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Urbana, IL, United States

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Site: http://www.nanotech-now.com/

Abstract: Researchers from the University of Illinois at Urbana-Champaign have demonstrated a new approach to modifying the light absorption and stretchability of atomically thin two-dimensional (2D) materials by surface topographic engineering using only mechanical strain. The highly flexible system has future potential for wearable technology and integrated biomedical optical sensing technology when combined with flexible light-emitting diodes. "Increasing graphene's low light absorption in visible range is an important prerequisite for its broad potential applications in photonics and sensing," explained SungWoo Nam, an assistant professor of mechanical science and engineering at Illinois. "This is the very first stretchable photodetector based exclusively on graphene with strain-tunable photoresponsivity and wavelength selectivity." Graphene--an atomically thin layer of hexagonally bonded carbon atoms--has been extensively investigated in advanced photodetectors for its broadband absorption, high carrier mobility, and mechanical flexibility. Due to graphene's low optical absorptivity, graphene photodetector research so far has focused on hybrid systems to increase photoabsorption. However, such hybrid systems require a complicated integration process, and lead to reduced carrier mobility due to the heterogeneous interfaces. According to Nam, the key element enabling increased absorption and stretchability requires engineering the two-dimensional material into three-dimensional (3D) "crumpled structures," increasing the graphene's areal density. The continuously undulating 3D surface induces an areal density increase to yield higher optical absorption per unit area, thereby improving photoresponsivity. Crumple density, height, and pitch are modulated by applied strain and the crumpling is fully reversible during cyclical stretching and release, introducing a new capability of strain-tunable photoabsorption enhancement and allowing for a highly responsive photodetector based on a single graphene layer. "We achieved more than an order-of-magnitude enhancement of the optical extinction via the buckled 3D structure, which led to an approximately 400% enhancement in photoresponsivity," stated Pilgyu Kang, and first author of the paper, "Crumpled Graphene Photodetector with Enhanced, Strain-tunable and Wavelength-selective Photoresponsivity," appearing in the journal, Advanced Materials. "The new strain-tunable photoresponsivity resulted in a 100% modulation in photoresponsivity with a 200% applied strain. By integrating colloidal photonic crystal--a strain-tunable optomechanical filter--with the stretchable graphene photodetector, we also demonstrated a unique strain-tunable wavelength selectivity." "This work demonstrates a robust approach for stretchable and flexible graphene photodetector devices," Nam added. "We are the first to report a stretchable photodetector with stretching capability to 200% of its original length and no limit on detection wavelength. Furthermore, our approach to enhancing photoabsorption by crumpled structures can be applied not only to graphene, but also to other emerging 2D materials." ### In addition to Nam and Kang, study co-authors include Michael Cai Wang and Peter M. Knapp in the Department of Mechanical Science and Engineering at Illinois. The optical characterizations and partial device fabrication were carried out in the Frederick Seitz Materials Research Laboratory and the Micro and Nano Technology Laboratory at Illinois. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Abstract: Researchers from the University of Illinois at Urbana-Champaign have developed a simplified approach to fabricating flat, ultra-thin optics. The new approach enables simple etching without the use of acids or hazardous chemical etching agents. "Our method brings us closer to making do-it-yourself optics a reality by greatly simplifying the design iteration steps," explained Kimani Toussaint, an associate professor of mechanical science and engineering who led the research published this week in Nature Communications. "The process incorporates a nanostructured template that can be used to create many different types of optical components without the need to go into a cleanroom to make a new template each time a new optical component is needed. "In recent years, the push to foster increased technological innovation and basic scientific and engineering interest from the broadest sectors of society has helped to accelerate the development of do-it-yourself (DIY) components, particularly those related to low-cost microcontroller boards," Toussaint remarked. "Simplifying and reducing the steps between a basic design and fabrication is the primary attraction of DIY kits, but typically at the expense of quality. We present plasmon-assisted etching as an approach to extend the DIY theme to optics with only a modest tradeoff in quality, specifically, the table-top fabrication of planar optical components." "Our method uses the intuitive design aspects of diffractive optics by way of simple surface modification, and the electric-field enhancement properties of metal nanoantennas, which are typically the building blocks of metasurfaces," stated Hao Chen, a former postdoctoral researcher in Toussaint's lab and first author of the paper, "Towards do-it-yourself planar optical components using plasmon-assisted etching." According to Chen, laser light scans the template--a 2D array of gold pillar-supported bowtie nanoantennas (with an area of 80 x 80 square micrometers)--which is submerged in water, in a desired pattern in a microscope. The light-matter interaction, enhanced by the nanoantennas, produces a strong heating effect. As a result, the gold layer of the nanoantennas undergoes thermal expansion that works against its adhesion with their glass substrate. With certain amount of optical power, the force provided by thermal expansion allows the gold layer to break away from the substrate, etching the metal. "Overall, the workload in the cleanroom is greatly reduced," Chen noted. "Once the template is ready, it is like a paper sheet. You can 'draw' all the optical elements you need on a 'canvas' using a conventional laser-scanning optical microscope." The study demonstrated fabrication of various ultra-thin (characteristic dimension less than the optical wavelength), flat optical components using the same template. The specific optical components fabricated by the researchers included a flat focusing lens (also known as a Fresnel zone plate) with focal length of ~150 micrometers, a diffraction grating, and a holographic converter that imparts angular momentum to a standard optical beam. According to the researchers, the PAE method and specialized template could also be used to enable preferential trapping and sorting of particles, to create so-called optofluidic channels "without walls." Toussaint directs the PROBE laboratory in the Department of Mechanical Science and Engineering at Illinois. In addition to Toussaint and Chen, study co-authors include graduate student Qing Ding, former graduate student Abdul Bhuiya, and Harley T. Johnson, a professor of mechanical science and engineering at Illinois. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article
Site: http://www.nanotech-now.com/

Abstract: Researchers from the University of Illinois at Urbana-Champaign have developed a one-step, facile method to pattern graphene by using stencil mask and oxygen plasma reactive-ion etching, and subsequent polymer-free direct transfer to flexible substrates. Graphene, a two-dimensional carbon allotrope, has received immense scientific and technological interest. Combining exceptional mechanical properties, superior carrier mobility, high thermal conductivity, hydrophobicity, and potentially low manufacturing cost, graphene provides a superior base material for next generation bioelectrical, electromechanical, optoelectronic, and thermal management applications. "Significant progress has been made in the direct synthesis of large-area, uniform, high quality graphene films using chemical vapor deposition (CVD) with various precursors and catalyst substrates," explained SungWoo Nam, an assistant professor of mechanical science and engineering at Illinois. "However, to date, the infrastructure requirements on post-synthesis processing--patterning and transfer--for creating interconnects, transistor channels, or device terminals have slowed the implementation of graphene in a wider range of applications." "In conjunction with the recent evolution of additive and subtractive manufacturing techniques such as 3D printing and computer numerical control milling, we developed a simple and scalable graphene patterning technique using a stencil mask fabricated via a laser cutter," stated Keong Yong, a graduate student and first author of the paper, "Rapid Stencil Mask Fabrication Enabled One-Step Polymer-Free Graphene Patterning and Direct Transfer for Flexible Graphene Devices appearing in Scientific Reports. "Our approach to patterning graphene is based on a shadow mask technique that has been employed for contact metal deposition," Yong added. "Not only are these stencil masks easily and rapidly manufactured for iterative rapid prototyping, they are also reusable, enabling cost-effective pattern replication. And since our approach involves neither a polymeric transfer layer nor organic solvents, we are able to obtain contamination-free graphene patterns directly on various flexible substrates." Nam stated that this approach demonstrates a new possibility to overcome limitations imposed by existing post-synthesis processes to achieve graphene micro-patterning. Yong envisions this facile approach to graphene patterning sets forth transformative changes in "do It yourself" (DIY) graphene-based device development for broad applications including flexible circuits/devices and wearable electronics. "This method allows rapid design iterations and pattern replications, and the polymer-free patterning technique promotes graphene of cleaner quality than other fabrication techniques," Nam said. "We have shown that graphene can be patterned into varying geometrical shapes and sizes, and we have explored various substrates for the direct transfer of the patterned graphene." ### In addition to Nam and Yong, study co-authors include Ali Ashraf and Pilgyu Kang from the Department of Mechanical Science and Engineering at Illinois. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


"Our method brings us closer to making do-it-yourself optics a reality by greatly simplifying the design iteration steps," explained Kimani Toussaint, an associate professor of mechanical science and engineering who led the research published this week in Nature Communications. "The process incorporates a nanostructured template that can be used to create many different types of optical components without the need to go into a cleanroom to make a new template each time a new optical component is needed. "In recent years, the push to foster increased technological innovation and basic scientific and engineering interest from the broadest sectors of society has helped to accelerate the development of do-it-yourself (DIY) components, particularly those related to low-cost microcontroller boards," Toussaint remarked. "Simplifying and reducing the steps between a basic design and fabrication is the primary attraction of DIY kits, but typically at the expense of quality. We present plasmon-assisted etching as an approach to extend the DIY theme to optics with only a modest tradeoff in quality, specifically, the table-top fabrication of planar optical components." "Our method uses the intuitive design aspects of diffractive optics by way of simple surface modification, and the electric-field enhancement properties of metal nanoantennas, which are typically the building blocks of metasurfaces," stated Hao Chen, a former postdoctoral researcher in Toussaint's lab and first author of the paper, "Towards do-it-yourself planar optical components using plasmon-assisted etching." According to Chen, laser light scans the template—a 2D array of gold pillar-supported bowtie nanoantennas (with an area of 80 x 80 square micrometers)—which is submerged in water, in a desired pattern in a microscope. The light-matter interaction, enhanced by the nanoantennas, produces a strong heating effect. As a result, the gold layer of the nanoantennas undergoes thermal expansion that works against its adhesion with their glass substrate. With certain amount of optical power, the force provided by thermal expansion allows the gold layer to break away from the substrate, etching the metal. "Overall, the workload in the cleanroom is greatly reduced," Chen noted. "Once the template is ready, it is like a paper sheet. You can 'draw' all the optical elements you need on a 'canvas' using a conventional laser-scanning optical microscope." The study demonstrated fabrication of various ultra-thin (characteristic dimension less than the optical wavelength), flat optical components using the same template. The specific optical components fabricated by the researchers included a flat focusing lens (also known as a Fresnel zone plate) with focal length of ~150 micrometers, a diffraction grating, and a holographic converter that imparts angular momentum to a standard optical beam. According to the researchers, the PAE method and specialized template could also be used to enable preferential trapping and sorting of particles, to create so-called optofluidic channels "without walls." Toussaint directs the PROBE laboratory in the Department of Mechanical Science and Engineering at Illinois. In addition to Toussaint and Chen, study co-authors include graduate student Qing Ding, former graduate student Abdul Bhuiya, and Harley T. Johnson, a professor of mechanical science and engineering at Illinois. More information: Hao Chen et al. Towards do-it-yourself planar optical components using plasmon-assisted etching, Nature Communications (2016). DOI: 10.1038/ncomms10468


Han K.,Mechanical Science and Engineering | Kim J.H.,Mechanical Science and Engineering | Bahl G.,Mechanical Science and Engineering
Optics Express | Year: 2014

Recently, the first microfluidic optomechanical device was demonstrated, capable of operating with non-solid states of matter (viscous fluids, bioanalytes). These devices exhibit optomechanical oscillation in both the 10-20 MHz and 10-12 GHz regimes, driven by radiation pressure (RP) and stimulated Brillouin scattering (SBS) respectively. In this work, we experimentally investigate aerostatic tuning of these hollow-shell oscillators, enabled by geometry, stress, and temperature effects. We also demonstrate for the first time the simultaneous actuation of RP-induced breathing mechanical modes and SBS-induced whispering gallery acoustic modes, through a single pump laser. Our result is a step towards completely self-referenced optomechanical sensor technologies.©2014 Optical Society of America. Source

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