Left: Shape of nanostructures made of lead sulphide, computer reconstructed based on series of transmission electron microscopy images; the left straight stripe behaves like a semiconductor and the right zigzag nanowire behaves like a metal. Right: Electrical device consisting of two gold electrodes contacting a nanowire (in red) on a silicon chip (in blue). Image: Hungria/Universidad de Cádiz, Ramin/DESY, Klinke/University of Rostock and Swansea University.A team of European researchers has shown that the crystal structure at the surface of semiconductor materials can make them behave like metals and even like superconductors. This discovery, reported in a paper in Advanced Functional Materials, potentially opens the door to advances like more energy-efficient electronic devices.
Semiconductors are the active parts of transistors, integrated circuits, sensors and LEDs. These materials, mostly based on silicon, are at the heart of today's electronics industry. We use their products almost continuously, in modern TV sets, in computers, as illumination elements, and of course in mobile phones. Metals, on the other hand, wire the active electronic components together and provide the framework for these devices.
The research team, led by Christian Klinke of Swansea University in the UK and the University of Rostock in Germany, analyzed the crystals at the surface of semiconductor materials. Applying a method called colloidal synthesis to lead sulfide nanowires, the team showed that the lead and sulfur atoms making up the crystals could be arranged in different ways. Crucially, they saw that this affected the material's properties.
In most configurations, the two types of atoms are mixed and the whole structure shows semiconducting behavior as expected. However, the team found that one particular ‘cut’ through the crystal, with so-called {111} facets on the surface, which contains only lead atoms, shows metallic character.
This means that nanowires with these facets carry much higher currents, their transistor behavior is suppressed, they do not respond to illumination, as semiconductors would, and they show inverse temperature dependency, typical for metals.
"After we discovered that we can synthesize lead sulfide nanowires with different facets, which makes them look like straight or zigzag wires, we thought that this must have interesting consequences for their electronic properties," said Mehdi Ramin from Swansea University. "But these two behaviors were quite a surprise to us. Thus, we started to investigate the consequences of the shape in more detail."
The team then made a second discovery: at low temperatures, the skin of the nanostructures even behaves like a superconductor. This means that the electrons are transported through the structures with significantly lower resistance.
"This behavior is astonishing and certainly needs to be further studied in much more detail," said Klinke. "But it already gives new exciting insights into how the same material can possess different fundamental physical properties depending on its structure and what might be possible in the future. One potential application is lossless energy transport, which means that no energy is wasted.
"Through further optimization and transfer of the principle to other materials, significant advances can be made, which might lead to new efficient electronic devices. The results presented in the article are merely a first step in what will surely be a long and fruitful journey towards new thrilling chemistry and physics of materials."
This story is adapted from material from Swansea University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.