Fabrication, Characterizations And Optical Properties Of One-dimensional Cadmium Sulfide Nanostructures

CdS, which is an important II-VI group semiconductor with a wide direct bandgap of 2.42 eV in the visible range at 300 K, has attracted considerable attention owing to its unique properties such as strong emission in the visible range,excellent photoconductive characteristics. Since the properties of the material greatly depend on their morphological features, nanostructured CdS with different sizes and morphologies has been fabricated and characterized and has been widely investigated in areas such as laser, waveguide, transistors, logic gates, flat panel displays, light emitting diodes, nonlinear optical devices, and solar cells. Over the past decade, much effort has been devoted to manipulating the size, morphology, and crystal structure of CdS nanomaterials. The detailed contents are as the following three aspects:(1) High-quality corrugated CdS nanoribbons were synthesized through thermal evaporation of CdS powder (1.44 g). The length of periodicity could be tuned simply by varying the deposition temperature. Also, when the CdS source was reduced to 0.144 g, the product was slick nanobelts. The hexagonal wurtzite phase and single crystal of products were verified by XRD and SAED, respectively. The mechanism for the growth of nanoribbons has been described. In photoluminescence studies, a sharp peak due to near-band-edge emission and a broad band due to surface-trapped states or Cd vacancy emission were observed. CdS nanoribbons with corrugated structures have not been reported before and their presence makes the investigation of CdS nanostructures more interesting and intriguing.(2) High-quality morphology-tunable CdxZn1-xS nanostructures were synthesized through a one-step thermal evaporation process. They are in the forms of nanoswords, super-long nanowires, cubic nanopillars, heterogeneous nanobelts, branched nanorods, and nanocombs. The morphology and composition of the as-prepared CdxZnl2xS nanomaterials were regulated by controlling (i) distance between source materials, (ii) deposition temperature, and (iii) flow of protecting gas. The hexagonal wurtzite phase of the CdxZn1-xS nanostructures was verified by XRD, and the single crystal was confirmed by SAED analysis. In the photoluminescence (PL) study, the emission bands ranged from 448 to 474 nm, which indicates the formation of ZnxCdl2xS nanocrystals rather than CdS, ZnS, or core-shell structured nanocrystals. The result of the cathodoluminescence (CL) investigation reveals that the nanoswords are thick at the middle and thin at the two edges, just as the name "nanoswords" indicates. It is worth pointing out that the low-cost, environment-friendly approach adopted in the present study can be applied to synthesize nanostructures of other compounds such as ternary MgxZn1-xS, CuxCd1-xS and quaternary CuCdMgS semiconductors.