We report the direct observation of solidlike ordering at room temperature of thin films of [Bmim][NTf2] ionic liquid on mica, amorphous silica, and oxidized Si(110). A statistical quantitative analysis of atomic force microscopy topographies shows that on these surfaces [Bmim][NTf2] forms layered structures, characterized by a perpendicular structural periodicity of approximately 0.6 nm. Remarkably, even the highest structures, up to 50 nm high, behave solidlike against the AFM probe. Conversely, on highly oriented pyrolitic graphite the ionic liquid forms nanometer-sized, liquidlike domains. The results of this study are directly relevant for those applications where ILs are employed in form of thin films supported on solid surfaces, such as in microelectromechanical or microelectronic devices. More generally, they suggest that at the liquid/solid interface the structural properties of ILs can be far more complex than those depicted so far, and prompt new fundamental investigations of the forces that drive supported ILs through a liquidlike-to-solidlike transition.

A paradigm in transcriptional regulation is that graded increases in transcription factor (TF) concentration are translated into on/off transcriptional responses by cooperative TF binding to adjacent sites. Digital transcriptional responses underlie the definition of anatomical boundaries during development. Here we show that NF-kappaB, a TF controlling inflammation and immunity, is conversely an analog transcriptional regulator that uses clustered binding sites noncooperatively. We observed that increasing concentrations of NF-kappaB are translated into gradual increments in gene transcription. We provide a thermodynamic interpretation of the experimental observations by combining quantitative measurements and a minimal physical model of an NF-kappaB-dependent promoter. We demonstrate that NF-kappaB binds independently to adjacent sites to promote additive RNA Pol II recruitment and graded transcriptional outputs. These findings reveal an alternative mode of operation of clustered TF binding sites, which might function in biological conditions where the transcriptional output is proportional to the strength of an environmental input.

Ab-initio calculations within Density Functional Theory combined with experimental Raman spectra on cluster-beam deposited pure carbon films provide a consistent picture of sp-carbon chains stabilized by sp 3 or sp 2 terminations, the latter being sensitive to torsional strain. This unexplored effect promises many exciting applications since it allows one to modify the conductive states near the Fermi level and to switch on and off the on-chain π-electron magnetism.

A novel, pulsed, supersonic, cluster-beam source based on microplasma ablation has been realized and tested. Its intensity and stability allows one to overcome the limitations encountered in laser vaporization and pulsed arc cluster sources. Supersonic carbon cluster beams have been obtained and characterized. Target ablation processes and cluster growth have been investigated, showing the presence of mechanisms substantially different from those observed in other plasma-based sources. In particular, we show that the precise confinement of the ablation plasma in the source is of fundamental importance for the production of cluster beams with high intensity and stability. This opens new opportunities for the study of free and supported clusters and for the synthesis of nanostructured materials.

Atomic force microscopy images for [bmim][Tf(2)N] films deposited at ambient conditions by drop-casting show a population of terraced islands of mesoscopic area (1-100 μ(2)) and ∼50 nm height. The regularity of terraces and steps, stiff mechanical properties and a fragile fracture mode all suggest that the islands are solid-like, even though bulk [bmim][Tf(2)N] is liquid at the temperature of the experiment. Molecular dynamics simulations for a homogeneous [bmim][Tf(2)N] film 4 nm thick on silica also display marked layering in proximity to silica of periodicity closely matching the experimental estimate of the step height. The density modulation of the simulated sample, however, decays into an approximatively homogeneous and fluid-like density distribution ∼2 nm from the solid surface. The detailed comparison of experiments and simulations is contained in the closing section of the paper.