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Two-dimensional (2D) transition metal dichalcogenides (TMDCs) provide an opportunity to investigate diverse scientific phenomena at an atomic level and have effective technological potential. In recent times, unlike conventional TMDCs, platinum diselenide (PtSe2) has garnered considerable attention owing to its i) fascinating electrical and optical features coupled with mechanical strain and ii) scalable synthesis method. However, its local electrical/tribological/mechanical properties are yet to be examined in detail. In this study, we prepared two different types of PtSe2 layers by controlling the thickness of the Pt-seed film: i) one with horizontal alignments, which are made from ultrathin Pt films and ii) one with vertical and horizontal alignments, which are made from a relatively thick Pt film. Then, the local tribological, mechanical, and electrical properties of PtSe2 were evaluated mainly with scanning probe microscopy (SPM). The local friction study unveiled the marked friction variation depending on the layer directions. An additional study on the local mechanical property indicated that the apparent modulus difference between the two growth directions can lead to dissimilar friction behaviors. Furthermore, local current probing using SPM showed that PtSe2 with both layer directions provides ohmic features to both directions, although the magnitude of conductance along the horizontal direction is ~100 times smaller than that along the vertical one. On the contrary, PtSe2 with only in-plane alignments is configured with multiple horizontal PtSe2 layers, densely stitching themselves together one after another with a very narrow trench region at their boundary. Surprisingly, a local current–voltage spectroscopy analysis showed a small current gap on the bridged trench region, in contrast to the ohmic behavior of the grain interior. This indicates that the local metal-to-semiconductor transition is available, owing to thin PtSe2 layers in the trench regions. The following study at macroscale showed how the overall electrical and thermoelectric properties of PtSe2 can be influenced by local structures triggered by the variation in Pt-seed thickness. The results not only provide a new insight on better understanding the intrinsic features of 2D PtSe2, but also offer important characterization guidance on tailoring their functionalities.

This paper reports the results of a study on the microstructure evolution of sputtered BiSb–Te thermoelectric films during post-annealing and its effects on their electronic transport and thermoelectric properties. Combining X-ray diffraction, transmission electron microscopy, and Raman spectroscopy, we illuminate the fundamental aspects of the microstructure evolution: the as-deposited film was Bi0.5Sb1.5Te3 compound in the Bi2Te3-type phase with a nano-crystalline microstructure and the post-annealing prompted a drastic grain growth. The electrical and thermoelectric properties also closely changed following the trend of the grain growth. The Seebeck coefficient, electron mobility, and thermal conductivity increase while the carrier concentration remains flat. The ZT value escalates systematically with the annealing time increasing, reaching around 0.94 after 12 h annealing.

This paper investigates the effects of the Sb content (х) on (Bi1−xSbx–2Te3 thermoelectric films with х changing widely from 0 (Sb2Te3) to 1 (Bi2 Te3). First, the XRD analysis discloses that with the Sb content (x) increasing, the phase changed gradually from Bi2Te3 to Sb2Te3 as Sb atoms replaced substitutionally Bi atoms. Further microstructure analysis reveals that an extensive grain growth occurred during post-annealing for the samples with high Sb contents. According to the measurement of electrical and thermoelectric properties, the polarity of the charge carrier and Seebeck coefficient switched n-type to p-type in the range of x = 0.45∼0.63. For the n-type samples, the power factor is highest when x = 0.18 around 46.01 μW/K2 whereas Sb2Te3, for the p-type samples, shows the highest value, 62.48 μW/K2cm.

This study examined the sensitive effects of composition on the microstructure evolution and thermoelectric properties of sputtered Bi-Te films. Bi-Te films of various Te compositions (49 at.% to 60 at.%) were grown by cosputtering deposition and annealed at 200°C for different durations. We examined the microstructure of the films using x-ray diffraction (XRD) and transmission electron microscopy (TEM), and measured the electronic transport and thermoelectric properties. As the Te composition of the films changed from 49 at.% to 60 at.%, the phase of the as-sputtered film changed from the rhombohedral BiTe-type phase to the metastable rock-salt phase, which eventually transformed to the Bi2Te3-type phase upon annealing, instigating microstructure evolution. This phase transformation profoundly influenced the electrical and thermoelectric properties of the films.

This paper reports the microstructure evolution of Bi-Te thermoelectric films upon post-annealing and its effects on the thermoelectric properties. Bi-Te films with the composition of around 61at.% Te and the thickness of 300nm were deposited onto SiO"2-coated Si substrates by using bismuth and tellurium targets in a radio frequency (RF) magnetron sputtering system. We annealed the films at different temperatures (100, 150 and 200^oC) under N"2 ambient for 8h, and characterized the crystallinity and morphology of the Bi-Te films. Microstructure characterization using X-ray diffraction and scanning electron microscopy disclosed that the post-annealing treatment entailed a drastic microstructural evolution by inducing the development of a strong texture of grains with their c-axis oriented normal to the substrate. In addition, we measured the electrical transport and thermoelectric properties of the films to reveal their close link with the microstructure changes. The electron mobility and Seebeck coefficient increase significantly, leading to a remarkable improvement in the power factor from [email protected]/K^2cm for the as-deposited sample to [email protected]/K^2cm for the 200^oC-annealed sample.

In this study, we explore various electrode materials (Au, Ti, and Sb) for use as contact materials on Bi2Te3 and Sb2Te3 thermoelectric films. Using the transmission line method (TLM), we measured the specific resistivity of the contacts, which showed that Au has the lowest contact resistivity for both the thermoelectric films (after annealing): 2.7 × 10−10 Ω m2 for Bi2Te3 and 2.9 × 10−11 Ω m2 for Sb2Te3. The specific contact resistivity data suggest that the dominant factor for the contact properties is interface states. After annealing, the contact resistivity does not change much for the Bi2Te3 contacts while it drops greatly for the Sb2Te3 ones. Analysis of the carrier transport mechanism across the contacts discloses that changes in the carrier concentration in the thermoelectric films after annealing are responsible for the different behaviors.