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.

RTNN researchers create first flexible memory device

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Researchers at NC State were able to deposit an ultra-thin oxide ferroelectric film onto a flexible polymer substrate for the first time. The team uses the flexible films to make non-volatile memory devices that are wearable and resilient. Ferroelectric materials can store charge, which is an ideal property for non-volatile memory devices. However, ferroelectric materials tend to be brittle and are typically made at high temperatures, which would destroy most polymers. Researchers were able to grow an extremely thin film of hafnia (20-50 nm) onto plastic substrates at low temperatures. The resulting prototype remained stable and flexible during testing and can be used in numerous applications from defense to space.

A press release can be found here.

“Flexible Inorganic Ferroelectric Thin Films for Non-Volatile Memory Devices”

Authors: Hyeonggeun Yu, Ching-Chang Chung, Nate Shewmon, Szuheng Ho, Joshua H. Carpenter, Ryan Larrabee, Tianlei Sun, Jacob L. Jones, Harald Ade, Brendan T. O’Connor, and Franky So, North Carolina State University

Published: April 12, 2017 in Advanced Functional Materials

Abstract: Next-generation wearable electronics calls for flexible non-volatile devices for ubiquitous data storage. Thus far, only organic ferroelectric materials have shown intrinsic flexibility and processibility on plastic substrates. Here, we discovered that by controlling the heating rate, ferroelectric hafnia films can be grown on plastic substrates. The resulting highly flexible capacitor with a film thickness of 30 nm yielded a remnant polarization of 10 μC cm-2. Bending test shows that the film ferroelectricity can be retained under a bending radius below 8 mm with bending cycle up to 1,000 times. The excellent flexibility is due to the extremely thin hafnia film thickness. Using the ferroelectric film as a gate insulator, a low voltage non-volatile vertical organic transistor was demonstrated on a plastic substrate with an extrapolated date retention time up to 10 years.

Scientific Art Competition – Submit your image!

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The Chapel Hill Analytical and Nanofabrication Laboratory (CHANL) is hosting its 9th annual Scientific Art Competition! The Scientific Art Competition provides an opportunity to showcase scientific data with artistic appeal. The deadline for submission is March 31, 2017. Submissions should be sent to Dr. Amar Kumbhar (akumbha@gmail.com) along with a submission form.  Anyone can submit to the CHANL scientific art competition, and the work does not need to be produced on CHANL equipment.

This year there will be twelve CASH prizes!
1)  Artist’s Choice: 1st Place: $ 50.00, and 3 finalists: $20.00 each
2)  People’s Choice: 1st Place: $ 50.00, and 3 finalists: $20.00 each
3)  Students’ Choice: 1st Place: $ 50.00, and 3 finalists: $20.00 each

Winners will be announced the week of April 23 at a lunch reception and the CHANL MRS seminar.

Please contact rtnanonetwork@ncsu.edu with questions or concerns.

 

 

New Graduate Student Opportunity: Science Outside the Lab

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“Science Outside the Lab” brings a small cohort of graduate student scientists and engineers to Washington, D.C. to explore the relationships among science, innovation, policy, and societal outcomes. This customized free one week version (June 4-10, 2017), sponsored by the Nanotechnology Collaborative Infrastructure Southwest (NCI-SW), will investigate the context of nanotechnology decision-making in government and business at the local, state, federal, and international levels. During the week-long workshop participants meet and interact with groups of people who fund, regulate, shape, critique, publicize, and study nanotechnology and other emerging technologies. This includes people like congressional staffers, lobbyists, funding agency officers, regulators, journalists, academics, museum curators, and others.

To apply to the program, complete this application and email as an attachment to CENTSS@asu.edu or fax to (480-727-8791). Application deadline: March 10, 2017. For more information, please contact Andra Williams at andra.williams@asu.edu. 

Silver nanocubes for multispectral imaging and printing

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Researchers at Duke University recently published a paper in Advanced Materials describing the development of a technique to detect light across the electromagnetic spectrum. As opposed to using materials that absorb specific wavelengths of light, silver nanocube structures trap different types of light. This can be controlled by changing the size and arrangement of the nanocubes. To learn more see the Duke press release or read the article.

“Toward Multispectral Imaging with Colloidal Metasurface Pixels“
Jon W. Stewart, Gleb M. Akselrod, David R. Smith, and Maiken H. Mikkelsen

Abstract: Multispectral colloidal metasurfaces are fabricated that exhibit greater than 85% absorption and ≈100 nm linewidths by patterning film-coupled nanocubes in pixels using a fusion of bottom-up and top-down fabrication techniques over wafer-scale areas. With this technique, the authors realize a multispectral pixel array consisting of six resonances between 580 and 1125 nm and reconstruct an RGB image with 9261 color combinations.