Surface coating with inorganic materials such as SiO 2 , [31][32][33] TiO 2 , [34][35][36] or yttria-stabilized zirconia [37] has been commonly used to achieve thermal stability of various individual nanoparticles including GNRs [38][39][40] or nanoporous gold. [41] Encapsulation of individual GNRs with silica, forming core-shell structure, makes GNRs stable up to 700 and 800 °C [39] while surfactant or polymer-coated GNRs become degraded at temperature as low as 100 °C. [29,42] This encapsulation approach, however, has not been successfully applied for GNR superlattices yet. Recently, an impregnation method has been used to protect the GNR superlattices with porous silica, in which a preformed GNR superlattice on substrate was immersed in a silica precursor solution. [43] While the GNR superlattice made by the impregnation method was quite stable in water, it became significantly degraded at 150 °C because silica layer was formed over the superlattice and between the individual lamellae of GNRs inside the structure without covering the individual GNRs. [43] To achieve the stability of GNR superlattice at high temperature, therefore, a new method to protect individual GNRs in the superlattice should be developed.In this study, we developed a new method to fabricate 2D hexagonal GNR superlattices on substrate in which each GNR is individually encapsulated with silica, providing an excellent stability at high temperature and in solvents of different polarities. In this method, cetyltrimethylammonium bromide (CTAB) bilayer-covered GNRs dispersed in silica precursor solution at a highly acidic condition are self-assembled into the 2D monolayer superlattice upon drop casting on substrate, during which the condensation of silica precursors adsorbed on the CTAB bilayer and the slow solvent evaporation occur simultaneously. The GNR superlattices embedded in the silica matrix are stable at temperature as high as 500 °C and in various solvents of different polarity, well maintaining the cylindrical shape of GNRs and their hexagonal packing. The structural stability makes the GNR superlattice embedded in the silica matrix a highly reusable surface-enhanced Raman scattering (SERS) active substrate for molecular detection, as evidenced by the signal intensities well maintained over 10 cycles. To the best of our knowledge, this is the GNR superlattice with the highest thermal and solvent stability reported so far.A facile method to fabricate 2D hexagonal monolayer superlattices of gold nanorods (GNRs) individually embedded in silica matrix on a substrate is developed. In this method, the cetyltrimethylammonium bromide (CTAB) bilayer-coated GNRs are self-assembled into a hexagonally packed monolayer superlattice on the substrate by slow evaporation in the presence of silica precursors in the solution at a highly acidic condition. The GNR superlattices fabricated by this method show excellent structural stability at high temperature as high as 500 °C and in solvents of a wide range of polarities including water, ethanol, toluene...

A facile method to fabricate self‐assembled 2D hexagonal monolayer superlattices of gold nanorods (GNRs) individually embedded in silica matrix on a substrate is developed. The GNR superlattices show excellent structural stability at high temperature and in various solvents, making the GNR superlattices highly reusable surface‐enhanced Raman scattering (SERS) active substrates for sensitive molecular detection. More details can be found in article number 1900986 by Sung‐Hwan Lim, Sung‐Min Choi, and co‐workers.