Laurence Masson

A novel self-ordered sub-10 nm nanopore template for nanotechnology.

The fabrication of cost-efficient wafer scale self-ordered arrays of vertical and insulating sub-10 nm nanopores with low porosity is demonstrated. These meet challenging applications like read heads with perpendicular to the plane giant magnetoresistance, calling for strongly localized currents. Purely electrical sequencing of DNA strands, requiring insulating membranes with reduced pore diameters can also be considered.

Large-scale ordered plastic nanopillars for quantitative live-cell imaging.

Surfaces exhibiting ordered nanopillars have a wide range of potential biomedical applications based on the altered adhesivity of living cells on nanopatterned surfaces compared to planar ones. Examples include scaffolding for tissue engineering, designer bandages for wound dressing, and antifouling surfaces for implants. Although numerous experiments performed over the last decade have confirmed that cells respond to the chemistry (biochemical 2D imprint) and geometry (topographical 3D relief) of their surroundings at the nanoscale, the fundamental processes by which cells recognize nanostructures is a subject of on-going research. In this context, there is a need to ensure that the nanostructured surfaces have large-scale coverage and are compatible with quantitative optical microscopy (QOM), an important tool for studying living cells, especially the dynamics thereof. While biochemical patterning is not expected to pose a special challenge for QOM, topographical patterning may do so. Well-known techniques for topographical patterning are nanoimprint lithography (NIL, including thermal embossing and UV curing) and self-assembly based on colloidal beads or phase separation of polymers, all of which achieve large coverage. NIL is relatively resource intensive and usually depends on conventional techniques like electron-beam lithography for the initial stamp. Self-assembly, although increasingly refined, has limited flexibility for the choice of motif. Transparent substrates made using these

Metal-rich Au-silicide nanoparticles for use in nanotechnology

We present a route to functionalize chemically and magnetically silicon surfaces by a local passivation, taking advantage of Stranski–Krastanov growth mode of the Au–Si(111) system. Metal-rich Au-silicide nanoparticles, supported on a Si-rich two-dimensional Au-silicide layer, are obtained. Subsequently deposited Co is used to form magnetic nanostructures. The two Au silicides display a different chemical reactivity with Co enabling the fabrication of localized magnetic Co nanodots. These magnetic nanostructures can be aligned along step bunches of a vicinal Si(111) surface. By varying the growth parameters, the particle density can be tuned from 109 to the low 1012 dots/in.2.

Growth of Co nanolines on self-assembled Si nanostripes

One-dimensional Si nanostructures, grown on a Ag(110) substrate, have been used as a template to grow Co nanolines. Before Co deposition, the self-assembled Si nanostripes were characterized by high-resolution scanning tunneling microscopy. From this, an original atomic arrangement of silicon adatoms forming nanostripes can be proposed. The early stages of the Co deposition at room temperature on the Si nanostripes have then been studied by scanning tunneling microscopy, enabling the localization of adsorbed Co atoms. We show that Co is adsorbed on top of the Si nanostripes forming nanolines. No Co adsorption was detected on the pure Ag-surface in between the stripes. The preparation of an interesting one-dimensional Co-Si nanosystem is demonstrated.

Anodic 3D nanostructuring for tailored applications

Electrochemistry can be used to fabricate different three dimensional objects on the nanometre scale. Porous anodic aluminium oxide (AAO) membranes with varying but controlled morphologies are used in several complementary experiments in physics and biology. The present paper gives a description of the membrane fabrication procedure and presents a selection of applications based on the use of the membranes as evaporation masks in crystal growth experiments, as masks in reactive ion etching experiments or as moulds to fabricate arrays of ordered polymer nanopillars. Applications in energy storage are also briefly mentioned. Finally the fabrication of TiO2 nanotubes (TNT) is described. Their anodic formation is very close to that of the AAO membranes and TNTs offer additional perspectives for applications.

A graphene electron lens

An epitaxial layer of graphene was grown on a pre patterned 6H-SiC(0001) crystal. The graphene smoothly covers the hexagonal nano-holes in the substrate without the introduction of small angle grain boundaries or dislocations. This is achieved by an elastic deformation of the graphene by ~0.3% in accordance to its large elastic strain limit. This elastic stretching of the graphene leads to a modification of the band structure and to a local lowering of the electron group velocity of the graphene. We propose to use this effect to focus two-dimensional electrons in analogy to simple optical lenses.

Nanoscale template for the growth of one-dimensional nanostructures

The functionalization of the anisotropic Ag(110) surface with a self-assembled silicon nanostripe grating prior to Co deposition has been studied in situ with scanning tunneling microscopy. At room temperature, Co atoms are adsorbed on top of the silicon nanostructures. As the diffusion rate of Co into the Si nanostripes is very low at this temperature, the formation of well-organized, identical Co nanolines arranged in parallel rows is observed. Upon annealing at 100 °C, Co atoms massively diffuse into the nanostripes, leading to the destruction of the Si array. The early stages of growth at room temperature indicate that the parallel Co nanolines are coupled and display short-range interaction. Our results show that the Ag(110) surface covered with a silicon nanostripe grating can be used as a template for the growth of identical and well-ordered one-dimensional nanostructures of various materials.

Si Nanoribbons on Ag(110) Studied by Grazing-Incidence X-Ray Diffraction, Scanning Tunneling Microscopy, and Density-Functional Theory: Evidence of a Pentamer Chain Structure

We report a combined grazing incidence x-ray diffraction (GIXD), scanning tunneling microscopy (STM), and density-functional theory (DFT) study which clearly elucidates the atomic structure of the Si nanoribbons grown on the missing-row reconstructed Ag(110) surface. Our study allows us to discriminate between the theoretical models published in the literature, including the most stable atomic configurations and those based on a missing-row reconstructed Ag(110) surface. GIXD measurements unambiguously validate the pentamer model grown on the reconstructed surface, obtained from DFT. This pentamer atomistic model accurately matches the high-resolution STM images of the Si nanoribbons adsorbed on Ag(110). Our study closes the long-debated atomic structure of the Si nanoribbons grown on Ag(110) and definitively excludes a honeycomb structure similar to that of freestanding silicene.

KCl ultra-thin films with polar and non-polar surfaces grown on Si(111)7 × 7

The growth of ultra-thin KCl films on the Si(111)7 × 7 reconstructed surface has been investigated as a function of KCl coverage and substrate temperature. The structure and morphology of the films were characterized by means of scanning tunneling microscopy (STM) under ultra-high vacuum (UHV) conditions. Detailed analysis of the atomically resolved STM images of islands grown at room and high temperatures (400 K–430 K) revealed the presence of KCl(001) and KCl(111) islands with the ratio between both structures depending on the growth temperature. At room temperature, the growth of the first layer, which covers the initial Si(111)7 × 7 surface, contains double/triple atomic layers of KCl(001) with a small fraction of KCl(111) islands. The high temperature growth promotes the appearance of large KCl(111) areas, which are built up by three atomic layers. At room and high temperatures, flat and atomically well-defined ultra-thin KCl films can be grown on the Si(111)7 × 7 substrate. The formation of the above mentioned (111) polar films is interpreted as a result of the thermally activated dissociative adsorption of KCl molecules on Si(111)7 × 7, which produces an excess of potassium on the Si surface.

AAO-based nanoreservoir arrays: A quick and easy support for TEM characterization

Large-scale arrays of calibrated, nanometer sized reservoirs are prepared by adapting the well-established electrochemical method used so far for the preparation of anodic aluminium oxide (AAO) membranes. The bottom plane of the assembly is prepared to be transparent for high-energy electrons, enabling their use as a universal sample support for transmission electron microscopy studies of nanoparticles. The nanoreservoir substrates can be cleaned under ultra-high-vacuum conditions and filled, by evaporating different materials. Filled nanoreservoirs can locally be sealed with a thin carbon layer using focused-ion-beam–induced deposition (FIBID). Nanoparticles, grow at various adsorption places on the walls and bottom planes inside the nanoreservoirs. They can be characterized by transmission electron microscopy (TEM) without further sample preparation in different crystallographic directions. Due to the dense array-arrangement of the reservoirs, very good statistics can already be obtained on one single sample. The controlled fabrication of the nanoreservoir array and first TEM results obtained on Au nanoparticles before and after sealing of the reservoirs, are presented.