Uniaxial magnetic anisotropy tuned by nanoscale ripple formation: ion-sculpting of Co/Cu(001) thin films

We have investigated the growth of surface nanostructures on a Co/Cu(001) film and the growth of Co films on a nanostructured Cu(001) substrate as well as the effect of nanoscale pattern formation on the film magnetic properties. Here we demonstrate by scanning tunneling microscopy measurements and magneto-optic Kerr effect hysteresis curves that low-temperature grazing-incidence ion sputtering can be used to induce the formation of nanoscale ripples which reduce the four-fold symmetry of the Co film to two-fold, thus generating a strong in-plane uniaxial magnetic anisotropy. The nanostructures and the associated uniaxial magnetic anisotropy were found to be stable up to room temperature

Label-free, atomic force microscopy-based mapping of DNA intrinsic curvature for the nanoscale comparative analysis of bent duplexes

We propose a method for the characterization of the local intrinsic curvature of adsorbed DNA molecules. It relies on a novel statistical chain descriptor, namely the ensemble averaged product of curvatures for two nanosized segments, symmetrically placed on the contour of atomic force microscopy imaged chains. We demonstrate by theoretical arguments and experimental investigation of representative samples that the fine mapping of the average product along the molecular backbone generates a characteristic pattern of variation that effectively highlights all pairs of DNA tracts with large intrinsic curvature. The centrosymmetric character of the chain descriptor enables targetting strands with unknown orientation. This overcomes a remarkable limitation of the current experimental strategies that estimate curvature maps solely from the trajectories of end-labeled molecules or palindromes. As a consequence our approach paves the way for a reliable, unbiased, label-free comparative analysis of bent duplexes, aimed to detect local conformational changes of physical or biological relevance in large sample numbers. Notably, such an assay is virtually inaccessible to the automated intrinsic curvature computation algorithms proposed so far. We foresee several challenging applications, including the validation of DNA adsorption and bending models by experiments and the discrimination of specimens for genetic screening purposes

Ripples and ripples : from sandy deserts to ion-sputtered surfaces

Abstract. We study the morphological evolution of surfaces during ion sputtering and we compare their dynamical corrugation with aeolian ripple formation in sandy deserts. We show that, although the two phenomena are physically different, they must obey similar geometrical constraints and therefore they can be described within the same theoretical framework. The present theory distinguishes between atoms that stay bounded in the bulk and others that are mobile on the surface. We describe the excavation mechanisms, the adsorption and the surface mobility by means of a continuous equation derived from the study of dune formation on sand.We explore the spontaneous development of ordered nanostructures and explain the different dynamical behaviours experimentally observed in metals or in semiconductors or in amorphous systems.We also show that this novel approach can describe the occurrence of rotation in the ripple direction and the formation of other kinds of self-organized patterns induced by changes in the sputtering incidence angle

Permeability thickness dependence of polydimethylsiloxane (PDMS) Membranes

The paper describes a reliable technique to prepare PDMS membrane used to determine the permeability to CO2 and He. SEM controls morphology of surface membrane and SEM/FIB measures the membrane thickness. The data show that permeability becomes thickness dependent below some tens of micrometers. The Islam\u5f3s model, based on the non-equilibrium sorption\u2013desorption process at the interface, fits quite well with the experimental data. The comparison shows that flux models based on interface reaction could apply to describe quantitatively the thickness-dependence of the permeability. The model allows to determine the surface reactions rate constants for CO2 and He on PDMS. The introduction of a specific characteristic thickness Lc provides a functional form, which describes very accurately the results of the present paper and other experiments on polymers. By reducing the membrane thickness below 200 nm, both permeability and selectivity change, indicating Knudsen diffusion as flux mechanisms responsible for permeation. In this range of thickness, SEM images reveal membrane defects

Temperature and time evolution of ripple structure induced by ion sputtering on Cu(110)

The surface morphology generated by ion sputtering on a Cu(110) crystal has been investigated by Scanning Tunneling Microscopy (STM). A ripple structure is observed for all the considered values of the incident ion beam angle theta (0 degrees < theta < 70 degrees). In particular, normal:sputtering produces a well defined ripple structure whose wave vector rotates from (001) to (1 (1) over bar 0) by increasing the substrate temperature. Moreover, for theta = 45 degrees the ripple wavelength lambda increases in time following a scaling law lambda proportional to t(z), with z = 0.26 +/- 0.02. These results are described by a continuum equation which includes, in addition to the surface curvature dependent erosion terms, a diffusion term that takes into account both the surface anisotropy and the effect of an Ehrlich-Schwoebel barrier