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

Thermomechanical sensitivity of microcantilever in the mid-infrared spectral region

This paper reports the thermomechanical sensitivity of bimaterial cantilevers over a mid-infrared (IR) spectral range (5-10 µm) that is critical both for chemical analysis via vibrational spectroscopy and for direct thermal detection in the 300-700 K range. Mechanical bending sensitivity and noise were measured and modeled for six commercially available microcantilevers, which consist of either an aluminum film on a silicon cantilever or a gold film on a silicon nitride cantilever. The spectral sensitivity of each cantilever was determined by recording cantilever deflection when illuminated with IR light from a monochromator. Rigorous modeling and systematic characterization of the optical system allowed for a quantitative estimate of IR energy incident upon the cantilever. Separately, spectral absorptance of the cantilever was measured using Fourier transform infrared (FT-IR) microscopy, which was compared with analytical models of radiation onto the cantilever and heat flow within the cantilever. The predictions of microcantilever thermomechanical bending sensitivity and noise agree well with measurements, resulting in a ranking of these cantilevers for their potential use in IR measurements

Development of microcantilever mid-infrared detectors and sources and their application in infrared spectroscopy

Mid-infrared (mid-IR) light is an electromagnetic radiation with the wavelengths of 3 – 30 um. This spectral range includes the dominant wavelengths of the thermal radiation emitted by objects at or near room temperature, and vibrational and rotational resonance frequencies of many molecules. The detection and generation of mid-IR light, thus, have been extensively studied for the applications in thermal and chemical sensing. However, the mid-IR light detection with a high resolution at room temperature has been a difficult task, since the thermal noise is significant in the traditional detection methods. In addition, there have been few mid-IR light sources available for microscopic and rapid experiments. This study presents the development of microcantilever mid-IR detectors and sources. First, this research investigates the dynamic thermomechanical response of bimaterial cantilevers to periodic heating by an IR laser. A model relates incident IR radiation, heat transfer, temperature distribution in the cantilever, and thermal expansion mismatch to find the cantilever displacement. Silicon nitride-aluminum bimaterial cantilevers are designed, fabricated, and tested for validating the developed model. The custom-fabricated cantilevers show 9X or 190X improvements in IR detection sensitivity compared to commercial cantilevers. To improve the sensitivity of silicon based bimaterial cantilever IR detectors, this research introduces the integration of black silicon nanocone arrays into commercially available silicon-aluminum cantilevers. The black silicon consists of nanometer-scale silicon cones. Compared to a cantilever with smooth single crystal silicon, the cantilever with black silicon has about 2X increased responsivity at the wavelengths of 5 – 9 um. Developed model also provides further insights into the influence of the nanocone height on the IR absorbance and responsivity of the cantilever. Next, this study introduces the integration of one-dimensional high-contrast grating into silicon-aluminum bimaterial cantilevers which enhances the amplitude and bandwidth of the IR absorbance as well as the responsivity. With the integrated grating, the silicon layer acts as a grating coupler and waveguide, while the aluminum layer acts as an IR absorber. At the wavelengths of 3 – 11 um, the cantilevers with high-contrast grating show about 2X larger bandwidth for the IR absorbance > 0.2 and an order of magnitude larger responsivity as compared to a commercial silicon-aluminum cantilever. Bimaterial cantilever with a sharp tip can perform standard atomic force microscope (AFM) imaging and also detect IR light. This study reports nanotopography and IR microspectroscopy measurements performed using a bimaterial cantilever in the same AFM system. This system uses micrometer scale engineered skin and three-dimensional cell culture samples for the demonstration. Finally, this research investigates the IR emission of two silicon cantilevers with integrated solid-state heaters over the 2500 – 3000 cm-1 spectral range. A model calculates the spectral power emitted by the cantilever based on the Planck function, dielectric function of the doped silicon at elevated temperatures, and cantilever spectral emissivity. Measurements of the cantilever spectral power compare well with predictions. The cantilevers provide radiative powers on the order of 1 – 100 µW at the temperature near 1000 K

Strain-Mediated Phase Stabilization: A New Strategy for Ultrastable alpha-CsPbI3 Perovskite by Nanoconfined Growth

All-inorganic cesium lead triiodide (CsPbI3) perovskite is considered a promising solution-processable semiconductor for highly stable optoelectronic and photovoltaic applications. However, despite its excellent optoelectronic properties, the phase instability of CsPbI3 poses a critical hurdle for practical application. In this study, a novel stain-mediated phase stabilization strategy is demonstrated to significantly enhance the phase stability of cubic a-phase CsPbI3. Careful control of the degree of spatial confinement induced by anodized aluminum oxide (AAO) templates with varying pore sizes leads to effective manipulation of the phase stability of alpha-CsPbI3. The Williamson-Hall method in conjunction with density functional theory calculations clearly confirms that the strain imposed on the perovskite lattice when confined in vertically aligned nanopores can alter the formation energy of the system, stabilizing alpha-CsPbI3 at room temperature. Finally, the CsPbI3 grown inside nanoporous AAO templates exhibits exceptional phase stability over three months under ambient conditions, in which the resulting light-emitting diode reveals a natural red color emission with very narrow bandwidth (full width at half maximum of 33 nm) at 702 nm. The universally applicable template-based stabilization strategy can give in-depth insights on the strain-mediated phase transition mechanism in all-inorganic perovskites.11Nsciescopu

Multi-floor cascading ferroelectric nanostructures: multiple data writing-based multi-level non-volatile memory devices

Multiple data writing-based multi-level non-volatile memory has gained strong attention for next-generation memory devices to quickly accommodate an extremely large number of data bits because it is capable of storing multiple data bits in a single memory cell at once. However, all previously reported devices have failed to store a large number of data bits due to the macroscale cell size and have not allowed fast access to the stored data due to slow single data writing. Here, we introduce a novel three-dimensional multi-floor cascading polymeric ferroelectric nanostructure, successfully operating as an individual cell. In one cell, each floor has its own piezoresponse and the piezoresponse of one floor can be modulated by the bias voltage applied to the other floor, which means simultaneously written data bits in both floors can be identified. This could achieve multi-level memory through a multiple data writing process.1142sciescopu

Continuous Nanoparticle Patterning Strategy in Layer-Structured Nanocomposite Fibers

Anisotropic polymer/nanoparticle composites display unique mechanical, thermal, electrical, and optical properties depending on confirmation and configuration control of the composing elements. Processes, such as vapor deposition, ice-templating, nanoparticle self-assembly, additive manufacturing, or layer-by-layer casting, are explored to design and control nanoparticle microstructures with desired anisotropy or isotropy. However, limited attempts are made toward nanoparticle patterning during continuous fiber spinning due to the thin-diameter cross section and 1D features. Thus, this research focuses on a new patterning technique to form ordered nanoparticle assembly in layered composite fibers. As a result, distinct layers can be retained with innovative tool design, unique material combinations, and precise rheology control during fiber spinning. The layer multiplying-enabled nanoparticle patterning is demonstrated in a few material systems, including polyvinyl alcohol (PVA)-boron nitride (BN)/PVA, polyacrylonitrile (PAN)-aluminum (Al)/PAN, and PVA-BN/graphene nanoplatelet (GNP)/PVA systems. This approach demonstrates an unprecedentedly reported fiber manufacturing platform for well-managed layer dimensions and nanoparticle manipulations with directional thermal and electrical properties that can be utilized in broad applications, including structural supports, heat exchangers, electrical conductors, sensors, actuators, and soft robotics.W.X. and R.F. contributed equally to this work. This work was funded by the Global Sports Institute (GSI) at Arizona State University and the U.S. National Science Foundation (NSF, EAGER 1902172).Scopu