Search

Intelligent matter with smart responses to environmental stimulation paves the way to implement data-centric tactics with in-sensor computing, which bypasses redundant data shuttling.

The ability to perform broadband optical spectroscopy with sub-diffraction-limit resolution is highly sought-after for a wide range of critical applications. However, sophisticated tip-enhanced techniques are currently required to achieve this goal. We bypass this challenge by demonstrating an extremely broadband photodetector based on a two-dimensional (2D) van der Waals heterostructure that is sensitive to light across over a decade in energy from the mid-infrared (MIR) to deep-ultraviolet (DUV) at room temperature. The devices feature high detectivity (> 10^9 cm Hz^1/2 W^-1) together with high bandwidth (2.1 MHz). The active area can be further miniaturized to submicron dimensions, far below the diffraction limit for the longest detectable wavelength of 4.1 um, enabling such devices for facile measurements of local optical properties on atomic-layer-thickness samples placed in close proximity. This work can lead to the development of low-cost and high-throughput photosensors for hyperspectral imaging at the nanoscale., 12 pages: 7 pages main text, 5 pages figures

We report the direct joining of carbon nanofibers (CNFs) to silver nanowire (Ag NWs) by controlled irradiation with femtosecond (fs) laser pulses. Two separate types of nano-junction dependent on joint geometry, laser fluence and irradiation time are identified in irradiated mixtures. In one type of junction, the tip of an Ag NW is melted and flows to form a bond with an adjacent CNF. The second type of junction occurs without significant heating of the Ag NW and involves the softening and flow of carbon in the CNF in response to the transfer of plasmonic energy from the Ag NW into the CNF. Bonding in a T-type joint configuration can be of either kind depending on the relative orientation of the incident optical field and the long axis of the Ag NW. FDTD simulations were used to explore this effect for different joint geometries and laser polarization. The electrical properties of a heterojunction involving a single Ag NW-CNF structure have been measured, and it is found that the junction resistance can be reduced by six orders of magnitude after laser joining. Finally, we have investigated the properties of a strain sensor based on an Ag NW-CNF hybrid nanowire network and find that this device can exhibit high sensitivity. This sensitivity occurs as nano-junctions induced by fs laser irradiation greatly reduces the initial resistance. This laser-based technique for direct nanojoining of CNF and Ag NWs may enable the design of robust nanowire structures for application in a variety of new devices.

We report the development of low-cost triboelectric nanogenerators (TENGs) based on polypropylene (PP) fabrics formulated via an inexpensive melt-blowing process with an output voltage as high as 50 V. By disinfection methods such as exposure to steam, ethanol, and dry heat at 75 °C, the commercial medical masks and N95 filtering facepiece respirators (FFRs) can be reused to fabricate PP fiber based TENGs, which provide a novel regime for energy-harvesting devices based on reusable materials. As a power source, the output of one TENG can drive 15 serially connected light-emitting diodes (LEDs) or a commercial electric calculator. PP fabric TENGs can also work as self-powered sensors for the high-sensitivity detection of mechanical impact. We provide examples where the TENG is used to detect biomechanical motion such as that associated with the extension of an elbow, the touch of a finger, the impact of footsteps, and the bending of a knee without an external power supply. Most importantly, these PP fabrics for TENGs can be obtained from decontaminated medical masks that are generated as tremendous wastes every day, which provide a great potential as sustainable energy. These properties suggest that PP fabric based TENGs are promising for harvesting energy from biological systems and that they may facilitate the large-scale production of a new range of inexpensive self-powered multifunctional wearable sensors for applications in healthcare, security, and information networks.

Harvesting energy from ambient moisture and natural water sources is currently of great interest due to the need for standalone self-powered nano/micro-systems. In this work, we report on the development of a cost-effective nanogenerator based on a carbon paper-Al2O3 nanoparticle layer-carbon paper (CAC) sandwich structure, where the 3D Al2O3 layer is deposited via vacuum filtration. This type of device can produce an open-circuit voltage (UOC) of up to 4 V and a short-circuit current (ISC) of ∼18 μA with only an 8 μL water droplet applied. To our knowledge, this is the highest voltage yet reported from a single moisture/water-induced electricity nanogenerator using solid oxides and carbon-based materials. A remarkable output power of 14.8 μW can be reached with an optimized resistive load. An LED with a working voltage of 3-3.2 V can operate for a short time with the power from a single CAC device exposed to one 8 μL water droplet. Furthermore, a CAC generator adsorbing as little as 2 μL water droplets every 3 min can also give a UOC of 3.63 V. We show that CAC devices provide a robust electrical output over more than 200 wet-dry cycles without any deterioration in performance. These units demonstrate much promise as cost-effective electricity generators for harvesting energy from natural sources like rainwater, tap water, snow runoff, and dew. The response time of CAC devices can be as fast as 10-100 ms, making them ideal for applications as self-powered water detectors. The generation of power in this device arises from the streaming current. To assist in the optimization of these devices, we have analyzed how their response is related to such factors as layer thickness, time interval between application of water droplets, and the volume of each water droplet.

The memristor-based neuromorphic computing application, which is highly flexible and capable of handling large amounts of parallel information, is one of the major breakthroughs in the past decade....

Using the earth-abundant natural biomaterials to manufacture functional electronic devices meets the sustainable requirement of green electronics, especially for the practical application of memristors in data storage and neuromorphic computing. However, the sneak currents flowing though the unselected cells in a large-scale cross-bar memristor array is one of the major problems which need to be tackled. The self-selecting memristors can solve the problem to develop compact and concise integrated circuits. Here, a sustainable natural biomaterial (anthocyanin, C

The information technologies have been increasing exponentially following Moore's law over the past decades. This has fundamentally changed the ways of work and life. However, further improving data process efficiency is facing great challenges because of physical and architectural limitations. More powerful computational methodologies are crucial to fulfill the technology gap in the post-Moore's law period. The memristor exhibits promising prospects in information storage, high-performance computing, and artificial intelligence. Since the memristor was theoretically predicted by L. O. Chua in 1971 and experimentally confirmed by HP Laboratories in 2008, it has attracted great attention from worldwide researchers. The intrinsic properties of memristors, such as simple structure, low power consumption, compatibility with the complementary metal oxide-semiconductor (CMOS) process, and dual functionalities of the data storage and computation, demonstrate great prospects in many applications. In this review, we cover the memristor-relevant computing technologies, from basic materials to in-memory computing and future prospects. First, the materials and mechanisms in the memristor are discussed. Then, we present the development of the memristor in the domains of the synapse simulating, in-memory logic computing, deep neural networks (DNNs) and spiking neural networks (SNNs). Finally, the existent technology challenges and outlook of the state-of-art applications are proposed.

Nanostructures incorporating copper oxide (CuO), a narrow bandgap p-type semiconductor, are well suited for applications such as gas/biosensors, field emission devices, and photodetectors. However, the use of CuO nanocomponents in these applications is currently limited by the availability of fabrication and in situ processing techniques. In this paper, we show that the electrical and mechanical properties of CuO nanowire (NW) networks can be adjusted through sequential processing with nanosecond laser radiation. This new two-stage process involves selective breakage/cleaving of CuO NWs with an initial set of laser pulses, followed by irradiation with a second set of laser pulses applied in an optimized orientation to tailor bonding and junction formation between pairs and bundles of previously separated CuO NWs. We find that stage one processing introduces a high concentration of oxygen vacancies in NWs leading to the nucleation of dislocations and high strain. This localized strain is responsible for the breaking of individual NWs, while the high oxygen vacancy concentration modifies the electrical conductivity within each NW. The second stage involves re-orientation of the laser beam, followed by additional laser irradiation of the NW network. This has been found to result in the bonding of NWs and the creation of junctions in regions where CuO NWs are in contact. Laser-induced heating under these conditions produces melting in the contact areas between NWs and is accompanied by the reduction of CuO to form Cu2O as verified via XPS and Raman analysis. XRD and TEM observations demonstrate that plastic deformation within CuO NWs dominates in stage one laser processing. The enhancement of electrical conductivity observed, following stage two processing, is attributed due to an increase in the concentration of laser-induced oxygen vacancies as well as the formation of localized bridging and junction sites in the overall NW network.

The memristor is a promising candidate to implement high-density memory and neuromorphic computing. Based on the characteristic retention time, memristors are classified into volatile and non-volatile types. However, a single memristor generally provides a specific function based on electronic performances, which poses roadblocks for further developing novel circuits. Versatile memristors exhibiting both volatile and non-volatile properties can provide multiple functions covering non-volatile memory and neuromorphic computing. In this work, a versatile memristor with volatile/non-volatile bifunctional properties was developed. Non-volatile functionality with a storage window of 4.0 × 10

Materials science and engineering / A 839, 142830 (2022). doi:10.1016/j.msea.2022.142830, During laser welding of Al���Si coated 22MnB5 steel, the melted Al���Si coating alloys with the molten weld pool promoting ��-ferrite phase formation during the heat-treatment stage of hot-stamping, which results in a fusion-zone (FZ) microstructure consisting of ��-ferrite islands disbursed through a martensitic matrix. The presence of the softer ferrite phase is the main cause for premature failure of laser-welded 22MnB5 joints in the hot-stamped condition. This work showed that surface modification of the Al���Si coating using an additive manufacturing technique called electro-spark deposition (ESD) prior to laser welding prevented ��-ferrite formation in the FZ post-welding and hot-stamping. This was achieved by the in-situ alloying of ferrite-suppressing carbides and austenite-stabilizing elements. These alloying agents were added to the FZ by applying different ESD-modified coatings to the material surface, which melted into the molten weld pool during laser welding, leading to the simultaneous dispersion and solid-solution strengthening of the FZ after hot-stamping, respectively. The modification of the Al���Si coating prior to welding using tungsten-carbide (WC) and Inconel 625 (In625) resulted in drastically improved mechanical properties of the welded joint in the hot-stamped condition. In fact, this study showed that by carefully modifying the as-received Al���Si coating using ESD prior to laser welding could be used as an effective method to shift failure from the FZ, where it normally occurs, to the base material (BM). This work is highly relevant to the on-going discussion in the advanced manufacturing and materials science communities regarding the production of functionally-graded components as it proposes the implementation of an advanced processing technique to achieve the production of novel materials with highly optimized properties., Published by Elsevier, Amsterdam

Single nanowire memory units are of particular interest in the design of high-density nanoelectronic circuits, but the performance due to weak contact state remains a major problem. In this paper, bonding between core/shell SiC/SiO2 nanowire and Au electrodes can be improved via local contact engineering with femtosecond (fs) laser irradiation. An optimized heterojunction (Au-SiO2-SiC) is possible since plasmonic enhanced optical absorption can be localized at the metal-oxide (Au-SiO2) interface. Electron transport across the barrier and charge accumulation at the oxide-semiconductor (SiO2-SiC) interface are improved in nanowire circuits. A fast and stable resistance change can be achieved after only one biasing cycle ('write') and the written state can be read/extracted at a low voltage (∼ 0.5 V). Unlike other as-built nanowire circuits, the resistance state can be retained for 10 min in the absence of external power, indicating that these devices can be used for short-term memory units. High current tolerance is also provided in the circuit by the surface oxide shell which acts to protect the inner SiC core. The current density carried by the single SiC/SiO2 nanowire circuit can be as high as ∼3 × 106 A cm-2 before break down, and that breakdown occurs as a two-stage process.

In this work, solid-state metal transport from internal metal nanolayers onto the surface of metal/ceramic nano-multi-layers (NMLs) has been directed in a controlled way by femtosecond (fs) laser irradiation and subsequent low temperature thermal annealing. Laser irradiation induced modifications of the NML microstructures and stress states can be limited within the first few top nanolayers due to the focused laser energy input at the metal/ceramic interface by exploiting the local plasmonic effect. Accompanied laser peening can further refine the crystallites and introduce compressive stress at the laser-irradiated region, which reduces the activation energies for vacancy formation and migration of metal atoms in the nano-confinement. Patterned Cu surface nanostructures (outflow) appear selectively along the laser path after air annealing at temperatures down to 360 ℃. For the solid-state diffusion of Cu in confinement, in-plane metal transport along the Cu-AlN interfaces is much faster than the outward ...

Bonding a large-area die by Ag nanoparticle paste sintering faces a lot of challenges, and the voids/cracks caused by residual organics of the paste are some of the obstacles. The organic burnt out during the sintering process and degassing of the residue organics during service cause significant concerns. In this study, organic-free Ag nanoparticle material has been developed by pulsed laser deposition technology. Oweing to being organic-free, no void, crack and delamination were observed in the sintered Ag layer of die-attachment, and the large-area die-attachment could be carried out by a simple sintering profile at low temperature. The die shear test indicated that the bonding strength was superior to the standard. Porosity and densification of the sintered Ag layer could be controlled by sintering profiles, including the processing pressure, temperature and time.

The presence of pharmaceutical and personal care products (PPCPs) in aquatic systems has been a growing cause for concern. Advanced oxidation processes such as UV/TiO2 (ultraviolet light/titanium dioxide) can break down PPCPs into smaller constituents, reducing the pharmaceutical activity. However, this process is limited by low photonic efficiency under UV systems. Controlled periodic illumination (CPI) is a promising solution to overcome the issues concerning low photonic efficiencies. Using a CPI controlled UV-LED/TiO2 process, a mixture of eighteen PPCP compounds were analyzed for their degradation removal on porous titanium – titanium dioxide (PTT) substrates. The kinetic rate constants of PPCPs may be analyzed using multiple regression analysis with parameters such as net charge at experimental pH, solubility, and molecular weight. Negatively charged PPCP compounds were found to have the highest removal compared to neutral and positively charged compounds due to electrostatic attraction forces. Decreasing the duty cycle under CPI or the UV-LED illumination period did not significantly change the individual and cumulative PPCP compound removal, suggesting that the CPI controlled UV-LED/TiO2 processes using PTT substrates were effective in reducing energy requirements without sacrificing removal performance.

In this work, plasmon-induced heterointerface thinning for Schottky barrier modification of core/shell SiC/SiO2 nanowires is conducted by femtosecond (fs) laser irradiation. The incident energy of ...

Nano-Ag sintering technology is a promising die attach method for power semiconductors in high reliability and high temperature (i.e. 300°C) applications. However, the present predictive models for thermal conductivity of multiphase materials are not suitable for the porous sintered Ag due to the model limitations of low porosity, i.e.

ZnO nanomaterials have received much attention due to their suitability for applications such as gas sensors, UV detectors, and solar collectors. However, the functionality of ZnO in optical applications is often limited by its wide bandgap (3.15 eV) which restricts the response to shorter wavelengths. In view of this limitation, there has been much interest in tuning the optical properties of ZnO through defect engineering. In this work, we show that processing ZnO thin films with nanosecond (ns) laser irradiation is a simple and effective way to introduce interband defects lowering the bandgap and increasing the sensitivity of ITO/ZnO/ITO photodetector structures at longer wavelengths. In particular, we show that the concentration of oxygen vacancies in ZnO is proportional to laser fluence below 700 mJ/cm2, but that an increase in laser fluence above this value results in thermal heating that anneals the film and lowers the relative abundance of oxygen vacancies. On the other hand, the surface morphology of ZnO does not change significantly even though the fluence reaches 700 mJ/cm2. To illustrate the way in which laser processing can be utilized to improve the optical properties of ZnO films in photodetector applications, we have fabricated transparent ITO/ZnO/ITO stacked structures and measured their response at various optical wavelengths. We find that processing with ns laser radiation is effective in enhancing the responsivity and detectivity of these devices at blue (460 nm) and UV (390 nm) wavelengths. The response of the photodetector is also increased at green wavelengths (570 nm) and red wavelengths (620 nm) when processed with laser fluences in the 480–600 mJ/cm2 range.

Ag or Cu metal nanoparticle paste can be used as a bonding material for electronic packaging applications. However, Ag nanoparticle paste has some drawbacks including high cost and being prone to ion migration in high-humidity conditions. The main obstacle to using Cu nanoparticle paste is rapid oxidation in air during heating. In this work, we describe a method to prepare Ag-Cu alloy nanoparticle paste by a polyol chemical reduction method combined with subsequent concentration. Characterization with ultraviolet–visible spectroscopy, transmission electron microscopy, x-ray photoelectron spectroscopy and energy dispersive spectrometry confirm the formation of the Ag-Cu alloy structure. During the synthesis of Ag-Cu alloy nanoparticles, an Ag core forms initially, followed by codeposition of Ag and Cu. Most of the Ag-Cu alloy nanoparticles have a truncated octahedral shape with twin structures located at the edges. This Ag-Cu alloy nanoparticle paste has a good oxidation resistance up to 350°C in air atmosphere. Using the Ag-Cu alloy nanoparticle paste, joints were formed at a low sinter-bonding temperature of 160°C. Shearing tests confirm the formation of robust joints, with an average shear strength of 50 MPa.

It is widely accepted that nano pores of sintered nanoparticles can coalesce into micro pores during high temperature service. When applying sintered nanoparticles in power electronics, the pore segregation and delamination seriously degrade the bond strength and thermal conductivity, but the reason is still not well understood. In this paper, both finite element analysis and experimental results confirmed that thermal stress is the main driving force for this phenomenon, which was not considered in the previous study. The effect of pore segregation on performance and reliability of power devices is also discussed.

The newly developed quenching and partitioning (QP) steel QP980 and boron alloyed martensitic steel B1500HS were butt-welded using fiber laser at a constant laser power 4.5 kW and various welding speeds of 4∼10 m/min. Retained austenite was measured in the super-critical HAZ of B1500HS (0.9%), inter-critical HAZ of B1500HS (3.4%) and inter-critical HAZ of QP980 (0.6%), while the sub-critical HAZ of QP980 witnessed decomposition of retained austenite from 8.4% to 4.4%. The joints welded at 4 m/min achieved the highest tensile strength, while the significantly softened HAZ of the B1500HS was the weakest region. The dissimilar joint welded at 6∼8 m/min fractured at the base metal of QP980, which were preferred as more crash energy can be absorbed. However, the Erichsen values of these welded joints (∼4.06 mm) significantly decreased compared with the base metal of B1500HS (7.46 mm) and QP980 steel (8.67 mm), as the crack propagated along the softened HAZ of B1500HS.

Four linear engineered TiO2 nanomaterials (LENs) were synthesized and evaluated in terms of settlability and their ability to remove natural organic matter (NOM) from river water. The size, surface characteristics, and crystallinity of the LENs were manipulated by varying the temperatures used during the synthesis procedure. All four LENs settled out of purified water more effectively than standard Degussa Evonik Aeroxide P25 nanoparticles. The settling behaviour of the nanomaterials was impacted by surface charge effects and interactions with NOM and ionic species in the river water matrix. The reduction of two disinfection byproduct precursor surrogate parameters, DOC and UV254, by the LENs via adsorption (no irradiation) and photocatalytic degradation under UVA LED irradiation was compared to that by P25 nanoparticles. After 60 min of irradiation DOC removal by the LENs ranged from 20 to 50% and UV254 reduction ranged from 65 to 90%. Two of the most promising LENs were reused multiple times and although both materials experienced decreases in treatment efficacy over successive reuse cycles, the reusability of both LENs was equal to or superior to that of P25 nanoparticles. The electrical energy per order required to remove DOC and UV254 from the water ranged from 8 to 36 times higher than that required for UV/H2O2 treatment but comparable to results reported by other researchers using UV/TiO2 for NOM removal. A subset of the nanomaterials evaluated in this study may prove to be a viable alternative to standard TiO2 nanoparticles for the removal of DBP precursors from drinking water, but the characteristics of the water matrix have important effects on settling efficiency and will require site-specific evaluation.