Catalyst-Assisted Solution−Liquid−Solid Synthesis of CdS/CdSe Nanorod Heterostructures

Abstract

We report the synthesis and characterization of axial nanorod heterostructures composed of cadmium selenide (CdSe) and cadmium sulfide (CdS). The synthesis employs a solution-liquid-solid (SLS) mechanism with the assistance of bismuth nanocrystals adhered to a substrate (silicon or a III-V semiconductor). Transmission electron microscopy (TEM) and diffraction studies show that CdSe and CdS segments exhibit the wurtzite (hexagonal) crystal structure with <5% stacking faults. Both of these segments grow along the [002] direction with an epitaxial interface between them. Energy-dispersive X-ray (EDX) spectrometry using a high-resolution TEM operating in scanning mode confirms the alloy-free composition modulation in the nanorod heterostructures, showing that Se and S are localized in the CdSe and CdS portions of the nanorod heterostructures, respectively. This study demonstrates that SLS synthesis provides an alternate route to prepare axial nanorod heterostructures that have been difficult to generate using either vapor-liquid-solid growth or catalyst-free solution-phase synthesis.

Formation Mechanism and Properties of CdS-Ag2S Nanorod Superlattices

“…4,5 However, to date, published preparations of 1D superlattices using colloidal growth 6 have been cumbersome with the resulting 1D superlattices, which have only a few layers before the procedure is too difficult. 7 Therefore, instead of relying on sequential methods which require iterated syntheses to produce ordering, it is highly desirable to develop spontaneous ordering methods, where a pattern of nanostructures emerges naturally due to intrinsic interactions on the nanoscale. For instance, in growth of 2D and 3D structures, lattice strain has been used to drive pattern formation on the nanoscale, yielding self-assembled quantum dots and their ordered arrays following epitaxial growth.…”

Effect of Tributylphosphine for the Solution-Liquid-Solid Synthesis of CdSe Nanowires

“…8,[16][17][18] Bi nanocrystals have recently been demonstrated as an ideal catalyst to assist 1D growth of CdSe NWs in solution at relatively low temperatures based on the SLS mechanism.…”

“…16 The main advantage of using substrate-bound catalyst particles is that massive purification and reconcentration step for reaction products are not necessary during the following procedures. And, based on the fact that most of the reaction products were found on substrates, with very few Bi-bound CdSe NWs found in the TOPO solution, it should be noted that the Cr underlayer is critical for the adhesion of the nanocrystals to the substrates.…”

“…Recently, SLS methods for synthesizing CdSe nanowires using bismuth (Bi) thin film as nanocatalyst 16 instead of Bi nanoparticles was introduced. It uses tributylphosphine (TBP) as the solvent of Se powders, and Se/TBP precursor was injected into tri-n-octylphosphine oxide (TOPO) solution containing Cd.…”

Electrically Controlled Catalytic Nanowire Growth from Solution

“…Well-established methods for the wet chemical synthesis of monodisperse CdSe nanocrystals [14][15][16] have recently been extended to yield high-quality CdSe nanowires utilizing the SLS mechanism. [17][18][19][20][21] One aspect that has largely been ignored is the impact of the electrochemical potential of the metal seed particles on the growth process. In the following, we investigate the influence of voltage and electric field on CdSe-nanowire growth off bismuth catalyst particles on platinum electrodes in solution, with the goal of in situ device fabrication.…”