The unique carrier mobility of Janus MoSSe/GaN heterostructures

Heterostructure is an effective approach in modulating the physical and chemical behavior of materials. Here, the first-principles calculations were carried out to explore the structural, electronic, and carrier mobility properties of Janus MoSSe/GaN heterostructures. This heterostructure exhibits a superior high carrier mobility of 281.28 cm²·V⁻¹·s⁻¹ for electron carrier and 3951.2 cm²·V⁻¹·s⁻¹ for hole carrier. Particularly, the magnitude of the carrier mobility can be further tuned by Janus structure and stacking modes of the heterostructure. It is revealed that the equivalent mass and elastic moduli strongly affect the carrier mobility of the heterostructure, while the deformation potential contributes to the different carrier mobility for electron and hole of the heterostructure. These results suggest that the Janus MoSSe/GaN heterostructures have many potential applications for the unique carrier mobility.     

Negative thermal expansion: Mechanisms and materials

Negative thermal expansion (NTE) of materials is an intriguing phenomenon challenging the concept of traditional lattice dynamics and of importance for a variety of applications. Progresses in this field develop markedly and update continuously our knowledge on the NTE behavior of materials. In this article, we review the most recent understandings on the underlying mechanisms (anharmonic phonon vibration, magnetovolume effect, ferroelectrorestriction and charge transfer) of thermal shrinkage and the development of NTE materials under each mechanism from both the theoretical and experimental aspects. Besides the low frequency optical phonons which are usually accepted as the origins of NTE in framework structures, NTE driven by acoustic phonons and the interplay between anisotropic elasticity and phonons are stressed. Based on the data documented, some problems affecting applications of NTE materials are discussed and strategies for discovering and design novel framework structured NET materials are also presented.     

Assessing Earthquake Forecast Performance Based on b Value in Yunnan Province,China

Many studies have shown that b values tend to decrease prior to large earthquakes. To evaluate the forecast information in b value variations, we conduct a systematic assessment in Yunnan Province, China, where the seismicity is intense and moderate–large earthquakes occur frequently. The catalog in the past two decades is divided into four time periods (January 2000–December 2004, January 2005–December 2009, January 2010–December 2014, and January 2015–December 2019). The spatial b values are calculated for each 5-year span and then are used to forecast moderate-large earthquakes (M ≥ 5.0) in the subsequent period. As the fault systems in Yunnan Province are complex, to avoid possible biases in b value computation caused by different faulting regimes when using the grid search, the hierarchical space–time point-process models (HIST-PPM) proposed by Ogata are utilized to estimate spatial b values in this study. The forecast performance is tested by Molchan error diagram (MED) and the efficiency is quantified by probability gain (PG) and probability difference (PD). It is found that moderate–large earthquakes are more likely to occur in low b regions. The MED analysis shows that there is considerable precursory information in spatial b values and the forecast efficiency increases with magnitude in the Yunnan Province. These results suggest that the b value might be useful in middle- and long-term earthquake forecasts in the study area.     

HL-2M装置真空室预装阶段检漏试验

通过在加工现场和安装现场搭建的真空辅助系统、四极质谱计及氦检漏仪组成的检漏系统,运用残余气体分析和氦质谱检漏方法在冷态下对HL-2M真空室扇形段及真空室整体进行了真空检漏试验.对漏点进行修复后,测试了真空室的极限真空度和总漏气率等.真空室经过72h的抽气后,真空度达到3.7×10?5Pa,超过了1.0×10?4Pa的预...     

HL-2M初始等离子体放电阶段的辉光放电清洗系统电极的设计与分析

针对HL-2M装置初始等离子体放电阶段所需的直流辉光放电清洗系统的电极进行了设计.对辉光放电清洗系统在不同工况下的系统负载进行了分析和拟定,并确定了电极结构设计分析标准.根据系统电极的结构特点并结合系统负载规范与分析标准,依据不同的失效模式对电极进行了失效分析.分析结果表明,此针对初始等离子体放电的电极设计能可靠安全运...     

近玻尔速度Ne2+离子穿过碳膜引起的电子发射

本文测量了入射能为2–25 keV/u的Ne²⁺离子穿过不同厚度碳膜诱导的前向、后向 (分别对应出射表面和入射表面) 电子发射产额. 实验中通过改变炮弹离子的能量, 系统的研究了势能沉积、电子能损以及反冲原子对前向、后向电子发射产额的贡献. 结果表明, 离子的势能沉积只对后向电子发射有贡献, 前向、后向电子发射产额分别与Ne²⁺离子在薄膜出射、入射表面的电子能损近似成正比关系, 其中电子能损很低 (对应于离子能量很低) 的时候, 反冲原子对电子发射的贡献不能忽略. 关键词： 近玻尔速度 电子发射 电子能损 反冲原子     

TiO2 Nanotube Array/Monolayer Graphene Film Schottky Junction Ultraviolet Light Photodetectors

Schottky junctions made from a titanium dioxide nanotube (TiO₂NT) array in contact with a monolayer graphene (MLG) film are fabricated and utilized for UV light detection. The TiO₂NT array is synthesized by the anodization and the MLG through a simple chemical vapor deposition process. Photoconductive analysis shows that the fabricated Schottky junction photodetector (PD) is sensitive to UV light illumination with good stability and reproducibility. The corresponding responsivity (R), photoconductive gain (G), and detectivity (D*) are calculated to be 15 A W^?1, 51, and 1.5 × 10¹² cm Hz^1/2 W^?1, respectively. It is observed that the fabricated PD exhibits spectral sensitivity and a simple power‐law dependence on light intensity. Moreover, the height of the Schottky junction diode is derived to be 0.59 V by using a low temperature I–V measurement. Finally, the working mechanism of the TiO₂NT array/MLG film Schottky junction PD is elucidated.     

含磁控和荷控两种忆阻器的混沌电路设计与仿真

利用惠普实验室荷控和磁控两种忆阻器模型设计了一个五阶混沌电路. 数值仿真结果表明该电路在参数变化情况下能产生Hopf分岔和反倍周期分岔两种分岔行为,并能产生双涡卷、单涡卷、周期态等不同相轨道. 为了验证电路的混沌行为,利用基本元器件设计了惠普实验室荷控和磁控忆阻器模拟器,并将其应用到对所设计电路中进行Pspice仿真,电路仿真结果验证了理论分析的正确性. 关键词： 混沌电路 HP忆阻器 模拟器 Pspice仿真     

周期性纳米洞内边缘氧饱和石墨烯纳米带的电子特性

利用基于密度泛函理论的第一性原理方法,研究了内边缘氧饱和的周期性凿洞石墨烯纳米带（G NR）的电子特性. 研究结果表明：对于凿洞锯齿形石墨烯纳米带（ZGNRs）,在非磁性态时不仅始终为金属,且金属性明显增强;反铁磁态（AFM）时为半导体的ZGNR,凿洞后可能成为金属;但铁磁态（FM）为金属的ZGNR,凿洞后一般变为半导体或半金属. 而对于凿洞的扶手椅形石墨烯（AGNRs）,其带隙会明显增加. 深入分析发现：这是由于氧原子对石墨烯纳米带边的电子特性有重要的影响,以及颈次级纳米带（NSNR）及边缘次级纳米带（ESNR）的不同宽度及边缘形状（锯齿或扶手椅形）能呈现出不同的量子限域效应. 这些研究对于发展纳米电子器件有重要的意义. 关键词： 石墨烯纳米带 纳米洞 内边缘氧饱和 电子特性     

Thermal and Thermo-Oxidative Degradation of Biodegradable Poly(Ester Urethane) Containing Poly(L-Lactic Acid) and Poly(Butylene Succinate) Blocks

A novel biodegradable poly(ester urethane; PEU) was synthesized by chain extension reaction of dihydroxylated poly(L-lactic acid; PLLA) and poly(butylene succinate; PBS) using diisocyanate as a chain extender. The kinetics of thermal and thermo-oxidative degradation of PEU containing PLLA and PBS blocks were studied by thermogravimetric analysis (TGA). TGA results indicated that PEU was more stable in air than in nitrogen and went through a two-stage degradation process irrespective of the experimental atmosphere. Activation energy of each stage was calculated by means of Kissinger, Kim-Park, Friedman, Flynn-Wall-Ozawa, and Kissinger-Akahira-Sunose methods. For the first stage, the activation energy value obtained in air was slightly higher than the corresponding value obtained in nitrogen; and for the second stage, the activation energy showed a much higher value in air than in nitrogen. The Coats-Redfern method was employed to study the degradation mechanism of each stage. The results indicated that the degradation of the first stage follows the P3/4 mechanism irrespective of the experimental atmosphere; the degradation of the second stage of PEU obeys the P1 mechanism in nitrogen while P3/2 in air.