New quantum dot technique combines best of optical and electron microscopy
June 12, 2013 — It's not reruns of "The Jetsons," but researchers working at the National Institute of Standards and Technology (NIST) have developed a new microscopy technique that uses a process similar to how an old tube television produces a picture -- cathodoluminescence -- to image nanoscale features. Combining the best features of optical and scanning electron microscopy, the fast, versatile, and high-resolution technique allows scientists to view surface and subsurface features potentially as small as 10 nanometers in size.
The new microscopy technique, described in the journal AIP Advances, uses a beam of electrons to excite a specially engineered array of quantum dots, causing them to emit low-energy visible light very close to the surface of the sample, exploiting so-called "near-field" effects of light. By correlating the local effects of this emitted light with the position of the electron beam, spatial images of these effects can be reconstructed with nanometer-scale resolution.
The technique neatly evades two problems in nanoscale microscopy, the diffraction limit that restricts conventional optical microscopes to resolutions no better than about half the wavelength of the light (so about 250 nm for green light), and the relatively high energies and sample preparation requirements of electron microscopy that are destructive to fragile specimens like tissue.
NIST researcher Nikolai Zhitenev, a co-developer of the technique, had the idea a few years ago to use a phosphor coating to produce light for near-field optical imaging, but at the time, no phosphor was available that was thin enough. Thick phosphors cause the light to diverge, severely limiting the image resolution. This changed when the NIST researchers teamed with researchers from a company that builds highly engineered and optimized quantum dots for lighting applications. The quantum dots potentially could do the same job as a phosphor, and be applied in a coating both homogenous and thick enough to absorb the entire electron beam while also sufficiently thin so that the light produced does not have to travel far to the sample.
The collaborative effort found that the quantum dots, which have a unique core-shell design, efficiently produced low-energy photons in the visible spectrum when energized with a beam of electrons. A potential thin-film light source in hand, the group developed a deposition process to bind them to specimens as a film with a controlled thickness of approximately 50 nm.
Much like in an old tube television where a beam of electrons moves over a phosphor screen to create images, the new technique works by scanning a beam of electrons over a sample that has been coated with the quantum dots. The dots absorb the electrons' energy and emit it as visible light that interacts with and penetrates the surface over which it has been coated. After interacting with the sample, the scattered photons are collected using a closely placed photodetector, allowing an image to be constructed. The first demonstration of the technique was used to image the natural nanostructure of the photodetector itself. Because both the light source and detector are so close to the sample, the diffraction limit doesn't apply, and much smaller objects can be imaged.
"Initially, our research was driven by our desire to study how inhomogeneities in the structure of polycrystalline photovoltaics could affect the conversion of sunlight to electricity and how these devices can be improved," says Heayoung Yoon, the lead author of the paper. "But we quickly realized that this technique could also be adapted to other research regimes, most notably imaging for biological and cellular samples, wet samples, samples with rough surfaces, as well as organic photovoltaics. We are anxious to make this technique available to the wider research community and see the results."
This work was a collaboration among researchers from NIST; the Maryland NanoCenter at the University of Maryland, College Park; Worcester Polytechnic Institute; QD Vision; and Sandia National Laboratories.
Welcome to SUV System Ltd!
SUV System Ltd is ISO 90012008 Certified electronics distributor with 10 years of experiences.
We have built up long term business relationship with about many companies which are stockers and authorized agents. we have a steady and reliable supply to meet customer's demands to the greatest extent .Confidently, we are able to lower your cost and support your business with our years of professional service.
SUV System Ltd is Electronic Components Distributor Supplies,Find Quality Electronic Components Supplies Products IC(Integrated Circuits),Connectors,Capacitor,Resistors,Diodes,Transistors,LED at Suvsystem.com. Sourcing Other Energy, Environment, Excess Inventory Products from Manufacturers and Suppliers at Suvsystem.com
Electronic Components distributor:http://www.suvsystem.com
Connectors Distributor:http://www.suvsystem.com/l/Connectors-1.html
IC Distributor:http://www.suvsystem.com/l/IC(Integrated-Circuits)-1.html
LED Distributor:http://www.suvsystem.com/l/LED-1.html
Capacitor Distributor:http://www.suvsystem.com/l/Capacitor-1.html
Transistor Distributor:http://www.suvsystem.com/l/Transistors-1.html
Resistor Distributor:http://www.suvsystem.com/l/Resistors-1.html
Diode Distributor:http://www.suvsystem.com/l/Diodes-1.html
SUV System Ltd insists on the managing faith ofsincereness,speciality,foresight, win-win,so we build up stable-relationship customers located all over the world, including the States, Europe, Argentina, UAE, Malaysia, Australia,and India etc
we are focus on the following fields,and hope we can help you.
C1206T919D1GAL7800 C1206T824J3RAL7800 C1206T824J3RAL C1206T685K4RCL C1206T683J5GAL C1206T680J5GAC7800 C1206T680J5GAC C1206T475M3RAC C1206T475K8RCC7800 C1206T475K8RAC C1206T475K4RAL C1206T475K4RAC C1206T475K3RCL C1206T475K3RAC C1206T475K3PAL C1206T475K3PAC C1206T474K3RAL7800 C1206T474K3RAC C1206T470J5GCL C1206T470J5GAL7800 C1206T470J5GAL C1206T455K3PAC C1206T395K4RAL C1206T334K5RAL C1206T333K1RAL C1206T330J5GAL C1206T272G2GAL C1206T272G1GAL C1206T272G1GAC C1206T226M9PAC C1206T225K5RCL C1206T225K4RCL C1206T225K4RAL C1206T225K4RAC C1206T225K3RCG C1206T225J4RAC C1206T224K5RCL C1206T223K1RCL7800 C1206T223K1RCL C1206T223K1RAL
http://www.suvsystem.com/a/2834.aspx
没有评论:
发表评论