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The cuticle of mussel byssal threads is a robust natural coating that combines high extensibility with high stiffness and hardness. In this study, fluorescence microscopy and elemental analysis were exploited to show that the 3,4-dihydroxyphenyl-L-alanine (dopa) residues of mussel foot protein-1 colocalize with Fe and Ca distributions in the cuticle of Mytilus galloprovincialis mussel byssal threads. Chelated removal of Fe and Ca from the cuticle of intact threads resulted in a 50% reduction in cuticle hardness, and thin sections subjected to the same treatment showed a disruption of cuticle integrity. Dopa-metal complexes may provide significant interactions for the integrity of composite cuticles deformed under tension.

The structure of asymmetric poly(styrene-b-2-vinylpyridine) (PS-PVP) diblock copolymers allowed to order in a thin film is observed by a combination of secondary ion mass spectrometry and scanning force microscopy. The surface/interface-induced ordering persists over a surprisingly long range (more than 1 μm). The 2-D structure in the layer parallel to a surface is mainly a distorted hexagonal structure similar to that of the (110) plane of a body-centered cubic structure. In contrast to the long-range order in the direction perpendicular to the surfaces, the in-plane structure shows only short-range order. The surface has a very strong effect on the structure only in the direction perpendicular to it. The development of the layered structure induced by the surfaces was also investigated as a function of temperature. When the molecular weight of PS-PVP is low but the copolymer still forms the spherical structure, the layered structure decays more rapidly with distance from the free surface as the temperature is increased. We find that the layered structure changes from an order that is nearly liquid-like near the surface to a long-range-ordered structure continuously as the temperature is decreased, which suggests that the ultimate range of order of the layered structure is governed by thermodynamics. When the molecular weight of PS-PVP is high, the propagation of the layered structure is kinetically limited due to slow diffusion. Similar to symmetric diblock copolymers with a lamellar structure, asymmetric diblock copolymers with a layered spherical domain structure form islands or holes at the free surface when the film is thin and the film thickness does not correspond to an integral number of layers of spheres. As the film becomes thick, the shape of the edge of the island or hole structure changes from a step function to a tanh function, and finally these islands or holes disappear.

We report on the plasma-assisted molecular-beam epitaxy of Mg-doped ͑1010͒ GaN on ͑1010͒ 6H-SiC. Secondary ion mass spectroscopy measurements show the incorporation of Mg into the GaN films with an enhanced Mg incorporation under N-rich conditions relative to Ga-rich growth. Transport measurements of Mg-doped layers grown under Ga-rich conditions show hole concentrations in the range of p =1ϫ 10 18 to p =7ϫ 10 18 cm −3 and a dependence between hole concentration and Mg beam equivalent pressure. An anisotropy in in-plane hole mobilities was observed, with the hole mobility parallel to ͓1120͔ being higher than that parallel to ͓0001͔ for the same hole concentration. Mobilities parallel to ͓1120͔ were as high as ϳ11.5 cm 2 /Vs ͑at p ϳ 1.8 ϫ 10 18 cm −3 ͒.

We report on an extensive study of the two-dimensional electron gas (2DEG) structures containing AlN layers. It is shown that the presence of large polarization fields in the AlN barrier layer in AlN/GaN heterostructures results in high values of the 2DEG sheet density of up to 3.6×1013 cm−2. Room-temperature sheet resistance of 180 Ω/□ is demonstrated in the AlN/GaN structure with a 35 Å AlN barrier. As a result of reduced alloy disorder scattering, low-temperature electron mobility is significantly enhanced in AlN/GaN heterostructures in comparison to AlGaN/GaN structures with similar values of the 2DEG sheet density. The growth of GaN cap layers on top of AlN/GaN structures with relatively thick (∼35 Å) AlN barriers is found to lead to a significant decrease in the 2DEG sheet density. However, inserting a thin (∼10 Å) AlN layer between AlxGa1−xN and GaN in the AlxGa1−xN/GaN (x∼0.2–0.45) 2DEG structures does not affect the 2DEG sheet density and results in an increase of the low-temperature electron mobility in comparison to standard AlGaN/GaN structures. At room temperature, a combination of the high 2DEG sheet density of 2.15×1013 cm−2 and high electron mobility of 1500 cm2/V s in Al0.37Ga0.63N/AlN/GaN yielded a low sheet resistance value of 194 Ω/□.

Highly stable glasses of tris-naphthylbenzene transform into a liquid when annealed above the glass transition temperature T_{g}. In contrast to the predictions of standard models, the observed transformation is spatially inhomogeneous. Secondary ion mass spectrometry experiments on isotopically labeled multilayer films show that the liquid grows into the stable glass with sharp growth fronts initiated at the free surface and at the interface with the substrate. For the free surface, the growth velocity is constant in time and has the same temperature dependence as self-diffusion in the equilibrium supercooled liquid. These stable glasses are packed so efficiently that surfaces and interfaces are required to initiate the transformation to the liquid even well above T_{g}.

We have measured self-diffusion coefficients for deeply supercooled tris-naphthylbenzene using secondary ion mass spectrometry. Isotopically labeled multilayer films were prepared by vapor deposition. For samples deposited within a few K of T(g), the evolution of the concentration profile was observed to be Fickian on all accessible length and time scales. Diffusion is enhanced by a factor of approximately 100 at 338 K when compared to the prediction of the Stokes-Einstein model. In combination with previous neutron reflectivity experiments, these measurements quantify the length scale at which dynamics cross over to non-Fickian behavior in supercooled TNB. Comparisons are made between this diffusion data and other measurements of dynamics in supercooled TNB, including probe diffusion and crystal growth rates. An earlier report of self-diffusion coefficients for TNB was in error because the samples were prepared by vapor deposition at T(g) - 50 K, creating very stable glasses in which the concentration profile does not evolve by Fickian diffusion.

Due to its perfect cleavage that provides large areas of molecularly smooth, chemically inert surfaces, mica is the most commonly used natural substrate in measurements with the surface forces apparatus (SFA), in atomic force microscopy (AFM), and in many adsorption studies. However, preparing mica surfaces that are truly clean is not easy since mica is a high-energy surface that readily adsorbs water, organic contaminants, and gases from the atmosphere. Mica can also become charged on cleaving, which makes it prone to picking up oppositely charged particles or mica flakes from the surroundings. High refractive index particles, such as metals, will adhere to mica through van der Waals forces. Recent articles have demonstrated that particle contamination is obtained when inappropriate cutting and handling procedures for the mica are used. In this paper, we show that both particle and other critical contamination is easy to detect and provide proper steps to take during the sample preparation process.