Using grazing-incidence x-ray diffraction and scanning tunneling microscopy (STM), we show that the thermal decomposition of an electronic-grade wafer of 6H-SiC after annealing at increasing temperatures TA between 1080 and 1320 °C leads to the layer-by-layer growth of unconstrained, heteroepitaxial single-crystalline graphite. The limited width of the in-plane diffraction rod profiles of graphite reveals large terraces, with an average size larger than 200 Å and a very small azimuthal disorientation. The overlayer is unstrained and adopts the crystalline parameter of bulk graphite even at the smallest coverage studied, which corresponds to a single graphene plane, as inferred from the flat out-of-plane diffraction profile. By increasing TA, additional graphene planes can be grown below this graphite layer from the solid-state decomposition of SiC, forming the AB stacking of Bernal graphite. A C-rich precursor is evidenced in STM by an intrinsic (6×6) reconstruction made of ordered ring or starlike structures. The resulting epitaxial film is indistinguishable from a bulk graphite single crystal.

Synthetic methods that allow for the controlled design of well-defined Pt nanoparticles are highly desirable for fundamental catalysis research. In this work, we propose a strategy that allows precise and independent control of the Pt particle size and coverage. Our approach exploits the versatility of the atomic layer deposition (ALD) technique by combining two ALD processes for Pt using different reactants. The particle areal density is controlled by tailoring the number of ALD cycles using trimethyl(methylcyclopentadienyl)platinum and oxygen, while subsequent growth using the same Pt precursor in combination with nitrogen plasma allows for tuning of the particle size at the atomic level. The excellent control over the particle morphology is clearly demonstrated by means of in situ and ex situ X-ray fluorescence and grazing incidence small angle X-ray scattering experiments, providing information about the Pt loading, average particle dimensions, and mean center-to-center particle distance.

Combining optical microscopy, synchrotron X-ray diffraction and ellipsometry, we studied the internal structure of linear defect domains (oily streaks) in films of a smectic liquid crystal 8CB with thicknesses in the range of 100-300 nm. These films are confined between air and a rubbed PVA polymer substrate which imposes hybrid anchoring conditions (normal and unidirectional planar, respectively). We show how the presence or absence of dislocations controls the structure of highly deformed thin smectic films. Each domain contains smectic layers curved in the shape of flattened hemicylinders to satisfy both anchoring conditions, together with grain boundaries whose size and shape are controlled by the presence of dislocation lines. A flat grain boundary normal to the interface connects neighboring hemicylinders, while a rotating grain boundary (RGB) is located near the axis of curvature of the cylinders. The RGB shape appears such that dislocation lines are concentrated at its summit close to the air interface. The smectic layers reach the polymer substrate via a transition region where the smectic layer orientation satisfies the planar anchoring conditions over the entire polymer substrate and whose thickness does not depend on that of the film. The strength of planar anchoring appears to be high, larger than 10(-2) mJ m(-2), compensating for the high energy cost of creating an additional 2D defect between a horizontal smectic layer and perpendicular ones of the transition region. This 2D defect may be melted, in order to avoid the creation of a transition region structure composed of a large number of dislocations. As a result, linear defect domains can be considered as arrays of oriented defects, straight dislocations of various Burger vectors, whose location is now known, and 2D nematic defects. The possibility of easy variation between the present structure with a moderate amount of dislocations and a structure with a large number of dislocations is also demonstrated.

Spin-crossover molecules are very appealing for use in multifunctional spintronic devices because of their ability to switch between high-spin and low-spin states with external stimuli such as voltage and light. In actual devices, the molecules are deposited on a substrate, which can modify their properties. However, surprisingly little is known about such molecule−substrate effects. Here we show for the first time, by grazing incidence X-ray diffraction, that an Fe II spin-crossover molecular layer displays a well-defined epitaxial relationship with a metal substrate. Then we show, by both density functional calculations and a mechanoelastic model, that the resulting epitaxial strain and the related internal pressure can induce a partial spin conversion at low temperatures, which has indeed been observed experimentally. Our results emphasize the importance of substrate-induced spin state transitions and raise the possibility of exploiting them.