Joint project details charge transport in polymeric carbon nitride for first time
Polymeric carbon nitrides are organic compounds synthesised to form a yellow powder of a myriad of nanocrystals. The crystalline structure resembles that of graphite because the carbon nitride groups are chemically bound only in layers, while just weak Van der Waals forces provide cohesion between these layers.
Charge carriers in polymeric carbon nitrides always take paths perpendicular to the sheets, as Merschjann's group has now shown. Light creates an electron-hole pair. The opposite happens when an electron and hole meet under certain conditions (forming a singlet exciton) and emit light (fluorescence).
Credit: C. Merschjann
It was already known that light is able to create an electron-hole pair in this class of materials. So there have already been numerous attempts to employ polymeric carbon nitrides as cost-effective photocatalysts for solar-powered water splitting. However, the efficiency levels so far have remained comparatively low.
Light creates charge carriers
Now a team headed by Dr. Christoph Merschjann (HZB and Freie Universität Berlin) and Prof. Stefan Lochbrunner (University of Rostock) have for the first time precisely probed the processes occurring during light-induced charge separation.
"The most interesting result has been that charges are basically only transported along one dimension during this process, perpendicular to the graphite-like layers", explains Merschjann. The light creates an electron-hole pair that subsequently migrates in opposing directions.
Using femtosecond spectroscopy as well as other spectroscopic time-domain methods, the researchers were able to make the first quantitative mobility and lifetime measurements on the charge carriers. This revealed that the charge mobility attains values similar to those in conventional organic semiconductor materials. Moreover, the charge carriers are long-lived before recombining again.
New material for organic electronics
Polymeric carbon nitrides are not only non-toxic and cost-effective, they are also extremely durable because they are chemically very stable and can withstand temperatures of up to about 500 °C. Components made of these kinds of compounds might therefore be employed in environments that are unsuitable for today's organic electronics.
Merschjann finds the prospect of growing these compounds on ordered substrates, such as graphene for example, especially interesting though. This is because graphene possesses extremely high in-plane conductivity, while carbon nitrides primarily conduct perpendicular to the sheets.
"Carbon nitrides need not fear the competition with conventional organic semiconductor materials. On the contrary, completely new kinds of all-organic optoelectronic components might be built using their property of being essentially one-dimensional semiconductors", Merschjann hopes. He is currently working on making direct measurements of the charge carriers in a DFG-funded research project at Freie Universität Berlin.
The cooperation was initiated by the BMBF-Cluster-Projekct „Light2Hydrogen".
The results have been published in the renowned periodical Advanced Materials: Complementing Graphenes: 1D Interplanar Charge Transport in Polymeric Graphitic Carbon Nitrides
Antonia Roetger | EurekAlert!
Further reports about: > Advanced Materials > Carbon > Helmholtz-Zentrum > Polymeric > cohesion > conventional > crystalline structure > electron-hole pair > femtosecond spectroscopy > graphene > materials > measurements > optoelectronic > organic compounds > research project > semiconductor > semiconductor materials
New biomaterial could replace plastic laminates, greatly reduce pollution
21.09.2017 | Penn State
Stopping problem ice -- by cracking it
21.09.2017 | Norwegian University of Science and Technology
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
22.09.2017 | Life Sciences
22.09.2017 | Medical Engineering
22.09.2017 | Physics and Astronomy