Soft Composites with Tunable Optical and Electrical Properties

Ionogels, with wide applications in tissue engineering, soft robotics, and flexible iontronic devices, require tunable optical, mechanical, and electrical properties for advanced functionality applications. Here, a facile strategy is reported to tune a set of properties of ionogels via tuning the redox states of the added polyoxometalate (POM) clusters. Upon external electrical stimuli, the POM clusters in the ionogels can be reversibly tuned from a transparent, oxidized state to a blue, reduced state. The redox states of the POM anions influence the POM‐polymer interactions, which promotes the in situ modulation of the ionogel properties reversibly over a large window: optical transparency from 91% to 7%, dissipated energy from 0.9 to 3.1 MJ m−3, elastic modulus from 1.5 to 2 MPa, conductivity from 1.6 × 10−4 to 2.2 × 10−4 S cm−1. Meanwhile, the sensory properties of the ionogels can be modulated simultaneously. For strain sensing and pressure sensing, the GF can be tuned from 2.3 to 7.2, and the sensitivity can be tuned from 0.8 to 1.2 kPa−1. Such an ionogel with tunable optical, mechanical, and electrical properties may find a variety of applications meeting specific demands. The POM functionalization strategy may also bring new insights into the design of the stimuli‐responsive ionogels.

Carbon nanosheets are mechanically stable, free‐standing two‐dimensional materials with a thickness of ≈1 nm and well defined physical and chemical properties. They are made by radiation‐induced cross‐linking of aromatic self‐assembled monolayers. Herein, a route is presented to the scalable fabrication of multilayer nanosheets with tunable electrical, optical, and chemical properties on insulating substrates. Stacks of up to five nanosheets with sizes of ≈1 cm2 on oxidized silicon are studied. Their optical characteristics are investigated by visual inspection, optical microscopy, UV–vis reflection spectroscopy, and model calculations. Their chemical composition is studied by X‐ray photoelectron spectroscopy. The multilayer samples are then annealed in an ultrahigh vacuum at various temperatures up to 1100 K. A subsequent investigation by Raman, X‐ray photoelectron, and UV–vis reflection spectroscopy, as well as by electrical four‐point probe measurements, demonstrates that the layered nanosheets transform into nanocrystalline graphene. This structural and chemical transformation is accompanied by changes in the optical properties and electrical conductivity and opens up a new path for the fabrication of ultrathin functional conductive coatings.

Ionic solution-processable Ag nanostructures with tunable optical and electrical properties and strong adhesion to general substrates

The tunable electronic, electrical and optical properties of graphene oxide (GO) sheets were investigated using a controlled reduction by 500 keV Ar+-ion irradiation. The carbon to oxygen ratio of the GO sheets upon the ion beam reduction has been estimated using resonant Rutherford backscattering spectrometry analyses and its effect on the electrical and optical properties of GO sheets has been studied using sheet resistance measurements and photoluminescence (PL) measurements. The restoration of sp2-hybridized carbon atoms within the sp3 matrix is found to be increases with increasing the Ar+-ion fluences as evident from Fourier transform infrared, and x-ray absorption near-edge structure measurements. The decrease in the number of disorder-induced local density of states (LDOSs) within the π–π* gap upon the reduction causes the shifting of PL emission from near infra-red to blue region and decreases the sheet resistance. The improved electrical and optical properties of GO sheets were correlated to the decrease in the number of LDOSs within the π–π* gap. Our experimental investigations suggest ion beam irradiation is one of an effective approaches to reduce GO to RGO and to tailor its electronic, electrical and optical properties.

Thin film transistors fabricated using ZnSe thin films synthesized using chemical bath deposition.

Modern wearable electronics require scalable, flexible, and conductive electrodes with tunable properties. Abundant materials such as graphite as a conductive component and polymer as a flexible component forming a composite film (electrode) via simple synthesis technique are particularly captivating. This approach conveniently satisfies the fundamental needs of an ideal electrode yet provides a conductive platform to accommodate a secondary material for various purposes in electrochemical energy conversion and storage. Accordingly, we optimize a graphite-polymer composite film with good conductivity and flexibility to incorporate two-dimensional (2D) VSx (mixed phase predominated by V5S8) as an active material within the film. We exemplify the dual functionalities of the VSx/graphite flexible electrode as i) a photo-electrocatalyst for enhanced hydrogen evolution reaction by visible and near-infrared light irradiation (overpotential ≈500 mV at the current density of −10 mA cm−2), and ii) a conductive electrode for symmetrical solid-state supercapacitor with pseudocapacitive charge storage mechanism (areal capacitance of 123 mF cm−2 and areal capacity of 34 µAh cm−2 at the current density of 0.5 mA cm−2). Our work demonstrates the versatility of graphite films in terms of size, shape, flexibility, and scalability, with tunable physical, optical, and electrical properties by integrating other secondary materials. We combine flexible graphite film and 2D vanadium sulfide with near-infrared photoresponse and pseudocapacitive properties, as an economically feasible avenue for energy harvesting, outer space application, and wearable devices.

In this paper, we experimentally investigate the effect of annealing and ligand removal on the electrical and photovoltaic properties of polycrystalline films formed from a colloidal solution of heterostructured CdSe/CdS nanoparticles in chlorobenzene using the drop-casting method. Annealing leads to a significant increase in photoconductivity, up to 4 orders of magnitude, while the band gap of the CdSe/CdS nanoplatelet film remains unchanged. Moreover, it was shown that the annealing causes a change in the dominant recombination mechanism from monomolecular to bimolecular due to an increase in charge carrier mobility. These findings directly demonstrate the possibility of creating highly photoconductive nanocrystalline films with tunable optical and electrical properties. Moreover, annealing also provides the growth of photosensitivity from approximately 0.87 to 2.75 A/W for photons with 2.12 eV energy, which is a record value for such nanocrystalline films. Considered films have the potential to significantly enhance the sensitivity of photodetectors and solar cell efficiency.

Black phosphorus, which is a relatively rare allotrope of phosphorus, was first discovered by Bridgman in 1914. Since the advent of two-dimensional (2D) black phosphorus (which is known as phosphorene due to its resembling graphene sheets) in early 2014, research interest in the arena of black phosphorus was reignited in the scientific and technological communities. Henceforth, a myriad of research studies on this new member of the 2D world have been extensively emerged. Fascinatingly, 2D black phosphorus exhibits a distinctive wrinkled structure with the high hole mobility up to 1000 cm2 V−1 s−1, excellent mechanical properties, tunable band structures, anisotropic thermal, electrical and optical properties, thus leading to its marvelous prospects in device applications. This review firstly introduces the state-of-the-art development, structural properties and preparation routes of black phosphorus. In particular, anisotropy involved in mechanical properties, thermal conductivity, carrier transport as well as optical properties is comprehensively discussed. Apart from discussing the recent progress in black phosphorus which is applied to devices (i.e. field effect transistors and optoelectronic), the review also highlights the bottlenecks encountered by the society and finally casts an invigorating perspective and insightful outlook on the future direction of the next-generation 2D black phosphorus by harnessing its remarkable characteristics for energy production.

As an eye‐catching 2D material, MoS2 has tunable optical and electrical properties. However, the rapid recombination of electron‐hole pairs intrinsically significantly hinders the performance improvement of MoS2 photodetectors. Achieving carrier manipulation to suppress recombination is crucial and challenging for MoS2 photodetectors. Herein, we report three MoS2 photodetectors decorated with platinum single atoms (Pt SAs), platinum single‐layer clusters (Pt SCs), and platinum nanoclusters (Pt NCs) via an impregnation method. Carrier recombination in MoS2 is suppressed by growing Pt SAs, Pt SCs, and Pt NCs. Furthermore, Pt SAs, Pt SCs, and Pt NCs have different effects on carrier behavior due to the size effect and disparate interactions with MoS2. Among the Pt SA/MoS2, Pt SC/MoS2, and Pt NC/MoS2 devices, Pt SC/MoS2 exhibits a responsivity (R) of 1.44 × 102 A W−1 and a specific detectivity (D*) of 1.07 × 1010 Jones under 532 nm illumination with a power density of 0.5 mW cm−2. This work will deepen the understanding of the relationship between the size effect and carrier behavior and provide a theoretical basis for carrier manipulation of photodetectors.

Photoluminescence properties and DFT simulations of the Cr ion-implanted (100)-oriented β-Ga2O3 single crystals

ZnS/Ag/ZnS coating as transparent anode for organic light emitting diodes

Special interest continues to grow in the achievement of fundamental understanding of nanostructured assemblies that potentially open new horizons for creating novel energy conversion systems. When one-dimensional (1D) nanostructures based on nanotubes or nanowires are integrated into the assembly of well-ordered architectures, they exhibit a variety of tunable optical and electrical properties that can offer exciting opportunities in creating the next generation of solar cells. Recently, particular focus has been placed on nanostructured solar cells that can tolerate a higher level of defects and impurities. To realize their potential, semiconducting 1D nanostructures that serve as conducting scaffolding and absorbing layers should be controlled in a predictable and precise fashion in order to efficiently tailor photon harvesting and transport charge carriers [1,2,3]. While the past several years have witnessed great progress in the area of nanotechnologies, structural dimensions (height, thickness, and spacing) and spatial alignment of 1D nanostructures have not been shown to be selectively controllable with high precision [4]. Accordingly, current nanofabrication technologies allowing for precise control over the assembly of 1D nanostructures yielding optimal architectures of nanostructured solar cells are still in their infancy. Hence, a scarcity of ideal platforms consisting of highly-controlled nanostructure assemblies makes use of non-ideal systems, thereby preventing systematic studies of energy conversion processes within the cell and at the heterojunction interfaces. Therefore, we provide novel approaches to investigate material synthesis for highly arrayed nanostructured systems for solar cell applications.We developed a new process technology that can make full use of the porous template while structural dimensions such as spacing and thickness of nanostructures are also precisely controlled. Particularly, our technologies enable highly arrayed nanostructures having various material combinations such as insulators, semiconductors, and/or metals. In addition, they allow for large-scale production of such highly arrayed nanostructures. Currently, we are integrating highly arrayed nanostructures into glass or plastic substrates. Our nanofabrication technologies will provide a new class of highly arrayed, multi-walled nanostructures suitable for many optoelectronic applications including new-generation solar cells. References Z. Fan, H. Razavi, J. W. Do, A. Moriwaki, O. Ergen, Y. L. Chuen, P.W. Leu, J.C. Ho, T. Takahashi, L. A. Reichertz, S. Neale, K. Yu, M. Wu, J.W. Ager, and A. Javey, Nat. Mater. 8, 648 (2009)L. Sun, S.Zhang, X. Sun, and X. He, J. Nanosci. Nanotechnol., 10, 4551 (2010)V. Thavasi, V. Renugopalakrishnan, R. Jose, and S. Ramakrishna, Mater. Sci. Eng. R. 63, 81(2009) A. Belaidi, Th. Dittrich, D. Kieven, J. Tornow, K. Schwarzburg, M. Kunst, N. Allsop, M.-Ch. Lux-Steiner, and S. Gavrilov, Sol. Energy Mater. Sol. Cells, 93, 10336 (2009)

Van der Waals semiconductor based self-powered transparent broadband photodetector

Optically controlled nongenetic neuromodulation represents a promising approach for the fundamental study of neural circuits and the clinical treatment of neurological disorders. Among the existing material candidates that can transduce light energy into biologically relevant cues, silicon (Si) is particularly advantageous due to its highly tunable electrical and optical properties, ease of fabrication into multiple forms, ability to absorb a broad spectrum of light, and biocompatibility. This protocol describes a rational design principle for Si-based structures, general procedures for material synthesis and device fabrication, a universal method for evaluating material photoresponses, detailed illustrations of all instrumentation used, and demonstrations of optically controlled nongenetic modulation of cellular calcium dynamics, neuronal excitability, neurotransmitter release from mouse brain slices, and brain activity in the mouse brain in vivo using the aforementioned Si materials. The entire procedure takes ~4-8 d in the hands of an experienced graduate student, depending on the specific biological targets. We anticipate that our approach can also be adapted in the future to study other systems, such as cardiovascular tissues and microbial communities.

This study investigates a class of materials known as polymer nanodielectrics, which are formed by incorporating ceramic fillers into polymers. These materials offer the unique advantage of tunable electrical and optical properties. The research focuses on the incorporation of high-purity stannic oxide nanoparticles (SnO2 NPs) into a ternary blend matrix of hydroxypropyl methylcellulose (HPMC) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) using a solution casting method. Characterization techniques like X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) revealed alterations in the amorphous nature of the HPMC/PEDOT:PSS blend upon the introduction of SnO2 NPs. These analyses also suggest the formation of interactions between the polymer and nanoparticles. Scanning electron microscopy (SEM) images confirmed the successful dispersion of SnO2 NPs on the surface of the polymer blend, particularly at lower concentrations. The optical properties of the nanocomposite films were investigated using UV-vis spectrophotometry. This analysis allowed for the calculation of optical constants like the bandgap and refractive index. The results showed a dual-bandgap structure, with the direct and indirect bandgaps ranging from 4.92 eV to 4.26 eV and 3.52 eV to 1.68 eV, respectively. Electrical characterization using AC conductivity and dielectric permittivity measurements revealed a dependence on the SnO2 NPs concentration within the frequency range of 0.1 Hz to 10 MHz. The relaxation processes and interfacial polarization effects within these nanocomposites are further discussed in the study. At a frequency of 10 Hz, the AC conductivity exhibited a significant increase, rising from 1.85 × 10-12 S m-1 to 1.04 × 10-9 S m-1 upon the addition of 0.7 wt% SnO2 NPs. These findings highlight the multifunctional nature of the developed nanocomposites. They hold promise for various applications, including UV blockers, optical bandgap tuners, and optical coatings in advanced optoelectronic devices. Additionally, their tunable high permittivity suggests potential use as dielectric substrates for next-generation, high-performance energy storage devices.