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A strong correlation is observed between the structure and the microwave dielectric properties of epitaxial Ba0.5Sr0.5TiO3 (BST) thin films deposited onto (001) MgO by pulsed laser deposition. Films were deposited at 750 °C in an oxygen pressure that was varied from 3 to 1000 mTorr. The tetragonal distortion (ratio of in-plane and surface normal lattice parameters, D=a/c) of the films depends on the oxygen deposition pressure. D varied from 0.996 at 3 mTorr to 1.003 at 800 mTorr. At microwave frequencies (1–20 GHz), BST films with low distortion have higher dielectric constants (ε∼500), and lower dielectric loss (tan δ∼0.02) compared to films with higher distortion. The correlation of the microwave properties with the film structure can be attributed to stresses and polarizability in the film. The BST film grown at the oxygen deposition pressure of 50 mTorr exhibits a large dielectric constant change and a low dielectric loss at the same time, which corresponds to the film in low stress (D=1.0004). For tunable microwave applications, BST films with low stress are desirable in order to achieve both low dielectric loss and large tunability.

In order to study the effect of organic surface chemistry on calcite nucleation, attachment, and growth, calcium carbonate was precipitated in the presence of various ultrathin-film organosilane-modified silicon wafers. The chemistry of the aminosilane surfaces was systematically changed by the coupling of various acidic molecules, without creating a geometric lattice of acidic functional groups. Optical microscopy, scanning electron microscopy with image analysis, and X-ray scattering were employed to characterize crystallite density and orientation normal to the surface. Calcite grown on amino-modified surfaces was produced with the equilibrium rhombohedral habit and had the 〈104〉 orientation. Surfaces of the silicon oxide, carboxylate, iminodiacetate, or phosphoramidate tended to favor the orientation of surface crystals along 〈001〉 or near the 〈001〉 axes of the crystal. Primarily this is a result of the affinity of the surface for cations, but functional-group-mediated ion ordering and/or stereochemical matching is also suggested by the much greater amount of crystal nucleation on the long-chain carboxylates when compared to shortchain carboxylates. Coupling of nitrilotriacetic acid (NTA) favored appearance of 〈110〉, 〈113〉, and 〈116〉 oriented crystals when compared to the other acid surfaces. Growth of calcite with relatively larger {110} faces was observed when the microcrystals were synthesized in the presence of freely soluble NTA. Appearance of these faces is a result of a relatively suppressed growth rate due to face-specific adsorption on the growing crystallites. Similarly, the enhancement of specific crystal surface binding by the substrate bound NTA is probably the mechanism influencing orientation of surface microcrystals. Two common structural features of the {110}, {113}, and {116} faces are the tilt of the carbonate plane at large angles from the face and the same angle of rotation of the carbonates about their 3-fold symmetry axes. That angle may enhance the ability of two NTA carboxylates to simultaneously occupy carbonate sites of these calcite faces. The fact that crystallite density and orientation are influenced by submonolayers of functional groups attests to the importance of electrostatic and stereochemical recognition of certain crystal faces even without matching of the geometric lattice.

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At elevated pressure, PbS undergoes a first order phase transition from the NaCl or B1 structure to an orthorhombic structure. The effects of particle sizes in the nanometer range on this transition have been investigated using energy-dispersive x-ray diffraction of synchrotron produced wiggler radiation. Relative to the bulk crystals, the onset of transition pressure showed a significant increase with decreasing particle size. The results also show that compressibility increases with decreasing particle size: this increase is continuous through the phase transition.