Scalable Synthesis of Switchable Assemblies of Gold Nanorod Lyotropic Liquid Crystal Nanocomposites

A new class of solvent free, lyotropic liquid crystal nanocomposites based on gold nanorods (AuNRs) with high nanorod content is reported. Application of shear results in switchable, highly ordered alignment of the nanorods over several centimeters with excellent storage stability for months. For the synthesis, AuNRs are surface functionalized with a charged, covalently tethered corona, which induces fluid‐like properties. This honey‐like material can be deposited on a substrate and a high orientational order parameter of 0.72 is achieved using a simple shearing protocol. Switching shearing direction results in realignment of the AuNRs. For a film containing 75 wt% of AuNRs the alignment persists for several months. In addition to the lyotropic liquid crystal characteristics, the AuNRs films also exhibit anisotropic electrical conductivity with an order of magnitude difference between the conductivities in direction parallel and perpendicular to the alignment of the AuNRs.     

Unveiling the Dynamical Assembly of Magnetic Nanocrystal Zig‐Zag Chains via In Situ TEM Imaging in Liquid

The controlled assembly of colloidal magnetic nanocrystals is key to many applications such as nanoelectronics, storage memory devices, and nanomedicine. Here, the motion and ordering of ferrimagnetic nanocubes in water via liquid‐cell transmission electron microscopy is directly imaged in situ. Through the experimental analysis, combined with molecular dynamics simulations and theoretical considerations, it is shown that the presence of highly competitive interactions leads to the formation of stable monomers and dimers, acting as nuclei, followed by a dynamic growth of zig‐zag chain‐like assemblies. It is demonstrated that such arrays can be explained by first, a maximization of short‐range electrostatic interactions, which at a later stage become surpassed by magnetic forces acting through the easy magnetic axes of the nanocubes, causing their tilted orientation within the arrays. Moreover, in the confined volume of liquid in the experiments, interactions of the nanocube surfaces with the cell membranes, when irradiated at relatively low electron dose, slow down the kinetics of their self‐assembly, facilitating the identification of different stages in the process. The study provides crucial insights for the formation of unconventional linear arrays made of ferrimagnetic nanocubes that are essential for their further exploitation in, for example, magnetic hyperthermia, magneto‐transport devices, and nanotheranostic tools.     

Memory effect in an ionic liquid matrix containing single-walled carbon nanotubes and polystyrene

We report the use of an ionic liquid (IL) gel matrix containing a blend of single-walled carbon nanotubes (SWNTs) and polystyrene (PS) as a memory device. SWNTs and PS beads were mixed in a room-temperature IL, 1-butyl-3-methyl-hexafluorophosphate ([BMIM][PF(6)]). The composite gel was sandwiched between a bottom ITO glass and a top aluminium electrode. By merely changing the concentrations of SWNTs in the inert insulating PS matrix, we observed several distinct electrical properties of the device, such as an insulator, a memory in terms of switching and negative differential resistance (NDR), and a conductor. The electric bistable switching hops between a higher impedance (OFF) state and a lower impedance (ON) state which is approximately equal to five orders of current decays.     

Springtail‐Inspired Superamphiphobic Ordered Nanohoodoo Arrays with Quasi‐Doubly Reentrant Structures

The skin of springtails is well‐known for being able to repel water and organic liquids using their hexagonally arranged protrusions with reentrant structures. Here, a method to prepare 100 nm‐sized nanohoodoo arrays with quasi‐doubly reentrant structures over square centimeters through combining the nanosphere lithography and the template‐protected selective reactive ion etching technique is demonstrated. The top size of the nanohoodoos, the intra‐nanohoodoo distance, and the height of the nanohoodoos can be readily controlled by the plasma‐etching time of the polystyrene (PS) spheres, the size of the PS spheres used, and the reactive ion etching time of silicon. The strong structural control capability allows for the study of the relationship between the nanohoodoo structure and the wetting property. Superamphiphobic nanohoodoo arrays with outstanding water/organic liquid repellent properties are finally obtained. The superamphiphobic and liquid repellent properties endow the nanohoodoo arrays with remarkable self‐cleaning performance even using hot water droplets, anti‐fogging performance, and the surface‐enhanced Raman scattering sensitivity improvement by enriching the analyte molecules on the nanohoodoo arrays. Overall, the simple and massive production of the superamphiphobic nanohoodoo structures will push their practical application processes in diverse fields where wettability and liquid repellency need to be carefully engineered.     

A UV‐Responsive Multifunctional Photoelectric Device Based on Discotic Columnar Nanostructures and Molecular Motors

Orientation control of ordered materials would not only produce new physical phenomenon but also facilitate the development of fancy devices. Discotic liquid crystals (DLCs) form 1D charge transport pathway by self‐organizing into columnar nanostructures via π–π stacking. However, controlling the electrical properties in such nanostructures with some direct and instant way is a formidable task for their high viscosity and insensitivity to external stimuli. Herein, the arbitrary control over electrical conductivity of such columnar nanostructures is achieved with UV light by incorporating DLCs with molecular motors. Highly ordered DLC microstripe arrays are generated on desired substrate through a capillary bridge dewetting strategy. The conductivity of the microstripes could be continuously modulated by 365 nm light due to the influence of molecular motion under UV irradiation on the electron orbital overlap of columnar nanostructures. This is so because the disorder degree of the DLC molecules is associated with the intensity of UV light and the doping concentration of molecular motors. Moreover, the device shows memory effect and reversible conductivity change. The DLC microstripe arrays are very promising for the applications in UV detectors, memory devices, optical switches, and so on.     

电化学刻蚀参数对高阻厚壁宏孔硅阵列表面形貌的影响

采用光电化学刻蚀方法,在电阻率为4～5 kΩ·cm的n-型[100]单晶硅片上制备了厚壁有序宏孔硅阵列。通过对比有限元法模拟诱导坑周围的电场分布,研究了刻蚀参数(电解液、光照、电压)对阵列表面形貌的影响。在刻蚀成孔的过程中,诱导坑对孔的限制受电场分布和实验条件的共同影响,出现刻蚀偏离的现象。模拟结果显示,诱导坑上的电场强度沿着单晶硅的[100]和[110]晶向的分布。这种分布的结果是,随着光照强度的提高和刻蚀溶液表面自由能的降低刻蚀由原光刻图形的(110)面向(100)面偏离。提高刻蚀电压可抑制刻蚀偏离,有利于诱导坑快速刻蚀成孔,从而形成规整的厚壁宏孔硅阵列。     

Iodine Vacancy Redistribution in Organic–Inorganic Halide Perovskite Films and Resistive Switching Effects

Organic–inorganic halide perovskite (OHP) materials, for example, CH₃NH₃PbI₃ (MAPbI₃), have attracted significant interest for applications such as solar cells, photodectors, light‐emitting diodes, and lasers. Previous studies have shown that charged defects can migrate in perovskites under an electric field and/or light illumination, potentially preventing these devices from practical applications. Understanding and control of the defect generation and movement will not only lead to more stable devices but also new device concepts. Here, it is shown that the formation/annihilation of iodine vacancies (V_I's) in MAPbI₃ films, driven by electric fields and light illumination, can induce pronounced resistive switching effects. Due to a low diffusion energy barrier (≈0.17 eV), the V_I's can readily drift under an electric field, and spontaneously diffuse with a concentration gradient. It is shown that the V_I diffusion process can be suppressed by controlling the affinity of the contact electrode material to I^? ions, or by light illumination. An electrical‐write and optical‐erase memory element is further demonstrated by coupling ion migration with electric fields and light illumination. These results provide guidance toward improved stability and performance of perovskite‐based optoelectronic systems, and can lead to the development of solid‐state devices that couple ionics, electronics, and optics.     

Complementary Resistive Switching Using Metal–Ferroelectric–Metal Tunnel Junctions

Complementary resistive switching (CRS) devices are receiving attention because they can potentially solve the current‐sneak and current‐leakage problems of memory arrays based on resistive switching (RS) elements. It is shown here that a simple anti‐serial connection of two ferroelectric tunnel junctions, based on BaTiO₃, with symmetric top metallic electrodes and a common, floating bottom nanometric film electrode, constitute a CRS memory element. It allows nonvolatile storage of binary states (“1” = “HRS+LRS” and “0” = “LRS+HRS”), where HRS (LRS) indicate the high (low) resistance state of each ferroelectric tunnel junction. Remarkably, these states have an identical and large resistance in the remanent state, characteristic of CRS. Here, protocols for writing information are reported and it is shown that non‐destructive or destructive reading schemes can be chosen by selecting the appropriate reading voltage amplitude. Moreover, this dual‐tunnel device has a significantly lower power consumption than a single ferroelectric tunnel junction to perform writing/reading functions, as is experimentally demonstrated. These findings illustrate that the recent impressive development of ferroelectric tunnel junctions can be further exploited to contribute to solving critical bottlenecks in data storage and logic functions implemented using RS elements.     

High-efficiency ordered silicon nano-conical-frustum array solar cells by self-powered parallel electron lithography

Nanostructured silicon thin film solar cells are promising, due to the strongly enhanced light trapping, high carrier collection efficiency, and potential low cost. Ordered nanostructure arrays, with large-area controllable spacing, orientation, and size, are critical for reliable light-trapping and high-efficiency solar cells. Available top-down lithography approaches to fabricate large-area ordered nanostructure arrays are challenging due to the requirement of both high lithography resolution and high throughput. Here, a novel ordered silicon nano-conical-frustum array structure, exhibiting an impressive absorbance of 99% (upper bound) over wavelengths 400-1100 nm by a thickness of only 5 μm, is realized by our recently reported technique self-powered parallel electron lithography that has high-throughput and sub-35-nm high resolution. Moreover, high-efficiency (up to 10.8%) solar cells are demonstrated, using these ordered ultrathin silicon nano-conical-frustum arrays. These related fabrication techniques can also be transferred to low-cost substrate solar energy harvesting device applications.     

Physically Transient Threshold Switching Device Based on Magnesium Oxide for Security Application

Transient memristors are prospective candidates for both secure memory systems and biointegrated electronics, which are capable to physically disappear at a programmed time with a triggered operation. However, the sneak current issue has been a considerable obstacle to achieve high‐density transient crossbar array of memristors. To solve this problem, it is necessary to develop a transient switch device to turn the memory device on and off controllably. Here, a dissolvable and flexible threshold switching (TS) device with a vertically crossed structure is introduced, which exhibits a high selectivity of 10⁷, steep turn‐on slope of <8 mV dec⁻¹, and fast ON/OFF switch speed within 50/25 ns. Triggered failure could be achieved after soaking the device in deionized water for 8 min at room temperature. Furthermore, a water‐assisted transfer printing method is used to fabricate flexible and transient TS device arrays for bioresorbable systems, in which none of any significant degradation is observed under a bending radius of 2 mm. Integrating the selector with a transient memristor is capable of 10⁷ Gb memory implementation, indicating that the transient TS device could provide great opportunities to achieve highly integrated transient memory arrays.     

Focused Orientation and Position Imaging (FOPI) of Single Anisotropic Plasmonic Nanoparticles by Total Internal Reflection Scattering Microscopy

The defocused orientation and position imaging (DOPI) and polarization-based in-focus imaging techniques have been widely used for detecting rotational motions with anisotropic gold nanorods (AuNRs) as orientation probes. However, these techniques have a number of significant limitations, such as the greatly reduced signal intensity and relatively low spatial and temporal resolutions for out-of-focus AuNRs and the angular degeneracy for in-focus AuNRs. Herein, we present a total internal reflection (TIR) scattering-based focused orientation and position imaging (FOPI) of AuNRs supported on a 50 nm thick gold film, which enables us to overcome the aforementioned limitations. Imaging AuNRs under the TIR scattering microscope provides excellent signal-to-noise ratio and results in no deteriorating images. The scattering patterns of AuNRs on the gold substrate are affected by the strong interaction of the excited dipole in the AuNR with the image dipole in the gold substrate. The doughnut-shaped scattering field distribution allows for high-throughput determination of the three-dimensional spatial orientation of in-focus AuNRs within a single frame without angular degeneracy. Therefore, the TIR scattering-based FOPI method is demonstrated to be an outstanding candidate for studying dynamics of functionalized nanoparticles on a large variety of functional surfaces.     

Sensing array for coherence analysis of modulated aquatic chemical plumes

Here we show that an array of sensors can provide information about the spatial and temporal distribution of chemicals in liquid turbulent plumes. Planar laser induced fluorescence (PLIF) and amperometric sensor arrays were used to record signals from modulated chemical plumes released into a recirculating flume. Coherence analysis was applied to extract the frequency components contained in the sensor response. Effects due to release distance, modulation frequency, and array orientation were investigated. This study has demonstrated that frequency encoded information can be extracted from a turbulent chemical plume using an array of amperometric sensors with optimized three-dimensional geometry and tuning.     

光照可逆调控侧链液晶聚合物膜的表面能

对侧链液晶聚合物聚甲基丙烯酸(5-[4-(4-氰基偶氮苯)苯氧基]戊酯)进行溶液铸膜,用473nm线偏振光(LPL)照射使聚合物膜发生光致取向,用锥光成像的方法表征了侧链液晶聚合物的取向。取向前接触角为71.8°,取向后为86.4°;用365nm紫外光照射后,薄膜发生了解取向,解取向后接触角为72.3°。取向使膜表面能由40.1变为30.8mJ/m2,解取向后又恢复到39.8mJ/m2。表明光照能可逆调控侧链液晶聚合物表面能。     

固态拖线阵和液态拖线阵的试验分析

拖曳线列阵声纳以低频、大孔径等特点而受到关注。作为湿端的主要组成部分,拖线阵的发展也比较迅速。由于应用较早,液态拖线阵技术已经比较成熟。相比于液态拖线阵,固态拖线阵具有自身的特点,因此近年来对固态拖线阵的研究也逐渐增多。为了比较两种成阵工艺对拖曳线列阵性能的影响,进行了湖试,通过对湖试数据进行分析,比较两种拖线阵中阵元一致性和拖线阵波束形成性能的差异。结果表明,在阵元一致性方面,液态拖线阵和固态拖线阵的性能基本相似;在波束形成性能方面,静态时两者性能无明显的差别;在拖曳状态下,固态拖线阵对拖曳时产生的噪声敏感性低,因而具有更好的波束形成性能。     

Signal sensing and magnetic film memory array design

A signal-to-noise analysis is presented to show its influence on the design of magnetic film memory arrays. The device geometry and array dimensions are varied independently to find the design limits within which reliable signal detection can be performed, that is, the range within which adequate signal-to-noise ratio is obtained at the sense amplifier. The result is a plot of the required number of READ pulses for any combination of line width and line length in the range of interest. Line widths between 1/2- and 4-Mil and array sizes up to 4096 × 4096 bits were investigated. Multipulse readout is required for line widths less than 1.5-mils. A 256 × 256 array of 1/2-mil lines on 1-mil centers requires 12 signal pulses of 3-ns duration each, whereas a 1024 × 1024 array of 1-mil lines on 2-mil centers requires 7 signal pulses. It should be noted that in addition to adequate signal-to-noise ratio, a minimum of signal is needed (not obtainable through multiple READs) commensurate with the gain of the sense amplifier. These considerations are all combined in a set of design curves which can be used to make design tradeoffs between device size, array size, and cycle time.     

Si/a-Si core/shell nanowires as nonvolatile crossbar switches

Radial core/shell nanowires (NWs) represent an important class of nanoscale building blocks with substantial potential for exploring fundamental electronic properties and realizing novel device applications at the nanoscale. Here, we report the synthesis of crystalline silicon/amorphous silicon (Si/a-Si) core/shell NWs and studies of crossed Si/a-Si NW metal NW (Si/a-Si x M) devices and arrays. Room-temperature electrical measurements on single Si/a-Si x Ag NW devices exhibit bistable switching between high (off) and low (on) resistance states with well-defined switching threshold voltages, on/off ratios greater than 10(4), and current rectification in the on state. Temperature-dependent switching experiments suggest that rectification can be attributed to barriers to electric field-driven metal diffusion. Systematic studies of Si/a-Si x Ag NW devices show that (i) the bit size can be at least as small as 20 nm x 20 nm, (ii) the writing time is <100 ns, (iii) the retention time is >2 weeks, and (iv) devices can be switched >10(4) times without degradation in performance. In addition, studies of dense one-dimensional and two-dimensional Si/a-Si x Ag NW devices arrays fabricated on crystalline and plastic substrates show that elements within the arrays can be independently switched and read, and moreover that bends with radii of curvature as small as 0.3 cm cause little change in device characteristics. The Si/a-Si x Ag NW devices represent a highly scalable and promising nanodevice element for assembly and fabrication of dense nonvolatile memory and programmable nanoprocessors.     

A 1D Vanadium Dioxide Nanochannel Constructed via Electric‐Field‐Induced Ion Transport and its Superior Metal–Insulator Transition

Nanoscale manipulation of materials' physicochemical properties offers distinguished possibility to the development of novel electronic devices with ultrasmall dimension, fast operation speed, and low energy consumption characteristics. This is especially important as the present semiconductor manufacturing technique is approaching the end of miniaturization campaign in the near future. Here, a superior metal–insulator transition (MIT) of a 1D VO₂ nanochannel constructed through an electric‐field‐induced oxygen ion migration process in V₂O₅ thin film is reported for the first time. A sharp and reliable MIT transition with a steep turn‐on voltage slope of <0.5 mV dec^?1, fast switching speed of 17 ns, low energy consumption of 8 pJ, and low variability of <4.3% is demonstrated in the VO₂ nanochannel device. High‐resolution transmission electron microscopy observation and theoretical computation verify that the superior electrical properties of the present device can be ascribed to the electroformation of nanoscale VO₂ nanochannel in V₂O₅ thin films. More importantly, the incorporation of the present device into a Pt/HfO₂/Pt/VO₂/Pt 1S1R unit can ensure the correct reading of the HfO₂ memory continuously for 10⁷ cycles, therefore demonstrating its great possibility as a reliable selector in high‐density crossbar memory arrays.     

Facile, hetero-sized nanocluster array fabrication for investigating the nanostructure-dependence of nonvolatile memory characteristics

A facile fabrication of a hetero-sized nanocluster array has been demonstrated by using inert-gas condensation at room temperature. The array consisted of 1.5 and 3.2 nm sized gold clusters. The nonvolatile memory characteristics of a memory cell that had a hetero-sized nanocluster array to be used as a charge-trapping layer were compared to those of two cells that had 1.5 and 3.2 nm sized cluster arrays, respectively. While the average cluster size or the average number of electrons trapped in a cluster was reflected in the programming/erasing characteristics, the nanostructure effect was revealed in the retention characteristics, i.e. the proposed cell was found to have the gentlest degradation of the memory window. This can be explained by a preferential pathway for charge-carrier redistribution, caused by the ionization potential difference between the two nanoclusters of different sizes.     

表面稳定铁电液晶器件特性的PSPICE模拟研究

以铁电液晶（FELC）等效电路模型为基础，通过开发Pspice光合混合系统模块，灵活地调整多种时序脉冲及驱动源波形，优化FELC晶胞厚度，面积，粘滞系数，入射偏振角和自发极化强度等结构参数，成功地实现了FELC开关响应，记忆和存储特性的动态模拟，也为其他光子器件和混合集成系统的EDA仿真研究做了技术铺垫。     

Self‐Regulating Iris Based on Light‐Actuated Liquid Crystal Elastomer

The iris, found in many animal species, is a biological tissue that can change the aperture (pupil) size to regulate light transmission into the eye in response to varying illumination conditions. The self‐regulation of the eye lies behind its autofocusing ability and large dynamic range, rendering it the ultimate “imaging device” and a continuous source of inspiration in science. In optical imaging devices, adjustable apertures play a vital role as they control the light exposure, the depth of field, and optical aberrations of the systems. Tunable irises demonstrated to date require external control through mechanical actuation, and are not capable of autonomous action in response to changing light intensity without control circuitry. A self‐regulating artificial iris would offer new opportunities for device automation and stabilization. Here, this paper reports the first iris‐like, liquid crystal elastomer device that can perform automatic shape‐adjustment by reacting to the incident light power density. Similar to natural iris, the device closes under increasing light intensity, and upon reaching the minimum pupil size, reduces the light transmission by a factor of seven. The light‐responsive materials design, together with photoalignment‐based control over the molecular orientation, provides a new approach to automatic, self‐regulating optical systems based on soft smart materials.