Compared with 2D or 3D assembly models, 1D assembly of functional nanoparticles (NPs) is more difficult to prepare due to its higher surface energy. Despite the fabrication difficulty, 1D assembly of NPs exhibits many unique properties, and can directionally transport excitons, photons, phonons, etc., which generate great interest in considerable applications in biomedicine, data storage, waveguiding, highly sensitive sensors, color displays, microcircuits and others. The unique features of 1D assembly of NPs can bridge fabrication of NPs with their practical device applications. The aim of this Tutorial Review is to introduce the general mechanisms to assemble NPs in one direction. To achieve 1D assembly of NPs, different kinds of traditional and newly developed assembly strategies will be discussed. Finally, some examples will be demonstrated to illustrate the applications of NP 1D assemblies in the fields of optics, electronics and magnetics.

What is static charge? Despite the long history of research, the identity of static charge and mechanism by which static is generated by contact electrification are still unknown. Investigations are challenging due to the complexity of surfaces. This study involves the molecular-scale analysis of contact electrification using highly well-defined surfaces functionalized with a self-assembled monolayer of alkylsilanes. Analyses show the elementary molecular steps of contact electrification: the exact location of heterolytic cleavage of covalent bonds (i.e., Si-C bond), exact charged species generated (i.e., alkyl carbocation), and transfer of molecular fragments. The strong correlation between charge generation and molecular fragments due to their signature odd-even effects further shows that contact electrification is based on cleavage of covalent bonds and transfer of ionic molecular fragments. Static charge is thus an alkyl carbocation; in general, it is an ionic molecular fragment. This mechanism based on cleavage of covalent bonds is applicable to general types of insulating materials, such as covalently bonded polymers. The odd-even effect of charging caused by the difference of only one atom explains the highly sensitive nature of contact electrification.