Nanotechnology is touted as the next logical sequence in technological evolution. This has led to a substantial surge in research activities pertaining to the development and fundamental understanding of processes and assembly at the nanoscale. Both top-down and bottom-up fabrication approaches may be used to realize a range of well-defined nanostructured materials with desirable physical and chemical attributes. Among these, the bottom-up self-assembly process offers the most realistic solution toward the fabrication of next-generation functional materials and devices. Here, we present a comprehensive review on the physical basis behind self-assembly and the processes reported in recent years to direct the assembly of nanoscale functional blocks into hierarchically ordered structures. This paper emphasizes assembly in the synthetic domain as well in the biological domain, underscoring the importance of biomimetic approaches toward novel materials. In particular, two important classes of directed self-assembly, namely, (i) self-assembly among nanoparticle-polymer systems and (ii) external field-guided assembly are highlighted. The spontaneous self-assembling behavior observed in nature that leads to complex, multifunctional, hierarchical structures within biological systems is also discussed in this review. Recent research undertaken to synthesize hierarchically assembled functional materials have underscored the need as well as the benefits harvested in synergistically combining top-down fabrication methods with bottom-up self-assembly.

Hydrogen generation and storage is an essential component in the increasingly important field of energy storage. Electrochemical generation of hydrogen atoms at the surface of Pt like metals at select potentials is a widely accepted phenomenon. However, moving these adsorbed hydrogen atoms to high surface area support systems for storage is an issue. We show spillover of these adsorbed hydrogen atoms to the supporting structure for sub-2 nm Pt nanoparticles sputtered on Fluorine Doped Tin Oxide (FTO) and on few layer graphene (FLG) supports. Evidence of size-dependent hydrogen spillover was observed for Pt nanoparticles deposited using tilted target sputtering and a correlation between nanoparticle size, crystallinity, support characteristics, and hydrogen spillover is also reported. Evidence of C–H bonds formed on the FLG surface due to H spillover from 0.9 nm Pt nanoparticles was also confirmed through XPS analysis.