Joseph Tedesco - Academia.edu (original) (raw)
Papers by Joseph Tedesco
Proceedings of the IEEE, 2000
In addition to the potential for memristors to be used in logic, memory, smart interconnects, and... more In addition to the potential for memristors to be used in logic, memory, smart interconnects, and biologically inspired architectures that could transform traditional silicon-based computing, memristors may enable such transformative technologies on physically flexible substrates. The simple structure of a memristor, which generally consists of a thin film of oxide sandwiched between two metal contacts, contributes to its compatibility with
Nanotechnology, 2012
Memristors are emerging as unique electrical devices with potential applications in memory, recon... more Memristors are emerging as unique electrical devices with potential applications in memory, reconfigurable logic and biologically inspired computing. Due to the novelty of these devices, the complete details of their switching mechanism is not yet well established. In this work, the switching mechanism of our solution-processed titanium dioxide-based memristor is investigated by studying how variations in the device area and film thickness affect electrical behavior and correlating these behavioral changes to proposed switching mechanisms. The conduction path of the switching is also investigated through electrical characterization of devices both before and after physically cutting the devices in half, as well as through infrared imaging of the devices during operation. The results suggest that the electrical behavior of these devices is dominated by a localized, charge-based phenomenon that exhibits a dependence on device area.
In order to study the conduction and loss mechanisms behind their operation, flexible sol-gel bas... more In order to study the conduction and loss mechanisms behind their operation, flexible sol-gel based memristors were fabricated with differing oxide film thicknesses and device sizes. XPS, TEM, EELS, and VASE measurements indicated the oxide was amorphous TiO2, with a significant fraction of organic material. Analysis of the bias and sweep rate dependence of the devices suggested the switching mechanism
ABSTRACT Flexible memristors consisting of an oxide film generated through hydrolysis of a spun-o... more ABSTRACT Flexible memristors consisting of an oxide film generated through hydrolysis of a spun-on sol-gel were fabricated on polyethylene terephthalate substrates. X-ray photoelectron spectroscopy, spectroscopic ellipsometry, transmission electron microscopy, and electron energy loss spectroscopy measurements indicated that the oxide films contained amorphous TiO2 as well as a significant fraction of organic material. This characterization indicated that the oxide film has a different structure and morphology than sputter-deposited TiO2 memristors ("traditional memristors"). Despite the structural differences between sol-gel and traditional memristors, these flexible memristors exhibit switching behavior that is similar to sputter-deposited devices. Current-voltage (I-V) measurements suggest that this switching is not directly due to the electric field in the memristors. Additionally, thermal imaging measurements and I-V measurements performed after sectioning the memristors suggest that conduction occurred via localized conduction pathways. Capacitance-frequency and conductance-frequency measurements were also performed to further investigate conduction and loss mechanisms in these memristors.
Scientific Reports, 2013
The remarkable electronic properties of graphene strongly depend on the thickness and geometry of... more The remarkable electronic properties of graphene strongly depend on the thickness and geometry of graphene stacks. This wide range of electronic tunability is of fundamental interest and has many applications in newly proposed devices. Using the mid-infrared, magneto-optical Kerr effect, we detect and identify over 18 interband cyclotron resonances (CR) that are associated with ABA and ABC stacked multilayers as well as monolayers that coexist in graphene that is epitaxially grown on 4H-SiC. Moreover, the magnetic field and photon energy dependence of these features enable us to explore the band structure, electron-hole band asymmetries, and mechanisms that activate a CR response in the Kerr effect for various multilayers that coexist in a single sample. Surprisingly, we find that the magnitude of monolayer Kerr effect CRs is not temperature dependent. This unexpected result reveals new questions about the underlying physics that makes such an effect possible. OPEN SUBJECT AREAS: MAGNETO-OPTICS ELECTRONIC PROPERTIES AND MATERIALS
Nano Letters, 2009
We present X-ray photoelectron spectroscopy, van der Pauw Hall mobilities, low-temperature far-in... more We present X-ray photoelectron spectroscopy, van der Pauw Hall mobilities, low-temperature far-infrared magneto transmission (FIR-MT), and atomic force microscopy (AFM) results from graphene films produced by radiative heating in an ultrahigh vacuum (UHV) chamber or produced by radio frequency (RF) furnace annealing in a high vacuum chemical vapor deposition system on Si-and C-face 4H SiC substrates at 1200-1600°C. Although the vacuum level and heating methods are different, graphene films produced by the two methods are chemically similar with the RF furnace annealing typically producing thicker graphene films than UHV. We observe, however, that the formation of graphene on the two faces is different with the thicker graphene films on the C-face RF samples having higher mobility. The FIR-MT showed a 0(-1) f 1(0) Landau level transition with a B dependence and a line width consistent with a Dirac fermion with a mobility >250 000 cm 2 ·V -1 ·s -1 at 4.2 K in a C-face RF sample having a Hall-effect carrier mobility of 425 cm 2 ·V -1 ·s -1 at 300 K. AFM shows that graphene grows continuously over the varying morphology of both Si and C-face substrates.
In this work we present mid-infrared (114 meV-224 meV) polarization-sensitive measurements on mul... more In this work we present mid-infrared (114 meV-224 meV) polarization-sensitive measurements on multilayer epitaxial graphene, which reveal graphene's rich and complex cyclotron resonant (CR) structure. By using Fourier transform Kerr spectroscopy we are able to separate and identify cyclotron resonances from graphene multilayers with various stacking orders and thicknesses. Moreover, from the identification of the layers present and their measured fundamental band parameters we are able to use these results to better understand previously unexplained CR features in far-infrared (0.1 meV -87 meV) transmission measurements performed on the same sample.
Eprint Arxiv 0907 5029, Jul 1, 2009
Graphene was epitaxially grown on both the C- and Si-faces of 4H- and 6H-SiC(0001) under an argon... more Graphene was epitaxially grown on both the C- and Si-faces of 4H- and 6H-SiC(0001) under an argon atmosphere and under high vacuum conditions. Following growth, samples were imaged with Nomarski interference contrast and atomic force microscopies and it was found that growth under argon led to improved morphologies on the C-face films but the Si-face films were not significantly affected. Free carrier transport studies were conducted through Hall effect measurements, and carrier mobilities were found to increase and sheet carrier densities were found to decrease for those films grown under argon as compared to high vacuum conditions. The improved mobilities and concurrent decreases in sheet carrier densities suggest a decrease in scattering in the films grown under argon.
ECS Transactions, 2009
An in vacuo thermal desorption process has been accomplished to form epitaxial graphene (EG) on 4... more An in vacuo thermal desorption process has been accomplished to form epitaxial graphene (EG) on 4H-and 6H-SiC substrates using a commercial chemical vapor deposition reactor. Correlation of growth conditions and the morphology and electrical properties of EG are described. Raman spectra of EG on Si-face samples were dominated by monolayer thickness. This approach was used to grow EG on 50 mm SiC wafers that were subsequently fabricated into field effect transistors with f max of 14 GHz.
Carbon Nanotubes, Graphene, and Associated Devices III, 2010
Epitaxial graphene (EG) grown on the carbon-face of SiC has been shown to exhibit higher carrier ... more Epitaxial graphene (EG) grown on the carbon-face of SiC has been shown to exhibit higher carrier mobilities in comparison graphene grown via most other methods, while also remaining amenable to wafer-scale growth and fabrication. The ability to transfer large area (>mm2), continuous graphene films to arbitrary substrates while maintaining the electrical and structural integrity of the film is desirable. We
2010 Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems (SiRF), 2010
Abstract We will present recent development of graphene FET technology on a wafer scale, includ... more Abstract We will present recent development of graphene FET technology on a wafer scale, including epitaxial graphene growth, device fabrication and characterization. The epitaxial growth of graphene on 2-inch wafers were fabricated via graphitization of Si-face ...
ECS Transactions, 2009
Graphene was epitaxially grown on both the C-and Si-faces of 4H-and 6H-SiC(0001) under an argon a... more Graphene was epitaxially grown on both the C-and Si-faces of 4H-and 6H-SiC(0001) under an argon atmosphere and under high vacuum conditions. Following growth, samples were imaged with Nomarski interference contrast and atomic force microscopies and it was found that growth under argon led to improved morphologies on the C-face films but the Si-face films were not significantly affected. Free carrier transport studies were conducted through Hall effect measurements, and carrier mobilities were found to increase and sheet carrier densities were found to decrease for those films grown under argon as compared to high vacuum conditions. The improved mobilities and concurrent decreases in sheet carrier densities suggest a decrease in scattering in the films grown under argon.
MRS Proceedings, 2010
... J. Anderson, Karl D. Hobart, Glenn G. Jernigan, James C. Culbertson, Fritz J. Kub, Joseph L. ... more ... J. Anderson, Karl D. Hobart, Glenn G. Jernigan, James C. Culbertson, Fritz J. Kub, Joseph L. Tedesco, Jennifer K. Hite, Michael A. Mastro, Rachael L. Myers ... The tape/EG/SiC 'stack' was then placed on a silicon wafer within the bore of an EVG EV501 wafer bonding apparatus. ...
Materials Science Forum, 2010
... Conclusions: In summary, we have used UVPL, HRXT, and micro-Raman mapping to investigate the ... more ... Conclusions: In summary, we have used UVPL, HRXT, and micro-Raman mapping to investigate the structure ... 353356 (2001), p. 299 [6] H. Lendenmann, F. Dahlquist, N. Johansson, R. Soderholm, PA Nilsson ... 457460 (2004) p. 533 [9] SI Maximenko and TS Sudarshan, J. Appl ...
Materials Science Forum, 2009
Graphene layers were created on both C and Si faces of semi-insulating, on-axis, 4H-and 6H-SiC su... more Graphene layers were created on both C and Si faces of semi-insulating, on-axis, 4H-and 6H-SiC substrates. The process was performed under high vacuum (<10 -4 mbar) in a commercial chemical vapor deposition SiC reactor. A method for H 2 etching the on-axis substrates was developed to produce surface steps with heights of 0.5 nm on the Si-face and 1.0 to 1.5 nm on the C-face for each polytype. A process was developed to form graphene on the substrates immediately after H 2 etching and Raman spectroscopy of these samples confirmed the formation of graphene. The morphology of the graphene is described. For both faces, the underlying substrate morphology was significantly modified during graphene formation; surface steps were up to 15 nm high and the uniform step morphology was sometimes lost. Mobilities and sheet carrier concentrations derived from Hall Effect measurements on large area (16 mm square) and small area (2 and 10 m square) samples are presented and shown to compare favorably to recent reports.
ABSTRACT Flexible memristors consisting of an oxide film generated through hydrolysis of a spun-o... more ABSTRACT Flexible memristors consisting of an oxide film generated through hydrolysis of a spun-on sol-gel were fabricated on polyethylene terephthalate substrates. X-ray photoelectron spectroscopy, spectroscopic ellipsometry, transmission electron microscopy, and electron energy loss spectroscopy measurements indicated that the oxide films contained amorphous TiO2 as well as a significant fraction of organic material. This characterization indicated that the oxide film has a different structure and morphology than sputter-deposited TiO2 memristors ("traditional memristors"). Despite the structural differences between sol-gel and traditional memristors, these flexible memristors exhibit switching behavior that is similar to sputter-deposited devices. Current-voltage (I-V) measurements suggest that this switching is not directly due to the electric field in the memristors. Additionally, thermal imaging measurements and I-V measurements performed after sectioning the memristors suggest that conduction occurred via localized conduction pathways. Capacitance-frequency and conductance-frequency measurements were also performed to further investigate conduction and loss mechanisms in these memristors.
Cobalt disilicide (CoSi2) islands have been formed on Si(111) and Si(100) through UHV deposition ... more Cobalt disilicide (CoSi2) islands have been formed on Si(111) and Si(100) through UHV deposition and annealing. Current-voltage (I-V) and temperature-dependent current-voltage (I-V-T) curves have been measured on the islands using conducting atomic force microscopy ( c-AFM) with a doped diamond like carbon cantilever. Thermionic emission theory has been applied to the curves and the Schottky barrier heights, phi B, and ideality factors, n, for each island have been calculated. Barrier heights and ideality factors are evaluated as functions of temperature, island area, and each other. While all islands were prepared in UHV conditions, one set was removed from UHV and measurements were performed in ambient conditions while the other set remained in UHV. The islands measured in ambient conditions were known as "air-exposed samples" due to the fact that the surface was assumed to be passivated upon exposure to atmospheric conditions. The islands measured in UHV were known as &...
Proceedings of the IEEE, 2000
In addition to the potential for memristors to be used in logic, memory, smart interconnects, and... more In addition to the potential for memristors to be used in logic, memory, smart interconnects, and biologically inspired architectures that could transform traditional silicon-based computing, memristors may enable such transformative technologies on physically flexible substrates. The simple structure of a memristor, which generally consists of a thin film of oxide sandwiched between two metal contacts, contributes to its compatibility with
Nano Letters, 2009
] is not only highly dependent on thickness uniformity but also on monolayer s st tr ra ai in n u... more ] is not only highly dependent on thickness uniformity but also on monolayer s st tr ra ai in n uniformity. Only when both thickness and strain are uniform over a significant fraction (> 40%) of the device active area does the mobility exceed 1000 cm 2 /V-s. Additionally, we achieve high mobility epitaxial graphene (18,100 cm 2 /V-s at room temperature) on the C-face of SiC [SiC(000-1)] and show that carrier mobility depends strongly on the graphene layer stacking. These findings provide a means to rapidly estimate carrier mobility and provide a guide to achieve very high mobility in epitaxial graphene. Our results suggest that ultra-high mobilities (>50,000 cm 2 /V-s) are achievable via the controlled formation of uniform, rotationally faulted epitaxial graphene.
Nano Letters, 2009
We present X-ray photoelectron spectroscopy, van der Pauw Hall mobilities, low-temperature far-in... more We present X-ray photoelectron spectroscopy, van der Pauw Hall mobilities, low-temperature far-infrared magneto transmission (FIR-MT), and atomic force microscopy (AFM) results from graphene films produced by radiative heating in an ultrahigh vacuum (UHV) chamber or produced by radio frequency (RF) furnace annealing in a high vacuum chemical vapor deposition system on Si-and C-face 4H SiC substrates at 1200-1600°C. Although the vacuum level and heating methods are different, graphene films produced by the two methods are chemically similar with the RF furnace annealing typically producing thicker graphene films than UHV. We observe, however, that the formation of graphene on the two faces is different with the thicker graphene films on the C-face RF samples having higher mobility. The FIR-MT showed a 0(-1) f 1(0) Landau level transition with a B dependence and a line width consistent with a Dirac fermion with a mobility >250 000 cm 2 ·V -1 ·s -1 at 4.2 K in a C-face RF sample having a Hall-effect carrier mobility of 425 cm 2 ·V -1 ·s -1 at 300 K. AFM shows that graphene grows continuously over the varying morphology of both Si and C-face substrates.
Proceedings of the IEEE, 2000
In addition to the potential for memristors to be used in logic, memory, smart interconnects, and... more In addition to the potential for memristors to be used in logic, memory, smart interconnects, and biologically inspired architectures that could transform traditional silicon-based computing, memristors may enable such transformative technologies on physically flexible substrates. The simple structure of a memristor, which generally consists of a thin film of oxide sandwiched between two metal contacts, contributes to its compatibility with
Nanotechnology, 2012
Memristors are emerging as unique electrical devices with potential applications in memory, recon... more Memristors are emerging as unique electrical devices with potential applications in memory, reconfigurable logic and biologically inspired computing. Due to the novelty of these devices, the complete details of their switching mechanism is not yet well established. In this work, the switching mechanism of our solution-processed titanium dioxide-based memristor is investigated by studying how variations in the device area and film thickness affect electrical behavior and correlating these behavioral changes to proposed switching mechanisms. The conduction path of the switching is also investigated through electrical characterization of devices both before and after physically cutting the devices in half, as well as through infrared imaging of the devices during operation. The results suggest that the electrical behavior of these devices is dominated by a localized, charge-based phenomenon that exhibits a dependence on device area.
In order to study the conduction and loss mechanisms behind their operation, flexible sol-gel bas... more In order to study the conduction and loss mechanisms behind their operation, flexible sol-gel based memristors were fabricated with differing oxide film thicknesses and device sizes. XPS, TEM, EELS, and VASE measurements indicated the oxide was amorphous TiO2, with a significant fraction of organic material. Analysis of the bias and sweep rate dependence of the devices suggested the switching mechanism
ABSTRACT Flexible memristors consisting of an oxide film generated through hydrolysis of a spun-o... more ABSTRACT Flexible memristors consisting of an oxide film generated through hydrolysis of a spun-on sol-gel were fabricated on polyethylene terephthalate substrates. X-ray photoelectron spectroscopy, spectroscopic ellipsometry, transmission electron microscopy, and electron energy loss spectroscopy measurements indicated that the oxide films contained amorphous TiO2 as well as a significant fraction of organic material. This characterization indicated that the oxide film has a different structure and morphology than sputter-deposited TiO2 memristors ("traditional memristors"). Despite the structural differences between sol-gel and traditional memristors, these flexible memristors exhibit switching behavior that is similar to sputter-deposited devices. Current-voltage (I-V) measurements suggest that this switching is not directly due to the electric field in the memristors. Additionally, thermal imaging measurements and I-V measurements performed after sectioning the memristors suggest that conduction occurred via localized conduction pathways. Capacitance-frequency and conductance-frequency measurements were also performed to further investigate conduction and loss mechanisms in these memristors.
Scientific Reports, 2013
The remarkable electronic properties of graphene strongly depend on the thickness and geometry of... more The remarkable electronic properties of graphene strongly depend on the thickness and geometry of graphene stacks. This wide range of electronic tunability is of fundamental interest and has many applications in newly proposed devices. Using the mid-infrared, magneto-optical Kerr effect, we detect and identify over 18 interband cyclotron resonances (CR) that are associated with ABA and ABC stacked multilayers as well as monolayers that coexist in graphene that is epitaxially grown on 4H-SiC. Moreover, the magnetic field and photon energy dependence of these features enable us to explore the band structure, electron-hole band asymmetries, and mechanisms that activate a CR response in the Kerr effect for various multilayers that coexist in a single sample. Surprisingly, we find that the magnitude of monolayer Kerr effect CRs is not temperature dependent. This unexpected result reveals new questions about the underlying physics that makes such an effect possible. OPEN SUBJECT AREAS: MAGNETO-OPTICS ELECTRONIC PROPERTIES AND MATERIALS
Nano Letters, 2009
We present X-ray photoelectron spectroscopy, van der Pauw Hall mobilities, low-temperature far-in... more We present X-ray photoelectron spectroscopy, van der Pauw Hall mobilities, low-temperature far-infrared magneto transmission (FIR-MT), and atomic force microscopy (AFM) results from graphene films produced by radiative heating in an ultrahigh vacuum (UHV) chamber or produced by radio frequency (RF) furnace annealing in a high vacuum chemical vapor deposition system on Si-and C-face 4H SiC substrates at 1200-1600°C. Although the vacuum level and heating methods are different, graphene films produced by the two methods are chemically similar with the RF furnace annealing typically producing thicker graphene films than UHV. We observe, however, that the formation of graphene on the two faces is different with the thicker graphene films on the C-face RF samples having higher mobility. The FIR-MT showed a 0(-1) f 1(0) Landau level transition with a B dependence and a line width consistent with a Dirac fermion with a mobility >250 000 cm 2 ·V -1 ·s -1 at 4.2 K in a C-face RF sample having a Hall-effect carrier mobility of 425 cm 2 ·V -1 ·s -1 at 300 K. AFM shows that graphene grows continuously over the varying morphology of both Si and C-face substrates.
In this work we present mid-infrared (114 meV-224 meV) polarization-sensitive measurements on mul... more In this work we present mid-infrared (114 meV-224 meV) polarization-sensitive measurements on multilayer epitaxial graphene, which reveal graphene's rich and complex cyclotron resonant (CR) structure. By using Fourier transform Kerr spectroscopy we are able to separate and identify cyclotron resonances from graphene multilayers with various stacking orders and thicknesses. Moreover, from the identification of the layers present and their measured fundamental band parameters we are able to use these results to better understand previously unexplained CR features in far-infrared (0.1 meV -87 meV) transmission measurements performed on the same sample.
Eprint Arxiv 0907 5029, Jul 1, 2009
Graphene was epitaxially grown on both the C- and Si-faces of 4H- and 6H-SiC(0001) under an argon... more Graphene was epitaxially grown on both the C- and Si-faces of 4H- and 6H-SiC(0001) under an argon atmosphere and under high vacuum conditions. Following growth, samples were imaged with Nomarski interference contrast and atomic force microscopies and it was found that growth under argon led to improved morphologies on the C-face films but the Si-face films were not significantly affected. Free carrier transport studies were conducted through Hall effect measurements, and carrier mobilities were found to increase and sheet carrier densities were found to decrease for those films grown under argon as compared to high vacuum conditions. The improved mobilities and concurrent decreases in sheet carrier densities suggest a decrease in scattering in the films grown under argon.
ECS Transactions, 2009
An in vacuo thermal desorption process has been accomplished to form epitaxial graphene (EG) on 4... more An in vacuo thermal desorption process has been accomplished to form epitaxial graphene (EG) on 4H-and 6H-SiC substrates using a commercial chemical vapor deposition reactor. Correlation of growth conditions and the morphology and electrical properties of EG are described. Raman spectra of EG on Si-face samples were dominated by monolayer thickness. This approach was used to grow EG on 50 mm SiC wafers that were subsequently fabricated into field effect transistors with f max of 14 GHz.
Carbon Nanotubes, Graphene, and Associated Devices III, 2010
Epitaxial graphene (EG) grown on the carbon-face of SiC has been shown to exhibit higher carrier ... more Epitaxial graphene (EG) grown on the carbon-face of SiC has been shown to exhibit higher carrier mobilities in comparison graphene grown via most other methods, while also remaining amenable to wafer-scale growth and fabrication. The ability to transfer large area (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;mm2), continuous graphene films to arbitrary substrates while maintaining the electrical and structural integrity of the film is desirable. We
2010 Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems (SiRF), 2010
Abstract We will present recent development of graphene FET technology on a wafer scale, includ... more Abstract We will present recent development of graphene FET technology on a wafer scale, including epitaxial graphene growth, device fabrication and characterization. The epitaxial growth of graphene on 2-inch wafers were fabricated via graphitization of Si-face ...
ECS Transactions, 2009
Graphene was epitaxially grown on both the C-and Si-faces of 4H-and 6H-SiC(0001) under an argon a... more Graphene was epitaxially grown on both the C-and Si-faces of 4H-and 6H-SiC(0001) under an argon atmosphere and under high vacuum conditions. Following growth, samples were imaged with Nomarski interference contrast and atomic force microscopies and it was found that growth under argon led to improved morphologies on the C-face films but the Si-face films were not significantly affected. Free carrier transport studies were conducted through Hall effect measurements, and carrier mobilities were found to increase and sheet carrier densities were found to decrease for those films grown under argon as compared to high vacuum conditions. The improved mobilities and concurrent decreases in sheet carrier densities suggest a decrease in scattering in the films grown under argon.
MRS Proceedings, 2010
... J. Anderson, Karl D. Hobart, Glenn G. Jernigan, James C. Culbertson, Fritz J. Kub, Joseph L. ... more ... J. Anderson, Karl D. Hobart, Glenn G. Jernigan, James C. Culbertson, Fritz J. Kub, Joseph L. Tedesco, Jennifer K. Hite, Michael A. Mastro, Rachael L. Myers ... The tape/EG/SiC 'stack' was then placed on a silicon wafer within the bore of an EVG EV501 wafer bonding apparatus. ...
Materials Science Forum, 2010
... Conclusions: In summary, we have used UVPL, HRXT, and micro-Raman mapping to investigate the ... more ... Conclusions: In summary, we have used UVPL, HRXT, and micro-Raman mapping to investigate the structure ... 353356 (2001), p. 299 [6] H. Lendenmann, F. Dahlquist, N. Johansson, R. Soderholm, PA Nilsson ... 457460 (2004) p. 533 [9] SI Maximenko and TS Sudarshan, J. Appl ...
Materials Science Forum, 2009
Graphene layers were created on both C and Si faces of semi-insulating, on-axis, 4H-and 6H-SiC su... more Graphene layers were created on both C and Si faces of semi-insulating, on-axis, 4H-and 6H-SiC substrates. The process was performed under high vacuum (<10 -4 mbar) in a commercial chemical vapor deposition SiC reactor. A method for H 2 etching the on-axis substrates was developed to produce surface steps with heights of 0.5 nm on the Si-face and 1.0 to 1.5 nm on the C-face for each polytype. A process was developed to form graphene on the substrates immediately after H 2 etching and Raman spectroscopy of these samples confirmed the formation of graphene. The morphology of the graphene is described. For both faces, the underlying substrate morphology was significantly modified during graphene formation; surface steps were up to 15 nm high and the uniform step morphology was sometimes lost. Mobilities and sheet carrier concentrations derived from Hall Effect measurements on large area (16 mm square) and small area (2 and 10 m square) samples are presented and shown to compare favorably to recent reports.
ABSTRACT Flexible memristors consisting of an oxide film generated through hydrolysis of a spun-o... more ABSTRACT Flexible memristors consisting of an oxide film generated through hydrolysis of a spun-on sol-gel were fabricated on polyethylene terephthalate substrates. X-ray photoelectron spectroscopy, spectroscopic ellipsometry, transmission electron microscopy, and electron energy loss spectroscopy measurements indicated that the oxide films contained amorphous TiO2 as well as a significant fraction of organic material. This characterization indicated that the oxide film has a different structure and morphology than sputter-deposited TiO2 memristors ("traditional memristors"). Despite the structural differences between sol-gel and traditional memristors, these flexible memristors exhibit switching behavior that is similar to sputter-deposited devices. Current-voltage (I-V) measurements suggest that this switching is not directly due to the electric field in the memristors. Additionally, thermal imaging measurements and I-V measurements performed after sectioning the memristors suggest that conduction occurred via localized conduction pathways. Capacitance-frequency and conductance-frequency measurements were also performed to further investigate conduction and loss mechanisms in these memristors.
Cobalt disilicide (CoSi2) islands have been formed on Si(111) and Si(100) through UHV deposition ... more Cobalt disilicide (CoSi2) islands have been formed on Si(111) and Si(100) through UHV deposition and annealing. Current-voltage (I-V) and temperature-dependent current-voltage (I-V-T) curves have been measured on the islands using conducting atomic force microscopy ( c-AFM) with a doped diamond like carbon cantilever. Thermionic emission theory has been applied to the curves and the Schottky barrier heights, phi B, and ideality factors, n, for each island have been calculated. Barrier heights and ideality factors are evaluated as functions of temperature, island area, and each other. While all islands were prepared in UHV conditions, one set was removed from UHV and measurements were performed in ambient conditions while the other set remained in UHV. The islands measured in ambient conditions were known as "air-exposed samples" due to the fact that the surface was assumed to be passivated upon exposure to atmospheric conditions. The islands measured in UHV were known as &...
Proceedings of the IEEE, 2000
In addition to the potential for memristors to be used in logic, memory, smart interconnects, and... more In addition to the potential for memristors to be used in logic, memory, smart interconnects, and biologically inspired architectures that could transform traditional silicon-based computing, memristors may enable such transformative technologies on physically flexible substrates. The simple structure of a memristor, which generally consists of a thin film of oxide sandwiched between two metal contacts, contributes to its compatibility with
Nano Letters, 2009
] is not only highly dependent on thickness uniformity but also on monolayer s st tr ra ai in n u... more ] is not only highly dependent on thickness uniformity but also on monolayer s st tr ra ai in n uniformity. Only when both thickness and strain are uniform over a significant fraction (> 40%) of the device active area does the mobility exceed 1000 cm 2 /V-s. Additionally, we achieve high mobility epitaxial graphene (18,100 cm 2 /V-s at room temperature) on the C-face of SiC [SiC(000-1)] and show that carrier mobility depends strongly on the graphene layer stacking. These findings provide a means to rapidly estimate carrier mobility and provide a guide to achieve very high mobility in epitaxial graphene. Our results suggest that ultra-high mobilities (>50,000 cm 2 /V-s) are achievable via the controlled formation of uniform, rotationally faulted epitaxial graphene.
Nano Letters, 2009
We present X-ray photoelectron spectroscopy, van der Pauw Hall mobilities, low-temperature far-in... more We present X-ray photoelectron spectroscopy, van der Pauw Hall mobilities, low-temperature far-infrared magneto transmission (FIR-MT), and atomic force microscopy (AFM) results from graphene films produced by radiative heating in an ultrahigh vacuum (UHV) chamber or produced by radio frequency (RF) furnace annealing in a high vacuum chemical vapor deposition system on Si-and C-face 4H SiC substrates at 1200-1600°C. Although the vacuum level and heating methods are different, graphene films produced by the two methods are chemically similar with the RF furnace annealing typically producing thicker graphene films than UHV. We observe, however, that the formation of graphene on the two faces is different with the thicker graphene films on the C-face RF samples having higher mobility. The FIR-MT showed a 0(-1) f 1(0) Landau level transition with a B dependence and a line width consistent with a Dirac fermion with a mobility >250 000 cm 2 ·V -1 ·s -1 at 4.2 K in a C-face RF sample having a Hall-effect carrier mobility of 425 cm 2 ·V -1 ·s -1 at 300 K. AFM shows that graphene grows continuously over the varying morphology of both Si and C-face substrates.