Nanotech Tech Digest - December 2016

Nanotubes strengthen composite materials

New technology that could enhance electrical and thermal conductivity in composite materials has resulted from collaboration between the Universities of Surrey and Bristol, together with aerospace company Bombardier. Their research shows that growing carbon nanotubes on a substrate of carbon fibre improves electrical conductivity by two, three or four times dependant on direction of current. It was also shown that through-thickness thermal conductivity (i.e. conductivity through the Z axis, perpendicular to the rolled (X&Y axes) surface of carbon fibre) increased by 107 per cent. The researchers see this having application in lightening-strike protection and de-icing solutions for the aerospace industry. It could also allow for composites to integrate sensors, energy harvesting lighting systems – which the researchers say they are already working on – and communication antennae, without compromising structural integrity. 

Rewritable circuits

In a study published by Nanoletters, Yuebing Zheng from the Cockrell School of Engineering at the University of Texas, outlines his team’s work on a nanomaterial that could be used to create rewritable photonic nanocircuits. Owing to the materials’ molecules’ sensitivity to light, a UV or other specific wavelength of light can be used to write or delete information to or from the material, similar to a rewritable CD. 
The material is composed of a plasmonic surface made up of aluminium nanoparticles (first quantum system), and on top of this is a layer of nanoscale polymers embedded with light responsive molecules (second quantum system). Depending on its state the material can either absorb light or transfer it across its surface. The material can be in two light-transporting modes simultaneously (hybrid mode).
Using a green laser to change the relative quantum states of the device’s composite materials, the researchers developed a waveguide (a device which channels light waves) on the nanomaterial. The waveguide – providing modulation of direction, amplitude, frequency and phase of the light waves –constrains the light wave forcing it to travel on a two-dimensional plane. The team then used an ultraviolet light to erase the waveguide, and then rewrote it, using the green laser, on the same material. 
Zheng’s team believes that their material could be used to create rewritable photonic circuits that could be smaller, faster and more energy efficient than silicon based chips. 

Doping quantum dots could reduce greenhouse gas

Nitrogen-doped quantum dots (NDQDs – semiconducting nanocrystals that are primarily being tested for their potential to be used in experimental display technologies) have the property of being able to convert carbon dioxide into complex hydrocarbons. A team led by Pulickel Ajayan from Rice University, has demonstrated using electrocatalysis to convert carbon dioxide into small amounts of ethylene and ethanol. Currently, copper is considered one of the materials with the best potential for this sort of catalysis. However, the researchers found that NDQDs are nearly as efficient as copper. NDQDs can reduce carbon dioxide by up to 90 per cent, converting 45 per cent of that into ethylene or alcohol. Industry currently uses scalable thermal catalysis to produce fuels and chemicals, therefore Ajayan is pessimistic about the potential of speedy adoption of his method by industry any time soon.

Nanowire wonderfilm 

A transparent, electrically conductive, bendable and ultrathin film has been produced by a team of researchers from the University of Illinois at Chicago, and Korea University. It is created by spraying silver-nanowires at supersonic speed, resulting in a film which, according to the researchers, has comparable conductivity to silver, but is as transparent as glass. As the wires are smaller than the wavelength of visible light they cause minimal light scattering and seem transparent. According to the researchers, the film can be bent repeatedly and stretched to seven times its length and continue to work. 

Nanotechnology device could be used for development of blood test for cancer

Engineers at Worcester Polytechnic Institute (WPI) have developed a chip that can trap and identify metastatic cancer cells (cells produced when the cancer is spreading to another area of the body) in a small amount of blood. Antibodies, attached to nanotubes in wells on the device, attract and then bind with the cancer cells after they have sunk to the well bottom, with a mean capture efficiency of 62%. The device produces an electrical signal when cancerous cells have been captured. Currently the research has focused on breast cancer cells, but the researchers believe the device could be set up to detect other tumour types.

Nanotubes used in printing

A team of scientists at Massachusetts Institute of Technology have developed a way to print utilising carbon nanotubes – by using stamping. Using a stamp with a nanoporous surface (covered in nanoscale holes) to channel ink to its destination, they say they’ve managed to overcome the problem with previous stamping techniques of image blur. The nanotube ‘forest’ was grown on a bed of silicon, then coated with polymers to enable the ink to flow smoothly through the quill like tubes, also increasing their ability to resist printing pressures. To calculate a suitable and evenly applied pressure for the stamping process – essential for printed image clarity – the team developed a computer model. They found that they could print at a speed of 200 millimetres per second, which they claim far surpasses printing rates in industrial printing technologies.

Flawed diamonds used as radio receiver

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences have demonstrated a tiny radio receiver. Nitrogen-vacancy (NV) centres (tiny, human engineered holes – some as small as two atoms) in diamonds are sensitive to electromagnetic fields, including FM radiowaves. The electrons in the NV centres were powered by green laser light. When they receive FM radiowaves they emit an audio signal as red light, which is then converted by a photodiode into a current that can be converted into sound via a speaker or earphone. Due to the strength of diamond the radio is able to work at extreme temperatures, the team demonstrated the device producing audio at temperatures as high as 350°C.

Uniform nanotubes

Scientists from Lawrence Berkeley National Laboratory, have discovered a family of synthetic materials which when placed in water assemble into nanotubes with uniform diameter. The materials, monodisperse amphiphilic diblock copolypeptoids, are ring-shaped, and can be used as building blocks. After submersion in water, each ring-shaped unit is stacked on top of another causing the formation of hollow, crystalline nanotube structures.The polymers tile-units can be built up to create precision supramolecular structures (i.e., nanotubes with defined lengths and widths). 

Colour cubed

A team of scientists at Duke University have developed a cheap way to apply plasmonics knowledge to detectors and printers. They have built a light detector which has pixels composed of variously sized silver nanocubes. When the light hits the cubes they each react in their own way, and the data of how each nanocube reacts is then run through a computer to determine the light’s original colour. 
Plasmonics is the use of nanoscale physical phenomena to trap certain frequencies of light. Using knowledge from this field engineers make 100 nanometre wide silver cubes and position them nanometres above a thin gold foil. When incoming light hits the nanocube it causes silver electrons to become excited and traps the lights energy. The trapped light’s frequency is determined by the cube’s size and distance from the gold foil. By adjusting these factors one can tune into any wavelength one desires – from visible light to infrared. This is how it is setup for use as a sensor or detector, but its setup can be altered for use as a printer. 
To print an image onto a gold wafer the detector is altered so as to have three bars of pixels which are individually responsible for reflecting red, blue or green. By controlling the length of each bar they can determine the colour the pixel reflects. The scientists are excited about the potential of this method to print infrared and visible light spectrum images onto the same substrate. 

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