The direct identification of mineral species in raw rocks was performed using laser induced breakdown spectroscopy (LIBS). A total of 162 sulfide rocks with mineralogical relevance in the copper industry were analyzed. These contained bornite (Cu5FeS4), chalcocite (Cu2S), chalcopyrite (CuFeS2), covellite (CuS), enargite (Cu3AsS4), molybdenite (MoS2), and pyrite (FeS2). The samples were collected from different mining locations to account for sample variability. Unsupervised multivariate methods like principal component analysis (PCA) and dendrogram analysis were explored, while supervised pattern recognition techniques, such as soft independent modelling of class analogy (SIMCA), partial least squares discriminant analysis (PLS-DA), K-nearest neighbor (KNN), decision tree analysis and artificial neural networks (ANNs) were compared. The sensitivity test performed on the LIBS data shows that the models KNN, SIMCA, PLS-DA and ANN achieve an average classification accuracy of 96.2, 98.1, 90.6 and 100%, respectively. In contrast, the robustness test of the models SIMCA and PLS-DA yields accuracies of 97.7 and 98.8%, respectively. The correct identification of very similar species in terms of their elemental composition such as bornite/chalcopyrite and chalcocite/covellite is also achieved.

Determination of copper-based mineral species by laser induced breakdown spectroscopy and chemometric methods

The two-dimensional layered material CuInP2S6 (CIPS) has attracted significant research attention due to its nontrivial physical properties, including room-temperature ferroelectricity at the ultrathin limit and substantial ionic conductivity. Despite many efforts to control its ionic conductance and develop electronic devices, such as memristors, improving the stability of these devices remains a challenge. This work presents a highly stable threshold-switching device based on the Cu/CIPS/graphene heterostructure, achieved after a comprehensive investigation of the activation of Cu's ionic conductivity. The device exhibits exceptional threshold-switching performance, including good cycling endurance, a high on/off ratio of up to 104, low operation voltages, and an ultrasmall subthreshold swing of less than 1.8 mV/decade for the resistance-switching process. Through temperature-dependent electrical and Raman spectroscopy measurements, the stable resistive-switching mechanism is interpreted with a drifting and diffusion model of Cu ions under the electric field, rather than the conventional conducting filament mechanism. These results make the layered ferroionic CIPS material a promising candidate for information storage devices, demonstrating a compelling approach to achieving high-performance threshold-switching memristor devices.

Robust Threshold-Switching Behavior Assisted by Cu Migration in a Ferroionic CuInP2S6 Heterostructure.

With the development of information processing, various neuromorphic synaptic devices have been proposed, including novel devices mimicking multiple sensory systems in the biosome, in which vision is a vital source of information. Due to the pressing issue of high energy consumption and the ever‐increasing complexity of practical application scenarios, there is an urgent need to investigate optoelectronic synapses with simple structure but multifunctional capabilities, thereby broadening their application scope. Here, remarkable performances in both electrical and optical operation modes are achieved in multilayer graphene/CuInP2S6/Au electronic/optoelectronic device. By modulating the electrical and optical pulses, both short‐term and long‐term memory can be emulated in the same device, while visual perception, processing, and memorizing functions are demonstrated in this single cell with relatively low energy consumption. In addition, light adaptive behavior can also be simulated through optical–electrical cooperative modulation in the device, further providing a novel and promising strategy for future applications in artificial visual systems.

CuInP2S6‐Based Electronic/Optoelectronic Synapse for Artificial Visual System Application

Two-dimensional (2D) ferroelectric materials have attracted intensive attention in recent years for academic research. However, the synthesis of large-scale 2D ferroelectric materials for electronic applications is still challenging. Here, we report the successful synthesis of centimeter-scale ferroelectric In2Se3 films by selenization of In2O3 in a confined space chemical vapor deposition method. The as-grown homogeneous thin film has a uniform thickness of 5 nm with robust out-of-plane ferroelectricity at room temperature. Scanning transmission electron microscopy and Raman spectroscopy reveal that the thin film is 2H stacking α-In2Se3 with excellent crystalline quality. Electronic transport measurements of In2Se3 highlight the current-voltage hysteresis and polarization modulated diode effect due to the switchable Schottky barrier height (SBH). First-principles calculations reveal that the polarization modulated SBH is originated from the competition between interface charge transfer and polarized charge. The large area growth of epitaxial In2Se3 opens up potential applications of In2Se3 in novel nanoelectronics.

Epitaxial Growth of Large Area Two-Dimensional Ferroelectric α-In2Se3.

Fiber-tip sensors based on the Fabry-Perot interferometer (FPI) are one of the most widely used devices for temperature and pressure measurements in space-confined scenarios. However, the deposited metal films with a polycrystalline structure tend to form microcracks under strain, which can undermine the optical quality factor and thus sensing performance of these fiber-tip sensors. Here, we demonstrate an atomically smooth gold microflake (GMF)-enabled fiber-tip FPI sensor with a Q factor as high as 628. Benefiting from the high reflectivity and flexibility of GMFs and the elasticity of the PDMS spacer, the fiber-tip FPI can maintain stable sensing performance under large deformation. For temperature sensing, the fiber-tip sensor exhibits a linear response to the temperature in the range 28-40 °C with a sensitivity as high as 1.74 nm °C-1. To realize linear and sensitive pressure sensing, we design and fabricate a PDMS clamped-beam structure on the fiber tip using a soft lithography technique, achieving a sensitivity of 11.48 nm kPa-1. Moreover, simultaneous measurement of the temperature and pressure is also demonstrated using the wavelength demodulation method. The simple and cost-effective fabrication of the clamped beam and the transferable GMFs allow for the facile integration of high-quality FP cavities on fiber tips, opening new opportunities for developing optical sensors with miniaturized sizes.

Atomically Smooth Gold Microflake-Enabled Fiber-Tip Fabry-Perot Interferometer for Temperature and Pressure Sensing.

Nanoparticle-on-mirror plasmonic nanocavities, capable of extreme optical confinement and enhancement, have triggered state-of-the-art progress in nanophotonics and development of applications in enhanced spectroscopies. However, the optical quality factor and thus performance of these nanoconstructs are undermined by the granular polycrystalline metal films (especially when they are optically thin) used as a mirror. Here, we report an atomically smooth single-crystalline platform for low-loss nanocavities using chemically synthesized gold microflakes as a mirror. Nanocavities constructed using gold nanorods on such microflakes exhibit a rich structure of plasmonic modes, which are highly sensitive to the thickness of optically thin (down to ∼15 nm) microflakes. The microflakes endow nanocavities with significantly improved quality factor (∼2 times) and scattering intensity (∼3 times) compared with their counterparts based on deposited films. The developed low-loss nanocavities further allow for the integration with a mature platform of fiber optics, opening opportunities for realizing nanocavity-based miniaturized photonic devices for practical applications.

/pdf/atomically-smooth-single-crystalline-platform-for-low-loss-1n86nxi2.pdf

Atomically Smooth Single-Crystalline Platform for Low-Loss Plasmonic Nanocavities.

As basic building blocks for next-generation information technologies devices, high-quality p-n junctions based on van der Waals (vdW) materials have attracted widespread interest. Compared to traditional two-dimensional (2D) heterojunction diodes, the emerging homojunctions are more attractive owing to their intrinsic advantages, such as continuous band alignments and smaller carrier trapping. Here, utilizing the long-range migration of Cu+ ions under an in-plane electric field, a lateral p-n homojunction was constructed in the 2D layered copper indium thiophosphate (CIPS). The symmetric Au/CIPS/Au devices demonstrate an electric-field-driven resistance switching (RS) accompanied by a rectification behavior without any gate control. Moreover, such rectification behavior can be continuously modulated by poling voltage. We deduce that the reversable rectifying RS behavior is governed by the effective lateral build-in potential and the change of the interfacial barrier during the poling process. Furthermore, the CIPS p-n homojuction is evidenced by the photovoltaic effect, with the spectral response extending up to the visible region due to the better photogenerated carrier separation efficiency. Therefore, this work provides a facile route to fabricate homojunctions through electric-field-driven ionic migration.

/pdf/highly-tunable-lateral-homojunction-formed-in-two-16p1bodj.pdf

Highly Tunable Lateral Homojunction Formed in Two-Dimensional Layered CuInP2S6 via In-Plane Ionic Migration.

Optical microfibers drawn from conventional fibers have attracted considerable interests and have found many novel applications. Here, we review recent advances in ultrafast fiber lasers based on optical microfibers. Starting with characteristics and fabrication of optical microfibers, which are closely related to ultrafast fiber lasers, we show that characteristics of large portion of evanescent field, tailorable dispersion, high optical nonlinearity, very low optical loss and full compatibility with conventional fibers are greatly beneficial to novel ultrafast fiber lasers. We then highlight recent works on ultrafast fiber lasers based on optical microfibers in terms of fast saturable absorbers made from optical microfiber-supported nanomaterials, dispersion management and high optical nonlinearity, as well as some other novel ultrafast fiber lasers. Finally, we briefly discuss future opportunities for optical microfiber-based ultrafast fiber lasers, such as high-order dispersion management, nonlinearity management and applications for sensing and measurement.

Optical microfiber-based ultrafast fiber lasers

Ultrafast interfacing of electrical and optical signals at the nanoscale is highly desired for on-chip applications including optical interconnects and data processing devices. Here, we report electrically driven nanoscale optical sources based on metal–insulator–graphene tunnel junctions (MIG-TJs), featuring waveguided output with broadband spectral characteristics. Electrically driven inelastic tunneling in a MIG-TJ, realized by integrating a silver nanowire with graphene, provides broadband excitation of plasmonic modes in the junction with propagation lengths of several micrometers (∼10 times larger than that for metal–insulator–metal junctions), which therefore propagate toward the junction edge with low loss and couple to the nanowire waveguide with an efficiency of ∼70% (∼1000 times higher than that for metal–insulator–metal junctions). Alternatively, lateral coupling of the MIG-TJ to a semiconductor nanowire provides a platform for efficient outcoupling of electrically driven plasmonic signals to low-loss photonic waveguides, showing potential for applications at various integration levels.

https://doi.org/10.1021/acs.nanolett.2c04975

Waveguide-Integrated Light-Emitting Metal–Insulator–Graphene Tunnel Junctions

Narrow bandgap materials have garnered significant attention within the field of broadband photodetection. However, the performance is impeded by diminished absorption near the bandgap, resulting in a rapid decline in photoresponsivity within the mid‐wave infrared (MWIR) and long‐wave infrared (LWIR) regions. Furthermore, they mostly worked in cryogenic temperature. Here, without the assistance of any complex structure and special environment, it is realized high responsivity covering ultra‐broadband wavelength range (Ultraviolet (UV) to LWIR) in a single quasi‐1D pseudogap (PG) system (TaSe4)2I nanoribbon, especially high responsivity (From 23.9 to 8.31 A W−1) within MWIR and LWIR region at room temperature (RT). Through direct probing the carrier relaxation process with broadband time‐resolved transient absorption spectrum measurement, the underlying mechanism of majorly photoconductive effect is revealed, which causes an increased spectral weight extended to PG region. This work paves the way for realizing high‐performance uncooled MWIR and LWIR detection by using quasi‐1D PG materials.

Ultrabroadband High Photoresponsivity at Room Temperature Based on Quasi‐1D Pseudogap System (TaSe4)2I

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