Rolled-up Structure Research Articles

Flexible Mesopores in Nanoscrolls: Extraordinarily Large Alteration of Pore Sizes and Their Reversibility.

Flexible porous materials have gained considerable interest for their potential applications in selective absorption and controlled release/storage of specific molecules or compounds. Here, nanoscrolls are proposed as a type of inorganic solids with reversibly flexible mesopores. Nanoscrolls exhibit a rolled-up structure composed of nanosheets with a 1D rod-like morphology, possessing two distinct nanospaces. The first space comprises 1D tubular mesopores located at the center of the rod, while the second space exists in the interlayer regions on the wall of the mesopore, resulting from the layer stacking caused by the scrolling of nanosheets. By replacing the interlayer cations on the nanoscroll walls with other cations, a drastic alteration in the size of the 1D mesopores is observed. For instance, exchanging bulky dodecylammonium cations with small NH4 + cations leads to a substantial change in pore size, with differences ranging from 10 to 20nm-a notably larger variation compared to previous reports on flexible porous materials. Importantly, the alteration of pore size induced by the exchange reaction is found to be reversible. This reversible alteration in pore size holds promise for applications in host-guest chemistry involving large moieties such as nanoparticles and enzymes.

Tailored fabrication of a self-rolled-up AlGaN/GaN tubular structure with photoelectrochemical etching.

Group III-nitride semiconductors with tubular structures offer significant potential across various applications, including optics, electronics, and chemical sensors. However, achieving tailored fabrication of these structures remains a challenge. In this study, we present a novel, to the best of our knowledge, method to fabricate micro-sized tubular structures by rolling the layered membrane of group III-nitride alloys utilizing the photoelectrochemical (PEC) etching. To customize the geometry of the tubular structure, we conducted an analytic calculation to predict the strain and deformation for the layered membrane. Based on the calculations, we designed and fabricated an AlGaN/GaN/InGaN/n-GaN/ sapphire structure using metal-organic chemical vapor deposition (MOCVD). Photolithography and PEC etching were employed to selectively etch the sacrificial InGaN layer. We investigated the changes of optical properties of the rolled-up structure by utilizing micro-photoluminescence (µ-PL) and micro-Raman spectroscopy.

Characteristics of a Rollable Dielectric Barrier Discharge Plasma and Its Effects on Spinach-Seed Germination

We investigated the characteristics of a rollable dielectric barrier discharge (RDBD) and evaluate its effects on seed germination rate and water uptake. The RDBD source was composed of a polyimide substrate and copper electrode, and it was mounted in a rolled-up structure for omnidirectional and uniform treatment of seeds with flowing synthetic air gas. The rotational and vibrational temperatures were measured to be 342 K and 2860 K, respectively, using optical emission spectroscopy. The chemical species analysis via Fourier-transform infrared spectroscopy and 0D chemical simulation showed that O3 production was dominant and NOx production was restrained at the given temperatures. The water uptake and germination rate of spinach seeds by 5 min treatment of RDBD was increased by 10% and 15%, respectively, and the standard error of germination was reduced by 4% in comparison with the controls. RDBD enables an important step forward in non-thermal atmospheric-pressure plasma agriculture for omnidirectional seed treatment.

An UWB 3-D Rolled-Up Delay Line for Phased Array Systems in the 5G Sub-6 GHz Frequency Band

To reduce the area occupied by delay lines for the 5G sub-6-GHz frequency band, a 3-D rolled-up structure is presented in this letter. According to the rules proposed in this letter, a conventional planar interdigital delay line is rolled up, transforming the initially planar device into a 3-D spiral geometry. When rolling the device into 1 turn, the area occupied by the rolled-up interdigital delay line is reduced by over 65% while maintaining similar performance to the unrolled device. From 1 to 6 GHz, the return loss of the input and outputs port is greater than 13.1 dB, and the insertion loss is less than 3 dB. The group delay is 1.8 ns±5% over the operating band.

Physical Modeling of Monolithic Self-Rolled-Up Microtube Interdigital Capacitors

This article presents a physical model for monolithic self-rolled-up microtube interdigital capacitors and elaborates their working mechanisms in comparison to on-chip planar interdigital capacitors. Besides the high-frequency phenomena such as the skin effect in thin, wide metal films, the model accounts for the complexities resulting from all possible 3-D electrode configurations, such as the inner diameter-dependent overlapping capacitances and edge capacitances between electrodes, as well as parasitic inductances within the rolled-up structure between the fingers, for integer and noninteger number of turns. The model is validated by the measured results of fabricated self-rolled-up membrane (S-RuM) interdigital capacitors over a wide range of layout and process parameters. This fully enables the structural design optimization for electrical performance of this 3-D device architecture.

Creating Ferroic Micropatterns through Geometrical Transformation.

The functionality of a ferroic device is intimately coupled to the configuration of domains, domain boundaries, and the possibility for tailoring them. Exemplified with a ferromagnetic system, we present a novel approach which allows the creation of new, metastable multidomain patterns with tailored wall configurations through a self-assembled geometrical transformation. By preparing a magnetic layer system on a polymeric platform including swelling layer, a repeated self-assembled rolling into a multiwinding tubular structure and unrolling of the functional membrane is obtained. When polarizing the rolled-up 3D structure in a simple homogeneous magnetic field, the imprinted configuration translates into a regularly arranged multidomain configuration once the tubular structure is unwound. The process is linked to the employed magnetic anisotropy with respect to the surface normal, and the geometrical transformation connects the angular with the lateral degrees of freedom. This combination offers unparalleled possibilities for designing new magnetic or other ferroic micropatterns.

Dependence of the nonlinear optical response of CdSe nanoscrolls on coating with oleic or acetic acid

The photoluminescence and nonlinear transmission of atomically thin population of colloidal CdSe rolled-up nanosheets were investigated at the one-photon stationary excitations of excitons by the third harmonic of Nd3+:YAP laser pulses. It was revealed that the nonlinear optical response of the nanoscrolls is strongly influenced by multiwalled rolled-up structure. The broadening of exciton band and the red shift of the photoluminescence were observed and explained by coupling effect within the folded scroll-layers.

Kelvin-Helmholtz instability in anisotropic viscous magnetized fluid

Kelvin-Helmholtz instability in anisotropic viscous fluid with uniform density in the presence of magnetic field is simulated through solving the non-ideal magnetohydrodynamic equations. The magnetic field is uniform and parallel to the stream. The magnetohydrodynamic equations are solved by corner transport upwind algorithm and constrained transport algorithm. In this paper, the influence of viscous anisotropy on Kelvin-Helmholtz instability is studied. The viscous anisotropy is embodied in the direction of the magnetic field, that is, viscosity parallel to the direction of the magnetic field line is much larger than that in the other directions. The results in the isotropic and the anisotropic viscous cases are compared from the aspects of flow structure, vortex evolution, and magnetic field distribution. It shows that the viscous anisotropy is more advantageous to the stability in a magnetized shear layer than the viscous isotropy. The flow structure evolves similarly in large scales but vortices evolve differently in small scales. Due to the decrease of the shear rate in the direction of the magnetic field lines, the rolling-up degree of interface and the number of laps decrease; the multiplication and merging of small vortices in the rolled-up structure destroy the regular growth of the vortex, which contributes to the stability of the flow. The increase of the magnetic energy at the sheared interface slows down effectively by the viscous anisotropy, which weakens the growth of the transverse magnetic pressure and anti-bending magnetic tension. However, viscous anisotropy shows much greater influence on the transverse magnetic pressure than on the anti-bending magnetic tension. The total enstrophy decreases slowly in viscous isotropy and anisotropy case. It increases quickly in late time in the former case, but is heavily suppressed in the latter case.

Transforming Monolayer Transition-Metal Dichalcogenide Nanosheets into One-Dimensional Nanoscrolls with High Photosensitivity.

One-dimensional (1D) nanoscrolls derived from two-dimensional (2D) nanosheets own unusual physical and chemical properties that arise from the spiraled 1D morphology and the atomic thin 2D building blocks. Unfortunately, preparation of large-sized nanoscrolls of transition-metal dichalcogenides (TMDCs) remains a big challenge, which greatly restricts the fabrication of single-scroll devices for their fundamental studies and further applications. In this work, we report a universal and facile method, by making use of the evaporation process of volatile organic solvent, to prepare TMDC (e.g., MoS2 and WS2) nanoscrolls with lengths of several tens to one hundred micrometers from their 2D precursors presynthesized by chemical vapor deposition on Si/SiO2. Both atomic force microscopy and electron microscopy characterizations confirmed the spirally rolledup structure in the resulting nanoscrolls. An interlayer spacing of as small as ∼0.65 nm was observed, suggesting the strong coupling between adjacent layers, which was further evidenced by the emergence of new breathing mode peaks in the ultralow frequency Raman spectrum. Importantly, compared with the photodetector fabricated from a monolayer MoS2 or WS2 nanosheet, the device based on an MoS2 or WS2 nanoscroll showed the much enhanced performance, respectively, with the photosensitivity greatly increased up to 2 orders of magnitude. Our work suggests that turning 2D TMDCs into 1D scrolls is promising in achieving high performances in various electronic/optoelectronic applications, and our general method can be extended to the preparation of large-sized nanoscrolls of other kinds of 2D materials that may bring about new properties and phenomena.

Transfer and Dynamic Inversion of Coassembled Supramolecular Chirality through 2D-Sheet to Rolled-Up Tubular Structure.

Transfer and inversion of supramolecular chirality from chiral calix[4]arene analogs (3D and 3L) with an alanine moiety to an achiral bipyridine derivative (1) with glycine moieties in a coassembled hydrogel are demonstrated. Molecular chirality of 3D and 3L could transfer supramolecular chirality to an achiral bipyridine derivative 1. Moreover, addition of 0.6 equiv of 3D or 3L to 1 induced supramolecular chirality inversion of 1. More interestingly, the 2D-sheet structure of the coassembled hydrogels formed with 0.2 equiv of 3D or 3L changed to a rolled-up tubular structure in the presence of 0.6 equiv of 3D or 3L. The chirality inversion and morphology change are mainly mediated by intermolecular hydrogen-bonding interactions between the achiral and chiral molecules, which might be induced by reorientations of the assembled molecules, confirmed by density functional theory calculations.

Piezoelectrically and triboelectrically hybridized self-powered sensor with applications to smart window and human motion detection

In this paper, we demonstrate a hybrid generator, derived from the concurrent adoption of piezoelectric and triboelectric mechanisms in one press-and-release cycle, called a Hybridized Self-Powered sensor (HSPS). A new integration of print circuit board (PCB) technology-based piezoelectric generator (PG) concurrently adopted the direct-write, near-field electrospun polyvinylidene fluoride (PVDF) nano/micro-fibers as piezoelectric source materials. On the other hand, triboelectric nanogenerators have the advantages of a high output performance with a simple structure which is also concurrently combined with the PG. The working mechanism of the HSPS includes the PCB-based substrate mounted with parallel aligned piezoelectric PVDF fibers in planar configuration which first bended and generated the electric potential via the effect of piezoelectricity. In what follows, the deformation of a cylindrical rolled-up piezoelectric structure is exercised, and finally, the triboelectric contact of Cu and PTFE layers is physically rubbed against each other with a separation to induce the triboelectric potential. This hybridized generator with a double domed shape design simultaneously combines piezoelectric output and triboelectric output and offers a built-in spacer with automatically spring back capability, which produces a peak output voltage of 100 V, a current of 4 μA, and a maximum power output of 450 nW. A self-powered smart window system was experimentally driven through finger-induced strain of HSPS, showing the optical properties with reversibly tunable transmittances. This research is a substantial advancement in the field of piezoelectric PVDF fibers integration toward the practical application of the whole self-powered system.

Single cell detection using 3D magnetic rolled-up structures

A 3D rolled-up structure made of a SiO2 layer and a fishbone-like magnetic thin film was proposed here as a biosensor. The magnetoresistance (MR) measurement results of the sensor suggest that the presence of the stray field, which is induced by the magnetic nanoparticles, significantly increased the switching field. Comparing the performance of the 2D sensor and 3D sensor designed in this study, the response in switching field variation was 12.14% in the 2D sensor and 62.55% in the 3D sensor. The response in MR ratio variation was 4.55% in the 2D sensor and 82.32% in the 3D sensor. In addition, the design of the 3D sensor structure also helped to attract and trap a single magnetic cell due to its stronger stray field compared with the 2D structure. The 3D magnetic biosensor designed here can provide important information for future biochip research and applications.

A nanofibrous hydrogel templated electrochemical actuator: From single mat to a rolled-up structure

A flexible conducting polymer actuator was fabricated using an electrospun poly(vinyl alcohol) (PVA) nanofibrous mat followed by in situ chemical polymerization with aniline. The PVA/polyaniline (PVA/PANi) hybrid mat consisted of nanostructured PANi grown on the surface of individual PVA nanofibers. The resulting structure with large surface area and porosity enabled the easy diffusion of ions to cause efficient electrochemical reaction. The PVA/PANi hybrid mat showed an electrical conductivity of 2.35 S/cm and a single strip produced a maximum linear actuation strain of 1.8% while cycling the potential between specified ranges in 1 M methane sulfonic acid solution. The hybrid mat could be stably actuated during extended electrochemical cycling up to 250 cycles. Actuation performance of the hybrid fibrous mat (for a single strip) was explained from the viewpoint of mechanical properties, and it was demonstrated that the flexible structure can generate higher strain than the brittle structure such as a carbon nanotube/conducting polymer composite actuator. Based on the flexible nature and the mechanical stability provided by highly entangled hydrogel nanofibers, the PVA/PANi hybrid mat was conveniently rolled-up into multilayered assembly of cylindrical structures. The interlayer spacing of the rolled-up structure and the huge surface area per unit volume accessible to electrolytes contributed to high current and enabled enhanced actuation performance and fast response.

Application of Vortex Invariants to Roll Up of Vortex Pairs

A method developed by Betz for the rolled-up structure of vortices shed by isolated wing tips is extended to vortex pairs (two vortical regions of opposite sign), which are shed by wings of finite span. The present analysis again uses the invariants for the two-dimensional time-dependent motion of vortex systems, but the extension made here to vortex pairs depends primarily on the invariant for kinetic energy. It is found that the total energy in the flowfield can be separated into a part that governs the structure of each vortical region and a part that governs the spanwise distance between the centroids of the vortical regions. As a consequence, the rules for the rolled-up structure of vortical regions are the same as the one derived by Betz. Because the analysis does not apply a constraint that forces the circular contours of constant circulation to coincide with streamline paths, the solution is labeled first order. A method that can be used to obtain second- and higher-order approximations is described. Application of the first-order method to the vortex wake of an elliptically loaded wing indicates that a first-order solution for vortex pairs is adequate for many engineering purposes. The method derived here for single vortex pairs also justifies the superposition of axially symmetric vortical cores to simulate complex vortex wakes.

On the Inviscid Rolled-Up Structure of Lift-Generated Vortices

A simple form is presented of the relationships for the inviscid, fully developed structure of lift-generated vortices behind aircraft wings. The method is then extended to arbitrary span-load distributions by inferring guidelines for the selection of rollup centers for the vortex sheet, along with rules for calculating the fully developed structure of the resulting multiple vortices. These techniques yield realistic estimates of the rolled-up structure of vortices produced by a wider variety of span-load distributions than possible with the original form of the theory.