Tungsten Carbide Nanolayer Formation by Ion Beam Mixing with Argon and Xenon Ions for Applications as Protective Coatings.

A novel nanolayer is formed by means of ion irradiation applicable as protective coating. Tungsten carbide (WC)-rich nanolayers were produced at room temperature by applying ion beam mixing of various carbon/tungsten (C/W) multilayer structures using argon and xenon ions with energy in the range of 40-120 keV and fluences between 0.25 and 3 × 1016 ions/cm2. The hardness of the nanolayers was estimated by means of standard scratch test applying an atomic force microscope equipped with a diamond-coated tip (radius < 10 nm); the applied load was 2 µN. The irradiation-induced hardness of the nanolayers correlated with the areal density of the WC; with the increasing amount of WC, the hardness of the nanolayer increased. The produced layers had an order of magnitude better corrosion resistance than a commercially available WC cermet circular saw. If the WC amount was high enough, the hardness of the layer became higher than that of the investigated WC cermet. These findings allow us to tune and design the mechanical and chemical properties of the WC protective coatings.

Large-area nanoengineering of graphene corrugations for visible-frequency graphene plasmons.

Quantum confinement of the charge carriers of graphene is an effective way to engineer its properties. This is commonly realized through physical edges that are associated with the deterioration of mobility and strong suppression of plasmon resonances. Here, we demonstrate a simple, large-area, edge-free nanostructuring technique, based on amplifying random nanoscale structural corrugations to a level where they efficiently confine charge carriers, without inducing significant inter-valley scattering. This soft confinement allows the low-loss lateral ultra-confinement of graphene plasmons, scaling up their resonance frequency from the native terahertz to the commercially relevant visible range. Visible graphene plasmons localized into nanocorrugations mediate much stronger light-matter interactions (Raman enhancement) than previously achieved with graphene, enabling the detection of specific molecules from femtomolar solutions or ambient air. Moreover, nanocorrugated graphene sheets also support propagating visible plasmon modes, as revealed by scanning near-field optical microscopy observation of their interference patterns.

Interface induced diffusion.

Interface induced diffusion had been identified in a thin film system damaged by electron bombardment. This new phenomenon was observed in Al2O3 (some nm thick)/Si substrate system, which was subjected to low energy (5 keV) electron bombardment producing defects in the Al2O3 layer. The defects produced partially relaxed. The rate of relaxation is, however, was different in the vicinity of the interface and in the "bulk" parts of the Al2O3 layer. This difference creates an oxygen concentration gradient and consequently oxygen diffusion, resulting in an altered layer which grows from the Al2O3/Si substrate interface. The relative rate of the diffusion and relaxation is strongly temperature dependent, resulting in various altered layer compositions, SiO2 (at room temperature), Al2O3 + AlOx + Si (at 500 °C), Al2O3 + Si (at 700 °C), as the temperature during irradiation varies. Utilizing this finding it is possible to produce area selective interface patterning.

Inelastic mean free path data for Si corrected for surface excitation.

Surface-sensitive electron spectroscopies, like Auger electron spectroscopy, X-ray photoelectron spectroscopy and elastic peak electron spectroscopy (EPES) are suitable techniques to investigate surfaces and thin layers. A theoretical model for electron transport is needed to process the observed electron spectra. Electron transport descriptions are based on the differential elastic cross sections for the sample atoms and the inelastic mean free path (IMFP) of backscattered electrons. An electron impinging on the sample can lose energy either due to surface or volume excitations. In the present work a Monte Carlo (MC) simulation of the elastic peak of Si, Ag, Ni, Cu, and Au for surface analysis is presented. The IMFP of Si was determined applying the EPES method. The integrated elastic peak ratio of Si with the standard metal reference samples corrected for surface excitation provided IMFP values of Si in the energy range E = 0.2-2.0 keV. Experiments were made with the ESA 31 HSA (ATOMKI) and with the DESA-100 (Staib) spectrometers. Surface correction was based on the application of Chen's model and material parameters. The Monte Carlo simulations of elastically backscattered electron trajectories were made using new EPESWIN software of Jablonski. An improvement of IMFP experimental results was achieved applying the presented procedure.

Calculation of the surface excitation parameter for Si and Ge from measured electron backscattered spectra by means of a Monte-Carlo simulation.

A new Monte Carlo method has been developed for simulating backscattered electron spectra, and this was applied for determining the surface excitation parameter (SEP). The simulation is based on direct tracking of electron trajectories in the solid, taking into account elastic and inelastic events. The elastic scattering cross sections are taken from literature, while inelastic cross section data are obtained by a fitting procedure. After some iterations, the program produces electron spectra fitting well to the experimental ones. Si and Ge electron spectra were simulated and SEP values were calculated. The SEP values are compared to other ones from literature.