contacts and studied the effect of barrier height at the P3HT:PCBM/electrode interface on the device output and transport properties. The study showed a clear effect of varying the contact material on the charge injection mechanism and on the carriers mobilities. The results have also shown that Au with high hole mobility and on current in the p-channel can be used as an anode (holes extractor) in the P-OPV device while In, Cr, and Ti that showed a reasonable value of electron mobility can be good candidates for cathode (electron extractor). We also found that, Ag, Al, and Mg showed large barrier which resulted in large threshold voltage in the I-V curve making them undesired cathode materials in the P-OPV device. We then fabricated P-OPV devices with Au as an anode material and varied the cathode material to study the effect of the interface between the P3HT:PCBM layer and the cathode material. When Al, Mg, or Ag used as a cathode material no PV behavior was observed, while PV behavior was observed for In, Cr, and Ti cathode materials. The PV behavior and the characteristic parameters including Voc, Isc, FF and PCE were affected by varying the cathode material. The results have shown that the P-OPV device performance can be affected by the cathode material depending on the properties and the work function of the metal.We have also studied the effect of varying the P3HT:PCBM layer thickness at a fixed channel length for Cr and Ti cathode materials and Au as anode. While Voc and FF values do not change, Isc and PCE increase with increasing the layer thickness due to the increase of the light absorption and charges generation. Moreover, we studied the effect of varying the channel length at a fixed film thickness; and showed that the values of Isc and PCE increase with decreasing channel length while Voc and FF maintain the same value. In this thesis we will also present the results on experimentally defining and testing the illuminated area in the P-OPV device by using different measurement set-ups and different electrodes patterns. The results prove that the illuminated area in the P-OPV device is the area enclosed between the two electrodes. Lastly, we will present the effect of the P3HT:PCBM ratio on the P-OPV device performance. We show that 1:2 ratio is the optimized ratio for the P-OPV device. The detailed results in this thesis show a potential opportunity to help improving and understanding the design of OPV device by understanding the effects of the device structural parameters.
Show less - Date Issued
- 2013
- Identifier
- CFE0004804, ucf:49754
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004804
- Title
- 1, 2, and 3 Dimension Carbon/Silicon Carbon Nitride Ceramic Composites.
- Creator
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Calderon Flores, Jean, Zhai, Lei, Campiglia, Andres, Yestrebsky, Cherie, Zou, Shengli, Khondaker, Saiful, University of Central Florida
- Abstract / Description
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Polymer-derived ceramics (PDCs) are exceptional ultra-high temperature and stable multifunctional class of materials that can be synthesized from a polymer precursor through thermal decomposition. The presented research focuses on 1-D nanofibers, 2-D films and 3-D bulk, carbon-rich silicon carbon nitride (SiCN) ceramics. 1-D nanofibers were prepared via electrospinning for light weight, flame retardant and conductive applications. The commercially available CerasetTM VL20, a liquid...
Show morePolymer-derived ceramics (PDCs) are exceptional ultra-high temperature and stable multifunctional class of materials that can be synthesized from a polymer precursor through thermal decomposition. The presented research focuses on 1-D nanofibers, 2-D films and 3-D bulk, carbon-rich silicon carbon nitride (SiCN) ceramics. 1-D nanofibers were prepared via electrospinning for light weight, flame retardant and conductive applications. The commercially available CerasetTM VL20, a liquid cyclosilazane pre-ceramic precursor, was mixed with polyacrylonitrile (PAN) in order to make the cyclosilazane electrospinnable. Carbon-rich PDC nano?bers were fabricated by electrospinning various ratios of PAN/cyclosilazane solutions followed by pyrolysis. Surface morphology of the electro spun nanofibers characterized by SEM show PDC nano?bers with diameters ranging from 100-300 nm. Also, thermal stability towards oxidation showed a 10% mass loss at 623oC. 2-D carbon/SiCN films were produced by drop-casting a mixture of PAN/cyclosilazane onto a glass slide followed by pyrolysis of the film. Samples ranging from 10:1 to 1:10 PAN:cyclosilazane were made by dissolving the solutes into DMF to produce solutions ranging from 1% to 12% by weight. Green, heat-stabilized, and pyrolyzed 8% films were examined with FTIR to monitor the change in chemical structure at each step of the ceramization. SEM shows that high PAN samples produced films with ceramic embedded spheroid components in a carbon matrix, while high cyclosilazane samples produced carbon embedded spheroid.Finally, this research focuses on the challenge of making fully dense, 3-D bulk PDCs materials. Here we present a composite of SiCN with reduced graphene oxide (rGO) aerogels as a route for fully dense bulk PDCs. Incorporation of the rGO aerogel matrix into the SiCN has its pros and cons. While it lowers the strength of the composite, it allows for fabrication of large bulk samples and an increase in the electrical conductivity of the PDC. The morphology, mechanical, electrical properties and thermal conductivity of graphene-SiCN composite with varying rGO aerogel loading (0.3-2.4%) is presented. The high temperature stability, high electrical conductivity and low thermal conductivity of these composites make them excellent candidates for thermoelectric applications. Generally, carbon-rich SiCN composites with improved thermal and electrical properties are of great importance to the aerospace and electronics industries due to their expected harsh operating environments.
Show less - Date Issued
- 2015
- Identifier
- CFE0005768, ucf:50095
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005768