In recent years, flexible electronics has attracted worldwide attention and has been rapidly developed, and is believed to bring about an electronic technological revolution. It is an emerging electronic technology for fabricating organic/inorganic material electronic devices on flexible substrates. With its unique deformability and high-efficiency, low-cost manufacturing process, it has broad application prospects in the fields of information, energy, medical care, defense, etc. However, current inorganic materials, especially semiconductors, are brittle materials with large bending and large deformation. In addition, or under tensile conditions, it is prone to cracking and leading to device failure. In addition, organic semiconductors have a relatively low migration rate relative to inorganic semiconductors, and the electrical performance can be adjusted in a relatively small range, failing to satisfy the vigorous development needs of the semiconductor industry. Therefore, development has A good ductility and bendability of inorganic semiconductor materials, to achieve a breakthrough in the integration of flexible electronic technology equipment and manufacturing processes, is the urgent need for the development of flexible electronics.
Recently, Shi Xun, a researcher at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, and Chen Lidong teamed up with Professor Yuri Grin of Germany's Max Prof. to find a semiconductor material whose room temperature is the same as that of a metal. The study found that α-Ag2S is a kind of A typical semiconductor, but with very anomalous and metal-like mechanical properties, in particular, it has good ductility and bendability, is expected to be widely used in flexible electronics. Related research published in the "Nature - Materials" magazine (Nature Materials).
The room temperature α-Ag2S has a zig-zag wrinkled layered monoclinic structure. Four S and four Ag atoms form an 8-atom ring, and the ring and the ring are connected by an S atom. α- Ag2S is a typical semiconductor with a bandgap energy band around 1 eV. Undoped α-Ag2S is mainly electronically conductive. Its electron concentration is relatively low, its conductivity is relatively small, and its mobility is around 0.01Sm-1. Larger, about 100 cm2V-1s-1. The electron concentration and conductivity of α-Ag2S can be increased by several orders of magnitude with elemental doping, and its electrical properties can be freely controlled in the semiconductor region.
Compared to other semiconductors or ceramics, α-Ag2S has very unique and unique mechanical properties. It has the same ductility and deformability as metal. It does not break or break material under external force and large strain. Its material processing Debris is also similar to metal as a piece of slender winding filaments, while ceramic and semi-conductor processing debris is usually fine particles or powder. Further characterization of its mechanical properties found that α-Ag2S compression deformation can reach up to 50% Above, the three-point bending test shows that the maximum deformation of its bending exceeds 20%, and the tensile test shows that the tensile deformation of α-Ag2S can reach 4.2%. All these values far exceed the known ceramic and semiconductor materials, and Some metals have similar mechanical properties.
The research team further studied the mechanism and mechanism of these abnormal mechanical properties of α-Ag2S. For a material with good sliding properties and ductility, two basic conditions must be met: First, there is a slip surface with a small energy barrier. The sliding can occur under the action of external forces; the second is that no decomposition occurs during the sliding process, and the integrity and integrity of the material are still maintained. The researchers used a first-principles calculation to simulate a series of materials including α-Ag2S, NaCl, In the slip process of graphite, diamond, metallic Mg and Ti, it was found that α-Ag2S, NaCl, graphite, metallic Mg and Ti all have slip planes with small energy barriers, and the slip plane of α-Ag2S is (100) In the sliding process, diamond has a large barrier and there is no slip surface. It has also been found that the interaction between α-Ag2S, metal Mg and Ti sliding surfaces is relatively large, during the material slip. Cracks and dissociation are difficult to maintain, and the integrity and integrity of the material are maintained. However, the forces between the slip surfaces of graphite and diamond are too small, and the material is easily cracked and dissociates during the sliding process. Quantum chemistry calculations revealed -The origin and mode of action of the force between the sliding planes of Ag2S, found that within one crystal period, except for intermolecular forces, there are only two yellow S atoms and six gray Ag atoms between the (100) slip planes. In the sliding process, the two S atoms move along the slides formed by the six Ag atoms. At this point, the old Ag-S bonds are constantly weakened or even broken, and there are new Ag- The S bond is strengthened or even generated. Therefore, the force between the (100) slip planes is always maintained in the Ag-S bond state, and the energy fluctuation during the slip is small, resulting in a small slip energy barrier. At the same time, the keying state ensures a strong force between these sliding surfaces, avoiding the occurrence of cracks or even the dissociation of materials during the sliding process.
For the application of flexible electrons, the team also prepared α-Ag2S thin films and found that it has greater deformability than bulk materials. At the same time, it also characterized the electrical properties of α-Ag2S deformation, found dozens, hundreds of repeats After bending deformation, its electrical properties remain basically unchanged or change little.
Unlike known brittle ceramic and semiconducting materials, α-Ag2S semiconductors have metal-like mechanical properties that maintain the integrity and electrical properties of the material under bending and deformation. Its wide range of adjustable electrical properties, suitable bandwidth The large mobility rate makes it possible to be widely used in the field of flexible electronics. At the same time, this work will also open up the search for and discover other semiconductor materials with similar mechanical properties of metals.
The research work was funded and supported by the National Natural Science Foundation of China (51625205 and 51632010), the key deployment project of the Chinese Academy of Sciences (KFZD-SW-421), the Shanghai Major Foundation Project (15JC1400301), and the academic leaders (16XD1403900).
