Manufacturing Bits: Oct. 23
Carbon Nanotube Uniforms
Using a carbon nanotube fabric, Lawrence Livermore National Laboratory (LLNL) is developing a new military uniform material that repels chemical and biological agents.
The material can move from a breathable to a protective state. In theory, if a chemical warfare agent hits the carbon nanotube fabric then the functional groups on the carbon nanotube membrane will sense and block the threat. Then, a second response scheme also will be developed. “Similar to how a living skin peels off when challenged with dangerous external factors, the fabric will exfoliate upon reaction with the chemical agent,” according to researchers. In turn, the fabric will be able to block chemical agents such as sulfur mustard, GD and VX nerve agents, toxins such as staphylococcal enterotoxin, and biological spores such as anthrax.
The highly breathable membranes have pores made of a few nanometer-wide vertically aligned carbon nanotubes that are surface modified with a chemical warfare agent-responsive functional layer.
“The uniform will be like a smart second skin that responds to the environment,” said Francesco Fornasiero, LLNL’s principal investigator for the Defense Threat Reduction Agency (DTRA)-funded project, on LLNL’s Web site. “Without the need of an external control system, the fabric will be able to switch reversibly from a highly breathable state to a protective one in response to the presence of the environmental threat. In the protective state, the uniform will block the chemical threat while maintaining a good breathability level.”
The new uniforms could be deployed in the field in less than 10 years.
Chicken Wire Chips
Ferromagnetism in non-magnetic materials, such as the edge states in graphene nano-ribbons and defects in graphite, have attracted attention in R&D circles.
The Department of Energy’s Oak Ridge National Laboratory and others have made a surprising discovery: Nano-ribbons of silicon configured so the atoms resemble chicken wire could hold the key to data storage. Researchers investigated electron spins arising from intrinsic broken bonds at the step edges. They used scanning tunneling spectroscopy (STS).
In the lab, the step edges on the silicon-gold surface underwent a 1 × 3 reconstruction at low temperature. Oak Ridge, Argonne National Laboratory, the University of Wisconsin and Naval Research Laboratory showed that the electron spins are ordered anti-ferromagnetically. The up and down spin-polarized atoms serve as effective substitutes for conventional “0s” and “1s” common to electrons.
“By exploiting the electron spins arising from intrinsic broken bonds at gold-stabilized silicon surfaces, we were able to replace conventional electronically charged zeros and ones with spins pointing up and down,” said Paul Snijders of the Department of Energy’s Oak Ridge National Laboratory. “For the first time we were able to clearly establish that the edges of nano-ribbons feature magnetic silicon atoms.”
This confirms the prediction of spin-polarization in silicon. It also provides an avenue for studying low-dimensional magnetism. Most importantly, silicon–gold surfaces provide a precise template for single-spin devices at the ultimate limit of high-density data storage and processing.
Vortex Devices
Researchers from the Universities of Bristol, the University of Glasgow, Sun Yat-sen University and Fudan University have demonstrated integrated arrays of emitters of “optical vortex beams” in silicon chips. The quantum mechanical properties of optical vortices can be applied in quantum communications and computation.
The research contradicts the conception that light moves in straight rays. Instead, researchers demonstrated that the energy travels in a spiral fashion in a conical beam shape.
The research is related to the orbital angular momentum (OAM) of photons, in which photons orbit around a beam axis. Researchers demonstrated silicon-integrated optical vortex emitters using angular gratings with high OAM. The smallest device has a radius of 3.9 micrometers.
Siyuan Yu, professor of photonics information systems in the Photonics Research Group at the University of Bristol, said: “Our microscopic optical vortex devices are so small and compact that a silicon micro-chip containing thousands of emitters could be fabricated at a very low cost and in high volume. Such integrated devices and systems could open up entirely new applications of optical vortex beams previously unattainable using bulk optics.”
Mark Thompson, deputy director of the Centre for Quantum Photonics at the University of Bristol, added: “Perhaps one of the most exciting applications is the control of twisted light at the single photon level, enabling us to exploit the quantum mechanical properties of optical vortices for future applications in quantum communications and quantum computation.”
Misbehaving MEMS
Researchers can calculate the movement of tiny MEMS devices. The impression is that MEMS devices move in uniform increments. However, the National Institute of Standards and Technology (NIST) made a new and surprising finding: MEMS do not march in uniform steps.
To track a MEMS device, NIST has devised a super-resolution fluorescence microscopy technology. This technology is said to measure a MEMS device in motion across a surface. More specifically, NIST tracked a MEMS device called a “scratch drive actuator.” This device is said to drag itself over a surface by repeatedly flexing and relaxing a hooked arm.
A micromachine called a scratch drive actuator, labeled with fluorescent dots, (top) rests atop a platform underlain by an electric circuit that initiates the device’s step-by-step movements. Under a fluorescence microscope, the nanoparticles appear as points of light in a starlike constellation (bottom), making it possible to measure small changes in the position and orientation of the device at each step. Credit: NIST
The device is imaged by widefield epi-fluorescence microscopy. The image is then placed into a Gaussian distribution model to calculate its position. NIST calculated the size of each movement to within 1.85nm. This technique is also used to measure the stepwise motion of a scratch drive actuator across each of 500 duty cycles with a 130nm localization precision.
“Our method revealed very irregular step sizes, which had neither been observed previously nor predicted by established models of MEMS behavior,” said Craig McGray of NIST on the organization’s Web site. Super-resolution fluorescence microscopy can be used in MEMS R&D and other applications.
—Mark LaPedus
Tags: Argonne National Laboratory, California Institute of Technology, Fudan University, Lawrence Livermore National Laboratory, MEMS, nanotubes, National Institute of Standards and Technology, Naval Research Laboratory, Oak Ridge National Laboratory, Sun Yat-sen University, University of Bristol, University of Glasgow, University of Rochester, University of Wisconsin