Multiple generations of grain aggregation in different environments preceded solar system body formation.

The solar system formed from interstellar dust and gas in a molecular cloud. Astronomical observations show that typical interstellar dust consists of amorphous (-) silicate and organic carbon. Bona fide physical samples for laboratory studies would yield unprecedented insight about solar system formation, but they were largely destroyed.

Detection of solar wind-produced water in irradiated rims on silicate minerals.

The solar wind (SW), composed of predominantly ∼1-keV H(+) ions, produces amorphous rims up to ∼150 nm thick on the surfaces of minerals exposed in space. Silicates with amorphous rims are observed on interplanetary dust particles and on lunar and asteroid soil regolith grains. Implanted H(+) may react with oxygen in the minerals to form trace amounts of hydroxyl (-OH) and/or water (H2O).

Noncrystalline-to-crystalline transformations in Pt nanoparticles.

We show that the noncrystalline-to-crystalline transition of supported Pt nanoparticles (NPs) in the subnanometer to nanometer size range is statistical in nature, and strongly affected by particle size, support, and adsorbates (here we use H2). Unlike in the bulk, a noncrystalline phase exists and is stable in small NPs, reflecting a general mesoscopic feature. Observations of >3000 particles by high-resolution transmission electron microscopy show a noncrystalline-to-crystalline transition zone that is nonabrupt; there is a size regime where disordered and ordered NPs coexist.

Synthesis and characterization of visible light absorbing (GaN)(1-x)(ZnO)x semiconductor nanorods.

Although the (GaN)(1-x)(ZnO)x solid solution is one of the most effective systems for driving overall solar water splitting with visible light, its quantum yield for overall water splitting using visible light photons has not yet reached ten percent. Understanding and controlling the nanoscale morphology of this system may allow its overall conversion efficiency to be raised to technologically relevant levels. We describe the use a Ga2O3(ZnO)16 precursor phase in the synthesis of this phase which naturally results in the production of arrays of nanorods with favorable diameters (∼100 nm) and band gaps (∼2.

Fitting valence charge densities at a crystal surface.

A procedure is reported for obtaining a much better initial parameterization of the charge density than that possible from a neutral atom model. This procedure involves the parameterization of a bulk charge density model in terms of simple variables such as bond lengths, which can then be transferred to the problem of interest, for instance a surface. Parameterization is accomplished through the fitting of density functional theory calculations for a variety of crystal distortions.