No abstract

Colloidal nanoparticle assembly methods can serve as ideal models to explore the fundamentals of homogeneous crystallization phenomena, as interparticle interactions can be readily tuned in order to modify crystal nucleation and growth. However, heterogeneous crystallization at interfaces is often more challenging to control, as it requires that both interparticle and particle-surface interactions be manipulated simultaneously. Here we demonstrate how programmable DNA hybridization enables the formation of single-crystal Winterbottom constructions of substratebound nanoparticle superlattices with defined sizes, shapes, orientations, and degrees of anisotropy. Additionally, we

ABSTRACT:We report here and experimentally demonstrate an actively controlled gate-tunable plasmonic metasurface operating in the visible region of the electromagnetic spectrum, wherestrikingly -the operating voltages for reflectance modulation are much less than 1V. The electrically tunable metasurface consists of inverse dolmen structures (iDolmen) patterned on silver and chromium on a quartz substrate and subsequently covered with a 5 nm thin layer of Al2O3 followed by a 110 nm indium tin oxide (ITO) layer, which acts as a transparent electrode.Our designed structures show up to 78% change in reflection upon applying small voltages (<1V).We explain this behaviour via ion conductance of silver through Al2O3 and ITO, leading to active

Decades of research efforts into atomic crystallization phenomenon have led to a comprehensive understanding of the pathways through which atoms form different crystal structures. With the onset of nanotechnology, methods that use colloidal nanoparticles (NPs) as nanoscale “artificial atoms” to generate hierarchically ordered materials are being developed as an alternative strategy for materials synthesis. However, the assembly mechanisms of NP‐based crystals are not always as well‐understood as their atomic counterparts. The creation of a tunable nanoscale synthon whose assembly can be explained using the context of extensively examined atomic crystallization will therefore provide significant advancement in nanomaterials synthesis. DNA‐grafted NPs have emerged as a strong candidate for such a “programmable atom equivalent” (PAE), because the predictable nature of DNA base‐pairing allows for complex yet easily controlled assembly. This Review highlights the characteristics of these PAEs that enable controlled assembly behaviors analogous to atomic phenomena, which allows for rational material design well beyond what can be achieved with other crystallization techniques.

Hierarchical structural control across multiple size regimes requires careful consideration of the complex energy- and time-scales which govern the system’s morphology at each of these different size ranges. At the nanoscale, synthetic chemistry techniques have been developed to create nanoparticles of well-controlled size and composition. At the macroscale, it is feasible to directly impose material structure via physical manipulation. However, in between these two size regimes at the mesoscale, structural control is more challenging as the physical forces that govern material assembly at larger and smaller scales begin to interfere with one another. In this work, the interplay of structure-directing forces at multiple length-scales is investigated by utilizing optical processing to influence both nanoscale and microscale features of self-assembled, DNA-grafted nanoparticle films. Optical processing is used to generate heat, which causes the self-assembled particles to rearrange from a kinetically trapped, amorphous state into a thermodynamically preferred superlattice structure. The gradient in the heat profile, however, also induces thermophoretic motion within the nanoparticle film, resulting in microscale movement at a comparable time-scale. By utilizing precise exposure times enabled by optical processing, crystallization and thermophoresis occur concurrently in the self-assembling nanoparticle system, enabling a dynamic growth mechanism whereby nucleation and growth occur in separate regions of the material. Furthermore, utilizing sufficiently short processing times allows for the formation of a fluidlike state of the DNA-functionalized nanoparticle materials that is inaccessible via typical thermal processing setups. This unique phase of the material allows for both pathway-dependent and pathway-independent growth phenomena, as appropriately tuning the experimental conditions enables the formation of morphologically equivalent nanoparticle lattices that are generated through different intermediate states (pathway-independent structures), or kinetically preprocessing a material to yield unique thermodynamic arrangements of particles once fully annealed (pathway-dependent structures).