---
title: "Nanoelectromechanical systems"
chunk: 2/4
source: "https://en.wikipedia.org/wiki/Nanoelectromechanical_systems"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:55:36.112304+00:00"
instance: "kb-cron"
---

Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. They can be considered a rolled up graphene. When rolled at specific and discrete ("chiral") angles, and the combination of the rolling angle and radius decides whether the nanotube has a bandgap (semiconducting) or no bandgap (metallic).
Metallic carbon nanotubes have also been proposed for nanoelectronic interconnects since they can carry high current densities.  This is a useful property as wires to transfer current are another basic building block of any electrical system. Carbon nanotubes have specifically found so much use in NEMS that methods have already been discovered to connect suspended carbon nanotubes to other nanostructures.  This allows carbon nanotubes to form complicated nanoelectric systems.  Because carbon based products can be properly controlled and act as interconnects as well as transistors, they serve as a fundamental material in the electrical components of NEMS.

==== CNT-based NEMS switches ====
A major disadvantage of MEMS switches over NEMS switches are limited microsecond range switching speeds of MEMS, which impedes performance for high speed applications. Limitations on switching speed and actuation voltage can be overcome by scaling down devices from micro to nanometer scale. A comparison of performance parameters between carbon nanotube (CNT)-based NEMS switches with its counterpart CMOS revealed that CNT-based NEMS switches retained performance at lower levels of energy consumption and had a subthreshold leakage current several orders of magnitude smaller than that of CMOS switches. CNT-based NEMS with doubly clamped structures are being further studied as potential solutions for floating gate nonvolatile memory applications.

==== Difficulties ====
Despite all of the useful properties of carbon nanotubes and graphene for NEMS technology, both of these products face several hindrances to their implementation.  One of the main problems is carbon's response to real life environments.  Carbon nanotubes exhibit a large change in electronic properties when exposed to oxygen.  Similarly, other changes to the electronic and mechanical attributes of carbon based materials must fully be explored before their implementation, especially because of their high surface area which can easily react with surrounding environments. Carbon nanotubes were also found to have varying conductivities, being either metallic or semiconducting depending on their helicity when processed.  Because of this, special treatment must be given to the nanotubes during processing to assure that all of the nanotubes have appropriate conductivities.  Graphene also has complicated electric conductivity properties compared to traditional semiconductors because it lacks an energy band gap and essentially changes all the rules for how electrons move through a graphene based device.  This means that traditional constructions of electronic devices will likely not work and completely new architectures must be designed for these new electronic devices.

==== Nanoelectromechanical accelerometer ====
Graphene's mechanical and electronic properties have made it favorable for integration into NEMS accelerometers, such as small sensors and actuators for heart monitoring systems and mobile motion capture. The atomic scale thickness of graphene provides a pathway for accelerometers to be scaled down from micro to nanoscale while retaining the system's required sensitivity levels.
By suspending a silicon proof mass on a double-layer graphene ribbon, a nanoscale spring-mass and piezoresistive transducer can be made with the capability of currently produced transducers in accelerometers. The spring mass provides greater accuracy, and the piezoresistive properties of graphene converts the strain from acceleration to electrical signals for the accelerometer. The suspended graphene ribbon simultaneously forms the spring and piezoresistive transducer, making efficient use of space in while improving performance of NEMS accelerometers.

=== Polydimethylsiloxane (PDMS) ===
Failures arising from high adhesion and friction are of concern for many NEMS. NEMS frequently utilize silicon due to well-characterized micromachining techniques; however, its intrinsic stiffness often hinders the capability of devices with moving parts.
A study conducted by Ohio State researchers compared the adhesion and friction parameters of a single crystal silicon with native oxide layer against PDMS coating. PDMS is a silicone elastomer that is highly mechanically tunable, chemically inert, thermally stable, permeable to gases, transparent, non-fluorescent, biocompatible, and nontoxic. Inherent to polymers, the Young's Modulus of PDMS can vary over two orders of magnitude by manipulating the extent of crosslinking of polymer chains, making it a viable material in NEMS and biological applications. PDMS can form a tight seal with silicon and thus be easily integrated into NEMS technology, optimizing both mechanical and electrical properties. Polymers like PDMS are beginning to gain attention in NEMS due to their comparatively inexpensive, simplified, and time-efficient prototyping and manufacturing.
Rest time has been characterized to directly correlate with adhesive force, and increased relative humidity lead to an increase of adhesive forces for hydrophilic polymers. Contact angle measurements and Laplace force calculations support the characterization of PDMS's hydrophobic nature, which expectedly corresponds with its experimentally verified independence to relative humidity. PDMS' adhesive forces are also independent of rest time, capable of versatilely performing under varying relative humidity conditions, and possesses a lower coefficient of friction than that of Silicon. PDMS coatings facilitate mitigation of high-velocity problems, such as preventing sliding. Thus, friction at contact surfaces remains low even at considerably high velocities. In fact, on the microscale, friction reduces with increasing velocity. The hydrophobicity and low friction coefficient of PDMS have given rise to its potential in being further incorporated within NEMS experiments that are conducted at varying relative humidities and high relative sliding velocities.