Abstract
As device miniaturization in modern electronics accelerates, thermal management emerges as a critical challenge due to increasing power densities and local heat accumulation. Efficient heat dissipation and thermoelectric energy conversion are essential for sustaining reliable, high-performance operation in next-generation nanoelectronic systems. Two-dimensional (2D) materials with tunable thermal and electrical transport properties offer a compelling platform to address these challenges. This thesis investigates in-plane thermal and electronic transport behavior in two such materials: metallic cobalt-intercalated 2H-TaS₂ (2H-CoxTaS₂) and semiconducting n-doped γ-phase indium selenide (γ-InSe), with the goal of advancing their applicability in thermal management and energy conversion technologies.
For 2H-CoxTaS₂ (where x<0.2), a metallic transition metal dichalcogenide (TMD), exfoliated flakes with nanometer-scale thickness were studied using thermoreflectance-based heat diffusion imaging (HDI) and four-probe electrical transport measurements. The temperature-dependent thermal conductivity reveals a dominant electronic contribution at low temperatures with a balanced phonon–electron heat transport across most of the measured range, including room temperature. The highest in-plane thermal conductivity reaches 10.41 W/m·K at 384.5 K, with an electrical conductivity exceeding 6.23 × 10⁵ S/m at room temperature. The observed low resistivity and high thermal conductivity alongside structural coherence and absence of magnetic ordering highlight the high crystalline quality and well-ordered intercalant distribution in the thin flakes. Comparative studies with a second 90 nm sample affirm the intrinsic transport behavior, making 2H-CoxTaS₂ a promising candidate for on-chip thermoelectric cooling and 2D metallic interconnects.
The second system, γ-InSe, a semiconducting III–VI layered material, was studied in n-doped (53 nm and 37 nm) forms. The HDI method was employed to extract in-plane thermal conductivity across a temperature range of 51–300 K. The room-temperature thermal conductivity measured 7.58 W/m·K in the n-doped sample, revealing the influence of impurity scattering on phonon transport. Wiedemann–Franz analysis confirmed the negligible electronic contribution, indicating that heat transport is phonon-dominated. A thermal conductivity transition near 141 K, consistent with a shift from boundary to Umklapp phonon scattering, was observed in both samples.
Together, these findings offer new insights into thermal and thermoelectric transport in two structurally and electronically distinct 2D layered materials. The HDI technique enables precise, non-contact thermal characterization in ultrathin geometries, providing a valuable tool for nanoscale device design. The results identify 2H-CoxTaS₂ as a strong candidate for on-chip thermal management and 2D interconnects, while highlighting γ-InSe’s potential in thermoelectric and nanoelectronic applications.
