FOCUS RESEARCH NEWS
Atom-thick crystal to advance 2D optoelectronics
A diode made from crystalline material with layers just a few atoms thick has been produced by a team of researchers from the Institute of Photonics at Vienna University of Technology in Austria. The work, published in Nature Nanotechnology, constitutes significant progress in 2D optoelectronics. The properties of such ultra-thin crystals open up new possibilities for solar cells, photodiodes and LEDs. Semiconductors used in electronic devices are usually made from crystalline silicon made from 3D crystals, which are expensive to manufacture. 2D crystals – crystalline material layers with a thickness of just one or a few atoms – can be produced economically on a large scale and exhibit all the advantages of crystalline materials. The Austrian team succeeded in producing the first diode with a p-n junction from 2D crystals, thus laying the foundation for radical changes in optoelectronics. The starting material used by the team led by Professor Thomas Mueller was tungsten diselenide (WSe2
in monolayer crystalline
Live super resolution cell imaging possible with new microscope
A
microscope developed at Queen Mary University of London’s Blizard Institute has been unveiled that opens up new
opportunities in biological imaging. The spinning disk super resolution imaging (SDSI) microscope is able to produce pictures with a resolution of 80nm and allow artefacts such as protein complexes in the nucleus to be viewed, which currently can’t be seen using standard PALM and STORM super-resolution techniques. The team that developed the microscope was
led by Dr Ann Wheeler, head of imaging at the Blizard Institute, and Professor Martin Knight of Queen Mary’s School of Engineering and Materials Science.
), which has a band gap. The
material was mechanically ‘peeled’ from 3D crystals to create layers 0.7nm thick. ‘WSe2
form is theoretically an ideal starting material for p-n diodes and optoelectronics – but no one had ever proven it before. We have now done just that. We measured an efficiency of 0.5 per cent in converting light to electrical energy,’ commented Mueller, adding that this is the first worldwide demonstration of the photovoltaic characteristics of a 2D crystalline material.
Recurring lettering imprinted on a steel foil using the multi-beam scanner
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l Trumpf’s Leibinger points to strong China and UK markets for laser machining
www.electrooptics.com/news 6 ELECTRO OPTICS l APRIL 2014
Pulsar Photonics, a spin-off of the Fraunhofer Institute for Laser Technology (ILT), has developed a modified ultrashort laser system. The system uses a multi-beam approach to increase the cost effectiveness of using ultrashort pulsed techniques to process materials. The new technique allows a workpiece to be processed at 100 places at once, with the additional option to segment the laser beam. The
system and multi-beam scanner will be presented for the first time to the public on 7-11 April at the Hannover Messe trade fair in Germany. The multi-beam technology, which speeds up processing, is primarily suited to the manufacture of components that feature recurring patterns and set structural arrangements, or else for working on several components with the same structure simultaneously.
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The SDSI microscope was developed by combining the single focus plane technology of a spinning disk system with the super resolution techniques of Photoactivation Light-Microscopy (PALM) and Stochastic Optical Reconstruction Microscopy (STORM). It allows imaging in live cells, which other super resolution microscopy techniques would find difficult. Dr Wheeler, Professor Knight and their team used piezo-driven, capacitive sensor feedback
nano-positioning technology from Physik Instrumente (PI) to provide long-term stability for the SDSI microscope. Currently PALM and STORM super-resolution techniques use TIRF to collect fluorescent images over an extended time period and then use complex algorithms to process the data. The high laser power required for TIRF illumination can cause photo-bleaching in live cells, which limits the technique’s range of use. Also, the penetration depth of TIRF is limited to 100nm, therefore preventing access to the cell nucleus. The microscope at the Blizard Institute uses a spinning disk to acquire the image and then processes the data using super resolution algorithms. Acquiring the images using the spinning disc allows both a lower laser power to be used and penetration depths to reach the level of the nucleus. The technique produces pictures with a resolution of 80nm and can be used to view protein complexes in the nucleus. Each set of data taken from a single image plane is acquired over several minutes. During data collection the sample must remain stable relative to the focal plane.
Multi-beam ultrafast laser to optimise machining
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