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Electronic devices with touch screens are ubiquitous, and their possible makes one key thing: transparent semiconductors. However, the cost and physical limitations of the material out of which usually make these semiconductors are hindering progress towards flexible devices with touch screens.
Fortunately, the research team at the University of Pennsylvania and Duke University has discovered a new way of developing transparent conductors using metal nanowires that could bring production of inexpensive and flexible touch screens on the high road.
The study was published in the journal ACS Nano.
Currently, the standard material for a transparent conductor of indium tin oxide (ITO), which is deposited in the form of two thin layers on both sides of the separation film. Contact in the form of a finger or stylus changes the electrical resistance between two layers of ITO enough to capture when the user touches the screen. Although this material works well, its shortcomings have led to the fact that the leading academics in this sphere began to look for an alternative.
“There are two problems associated with ITO: Indium is a rare, so its cost and availability are a significant problem, and what is more important in the production of flexible devices – it is fragile,” – said Professor Karen Wynn working on the project. – “We would have done better touch screens that use a thin, flexible nanowire, but to predict and optimize the properties of such nanoscale networks is very problematic.”
We have previously written that rare and expensive elements in mobile devices could soon come to an end .
Metallic nanowires relatively inexpensive and well preserved, they are liquid and easily drawn, or sprayed onto a flexible or rigid substrate and can not be grown in a vacuum as in the case of ITO. The only problem is that the first process forms the random network layer was not uniform as ITO.
The quality of the sheet of material in this context depends on two parameters, each of which can be separated from the material properties of transparency, which should be high, and the total electrical resistance, which should be low. To determine the electrical properties of the network of nanowires, however, need to know the length and diameter of the wire, the area that it covers, and the property known as the contact resistance. As the four independent parameters will affect the electrical and optical properties of the nanowires is not yet clear.
“What does that mean? People will synthesize nanowires to create one network, to measure the total resistance and optical properties of the network, and then declare victory when the measurements show a good result, “- says Wynn. – “The problem is that they do not know why good is good and what is worse, they do not necessarily know why bad is bad.”
For example, a low total resistance may be the result of the synthesis method, which produced unexpectedly long wiring, or a method of treatment, which resulted in decreased contact resistance between the nanowires. Without the possibility of release of these factors, the researchers could not determine what combination of parameters will be most successful.
Earlier, a group of Huayna worked on modeling of three-dimensional network of nanowires in nanocomposites, in particular, the number of nanowires considered necessary in order to create a connection path from one end of the system to another. Professor Benjamin Wiley of Duke contacted Wynn and asked if she wanted to join in the work of the two-dimensional modeling, which can be applied to the creation of silver nanowires fabricated by his group.
While the group has been able to Wylie desired length, diameter and area of the network of nanowires, the team was able to use the simulation of Huayna to work in the opposite direction, the total electrical resistance of the network to uncover the elusive contact resistance. Alternative methods for finding the contact resistance are labor-intensive, and incompatible with the typical methods of processing network.
“As soon as we get reliable and relevant contact resistance, we can begin to wonder how we can improve the overall resistance of the sheet by changing other variables. In a game with such a simulation, we can see how we get a better network if, for example, increases the length of the nanowires. ”
Researchers are searching for the best balance settings for a specific application of their system. For example, increased coverage nanowires always reduces the total electrical resistance, but also reduces the transparency, as more and more nanowires are formed in the network, whereby it is no longer transparent and becomes gray.
Different applications require different types of nanowires. Simulation allows scientists to understand how much you need to put the nanowires to achieve the Goldilocks zone, where it will be the best combination of transparency and resistance. Well, on the way to nanotechnology we need to master the nanowires.
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Tags: Flexible displays , Nanotechnology , Semiconductors .
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