Introduction, Application and Challenges of Nanoelectromechanical Systems (NEMS)

NanoElectroMechanical Systems (NEMS) have critical structural elements at or below 100 nm. This distinguishes them from MicroElectroMechancial Systems (MEMS), where the critical structural elements are on the micrometer length scale. Compared to MEMS, NEMS combine smaller mass with higher surface area to volume ratio and are therefore most interesting for applications regarding high frequency resonators and ultrasensitive sensors.

NEMS applications are envisaged in sensing, displays, portable power generation, energy harvesting, drug delivery and imaging¹. Examples for NEMS comprise nanoresonators^2,3 and nanoaccelerometers⁴, integrated peizoresistive detection devices⁵. Applications that have either already reached the market or are available as research prototypes comprise ultrasharp tips for atomic force microscopy (e.g., single-walled carbon nanotubes mounted on the tip of an atomic force microscopy cantilever⁶), a nonvolatile NEMS memory⁷, NEMS sensors^8,9, Carbon nanotube single electron transistors¹⁰, nanoelectrometers¹¹, relays and switches with nanotubes^12,13, pH sensors¹⁴, protein concentration detectors¹⁵, etc.

NEMS can either be produced bottom-up (e.g. chemical self assembly methods, CVD methods, hot plate technique), top-down (e.g. metallic thin films or etched semiconductor layers that are produced with the help of etching, with scanning probe tools or with nanolithography methods) or via combined methods where molecules are integrated into a top-down framework¹⁶. Carbon (graphene, carbon nanotubes) is a major material used in current NEMS.

Current challenges in NEMS concern the tailored production of metallic or semiconducting Carbon nanotubes¹⁷ as well as stiction and lubrication issues¹⁸. Monomolecular lubricant films are a hot topic of research¹⁹.

Bioinspiration: In MEMS and NEMS technology - comparable to biology - a limited number of base materials is used, providing a wide range of functional and structural properties. The complexity of the approach (in biology as well as in engineering) increases with decreasing number of base materials. Biomimetics, i.e., technology transfer from biology to engineering, is especially promising in MEMS development because of the material constraints in both fields²⁰.

Diatoms²¹ are single celled organisms that have moving parts in relative motion on the nanoscale. They are high-potential biological systems that can inspire emerging NEMS technologies: Diatoms such as Eunotia sudetica, Bacillaria paxillifer and species of Ellerbeckia have hinges and interlocking devices on the several 100 nanometer scale²⁰, the diatoms Corethron pennatum and Corethron criophilum exhibit click-stop mechanisms on the micrometer lengthscale and below and the unfolding of cells of these species after cell division is an excellent example on how to obtain 3D structures from fabricated 2D structures²⁰. Even springs and micropumps might be realized on the micro- and nanoscale, e.g. in the diatoms Rutilaria grevilleana and Rutilaria philipinnarum^22,23, although these are still topics of discussion.

Outlook

Future applications of NEMS are hard to predict. The prototype NEMS that would be economically most interesting are the ones that are most hard to be commercialized. Applications that combine biology and nanotechnology seem to be the most promising ones²⁴. Nanoresonators would have direct consequences for the wireless communication technologies.

Possible applications of nanomotors might be nanofluidic pumps for biochips or sensors. According to Alex Zettl from Berkeley University, CA, USA, emerging NEMS might also path the way for novel MicroElectroMechanical Systems (MEMS) that currently have major problems with stiction; integrated systems from NEMS and MEMS might be of high relevance (such as MEMS sensors with NEMS as core components), compared to the natural systems in biology, where cells, true micro-objects, have various nanoparts as integrative components.

Recent work by the department of Transducers Science and Technology of the University of Twente, Holland, is concentrated on the construction of truly three-dimensional nanostructures. The fields of applications are not yet fully explored but first studies on cell trapping in 3D nanoconfined objects and self-organizing nanoparticles are underway. Recent studies in 3D sculpturing are on corner lithography for advanced probing (smarticles) and ultimately sharp probe tips²⁵. This research might lead to interesting emerging MEMS.

References

1. Cimalla V., Niebelschütz F., Tonisch K., Foerster Ch., Brueckner K., Cimalla I., T., Friedrich, Pezoldt J., Stephan R., Hein M. and Ambacher O. Nanoelectromechanical devices for sensing applications, Functional Materials for Micro and Nanosystems - EMRS, Sensors and Actuators B: Chemical 126(1), 2007, 24-34, doi: 10.1016/j.snb.2006.10.049
2. LaHaye M.D., Buu O., Camarota B. and Schwab K.C. Approaching the quantum limit of a nanomechanical resonator, Science 304(5667), 2004, 74-77, doi: 10.1126/science.1094419
3. Peng H.B., Chang C.W., S Aloni., Yuzvinsky T.D. and Zettl A. Microwave electromechanical resonator consisting of clamped carbon nanotubes in an abacus arrangement, Phys. Rev. B 76(3), 2007, 035405(5p)
4. Fennimore A.M., Yuzvinsky T.D., Han W.-Q., Fuhrer M.S., Cumings J. and Zettl A. Rotational actuators based on carbon nanotubes, Nature 424, 2003, 408-410, doi: 10.1038/nature01823
5. Li M., Tang H.X. and Roukes M.L. Ultra-sensitive NEMS-based cantilevers for sensing, scanned probe and very high-frequency applications, Nature Nanotech. 2, 2006, 114-120, doi: 10.1038/nnano.2006.208
6. Bunch J.S., Rhodin T.N. and McEuen P.L. Noncontact-AFM imaging of molecular surfaces using single-wall carbon nanotube technology, Nanotechnology 15, 2004, S76-S78
7. Tsuchiya Y., Takai K., Momo N., Nagami T., Mizuta H. and Oda S. Nanoelectromechanical nonvolatile memory device incorporating nanocrystalline Si dots, J. Appl. Phys. 100(9), 2006, 094306
8. Besteman K., Lee J.O., Wiertz F.G.M., Heering H.A. and Dekker C. Enzyme-coated carbon nanotubes as single-molecule biosensors, Nano Letters 3(6), 2003, 727-730
9. Cui Y., Wei Q., Park H. and Lieber C.M. Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species, Science 293, 2001, 1289-1292
10. Postma H.W.Ch., Teepen T., Yao Z., Grifoni M. and Dekker C. Carbon nanotube single-electron transistors at room temperature, Science 293(5527), 2001, 76 - 79, doi: 10.1126/science.1061797
11. Cleland A.N. and Roukes M.L. Nanostructure-based mechanical electrometry, Nature 392, 1998, 160
12. Kinaret J.M., Nord T. and Viefers S. A carbon-nanotube-based nanorelay, Appl. Phys. Lett. 82(8), 2003, 1287-1289
13. Kaul A.B., Wong E.W., Epp L.and Hunt B.D., Electromechanical carbon nanotube switches for high-frequency applications, Nano Lett. 6(5), 2006, 942-947
14. Chen Y., Wang X., Erramilli S., Mohantya P. and Kalinowski A. Silicon-based nanoelectronic field-effect pH sensor with local gate control, Appl. Phys. Lett. 89, 2006, 223512
15. Lee W.C., Cho Y.H. and Pisano A. Nanomechanical protein concentration detector using a nanogap squeezing actuator with compensated displacement monitoring electrodes, J. Microelectromechanical Systems 16(4), 2007, 802-808
16. Mahalik N.P. Micromanufacturing & Nanotechnology, Springer 2006
17. Ebbesen T.W., Lezec H.J., Hiura H., Bennett J.W., Ghaemi H.F. and Thio T. Electrical conductivity of individual carbon nanotubes, Nature 382, 1996, pp. 54 - 56. doi: 10.1038/382054a0
18. Bhushan B. Nanotribology and Nanomechanics: An Introduction, Springer Publishing, 2008
19. Tomala A., Werner W.S.M., Gebeshuber I.C., Doerr N. and Stoeri H. Tribochemistry of monomolecular lubricant films of ethanolamine oligomers, Trib. Int. 42(10), 2009, 1513-1518, doi: 10.1016/j.triboint.2009.06.004
20. Gebeshuber I.C., Stachelberger H., Ganji B.A., Fu D.C., Yunas J. and Majlis B.Y. Exploring the innovational potential of biomimetics for novel 3D MEMS, Adv. Mat. Res. 74, 2009, 265-268, doi: 10.4028/www.scientific.net/AMR.74.265
21. Round F.E., Crawford R.M. and Mann D.G. The diatoms: biology and morphology of the genera, Cambridge University Press, Cambridge, UK, 1990
22. Crawford R.M. and Sims P.A. Some principles of chain formation as evidenced by the early diatom fossil record, Nova Hedwigia Beiheft 133, 2007, 171-186
23. Srajer J., Majlis B.Y. and Gebeshuber I.C. Microfluidic simulation of a colonial diatom chain reveals oscillatory movement, Acta Bot. Croat. 68 (2), 2009, 431-441
24. Madou M.J. From MEMS to Bio-MEMS and Bio-NEMS: Manufacturing Techniques and Applications, CRC Press, 2010
25. Berenschot E., Tas N.R., Jansen H.V. and Elwenspoek M. 3D-Nanomachining using corner lithography. 3rd IEEE International Conference on Nano/Micro Engineered and Molecular Systems, NEMS, 2008, art. no. 4484432, 729-732