24-07-2014, 11:19 AM
Molecular electronics
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ABSTRACT
Molecular electronics (sometimes called moletronics) is an interdisciplinary theme that spans physics, chemistry, and materials science. The unifying feature of this area is the use of molecular building blocks for the fabrication of electronic components, both passive (e.g. resistive wires) and active (e.g. transistors). The concept of molecular electronics has aroused much excitement both in science fiction and among scientists due to the prospect of size reduction in electronics offered by molecular-level control of properties. Molecular electronics provides a means to extend Moore's Law beyond the foreseen limits of small-scale conventional silicon integrated circuits.
The field of molecular electronics seeks to use individual molecules to perform functions in electronic circuitry now performed by semiconductor devices. Individual molecules are hundreds of times smaller than the smallest features conceivably attainable by semiconductor technology. Because it is the area taken up by each electronic element that matters, electronic devices constructed from molecules will be hundreds of times smaller than their semiconductor based counterparts.
Moreover individual molecules are easily made exactly the same by billions & trillions. The dramatic reductions in size, and the sheer enormity of numbers in manufacture, are the principle benefits promised by the field of molecular electronics
The notion 'molecular electronics' has been used more frequently since the 1970s and summarizes a series of physical phenomena and ideas for their application in connection with organic molecules, oligomers, polymers, organic aggregates and solids. The properties studied in this field were connected to optical and electrical phenomena, such as optical absorption, fluorescence, nonlinear optics, energy transport, charge transfer, electrical conductance, and electron and nuclear spin-resonance. The final goal was and is to build devices which can compete or surpass some aspects of inorganic semiconductor devices. For example, on the basis of organic molecules there exist rectifiers, transistors, molecular wires, organic light emitting diodes, elements for photovoltaics, and displays. With respect to applications, one aspect of the organic materials is their broad variability and the lower effort and costs for their processability
INTRODUCTION
Molecular electronics, one of the major fields of current efforts in nanoscience, involves the exploration of the electronic level structure, response and transport, together with the development of electronic devices and applications that depend on the properties of matter at the molecular scale. This includes single molecules, molecular arrays and molecular networks connected to other electronic components. Its major application areas include sensors, displays, smart materials, molecular motors, logic and memory devices, molecular scale transistors and energy transduction devices. Often molecular electronics is envisioned as the next step in device miniaturization. The importance of molecules in device applications stems not only from their electronic properties, but also from their ability to bind to one another, recognize each other, assemble into larger structures, and exhibit dynamical stereochemistry
Molecular Electronics an Overview
Molecular electronics (sometimes called moletronics) is a branch of applied physics which aims at using molecules as passive (e.g. resistive wires) or active (e.g. transistors) electronic components.
The concept of molecular electronics has aroused much excitement both in science fiction and among scientists due to the prospect of size reduction in electronics offered by such minute components. It is an enticing alternative to extend Moore's Law beyond the foreseen limits of small-scale conventional silicon integrated circuits. As a result, molecular electronics is currently a very active research field.
Among the important issues is the determination of the resistance of a single molecule (both theoretical and experimental). Another problem faced by this field is the difficulty to perform direct characterization since imaging at the molecular scale is often impossible in many experimental devices.
About Molecular Electronics
The guiding principle of this research is that biological systems can provide useful paradigms for developing electronic and computational devices at the molecular level. For example, natural photosynthetic reaction centers are photovoltaic devices of molecular dimensions, and the principles dictating the operation of reaction centers may be useful in the design of synthetic optoelectronic switches. In this project, several classes of molecular photovoltaic species are being synthesized and studied. These include porphyrin-fullerene dyads, carotenoid-fullerene dyads, a carotenoid-porphyrin-fullerene triad, carotene-porphyrin-imide triads, and molecular dyads and triads containing two porphyrin moieties.
The approach involves the design and synthesis of dyads, triads and other super molecular species using the techniques of organic chemistry. The newly-prepared molecules are then studied by a variety of physical methods, including time-resolved laser spectroscopy, NMR spectroscopy, and cyclic voltammetry in order to determine how and how well they functioned as molecular electronic elements. The information gained can then be used to design new generations of these molecules.
Once functional molecular photovoltaics, logic gates, or other elements have been prepared, ways must be developed for interfacing these with electronic circuits. Possibilities are being investigated in a collaborative project with Professor Michael Kozicki, in the Department of Electrical Engineering.
Molecular Electronics Technology
The field of molecular electronics seeks to use individual molecules to perform functions in electronic circuitry now performed by semiconductor devices. Individual molecules are hundreds of times smaller than the smallest features conceivably attainable by semiconductor technology. Because it is the area taken up by each electronic element that matters, electronic devices constructed from molecules will be hundreds of times smaller than their semiconductor-based counterparts. Moreover, individual molecules are easily made exactly the same by the billions and trillions. The dramatic reduction in size, and the sheer enormity of numbers in manufacture, is the principle benefits offered by the field of molecular electronics.
At the heart of the semiconductor industry is the semiconductor switch. Because semiconductor switches can be manufactured at very small scales and in combination can be made to perform all desired computational functions, the semiconductor switch has become the fundamental device in all of modern electronics. California Molecular Electronics Corporation's Chiropticene® Switch is a switchable device that goes beyond the semiconductor switch in size reduction. This switch is a single molecule that exhibits classical switching properties.
The material listed herein provides insight into important technology areas of molecular electronics. The documents are a "collection of works" on various topics in the field of molecular electronics assembled by California Molecular Electronics Corporation (CALMEC®) for the purposes of informing the non-scientific community on the exciting technology of molecular electronics. At present, the topics include an introduction to CALMEC's Chiropticene Molecular Switch Design, the principles behind the Chiropticene Switch technology, its molecular engineering, and the patents that protect the Chiropticene Switch technology.
Electrode effects
The molecule–electrode interface is a critically important component of a molecular junction: It may limit current flow or completely modify the measured electrical response of the junction. Most experimental platforms for constructing molecular-electronic devices are based on practical considerations. This pragmatic approach is, in many ways, the boon and the bane of the field. For example, the sulfur–gold bond is a terrific chemical handle for forming self-assembled, robust organic monolayer on metal surfaces. Other methods, such as using a scanning probe tiptop contact the molecule, are frequently employed; in part because they avoid processing steps that can damage or unpredictably modify the molecular component. Ideally, the choice of electrode materials would be based not on the ease of fabrication or measurement, but rather on first principles considerations of molecule–electrode interactions. However, the current state of the art for the theory of molecule–electrode interfaces is primitive. Poor covalent bonding usually exists between the molecule and electrode. Consequently, at zero applied bias some charge must flow between molecule and electrodes to equilibrate the chemical potential across the junction. That flow can cause partial charging of the molecule, and local charge buildup gives Scotty-like barriers to charge flow across the interface. Such barriers, which can partially or fully mask the molecule’s electronic signature, increase for larger electro negativity differences. For this reason—and others, including stability, reproducibility, and generality—chemical bonds such as carbon–carbon or carbon–silicon will likely be preferred over gold–sulfur linkage sat the interfaces. Very little theory exists that can adequately predict how the molecular orbital’ energy levels will align with the Fermi energy of the electrode. Small changes in the energy levels can dramatically affect junction conductance, so understanding how the interface energy levels correlate is critical and demands both theoretical and experimental study. A related consideration involves how the chemical nature of the molecule–electrode interface affects the rest of the
Molecule. The zero-bias coherent conductance of a molecular junction may be described as a product of functions that describe the molecule’s electronic structure and the molecule–electrode interfaces (see box 1 on page 46). However, the chemical interaction between the molecule and the electrode will likely modify the molecule’s electron density in the vicinity of the contacting atoms and, in turn, modify the molecular energy levels or the barriers within the junction. The clear implication (and formal result) is that the molecular and interface functions are inseparable and thus muster considered as a single system.
CONCLUSION
Molecular electronics clearly has the advantage of size. The components of these circuits are molecules, so the circuit size would inherently range between 1 to 100 NM.
Molecular systems, or systems based on small organic molecules, possess interesting and useful electronic properties. The rapidly developing area of organic -or plastic- electronics is based on these materials. The investigations of molecular systems that have been performed in the past have been strongly influenced.
Molecular electronics is reaching a stage of trustable and reproducible experiments. This has lead to a variety of physical and chemical phenomena recently observed for charge currents owing through molecular junctions, posing new challenges to theory.
The potential application of molecular electronics has already attracted the interest of some large corporate
[attachment=66181]
ABSTRACT
Molecular electronics (sometimes called moletronics) is an interdisciplinary theme that spans physics, chemistry, and materials science. The unifying feature of this area is the use of molecular building blocks for the fabrication of electronic components, both passive (e.g. resistive wires) and active (e.g. transistors). The concept of molecular electronics has aroused much excitement both in science fiction and among scientists due to the prospect of size reduction in electronics offered by molecular-level control of properties. Molecular electronics provides a means to extend Moore's Law beyond the foreseen limits of small-scale conventional silicon integrated circuits.
The field of molecular electronics seeks to use individual molecules to perform functions in electronic circuitry now performed by semiconductor devices. Individual molecules are hundreds of times smaller than the smallest features conceivably attainable by semiconductor technology. Because it is the area taken up by each electronic element that matters, electronic devices constructed from molecules will be hundreds of times smaller than their semiconductor based counterparts.
Moreover individual molecules are easily made exactly the same by billions & trillions. The dramatic reductions in size, and the sheer enormity of numbers in manufacture, are the principle benefits promised by the field of molecular electronics
The notion 'molecular electronics' has been used more frequently since the 1970s and summarizes a series of physical phenomena and ideas for their application in connection with organic molecules, oligomers, polymers, organic aggregates and solids. The properties studied in this field were connected to optical and electrical phenomena, such as optical absorption, fluorescence, nonlinear optics, energy transport, charge transfer, electrical conductance, and electron and nuclear spin-resonance. The final goal was and is to build devices which can compete or surpass some aspects of inorganic semiconductor devices. For example, on the basis of organic molecules there exist rectifiers, transistors, molecular wires, organic light emitting diodes, elements for photovoltaics, and displays. With respect to applications, one aspect of the organic materials is their broad variability and the lower effort and costs for their processability
INTRODUCTION
Molecular electronics, one of the major fields of current efforts in nanoscience, involves the exploration of the electronic level structure, response and transport, together with the development of electronic devices and applications that depend on the properties of matter at the molecular scale. This includes single molecules, molecular arrays and molecular networks connected to other electronic components. Its major application areas include sensors, displays, smart materials, molecular motors, logic and memory devices, molecular scale transistors and energy transduction devices. Often molecular electronics is envisioned as the next step in device miniaturization. The importance of molecules in device applications stems not only from their electronic properties, but also from their ability to bind to one another, recognize each other, assemble into larger structures, and exhibit dynamical stereochemistry
Molecular Electronics an Overview
Molecular electronics (sometimes called moletronics) is a branch of applied physics which aims at using molecules as passive (e.g. resistive wires) or active (e.g. transistors) electronic components.
The concept of molecular electronics has aroused much excitement both in science fiction and among scientists due to the prospect of size reduction in electronics offered by such minute components. It is an enticing alternative to extend Moore's Law beyond the foreseen limits of small-scale conventional silicon integrated circuits. As a result, molecular electronics is currently a very active research field.
Among the important issues is the determination of the resistance of a single molecule (both theoretical and experimental). Another problem faced by this field is the difficulty to perform direct characterization since imaging at the molecular scale is often impossible in many experimental devices.
About Molecular Electronics
The guiding principle of this research is that biological systems can provide useful paradigms for developing electronic and computational devices at the molecular level. For example, natural photosynthetic reaction centers are photovoltaic devices of molecular dimensions, and the principles dictating the operation of reaction centers may be useful in the design of synthetic optoelectronic switches. In this project, several classes of molecular photovoltaic species are being synthesized and studied. These include porphyrin-fullerene dyads, carotenoid-fullerene dyads, a carotenoid-porphyrin-fullerene triad, carotene-porphyrin-imide triads, and molecular dyads and triads containing two porphyrin moieties.
The approach involves the design and synthesis of dyads, triads and other super molecular species using the techniques of organic chemistry. The newly-prepared molecules are then studied by a variety of physical methods, including time-resolved laser spectroscopy, NMR spectroscopy, and cyclic voltammetry in order to determine how and how well they functioned as molecular electronic elements. The information gained can then be used to design new generations of these molecules.
Once functional molecular photovoltaics, logic gates, or other elements have been prepared, ways must be developed for interfacing these with electronic circuits. Possibilities are being investigated in a collaborative project with Professor Michael Kozicki, in the Department of Electrical Engineering.
Molecular Electronics Technology
The field of molecular electronics seeks to use individual molecules to perform functions in electronic circuitry now performed by semiconductor devices. Individual molecules are hundreds of times smaller than the smallest features conceivably attainable by semiconductor technology. Because it is the area taken up by each electronic element that matters, electronic devices constructed from molecules will be hundreds of times smaller than their semiconductor-based counterparts. Moreover, individual molecules are easily made exactly the same by the billions and trillions. The dramatic reduction in size, and the sheer enormity of numbers in manufacture, is the principle benefits offered by the field of molecular electronics.
At the heart of the semiconductor industry is the semiconductor switch. Because semiconductor switches can be manufactured at very small scales and in combination can be made to perform all desired computational functions, the semiconductor switch has become the fundamental device in all of modern electronics. California Molecular Electronics Corporation's Chiropticene® Switch is a switchable device that goes beyond the semiconductor switch in size reduction. This switch is a single molecule that exhibits classical switching properties.
The material listed herein provides insight into important technology areas of molecular electronics. The documents are a "collection of works" on various topics in the field of molecular electronics assembled by California Molecular Electronics Corporation (CALMEC®) for the purposes of informing the non-scientific community on the exciting technology of molecular electronics. At present, the topics include an introduction to CALMEC's Chiropticene Molecular Switch Design, the principles behind the Chiropticene Switch technology, its molecular engineering, and the patents that protect the Chiropticene Switch technology.
Electrode effects
The molecule–electrode interface is a critically important component of a molecular junction: It may limit current flow or completely modify the measured electrical response of the junction. Most experimental platforms for constructing molecular-electronic devices are based on practical considerations. This pragmatic approach is, in many ways, the boon and the bane of the field. For example, the sulfur–gold bond is a terrific chemical handle for forming self-assembled, robust organic monolayer on metal surfaces. Other methods, such as using a scanning probe tiptop contact the molecule, are frequently employed; in part because they avoid processing steps that can damage or unpredictably modify the molecular component. Ideally, the choice of electrode materials would be based not on the ease of fabrication or measurement, but rather on first principles considerations of molecule–electrode interactions. However, the current state of the art for the theory of molecule–electrode interfaces is primitive. Poor covalent bonding usually exists between the molecule and electrode. Consequently, at zero applied bias some charge must flow between molecule and electrodes to equilibrate the chemical potential across the junction. That flow can cause partial charging of the molecule, and local charge buildup gives Scotty-like barriers to charge flow across the interface. Such barriers, which can partially or fully mask the molecule’s electronic signature, increase for larger electro negativity differences. For this reason—and others, including stability, reproducibility, and generality—chemical bonds such as carbon–carbon or carbon–silicon will likely be preferred over gold–sulfur linkage sat the interfaces. Very little theory exists that can adequately predict how the molecular orbital’ energy levels will align with the Fermi energy of the electrode. Small changes in the energy levels can dramatically affect junction conductance, so understanding how the interface energy levels correlate is critical and demands both theoretical and experimental study. A related consideration involves how the chemical nature of the molecule–electrode interface affects the rest of the
Molecule. The zero-bias coherent conductance of a molecular junction may be described as a product of functions that describe the molecule’s electronic structure and the molecule–electrode interfaces (see box 1 on page 46). However, the chemical interaction between the molecule and the electrode will likely modify the molecule’s electron density in the vicinity of the contacting atoms and, in turn, modify the molecular energy levels or the barriers within the junction. The clear implication (and formal result) is that the molecular and interface functions are inseparable and thus muster considered as a single system.
CONCLUSION
Molecular electronics clearly has the advantage of size. The components of these circuits are molecules, so the circuit size would inherently range between 1 to 100 NM.
Molecular systems, or systems based on small organic molecules, possess interesting and useful electronic properties. The rapidly developing area of organic -or plastic- electronics is based on these materials. The investigations of molecular systems that have been performed in the past have been strongly influenced.
Molecular electronics is reaching a stage of trustable and reproducible experiments. This has lead to a variety of physical and chemical phenomena recently observed for charge currents owing through molecular junctions, posing new challenges to theory.
The potential application of molecular electronics has already attracted the interest of some large corporate