These are the slides from the May Science Cafe featuring Dr. MVS Chandrashekhar. During this cafe he discussed his work with graphene a new, clean energy source.
Solar Cells Lecture 3: Modeling and Simulation of Photovoltaic Devices and Sy...Tuong Do
The document provides information about a summer school on modeling and simulation of photovoltaic devices and systems being held in July 2011. It outlines the course, which will cover objectives of PV modeling and simulation, device modeling, fundamental limits, system modeling of multijunction devices, and detailed numerical simulation. The instructor is Prof. Jeffery L. Gray of Purdue University and the material is provided under a Creative Commons license.
This document discusses trions, which are charged exciton-electron complexes, and their properties. It covers:
1. Trions can exist in singlet or triplet spin states at low electron densities. Modulation doping is used to control electron density in quantum wells.
2. Trions appear in optical spectra and their binding energy depends on the quantum well width. Magnetic fields affect the trion energy levels and allow determination of electron concentration.
3. At high electron densities, combined exciton-electron and trion-electron processes influence photoluminescence spectra. Trion Zeeman splitting also occurs in magnetic fields.
Introduction to the phenomenology of HiTc superconductors.ABDERRAHMANE REGGAD
1. The document provides an introduction to the phenomenology of high-temperature superconductors (HiTc).
2. It discusses the basic physics of doped Mott insulators and experimental methods used to study HiTc superconductors such as thermodynamic measurements, transport properties, neutron scattering, and ARPES.
3. It also covers topics such as the pseudo-gap phase, the one-hole problem, properties at small doping levels, and properties of the superconducting state.
Solar Cells Lecture 3: Modeling and Simulation of Photovoltaic Devices and Sy...Tuong Do
The document provides information about a summer school on modeling and simulation of photovoltaic devices and systems being held in July 2011. It outlines the course, which will cover objectives of PV modeling and simulation, device modeling, fundamental limits, system modeling of multijunction devices, and detailed numerical simulation. The instructor is Prof. Jeffery L. Gray of Purdue University and the material is provided under a Creative Commons license.
This document discusses trions, which are charged exciton-electron complexes, and their properties. It covers:
1. Trions can exist in singlet or triplet spin states at low electron densities. Modulation doping is used to control electron density in quantum wells.
2. Trions appear in optical spectra and their binding energy depends on the quantum well width. Magnetic fields affect the trion energy levels and allow determination of electron concentration.
3. At high electron densities, combined exciton-electron and trion-electron processes influence photoluminescence spectra. Trion Zeeman splitting also occurs in magnetic fields.
Introduction to the phenomenology of HiTc superconductors.ABDERRAHMANE REGGAD
1. The document provides an introduction to the phenomenology of high-temperature superconductors (HiTc).
2. It discusses the basic physics of doped Mott insulators and experimental methods used to study HiTc superconductors such as thermodynamic measurements, transport properties, neutron scattering, and ARPES.
3. It also covers topics such as the pseudo-gap phase, the one-hole problem, properties at small doping levels, and properties of the superconducting state.
Optical spectroscopy techniques such as transmission, reflection, absorption, and photoluminescence measurements are important tools for characterizing the optical properties of semiconductor materials for photovoltaic applications. These techniques can determine the band gap type and energy, which are crucial for a material's suitability as a solar cell absorber. A direct band gap is preferable to an indirect band gap. Temperature-dependent absorption measurements provide insight into the temperature dependence of the band gap and allow comparison to density functional theory calculations. Characterizing defects through photoluminescence is also useful. Together, optical measurements provide essential information for understanding and improving photovoltaic materials.
Magnetic semiconductors: classes of materials, basic properties, central ques...ABDERRAHMANE REGGAD
This document discusses magnetic semiconductors and their properties. It covers:
1) Concentrated magnetic semiconductors like chromium chalcogenides and europium chalcogenides which are ferromagnetic due to kinetic exchange and Coulomb interactions between localized magnetic moments.
2) Diluted magnetic semiconductors (DMS) where magnetic ions substitute into semiconductor hosts, including II-VI, oxide, and III-V semiconductors. Many DMS show carrier-mediated ferromagnetism driven by holes.
3) Key open questions about the mechanism of ferromagnetism, the nature of carrier states, and the origin of metal-insulator transitions and resistivity maxima observed
The document discusses room temperature superconductivity and summarizes past research on high temperature superconductivity. It also examines the electronic structure and superconducting properties of NaxCoO2. Specifically:
1) Prior research from the 1970s explored whether high temperature superconductivity was possible.
2) Calculations and experiments on NaxCoO2 suggest it has unusual magnetic and electronic properties, including spin fluctuations that may be important to superconductivity.
3) Studies of the superconducting state in NaxCoO2 indicate it is unconventional and not fully gapped, with triplet f-wave pairing being a leading hypothesis to explain experimental results.
This document presents theoretical problems related to ionic crystal structures. It discusses the Coulomb and repulsive potentials acting on ions in the crystal lattice. Two models are provided to describe the repulsive potential: an exponential function and an inverse power function. Experimental data for several ionic crystals is given. The problems involve deriving expressions for the net potential energy, determining equilibrium positions, estimating potential parameters from experimental dissociation energies, and calculating ionization energies. The solutions show that the Coulomb and Pauli potentials contribute to the net potential energy in a 9:1 proportion for NaCl.
Introduction to Modern Methods and Tools for Biologically Plausible Modelling...SSA KPI
This document provides an overview of modern methods and tools for biologically plausible modeling of neural structures in the brain. It discusses modeling at different levels, from the system level looking at the brain as a whole, down to the subcellular and molecular levels examining individual neurons and ion channels. At each level, it outlines key research methods used to study the brain experimentally and different modeling approaches, including population and dynamical models, formal neural networks, and detailed single-cell models. The document also reviews seminal work in neuroscience like Hodgkin and Huxley's equations for modeling ion channel dynamics and spike generation in neurons.
- The document discusses strongly interacting atoms in optical lattices and lattice-induced Feshbach resonances.
- It presents exact calculations of two atoms in a 1D lattice and finds avoided crossings between molecular bands and continuum states that depend on the lattice quasimomentum.
- An effective Hamiltonian is constructed that qualitatively captures these effects and introduces a momentum-dependent atom-dimer coupling parameter.
1. Diluted magnetic semiconductors aim to integrate semiconductor processing and ferromagnetic data storage on a single chip. Magnetic semiconductors are classes of materials that exhibit both semiconducting and magnetic properties.
2. The lecture discusses the theoretical picture of magnetic impurities in semiconductors based on the Zener model and mean-field theory. It also covers disorder, transport properties, and the anomalous Hall effect in diluted magnetic semiconductors.
3. The final sections discuss magnetic properties in the presence of disorder and recent developments, as well as open questions for the future of magnetic semiconductors.
This document provides an overview of density functional theory and methods for modeling strongly correlated materials. It discusses the limitations of standard DFT approaches like LDA for strongly correlated systems and introduces model Hamiltonians and correction methods like LDA+U, LDA+DMFT, self-interaction correction, and generalized transition state to better account for electron correlation effects. The document outlines the basic theory and approximations of DFT, including Kohn-Sham equations and the local density approximation, and discusses basis set approaches like plane waves, augmented plane waves, and pseudopotentials.
The document summarizes the LDA+U method for treating strongly correlated materials and applies it to two cases - CaFeO3 and La1/2Sr2/3FeO3. LDA+U adds an on-site Coulomb interaction term U to the LDA functional to better describe localized d-orbitals. It shows how LDA+U predicts charge disproportionation and an insulating state in both materials, driven by factors like lattice distortions, correlations, and disorder.
This document provides an overview of strongly correlated electronic systems. It begins with a list of some historical landmarks in the field, including early works developing band theory and models like the Hubbard model. It then contrasts the band structure approach with an atomic physics perspective that considers local electron-electron interactions. The document discusses how transition metal and rare earth compounds exhibit a range of behaviors between itinerant and localized electron limits depending on the relative sizes of the hopping integral and on-site Coulomb interaction. It provides examples of ordered phases that can emerge in correlated systems and how spectral weight is transferred with doping.
Module01 nuclear physics and reactor theorysirwaltz73
This document provides an overview of a basic professional training course on nuclear physics and reactor theory. It covers topics like atomic structure, the structure of the atom including electrons and the nucleus, isotopes, radioactive decay, and nuclear reactions. The document is divided into several modules, with learning objectives provided for each section. It includes diagrams and examples to illustrate key concepts in nuclear physics.
1) Atoms can exist in excited states with quantized, higher energy levels. Electrons can jump between these levels by absorbing or emitting photons with specific frequencies and wavelengths.
2) Bohr's model of the hydrogen atom successfully explained its observed emission spectrum, proposing that electrons orbit the nucleus at discrete energy levels corresponding to specific orbital radii.
3) Transitions between these quantized energy levels result in the emission or absorption of electromagnetic radiation in the form of photons. The energy and frequency of photons are related by Planck's constant.
Introduction to modern methods and tools for biologically plausible modeling ...SSA KPI
AACIMP 2010 Summer School lecture by Ruben Tikidji-Hamburyan. "Physics, Chemistry and Living Systems" stream. "Introduction to Modern Methods and Tools for Biologically Plausible Modeling of Neurons and Neural Networks" course. Part 1.
More info at http://summerschool.ssa.org.ua
The document discusses key concepts in quantum mechanics including:
1) Classical mechanics fails to fully explain phenomena like the photoelectric effect and wave-particle duality.
2) Planck's quantum hypothesis and Einstein's explanation of the photoelectric effect using light quanta (photons) helped establish quantum theory.
3) Heisenberg's uncertainty principle limits the simultaneous knowledge of conjugate variables like position and momentum.
4) De Broglie proposed that all matter has wave-particle duality properties defined by the de Broglie relations.
5) Schrödinger's wave equation describes how a wave function can be used to predict the behavior of a system.
The document summarizes the metal-insulator transition in VO2, which occurs at 340K. In the metallic phase, VO2 exhibits bad metal behavior with short electron mean free paths. The insulating phase has two possible structures - M1 and M2. M1 involves pairing of V atoms and splitting of orbitals. M2 involves formation of zig-zag V chains. The transition may involve both Mott-Hubbard localization and a Peierls instability driven by soft phonon modes near the R point of the Brillouin zone. Precise values are estimated for the electronic parameters characterizing the insulating M1 phase, including Hubbard U, spin gap Δσ, and charge gap Δρ.
Theoretical picture: magnetic impurities, Zener model, mean-field theoryABDERRAHMANE REGGAD
The document summarizes the theoretical picture of dilute magnetic semiconductors (DMS). It describes the Zener model where magnetic impurities interact with charge carriers via exchange interaction. It then discusses the mean field approximation used to calculate the Curie temperature. For higher doping concentrations, a virtual crystal approximation is used to replace impurity spins with a smooth spin density. The model explains several experimental observations but cannot explain some properties like the shape of magnetization curves. At very low doping, a bound magnetic polaron model applies where carriers hop between localized acceptor levels aligned with impurity spins.
The document discusses the structure of atoms and the development of atomic models. It summarizes:
1) The subatomic particles that make up atoms - electrons, protons, and neutrons - along with their relative charges and masses.
2) Early experiments that led to the discovery of electrons and the Thomson and Rutherford atomic models.
3) Quantum numbers like atomic number and mass number that are used to describe atoms.
4) Developments in quantum theory that resulted in Bohr's model of the hydrogen atom and explanation of atomic spectra through quantized energy levels.
The document discusses radioactivity, which is the spontaneous emission of particles or radiation from radioactive substances. It explains that there are three types of rays - alpha, beta, and gamma rays - produced by the decay or breakdown of radioactive materials, and each type is affected differently by electric or magnetic fields. The penetrating abilities of the different types of rays through materials like lead is also illustrated.
[L'angolo del PhD] Sara Borroni - XXIII Ciclo - 2010accatagliato
This thesis is focused on the study of the Z -> µ+ µ- process. This process is quite interesting. From the detector performance point of view, it can be used to measure from data muon trigger and reconstruction efficiencies. To extract these efficiencies, in the past three years I developed and optimized a method, called Tag&Probe, using Monte Carlo simulation. In the past few months, with the first ATLAS data, it allowed to measure the muon efficiencies from data for the first time. A data sample of 1.3 pb^-1 of integrated luminosity has been used and the results have been compared with the MC expectations.
The efficiencies estimation is also relevant for the cross-section measurement of all processes involving muons. In fact, when comparing the measured cross-section from data with the theoretical expectations, one has to correct for the detector inefficiencies, which at the start-ip are not perfectly reproduced in the simulation. In this thesis, these muon efficiencies have been used for a first data/MC comparison of the Z -> µ+ µ- cross-section, both inclusive and differential as a function of the jet multiplicity.
This document discusses brain-machine interfaces (BMI) and how carbon nanotubes could be used to improve them. It defines BMI as a collaboration where the brain controls a mechanical device. It then describes different types of invasive and noninvasive BMI and how diamond chips and carbon nanotubes could replace silicon in BMI circuits for benefits like higher temperatures and speeds. Potential applications discussed include using BMI for rehabilitation, daily tasks, communication, and enhancing military performance.
This document summarizes research on plasmonics and surface plasmon polaritons (SPPs). It discusses two types of excitations - localized surface plasmon resonance and propagating SPPs. Applications mentioned include spectroscopy, molecular detection, cancer treatment, photonic devices, integrated photonics, and optical data storage. Challenges include losses, thermal effects, and limitations of nanofabrication techniques. The document also reviews using SPPs for applications such as beam collimation, near-field microscopy, solar cells, and metamaterials.
Optical spectroscopy techniques such as transmission, reflection, absorption, and photoluminescence measurements are important tools for characterizing the optical properties of semiconductor materials for photovoltaic applications. These techniques can determine the band gap type and energy, which are crucial for a material's suitability as a solar cell absorber. A direct band gap is preferable to an indirect band gap. Temperature-dependent absorption measurements provide insight into the temperature dependence of the band gap and allow comparison to density functional theory calculations. Characterizing defects through photoluminescence is also useful. Together, optical measurements provide essential information for understanding and improving photovoltaic materials.
Magnetic semiconductors: classes of materials, basic properties, central ques...ABDERRAHMANE REGGAD
This document discusses magnetic semiconductors and their properties. It covers:
1) Concentrated magnetic semiconductors like chromium chalcogenides and europium chalcogenides which are ferromagnetic due to kinetic exchange and Coulomb interactions between localized magnetic moments.
2) Diluted magnetic semiconductors (DMS) where magnetic ions substitute into semiconductor hosts, including II-VI, oxide, and III-V semiconductors. Many DMS show carrier-mediated ferromagnetism driven by holes.
3) Key open questions about the mechanism of ferromagnetism, the nature of carrier states, and the origin of metal-insulator transitions and resistivity maxima observed
The document discusses room temperature superconductivity and summarizes past research on high temperature superconductivity. It also examines the electronic structure and superconducting properties of NaxCoO2. Specifically:
1) Prior research from the 1970s explored whether high temperature superconductivity was possible.
2) Calculations and experiments on NaxCoO2 suggest it has unusual magnetic and electronic properties, including spin fluctuations that may be important to superconductivity.
3) Studies of the superconducting state in NaxCoO2 indicate it is unconventional and not fully gapped, with triplet f-wave pairing being a leading hypothesis to explain experimental results.
This document presents theoretical problems related to ionic crystal structures. It discusses the Coulomb and repulsive potentials acting on ions in the crystal lattice. Two models are provided to describe the repulsive potential: an exponential function and an inverse power function. Experimental data for several ionic crystals is given. The problems involve deriving expressions for the net potential energy, determining equilibrium positions, estimating potential parameters from experimental dissociation energies, and calculating ionization energies. The solutions show that the Coulomb and Pauli potentials contribute to the net potential energy in a 9:1 proportion for NaCl.
Introduction to Modern Methods and Tools for Biologically Plausible Modelling...SSA KPI
This document provides an overview of modern methods and tools for biologically plausible modeling of neural structures in the brain. It discusses modeling at different levels, from the system level looking at the brain as a whole, down to the subcellular and molecular levels examining individual neurons and ion channels. At each level, it outlines key research methods used to study the brain experimentally and different modeling approaches, including population and dynamical models, formal neural networks, and detailed single-cell models. The document also reviews seminal work in neuroscience like Hodgkin and Huxley's equations for modeling ion channel dynamics and spike generation in neurons.
- The document discusses strongly interacting atoms in optical lattices and lattice-induced Feshbach resonances.
- It presents exact calculations of two atoms in a 1D lattice and finds avoided crossings between molecular bands and continuum states that depend on the lattice quasimomentum.
- An effective Hamiltonian is constructed that qualitatively captures these effects and introduces a momentum-dependent atom-dimer coupling parameter.
1. Diluted magnetic semiconductors aim to integrate semiconductor processing and ferromagnetic data storage on a single chip. Magnetic semiconductors are classes of materials that exhibit both semiconducting and magnetic properties.
2. The lecture discusses the theoretical picture of magnetic impurities in semiconductors based on the Zener model and mean-field theory. It also covers disorder, transport properties, and the anomalous Hall effect in diluted magnetic semiconductors.
3. The final sections discuss magnetic properties in the presence of disorder and recent developments, as well as open questions for the future of magnetic semiconductors.
This document provides an overview of density functional theory and methods for modeling strongly correlated materials. It discusses the limitations of standard DFT approaches like LDA for strongly correlated systems and introduces model Hamiltonians and correction methods like LDA+U, LDA+DMFT, self-interaction correction, and generalized transition state to better account for electron correlation effects. The document outlines the basic theory and approximations of DFT, including Kohn-Sham equations and the local density approximation, and discusses basis set approaches like plane waves, augmented plane waves, and pseudopotentials.
The document summarizes the LDA+U method for treating strongly correlated materials and applies it to two cases - CaFeO3 and La1/2Sr2/3FeO3. LDA+U adds an on-site Coulomb interaction term U to the LDA functional to better describe localized d-orbitals. It shows how LDA+U predicts charge disproportionation and an insulating state in both materials, driven by factors like lattice distortions, correlations, and disorder.
This document provides an overview of strongly correlated electronic systems. It begins with a list of some historical landmarks in the field, including early works developing band theory and models like the Hubbard model. It then contrasts the band structure approach with an atomic physics perspective that considers local electron-electron interactions. The document discusses how transition metal and rare earth compounds exhibit a range of behaviors between itinerant and localized electron limits depending on the relative sizes of the hopping integral and on-site Coulomb interaction. It provides examples of ordered phases that can emerge in correlated systems and how spectral weight is transferred with doping.
Module01 nuclear physics and reactor theorysirwaltz73
This document provides an overview of a basic professional training course on nuclear physics and reactor theory. It covers topics like atomic structure, the structure of the atom including electrons and the nucleus, isotopes, radioactive decay, and nuclear reactions. The document is divided into several modules, with learning objectives provided for each section. It includes diagrams and examples to illustrate key concepts in nuclear physics.
1) Atoms can exist in excited states with quantized, higher energy levels. Electrons can jump between these levels by absorbing or emitting photons with specific frequencies and wavelengths.
2) Bohr's model of the hydrogen atom successfully explained its observed emission spectrum, proposing that electrons orbit the nucleus at discrete energy levels corresponding to specific orbital radii.
3) Transitions between these quantized energy levels result in the emission or absorption of electromagnetic radiation in the form of photons. The energy and frequency of photons are related by Planck's constant.
Introduction to modern methods and tools for biologically plausible modeling ...SSA KPI
AACIMP 2010 Summer School lecture by Ruben Tikidji-Hamburyan. "Physics, Chemistry and Living Systems" stream. "Introduction to Modern Methods and Tools for Biologically Plausible Modeling of Neurons and Neural Networks" course. Part 1.
More info at http://summerschool.ssa.org.ua
The document discusses key concepts in quantum mechanics including:
1) Classical mechanics fails to fully explain phenomena like the photoelectric effect and wave-particle duality.
2) Planck's quantum hypothesis and Einstein's explanation of the photoelectric effect using light quanta (photons) helped establish quantum theory.
3) Heisenberg's uncertainty principle limits the simultaneous knowledge of conjugate variables like position and momentum.
4) De Broglie proposed that all matter has wave-particle duality properties defined by the de Broglie relations.
5) Schrödinger's wave equation describes how a wave function can be used to predict the behavior of a system.
The document summarizes the metal-insulator transition in VO2, which occurs at 340K. In the metallic phase, VO2 exhibits bad metal behavior with short electron mean free paths. The insulating phase has two possible structures - M1 and M2. M1 involves pairing of V atoms and splitting of orbitals. M2 involves formation of zig-zag V chains. The transition may involve both Mott-Hubbard localization and a Peierls instability driven by soft phonon modes near the R point of the Brillouin zone. Precise values are estimated for the electronic parameters characterizing the insulating M1 phase, including Hubbard U, spin gap Δσ, and charge gap Δρ.
Theoretical picture: magnetic impurities, Zener model, mean-field theoryABDERRAHMANE REGGAD
The document summarizes the theoretical picture of dilute magnetic semiconductors (DMS). It describes the Zener model where magnetic impurities interact with charge carriers via exchange interaction. It then discusses the mean field approximation used to calculate the Curie temperature. For higher doping concentrations, a virtual crystal approximation is used to replace impurity spins with a smooth spin density. The model explains several experimental observations but cannot explain some properties like the shape of magnetization curves. At very low doping, a bound magnetic polaron model applies where carriers hop between localized acceptor levels aligned with impurity spins.
The document discusses the structure of atoms and the development of atomic models. It summarizes:
1) The subatomic particles that make up atoms - electrons, protons, and neutrons - along with their relative charges and masses.
2) Early experiments that led to the discovery of electrons and the Thomson and Rutherford atomic models.
3) Quantum numbers like atomic number and mass number that are used to describe atoms.
4) Developments in quantum theory that resulted in Bohr's model of the hydrogen atom and explanation of atomic spectra through quantized energy levels.
The document discusses radioactivity, which is the spontaneous emission of particles or radiation from radioactive substances. It explains that there are three types of rays - alpha, beta, and gamma rays - produced by the decay or breakdown of radioactive materials, and each type is affected differently by electric or magnetic fields. The penetrating abilities of the different types of rays through materials like lead is also illustrated.
[L'angolo del PhD] Sara Borroni - XXIII Ciclo - 2010accatagliato
This thesis is focused on the study of the Z -> µ+ µ- process. This process is quite interesting. From the detector performance point of view, it can be used to measure from data muon trigger and reconstruction efficiencies. To extract these efficiencies, in the past three years I developed and optimized a method, called Tag&Probe, using Monte Carlo simulation. In the past few months, with the first ATLAS data, it allowed to measure the muon efficiencies from data for the first time. A data sample of 1.3 pb^-1 of integrated luminosity has been used and the results have been compared with the MC expectations.
The efficiencies estimation is also relevant for the cross-section measurement of all processes involving muons. In fact, when comparing the measured cross-section from data with the theoretical expectations, one has to correct for the detector inefficiencies, which at the start-ip are not perfectly reproduced in the simulation. In this thesis, these muon efficiencies have been used for a first data/MC comparison of the Z -> µ+ µ- cross-section, both inclusive and differential as a function of the jet multiplicity.
This document discusses brain-machine interfaces (BMI) and how carbon nanotubes could be used to improve them. It defines BMI as a collaboration where the brain controls a mechanical device. It then describes different types of invasive and noninvasive BMI and how diamond chips and carbon nanotubes could replace silicon in BMI circuits for benefits like higher temperatures and speeds. Potential applications discussed include using BMI for rehabilitation, daily tasks, communication, and enhancing military performance.
This document summarizes research on plasmonics and surface plasmon polaritons (SPPs). It discusses two types of excitations - localized surface plasmon resonance and propagating SPPs. Applications mentioned include spectroscopy, molecular detection, cancer treatment, photonic devices, integrated photonics, and optical data storage. Challenges include losses, thermal effects, and limitations of nanofabrication techniques. The document also reviews using SPPs for applications such as beam collimation, near-field microscopy, solar cells, and metamaterials.
Plasmonics aims to merge photonics and electronics at the nanoscale by using surface plasmons. Surface plasmons are electromagnetic waves that propagate along metal surfaces and can confine light to subwavelength dimensions, allowing the miniaturization of photonic components. This makes it possible to integrate optical and electronic circuits on the same chip. Plasmonic circuits use various geometries like thin metal films and arrays of gold nanoparticles as waveguides to guide surface plasmon signals while avoiding losses. This could enable the development of miniaturized optoelectronic components and circuits with subwavelength features bridging the gap between photonics and electronics.
These slides use concepts from my (Jeff Funk) course entitled analyzing hi-tech opportunities to analyze how the economic feasibility of flexible OLED displays are becoming better through newer and thinner materials, roll-to roll printing, and larger production equipment. Thinner materials along with new materials increase flexibility, reduce moisture permeation and thus increase the lifetime, and reduce cost. Flexibility enables displays that conform to complex shaped things such as wrists and backpacks and that can be fit inside pens and other tubes. Along with other technologies, this further facilitates information access.
The document discusses the Blue Eyes technology, which aims to develop computers that can understand users' emotions, identity, and presence through techniques like facial recognition and speech recognition. The technology uses non-obtrusive sensing methods to gather physiological data from users to determine their emotional states. This would allow computers to interact more naturally with humans. Experimental results showed that measures of skin conductivity, heart rate, finger temperature, and mouse movements can reliably predict a user's emotional state. Future work aims to improve these techniques with smaller, less intrusive sensors.
This document discusses OLED (Organic Light Emitting Diode) technology. It provides a definition of OLEDs as LEDs with an electroluminescent layer made of organic compounds. The history and development of OLEDs from the 1950s to today is covered. The architecture and types (passive vs active) of OLED displays are described. Current research focuses on improving efficiency and lifespan while reducing costs. Applications include TVs, phones, keyboards, lights, and more. Advantages over other technologies include thinner screens, wider viewing angles, and less energy use. Future uses may include flexible, transparent, and bendable displays.
Plasmonics is a new technology that uses plasmons, which are density waves of electrons created when light hits metal surfaces under certain conditions. Plasmonics could enable faster data transmission over very small wires by combining the best aspects of photonics and electronics. Researchers hope plasmonics can overcome limitations of conventional communication systems and allow for information transfer with greater control at the nanoscale. Potential applications of plasmonics include solar cells, LEDs, invisibility cloaks, cancer treatment, and quantum dot devices for fast computing. However, challenges remain in developing active plasmonic components that can operate at ultra-high bandwidths and low power.
Smart dust are tiny wireless sensor devices that combine sensing, computing, communication and power into a small volume. They can monitor environments without disruption and transmit data wirelessly. Communication methods include passive optical using retroreflectors, active laser, and fiber optic. Challenges include fitting all components into a small size while conserving energy. Potential applications include environmental monitoring, health, security, and industrial automation.
Finding Our Happy Place in the Internet of ThingsPamela Pavliscak
In the future, technology will work together and make decisions for us, though it may not truly understand humans. Currently, technology can have negative effects like distracting and isolating people. However, if designed well with a focus on empathy, emotional intelligence, and human well-being, technology could have positive impacts like strengthening relationships and empowering personal growth. Creating technology with emotional sensitivity, transparency, and a wellness model may lead to a more human future.
We suddenly live in a strange and wonderful nexus of digital and physical. Touchscreens let us hold information in our hands, and we touch, stretch, crumple, drag, and flick data itself. Our sensor-packed phones even reach beyond the screen to interact directly with the world around us. While these digital interfaces are becoming physical, the physical world is becoming digital, too. Objects, places, and even our bodies are lighting up with with sensors and connectivity. We’re not just clicking links anymore; we’re creating physical interfaces to digital systems. This requires new perspective and technique for web and product designers. The good news: it’s all within your reach. With a rich trove of examples, Designing for Touch author Josh Clark explores the practical, meaningful design opportunities for the web’s newly physical interfaces.
Spectroscopic ellipsometry is a technique for investigating the optical properties and electrodynamics of materials. It has several advantages over other optical techniques:
1) It provides an exact numerical inversion with no need for Kramers-Kronig transformations, allowing consistency checks.
2) Measurements are non-invasive and highly reproducible as they do not require reference samples.
3) It is very sensitive to thin film properties due to its ability to measure at oblique angles of incidence.
Ellipsometry has been used to study phenomena like superconductivity in cuprates and pnictides by measuring changes in spectral weight, and collective charge ordering in oxide superlattices.
Widom and Larsen ULM Neutron Catalyzed LENRs on Metallic Hydride Surfaces-EPJ...Lewis Larsen
This document discusses ultra low momentum neutron catalyzed nuclear reactions on metallic hydride surfaces. Weak interaction catalysis initially occurs when neutrons (along with neutrinos) are produced from protons that capture "heavy" electrons. Surface electron masses are shifted upwards by localized condensed matter electromagnetic fields. Condensed matter quantum electrodynamic processes may also shift the densities of final states, allowing an appreciable production of extremely low momentum neutrons, which are thereby efficiently absorbed by nearby nuclei. No Coulomb barriers exist for the weak interaction neutron production or other resulting catalytic processes.
UCSD NANO 266 Quantum Mechanical Modelling of Materials and Nanostructures is a graduate class that provides students with a highly practical introduction to the application of first principles quantum mechanical simulations to model, understand and predict the properties of materials and nano-structures. The syllabus includes: a brief introduction to quantum mechanics and the Hartree-Fock and density functional theory (DFT) formulations; practical simulation considerations such as convergence, selection of the appropriate functional and parameters; interpretation of the results from simulations, including the limits of accuracy of each method. Several lab sessions provide students with hands-on experience in the conduct of simulations. A key aspect of the course is in the use of programming to facilitate calculations and analysis.
This document provides an overview of nanomaterials and their optical properties. It begins with an introduction to nanomaterials and their history. It then discusses how the optical properties of nanomaterials differ from bulk materials due to their small size and large surface area. Specifically, it describes how semiconductor nanomaterials exhibit size-dependent band gaps and excitonic effects. For metallic nanomaterials, it explains surface plasmon resonance and how this results in strong light absorption. Different characterization techniques for studying nanomaterials are also summarized, including electron microscopy methods. Finally, common synthesis routes like colloidal methods are outlined.
Apartes de la Conferencia de la SJG del 14 y 21 de Enero de 2012Nonlinear ele...SOCIEDAD JULIO GARAVITO
This document summarizes a research article about nonlinear electrodynamics and its effects on the polarization of the cosmic microwave background radiation. It introduces nonlinear electrodynamics models as alternatives to Maxwell's electrodynamics. The document then discusses how nonlinear electrodynamics is minimally coupled to gravity and derives the relevant equations of motion. It focuses on analyzing the Pagels-Tomboulis nonlinear electrodynamics Lagrangian and computing the polarization angle of photons propagating in an expanding universe with planar symmetry. Constraints on the nonlinear electrodynamics parameter are obtained using data on cosmic magnetic field strengths and the rotation of CMB polarization spectra measured by experiments.
Dielectrics are materials that have a permanent electric dipole moment. They are used to store electrical energy as they are electrical insulators. A dipole is formed when there is a separation of equal and opposite charges. The dipole moment is calculated as the product of the charge and the distance between them.
The dielectric constant is the ratio of the permeability of the material to the permeability of free space. It determines the polarization characteristics of a dielectric. Polarization occurs when an applied electric field causes a separation of charges in the material, creating electric dipoles. The different types of polarization are electronic, ionic, orientational and space charge polarization.
This document summarizes research on excitonic quasimolecules formed of two spatially separated quantum dots. It presents a theoretical model of an excitonic quasimolecule consisting of two copper oxide quantum dots separated by a distance D in a silicate glass matrix. Calculations using the variational method show that the binding energy of the biexcitonic ground state is maximized at a critical spacing D1 = 3.0 nm, corresponding to a binding energy of -1.144 meV. Below this critical spacing, quantum confinement effects destroy the binding energy. The major contribution to binding comes from electron-hole exchange interaction rather than Coulomb interaction. Experimental data on absorption peaks in similar samples is consistent with predictions of
1) Circular dichroism arises from the differential absorption of left and right circularly polarized light by chiral molecules.
2) CD spectra are more sensitive to conformational changes in proteins and nucleic acids than absorption spectra.
3) CD spectra can provide information about secondary structure in proteins.
The quantum bounce of neutrons has been observed at the peV energy level. An application of Ramsey's method of oscillating fields allows high-precision spectroscopy of neutrons bouncing on a surface. This technique could improve the sensitivity for testing neutron couplings to hypothetical short-range forces and influences on gravity. Future experiments aim to reach sensitivities needed to probe certain axion dark matter models and non-Newtonian gravity potentials.
(1) The document discusses doping of semiconductors and transition metal oxides, including n-type and p-type doping of silicon. It also covers band structure diagrams and density of states plots.
(2) Preparation methods for metal oxides include molecular synthesis and solid state synthesis. Modification of solids can occur through ion exchange or intercalation. Lithium ion batteries operate through lithium intercalation into graphite.
(3) Characterization techniques covered are XRD for crystal structure analysis and electron microscopy. Magnetic properties depend on temperature; ferromagnets become paramagnetic above the Curie temperature. Spinels can exhibit ferrimagnetism from opposing sublattice
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Science Cafe Discovers a New Form of Alternative Energy
1. Clean Energy Lab (CEL)
Towards Plasmonics in Epitaxial Graphene
M.V.S. Chandrashekhar
Department of Electrical and Computer Engineering,
University of South Carolina
USC CMU MPI/Pisa
G.Koley R. Feenstra U. Starke
T.S. Sudarshan N. Srivastava C. Colletti
C. Williams
J. Weidner
1
B.K. Daas
K.M. Daniels
S. Shetu
O. Sabih
A. Obe
2. Clean Energy Lab (CEL) @ USC
OUTLINE
•What is Graphene?
•Why Plasmonics?
• Viability of IR Plasmonics in EG on SiC
• Infrared carrier transport in EG/SiC
• Molecular doping studies using IR
•Interband processes
•Electrochemical Functionalization of EG
•Summary
3. WHAT IS GRAPHENE?
Single atomic layer of graphitic carbon “discovered” in 2005-
Physics Nobel in 2010 Geim & Novoselov, U. Manchester
Electrons behave like they have no mass-am I crazy?
Strongest material known -space elevator E=1.25TPa
Highest thermal conductivity in-plane
It is all surfacesensitive to surroundings
Very transparent and highly conductive-touch screens?
4. Clean Energy Lab (CEL) @ USC
WHAT IS A PLASMON POLARITON?
Polariton: Collective oscillation of electrons (Plasmon), generated by the
electromagnetic field that excites the metal/dielectric interface [1]. It is a near-field
phenomenon. Like waves in water.
Electromagnetic wave Electric or magnetic Dipole
Polariton
(Bosonic-quasiparticles)
Phonon-Polariton (IR photon + Optic phonon)
Exiciton-Polariton ( Visible light + exciton)
Intersubband Polarition (IR photon + intersubband-excition)
Surface plasmon-Polariton , SPP (Surface plasmons +light)
[1] W.L. Barnes, A.Dereux, T.W. Ebbesen, Nature 424 (2003) 824-830
5. Clean Energy Lab (CEL) @ USC
MOTIVATION: THE PLASMONIC CHIP
1. Overcome diffraction limit of light (d<λ/2) using SPP
2. Merge electronics and optics together in nano scaled range
3. Important for data processing, super lensing, sensing etc.
ωp2
ε m (ω ) = 1 − 2
Surface Plasmon Polariton at metal/dielectric interface ω
Whenε m<0, K is imaginary
Surface confinement
5
SPP
CHALLENGE: Couple Collective SPP to Single particle excitations
[2] M. Dragoman, D. Dragoman, Nanoelectronics: Principles and Devices, Artech House, Boston, 2006
6. Clean Energy Lab (CEL) @ USC
HOW DO PLASMONICS WORK?
•SPP propagation mediated by intra band processes
•SPP detection mediated by inter band processes
Graphene
e2
π h2 ∞ ∂f ( E − EF )
σ int ra ( ω ) = i ∫ dE ]E
i −∞ ∂E
ω+
τ
∆2
(1 + 2 )
e2 (ω + iΓ ) ∞ E
σ int er ( ω ) = i ∫∆ dE ( 2E ) 2 − ( hω + iΓ ) 2 [ f ( E − EF ) − f (− E − EF )]
π
Unlike a metal, there is significant interband conductivity even at low energies.
KEY: How to convert plasmon to e-h pair and vice versa?
-high speed computation
-new paradigm in plasmonic light sources
7. Clean Energy Lab (CEL) @ USC
SIC SUBSTRATE DIELECTRIC FUNCTION
ω 2 − ωLO + iΓ1ω
2
ε SiC = ε SiC (ω ) = ε ∞ 2
ω − ωTO + iΓ 2ω
2
WLO= Longitudinal optical phonon (972cm-1)
WTO= Transversal optical phonon (796cm-1)
ε
At high frequency SiC ~6.5 [8]
ε
At low frequency SiC ~9.52
ε (0) ωL
2
LST relation: = 2
ε (∞) ωT Negative dielectric function
n imaginary, damped wave gives
SPP surface confinement
SiC’s negative dielectric function in restrahlen band
n is imaginary, damped wave
confines SPP vertically
Role of metal and dielectric reversed.
[8] Dmitriy Korobkin, Yaroslav Urzhumov, and Gennady Shvets; J. Opt. Soc. Am. B, 23,3,468 (2006)
8. Clean Energy Lab (CEL) @ USC
Viability of Plasmonics in EG on SiC
TM modes are found by assuming that the electric field
has the form as..
When x>0 Ex = Beiqz −Q x and Ez = Aeiqz −Q x E y = 0
1 1
When x<0 Ex = Deiqz +Q x and Ez = Ceiqz +Q x
2 2
Ey = 0
Dispersion relation for TM mode is given by
ε1 ε2 σ (ω , q)i
+ =
ε1ω 2 ε 2ω 2 ωε 0
q − 2
2
q − 2
2
c c
Assuming we are in low q, so q<w/c, SPP
dispersion relation is.
ω2 1
q = 2 [1 −
2
]
c σ (ω , q )
( + ε2 ) 2
450
ε 0c
ω
Free space dispersion relation is q =
c
Fig: SPP dispersion relation plot with free space dispersion
8
SPP dispersion intersects the free space dispersion -coupling of
SPP into free space radiation- SiC substrate essential.
9. Clean Energy Lab (CEL) @ USC
Viability of Plasmonics in Epitaxial Graphene
q= wave vector
Coupling between SPP and Single Particle Excitations ω= frequency
•Intersection between SPP and free space ω1 = vF q
•Coupling to free space
•Intersection region has to be dominated by
interband scattering
•Energy to create e-h pairs, not heat
•SPP detection
•Potential for tuning this process
•Change Ef by gating to suppress e-h
•SPP guiding.
ω2 = 0 q < 2k F ω2 = γ q − 2 EF q > 2 k F
Applying single particle excitation boundary
condition for intra and inter band scattering
Comes from graphene E-k bands 9
(developed by S.Das Sarma)
10. Clean Energy Lab (CEL) @ USC
MODULATING EPITAXIAL GRAPHENE
PLASMON WAVEGUIDE BY DOPING
‘OFF’: When Ef is low, only ‘ON’: When Ef is high,
interband transitions allowed. interband transitions not
Can transform plasmon to DC allowed. Can propagate signal
current and vice-versa. without significant damping.
Electrical manipulation of
plasmonic signals.
11. Clean Energy Lab (CEL) @ USC
Graphene
Exfoliated graphene Epitaxial graphene
( single layer) (single or multi layer)
Silicon (Si) GaAs 4H-SiC Metal Graphene
(Ag)
Supporting TE --- --- ---- No Yes [2]
mode
Dispersion Parabolic parabolic parabolic parabolic linear –EHP at
relation
any wavelength
Band gap 1.12eV 1.42eV 3.23eV 0 0
Electron Mobility <1400 <8500 <900 200000
(cm2/v-s)
RMS roughness --- ---- ------- ~1nm <0.5nm
SPP Detection ----- ------ -------- Metal to Single material
and guiding
guide, for guiding and
materials 11
Semi to detection,
detect
[3] L A Falkovsky “Optical properties of graphene” . Phys.: Conf. Ser., Volume 129, Number 1 (2008)
[4] M.Jablan, H. buljan, M. Soljacic “Plasmonics in Graphene at infrared frequencies” Phy.ReV. B 80 245435 (2009)
12. Clean Energy Lab (CEL) @ USC
Epitaxial Graphene Growth
Raman XPS & ARPES
6H-SiC Graphene
A
B
D peak (1345 cm-1)…..due to induced
disorder
C
A G peak (1585cm-1)… due to in plane
vibration
C
B
2D peak (2670cm-1)…..due to double
A
resonant process
A B C
FiG: Realization of Graphene from 6H-SiC ID/IG…Disorder ratio <0.2 [5]
12
[5] A.C Ferrari and J. Robertson “Interpretation of Raman spectra of disordered and amorphous carbon” Phys. Rev B 61 vol 61 num 20 (2000)
[6] P.J.Cumpson; “The Thickogram: a method for easy film thickness measurement in XPS”Surf.Interface.Anal,29,403 (2000)
13. NON-POLAR FACE GROWTH-6H SIC
EG on Si face EG on C face
5µm× 5µm×
5µm 5µm
What Growth
Growth mechanism is
happens
mechanism is defect&step
in
step flow mediated [**]
between?
mediated [*]
[*] M. Hupalo, E. Conrad, M. C. Tringides http://arxiv.org/abs/0809.3619
[**] Appl. Phys. Lett. 96, 222103 (2010)
14. Clean Energy Lab (CEL) @
USC 13000C 13500C 14000C 14500C
Si face
A plane
M plane
C face
15. Clean Energy Lab (CEL) @
USC
Raman Characterization
Si face
C face
All peaks are red shifted with increasing temp.
What would a H2 etch do? Decreasing stress with temperature increase
2D peaks narrow with increasing temperature
16. Clean Energy Lab (CEL) @ USC
Surface Plasmon Polariton (SPP) in Epitaxial Graphene
Our approach
Mathematical Model [7]
Experiment:
Blank SiC is used as reference. ω 2 − ωLO + iΓ1ω
2
ε 2 = ε 2(ω ) = ε ∞ 2
ω − ωTO + iΓ 2ω
2
∆2
(1 +)
e 2 (ω + iΓ ) ∞ E2
σ int er ( ω ) = i ∫∆ dE ( 2 E ) 2 − ( hω + iΓ ) 2 [ f ( E − EF ) − f (− E − EF )]
π
e2
∂f ( E − EF )
σ int ra ( ω ) = i π h
2 ∞
i ∫
−∞
dE
∂E
]E
ω+
τ
2
ε1Nσ (ω) ×cos(Φ
( ε1ε 2ε 0 / α + ) c
1)
−ε1ε 0
Fig: Schematic view of FTIR differential R= 2
reflection spectra setup ε1Nσ (ω) ×cos(Φ
( ε1ε 2ε 0 / α + ) c
1)
+ε1ε 0
n1
1 − [( sin Φ1)]2
α= n2
cos Φ1 16
[7] T. Stauber, N.M.R Peres, A.K. Geim; “Optical conductivity of graphene in the visible region of the spectrum”Phy.Rev. B 78 085432 (2008)
17. Clean Energy Lab (CEL) @ USC
Surface Plasmon Polariton (SPP) in Epitaxial Graphene….(Cont.)
Results of developed mathematical model
Fig: Variation of number of layer Fig: Variation of Fermi level
2
ε1Nσ (ω) ×cos(Φ
( )
ε1ε 2ε 0 / α +
c
1)
−ε1ε 0
R= 2
ε1Nσ (ω) ×cos(Φ
( )
ε1ε 2ε 0 / α +
c
1)
+ε1ε 0
Variable Parameter
Number of Layer, N
Fermi Energy Ef
17
Scattering time τ
Fig: Variation of scattering time
18. Clean Energy Lab (CEL) @ USC
Surface Plasmon Polariton (SPP) in EG/SiC interface
Experimental results from FTIR: Evidence of SPP at EG/SiC interface
Fig: AFM image of SiC Substrate Fig: IR reflection of SiC Substrate with SiC as reference
ωLO
18
ωTO
Fig: AFM image of EG (2ML)on SiC Fig: IR reflection of EG with SiC as reference
19. Clean Energy Lab (CEL) @ USC
EG transport properties extraction using FTIR
Extracted Parameters:
•No of Layer N=2-17
•Fermi Energy Ef=10535meV
•Scattering time, τ=4-17fs
Interband broadening is assumed
constant=10meV i.e. only intraband
scattering considered.
Extracted No of layer matches well with
XPS measurements.
Fig: IR reflection measurement and mathematical
model are consistent
20. Clean Energy Lab (CEL) @ USC
EG transport properties extraction using FTIR
B,K. Daas…MVS et al JAP (2012)
∞
Carrier density ns = ∫ D( E ) f ( E − EF )dE
0
D ( E ) = 2 E / π ( hv F ) 2
Fig: Fermi level Vs No of layer
1
τ = k1( ) / vF
ns
1
Short range scattering[9] τ∝
ns
Fig: Scattering time Vs avg. carrier density
Coulomb scattering[9] τ ∝ ns
Mobility, µ= eτ vF / EF
2
20
Fitting value of k1=0.6 suggests our EG is
Mobility (1000-10,000) cm /V-s 2
dominated by short-range scattering.
[9] L A Falkovsky “Optical properties of graphene” . Phys.: Conf. Ser., Volume 129, Number 1 (2008)
21. CORRELATION WITH ULTRAFAST
SPECTROSCOPY OF EPITAXIAL
GRAPHENE
If states are occupied by pump,
probe signal will not be absorbed,
transmission increases
85fs, ~10nJ 785nm laser, pump &probe
Measures ENERGY relaxation time, not momentum
τenergy>>τmomentum, supports short range scattering
22. THZ PROBE, OPTICAL PUMP
Non-linear power dependence, quadratic fit works
well-intervalley phonon scattering & Auger dominate
Explains full behavior, withτrec~200fs , B~1-3cm2/s
23. MOLECULAR DOPING OF EG-LONG
Clean Energy Lab (CEL) @ USC
RANGE?
Mirror
Collecting Incoming
•Pure N2 - inert gas
light light
signal source
•15ppm NO2 -electron accepting gas
•500ppmNH3 -electron donating gas
Sensing
element
Graphene
SiC Substrate SPP
Graphene
Fig: Experimental setup
Findings:
Reflection amplitude changes
-Looks like change of thickness
but thickness can’t change 23
24. Clean Energy Lab (CEL) @ USC
Conductivity Matching:
Optical Conductivity:
∆2
(1 + 2 )
e2 (ω + iΓ ) ∞ E
σ int er ( ω ) = i ∫∆ ( 2E ) 2 − ( hω + iΓ ) 2 [ f ( E − EF ) − f (− E − EF )]
dE
π
e2
σ int ra ( ω ) = i π h 2 ∞ dE ∂f ( E − EF ) ] E
i ∫−∞ ∂E
ω+
RPA approximation: τ
e2 ns n F [4rs / (2 − π rs )]
σ RPA
T =0 = [ + i ]
π h ni G[4rs / (2 − π rs )] 4ns
Fig: Dielectric function of SiC
Intraband-low f Interband high f
2π
e2 2 2π
sin θ
2 x2 (1 − cos θ ) 2
rs =
4πε 0ε SiC vF h
G ( x) =
x
8 ∫ θ
dθ F ( x) =
8 ∫ θ
dθ
0 (sin + x) 2 0 (sin + x) 2
2 2
Here, Γ=h/2πτintra is not taken as constant but is allowed to vary.
This is needed to get a good fit to the data
Interband scattering
Extracted parameter ni
matters even at DC.
25. Clean Energy Lab (CEL) @ USC
C-FACE IR REFLECTIVITY
• Adsorbed molecules transfer
charge charged scatterers
• As ni increases, inter/intra
band scattering increase
• τ ~1/n i.e.
i,
conductivity decreases
• Assume each ni is an
adsorbed molecule
• From ΔEf, we can extract
carriers induced, n, using
D(E)
• 0.01e charge donated by
each NO2 molecule
Agrees with Kelvin probe
measurements
26. Clean Energy Lab (CEL) @ USC
No of Gas Fermi ni/ML Intra band Avg. Inter band
Layer level (cm-2) scattering scattering
(meV) time (fs) time(fs)
34 N2 25 2x1011 90-280 185 27-60
NH3 30 6x1012 60-90 75 1.6-2
NO2 35 2x1013 2-9 5 0.3-0.5
22 N2 45 3x1011 10-17 14 9-17
NH3 65 7.5x1012 2-9 5.5 0.2-2
NO2 95 6x1013 0.9 0.9 0.1-0.2
9 N2 70 5.1x1011 10-20 15 3-4
NH3 90 5.5x1013 0.8-1 0.9 0.2-0.5
NO2 120 1.5x1014 0.4-0.5 0.45 0.1-0.3
27. CORRELATION WITH ‘DC’
MEASUREMENTS
4ppm
NO2 makes the C-face more p-type
Implied δp~1012-13cm-2 -is this possible?
M. Qazi….MVS, Koley et al., Appl. Phys. Exp., 3, 075101 (2010)
28. CORRELATION WITH KELVIN
PROBE
~60% or more change in conductivity expected
Scattering from impurities not enough to explain
measured change in optical conductivity
Electron affinity of NO2 dominates!
Consistent with F.Schedin’s result of G/SiO2
Assume ΔEf~10meV for 4ppm. μchem ill-defined.
29. Clean Energy Lab (CEL) @ USC
No of Gas Fermi ni/ML Intra band Avg. Inter band
Layer level (cm-2) scattering scattering
(meV) time (fs) time(fs)
34 N2 25 2x1011 90-280 185 27-60
NH3 30 6x1012 60-90 75 1.6-2 From FTIR
NO2 35 2x1013 2-9 5 0.3-0.5
22 N2 45 3x1011 10-17 14 9-17
NH3 65 7.5x1012 2-9 5.5 0.2-2
NO2 95 6x1013 0.9 0.9 0.1-0.2
9 N2 70 5.1x1011 100-200 150 3-4
NH3 90 5.5x1013 0.8-1 0.9 0.2-0.5
NO2 120 1.5x1014 0.4-0.5 0.45 0.1-0.3
From ΔEf, we know δp(n)
Assume each ni is an NO2 molecule
So, each NO2 molecule donates δp/ni ~1%e for all
thicknesses-same as SKPM!
~(ΔEf/ΔSWF)2~0.3-2%e over various samples.
ni decrease with thickness-diffusion in C-face?
NOTE: interband broadening as large as 1eV!
30. REMEMBER PLASMONICS?
If interband broadening is large, even metallic
graphene plasmons will be damped, must control.
Periodic structures enable tuning using localized
plasmons-enable conversion of plasmon to e-h pair
31. SUMMARY FOR PART I
Plasmonic devices possible on EG/SiC
How clean is as-grown EG?
Gaseous molecular doping useful for transport
studies over wide energy range near K-point.
For FET’s, interband scattering could be
important at high carrier concentration, even at
DC. May influence realizing plasmonics.
Will we be able to convert SPP into e-h pair in
controllable fashion?
33. ELECTROCHEMICAL
FUNCTIONALIZATION-SI FACE
RMS: 0.57nm
Scale:
8nm
Before
RMS: 1.00nm
Scale:
8nm
After
H+ attracted to graphene cathode 1V, 1hr.
Can it react? V<1.2V, H2 formation potential
Goal: Bandgap in diamond-like graphanes.
34. FUNCTIONALIZATION BY RAMAN
SPECTROSCOPY
Single monolayer of graphene is more reactive than bulk
graphite
Up to ten times more reactive than bi-layer and multilayer graphene
Substrate
enhanced electron transfer
Emergence of D-peak indicates reaction in graphene
1200 D-peak red-shifts 1354-1335
cm-1.
1000
Raman Intensity (arb. units)
G peak broadens and
800 slightly blue shifts ~3 cm-1
New peak at ~2930
600
2 Indicative of C-
400 Hbond
G GraphaneD
200 D
Graphene
0
1200 1600 2000 2400 2800
-1
Wavenumber (cm )
34
• R. Sharma, et. al. Anomalously Large Reactivity of Single Graphene Layers and Edges toward Electron Transfer Chemistries, Nano Letters 10, 398-405 (2010)
35. H-FUNCTIONALIZATION SHOWN BY RAMAN
SLOPE
Increasing photoluminescence
background
Increasing hydrogen content
Ratio between slope m of the
linear background and the
intensity of the G peak
D peak m/I(G)
Raman Intensity
Measure of the bonded H content
G peak
Based on amourphous carbon
S≈ 18µm
results
Wavenumber
(cm-1)
maybe dominated by grain
Florescence is not seen in boundaries
carbon only hydrocarbons!!!
•B. Marchon, et.al. Photoluminescence and Raman Spectroscopy in Hydrogenated Carbon Films. IEEE Transactions on Magnetics, Vol. 33, NO. 5, Sept. 1997.
36. FLUORESCENCE BACKGROUND TO ESTIMATE
H-CONTENT
Damage distinguished from functionalization by a) damage has
unmesurable slope for a given D/G ratio b) D peak position
36
37. SUBSTRATE DEPENDENCE OF
FUNCTIONALIZATION
Table 1: Average Parameters From Each Substrate in Study
Substrate D-peak D-peak D/G D/G Normalized Normalized
Position Position Ratio Ratio Slope Slope
Before After Before After Before (µm) After(μm)
(cm-1) (cm-1)
SI(1°) 1348 1330 0.21 1.91 3.66 14.4
SI2(on) 1344 1332 0.17 1.32 4.24 18.9
SI3(0.5) 1347 1331 0.13 0.6 3.93 4.42
* All substrate averages contain at least three samples
• Substrate Limited Functionalization
– Possible Causes
• Off-cut angle
• Substrate Resistivity
• Residual Damage in Graphene
Problem: Issue with conversion control?
Solution: Enhance reactivity with metal? 37
38. RAMAN SPECTRA OF
FUNCTIONALIZATION WITH AND
WITHOUT PT NANOPARTICLES
Chemically Deposited • Raman Shows:
Platinum – Incredibly large D/G ratio~4.5 38
– Emergence of Fluorescence
H2PtCl6 · 6H2O + DI water – Addition to D’ shoulder peak
– C-H peak at ~2930
39. RESULTS OF EVAPORATED METAL
CATALYSIS FUNCTIONALIZATION
Increased reactivity seen in Au and Pt enhanced conversions
D/G ratio>1.0 for Au and Pt
Fluorescence> Noise Threshold (5 µm) 39
40. SUMMARY: METAL CATALYSIS
D Position D Position ID/IG ID/IG Normalized Normalized
Before After Ratio Ratio Slope Slope
(cm-1) (cm-1) Before After Before (µm) After (µm)
SI 1348 1330 0.21 1.91 3.66 14.4
SI2 1344 1332 0.17 1.32 4.24 18.9
SI3 1347 1331 0.13 0.6 3.93 4.42
SI3 Au
Avg 1342 1330 0.22 1.05 4.42 7.86
SI3 Pt
Avg 1364 1330 0.086 1.24 3.81 17.69
Increased functionalization with metal catalyst
40
Increase in fluorescence bandgap?
41. SCANNING TUNNELING
SPECTROSCOPY
K.M. Daniels, …MVS, R. Feenstra… et.al, presented at EMC2011
accepted, JAP
Evidence of localized states
functionalized
unfunctionalized
*8x8mm
More evidence required to distinguish from damage
What are these states?
41
42. CYCLIC VOLTAMMETRY
Clear substrate dependence
Qualitatively different from bulk carbon
Clear peaks, not double-layer charging
Still investigating peak assignments
43. SUMMARY OF PART II
Electrochemical functionalization possible.
Evidence for hydrogen incorporation
More clarification needed
Functionalization is substrate dependent
Metal catalysts enhance functionalization
Evidence for localized states by STS
44. MASTER SUMMARY
Plasmonics in EG proposed
IR transport studies with molecular dopants
Electrochemical functionalization of EG
Evidence of localized states
We also gratefully acknowledge the
Southeastern Center for EE Education for support of this work
Editor's Notes
Without SiC, such an intersection is not possible.
Magnitude of conductivity or real part? When normalizing to SiC Substrate, what is the expression. Is there an angle?
4-nitrobenzene diazonium tetrafluoroborate
Fluorescence does not show in carbon but does show in hydrocarbons