Synthesis And Properties Of In, Sn- Chalcogenide Semiconductor Na Nocrystals

In the last decades, nanomaterials have attracted much scientist's attention. Na-noscience has been developed to an important content in science and technology revo-lution at 21 centuries. When the size of material reaches nanometer, many physical and chemical properties would be changed greatly. Nanomaterials would show quantum size effect, quantum tunneling effect, surface and interface effect, which induce poten-tial for optical, electronic and magnetic. Among these nanomaterials, semiconductor nanocrystals-quantum dot is a most important species. Because of the obvious quantum dot in semiconductor nanocrystals, the band gap in quantum dot can be turned by changing the size of nanocrystals. Semiconductor nanocrystals are good choice for fluorescent material, light detector and energy storage material. Coupled with the de-velopment of synthetic chemistry, various quantum dots have been produced. However, many problems are still existence in the investigation of quantum dot. Synthesis of new semiconductor nanocrystals is an important and efficient approach. In this paper, we synthesize and investigate the properties of a few new and nontoxic semiconductor nanocrystals.Till now, the investigation of semiconductor nanocrystals is focused on the II-VI group CdSe, CdTe, ZnSe, III-V group InP, InAs and IV-VI group PbSe, PbTe, other binary semiconductor nanocrystals are minor investigated. We have synthesized III-VI group In₂S₃ and In₂S₃ nanocrystals in this paper. By high temperature organic inject synthetic route, cubicβ-In₂S₃ nanoparticles with size of 7 nm have been produced. The UV-vis absorption and fluorescence emission spectra show obvious quantum size ef-fect in In₂S₃ nanoparticles. The UV-vis absorption peak is according to the band gap in In₂S₃ nanoparticles, the constant absorption peak indicates the size of In₂S₃ nanopar-ticles is not changed. The blue shift of emission peak shows the transformation from defect-related exciton recombination to electron-hole recombination for emission spectra. The nucleation of In₂S₃ nanoparticles is fast, and the growth process mainly includes passivation of surface defects and dangling bond, the size of In₂S₃ nanopar-ticles is constant. Then we investigate the similar indium selenide nanocrystals. We synthesize rare metastable cubic InSe nanocrystals. UV-vis absorption spectra of InSe give a peak at 610 nm, which has obvious red shift compared to the bulk InSe. InSe nanoparticles show distinct quantum size effect. The reaction temperature has impor-tant influence on the products. Selenium would appear when the reaction temperature is lower, and hexagonal In2Se3 would be the product when the reaction temperature is higher enough. The produced In2Se3 is nanosheets with size of 600 nm. We character-ize the samples taken at different time by XRD, and we find the transformation from cubic InSe to hexagonal In2Se3. The energy provided by reaction temperature can overcome the barrier for the phase transformation, and the battier for the transforma-tion from InSe to In2Se3 can be calculated to 0.052 eV. The drive force is reducing the free energy in the system.Recently, IV-VI group PbS, PbSe and PbTe nanocrystals have been investigated widely, however, the research about IV-VI group Sn based semiconductor nanocrystals are few. SnS and SnSe is the typical four layered semiconductor, the layered crystal structure induce many difficulties to synthesis these nanocrystals with smaller size. Till now, all most of the reported semiconductor nanocrystals have cubic or hexagonal crystal structure; the reports about layered crystal nanocrystals are few. Herein, we synthesize layered crystal structure SnS and SnSe nanocrystals. In the synthesis of semiconductor nanocrystals, the precursor is very important. We synthesize a new Sn precursor Sn₆O₄(OH)₄ to produce IV-VI group Sn based semiconductor nanocrystals. Moreover, we investigate the stability of Sn₆O₄(OH)₄ at different conditions. Pure Sn₆O₄(OH)₄ is very stable even at high temperature (160℃), however, Sn₆O₄(OH)₄ would compose to SnO nanocrystals with little water or free metal cations. By this new Sn precursor, we synthesize SnS nanocrystals, such as nanoparticles, nanoflowers and nanosheets. Size of SnS nanoparticles is 13 nm and the size distribution is uniform. In the synthesis of SnS nanoflowers, nanoflowers would integrate to bigger amorphous nanosheets with increasing reaction time. Coupled with integration of nanoflowers to nanosheets, an amorphization process is included. The main reason of the amorphiza-tion is the layered crystal structure of SnS, the layered crystal structure induce the ten-dency of compound growth to two-dimension nanosheets. We calculate the change of Gibbs free energy in the amorphization by thermodynamics, the result also support the amorphization process. Optical properties of SnS nanocrystals have also been investi-gated; obvious quantum size effect can be observed in SnS nanocrystals. Based on synthesis of SnS nanocrystals, we successfully synthesize SnSe nanoparticles with smaller size and uniform size distribution. By changing experimental conditions, the size and shape of SnSe nanoparticles can be controlled, and the influence of experi-mental conditions to the size and shape of SnSe nanoparticles has also been discussed. Indirect band gap is got in SnSe nanoparticles by UV-vis absorption spectra, which agrees with the previous theoretical result. The direct band gap and indirect band gap also show quantum size effect. The red shift in emission peak of SnSe nanocrystals with increasing the size of SnSe nanoparticles gives the further proof to the quantum size effect in SnSe nanoparticles. Typically, the electrochemical properties of SnSe nanoparticles as anode material for lithium battery have been investigated. We give a reaction mechanism of SnSe nanoparticles as anode material for lithium battery. The investigation of layered crystal SnS and SnSe nanocrystals would provide important reference to research other semiconductor nanocrystals with layered crystal structure.We have successfully synthesized IV-VI group layered crystal structure SnS and SnSe nanocrystals in front, the other IV-VI group Sn based semiconductor SnTe is an important middle infrared material. The middle infrared material mainly include III-V group Sb compound, but the high cost and narrow application range (3-5μm) hinders the potential in middle infrared material. SnTe with the band gap of 0.18 eV can cover the middle infrared range (3-7μm) and part of far infrared range, which have potential for middle infrared material. We synthesize SnTe nanocrystals with Sn₆O₄(OH)₄ as Sn precursor and the shape and size of SnTe nanocrystals can be turned by ligands. We investigate the experiment with octylamine as ligands. The produced SnTe nanopar-ticles with octylamine as ligands would aggregate to single crystal structure SnTe na-nowires with increasing the reaction time. These single crystal structure SnTe nano-wires would grow continual. The oriented attachment mechanism is used to explain the aggregation of nanoparticles to nanowires. The aggregation process can reduce the free energy in the system. The aggregation of SnTe nanoparticles to single crystal structure SnTe nanowires provide a typical example for oriented attachment.