Axially Segmented Semiconductor Heteronanowires

Abstract

Conspectus Programming nanoscale functional objects into complex, sophisticated heterostructures that tremendously outperform their solo objects and even bring about exotic chemical/physical properties offers exciting routes toward a spectrum of applications in photonics and electronics. The development in synthetic chemistry over past decades has enabled a library of hybrid nanostructures, such as core–shell, patchy, dimer, hierarchical/branched ones, etc. Nevertheless, the material combinations of these non-van der Waals solids are largely limited by the rule of lattice-matched epitaxy thereof. As an emerging class of heterostructures, axially segmented nanowires (ASNWs) offer an alternative but effective approach to epitaxially integrating the conventional non-van der Waals solids. The large lattice-mismatch tolerance in ASNWs permits vast material combinations, broad size modulations, and flexible interfacial strain engineering, signifying the great potentials for engineering their photon utilizations, band structures, features of charge carriers or excitons, and some other emerging properties. Unfortunately, ASNWs with on-demand, high-precision control over composition, shape, dimension, crystal phase, interface, and periodicity remain so far synthetically challenging. By steering the chemoselective reactions, one has access to high-precision ASNWs. In this Account, we describe the state-of-the-art synthetic strategies for chemoselectivity control. We categorize them into (i) unidirectional/bidirectional sequential additions, which include selective area epitaxy, catalyzed growth, and end-facet-seeded growth, and (ii) regiospecific one-off transformations, which include ionic exchange reaction, strain/thermal induced phase segregation and transition, Plateau-Rayleigh instability, regioselective heterogeneous nucleation as ruled by lattice match, defect, and surface charges, and nanomasking. We uncover the chemical principles behind from thermodynamic and kinetic aspects. Then we further offer insights into their fundamental physics (including carrier/photon/phonon confinement, mixed dimensionality, quantum dot–nanowire interaction, and interdot coupling effect) that are strongly correlated with a spectrum of applications, highlighting how the precise control of compositions and structures ultimately dictates their properties and functions. In the end, we conclude by describing current challenges and future directions of this field in terms of material synthesis, growth mechanism, exotic physics, and performance optimization. By crafting ASNWs at atomic precision, high-performance ASNWs with sophisticated electronic and phonon structures can be envisioned ultimately for applications in diverse fields, spanning from solar energy conversion and thermoelectrics to optoelectronics and quantum communications.

Selective Excitation of CdSe/CdS Dot‐in‐Rod Nanocrystals and Distinct Roles of Electrons and Holes in Photophysical and Photochemical Interactions with Ambient Air

“…Such fast separation of the photogenerated carriers can be explained by two facts. First, the diffusion length of carriers in CdS materials (such as bulk and polycrystals) is on the scale of at least tens of nanometers, [34,35] which is much greater than the diameter (about 5.1 nm) of the CdS nanorods. Second, the carrier capture by the CdSe QDs as well as the CdS surface is very efficient.…”

Generalized Colloidal Approach for Preparing Epitaxial 1D/2D Heterostructures

“…Therefore, the 1D/2D heterostructures require a distinct growth behavior during secondary growth compared with that of seeds. It is still a great challenge in epitaxial heterostructures because the growth of seeds and subsequent seeded growth easily yield materials of same dimensionalities, especially for materials with the same crystalline structures. − …”

One-Dimensional Superlattice Heterostructure Library

“…We took the view that epitaxially organizing synthetic functional nano-objects into axial superlattice nanowires (ASLNWs)  the one-dimensional derivatives of film superlatticesoffers a fertile ground for engineering such high-performance heterostructures (Figure c). Compositionally, the large lattice-mismatch tolerance in ASLNWs allows vast material combinations, therefore enabling unblocked, full utilization of solar irradiations, , strain engineering to modulate exciton binding energy, effective masses of charge carriers, and electronic density of states − as well as flexibly engineered type-II band alignment to achieve electron- or hole-involved processes at distinct sub-objects.…”