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Quantum Dots

Researchers develop quantum dot microscope for measuring electric potentials of atoms

A group of scientists from Jülich in collaboration with the University of Magdeburg has developed a new technique for measuring the electric potentials of a sample with accuracy to the atomic level. Using normal methods, it was almost impossible until now to measure the electric potentials which occur in the vicinity of individual molecules. The scanning quantum dot microscopy method, which was presented in the Nature Materials journal by researchers from Forschungszentrum Jülich in collaboration with other institutes, could open new possibilities in chip manufacturing or biomolecule characterization.

All matter consists of a positive nucleus of the atom and negative electrons. They generate electric potential fields which superpose and compensate the other, even at very small distances. Conventional methods do not allow for the measurements of these fields, that are responsible for many nanoscale properties and functions. Almost all the methods which are in use today are capable of imaging potentials which are based on the forces due to the electric charges. However, these forces are difficult to distinguish from other ones occurring at the nanoscale, that prevents measurements.

Researchers from Forschungszentrum Jülich, four years ago discovered a technique based on a different principle. Scanning quantum dot microscopy involves attachment of one organic molecule, quantum dot—to atomic microscope’s tip. This molecule acts as a  probe. Dr. Christian Wagner, lead researcher at the Controlled Mechanical Manipulation of Molecules group at Peter Grünberg Institute said that due to the small size of the molecule, individual electrons can be attached from atomic microscope’s tip to the molecule in a very controlled way.

Scientists recognized that this method can open up new avenues and hence filed a patent for it. But it could not be used in real experiments immediately. Initially, there were some limitations to its practical use. But now, the electric fields of individual atoms can be visualized and also precisely quantified. This was confirmed by comparing with theoretical calculations which were done by researchers at Luxembourg. Besides this, large areas of a sample can be imaged and the nanostructures can be displayed at once.

The researchers at Jülich spent a lot of time in investigating the technique and then developed a coherent theory for it. The very sharp images are possible due to the large separation from the sample which is permitted by the microscope tip, something beyond the ability of normal atomic force microscopes.

Engineers from Otto von Guericke University, Magdeburg developed a controller for automating the repeated sequence of scanning the sample. With the controller, now simply the whole surface can be scanned in an hour, whereas earlier it took 5-6 hours for a molecule. However, preparing the atomic dot takes lots of time but scientists are optimistic in overcoming this and applying it to challenging problems.

Quantum Dots with emission maxima in a 10-nm step are being produced at PlasmaChem in a kg scale

Researchers achieved near-perfect performance in low-cost semiconductors

Nowadays the whole world has become digitalized and for each and everything we have an electronic device. We have a television to entertain ourselves, an iPad to watch movies and work on the go, a mobile to receive calls when we are away from home. These electronic devices have something called as the semiconductor.

A semiconductor is a substance whose electrical conductance falls between metal and insulator. However, the conducting property can be altered by adding impurities into the crystal. Some commonly known semiconductors are silicon, germanium, and arsenide. Since it becomes very difficult to produce, semiconductor becomes very expensive.

Quantum dot is the solution and can be used in place of a semiconductor. Quantum dots are basically very small semiconductors which lie in the nanometre scale. Quantum dots change its properties even with a very small change in shape or size. The quantum dots have been used in electronic instruments like solar panels, camera sensors and medical imaging tools by researchers.

David Hanifi co-author of research on quantum dots said, “These quantum dots can be made in large number in labs in a more simple way as compared to semiconductor”.

When the research started in order to understand whether they could compete with semiconductors, the researchers focused on how efficiently the quantum dots could remit the light that they absorb, and the experiments showed that the performance of quantum dots was better as compared to a semiconductor.

This research work is the result of a collaboration between the labs of Alberto Salleo, professor of materials science and engineering at Stanford, and Paul Alivisatos, the Samsung Distinguished Professor of Nanoscience and Nanotechnology at the University of California, Berkeley, who is a pioneer in quantum dot research and senior author of the paper. However, this research is a part of the collection of projects of the Department of Energy at the Frontier Research Centre.

There are various benefits that quantum dots have. Being highly customizable, one of the biggest benefits of quantum dots is that it changes its shape due to which it can change the wavelength of light that they emit which is one of the biggest advantages in colour based applications like television.

Thus, quantum dots have hit the consumer market in the form of quantum dot TV or the QLED(where Q stands for quantum dots).

Samsung QLED TV

Samsung QLED TV 8K – 75 inches. Credit: Bretwa/ wikimedia

As we all know that everything in this universe comes with its own disadvantages, the disadvantage that the quantum dot has is that because of its smaller size – it takes many particles to come together in order to perform a particular task. In order to form so many quantum dots, the chances of something going wrong becomes highly possible, which indirectly means that the chances of some program to go wrong also becomes possible due to which there are chances of performance getting hampered.

The researchers are finding out measurement techniques in order to evaluate these particles.

The next step in the ongoing research involves even more precise measurements and if the researchers can determine that, these quantum dots could reach an efficiency of 99.9 percent or above.

With the increase in efficiency, we can have wonderful applications like:

  • New glowing dyes to enhance our ability to look at biology at the atomic scale.
  • Luminescent cooling and luminescent solar concentrators, which allow a relatively small set of solar cells to take in energy from a large area of solar radiation and many more things.

People working on these quantum dot materials have thought for more than a decade that dots could be as efficient as single crystal materials,” said Hanifi.

So, Let us hope for this research to go forward and get us many other efficient applications.

Published Researchhttp://science.sciencemag.org/content/363/6432/1199