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GeTe as one of the most promising medium temperature thermoelectrics has progressed leaps and bounds in recent years, largely thanks to a combination of its unique electronic, thermal and structural properties. Despite its various advantages, a major factor standing in the way of wide commercial adoptions lies in its unreliable mechanical properties. This work reports Re doping as a strategy to drastically enhance the mechanical properties of GeTe, resulting in Vickers microhardness as high as 342.6 Hv in Ge0.88Sb0.10Re0.02Te, which is more than double that of pristine GeTe (145 Hv). Ge0.88Sb0.10Re0.02Te also exhibited a Young's modulus of 64.1 GPa, substantially higher than many other binary chalcogenide thermoelectrics. The significant enhancement of GeTe in mechanical properties is mainly related to the mechanism of precipitation hardening. In addition, we found that while the electronic properties were slightly compromised with Re doping, the lattice thermal conductivity was reduced due to point defects scattering brought about by Re atoms. Therefore, a high zT value (>1.6) at 600–800 K is achieved in Ge0.88Sb0.10Re0.02Te. Furthermore, above 10% device efficiency can be expected for the operating temperature between 300–800 K. Such a solution to strengthen the mechanical properties of GeTe using Re doping is expected to play a major part in the push for full-scale GeTe-based thermoelectric devices.

Direct imprinting of metals is predominantly achieved by using polydimethylsiloxane (PDMS) molds to pattern metal nanoparticles and subsequently melting them to form continuous structures. Although such a combination can successfully imprint metals, the yield and reproducibility are usually low when sub-100 nm features over large areas are desired. In this work, we demonstrate a simple method involving the addition of a cross-linker ethylene glycol dimethacrylate (EDMA) to a palladium metal precursor, and its in situ free radical polymerization during imprinting, which not only dramatically increases the yield to ∼100% but also enables high reproducibility. Palladium mercaptide resist was formed by dissolving acetoxy(benzylthio)palladium, EDMA and azobis-(isobutyronitrile) in an organic solvent mixture. The resist underwent polymerization when imprinted using a silicon mold at 120 °C with pressures as low as 30 bar. Polymerization rigidly shapes the imprinted patterns, traps the metal atoms, reduces the surface energy and strengthens the structures, thereby giving ∼100% yield after demolding. Heat-treatment of the imprinted structures at 330 °C resulted in the loss of organics and their subsequent shrinkage without the loss of integrity or aspect ratio and converted them to palladium nanostructures as small as ∼35 nm wide, over areas >1 cm × 1 cm. With suitable precursors, our technique can potentially be extended to pattern noble metals such as platinum, gold and silver.

The use of polymerization to solidify, strengthen and imprint liquid organic materials is the basis of ultraviolet (UV) nanoimprint lithography. In spite of these advantages, the use of polymerization to pattern materials in thermal nanoimprint lithography is almost non-existent. In this study, we demonstrate a facile and general method to directly imprint a host of unary metal oxides (Fe2O3, ZrO2, TiO2, Nb2O5 and Ta2O5) at a very high resolution viain situ thermal free radical co-polymerization of various metal methacrylates in the presence of cross-linker ethylene glycol dimethacrylate using a silicon mold. Polymerization during nanoimprinting rigidly shapes the patterns, traps the metal atoms, reduces the surface energy and strengthens the structures, thereby giving ∼100% yield after demolding. It was found that the higher oxidation state of metal resulted in excessive cracking of imprinted structures. This could be due to a higher degree of cross-linking of the precursor leading to shrinkage-related stress. Optimization of the resin composition by partially replacing ethylene glycol dimethacrylate with methyl methacrylate alleviated this problem. Heat-treatment of the imprinted structures resulted in the loss of organics, their subsequent shrinkage and converted the patterns to their corresponding metal oxides with line-widths as small as 25 nm.