Crack-free, ligand-free, phase-pure nanostructured solids, using colloidal nanocrystals as precursors, are fabricated by a scalable and facile approach. Films produced by this approach have conductivities comparable to those of bulk crystals over more than 1 cm (1.370 S cm for PbS films).

Self-assembly is a critical process that can greatly expand the existing structures and lead to new functionality of nanoparticle systems. Multicomponent superstructures self-assembled from nanocrystals have shown promise as multifunctional materials for various applications. Despite recent progress in assembly of homogeneous nanocrystals, synthesis and self-assembly of Janus nanocrystals with contrasting surface chemistry remains a significant challenge. Herein, we designed a novel Janus nanocrystal platform to control the self-assembly of nanoparticles in aqueous solutions by balancing the hydrophobic and hydrophilic moieties. A series of superstructures have been assembled by systematically varying the Janus balance and assembly conditions. Janus Au-Fe3O4 dumbbell nanocrystals (<20 >nm) were synthesized with the hydrophobic ligands coated on the Au lobe and negatively charged hydrophilic ligands coated on the Fe3O4 lobe. We systematically fine-tune the lobe size ratio, surface coating, external conditions, and even additional growth of Au nanocrystal domains on the Au lobe of dumbbell nanoparticles (Au-Au-Fe3O4) to harvest self-assembly structures including clusters, chains, vesicles, and capsules. It was discovered that in all these assemblies the hydrophobic Au lobes preferred to stay together. In addition, these superstructures clearly demonstrated different levels of enhanced surface plasmon resonance that is directly correlated with the Au coupling in the assembly structure. The strong interparticle plasmonic coupling displayed a red-shift in surface plasmon resonance, with larger structures formed by Au-Au-Fe3O4 assembly extending into the nearinfrared region. Self-assembly of Janus dumbbell nanocrystals can also be reversible under different pH values. The biphasic Janus dumbbell nanocrystals offer a platform for studying the novel interparticle coupling and open up opportunities in applications including sensing, disease diagnoses, and therapy.

A common material in creating memristors is titanium dioxide (TiO 2 ), grown by atomic layer deposition, sputtering, or sol-gel process. In this letter, we study the memristive behavior in thin TiO 2 films fabricated by brief electrochemical anodization of titanium. The effects of different anodization times and annealing are explored. We discover that inherent oxygenvacancies at the bottom Ti/TiO 2 interface naturally lead to memristive switching in nonannealed films. Annealing induces extra oxygen vacancies near the top metal/oxide interface, which leads to symmetric and ohmic current-voltage characteristics with a collapse of memristive switching. No clear dependence on anodization time was observed for times between 1 s and 1 min.

The square antiprism/twisted square antiprism ratio in LnDOTA-tetraamide chelates is a critical parameter in governing water-exchange kinetics and ultimately the utility of a chelate as a PARACEST MRI contrast agent. In LnDOTA-tetraamide chelates with tertiary amides, this ratio and the rate of interconversion between these two structural isomers are found to be dramatically dependent upon the solvent and possibly other local environmental factors.The realization that Ln 3+ chelates with slowly exchanging inner-sphere water molecules could induce magnetic resonance imaging (MRI) contrast through a paramagnetic chemical exchange saturation transfer (PARACEST) mechanism has given rise to a recent upsurge in interest in LnDOTA-tetraamide chelates. 1,2 The large paramagnetic hyperfine chemical shifts induced by anisotropic 4f electrons effectively shift the resonance of the inner-sphere water far from that of solvent water. However, because unchelated Ln 3+ ions are toxic, suitable chelating ligands must be employed that both eliminate the toxic effects 3 of these ions and appropriately slow water exchange. 1,2,4,5 Ligands derived from cyclen have been widely accepted in the development of MRI contrast agents, 3 and the related DOTAtetraamide ligands (Chart 1) are now widely studied as PARACEST agents. Although DOTA-tetraamide chelates are kinetically inert, retaining the Ln 3+ ion throughout the in vivo residence of the chelate, 6,7 the use of DOTA-tetraamide ligands in vivo can be problematic. It has been shown that only when the cationic nature of these chelates is offset by anionic substituents, such as carboxylates, can the severe toxic effects intrinsic to cationic chelates be avoided at the relatively high dosing levels required for MRI. 6 A chelate incorporating four glycinateamide substituents has been shown to be safe for in vivo use. 6,7 The unique water-exchange characteristics of these chelates make them attractive as MRI sensors of various biological species such as glucose, Zn 2+ , or protons (pH), [8][9][10][11] species. In such situations, it may be desirable to incorporate the offsetting negative charges as tertiary amide substituents, leaving the sensing secondary amide substituents in place.However, DOTA-tetraamides with tertiary amide pendant arms have not been widely studied as PARACEST agents. Of particular relevance is the coordination chemistry of these chelates. LnDOTA-tetraamide chelates can adopt both a monocapped square antiprismatic (SAP) and a monocapped twisted square antiprismatic (TSAP) coordination geometry, 4,5 and it has been shown that water exchange in complexes that form a TSAP isomer is 1-2 orders of magnitude faster than that in complexes that form a SAP isomer. 4,5,12 Given the requirement for slow exchange kinetics in putative PARACEST agents, it is clearly preferable for the SAP coordination geometry to predominate. Indeed, to our knowledge, the rate of exchange observed in the TSAP isomers of these complexes is so fast that CEST arising from this species has not...

Amphiphilic Janus particles demonstrate unique assembly structures when dried on a hydrophilic substrate. Particle orientations are influenced by amphiphilicity and Janus balance. A three-stage model is developed to describe the process. Simulation further indicates the dominant force is capillary attraction due to the interface pinning at rough Janus boundaries.