Growth Mechanism of γ-MnS Nanorod-Arrays by Hydrothermal Method on Anodic Aluminum Oxide Template

Abstract

500 nm 500 nm 1 um 1 um 10 um 20 um Figure 1. (a) SEM image of anodic aluminum oxide template, inset cross-section image of anodic aluminum oxide template (b)-(e) SEM images of the products on different substrates respectively corresponding to anodic aluminum oxide template, one-step anodization Al foil, Al foil (dipped in HNO3 solution) and silicon wafer.MnS, as a p-type semiconductor with a wide gap (Eg = 3.7 eV), has a potential application in solar cell as a window/buffer, but also is linked with the study of diluted magnetic semiconductor (DMS).1 So far, a number of methods have been developed to fabricate different nanostructure MnS such as solvothermal method for preparing hierarchical architectures MnS, 2 biomolecule-assisted method for synthesizing porous MnS networks, 3 and chemical bath deposition method for making crystalline MnS thin film. 4 Hydrothermal method is a general, low-cost and convenience method which was utilized for synthesis of nanomaterials.5-7 Our research group has reported that oriented MnS nanorods on anodic aluminum oxide template were synthesized under a hydrothermal condition and demonstrated the effect of precursor content on the morphology evolution of assamples. 8 In order to research the growth mechanism of the arrays, herein we synthesized MnS nanorod arrays by combination of anodic aluminum oxide template and hydrothermal method on different substrates.Through-hole anodic aluminum oxide templates were prepared using Al foil (99.999%) via a two-step anodization process as described in literature.8 To investigate the effect of different substrates on the morphology of the-products, different substrates including anodic aluminum oxide template (sample A), one-step anodization Al foil (sample B, which was prepared by first anodizing Al foil for 10h and then removing the alumina layer with the mixed acid (0.6 M H 3 PO 4 and 0.15 M H 2 CrO 4 ), where the foil still kept the close-packed concave nano-pits consistently with the nanopole of anodic aluminum oxide template), Al foil (sample C, dipped in HNO 3 solution and covered by a compact alumina layer), Si wafer (sample D) respectively were put into Teflon-lined stainless steel autoclaves of 20 mL capacity filled with 16 mL mixed solution consisting of 2 mol/L MnCl4 and 2 mol/L thiourea. We kept the reaction at 150 o C for 20 h. When reactions completed the products were washed three times with distilled water and absolute ethanol, respectively. Then the products were dried in an oven at 60 o C. The powder XRD patterns (not showed here) reveal that the as-prepared products on different substrates were γ-MnS with lattice constants of a = 3.979 Å and c = 6.447 Å (JCPDS, No. 40-1289). And Figure 1 shows the typical SEM images of anodic aluminum oxide template and the as-prepared products on different substrates. b) -e) are respectively corresponding to on sample A ~ D. Figure 1a reveals that the anodic aluminum oxide template has highly ordered pores with a diameter of about 60 nm. The similar grass-like, packed nanorod arrays co...