- Email: [email protected]
New hybrid films could make touch screens more durable
Materials Today Volume 18, Number 6 July/August 2015
NEWS
Electrons help image light as both particle and wave An innovative experimental technique by a team from the E´cole Polytechnique Fe´de´rale de Lausanne (EPFL) in Switzerland has helped produce the first image of light behaving simultaneously as a particle and a wave. The approach allows for the control and visualization of plasmonic fields at the nanoscale, offering potential for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits, as well as potential benefits in optical data storage devices and biosensing applications. Although previous studies have demonstrated light as either a wave or a particle, this was at different times – no experiment has managed to photograph light behaving simultaneously as both a wave and a stream of particles, despite quantum mechanics showing that light can show both natures at the same time. The experiment, as reported in Nature Communications [Piazza, et al., Nat. Commun. (2015), doi:10.1038/ncomms7407], used a pulse of laser light fired at a metallic nanowire, which added energy to the charged particles in the nanowire, resulting
Light confined on a nanowire, behaving as both particle and wave.
in it vibrating. The light can move along the wire in either direction; when waves traveling in opposite directions meet each other, they form a new wave that appears to not be moving. This standing wave then becomes the source of light for the experiment, radiating around the nanowire. At this point, the team fired a stream of electrons close to the nanowire, using them
to image the standing wave of light. As the electrons pass near to and interact with the light, they collide with the light’s particles, the photons, changing their speed. Ultrafast microscopy was used to image the position at which this change in speed took place, and visualize the standing wave. The change in speed resembles an exchange of energy ‘‘packets’’ (quanta) between the electrons and photons, proving the light on the nanowire is behaving as a particle. As team leader Fabrizio Carbone said, ‘‘This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly.’’ The researchers are continuing their measurements to expose other aspects of the complementarity principle, and investigate their implications for circuits that exploit confined electromagnetic fields for quantum devices. They are also investigating developing and characterizing photonics circuits using the same methodology. As Carbone explains, ‘‘Being able to image and control quantum phenomena at the nanometer scale like this opens up a new route towards quantum computing.’’ Laurie Donaldson
New hybrid films could make touch screens more durable A type of hybrid thin-layer film that could make touch screen displays in tablets, smart phones and computer monitors last longer has been developed in a new study by two polymer scientists from Kyungpook National University in Daegu, South Korea. The flexible thin films are comprised of both inorganic and organic materials using a sol–gel fabrication process, and could help in producing screens that are flexible and durable but still offer the same electrical and optical properties as existing screens. Touch screens are usually made up of layered thin films of indium–tin oxide of only billionths of a meter in thickness. This oxide is electrically conductive and allows electrical signals to travel from the touch location to the edge of the display where they can be sensed by the device. However, these inorganic materials are brittle and shatter easily, and use acids that corrode
the metals and metal oxides in the electronic components. An acid-free sol–gel method of synthesizing organic–inorganic hybrid materials was therefore required for optical thin-film applications. The research by Soo-Young Park and A-Ra Cho, as published in Optical Materials Express [Cho, Park, Opt. Mater. Express (2015), doi:10.1364/OME.5.000690], involved a copolymer composed of two organic materials combined with a co-polymer called trialkoxysilane. When this reacts with two other inorganic chemicals, it synthesizes hybrid layers with high and low refractive indexes. The refractive index measures the amount that light is bent as it passes through the material. However, inorganic thin-layer and hybrid films have layers with different refractive indexes, which helps tune the wavelengths of the light passing through the film (or
touch screen). Tests undertaken on the new hybrid films show that both the high and low refractive index layers are highly transparent compared to just glass. Also, films that have higher resistance have less electrical conductivity, so more voltage must be applied to send a signal through it, further degrading the material. For these new hybrid films, resistance increases less over time, allowing displays from this type of film to last longer. The materials were produced in solution and at low temperature, making their production much cheaper. In addition, the hybrid films demonstrated less depreciation in their flexibility after 10,000 bending cycles than the inorganic layered films. The process means multi-layered films can be created where the layers have thicknesses usable for anti-reflective coatings, leading to potential new applications. Laurie Donaldson
307
NEWS
Electrons help image light as both particle and wave An innovative experimental technique by a team from the E´cole Polytechnique Fe´de´rale de Lausanne (EPFL) in Switzerland has helped produce the first image of light behaving simultaneously as a particle and a wave. The approach allows for the control and visualization of plasmonic fields at the nanoscale, offering potential for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits, as well as potential benefits in optical data storage devices and biosensing applications. Although previous studies have demonstrated light as either a wave or a particle, this was at different times – no experiment has managed to photograph light behaving simultaneously as both a wave and a stream of particles, despite quantum mechanics showing that light can show both natures at the same time. The experiment, as reported in Nature Communications [Piazza, et al., Nat. Commun. (2015), doi:10.1038/ncomms7407], used a pulse of laser light fired at a metallic nanowire, which added energy to the charged particles in the nanowire, resulting
Light confined on a nanowire, behaving as both particle and wave.
in it vibrating. The light can move along the wire in either direction; when waves traveling in opposite directions meet each other, they form a new wave that appears to not be moving. This standing wave then becomes the source of light for the experiment, radiating around the nanowire. At this point, the team fired a stream of electrons close to the nanowire, using them
to image the standing wave of light. As the electrons pass near to and interact with the light, they collide with the light’s particles, the photons, changing their speed. Ultrafast microscopy was used to image the position at which this change in speed took place, and visualize the standing wave. The change in speed resembles an exchange of energy ‘‘packets’’ (quanta) between the electrons and photons, proving the light on the nanowire is behaving as a particle. As team leader Fabrizio Carbone said, ‘‘This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly.’’ The researchers are continuing their measurements to expose other aspects of the complementarity principle, and investigate their implications for circuits that exploit confined electromagnetic fields for quantum devices. They are also investigating developing and characterizing photonics circuits using the same methodology. As Carbone explains, ‘‘Being able to image and control quantum phenomena at the nanometer scale like this opens up a new route towards quantum computing.’’ Laurie Donaldson
New hybrid films could make touch screens more durable A type of hybrid thin-layer film that could make touch screen displays in tablets, smart phones and computer monitors last longer has been developed in a new study by two polymer scientists from Kyungpook National University in Daegu, South Korea. The flexible thin films are comprised of both inorganic and organic materials using a sol–gel fabrication process, and could help in producing screens that are flexible and durable but still offer the same electrical and optical properties as existing screens. Touch screens are usually made up of layered thin films of indium–tin oxide of only billionths of a meter in thickness. This oxide is electrically conductive and allows electrical signals to travel from the touch location to the edge of the display where they can be sensed by the device. However, these inorganic materials are brittle and shatter easily, and use acids that corrode
the metals and metal oxides in the electronic components. An acid-free sol–gel method of synthesizing organic–inorganic hybrid materials was therefore required for optical thin-film applications. The research by Soo-Young Park and A-Ra Cho, as published in Optical Materials Express [Cho, Park, Opt. Mater. Express (2015), doi:10.1364/OME.5.000690], involved a copolymer composed of two organic materials combined with a co-polymer called trialkoxysilane. When this reacts with two other inorganic chemicals, it synthesizes hybrid layers with high and low refractive indexes. The refractive index measures the amount that light is bent as it passes through the material. However, inorganic thin-layer and hybrid films have layers with different refractive indexes, which helps tune the wavelengths of the light passing through the film (or
touch screen). Tests undertaken on the new hybrid films show that both the high and low refractive index layers are highly transparent compared to just glass. Also, films that have higher resistance have less electrical conductivity, so more voltage must be applied to send a signal through it, further degrading the material. For these new hybrid films, resistance increases less over time, allowing displays from this type of film to last longer. The materials were produced in solution and at low temperature, making their production much cheaper. In addition, the hybrid films demonstrated less depreciation in their flexibility after 10,000 bending cycles than the inorganic layered films. The process means multi-layered films can be created where the layers have thicknesses usable for anti-reflective coatings, leading to potential new applications. Laurie Donaldson
307