Abstract
A facile method to fabricate large-scaled hexagonal close-packed metal nanocrystal arrays has been developed. The characterization of metal nanocrystals, investigation of their localized surface plasmon resonance (LSPR) properties, and further utilization of the LSPR substrates onto surface enhanced Raman scattering (SERS) applications are studied. The facile method combining colloidal lithography and surface energy driven dewetting process was demonstrated successfully to fabricate large-area, high density, hexagonal close-packed, single crystalline metal (Au, Ag) nanocrystal arrays with controllable crystal size of tens of nanometers, center to center spacing and uniform size distribution. The large-area hexagonal close-packed metal (Au, Ag) nanocrystal arrays with various sizes and center-to-center spacing were prepared and manipulated by regulation of thickness of metal and size of colloidal spheres. Appropriate surface treatments and metal deposition method were shown to be critical for obtaining metal nanocrystal arrays with uniform size. The quality of metal thin films can be improved by surface treatments and uniform metal thin films with the thickness below 4 nm are achieved, extending the controllability over the size of nanocrystal. Larger than 30 × 40 μm2 single superlattice domain of Au nanocrystal arrays were formed on Si and can be transferred to flexible substrates, illustrating the versatility of this method to realize metal nanocrystal arrays on various substrates. In addition to metal nanocrystal arrays, multiple metal/oxide (core/shell and core/dendrite) nanostructure arrays are also successfully fabricated by this method. The good controllability over geometrical parameters and structures of metal/oxide nanostructure arrays by control of the annealing temperature, atmosphere and time is demonstrated and the growth mechanism is proposed. The LSPR responses of metal nanocrystal arrays and metal/oxide nanostructure arrays were systematically measured. The LSPR responses can be manipulated by changing the variety, size of metal nanocrystal and the thickness of oxide shell of metal/oxide nanostructures. Simulations of their extinction (including absorption and scattering) spectra based on Mie theory are conducted for comparison. The experimental results exhibited high consistency with simulation, implying the high controllability of LSPR wavelength can be achieved by this method. Surface enhanced Raman resonance (SERS) properties utilizing the LSPR substrates with metal (Au, Ag) nanocrystal arrays are also demonstrated. Good sensitivity and reproducibility make these LSPR substrates promising candidates for future LSPR based biosensors applications. This method provides an inexpensive and facile route to fabricate a large-scaled close-packed single crystalline metal nanocrystal array with controllable sizes compared to the e-beam lithography method for precise regulation of LSPR wavelength and light scattering cross sections. It exhibits excellent versatility and controllability to fabricate large-scaled metal nanocrystal array and metal/oxide nanostructurs arrays with various size, morphology and structures on different substrates. Single crystallinity and long-range order of metal nanocrystal array can be achieved to enhance LSPR performance and benefit directional propagation, which can lead to significant applications on surface-enhanced Raman scattering (SERS) based biosensors, nanoantennas and other plasmonic optoelectronics.