Thermal transport across nanoscale damage profile in sapphire irradiated by swift heavy ions

Abstract

We studied the degradation of thermal conductivity in single crystal sapphire (α-Al2O3) irradiated by 167 MeV Xe swift heavy ions (SHIs) over the multiple fluences in the range of 1012–1014 ions/cm2. Thermal conductivity was measured primarily in the cross-plane direction using a noncontact ultrafast optical pump-probe technique called picosecond time domain thermoreflectance (TDTR). Multiple samples with variable ion fluences allowed us to probe distinct regions resulting from different regimes of microstructure evolution caused by electronic energy loss. By tuning the penetration depth of the thermal waves using different modulation frequencies, two regions with distinct conductivities were identified and the values of which were found to be consistent with phonon-mediated thermal transport models while the microstructure was confirmed by electron microscopy characterization. These damaged regions were determined to be a several micrometer thick ion track region and several tens of nanometer-thick amorphous layer present only above 5.0 × 1013 ions/cm2. These results demonstrate the applicability of TDTR to resolve thermal transport behavior in SHI irradiated oxides having nonhomogeneous damage profile on a nanometer scale. The presented approach facilitates future studies aiming at resolving the impact of distinct damage resulting from electronic and nuclear stopping regimes under irradiation.

Photothermal Effects and Heat Conduction in Nanogranular Silicon Films

“…When it comes to probe thermal transport properties of NP-based films, it is sufficient to use mild laser powers in contrast to the case of bulk materials, which would require much higher laser power inputs. To study heat propagation properties in nanostructured materials, a large variety of PT techniques, such as Raman spectroscopy [ 8 ], thermoreflectance [ 9 ], spectral radiometry [ 10 ] and others have been employed.…”

Thermal Energy Transport in Oxide Nuclear Fuel

“…The simplest form for the thermal wave penetration for the TDTR geometry is given as 𝐿 KL = H𝐷/(𝜋𝑓) , where D is the diffusivity of the substrate and f is the pump modulation frequency [406,569]. TDTR has been used to study a variety of ion irradiated materials including nuclear fuel [570], nuclear fuel cladding [571], silicon carbide [572] metallic multi-layers [571], silicon [571,573], sapphire [574], and diamond [575] across orders of magnitude in thermal conductivity. MTR, also referred to as spatial domain or beam-offset thermoreflectance [576,577,578,579,580,581], has been used in the majority of studies of ion irradiated actinide oxides and their surrogates.…”

Study of Degradation Mechanisms of Strength and Thermal-Physical Properties of Nitride and Carbide Ceramics—Promising Materials for Nuclear Energy

“…The most destructive consequences, in terms of destruction and amorphization processes, are two types of radiation damage. These are helium or hydrogen embrittlement due to processes associated with transmutation nuclear reactions under the impact of neutrons or during interaction with coolant, and the destruction of the near-surface layer due to interaction with products or fragments of nuclear fuel fission [ 16 , 17 , 18 ]. In both cases, the most vulnerable layer is the near-surface layer of structural materials, which is directly exposed to radiation.…”

“…Firstly, there is no unified theory of defect formation caused by the interaction of heavy charged particles with the structural damage material. Today there are several theoretical and experimental models attempting to describe these processes in various materials that are based on ideas about the energy exchange between the colliding particle and the material structure [ 18 , 19 , 20 , 21 , 22 ].…”