Soft epitaxy of nanocrystal superlattices

Abstract

Epitaxial heterostructures with precise registry between crystal layers play a key role in electronics and optoelectronics. In a close analogy, performance of nanocrystal (NC) based devices depends on the perfection of interfaces formed between NC layers. Here we systematically study the epitaxial growth of NC layers for the first time to enable the fabrication of coherent NC layers. NC epitaxy reveals an exceptional strain tolerance. It follows a universal island size scaling behaviour and shows a strain-driven transition from layer-by-layer to Stranski-Krastanov growth with non-trivial island height statistics. Kinetic bottlenecks play an important role in NC epitaxy, especially in the transition from sub-monolayer to multilayer coverage and the epitaxy of NCs with anisotropic shape. These findings provide a foundation for the rational design of epitaxial structures in a fundamentally and practically important size regime between atomic and microscopic systems.

The mobility of PEG chains versus micellar stability towards the formation of PE‐b‐PEG nanohybrid shish‐kebab on carbon nanotubes

“…Two main factors that control the polymer chain orientation on CNTs during crystal growth are epitaxy and geometrical confinement. When the radius of gyration of a polymer is comparable to CNTs diameter, the polymer chains are forced to align to the CNT's long axis, regardless of the CNTs chirality . In PE‐b‐PEG, PE is the portion of the copolymer that plays the main role because its radius of gyration is comparable with CNTs diameter.…”

“…The prefix number for each segment represents for their weight percentage (Table ). In our previous work, we found that values of the NHSK parameters (diameter, thickness, and periodicity) are the functions of crystallization time, so we selected crystallization time as 1 hour and 6 hours. The results are presented in the preceding sections.…”

“…This time‐dependent increase in the periodic spacing indicates that the polymer crystals might have adjusted along the nanotubes with time. Zheng et al proposed that PE crystals tend to slide down the tubes . This sliding down of PE will provide more room for PEG chains to cohere and attach on CNTs.…”

The nature and implications of uniformity in the hierarchical organization of nanomaterials

“…6B) (82,83). Using the principle of epitaxy, nanoparticle superlattices of one type can even be used as a template for the growth of subsequent nanoparticle crystals of a different type (75). To realize the full potential of this approach, it would be advantageous to develop high-throughput printing techniques that could define nanoscale features into microscale patterns over millimeter lengths.…”

“…Criterion 2: Orientation. The vast majority of nanoparticle assemblies reported use spherical building blocks that, as a result of their continuous rotational symmetry, can adopt any orientation in a crystal and remain equivalent (57,62,(73)(74)(75). The use of anisotropic nanoparticles as building blocks breaks this symmetry and generates inequivalent particle orientations (Fig.…”