The present study reports a strong thickness-dependence and anomalously large enhancement in the values of the Seebeck coefficient and electrical conductivity in Bi2Te3 films at ultralow thickness. An opposite sign of the Hall coefficient (negative) and Seebeck coefficient (positive) is observed in an ultrathin Bi2Te3 film (65 nm) as compared to the normally observed identical sign in the case of Bi2Te3 thin films (520 nm). A simultaneous enhancement in the values of electrical conductivity and the Seebeck coefficient results in a giant enhancement in the value of power factor from 1.86 mW/m K2 to 18.0 mW/m K2 at 416 K, with a reduction in thickness. X-ray photoelectron spectroscopy investigation reveals the absence of any significant change in stoichiometry and chemical bonding upon reduction of thickness. Magnetoresistance vs magnetic field data show a sharp dip at the lower magnetic field values, indicating a weak antilocalization effect in the case of the ultrathin film sample suggesting the role of strong spin–orbit coupling toward the carrier filtering effect resulting in enhancement of thermoelectric properties. Observation of the large Seebeck coefficient and the power factor at lower thickness values and its relationship with spin–orbit coupling is an important result, both for practical applications and for better understanding of the thermoelectric properties.

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In this study, the effect of incorporation of 2D nanoflakes on an n type and a p type thermoelectric matrixes, Bi2Te3 and Sb2Te3, respectively, has been studied. MoS2 has been used to prepare nanocomposite bulk samples having n-n or n-p 2D interfaces. Kelvin probe force microscopy based measurements were used to characterize nanocomposite samples which revealed a difference in potentials barrier at the 2D interface for Bi2Te3:MoS2 and Sb2Te3:MoS2 samples, respectively. The electrical conductivity of Bi2Te3:MoS2 was observed to be lower as compared to the pristine Bi2Te3 due to increased electron scattering at 2D interfaces, whereas in the case of Sb2Te3:MoS2, the incorporation of MoS2 led to the increase in the value of electrical conductivity due to higher carrier mobility. In Bi2Te3:MoS2, a large decrease in thermal conductivity due to reduced electronic contribution is observed in contrast to no change in the case of the Sb2Te3:MoS2 nanocomposite sample. The Seebeck coefficient is observed to increase in both the types of nanocomposite samples but owing to different mechanisms. The presence of potential barrier for electrons restricts the flow of majority carriers in the Bi2Te3:MoS2 nanocomposite, whereas in the case of Sb2Te3:MoS2 nanocomposite samples, the increased potential barrier helps in assisting the flow of holes, thereby increasing the mobility of carriers in the case of Sb2Te3:MoS2.

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Efficient thermoelectric (TE) conversion of waste heat to usable energy is a holy grail promising to address major societal issues related to energy crisis and global heat management. For these to be economical, synthesis of a solid‐state material with a high figure‐of‐merit (ZT) values is the key, with characterization methods quantifying TE and heat transport properties being indispensable for guiding the development of such materials. In the present study, a large enhancement of the TE power factor in Sb2Te3/MoS2 multilayer structures is reported. A new approach is used to simultaneously experimentally determine the values of in‐plane (kxy) and out‐of‐pane (kz) thermal conductivities for multilayer samples with characteristic layer thickness of few nanometres, essential for the quantification of the ZT, the key parameter for the TE material. Combining simultaneous enhancement in the value of in‐plane power factor (to (4.9 ± 0.4) × mWm−1 K−2) and reduction of the in‐plane value of the thermal conductivity (to 0.7 ± 0.1 Wm−1 K−1) for Sb2Te3/MoS2 multilayer sample led to high values of ZT of 2.08 ± 0.37 at room temperature. The present study, therefore, sets the foundation for a new methodology of exploiting the properties of 2D/3D interfaces for the development of novel fully viable thermoelectric materials.

In the present study, 2D-3D MoS2/Sb2Te3 (n-p) and MoS2/Bi2Te3 (n-n) heterojunctions with varying MoS2 thicknesses have been investigated using the Kelvin Probe Force Microscopy technique. Nanoscale maps of interface measurements based on the difference of surface potential (SP) maps in surface charge and back natural modes have been carried out. The 2D-3D heterojunctions with lower MoS2 thickness show a large difference in SP values in the two modes, which is observed to increase with a decrease in the MoS2 thickness. In comparison, samples with larger (bulk-like) MoS2 thickness show negligible SP differences, indicating complete Fermi level alignment, as expected in a normal bulk junction. The difference in the SP value in two modes represents large surface charge accumulation in the 2D layer due to a relatively high value of the depletion width required for achieving equilibrium in comparison to the atomic scale thickness of 2D MoS2. In limited earlier reports, the current-voltage behavior of metal—2D MoS2 junctions is explained on the basis of the Fermi level pinning effect, which is a very generic explanation given for bulk p-n heterojunctions and may not be applicable in 2D materials. The present study shows that surface charge accumulation has a large influence on the I-V characteristic of 2D junctions, and this may be a key factor influencing the physics of the 2D interface and their potential applications.

Hot energy carrier filtering as a means to improve the thermoelectric (TE) property in Sb 2 Te 3 thin film samples having size-selected Au nanoparticles (NPs) is investigated in the present study. Nonagglomerated Au NPs with a very narrow size distribution grown by an integrated gas-phase synthesis setup are incorporated into the Sb 2 Te 3 thin film synthesized by RF magnetron sputtering. TE properties have been investigated as a function of size-selected Au NP concentrations and compared with that of a nanocomposite sample having non-size-selected Au NPs. An increase in the Seebeck coefficient and power factor, along with a slight decrease in electrical conductivity, is observed for samples with a NP size of minimum variance. Further, the Kelvin probe force microscopy and conducting atomic force microscopy techniques were employed to understand the nature of the interface and charge transport across the Sb 2 Te 3 matrix and Au NPs. The study provides an opportunity to modulate the TE properties in Sb 2 Te 3 thin films by constructing a metal−semiconductor heterostructure through controlling the concentration and randomness to achieve a high TE performance.