Generalised optical printing of photocurable metal chalcogenides

Optical three-dimensional (3D) printing techniques have attracted tremendous attention owing to their applicability to mask-less additive manufacturing, which enables the cost-effective and straightforward creation of patterned architectures. However, despite their potential use as alternatives to traditional lithography, the printable materials obtained from these methods are strictly limited to photocurable resins, thereby restricting the functionality of the printed objects and their application areas. Herein, we report a generalised direct optical printing technique to obtain functional metal chalcogenides via digital light processing. We developed universally applicable photocurable chalcogenidometallate inks that could be directly used to create 2D patterns or micrometre-thick 2.5D architectures of various sizes and shapes. Our process is applicable to a diverse range of functional metal chalcogenides for compound semiconductors and 2D transition-metal dichalcogenides. We then demonstrated the feasibility of our technique by fabricating and evaluating a micro-scale thermoelectric generator bearing tens of patterned semiconductors. Our approach shows potential for simple and cost-effective architecturing of functional inorganic materials

Cu2Se-based thermoelectric cellular architectures for efficient and durable power generation

Thermoelectric power generation offers a promising way to recover waste heat. The geometrical design of thermoelectric legs in modules is important to ensure sustainable power generation but cannot be easily achieved by traditional fabrication processes. Herein, we propose the design of cellular thermoelectric architectures for efficient and durable power generation, realized by the extrusion-based 3D printing process of Cu2Se thermoelectric materials. We design the optimum aspect ratio of a cuboid thermoelectric leg to maximize the power output and extend this design to the mechanically stiff cellular architectures of hollow hexagonal column- and honeycomb-based thermoelectric legs. Moreover, we develop organic binder-free Cu2Se-based 3D-printing inks with desirable viscoelasticity, tailored with an additive of inorganic Se-8(2-) polyanion, fabricating the designed topologies. The computational simulation and experimental measurement demonstrate the superior power output and mechanical stiffness of the proposed cellular thermoelectric architectures to other designs, unveiling the importance of topological designs of thermoelectric legs toward higher power and longer durability

Fabrication of high-performance SnSe<sub>2</sub> thermoelectric thin films with preferred crystallographic orientation

SnSe2 has been of great interest as the n-type semiconductor exhibits high thermoelectric (TE) performance. Because material's thermoelectric properties are highly anisotropic, controlling the crystallographic orientation in the microstructure is one of the key factors for enhancing the TE performance. However, reports of SnSe2 with preferred crystallographic orientation have been limited due to the difficulty in fabrication. As a solution for this challenge, in this study, we report solution-processed fabrication of textured SnSe2 thin films. Following heat treatment optimization, the thin films possessed exceptionally strong crystallographic orientation order in the a???b plane, as demonstrated with x-ray diffraction analyses. Moreover, controlled defect formation through processing conditions realizes high electron concentrations of an order of ???1020???cm???3. In particular, we demonstrate that the microstructure of the SnSe2 thin films determined their electronic transport properties, where the electron mobility increases with stronger crystallographic orientation. Finally, the thin film with the optimal structure exhibits the enhanced thermoelectric power factor of 3.69?????W???cm???1???K???2. Our findings will offer a way to enhance the thermoelectric and electronic properties of highly anisotropic materials

Synthesis of inorganic-organic two-dimensional CdSe slab-diamine quantum nets

Porous semiconductors attract great interest due to their unique structural characteristics of high surface area as well as their intrinsic optical and electronic properties. In this study, synthesis of inorganic-organic 2D CdSe slabs‐diaminooctane (DAO) porous quantum net structures is demonstrated. It is found that the hybrid 2D CdSe‐DAO lamellar structures are disintegrated into porous net structures, maintaining an ultrathin thickness of ≈1 nm in CdSe slabs. Furthermore, the CdSe slabs in quantum nets show the highly shifted excitonic transition in the absorption spectrum, demonstrating their strongly confined electronic structures. The possible formation mechanism of this porous structure is investigated with the control experiments of the synthesis using n‐alkyldiamines with various hydrocarbon chain lengths and ligand exchange of DAO with oleylamine. It is suggested that a strong van der Waals interaction among long chain DAO may exert strong tensile stress on the CdSe slabs, eventually disintegrating slabs. The thermal decomposition of CdSe‐DAO quantum nets is further studied to form well‐defined CdSe nanorods. It is believed that the current CdSe‐DAO quantum nets will offer a new type of porous semiconductors nanostructures under a strong quantum‐confinement regime, which can be applied to various technological areas of catalysts, electronics, and optoelectronics

Polyphosphide Precursor for Low-Temperature Solution-Processed Fibrous Phosphorus Thin Films

Crystalline red phosphorus has very recently emerged as a stable and cost-effective semiconductor material. However, despite its potentiality in electronics and optoelectronics, the widespread application of this material is still hampered by the limited synthetic route of the ampoule-based chemical vapor deposition that critically requires mineralizing agents. To address this issue, we report the chemical synthesis of soluble polyphosphide precursors that serve as inks for the solution-processed fabrication of crystalline fibrous phosphorus thin films. The purified polyphosphide precursor formed crystalline fibrous phosphorus via thermal annealing at a temperature as low as 250 ??C without any mineralizing agents. This anionic polyphosphide functioned as a surface-capping ligand for nanoparticles including metals, semiconductors, and magnets. Therefore, the study investigates the possibility of solution-processed fibrous phosphorus thin films as active channel layers in field-effect transistors as well as photodetectors and demonstrates their initial performances on the charge-transport and photoresponsive characteristics of these devices. The effect of semiconducting PbS nanoparticles embedded in the fibrous phosphorus thin films on device performance was also studied. The synthesized polyphosphide precursor offers a vast opportunity for the facile preparation of crystalline red phosphorus and chemical design of nanoparticles

Solution-Processed Stretchable Ag2S Semiconductor Thin Films for Wearable Self-Powered Nonvolatile Memory

Compared with the large plastic deformation observed in ductile metals and organic materials, inorganic semiconductors have limited plasticity (<0.2%) due to their intrinsic bonding characters, restricting their widespread applications in stretchable electronics. Herein, the solution-processed synthesis of ductile alpha-Ag2S thin films and fabrication of all-inorganic, self-powered, and stretchable memory devices, is reported. Molecular Ag2S complex solution is synthesized by chemical reduction of Ag2S powder, fabricating wafer-scale highly crystalline Ag2S thin films. The thin films show stretchability due to the intrinsic ductility, sustaining the structural integrity at a tensile strain of 14.9%. Moreover, the fabricated Ag2S-based resistive random access memory presents outstanding bipolar switching characteristics (I-on/I-off ratio of approximate to 10(5), operational endurance of 100 cycles, and retention time >10(6) s) as well as excellent mechanical stretchability (no degradation of properties up to stretchability of 52%). Meanwhile, the device is highly durable under diverse chemical environments and temperatures from -196 to 300 degrees C, especially maintaining the properties for 168 h in 85% relative humidity and 85 degrees C. A self-powered memory combined with motion sensors for use as a wearable healthcare monitoring system is demonstrated, offering the potential for designing high-performance wearable electronics that are usable in daily life in a real-world setting

Controlled Grafting of Colloidal Nanoparticles on Graphene through Tailored Electrostatic Interaction

Nanoparticle/graphene hybrid composites have been of great interest in various disciplines due to their unique synergistic physicochemical properties. In this study, we report a facile and generalized synthesis method for preparing nanoparticle/exfoliated graphene (EG) composites by tailored electrostatic interactions. EG was synthesized by an electrochemical method, which produced selectively oxidized graphene sheets at the edges and grain boundaries. These EG sheets were further conjugated with polyethyleneimine to provide positive charges at the edges. The primary organic ligands of the colloidal nanoparticles were exchanged with Cl- or MoS42- anions, generating negatively charged colloidal nanoparticles in polar solvents. By simple electrostatic interactions between the EG and nanoparticles in a solution, nanoparticles were controllably assembled at the edges of the EG. Furthermore, the generality of this process was verified for a wide range of nanoparticles, such as semiconductors, metals, and magnets, on the EG. As a model application, designed composites with size-controlled FeCo nanoparticle/EG were utilized as electromagnetic interference countermeasure materials that showed a size-dependent shift of the frequency ranges on the electromagnetic absorption properties. The current generalized process will offer great potential for the large-scale production of well-designed graphene nanocomposites for electronic and energy applications

Thiometallate precursors for the synthesis of supported Pt and PtNi nanoparticle electrocatalysts: Size-focusing by S capping

Herein, we report for the first time the successful preparation of thiometallate-based precursors for use in a bottom-up synthetic process of supported Pt and PtNi nanoparticle catalyst. This precursor enabled the monodisperse synthesis of supported Pt nanoparticles and the in situ formation of S, which were caught directly in a collection system by the nanoparticle synthetic processes consisting of impregnation and thermal processes. S is proven to act as a capping agent in generating highly stable nanoparticles with the size ranging from 2 nm to 3 nm and further favors the formation of monodispersed particles by solid-state digestive ripening. The proposed synthetic methodology can be applied to high-quality PtNi alloy nanoparticle systems. The current route is readily scalable, and multi-gram quantities can be prepared. The prepared carbon-supported Pt and PtNi nanoparticles were characterized as electrocatalysts for the oxygen reduction reaction and exhibited superior performance and durability to commercial Pt/C

Colloidal Suprastructures Self-Organized from Oppositely Charged All-Inorganic Nanoparticles

The self-organization of colloidal nanoparticles into programmed suprastructures is an important research area in various disciplines of nano, colloid, and polymer sciences. However, despite the recent advances in their fundamental understanding and practical applications, the self-organization of organic-free inorganic nanoparticles remains unexplored. Herein, we present the controlled organization of oppositely charged allinorganic nanoparticles through the electrostatic interaction and the colloidal behaviors of organized suprastructures. Depending on the charge states of the assembled suprastructures, three different phases, including patchy, patchy bridged, and fully coated particles, are identified, enabling the construction of the phase diagram with nanoparticle concentrations. Especially, the fully coated particles exhibit unexpected colloidal stability through the action of nanoparticles as surface stabilizers to induce the overcharged surface state; thus, we propose the concept of "nanoligands". It is demonstrated that this concept can be extended to a wide range of material combinations, including semiconducting, metallic, and oxide nanoparticles. The currently developed approach will enable the chemical designing of self-organized nanostructures

Solution-Processed Hole-Doped SnSe Thermoelectric Thin-Film Devices for Low-Temperature Power Generation

Owing to the increase in the demand for energy autonomy in electronic systems, there has been increased research interest in thermoelectric thin-film-based energy harvesters. However, the fabrication of such devices is challenging when considering material performance and integration processes. SnSe has emerged as among the best bulk thermoelectric materials capable of functioning at high temperatures; however, the thermoelectric performance of thin films is still limited. Herein, we present a solution-processed fabrication of high-performance Ag-doped SnSe thin films operable in a low-temperature range. The Ag doping induces the preferred crystallographic orientation and grain growth in the b-c plane (in-plane) of SnSe, consequently enhancing thermoelectric performance at low temperatures. Moreover, thin-film wrinkling and photolithography are employed in the fabrication of stretchable and patterned devices, in which power generation performance is then evaluated, thereby demonstrating the feasibility of the proposed thin films as an energy harvester in emerging electronic systems