Anomalous Plastic Deformation and Sputtering of Ion Irradiated Silicon Nanowires.

Silicon nanowires of various diameters were irradiated with 100 keV and 300 keV Ar(+) ions on a rotatable and heatable stage. Irradiation at elevated temperatures above 300 °C retains the geometry of the nanostructure and sputtering can be gauged accurately. The diameter dependence of the sputtering shows a maximum if the ion range matches the nanowire diameter, which is in good agreement with Monte Carlo simulations based on binary collisions. Nanowires irradiated at room temperature, however, amorphize and deform plastically. So far, plastic deformation has not been observed in bulk silicon at such low ion energies. The magnitude and direction of the deformation is independent of the ion-beam direction and cannot be explained with mass-transport in a binary collision cascade but only by collective movement of atoms in the collision cascade with the given boundary conditions of a high surface to volume ratio.

Utilizing dynamic annealing during ion implantation: synthesis of silver nanoparticles in crystalline lithium niobate.

Silver nanoparticles (NPs) embedded in lithium niobate were fabricated via ion beam synthesis and are suitable for various plasmonic applications, e.g. enhancement of optical nonlinear effects. After room temperature silver implantation, annealing in the temperature range of 400-600 °C was performed in order to recrystallize the damaged lithium niobate surface layer. The shape of the silver NPs, their optical properties as well as the structural properties of their surrounding matrix have been analyzed for various annealing steps. TEM investigations show that annealing at 400 °C does not lead to recrystallization of the damaged lithium niobate. A recrystallization occurs upon increasing the annealing temperature to 500 or 600 °C, but simultaneously a second phase consisting of lithium triniobate forms. This is additionally supported by XRD measurements. By utilizing dynamic annealing, i.e. implanting silver at elevated temperatures of 400 °C, it is shown that the LiNbO3 matrix stays single crystalline during ion implantation and no LiNb3O8 is formed. This is additionally verified by comparing the positions of the surface plasmon resonances with calculations based on Mie's scattering theory.

Mechanism of oxide layer growth during annealing of NiTi.

After annealing at 540°C, NiTi is covered by a characteristic oxide layer with an Ni-containing outer and an Ni-free inner titanium oxide region. To elucidate details of the yet unclear formation process, samples were annealed in an atmosphere containing different oxygen isotopes at a time and analyzed by nondestructive ion beam techniques at different stages of the oxidation. During the heating stage, an oxygen permeable "low Ni" titanium oxide forms, and the oxide layer grows inward. Subsequently, when the annealing temperature of 540°C is reached, Ni-free stoichiometric titanium oxide forms and inhibits the transport of oxygen toward the bulk. Thus, the oxide layer growth changes to outward, and the final location of the reaction front between O and Ti is inside the oxide layer at the transition of "low Ni" oxide to "Ni-free" oxide. Consequently, the annealing conditions during inward oxide layer growth govern the surface properties, whereas the conditions during outward oxide layer growth are uncritical with respect to the surface properties. The findings are directly applicable to set the amount of surface Ni of NiTi devices, provide basis for detailed interpretation of experimental results involving annealing of NiTi, and can further respective modeling.

Ultrathin membranes in x-cut lithium niobate.

Ion-beam enhanced etching is used to pattern a bulk lithium niobate crystal with ultrathin membranes. By the implementation of an air gap beneath the membrane, high index contrast is achieved. A buried amorphous layer, created by irradiation with He ions, is removed by means of wet chemical etching in hydro-fluoric acid. Membranes having thicknesses down to 200 nm are fabricated. The etched air gaps and the membranes exhibit a uniform thickness over the entire etched area, and their widths can be purposefully adjusted over a wide range by choosing appropriate ion energies and fluences as well as annealing conditions.

Fabrication of ridge waveguides in zinc-substituted lithium niobate by means of ion-beam enhanced etching.

We present results on the fabrication and characterization of ridge waveguides in zinc-substituted lithium niobate. High-quality waveguides were fabricated by a combination of liquid-phase epitaxy and multiple applications of ion-beam enhanced etching. The two major demands on ridge waveguides, a very low side-wall roughness and a rectangle shape with side-wall angles close to 90 degrees , were realized simultaneously by using this technique. Single-mode waveguiding at a wavelength of 1064 nm was demonstrated with attenuation values of 0.9 dB/cm.

Amorphous silicon exhibits a glass transition.

Amorphous silicon is a semiconductor with a lower density than the metallic silicon liquid. It is widely believed that the amorphous-liquid transition is a first-order melting transition. In contrast to this, recent computer simulations and the experimental observation of pressure-induced amorphization of nanoporous silicon have revived the idea of an underlying liquid-liquid phase transition implying the existence of a low-density liquid and its glass transition to the amorphous solid. Here we demonstrate that during irradiation with high-energy heavy ions amorphous silicon deforms plastically in the same way as conventional glasses. This behaviour provides experimental evidence for the existence of the low-density liquid. The glass transition temperature for a timescale of 10 picoseconds is estimated to be about 1,000 K. Our results support the idea of liquid polymorphism as a general phenomenon in tetrahedral networks.