Inorganic Double Helix
Discovered
A flexible semiconductor for electronics, solar technology and photo catalysis
University
of Munich , August 28,
2016
It is the double helix, with its stable and flexible structure of genetic information, that made life on Earth possible in the first place. Now a team from theTechnical University of Munich
(TUM) has discovered a double helix structure in an inorganic material. The
material comprising tin, iodine and phosphorus is a semiconductor with
extraordinary optical and electronic properties, as well as extreme mechanical
flexibility.
Countless application possibilities
Just at the beginning
Interdisciplinary cooperation
A flexible semiconductor for electronics, solar technology and photo catalysis
It is the double helix, with its stable and flexible structure of genetic information, that made life on Earth possible in the first place. Now a team from the
Flexible yet robust – this is one reason why nature codes genetic
information in the form of a double helix. Scientists at TU Munich have now
discovered an inorganic substance whose elements are arranged in the form of a
double helix.
The substance called SnIP, comprising the elements tin (Sn), iodine (I) and
phosphorus (P), is a semiconductor. However, unlike conventional inorganic
semiconducting materials, it is highly flexible. The centimeter-long fibers can
be arbitrarily bent without breaking.
"This property of SnIP is clearly attributable to the double
helix," says Daniela Pfister, who discovered the material and works as a
researcher in the work group of Tom Nilges, Professor for
Synthesis and Characterization of Innovative Materials at TU Munich. "SnIP
can be easily produced on a gram scale and is, unlike gallium arsenide, which
has similar electronic characteristics, far less toxic."
Countless application possibilities
The semiconducting properties of SnIP promise a wide range of application
opportunities, from energy conversion in solar cells and thermoelectric
elements to photocatalysts, sensors and optoelectronic elements. By doping with
other elements, the electronic characteristics of the new material can be adapted
to a wide range of applications.
Due to the arrangement of atoms in the form of a double helix, the fibers,
which are up to a centimeter in length can be easily split into thinner
strands. The thinnest fibers to date comprise only five double helix strands
and are only a few nanometers thick. That opens the door also to nanoelectronic
applications.
"Especially the combination of interesting semiconductor properties
and mechanical flexibility gives us great optimism regarding possible
applications," says Professor Nilges. "Compared to organic solar
cells, we hope to achieve significantly higher stability from the inorganic
materials. For example, SnIP remains stable up to around 500°C (930 °F)."
Just at the beginning
"Similar to carbon, where we have the three-dimensional (3D) diamond,
the two dimensional graphene and the one dimensional nanotubes," explains
Professor Nilges, "we here have, alongside the 3D semiconducting material
silicon and the 2D material phosphorene, for the first time a one dimensional
material – with perspectives that are every bit as exciting as carbon
nanotubes."
Just as with carbon nanotubes and polymer-based printing inks, SnIP double
helices can be suspended in solvents like toluene. In this way, thin layers can
be produced easily and cost-effectively. "But we are only at the very
beginning of the materials development stage," says Daniela Pfister.
"Every single process step still needs to be worked out."
Since the double helix strands of SnIP come in left and right-handed
variants, materials that comprise only one of the two should display special
optical characteristics. This makes them highly interesting for optoelectronics
applications. But, so far there is no technology available for separating the
two variants.
Theoretical calculations by the researchers have shown that a whole range
of further elements should form these kinds of inorganic double helices.
Extensive patent protection is pending. The researchers are now working
intensively on finding suitable production processes for further materials.
Interdisciplinary cooperation
An extensive interdisciplinary alliance is working on the characterization
of the new material: Photoluminescence and conductivity measurements have been
carried out at the Walter Schottky Institute of the TU Munich. Theoretical
chemists from the University
of Augsburg collaborated
on the theoretical calculations. Researchers from the University
of Kiel and the Max Planck Institute
of Solid State Research in Stuttgart
performed transmission electron microscope investigations. Mössbauer spectra
and magnetic properties were measured at the University of Augsburg ,
while researchers of TU Cottbus contributed thermodynamics measurements.
The research was funded by the DFB (SPP 1415), the international graduate
school ATUMS (TU Munich and the University
of Alberta , Canada )
and the TUM Graduate School .
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