Dynamical Self-assembly during Colloidal Droplet Evaporation Studied by in situ Small Angle X-ray Scattering

The nucleation and growth kinetics of highly ordered nanocrystal superlattices during the evaporation of nanocrystal colloidal droplets was elucidated by in situ time resolved small-angle x-ray scattering. We demonstrated for the first time that evaporation kinetics can affect the dimensionality of the superlattices. The formation of two-dimensional nanocrystal superlattices at the liquid-air interface of the droplet has an exponential growth kinetics that originates from interface "crushing".Comment: 4 pages, 4 figure

A plasmonic fluid with dynamically tunable optical properties

We report the first synthesis of a gold nanorod (GNR)-based nanocomposite that exhibits solid-like plasmonic properties while behaving in a liquid-like manner. Tuning the degree of GNR clustering controls the material's responsiveness to external stimuli, such as mechanical shearing, due to the sensitivity of the localized surface plasmon resonance to interparticle interactions.We would like to acknowledge Prof. Lynden Archer for helpful discussions. This work was made possible by Award No. KUS-C1-018-02 made by King Abdullah University of Science and Technology(KAUST). We acknowledge use of facilities at the Cornell Center for Materials Research, a National Science Foundation Materials Research Science and Engineering Center (NSF DMR-0520404), and the Cornell High Energy Synchrotron Source, also supported by the National Science Foundation and NIH-NIGMS(NSF DMR-0225180)

X-ray scattering from surfaces of organic crystals

X-ray scattering experiments have been performed on the surfaces of organic crystals. The (010) cleavage planes of β-alanine and α-glycine were investigated, and both specular and off-specular crystal truncation rods were measured. This allowed a determination of the molecular layering at the cleavage planes. Furthermore, the surfaces were investigated during growth and dissolution. No change in surface structure was observed, suggesting that the growth and dissolution is performed via the step edges. Finally, experiments on stereospecific adsorption of methionine on α-glycine were performed, showing that the (S)-methionine molecules are orderly attached to the surface of α-glycine and also attached to the (010) surface, but not in registry with the substrate

Transition between dynamic regimes in the sputter ablation of Ge(001)

We have studied the dynamic behavior of the Ge(001) surface during sputtering using in situ, real-time synchrotron X-ray diffraction. Two dynamic regimes were found which are characterized by kinetic roughening exponents β of 0.1 and 0.4, respectively. We observed an abrupt transition of the system between these two dynamic regimes both as a function of temperature and ion current. From the boundary between the regimes we derive an activation energy of the relevant diffusion process of 1.1 eV