Dopant‐Induced Formation of Branched CdS Nanocrystals

Abstract

The dimensions and structures of semiconductor nanocrystals (NCs) play an important role in determining the electronic and optical properties of the materials. In the past few years, much effort has been expended to control the size and shape of these materials. One way to control NC structures is to enhance anisotropic growth using an external catalytic medium such as the metallic nanoparticles employed in vapor–liquid–solid (VLS) and solution–liquid–solid (SLS) processes. Another common approach using surfactants as capping agents or soft templates can be utilized in a solution system to facilitate anisotropic crystal growth. Tetrapods, a unique example of these anisotropically shaped NCs, find potential applications in nanocomposites and nanoscale devices. For example, because of the three-dimensionally extending structures, tetrapods may be a promising building unit for the preparation of interesting superstructures for nanoelectronics, especially three-dimensional (3D) prototypes. In addition, semiconductor tetrapods have potential advantages in hybrid NC/ polymer photovoltaic devices because their 3D structures make it facile for them to orderly align toward the electrodes within the polymer film, providing a direct charge-carrier transportation pathway to improve the device performance. Up to now, nanometer-sized tetrapod crystals have been synthesized for a variety of II–VI semiconductors including ZnO, CdS, CdSe, and CdTe. The most often observed crystallographic feature of these tetrapod NCs is one cubic zinc blende (ZB) core attached with four hexagonal wurtzite (WZ) arms. Evidently, to form such novel architecture, one should have the crystals nucleate in the ZB phase followed by anisotropic growth in the WZ phase. The former stage can be achieved through kinetic control of the reaction