The {100}-oriented (CaxSr1-x)Si2 thin films have been prepared by co-sputtering method at various deposition temperatures. Constituent phase of the films primarily depends on the deposition temperature and the composition x. Although CaSi2 films consisted of layered structure regardless of deposition temperature, the phase was changed by the deposition temperature: the majority phases of the film deposited at 600°C, 650°C and 700°C were 1T layered structure, 1T layered structure + 2H layered structure and 1T layered structure + 6R layered structure, respectively. When the (CaxSr1-x)Si2 films deposited at 700°C, the α-SrSi2-type phase was mainly confirmed below x = 0.17, which is the most stable phase of SrSi2. However, the main phase of all CaxSr1-xSi2 films deposited at 600°C changed to be 1T-type layered structure. Substitution with Ca below x = 0.50 in the film deposited at 600°C led to the decrease in the electrical resistivity compared with that of pure SrSi2.

Fused deposition modelling (FDM) type of 3D printing is widely used for manufacturing complex shaped polymer products. Recently, the metal/polymer composite products can be made by 3D printer using metal/polymer composite filament. Now, we are planning to develop a new manufacturing process of the thermoelectric (TE) elements or modules by combining the FDM-type 3D printing and the degreasing-sintering process. In this work, we focused on the degreasing-sintering process of the mixture of Mg2Si and polylactic acid (PLA) powders. Mg2Si compound powder was synthesized by a liquid-solid phase reaction (LSPR) method. The powder mixtures of Mg2Si, Al and PLA were pressed and heated in a pulse discharge sintering (PDS) chamber under a vacuum in various degreasing conditions. Following the degreasing, the sintering of Mg2Si was carried out in the same PDS chamber at various starting sintering temperatures. Sintered density, Seebeck coefficient and electrical resistivity of the consolidated Mg2Si were measured and the power factor as a TE performance was estimated from the TE properties. The optimum conditions of degreasing-sintering process maximizing the sintered density and the TE performance of Al-doped Mg2Si were investigated. Furthermore, the influences of the additive amount of Al on the sintered density and the TE performance of Mg2Si fabricated via the optimized degreasing-sintering process were investigated.

Thermoelectric (TE) materials, or materials that can generate an electrical energy from temperature gradient, are promising for renewable energy technology. One fundamental aspect in the TE research is the demand to maximize the TE power-factor, PF = S2 σ, by having as large Seebeck coefficient (S) and electrical conductivity (σ) as possible. In the early 90s, Hicks and Dresselhaus proposed the PF enhancement by using low-dimensional materials, in which electrons are confined in certain directions and they move freely in the other directions. This quantum effect is known as the confinement length (L) effect, in which L is the thickness or diameter of the two-dimensional (2D) or one-dimensional materials, respectively. However, a key challenge is to understand the critical value of L, at which the PF can be significantly enhanced. Recently, we reevaluated the confinement theory of the low-dimensional materials to solve this issue. We showed that electrons are fully confined only when L is smaller than an intrinsic length Λ, the so-called thermal de Broglie wavelength, which depends on the materials and can be experimentally measured. Monolayer 2D materials naturally satisfy the condition of L < Λ since their confinement length is ∼ 1 nm, while their thermal de Broglie wavelength is ∼ 5-10 nm. Therefore, they could be a good candidate for TE materials. In this review article, we first review the TE materials with low dimensions. Then, we show the basic concept of the confinement effect and the consequence of such an effect. Finally, based on this effect, we turn our attention to the progress achieved recently in the TE properties of the 2D materials such as monolayer InSe, GaN electron gas, and SrTiO3 superlattices.

We examined a working hypothesis of sticky thermoelectric (TE) materials, which is inversely designed to mass-produce flexible TE sheets with lamination or roll-to-roll processes without electric conductive adhesives. Herein, we prepared p-type and n-type sticky TE materials via mixing antimony and bismuth powders with low-volatilizable organic solvents to achieve a low thermal conductivity. Since the sticky TE materials are additionally injected into punched polymer sheets to contact with the upper and bottom electrodes in the fabrication process, the sticky TE modules of ca. 2.4 mm in thickness maintained temperature differences of ca. 10°C and 40°C on a hot plate of 40 °C and 120°C under a natural-air cooling condition with a fin. In the single-cell resistance analysis, we found that 75∼150-µm bismuth powder shows lower resistance than the smaller-sized one due to the fewer number of particle-particle interfaces in the electric pass between the upper and bottom electrodes. After adjusting the printed wiring pattern for the upper and bottom electrodes, we achieved 42 mV on a hot plate (120°C) with the 6 x 6 module having 212 Ω in the total resistance. In addition to the possibility of mass production at a reasonable cost, the sticky TE materials provide a low thermal conductivity for flexible TE modules to capture low-temperature waste heat under natural-air cooling conditions with fins for the purpose of energy harvesting.

Polymeric conjugated materials are very promising for developing future soft material-based semiconductors, conductors, electronic and optoelectronic devices due to their inherent advantages such as lightweight, flexible shape, low-cost, ease of processability, ease of scalability, etc. There are a number of ways to tune material properties via post-processing treatments such as annealing, solvent additives, or doping. One challenge of solution processed organic thin film electronics is the repeatable and well-defined morphological control of the resulting films after deposition. In this study, we observed how the addition of diiodo-alkanes to poly-3-hexyl-thiophene (P3HT) solutions effect the formation of resulting thin films. These additives have various boiling points that will affect the drying properties of cast thin films. We also sought to observe if any halogen bonding interaction between iodine and sulfur occurs and if this interaction can be used to promote polymer morphological self-assembly. Techniques such as UV/Vis spectroscopy, X-ray diffraction, and Atomic Force Microscopy were used to probe the evolution of the film morphology as the additives were added to the solutions. 1,8-diiodooctane doped films showed the best overall device performance. This could be due to its favorable interaction with the side chain of P3HT as seen in it morphological properties. This study may result in a new technique that can be used to enhance the solid-state morphology of thin films for high performance electronic applications.

In the present study we employ electronic structure calculations (based on Density Functional Theory -DFT approach) and Fully Atomistic Reactive Molecular Dynamics (FARMD) simulations (based on ReaxFF reactive force field) to evaluate the reactivity of branched polyfuran (PF) derivatives and identify promising systems for chemical sensing. Condensed-to-atoms Fukui indexes (CAFI) were employed to identify the most reactive sites on the oligomers structure. The chemical sensing abilities of the most promising systems were evaluated via FARMD simulations in the presence of distinct gaseous compounds. The results indicate the derivatives PF-CCH and PF-NO₂ (i.e. CCH and NO2 as side groups) as the most promising systems for chemical sensor applications, presenting higher reactivity on the most accessible sites. An interesting correspondence between DFT and MD results was also identified, suggesting the plausibility of using CAFI parameters for the identification of improved materials for chemical sensors.

The emerging breakthroughs in space exploration, smart textiles, and novel automobile designs have increased technological demand for high temperature electronics. In this snapshot review we first discuss the fundamental challenges in achieving electronic operation at elevated temperatures, briefly review current efforts in finding materials that can sustain extreme heat, and then highlight the emergence of organic semiconductors as a new class of materials with potential for high temperature electronics applications. Through an overview of the state-of-the art materials designs and processing methods, we will layout molecular design principles and fabrication strategies towards achieving thermally stable operation in organic electronics.