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
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
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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