基于氧化石墨烯的长周期光纤光栅的全光控制

实验验证了一种通过将氧化石墨烯分散液沉积在长周期光纤光栅的全光控制的相关研究。通过外加的垂直泵浦光的作用,氧化石墨烯吸收泵浦光产生热量,改变长周期光纤光栅的包层模式的相位差,由于热膨胀的作用改变了氧化石墨烯所覆盖部分的光栅周期,使得谐振谱发生了移动,其最大调制深度可达10.6 dB,谐振谱最大可红移12.8 nm。通过实验发现,沉积相同浓度氧化石墨烯分散液的次数影响实验结果,通过在相同光栅的相同位置分别沉积三次,发现沉积三次可以在光纤表面获得更加均匀的氧化石墨烯膜,进行了时间响应的测试,其中沉积三次后的长周期光纤光栅的响应速度可达0.61 ms,沉积多次氧化石墨烯分散液可以在光纤表面沉积得更加平整均匀,从而获得更大的导热性能。     

Localized electric-field-enhanced low-light detection by a 2D SnS visible-light photodetector

Due to their excellent carrier mobility, high absorption coefficient and narrow bandgap, most 2 D IVA metal chalcogenide semiconductors(GIVMCs, metal = Ge, Sn, Pb;chalcogen = S, Se) are regarded as promising candidates for realizing high-performance photodetectors. We synthesized high-quality two-dimensional(2 D) tin sulfide(Sn S) nanosheets using the physical vapor deposition(PVD) method and fabricated a 2 D Sn S visible-light photodetector. The photodetector exhibits a high photoresponsivity of 161 A·W~(-1) and possesses an external quantum efficiency of 4.45 × 10~4%, as well as a detectivity of 1.15 × 10~9 Jones under 450 nm blue light illumination. Moreover, under poor illumination at optical densities down to 2 m W·cm~(-2), the responsivity of the device is higher than that at stronger optical densities. We suggest that a photogating effect in the 2 D Sn S photodetector is mainly responsible for its low-light responsivity. Defects and impurities in 2 D Sn S can trap carriers and form localized electric fields, which can delay the recombination process of electron-hole pairs,prolong carrier lifetimes, and thus improve the low-light responsivity. This work provides design strategies for detecting low levels of light using photodetectors made of 2 D materials.     

Orientation dependence in high harmonics of ZnO with polarization corrections to counteract the birefringent effect

We investigate the influence of the birefringence on the high-order harmonics in an a-cut Zn O crystal with midinfrared laser pulses. The high harmonics exhibit strong dependence on the alignment of the crystal with respect to the laser polarization. We introduce the Jones calculus to counteract the birefringent effect and obtain the harmonics with polarization corrections in Zn O. We show that the birefringent effect plays an important role in the orientation dependence of HHG.     

Vertical WS_2 spin valve with Ohmic property based on Fe_3GeTe_2 electrodes

The two-dimensional(2 D) transition-metal dichalcogenides(TMDCs) have been recently proposed as a promising class of materials for spintronic applications. Here, we report on the all-2 D van der Waals(vd W) heterostructure spin valve device comprising of an exfoliated ultra-thin WS_2 semiconductor acting as the spacer layer and two exfoliated ferromagnetic Fe_3 GeTe_2(FGT) metals acting as ferromagnetic electrodes. The metallic interface rather than Schottky barrier is formed despite the semiconducting nature of WS_2, which could be originated from the strong interface hybridization. The spin valve effect persists up to the Curie temperature of FGT. Moreover, our metallic spin valve devices exhibit robust spin valve effect where the magnetoresistance magnitude does not vary with the applied bias in the measured range up to 50 μA due to the Ohmic property, which is a highly desirable feature for practical application that requires stable device performance. Our work reveals that WS_2-based all-2 D magnetic vd W heterostructure, facilitated by combining 2 D magnets, is expected to be an attractive candidate for the TMDCs-based spintronic applications.     

Effects of low-LET radiations on CR-39 track detector

The effects of Co-60 gamma-rays and about 25-MeV pulsed electrons have been investigated on CR-39 plastic nuclear track detector. The bulk etch rate was measured as a function of the absorbed dose under three different irradiation conditions; gamma-ray exposure in air at the dose rate of 6 kGy/h, that in vacuum and electron shower in air at 126 kGy/h on average. It was found that the bulk etch rate (V) increased nearly exponentially with the dose (D); V=V₀exp(kD), and the characteristic parameter (k) was 35, 9 and 12 MGy⁻¹, respectively. It is considered that a lack of oxygen in damage formation processes could occur momentarily during a short electron pulse, just similarly to the vacuum effect of reduction in track etch rates in outgassed CR-39 plastic.     

Magnetoelectric effects in multiferroic Y-type hexaferrites Ba_(0.3)Sr_(1.7)Co_xMg_(2-x)Fe_(12)O_(22)

Y-type hexaferrites with tunable conical magnetic structures are promising single-phase multiferroics that exhibit large magnetoelectric effects. We have investigated the influence of Co substitution on the magnetoelectric properties in the Y-type hexaferrites Ba(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22)(x = 0.0, 0.4, 1.0, 1.6). The spin-induced electric polarization can be reversed by applying a low magnetic field for all the samples. The magnetoelectric phase diagrams of BaBa(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22) are obtained based on the measurements of magnetic field dependence of dielectric constant at selected temperatures. It is found that the substitution of Co ions can preserve the ferroelectric phase up to a higher temperature, and thus is beneficial for achieving single-phase multiferroics at room temperature.     

Survival probability in one dimension for theA+B→B reaction with hard-core repulsion

We study the effect of hard-core repulsion (known as the bus effect) betweenB particles on the reaction-diffusion systemA+BB in the continuous-time random walk model in one dimension with theA particles stationary. We show rigorously that the survival probability of theA particles is asymptotically bounded asC ₁lim _t{[–logS(t)]/t ^0.5}C ₂, whereC ₁ andC ₂ are constants. We also do simulations to confirm our results.     

声电光效应的耦合波方程理论

将声光效应与电光效应的耦合波方程相结合，统一为声电光效应的耦合波方程，并对之进行求解，给出声电光效应的衍射效率公式。     

我国城乡居民收入差距的反事实因素分解

首先,对我国城乡居民收入差距进行了简单的统计描述;然后,构建线性分位数回归方程,对影响收入变化的因素进行了较为细致的分析;最后,基于线性分位数回归模型,借助于反事实分析方法,将我国城乡居民收入差距分解为要素报酬效应、变量效应和残差效应,其中要素报酬效应在任何分位点处均表现最为突出,说明无论是针对较低的收入的工种,还是针对中高收入的工种,农民或多或少地被打上户籍标签,较低的要素报酬率使农民在获得收入的过程中,存在很大的劣势.     

Enhanced magnetocaloric effect in Eu-doped La0.7Ca0.3MnO3 compounds

Orthorhombic La_0.7-xEu_xCa_0.3MnO₃ samples (x = 0.04–0.12) with apparent density of ρ = 3.9–4.1 g/cm³ prepared by solid-state reactions have been studied. The analysis of temperature-dependent magnetization for an applied field H = 500 Oe indicated a decrease of the Curie temperature (T_C) from about 225 K for x = 0.04 through 189 K for x = 0.08–146 K for x = 0.12. The magnetocaloric (MC) study upon analyzing M(H, T) data has revealed that the magnetic entropy change around T_C reaches the maximum (|ΔS_max|), which is dependent on both x and H. For an applied field interval of ΔH = 60 kOe, |ΔS_max| values are about 5.88, 4.93, and 4.71 J/kg⋅K for x = 0.04, 0.08, and 0.12, respectively. Though |ΔS_max| decreases with increasing x, relative cooling power (RCP) increases remarkably from 383 J/kg for x = 0.04 to about 428 J/kg for x = 0.08 and 0.12. This is related to the widening of the ferromagnetic-paramagnetic transition region when x increases. Particularly, if combining two compounds with x = 0.04 and 0.08 (or 0.12) as refrigerant blocks for MC applications, a cooling device can work in a large temperature range of 145–270 K, corresponding to RCP ≈ 640 J/kg for H = 60 kOe. M(H) analyses around T_C have proved x = 0.04 exhibiting the mixture of first- and second-order phase transitions while x = 0.08 and 0.12 exhibit a second-order nature. The obtained results show potential applications of Eu-doped La_0.7Ca_0.3MnO₃ materials for magnetic refrigeration below room temperature.