Ultrafast Speed Research Articles

A Bubble-Dragged Catalytic Polymer Microrocket.

We report the bubble dragged microrocket consisting of functionalized multilayer polymer covered asymmetrically by platinum nanoparticles. The microrocket is pushed back during bubble growth over a small step and dragged forward over a big step during bubble explosion. Each bubble explosion induced a shock wave of gas which propagates in water at ultrafast speed. The bubble dragged microrocket can move along an approximate straight line instead of a fluctuating circle which is the trajectory of a bubble-pushed microrocket in most cases, which makes it a promising candidate for drug delivery and simulating rod-shaped bacteria.

Science opportunities and challenges associated with SKA big data

The upcoming Square Kilometre Array (SKA) radio telescope will become the largest astronomical observation facility, and is expected to introduce revolutionary changes in major fields of natural sciences. These revolutionary changes help us to answer the fundamental questions related to the origins of the universe, life, cosmic magnetic field, the nature of gravity, and to search for extraterrestrial civilizations. The unprecedented power of the SKA is characterized by an extremely high sensitivity, wide field of view, ultra-fast survey speed, and ultra-high time, space, frequency resolutions, which ensures that SKA will have a leading position in radio astronomy in future; this will be accompanied by a vast amount of observational data at exabyte (EB) level. The transportation, storage, reading, writing, computation, curation, and archiving of the SKA-level data and the release of SKA science products are posing serious challenges to the field of information communication technology (ICT). The China SKA science team will work together with the information, communication and computer industries to tackle the challenges associated with the SKA big data, which will not only promote major original scientific discoveries, but also apply the obtained technological achievements for stimulating the national economy.

Si/CuIn0.7Ga0.3Se2 Core–Shell Heterojunction for Sensitive and Self‐Driven UV–vis–NIR Broadband Photodetector

AbstractDesigning Si nanowire‐based heterostructures provides a promising path to construct self‐driven and broadband photodetectors, which are the key components for optoelectronic systems. Herein, the first fabrication of a p‐CuIn0.7Ga0.3Se2 nanoparticles/n‐Si nanowire array core–shell structure through a simple two‐stage process—spin coating and selenization treatment—and its integration into a self‐driven photodetector are reported. The heterojunction photodetector is sensitive to broad wavelength range from UV light to visible and near‐infrared light, with high detectivity of up to 1.6 × 1013 Jones, large responsivity of 0.33 A W−1, and an ultrafast response speed of 823/356 µs at zero bias. Additionally, this core–shell nanostructure exhibits good air stability and strong ability to detect weak light sources such as fluorescent lamp and lighter. The superior performance can be attributed to the strong light absorption of both Si and CuIn0.7Ga0.3Se2, the unique vertically standing core–shell structure, and effective photogenerated carriers' separation and transportation at the heterojunction interface.

Solution‐Processed Self‐Powered Transparent Ultraviolet Photodetectors with Ultrafast Response Speed for High‐Performance Communication System

AbstractTransparent ultraviolet (UV) photodetectors are an essential component of next‐generation “see‐through” electronics. However, the current photodetectors often suffer from relatively slow response speeds and high driving voltages. Here, all‐solution‐processed UV photodetectors are reported that are facilely prepared from environmentally friendly and abundant materials. The UV photodetectors are composed of a titanium dioxide thin film as the photosensitive layer sandwiched between two different transparent electrodes to form asymmetric Schottky junctions. The photodetector with high optical transparency can operate at zero bias because of spontaneous separation of photogenerated electron–hole pairs by the built‐in electric field. The resulting self‐powered photodetector displays high sensitivity to broadband UV light (200–400 nm). In particular, an ultrafast response speed up to 44 ns is obtained, representing a significant improvement over those of the conventional transparent photodetectors. Moreover, the photodetector has been successfully applied, for the first time, in a UV communication system as the self‐powered signal receiver. This work uniquely combines the features of high optical transparency and self‐power ability into UV photodetectors and would enable a broad range of optoelectronic applications.

Focus on the ferroelectric polarization behavior of four-layered Aurivillius multiferroic thin film

The well-saturated ferroelectric hysteresis loops with double remnant polarization up to 50 μC/cm2 were obtained in four layered Aurivillius-type multiferroic Bi5FeTi3O15 thin film. Pulsed positive-up negative-down polarization measurements demonstrate the intrinsic ferroelectric polarization, which present optimal rectangularity and polarization value. The hysteresis loops measurements with larger frequency range of 0.2–100 kHz indicate stable and ultra-fast switching speed of ferroelectric domains. Persistent retention properties were observed, and they are also independent of the applied electric field. In fatigue test an increased dielectric constant is observed along with the suppression of switchable polarization. Both of them can be restored partly to their original values via the stimulating of high electric field. The block domain switching due to the oxygen vacancies aggregated on domain walls are discussed for those characteristics. It is providing important contributions of domain wall pinning in the polarization degradation of Aurivillius-type ferroelectric films with four layers.

Ultrafast Photovoltaic-Type Deep Ultraviolet Photodetectors Using Hybrid Zero-/Two-Dimensional Heterojunctions.

Deep ultraviolet (DUV) photodetectors have wide-range applications in satellite communications, air purification, and missile-plume detection. However, the critical barriers for the currently available wide-band gap semiconductor film-based DUV photodetectors are their low efficiency, complicated processes, and lattice mismatch with the substrate. Quantum dot (QD) devices prepared using solution-based methods can solve these problems. However, so far, there are no reports on photovoltaic-type DUV photodetectors using QDs. In this study, we propose a novel methodology to construct a hybrid zero-/two-dimensional DUV photodetector (p-type graphene/ZnS QDs/4H-SiC) with photovoltaic characteristics. The device exhibits excellent selectivity for the DUV light and has an ultrafast response speed (rise time: 28 μs and decay time: 0.75 ms), which are much better than those reported for conventional photoconductive photodetectors.

Symmetric Ultrafast Writing and Erasing Speeds in Quasi-Nonvolatile Memory via van der Waals Heterostructures.

Due to the large gap in timescale between volatile memory and nonvolatile memory technologies, quasi-nonvolatile memory based on 2D materials has become a viable technology for filling the gap. By exploiting the elaborate energy band structure of 2D materials, a quasi-nonvolatile memory with symmetric ultrafast write-1 and erase-0 speeds and long refresh time is reported. Featuring the 2D semifloating gate architecture, an extrinsic p-n junction is used to charge or discharge the floating gate. Owing to the direct injection or recombination of charges from the floating gate electrode, the erasing speed is greatly enhanced to nanosecond timescale. Combined with the ultrafast write-1 speed, symmetric ultrafast operations on the nanosecond timescale are achieved, which are ≈106 times faster than other memories based on 2D materials. In addition, the refresh time after a write-1 operation is 219 times longer than that of dynamic random access memory. This performance suggests that quasi-nonvolatile memory has great potential to decrease power consumption originating from frequent refresh operations, and usher in the next generation of high-speed and low-power memory technology.

Thermal Barrier Phase Change Memory

Phase change memory is widely considered as the most promising candidate as storage class memory (SCM), bridging the performance gaps between dynamic random access memory and flash. However, high required operation current remains the major limitation for the SCM application, even after using defect engineering materials, for example, Ti-doped Sb2Te3. Here, we demonstrate that ∼87% current can be reduced by spatially separating Sb2Te3 and TiTe2 layers, thanks to semimetallic TiTe2 serving as a thermal barrier in the reset process. Moreover, the stable crystalline TiTe2 layer provides an ordered interface to speed up the crystallization process of the amorphous Sb2Te3 layer, enabling ∼10 ns ultrafast crystallization speed. An outstanding device lifetime, up to ∼2 × 107 cycles, has been obtained, which is twice as long as that of alloy-based cells. Correlative electron microscopy and atom probe tomography provide evidence that the TiTe2/Sb2Te3 multilayer can keep a layer-stacked structure, avoiding phase segregation found in alloys and strong element intermixing in the GeTe/Sb2Te3 superlattice, which enables excellent cyclability. This study suggests that adding a semimetallic layer in the phase change layer, such as TiTe2 and TiSe2, can yield a phase change memory with superior properties.

Ultrahigh Energy‐Storage Density in Antiferroelectric Ceramics with Field‐Induced Multiphase Transitions

AbstractThe excellent energy‐storage performance of ceramic capacitors, such as high‐power density, fast discharge speed, and the ability to operate over a broad temperature range, gives rise to their wide applications in different energy‐storage devices. In this work, the (Pb0.98La0.02)(Zr0.55Sn0.45)0.995O3 (PLZS) antiferroelectric (AFE) ceramics are prepared via a unique rolling machine approach. The field‐induced multiphase transitions are observed in polarization–electric field (P–E) hysteresis loops. All the PLZS AFE ceramics possess high energy‐storage densities and discharge efficiency (above 80%) with different sintering temperatures. Of particular significance is that an ultrahigh recoverable energy‐storage density of 10.4 J cm‐3 and a high discharge efficiency of 87% are achieved at 40 kV mm‐1 for PLZS ceramic with a thickness of 0.11 mm, sintered at 1175 °C, which are by far the highest values ever reported in bulk ceramics. Moreover, the corresponding ceramics exhibit a superior discharge current density of 1640 A cm‐2 and ultrafast discharge speed (75 ns discharge period). This great improvement in energy‐storage performance is expected to expand the practical applications of dielectric ceramics in numerous electronic devices.

Glass–ceramic dielectric materials with high energy density and ultra-fast discharge speed for high power energy storage applications

Ferroelectric glass–ceramic materials have been widely used as dielectric materials for energy storage capacitors because of their ultrafast discharge speed, excellent high temperature stability, stable frequency, and environmental friendliness.

Superior discharge energy density and efficiency in polymer nanocomposites induced by linear dielectric core–shell nanofibers

Novel SrTiO3@Al2O3/PVDF composite film capacitors have remarkably large discharge energy density (15.3 J cm−3) along with high discharge efficiency (68.52%) and ultrafast discharge speed (127 ns).

Crystallization Properties of Mg35Sb65/Sb Nanocomposite Multilayer Films for Phase Change Memory Application

The phase transition properties of Mg35Sb65/Sb multilayer thin films were studied, including the crystallization mechanism, surface morphology, atomic bonding mode and adhesion strength. With the increase of the thickness of Mg35Sb65 interlayers, Mg35Sb65/Sb thin film had better thermal stability and lower electrical conductivity. The growth-dominated crystallization mechanism made Mg35Sb65/Sb have ultra-fast phase change speed. The subtle change on surface morphology was ascribed to the grain growth and interface stress during crystallization. The scratch test revealed the adhesion strength contrast before and after crystallization. This work showed that Mg35Sb65/Sb multilayer film was a potential material with fast speed and good thermal stability for phase change memory application.

Silicon nitride nanopore created by dielectric breakdown with a divalent cation: deceleration of translocation speed and identification of single nucleotides.

Nanopore DNA sequencing with a solid-state nanopore requires deceleration of the ultrafast translocation speed of single-stranded DNA (ssDNA). We report an unexpected phenomenon: controlled dielectric breakdown (CBD) with a divalent metal cation, especially Ca2+, provides a silicon nitride nanopore with the ability to decelerate ssDNA speed to 100 μs per base even after solution replacement. This speed is two orders of magnitude slower than that for CBD with a conventional monovalent metal cation. Temperature dependence experiments revealed that the enthalpic barrier for a nanopore created via CBD with Ca2+ is 25-30kBT, comparable to that of a biological nanopore. The slowing effect originates from the strong interaction between ssDNA and divalent cations, which were coated on the sidewall of the nanopore during the CBD process. In addition, we found that the nanopore created via CBD with Ca2+ can decelerate the speed of even single-nucleotide monomers, dNMPs, to 0.1-10 ms per base. The four single nucleotides could be statistically identified according to their blockade currents. Our approach is simple and practical because it simultaneously allows nanopore fabrication, ssDNA deceleration and the identification of nucleotide monomers.

Multi-Port 1R1W Transpose Magnetic Random Access Memory by Hierarchical Bit-Line Switching

Emerging Magnetic Random-Access Memory (MRAM) has shown a great potential to replace Static-RAM (SRAM) and Dynamic-RAM (DRAM) in the working memories including Cache and main memory. MRAM benefits from its high-density, fast speed, low standby power, and non-volatility, which provides the possibility to accelerate the computation. In this paper, we present a transpose MRAM (T-MRAM) based on the current MRAM family (Spin-Transfer Torque or STT, Spin-Orbit Torque or SOT, -MRAM) to support read/write operations both in vertical and horizontal dimensions. More importantly, a multi-port 1-Read-1-Write (1R1W) scheme is developed for the proposed T-SOT-MRAM. Thanks to the ultra-fast speed and high power-efficiency, the proposed T-SOT-MRAM can be used to accelerate the computation of Convolution Neural Networks (CNNs) and video coding. The functional validation is performed under a hybrid CMOS/MRAM simulation. According to the evaluation results, the proposed T-SOT-MRAM obtains $1.8 \times $ speedup and 28% energy saving of 1R1W operations, compared to the baseline. In addition, T-MRAMs consume less leakage power consumption than the other counterparts. Furthermore, the smaller cell area of the proposed T-MRAMs allows increasing the capacity in order to improve performance efficiency.

Voltage-controlled magnetoelectric memory and logic devices

Abstract

Amorphous-MgGaO Film Combined with Graphene for Vacuum-Ultraviolet Photovoltaic Detector.

Vacuum-ultraviolet (VUV) detector equipped on satellites has extensive application in space exploration and cosmic science. For a VUV detector, a semiconductor material with a sufficiently wide band gap is eagerly desired. In this work, a wide-band gap amorphous-MgGaO (a-MGO) film was epitaxially grown on n-type GaN substrate by atomic layer deposition and a p-i-n-type heterojunction device for VUV detection was constructed with a-MGO film as a photosensitive layer and p-type graphene as a transparent conductive layer. The device exhibits a good spectral selectivity of VUV with photovoltaic response, a high responsivity (2 mA W-1) under zero bias, and an ultrafast response speed (rise and decay time of 0.76 μs and 0.56 ms, respectively) under nanosecond VUV pulse irradiation. This newly developed device shows great potential in VUV detection for space exploration.

Ultracompact ultrafast-switching-speed all-optical 4 × 2 encoder based on photonic crystal

A novel two-dimensional photonic-crystal-based all-optical encoder was designed, tested, and optimized. The structure is built on a linear square-lattice photonic crystal platform. An ultracompact, simple design occupying an area of only 128.52 μm2 is constructed, 50 % smaller than the smallest design known to date. Ultrafast switching speed with the lowest known delay time is achieved. The proposed design consists of one ring resonator with cylindrical silicon rods suspended in air. No auxiliary or bias input is required for its operation. The proposed platform is not sensitive to the applied input phase shift. Finite-difference time-domain and plane-wave expansion methods were used to analyze the structure and optimize the radius of the rods at 1.525 µm, with radius of the inner rods of 0.19a, for successful operation, resulting in ultrafast switching speed of 10 THz and shorter delay time reaching 0.1 ps. This maximum switching speed is two times faster than recent literature reports. The contrast ratio is calculated to reach an acceptable record of 7.1138 dB. The trade-off between the switching speed and contrast ratio was also examined.

Shortening Nucleation Time to Enable Ultrafast Phase Transition in Zn1Sb7Te12 Pseudo-Binary Alloy.

Zn1Sb7Te12 thin films have been deposited by magnetron co-sputtering of ZnTe and Sb2Te3 targets. The microstructure, phase-change speed, optical cycling stability, and crystallization kinetics have been investigated during thermal annealing and laser irradiation. The thermal-annealed and laser-irradiated films give a clear evidence of the coexistence of trigonal Sb2Te3 and cubic ZnTe phases, which are homogeneously distributed in a single alloy as confirmed by advanced scanning transmission electron microscopy. The formation of both phases increases the initial nucleation sites, leading to the rapid phase-change speed in the Zn1Sb7Te12 film. The film has a minimum crystallization time of ∼3 ns at 70 mW with almost no incubation period for the formation of critical nuclei compared to Ge2Sb2Te5 and other Zn-based films. Moreover, the complete crystallization of Zn1Sb7Te12 thin films is achieved within 10 ns. The ultrafast two-dimensional nucleation and crystal growth speed in Zn1Sb7Te12 obtained from the laser-irradiated system is almost 7 times faster compared to that in Ge2Sb2Te5 film. Controlling the crystallization process through doping ZnTe into Sb2Te3 is thus promising for the development of high-speed optical switching technology.

Potential of ITO thin film for electrical probe memory applications

ABSTRACTElectrical probe memory has received considerable attention during the last decade due to its prospective potential for the future mass storage device. However, the electrical probe device with conventional diamond-like carbon capping and bottom layers encounters with large interfacial contact resistance and difficulty to match the experimentally measured properties, while its analog with titanium nitride capping and bottom layers also faces serious heat dissipation through either probe and silicon substrate. Therefore, the feasibility of using indium tin oxide (ITO) media for the capping and bottom layers of the electrical probe device is investigated by tailoring the thickness and electrothermal properties of the ITO capping and bottom layers within experimentally established range and subsequently calculating the resultant temperature at several predefined points based on a previously developed three-dimensional model. To meet the required temperature and to fit the experimentally reported values, the thickness, electrical conductivity, and thermal conductivity of the ITO capping and bottom layers are found to be 5 nm, 103 Ω−1 m−1, 0.84 W m−1 K−1, and 200 nm, 1.25 × 106 Ω−1 m−1, 0.84 W m−1 K−1, respectively. The practicality of using this optimized device to achieve ultrahigh density, ultralow energy consumption, ultrafast switching speed, low interfacial contact resistance, and high thermal reliability has also been demonstrated.

Niobium doped tungsten oxide mesoporous film with enhanced electrochromic and electrochemical energy storage properties

Exploring high performance cathode materials is of great means for the development of bi-functional electrochromic energy storage devices. Herein, Nb-doped WO3 mesoporous films as integrated high-quality cathode are successfully constructed via a facile sol-gel method. Chemical state and crystallinity of the WO3 based films are significantly influenced by doping concentration. Compared with the pure WO3, the optimal Nb-doped film shows improved optical-electrochemical properties with high specific capacity (74.4 mAh g−1 at 2 A g−1), excellent high-rate capability, large optical contrast (61.7% at 633 nm), and ultra-fast switching speed (3.6 s and 2.1 s for coloring and bleaching process, respectively). These positive features suggest the potential application of Nb-doped WO3 mesoporous cathode. Our research paves the way for the development of multifunctional photoelectrochemical energy devices.