No abstract

We report a thermomechanical nanomolding method for crystalline metals. Based on atomic diffusion, this process becomes easier with decreasing mold diameter. As the responsible underlying diffusion mechanism is present in all metals and alloys, discovered nanomolding process provides a toolbox to shape essentially any metal and alloy into nanofeatures. Technologically, this highly versatile and practical thermomechanical nanomolding technique offers a method to fabricate high-surface area metallic nanostructures which are impactful in diverse fields of applications including catalysts, sensors, photovoltaics, microelectronics, and plasmonics. Molding is a manufacturing process in which a pliable or moldable material is formed to replicate a mold. It is used as a processing technique for all major material classes, and the most versatile manufacturing technique for shaping of thermoplastics. The moldability of a material is typically associated with its flow-ability. Such flow-ability is high in thermoplastics, gels, and some glasses, however, low in crystalline metals [1,2]. Metals are either too hard in their crystalline state or too fluid and reactive in their liquid state to be considered for molding. The difficulty of a shape to be molded can be quantified in the aspect ratio between mold cavity depth, L, and mold cavity diameter, d. In general, molding is increasingly more challenging with decreasing d, which can originate from capillary forces [3] or intrinsic size effects, typically related with the length-scale of flow units [4]. Such flow units can be grains in crystalline metals (typically microns) or chain length in plastics (typically nanometers), or shear transformation

No abstract

The fabrication of nanotips has been driven by the increasing industrial demands in developing high-performance multifunctional nanodevices. In this work, we proposed a controlled, rapid as well as low cost nanomolding-necking technology to fabricate gold nanotips arrays. The geometries of gold nanotips having cone angle range of ∼28–77° and curvature radii of <5 nm can be prepared by tailoring the diameters of raw nanorods in nanomolding process or modulating the necking temperature. Molecular dynamics simulation reveals that the formation of the nanotip geometry is determined by the interplay between dislocation-based and diffusion-based deformation mechanisms, intrinsically arising from the nonlinear dependence of atom diffusion on temperature and sample size. The good controllability, mass production and low cost of the developed nanomolding-necking technology make it highly promising in developing nanodevices for a wide range of applications, such as probing, sensing, antireflection coating and nanoindentation.

No abstract