Quantan Wu

Reversible phase transition between amorphous and crystalline in Zr41.2Ti13.8Cu12.5Ni10Be22.5 under high pressure at room temperature

A reversible phase transition between amorphous and crystalline in bulk metallic glass (BMG) Zr41.2Ti13.8Cu12.5Ni10Be22.5 has been investigated under high pressure at room temperature. The BMG displayed a structure memory under high pressure as detected by in situ synchrotron radiation of x-ray diffraction and resistance measurement in a diamond anvil cell. Direct experimental observations found that the crystallization of the BMG occurred at 24 GPa on uploading and the crystalline phase reverted back to the amorphous state during downloading. This unusual phenomenon was discussed thermodynamically

Ionized‐cluster‐beam deposition and electrical bistability of C60–tetracyanoquinodimethane thin films

We report an ionized‐cluster‐beam (ICB) deposition and the electrical bistability of C60–tetracyanoquinodimethane (TCNQ) thin films. The films are fabricated by using an ionized‐cluster‐beam deposition method in a high vacuum system. The as‐deposited films were characterized by transmission electron microscopy and optical absorption spectroscopy, which verified the formation of the charge‐transfer complex system in C60–TCNQ thin films and the microstructure of these thin films. The structure and the electrical property of the ICB deposited Ag‐TCNQ thin films are also presented. The possible conductive mechanism of these ICB deposited thin films is discussed in the letter.

Electronic origin of spatial self-phase modulation: Evidenced by comparing graphite with C60 and graphene

We report unambiguous observation of spatial self-phase modulation (SSPM) in a dispersive suspension of graphite flakes. This coherent nonlinear optical effect in bulk graphite is found to be broadband and large, with a third-order nonlinear susceptibility χ(3) of 2.2u2009×u200910−9 esu (i.e., 3.1u2009×u200910−17 m2/V2 in SI units) at 532u2009nm excitation. Comparison with other carbon allotropes shows that this value is 5u2009×u2009107 times higher than that of C60 but ∼50 times lower than that of graphene, fully exhibiting the electronic origin of SSPM.

Synthesis, structure, and magnetic properties of Nd-Y-Fe-Mo-B bulk nanocomposite magnets

NdxY6−xFe68Mo4B22 (xu2009=u20091–5) nanocomposites were prepared directly by the devitrification of amorphous rods. The effects of Y doping on the glass-forming ability, microstructure, and magnetic properties of the alloys were also investigated. GFA of the alloys was found to get enhanced through substituting Nd with Y and to increase with the growth of Y contents. Results also showed that the best glass former was Nd1Y5Fe68Mo4B22 with a critical diameter of 4 mm. The coercivity first increased after subsequent crystallization and then decreased with the reduction of Y content, which was closely related to the phase transition during the crystallization. The devitrified Nd3Y3Fe68Mo4B22 exhibited a maximal coercivity of 364.1 kA/m, resulting from strong exchange coupling between the hard and the soft phases.

Emulating Short-Term and Long-Term Plasticity of Bio-Synapse Based on Cu/a-Si/Pt Memristor

Short-term plasticity and long-term plasticity of bio-synapse are thought to underpin critical physiological functions in neural circuits. In this letter, we vividly emulated the short-term and long-term synaptic functions in a single Cu/a-Si/Pt memristor. By controlling the injection quantity of Cu cations into the a-Si layer, the device showed volatile and non-volatile resistive switching behaviors. Owing to the unique characteristics of Cu/a-Si/Pt device, the short-term synaptic functions, i.e., short-term potentiation, pair-pulse facilitation, and long-term functions, i.e., long-term potentiation/depression, spike-timing-dependent plasticity, were mimicked in the memristor successfully. Furthermore, the transition from short-term memory to long-term memory of the device was also observed under repeated stimuli. The experimental results confirm that the Cu/a-Si/Pt memristor with various synaptic behaviors has a potential application in the brain-inspired computing systems.

Magnetic hardening mechanism of SmCo6.6Nb0.4 nanoflakes prepared by surfactant-assisted ball milling method

In this paper, we studied the magnetic hardening mechanism of SmCo6.6Nb0.4 nanoflakes prepared by surfactant-assisted high energy ball milling. The hysteresis loop with the initial magnetization curve and the corresponding differential susceptibility curve of thermally demagnetized SmCo6.6Nb0.4 nanoflakes were studied. It is concluded that the magnetization reversal process of the specimen is determined by domain wall motion, i.e., the magnetic hardening mechanism of the magnetic powders is dominated by domain wall pinning. Moreover, the dependence of coercive field of the nanoflakes on the maximum applied field derived from minor hysteresis loops also confirms the pinning effect in the magnetization reversal.

Fullerene-tetracyanoquinodimethane thin film and novel electrical bistability

We report the electrical bistability of C 60-tetracyanoquinodimethane (TCNQ) thin films fabricated by using an ionized-cluster-beam method in a high vacuum system. The films were characterized by transmission electron microscopy and electronic absorption spectroscopy. The spectroscopic results showed evidence of the formation of the charge-transfer complex system in C60-TCNQ thin films, and the TEM results revealed the microstructure of the films. The film thickness is ,100 nm. The electromotive intensity at the transition point was of the order of 10 6 Vym. The possible mechanism of the electrical phenomena of the films is discussed in the paper.

Improvement of Device Reliability by Introducing a BEOL-Compatible TiN Barrier Layer in CBRAM

Negative-SET behavior, induced by nano-filament overgrowth phenomenon, takes major responsibility to the reset failure phenomenon in conductive bridge random access memory (CBRAM). The unexpected negative-SET behavior in CBRAM devices can result in serious reliability issues and has been an obstacle on the way to mass production. In this letter, we have proposed a back-end-of-line (BEOL) compatible TiN barrier layer to improve the device reliability in CBRAM devices by eliminating the nano-filament overgrowth phenomenon and negative-SET behavior. Thus, a higher reset voltage can be applied to the TiN barrier layer devices to achieve more complete reset process and obtain better resistive switching performance. The results show that the Cu/HfO2/TiN/Ru device with one transistor structure has excellent comprehensive memory properties, including high reliability, fast switching speed, high resistance state uniformity, high endurance, long retention, and multi-level storage ability.

A new surface-potential-based compact model for the MoS2 field effect transistors in active matrix display applications

We present a continuous surface-potential-based compact model for molybdenum disulfide (MoS2) field effect transistors based on the multiple trapping release theory and the variable-range hopping theory. We also built contact resistance and velocity saturation models based on the analytical surface potential. This model is verified with experimental data and is able to accurately predict the temperature dependent behavior of the MoS2 field effect transistor. Our compact model is coded in Verilog-A, which can be implemented in a computer-aided design environment. Finally, we carried out an active matrix display simulation, which suggested that the proposed model can be successfully applied to circuit design.

Improvement of durability and switching speed by incorporating nanocrystals in the HfOx based resistive random access memory devices

Resistive random access memory (RRAM) has attracted significant interest for next-generation nonvolatile memory applications. However, it is somehow difficult to design a high speed RRAM device with enhanced data reliability. This paper deals with the improvement of high speed durable switching in nanocrystals based RRAM (NC-RRAM) devices. The high performance RRAM devices were prepared by incorporating the NCs into the HfOx oxide layer. As compared to the without (w/o) NC devices, the NC-RRAM devices are capable to execute uniform switching with higher set speed of 100u2009ns and reset speed of 150u2009ns, longer retention time and higher endurance of 108 cycles at 85u2009°C. The possible switching mechanism is due to the formation and rupture of the conductive filaments (CFs) inside the oxide film. The improvement of the NC-RRAM devices is due to the enhanced electric field intensity on the surface of the NCs, which can effectively facilitate the formation and rupture of the CFs.