Investigations of Ar ion irradiation effects on nanocrystalline SiC thin films
Introduction
Due to its excellent mechanical, optical, thermochemical, electronic, and electrical properties coupled with a low neutron absorption cross section, SiC has been extensively investigated for potential uses in environments where there is a high level of radiation [1], [2]. Such thin films have been used for applications in the nuclear industry as components in composite materials [3], encapsulating coatings for nuclear fuel particles used in the next generation reactors [4], [5] or as a wall material in fusion experiments [6]. The effect of radiation on the structure, mechanical and electronic properties of SiC has been investigated in detail for single crystals that are mainly used for microelectronics applications [7], [8], [9]. However, the deposited films used as coatings for the encapsulation and protection of nuclear fuel or on the walls are either amorphous or polycrystalline, containing many polytypes and a high density of defects. The effect of radiation on such coatings has been only recently investigated [10], [11], [12]. It was reported that some results were quite different from those observed for single crystalline SiC samples. For example, the amorphization fluence threshold was found to be higher for nanocristalline SiC than its value measured for single crystals [10], [11]. Since the depth of the radiation damaged region for medium energy ions is of the order of hundreds of nm, nanoindentation investigations have been recently used to assess changes of the mechanical properties induced by radiation [13], [14]. However, nanoindentation investigations of polycrystalline SiC films have not been yet reported, because the errors caused by the high surface roughness of the investigated films were too large [15]. Using the pulsed laser deposition (PLD) technique, SiC films were deposited on Si substrates and their structure and properties investigated [10], [16], [17], [18], [19]. Results showed that PLD grown films were dense (around 3.20 g/cm3, similar to single crystal values), nanocrystalline, contained low O concentrations and possessed smooth surfaces (rms values below 1 nm) [19]. Because of its ability to manufacture very smooth thin films, the PLD technique offers then the unique opportunity to perform nano-indentation and to probe the damaged area with the glancing incidence X-ray diffraction (GIXRD) and X-ray reflectivity (XRR) techniques and extract information on the mechanical properties, structure and the microstructure of irradiated samples [20], [21], [22], [23]. Even if the surface morphology of PLD grown film could be quite different from that of films deposited using other techniques, the combination of nano-indentation, XRR and GIXRD investigations allows for the observation of the structural (unit cell parameter) and the microstructural (strain field) evolution of SiC samples versus the irradiation fluence and their influence on the mechanical properties. To illustrate these advantages, PLD grown SiC samples were irradiated by 800 keV Ar ions and the changes of the mechanical properties, surface morphology and structure were investigated.
Section snippets
Experimental details
The PLD setup uses a KrF excimer laser (λ = 248 nm, pulse duration τ = 25 ns, fluence around 6 J/cm2, 40 Hz repetition rate) to ablate a SiC polycrystalline target in a stainless steel chamber [19]. The ultimate pressure in the deposition chamber was in the low 10−6 Pa to minimize oxygen incorporation. Films were deposited using our previous optimized conditions (nominal substrate temperature of 1000 °C under a high purity of 2 × 10−3 Pa CH4) on p++ (100) Si substrates (MEMC Electronic Materials, Inc.) for
Results and discussion
In order to study the structural stability of SiC thin film under irradiation, ion beam irradiation was performed. The nature and the energy of the ion beam were selected to mimic the recoils spectrum induced by a typical pressurized water reactor (PWR) neutron flux at the same temperature. This simulation was performed using the DART code [27]. Fig. 1 displays the comparison of the weighted recoil spectra computed within the binary collision approximation [27] for 1 MeV electron, 800 keV He, 800
Conclusions
Dense and nanocrystalline SiC films grown by the PLD technique on Si substrates were irradiated at room temperature by 800 keV Ar ions at a fluence of 2.6 × 1014 at/cm2. After irradiations, a relative decrease of the fraction of hexagonal crystalline regions and an increase in the fraction of the cubic regions was observed by GIXRD investigations. The films were rather smooth and allowed for the measurement of the XRR curves. The simulations of the XRR curves indicated a slight decrease of the
Acknowledgements
This work was supported by a grant IFA-CEA C3-03. S.B. would like to thank the financial support from Florida International University Doctoral Evidence Acquisition Fellowship. The authors also acknowledge the help of N. Nabillon and N. Moncoffre of the team ACE of the CNRS/IPNL for having performed the Ar ion irradiations. VC acknowledges the support of a JSPS fellowship S-14058 and the NUCLEU program.
References (35)
- et al.
An XPS study to investigate the dependence of carbon ion fluences in the formation of buried SiC
Nucl. Instrum. Methods Phys. Res. Sect. B: Beam Interact. Mater. Atoms
(2012) - et al.
Physical properties of ECR-CVD polycrystalline SiC films for micro-electro-mechanical systems
Diam. Relat. Mater.
(2003) - et al.
The reprocessing of reactor core materials
Nucl. Eng. Des.
(2014) - et al.
Creation of leak-proof silicon carbide diffusion barriers by means of pulsed laser deposition
Nucl. Eng. Des.
(2014) - et al.
Radiation effects in SiC for nuclear structural applications
Curr. Opin. Solid State Mater. Sci.
(2012) - et al.
Irradiation-induced microstructural change in helium-implanted single crystal and nano-engineered SiC
J. Nucl. Mater.
(2014) - et al.
SEM analysis of ion implanted SiC
Nucl. Instrum. Methods Phys. Res. B
(2013) - et al.
Evolution of defects in silicon carbide implanted with helium ions
Nucl. Instrum. Methods Phys. Res. B
(2014) - et al.
Radiation effects in carbides: TiC and ZrC versus SiC
Nucl. Instrum. Methods Phys. Res. B
(2014) - et al.
Experimental and ab initio study of enhanced resistance to amorphization of nanocrystalline silicon carbide under electron irradiation
J. Nucl. Mater.
(2014)
Competing effects of electronic and nuclear energy loss on microstructural evolution in ionic-covalent materials
Nucl. Instrum. Methods Phys. Res. B
Nanomechanical measurements of irradiated layers: methodology, possibilities and pitfalls
Vacuum
Issues to consider using nanoindentation on shallow ion beam irradiated materials
J. Nucl. Mater.
Amorphous to crystalline phase transition in pulsed laser deposited silicon carbide
Appl. Surf. Sci.
Pulsed laser deposition of nanocrystalline SiC films
Appl. Surf. Sci.
Grazing incidence X-ray diffraction for the study of polycrystalline layers
Thin Solid Films
Structural behaviour of nearly stoichiometric ZrC under ion irradiation
Nucl. Instrum. Methods Phys. Res. Sect. B – Beam Interact. Mater. Atoms
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2022, Ceramics InternationalCitation Excerpt :Fig. 8 displays a C 1s high-resolution spectra. In addition to the C related surface components (BE > 285 eV), a dominant peak located at 283.8 eV associated with the Si–C bond and a shoulder peak at 284.8 eV associated with the C–C bond were observed in the original sample [33]. Although the formation of new bonds was not observed, the implantation of Si5+ ions still affected the bonding state of the sample significantly.