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.
Atomic force microscopy: Atomic force microscopy is a type of scanning probe microscopy. A sharp tip mounted on top of a flexible cantilever is raster scanned over a surface, and various surface parameters such as topography and viscoelastic properties can be recorded. The sharpness of the tip contributes to the resolution of the microscope; therefore, carbon nanotubes with their small diameter and high aspect ratio mounted to the tip are used for specific applications.
Carbon nanotubes: Carbon nanotubes are molecular tubes made of carbon, with a diameter between 1nm and 50nm, and various lengths. There are single walled carbon nanotubes, double wall carbon nanotubes and multiwall carbon nanotubes. Carbon nanotubes can for example be used for functionalization of AFM tips, in nanocomposites, and as wires in nanotechnological applications.
Graphene: Graphene sheets are single layers of graphite with uniform honeycomb-like structure. They are strong and stable, and excellent electrical charge carriers.
MEMS: MEMS stands for MicroElectroMechanical Systems. Currently, the word MEMS denotes man-made mechanical elements, sensors, actuators and electronics that that were produced using microfabrication technology and are integrated on a silicon substrate. Increasingly, the word MEMS is used for miniaturized devices that are based on Silicon technology or traditional precision engineering, chemical or mechanical.
Nanoelectronics: Nanoelectronics extends miniaturization further toward the ultimate limit of individual atoms and molecules. On such a small scale, billions of devices could be integrated into a single nanoelectronical system. Nanoelectronics is often considered a disruptive technology because present candidates for nanoelectronical functional elements are significantly different from traditional transistors.
Nanofabrication: Nanofabrication refers to the fabrication of materials, physical structures or devices with at least one of their dimensions in the range of 1-100 nm. Various nanofabricated devices exhibit functional properties, phenomena and behavior that clearly distinguish them from their macroscale counterparts.
NEMS: NEMS stands for NanoElectroMechanical Systems. NEMS extend miniaturization further toward the ultimate limit of individual atoms and molecules. NEMS are man-made devices with functional units on a length scale between 1 and 100 nm. Some NEMS are based on the movement of nanometer-scale components.
NEMS applications are envisaged in sensing, displays, portable power generation, energy harvesting, drug delivery and imaging1. Examples for NEMS comprise nanoresonators2,3 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 sensors8,9, Carbon nanotube single electron transistors10, nanoelectrometers11, relays and switches with nanotubes12,13, 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 philipinnarum22,23, although these are still topics of discussion.
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.
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