Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New quantum dot technique combines best of optical and electron microscopy

13.06.2013
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.


Much like in an old tube television where a beam of electrons moves over a phosphor screen to create images, the new microscopy technique works by scanning a beam of electrons over a sample that has been coated with specially engineered quantum dots. The dots absorb the energy and emit it as visible light that interacts with the sample at close range. The scattered photons are collected using a similarly closely placed photodetector (not depicted), allowing an image to be constructed.

Credit: Dill/NIST

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.

* H. Yoon, Y, Lee, C. Bohn, S. Ko, A. Gianfrancesco, J. Steckel, S. Coe-Sullivan, A. Talin and N. Zhitenev. High-resolution photocurrent microscopy using near-field cathodoluminescence of quantum dots. AIP Advances. Published online 10 June 2013.

Mark Esser | EurekAlert!
Further information:
http://www.nist.gov

More articles from Physics and Astronomy:

nachricht SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University

nachricht Molecule flash mob
19.01.2017 | Technische Universität Wien

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>