Laser-induced modification of dog-bone-like Au nanorods for accurate growth of well-defined cylindrical structures

Abstract

Gold nanorods (Au NRs) with regular cylindrical structures can be prepared by the conventional seed-mediated growth method. But for every success, there are dozens of failures. In most cases, a significant fraction of irregular Au NRs with dog-bone-like structures are also frequently formed. Therefore, a complementary way (the reshaping of irregular rods, etc.) to reduce the defective rate in the fabrication of regular Au NRs is urgently desired. In this paper, a novel and effective strategy for accurate growth of well-defined cylindrical Au NR structures with fairly good uniformity is developed by laser-induced shape-modification of dog-bone-like Au NRs. In the first step, large-scale irregular shaped Au NRs with dog-bone-like structures were prepared by the standard seed-mediated growth approach. Subsequently, highly mono-dispersed perfect Au NRs with ultra-smooth surfaces can be obtained by non-focused laser irradiation of the irregular Au NR solution. The irradiation parameters such as laser power density, irradiation time and laser wavelength play an important role in the accurate growth of Au NRs. At optimum conditions (∼5 W cm⁻², <100 s, 1064 nm), a laser-induced reshaping process in the growth solution can also be employed to grow the cylindrical Au NRs into longer structures with aspect ratios ranging from about 2.3 to 5.6. After laser irradiation, the absorption spectra of the Au NRs show that longitudinal localized surface plasmon resonance (LSPR) peaks can be effectively modulated from about 750 nm to 810 nm. On the other hand, by adding some H₂PtCl₆ in the as-prepared Au NR growth solution, laser irradiation will lead to a guided growth behavior of a Pt–Ag structure, resulting in the fabrication of Pt–Ag nano-islands on Au NRs. Thus, it can be seen that the laser-induced modification is a simple, low-cost and high-throughput strategy to prepare noble metal perfectly cylindrical nano-structures with multiple structural controlling capabilities.