Crystals shape-shift with UV exposure

May 1, 2001
Strange crystals studied using atomic force microscopy (ATM) have been found by researchers to change shape upon exposure to ultraviolet (UV) light.
Th 0501news09

Strange crystals studied using atomic force microscopy (ATM) have been found by researchers to change shape upon exposure to ultraviolet (UV) light. The surface of the colorless crystal also underwent a thermally stable color change to blue, but returned to its original shape and clear color upon re-radiation with visible light. Such morphological change may have application in switching or redirecting optical signals without the need for electronics or microelectromechanical systems with moving parts.

Masahiro Irie, Seiya Kobatake, and Masashi Horichi of the Department of Chemistry and Biochemistry at Kyushu Univeristy, and CREST, Japan Science and Technology Corporation (Fukoka, Japan), illuminated the surface of diarylethene single crystals with UV light (366 nm) for a minimum of 10 s at 12 mW/cm2. This drove reversible photocyclization reactions that created a series of 5 to 10 steps on the (100) surface. The step height of 1.0 ± 0.1 nm corresponds to one molecular layer. With prolonged irradiation time, more steps with heights of 2.0 ± 0.2 nm and 3.0 ± 0.3 nm appeared. The height was always a multiple of the minimum step height (1.0 ± 0.1 nm), and the team did not observe any steps with a height lower than one molecular layer (see figure).

The steps remained stable until exposed to visible light (500 nm), which restored the colorless, smooth-surface topology. The light-dependent coloration-decoloration cycles were repeatable more than 10,000 times without changing the shape of the crystal. In addition, the photo-generated color states remained stable at temperatures up to 100°C.

Using absorption anisotropy (polar plot) analysis, Irie and colleages found that the UV-irradiated single crystal undergoes a shortening in the distance between the phenyl ring edges. The shrinking of molecular layers produces vacancies in the crystal bulk, which allows the surface to sink as much as one layer. The reactions take place as deep as 500 µm.

Photochromism is the color change of a chemical species by photoirradiation. Although various kinds of photochromic crystals have been developed, the reversible quality is very rare. Photochromic single crystals may have use in holographic and three-dimensional memories. The reversible morphological changes discovered may have use in photodriven, nanometer-scale actuators.

About the Author

Valerie Coffey-Rosich | Contributing Editor

Valerie Coffey-Rosich is a freelance science and technology writer and editor and a contributing editor for Laser Focus World; she previously served as an Associate Technical Editor (2000-2003) and a Senior Technical Editor (2007-2008) for Laser Focus World.

Valerie holds a BS in physics from the University of Nevada, Reno, and an MA in astronomy from Boston University. She specializes in editing and writing about optics, photonics, astronomy, and physics in academic, reference, and business-to-business publications. In addition to Laser Focus World, her work has appeared online and in print for clients such as the American Institute of Physics, American Heritage Dictionary, BioPhotonics, Encyclopedia Britannica, EuroPhotonics, the Optical Society of America, Photonics Focus, Photonics Spectra, Sky & Telescope, and many others. She is based in Palm Springs, California. 

Sponsored Recommendations

Monolithic integration of functional structures into micro-optical elements

Dec. 6, 2023
A polymer-only ultraviolet imprint process potentially saves costs, simplifies the process, and increases the reliability of the optical element.

Manufacturing thin films with tailor-made electronic properties

Dec. 5, 2023
Unlock the future of optoelectronics as researchers at Leibniz IPHT in Jena, Germany unveil an innovative technique for precision deposition of thin organic semiconductor films...

Quantitative Microscopy with Deep Learning

Dec. 5, 2023
Explore the untapped potential of deep learning in video microscopy with our cutting-edge software, DeepTrack 2.2. Overcoming the steep learning curve, this innovative application...

Stimulated Brillouin scattering enhances CMOS chip for microwave signal processing

Dec. 5, 2023
University of Sydney Nano Institute researchers are pioneering photonic silicon chips and helping spur growth in Australia’s semiconductor industry.

Voice your opinion!

To join the conversation, and become an exclusive member of Laser Focus World, create an account today!