Generalised optical printing of photocurable metal chalcogenides

The Latest Advances in Ink-Based Nanogenerators: From Materials to Applications

Nanogenerators possess the capability to harvest faint energy from the environment. Among them, thermoelectric (TE), triboelectric, piezoelectric (PE), and moisture-enabled nanogenerators represent promising approaches to micro-nano energy collection. These nanogenerators have seen considerable progress in material optimization and structural design. Printing technology has facilitated the large-scale manufacturing of nanogenerators. Although inks can be compatible with most traditional functional materials, this inevitably leads to a decrease in the electrical performance of the materials, necessitating control over the rheological properties of the inks. Furthermore, printing technology offers increased structural design flexibility. This review provides a comprehensive framework for ink-based nanogenerators, encompassing ink material optimization and device structural design, including improvements in ink performance, control of rheological properties, and efficient energy harvesting structures. Additionally, it highlights ink-based nanogenerators that incorporate textile technology and hybrid energy technologies, reviewing their latest advancements in energy collection and self-powered sensing. The discussion also addresses the main challenges faced and future directions for development.

Thermoelectric nanowires for dense 3D printed architectures

The large-scale employment of 3D printed inorganic thermoelectrics is primarily constrained because of their lower efficiencies as compared to those fabricated from conventional methods such as spark plasma sintering and hot-pressing. This originates from the significant challenge in the densification of printed parts, particularly through the direct-ink-writing fabrication process, which demands a high binder content for printability. To achieve high-density printed thermoelectrics, the ink formulation process often involves the addition of substantial filler content and sintering aids, coupled with prolonged sintering periods. Here, we propose a strategy to resolve the low densification issue of 3D printed thermoelectrics through a binder-less and sintering aid-free thermoelectric nanowire ink system that can achieve dense thermoelectric structures (up to 82.5% theoretical density). The increase in density and corresponding enhancement of thermoelectric material efficiency are attained in a more tunable and controlled manner without compromising the material composition. A high filler-derived density index (FDI) of 2.51 is also achieved, implying the potential to obtain high-density parts with minimal filler content, thus unlocking a cascade of profound impacts. Crucially, this advancement enables the possibilities of anisotropic engineering in thermoelectric materials, thereby shattering the limitations that have hindered the widespread adoption of 3D printed inorganic thermoelectrics.

Phase-Change Memory from Molecular Tellurides

Phase-change memory (PCM) is an emerging memory technology based on the resistance contrast between the crystalline and amorphous states of a material. Further development and realization of PCM as a mainstream memory technology rely on innovative materials and inexpensive fabrication methods. Here, we propose a generalizable and scalable solution-processing approach to synthesize phase-change telluride inks in order to meet demands for high-throughput material screening, increased energy efficiency, and advanced device architectures. Bulk tellurides, such as Sb2Te3, GeTe, Sc2Te3, and TiTe2, are dissolved and purified to obtain inks of molecular metal telluride complexes. This allowed us to unlock a wide range of solution-processed ternary tellurides by the simple mixing of binary inks. We demonstrate accurate and quantitative composition control, including prototype materials (Ge-Sb-Te) and emerging rare-earth-metal telluride-doped materials (Sc-Sb-Te). Spin-coating and annealing convert ink formulations into high-quality, phase-pure telluride films with preferred orientation along the (00l) direction. Deposition engineering of liquid tellurides enables thickness-tunable films, infilling of nanoscale vias, and film preparation on flexible substrates. Finally, we demonstrate cyclable and non-volatile prototype memory devices, achieving performance indicators such as resistance contrast and low reset energy on par with state-of-the-art sputtered PCM layers.

Nanoscale Vertical Resolution in Optical Printing of Inorganic Nanoparticles

Direct optical printing of functional inorganics shows tremendous potential as it enables the creation of intricate two-dimensional (2D) patterns and affordable design and production of various devices. Although there have been recent advancements in printing processes using short-wavelength light or pulsed lasers, the precise control of the vertical thickness in printed 3D structures has received little attention. This control is vital to the diverse functionalities of inorganic thin films and their devices, as they rely heavily on their thicknesses. This lack of research is attributed to the technical intricacy and complexity involved in the lithographic processes. Herein, we present a generalized optical 3D printing process for inorganic nanoparticles using maskless digital light processing. We develop a range of photocurable inorganic nanoparticle inks encompassing metals, semiconductors, and oxides, combined with photolinkable ligands and photoacid generators, enabling the direct solidification of nanoparticles in the ink medium. Our process creates complex and large-area patterns with a vertical resolution of ∼50 nm, producing 50-nm-thick 2D films and several micrometer-thick 3D architectures with no layer height difference via layer-by-layer deposition. Through fabrication and operation of multilayered switching devices with Au electrodes and Ag-organic resistive layers, the feasibility of our process for cost-effective manufacturing of multilayered devices is demonstrated.