J. Gierak

Dynamics of completely unfolded and native proteins through solid-state nanopores as a function of electric driving force.

We report experimentally the dynamic properties of the entry and transport of unfolded and native proteins through a solid-state nanopore as a function of applied voltage, and we discuss the experimental data obtained as compared to theory. We show an exponential increase in the event frequency of current blockades and an exponential decrease in transport times as a function of the electric driving force. The normalized current blockage ratio remains constant or decreases for folded or unfolded proteins, respectively, as a function of the transmembrane potential. The unfolded protein is stretched under the electric driving force. The dwell time of native compact proteins in the pore is almost 1 order of magnitude longer than that of unfolded proteins, and the event frequency for both protein conformations is low. We discuss the possible phenomena hindering the transport of proteins through the pores, which could explain these anomalous dynamics, in particular, electro-osmotic counterflow and protein adsorption on the nanopore wall.

Epitaxial graphene on cubic SiC(111)/Si(111) substrate

Epitaxial graphene films grown on silicon carbide (SiC) substrate by solid state graphitization is of great interest for electronic and optoelectronic applications. In this paper, we explore the properties of epitaxial graphene films on 3C-SiC(111)Si(111) substrate. X-ray photoelectron spectroscopy and scanning tunneling microscopy were extensively used to characterize the quality of the few-layer graphene (FLG) surface. The Raman spectroscopy studies were useful in confirming the graphitic composition and measuring the thickness of the FLG samples.

Focused ion beam technology and ultimate applications

In this topical review, the potential of the focused ion beam (FIB) technology and ultimate applications are reviewed. After an introduction to the technology and to the operating principles of liquid metal ion sources (LMIS), of ion optics and instrument architectures, several applications are described and discussed. First, the application of FIB for microcircuit inspection, metrology and failure analysis is presented. Then, we introduce and illustrate some advanced patterning schemes we propose as next generation FIB processing examples. These patterning schemes are (i) local defect injection or smoothing in magnetic thin film direct patterning, (ii) functionalization of graphite substrates to guide organization of clusters, (iii) local and selective epitaxy of III‐V semiconductor quantum dots and (iv) FIB patterned solid-state nanopores for biological molecules manipulation and analysis. We conclude this work by giving our vision of the future developments for FIB technology. (Some figures in this article are in colour only in the electronic version)

Efficient generation of surface plasmon by single-nanoslit illumination under highly oblique incidence

Using scanning near-field optical microscopy, we investigate the ability of nanoslits in metallic films to launch surface plasmon polaritons (SPPs) under highly oblique incidence at λ=975 nm. The SPP generation efficiency is inferred by fitting the recorded near-field data with a simple analytical model. We find a remarkably large efficiency of 20% for the front side of the slit, which is in agreement with recent theoretical predictions relying on a fully vectoral electromagnetic formalism. An even larger efficiency is predicted experimentally (44%) and theoretically (33%) for the rear side. The present near-field analysis provides a direct approach to measure SPP generation efficiencies and may find applications for characterizing SPP devices.

Modification of Co/Pt multilayers by gallium irradiation - Part 1: The effect on structural and magnetic properties

Atomic force microscopy, transmission electron microscopy, optical, and magneto-optical microscopy have been used to study how structural and magnetic properties are changed when a Co/Pt multilayer is quasihomogeneously irradiated with Ga ions. Under low irradiation fluence, both grain size and texture in the multilayer increase. These effects continue for fluences in excess of 1×1015 Ga ions/cm2, but beyond this dose significant thinning of the multilayer is also observed. Three distinct irradiation-induced magnetic regimes with sharp transitions between each were identified. For Ga fluences less than 5×1012 ions/cm2, the irradiated region retains perpendicular uniaxial anisotropy but with coercivity lower than that of the as-grown film. For fluences between 5×1012 and 1×1013 Ga ions/cm2, a transition from perpendicular to in-plane magnetization was experienced. Very little change of the in-plane magnetic properties of irradiated multilayers is then observed until the sample experiences a ferromagnetic t...

Dynamics of colloids in single solid-state nanopores.

We use solid-state nanopores to study the dynamics of single electrically charged colloids through nanopores as a function of applied voltage. We show that the presence of a single colloid inside of the pore changes the pore resistance, in agreement with theory. The normalized ionic current blockade increases with the applied voltage and remains constant when the electrical force increases even more. We observe short and long events of current blockades. Their durations are associated, respectively, with low and high current variation. The ratio of long events increases with the electrical force. The events frequency increases exponentially as a function of applied voltage and saturates at high voltage. The dwelling time decreases exponentially at low and medium voltages when the electrical force increases. At large voltages, this time decreases inversely proportionally to the applied voltage. The long events are associated with translocation events. We show that the dynamics of colloids through the nanopore is governed mainly by two mechanisms, by the free-energy barrier at relatively low and medium voltages and by the electrophoresis mechanism at high voltage.

Organizing nanoclusters on functionalized surfaces

This letter reports on the synthesis and observation of periodic arrangements of nanometric size gold islands. Samples are produced by deposition of preformed gold clusters on a functionalized graphite surface. The evolution of the cluster organization with artificial defects nature and periodicity is studied experimentally and analyzed in the framework of Kinetic Monte Carlo (KMC) simulations. This study points out the potentialities of the technique to organize nanostructures on patterned surfaces.

Modifications of magnetic properties of Pt/Co/Pt thin layers by focused gallium ion beam irradiation

We show how the magnetic properties of the Pt/Co ultrathin film structure can be modified and even controlled under uniform irradiation by Ga+ ions at low fluence in the 20–100 keV range. A systematic magneto-optical study is presented for the Pt/Co(1.4 nm)/Pt(111) ultrathin-film structure. At ion fluences below D=1014 Ga+/cm2, the coercive field is steadily reduced when increasing the fluence. At large fluences, in the range D=(5–10)×1014 Ga+ ions/cm2, the magnetization of the Co layer drops rapidly and the film finally becomes paramagnetic at room temperature for D>2×1015 Ga+ ions/cm2. We demonstrate that these magnetic changes are related to the effect of ion-induced collisional intermixing of the Co/Pt interfaces, leading to the formation of stable Co–Pt alloys with varying composition across the interfaces. A simple model is derived to relate the ion beam-induced mixing to the changes in magnetic properties. The present work allows us to gain a quantitative understanding of previous experiments using...

New characterization method of ion current‐density profile based on damage distribution of Ga+ focused‐ion beam implantation in GaAs

A new method is reported for characterizing focused ion probe current distributions based on the comparison between damage simulations and transmission electron microscopy observations. Several focused‐ion beam operation conditions were modeled, such as low‐to‐high source emission currents and variable beam acceptances. At low current and small acceptance, the ion spot exhibits a nearly Gaussian profile, otherwise larger tails are evidenced which can be modeled either by Pearson or ‘‘bi‐Gaussian’’ distributions. The sensitivity of the procedure to the tail extension is highlighted.

Optimization of experimental operating parameters for very high resolution focused ion beam applications

We report an experimental procedure to optimize the current profile of a focused ion beam probe, with a special emphasis on high resolution applications. The optimized operating conditions are given for three specific cases: specimen thinning for electron microscopy, nanoetching, and nanolithography. We present high quality membranes for transmission electron microscopy, arrays of nanoholes with reproducible dimensions of 17 nm etched on a nickel membrane, and finally nanolithography operations with a 10 nm resolution. Due to the conventional design of our focused ion beam system, the operating conditions that we have established for each nanofabrication application, should be successfully applied to a wide variety of ion columns.