Aligned Nanostructures Research Articles

Boosting through-plane electrical conductivity: chitosan composite films with carbon-sepiolite and multiwalled carbon nanotubes

Flexible and electrically conductive materials are gaining significant attention across various domains, notably in electronics, biomedicine and food industry. One promising strategy involves the integration of electrically conductive nanostructures into a polymeric matrix to fabricate composite materials. However, achieving uniform through-plane electrical conductivity remains a challenge due to the preferential alignment of carbon nanostructures in the in-plane direction. Herein, we report the development of electrically conductive chitosan (CS)-based biocomposite films incorporating a multicomponent filler system. By combining carbon supported on sepiolite clay (CARSEP) with multiwalled carbon nanotubes (MWCNT), it is aimed to facilitate an interconnected distribution in both in-plane and through-plane directions. The optimized film, featuring a CS/CARSEP/MWCNT mass ratio of 50/40/10, exhibited a maximum electrical conductivity of 55.5 S/m and 0.1 S/m in the in-plane and through-plane directions, respectively. Additionally, migration studies demonstrated the absence of harmful compounds upon heating the film up to 60 °C in air, ethanol, or hexane. These findings highlight the potential of these flexible and electrically conductive biocomposite films, primarily composed of biobased materials, for applications requiring through-plane electrical conductivity.

Self – assembled aligned single – walled carbon nanotubes as an anisotropic polarizer and saturable absorber in erbium-doped femtosecond fiber laser

We report the production of a saturable absorber (SA) based on aligned single-walled carbon nanotubes SWCNTs by the self-assembly method. The ultrafast saturation behavior of prepared aligned and random nanostructures shows an increase of modulation depth by 6% due to the alignment method. We also observed the dependence of aligned SWCNTs loss on the polarization direction of laser radiation. All-fiber Er-doped hybrid mode-locked fiber laser was demonstrated based on the aligned /random SWCNTs-based SAs. We achieved the generation of stable stretched pulses with a pulse duration of 490/569 fs and an average output power of 20.7/18.25 mW. We also investigated the advantages of using aligned SWCNTs compared to the typical structure with random tube distribution. We show that the use of aligned SWCNTs film increased the SNR by 24.5, decreased the mode-locking threshold power by 42 mW, and decreased the RIN level by (20-25) dB in the frequency range [∼ 0 Hz- 100 kHz] and ∼ 8 dB in the range [100 kHz – 1 MHz].

Hetero-integration of cadmium sulfide nanorod arrays on graphite substrates to guide electron pathways for effective photocatalytic and photoelectrochemical activities

One-dimensional (1D) cadmium sulfide (CdS) nanostructures in photosynthetic systems have attracted attention because of their effective transport pathways for charge extraction which are essential for efficient photocatalytic and photoelectrochemical systems. Despite the numerous benefits of aligned 1D CdS nanostructures in photosynthetic systems, limited attention has been paid to hetero-integrating 1D CdS arrays on substrates with rapid charge extraction capabilities and practical applicability. Herein, we report the fabrication of vertically aligned CdS nanorod arrays on graphite substrates, in which electron transport pathways are rationally designed for effective photocatalysts and photoanodes. Specifically, CdS nanorod arrays integrated on graphite substrates exhibited photocatalytic reactions with excellent reusability and photostability owing to their superior bifacial properties compared to the control free-standing nanostructures. The proposed system also demonstrated excellent photoelectrochemical performance relative to control CdS nanorod arrays integrated on fluorine-doped tin oxide substrates because of the enhanced separation and extraction of photogenerated electrons combined with curvilinear surfaces.

Synergistic Molecular Alignment and Dipole Polarization in Stretched Nafion/Poly(vinylidene fluoride) Blend Membranes for High Proton Conduction in PEMFCs.

The nanostructure of Nafion and poly(vinylidene fluoride) (PVDF) blend membranes is successfully aligned through a mechanical uniaxial stretching method. The phase-separated morphology of Nafion molecules distinctly forms hydrophilic proton channels with increased connectivity, resulting in enhanced proton conductivity. Additionally, the crystalline phase of PVDF molecules undergoes a successful transformation from the α- to β-phase during membrane stretching, demonstrating an alignment of fluorine and hydrogen atoms with a TTTT(trans) structure. The aligned nanostructure of the blend film, combined with the dipole polarization of the β-phase PVDF, synergistically enhances the proton conduction through the membrane for operating proton-exchange membrane fuel cells (PEMFCs). The controlled structures of the blend membranes are thoroughly investigated using atomic force microscopy and small-angle X-ray scattering. Furthermore, the improved in-plane proton conductivity facilitates increased proton conduction at the interface between the membrane and catalyst layer in the membrane-electrode assembly, ultimately enhancing the power generation of PEMFCs.

Achieving Long‐Range Arbitrary Uniform Alignment of Nanostructures in Magnetic Fields

AbstractFor magnetic field orientation of nonstructures to become a viable method to create high performance multifunctional nanocomposites, it is of paramount importance to develop a method that is easy to implement and that can induce long‐range uniform nanostructural alignment. To overcome this challenge, inspired by low field nuclear magnetic resonance (NMR) technology, a highly uniform, high field strength, and compact magnetic‐field nanostructure orientation methodology is presented for polymeric nanocomposites using a Halbach array, for the first time. Potential new advances are showcased for applications of graphene polymer composites by considering their electro‐thermal and antibacterial properties in highly oriented orthogonal morphologies. The high level of anisotropy induced in the graphene nanocomposites studied stands out through: 1) up to four decades higher electrical conductivities recorded in comparison to their randomly oriented counterparts, at concentrations where the latter show minimal improvements compared to the unfilled polymer; 2) over 1200% improvement in thermal conductivity, 3) antibacterial surfaces at field benchmark levels with lower filler content and with the added versatility of arbitrary orientation of the nanofillers. Overall, the new method and variations thereof can open up new horizons for tailoring nanostructure and performance for virtually all major nanocomposite applications based on graphene and other types of fillers.

Double-sided semitransparent titania photoelectrode with enhanced light harvesting

In this work, unique semitransparent electrodes were prepared by the anodization of titanium layers (540 nm thick) initially deposited on the both sides of glass substrates employing indium-tin oxide interface layers serving as a current collector for the induced photocurrent. The anodization strategy used in this study enables fabrication of semitransparent titanium dioxide nanotube arrays with either aligned or spaced architecture on the two sides of the planar substrate. This study aims to perform a detailed investigation of this novel photoelectrode system (crystal structure, morphology and optical properties) to reveal their photoelectrochemical features. It was found that the photoelectrode exhibits enhanced photocurrent density about 1.9 times higher (4.6 μAcm−2 at +0.5 V) for aligned nanotubes compared to a substrate overgrown symmetrically by separated nanotubes (2.4 μAcm−2 at +0.5 V). This can be effectively explained by the higher tube density in the case of aligned nanostructures, which provide more channels for charge percolation. In addition, both the high donor concentration (6.4 × 1020 cm−3) together with the low charge transfer resistance of the semitransparent electrode of the aligned nanotubes make the material promising for application in photoelectrochemical systems and smart light management.

High-aligned oppositely-charged nanocellulose/MXene aerogel membranes through synergy of directional freeze-casting and structural densification for osmotic-energy harvesting

Optimization of ion-transport paths can considerably improve ion-transport capabilities in charged nanochannels. Thus, the assembly of high-charge-density one- and two-dimensional nanomaterials into aligned nanochannels is necessary for high-performance osmotic-energy harvesting. Herein, we prepared cellulose/MXene aerogel membranes with opposite charges and aligned nanochannels via chemical modification on algal cellulose nanofibers and MXene nanosheets, unidirectional freeze casting, and structural densification to considerably enhance the ionic conductivity in low-concentration solutions (maximum conductivity of 2.88 × 10−3 S cm−1). In particular, the aligned membrane had an output power density of 2.97 and 4.89 times higher than membranes used for suction filtration and isotropic nanochannels, respectively, demonstrating the necessity for nanostructure control. In addition, due to the photothermal effect of MXene, the positively–negatively (P–N) charged unit produced a maximum output power density of 8.87 W m−2 under a concentration gradient of artificial seawater and river water and simulated sunlight. Moreover, the unit maintained 90.4% of its original output capacity after 168 h of operation. As a proof of concept, we created nine series of P–N units and successfully powered an electronic calculator with an output voltage of 1.85 V. This study reveals improvements in developing renewable materials with an aligned nanostructure for high-performance osmotic-energy conversion.

Graphene Hybrid Tough Hydrogels with Nanostructures for Tissue Regeneration.

Over the past few decades, hydrogels have attracted considerable attention as promising biomedical materials. However, conventional hydrogels require improved mechanical properties, such as brittleness, which significantly limits their widespread use. Recently, hydrogels with remarkably improved toughness have been developed; however, their low biocompatibility must be addressed. In this study, we developed a tough graphene hybrid hydrogel with nanostructures. The resultant hydrogel exhibited remarkable mechanical properties while representing an aligned nanostructure that resembled the extracellular matrix of soft tissue. Owing to the synergistic effect of the topographical properties, and the enhanced biochemical properties, the graphene hybrid hydrogel had excellent stretchability, resilience, toughness, and biocompatibility. Furthermore, the hydrogel displayed outstanding tissue regeneration capabilities (e.g., skin and tendons). Overall, the proposed graphene hybrid tough hydrogel may provide significant insights into the application of tough hydrogels in tissue regeneration.

Layered-Double-Hydroxide (LDH) pyroelectric nanogenerators

Layered Double Hydroxides (LDHs) have outstanding properties, including straightforward fabrication and connection of high-density arrays of aligned nanostructures on almost every (e.g., large area and flexible) substrates, high surface-to-volume ratios, biocompatibility, flame retardancy and several degrees of freedom (divalent and trivalent cations, trivalent/divalent cations ratio, intercalated anions and geometries) for tuning their properties as well as their band diagrams. Nevertheless, LDH pyroelectric devices have never been reported. Here we suggest that LDHs can be ideal building blocks for pyroelectric nanogenerators because of high gradients of both composition and energy-levels, size effects and extraordinary simplicity of fabrication and tuning. For validation, we fabricated several LDH nanoplatelets pyroelectric nanogenerators and found that, without any poling, the equivalent pyroelectric coefficients can be positive, up to 150 µC/(K*m2), or negative, down to – 160 µC/(K*m2), for nanogenerators made of ZnAl LDH or MgAl LDH nanoplatelets, respectively. Beside demonstrating extremely simple and low cost pyroelectric nanogenerators, our results suggest that LDHs are outstanding candidates for high performance pyroelectric nanodevices as, first, the areas of the fabricated devices are orders of magnitude larger than the areas of the nanoplatelet-to-metal junctions and, second, the high number of degrees of freedom of LDHs leaves room for significant improvements.

Directed self‐assembly of block copolymer thin films via momentary thickness gradients

AbstractIn this study, a novel method to fabricate highly aligned lamellar nanostructures in a millimeter‐scale large area was demonstrated by directing the self‐assembly of block copolymer (BCP) thin films with a temporary thickness‐gradient micropattern via simple two‐step thermal annealing. In the first step of thermal annealing, the BCP nanostructure is latently guided by a phenomenon known as “geometric anchoring” for the area with a thickness gradient. The second annealing step causes thermal reflow of the height gradient micropattern with a sufficiently large curvature to flatten the micropattern. The shear stress generated by thermal reflow enlarged the grain of the BCP nanostructure, resulting in a highly aligned lamellar pattern over the entire area. Finally, the formation of periodic nanopatterns in large area was ensured by performing grazing‐incidence small‐angle x‐ray scattering. This innovative approach in directing the BCP self‐assembly promotes the fabrication of highly aligned nanostructures in large areas through cost‐effective and simple thermal imprinting method and designed two‐step heat treatment.

Room temperature excitonic emission in highly aligned ZnO nanostructures prepared by glancing angle Xe+ ion irradiation

Highly aligned ZnO nanostructures have been prepared using glancing angle ion irradiation technique. ZnO thin films were deposited on Si substrates using pulsed laser deposition method. These films were irradiated with 100 keV Xe+ ions of different fluencies ranging from 1 × 1016 to 1 × 1017 ions/cm2 at a glancing angle of 70° with respect to the sample normal. The scanning electron and atomic force microscopy studies reveal a randomly oriented flower petal like structure in the pristine ZnO film. However after ion irradiation, these petals are aligned in the beam direction. Further, with the increase of the ion fluence the petals are transformed to the nanostripe, nanowire like structures and at highest fluence wrinkled structure are formed. Interestingly, on closer examination, these wrinkles consist of nanopillar like structures aligned in the beam direction. The X-ray diffraction analysis reveals that the formed ZnO nanostructures are of hexagonal wurtzite structure with preferred orientation along the c-axis. Further, the ion beam modified nanostructures exhibit interesting photoluminescence emissions in the UV regime. The exciton emission of these ion beam modified ZnO nanostructures has been discussed with the aid of X-ray absorption near edge spectroscopy at O K-edge.

Aligned regenerated cellulose-based nanofluidic fibers with ultrahigh ionic conductivity and underwater stability for osmotic energy harvesting

The growing interest in biomass-based nanofluids has revealed flaws in large-scale manufacturing, customizable aligned nanostructures, and the weak interaction of structural components, resulting in low ionic conductivity, unsatisfactory long-term reliability underwater, and insufficient energy conversion efficiency. Herein, we present a bottom-up strategy integrating cellulose dissolution, orientation, regeneration, and densification to construct regenerated cellulose-based nanofluidic fibers (RCNFs) comprising a high weight content of acidified carbon nanotubes (40 %), aligned nanochannels (3–4 nm), and negatively charged surfaces (–3.05 mC m−2). Benefited from the synergistic alignment and spatial confinement of CNTs by the cross-linked cellulose network, the RCNFs realized a high underwater strength (29 MPa), unprecedentedly high ionic conductivity (0.07 S cm−1) at low salt concentrations (<0.001 M), and high long-term output power density (2.57 W m−2 over 43 days) in an artificial river water–seawater system. In a proof-of-concept experiment, customizable RCNF-based devices connected in series powered a calculator and LED lights at a 50-fold concentration gradient. This work can promote the application of regenerated cellulose in high-performance osmotic energy conversion systems.

Taming quantum dots’ nucleation and growth enables stable and efficient blue-light-emitting devices

Controlling quantum dots’ emission, nanostructure, and energy level alignment to achieve stable and efficient blue emission is of great significance for electroluminescence devices but remains a challenge. Here, a series of blue ZnCdSeS/ZnS quantum dots was optimized in preparation by taming their nucleation and growth kinetics. Controlling anion precursor reactive properties to modulate quantum dots’ nucleation and growth tailors their alloy core and continuous gradient energy band nanostructure. These results not only elevate the thermal stability of blue quantum dots but also further enhance the injection/transportation of carriers and improve the radiative recombination efficiency in the device. The blue ZnCdSeS/ZnS quantum dots applied in light-emitting devices show superior performance, including maximum current efficiency and external quantum efficiency of, respectively, 8.2 cd/A and 15.8% for blue, 2.6 cd/A and 10.0% for blue-violet, and 10.9 cd/A and 13.4% for sky-blue devices. The blue and sky-blue devices exhibit lifetimes of more than 10,000 h. The proposed methodology for tailoring quantum dots is expected to pave new guidelines for further facilitating visible optoelectronic device exploration.

Scalar‐Superposition Metasurfaces with Robust Placement of Quantum Emitters for Tailoring Single‐Photon Emission Polarization

AbstractDue to nanometric hotspots in a metallic nanoantenna or phase sensitivities in a metasurface, precise placement of a quantum emitter is rigorously required to tailor single‐photon emission, which considerably increases alignment and fabrication difficulties. Here, a scalar‐superposition metasurface is proposed to achieve robust placement of a quantum emitter and meanwhile tailor the single‐photon emission to a desired polarization (e.g., linear, circular, or elliptical polarization). In this metasurface, the far‐field interference of the scattered fields from all unit nanostructures can be simplified as a scalar‐superposition process. As a result, the emission polarization state is insensitive to the phase or the position of the quantum emitter. The simualtion and experiment show that the placement accuracy of the quantum emitter relative to the center of the metasurface is released to about 3λ (wavelength), which is dozens of times greater than that in previous works. This high placement robustness together with the deflection effect of emission directions of the metasurfaces further enable to tailor the polarization of multiple single‐photon emission spots. The strategy of the scalar‐superposition metasurfaces with robust placement makes the nanostructure design and alignment easy, and it also might provide new possibilities for realizing multifunctional and novel quantum nanophotonic devices.

Study of the Thermoelectric Properties of Bi2Te3/Sb2Te3 Core-Shell Heterojunction Nanostructures.

Thermoelectric materials convert heat energy into electricity, hold promising capabilities for energy waste harvesting, and may be the future of sustainable energy utilization. In this work, we successfully synthesized core-shell Bi2Te3/Sb2Te3 (BTST) nanostructured heterojunctions via a two-step solution route. Samples with different Bi2Te3 core to Sb2Te3 shell ratios could be synthesized by controlling the reaction precursors. Scanning electron microscopy images show well-defined hexagonal nanoplates and the distinct interfaces between Bi2Te3 and Sb2Te3. The similarity of the area ratios with the precursor ratios indicates that the growth of the Sb2Te3 shell mostly took place on the lateral direction rather than the vertical. Transmission electron microscopy revealed the crystalline nature of the as-synthesized Bi2Te3 core and Sb2Te3 shell. Energy-dispersive X-ray spectroscopy verified the lateral growth of a Sb2Te3 shell on the Bi2Te3 core. Thermoelectric properties were measured on pellets obtained from powders via spark plasma sintering with two different directions, in-plane and out-of-plane, showing anisotropic properties due to the nanostructure alignment in the pellets. All samples showed a degenerate semiconducting character with the electrical resistivity increasing with the temperature. Starting from Sb2Te3, the electrical resistivity increases with the increase in amounts of Bi2Te3. Thermal conductivity is lowered due to the increase in interfaces and additional phonon scattering. We show that the out-of-plane direction of the BTST 1-3 sample (where 1-3 indicates the ratio of BT to ST) demonstrates a high Seebeck value of 145 μV/K at 500 K which may be attributed to an energy filtering effect across the heterojunction interfaces. The highest overall zT is observed for the BTST 1-3 sample in the out-of-plane direction at 500 K. The zT values increase continuously over the measured temperature range, indicating a probable higher value at increased temperatures.

A Constrained Assembly Strategy for High-Strength Natural Nanoclay Film.

Developing high-performance materials from existing natural materials is highly desired because of their environmental friendliness and low cost; two-dimensional nanoclay exfoliated from layered silicate minerals is a good building block to construct multilayered macroscopic assemblies for achieving high mechanical and functional properties. Nevertheless, the efforts have been frustrated by insufficient inter-nanosheet stress transfer and nanosheet misalignment caused by capillary force during solution-based spontaneous assembly, degrading the mechanical strength of clay-based materials. Herein, a constrained assembly strategy that is implemented by in-plane stretching a robust water-containing nanoclay network with hydrogen and ionic bonding is developed to adjust the 2D topography of nanosheets within multilayered nanoclay film. In-plane stretching overcomes capillary force during water removal and thus restrains nanosheet conformation transition from nearly flat to wrinkled, leading to a highly aligned multilayered nanostructure with synergistic hydrogen and ionic bonding. It is proved that inter-nanosheet hydrogen and ionic bonding and nanosheet conformation extension generate profound mechanical reinforcement. The tensile strength and modulus of natural nanoclay film reach up to 429.0 MPa and 43.8 GPa and surpass the counterparts fabricated by normal spontaneous assembly. Additionally, improved heat insulation function and good nonflammability are shown for the natural nanoclay film and extend its potential for realistic uses.

Advances in electrospun TiO2 nanofibers: Design, construction, and applications

• Structure control of electrospun TiO 2 NFs through various strategies was summarized. • Mechanical flexibility adjusting of electrospun TiO 2 NFs and related deformation mechanism were discussed. • Multifunctional applications of electrospun TiO 2 NFs in environment, energy, and sensors were introduced. • Current challenges and future perspectives on the development of electrospun TiO 2 NFs were proposed. One dimensional (1D) TiO 2 nanomaterials, as one of the most important semiconductor materials, which have attracted much attention due to their unique structural feature, outstanding optical or electronic properties. Electrospinning is one of the most facile and highly versatile approaches to fabricate 1D TiO 2 nanofibers (NFs) with high porosity, controllable dimensions, designed structures, and adjustable mechanics, which hold great promise in many areas including photocatalytic degradation, solar cells, lithium-ion batteries, water splitting, sensors, and catalyst supports. In this review, progress in structure/mechanics design, fabrication and multifunctional applications of electrospun TiO 2 NFs are presented. The strategies to prepare electrospun TiO 2 NFs with diverse structures involving porous, hollow, hierarchical, aligned, and 3D self-assembled nanostructures are introduced and analyzed. Moreover, the recent breakthrough in the construction of flexible TiO 2 nanofibrous materials and corresponding deformation mechanism have been concerned. Furthermore, some achievements associated with the potential applications of electrospun TiO 2 NFs in the areas of environmental remediation, energy, and sensors are discussed. Finally, a straightforward summary, main challenges and future outlooks about electrospun TiO 2 NFs are proposed. It is anticipated that this review could provide guidelines for designing and constructing novel TiO 2 -based nanofibrous materials for advanced applications.

Micro and Nanopatterned Ion Exchange Membranes for Applications in Electrochemical Devices

Topographical patterns on ion exchange membranes’ (IEMs’) surfaces have been show to improve the performance and energy efficiency in electrochemical energy conversion and water treatment processes. Substituting flat IEMs with patterned/profiled IEMs in electrodialysis reduces spacer channel mass transfer limitations by increasing the interfacial area between the liquid solution and membrane materials. Additionally, the extended surface of the profiled cation-exchange and anion-exchange membranes augment the spacer channel conductivity without obfuscating bulk liquid flow. Topographically patterned ion exchange membranes are fabricated using several methodologies that include photo-/soft-lithography, hot pressing, solution casting and 3D printing. The minimum lateral feature size that can be obtained by these methods is practically on the order of a few microns and potentially could be as low as few hundred nanometers. Block copolymer (BCP) lithography is a nanopatterning platform that generates lateral feature sizes of 5 to 50 nm. Thin films of diblock copolymers can self-assemble on a neutral layer resulting in lamella, cylinder, or sphere morphologies when the film is thermal or solvent vapor annealed. The morphology of the film primarily depends on volume fraction (fA, fB) of each block and interaction parameter between the blocks (χ). Poly(styrene-block-methylmethacrylate) (PS-b-PMMA) is one of the most studied block copolymer for BCP lithography because it form perpendicular aligned nanostructures via thermal annealing without topcoat layers to control the free surface interfacial energy. The etch contrast between the styrene and MMA blocks also makes it easier to transfer the pattern onto substrates – especially if sequential infiltration synthesis (SIS) is used.In this work, for the first time, a method to prepare nanopatterned IEMs using BCP lithography is reported. The SIS process post PS-b-PMMA self-assembly converts MMA into alumina creating organic-inorganic hard mask. The styrene block is removed via oxygen plasma in a reactive ion-etcher leaving behind a nanoporous alumina template on a silicon wafer. Sulfonated poly(arylene ether ether ketone) (SPEEK) is dropcasted onto the nanoporous alumina and the solvent is evaporated. Once releasing the SPEEK from the substrate, a nanopatterned cation-exchange membrane is attained. The electrochemical properties of the nanopatterned membrane such as conductivity, permselectivity and transference number are measured and compared to a flat, non-patterned membrane. The efficiency of these nanopatterned membranes for simple electrochemical devices, like a hydrogen pump, will also be presented.This work is supported from NSF Award # 1703307. Figure 1

Dual-encryption freedom via a monolayer-nanotextured Janus metasurface in the broadband visible.

As an emerging category of two-faced 2D architecture, the Janus metasurface aims to explore another universal optical property, that is, the wavevector direction (k-direction), and to enable the asymmetric transmission between the opposite directional incidences. It exhibits significant potential in creating versatile multiplexing metasurfaces and an optical isolator in optical communication applications. However, most previous asymmetric functionality shows merely one-way functionality with the other-way simply muted or demands multilayered nanostructure fabrication and alignment. Hence, it remains a great challenge to make a monolayer-nanotextured Janus metasurface with dual-encryption freedom and conquering the difficulty for multilayer alignment and practical operation bandwidth. In this work, we have proposed and experimentally demonstrated a new strategy of a dual-encryption Janus metasurface design with a simple monolayer-nanotextured metasurface coupled with a commercialized film of the half-wave plate. Utilizing the hybridization from two independent geometrical dimensions of rectangular-antennas, our approach ingeniously transforms the polarization-multiplexing into the dual-directional channels. A series of calculations and experimental results demonstrate that our asymmetric approach simultaneously constructs completely independent imaging encryptions for both forward and backward directions. Additionally, our proposed approach becomes a practical scheme with broadband visible-frequency operation and great simplicity in design and nanofabrication. We believe the universal scheme could facilitate to increase the information encoding capacity and holographic multiplexing channels by expanding the illumination wavevector to the full-space (+/-), and it paves the route toward the potential applications in on-chip integration, telecommunications, encryption, information processing, and communication.

Tunable and high-performance self-powered ultraviolet detectors using leaf-like nanostructural arrays in ternary tin zinc sulfide system

Recently, self-powered ultraviolet (UV) detectors have received increasing attention for developing the future demands for optoelectronic devices due to their distinguished photoresponse properties. In this study, an emerging type of self-powered UV detectors using the ternary SnxZn1-xS alloy thin films (0.20 ≤ x ≤ 0.40 mol) were fabricated using the solvothermal process. The structural study showed the formation of two distinct phases of ZnS and SnS for the samples with high content Sn2+ ions. According to the ideal crystal-growth mechanism proposed by periodic bond chain theory, a morphological evolution from nanorods to nanoflakes and unique aligned three-dimensional leaf-like nanostructures was achieved by enhancing the Sn2+ content up to the maximum value of 0.40 mol. The optical properties featured the less influence of band tailing on the band gap energy at the high concentration of Sn2+ ions, resulting in the widening of the band gap energy up to 4.56 eV thanks to the Burstein-Moss effect. From the photosensing measurements, the Schottky barrier heights of the devices were found to significantly reduce under UVB exposure as the Sn2+ content increases, confirming a high Ion/Ioff ratio (>103) for the devices. The UV detectors exhibited superior self-powered characteristics under UVB illumination, having high photosensitivity and fast photoswitching response times (τr = 1.9 and τd = 2.6 ms) at zero voltage. Interestingly, the photoresponse performance of UV detectors can be adjusted by varying the content of Sn2+ ions, which signifies that tunable self-powered UV detectors can be designed by varying the Sn2+ concentration in the ternary SnxZn1-xS system.