The fabrication of well-ordered metal-nanoparticle (NP) arrays on either rigid or flexible substrates is of considerable interest in modern science and technology for applications as diverse as electronics, photonics, informatics, sensors, and catalysis.[1] For example, nanofabrication on optically transparent flexible substrates is spawning novel and unique applications, including plastic electronics and organic light-emitting displays.[2] A template-assisted nanofabrication strategy based on self-assembled nanostructures is one promising method for macroscopically manipulating nanopatterned surfaces for practical applications. [1][2][3][4][5][6][7][8][9] Among the potential self-assembled templates, phase-segregated block copolymers have drawn much attention because they can give rise to tunable periodic nanostructures with various geometries. [3][4][5][6][7][8][9][10] Many approaches, including physical vapor deposition, [11,12] chemical vapor deposition, [13][14][15] electroless deposition, [16,17] galvanic displacement, [18,19] electrochemical plating, [20,21] sol-gel chemistry, [22] chemical reduction, [23] and pyrolysis, [24] have been widely explored as options for arranging metal NPs onto robust substrates by using a block copolymer template. For example, very recently our group has demonstrated that Au NPs can be assembled via a site-specific recognition between hydrophilic/ hydrophobic NPs and the nanodomains of phase-segregated, amphiphilic, diblock copolymer films. [25] In contrast, a novel hybrid nanofabrication process, block copolymer lithography, [26][27][28][29][30][31][32] has recently been extensively investigated because it successfully combines advantages of both the top-down (lithography) and bottom-up (block copolymer template) techniques, where high-energy irradiation, such as laser, [26] plasma, [27][28][29] electron beam, [30] or ion beam, [31,32] has been utilized to both generate periodic arrays of nano-objects and remove the copolymer template in a single step. [3][4][5][6][7][8][9] Unfortunately, less attention has been paid to the site-selective metallization of long-range-ordered nanostructures on optically transparent polymer substrates, potentially leading to flexible electronic and photonic devices beyond conventional Si-based technology.[1] A further challenge is to develop a versatile procedure for efficient nanostructure fabrication on both soft and hard substrates.[2] Herein, we demonstrate the simple but widely applicable vacuum ultraviolet (VUV)-assisted nanofabrication of a hexagonally arranged, high-density Ag-NP array with a tunable interparticle distance on either a rigid or flexible substrate over a large area. The key to the nanofabrication process described here is that the VUV irradiation drives both the photoreduction of the selectively infiltrated Ag + to metallic Ag NPs and the etching of the template of the copolymer film in one step. It is well known that Ag + can be photochemically reduced in the presence of an appropriate electron donor, [33] and this appro...