Vertically Oriented Porous PET as Template to Integrated Metal Halide for High-Performance Large-Area and Ultra-Flexible X-Ray Detector.

High-performance X-ray detectors have immense potential in medical and security inspections. However, the current X-ray detectors are limited in flexible, high-spatial-resolution large-scale detection, and integration for imaging. Here, nuclear track-etched porous polyethylene terephthalate (PET) is developed as the template for preparing uniform, large-area (≥105 cm2 ), and flexible metal halide (MH)-based X-ray detectors. Adjustable high-density vertically oriented porous PET with adjustable thickness can provide proper physical support for flexible thick absorption film, thus improving X-ray absorption ability with excellent bending stability. Moreover, vertical channels can block the ion migration, lateral charge diffusion, and water/oxygen attacks, increasing activation energy for ionic transport, charge collection rate of electrodes, and environmental stability. Hence, the related detectors eventually obtain large sensitivity (6722 µC Gyair -1 cm-2 ), low detection limit (1.87 nGyair s-1 ), and high spatial resolution (5.17 lp mm-1 ) compared to the detectors without porous PET template. Meanwhile, the device shows no degradation after storage or working under various thermal attacks. MH-filled-PET is also monolithically integrated on the bottom circuit with different MHs and it is applied to single-pixel mode and fast linear-array imaging in a broad range of X-rays photon energy (20 to 160 keV).

Elliptical gold nanowires: controlled fabrication and plasmonic Fabry-Pérot resonances.

Nanowires (NWs) are essential building blocks of photonic devices for guiding light waves. However, the controlled synthesis of non-circular NWs remains challenging. Herein, we develop a bottom-up approach for the fabrication of high-quality elliptical gold NWs with finely tuned geometry engineering by using an advanced ion-track template technology. Compared to ordinary NWs, the rotational symmetry breaking leads to highly polarization-dependent plasmonic responses. Modal analysis shows that the lowest dipolar HE1 mode splits into two branches where the attenuation of the long-range branch decreases by 40%, while the short-range branch has a stronger enhanced near-field. Novel, to the best of our knowledge, plasmonic Fabry-Pérot resonances on finite NWs are measured. Our method can be extended to fabricate non-circular NWs with other materials, holding potential for novel applications from quantum to collective scales.

Metric-Torsion Duality of Optically Chiral Structures.

We develop a metric-torsion theory for chiral structures by using a generalized framework of transformation optics. We show that the chirality is uniquely determined by a metric with the local rotational degree of freedom. In analogy to the dislocation continuum, the chirality can be alternatively interpreted as the torsion tensor of a Riemann-Cartan space, which is mimicked by the anholonomy of the orthonormal basis. As a demonstration, we reveal the equivalence of typical three-dimensional chiral metamaterials in the continuum limit. Our theory provides an analytical recipe to design optical chirality.

Mechanical metamaterials made of freestanding quasi-BCC nanolattices of gold and copper with ultra-high energy absorption capacity.

Nanolattices exhibit attractive mechanical properties such as high strength, high specific strength, and high energy absorption. However, at present, such materials cannot achieve effective fusion of the above properties and scalable production, which hinders their applications in energy conversion and other fields. Herein, we report gold and copper quasi-body centered cubic (quasi-BCC) nanolattices with the diameter of the nanobeams as small as 34 nm. We show that the compressive yield strengths of quasi-BCC nanolattices even exceed those of their bulk counterparts, despite their relative densities below 0.5. Simultaneously, these quasi-BCC nanolattices exhibit ultrahigh energy absorption capacities, i.e., 100 ± 6 MJ m-3 for gold quasi-BCC nanolattice and 110 ± 10 MJ m-3 for copper quasi-BCC nanolattice. Finite element simulations and theoretical calculations reveal that the deformation of quasi-BCC nanolattice is dominated by nanobeam bending. And the anomalous energy absorption capacities substantially stem from the synergy of the naturally high mechanical strength and plasticity of metals, the size reduction-induced mechanical enhancement, and the quasi-BCC nanolattice architecture. Since the sample size can be scaled up to macroscale at high efficiency and affordable cost, the quasi-BCC nanolattices with ultrahigh energy absorption capacity reported in this work may find great potentials in heat transfer, electric conduction, catalysis applications.

Double-sided plasmonic metasurface for simultaneous biomolecular separation and SERS detection.

Porous membrane-based nanofiltration separation of small biomolecules is a widely used biotechnology for which size-based selectivity is a critical parameter of technological relevance. Efficient determination of size selectivity calls for an advanced detection method capable of performing sensitive, rapid, and on-membrane examination. Surface-enhanced Raman spectroscopy (SERS) is such a detection method that has been widely recognized as an ultrasensitive technique for trace-level detection with sensitivity down to the single-molecule level. In this work, we for the first time develop a double-sided hierarchical porous membrane-like plasmonic metasurface to realize high-selectivity bimolecular separation and simultaneous ultrasensitive SERS detection. This highly flexible device, consisting of subwavelength nanocone pairs surrounded by randomly orientated sub-5 nm nanogrooves, was prepared by combining customized "top-down" fabrication of conical nanopores in an ion-track registered polycarbonate membrane and self-assembly of nanogrooves on the membrane surface through physical vapor deposition. The unique tip-to-tip oriented conical nanopores in the device enables excellent size-based molecular selectivity; the hierarchical groove-pore structure supports a peculiar cascaded electromagnetic near-field enhancement mechanism, endowing the device with SERS-based molecular detection of ultrahigh sensitivity, uniformity, repeatability, and polarization independence. With such dual structural merits and performance enhancement, we demonstrate effective nanofiltration separation of small-sized adenine from big-sized ss-DNA and synergistic SERS determination of their species. We experimentally demonstrate an ultrasensitive detection of 4-mercaptopyridine down to 10 pM. Together with its unparalleled mechanical flexibility, this double-side-responsive plasmonic metasurface membrane can find great potential in real-world molecular filtration and detection under extremely complex working conditions.

Direct Fabrication of PET-Based Thermotolerant Separators for Lithium-Ion Batteries with Ion Irradiation Technology.

Lithium-ion batteries (LIBs) play a pivotal role as essential components in various applications, including mobile devices, energy storage power supplies, and electric vehicles. The widespread utilization of LIBs underscores their significance in the field of energy storage. High-performance LIBs should exhibit two key characteristics that have been persistently sought: high energy density and safety. The separator, a critical part of LIBs, is of paramount importance in ensuring battery safety, thus requiring its high thermal stability and uniform nanochannels. Here, the novel ion-track etched polyethylene terephthalate (ITE PET) separator is controllably fabricated with ion irradiation technology. Unlike conventional polypropylene (PP) separators, the ITE PET separator demonstrated vertically aligned nanochannels with uniform channel size and distribution. The remarkable characteristics of the ITE PET separator include not only high electrolyte wettability but also exceptional thermal stability, capable of withstanding temperatures as high as 180 °C. Furthermore, the ITE PET separator exhibits a higher lithium-ion transfer number (0.59), which is advantageous in enhancing battery performance. The structural and inherent advantages of ITE PET separators contribute to enhance the C-rate capacity, electrochemical, and long-term cycling (300 cycles) stability observed in the corresponding batteries. The newly developed method for fabricating ITE PET separators, which possess high thermal stability and a uniform channel structure, fulfills the demand for high-temperature-resistant separators without requiring any modification procedures. Moreover, this method can be easily scaled up using simple processes, making it a competitive strategy for producing thermotolerant separators.

High-Performance Osmotic Power Generators Based on the 1D/2D Hybrid Nanochannel System.

Extracting clean energy by converting the salinity gradient between river and sea into energy is an effective way to reduce the global pollution and carbon emissions. Reverse electrodialysis (RED) is of great importance to realize the energy conversion assisting the ion-selective membrane. However, its higher ion resistance and lower conversion efficiency results in the undesirable power conversion performance. Here, we demonstrate a 1D/2D hybrid nanochannel system to achieve high osmotic energy conversion and output power. This heterogeneous structure is composed of two structures, in which the subnanometer nanochannels in graphene oxide membrane (GOM) can serve as a selective layer and reduce the ion diffusion energy barrier, while the nanochannel in the polymer can introduce asymmetry to enhance ionic rectification and conversion efficiency. This heterogeneous membrane exhibits excellent cation selectivity and enhanced ionic current rectification (ICR) performance. The application of the GOM/PET hybrid nanochannel system in osmotic energy harvesting is evaluated, and the output power can reach up to 118.2 pW with the energy conversion efficiency of 40.3%. Theoretical calculation indicates that the 1D/2D hybrid system can effectively take the advantage of excellent cation selectivity of 2D lamellar nanochannels to improve its RED performance significantly.

Fast synthesis of gold nanostar SERS substrates based on ion-track etched membrane by one-step redox reaction.

Surface-enhanced Raman scattering (SERS), due to its high detecting sensitivity and rapid data acquisition ability, has been considered as a powerful technique for label-free ultrasensitive detection of chemical and biochemical analytes. As an important part, the uniform SERS substrate is the prerequisite for this technology being used in all the related areas. Therefore, seeking the fast, convenient and low-cost way to obtain the SERS substrate with high performance and reproducibility never stops in recent decades. In this work, the PC membrane with uniform nanopores obtained by ion irradiation and chemical etching (i.e., ion-track etched PC membrane) was first used to prepare the gold nanostar SERS substrate. The monolayer gold nanostars can be obtained through a one-step redox reaction on the surface of the PC membrane, which not only can act as the base of SERS substrate but also can work as the reaction adjuster. By optimizing the growth conditions, the SERS substrate with uniform monolayer gold nanostars can be fabricated without any complicated procedures and costly equipment fast (in 20 mins). Meanwhile, the prepared flexible gold nanostar SERS substrate exhibits excellent Raman performance, which can effectively detect the analyte R6G with the concentration as low as 1 × 10-10 M and the SERS enhancement factors can be around 3.70 × 105. The new facile SERS substrate preparation method is cost-effective, convenient, fast and easily scale up, which can satisfy the requests of the real applications in many fields.

Ionic Transport and Sieving Properties of Sub-nanoporous Polymer Membranes with Tunable Channel Size.

Bioinspired nanoporous membranes show great potential in ionic separation and water filtration by offering high selectivity with less permeation resistance. However, complex processes always limit their applications. Here, we report a convenient approach to introduce ionic selective channels in a micron-thick polycarbonate membrane through swift heavy ion irradiation accompanied by UV sensitization and pulsed-electrical etching. The characteristic dimension of channels was tuned through regulating energy loss of the incident ion and UV sensitization time of the membrane, resulting in the sub-nanoporous membranes with mean channel diameter ranging from <2.4 to 9.7 Å. These membranes showed the voltage-activated ionic transport properties associated with the dehydration effect, and the corresponding I-V characteristics were related to ionic strength, solution pH, ionic type, and channel diameter. It was found that the transmembrane conduction of multivalent ions was severely suppressed compared to monovalent ions, until the size of the membrane channel was comparable to the hydrated diameter of multivalent ions. Ionic sieving experiments also demonstrated the excellent ionic valence selectivity of the membrane. Even for the membrane with a channel diameter close to 1 nm, the Li+/Mg2+ separation ratio was still as high as 40, and an even higher separation ratio was found for Li+/La3+ (>3000).

Controlled crystallinity and crystallographic orientation of Cu nanowires fabricated in ion-track templates.

The hallmark of materials science is the ability to tailor the structures of a given material to provide a desired response. In this work, the structures involving crystallinity and crystallographic orientation of Cu nanowires electrochemically fabricated in ion-track templates have been investigated as a function of fabrication condition. Both single crystalline and polycrystalline nanowires were obtained by adjusting applied voltages and temperatures of electrochemical deposition. The anti-Hall-Petch effect was experimentally evidenced in the polycrystalline nanowires. The dominant crystallographic orientations of wires along [111], [100], or [110] directions were obtained by selecting electrochemical deposition conditions, i.e., H(2)SO(4) concentration in electrolyte, applied voltage, and electrodeposition temperature.

Parallel Aligned Nickel Nanocone Arrays for Multiband Microwave Absorption.

Magnetic nanostructures with conical shape are highly desired for pursuing extraordinary magnetic properties and microwave absorption. However, the fabrication of such nanostructures with controlled shape and size uniformities and alignment is not yet realized. Accordingly, the magnetic properties and their application as microwave absorber are not well understood. Here, we report on the first demonstration of controlled fabrication of soft magnetic nickel nanocone arrays with sharp geometry, large aspect ratio, uniform size, and parallel alignment. The imaginary part of the relative complex permeability shows multiband absorption in the 2-17 GHz range. Such an exceptional microwave absorption results from the uniform conical shape and size and the parallel alignment. The absorption mechanisms are discussed under the framework of natural resonance and exchange resonance. The natural resonance is dependent on the shape anisotropy and facilitated by the conical geometry. The exchange resonance is well explained by the observation of the bulk spin waves with exchange coupling at the tip of nanocones using the inelastic light scattering and is consistent with exchange theory predictions for the quantization of bulk spin waves. We expect that our work will shed light on the physical insights into the magnetic properties of nanocones and find great potential in applications of microwave absorption.

Selectively Enhanced Ion Transport in Graphene Oxide Membrane/PET Conical Nanopore System.

Graphene oxide (GO) has become a promising 2D material in many areas, such as gas separation, seawater desalination, antibacterial materials, and so on because of its abundant oxygen-containing functional groups and excellent dispersibility in various solvents. The graphene oxide membrane (GOM), a laminar and channel-rich structure assembled by stacked GO nanosheets, served as a kind of precise and ultrafast separation material has attracted widespread attention in membrane separation field. To break the trade-off between ion permeability and ion selectivity of separation membrane based on GOM, GOM/conical nanopore system is obtained by spin-coating ultrathin GOM on PET conical nanopore, which possesses ion rectification property. Comparing to pure PET conical nanopore, the existence of GOM not only enhances the cation conductance but also makes the ion rectification ratio increase from 4.6 to 238.0 in KCl solution. Assisted by COMSOL simulation, it is proved that the GOM can absorb large amount of cations and act as cation source to improve the ion selectivity and rectification effect of GOM/conical nanopore system. Finally, the chemical stability of GOM/conical nanopore is also investigated and the corresponding results reveal that the GOM/conical nanopore system can perform the ion rectification behavior in a wider pH range than pure PET conical nanopore. The presented findings demonstrate the great potential applications of GOM/conical nanopore system in ionic logic circuits and sensor systems.

Large Rectification Effect of Single Graphene Nanopore Supported by PET Membrane.

Graphene is an ideal candidate for the development of solid state nanopores due to its thickness at the atomic scale and its high chemical and mechanical stabilities. A facile method was adopted to prepare single graphene nanopore supported by PET membrane (G/PET nanopore) within the three steps assisted by the swift heavy ion irradiation and asymmetric etching technology. The inversion of the ion rectification effect was confirmed in G/PET nanopore while comparing with bare PET nanopore in KCl electrolyte solution. By modifying the wall charge state of PET conical nanopore with hydrochloric acid from negative to positive, the ion rectification effect of G/PET nanopore was found to be greatly enhanced and the large rectification ratio up to 190 was obtained during this work. Moreover, the high ionic flux and high ion separation efficiency was also observed in the G/PET nanopore system. By comparing the "on" and "off" state conductance of G/PET nanopore while immersed in the solution with pH value lower than the isoelectric point of the etched PET (IEP, pH = 3.8), the voltage dependence of the off conductance was established and it was confirmed that the large rectification effect was strongly dependent on the particularly low off conductance at higher applied voltage.

Surface Modification and Damage of MeV-Energy Heavy Ion Irradiation on Gold Nanowires.

Gold nanowires with diameters ranging from 20 to 90 nm were fabricated by the electrochemical deposition technique in etched ion track polycarbonate templates and were then irradiated by Xe and Kr ions with the energy in MeV range. The surface modification of nanowires was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations. Different craters with and without protrusion on the gold nanowires were analyzed, and the two corresponding formation mechanisms, i.e., plastic flow and micro-explosion, were investigated. In addition, the sputtered gold nanoparticles caused by ion irradiation were studied and it was confirmed that the surface damage produced in gold nanowires was increased as the diameter of the nanowires decreased. It was also found that heavy ion irradiation can also create stacking fault tetrahedrons (SFTs) in gold nanowires and three different SFTs were confirmed in irradiated nanowires. A statistical analysis of the size distribution of SFTs in gold nanowires proved that the average size distribution of SFT was positively related to the nuclear stopping power of incident ions, i.e., the higher nuclear stopping power of incident ions could generate SFT with a larger average size in gold nanowires.

Temperature- and Angle-Dependent Magnetic Properties of Ni Nanotube Arrays Fabricated by Electrodeposition in Polycarbonate Templates.

Parallel arrays of Ni nanotubes with an external diameter of 150 nm, a wall thickness of 15 nm, and a length of 1.2 ± 0.3 µm were successfully fabricated in ion-track etched polycarbonate (PC) templates by electrochemical deposition. The morphology and crystal structure of the nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Structural analyses indicate that Ni nanotubes have a polycrystalline structure with no preferred orientation. Angle dependent hysteresis studies at room temperature carried out by using a vibrating sample magnetometer (VSM) demonstrate a transition of magnetization between the two different magnetization reversal modes: curling rotation for small angles and coherent rotation for large angles. Furthermore, temperature dependent magnetic analyses performed with a superconducting quantum interference device (SQUID) magnetometer indicate that magnetization of the nanotubes follows modified Bloch's law in the range 60-300 K, while the deviation of the experimental curve from this law below 60 K can be attributed to the finite size effects in the nanotubes. Finally, it was found that coercivity measured at different temperatures follows Kneller's law within the premises of Stoner-Wohlfarth model for ferromagnetic nanostructures.

Controlled Structure of Electrochemically Deposited Pd Nanowires in Ion-Track Templates.

Understanding and controlling structural properties of the materials are crucial in materials research. In this paper, we report that crystallinity and crystallographic orientation of Pd nanowires can be tailored by varying the fabrication conditions during electrochemical deposition in polycarbonate ion-track templates. By changing the deposition temperature during the fabrication process, the nanowires with both single- and poly-crystallinities were obtained. The wires with preferred crystallographic orientations along [111], [100], and [110] directions were achieved via adjusting the applied voltage and temperature during electrochemical deposition.