Three Synthesis Routes of Single-Crystalline PbS Nanowires and Their Electrical Transport Properties
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Three Synthesis Routes of Single-Crystalline PbS Nanowires and Their Electrical Transport Properties So Young Jang, Yun Mi Song, Han Sung Kim, Yong Jae Cho, Young Suk Seo, Gyeong Bok Jung, Chi-Woo Lee, Jeunghee Park Department of Chemistry, Korea University, Jochiwon 339-700, Korea ABSTRACT Single-crystalline rock-salt PbS nanowires (NWs) were synthesized using three different routes; the solvothermal, chemical vapor transport, and gas-phase substitution reaction of pre-grown CdS NWs. They were uniformly grown with the [100] or [110], [112] direction in a controlled manner. In the solvothermal growth, the oriented attachment of the octylamine (OA) ligands enables the NWs to be produced with a controlled morphology and growth direction. As the concentration of OA increases, the growth direction evolves from the [100] to the higher surfaceenergy [110] and [112] directions. In the synthesis involving chemical vapor transport and the substitution reaction, the use of a lower growth temperature causes the higher surface-energy growth direction to change from [100] to [110]. We fabricated field effect transistors using single PbS NW, which showed intrinsic p-type semiconductor characteristics for all three routes. For the PbS NW with a thinner oxide layer, the carrier mobility was measured to be as high as 10 cm2V−1s−1. INTRODUCTION Since the discovery of carbon nanotubes (CNTs), a tremendous amount of research has been conducted on the synthesis and utilization of one-dimensional (1D) as well-defined building blocks.1-2 The success of various applications depends on the quality control of the nanostructures.3-5 As one of the important IV-VI semiconductor materials, rock-salt (facecentered cubic) structured PbS nanostructures have been the object of particular attention, because of the narrow band gap (0.41 eV at room temperature) and its large Bohr radius (ca. rB = 18 nm).6 The synthesis of PbS NWs has been reported using various methods including template-assisted deposition,7-9 hydrotherthermal,10-12 solvothermal,13-15 chemical vapor transport (CVT),16-18 , and electron-beam irradiation.19 However, developing an improved synthesis method that increases the yield of PbS NWs with controlled morphology and crystal structure (i.e., single crystallinity, growth direction, etc.) remains still quite a challenge. In the present work, we report single-crystalline PbS NWs synthesized using three methods; (i) the solvothermal reaction, (ii) CVT, and (iii) gas-phase conversion reaction of pre-grown CdS NWs as templates. In the solvothermal growth, octylamine was used as a ligand offering “sufficient” protection, which causes the progressive evolution of the morphology and growth direction of the PbS NWs. The CVT method using PbCl2 and S as the precursors under argon flow enables single-crystalline PbS NWs to be grown. The gas-phase conversion of the CdS NWs into PbS NWs involves the substitution reaction. For both the CVT and substitution methods, we demonstrated that the growth direction is controllable, mainly by ad
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