Z. Zolnai

Magnetic patterning perpendicular anisotropy FePd alloy films by masked ion irradiation

The nanopatterning of magnetic films by ion implantation is reported. Highly L10-ordered Fe47Pd53 epitaxial alloy films on a MgO(001) substrate were covered by a monolayer of silica spheres in a Langmuir film balance. Using this sphere layer as an implantation mask, the samples were irradiated by Ne+ or Fe+ ions with energies of 35 keV and 100 keV, respectively. After the silica mask was removed, the samples were characterized via conversion electron Mossbauer spectroscopy, longitudinal and polar magneto-optical Kerr effect, and atomic force and magnetic force microscopy. We find that the magnetic stripe domains observed in the nonirradiated sample were converted into a regular 2D magnetic pattern of hcp character upon 1 × 1015/cm2 35 keV neon or 1 × 1014/cm2 100 keV iron irradiation, with the direction of magnetization remaining out of plane in the nodes of the hcp lattice and relaxed into the film plane in the inter-node region, resulting in an overall in-plane magnetic softening of the film.

Antibacterial properties of Ag-TiO2 composite sol-gel coatings

In this work the long-term antibacterial activity of silver doped titania coatings is studied systematically as a function of the titania layer structure (with and without molecular template) and the amount and physical properties of the silver dopant. Silver was incorporated in two different ways into the titania sol–gel films, either by co-deposition, i.e., adding the silver ions directly to the precursor sol of the layer or by post-synthetic impregnation of the mesoporous titania coating. The structure and morphology of the layers were investigated using transmission and scanning electron microscopy, whereas the silver content was determined by Rutherford backscattering spectrometry. Antibacterial properties against Escherichia coli bacteria were studied by colony forming unit assay and agar diffusion method. It was found that directly after preparation, all composite coatings show antibacterial activity both in the dark and under visible light illumination. The antibacterial activity of the co-deposited samples vanished after the first use despite their high and constant remaining silver content (2.597 at%). This type of coating was not effective in agar diffusion tests at all. The antibacterial activity of the impregnated coatings with lower silver contents (0.596 at% and 1.961 at%), however, showed long-lasting antibacterial effect both in the colony forming unit assay and in agar diffusion tests as well. This can be attributed to the fact that the silver content is distributed over the mesoporous network of the titania coating and is effective during the long-term tests.

Damage accumulation in nitrogen implanted 6H-SiC: Dependence on the direction of ion incidence and on the ion fluence

The influence of crystallographic orientation and ion fluence on the shape of damage distributions induced by 500keV N+ implantation at room temperature into 6H‐SiC is investigated. The irradiation was performed at different tilt angles between 0° and 4° with respect to the ⟨0001⟩ crystallographic axis in order to consider the whole range of beam alignment from channeling to random conditions. The applied implantation fluence range was 2.5×1014–3×1015cm−2. A special analytical method, 3.55MeV He+4 ion backscattering analysis in combination with channeling technique (BS∕C), was employed to measure the disorder accumulation simultaneously in the Si and C sublattices of SiC with good depth resolution. For correct energy to depth conversion in the BS∕C spectra, the average electronic energy loss per analyzing He ion for the ⟨0001⟩ axial channeling direction was determined. It was found that the tilt angle of nitrogen implantation has strong influence on the shape of the induced disorder profiles. Significantl...

Target dependent femtosecond laser plasma implantation dynamics in enabling silica for high density erbium doping

Chemical dissimilarity of tellurium oxide with silica glass increases phase separation and crystallization tendency when mixed and melted for making a glass. We report a novel technique for incorporating an Er3+-doped tellurite glass composition into silica substrates through a femtosecond (fs) laser generated plasma assisted process. The engineered material consequently exhibits the spectroscopic properties of Er3+-ions, which are unachievable in pure silica and implies this as an ideal material for integrated photonics platforms. Formation of a well-defined metastable and homogeneous glass structure with Er3+-ions in a silica network, modified with tellurite has been characterized using high-resolution cross-sectional transmission electron microscopy (HRTEM). The chemical and structural analyses using HRTEM, Rutherford backscattering spectrometry (RBS) and laser excitation techniques, confirm that such fs-laser plasma implanted glasses may be engineered for significantly higher concentration of Er3+-ions without clustering, validated by the record high lifetime-density product 0.96 × 1019 s.cm−3. Characterization of planar optical layers and photoluminescence emission spectra were undertaken to determine their thickness, refractive indices and photoluminescence properties, as a function of Er3+ concentration via different target glasses. The increased Er3+ content in the target glass enhance the refractive index and photoluminescence intensity of the modified silica layer whilst the lifetime and thickness decrease.

Doping silica beyond limits with laser plasma for active photonic materials

The limited solubility of rare-earths in silica hampers the development of loss-compensated photonic integrated circuits. We report a novel method using femtosecond laser plasma assisted hybrid material integration of rare-earth-doped tellurite with silica, achieving high doping concentration of Er3+ and Yb3+-ions, 1.63 × 1021 atoms.cm−3,without segregation validated by Er3+:4I13/2 lifetime of 9.1 ms. The sequential ablation of two individual rare-earth (Er3+/Yb3+) doped-tellurite glass targets produces an exceptional intermixing of Er3+ and Yb3+-ions extending to the pristine silica with sharp interface. Formation of such homogeneous glass structure with Er3+-Yb3+-ions in a matrix of silica is not possible to realise by conventional methods.

Slab optical waveguides in Er3-doped tellurite glass by N + ion implantation at 1.5 MeV

Slab optical waveguides were fabricated in tung-sten-tellurite glass doped with Er3 + ions by means of nitrogen ion implantation at 1.5 MeV. A wide range of ion doses (from 5·1012 to 8·1016 ions/cm2) was used. Optical characterization, performed by dark-line spectroscopy, revealed that the waveguides were of optical barrier type: the implanted layer exhibited a decrease of the refractive index with respect to the virgin bulk glass, while the region comprised between the sample surface and the end of the ion track acted as an optical guiding structure. It was also demonstrated that a post-implantation annealing process, performed at various temperatures on the samples implanted at higher doses, contributes to the reduction of the barrier region.

Introducing nanoscaled surface morphology and percolation barrier network into mesoporous silica coatings

Mesoporous silica thin films were patterned at the sub-micron scale utilizing the ion hammering effect in order to combine the advantages of mesoporous character and surface morphology, while preserving the interconnected pore system or creating laterally separated porous volumes surrounded by nonpermeable compact zones. Porous silica coatings were prepared by a sol–gel method with an ordered and disordered pore system using micellar templates. A hexagonally ordered Langmuir–Blodgett type monolayer of silica spheres was applied as a mask against Xe+ ion irradiation. The ion energy was chosen according to Monte-Carlo simulations to achieve structures with high lateral contrast between irradiated and unirradiated, i.e., masked areas. The disordered pore system proved to be more resistant against ion bombardment. Although the created surface morphologies were similar, the main character of the pore system could be tailored to be interconnected or separated by controlling the ion fluence. Confocal fluorescence images and ellipsometric porosimetry measurements confirmed that the contribution of transition zone between the intact masked and damaged regions to the porosity is negligible. Furthermore, the majority of the porous volume can be preserved as an interconnected pore system by the application of low ion fluence. By increasing the fluence value, however, separated porous volumes can be created at the expense of the total pore volume.

Fabrication of barrier-type slab waveguides in Er 3+-doped tellurite glass by single and double energy MeV N + ion implantation

Ion implantation proved to be a universal technique for producing waveguides in most optical materials. Tellurite glasses are good hosts of rare-earth elements for the development of fibre and integrated optical amplifiers and lasers covering all the main telecommunication bands. Er 3+ - doped tellurite glasses are good candidates for the fabrication of broadband amplifiers in wavelength division multiplexing around 1.55 μm, as they exhibit large stimulated cross sections and broad emission bandwidth. Fabrication of channel waveguides in such a material via N+ ion implantation was reported recently. Parameters of waveguide fabrication in an Er-doped tungsten-tellurite glass via implantation of N + ions were optimized. First single-energy implantation at 3.5 MeV with fluences between 1·10 16 and 8·10 16 ions/cm2 was applied. Waveguide operation up to 1.5 μm was observed. Then double-energy implantations at a fixed upper energy of 3.5 MeV and lower energies between 2.5 and 3.0 MeV were performed to suppress leaky modes by increasing barrier width. Improvement of waveguide characteristics was found by m-line spectroscopy and spectroscopic ellipsometry.

Structural and functional characterisation of slab waveguides written in Er 3+ - doped tellurite glass, CaF 2 , Bi 4 (GeO 4 ) 3 and Bi12GeO20 crystals via implantation of MeV N + ions

Ion implantation proved to be a universal technique for producing waveguides in most optical materials. Tellurite glasses are used as hosts of rare-earth elements for the development of fibre and integrated optic amplifiers and lasers covering all the main telecommunication bands. Er 3+ - doped tellurite glasses are very attractive materials for the fabrication of broadband amplifiers in wavelength division multiplexing (WDM) around 1.55 μm, as they exhibit large stimulated cross sections and broad emission bandwidth. First objective of the present research was to optimise parameters of waveguide fabrication in the Er: tellurite glass via implantation of MeV energy N + ions in a wide range of implanted doses. Besides of glasses, slab optical waveguides were designed and fabricated in CaF2, Bi4Ge3O12 and Bi12GeO20 crystals, also using MeV energy N + ions. Waveguides were characterised using UV/VIS and NIR absorption spectroscopy, spectroscopic ellipsometry and m-line spectroscopy. Part of the implanted samples was annealed to improve waveguide properties. We report on first working slab waveguides fabricated in CaF2 crystals using implantation of MeV-energy medium-mass ions.

Ion Beam Analysis and Computer Simulation of Damage Accumulation in Nitrogen Implanted 6H-SiC: Effects of Channeling

500 keV nitrogen implantations at different tilt angles (0o, 0.5o, 1.2o, 1.6o, 4o) with respect to the c-axis of 6H-SiC were carried out. Radiation damage distributions have been investigated by Backscattering Spectrometry combined with channeling technique (BS/C) using 3550 keV 4He+ ion beam. A comparative simultaneous evaluation of the damage depth distributions in the Si and C sublattices of 6H-SiC led to a correction factor of 0.8 in the electronic stopping power of 4He+ ions along <0001> channel. Full-cascade Crystal-TRIM simulations with the same set of damage accumulation model parameters could reconstruct the measured shapes and heights of damage distributions for all implantation tilt angles. Secondary defect generation effects in addition to the primary point defect accumulation were assumed in the analysis.