Semiconductor nanowires (NWs) have been studied extensively for over two decades for their novel electronic, photonic, thermal, electrochemical and mechanical properties. This comprehensive review article summarizes major advances in the synthesis, characterization, and application of these materials in the past decade. Developments in the understanding of the fundamental principles of "bottom-up" growth mechanisms are presented, with an emphasis on rational control of the morphology, stoichiometry, and crystal structure of the materials. This is followed by a discussion of the application of nanowires in i) electronic, ii) sensor, iii) photonic, iv) thermoelectric, v) photovoltaic, vi) photoelectrochemical, vii) battery, viii) mechanical, and ix) biological applications. Throughout the discussion, a detailed explanation of the unique properties associated with the one-dimensional nanowire geometry will be presented, and the benefits of these properties for the various applications will be highlighted. The review concludes with a brief perspective on future research directions, and remaining barriers which must be overcome for the successful commercial application of these technologies.

Abstract:The kinetics and uniformity of ion insertion reactions at the solid/liquid interface govern the rate capability and lifetime, respectively, of electrochemical devices such as Li-ion batteries.We develop an operando X-ray microscopy platform that maps the dynamics of the Li composition and insertion rate in LiXFePO4, and show that nanoscale spatial variations in rate and in composition control the lithiation pathway at the sub-particle length scale. Specifically, spatial variations in the insertion rate constant lead to the formation of nonuniform domains, and the composition dependence of the rate constant amplifies nonuniformities during delithiation but suppresses them during lithiation, and moreover stabilizes the solid solution during lithiation. This coupling of lithium composition and surface reaction rates controls the kinetics and uniformity during electrochemical ion insertion.One Sentence Summary: X-ray microscopy reveals the nanoscale evolution of composition and reaction rate inside a Li-ion battery during cycling Main Text: The insertion of a guest ion into the host crystal is the fundamental reaction underpinning insertion electrochemistry and has been applied to store energy (1), tune catalysts (2), and switch optoelectronic properties (3). In Li-ion batteries, for example, Li ions from the 2 liquid electrolyte insert into solid host particles in the electrode. Nanoscale intraparticle electrochemical inhomogeneities in phase and in composition are responsible for mechanical strain and fracture which decrease the reversibility of the reaction (4). Moreover, these nonuniformities make it difficult to correlate current-voltage measurements to microscopic ion insertion mechanisms. Simultaneously quantifying nonuniform nanoscale reaction kinetics and the underlying material composition at the solid-liquid interface holds the key to improving device performance.A gold standard material for investigating ion insertion reactions is LiXFePO4 (0