Morphology evolution of thermally annealed polycrystalline thin films

Investigation of the morphology evolution of annealed polycrystalline Au(111) films by atomic force microscopy and x-ray diffraction leads to a continuous model that correlates such an evolution to local interactions between grains triggering different mechanisms of stress accommodation (grain zipping and shear strain) and relaxation (gap filling and grain rotation). The model takes into consideration findings concerning the in-plane reorientation of the grains during the coalescence to provide a comprehensive picture of the grain-size dependence of the interactions (underlying the origin of the growth stress in polycrystalline systems); and in particular it sheds light on the postcoalescence compressive stress as a consequence of the kinetic limitations for the reorientation of larger surface structuresThis paper was supported by the projects F1-54173 (bilateral program CSIC-Conacyt) 200960I182 (CSIC), and CCG10-UAM/MAT-5537 (DGUI-Comunidad de Madrid and Universidad Aut´onoma deMadrid). A.G.G. acknowledges the financial support of the MICINN Spanish Ministry under the project ESP2006-14282-C02-0

Morphology Analysis of Si Island Arrays on Si(001)

The formation of nanometer-scale islands is an important issue for bottom-up-based schemes in novel electronic, optoelectronic and magnetoelectronic devices technology. In this work, we present a detailed atomic force microscopy analysis of Si island arrays grown by molecular beam epitaxy. Recent reports have shown that self-assembled distributions of fourfold pyramid-like islands develop in 5-nm thick Si layers grown at substrate temperatures of 650 and 750°C on HF-prepared Si(001) substrates. Looking for wielding control and understanding the phenomena involved in this surface nanostructuring, we develop and apply a formalism that allows for processing large area AFM topographic images in a shot, obtaining surface orientation maps with specific information on facets population. The procedure reveals some noticeable features of these Si island arrays, e.g. a clear anisotropy of the in-plane local slope distributions. Total island volume analysis also indicates mass transport from the substrate surface to the 3D islands, a process presumably related to the presence of trenches around some of the pyramids. Results are discussed within the framework of similar island arrays in homoepitaxial and heteroepitaxial semiconductor systems

Sonic hedgehog negatively regulates pre-TCR–induced differentiation by a Gli2-dependent mechanism

Hedgehog signaling regulates differentiation, survival, and proliferation of the earliest double-negative (DN) thymocytes, but its importance at later stages of T-cell development is controversial. Here we use loss- and gain-of-function mouse models to show that Shh, by signaling directly to the developing thymocyte, is a negative regulator of pre-TCR–induced differentiation from DN to double-positive (DP) cell. When hedgehog signaling was reduced, in the Shh−/− and Gli2−/− thymus, or by T lineage–specific transgenic expression of a transcriptional-repressor form of Gli2 (Gli2ΔC2), differentiation to DP cell after pre-TCR signal transduction was increased. In contrast, when Hh signaling was constitutively activated in thymocytes, by transgenic expression of a constitutive transcriptional-activator form of Gli2 (Gli2ΔN2), the production of DP cells was decreased. Gene expression profiling showed that physiologic Hh signaling in thymocytes maintains expression of the transcription factor FoxA2 on pre-TCR signal transduction

B cell/stromal cell crosstalk in health, disease, and treatment: Follicular lymphoma as a paradigm

International audienceStromal cells organize specific anatomic compartments within bone marrow (BM) and secondary lymphoid organs where they finely regulate the behavior of mature normal B cells. In particular, lymphoid stromal cells (LSCs) form a phenotypically heterogeneous compartment including various cell subsets variably supporting B-cell survival, activation, proliferation, and differentiation. In turn, activated B cells trigger in-depth remodeling of LSC networks within lymph nodes (LN) and BM. Follicular lymphoma (FL) is one of the best paradigms of a B-cell neoplasia depending on a specific tumor microenvironment (TME), including cancer-associated fibroblasts (CAFs) emerging from the reprogramming of LN LSCs or poorly characterized local BM precursors. FL-CAFs support directly malignant B-cell growth and orchestrate FL permissive cell niche by contributing, through a bidirectional crosstalk, to the recruitment and polarization of immune TME subsets. Recent studies have highlighted a previously unexpected level of heterogeneity of both FL B cells and FL TME, underlined by FL-CAF plasticity. A better understanding of the signaling pathways, molecular mechanisms, and kinetic of stromal cell remodeling in FL would be useful to delineate new predictive markers and new therapeutic approaches in this still fatal malignancy