Synthesis And Properties Of One Dimensional Bi₂S₃ With Nano/Micro-Structure

As an important member of the main group metal chalcogenides, Bi2S3’s band gap is 1.3e V, which has many potential applications, such as photovoltaic converters, thermoelectric generation, and electrochemical hydrogen storage and so on. In this paper, we have successfully synthesized one dimensional Bi2S3 nanowires and nanobelts, and examined their crystalline structure and morphologies, and also made a research on their properties of thermoelectric, photoelectric and photocatalytic degradation. We abstract the main content of this dissertation as following:(1) The orthorhombic Bi2S3 nanostructure materials have been synthesized by the modified composite molten salt method, the morphology and size can be controlled by the condition of reaction temperature, growing time, the amount of water, and we obtained the uniform, highly crystallized and long nanowires with length up to 20 μm by this method. We measured the band gaps of three samples we synthesized with different morphologies. The morphologies of the three samples are mixture of nanowires and sheets(P1), nanowires(P3) and sheets(P8). We have pressed the three samples into films, and measured the surface morphology, resistivity, Seebeck coefficient of these films. From the result, we find that the power factor of the film made from nanowires is much larger than that of the rest two films due to its lower resistivity and large Seebeck coefficient. Furthermore, the low resistivity of the nanowires film is a result of the high carrier concentration and high carrier mobility due to the high orientation degree and better crystallization. The introduction of many interfaces from smaller size of grains, which scatter phonons more effectively than electrons, or serve to filter out the low-energy electrons at the interfacial energy barriers, allows the enhancement of Seebeck coe?cient.(2) The Au electrode pattern was defined with photolithography and magnetron sputtering on a Si O2/Si substrate. A long enough nanowire near or on the electrodes was chosen to be transferred to across two Au electrodes by using a thin needle under microscope. We have obtained two single nanowire devices by this method, and then, for one device, used focused ion beam to deposit Pt on the contacts between the nanowire and the Au electrodes for eliminating the Schottky barriers and forming high quality Ohmic contacts. Another single nanowire device doesn’t use FIB. Besides, a Bi2S3 nanowires film is obtained by pressing the rest Bi2S3 nanowires powder, and a film device is fabricated in sandwich structure of FTO/Bi2S3/FTO, and the photoelectric properties of the three devices were measured. Photoelectric properties of the two single nanowire devices were systematically investigated under simulation sunlight illumination at room temperature in the open air, both single nanowire devices exhibit high sensitive photoelectric responses that are fully reversible and periodic. The device with the deposition of Pt shows a better stability and the device without the deposition of Pt shows a faster photoconductive response. In addition, both single nanowire devices exhibit better performance compared with the thin ?lm device made of Bi2S3 NWs. The results imply that single Bi2S3 NW device is a promising candidate for fabricating optical detectors or optical switches.(3) Using Bi(NO3)3·5H2O and Na2S2O3 as the reactant, a mixture of distilled water and glycerol as reaction solution, Na OH as a catalyzer, we have synthesized orthorhombic Bi2S3 nanoribbons with length up to several millimeters. Observed from the SEM, we found that the samples are a mixture of nanowires and nanoribbons, and the diameter is range from about 100 nm to several microns. We also found that some nanoribbons are consists of smaller nanowires and nanoribbons. For further study, we measured the TEM, and found the two nanoribbons are growing toghther, and made a HRTEM on the region of the intersection. After remove the noise, we got the lattice fringe image of the region, make us a better understand of the growth of nanoribbons. A Cd S/Bi2S3 heterostructure has been successfully realized by depositing Cd S nanoparticles on the surface of the nanoribbons, and evaluated its photocatalytic activity by the photocatalytic degradation of methylene blue(MB). The heterostructure of Cd S / Bi2S3 could degrade 85% percent of the methylene blue after 7 hours; the results indicated that it has a good photocatalytic performance.