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 Turmoil in sluggish electrons’ existence
23.05.2017 | Max-Planck-Institut für Quantenoptik

nachricht Physicists discover that lithium oxide on tokamak walls can improve plasma performance
22.05.2017 | DOE/Princeton Plasma Physics Laboratory

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: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

Im Focus: Using graphene to create quantum bits

In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.

In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...

Im Focus: Bacteria harness the lotus effect to protect themselves

Biofilms: Researchers find the causes of water-repelling properties

Dental plaque and the viscous brown slime in drainpipes are two familiar examples of bacterial biofilms. Removing such bacterial depositions from surfaces is...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

Innovation 4.0: Shaping a humane fourth industrial revolution

17.05.2017 | Event News

 
Latest News

Supercomputing helps researchers understand Earth's interior

23.05.2017 | Earth Sciences

Study identifies RNA molecule that shields breast cancer stem cells from immune system

23.05.2017 | Life Sciences

Turmoil in sluggish electrons’ existence

23.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>