Feb 17 2015
North Carolina State University (NC State) has led a team of researchers that has synthesized a material for creating plasmonic devices that respond efficiently to mid-infrared (IR) range light. This material has potential applications in various fields including solar energy, biomedical devices and high-speed computers.
When the interface between an insulating material and a conducting material are illuminated, the surface plasmon resonance phenomenon comes into play. The electrons in the conductor commence oscillating when the incoming light has suitable wavelength, polarization and angle. An intense electric field is created by this oscillation that extends into the insulator, and this field can be used in a wide range of applications including solar cells, opto-electronic devices and biomedical sensors.
The conductive material’s nature influences the wavelength of light that creates these oscillations. Materials such as metals have a high density of free electrons. These materials respond to light in the ultraviolet range and other such short wavelengths of light. However, researchers have not been able to identify materials that have the ability to support surface plasmon resonance efficiently, when targeted with light in the mid-IR range wavelength, which would be in the range between 1,500 and 4,000 wavenumbers.
There are at least three practical reasons for wanting to identify materials that exhibit surface plasmon resonance in response to mid-IR light. First, it could make solar harvesting technology more efficient by taking advantage of the mid-IR wavelengths of light – that light wouldn’t be wasted. Second, it would allow us to develop more sophisticated molecular sensing technology for use in biomedical applications. And third, it would allow us to develop faster, more efficient opto-electronic devices.
Dr. Jon-Paul Maria, corresponding author of a paper on the work and a professor of materials science and engineering at NC State.
“We’ve now synthesized such a material, and shown that it effectively exhibits low-loss surface plasmon resonance in the mid-IR range,” Maria says. This would mean that mid-IR light is converted into oscillating electrons efficiently.
The researchers had doped cadmium oxide with dysprosium, which is a rare earth element. The doping process means that without changing the crystal structure of cadmium oxide, dysprosium has been added in very small quantities. This doping leads to the creation of free electrons in the material and also increases the electron’s mobility. The doping process enables mid-IR light to efficiently stimulate oscillations in the electrons.
Usually when you dope a material, electron mobility goes down, but in this case we found the opposite – more dysprosium doping increases this critical characteristic. In technical terms, our experiments revealed that Dy-doping reduces the number of oxygen vacancies in a CdO crystal. Oxygen vacancies, which correspond to locations where oxygen atoms are missing, are strong electron scatterers and interfere with electron motion. In the most basic terms, by removing these defects, electrons scatter less and become more mobile.
Dr. Jon-Paul Maria, corresponding author of a paper on the work and a professor of materials science and engineering at NC State.
This study has been published in the journal Nature Materials as a paper titled “Dysprosium doped cadmium oxide: A gateway material for mid-infrared plasmonics.” Edward Sachet, an NC State Ph.D. student is the lead author of this paper. The study’s coauthors include Christopher Shelton, Benjamin Gaddy, Stefan Franzen, Joshua Harris, and Drs. Doug Irving from NC State; Drs. Ana Lima Sharma, Jon Ihlefeld and Peter Sharma from the Sandia National Laboratories; Dr. Patrick Hopkins and Brian Donovan from the University of Virginia; and Dr. Stefano Curtarolo from the Duke University.
The National Science Foundation, the Air Force Office of Scientific Research and the Office of Naval Research had supported this project with grants.
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