Richard W. Siegel
Materials Science and Engineering Department
Rensselaer Polytechnic Institute
Troy, New York 12180, USA
Under the auspices of the World Technology Evaluation Center (WTEC) of the International Technology Research Institute at Loyola College in Maryland, we are in the process of conducting a year-long, worldwide study of research and development activities in nanoparticles, nanostructured materials, and nanodevices. The study is funded by the U.S. National Science Foundation (NSF), with additional support from several other agencies of the U.S. government, including the Office of Naval Research, the Air Force Office of Scientific Research, the Department of Commerce and its National Institute of Standards and Technology (NIST), the National Aeronautics and Space Administration (NASA), the National Institute of Health, and the Department of Energy.
The purposes of the WTEC study are to:
The study is focused on nanoscale building blocks, atom clusters or nanoparticles smaller than 100 nm (Fig. 2.1), and the nanostructured materials made therefrom. The features that unify all these materials are (1) that they are synthetic materials with structures modulated in 0 to 3 dimensions, (2) that they have a size constraint or 'confinement' <100 nm, and (3) that there is a significant volume fraction (>1%) of their interfaces. The study thus examines the assembly of these building blocks in controlled ways to make materials with new properties and to fabricate these materials into useful devices and parts. Hence, a hierarchy of (1) atomically engineered building blocks, (2) assembly and materials fabrication, and (3) applications forms the basic organization of the study. All physical, chemical, and biological routes for the synthesis and processing of nanostructures are being considered. The applications can be roughly divided (with significant overlaps) into four areas (Fig. 2.2): dispersions and coatings (e.g., optical, thermal, diffusion barriers); high surface area materials (e.g., catalysts, sensors, filters); functional nanostructures (e.g., magnetic, electronic, optical devices); and consolidated materials and parts (e.g., structural parts, magnets). The WTEC study panel of eight members from industry and academia was selected with these areas of concentration in mind: Richard Siegel, panel chair; Evelyn Hu, panel co-chair; Donald Cox; Herb Goronkin; Lynn Jelinski; Carl Koch; John Mendel; and David Shaw. Panel members' affiliations and addresses are listed on the inside front cover of this document. Two other reports from this study are being published by WTEC. One is a summary of U.S. activity in the field.1 The other is the final report comparing research in the field worldwide.2
Fig. 2.1. Schematic of nanostructured materials of various modulation dimensionalities from 0 to 3: 0 = clusters: 1 £ aspect ratio £ ¥; 1 = multilayers; 2 = ultrafine-grained overlayers; 3 = nanophase materials.
The work of the panel commenced around the beginning of 1997 and, as a first significant step, a review workshop was organized during May 8-9 in order to benchmark the research and development status and trends in nanoparticles, nanostructured materials, and nanodevices in the United States. About 25 experts in the field were invited to the workshop in suburban Washington, D.C., to share their thoughts on the field with the panel, as seen from their own perspective. Among the questions asked were the following:
1R&D Status and Trends in Nanoparticles, Nanostructured Materials, and Nanodevices in the United States is available from the National Technical Information Service as publication PB98-117914 and also on the World Wide Web at http://itri.loyola.edu/nano/US.Review/.
2Nanostructure Science and Technology: R&D Status and Trends in Nanoparticles, Nanostructured Materials, and Nanodevices is available from Kluwer Academic Publishers, and on the World Wide Web at http://itri.loyola.edu/nano/IWGN.Worldwide.Study/.
Fig. 2.2. Schematic of the field of nanostructure science and technology and the structure of the WTEC study.
In addition, about 20 brief summary presentations were made by program leaders of the participating U.S. government agencies on activities in the field funded from their programs. The focus of the workshop was to (1) assess the state of the art of U.S. nanoparticle/nanostructure/nanodevice technology and applications, (2) develop a baseline against which to compare activities in other countries, and (3) develop a document summarizing the current U.S. status to be included in the panel's final report and to be presented in draft form to our hosts abroad. A copy of this document has been left with our Russian hosts, and additional copies can be supplied by WTEC on request.
The panel's first visits abroad occurred during a week-long visit to Japan in July. Our second such event is this workshop in St. Petersburg, to which about 12 Russian experts were invited to share with the panel chair, co-chair, and principal sponsor (M.C. Roco, NSF) their thoughts on the field of nanoparticle/nanostructure/nanodevice technology and applications and its status in Russia and, to the extent possible, the other countries of the former Soviet Union.
The following material, taken from the viewgraphs R. W. Siegel used at the workshop, reviews the findings from an earlier workshop regarding research on nanoparticles and nanostructures in the United States.
There is a wide range of methods now being investigated including aerosols with solid, liquid, or gas precursors; liquid phase chemical reactions including precipitation, templating, and self-assembly; mechanical attrition and severe plastic deformation; and patterning that includes soft lithography and electron beam lithography. Many of these methods are being used in the laboratory, but very few are already used in commercial production.
Among the questions raised in the area of synthesis and assembly are the following:
The areas of current activity are many and diverse, including quantum dots, photoresists, oxide systems, photographic emulsions, inks, magnetic recording media, fillers, paper coatings, cosmetics, and drug delivery. A wide variety of synthetic materials are being used from laboratory to commercial levels (102- 105 tons /year) of production.
Among the critical issues raised in this area are controlling raw material and process uniformity, preparing the dispersion, stabilizing the dispersed phase, characterizing the interfacial properties, controlling the process and scale-up to manufacturing, and applying subsequent nanoparticle coatings.
The areas of current activity are diverse, including materials for adsorption and separation processes (e.g., H2O, H2S, and CO2 removal, H2 and CH4 storage, and O2 /N2 and H2 /HC5 separation), catalysts for petroleum processing applications, thermal barrier materials, battery and capacitor elements, biochemical and pharmaceutical separations, radioisotope separation, and interfacial bonding. A variety of synthetic materials are being used in the laboratory (mostly) and on a commercial scale.
Among the major challenges in this area are critical dimensional control at the atomic level of nanoscale structure over long periods of time, and varying conditions and thermal and chemical stability control of the fabricated nanostructure.
There are several areas of interest and activity that are leading to generally longer-term applications. These include solar cells, light-emitting devices, nanoscale transistors, batteries and capacitors, sensors, and magnetic read/write heads. A variety of synthesis methods are being used, but most of these are still in the laboratory.
The major challenges in this area include critical dimensional control, impurity control, interconnects, reliability, single electron circuit architecture, arrays and self-assembled fabrication, and theoretical models.
A variety of efforts are being made to synthesize nanostructured metals, intermetallics, ceramics, and composites for structural and magnetic applications. These areas include wear-resistant parts, cutting tools, lighting envelopes, permanent magnets (hard and soft), and magnetostrictive materials. These are made using a variety of methods. Most are still at the laboratory level, but commercial applications are beginning to appear.
Among the major challenges in this area are engineering reliability, process control and defects, and scaling up to manufacturing.