A cluster of 1,000 or more atoms known as a quantum dot functions as a single big “super-atom.” These dots’ electrical characteristics may be precisely designed by adjusting their size. However, a significant number of dots need to be merged into a new material in order to produce functioning devices. The characteristics of the dots are frequently lost throughout this procedure. A highly conductive optoelectronic metamaterial has now been created by self-organization by a team under the direction of Maria Antonietta Loi, professor of photophysics and optoelectronics at the University of Groningen. The metamaterial is discussed in the article published on October 29 in the journal Advanced Materials.
Lead selenide or lead sulphide quantum dots have the ability to transform shortwave infrared light into an electrical current. Making detectors or a switch for telecommunications can benefit from this characteristic. However, a gadget is not created by a single dot. Additionally, Loi notes that when dots are merged, the assembly frequently loses the distinctive optical characteristics of individual dots or, if they do keep them, their ability to carry charge carriers deteriorates significantly. This is because making an ordered substance out of dots is challenging.
In collaboration with colleagues at the University of Groningen’s Faculty of Science and Engineering, Loi tested a technique that enables the creation of a metamaterial from a colloidal solution of quantum dots. These five to six nanometer-sized dots exhibit extremely high conductivity when arranged in an ordered array while retaining their visual characteristics.
Dots may self-organize into a two-dimensional, ordered layer, as we were aware from the literature. According to Loi, “We intended to develop this to a 3D substance.” To do this, scientists put liquid in tiny containers, which served as a sort of “mattress” for the colloidal quantum dots. We produced a 2D substance by injecting a little quantity onto the liquid’s surface. Then, it was discovered that producing more quantum dots produced an organized 3D substance.
To reach a low energy state, the dots self-orient on the surface rather than being immersed in the liquid. According to Loi, “The dots have a truncated cubic shape, and when they are combined, they form an organized structure in three dimensions called a superlattice, where the dots operate like atoms in a crystal.” The maximum electron mobility ever recorded for a quantum dot assembly may be seen in this superlattice made of quantum dot superatoms.
It requires specialized tools to determine the new metamaterial’s appearance. The team’s electron microscope, which possesses atomic resolution, was utilized to display the material’s finer features. Grazing-incidence small-angle X-ray scattering was used to “image” the material’s large-scale structure as well. Thanks to my colleagues Bart Kooi and Giuseppe Portale, respectively, these methodologies are now available at the Zernike Institute, which was a big assistance, says Loi
The material’s electrical properties have been measured, and they reveal that although it has dot-like optical characteristics, it closely approaches that of a bulk semiconductor. The experiment therefore paves the door for the development of novel quantum dot-based metamaterials. Because of the dots’ infrared light sensitivity, optical switches for telecommunications equipment may be developed. Additionally, they might be utilized in infrared detectors for driverless vehicles and night vision.
Loi is overjoyed with the experiment’s findings: “People have been hoping for this since the 1980s. That much time has been spent trying to put together quantum dots into useful materials. Beyond our wildest dreams, we were able to control the construction and the properties. Loi recently received an Advanced Grant from the European Research Council for her work on comprehending and developing the technology to construct extended superlattices using quantum dots, but she also intends to do it with other building blocks. “Our next step is to refine the method to make the materials more precise and manufacture photodetectors with them,” the researcher said.