Employees of the Faculty of Chemistry and the Faculty of Materials Science of the MVLomonosov Moscow State University, together with foreign colleagues, discovered that two-dimensional sheets of cadmium telluride can spontaneously coagulate into nanotubes, which can find application in electronics and photonics. The results of the study were published in the highly rated journal Chemistry of Materials.
In the course of the work, scientists studied two-dimensional semiconductor materials. These include, for example, graphene, phosphorene, two-dimensional layers of molybdenum disulphide, two-dimensional perovskites – recently they have attracted a huge interest of scientists. Such materials are atomic-thin crystals with two-dimensional electronic properties. Scientists suggest that these two-dimensional materials can be used to create new instruments.
“We studied two-dimensional cadmium telluride CdTe and discovered the unexpected effect of spontaneous folding of two-dimensional sheets of this semiconductor, which are ultrathin, only one nanometer thick, which are otherwise called colloidal quantum wells,” said one of the authors Roman Vasiliev, Ph.D., associate professor of the chemical faculty and faculty Materials Science of Moscow State University named after MV Lomonosov.
Colloidal quantum wells are a new generation of colloidal quantum dots. Quantum dots have pronounced luminescent properties and have already found application in commercially available devices, for example, television sets. Quantum wells – a two-dimensional version of quantum dots – are only being investigated, but they have extremely narrow luminescence bands, which is of great importance for high color purity in light-emitting devices.
The scientists studied the properties of two-dimensional sheets of cadmium telluride, changing organic molecules that were “sewn” to their surface and ensured the stability of nanoparticles. For the synthesis of nanoparticles of two-dimensional cadmium telluride, chemists used a colloidal method and received them in a flask. To this end, the scientists carried out the reaction in an organic solvent in the presence of surfactants. By selecting the conditions, the researchers were able to achieve the growth of nanoparticles in the form of atomic-thin sheets.
First, the authors grew flat two-dimensional flists coated with a stabilizer-oleic acid. It was possible to obtain sheet sizes of hundreds of nanometers at a thickness of strictly one nanometer. Then scientists began to replace the molecules of oleic acid with other organic molecules and analyze the size, shape of the resulting nanoparticles, their composition and crystal structure. For this they used the electron microscope of the Center for Collective Use of the Moscow State University.
During the work, they found that when using a special class of thiol stabilizers, flat cadmium telluride sheets curled into neat and uniform tubes. Adhering to the surface of the sheet, thiol molecules increase the thickness by exactly one monolayer (0.15 nanometers) and cause mechanical stresses that lead to folding of the sheet in a strictly defined crystallographic direction. Folding occurs at all nanoparticles simultaneously, and the radius “convolution” is the same for all nanostructures.
“This research opens up new opportunities for manipulating two-dimensional materials and nanoparticles. A very unexpected folding effect resembles origami, only in our case sheets have a thickness of one nanometer. The ability to control the spatial shape of nanoparticles can find application in the creation of optical materials with anisotropic properties and with polarized luminescence. With their help, it is possible to develop active light-emitting matrixes for displays that will reduce power consumption and increase the brightness and contrast of the device. We can also assume the possibility of designing new nanodevices, for example, transistors with a tube shape. These interesting properties can be in demand in new generations of light-emitting and sensory devices, in optical and optoelectronic technologies and nanotechnologies,
Source : Moscow State University