平特五不中

Metamaterials describe a class of materials in which material properties arise from the interaction of electromagnetic waves with the sub-wavelength sized component structures that constitute them. It has become clear that producing nano-based materials with properties not found in nature, such as metamaterials active at optical frequencies, requires breakthroughs in the ability to position materials with nanometer precision. This desire has led to a growing interest in bottom-up, self-assembling systems. In this talk, I will discuss recent developments in two approaches to self-assembly of plasmonic nanoparticles.

One such approach is to use ligands that can trigger self-assembly. We demonstrate that 14-nm silver nanoparticles can quickly and spontaneously self-assemble into highly anisotropic structures in solution using controlled amounts of one of three short ditopic ligands: cysteamine, DTT or cysteine. The self-assembled chain-based structures are bound together through hydrogen bonding, making them reasonably robust over a wide range of solution conditions and temperatures. The degree of self-assembly, and thus the resulting optical properties can be readily dictated by the ligand concentration, pH and solvent. The highly anisotropic spectra are reminiscent of high aspect ratio 1D nanoparticles such as rods, and have not been previously demonstrated to this extent with silver nanoparticles.

Another such approach is to use biomolecules as scaffolds because of the specificity and versatility they provide. In particular, the use of viruses as nanoscale scaffolds offers the promise of exquisite control for positioning on the nanoscale, using a particle that can undergo further self-assembly into extended structures, and allowing the simultaneous creation of many identical complex submicron geometrical structures. We use the TMVcp (Tobacco Mosaic Virus coat protein) command surface to grow and assemble silver nanoparticles. The versatility of TMV allows the formation of continuous in addition to rings of discrete nanoparticles that are characterized by UV-vis and TEM. TEM clearly showed the formation of the rings composed of an average of 5-6 nanoparticles per ring as well as a central nanoparticle under appropriate pH conditions. Discrete Dipole Approximation of AgNPs rings excited by plane wave incident field shows plasmon broadening and red-shift in agreement with the experimental measurements. Our silver rings are believed to be the smallest to date, and they can offer a testing material for existing theories.