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Seeing in the dark
RESEARCH NEWS
Seeing in the dark OPTICAL MATERIALS Over the last two decades, significant research effort has been applied to developing organic light-emitting diodes (OLEDs). To date, this area has focused on devices that emit in the visible part of the spectrum, with recent interest growing in OLEDs that emit in the near-infrared (NIR) region (700-2500 nm). A team of researchers from the University of Southern California (USC), Princeton University, the University of Michigan, and Universal Display Corporation has synthesized a highly efficient NIR OLED based on a phosphorescent Pt-metalloporphyrin complex [Borek et al., Angew. Chem., Int. Ed. (2007) 46, 1109]. This development opens the door for the use of these NIR OLEDs in applications such as night-visionreadable displays and sensors. OLEDs have emissive layers that, until now, have been doped with fluorescent dyes. However, the efficiency of OLEDs improves significantly if the fluorescent emissive dopants are replaced with phosphorescent heavymetal complexes. In this work, the researchers focused on PtII-tetraphenyltetrabenzoporphyrin [Pt(tpbp)] as a phosphorescent dopant. Their results demonstrate that the [Pt(tpbp)] devices are stable at high currents, although further study is required to determine the device lifetime at radiances suitable for display use, assuming the viewer is using night-vision goggles. The half-life of the device is too long to measure, but the researchers report ~90% lifetime of >1000 hours, when the device is run at 40 mA/cm2 and a brightness of over 0.7 mW/cm2. “Our next step is to push the emission energy deeper into the NIR to see how far we can go,” comments lead researcher, Mark E. Thompson of USC.
Catherine Reinhold
Nanocolumns respond to stimuli NANOTECHNOLOGY
in a fast reversible reorientation Materials and devices that of the nanocolumns with respect change properties and function to the surface, from tilted to in response to external stimuli perpendicular. One of the major are the focus of research strengths of this system is the from across the scientific ability to form a variety of and engineering community. elaborate micropatterns with Researchers from Bell complex geometries by controlling Laboratories/Alcatel-Lucent the stress field in the hydrogel. and the Max Planck Institute “The design was inspired by of Colloids and Interfaces, An example of a complex hybrid architecture biological structures, such as Germany have demonstrated pattern, showing an array of microtraps, carnivorous plants or pedicellaria an unprecedented phenomenon in which every group of four attached – surface nanostructures that nanocolumns is held together by the hydrogel. (multijawed microforcepslike structures found on dynamically and reversibly (© 2007 AAAS.) Echinoderms),” says Joanna change their orientation in Aizenberg of Bell Laboratories. “But we took it from the response to external stimuli, forming highly-controlled, macroscale (as seen in plants) or from the 100 micron complex microstructures [Sidorenko et al., Science scale (as seen in Echinoderms) to a nanometer scale.” (2007) 315, 487]. A detailed mechanical assessment of the system These remarkable, reversible rearrangements of surface suggests that it is possible to design a hydrogel/ features in a controlled and ordered fashion have not nanocolumn combination that enables a desired degree been reported either for all-soft, all-hard, or hybrid of directed actuation. The results provide evidence that structures. it might be possible to exploit the variety of unique, The team have designed a dynamic actuator by complex movements of the nanostructures to create integrating high-aspect-ratio Si nanocolumns, either patterns at the micron scale, for example in actuators, free-standing or substrate-attached, with a hydrogel microfluidics, tunable photonic structures, and artificial layer. The nanocolumns are set in motion by the muscle. ‘muscle’ of the hydrogel, which swells or contracts Catherine Reinhold depending on the humidity level. This movement results
Memory circuit shrinks further ELECTRONIC MATERIALS Development of dynamic random A monolayer of bistable, [2]rotaxane access memory (DRAM) circuits will molecules serves as the data storage be an intergral part of improving elements. Although the fabricated integrated circuit (IC) technology circuit has large numbers of defects, in the future. Improving DRAM these can be identified through requires reduction in the size of the electronic testing and isolated using memory cell and also the spacing, software coding. The working bits or pitch, between the most closely are then configured to form a fully spaced wires within a DRAM circuit. functional random access memory However, a large proportion of circuit for storing and retrieving Electron micrograph showing some of the the patterning and materials information. The fabricated electronic detail of the memory circuit. (Courtesy of James R. Heath.) requirements that are expected to memory circuit is about 40 times be required for the construction of more dense than existing circuits. new IC technologies in the 2013 timeframe currently have “The research was a scientific demonstration rather than no known solution. Researchers from the California Institute a technology demonstration,” emphasises lead researcher, of Technology and the University of California, Los Angeles James R. Heath. “Our memory worked, but it has a long way have brought a solution a step closer by fabricating a 160 kB to go before it could even be considered for commercial memory circuit with a density of 1011 bits/cm2 [Green et al., applications.” Nature (2007) 445, 414]. Catherine Reinhold
MARCH 2007 | VOLUME 10 | NUMBER 3
13
Seeing in the dark OPTICAL MATERIALS Over the last two decades, significant research effort has been applied to developing organic light-emitting diodes (OLEDs). To date, this area has focused on devices that emit in the visible part of the spectrum, with recent interest growing in OLEDs that emit in the near-infrared (NIR) region (700-2500 nm). A team of researchers from the University of Southern California (USC), Princeton University, the University of Michigan, and Universal Display Corporation has synthesized a highly efficient NIR OLED based on a phosphorescent Pt-metalloporphyrin complex [Borek et al., Angew. Chem., Int. Ed. (2007) 46, 1109]. This development opens the door for the use of these NIR OLEDs in applications such as night-visionreadable displays and sensors. OLEDs have emissive layers that, until now, have been doped with fluorescent dyes. However, the efficiency of OLEDs improves significantly if the fluorescent emissive dopants are replaced with phosphorescent heavymetal complexes. In this work, the researchers focused on PtII-tetraphenyltetrabenzoporphyrin [Pt(tpbp)] as a phosphorescent dopant. Their results demonstrate that the [Pt(tpbp)] devices are stable at high currents, although further study is required to determine the device lifetime at radiances suitable for display use, assuming the viewer is using night-vision goggles. The half-life of the device is too long to measure, but the researchers report ~90% lifetime of >1000 hours, when the device is run at 40 mA/cm2 and a brightness of over 0.7 mW/cm2. “Our next step is to push the emission energy deeper into the NIR to see how far we can go,” comments lead researcher, Mark E. Thompson of USC.
Catherine Reinhold
Nanocolumns respond to stimuli NANOTECHNOLOGY
in a fast reversible reorientation Materials and devices that of the nanocolumns with respect change properties and function to the surface, from tilted to in response to external stimuli perpendicular. One of the major are the focus of research strengths of this system is the from across the scientific ability to form a variety of and engineering community. elaborate micropatterns with Researchers from Bell complex geometries by controlling Laboratories/Alcatel-Lucent the stress field in the hydrogel. and the Max Planck Institute “The design was inspired by of Colloids and Interfaces, An example of a complex hybrid architecture biological structures, such as Germany have demonstrated pattern, showing an array of microtraps, carnivorous plants or pedicellaria an unprecedented phenomenon in which every group of four attached – surface nanostructures that nanocolumns is held together by the hydrogel. (multijawed microforcepslike structures found on dynamically and reversibly (© 2007 AAAS.) Echinoderms),” says Joanna change their orientation in Aizenberg of Bell Laboratories. “But we took it from the response to external stimuli, forming highly-controlled, macroscale (as seen in plants) or from the 100 micron complex microstructures [Sidorenko et al., Science scale (as seen in Echinoderms) to a nanometer scale.” (2007) 315, 487]. A detailed mechanical assessment of the system These remarkable, reversible rearrangements of surface suggests that it is possible to design a hydrogel/ features in a controlled and ordered fashion have not nanocolumn combination that enables a desired degree been reported either for all-soft, all-hard, or hybrid of directed actuation. The results provide evidence that structures. it might be possible to exploit the variety of unique, The team have designed a dynamic actuator by complex movements of the nanostructures to create integrating high-aspect-ratio Si nanocolumns, either patterns at the micron scale, for example in actuators, free-standing or substrate-attached, with a hydrogel microfluidics, tunable photonic structures, and artificial layer. The nanocolumns are set in motion by the muscle. ‘muscle’ of the hydrogel, which swells or contracts Catherine Reinhold depending on the humidity level. This movement results
Memory circuit shrinks further ELECTRONIC MATERIALS Development of dynamic random A monolayer of bistable, [2]rotaxane access memory (DRAM) circuits will molecules serves as the data storage be an intergral part of improving elements. Although the fabricated integrated circuit (IC) technology circuit has large numbers of defects, in the future. Improving DRAM these can be identified through requires reduction in the size of the electronic testing and isolated using memory cell and also the spacing, software coding. The working bits or pitch, between the most closely are then configured to form a fully spaced wires within a DRAM circuit. functional random access memory However, a large proportion of circuit for storing and retrieving Electron micrograph showing some of the the patterning and materials information. The fabricated electronic detail of the memory circuit. (Courtesy of James R. Heath.) requirements that are expected to memory circuit is about 40 times be required for the construction of more dense than existing circuits. new IC technologies in the 2013 timeframe currently have “The research was a scientific demonstration rather than no known solution. Researchers from the California Institute a technology demonstration,” emphasises lead researcher, of Technology and the University of California, Los Angeles James R. Heath. “Our memory worked, but it has a long way have brought a solution a step closer by fabricating a 160 kB to go before it could even be considered for commercial memory circuit with a density of 1011 bits/cm2 [Green et al., applications.” Nature (2007) 445, 414]. Catherine Reinhold
MARCH 2007 | VOLUME 10 | NUMBER 3
13