Semiconductor nanostructures are poised to play a big role in future solar-powered hydrogen generation systems, according to a new study by researchers at the A*STAR Institute of High Performance Computing1. Hui Pan and Yong-Wei Zhang report that model interfaces made from gallium nitride (GaN) and zinc oxide (ZnO) semiconductors have tunable magnetic and light-harvesting capabilities — factors that can greatly improve the photocatalytic transformation of water into hydrogen fuel.
Semiconductors fabricated into stacked, nanometer-thin layers (left, schematic illustration; right, atomic structure) can harvest solar energy with striking efficiency.
© 2012 Elsevier
Most photoelectrochemical cells use titanium dioxide electrodes to absorb light and split water molecules into hydrogen and oxygen gas. But because this mineral has a large bandgap — a measure of energy needed to initiate photoreactions — these devices respond only to a tiny fraction of the solar spectrum. A promising way to boost this efficiency is with ‘superlattice’ materials that stack two different semiconductors into alternate, nanometer-thin layers.
The two-dimensional channels that emerge from superlattices resemble conductive nanowires for swift charge-carrier movement. Bandgaps in these hetero-nanostructures have a demonstrated dependence on semiconductor composition and layer thickness.
Pan and Zhang investigated superlattices based on stacked GaN and ZnO layers, two semiconductors with similar electronic and structural properties that are widely used in optoelectronic devices. Using density functional theory calculations, they optimized a periodic GaN–ZnO model superlattice (see image). These computations, which describe the charge and electron spin states of materials, showed that the two semiconductor layers formed crystalline nanowire arrangements with no magnetic characteristics.
The duo then systematically introduced small defects — atomic substitutions that slightly disrupt semiconductor crystallinity — into the GaN–ZnO superlattice. To Pan and Zhang’s surprise, they observed significant magnetism at several types of defect interface.
According to Pan, this extraordinary activity is due to ‘polar discontinuities’ that form when positively charged defects partially neutralize negative charges at Ga–O interface points. Unpaired electrons then accumulate around Zn–N connections and generate magnetic forces that can boost charge separation and mobility during the reaction known as photocatalysis.
The researchers also found that engineered polar discontinuities could significantly alter semiconductor bandgaps by generating intermediate energy levels. These zones act as ‘stepping stones’ that make it easier for photons, or light-transmitting particles, to excite electrons for water-splitting reactions.
Pan notes that once these intriguing properties of GaN–ZnO nanostructures are verified through laboratory studies, the materials may find application in energy-harvesting solar cells. “If this design proves efficient in both theory and experiment, we would then look for commercial applications by collaborating with industry,” he says.
The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing
Pan, H. & Zhang, Y.-W. GaN/ZnO superlattice nanowires as photocatalyst for hydrogen generation: A first-principles study on electronic and magnetic properties. Nano Energy 1, 488–493 (2012)
Electron tomography technique leads to 3-D reconstructions at the nanoscale
24.05.2018 | The Optical Society
These could revolutionize the world
24.05.2018 | Vanderbilt University
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences