Thermal transport properties for the isotropic and anisotropic characterization of nanolayers have been a significant gap in the research over the last decade. Multiple studies have been close to determining the thermal conductivity, diffusivity, and boundary resistance between the layers. The methods detailed in this work involve non-contact frequency domain pump-probe thermoreflectance (FDTR) and photothermal radiometry (PTR) methods for the ultraprecise determination of in-plane and cross-plane thermal transport properties. The motivation of one of the works is the advantage of the use of amplitude (TR signal) as one of the input parameters along with the phase for the determination of thermal parameters. In this article, we present a unique strategy for measuring the thermal transport parameters of thin films, including cross-plane thermal diffusivity, in-plane thermal conductivity, and thermal boundary resistance as a comprehensively reviewed article. The results obtained for organic and inorganic thin films are presented. Precise ranges for the thermal conductivity can be across confidence intervals for material measurements between 0.5 and 60 W/m-K for multiple nanolayers. The presented strategy is based on frequency-resolved methods, which, in contrast to time-resolved methods, make it possible to measure volumetric-specific heat. It is worth adding that the presented strategy allows for accurate (the signal in both methods depends on cross-plane thermal conductivity and thermal boundary resistance) and precise measurement.

We demonstrate that dopant inhomogeneity strongly suppresses thermal conductivity in Cd/Eu co-doped, non-polar a-plane-oriented ZnO films grown on r-plane sapphire (Al₂O₃) by plasma-assisted molecular beam epitaxy. X-ray diffraction confirms the a-plane-oriented ZnO without detectable secondary phases. Cross-sectional scanning electron microscopy shows continuous films with well-defined interfaces, and secondary-ion mass spectrometry depth profiling identifies Cd/Eu incorporation through the film thickness and a sharp Zn/O drop at the substrate interface. Cross-plane thermal transport was measured at room temperature using frequency-domain photothermal infrared radiometry (PTR) and analyzed by fitting the complex PTR amplitude and phase with a multilayer heat-diffusion model. The extracted thermal conductivity ($\kappa$) spans ~3.7–6.3 W·m⁻¹·K⁻¹. The lowest $\kappa$ values correlate with increased Eu-distribution inhomogeneity, consistent with enhanced phonon scattering and reduced effective cross-plane heat transport.

We demonstrate that dopant inhomogeneity strongly suppresses thermal conductivity in Cd/Eu co-doped, non-polar a-oriented ZnO films grown on r-plane sapphire (Al₂O₃) by plasma-assisted molecular beam epitaxy. Structural characterization by θ-2θ XRD confirms a-oriented ZnO without detectable secondary phases. Cross-sectional SEM shows continuous films with well-defined interfaces, and SIMS depth profiling verifies Cd/Eu incorporation through the film thickness and a sharp Zn/O drop at the substrate interface. Optical transmittance and Tauc analysis reveal composition-dependent shifts of the absorption edge and band gap. Cross-plane thermal transport was measured at room temperature using frequency-domain photothermal infrared radiometry (PTR) and analyzed by fitting the complex PTR amplitude and phase with a multilayer heat-diffusion model. The extracted thermal conductivity spans ~3.7 - 6.3 Wm-1K-1. The lowest k values correlate with increased defect non-uniformity, consistent with enhanced phonon scattering and reduced effective cross-plane heat transport.