Tunable and highly sensitive temperature sensor based on graphene photonic crystal fiber

Optical fiber temperature sensors have been widely employed in enormous areas ranging from electric power industry, medical treatment, ocean dynamics to aerospace. Recently, graphene optical fiber temperature sensors attract tremendous attention for their merits of simple structure and direct power detecting ability. However, these sensors based on transfer techniques still have limitations in the relatively low sensitivity or distortion of the transmission characteristics, due to the unsuitable Fermi level of graphene and the destruction of fiber structure, respectively. Here, we propose a tunable and highly sensitive temperature sensor based on graphene photonic crystal fiber (Gr-PCF) with the non-destructive integration of graphene into the holes of PCF. This hybrid structure promises the intact fiber structure and transmission mode, which efficiently enhances the temperature detection ability of graphene. From our simulation, we find that the temperature sensitivity can be electrically tuned over four orders of magnitude and achieve up to ～ 3.34×10^-3 dB/(cm·℃) when the graphene Fermi level is ～ 35 meV higher than half the incident photon energy. Additionally, this sensitivity can be further improved by ～ 10 times through optimizing the PCF structure (such as the fiber hole diameter) to enhance the light-matter interaction. Our results provide a new way for the design of the highly sensitive temperature sensors and broaden applications in all-fiber optoelectronic devices.     

金属衬底上石墨烯的红外近场光学

对石墨烯/铜体系开展了系统性的近场光学实验研究,成功观测到了区别于铜衬底的、来自石墨烯的近场光学响应信号,发现在表面台阶几何参数相同的铜衬底上的不同石墨烯样品表现出了截然不同的近场光学响应.     

Orbit-Transfer Torque Driven Field-Free Switching of Perpendicular Magnetization

he reversal of perpendicular magnetization （PM） by electric control is crucial for high-density integration of low-power magnetic random-access memory.Although the spin-transfer torque and spin-orbit torque technologies have been used to switch the magnetization of a free layer with perpendicular magnetic anisotropy,the former has limited endurance because of the high current density directly through the junction,while the latter requires an external magnetic field or unconventional configuratio...     

基于硒化镓纳米片填充的空芯光纤超高二次谐波增强

与传统的光学晶体相比,全光纤功能器件由于和光纤系统的天然兼容性,被认为是下一代集成光学的重要研究方向,吸引了人们的广泛关注。然而,由于二氧化硅固有的中心反演对称性质,光纤中的二阶非线性光学过程仍有待探索,这在可调谐超快激光、全光信号处理、成像和光通信等商业全光纤非线性光学应用中具有重要意义。因此,我们提出了一种新的溶液填充方法,可有效地将具有高非线性的硒化镓纳米片直接沉积在长度达半米的空芯光纤(HCF)的内孔壁上。此外,采用制备的硒化镓纳米片-空芯光纤(GaSe-HCF)作为光频率转换器,其二次谐波(SHG)比嵌入MoS₂的HCF和普通HCF分别提高了2个数量级和3个数量级。我们的研究成果将拓展其它非线性材料在全光纤高端非线性光学和光电子学中的应用,并提供新的制备思路。     

石墨烯的透射电子显微学研究

石墨烯(Graphene)是近几年迅速发展起来的研究热点材料之一,利用透射电子显微镜(TEM)研究Gra-phene的结构特征和原子动态过程,是Graphene研究的重要进展,文章评述了利用透射电子衍射方法对Graphene的层数、堆垛方式、取向和表面形貌等结构特征进行的研究工作,介绍了利用高分辨透射电子显微术在Graphene的表面缺陷、边缘结构及吸附原子等研究领域取得的最新结果.     

表界面调控米级二维单晶原子制造

随着芯片尺寸不断缩小,短沟道效应、热效应日趋显著.开发全新的量子材料体系以实现高性能芯片器件应用已成为当前科技发展的迫切需求.二维材料作为一类重要的量子材料,其天然具备原子层厚度和平面结构,能够有效克服短沟道效应并兼容当代微纳加工工艺,非常有望应用于新一代高性能器件方向.与硅基芯片发展类似,二维材料芯片级器件应用必须基于高质量、大尺寸的二维单晶材料制造.然而,由于二维材料的表界面特性,现有体单晶制备技术不能完全适用于单原子层结构的二维单晶制造.因此,亟需发展新的制备策略以实现大尺寸、高质量的二维单晶原子制造.有鉴于此,本文重点综述表界面调控二维单晶大尺寸制备技术发展现状,总结梳理了米级二维单晶原子制造过程中的3个关键调控方向,即单畴生长调控、单晶衬底制备和多畴取向控制.最后,系统展望了大尺寸二维单晶在未来规模化芯片器件方向的潜在应用前景.     

Tuning energy transfer efficiency in quantum dots mixture by controling donor/acceptor ratio

Improving the emission performance of colloidal quantum dots (QDs) is of paramount importance for their applications on light-emitting diodes (LEDs), displays and lasers. A highly promising approach is to tune the carrier recombination channels and lifetime by exploiting the energy transfer process. However, to achieve this precise emission optimization, quantitative modulation on energy transfer efficiency is highly desirable but still challenging. Here, we demonstrate a convenient approach to realize tunable energy transfer efficiency by forming QDs mixture with controllable donor/acceptor (D/A) ratio. With the mixing ratio ranging from 16/1 to 1/16, the energy transfer efficiency could be effectively tuned from near zero to ~70%. For the high mixing ratio of 16/1, acceptors obtain adequate energy supplied by closely surrounding donors, leading to~2.4-fold PL enhancement. While for the low mixing ratio, the ultrafast and efficient energy extraction process directly suppresses the multi-exciton and Auger recombination in the donor, bringing about a higher threshold. The facile modulation of emission performance by controllably designed mixing ratio and quantitatively tunable energy transfer efficiency will facilitate QD-based optoelectronic and photovoltaic applications.     

Growth,characterization, and Raman spectra of the 1T phases of TiTe2, TiSe2, and TiS2

High-quality large 1$T$ phase of Ti$X_2$ ($X ={\rm Te}$, Se, and S) single crystals have been grown by chemical vapor transport using iodine as a transport agent. The samples are characterized by compositional and structural analyses, and their properties are investigated by Raman spectroscopy. Several phonon modes have been observed, including the widely reported $A_{1g}$ and $E_g$ modes, the rarely reported $E_u$ mode ($\sim$183 cm$^{-1}$ for TiTe$_2$, and $\sim$185 cm$^{-1}$ for TiS$_2$), and even the unexpected $K$ mode ($\sim$85 cm$^{-1}$) of TiTe$_2$. Most phonons harden with the decrease of temperature, except that the $K$ mode of TiTe$_2$ and the $E_u$ and "$A_{2u}$/Sh" modes of TiS$_2$ soften with the decrease of temperature. In addition, we also found phonon changes in TiSe$_2$ that may be related to charge density wave phase transition. Our results on Ti$X_2$ phonons will help to understand their charge density wave and superconductivity.     

基于石墨烯光子晶体光纤的流体传感器

与传统的传感器设备阵列相比,由于结构更为简单,具有广泛检测兼容性的光纤系统逐渐成为分布式监测的有力候选者。然而,受工作机制的限制,大多数光纤传感器仍局限于对折射率等物理参数进行探测,一种用于环境化学监测的全光纤分布式传感系统亟待研发。本工作中,我们向化学气相沉积法生长的石墨烯光子晶体光纤(Gr-PCF)中引入了一种化学传感机制。初步结果表明,石墨烯光子晶体光纤可以选择性地检测浓度为ppb级的二氧化氮气体,并在液体中表现出离子敏感性。石墨烯光子晶体光纤与光纤通信系统的波分、时分复用技术结合后,将为实现分布式光学传感环境问题提供巨大的潜力和机会。     

Strain Tunable Berry Curvature Dipole,Orbital Magnetization and Nonlinear Hall Effect in WSe_2 Monolayer

The electronic topology is generally related to the Berry curvature,which can induce the anomalous Hall effect in time-reversal symmetry breaking systems.Intrinsic monolayer transition metal dichalcogenides possesses two nonequivalent K and K’ valleys,having Berry curvatures with opposite signs,and thus vanishing anomalous Hall effect in this system.Here we report the experimental realization of asymmetrical distribution of Berry curvature in a single valley in monolayer WSe₂ via applying uniaxial strain to break C_3v symmetry.As a result,although the Berry curvature itself is still opposite in K and K’ valleys,the two valleys would contribute equally to nonzero Berry curvature dipole.Upon applying electric field E,the emergent Berry curvature dipole D would lead to an out-of-plane orbital magnetization M ∝ D·E,which further induces an anomalous Hall effect with a linear response to E²,known as nonlinear Hall effect.We show the strain modulated transport properties of nonlinear Hall effect in monolayer WSe₂ with moderate hole-doping by gating.The second-harmonic Hall signals show quadratic dependence on electric field,and the corresponding orbital magnetization per current density M/J can reach as large as 60.In contrast to the conventional Rashba-Edelstein effect with in-plane spin polarization,such current-induced orbital magnetization is along the out-of-plane direction,thus promising for high-efficient electrical switching of perpendicular magnetization.