CiteULike: dchen's nano

Soft Nanopolyhedra as a Route to Multivalent Nanoparticles

Jiunn Roan — 2008-05-05T15:43:40-00:00

Physical Review Letters, Vol. 96, No. 24. (2006)

Computer simulations show that end-grafted immiscible homopolymers can confer multivalence to nanoparticles, resulting in soft nanopolyhedra with structures identical to those found in small clusters of colloidal microspheres. Unprecedented structure tunability is demonstrated by several structure transition sequences, including a reentrant transition, induced by varying composition, polymer lengths, or grafting patterns. These results suggest a new method for fabricating nanoparticles with precisely controlled numbers and locations of functional sites (i.e., multivalent nanoparticles).

Superstability of Surface Nanobubbles

Bram Borkent — 2008-05-04T16:08:51-00:00

Physical Review Letters, Vol. 98, No. 20. (2007)

Shock wave induced cavitation experiments and atomic force microscopy measurements of flat polyamide and hydrophobized silicon surfaces immersed in water are performed. It is shown that surface nanobubbles, present on these surfaces, do not act as nucleation sites for cavitation bubbles, in contrast to the expectation. This implies that surface nanobubbles are not just stable under ambient conditions but also under enormous reduction of the liquid pressure down to -6 MPa. We denote this feature as superstability.

Time-Resolved Shadowgraphs of Material Ejection in Intense Femtosecond Laser Ablation of Aluminum

Nan Zhang — 2008-05-03T23:46:49-00:00

Physical Review Letters, Vol. 99, No. 16. (2007)

The dynamic process of intense 50 fs laser ablation of aluminum is investigated by ultrafast time-resolved microscopy. A stripe pattern preceding phase explosion is clearly seen in the shadowgraph of 1 ns time delay. Intermittent material ejections are observed within the ejected plume after 2.5 and 7 ns time delay, respectively, which may be attributed to the material response to the generation of an extremely strong thermoelastic wave. Similar processes are also recorded in the ablation of silicon and glass samples, except for the glass samples, the intermittent material ejections are not found.

Imaging Surface Topography using Lloyd's Mirror in Photoemission Electron Microscopy

DE Jesson — 2008-05-03T18:26:53-00:00

Physical Review Letters, Vol. 99, No. 1. (2007)

We use Lloyd's mirror to modulate electron photoemission in photoemission electron microscopy. This results in the projection of Lloyd's fringes on to three-dimensional (3D) surface objects. An iterative reconstruction method is used to correct for distortions in the fringe pattern due to the cathode immersion lens, thereby providing a quantitative interpretation of surface shape. It is therefore possible to extract 3D height information directly from a two-dimensional, plan-view image. The technique is of sufficient intensity and contrast to study real-time changes in surface topography and we apply the method to study unusual contact-line dynamics during the reactive wetting of metal droplets.

Nanoparticle Assembly at Fluid Interfaces: Structure and Dynamics

Y Lin — 2008-04-29T22:19:44-00:00

Langmuir, Vol. 21, No. 1. (4 January 2005), pp. 191-194.

Abstract: The self-assembly of nanoparticles at fluid interfaces, driven by the reduction in interfacial energy, was investigated. With spherical, tri-n-octyl-phosphine-oxide covered cadium selenide (CdSe) nanoparticles (1-8 nm), thermal fluctuations compete with the interfacial segregation giving rise to a size-dependent self-assembly of the particles. The structure of the nanoparticle assembly was studied using electron microscopy, atomic force microscopy, and X-ray scattering in situ, which indicate that the particles form a densely packed monolayer. The energetics of the adsorption of nanoparticles onto the interface was revealed by time-dependent fluorescence studies on a mixture of two different sized nanoparticles at the interface. The dynamics of the nanoparticles at the fluid interface, probed using fluorescence photobleaching methods, suggests a liquid-like behavior. The results have implications in the design of hierarchical self-assemblies of nanoparticles for the one-step fabrication of devices on multiple length scales.

Microrheology with modulated optical nanoprobes (MOONs)

Caleb Behrend — 2007-07-26T18:15:07-00:00

Journal of Magnetism and Magnetic Materials, Vol. 293, No. 1. (May 2005), pp. 663-670.

Metal-capping of one hemisphere of a nano or microparticle breaks the particle's optical symmetry, allowing its orientation to be tracked using fluorescence and reflection. Tracking orientation and rotation allows the torques acting on the particles be inferred. In addition to serving as rotational nanoviscometers these probes report on local Brownian, magnetic and biomechanical torques.

From Micro- to Nanofabrication with Soft Materials

Stephen Quake — 2007-09-27T08:45:33-00:00

Science, Vol. 290, No. 5496. (24 November 2000), pp. 1536-1540.

10.1126/science.290.5496.1536

Hard-X-Ray Lensless Imaging of Extended Objects

JM Rodenburg — 2008-03-19T17:07:12-00:00

Physical Review Letters, Vol. 98, No. 3. (2007)

We demonstrate a hard-x-ray microscope that does not use a lens and is not limited to a small field of view or an object of finite size. The method does not suffer any of the physical constraints, convergence problems, or defocus ambiguities that often arise in conventional phase-retrieval diffractive imaging techniques. Calculation times are about a thousand times shorter than in current iterative algorithms. We need no a priori knowledge about the object, which can be a transmission function with both modulus and phase components. The technique has revolutionary implications for x-ray imaging of all classes of specimen.

Two-Dimensional Dynamics of Metal Nanoparticles on the Surface of Thin Polymer Films Studied with Coherent X Rays

S Streit — 2008-03-19T17:03:19-00:00

Physical Review Letters, Vol. 98, No. 4. (2007)

X-ray photon-correlation spectroscopy is used to measure the dynamic structure factor f(q,) of gold particles moving on the surface of thin polymer films. Above the glass transition of the polymer the peculiar form f(q,)~exp[-()] is found with 0.7<<1.5, depending on sample age and temperature. The relaxation rates scale linearly with q, excluding a simple Brownian diffusive motion. This type of behavior, already observed in aging bulk soft matter systems, is explained by a power law distribution of particle velocities due to ballistic motion.

Polymer Chain Swelling Induced by Dispersed Nanoparticles

Anish Tuteja — 2008-03-17T22:54:34-00:00

Physical Review Letters, Vol. 100, No. 7. (2008)

The dimensions of individual deuterated polystyrene (d-PS) chains in a well-dispersed mixture of protonated polystyrene and chemically identical nanoparticles was determined by neutron scattering. A 10%–20% increase in the radius of gyration of d-PS was found when the nanoparticles are homogeneously dispersed in the polymer, an effect that occurs only when the radius of gyration of the polymer is larger than the nanoparticle radius. These results are reconciled with the existing literature.