Tag Archives: semiconductor

Strain Improves Performance of Atomically Thin Semiconductor

Researchers in UConn’s Institute of Materials Science significantly improved the performance of an atomically thin semiconductor material by stretching it, an accomplishment that could prove beneficial to engineers designing the next generation of flexible electronics, nano devices, and optical sensors.

In a study appearing in the research journal Nano Letters, Michael Pettes, assistant professor of mechanical engineering, reports that a six-atom thick bilayer of tungsten diselenide exhibited a 100-fold increase in photoluminescence when it was subjected to strain. The material had never exhibited such photoluminescence before.

The findings mark the first time scientists have been able to conclusively show that the properties of atomically thin materials can be mechanically manipulated to enhance their performance, Pettes says. Such capabilities could lead to faster computer processors and more efficient sensors.

The process the researchers used to achieve the outcome is also significant in that it offers a reliable new methodology for measuring the impact of strain on ultrathin materials, something that has been difficult to do and a hindrance to innovation.

Experiments involving strain are often criticized since the strain experienced by these atomically thin materials is difficult to determine and often speculated as being incorrect,” says Pettes. “Our study provides a new methodology for conducting strain-dependent measurements of ultrathin materials, and this is important because strain is predicted to offer orders of magnitude changes in the properties of these materials across many different scientific fields.”

Source: https://today.uconn.edu/

A stamp-sized nanofilm stores more data than 200 DVDs

Ninety percent of the world’s data has been created in the last two years, with a massive 2.5 quintillion bytes generated every single day. As you might suspect, this causes some challenges when it comes to storage. While one option is to gradually turn every square inch of free land into giant data centers, researchers from the  Center for Advanced Optoelectronic Functional Material Research, Northeast Normal University (China) may have come up with a more elegant solution. In a potential breakthrough, they have developed a new nanofilm80 times thinner than a human hair — that is able to store large amounts of data holographically. A single 10-by-10 cm piece of this film could archive more than 1,000 times the amount of data found on a DVD. By our count, that means around 8.5 TB of data. This data can also be retrieved incredibly quickly, at speeds of up to 1GB per second: The equivalent of 20 times the reading speed of modern flash memory.

In the journal Optical Materials Express, the researchers detail the fabrication process of the new film. This involves using a laser to write information onto silver nanoparticles on a titanium dioxide (titania) semiconductor film. This stores the data in the form of 3D holograms, thereby allowing it to be compressed into smaller spaces than regular optical systems.

That’s exciting enough, but what really makes the work promising is the fact that the data is stored in a way that is stable. Previous attempts at creating films for holographic data storage have proven less resilient than alternate storage methods since they can be wiped by exposure to ultraviolet light. That makes them less-than-viable options for long-term information storage. The creators of this new film, however, have shown that it has a high stability even in the presence of such light. This environmental stability means that the device could be used outside — or even conceivably in harsher radiation conditions like outer space.

Going forward, the researchers aim to test their new film by putting it through its paces outdoors. Should all go according to plan, it won’t be too long before this is available on the market. We might be willing to throw down a few bucks on Kickstarter for a piece!

Source: https://www.osapublishing.org

Squeeze And Get More Power Out Of Solar Cells

Physicists at the University of Warwick have published new research in the Journal Science  that could literally squeeze more power out of solar cells by physically deforming each of the crystals in the semiconductors used by photovoltaic cells. The paper entitled the “Flexo-Photovoltaic Effect” was written by Professor Marin Alexe, Ming-Min Yang, and Dong Jik Kim who are all based in the University of Warwick’s Department of Physics.

The Warwick researchers looked at the physical constraints on the current design of most commercial solar cells which place an absolute limit on their efficiency. Most commercial solar cells are formed of two layers creating at their boundary a junction between two kinds of semiconductors, p-type with positive charge carriers (holes which can be filled by electrons) and n-type with negative charge carriers (electrons). When light is absorbed, the junction of the two semiconductors sustains an internal field splitting the photo-excited carriers in opposite directions, generating a current and voltage across the junction. Without such junctions the energy cannot be harvested and the photo-exited carriers will simply quickly recombine eliminating any electrical charge. That junction between the two semiconductors is fundamental to getting power out of such a solar cell but it comes with an efficiency limit. This Shockley-Queisser Limit means that of all the power contained in sunlight falling on an ideal solar cell in ideal conditions only a maximum of 33.7% can ever be turned into electricity.

There is however another way that some materials can collect charges produced by the photons of the sun or from elsewhere. The bulk photovoltaic effect occurs in certain semiconductors and insulators where their lack of perfect symmetry around their central point (their non-centrosymmetric structure) allows generation of voltage that can be actually larger than the band gap of that material. Unfortunately the materials that are known to exhibit the anomalous photovoltaic effect have very low power generation efficiencies, and are never used in practical power-generation systems. The Warwick team wondered if it was possible to take the semiconductors that are effective in commercial solar cells and manipulate or push them in some way so that they too could be forced into a non-centrosymmetric structure and possibly therefore also benefit from the bulk photovoltaic effect.

Extending the range of materials that can benefit from the bulk photovoltaic effect has several advantages: it is not necessary to form any kind of junction; any semiconductor with better light absorption can be selected for solar cells, and finally, the ultimate thermodynamic limit of the power conversion efficiency, so-called Shockley-Queisser Limit, can be overcome“,  explains Professor Marin Alexe  (University of Warwick).

Source: https://warwick.ac.uk/