Tag Archives: light

Researchers Use Gold Nanoparticles to Unfold 3-D Structures

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Researchers at NC State have developed a technique that uses nanoparticles, nanospheres and nanorods, to trigger shape changes in polymers. These differently shaped nanoparticles exhibit different surface plasmon resonances and will heat when exposed to specific wavelengths of light. When embedded in polymers, this causes the material to heat and change its shape. This work has the potential for use in soft robotics applications like biomedical implants. For more on this work, please see the NC State press release.

“Sequential Actuation of Shape-Memory Polymers through Wavelength-Selective Photothermal Heating of Gold Nanospheres and Nanorods”

Authors: Sumeet R. Mishra and Joseph B. Tracy, North Carolina State University

Published: June 15, Applied Nano Materials

DOI: 10.1021/acsanm.8b00394

Abstract: Photothermal triggering of shape-memory polymers is an appealing noncontact mode of actuation for responsive materials and soft robotics. Wavelength-selective photothermal triggering of shape recovery is reported in thermoplastic polyurethane shape-memory polymers with embedded gold (Au) nanospheres and nanorods. Light-emitting diodes with wavelengths of 530 and 860 nm matched to the surface plasmon resonances drive selective shape recovery. Wavelength-selective shape recovery enables sequential actuation, as demonstrated in a wavelength-controlled stage with optically controlled height and tilt angle using legs of shape-memory-polymer films with embedded Au nanospheres and nanorods.

 

Researchers use electric fields to control light

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Scientists at NC State have developed a new method to control light. To do this, they use electric fields to change the refractive index of materials. Researchers investigated thin films of semiconductor materials: molybdenum sulfide, tungsten sulfide and tungsten selenide. In some of these materials, the refractive index was changed by as much as 60 percent.

A press release can be found here.

“Giant Gating Tunability of Optical Refractive Index in Transition Metal Dichalcogenide Monolayers”

Authors: Yiling Yu, Yifei Yu, Lujun Huang and Linyou Cao, North Carolina State University; Haowei Peng, Temple University; and Liwei Xiong, Wuhan Institute of Technology

Published: May 15, 2017, Nano Letters

Abstract: We report that the refractive index of transition metal dichacolgenide (TMDC) monolayers, such as MoS2, WS2, and WSe2, can be substantially tuned by > 60% in the imaginary part and > 20% in the real part around exciton resonances using CMOS-compatible electrical gating. This giant tunablility is rooted in the dominance of excitonic effects in the refractive index of the monolayers and the strong susceptibility of the excitons to the influence of injected charge carriers. The tunability mainly results from the effects of injected charge carriers to broaden the spectral width of excitonic interband transitions and to facilitate the interconversion of neutral and charged excitons. The other effects of the injected charge carriers, such as renormalizing bandgap and changing exciton binding energy, only play negligible roles. We also demonstrate that the atomically thin monolayers, when combined with photonic structures, can enable the efficiencies of optical absorption (reflection) tuned from 40% (60%) to 80% (20%) due to the giant tunability of refractive index. This work may pave the way towards the development of field-effect photonics in which the optical functionality can be controlled with CMOS circuits.

National Nanotechnology Day

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National Nanotechnology Day will be held on October 9, 2016. Several events have been scheduled in celebration. More details regarding these events can be found here.