Thermal conductivity profile determination in proton-irradiated ZrC by Spatial and frequency scanning thermal wave methods

Using complementary thermal wave methods, the irradiation damaged region of zirconium carbide (ZrC) is characterized by quantifiably profiling the thermophysical property degradation. The ZrC sample was irradiated by a 2.6 MeV proton beam at 600 °C to a dose of 1.75 displacements per atom. Spatial scanning techniques including scanning thermal microscopy (SThM), lock-in infrared thermography (lock-in IRT), and photothermal radiometry (PTR) were used to directly map the in-depth profile of thermal conductivity on a cross section of the ZrC sample. The advantages and limitations of each system are discussed and compared, finding consistent results from all techniques. SThM provides the best resolution finding a very uniform thermal conductivity envelope in the damaged region measuring ∼52 ± 2 μm deep. Frequency-based scanning PTR provides quantification of the thermal parameters of the sample using the SThM measured profile to provide validation of a heating model. Measured irradiated and virgin thermal conductivities are found to be 11.9 ± 0.5 W m−1 K−1 and 26.7 ±1 W m−1 K−1, respectively. A thermal resistance evidenced in the frequency spectra of the PTR results was calculated to be (1.58 ± 0.1) × 10−6 m2 K W−1. The measured thermal conductivity values compare well with the thermal conductivity extracted from the SThM calibrated signal and the spatially scanned PTR. Combined spatial and frequency scanning techniques are shown to provide a valuable, complementary combination for thermal property characterization of proton-irradiated ZrC. Such methodology could be useful for other studies of ion-irradiated materials

Scanning thermal microscopy based on a modified atomic force microscope combined with pyroelectric detection

We propose a novel approach in scanning thermal microscopy of layered samples. The thermal probe (ThP) (Wollaston wire) acts as a local a.c. heat source at the front of a sample layer deposited on a pyroelectric (PE) sensor. The PE signal is proportional to the heat wave transmitted through the sample. The ThP and PE signals can be used to generate complementary thermal conductivity maps and with some restrictions, thermal diffusivity maps of the sample. Additionally, the topography map is obtained in the usual way from the atomic force microscope. We give the theoretical background for the interpretation of PE signal obtained at low and at high frequency, and we demonstrate that it carries information on the thermal diffusivity of a test sample (12 $\mu$m thick PET polymer sheet). Finally, we discuss the contributions of heat transfer channels between ThP and sample, and the role of contact thermal resistance

Thermal characterization of micro-structured NiTi samples by 3ω scanning thermal microscopy

The lateral modification of the thermal conductivity of a NiTi sample have been measured by scanning thermal microscope using the 3ω-technique. Squares of lateral length in the micrometer range had been drawn in a polycrystalline NiTi sample by a focussed ion beam of Ga. Amplitude and phase of the 3ω-signal have been recorded at some selected positions as a function of frequency between 10 Hz and 10 KHz and as a function of position at selected modulation frequencies. The 3ω-signals are modified inside the squares as well as the border lines and also change when the temperature is increased above the martensite-austenite transition temperature

Sensing thermal conductivity and structural effects at the nanoscale by scanning thermal microscopy (SThM)

We introduce the theoretical description of $3\omega$ signal from the Wollaston probe of a scanning thermal microscope (SThM) in terms of an equivalent low-pass filter. We performed thermal conductivity $k$ measurements with lateral resolution of about 100 nm. The first application concerns NiTi shape memory alloys microstructured by focused ion beam implantation. Local martensite to austenite structural phase transition has been identified upon heating the sample from room temperature to 100$^{\circ}$C. The $3\omega$ signal changes were -1.95% in amplitude and 0.6$^{\circ}$ in phase, corresponding to thermal conductivity $k$ increase of 13.5%. The second application consists of static measurement of local $k$ on points situated on flat faces of bare diamond crystallites 300 $\mu$m in diameter, and on crystallites coated with Cr, Cu and Cu/Cr layers with thickness in the range 0.5-30 $\mu$m. The high $k$ advantage of bare crystallites is lost upon coating the particles, but the thermal barrier depends also on the specific configuration when the particles are in contact to one another in materials obtained from such powders

Photothermal and micro-thermal characterization of metal coated diamond crystallites

Photoacoustic effect and scanning near field microscopy have been applied to characterise the thermal properties of diamond crystallites which were coated by a Cu film, a Cr-film and a Cr-Cu film. The Cu-coated diamond exhibits a considerable thermal barrier at the Cu-diamond interface which had disappeared for the crystallites with a thin bond Cr-layer between diamond and Cu. The local inspection of the thermal conductivity with a thermal nano-probe operated in the 3ω-mode reveals slight local variations of the thermal conductivity of the Cr-coated crystallite

Experimental modeling of nonlinear photothermal effects in composite materials

An experimental model system was developed in order to investigate the nonlinear effects that originate from vibrating boundaries in photothermal techniques. It followed a primary investigation that demonstrated the effect of thermoelastic bending particularly studied in fiber reinforced composite laminates. The model consisted of such a laminate with a hole and a metallic piston piece that was made to fit exactly inside the hole. The piston position, and consequently the width of the air gap between laminate and piston, was periodically varied while collecting a IR radiometric photothermal signal. The nonlinear effect caused by the varying boundary condition experiment resulted in the generation of mixing frequency components in the photothermal signal

Photothermal and micro-thermal characterization of metal coated diamond crystallites

Photoacoustic effect and scanning near field microscopy have been applied to characterise the thermal properties of diamond crystallites which were coated by a Cu film, a Cr-film and a Cr-Cu film. The Cu-coated diamond exhibits a considerable thermal barrier at the Cu-diamond interface which had disappeared for the crystallites with a thin bond Cr-layer between diamond and Cu. The local inspection of the thermal conductivity with a thermal nano-probe operated in the 3ω-mode reveals slight local variations of the thermal conductivity of the Cr-coated crystallite

Nucleation Phase and Dynamic Inversion of the Mw 6.9 Valparaíso 2017 Earthquake in Central Chile

The Valparaiso 2017 sequence occurred in the Central Chile megathrust, an active zone where the last mega-earthquake occurred in 1730. Intense seismicity started 2 days before the Mw 6.9 mainshock, a slow trenchward movement was observed in the coastal GPS antennas and was accompanied by foreshocks and repeater-type seismicity. To characterize the rupture process of the mainshock, we perform a dynamic inversion using the strong-motion records and an elliptical patch approach. We suggest that a slow slip event preceded and triggered the Mw 6.9 earthquake, which ruptured an elliptical asperity (semiaxis of 10 km and 5 km, with a subshear rupture, stress drop of 11.71 MPa, yield stress of 17.21 MPa, slip weakening of 0.65 m, and kappa value of 1.98). This earthquake could be the beginning of a long-term nucleation phase to a major rupture, within the highly coupled Central Chile zone where a megathrust earthquake like 1730 is expected

Nucleation Phase and Dynamic Inversion of the M<SUB>w</SUB> 6.9 Valparaíso 2017 Earthquake in Central Chile

International audienceThe Valparaiso 2017 sequence occurred in the Central Chile megathrust, an active zone where the last mega-earthquake occurred in 1730. Intense seismicity started 2 days before the Mw 6.9 mainshock, a slow trenchward movement was observed in the coastal GPS antennas and was accompanied by foreshocks and repeater-type seismicity. To characterize the rupture process of the mainshock, we perform a dynamic inversion using the strong-motion records and an elliptical patch approach. We suggest that a slow slip event preceded and triggered the Mw 6.9 earthquake, which ruptured an elliptical asperity (semiaxis of 10 km and 5 km, with a subshear rupture, stress drop of 11.71 MPa, yield stress of 17.21 MPa, slip weakening of 0.65 m, and kappa value of 1.98). This earthquake could be the beginning of a long-term nucleation phase to a major rupture, within the highly coupled Central Chile zone where a megathrust earthquake like 1730 is expected