Strain engineering and hydrogen effect for two-dimensional ferroelectricity in monolayer group-Ⅳmonochalcogenides MX(M=Sn,Ge;X=Se,Te,S)

Two-dimensional(2D)ferroelectric compounds are a special class of materials that meet the need for devices miniaturization,which can lead to a wide range of applications.Here,we investigate ferroelectric properties of monolayer group-IV monochalcogenides MX(M=Sn,Ge;X=Se,Te,S)via strain engineering,and their effects with contaminated hydrogen are also discussed.GeSe,GeTe,and GeS do not go through transition up to the compressive strain of-5%,and consequently have good ferroelectric parameters for device applications that can be further improved by applying strain.According to the calculated ferroelectric properties and the band gaps of these materials,we find that their band gap can be adjusted by strain for excellent photovoltaic applications.In addition,we have determined the most stable hydrogen occupancy location in the monolayer SnS and SnTe.It reveals that H prefers to absorb on SnS and SnTe monolayers as molecules rather than atomic H.As a result,hydrogen molecules have little effect on the polarization and electronic structure of monolayer SnTe and SnS.

Two-Dimensional Materials for Highly Efficient and Stable Perovskite Solar Cells

Perovskite solar cells(PSCs)offer low costs and high power conversion efficiency.However,the lack of long-term stability,primarily stemming from the interfacial defects and the sus-ceptible metal electrodes,hinders their practical application.In the past few years,two-dimensional(2D)materials(e.g.,graphene and its derivatives,transitional metal dichalcogenides,MXenes,and black phosphorus)have been identified as a promising solution to solving these problems because of their dangling bond-free surfaces,layer-dependent electronic band structures,tunable functional groups,and inherent compactness.Here,recent progress of 2D material toward efficient and stable PSCs is summarized,including its role as both interface materials and electrodes.We discuss their beneficial effects on perovskite growth,energy level alignment,defect passivation,as well as blocking external stimulus.In particular,the unique properties of 2D materials to form van der Waals heterojunction at the bottom interface are emphasized.Finally,perspectives on the further development of PSCs using 2D materials are provided,such as designing high-quality van der Waals heterojunction,enhancing the uniformity and coverage of 2D nanosheets,and developing new 2D materials-based electrodes.

Defect engineering in two-dimensional materials

Since the discovery of graphene in 2004, two-dimensional (2D) materials have attracted worldwide interest. They are proved to be the most promising materials for next generation electronic and optoelectronic devices, including transistor, photodetector, sensor, modulator and light-emitting diode. Defects, e.g. vacancies, adatoms, edges, grain boundaries, and substitutional impurities, are inevitable in 2D materials[1]. They will influence the performance of the materials in many aspects such as mechanical, electrical, optical and optoelectronic properties. For example, the presence of sulfur vacancies (SVs) leads to electron donor states within the electronic bandgap. This increases electron concentration and results in n-type characteristic in as-prepared MoS2. They could also give rise to hopping transport behavior in low carrier density and act as scattering centers to reduce the carrier mobility in MoS2. Thus, defect engineering, namely, eliminating the unfavorable defects and introducing beneficial defects is very meaningful, and would be a promising strategy to realize high performance electronic and optoelectronic devices based on 2D materials.

Contact engineering for two-dimensional semiconductors

Two-dimensional(2D)layered materials,including graphene,black phosphorus(BP)and transition metal dichalcogenide(TMD)such as molybdenum disulfide(Mo S2),tungsten diselenide(WSe2),have attracted increasing attention for the application in electronic and optoelectronic devices.Contacts,which are the communication links between these 2D materials and external circuitry,have significant effects on the performance of electronic and optoelectronic devices.However,the performance of devices based on 2D semiconductors(SCs)is often limited by the contacts.Here,we provide a comprehensive overview of the basic physics and role of contacts in 2D SCs,elucidating Schottky barrier nature and Fermi level pinning effect at metal/2D SCs contact interface.The progress of contact engineering,including traditional metals contacts and metallic 2D materials contacts,for improving the performance of 2D SCs based devices is presented.Traditional metal contacts,named 3D top and edge contacts,are discussed briefly.Meanwhile,methods of building 2D materials contacts(2D top contact and 2D edge contact)are discussed in detail,such as chemical vapor deposition(CVD)growth of 2D metallic material contacts,phase engineered metallic phase contacts and intercalation induced metallic state contacts.Finally,the challenges and opportunities of contact engineering for 2D SCs are outlined.

Two-dimensional silicon nanomaterials for optoelectronics

Silicon nanomaterials have been of immense interest in the last few decades due to their remarkable optoelectronic responses,elemental abundance,and higher biocompatibility.Two-dimensional silicon is one of the new allotropes of silicon and has many compelling properties such as quantum-confined photoluminescence,high charge carrier mobilities,anisotropic electronic and magnetic response,and non-linear optical properties.This review summarizes the recent advances in the synthesis of two-dimensional silicon nanomaterials with a range of structures(silicene,silicane,and multilayered silicon),surface ligand engineering,and corresponding optoelectronic applications.

Research on railway BIM platform framework based on homemade graphics engine

At present,BIM platforms rely on foreign software.Homemade software and industry applications are mostly secondary developments,which present stranglehold problems caused by interruptions to the software supply.To solve the problem,key technical research on the 3D integrated design of railway engineering was stuedied based on homemade graphics engines to propose an innovative railway BIM platform framework.The entire process was completed from the top-level design to the engineering verification of the platform.The co-designed mechanism of a"center model and link"hybrid mode was constructed,which solved the difficulties of data management and increment synchronization at a large scale,achieving teamwork among surveying and mapping,alignments,and bridges.The results of this study could provide strong support for the development of BIM software for a whole railway and all majors.

Solution to new word perplexity in immersion bilingual teaching of engineering graphics

Numerous and specialized words are main obstacles in immersion bilingual teaching of engineering graphics. A feasible solution to this problem is given by classifying new words into three categories. The fear of new words among students is overcome and the effect of bilingual teaching is greatly improved .

Two-Dimensional Materials in Large-Areas: Synthesis, Properties and Applications

Large-area and high-quality two-dimensional crystals are the basis for the development of the next-generation electronic and optical devices.The synthesis of two-dimensional materials in wafer scales is the first critical step for future technology uptake by the industries;however,currently presented as a significant challenge.Substantial efforts have been devoted to producing atomically thin two-dimensional materials with large lateral dimensions,controllable and uniform thicknesses,large crystal domains and minimum defects.In this review,recent advances in synthetic routes to obtain high-quality two-dimensional crystals with lateral sizes exceeding a hundred micrometres are outlined.Applications of the achieved large-area two-dimensional crystals in electronics and optoelectronics are summarised,and advantages and disadvantages of each approach considering ease of the synthesis,defects,grain sizes and uniformity are discussed.

Teaching Reform and Practice in Engineering Drawing Based on 3D Modeling with Computer

Based on the necessity of three dimensional modeling with computer in teaching reform, this paper is the summarization of reform practice of teaching engineering drawing in our institute. The teaching reform begins with three dimensional modeling that used computer instead of board. On the basis of target of teaching reform, set of teaching content, arrangement of class hour and teaching method, the research of teaching practice have been done, and very good effects in teaching of engineering drawing have been achieved.

Combination of Splicing Visualization and Assembling Visualization in Engineering Drawing Education Carried by Self-optimizing Student Presentation

A pioneering self-optimizing teaching method in student-centric seminars was introduced in this paper, in which each student will establish preferred engineering drawing process directed by educators and necessary principles. We presented the working-memory centered mechanism in mental aspect to explain the phenomena. The theoretical mechanism is based on the typical translation between orthographic projection image and perspective image. The first is bonding object into a whole solid. The second is splicing the selected surfaces of objects and tailored them together. Two study groups were determined： an experimental group, who were directed to combine the object-based and surface-based construction methods in the presentations, and a control group, who learned through regular presentations made by an experienced teacher during the same period. The results showed that a significant enhancement in average scores has been achieved in the test among the experimental group in comparison with the control group. The variance of the scores is obviously reduced through the self-optimizing learning strategy, indicating a significant advantage on filling up the ability gaps among students. In fact, the results also indicated that the educator did keep the lesson in high quality. But it is worthy of more attention that the difference of mental manipulation habits between some students and educator may lead to a polarization in score distribution. So the seminar is a promising method to help the students to combine the object-based and surface-based construction methods.

COMPUTER SIMULATION IN MAN-MACHINE-ENVIRONMENT SYSTEM ENGINEERING

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Magnetic and electronic properties of two-dimensional metal-organic frameworks TM_(3)(C_(2)NH)_(12)

The ferromagnetism of two-dimensional(2D)materials has aroused great interest in recent years,which may play an important role in the next-generation magnetic devices.Herein,a series of 2D transition metal-organic framework materials(TM-NH MOF,TM=Sc-Zn)are designed,and their electronic and magnetic characters are systematically studied by means of first-principles calculations.Their structural stabilities are examined through binding energies and ab-initio molecular dynamics simulations.Their optimized lattice constants are correlated to the central TM atoms.These 2D TM-NH MOF nanosheets exhibit various electronic and magnetic performances owing to the effective charge transfer and interaction between TM atoms and graphene linkers.Interestingly,Ni-and Zn-NH MOFs are nonmagnetic semiconductors(SM)with band gaps of 0.41 eV and 0.61 eV,respectively.Co-and Cu-NH MOFs are bipolar magnetic semiconductors(BMS),while Fe-NH MOF monolayer is a half-semiconductor(HSM).Furthermore,the elastic strain could tune their magnetic behaviors and transformation,which ascribes to the charge redistribution of TM-3d states.This work predicts several new 2D magnetic MOF materials,which are promising for applications in spintronics and nanoelectronics.

Phase engineering two-dimensional nanostructures for electrocatalytic hydrogen evolution reaction

Hydrogen(H2)is considered to be a promising substitute for fossil fuels.Two-dimensional(2D)nanomaterials have exhibited an efficient electrocatalytic capacity to catalyze hydrogen evolution reaction(HER).Particularly,phase engineering of 2D nanomaterials is opening a novel research direction to endow 2D nanostructures with fascinating properties for deep applications in catalyzing HER.In this review,we briefly summarize the research progress and present the current challenges on phase engineering of 2D nanomaterials for their applications in electrocatalytic HER.Our summary will be of significance to provide fundamental understanding for designing novel 2D nanomaterials with unconventional phases to electrochemically catalyze HER.

Information and communication technology in science learning as a tool for “scientific thinking” in engineering education

New methodologies in science (also mathemat- ics) learning process and scientific thinking in the classroom activity of engineer students with ICT (information and communication technology, including also graphic calculator) are presented: visual modelling with ICT, action research with graphic calculator, insight in classroom, com- munications and reflection of integrative ac- tions. How can we show our students the beauty of science (and mathematics) with ICT and the way scientists think and try to find the truth? Is it possible to create the motivation in science learning for students using ICT or graphic cal- culator? How can we organize the engineer training on such professional activity in class- room? In this paper we try to answer the ques- tions using methodology of visual modelling and technology of resource lessons in high en- gineering school.

Raster to Vector Conversion for Engineering Drawings:Survey and Prospect

Recent development and recognition methods of raster to vector conversion for engineering drawings are presented. The advantages and disadvantages of all existing models are analyzed. Some research challenges and future directions are discussed.

Defect engineering of two-dimensional materials towards nextgeneration electronics and optoelectronics

The ultrathin body of two-dimensional(2D)materials provides potential for next-generation electronics and optoelectronics.The unavoidable atomic defects substantially determine the physical properties of atomic-level thin 2D materials,thus enabling new functionalities that are impossible in three-dimensional semiconductors.Therefore,rational design of atomic defects provides an alternative approach to modulate the physical properties of 2D materials.In this review,we summarize the recent progress of defect engineering in 2D materials,particularly in device performance enhancement.Firstly,the common defects in 2D materials and approaches for generating and repairing defects,including synthesis and post-growth treatments,are systematically introduced.The correlations between defects and optical,electronic,and magnetic properties of 2D materials are then highlighted.Subsequently,defect engineering for high performance electronics and optoelectronics is emphasized.At last,we provide our perspective on challenges and opportunities in defect engineering of 2D materials.

Highly Fluorescent Semiconducting Two-Dimensional Conjugated Polymer Films Achieved by Side-Chain Engineering Showing Large Exciton Diffusion Length

Semiconducting two-dimensional conjugated polymers(2DCPs)with strong fluorescence emission have great potential for various optoelectronic applications.However,it is enormously challenging to achieve this goal due to the significant compact interlayerπ-πstacking-induced quenching effect in these systems.In this work,we found that highly fluorescent semiconducting 2DCPs can be prepared through an effective side-chain engineering approach in which interlayer spacers are introduced to reduce the fluorescence quenching effect.The obtained two truxene-based 2DCP films that,along with-C6H13 and-C_(12)H_(25)alkyl side chains as interlayer spacers both demonstrate superior fluorescence properties with a high photoluminescence quantum yield of 5.6%and 14.6%,respectively.These are among the highest values currently reported for 2DCP films.Moreover,an ultralong isotropic quasi-twodimensional exciton diffusion length constrained in the plane with its highest value approaching 110 nm was revealed by the transient photoluminescence microscopy technique,suggesting that theπ-conjugated structure in these truxene-based 2DCP films has effectively been extended.This work can enable a broad exploration of highly fluorescent semiconducting 2DCP films for more deeply fundamental properties and optoelectronic device applications.

工程图学混合式教学改革探索与实践

采用混合式教学方式对教学内容及教学目标优化重构,通过自主研发、与企业联合研发系统建立优势互补的教学内容。学生通过网络教学平台、MOOC建设、虚拟实验室进行线上自主学习,通过实体课堂动手测绘实验、动态演示实验、基于项目现场讨论交流、课外拓展训练等实现课前、课中、课后一体化教学设计,学生课上课下均有思考实现线上线下互进协作学习,选择学习时间自由性更大,充分调动自主学习能力,充分体现以产出为导向、以学生为中心的工程教学理念。

工程图学虚拟仿真模型系统设计及其教学分析

针对工科类专业工程测绘课程实验需求,基于云服务、虚拟模型技术和可视化仿真体验,开发了工程测绘虚拟仿真实验系统。该系统对工程测绘实验方案、互动环节和考核评价等内容的教学体系重构和数字化重建,以测绘对象三维建模代替零部件实物,降低实验教学成本投入;以虚拟实验室代替实际测绘实验室,减少实验室资源占用;以在线实验代替固定时间课内实验,提高课程教学灵活度。为校内外师生提供灵活交互、强沉浸感和高用户黏度的在线实验教学服务,驱动学生自主完成实验学习和在线互动等活动,从而使学生的空间思维、图感表达能力得到充分训练,有效提高学生的工程创新素质。

面向新工科的产品几何信息表达课程教学改革与实践

针对现代设计及加工方法对工程制图类课程提出的新要求,在机械创新班试点开设产品几何信息表达课程,以工程制图为基础,融合三维构形表达和基于模型定义技术,构建出一整套面向新工科的课程教学体系、教学模式及考核方式,满足学生自主学习、全面发展的需求。