Science Current Events | Science News |

Photonic gels are colorful sensors

October 11, 2012

Materials scientists at Rice University and the Massachusetts Institute of Technology (MIT) have created very thin color-changing films that may serve as part of inexpensive sensors for food spoilage or security, multiband optical elements in laser-driven systems and even as part of high-contrast displays.

The new work led by Rice materials scientist Ned Thomas combines polymers into a unique, self-assembled metamaterial that, when exposed to ions in a solution or in the environment, changes color depending on the ions' ability to infiltrate the hydrophilic (water-loving) layers.

The research was published in the American Chemical Society journal ACS Nano.

The micron-thick material called a photonic gel, far thinner than a human hair, is so inexpensive to make that, Thomas said, "We could cover an area the size of a football field with this film for about a hundred dollars."

But for practical applications, much smaller pieces would do. "Suppose you want a food sensor," said Thomas, the William and Stephanie Sick Dean of Rice's George R. Brown School of Engineering and former chair of the Department of Materials Science and Engineering at MIT. "If it's inside a sealed package and the environment in that package changes because of contamination or aging or exposure to temperature, an inspector would see that sensor change from blue to red and know immediately the food is spoiled."

Such visual cues are good, he said, "especially when you need to look at a lot of them. And you can read these sensors with low tech, either with your own eyes or a spectrophotometer to scan things."

The films are made of nanoscale layers of hydrophobic polystyrene and hydrophilic poly(2-vinyl pyridine). In the liquid solution, the polymer molecules are diffused, but when the liquid is applied to a surface and the solvent evaporates, the block copolymer molecules self-assemble into a layered structure.

The polystyrene molecules clump together to keep water molecules out, while the poly(2-vinyl pyridine), P2VP for short, forms its own layers between the polystyrene. On a substrate, the layers form into a transparent stack of alternating "nano-pancakes." "The beauty of self-assembly is that it's simultaneous, all the layers forming at once," Thomas said.

The researchers exposed their films to various solutions and found different colors depending on how much solvent was taken up by the P2VP layers. For example with a chlorine/oxide/iron solution that is not readily absorbed by the P2VP, the film is transparent, Thomas said. "When we take that out, wash the film and bring in a new solution with a different ion, the color changes."

The researchers progressively turned a clear film to blue (with thiocyanate), to green (iodine), to yellow (nitrate), to orange (bromine) and finally to red (chlorine). In each case, the changes were reversible.

Thomas explained that the direct exchange of counterions from the solution to the P2VP expands those layers and creates a photonic band gap - the light equivalent of a semiconducting band gap - that allows color in a specific wavelength to be reflected. "The wavelengths in that photonic band gap are forbidden to propagate," he said, which allows the gels to be tuned to react in specific ways.

"Imagine a solid in which you create a band gap everywhere but along a 3-D path, and let's say that path is a narrowly defined region you can fabricate within this otherwise photonic material. Once you put light in that path, it is forbidden to leave because it can't enter the material, due to the band gap.

"This is called molding the flow of light," he said. "These days in photonics, people are thinking about light as though it were water. That is, you can put it in these tiny pipes. You can turn light around corners that are very sharp. You can put it where you want it, keep it from where you don't want it. The plumbing of light has been much easier than in the past, due to photonics, and in photonic crystals, due to band gaps."

Co-authors of the paper are Rice research scientist Jae-Hwang Lee and MIT postdoctoral researchers Ho Sun Lim and Joseph Walish.

The work was supported by the U.S. Army Research Office, the U.S. Air Force and the Korea Research Foundation, funded by the Korean government.

Rice University

Related Photonic Current Events and Photonic News Articles

Growing perfect crystals by filling the gaps
Crystals are solid materials composed of microscopic building blocks arranged in highly ordered patterns.

This 'nanocavity' may improve ultrathin solar panels, video cameras and more
The future of movies and manufacturing may be in 3-D, but electronics and photonics are going 2-D; specifically, two-dimensional semiconducting materials.

Stochastic resonance, chaos transfer shown in an optomechanical microresonator
Researchers in the School of Engineering & Applied Science at Washington University in St. Louis have discovered a novel route to encode chaos on light in an optomechanical microresonator system.

Nature Photonics: Light source for quicker computer chips
Worldwide growing data volumes make conventional electronic processing reach its limits.

Quantum computing closer as RMIT drives towards first quantum data bus
RMIT University researchers have trialled a quantum processor capable of routing quantum information from different locations in a critical breakthrough for quantum computing.

Physicists promise a copper revolution in nanophotonics
Researchers from the Moscow Institute of Physics and Technology (MIPT) have for the first time experimentally demonstrated that copper nanophotonic components can operate successfully in photonic devices - it was previously believed that only gold and silver components have the required properties for this.

Moving electrons around loops with light: A quantum device based on geometry
While a classical bit found in conventional electronics exists only in binary 1 or 0 states, the more resourceful quantum bit, or 'qubit' is represented by a vector, pointing to a simultaneous combination of the 1 and 0 states.

New type of optical material discovered in the secret language of the mantis shrimp
A study into how animals secretly communicate has led to the discovery of a new way to create a polarizer - an optical device widely used in cameras, DVD players and sunglasses.

Nanoscale cavity strongly links quantum particles
Scientists have created a crystal structure that boosts the interaction between tiny bursts of light and individual electrons, an advance that could be a significant step toward establishing quantum networks in the future.

NASA engineers tapped to build first integrated-photonics modem
A NASA team has been tapped to build a new type of communications modem that will employ an emerging, potentially revolutionary technology that could transform everything from telecommunications, medical imaging, advanced manufacturing to national defense.
More Photonic Current Events and Photonic News Articles

Fundamentals of Photonics

Fundamentals of Photonics
by Bahaa E. A. Saleh (Author), Malvin Carl Teich (Author)

Now in a new full-color edition, Fundamentals of Photonics, Second Edition is a self-contained and up-to-date introductory-level textbook that thoroughly surveys this rapidly expanding area of engineering and applied physics. Featuring a logical blend of theory and applications, coverage includes detailed accounts of the primary theories of light, including ray optics, wave optics, electromagnetic optics, and photon optics, as well as the interaction of photons and atoms, and semiconductor optics. Presented at increasing levels of complexity, preliminary sections build toward more advanced topics,
such as Fourier optics and holography, guided-wave and fiber optics, semiconductor sources and detectors, electro-optic and acousto-optic devices, nonlinear optical devices, optical...

Silicon-Based Photonics

Silicon-Based Photonics
by Erich Kasper (Editor), Jingzhong Yu (Editor)

This book covers the basics of band structure of silicon and germanium and their influence on photonic properties and discusses system layout and key device components with the application background in mind. Special focus is given to SOI-based interconnects and passive waveguide devices and to germanium-on-silicon heterostructure devices for light detection, modulation, and emission. The high index contrast of SOI shows great promise for submicron waveguide structures suited to integration on chip scale. The Ge/Si heterostructures have already proved the expansion of the spectral range, high-speed operation of detection, efficient modulation and switching of optical signals, and enhanced emission properties. In the research focus are chip systems with more than 100 GHz speed. The book...

Silicon Photonics Design: From Devices to Systems

Silicon Photonics Design: From Devices to Systems
by Lukas Chrostowski (Author), Michael Hochberg (Author)

From design and simulation through to testing and fabrication, this hands-on introduction to silicon photonics engineering equips students with everything they need to begin creating foundry-ready designs. In-depth discussion of real-world issues and fabrication challenges ensures that students are fully equipped for careers in industry. Step-by-step tutorials, straightforward examples, and illustrative source code fragments guide students through every aspect of the design process, providing a practical framework for developing and refining key skills. Offering industry-ready expertise, the text supports existing PDKs for CMOS UV-lithography foundry services (OpSIS, ePIXfab, imec, LETI, IME and CMC) and the development of new kits for proprietary processes and clean-room based research....

Photonics: Optical Electronics in Modern Communications 6th Edition

Photonics: Optical Electronics in Modern Communications 6th Edition

Brand New

Silicon Photonics: Fueling the Next Information Revolution

Silicon Photonics: Fueling the Next Information Revolution
by Daryl Inniss (Author), Roy Rubenstein (Author)

Silicon photonics uses chip-making techniques to fabricate photonic circuits. The emerging technology is coming to market at a time of momentous change. The need of the Internet content providers to keep scaling their data centers is becoming increasing challenging, the chip industry is facing a future without Moore’s law, while telcos must contend with a looming capacity crunch due to continual traffic growth. Each of these developments is significant in its own right. Collectively, they require new thinking in the design of chips, optical components, and systems. Such change also signals new business opportunities and disruption. Notwithstanding challenges, silicon photonics’ emergence is timely because it is the future of several industries. For the optical industry, the...

Physics of Photonic Devices

Physics of Photonic Devices
by Shun Lien Chuang (Author)

The most up-to-date book available on the physics of photonic devices This new edition of Physics of Photonic Devices incorporates significant advancements in the field of photonics that have occurred since publication of the first edition (Physics of Optoelectronic Devices). New topics covered include a brief history of the invention of semiconductor lasers, the Lorentz dipole method and metal plasmas, matrix optics, surface plasma waveguides, optical ring resonators, integrated electroabsorption modulator-lasers, and solar cells. It also introduces exciting new fields of research such as: surface plasmonics and micro-ring resonators; the theory of optical gain and absorption in quantum dots and quantum wires and their applications in semiconductor lasers; and novel microcavity and...

Optoelectronics & Photonics: Principles & Practices (2nd Edition)

Optoelectronics & Photonics: Principles & Practices (2nd Edition)
by Safa O. Kasap (Author)

For one-semester, undergraduate-level courses in Optoelectronics and Photonics, in the departments of electrical engineering, engineering physics, and materials science and engineering.
This text takes a fresh look at the enormous developments in electo-optic devices and associated materials.

Diode Lasers and Photonic Integrated Circuits

Diode Lasers and Photonic Integrated Circuits
by Larry A. Coldren (Author), Scott W. Corzine (Author), Milan L. Mashanovitch (Author)

Diode Lasers and Photonic Integrated Circuits, Second Edition provides a comprehensive treatment of optical communication technology, its principles and theory, treating students as well as experienced engineers to an in-depth exploration of this field. Diode lasers are still of significant importance in the areas of optical communication, storage, and sensing. Using the the same well received theoretical foundations of the first edition, the Second Edition now introduces timely updates in the technology and in focus of the book. After 15 years of development in the field, this book will offer brand new and updated material on GaN-based and quantum-dot lasers, photonic IC technology, detectors, modulators and SOAs, DVDs and storage, eye diagrams and BER concepts, and DFB lasers....

Wave Propagation: From Electrons to Photonic Crystals and Left-Handed Materials

Wave Propagation: From Electrons to Photonic Crystals and Left-Handed Materials
by Peter Markos (Author), Costas M. Soukoulis (Author)

This textbook offers the first unified treatment of wave propagation in electronic and electromagnetic systems and introduces readers to the essentials of the transfer matrix method, a powerful analytical tool that can be used to model and study an array of problems pertaining to wave propagation in electrons and photons. It is aimed at graduate and advanced undergraduate students in physics, materials science, electrical and computer engineering, and mathematics, and is ideal for researchers in photonic crystals, negative index materials, left-handed materials, plasmonics, nonlinear effects, and optics. Peter Markos and Costas Soukoulis begin by establishing the analogy between wave propagation in electronic systems and electromagnetic media and then show how the transfer matrix can be...

Photonics and Lasers: An Introduction

Photonics and Lasers: An Introduction
by Richard S. Quimby (Author)

An introduction to photonics and lasers that does not rely on complex mathematics

This book evolved from a series of courses developed by the author and taught in the areas of lasers and photonics. This thoroughly classroom-tested work fills a unique need for students, instructors, and industry professionals in search of an introductory-level book that covers a wide range of topics in these areas. Comparable books tend to be aimed either too high or too low, or they cover only a portion of the topics that are needed for a comprehensive treatment.

Photonics and Lasers is divided into four parts:
* Propagation of Light
* Generation and Detection of Light
* Laser Light
* Light-Based Communication

The author has ensured that...

© 2017