Figure 1 shows the schematic of the TDTR experimental setup used in this study (Manufacturer – PicoTherm, Ibaraki, Japan). The output of the Er-doped fiber laser has a repetition frequency of 20 MHz. The pump beam of wavelength 1,550 nm heats the surface of a 135-nm-thick optothermal selleck chemicals Al transducer film deposited on the sample by sputtering. The pump beam thermally excites the sample creating a temperature-dependent reflectivity change. The reflectivity change is separately monitored with a time-delayed probe laser of wavelength 775 nm. The in-phase component (V in) and the out-of-phase component
(V out) of the probe signal variations were measured using a photodiode detector and audio frequency lock-in at 150 kHz. Figure 1 Schematic of the picosecond time domain thermoreflectance setup. The violet and red lines show the optical transport path of the pump beam and probe beam, respectively. The signals were analyzed assuming a unidirectional heat flow thermal model between the Al transducer film and the material . In brief, the analysis model accounts for thermal transport in layered structures from time periodic power source with a Gaussian intensity distribution . In our experiments, the modulation
frequency of the pump beam is 150 kHz. The pump CP673451 mw and probe beam spot sizes (1/e2 radius) are 37 μm and 14 μm, respectively. The Al transducer film thickness was measured as 135 nm using a profilometer. Results and discussion The thermal conductivity of single crystalline buy Captisol silicon with the Al transducer film was measured using TDTR and is found to be consistent with the literature value  within the experimental uncertainties of ±10%. The results of thermal conductivities of the HPT-processed samples measured using TDTR are shown in Figure 2. Figure 2a,b shows the example data sets and the corresponding
numerical fitting to the thermal model. The free parameters used in the model, the thermal interface conductance of the Al/sample and thermal conductivity of the HPT sample are adjusted to fit the experimental data at different delay Amisulpride times. Figure 2 Example data set of HPT-processed sample and corresponding fitting of thermal model (a) before and (b) after annealing. Figure 3 shows the thermal conductivity results of the HPT-processed silicon before and after annealing. The thermal conductivity of the HPT-processed silicon at 24 GPa was approximately 18 Wm−1 K−1 which is an order of magnitude less than the intrinsic literature value of 142 Wm−1 K−1 for single crystalline silicon. The thermal conductivity of HPT-processed samples reduces to approximately 7.6 Wm−1 K−1 when further strained by HPT processing. Figure 3 Thermal conductivities of the HPT-processed before and after annealing. An order of magnitude reduction in the thermal conductivity of Si upon HPT processing is observed.