Nanotech Tech Digest - January 2017

A new advance in making perovskite LEDs a reality

Researchers at Princeton have developed a method to cause perovskite particles to self-assemble. They say this produces more efficient, stable and durable perovskite LEDs that would be easier to manufacture than current LEDs, while emitting very strong light, that is easily tuned to display different colours. The crystal and diamond structure of perovskite exhibits either superconductivity or semi-conductivity depending on structure. The researchers’ advance was to add long-chain ammonium halide to the perovskite solution during processing, which constrained the formation of crystal in the film. Instead, what were formed were 5-10 nanometre crystallites which made the halide perovskite films far thinner and smoother. This meant that the LEDs emitted more photons per number of electrons entering the device than using alternative production methods.

Hot new conversion technique

Kyoto University, working with Osaka Gas, has built a proof-of-concept nanoscale semiconductor that narrows wavelength bandwidth to concentrate light energy in solar cells. Kyoto researchers claim that current solar cells are not good at converting visible light into electrical power, having just 20% efficiency. The scientists wanted to capture and convert light produced by gas flames, so they chose silicon as it can withstand temperatures of up to 1000 degrees Celsius. They  etched silicon plates to create a grid of identical, equidistant rods the structure of which could be altered to catch different wavelength bandwidths. Using this material, the scientists showed that they could raise the conversion efficiency of light to electricity by 40%. 

5D fingerprint to detect Alzheimer’s

Scientists believe that misshapen proteins, called amyloids, can clump together and form masses in the brain which block normal cell function, leading to neurodegenerative disorders such as Alzheimer’s. A team of researchers from the University of Michigan and the University of Fribourg have developed a technique to measure amyloids’ shapes, volume, electrical charge, rotation speed and binding propensity. They call this information a ‘5D fingerprint’. Having more measurement categories could enable doctors to better understand, treat and predict problems associated with amyloids. The researchers created a nanopore (holes of 10-30 nanometres diameter, small enough that only one protein molecule can pass through at a time) on a substrate. The nanopore was sandwiched between saline solution layers to which an electric current was applied. By reading fluctuations in the current as the molecule passes through the pore researchers were able to determine the molecule’s ‘5D fingerprint’. 

Colouring gold

Scientists from the Daegu Gyeongbuk Institute of Science and Technology in Korea have discovered a way to control colour changes by adding a coating of nanometres thick semiconducting materials to a metal substrate. Through the addition of a thin germanium film of 5-25 nanometres to a gold substrate the team could control the colour produced (through thin-film interference) – such as yellow, orange, blue and purple. The scientists hope that in the future a similar method could be used to create patterns or symbols on the substrate. 

COF colloids could carry drugs to target sites

Researchers at Northwest University have created a new type of nanomaterial called a COF colloid. Covalent organic frameworks (COFs) are strong polymers with many tiny pores which can be used to store for example energy, drugs or other cargo. These COFs usually come as a powdery substance which is, according to NWU, almost useless. However, the NWU team suspended the COF in a liquid ink which allows the material to be engineered to arbitrary sizes and thicknesses – opening up their potential use as designed carriers of drugs or other cargo  to specific locations within the body. Moreover, the team discovered that they could watch the process of how the molecules come together to create COF colloids by using a transmission electron microscope.

Tiny lasers

Researchers at Aalto University in Finland have created a nanoscale laser using nanoparticles. The device uses silver nanoparticles arranged in a periodic array. The optical feedback needed to generate the laser light is provided by radiative coupling (bouncing the captured light back and forth) between silver nanoparticles which effectively act as antennas. To produce a strong laser light the distance between particles was matched with the lasing wavelength to that they all radiate in unison. To provide the input energy for the laser organic fluorescent molecules were added. The benefits of such devices are that the laser can be made very small and very fast, which will be of use for chip-scale light sources in optical components.  

Microbial nanowires

Scientists at the University of Massachusetts Amherst have discovered a type of conductive natural nanowire produced by bacteria. The wires, known as microbial nanowires, are protein filaments which bacteria use to make electrical connections with other microbes or minerals. The team has been looking at several species of geobacter bacteria for their potential use in electronics. In the most recent study the scientists used genetically modified G. Sulfurreducens which produces more filaments and expresses filament genes from many different types of bacteria, and discovered that the microbial nanowires are highly conductive (around 5 mS/cm) which the scientists claim is comparable to that of metallic nanostructures. The scientists attribute the conductivity to a large amount of aromatic amino acid allowing for improved conductivity along the filament. As a result they believe these have good potential for use in electronics. 

Supercooled drum

A microscopic mechanical drum – a vibrating aluminium membrane – has been cooled to less than one-fifth of a single quantum (packet of energy), which is lower than quantum physics would predict. The work from the National Institute of Standards and Technology (NIST) provides the possibility of cooling an object to absolute zero which would make it more sensitive as a sensor, store information for longer, or even be used in quantum computing according to NIST scientists. To achieve this effect the scientists manipulated the resonance of the cavity through the application of a microwave tone at a frequency below the cavity’s resonance. The beating of the drum’s surface releases photons; with each photon that leaves the drum as a result of the microwave excitation the drum loses heat. 

Tight knot tied

Scientists at The University of Manchester have braided multiple molecular strands to enable the tying of a very tight knot. The knot has eight crossings in a 192-atom closed loop which is about 20 nanometres long. The knot was created by a technique known as self-assembly, in which molecular strands are woven around metal ions causing crossing points. The ends of the strands were then fused by a chemical catalyst to close the loop and create the knot. 
The scientists think that this will enable further study into how molecular knotting affects strength and elasticity of materials which could lead to the knowledge of how to weave polymer strands to create new materials. 

Rosetta Wearable Disk

The Rosetta Disk’s goal is to make a catalogue of languages and important documents to be preserved for the long term. On the small wearable pendant can be found microscopic pages. With the help of a microscope the preamble to the universal declaration of human rights can be read in 327 languages, a Swadesh Vocabulary List by PanLex Project (a phrasebook listing identical words and phrases in 719 languages), The Clock of The Long Now by Steward Brand and diagrams for the 10,000-year clock. This ‘wearable’ is made using a process similar to microchip lithography, which uses a laser bean to write onto a photosensitive material coated on a glass plate. These recorded features are then developed like a film, after which the plate is electroformed, which results in a disk made of solid nickel. The text is slightly raised from the surface, and requires optical magnification to read. 

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