Nano Science and Engineering in Mechanics and Materials

110Rev.Adv.Mater.Sci. 5 (2003) 110-116 Ken P. Chong

NANO SCIENCE AND ENGINEERING IN MECHANICS AND MATERIALS

Ken P. Chong

Directorate for Engineering, National Science Foundation, Arlington, VA 22230, USA

Abstract. The transcendent technologies include nanotechnology, microelectronics, information technology and biotechnology as well as the enabling and supporting mechanical and civil infrastructure systems and materials. These technologies are the primary drivers of the twenty first century and the new economy. Mechanics and materials are essential elements in all of the transcendent technologies. Research opportunities, education and challenges in mechanics and materials, including nanomechanics, carbon nano-tubes, bio-inspired materials, coatings, fire-resistant materials as well as improved engineering and design of materials are presented and discussed in this paper.

1. INTRODUCTION 10-6 m ELASTICITY; PLASTICITY; DISLO- CATION... Nanotechnology is the creation of new materials, 10-3 m MECHANICS OF MATERIALS devices and systems at the molecular level - phe- 10-0 m STRUCTURAL ANALYSIS nomena associated with atomic and molecular in- MULTI-SCALE ANALYSES & SIMULATIONS teractions strongly influence macroscopic material properties [according to I. Aksay, Princeton]; with The National Science Foundation has supported significantly improved mechanical, optical, chemical, basic research in engineering and the sciences in electrical... properties. Nobelist Richard Feynman the United States for a half century and it is ex- back in 1959 had the foresight to indicate there is pected to continue this mandate through the next plenty of room at the bottom. National Science century. As a consequence, the United States is Foundation [NSF] Director Rita Colwell in 2002 de- likely to continue to dominate vital markets, because clared nanoscale technology will have an impact diligent funding of basic research does confer a pref- equal to the Industrial Revolution. erential economic advantage (Wong, 1996). In the education area in order to do competitive Concurrently over this past half century, technolo- research in the nanotechnology areas, engineers gies have been the major drivers of the U. S. should also be trained in quantum mechanics, economy, and as well, NSF has been a major sup- molecular dynamics, etc. The following lists some porter of these technological developments. Accord- of the key topics across different scales. The au- ing to the former NSF Director for Engineering, Eu- thor has been advocating a summer institute to train gene Wong, there are three transcendental tech- faculty and graduate students to be knowledgeable nologies: in scales at and less than the micrometer (see: · Microelectronics Moores Law: doubling the http://tam.northwestrn.edu/summerinstitute/ capabilities every two years for the last 30 years; Home.htm) unlimited scalability; nanotechnology is essen- 10-12 m QUANTUM MECHANICS [TB, DFT, tial to continue the miniaturization process and HF ]* efficiency. 10-9 m MOLECULAR DYN. [LJ ]; *TB = TIGHT BINDING METHOD; DFT = DENSITY FTNAL NANOMECHANICS; MOLECULAR BIOLOGY; THEORY; HF = HATREE-FOCK APPROX.; LJ = LENNARD BIOPHYSICS JONES POTENTIAL

Corresponding author: Ken P. Chong, e-mail: [email protected]

· Information Technology [IT] NSF and DARPA as single-electron transistor; logic gate started the Internet revolution more than three as RAM on/off do not affect memory storage - decades ago; the confluence of computing and no booting needed. communications. Sources: · Biotechnology unlocking the molecular secrets CARBON NANOTUBES THE FIRST 10 YEARS, NATURE, of life with advanced computational tools as well 2001. as advances in biological engineering, biology, MECHANICAL ENGINEERING, ASME, NOV. 2000 chemistry, physics, and engineering including TECHNOLOGY REVIEW, MIT, MAR. 2002 mechanics and materials. Considerable NSF resources and funding will be Efficient mechanical and civil infrastructure sys- available to support basic research related to nano tems as well as high performance materials are science and engineering technologies. These op- essential for these technologies. By promoting re- portunities will be available for the individual search and development at critical points where investigator, teams, small groups and larger inter- these technological areas intersect, NSF can fos- disciplinary groups of investigators as well as cen- ter major developments in engineering. The solid ters. Nevertheless, most of the funding at NSF will mechanics and materials engineering (M&M) com- continue to support unsolicited proposals from indi- munities will be well served if some specific link- vidual investigator on innovative blue sky ideas in ages or alignments are made toward these tech- all areas including nano science and engineering nologies. technologies. Some thoughtful examples for the M&M and other engineering communities are: 2. NANOTECHNOLOGY · Bio-mechanics/materials Nanomechanics Workshop · Simulations/modeling Initiated by the author, with the organization and help · Thin-film mechanics/materials of researchers from Brown [K. S. Kim, et al.], · Micro-electro-mechanical systems (MEMS) Stanford, Princeton and other universities, a NSF · Wave Propagation/NDT Workshop on Nano- and Micro-Mechanics of Sol- · Smart materials/structures ids for Emerging Science and Technology was held · Nano-mechanics/materials at Stanford in October 1999. The following is ex- · Nano-electro-mechanical systems(NEMS) tracted from the Workshop Executive Summary. · Designer materials Recent developments in science have advanced · Fire Retardant Materials and Structures. capabilities to fabricate and control material sys- MEMs can be used as platforms for NEMS. tems on the scale of nanometers, bringing problems Another product of the nanotechnology is carbon of material behavior on the nanometer scale into the nano-tubes [CNT] which are self-assembled in depo- domain of engineering. Immediate applications of sition from C-rich vapors, consisted of honeycomb nanostructures and nano-devices include quantum lattices of carbon rolled into cylinders; nm in diam- electronic devices, bio-surgical instruments, micro- eter, micron in length. CNT have amazing proper- electrical sensors, functionally graded materials, and ties: many others with great promise for commercializa- 1/6 the weight of steel; 5 times its Youngs modu- tion. The branch of mechanics research in this lus; 100 times its tensile strength; 6 orders of emerging field can be termed nano- and micro-me- magnitude higher in electrical conductivity than chanics of materials, highly cross-disciplinary in copper; CNT strains up to 15% without breaking character. A subset of these, which is both scien- 10 times smaller than the smallest silicon tips tifically rich and technologically significant, has in Scanning Tunnel Microscope - STM [CNT is mechanics of solids as a distinct and unifying theme. the worlds smallest manipulator] The presentations at the workshop and the open CNT may have more impact than transistors discussion precipitated by them revealed the emer- ideal material for flat-screen TV [~2003] gence of a range of interesting lines of investigation similar diameter as DNA built around mechanics concepts that have poten- bridge different scales in mesoscale - useful as tial relevance to microelectronics, information tech- bldg. blocks ~ e.g. nanocomposites; gases stor- nology, bio-technology and other branches of age nanotechnology. It was also revealed, however, that metallic or semiconducting the study of complex behavior of materials on the nanometer scale is in its infancy. More basic re- 112 Ken P. Chong

Fig. 1. Instruments and techniques for experimental micro and nano mechanics [courtesy of K. S. Kim of Brown University] where HRTEM High Resolution Transmission Electron Microscopy, SRES Surface Roughness Evolution Spectroscopy, CFTM Computational Fourier Transform Moire, FGLM Fine Grating Laser Moiré, AFM Atomic Force Microscopy, LSI Laser Speckle Interferometry, SEM Scanning Electron Microscopy, DIC Digital Image Correlation, LDLM Large Deformation Laser Moire.

search that is well coordinated and that capitalizes To improve the speed and performance of the on progress being made in other disciplines is atomic force microscope, more optimal control of needed if this potential for impact is to be realized. the cantilever and more robust software to acquire Recognizing that this area of nanotechnology is and process the data as well as other improvements in its infancy, substantial basic research is needed are needed. A portable AFM has also been devel- to establish an engineering science base. Such a oped by IBM recently. commitment to nano- and micro-mechanics will lead The potential of various concepts in to a strong foundation of understanding and nanotechnology will be enhanced, in particular, by confidence underlying this technology based on exploring the nano- and micro-mechanics of coupled capabilities in modeling and experiment embody- phenomena and of multi-scale phenomena. Ex- ing a high degree of rigor. The instruments and tech- amples of coupled phenomena discussed in this niques available for experimental micro- and nano- workshop include modification of quantum states of mechanics are depicted in Fig. 1, courtesy of K. S. materials caused by mechanical strains, ferroelec- Kim of Brown University. tric transformations induced by electric field and One of the key instrument in nanotechnology is mechanical stresses, chemical reaction processes the atomic force microscope [AFM]. However the biased by mechanical stresses, and changes of bio- limitation is: molecular conformality of proteins caused by envi- AFM SCAN SPEED ~100HZ [TAKES ~30 MIN. FOR ronmental mechanical strain rates. Multi-scale phe- A SMALL IMAGE OF 20,000 PIXELS]. nomena arise in situations where properties of ma- Nano science and engineering in mechanics and materials 113 terials to be exploited in applications at a certain . Societal and educational implications of scientific size scale are controlled by physical processes and technological advances on the nanoscale. occurring on a size scale that is orders of magni- The National Nanotechnology Initiative started tude smaller. Important problems of this kind arise, in 2000 ensures that investments in this area are for example, in thermo-mechanical behavior of thin- made in a coordinated and timely manner (includ- film nanostructures, evolution of surface and bulk ing participating federal agencies NSF, DOD, DOE, nanostructures caused by various material defects, DOC [including NIST], NIH, DOS, DOT, NASA, EPA nanoindentation, nanotribological responses of sol- and others) and will accelerate the pace of revolu- ids, and failure processes of MEMS structures. tionary discoveries now occurring. Current request Details of this workshop report can be found by vis- of Federal agencies on NNI is about $710 million. iting http://en732c.engin.brown.edu/nsfreport.html. The NSF share of the budget is around $220 million [on NSE, part of NNI]. Nanoscale Science and Engineering Initiatives Coordinated by M. Roco (IWGN, 2000), NSF re- 3. CHALLENGES cently announced a multy year program [NSF 03- 043; see: www.nsf.gov] on collaborative research in The challenge to the mechanics and materials re- the area of nanoscale science and engineering search communities is: How can we contribute to (NSE). This program is aimed at supporting high these broad-base and diverse research agendas? risk/high reward, long-term nanoscale science and Although the mainstay of research funding will sup- engineering research leading to potential break- port the traditional programs for the foreseeable fu- throughs in areas such as materials and manufacture, considerable research funding will be directed turing, nanoelectronics, medicine and healthcare, toward addressing these research initiatives of na- environment and energy, chemical and pharmaceu- tional focus. At the request of the author [KPC], a tical industries, biotechnology and agriculture, com- NSF research workshop has been organized by putation and information technology, improving hu- F. Moon of Cornell University to look into the re- man performance, and national security. It also ad- search needs and challenges facing the mechan- dresses the development of a skilled workforce in ics communities. A website and report with recom- this area as well as the ethical, legal and social mendations of research needs and challenges avail- implications of future nanotechnology. It is part of able (see Mechanics, AAM, 32 (78) (2003)). the interagency National Nanotechnology Initiative Mechanics and materials engineering are really (NNI). Details of the NNI and the NSE initiative are two sides of a coin, closely integrated and related. available on the web at http://www.nsf.gov/nano or For the last decade this cooperative effort of the http://nano.gov. M&M Program has resulted in better understanding The NSE competition will support Nanoscale and design of materials and structures across all Interdisciplinary Research Teams (NIRT), Nanoscale physical scales, even though the seamless and re- Exploratory Research (NER), Nanoscale Science alistic modeling of different scales from the nano- and Engineering Centers (NSEC) and Nano Under- level to the system integration-level (Fig. 2) is not graduate Education (NUE). In addition, individual yet attainable. The major challenges are the sev- investigator research in nanoscale science and en- eral orders of magnitude in time and space gineering will continue to be supported in the rel- scales from the nano level to micro and to meso evant NSF Programs and Divisions outside of this levels. The following list summarizes some of the initiative. This NSE initiative focuses on seven high major methods in bridging the scales, top down or risk/high reward research areas, where special op- bottom up, and their limitations. portunities exist for fundamental studies in synthe- FIRST PRINCIPLE CALCULATIONS - TO sis, processing, and utilization of nanoscale sci- SOLVE SCHRODINGERS EQ. AB INITIO, e.g. ence and engineering. The seven areas are: HATREE- FOCK APPROX., DENSITY FUNC- . Biosystems at the nanoscale TIONAL THEORY, . Nanoscale structures, novel phenomena, and COMPUTIONAL INTENSIVE, O(N4) N is the quantum control number of orbitals. . Device and system architecture UP TO ~ 3000 ATOMS . Nanoscale processes in the environment MOLECULAR DYNAMICS [MD] pico sec. range . Multi-scale, multi-phenomena theory, modeling DETERMINISTIC, e.g. W/ LENNARD JONES and simulation at the nanoscale POTENTIAL . Manufacturing processes at the nanoscale 114 Ken P. Chong

Fig. 2. Physical scales in materials and structural systems (Boresi & Chong, 2000).

MILLIONS TIMESTEPS OF INTEGRATION; behavior into infrastructure systems performance, TEDIOUS and to model or extrapolate short term test results UP TO ~ BILLION ATOMS FOR NANO-SEC- into long term life-cycle behavior (NSF, 1998; Chong, ONDS 1999). Twenty-four awards were made totaling $7 COMBINED MD & CONTINUUM MECHANICS million. A grantees workshop was held recently in [CM], e.g. MAAD[Northwestern U.]; LSU; Berkeley and a book of proceedings has been pub- BRIDGING SCALE; lished (Monteiro et al., 2001). PROMISING, but bridging time and space Biomimetics or bio-inspired materials are to learn scales is the constraint... from natures millions of years of evolution and opti- INTERATOMIC POTENTIAL/CM HUANG [U. mization to see how to design and built stronger of Illinois UC]: EFFICIENT;MD STILL and high performance materials. An excellent ex- NEEDED IN TEMPERATURE, STRUCTURAL ample of natures design is the nacre [or the shell of CHANGES, DISLOCATIONS the red abalone], which has the nanostructured morphology and exceptional mechanical properties In the past, engineers and material scientists with just 2% of protein-binding agent. Katti, et al, have been involved extensively with the character- did a finite element modeling of nacre 2001. Re- ization of given materials. With the availability of searchers at Northwestern University and elsewhere advanced computing and new developments in ma- are also investigating different aspects of nacre. terial science, researchers can now characterize Tremendous progress is also being made in mi- processes and design and manufacture materials cro and nano sensors. Researchers at University of with desirable performance and properties. One of California Berkeley have been working on smart the challenges is to model short-term nano/micro- dust sensors with a target of a size of a cube scale material behavior, through meso-scale and 1mm on each side, capable of sensing [e.g. cracks macro-scale behavior into long-term structural sys- in materials] and transmitting wirelessly the data tems performance, Fig. 2. Accelerated tests to collected. Researchers at IBM Zurich and Basel simulate various environmental forces and impacts have developed the artificial nose to detect minute are needed (NSF, 1998). Supercomputers and/or analytes and air quality in the air [Fig. 3]. workstations used in parallel are useful tools to solve Researchers at NIST and other places have been this scaling problem by taking into account the large building nano-clay filled polymers with natural clay number of variables and unknowns to project micro- Nano science and engineering in mechanics and materials 115

Fig. 3. Cantilever detection mechanism [IBM Zurich].

form platelet [less than 1 nm in thickness] and 1 to for their comments and inputs during the writing of 5% by volume. These nano-clay filled polymers can this paper. Information on NSF initiatives, announce- dramatically improve fire resistance as well as me- ments and awards can be found in the NSF website: chanical properties. Metal oxide nanoparticles www.nsf.gov. Parts of this paper have been pre- have also been used in coatings for protection of sented elsewhere (Chong, 2002; 2003). Information UV light, self-disinfecting surfaces, solar cells, in- pertaining to NIST can be found on its website: door air cleaners, etc. In general, nanocomposites www.nist.gov. The opinions expressed in this ar- possess superior properties. ticle are the authors only, not necessarily those of the National Science Foundation. 4. SUMMARY, ACKNOWLEDGMENTS AND DISCLAIMER REFERENCES AND BIBLIOGRAPHY An overview of research opportunities and challenges Asif, S. A. S., Wahl, K. J., Colton, R. J., and of nanotechnology in mechanics and materials, in- Warren, O. L. (2001). Quantitative Imaging of cluding nanomechanics, carbon nano-tubes, bio- Nanoscale Mechanical Properties Using inspired materials, coatings, fire-resistant materi- Hybrid Nanoindentation and Force Modulation. als as well as improved engineering and design of J. Appl. Phys. 90, 5838-5838. materials are presented and discussed. Boresi, A. P. and Chong, K. P. (2000). Elasticity The author would like to thank his colleagues in Engineering Mechanics, John Wiley, New and many members of the research communities York. Boresi, A. P., Chong, K. P. and Saigal, S. (2002). Approximate Solution Methods in Engineering Mechanics, John Wiley, New York. Bhushan, B., Kulkarni, A. V., Banin, W., and Wyrobek, J. T. (1996). Nanoindentation and Picoindentation Measurements Using a Capacitive Transducer System in Atomic Force Microscopy. Phil. Mag. A 74, 1117-1128. Chong, K. P. (1998, 1999). Smart Structures Research in the U.S. Keynote paper, Proc. NATO Adv. Res. Workshop on Smart Struc- tures, held in Pultusk, Poland, 6/98, Smart Structures, Kluwer Academic Publ. 37-44 (1999). Chong, K. P., Research and Challenges in Nanomechanics 90-minute Nanotechnology Webcast, ASME, Oct. 2002; archived in Fig. 4. Below shows the stress-strain characteris- www.asme.org/nanowebcast. tics of nano-composites [L. Schadler, RPI]. 116 Ken P. Chong

Chong, K. P., Nano-scale Mechanics Research NSF. (1998). Long Term Durability of Materials and Challenges, Plenary Paper, Study of and Structures: Modeling and Accelerated Matter at Extreme Conditions Conference, Techniques. NSF 98-42, National Science Miami Beach, FL, 2003. Foundation, Arlington, VA. Interagency Working Group on Nano Science, NSF. (2001). Nanoscale Science and Engineer- Engineering and Technology (IWGN). (2000). ing. NSF 01-157, National Science Founda- Nanotechnology Research Directions. Kluwer tion, Arlington, VA. Academic Publ. 37-44. VanLandingham, M. R., Villarrubia, J. S., Guthrie, Katti, K. S., Katti, D. R., Tang, J., and Sarikaya, W. F., and Meyers, G. F. (2001). M. (2001), Proc. Mat. Res. Soc., Symp. AA, Nanoindentation of Polymers: An Overview. Spring 2001. Macromolecular Symposia 167: Advances in Monteiro, P. J. M., Chong, K. P., Larsen-Basse, J. Scanning Probe Microscopy of Polymers, and Komvopoulos, K., Eds. (2001). Long-term V. V. Tsukruk and N. D. Spencer, Eds., 15-44. Durability of Structural Materials, Elsevier, Wong, E. (1996). An Economic Case for Basic Oxford, UK. Research. Nature 381, 187-188.