Editor's note: An oversight by the laboratory staff four years ago led to an accidental discovery that ultimately resulted in a world-first process. Recently, the Quantum Dot Materials and Devices Research Group of the School of Materials Science and Engineering of Tianjin University has developed a new process for the synthesis of monodisperse quantum dots with environmental protection and efficiency. Physical methods synthesize monodisperse quantum dots, which are more efficient than chemical methods.
Since the concept of superlattice was proposed in 1970, it has been regarded as a landmark development in the field of semiconductor physics. It became a very popular research field in semiconductor physics in the 1980s and 1990s. The cascade resonance tunneling between the microstrip transport and the quantum well in the superlattice will cause a negative differential conductance effect, which makes the superlattice an ideal nonlinear system with multiple degrees of freedom.
Du Xiwen, the corresponding author of the paper and a professor at the School of Materials Science and Engineering of Tianjin University, said that when semiconductor materials are several nanometers in diameter, they can exhibit many unique physical properties. Like the well-known silicon, the maximum efficiency of converting solar energy into electrical energy at normal volume is 33%, but when the volume of silicon is about 4 nanometers, the efficiency can be increased to 66%. Some materials can emit special light. If you carry nano-level luminescent materials on the antibody drugs of the tumor, you can mark the location of the tumor very accurately, which can help doctors judge the disease and find the lesion. It is precisely because these quantum dots (also known as semiconductor nanocrystals) have such a magical ability, so it is currently a research and development hotspot of scientific researchers in various countries.
Many physical phenomena related to space-time nonlinear effects can be observed in superlattices, such as static electric field domains, periodic self-excited oscillations, and spontaneous chaotic oscillations. For a long time, these phenomena can only be observed in the low temperature environment below the temperature range of liquid nitrogen, which seriously limits the further research and practical promotion of superlattice devices. This is the main reason why the field of semiconductor superlattice research has become very deserted in recent years.
Du Xiwen said that the traditional mechanical process can crush semiconductor materials to the micron level at most, and the volume is thousands of times that of the nano level. In the past, quantum dot materials have been produced by wet chemical methods, using reactions between concentrated chemicals. However, this method takes a long time, ranging from a few hours to a few days, and also generates a large amount of pollutants, which causes a burden on the environment.
Four years ago, a student in Professor Du Xiwen's laboratory experimented with using a laser to break a metal target into metal particles. This experiment generally only needs to irradiate the metal target with a laser for about 3 minutes, but the students leave halfway and let the laser illuminate the metal target for more than 4 hours. The team then discovered that the metal target was beaten into metal particles with a size of a few nanometers, which was much more desirable than before. They turned to this "strange" phenomenon as a research focus, exploring how to use lasers to "knock" semiconductor materials into uniform nano-sized particles. Finally, it took 4 years to explore the physical method of synthesizing monodisperse quantum dots in this field.
Using the "hammer" of lasers, scientists can "change" the intensity according to actual needs and precisely control the specific size of semiconductor materials. Compared with the wet chemical method, this world-first method takes less time, and it only takes more than 20 minutes at a time. The quantum dots obtained are more uniform in size, without chemical drugs on the surface, and very clean. Du Xiwen said that it is expected that this process will help to obtain cheaper quantum dots in the future, making it play a more prominent role in the fields of disease diagnosis, water pollution detection, photoelectric conversion and other fields.
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