Synthesis and optical properties of CuS nanowires fabricated by electrodeposition with anodic alumina membrane Chien Wu a, Jen-Bin Shi b, Chih-Jung Chen a, Yu-Cheng Chen a, Ya-Ting Lin a, Po-Feng Wu b, Sung-Yen Wei b a The Graduate Institute of Electrical and Communications Engineering, Feng-Chia University, Taichung 40724, Taiwan b Department of Electronic Engineering, Feng-Chia University, Taichung 40724, Taiwan Received 7 June 2007; accepted 26 July 2007 Available online 1 August 2007 Advisor ： S.C.Wang Student ： Shih-Kai Shu

Outline Introduction Experimental Procedures Results and Discussion Conclusion Future work

Introduction

Metal nanowires are expected to be crucial components in future nanoscale devices for chemical, mechanical, electrical, magnetic, optical, and many other applications. During the past few years, considerable efforts have been spent to develop viable methods for the fabrication of metal nanowires. One-dimensional nanostructures have become the focus of intense research, because they provide a good system for investigating the dependence of electrical, optical, and thermal transport or mechanical properties on dimensionality and size confinement. As an important semiconductor material, copper sulfide has been found many applications for its metallike electrical conductivity, chemical-sensing capability and ideal characteristics for solar energy absorption.

There are many ways to prepare nanosized copper sulfide. Some methods, such as soft colloidal templates, in situ template-controlled (ISTC) method, microwave irradiation, template-free synthesis, biomolecule-assisted hydrothermal approach, solid-state reaction route, have been utilized to prepare one-dimensional CuS nanorods and nanowires, searching for a simple synthetic route is still an interesting subject worthy of further exploration. Herein we synthesize CuS nanowire by electrodepositing with the template method, a way for preparing one dimensional nanostructural materials, which entails fabricating the desired material within the pores of a template membrane.

The use of either direct current or alternate current for the nanowire deposition of a range of materials (such as CdSe, SnO 2, TiO 2, InO 2, Bi 2 S 3 etc) have already been shown to produce well ordered crystallized highly dense nanowire arrays. In this report, we use an AC and DC electrodeposition process at the same time to fabricate CuS nanowire arrays in AAM templates from a dimethylsulfoxide (DMSO) solution containing copper chloride and elemental sulfur. So far this is the first work to have successfully used electrodeposition to fabricate aligned CuS nanowire arrays and study its properties.

Experimental Procedures

Results and Discussion

XRD was performed to analyze the microstructure of the samples (shown in Fig. 1). In this measurement, we removed the AAM from the CuS nanowire arrays to avoid the effect of the AAM. When XRD pattern is compared with that of the standard powder diffraction pattern of CuS (JCPDS ) with hexagonal structure, the intensity of peak (110) is higher than other peaks, which is the highest intensity in the standard pattern, indicating that there was a [110] preferred orientation during the growth of the nanowires. In XRD data, we didn‘t find any phase about the elemental copper, sulfur and Cu 2 S.

Fig. 2(a)–(c) shows SEM images of the ordered nanowires in an anodic alumina membrane template and the nanowire arrays. SEM images show that the average diameter of the pores is around 60 nm. The nanowire arrays fill the nanochannels uniformly and the measured diameters of the nanowires are equal to the pore diameter. Fig. 2 (d) shows EDS spectrum of the CuS nanowire arrays without AAM which verifies that the nanowires consist of Cu and S, and quantitative analysis of the spectrum indicates that the atomic ratio of Cu to S is close to 1:1.

Fig. 3(a)–(d) show SEM images of the ordered CuS nanowires completely exposed after we dissolved the AAM. These spectrums show the nanowires are obviously entire and prolific. There are two supposed steps involving the electrodeposition of CuS in the DMSO solution containing CuCl 2 and elemental sulfur. First, the elemental sulfur of the solution diffuses to the electrode surface, is absorbed on the surface and then form in S 2− type. Secondly, the generated S 2− ions react with the Cu 2+ ion in the solution to form CuS crystalline core.

In addition, we proposed an alternate and directcurrent process to fabricate CuS nanowire arrays. Because of the alternate-current process, the alternation of the electric field will remove the undesired deposition that is deposited on the surface of the AAM, and then influence the rate of the deposition. For the direct-current process, the direction of the electric field makes a high density deposition to form highly aligned ordered CuS nanowire arrays. Finally we considered the above reasons in which an AC with DC method has successful produced highly quality CuS nanowire arrays.

UV–Vis optical absorption spectrum of CuS nanowires inside the deionized water is shown in Fig. 4. The inset in Fig. 4 depicts the energy scale of UV–Vis absorption spectrum (0.5 eV to 7.5 eV) in proportion to its wavelength. The spectrum shows a strong absorbance starts at around 550 nm, two absorption shoulders at short wavelength 242 nm and 400 nm, and one broad absorbance with a maximum at 825 nm in the near-IR region.

Conclusion

In summary, the high density, uniform 60 nm CuS nanowire arrays embedded in the pores of AAM template have been prepared by an alternate with direct-current electro- deposition in dimethylsulfoxide (DMSO) solution containing copper chloride and elemental sulfur. XRD and EDS present the microstructure of the CuS nanowire. Spectra show the good crystalline with hexagonal structure of the CuS nanowire arrays and almost a 1:1 composition ratio. In UV analysis we suggested that the absorption peaks at 242 nm and 400 nm might be due to the characteristic of Cu2S phase attributed from extreme few Cu2S composition and the near-IR absorption peak at 825 nm might be due to the characteristic of CuS phase attributed from major CuS nanowires.

Future work  Paper review  利用垂直基板和電化學沉積生成 CuS 奈米 線陣列，並於三月中進行 FIB 的作業。