 |
|
Ultraviolet Light Reveals Secrets of Nanoscale Electronic Materials
October 25, 2006An international team of scientists has used a novel technique to measure, for the first time, the precise conditions at which certain ultrathin materials spontaneously become electrically polarized. The research provides the fundamental scientific basis for understanding this "ferroelectric" state in materials needed for next-generation "smart card" memory chips and other devices. The research is published in a recent issue of the journal Science.
"We provide a complete picture of how the ferroelectric transition temperature changes when the electrical and mechanical conditions change within nanoscale ferroelectric materials," said Xiaoxing Xi, professor of physics and materials science and engineering at Penn State University, who led the research effort. The team is the first to use a technique known as ultraviolet Raman spectroscopy to reveal a range of temperatures, thicknesses, and structural configurations at which nanoscale barium titanate can store a switchable electric field. The scientists also performed theoretical calculations to predict the point at which materials transition into this ferroelectric state. The results of these calculations closely match the results of the team's experiments.
"The work led by Xiaoxing Xi on nano-thick ferroelectric multilayers is groundbreaking," comments Refik Kortan, a program manager at the Basic Energy Sciences division of the U. S. Department of Energy, one of the sponsors of the U.S.-funded research project. "It is truly remarkable that UV-Raman can resolve displacements in ultrathin films that are just a few atomic layers thick." Other sponsors include the National Science Foundation, the Office of Naval Research, and the National Aeronautics and Space Administration.
Various difficulties exist in fabricating materials that can retain their ferroelectric properties at small dimensions and at temperatures at or above room temperature. "How thin can a ferroelectric material be at room temperature?" is the fundamental question that lies at the root of efforts to determine how much data can be stored on next-generation electronic devices. "We found that a film of barium titanate (BaTiO3) whose thickness is just 4-tenths of a nanometer-or 4-hundred-millionths of a centimeter-can retain its ferroelectric properties when it is layered in thin sandwiches with non-ferroelectric layers of strontium titanate (SrTiO3)," said Darrell Schlom, professor of materials science and engineering at Penn State and a member of the research team. "This layer is just one molecule of barium titanate thick, the thinnest imaginable, but we have shown that it is ferroelectric at room temperature."
Xi explains, "The ferroelectric layer can induce ferroelectric properties in neighboring layers that normally are not ferroelectric, especially in materials that are easily polarized. For example, we found that even one layer of ferroelectric barium titanate is capable of polarizing 13 adjacent layers of strontium titanate." The scientists found that they could manipulate ferroelectricity by imposing different kinds of electrical and mechanical boundary conditions. The electrical conditions include the degree of resistance to polarization of the nonferroelectric material. The mechanical conditions included sandwiching ferroelectric layers between different layers of other materials, which mechanically restricts the movement of the atoms. By varying the thickness and composition of the nanoscale thin films, the researchers were able to change the phase-transition temperature by almost 500 Kelvin, obtaining ferroelectric properties more than 350 Kelvin-over 600 degrees Fahrenheit-above room temperature. "Our research shows that, under favorable conditions, room-temperature ferroelectricity can be strong and stable in nanoscale systems," Xi said.
The research team includes 22 scientists working in labs at Penn State, the University of Puerto Rico, the University of Wisconsin, the University of Michigan, Los Alamos National Laboratory, and Rutgers University in the United States, as well as at the National Atomic Energy Commission in Argentina and the University of Valencia in Spain. The collaboration grew over time with the addition of scientists who had access to the best high-performance Raman-spectroscopy devices and scientists who are specialists in materials fabrication, theoretical calculations, and structural characterization. "The number of names on this paper speaks well about teamwork and cooperation within and between different projects and across different universities," comments Lynnette Madsen, Program Director of Ceramics at the National Science Foundation.
The team successfully tackled Xi's goal of using ultraviolet Raman spectroscopy to detect the moment when vanishingly thin layers of materials developed ferroelectric properties under a variety of conditions-a goal that leading experts in the field initially told him was so difficult that it was "impossible" to achieve. "Because most measurement techniques that work for thick films don't work well for films less than 100-nanometers thick, a new technique was needed, and I believed that UV-Raman spectroscopy should work," Xi explained. "Our record thinnest detections so far with UV-Raman spectroscopy are a layered superlattice film just 24-nanometers thick and a single-layer film just 10-nanometers thick."
Raman spectroscopy is a technique that uses electromagnetic radiation to probe the properties of a material. The probe used in the technique is a photon-a quantum of light-which interacts in the material with a phonon-a quantum of sound. From the resulting change in the energy of the photon after it scatters off a material, scientists can measure the vibration energy of the lattice that is formed by the material's atoms. Typically, the radiation used for Raman spectroscopy has the energy of visible green light, but light with this energy is not absorbed effectively by nanoscale ferroelectric films, and so it does not reveal much information about them. Ultraviolet light, however, is able to be absorbed, so Xi reasoned that it could be used with the Raman-spectroscopy technique as an effective ferroelectricity detector for these nanoscale materials.
"We can take advantage of the change in the symmetry of the nanoscale material's crystal structure that occurs at the ferroelectric phase transition," Xi said. "Because Raman spectroscopy cannot detect the phonon above the phase transition, but it can detect it after the material becomes ferroelectric, we can use this technique to detect the temperature at which the ferroelectric phase transition occurs."
Ultraviolet Raman spectroscopy is a very new technology that is in the early stages of being developed, and few instruments exist that can achieve the resolution that Xi and his research colleagues require. "The number of photons that change their energies after interacting with phonons of lattice vibration is very small, and it is difficult to detect this weak signal at UV frequencies," Xi said. Xi overcame this obstacle by building a collaboration with scientists whose labs contained high-resolution UV Raman scattering systems, where his former postdoctoral fellow Dimitri Tenne, now an assistant professor of physics at Boise State University, made the measurements presented in the paper published in Science.
"We have demonstrated that we can use UV Raman spectroscopy to discover more about the unusual phenomena that occur in ultrathin ferroelectric materials, and that it is possible to tune the ferroelectric properties of nanoscale materials by changing the electrical and mechanical boundary conditions," Xi said. "It is exciting to realize that this is just the beginning of a whole new field of research."
Eberly College of Science
Various difficulties exist in fabricating materials that can retain their ferroelectric properties at small dimensions and at temperatures at or above room temperature. "How thin can a ferroelectric material be at room temperature?" is the fundamental question that lies at the root of efforts to determine how much data can be stored on next-generation electronic devices. "We found that a film of barium titanate (BaTiO3) whose thickness is just 4-tenths of a nanometer-or 4-hundred-millionths of a centimeter-can retain its ferroelectric properties when it is layered in thin sandwiches with non-ferroelectric layers of strontium titanate (SrTiO3)," said Darrell Schlom, professor of materials science and engineering at Penn State and a member of the research team. "This layer is just one molecule of barium titanate thick, the thinnest imaginable, but we have shown that it is ferroelectric at room temperature."
Xi explains, "The ferroelectric layer can induce ferroelectric properties in neighboring layers that normally are not ferroelectric, especially in materials that are easily polarized. For example, we found that even one layer of ferroelectric barium titanate is capable of polarizing 13 adjacent layers of strontium titanate." The scientists found that they could manipulate ferroelectricity by imposing different kinds of electrical and mechanical boundary conditions. The electrical conditions include the degree of resistance to polarization of the nonferroelectric material. The mechanical conditions included sandwiching ferroelectric layers between different layers of other materials, which mechanically restricts the movement of the atoms. By varying the thickness and composition of the nanoscale thin films, the researchers were able to change the phase-transition temperature by almost 500 Kelvin, obtaining ferroelectric properties more than 350 Kelvin-over 600 degrees Fahrenheit-above room temperature. "Our research shows that, under favorable conditions, room-temperature ferroelectricity can be strong and stable in nanoscale systems," Xi said.
The research team includes 22 scientists working in labs at Penn State, the University of Puerto Rico, the University of Wisconsin, the University of Michigan, Los Alamos National Laboratory, and Rutgers University in the United States, as well as at the National Atomic Energy Commission in Argentina and the University of Valencia in Spain. The collaboration grew over time with the addition of scientists who had access to the best high-performance Raman-spectroscopy devices and scientists who are specialists in materials fabrication, theoretical calculations, and structural characterization. "The number of names on this paper speaks well about teamwork and cooperation within and between different projects and across different universities," comments Lynnette Madsen, Program Director of Ceramics at the National Science Foundation.
The team successfully tackled Xi's goal of using ultraviolet Raman spectroscopy to detect the moment when vanishingly thin layers of materials developed ferroelectric properties under a variety of conditions-a goal that leading experts in the field initially told him was so difficult that it was "impossible" to achieve. "Because most measurement techniques that work for thick films don't work well for films less than 100-nanometers thick, a new technique was needed, and I believed that UV-Raman spectroscopy should work," Xi explained. "Our record thinnest detections so far with UV-Raman spectroscopy are a layered superlattice film just 24-nanometers thick and a single-layer film just 10-nanometers thick."
Raman spectroscopy is a technique that uses electromagnetic radiation to probe the properties of a material. The probe used in the technique is a photon-a quantum of light-which interacts in the material with a phonon-a quantum of sound. From the resulting change in the energy of the photon after it scatters off a material, scientists can measure the vibration energy of the lattice that is formed by the material's atoms. Typically, the radiation used for Raman spectroscopy has the energy of visible green light, but light with this energy is not absorbed effectively by nanoscale ferroelectric films, and so it does not reveal much information about them. Ultraviolet light, however, is able to be absorbed, so Xi reasoned that it could be used with the Raman-spectroscopy technique as an effective ferroelectricity detector for these nanoscale materials.
"We can take advantage of the change in the symmetry of the nanoscale material's crystal structure that occurs at the ferroelectric phase transition," Xi said. "Because Raman spectroscopy cannot detect the phonon above the phase transition, but it can detect it after the material becomes ferroelectric, we can use this technique to detect the temperature at which the ferroelectric phase transition occurs."
Ultraviolet Raman spectroscopy is a very new technology that is in the early stages of being developed, and few instruments exist that can achieve the resolution that Xi and his research colleagues require. "The number of photons that change their energies after interacting with phonons of lattice vibration is very small, and it is difficult to detect this weak signal at UV frequencies," Xi said. Xi overcame this obstacle by building a collaboration with scientists whose labs contained high-resolution UV Raman scattering systems, where his former postdoctoral fellow Dimitri Tenne, now an assistant professor of physics at Boise State University, made the measurements presented in the paper published in Science.
"We have demonstrated that we can use UV Raman spectroscopy to discover more about the unusual phenomena that occur in ultrathin ferroelectric materials, and that it is possible to tune the ferroelectric properties of nanoscale materials by changing the electrical and mechanical boundary conditions," Xi said. "It is exciting to realize that this is just the beginning of a whole new field of research."
Eberly College of Science
Ferroelectric Current Events and Ferroelectric News RSSORNL finding could help electronics industry enter new phase
Electronic devices of the future could be smaller, faster, more powerful and consume less energy because of a discovery by researchers at the Department of Energy's Oak Ridge National Laboratory.
Multiferroics -- making a switch the electric way
Multiferroics are materials in which unique combinations of electric and magnetic properties can simultaneously coexist.
Vise squad: Putting the squeeze on a crystal leads to novel electronics
A clever materials science technique that uses a silicon crystal as a sort of nanoscale vise to squeeze another crystal into a more useful shape may launch a new class of electronic devices that remember their last state even after power is turned off.
'Instant on' computing
The ferroelectric materials found in today's "smart cards" used in subway, ATM and fuel cards soon may eliminate the time-consuming booting and rebooting of computer operating systems by providing an "instant-on" capability as well as preventing losses from power outages.
Domain Walls that Conduct Electricity
The logic and memory functions of future electronic devices could shrink dramatically - to one or two nanometers (billionths of a meter) instead of the many tens of nanometers that characterize today's most advanced elements - if a way can be found to control domain walls, the ultrathin transition zones that separate regions of a material having different magnetic, electric, or other properties.
Capture of nanomagnetic 'fingerprints' a boost for next-generation information storage media
In the race to develop the next generation of storage and recording media, a major hurdle has been the difficulty of studying the tiny magnetic structures that will serve as their building blocks.
Polymer electric storage, flexible and adaptable
The proliferation of solar, wind and even tidal electric generation and the rapid emergence of hybrid electric automobiles demands flexible and reliable methods of high-capacity electrical storage. Now a team of Penn State materials scientists is developing ferroelectric polymer-based capacitors that can deliver power more rapidly and are much lighter than conventional batteries.
Disorder enables extreme sensitivity in piezoelectric materials
A research team working at the National Institute of Standards and Technology (NIST) has found an explanation for the extreme sensitivity to mechanical pressure or voltage of a special class of solid materials called relaxors.
The solution to a 7-decade mystery is crystal-clear to FSU chemist
A Florida State University researcher has helped solve a scientific mystery that stumped chemists for nearly seven decades. In so doing, his team's findings may lead to the development of more-powerful computer memories and lasers.
Landmark Modeling Study at Penn Reveals How Ferroelectric Computer Memory Works
A collaboration of University of Pennsylvania chemists and engineers has performed multi-scale modeling of ferroelectric domain walls and provided a new theory of behavior for domain-wall motion, the "sliding wall" that separates ferroelectric domains and makes high-density ferroelectric RAM (FeRAM) possible.
More Ferroelectric Current Events and Ferroelectric News Articles
 |
Principles and Applications of Ferroelectrics and Related Materials (Oxford Classic Text in the Physical Sciences) by M. E. Lines (Author), A. M. Glass (Author) Standard text for studying ferroelectric and pyroelectric devices. Develops the modern theory of ferroelectricity in terms of soft modes and lattice dynamics, covering modern techniques of measurement such as x-ray, optic, and neutron scattering. First published in 1977. Softcover. |
 |
Physics of Ferroelectrics: A Modern Perspective (Topics in Applied Physics) by Karin M. Rabe (Author), Karin M. Rabe (Editor), Charles H. Ahn (Editor), Jean-Marc Triscone (Editor) During the past two decades, revolutionary breakthroughs have occurred in the understanding of ferroelectric materials, both from the perspective of theory and experiment. First principles approaches, including the Berry phase formulation of ferroelectricity, now allow accurate, quantitative predictions of material properties, and single crystalline thin films are now available for fundamental studies of these materials. In addition, the need for high dielectric constant insulators and nonvolatile memories in semiconductor applications has motivated a renaissance in the investigation of these materials. This book addresses the paradigmatic shifts in understanding brought about by these breakthroughs, including the consideration of novel fabrication methods of single crystalline... |
|
Ferroelectric Crystals by Franco Jona (Author), G. Shirane (Author) | |
 |
Ferroelectric Devices, Second Edition by Kenji Uchino (Author) Discover a Strategy to Develop Bestselling Ferroelectric Devices Updating its bestselling predecessor, Ferroelectric Devices, Second Edition assesses the last decade of developments—and setbacks—in the commercialization of ferroelectricity. Field pioneer and esteemed author Uchino provides insight into why this relatively nascent and interdisciplinary process has failed so far without a systematic accumulation of fundamental knowledge regarding materials and device development. Filling the informational void, this collection of information reviews state-of-the-art research and development trends reflecting nano and optical technologies, environmental regulation, and alternative energy sources. Like the first edition, which became a standard... |
 |
Nanoscale Phenomena in Ferroelectric Thin Films (Multifunctional Thin Film Series) by Seungbum Hong (Editor) Nanoscale Phenomena in Ferroelectric Thin Films presents the recent advances in the field of nanoscale science and engineering of ferroelectric thin films. It consists of two main parts: electrical characterization in nanoscale ferroelectric capacitor, and nano domain manipulation and visualization in ferroelectric materials. Well-known leading experts both in relevant academia and industry over the world (U.S., Japan, Germany, Switzerland, Korea) were invited to contribute to each chapter. The objectives of the book are to provide the reader with the information needed to 1.) build, see and manipulate domain structures; 2.) understand the unexplained macroscopic phenomena; and 3.) create ferroelectric thin film that shows novel and significantly improved physical, chemical... |
 |
Microwave Dielectric Spectroscopy of Ferroelectrics and Related Materials (Ferroelectricity and Related Phenomena) by Grigas (Author) Recent technological advances affecting the size and useful frequency range of electronic elements depend heavily on the discovery of materials suitable for applications in the development of new radar systems, satellite broadcasting, and multichannel terrestrial and cosmic communications via the use of microwaves. Ferroelectrics and related materials have become of increasing importance for the utilization of microwave techniques, and in this monograph, the author summarizes the results of his 25 years of work in the field. This book provides a comprehensive review of methods available for microwave dielectric measurements and designated ferroelectric families. This volume will be an indispensable reference for researchers, engineers and graduate students of the physics of structural... |
 |
Ferroelectric Memories by James F. Scott (Author) Ferroelectric memories have changed in 10 short years from academic curiosities of the university research labs to commercial devices in large-scale production. This is the first text on ferroelectric memories that is not just an edited collection of papers by different authors. Intended for applied physicists, electrical engineers, materials scientists and ceramists, it includes ferroelectric fundamentals, especially for thin films, circuit diagrams and processsing chapters, but emphazises device physics. Breakdown mechanisms, switching kinetics and leakage current mechanisms have lengthly chapters devoted to them. The book will be welcomed by research scientists in industry and government laboratories and in universities. It also contains 76 problems for students, making it particularly... |
 |
Electromechanical Properties in Composites Based on Ferroelectrics (Engineering Materials and Processes) by Vitaly Yu. Topolov (Author), Christopher R. Bowen (Author) "Electromechanical Properties in Composites Based on Ferroelectrics" discusses the latest theoretical and experimental results on the effective electromechanical (piezoelectric, dielectric and elastic) properties in piezo-composites based on ferroelectrics. For the last decades, single-crystal, bulk ceramic and thin-film ferroelectrics have found a number of various applications as a result of their remarkable piezoelectric properties. Recent work in the field of smart materials demonstrates that both ferroelectricity and piezoelectricity represent an important link between solid state science and engineering. "Electromechanical Properties in Composites Based on Ferroelectrics" investigates the problem of prediction and non-monotonicity of the effective electromechanical properties in... |
 |
Ferroelectrics in Microwave Devices, Circuits and Systems: Physics, Modeling, Fabrication and Measurements (Engineering Materials and Processes) by Spartak Gevorgian (Author) Today’s wireless communications and information systems are heavily based on microwave technology, as are an increasing number of other industry sectors. Extensive research has been carried out into the development of new technologies to meet the increasingly complex requirements of such systems. Among these new technologies agile (tuneable, reconfigurable, and adaptable) microwave components based on ferroelectric materials, have great potential and are already gaining ground. Ferroelectrics in Microwave Devices, Circuits and Systems is an introduction to the field. It explores the emergence of new functionalities and components with enhanced performance that can meet the agility and cost requirements of modern microwave-based systems. The book provides the reader with... |
 |
Ferroelectric Devices (Materials Engineering, 16) by Kenji Uchino (Author) A comprehensive introduction to the fundamentals of ferroelectrics, including available materials, device designs, drive/control techniques, and essential applications - examining high-permittivity dielectrics, piezoelectric devices, pyroelectric sensors, and electro-optic devices. It focuses on highly adaptive polycrystalline ceramics and other materials used in thin/thick film devices. The book features the author's exclusive device development method. |
| © 2009 BrightSurf.com |