陕西汉中市1951-2015年气温变化特征

采用汉中市气象站1951—2015年的月气温数据,使用滑动平均、线性回归分析、小波分析和Mann-Kendal非参数检验方法,分析了汉中市1951—2015年来气温变化特征及其规律.结果表明:汉中市1951—2015年平均气温不断升高,线性倾向率为0.21℃/10 a,在2001年前后发生突变,并存在50～60 a和75～80 a的周期变化;各个季节平均气温也均在升高,其线性倾向率分别为0.289、0.106、0.201、0.245℃/10 a,其中春季增温最为明显;春、夏、秋季平均气温与年平均气温一致,升温趋势趋同,而冬季相对较早,突变节点在1996年.     

渐变耦合脊波导晶体管探测器光响应分析

为提高InP基光探测器的吸收效率和工作速度,设计了一种渐变耦合脊波导单载流子传输异质结光敏晶体管探测器。采用有效折射率法和光束传播法,分析渐变耦合脊波导的光传输模式,优化后波导宽度和波导长度分别为2.6μm和250μm,可实现单模传输和高的光吸收效率。由于渐变耦合脊波导单载流子传输异质结光敏晶体管光传输方向与载流子运动方向垂直,分别优化光敏晶体管的吸收效率和速度,器件输出光电流和特征频率均得到改善。渐变耦合脊波导单载流子传输异质结光敏晶体管的响应度为33.83A/W,饱和输出光电流为90mA,最高特征频率达到87GHz,其饱和输出电流和特征频率相比于台面单载流子传输异质结光敏晶体管分别提高了20%和24%。但渐变耦合脊波导单载流子传输异质结光敏晶体管吸收体积大,获得饱和电流时的光功率也比较大,因此渐变耦合脊波导单载流子传输异质结光敏晶体管的响应度略小于台面的单载流子传输异质结光敏晶体管的响应度。     

Local Density of States Modulated by Strain in Marginally Twisted Bilayer Graphene

In marginally twisted bilayer graphene, the Moiré pattern consists of the maximized AB(BA) stacking regions,minimized AA stacking regions and triangular networks of domain walls. Here we realize the strain-modulated electronic structures of marginally twisted bilayer graphene by scanning tunneling microscopy/spectroscopy and density functional theory(DFT) calculations. The experimental data show four peaks near the Fermi energy at the AA regions. DFT calculations indicate that the two new peaks ...     

Monolayer MoS2 of high mobility grown on SiO2 substrate by two-step chemical vapor deposition

We report a novel two-step ambient pressure chemical vapor deposition (CVD) pathway to grow high-quality MoS₂ monolayer on the SiO₂ substrate with large crystal size up to 110 μm. The large specific surface area of the pre-synthesized MoO₃ flakes on the mica substrate compared to MoO₃ powder could dramatically reduce the consumption of the Mo source. The electronic information inferred from the four-probe scanning tunneling microscope (4P-STM) image explains the threshold voltage variations and the n-type behavior observed in the two-terminal transport measurements. Furthermore, the direct van der Pauw transport also confirms its relatively high carrier mobility. Our study provides a reliable method to synthesize high-quality MoS₂ monolayer, which is confirmed by the direct 4P-STM measurement results. Such methodology is a key step toward the large-scale growth of transition metal dichalcogenides (TMDs) on the SiO₂ substrate and is essential to further development of the TMDs-related integrated devices.