Alenka Razpet

Fabrication of high-density ordered nanoarrays in silicon dioxide by MeV ion track lithography

Self-assembled nanoporous alumina films were employed as masks for MeV ion track lithography. Films with thickness of 2 μm and pore diameters of 30 and 70 nm were attached to thermally grown SiO2 covered with a thin gold layer. The samples were aligned with respect to the beam by detecting backscattered He+ ions with the initial energy of 2 MeV. The ordered pattern of the porous alumina films was successfully transferred into SiO2 after irradiation with a 4 MeV Cl2+ beam at fluence of 1014ions∕cm2, followed by chemical etching in a 5% HF solution.

Development of a time-of-flight telescope for ERDA at the JoŽef Stefan Institute

Abstract A new type of time detector in annular geometry for time-of-flight (TOF) telescope was designed and constructed. The start signal is triggered by the secondary electrons emitted from a thin carbon foil placed perpendicularly to the path of the fast ions. The secondary electrons are accelerated through the central hole of the microsphere plate (MSP) by the electric field between the carbon foil and the electrode at the rearside of the MSP. They are reflected to the active surface of the MSP by the mirror electrode. The stop signal is generated by a similar time detector with microchannel plates where the thin gold entrance window of the silicon detector serves as the secondary electron source. The performance of both time detectors was studied. The TOF detector performance was demonstrated in TOF-elastic recoil detection analysis (ERDA) measurements with a 9600 keV Cl5+ ion beam.

Nanopattern transfer to SiO2 by ion track lithography and highly selective HF vapor etching

The authors present a method for high aspect ratio nanopatterning of high density (1010pores∕cm2) self-assembled porous alumina membrane pattern into thermally grown SiO2 on silicon. The pattern transfer is accomplished by irradiating through 2μm thick porous alumina membrane with swift heavy ions (4MeV Cl2+). Ions passing through the nanopores in the mask at a fairly high fluence (typically 1014ions∕cm2) are impinging on the substrate and creating a continuous volume of overlapping ion tracks of damage. The damage is sufficient to be selectively etched by HF vapor from an aqueous HF solution. From an alumina mask with pores of 70nm diameter, a pattern of pores of 77nm in diameter and the same distance of 100nm between the centers of the pores was transferred. The deepest observed etched pores were 355nm, giving an aspect ratio of 5, which is up to 40 times larger compare to earlier work where HF wet etching was used. This ion track lithography technique shows a potential to produce nanostructures with ev...

Ion Beam Synthesis of Silicon Carbide

Formation and crystallization of a thin near-surface layer of silicon carbide on a silicon substrate, created by ion-beam synthesis (IBS), are discussed. 80 and 40 keV carbon ions were implanted into a (1 0 0) high-purity p-type silicon substrate at room temperature and 400 oC, respectively, using doses in excess of 1017 ions/cm2. Elastic recoil detection analysis (ERDA) technique, developed for routine atomic depth profiling at the Angstrom laboratory, Uppsala University, Sweden, was used to investigate the depth distributions of implanted-ions. Infrared transmittance measurement was used as an indication of SiC in the implanted Si substrate. For the samples implanted at high temperature, the results show the existence of a peak at 797 cm-1, indicating the presence of β-SiC, already directly formed during the implantation without postimplantation annealing. While for the samples implanted at room temperature, starting with the band of amorphous Si-C network, the crystalline SiC appears at the annealing temperature as low as 900 oC. In both cases, during further annealing in vacuum, the peak grows in height and narrows in width (according to the measured FWHM) with increasing annealing temperature, indicating a further growth of the SiC layer. However, for thermal annealing at 1000 oC in a vacuum furnace the SiC crystallization was not completed and crystal imperfection where still present. Complementary to IR, Raman scattering measurements were performed. Although no direct evidence of SiC vibrations were observed, the appearance and disappearance of both Si-Si and C-C related bands points out to the formation of silicon and carbon clusters in the implanted layer.

Properties of ordered nanoporous alumina as a template for pattern transfer by MeV ion irradiation

Properties of ordered nanoporous alumina as a template for pattern transfer by MeV ion irradiation