Three-Dimensionally Complex Phase Behavior and Collective Phenomena in Mixtures of Acoustically Powered Chiral Microspinners.

The process of dynamic self-organization of small building blocks is fundamental to the emergent function of living systems and is characteristic of their out-of-equilibrium homeostasis. The ability to control the interactions of synthetic particles in large groups could lead to the realization of analogous macroscopic robotic systems with microscopic complexity. Rotationally induced self-organization has been observed in biological systems and modeled theoretically, but studies of fast, autonomously moving synthetic rotors remain rare.

Enhanced Carrier Transport in Strongly Coupled, Epitaxially Fused CdSe Nanocrystal Solids.

Strongly coupled, epitaxially fused colloidal nanocrystal (NC) solids are promising solution-processable semiconductors to realize optoelectronic devices with high carrier mobilities. Here, we demonstrate sequential, solid-state cation exchange reactions to transform epitaxially connected PbSe NC thin films into CuSe nanostructured thin-film intermediates and then successfully to achieve zinc-blende, CdSe NC solids with wide epitaxial necking along {100} facets. Transient photoconductivity measurements probe carrier transport at nanometer length scales and show a photoconductance of 0.

Chemo- and Thermomechanically Configurable 3D Optical Metamaterials Constructed from Colloidal Nanocrystal Assemblies.

Nanofabrication has limited most optical metamaterials to 2D or, often with multiple patterning steps, simple 3D meta-atoms that typically have limited built-in tunability. Here, with a one-step scalable patterning process, we exploit the chemical addressability and structural adaptability of colloidal Au nanocrystal assemblies to transform 2D nanocrystal/Ti bilayers into complex, 3D-structured meta-atoms and to thermally direct their shape morphing and alter their optical properties. By tailoring the length, number, and curvature of 3D helical structures in each meta-atom, we create large-area metamaterials with chiroptical responses of as high as ∼40% transmission difference between left-hand (LCP) and right-hand (RCP) circularly polarized light (Δ = - ) that are suitable for broadband circular polarizers and, upon thermally configuring their shape, switch the polarity of polarization rotation.

Designing Strong Optical Absorbers Continuous Tuning of Interparticle Interaction in Colloidal Gold Nanocrystal Assemblies.

We program the optical properties of colloidal Au nanocrystal (NC) assemblies an unconventional ligand hybridization (LH) strategy to precisely engineer interparticle interactions and design materials with optical properties difficult or impossible to achieve in bulk form. Long-chain hydrocarbon ligands used in NC synthesis are partially exchanged, from 0% to 100%, with compact thiocyanate ligands by controlling the reaction time for exchange. The resulting NC assemblies show transmittance, reflectance, optical permittivity, and direct-current (DC) resistivity that continuously traverse a dielectric-metal transition, providing analog tuning of their physical properties, unlike the digital control realized by complete exchange with ligands of varying length.

Air-Stable CuInSe Nanocrystal Transistors and Circuits via Post-Deposition Cation Exchange.

Colloidal semiconductor nanocrystals (NCs) are a promising materials class for solution-processable, next-generation electronic devices. However, most high-performance devices and circuits have been achieved using NCs containing toxic elements, which may limit their further device development. We fabricate high mobility CuInSe NC field-effect transistors (FETs) using a solution-based, post-deposition, sequential cation exchange process that starts with electronically coupled, thiocyanate (SCN)-capped CdSe NC thin films.

Ultrasensitive, Mechanically Responsive Optical Metasurfaces via Strain Amplification.

Optical metasurfaces promise ultrathin, lightweight, miniaturized optical components with outstanding capabilities to manipulate the amplitude, phase, and polarization of light compared to conventional, bulk optics. The emergence of reconfigurable metasurfaces further integrates dynamic tunability with optical functionalities. Here, we report a structurally reconfigurable, optical metasurface constructed by integrating a plasmonic lattice array in the gap between a pair of symmetric microrods that serve to locally amplify the strain created on an elastomeric substrate by an external mechanical stimulus.

3D Nanofabrication via Chemo-Mechanical Transformation of Nanocrystal/Bulk Heterostructures.

Planar nanocrystal/bulk heterostructures are transformed into 3D architectures by taking advantage of the different chemical and mechanical properties of nanocrystal and bulk thin films. Nanocrystal/bulk heterostructures are fabricated via bottom-up assembly and top-down fabrication. The nanocrystals are capped by long ligands introduced in their synthesis, and therefore their surfaces are chemically addressable, and their assemblies are mechanically "soft," in contrast to the bulk films.

The Effect of Dielectric Environment on Doping Efficiency in Colloidal PbSe Nanostructures.

Doping, as a central strategy to control free carrier type and concentration in semiconductor materials, suffers from low efficiency at the nanoscale, especially in systems having high permittivity (ϵ) and large Bohr radii, such as lead chalcogenide nanocrystals (NCs) and nanowires (NWs). Here, we study dielectric confinement effects on the doping efficiency of lead chalcogenides nanostructures by integrating PbSe NWs in the platform of field effect transistors (FETs). Elemental Pb or In or elemental Se is deposited by thermal evaporation to remotely n- or p-dope the NWs.

Advanced Architecture for Colloidal PbS Quantum Dot Solar Cells Exploiting a CdSe Quantum Dot Buffer Layer.

Advanced architectures are required to further improve the performance of colloidal PbS heterojunction quantum dot solar cells. Here, we introduce a CdI-treated CdSe quantum dot buffer layer at the junction between ZnO nanoparticles and PbS quantum dots in the solar cells. We exploit the surface- and size-tunable electronic properties of the CdSe quantum dots to optimize its carrier concentration and energy band alignment in the heterojunction.