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Journal ArticleDOI

The electronic structure at the atomic scale of ultrathin gate oxides

24 Jun 1999-Nature (Nature Publishing Group)-Vol. 399, Iss: 6738, pp 758-761
TL;DR: In this paper, the authors used electron-energy-loss spectroscopy in a scanning transmission electron microscope to measure the chemical composition and electronic structure, at the atomic scale, across gate oxides as thin as one nanometre.
Abstract: The narrowest feature on present-day integrated circuits is the gate oxide—the thin dielectric layer that forms the basis of field-effect device structures. Silicon dioxide is the dielectric of choice and, if present miniaturization trends continue, the projected oxide thickness by 2012 will be less than one nanometre, or about five silicon atoms across1. At least two of those five atoms will be at the silicon–oxide interfaces, and so will have very different electrical and optical properties from the desired bulk oxide, while constituting a significant fraction of the dielectric layer. Here we use electron-energy-loss spectroscopy in a scanning transmission electron microscope to measure the chemical composition and electronic structure, at the atomic scale, across gate oxides as thin as one nanometre. We are able to resolve the interfacial states that result from the spillover of the silicon conduction-band wavefunctions into the oxide. The spatial extent of these states places a fundamental limit of 0.7 nm (four silicon atoms across) on the thinnest usable silicon dioxide gate dielectric. And for present-day oxide growth techniques, interface roughness will raise this limit to 1.2 nm.
Citations
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Journal ArticleDOI
TL;DR: In this paper, a review of the literature in the area of alternate gate dielectrics is given, based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success.
Abstract: Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...

5,711 citations

Journal ArticleDOI
TL;DR: The aim of this review is to present a unified view of the field of molecular machines by focusing on past achievements, present limitations, and future perspectives.
Abstract: The miniaturization of components used in the construction of working devices is being pursued currently by the large-downward (top-down) fabrication. This approach, however, which obliges solid-state physicists and electronic engineers to manipulate progressively smaller and smaller pieces of matter, has its intrinsic limitations. An alternative approach is a small-upward (bottom-up) one, starting from the smallest compositions of matter that have distinct shapes and unique properties-namely molecules. In the context of this particular challenge, chemists have been extending the concept of a macroscopic machine to the molecular level. A molecular-level machine can be defined as an assembly of a distinct number of molecular components that are designed to perform machinelike movements (output) as a result of an appropriate external stimulation (input). In common with their macroscopic counterparts, a molecular machine is characterized by 1) the kind of energy input supplied to make it work, 2) the nature of the movements of its component parts, 3) the way in which its operation can be monitored and controlled, 4) the ability to make it repeat its operation in a cyclic fashion, 5) the timescale needed to complete a full cycle of movements, and 6) the purpose of its operation. Undoubtedly, the best energy inputs to make molecular machines work are photons or electrons. Indeed, with appropriately chosen photochemically and electrochemically driven reactions, it is possible to design and synthesize molecular machines that do work. Moreover, the dramatic increase in our fundamental understanding of self-assembly and self-organizational processes in chemical synthesis has aided and abetted the construction of artificial molecular machines through the development of new methods of noncovalent synthesis and the emergence of supramolecular assistance to covalent synthesis as a uniquely powerful synthetic tool. The aim of this review is to present a unified view of the field of molecular machines by focusing on past achievements, present limitations, and future perspectives. After analyzing a few important examples of natural molecular machines, the most significant developments in the field of artificial molecular machines are highlighted. The systems reviewed include 1) chemical rotors, 2) photochemically and electrochemically induced molecular (conformational) rearrangements, and 3) chemically, photochemically, and electrochemically controllable (co-conformational) motions in interlocked molecules (catenanes and rotaxanes), as well as in coordination and supramolecular complexes, including pseudorotaxanes. Artificial molecular machines based on biomolecules and interfacing artificial molecular machines with surfaces and solid supports are amongst some of the cutting-edge topics featured in this review. The extension of the concept of a machine to the molecular level is of interest not only for the sake of basic research, but also for the growth of nanoscience and the subsequent development of nanotechnology.

2,099 citations

Journal ArticleDOI
31 Aug 2000-Nature
TL;DR: Development of higher permittivity dielectrics for dynamic random-access memories serves to illustrate the magnitude of the now urgent problem of identifying alternatives to silicon dioxide for the gate dielectric in logic devices, such as the ubiquitous field-effect transistor.
Abstract: The silicon-based microelectronics industry is rapidly approaching a point where device fabrication can no longer be simply scaled to progressively smaller sizes. Technological decisions must now be made that will substantially alter the directions along which silicon devices continue to develop. One such challenge is the need for higher permittivity dielectrics to replace silicon dioxide, the properties of which have hitherto been instrumental to the industry's success. Considerable efforts have already been made to develop replacement dielectrics for dynamic random-access memories. These developments serve to illustrate the magnitude of the now urgent problem of identifying alternatives to silicon dioxide for the gate dielectric in logic devices, such as the ubiquitous field-effect transistor.

1,179 citations

Journal ArticleDOI
TL;DR: The results of this detailed analysis reveal that the GO is rough with an average surface roughness of 0.6 nm and the structure is predominantly amorphous due to distortions from sp3 C-O bonds.
Abstract: We elucidate the atomic and electronic structure of graphene oxide (GO) using annular dark field imaging of single and multilayer sheets and electron energy loss spectroscopy for measuring the fine structure of C and O K-edges in a scanning transmission electron microscope. Partial density of states and electronic plasma excitations are also measured for these GO sheets showing unusual π* + σ* excitation at 19 eV. The results of this detailed analysis reveal that the GO is rough with an average surface roughness of 0.6 nm and the structure is predominantly amorphous due to distortions from sp3 C−O bonds. Around 40% sp3 bonding was found to be present in these sheets with measured O/C ratio of 1:5. These sp2 to sp3 bond modifications due to oxidation are also supported by ab initio calculations.

1,070 citations

Book
01 May 1999
TL;DR: In this paper, the authors describe the Network Centric Warfare concept and explain how it embodies the characteristics of the Information Age; identify the challenges in transforming this concept into a real operational capability; and suggest a prudent approach to meeting these challenges.
Abstract: : War is a product of its age. The tools and tactics of how we fight have always evolved along with technology. We are poised to continue this trend. Warfare in the Information Age will inevitably embody the characteristics that distinguish this age from previous ones. These characteristics affect the capabilities that are brought to battle as well as the nature of the environment in which conflicts occur. Often in the past, military organizations pioneered both the development of technology and its application. Such is not the case today. Major advances in Information Technology are being driven primarily by the demands of the commercial sector. Furthermore, Information Technology is being applied commercially in ways that are transforming business around the globe. The purposes of this book are to describe the Network Centric Warfare concept; to explain how it embodies the characteristics of the Information Age; to identify the challenges in transforming this concept into a real operational capability; and to suggest a prudent approach to meeting these challenges.

992 citations

References
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Book
31 Dec 1995
TL;DR: In this article, the authors present an overview of the basic principles of energy-loss spectroscopy, including the use of the Wien filter, and the analysis of the inner-shell of the detector.
Abstract: 1. An Introduction to Electron Energy-Loss Spectroscopy.- 1.1 Interaction of Fast Electrons with a Solid.- 1.2. The Electron Energy-Loss Spectrum.- 1.3. The Development of Experimental Techniques.- 1.4. Comparison of Analytical Methods.- 1.4.1. Ion-Beam Methods.- 1.4.2. Incident Photons.- 1.4.3. Electron-Beam Techniques.- 1.5. Further Reading.- 2. Instrumentation for Energy-Loss Spectroscopy.- 2.1. Energy-Analyzing and Energy-Selecting Systems.- 2.1.1. The Magnetic-Prism Spectrometer.- 2.1.2. Energy-Selecting Magnetic-Prism Devices.- 2.1.3. The Wien Filter.- 2.1.4. Cylindrical-Lens Analyzers.- 2.1.5. Retarding-Field Analyzers.- 2.1.6. Electron Monochromators.- 2.2. The Magnetic-Prism Spectrometer.- 2.2.1. First-Order Properties.- 2.2.2. Higher-Order Focusing.- 2.2.3. Design of an Aberration-Corrected Spectrometer.- 2.2.4. Practical Considerations.- 2.2.5. Alignment and Adjustment of the Spectrometer.- 2.3. The Use of Prespectrometer Lenses.- 2.3.1. Basic Principles.- 2.3.2. CTEM with Projector Lens On.- 2.3.3. CTEM with Projector Lens Off.- 2.3.4. Spectrometer-Specimen Coupling in a High-Resolution STEM.- 2.4. Recording the Energy-Loss Spectrum.- 2.4.1. Serial Acquisition.- 2.4.2. Electron Detectors for Serial Recording.- 2.4.3. Scanning the Energy-Loss Spectrum.- 2.4.4. Signal Processing and Storage.- 2.4.5. Noise Performance of a Serial Detector.- 2.4.6. Parallel-Recording Detectors.- 2.4.7. Direct Exposure of a Diode-Array Detector.- 2.4.8. Indirect Exposure of a Diode Array.- 2.4.9. Removal of Diode-Array Artifacts.- 2.5. Energy-Filtered Imaging.- 2.5.1. Elemental Mapping.- 2.5.2. Z-Contrast Imaging.- 3. Electron Scattering Theory.- 3.1. Elastic Scattering.- 3.1.1. General Formulas.- 3.1.2. Atomic Models.- 3.1.3. Diffraction Effects.- 3.1.4. Electron Channeling.- 3.1.5. Phonon Scattering.- 3.2. Inelastic Scattering.- 3.2.1. Atomic Models.- 3.2.2. Bethe Theory.- 3.2.3. Dielectric Formulation.- 3.2.4. Solid-State Effects.- 3.3. Excitation of Outer-Shell Electrons.- 3.3.1. Volume Plasmons.- 3.3.2. Single-Electron Excitation.- 3.3.3. Excitons.- 3.3.4. Radiation Losses.- 3.3.5. Surface Plasmons.- 3.3.6. Single, Plural, and Multiple Scattering.- 3.4. Inner-Shell Excitation.- 3.4.1. Generalized Oscillator Strength.- 3.4.2. Kinematics of Scattering.- 3.4.3. Ionization Cross Sections.- 3.5. The Spectral Background to Inner-Shell Edges.- 3.6. The Structure of Inner-Shell Edges.- 3.6.1. Basic Edge Shapes.- 3.6.2. Chemical Shifts in Threshold Energy.- 3.6.3. Near-Edge Fine Structure (ELNES).- 3.6.4. Extended Energy-Loss Fine Structure (EXELFS).- 4. Quantitative Analysis of the Energy-Loss Spectrum.- 4.1. Removal of Plural Scattering from the Low-Loss Region.- 4.1.1. Fourier-Log Deconvolution.- 4.1.2. Approximate Methods.- 4.1.3. Angular-Dependent Deconvolution.- 4.2. Kramers-Kronig Analysis.- 4.3. Removal of Plural Scattering from Inner-Shell Edges.- 4.3.1. Fourier-Log Deconvolution.- 4.3.2. Fourier-Ratio Method.- 4.3.3. Van Cittert'1. An Introduction to Electron Energy-Loss Spectroscopy.- 1.1 Interaction of Fast Electrons with a Solid.- 1.2. The Electron Energy-Loss Spectrum.- 1.3. The Development of Experimental Techniques.- 1.4. Comparison of Analytical Methods.- 1.4.1. Ion-Beam Methods.- 1.4.2. Incident Photons.- 1.4.3. Electron-Beam Techniques.- 1.5. Further Reading.- 2. Instrumentation for Energy-Loss Spectroscopy.- 2.1. Energy-Analyzing and Energy-Selecting Systems.- 2.1.1. The Magnetic-Prism Spectrometer.- 2.1.2. Energy-Selecting Magnetic-Prism Devices.- 2.1.3. The Wien Filter.- 2.1.4. Cylindrical-Lens Analyzers.- 2.1.5. Retarding-Field Analyzers.- 2.1.6. Electron Monochromators.- 2.2. The Magnetic-Prism Spectrometer.- 2.2.1. First-Order Properties.- 2.2.2. Higher-Order Focusing.- 2.2.3. Design of an Aberration-Corrected Spectrometer.- 2.2.4. Practical Considerations.- 2.2.5. Alignment and Adjustment of the Spectrometer.- 2.3. The Use of Prespectrometer Lenses.- 2.3.1. Basic Principles.- 2.3.2. CTEM with Projector Lens On.- 2.3.3. CTEM with Projector Lens Off.- 2.3.4. Spectrometer-Specimen Coupling in a High-Resolution STEM.- 2.4. Recording the Energy-Loss Spectrum.- 2.4.1. Serial Acquisition.- 2.4.2. Electron Detectors for Serial Recording.- 2.4.3. Scanning the Energy-Loss Spectrum.- 2.4.4. Signal Processing and Storage.- 2.4.5. Noise Performance of a Serial Detector.- 2.4.6. Parallel-Recording Detectors.- 2.4.7. Direct Exposure of a Diode-Array Detector.- 2.4.8. Indirect Exposure of a Diode Array.- 2.4.9. Removal of Diode-Array Artifacts.- 2.5. Energy-Filtered Imaging.- 2.5.1. Elemental Mapping.- 2.5.2. Z-Contrast Imaging.- 3. Electron Scattering Theory.- 3.1. Elastic Scattering.- 3.1.1. General Formulas.- 3.1.2. Atomic Models.- 3.1.3. Diffraction Effects.- 3.1.4. Electron Channeling.- 3.1.5. Phonon Scattering.- 3.2. Inelastic Scattering.- 3.2.1. Atomic Models.- 3.2.2. Bethe Theory.- 3.2.3. Dielectric Formulation.- 3.2.4. Solid-State Effects.- 3.3. Excitation of Outer-Shell Electrons.- 3.3.1. Volume Plasmons.- 3.3.2. Single-Electron Excitation.- 3.3.3. Excitons.- 3.3.4. Radiation Losses.- 3.3.5. Surface Plasmons.- 3.3.6. Single, Plural, and Multiple Scattering.- 3.4. Inner-Shell Excitation.- 3.4.1. Generalized Oscillator Strength.- 3.4.2. Kinematics of Scattering.- 3.4.3. Ionization Cross Sections.- 3.5. The Spectral Background to Inner-Shell Edges.- 3.6. The Structure of Inner-Shell Edges.- 3.6.1. Basic Edge Shapes.- 3.6.2. Chemical Shifts in Threshold Energy.- 3.6.3. Near-Edge Fine Structure (ELNES).- 3.6.4. Extended Energy-Loss Fine Structure (EXELFS).- 4. Quantitative Analysis of the Energy-Loss Spectrum.- 4.1. Removal of Plural Scattering from the Low-Loss Region.- 4.1.1. Fourier-Log Deconvolution.- 4.1.2. Approximate Methods.- 4.1.3. Angular-Dependent Deconvolution.- 4.2. Kramers-Kronig Analysis.- 4.3. Removal of Plural Scattering from Inner-Shell Edges.- 4.3.1. Fourier-Log Deconvolution.- 4.3.2. Fourier-Ratio Method.- 4.3.3. Van Cittert's Method.- 4.3.4. Effect of a Collection Aperture.- 4.4. Background Fitting to Ionization Edges.- 4.4.1. Energy Dependence of the Background.- 4.4.2. Background-Fitting Procedures.- 4.4.3. Background-Subtraction Errors.- 4.5. Elemental Analysis Using Inner-Shell Edges.- 4.5.1. Basic Formulas.- 4.5.2. Correction for Incident-Beam Convergence.- 4.5.3. Effect of Sample Orientation.- 4.5.4. Effect of Specimen Thickness.- 4.5.5. Choice of Collection Angle.- 4.5.6. Choice of Integration and Fitting Regions.- 4.5.7. Microanalysis Software.- 4.5.8. Calculation of Partial Cross Sections.- 4.6. Analysis of Extended Energy-Loss Fine Structure.- 4.6.1. Spectrum Acquisition.- 4.6.2. Fourier-Transform Method of Data Analysis.- 4.6.3. Curve-Fitting Procedure.- 5. Applications of Energy-Loss Spectroscopy.- 5.1. Measurement of Specimen Thickness.- 5.1.1. Measurement of Absolute Thickness.- 5.1.2. Sum-Rule Methods.- 5.2. Low-Loss Spectroscopy.- 5.2.1. Phase Identification.- 5.2.2. Measurement of Alloy Composition.- 5.2.3. Detection of Hydrogen and Helium.- 5.2.4. Zero-Loss Images.- 5.2.5. Z-contrast Images.- 5.2.6. Plasmon-Loss Images.- 5.3. Core-Loss Microanalysis.- 5.3.1. Choice of Specimen Thickness and Incident Energy.- 5.3.2. Specimen Preparation.- 5.3.3. Elemental Detection and Mapping.- 5.3.4. Quantitative Microanalysis.- 5.3.5. Measurement and Control of Radiation Damage.- 5.4. Spatial Resolution and Elemental Detection Limits.- 5.4.1. Electron-Optical Considerations.- 5.4.2. Loss of Resolution due to Electron Scattering.- 5.4.3. Statistical Limitations.- 5.4.4. Localization of Inelastic Scattering.- 5.5. Structural Information from EELS.- 5.5.1. Low-Loss Fine Structure.- 5.5.2. Orientation Dependence of Core-Loss Edges.- 5.5.3. Core-Loss Diffraction Patterns.- 5.5.4. Near-Edge Fine Structure.- 5.5.5. Extended Fine Structure.- 5.5.6. Electron-Compton Measurements.- Appendix A. Relativistic Bethe Theory.- Appendix B. FORTRAN Programs.- B.3. Incident-Convergence Correction.- B.4. Fourier-Log Deconvolution.- B.5. Kramers-Kronig Transformation.- Appendix C. Plasmon Energies of Some Elements and Compounds.- Appendix D. Inner-Shell Binding Energies and Edge Shapes.- Appendix E. Electron Wavelengths and Relativistic Factors Fundamental Constants.- References.

3,732 citations

Book
29 Apr 1988
TL;DR: Physics at Surfaces as discussed by the authors is a unique graduate-level introduction to the physics and chemical physics of solid surfaces and atoms and molecules that interact with solid surfaces, and it provides a synthesis of the entire field of surface physics from the perspective of a modern condensed matter physicist with a healthy interest in chemical physics.
Abstract: Physics at Surfaces is a unique graduate-level introduction to the physics and chemical physics of solid surfaces, and atoms and molecules that interact with solid surfaces. A subject of keen scientific inquiry since the last century, surface physics emerged as an independent discipline only in the late 1960s as a result of the development of ultra-high vacuum technology and high speed digital computers. With these tools, reliable experimental measurements and theoretical calculations could at last be compared. Progress in the last decade has been truly striking. This volume provides a synthesis of the entire field of surface physics from the perspective of a modern condensed matter physicist with a healthy interest in chemical physics. The exposition intertwines experiment and theory whenever possible, although there is little detailed discussion of technique. This much-needed text will be invaluable to graduate students and researchers in condensed matter physics, physical chemistry and materials science working in, or taking graduate courses in, surface science.

1,636 citations

Journal ArticleDOI
TL;DR: In this paper, the bonding of Si atoms at the SiO2/Si interface was determined via high-resolution core level spectroscopy with synchrotron radiation, and a model of the interface structure was obtained from the density and distribution of intermediate oxidation states.
Abstract: The bonding of Si atoms at the SiO2/Si interface is determined via high-resolution core level spectroscopy with synchrotron radiation. For oxides grown in pure O2, the SiO2/Si interface is found to contain Si atoms in intermediate oxidation states with a density of 1.5 ± 0.5 × 1015 cm−2. From the density and distribution of intermediate oxidation states, models of the interface structure are obtained. The interface is not abrupt, as evidenced by the non-ideal distribution of intermediate oxidation states and their high density (about 2 monolayers of Si). The finite width of the interface is explained by the bond density mismatch between SiO2 and Si. Annealing in H2 is found to influence the electrical parameters by removing the Pb centers that pin the Fermi level. The distribution of intermediate oxidation states is not affected.

1,543 citations

MonographDOI
01 Jan 1988

777 citations

Journal ArticleDOI
TL;DR: For example, electron energy-loss spectroscopy can be used to characterize interfaces buried deep in samples and to identify trace elements in biological specimens as discussed by the authors, and it can even look at an individual row of atoms in a crystal and identify the type of atoms and their bonding states.
Abstract: Solid-state scientists have many analytical techniques to choose from. But electron energy-loss spectroscopy does some things that no other technique can quite match. Electron energy-loss spectroscopy can, for example, form chemical maps of nanometre-sized regions in solid samples. It can be used to characterize interfaces buried deep in samples and to identify trace elements in biological specimens. It can even look at an individual row of atoms in a crystal and identify the type of atoms and their bonding states.

480 citations