Hydrogen kinetics in a-Si:H and a-SiC:H thin films investigated by real-time ERD

Hydrogen effusion from hydrogenated amorphous silicon (a-Si:H) and amorphous silicon carbide (a-Si1 xCx:H) thin films during a temperature ramp between RT and 600 C was studied by in situ realtime elastic recoil detection analysis. Point to point contour maps show the hydrogen depth profile and its evolution with the ramped temperature. This paper proposes a diffusion limited evolution model to study H kinetic properties from total retained H contents recorded in a single ramp. In a compact a-Si:H layer where H predominantly effuses at high temperatures between 500 and 600 C, an activation energy value of 1.50 eV and a diffusion pre-factor of 0.41 10 4 cm2/s were obtained. Applied to an non-stoichiometric a-Si1 xCx:H film in the same range of temperature, the model led to reduced values of activation energy and diffusion prefactor of 0.33 eV and 0.59 10 11 cm2/s, respectively.National Research Foundation of South Africa (Grant specific unique reference number (UID) 85961).http://www.elsevier.com/locate/nimbhb201

The new Heavy Ion ERDA set up at iThemba LABS Gauteng : multilayer thin film depth profiling using direct calculation and Monte Carlo simulation codes

We report here on the recently built Heavy Ion ERDA set up at iThemba LABS Gauteng; describing a typical application in the study of interfacial reactions in an Al2O3–Ti ceramic–metal multilayer structure annealed in vacuum at 800 C for 2 h. Depth profile extraction was found to be best obtained through combined use of direct calculation and Monte Carlo simulation codes as opposed to using just either of the methods. The obtained profile suggests a case of the Kirkendall effect, whereupon the inter-diffusion between the metal and the ceramic was largely due to the faster diffusion of the metal into the amorphous ceramic than diffusion of the ceramic elements into the metallic layer.National Research Foundation (iThemba LABS) and the International Atomic Energy Agency (IAEA).http://www.elsevier.com/locate/nimbhb201

Interface reactions between Pd thin films and SiC by thermal annealing and SHI irradiation

The solid-state reactions between Pd thin films and 6H-SiC substrates induced by thermal annealing, room temperature swift heavy ion (SHI) irradiation and high temperature SHI irradiation have been investigated by in situ and real-time Rutherford backscattering spectrometry (RBS) and Grazing incidence X-ray diffraction (GIXRD). At room temperature, no silicides were detected to have formed in the Pd/SiC samples. Two reaction growth zones were observed in the samples annealed in situ and analysed by real time RBS. The initial reaction growth region led to formation of Pd3Si or (Pd2Si+Pd4Si) as the initial phase(s) to form at a temperature of about 450 °C. Thereafter, the reaction zone did not change until a temperature of 640 °C was attained where Pd2Si was observed to form in the reaction zone. Kinetic analysis of the initial reaction indicates very fast reaction rates of about 1.55×1015 at.cm-2/s and the Pd silicide formed grew linear with time. SHI irradiation of the Pd/SiC samples was performed by 167 MeV Xe26+ ions at room temperature at high fluences of 1.07×1014 and 4×1014 ions/cm2 and at 400 °C at lower fluences of 5×1013 ions/cm2. The Pd/SiC interface was analysed by RBS and no SHI induced diffusion was observed for room temperature irradiations. The sample irradiated at 400 °C, SHI induced diffusion was observed to occur accompanied with the formation of Pd4Si, Pd9Si2 and Pd5Si phases which were identified by GIXRD analysis.http://www.elsevier.com/locate/nimb2017-03-31hb2016Physic

Formation and microstructure of cubic metastable iron silicides synthesized during pulsed laser annealing

The phase formation and crystallization processes of metastable [CsCl]Fe1-xSi phases were investigated by irradiating epsilon-FeSi/Si(111) thin films with a pulsed excimer laser in the energy density range 300-900 mJ/cm(2). The samples were analysed by Rutherford backscattering and channeling spectrometry (RBS/C), cross-sectional transmission electron microscopy (TEM) and conversion electron Mossbauer spectroscopy (CEMS). Laser irradiation results in mixing of the FeSi with the Si substrate, with the final concentration depending on the laser energy density. Due to the extremely rapid quench of the melt, a non-uniform Fe concentration is obtained. Analysis by cross-sectional transmission electron microscopy confirmed that this phase, which exhibits epitaxial ordering, corresponds to the metastable [CsCl]Fe1-xSi phase, which converts into the semiconducting beta-FeSi2 upon annealing at 600degreesC. CEMS indicates that no stable Fe- silicide phase nor a combination of stable phases have been formed. The CEM spectra consist of a distribution of quadrupole doublets and isomer shifts, in agreement with a [CsCl]Fe1-xSi phase that exhibits a (i) composition gradient and (ii) a random number of Fe vacancies in the neighbouring shells. These distributions make the CEM spectra hard to interpret. Full-Potential Linearized Augmented Plane Wave (FLAPW) calculations were performed to gain more insight in the hyperfine interaction parameters of the metastable [CsCl]Fe1-xSi phase and their dependence on a concentration variation. These calculations confirm the decreasing trend of the isomer shift with increasing number of laser pulses