PRODUCTS EDITOR’S CHOICE GRAPHENE PRODUCTION BREAKTHROUGH SILVER NANOINK PRINTING G


raphene has been hailed as a wonder material since it was first isolated from graphite in 2004. Graphene is just a


single atom thick but it is flexible, stronger than steel, and capable of efficiently conducting heat and electricity. However, widespread industrial adoption of graphene has so far been limited by the expense of producing it. Affordable graphene production could lead to a wide range of new


technologies reaching the market, including synthetic skin capable of providing sensory feedback to people with limb prostheses. That may be set to change now that researchers at the University of Glasgow have found a way to produce large sheets of graphene, using the same cheap type of copper used to manufacture lithium-ion batteries found in many household devices. In a new paper published in November in the journal Scientific Reports, a team led by Dr Ravinder Dahiya explain how they have been able to produce large-area graphene around 100 times cheaper than ever before. Graphene is often produced by a process known as chemical vapour deposition, or CVD, which turns gaseous reactants into a film of graphene on a special surface known as a substrate. The research team used a similar process to create high-quality graphene across the surface of commercially-available copper foils of the type often used as the negative electrodes in lithium-ion batteries. The ultra-smooth surface of the copper provided an excellent bed for the graphene to form upon. They found that the graphene they produced offered a stark improvement in the electrical and optical performance of transistors which they made compared to similar materials produced from the older process. Dr Dahiya, of the University of Glasgow’s School of Engineering,


said: “The commercially-available copper we used in our process retails for around one dollar per square metre, compared to around $115 for a similar amount of the copper currently used in graphene production. This more expensive form of copper often required preparation before it can be used, adding further to the cost of the process. Our process produces high-quality graphene at low cost, taking us one step closer to creating affordable new electronic devices with a wide range of applications, from the smart cities of the future to mobile healthcare. “Much of my own research is in the field of synthetic skin. Graphene could help provide an ultraflexible, conductive surface which could provide people with prosthetics capable of providing sensation in a way that is impossible for even the most advanced prosthetics today. “It’s a very exciting discovery and we’re keen to continue our research,” Dr Dahiya added. The research was conducted by the University of Glasgow in partnership with colleagues at Bilkent University in Turkey.


www.glasgow.ac.uk


Xaar and Lawter, along with its parent company Harima Chemicals Group (HCG), are collaborating to optimise the performance of a line of nanosilver conductive inks for the Xaar 1002 industrial inkjet printhead. The combined solution offers a robust and reliable method for printing antennas and sensors with silver nanoparticle ink. Industrial inkjet offers significant advantages over traditional print technologies to manufacturers of consumer electronics products. Inkjet is a cleaner process than other methods of printing silver inks; this is especially relevant when printing onto a substrate, such as a display, in which any yield loss is very expensive. With inkjet, manufacturers can very precisely control the amount of ink dispensed in certain areas of a pattern so that the ink or fluid deposited can be thicker in some areas and thinner in others. Similarly, inkjet enables the


deposition of a much thinner layer of fluids than traditional methods, which is significant for the manufacturers looking to produce thinner devices. In addition, inkjet is one of the few technologies able to print a circuit over a substrate that has a structured surface. “This is an excellent opportunity to showcase our latest technological breakthroughs and demonstrate the unique value that our revolutionary nanoparticle inkjet solutions can play as part of an integrated system solutions in the PE world,” says Dr Arturo Horta Ph.D., Business Development Manager for Lawter Innovation Group. HCG pioneered the development and


manufacture of silver nanoparticle conductive inks for the printed electronics industry over 20 years ago.


www.xaar.com


IMPROVED STABILITY COULD REVOLUTIONISE PEROVSKITE PHOTOVOLTAICS


Organo-lead halide perovskite materials, commonly used in high- efficiency perovskite solar cells, are materials that can easily decompose in moist conditions. They cannot survive even for one day without proper encapsulation. Due to the lead contained, perovskite solar cells may have limited applications as lead is not allowed in consumer electronic devices according to RoHS. Other potential applications require long-lifetime solar cells. Therefore, stability is the bottle neck for potentially large deployment of perovskite solar cells. Recently, Yang Yang group from UCLA


published a perovskite solar cell device with two layers of metal oxide as electron and hole transporting layers in Nature Nanotechnology. In this p-i-n structure, metal oxide layers also prevent perovskite from degradation. After 60 days storage in air at room


temperature, the device retained 90% of its initial efficiency (14.8% efficiency). Compared with the control device with organic transport layers (12.8% efficiency in the beginning), which degraded completely within 5 days. Since the first introduction of


ULTRA PRECISION THIN FILM SMD RESISTORS RELEASED


Willow Technologies has introduced a range of advanced ultra-precision chip resistors in Thin Film Technology, featuring ultra-tight tolerances down to ±0.01% and extremely low TCR down to ±2ppm/°C, with a power rating up to 1W. Available sizes supplied taped and reeled are from 0201 miniature up to a larger 2512 case size. The new thin film flat chip resistors combine proven reliability with an advanced level of precision. This combination has produced resistive devices


perfectly suited for applications such as medical equipment, precision test equipment, precision voltage dividers, industrial, automotive, aerospace, telecommunications and test apparatus.


The SAR range of thin film resistors has a standard resistance range from 1Ω to 3Mega Ω, with an operating temperature range of -55 to 155°C.


The company advises the


resistive element is based on NiCr film technology, with wrap around lead free terminations the device is


/ MICRO MATTERS


well suited for processing on automatic SMD assembly systems and for automatic soldering, using wave, reflow, or vapour phase. The resistors are RoHS


compliant and feature pure tin plating that provides compatibility with lead (Pb) free and lead (Pb) containing soldering processes. Samples and production


quantities of these new thin film resistors are available now from stock, & typical lead times of less than four weeks for larger orders.


www.willow.co.uk


perovskite solar cells in 2006, with an efficiency of 2.2%, they have experienced a remarkable learning curve, to the certified record of 20.1% at the end of 2014. The efficiency improvement of any other photovoltaic (PV) technologies are not comparable with perovskite’s. In addition, the low-cost and abundant materials used as the active layer, as well as the potential cheap manufacturing methods with solution processing capability are also advantages. Unlike the bulky, heavy, rigid and


opaque silicon solar cells, which dominate the current PV markets Perovskite solar cells can provide many value propositions including light- weight, flexibility, semi-transparency etc. They have attracted tremendous attention and this field becomes “crazy crowded” in the academia. Traditional PV companies also pay close attention to the new materials to make sure they will not lag behind when breakthrough is achieved. So far stability is one of the major issues in perovskite solar cells. Successfully tackling this issue may unlock perovskite solar cells as a game-changer.


www.ngsf.org


MICRO MATTERS | WINTER 2015 5


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