Dynamic effects induced by renormalization in anisotropic pattern forming systems

The dynamics of patterns in large two-dimensional domains remains a challenge in non-equilibrium phenomena. Often it is addressed through mild extensions of one-dimensional equations. We show that full 2D generalizations of the latter can lead to unexpected dynamical behavior. As an example we consider the anisotropic Kuramoto-Sivashinsky equation, that is a generic model of anisotropic pattern forming systems and has been derived in different instances of thin film dynamics. A rotation of a ripple pattern by $90^{\circ}$ occurs in the system evolution when nonlinearities are strongly suppressed along one direction. This effect originates in non-linear parameter renormalization at different rates in the two system dimensions, showing a dynamical interplay between scale invariance and wavelength selection. Potential experimental realizations of this phenomenon are identified.Comment: 5 pages, 3 figures; supplemental material available at journal web page and/or on reques

IBC - ION BEAM CENTER

In the Ion Beam Center (IBC), various set-ups – electrostatic accelerators, ion implanters, plasma-based ion implantation equipment, low-energy ion tools, an ion microscope etc. – are combined into a unique facility for research and applications using ion beams. Almost all ions from stable chemical nuclides are available in the ion energy range from 10 eV to about 60 MeV. In addition to broad beams, also focused (down to 1 nm) and highly-charged (charge state up to 45+) ion beams, or ions extracted from a plasma can be provided. In total, the IBC operates more than 30 dedicated tools or beamline end-stations. The specific expertise of IBC is the modification and analysis of solids by energetic ions aimed to develop novel materials for information technology, electronics or energy systems. In addition, ion beam analysis techniques became of increasing importance for interdisciplinary fields like geochemistry, climate or environmental research and resources technology. Special add-on services offered ensure a successful realization of user experiments. Based on a long-term expertise, specific equipment and common commercial procedures, the IBC is strongly active in the use of ion beam techniques for industrial applications aimed to initiate valuable product innovation

Implanting germanium into graphene

Incorporating heteroatoms into the graphene lattice may be used to tailor its electronic, mechanical and chemical properties. Direct substitutions have thus far been limited to incidental Si impurities and P, N and B dopants introduced using low-energy ion implantation. We present here the heaviest impurity to date, namely $^{74}$Ge$^+$ ions implanted into monolayer graphene. Although sample contamination remains an issue, atomic resolution scanning transmission electron microscopy imaging and quantitative image simulations show that Ge can either directly substitute single atoms, bonding to three carbon neighbors in a buckled out-of-plane configuration, or occupy an in-plane position in a divacancy. First principles molecular dynamics provides further atomistic insight into the implantation process, revealing a strong chemical effect that enables implantation below the graphene displacement threshold energy. Our results show that heavy atoms can be implanted into the graphene lattice, pointing a way towards advanced applications such as single-atom catalysis with graphene as the template.Comment: 20 pages, 5 figure

Nanopatterning of the (001) surface of crystalline Ge by ion irradiation at off-normal incidence : Experiment and simulation

Intricate topographical patterns can form on the surface of crystalline Ge(001) subject to low-energy ion irradiation in the reverse epitaxy regime, i.e., at elevated temperatures which enable dynamic recrystallization. We compare such nanoscale patterns produced by irradiation from varied polar and azimuthal ion incidence angles with corresponding calculated surface topographies. To this end, we propose a continuum equation including both anisotropic erosive and anisotropic diffusive effects. Molecular dynamics simulations provide the coefficients of angle-dependent sputter erosion for the calculations. By merely changing these coefficients accordingly, the experimentally observed surface morphologies can be reproduced, except for extreme ion incidence angles. Angle-dependent sputter erosion is thereby identified as a dominant mechanism in ion-induced pattern formation on crystalline surfaces under irradiation from off-normal incidence angles.Peer reviewe

Проблемы информационного обеспечения физической культуры и спорта

A formation process for semiconductor quantum dots based on a surface instability induced by ion sputtering under normal incidence is presented. Crystalline dots 35 nanometers in diameter and arranged in a regular hexagonal lattice were produced on gallium antimonide surfaces. The formation mechanism relies on a natural self-organization mechanism that occurs during the erosion of surfaces, which is based on the interplay between roughening induced by ion sputtering and smoothing due to surface diffusion

Morphological transitions in the patterning of the crystalline Ge(001) surface induced by ion irradiation

We investigate the morphologies of the Ge(001) surface that are produced by bombardment with a normally incident, broad argon ion beam at sample temperatures above the recrystallization temperature. Two previously-observed kinds of topographies are seen, i.e., patterns consisting of upright and inverted rectangular pyramids, as well as patterns composed of shallow, isotropic basins. In addition, we observe the formation of an unexpected third type of pattern for intermediate values of the temperature, ion energy and ion flux. In this type of transitional morphology, isolated peaks with rectangular cross sections stand above a landscape of shallow, rounded basins. We also extend past theoretical work to include a second order correction term that comes from the curvature dependence of the sputter yield. For a range of parameter values, the resulting continuum model of the surface dynamics produces patterns that are remarkably similar to the transitional morphologies we observe in our experiments. The formation of the isolated peaks is the result of a term that is not ordinarily included in the equation of motion, a second order correction to the curvature dependence of the sputter yield