Glass is usually considered a thermal insulator: that is precisely why it is inserted into windows. But a group of researchers led by Longji Cui of the University of Colorado Boulder has discovered that in the form of a thread one atom thick, glass behaves differently. The work was published in the journal Nature Nanotechnology.
In ordinary glass, atoms are arranged randomly, and this disorder scatters thermal vibrations. In a thread one atom wide, there is no room for disorder, so vibrations pass directly. Co-author Guilherme de Vilhena of the Institute of Materials Science in Madrid compared this to a window: glass retains heat, but stretched into an atomic thread it transmits it with an efficiency unprecedented for an insulator.
Moreover, the heat was transferred in separate portions. Each amounted to 40% of the maximum that a single channel can carry according to the laws of quantum physics. Such quantized, that is, divided into discrete steps, heat flow caused by atomic vibrations is being observed for the first time.
For the experiment, a scanning thermal probe microscope was used. It has a glass probe with a built-in thermometer: it senses the motion of atoms and molecules and measures heat flow through atomic-scale contacts. Cui compares the device to a tiny finger that reads temperature and heat flow through an individual atom.
During the experiment, two glass parts were pressed against each other and then slowly pulled apart. The contact narrowed to a thread one atom wide and eventually broke.
According to Cui, similar behavior may also occur in other materials. Researchers will now be able to study a wide variety of substances with this microscope, and the instrument may produce unexpected results. The scientist aims to create increasingly sensitive sensors for measuring invisible processes.
The discovery could be useful in developing miniature nanoelectronics. Silicon dioxide, that is, glass, is already used in computer chips as an insulating layer. Cui notes that semiconductors, the basis of nanoelectronic devices, are especially interesting: the new microscope will become a convenient diagnostic tool for studying their energy efficiency and reliability.
For now this is a laboratory discovery, and it is too early to speak of finished devices. But it shows that when moving to atomic sizes, the familiar properties of materials can change in the most unexpected ways.