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S. Feng and L.D. Zhang Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China (Received 18 October 2002; accepted 18 February 2003)

Large-scale single-crystal cubic PbS nanorods were successfully achieved by using ultrasound irradiation in certain ethylenediamine tetraacetic acid (EDTA) solutions, particularly in the solution of Pb:EDTA ⳱ 1:1. The obtained PbS nanorods were characterized using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersed x-ray spectrometry, selected area electronic diffraction, and high-resolution transmission electron microscopy. The results reveal that the PbS nanorods with straight and uniform structure have a diameter of about 70–80 nm and length of about 1000 nm, where the growth mechanism is tentatively discussed. The successful synthesis of these cubic structure semiconductor PbS nanorods may open up new possibilities for using these materials as building blocks to create functional two-dimensional or three-dimensional nanostructured materials.

I. INTRODUCTION

Quasi-one-dimensional (Q1D) nanostructured materials, such as nanorods, nanotubes, and nanowires, have received much attention due to their critical role in fabricating nanodevices with novel electrical, magnetic, and optical properties.1 Bulk PbS is a direct band gap semiconductor with Eg ⳱ 0.41 eV (at room temperature)2 and an exciton Bohr radius of 18 nm.3 The small band gap and large exciton Bohr radius make PbS an interesting system for studying the effect of size confinement. PbS nanostructured material may be one of the highest potential candidates for optical devices such as lightemitting diodes and optical switches due to its exceptional third-order nonlinear optical properties.3 This material is also potentially useful for making devices that require small band gap semiconductors with optical absorption and emission in the red and nearinfrared region of the spectrum.2–4 So synthesis of PbS nanoparticles has been rapidly developed using various techniques.3–7 However, the preparation of PbS Q1D nanostructured materials has rarely been reported.8,9 Recently, the sonochemical method developed by Suslick et al. has proved a useful technique for generating new nanomaterials with unusual properties.10 The

extremely high temperature (about 5000 K), pressure (>20 MP), and cooling rate (>109 K/s) attained during acoustic cavitation within the collapsing bubbles lead to many unique properties in the irradiated solution. Very recently, this method has extensively been used to fabricate various nanostructured materials. Our group has successfully synthesized CdS nanocrystallines with either hexagonal or cubic phase structure at room temperature.11 Sonochemical synthesis of WS2 nanorods12 as well as Ag nanowires13 has also been reported. Meanwhile, Wang et al.14 reported a sonochemical method for the preparation of Bi2S3 nanorods in different complexing agents; however, their nanorods are polycrystalline. Motivated by these works, in