Manufacturing Bits: Aug. 16

Safer drinking water; nanobead microscopes.


Safer drinking water
Two-dimensional materials are gaining steam in the R&D labs. 2D materials include graphene, boron nitride (BN) and the transition-metal dichalcogenides (TMDs).

These materials could one day enable future field-effect transistors (FETs). One TMD, molybdenum disulfide (MoS2), is also generating interest in other fields. Molybdenum disulfide consists of two elements–molybdenum and sulfur.

The Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have created a tiny nanostructured device based on molybdenum disulfide. The device kills 99.99% of the bacteria in wafer in just 20 minutes by using the visible part of the solar spectrum, according to SLAC.

The method doesn’t remove chemical pollutants from water. But it could one day enable safer drinking water in developing countries. In many parts of the world, one way to disinfect water is to boil it. This consumes fuel. Another way is to put water out in the sun in a plastic bottle. The ultraviolet (UV) rays will kill the microbes. The UV method takes six to 48 hours, limiting the amount of water people can disinfect this way.

To improve this process, SLAC and Stanford developed a device based on molybdenum disulfide. The surface of the device looks like a fingerprint. The lines are very thin films of molybdenum disulfide. The materials are stacked on edge, “like the walls of a labyrinth, atop a rectangle of glass,” according to SLAC.

Molybdenum disulfide is an industrial lubricant. But when these materials are transformed into layers at the atomic scale, they become photocatalysts. “When hit by incoming light, many of its electrons leave their usual places, and both the electrons and the ‘holes’ they leave behind are eager to take part in chemical reactions,” according to SLAC.

Researchers also develop these materials in order to absorb the full range of visible sunlight. “Our device looks like a little rectangle of black glass. We just dropped it into the water and put everything under the sun, and the sun did all the work,” said Chong Liu, a researcher at SLAC/Stanford.

Nanobead microscopes
Using a technology called nanobeads, Bangor University and Fudan University have developed a superlens for an optical microscope.

The new superlens, according to researchers, adds 5x magnification on top of an existing microscope.

Researchers devised a new “nano–solid-fluid assembly” fabrication method to build the lens. The lens itself is based on 15nm titanium dioxide (TiO2) nanoparticles enabling an all-dielectric metamaterial-based solid immersion lens (mSIL).

A lens could have millions of nanobeads. Each bead refracts light. It can produce an image at least around 45nm under an optical microscope. “We’ve used high-index titanium dioxide (TiO2) nanoparticles as the building element of the lens. These nanoparticles are able to bend light to a higher degree than water. To explain, when putting a spoon into a cup of this material, if it were possible, you’d see a larger bend where you spoon enters the material than you would looking at the same spoon in a glass of water,” said Zengbo Wang at Bangor University.

“Each sphere bends the light to a high magnitude and splits the light beam, creating millions of individual beams of light. It is these tiny light beams which enable us to view previously unseen detail,” Wang said.