Theoretical study of thermoelectric properties of MoS2Theoretical study of thermoelectric properties of MoS2Theoretical study of thermoelectric properties of MoS2

We systematically studied the thermoelectric properties of MoS2 with doping based on the Boltzmann transport theory and first-principles calculations. We obtained an optimal doping region （around 1019 cm-3） for thermoelectric properties along in-plane and cross-plane directions. MoS2 in the optimal doping region has a vanishingly small anisotropy of ther- mopower possibly due to the decoupling of in-plane and cross-plane conduction channels, but big anisotropies of electrical conductivity cr and electronic thermal conductivity ke arising from the anisotropic electronic scattering time. The ~ is comparable to the lattice counterpart k1 in the plane, while tq dominates over tee across the plane, The figure of merit ZT can reach 0.1 at around 700 K with in-plane direction preferred by doping.     

移动机器人履行系统配置优化研究——基于闭排队网络理论

本文对移动机器人履行系统中货架调度任务的履行过程进行分析,根据机器人在货架装载、搬运、拣选、卸载四个过程的作业特点建立闭排队网络模型。采用近似平均值分析算法求解,实现系统绩效的迅速评估。通过与仿真计算实验的对比证明,模型对系统绩效的评估误差不超过5%。利用闭排队网络模型评估拣选台、机器人利用率和调度任务履行能力,实现对系统设施配置的讨论和优化。研究表明,拣选台均匀分布于仓库较长的两侧能提高系统履行绩效;系统存在最优机器人投放数量使系统整体利用率较高。     

熔化法YBaKCuO块材的制备和性能

成功地制备了K掺杂的MTG-YBKCO单畴块材, 在70K时,Jc随H单调下降.但在55K时,Jc-H曲线在(2～4)T范围内呈现了第二峰即峰值效应,使能在较宽磁场中仍保持高Jc值.     

Unconventional lattice dynamics in few-layer h-BN and indium iodide crystals

Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increasing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional(2 D) systems, few-layer h-BN and indium iodide(In I). We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the competition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2 D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.     

Stacking stability of MoS_2 bilayer: An ab initio study

The study of the stacking stability of bilayer MoS2 is essential since a bilayer has exhibited advantages over single layer MoS2 in many aspects for nanoelectronic applications. We explored the relative stability, optimal sliding path between different stacking orders of bilayer MoS2, and （especially） the effect of inter-layer stress, by combining first-principles density functional total energy calculations and the climbing-image nudge-elastic-band （CI-NEB） method. Among five typical stacking orders, which can be categorized into two kinds （I： AA＇, AB and II： AA＇, AB＇, A＇B）, we found that stacking orders with Mo and S superposing from both layers, such as AA＇ and AB, is more stable than the others. With smaller computational efforts than potential energy profile searching, we can study the effect of inter-layer stress on the stacking stability. Under isobaric condition, the sliding barrier increases by a few eV/（uc.GPa） from AA＇ to ABt, compared to 0.1 eV/（uc.GPa） from AB to [AB]. Moreover, we found that interlayer compressive stress can help enhance the transport properties of AA＇. This study can help understand why inter-layer stress by dielectric gating materials can be an effective means to improving MoS2 on nanoelectronic applications.     

Tailoring electronic properties of two-dimensional antimonene with isoelectronic counterparts

Using ab initio density functional theory calculations, we explore the three most stable structural phases, namely, α,β, and cubic(c) phases, of two-dimensional(2D) antimonene, as well as its isoelectronic counterparts SnTe and InI. We find that the band gap increases monotonically from Sb to SnTe to InI along with an increase in ionicity, independent of the structural phases. The band gaps of this material family cover the entire visible-light energy spectrum, ranging from 0.26 eV to 3.37 eV, rendering them promising candidates for optoelectronic applications. Meanwhile, band-edge positions of these materials are explored and all three types of band alignments can be achieved through properly combining antimonene with its isoelectronic counterparts to form heterostructures. The richness in electronic properties for this isoelectronic material family sheds light on possibilities to tailor the fundamental band gap of antimonene via lateral alloying or forming vertical heterostructures.     

Fundamental band gap and alignment of two-dimensional semiconductors explored by machine learning

Two-dimensional(2D)semiconductors isoelectronic to phosphorene have been drawing much attention recently due to their promising applications for next-generation(opt)electronics.This family of 2D materials contains more than 400members,including(a)elemental group-V materials,(b)binary III–VII and IV–VI compounds,(c)ternary III–VI–VII and IV–V–VII compounds,making materials design with targeted functionality unprecedentedly rich and extremely challenging.To shed light on rational functionality design with this family of materials,we systemically explore their fundamental band gaps and alignments using hybrid density functional theory(DFT)in combination with machine learning.First,calculations are performed using both the Perdew–Burke–Ernzerhof exchange–correlation functional within the generalgradient-density approximation(GGA-PBE)and Heyd–Scuseria–Ernzerhof hybrid functional(HSE)as a reference.We find this family of materials share similar crystalline structures,but possess largely distributed band-gap values ranging approximately from 0 eV to 8 eV.Then,we apply machine learning methods,including linear regression(LR),random forest regression(RFR),and support vector machine regression(SVR),to build models for the prediction of electronic properties.Among these models,SVR is found to have the best performance,yielding the root mean square error(RMSE)less than 0.15 eV for the predicted band gaps,valence-band maximums(VBMs),and conduction-band minimums(CBMs)when both PBE results and elemental information are used as features.Thus,we demonstrate that the machine learning models are universally suitable for screening 2D isoelectronic systems with targeted functionality,and especially valuable for the design of alloys and heterogeneous systems.     

铁磁半导体 花落两维里

正三十余载觅磁稀今看低维若鹜依极限少层铬锗碲双重调控又双极载流双子两极缘电荷惺惺共自旋量子以为多靓颖其实几负丽人娟——带隙铁磁~1)1引子自古人类视觉追求立体、丰满、洞透,当下物理追求平面、细微、对称破缺。后者为之欲生欲死的对象之一就是"二维"这个字眼。她真是让人又爱又恨。爱者赞其丰富物理,可上天入地无所不能而酣畅淋漓。恨者斥其不可捉摸而迁怒于"炒作概念",就如朗道不喜、墨敏(Mermin)证毕一般,仅此而已。窃以为,二维材料的     

Theoretical study of thermoelectric properties of MoS2

We systematically studied the thermoelectric properties of MoS2 with doping based on the Boltzmann transport theory and first-principles calculations. We obtained an optimal doping region(around 1019cm 3) for thermoelectric properties along in-plane and cross-plane directions. MoS2in the optimal doping region has a vanishingly small anisotropy of thermopower possibly due to the decoupling of in-plane and cross-plane conduction channels, but big anisotropies of electrical conductivity σ and electronic thermal conductivity κearising from the anisotropic electronic scattering time. The κeis comparable to the lattice counterpart κlin the plane, while κldominates over κeacross the plane. The figure of merit ZT can reach 0.1 at around 700 K with in-plane direction preferred by doping.