B. Rauschenbach

Surface-enhanced fluorescence from metal sculptured thin films with application to biosensing in water

Surface-enhanced fluorescence from porous, metallic sculptured thin films (STFs) was demonstrated for sensing of bacteria in water. Enhancement factors larger than 15 were observed using STFs made of silver, aluminum, gold, and copper with respect to their dense film counterparts. The STFs used are assemblies of tilted, shaped, parallel nanowires prepared with several variants of the oblique-angle-deposition technique. Comparison between the different films indicates that the enhancement factor is higher when the tilt is either small ( 80 deg); thus, the enhancement is higher when only a single resonance in the nanowires is excited.

Ripple rotation, pattern transitions, and long range ordered dots on silicon by ion beam erosion

The importance of the ion incidence angle in self-organized pattern formation during low energy Xe+ ion beam erosion of silicon is elaborated. By a small step variation of the ion incidence angle, a variety of nanostructured patterns can develop. In this context, the angular distribution of ions within the ion beam is explored as an additional parameter controlling the evolution of the surface topography. Due to a controlled variation of these two parameters, hitherto unknown phenomena are found: (i) formation of rotated ripples, (ii) continuous transitions between patterns, and (iii) long range square ordered dot pattern.

Highly ordered self-organized dot patterns on Si surfaces by low-energy ion-beam erosion

Scanning force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM) have been used to investigate the complex topography evolution of Si surfaces during low-energy ion beam erosion. Depending on ion-beam parameters, a variety of different topographies can develop on the surface. At oblique ion-incidence angles, nanodots are formed for ion energies ⩾300eV upon sample rotation. Properly chosen parameters of the broad-beam ion source result in dots possessing a very high degree of lateral ordering with a mean dot size λ∼30nm. Both, degree of ordering and size homogeneity of these nanostructures increases with erosion time leading to the most ordered self-organized patterns on Si surfaces reported thus far.

In situ stress measurements during low-energy nitriding of stainless steel

Abstract Nitriding of austenitic stainless steel at moderate temperatures leads to the formation of a hard and wear-resistant surface layer of expanded austenite, characterised by an expansion of the lattice constant of up to 12%. This large expansion can be assumed to be accompanied by a corresponding high compressive stress parallel to the substrate at the interface between the implanted layer and the bulk substrate. In situ stress measurements using the beam bending method were performed to capacitively determine the curvature of thin samples, prepared from X5CrNi18.10 (DIN 1.4301, AISI 321), during low-energy nitrogen implantation. The thickness of the expanded austenite layer was derived afterwards from glow-discharge optical spectroscopy. Assuming an inversely parabolic growth rate for diffusion-limited growth, a rather high compressive stress of 1.4–1.5 GPa was reached after 90 s and stayed constant for 1 h. This value is near the plastic flow limit of stainless steel. Furthermore, while keeping the sample at 400 °C and switching off the nitrogen beam, the curvature of the sample almost instantaneously started to decrease exponentially by approximately 50% on a time scale of 15–30 min, indicating ongoing stress relaxation.

Experimental evidence for an angular dependent transition of magnetization reversal modes in magnetic nanotubes

We report on the experimental and theoretical investigation of the magnetization reversal in magnetic nanotubes that have been synthesized by a combination of glancing angle and atomic layer deposition. Using superconducting quantum interference device magnetometry the angular dependence of the coercive fields is determined and reveals a nonmonotonic behavior. Analytical calculations predict the crossover between two magnetization reversal modes, namely, the movement of different types of domain boundaries (vortex wall and transverse wall). This transition, already known in the geometrical dependences of the magnetization reversal in various nanotubes, is found within one type of tube in the angular dependence and is experimentally confirmed in this work.

Glancing angle sputter deposited nanostructures on rotating substrates: Experiments and simulations

Ordered arrays of Si nanorods and nanospirals have been produced by ion beam sputter glancing angle deposition of Si on rotating substrates. The substrates were prepatterned with honeycomb and hexagonal-closed-packed arranged Au dots obtained by nanosphere lithography. The effects of template type, substrate rotational speed, height of the artificial Au seeds, and deposition angle θ of the incident flux on the growth of the Si nanostructures is examined. Especially for the deposition of Si on honeycomb templates at different deposition angles, it is shown that the structure of the growing film changes drastically. A continuous film with honeycomblike arranged hillocks on top is deposited at normal incidence. With increased θ, the structure shifts to almost dense films with a mesh of hexagonally arranged pores (θ=70°). Finally, separated rodlike structures with triangular cross section are obtained under glancing angle conditions (θ=85°). In addition, the structural evolution of the glancing angle deposite...

Formation of TiN, TiC and TiCN by metal plasma immersion ion implantation and deposition

Abstract Titanium nitride, titanium carbide and titanium carbonitride are well known compounds displaying a rather high hardness and melting point, thus enabling their use as hard coatings. With a titanium cathode and both nitrogen and methane gas, a series of compound TiCxNy can be prepared with the final points TiN and TiC using metal plasma immersion ion implantation and deposition. The respective properties of the films are investigated by X-ray diffraction and Rutherford backscattering spectroscopy. With increasing pulse voltage, a decreasing carbon content and growth rate is found for the TiC series, while no such effect is observed for corresponding TiN films.

High-quality m-plane GaN thin films deposited on γ-LiAlO2 by ion-beam-assisted molecular-beam epitaxy

GaN(11¯00) thin films are deposited on γ-LiAlO2(100) by low-energy-ion-beam-assisted molecular-beam epitaxy. Structural properties of the epitaxial GaN films are investigated by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. X-ray diffraction measurements give evidence for a high crystalline quality far better than previously reported in literature. Cross-section transmission electron microscopy and atomic force microscopy show an anisotropy in defect structure and surface topography parallel and perpendicular to the GaN c axis. Optical properties are examined by photoluminescence spectroscopy at various temperatures. The spectra exhibit a strong and sharp near-band-gap transition, as well as a donor-acceptor pair transition.

Pattern transitions on Ge surfaces during low-energy ion beam erosion

During sputtering of Ge surfaces with Xe+ ions at 2keV ion energy at room temperature, self-organized ripple and dot nanostructures with a mean wavelength below 60nm emerge as the ion incidence angle is varied. Dots evolving at normal ion incidence pass into ripple patterns with increasing ion incidence angle. Furthermore, for ion incidence angles above 10deg to the surface normal a gradual transition from ripples to dots is observed. Guided by the previous existence of ripples these evolving dot patterns show a long range hexagonal ordering extending across the whole sample surface.

Heat balance during plasma immersion ion implantation

The substrate temperature was measured during plasma immersion ion implantation (PIII) of nitrogen as a function of the pulse bias voltage and the repetition frequency. The variation of the equilibrium frequency for temperatures between 150 and 500 °C and pulse voltages between -5 and -30 kV was investigated. Using these data, the relative dose per pulse for different voltages was obtained and its voltage dependence compared with different models for the plasma sheath expansion during PIII. A higher plasma density than measured for a static plasma without pulses, due to the interaction of secondary electrons with the plasma, must be assumed. Good agreement with dose measurements of N implanted in Si was also observed. For high pulse frequencies above 1 kHz a deviation was observed, clearly showing that depletion of the ions from the plasma during the pulses leads to reduced average plasma density at high repetition rates.