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| Solid State Research/Material Sciences |
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Solid State Research/Material Sciences
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The availability of materials with specific physical, chemical and technical functions has left a deep impression on the development of our civilization. It is for this reason that scientists are working on the characterization of material structures right down to the atomic range, to measure all their different properties and to develop an understanding as to how the properties of substances can be derived from their components and internal structures. Research is concentrating on both fundamental phenomena in solid state physics and chemistry and on a broad variety of functional materials, such as metals, ceramics, polymers, biomaterials and electronic, photonic and magnetic materials. The themes of the research range from the behavior and interactions of individual atoms and atom clusters through questions about the binding between atoms and their chemical reactivity, to the structure and properties of complex solids (see too  "European White Book on Fundamental Research in Materials Science", Max Planck Institute for Metal Research, Stuttgart: November 2001). What is particularly interesting is the behavior of materials under extreme conditions, such as high and low temperatures, extreme pressure, ultrastrong magnetic fields, or other exceptional environmental conditions. The interaction between materials and light is of special importance in this respect.
The discovery of unknown phenomena, the creation of new materials and progress in the understanding and control of material behavior and processing are often the consequence of the fruitful cohabitation of theory, experiments, computer-based modeling and simulation and the development of new instruments. Material science cooperates closely with chemistry, physics and engineering in this process. This area of research is also gaining more and more from participation of scientists from more remote disciplines, such as biochemistry, biology, geosciences, mathematics, information science and medicine.
The understanding, mastery and control of material phenomena at the microscopic level are important preconditions for the development of new materials for specific technological requirements, to optimize available substances and to able to produce products of higher quality, at lower costs and with less environmental pollution. Although in the past it was largely a question of the quantitative characterization of phenomena and the development of theories to explain them, modern scientists now have detailed knowledge of various electrical, magnetic, optical, mechanical and thermal phenomena. In the future, it will be a question of controlling material phenomena in the nanometer and femtosecond range. There are quite different goals for the different applications, such as
| • | The design of microstructures, for example, in multicomponent materials; |
| • | The control of phenomena, for example, in artificial structures with particular magnetic properties; |
| • | The exploitation of very small scale phenomena, for example, in colloids and biomimetic systems; |
| • | The production by systems of dynamic responses within very short intervals, for example, the conversion of disordered into ordered magnetic structures; |
| • | The investigation of phenomena under extreme conditions, for example, high pressure, high temperature or intense magnetic or electric fields; |
| • | - The understanding of highly complex surface and interfacial phenomena at the atomic level (friction, lubrication, corrosion, electrolysis). |
The controlled formation of structures of any order of magnitude in materials and components is a major challenge for material science. One particularly interesting problem is the assembly of complex materials at the nanometer scale with extreme combinations of properties. One of the most important goals today in the processing of materials is to exclude chance occurrences in structure formation, right down to atomic dimensions. The atomic scale is the domain of chemical bonds and the atomic structure can be adjusted by selection of the type and number of particles and the control parameters. The total synthesis of macroscopic materials includes the exploitation of deliberate heterogeneities, the combination of inorganic and organic materials and the integration of different types of materials and bonds. Problems which occur in the chemical reactions are solved in steps by the planned development of specific catalytic materials. It is now possible to use molecular beam techniques to assemble materials atom by atom and to employ scanning probe techniques at the atomic scale. Molecular machines are also conceivable.
Epoch-making new discoveries have been made at the “supramolecular” level, for example, with the fullerenes. The artificial structuring of low dimensional systems by lithographic methods, self-organization or by the complex biological processes of structure formation allow the production of quantum structures which exhibit electronic properties which are, in principle, novel. Innovations in chemical synthesis can greatly extend the molecular design of functional polymers. The development of new methods for the selective and environmentally friendly conversion of materials will increase in importance. More and more sophisticated active substances must be manufactured as drugs, for plant protection or as pure chemicals, and this is hardly conceivable without the development of active catalysts. Another area of research which is promising for the future is the manufacture of selective biocatalysts by in vivo selection. Current research is focused on:
| • | Miniaturization in the use of all materials, including their automatic parallel processing; |
| • | Biomimetic and biomaterials, for example, for medicine (implants, biosensors); |
| • | Complex structures from components, for example, from the self-organization of nanocomponents; |
| • | Design of interfaces, for example, to improve the properties of metals, ceramics, superconductors or biomaterials; |
| • | Modeling and automatization of material synthesis and processing, for example, of nanomaterials and biomaterials. |
Progress in material research is inseparably connected to the development of new analytical tools, which make it possible to examine the atomic and electronic structures of materials at the nanometer scale and to expose unknown phenomena and processes. New and improved microscopy techniques are most important, such as high resolution electron microscopy, which makes it possible to obtain images of individual atomic columns in a solid body. Scanning probe methods, such as force and tunnel microscopy, make it possible to analyze the surfaces of solids at atomic resolution and to obtain information about details of atomic bonding in this way. Spectroscopic methods permit statements about the binding relationships and the use of new synchrotron sources of radiation has greatly increased their accuracy. Moreover, dynamic processes can be followed with extreme accuracy, as a result of improved resolution in time and space. The combination of different measurement techniques is becoming more and more important. For example, analytical electron microscopy will soon combine spectroscopic information from synchrotron radiation with spatial resolution at the atomic scale. The use of lasers permits the study of chemical reactions in materials: Reactions which used to be described in terms of bond breaking can be seen at extremely high time resolution (femtosecond range) to involve a series of intermediate structures, which open new possibilities to direct the molecular design of materials.
The issues in instrument development are the maximum possible resolution, the maximum sensitivity and to lower the limit of detection as much as possible, combined with non-destructive in situ analysis. The barriers between refraction, microscopic and spectroscopic methods are becoming less and less clear during this process. Research is focused on:
| • | High resolution microscopy in the sub-Ångstrom and sub-electron volt range with 10 nanometer resolution in X-ray microscopy; |
| • | Real time characterization of materials and phenomena in the femtosecond range, to be able to follow atomic motion during chemical reactions. |
The successful evaluation of experiments is often only complete and satisfactory when a good theory is available. This applies particularly when there is a strong interaction between the medium and the object of investigation, which is for example characteristic of analytical electron microscopy and femtosecond laser spectroscopy. Theoretical research is, in principle, multidisciplinary, so that newly developed approaches can often be used in different areas of research. In the final analysis, the aim of the theoretical understanding of materials is the prediction of their macroscopic properties on the basis of their atomic or molecular properties.
Material modeling is also playing an increasingly important role in the design of materials and in understanding the fundamental and also very complex processes in solids. Both theory and modeling and powerful tools to predict of new structural and functional materials, to optimize complex materials, to improve the synthesis, processing, microstructure and properties of materials, to study phenomena which are not easily accessible to experiment and thus to save time and money in the development of new materials. Particularly interesting properties, such as the elasticity of a polymer, the thermal expansion of a glass ceramic, the water uptake of a membrane or the plasticity of a metallic tool can be determined by the overlapping use of different scales for time and space.
It is a particular challenge for material research when different properties of a material are to be exploited in a system at the same time. It is often not possible to optimize one property independently of the other. Examples would be lightness of construction against resistance to high temperatures in airplane construction or strength against conductivity in electrical and microelectronic elements. This conflict is especially complicated under extreme conditions, for example, with the materials exposed to plasma in nuclear fusion plants.
Functional materials are also of increasing importance, which perform reactions in response to environmental stimuli (“smart materials”, “adaptive systems”), or which can detect their activity (sensors), as are materials for energy conversion (batteries, fuel cells). It is specifically biology which raises new questions here, such as the extension of the multifunctionality of substances to biological functions (“biocompatibility” in medicine). In addition, it is becoming of increasing importance to bear in mind the methods of manufacturing and processing when new material concepts are being developed. Issues related to material cycles and energy and environmental balance belong to research on the manufacture and use of materials, as the practical importance of substances of increasingly complex structure is expanding continuously. This does not only concern the replacement of known materials with innovative materials with improved or really novel combinations of properties. It is rather the case that the implementation of new technologies is based on the availability of reliable and high performance materials. There are examples in the areas of energy conversion and storage, in information and communication technology and in many applications in biotechnology and medicine. Sensors will be used in environmental analysis to an increased extent and will help to influence environmental changes.
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