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- Title
- Electrostatic control over temperature-dependent tunneling across single-molecule junctions.
- Creator
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Rodriguez Garrigues, Alvar, Del Barco, Enrique, Flitsiyan, Elena, Ishigami, Masa, Hernandez, Eloy, University of Central Florida
- Abstract / Description
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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.
Show less - Date Issued
- 2016
- Identifier
- CFE0006171, ucf:51132
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006171
- Title
- Energy-Aware Reconfigurable Logic Device Using Spin-based Storage and Carbon Nanotube Switching.
- Creator
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Gopi Krishna, Mohan Krishna, DeMara, Ronald, Yuan, Jiann-Shiun, Del Barco, Enrique, University of Central Florida
- Abstract / Description
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Scaling of semiconductors to the 14-nanometer range and below nanometer range introduces serious design challenges that include high static power in memories and high leakage power, hindering further integration of CMOS devices. Thus, emerging devices are under intense analysis to overcome these drawbacks caused by transistor size scaling. Spintronics technology provides excellent features such as Non-Volatility, low read power, low read delay, higher scalability as well as easy integration...
Show moreScaling of semiconductors to the 14-nanometer range and below nanometer range introduces serious design challenges that include high static power in memories and high leakage power, hindering further integration of CMOS devices. Thus, emerging devices are under intense analysis to overcome these drawbacks caused by transistor size scaling. Spintronics technology provides excellent features such as Non-Volatility, low read power, low read delay, higher scalability as well as easy integration with CMOS in comparison with SRAM memories. In addition, Carbon-Nanotube Field-Effect Transistors (CNFETs) provide superior electrical conductivity, low delay and low power consumption in comparison with conventional CMOS technology. Thus in this thesis, a unique approach to amalgamate spintronics memory technology with CNFET for logic drive in a reconfigurable computing architecture, realizing ultimate circuit performance has been discussed. A Carbon Magnetic Look-Up Table (CM-LUT) is proposed, using a Magnetic Tunnel Junction (MTJ) spintronic device as memory element and CNFET to perform the logical operations to read the data stored in the aforementioned devices. The proposed circuit is radiation resilient, ultra-low power and high speed operation and the ability to withstand high temperature gradient, Ideal for low power high performance battery operated mobile applications. In addition, the performance of hybrid drive for LUT to leverage fabrication feasibility of CMOS and performance of CNFET to realize fabrication cost effective design. The proposed 4-input 1-output CM-LUT utilizes 41 CNFETs and 16 MTJs for read operation and 35 CNFETs to perform write operation. The results for CM-LUT show 38 times energy reduction and 5.8 times faster circuit operation in comparison with CMOS-based spin-LUT.
Show less - Date Issued
- 2016
- Identifier
- CFE0006109, ucf:51204
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006109
- Title
- Characterization of gold black and its application in un-cooled infrared detectors.
- Creator
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Panjwani, Deep, Peale, Robert, Chow, Lee, Del Barco, Enrique, Schoenfeld, Winston, University of Central Florida
- Abstract / Description
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Gold black porous coatings were thermally evaporated in the chamber backfilled with inert gas pressure and their optical properties were studied in near-far-IR wavelengths. The porosities of coatings were found to be extremely high around ~ 99%. Different approaches of effective medium theories such as Maxwell-Garnett, Bruggeman, Landau-Lifshitz-Looyenga and Bergman Formalism were utilized to calculate refractive index (n) and extinction coefficient (k). The aging induced changes on...
Show moreGold black porous coatings were thermally evaporated in the chamber backfilled with inert gas pressure and their optical properties were studied in near-far-IR wavelengths. The porosities of coatings were found to be extremely high around ~ 99%. Different approaches of effective medium theories such as Maxwell-Garnett, Bruggeman, Landau-Lifshitz-Looyenga and Bergman Formalism were utilized to calculate refractive index (n) and extinction coefficient (k). The aging induced changes on electrical and optical properties were studied in regular laboratory conditions using transmission electron microscopy, Fourier transform infrared spectroscopy, and fore-probe electrical measurements. A significant decrease in electrical resistance in as deposited coating was found to be consistent with changes in the granular structure with aging at room temperature. Electrical relaxation model was applied to calculate structural relaxation time in the coatings prepared with different porosities. Interestingly, with aging, absorptance of the coatings improved, which is explained using conductivity form of Bergman Formulism. Underlying aim of this work was to utilize gold blacks to improve sensitivity in un-cooled IR sensors consist of pixel arrays. To achieve this, fragile gold blacks were patterned on sub-mm length scale areas using both stenciling and conventional photolithography. Infrared spectral imaging with sub-micron spatial resolution revealed the spatial distribution of absorption across the gold black patterns produced with both the methods. Initial experiments on VOx-Au bolometers showed that, gold black improved the responsivity by 42%. This work successfully establishes promising role of gold black coatings in commercial un-cooled infrared detectors.
Show less - Date Issued
- 2015
- Identifier
- CFE0005680, ucf:50197
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005680
- Title
- TERAHERTZ AND SUB-TERAHERTZ TUNABLE RESONANT DETECTORS BASED ON EXCITATION OF TWO DIMENSIONAL PLASMONS IN InGaAs/InP HEMTs.
- Creator
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Nader Esfahani, Nima, Peale, Robert, Ishigami, Masa, Del Barco, Enrique, Buchwald, Walter, University of Central Florida
- Abstract / Description
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Plasmons can be generated in the two dimensional electron gas (2DEG) of grating-gated high electron mobility transistors (HEMTs). The grating-gate serves dual purposes, namely to provide the required wavevector to compensate for the momentum mismatch between the free-space radiation and 2D-plasmons, and to tune the 2DEG sheet charge density. Since the plasmon frequency at a given wavevector depends on the sheet charge density, a gate bias can shift the plasmon resonance. In some cases,...
Show morePlasmons can be generated in the two dimensional electron gas (2DEG) of grating-gated high electron mobility transistors (HEMTs). The grating-gate serves dual purposes, namely to provide the required wavevector to compensate for the momentum mismatch between the free-space radiation and 2D-plasmons, and to tune the 2DEG sheet charge density. Since the plasmon frequency at a given wavevector depends on the sheet charge density, a gate bias can shift the plasmon resonance. In some cases, plasmon generation results in a resonant change in channel conductance which allows a properly designed grating-gated HEMT to be used as a voltage-tunable resonant detector or filter. Such devices may find applications as chip-scale tunable detectors in airborne multispectral detection and target tracking.Reported here are investigations of InGaAs/InP-based HEMT devices for potential tunable resonant sub-THz and THz detectors. The HEMTs were fabricated from a commercial double-quantum well HEMT wafer by depositing source, drain, and semi-transparent gate contacts using standard photolithography processes. Devices were fabricated with metalized transmission gratings with multiple periods and duty cycles. For sub-THz devices, grating period and duty cycle were chosen to be 9 ?m and 22%, respectively; while they were chosen to be 0.5 ?m and 80% for the THz device. The gratings were fabricated on top of the gate region with dimensions of 250 ?m (&)#215; 195 ?m.The resonant photoresponse of the larger grating-period HEMT was investigated in the sub-THz frequency range of around 100 GHz. The free space radiation was generated by an ultra-stable Backward Wave Oscillator (BWO) and utilized in either frequency modulation (FM), or amplitude modulation (AM) experiments. The photoresponse was measured at 4K sample temperature as the voltage drop across a load resistor connected to the drain while constant source-drain voltages of different values, VSD, were applied. The dependence of such optoelectrical effect to polarization of the incident light, and applied VSD is studied. The results of AM and FM measurements are compared and found to be in agreement with the calculations of the 2D-plasmon absorption theory, however, a nonlinear behavior is observed in the amplitude and the line-shape of the photoresponse for AM experiments. For detection application, the minimum noise-equivalent-power (NEP) of the detector was determined to be 235 and 113 pW/Hz1/2 for FM and AM experiments, respectively. The maximum responsivity of the detector was also estimated to be ~ 200 V/W for the two experiments. The far-IR transmission spectra of the device with nanometer scale period was measured at 4 K sample temperature for different applied gate voltages to investigate the excitation of 2D-plasmon modes. Such plasmon resonances were observed, but their gate bias dependence agreed poorly with expectations.
Show less - Date Issued
- 2014
- Identifier
- CFE0005386, ucf:50461
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005386
- Title
- Structure-Property Relationship of the Two-Photon Circular Dichroism of Compounds with Axial and Helical Chirality.
- Creator
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Diaz, Carlos, Hernandez, Florencio, Uribe Romo, Fernando, Kuebler, Stephen, Masunov, Artem, Del Barco, Enrique, University of Central Florida
- Abstract / Description
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Back in 1894 Lord Kelvin coined the term (")chiral(") in order to refer to molecules whose mirror images were not superimposable with themselves. Over the years, research has demonstrated the important role that chiral molecules play in life, chemistry, and biology as well as their importance in the development of new drugs and technologies.The efforts to understand chiral systems have been mainly driven by spectroscopic methods that leverage on the opposite responses that enantiomers have to...
Show moreBack in 1894 Lord Kelvin coined the term (")chiral(") in order to refer to molecules whose mirror images were not superimposable with themselves. Over the years, research has demonstrated the important role that chiral molecules play in life, chemistry, and biology as well as their importance in the development of new drugs and technologies.The efforts to understand chiral systems have been mainly driven by spectroscopic methods that leverage on the opposite responses that enantiomers have to linear or circularly polarized light of both handedness. More specifically, Electronic Circular Dichroism (ECD) which measures the differences in linear absorption of left and right circularly polarized light has been the method par excellence for the spectroscopic characterization of chiral compounds. Unfortunately, the fact that ECD is based on linear absorption severely limits the use of this method in the near to far UV region. This is mainly due to the interferences generated by the strong linear absorption of common organic solvents and buffers in this portion of the light spectrum. Nevertheless, the fact remains that many chiral biomolecules of interest related to deceases like Alzheimer and Parkinson, exhibit most of their linear absorption in the near to far UV region where ECD cannot be employed for their study. Therefore, it has become an urgent necessity to develop spectroscopic methods to study chiral molecules that can circumvent the limitations of ECD at shorter wavelengths. In order to overcome the existent limitations in linear chiral spectroscopy, the nonlinear equivalent of ECD arises as a promising alternative, i.e. Two-Photon Circular Dichroism (TPCD). Although, this phenomenon was theoretically predicted in 1975, it was not until 2008, with the introduction of the double-L scan, that a reliable and versatile method for the measurement of TPCD was introduced. The high sensitivity of this method is based on the use of (")twin(") pulses that allow accounting for fluctuations in the excitation source that prevented the experimental realization of the measurement. The first measurement of a full TPCD spectrum was performed on BINOL enantiomers and the results were supported and discussed with the help of theoretical calculations. After that seminal work, we embarked in expanding the understanding of the structure-property relationship of TPCD by performing, systematically, a series of theoretical-experimental studies in chiral biaryl derivatives and compounds with helical chirality.In Chapter 2 we present the theoretical-experimental study of the effect of the ?-electron delocalization curvature on the TPCD of molecules with axial chirality. The targeted molecules for this part of our investigation were S-BINOL, S-VANOL, and S-VAPOL. Our findings revealed that an increase in the TPCD signal, within this series of compounds, was related to the curvature of the ?(-)electron delocalization. The contributions of the different transition moments to the two-photon rotatory strength support our outcomes. Then, in Chapter 3 we introduce the development of the Fragment-Recombination Approach (FRA) for the calculation of the TPCD spectra of large molecules. This simple but powerful method is based on the additivity of the TPCD signal, and is subject to a strict conditional fragmentation approach. FRA-TPCD is demonstrated, theoretically, in two hypothetical molecular systems from the biaryl derivatives family. Afterward, in Chapter 4 we show the first experimental demonstration of FRA-TPCD through the conformational analysis of an axially-chiral Salen ligand in solution (AXF-155). The FRA-TPCD spectra calculated for the different isomers of AXF-155 allowed narrowing the number of possible isomers of this complex molecule in THF solution to only two. This represents a significant improvement from previously reported results using ECD. Subsequently, in Chapter 5 we present the study of the effect of intramolecular charge transfer (ICT) in S-BINAP, an axially dissymmetric diphosphine ligand with strong ICT. The evaluation of the performance of two different exchange-correlation functional (XCF) confirmed that in order to properly predict the theoretical TPCD spectrum of a molecule exhibiting strong ICT, it is required to use an XCF such as CAM-B3LYP. In addition, our findings revealed the importance of considering an adequate number of excited states in order to be able to fully reproduce the experimental TPCD spectrum, thus avoiding wrong assignments of theoretical transitions to experimental spectral features. Finally, and expanding on our previous study, in Chapter 6 we investigated the effect of the nature of ICT on two hexahelicene derivatives. Our investigation demonstrated that the TPCD signal of chiral molecules with strong ICT does not only depend on the strength of this effect but on its nature, i.e. extension of the ?(-)electronic delocalization increasing beyond (EXO-ICT) or within (ENDO-ICT) the helicene core. In summary, with the results presented in this thesis we closed a first loop in the understanding of the structure-property relationship of TPCD. In the future, we expect to deepen in our knowledge of the structure-property relationship of this phenomenon by studying further helicene derivatives with donor-acceptor motif, and through the application of FRA-TPCD to the conformational analysis of amino acids in peptides. We foresee numerous applications of TPCD for the study of optically active molecules with implications in biology, medicine, and the drug and food industry, and applications in nanotechnology, asymmetric catalysis and photonics.
Show less - Date Issued
- 2015
- Identifier
- CFE0005787, ucf:50067
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005787
- Title
- Dynamical spin injection in graphene.
- Creator
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Singh, Simranjeet, Del Barco, Enrique, Mucciolo, Eduardo, Ishigami, Masa, Hill, Stephen, University of Central Florida
- Abstract / Description
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Within the exciting current trend to explore novel low-dimensional systems, the possibility to injectpure spin currents in graphene and other two-dimensional crystals has attracted considerableattention in the past few years. The theoretical prediction of large spin relaxation times and experimentally observed mesoscopic-scale spin diffusion lengths places graphene as a promising base system for future spintronics devices. This is due to the unique characteristics intrinsic to the two...
Show moreWithin the exciting current trend to explore novel low-dimensional systems, the possibility to injectpure spin currents in graphene and other two-dimensional crystals has attracted considerableattention in the past few years. The theoretical prediction of large spin relaxation times and experimentally observed mesoscopic-scale spin diffusion lengths places graphene as a promising base system for future spintronics devices. This is due to the unique characteristics intrinsic to the two-dimensional lattice of carbon atoms forming graphene, such as the lack of nuclear spins and weak spin-orbit coupling of the charge carriers. Interestingly for some spintronic applications, the latter can be chemically and physically engineered, with large induced spin-orbit couplings found in functionalized graphene sheets. Understanding spin injection, spin current and spin dynamics in graphene is of a great interest, both from the fundamental and applied points of view.This thesis presents an experimental study of dynamical generation of spin currents in macroscopic graphene sheets by means of spin pumping from the precessing magnetization of an adjacent ferromagnet. The spin pumping characteristics are studied by means of ferromagnetic resonance (FMR) measurements in Permalloy/graphene (Py/Gr) bilayers. Changes in the FMR linewidth induced by the presence of graphene (when compared to studies with only Py films) correspond to an increase in the Gilbert damping in the ferromagnetic layer (proportional to the FMR linewidth) and interpreted as a consequence of spin pumping at the Py/Gr interface driven by the Py magnetization dynamics (i.e., magnetic induced by the microwave stimulus). FMR experiments are performed on different FM/Gr interfaces, completing a set of studies designed to systematically identify and eliminate damping enhancement arising from processes other than spin pumping. Remarkably, a substantial enhancement of the Gilbert damping observed in Py/Gr strips with graphene protruding a few micrometers from the strip sides is univocally associated to spin pumping at the quasi-onedimensional interface between the Py strip edges and graphene. This increase in the FMR linewidth compares with observations in other bilayer systems, in where thick (thicker than the spin diffusionlength) layers of heavy metals with strong spin-orbit coupling are employed as the non-magneticlayer, indicating that spin relaxation in chemically grown graphene must be greatly enhanced in order to account for the losses of angular momentum lost by the ferromagnet. The fundamentalimplications of the results presented in this thesis point to a non-trivial nature of the spin pumping mechanism owing to the two-dimensionality of the non-magnetic layer (i.e., graphene).In addition, a spintronics device designed to interconvert charge and spin currents has been designed. A high-frequency microwave irradiation lock-in modulation technique is employed todetect the small electrical voltages generated by the inverse spin Hall effect (ISHE). As a proofof principle, a successful spin-charge interconversion in Py/Pt-based devices is experimentally demonstrated in this thesis. The challenges associated with the spin-charge interconversion in twodimensional devices are discussed and systematically addressed, and a potential device geometry for measuring the ISHE in Py/Gr-based systems is provided.
Show less - Date Issued
- 2014
- Identifier
- CFE0005552, ucf:50284
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005552
- Title
- QUANTITATIVE SCANNING TRANSMISSION ELECTRON MICROSCOPY OF THICK SAMPLES AND OF GOLD AND SILVER NANOPARTICLES ON POLYMERIC SURFACES.
- Creator
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Dutta, Aniruddha, Heinrich, Helge, Del Barco, Enrique, Chow, Lee, Chen, Bo, Kuebler, Stephen, University of Central Florida
- Abstract / Description
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Transmission Electron Microscopy (TEM) is a reliable tool for chemical and structural studies of nanostructured systems. The shape, size and volumes of nanoparticles on surfaces play an important role in surface chemistry. As nanostructured surfaces become increasingly important for catalysis, protective coatings, optical properties, detection of specific molecules, and many other applications, different techniques of TEM can be used to characterize the properties of nanoparticles on surfaces...
Show moreTransmission Electron Microscopy (TEM) is a reliable tool for chemical and structural studies of nanostructured systems. The shape, size and volumes of nanoparticles on surfaces play an important role in surface chemistry. As nanostructured surfaces become increasingly important for catalysis, protective coatings, optical properties, detection of specific molecules, and many other applications, different techniques of TEM can be used to characterize the properties of nanoparticles on surfaces to provide a path for predictability and control of these systems.This dissertation aims to provide fundamental understanding of the surface chemistry of Electroless Metallization onto Polymeric Surfaces (EMPS) through characterization with TEM. The research focuses on a single EMPS system: deposition of Ag onto the cross-linked epoxide (")SU8("), where Au nanoparticles act as nucleation sites for the growth of Ag nanoparticles on the polymer surface. TEM cross sections were analyzed to investigate the morphology of the Au nanoparticles and to determine the thicknesses of the Ag nanoparticles and of the Ag layers. A method for the direct measurement of the volume and thickness of nanomaterials has been developed in the project using High-Angle Annular Dark-Field (HAADF) Scanning Transmission Electron Microscopy (STEM). The morphology of Au and Ag NPs has been studied to provide reliable statistics for 3-D characterization. Deposition rates have been obtained as a function of metallization conditions by measuring the composition and thickness of the metal for EMPS. In the present work a calibration method was used to quantify the sensitivity of the HAADF detector. For thin samples a linear relationship of the HAADF signal with the thickness of a material is found. Cross-sections of multilayered samples provided by Triquint Semiconductors, FL, were analyzed as calibration standards with known composition in a TECNAI F30 transmission electron microscope to study the dependence of the HAADF detector signal on sample thickness and temperature.Dynamical diffraction processes play an important role in electron scattering for larger sample thicknesses. The HAADF detector intensity is not linearly dependent on sample thicknesses for thick samples. This phenomenon involves several excitation processes including Thermal Diffuse Scattering (TDS) which depends on temperature-dependent absorption coefficients. Multislice simulations have been carried out by Python programming using the scattering parameters available in the literature. These simulations were compared with experimental results. Wedge-shaped Focused Ion Beam (FIB) samples were prepared for quantitative HAADF-STEM intensity measurements for several samples and compared with these simulations. The discrepancies between the simulated and experimental results were explained and new sets of absorptive parameters were calculated which correctly account for the HAADF-STEM contrasts. A database of several pure elements is compiled to illustrate the absorption coefficients and fractions of scattered electrons per nanometer of the sample.In addition, the wedge-shaped FIB samples were used for studying the HAADF-STEM contrasts at an interface of a high- and a low-density material. The use of thick samples reveals an increased signal at the interfaces of high- and low-density materials. This effect can be explained by the transfer of scattered electrons from the high density material across the interface into the less-absorbing low-density material. A ballistic scattering model is proposed here for the HAADF-STEM contrasts at interfaces of thick materials using Python. The simulated HAADF-STEM signal is compared with experimental data to showcase the above phenomenon. A detailed understanding of the atomic number contrast in thick samples is developed based on the combination of experimental quantitative HAADF-STEM and simulated scattering. This approach is used to describe the observed features for Ag deposition on SU-8 polymers.
Show less - Date Issued
- 2014
- Identifier
- CFE0005485, ucf:50333
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005485
- Title
- Electronic transport and correlations in single magnetic molecule devices.
- Creator
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Romero, Javier, Mucciolo, Eduardo, Del Barco, Enrique, Stolbov, Sergey, Hernandez, Florencio, University of Central Florida
- Abstract / Description
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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.
Show less - Date Issued
- 2014
- Identifier
- CFE0005407, ucf:50420
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005407
- Title
- Electronic properties and atomic scale microscopy of two dimensional materials: graphene and molybdenum disulfide.
- Creator
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Katoch, Jyoti, Ishigami, Marsahir, Mucciolo, Eduardo, Del Barco, Enrique, Coffey, Kevin, University of Central Florida
- Abstract / Description
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Novel two dimensional nanoscale materials like graphene and metal dichalcogenides (MX2) have attracted the attention of the scientific community, due to their rich physics and wide range of potential applications.It has been shown that novel graphene based transparent conductors and radiofrequency transistors are competitive with the existing technologies. Graphene's properties are influenced sensitively by adsorbates and substrates. As such not surprisingly, physical properties of graphene...
Show moreNovel two dimensional nanoscale materials like graphene and metal dichalcogenides (MX2) have attracted the attention of the scientific community, due to their rich physics and wide range of potential applications.It has been shown that novel graphene based transparent conductors and radiofrequency transistors are competitive with the existing technologies. Graphene's properties are influenced sensitively by adsorbates and substrates. As such not surprisingly, physical properties of graphene are found to have a large variability, which cannot be controlled at the synthesis level, reducing the utility of graphene. As a part of my doctorate dissertation, I have developed atomic hydrogen as a novel technique to count the scatterers responsible for limiting the carrier mobility of graphene field effect transistors on silicon oxide (SiO2) and identified that charged impurities to be the most dominant scatterer. This result enables systematic reduction of the detrimental variability in device performance of graphene. Such sensitivity to substrates also gives an opportunity for engineering device properties of graphene using substrate interaction and atomic scale vacancies. Stacking graphene on hexagonal boron-nitride (h-BN) gives rise to nanoscale periodic potential, which influences its electronic graphene. Using state-of-the-art atomic-resolution scanning probe microscope, I correlated the observed transport properties to the substrate induced extrinsic potentials. Finally in efforts to exploit graphene's sensitivity to discover new sensor technologies, I have explored noncovalentfunctionalization of graphene using peptides.Molybdenum disulfide (MoS2) exhibits thickness dependent bandgap. Transistors fabricated from single layer MoS2 have shown a high on/off ratio. It is expected that ad-atom engineering can be used to induce on demand a metal-semiconductor transition in MoS2. In this direction, I have explored controlled/reversible fluorination and hydrogenation of monolayer MoS2 to potentially derive a full range of integrated circuit technology. The in-depth characterization of the samples is carried out by Raman/photoluminescence spectroscopy and scanning tunneling microscopy.
Show less - Date Issued
- 2014
- Identifier
- CFE0005190, ucf:50614
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005190
