RESUMO
This work reports a scaffold-templated, bottom-up synthesis of 3D anisotropic nanofeatures on periodic arrays of gold nanoparticles (AuNPs). Our method relies on substrate-bound AuNPs as large seeds with hemispherical shapes and smooth surfaces after the thermal annealing of as-fabricated particles. Spiky features were grown by immersing the patterned AuNPs into a growth solution consisting of a gold salt and Good's buffer; the number and length of spikes could be tuned by changing the solution pH and buffer concentration. Intermediate structures that informed the growth mechanism were characterized as a function of time by correlating the optical properties and spike features. Large-area (cm2) spiky AuNP arrays exhibited surface-enhanced Raman spectroscopy enhancement that was associated with increased numbers of high-aspect-ratio spikes formed on the AuNP seeds.
RESUMO
Cation exchange emerged as a versatile tool to obtain a variety of nanocrystals not yet available via a direct synthesis. Reduced reaction times and moderate temperatures make the method compatible with anisotropic nanoplatelets (NPLs). However, the subtle thermodynamic and kinetic factors governing the exchange require careful control over the reaction parameters to prevent unwanted restructuring. Here, we capitalize on the research success of CdSe NPLs by transforming them into PbSe NPLs suitable for optoelectronic applications. In a two-phase mixture of hexane/N-methylformamide, the oleate-capped CdSe NPLs simultaneously undergo a ligand exchange to NH4I and a cation exchange reaction to PbSe. Their morphology and crystal structure are well-preserved as evidenced by electron microscopy and powder X-ray diffraction. We demonstrate the successful ligand exchange and associated electronic coupling of individual NPLs by fabricating a simple photodetector via spray-coating on a commercial substrate. Its optoelectronic characterization reveals a fast light response at low operational voltages.