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1.
    
Understanding the thermal decomposition of metal salt precursors on carbon structures is essential for the controlled synthesis of metal-decorated carbon nanomaterials. Here, the thermolysis of a Ni precursor salt, NiCl2·6H2O, on amorphous carbon (a-C) and graphene oxide (GO) substrates is explored using in situ transmission electron microscopy. Thermal decomposition of NiCl2·6H2O on GO occurs at higher temperatures and slower kinetics than on a-C substrate. This is correlated to a higher activation barrier for Cl2 removal calculated by the density functional theory, strong Ni-GO interaction, high-density oxygen functional groups, defects, and weak van der Waals using GO substrate. The thermolysis of NiCl2·6H2O proceeds via multistep decomposition stages into the formation of Ni nanoparticles with significant differences in their size and distribution depending on the substrate. Using GO substrates leads to nanoparticles with 500% smaller average sizes and higher thermal stability than a-C substrate. Ni nanoparticles showcase the fcc crystal structure, and no size effect on the stability of the crystal structure is observed. These findings demonstrate the significant role of carbon substrate on nanoparticle formation and growth during the thermolysis of carbon–metal heterostructures. This opens new venues to engineer stable, supported catalysts and new carbon-based sensors and filtering devices.  相似文献   

2.
    
Vertically stacked low-dimensional heterostructures are outstanding systems both for exploring fundamental physics and creating new devices. Due to nanometer-scale building blocks, atomic scale phenomena become for them of fundamental importance, including during device operation. These can be accessed in situ in aberration-corrected scanning transmission electron microscopy (STEM) experiments. Here, the dynamics of a graphene-MoS2 heterostructure are studied under Joule heating, where the graphene serves as a high temperature atomically thin and electron transparent “hot plate” for the MoS2. Structural dynamics and evolution of the system are shown at the atomic scale, demonstrating that at the highest temperatures (estimated to exceed 2000 K), the continuous 2D MoS2 transforms into separated 3D nanocrystals, initiated by sulfur vacancy creation and migration followed by formation of voids and clustering at their edges. The resulting nanocrystals exhibit predominantly hexagonal shapes with the 2H and hybrid (2H/3R, 3R/TZ) polytypes. The observed morphology of the crystals is further discussed during and after the transformation, as well as their different edge configurations and stability under electron irradiation. These observations of MoS2 at extreme temperatures provide insights into the operation of devices based on graphene/MoS2 heterostructures and ultimately may help device fabrication techniques to create MoS2-based nanostructures, for example, in hydrogen evolution reaction applications.  相似文献   

3.
    
The nucleation and growth of nanoparticles are critical processes determining the size, shape, and properties of resulting nanoparticles. However, understanding the complex mechanisms guiding the formation and growth of colloidal multielement alloy nanoparticles remains incomplete due to the involvement of multiple elements with different properties. This study investigates in situ colloidal synthesis of multielement alloys using transmission electron microscopy (TEM) in a liquid cell. Two different pathways for nanoparticle formation in a solution containing Au, Pt, Ir, Cu, and Ni elements, resulting in two distinct sets of particles are observed. One set exhibits high Au and Cu content, ranging from 10 to 30 nm, while the other set is multi-elemental, with Pt, Cu, Ir, and Ni, all less than 4 nm. The findings suggest that, besides element miscibility, metal ion characteristics, particularly reduction rates, and valence numbers, significantly impact particle composition during early formation stages. Density functional theory (DFT) simulations confirm differences in nanoparticle composition and surface properties collectively influence the unique growth behaviors in each nanoparticle set. This study illuminates mechanisms underlying the formation and growth of multielement nanoparticles by emphasizing factors responsible for chemical separation and effects of interplay between composition, surface energies, and element miscibility on final nanoparticles size and structure.  相似文献   

4.
石墨烯－铜纳米颗粒复合物具有良好的电导率、电催化活性和化学可修饰性,在电化学和生物传感器等方面有广泛的应用前景。本文采用水合肼和KBH4原位化学还原氧化石墨烯和Cu2＋混合溶液制备石墨烯－铜纳米颗粒复合物。结果表明：石墨烯－铜纳米颗粒复合物只有在碱性或中性溶液中才能制备成功,水合肼比KBH4的还原效果好。水合肼还原后的石墨烯呈半透明薄纱状,铜纳米颗粒成功地、均匀地沉积在石墨烯纳米片上,独立存在不团聚,大小均匀,边长≈1μm,呈三角形或者六边形纳米片,正六边形纳米片的｛111｝面、不规则六边形和三角形纳米片的｛110｝面平行于石墨烯的二维平面。  相似文献   

5.
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Non-volatile memory(NVM)devices with non-volatility and low power consumption properties are important in the data storage field.The switching mechanism and packaging reliability issues in NVMs are of great research interest.The switch-ing process in NVM devices accompanied by the evolution of microstructure and composition is fast and subtle.Transmission electron microscopy(TEM)with high spatial resolution and versatile external fields is widely used in analyzing the evolution of morphology,structures and chemical compositions at atomic scale.The various external stimuli,such as thermal,electrical,mechanical,optical and magnetic fields,provide a platform to probe and engineer NVM devices inside TEM in real-time.Such ad-vanced technologies make it possible for an in situ and interactive manipulation of NVM devices without sacrificing the resolu-tion.This technology facilitates the exploration of the intrinsic structure-switching mechanism of NVMs and the reliability is-sues in the memory package.In this review,the evolution of the functional layers in NVM devices characterized by the ad-vanced in situTEM technology is introduced,with intermetallic compounds forming and degradation process investigated.The principles and challenges of TEM technology on NVM device study are also discussed.  相似文献   

6.
The deformation behavior of the epitaxial TiN/MgO (001) thin film/substrate system was studied through in-situ nanoindentation in a transmission electron microscope (TEM). The required sample geometry was prepared using Ga+ focused ion beam (FIB) etching. During room-temperature indentation, both the TiN film and the MgO substrate deformed through the motion of dislocations. The result was a localized hemispherical plastic zone in the TiN film directly under the indentation contact area, forming an 8° tilt boundary. These results show directly that small-scale plasticity in TiN can occur at room temperature through the motion of dislocations.  相似文献   

7.
    
Understanding and controlling the transformations of transition metal dichalcogenides (TMDs) from amorphous precursors into two‐dimensional (2D) materials is important for guiding synthesis, directing fabrication, and tailoring functional properties. Here, the combined effects of thermal energy and electron beam irradiation are explored on the structural evolution of 2D MoS2 flakes through the thermal decomposition of a (NH4)2MoS4 precursor inside an ultrahigh vacuum (10?9 Torr) scanning transmission electron microscope (STEM). The influence of reaction temperature, growth substrate, and the initial precursor morphology on the resulting 2D MoS2 flake morphology, edge structures, and point defects are explored. Although thermal decomposition occurs extremely fast at elevated temperatures and is difficult to capture using current STEM techniques, electron beam irradiation can induce local transformations at lower temperatures, enabling direct observation and interpretation of critical growth steps including oriented attachment and transition from single‐ to multilayer structures at atomic resolution. An increase in the number of layers of the MoS2 flakes from island growth is investigated using electron beam irradiation. These findings provide insight into the growth mechanisms and factors that control the synthesis of few‐layer MoS2 flakes through thermolysis and toward the prospect of atomically precise control and growth of 2D TMDs.  相似文献   

8.
    
The self-healing capability is highly desirable in semiconductors to develop advanced devices with improved stability and longevity. In this study, the automatic self-healing in silicon nanowires is reported, which are one of the most important building blocks for high-performance semiconductor nanodevices. A recovery of fracture strength (10.1%) on fractured silicon nanowires is achieved, which is demonstrated by in situ transmission electron microscopy tensile tests. The self-healing mechanism and factors governing the self-healing efficiency are revealed by a combination of atomic-resolution characterizations and atomistic simulations. Spontaneous rebonding, atomic rearrangement, and van der Waals attraction are responsible for the self-healing in silicon nanowires. Additionally, the self-healing efficiency is affected by the fracture surface roughness, the nanowire size, the nanowire orientation, and the passivation of dangling bonds on fracture surfaces. These new findings shed light on the self-healing mechanism of silicon nanowires and provide new insights into developing high-lifetime and high-security semiconductor devices.  相似文献   

9.
    
The precise mechanism governing the reversible semiconductor-to-metal transition (SMT) in V2O5 remains elusive, yet its investigation is of paramount importance due to the remarkable potential of V2O5 as a versatile “smart” material in advancing optoelectronics, plasmonics, and photonics. In this study, distinctive experimental insights into the SMT occurring in amorphous V2O5 through the application of highly sensitive, temperature-dependent, in situ analyses on a V2O5 thin film deposited on soda-lime glass are presented. The ellipsometry measurements reveal that the complete SMT occurs at ≈340 °C. Remarkably, the refractive index and extinction coefficients exhibit reversible characteristics across visible and near-infrared wavelengths, underscoring the switch-like behavior inherent to V2O5. The findings obtained from ellipsometry are substantiated by calorimetry and in situ secondary ion mass spectrometry analyses. In situ electron microscopy observations unveil a separation of oxidation states within V2O5 at 320 °C, despite the thin film retaining its amorphous state. The comprehensive experimental investigations effectively demonstrate that alterations in electronic state can trigger the SMT in amorphous V2O5. It is revealed for the first time that the SMT in V2O5 is solely contingent upon electronic state changes, independent of structural transitions, and importantly, it is a reversible transformation within the amorphous state itself.  相似文献   

10.
    
Developing high-capacity conversion-type anodes with superior durability substituting conventional graphite anodes is urgently desired to improve the energy density of lithium-ion batteries (LIBs). However, fatal capacity decay during cycling of the conversion-type anodes, which is primarily due to their inevitable structural degradation and continuous solid-electrolyte interphase reformation induced by drastic volume change, has highly restricted their commercialization. And, the interrelated effects of phase transformation, structural evolution, and electrochemical characteristics of the conversion-type anodes during cycling remain poorly understood. Herein, the findings on the fabrication and understanding of a previously unexplored entropy-stabilized spinel oxide, (Co0.2Mn0.2V0.2Fe0.2Zn0.2)3O4 as a promising conversion anode for LIBs, exhibiting not only moderate volume change character but also highly reversible capacities of ≈900 mAh g−1 for 500 cycles at 0.2 A g−1 and ≈500 mAh g−1 for 2000 cycles at 3 A g−1, respectively, are reported. Evidenced by in situ transmission electron microscopy coupled with theoretical calculations, its underlying mechanism underpinning highly reversible Li storage is explicitly revealed, which originates from reversible phase transformation and domain reconstruction during cycling. Moreover, the origin of small volume change is also clearly clarified. This work provides renewed mechanistic insights into designing high-capacity and durable conversion-type electrode materials for high-performance LIBs.  相似文献   

11.
    
Phase transition is established to govern electrostatic energy storage for antiferroelectric (AFE)-type dielectric capacitors. However, the source of inducing the phase transition and the pathway of storing the energy remains elusive so far given the ultrafast charging/discharging process under normal working conditions. Here, by slowing down the phase-transition speed using electron-beam irradiation as an external stimulus, the in situ dynamic energy-storage process in AFE PbZrO3 is captured by using atomic-resolution transmission electron microscopy. Specifically, it is found that oxygen-lead-vacancy-induced defect core acts as a seed to initiate the antiferrodistortive-to-ferrodistortive transition in antiparallel-Pb-based structural frames. Associated with polarity evolution of the compressively strained defect core, the ferroelectric (FE)–ferrodistortive state expands bilaterally along the b-axis direction and then develops into charged domain configurations during the energy-storage process, which is further evidenced by observations at the ordinary FE states. With filling the gap of perception, the findings here provide a straightforward approach of unveiling the unit-cell-wise energy storage pathway in chemical defect-engineered dielectric ceramics.  相似文献   

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13.
    
Direct observation of oxygen dynamics in an oxide-based second-order memristor can provide the valid evidence to clarify the memristive mechanism, however, which is still limited for now. In this study, the migration and diffusion of oxygen ions in the region of Pt/WO3-x Schottky interface are observed in the WO3-x second-order memristor by using the technique of in situ transmission electron microscopy (TEM) and the electron energy loss spectroscopy. Interestingly, the coexistence of memristive and memcapacitive switching can be implemented in this memristor. Combined with the analysis of depth-profile X-ray photoelectron spectroscopy (XPS), an interface-barrier-modulation second-order memristive model is proposed based on the above results. Notably, temporally correlative oxygen dynamics in the memristor offers the platform to integrate signals from multiple inputs, enabling the realization of the dendritic functions of synchronous and asynchronous integration for the application of logic operations with fault-tolerance capability and associative learning. These findings provide the experimental evidence to in-depth understanding of oxygen dynamics and switching mechanism in second-order memristor, which can support the optimization of memristive performance and the achievement of biorealistic synaptic functions.  相似文献   

14.
本文简述了透射电镜磁场双倾样品杆的设计方案,展示了Philips/FEI透射电镜磁场双倾样品杆的研制成果.利用该样品杆可以产生100 Oe的连续磁场,也可以产生140 Oe以上的瞬间磁场.通过“U”型磁组件和样品杯的巧妙设计,尽可能的减小了电子束在横向磁场中的偏移量.  相似文献   

15.
材料受周围环境的影响而产生的结构或成分变化一直都是材料科学和工业研发领域最关注的方向之一。随着材料研究的纳米化,外场导致的材料在亚纳米或原子尺度上的结构变化越来越成为认知材料宏观和纳米材料特性之根本。在诸如纳米催化剂的催化机制,材料的氧化-还原机制,纳米材料的生长或受力形变,电、磁场对材料纳米尺度结构的影响及微量气体探测等很多研究中有许多问题都需要一种特殊的电子显微镜即高分辨率原位环境电镜来帮助寻求答案。本文简要地回顾了环境透射电镜技术的发展思路,对于现代气体环境透射电镜的主流技术作了初步介绍,特别强调了高分辨率环境电镜的重要性以及在环境电镜中实现高分辨率所需要关注的一些技术环节,并力图通过具体实验实例使读者充分了解高分辨率原位环境电镜在材料科学研究中的重要性。  相似文献   

16.
    
Silicon based micro‐ and nanometer scale devices operating at various temperatures are ubiquitous today. However, thermo‐mechanical properties of silicon at the small scale and their underlying mechanisms remain elusive. The brittle‐to‐ductile transition (BDT) is one such property relevant to these devises. Materials can be brittle or ductile depending on temperature. The BDT occurs over a small temperature range. For bulk silicon, the BDT is about 545 °C. It is speculated that the BDT temperature of silicon may decrease with size at the nanoscale. However, recent experimental and computational studies have provided inconclusive evidence, and are often contradictory. Potential reasons for the controversy might originate from the lack of an in situ methodology that allows variation of both temperature and sample size. This controversy is resolved in the present study by carrying out in situ thermo‐mechanical bending tests on single crystal silicon samples with concurrent control of these two key parameters. It is unambiguously shown that the BDT temperature reduces with sample size. For example, the BDT temperature decreases to 293 °C for a sample size 720 nm. A mechanism‐based model is proposed to interpret the experimental observations.  相似文献   

17.
    
Potassium-ion batteries (PIBs) are promising alternatives to lithium-ion batteries because of the advantage of abundant, low-cost potassium resources. However, PIBs are facing a pivotal challenge to develop suitable electrode materials for efficient insertion/extraction of large-radius potassium ions (K+). Here, a viable anode material composed of uniform, hollow porous bowl-like hard carbon dual doped with nitrogen (N) and phosphorus (P) (denoted as N/P-HPCB) is developed for high-performance PIBs. With prominent merits in structure, the as-fabricated N/P-HPCB electrode manifests extraordinary potassium storage performance in terms of high reversible capacity (458.3 mAh g−1 after 100 cycles at 0.1 A g−1), superior rate performance (213.6 mAh g−1 at 4 A g−1), and long-term cyclability (205.2 mAh g−1 after 1000 cycles at 2 A g−1). Density-functional theory calculations reveal the merits of N/P dual doping in favor of facilitating the adsorption/diffusion of K+ and enhancing the electronic conductivity, guaranteeing improved capacity, and rate capability. Moreover, in situ transmission electron microscopy in conjunction with ex situ microscopy and Raman spectroscopy confirms the exceptional cycling stability originating from the excellent phase reversibility and robust structure integrity of N/P-HPCB electrode during cycling. Overall, the findings shed light on the development of high-performance, durable carbon anodes for advanced PIBs.  相似文献   

18.
本文综述了原子分辨率的原子序数衬度成像与原位电子能量损失谱分析、亚埃透射电子显微学、像差校正透射电子显微学和材料的微观结构表征与原位性能测试的最新发展和应用。在配置球差校正器、单色器和高能量分辨率过滤器的FEGTEM／STEM中,用相位衬度像／Z衬度成像与原位电子能量损失谱分析方法,在亚埃的空间分辨率和亚电子伏特能量分辨率下,可以研究各种材料的原子尺度界面和缺陷的原子和电子结构、价态、成键和成分等。配置球差校正器后,可明显提高透射电镜的点分辨率,把点分辨率延伸到信息分辨率,同时显著减小村度离住。随意改变球差系数Cs和离焦值△f,像差校正透射电子显微镜可提供新的成像模式。把特殊的样品杆插入电镜后,可把扫描隧道显微镜(STM)或原子力显微镜(AFM)功能相结合,开展材料的显微结构表征与原位的性能测试,不仅能得到物质的与显微像、成分、衍射有关的信息,同时还可以测量电学、力学性能,也可以研究在外场(温度、应力、电和磁场)作用下材料微观结构演变及结构与性能间的关系。  相似文献   

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20.
    
“Zero-strain” materials with little lattice strain and volume change during long-term cycling are ideal electrode choices for long-life lithium-ion batteries. However, the very limited “zero-strain” materials explored generally show small capacities ( < 200 mAh g?1), and the origin of “zero-strain” is still unclear. Here, Na2Ca(VO3)4 (NCVO) nanowires are explored as a new anode material capable of keeping single-phase-transition “zero-strain” during large-capacity (381 mAh g?1) Li+ intercalation. NCVO owns a crystal structure with isolated [V4O12]4? tetracycles separated by large-sized NaO6 octahedra and CaO8 square antiprism decahedra, generating large-sized quadrilateral and hexagonal channels ( ≈ 3.6 Å). During lithiation, two-electron transfer per vanadium is accomplished, introducing a large amount of Li+ into interstitial sites and increasing the size of reduced vanadium ions. The former and latter expansion effects are eliminated by the superior volume-buffering capabilities of the sufficiently large interstitial sites and electrochemical inactive Na-/Ca-based polyhedra, respectively, thus achieving “zero-strain” with the maximum volume variation of only 0.039% and mean strain of only 0.060%. Therefore, the NCVO nanowires exhibit exceptional cyclic stability, as demonstrated by 93.8%/93.2%/94.7% capacity retention over 2000/2000/7000 cycles at 1C/2C/10C. The understanding of the crystal-structural features for “zero-strain” provides a guide for the future designs of “zero-strain” energy-storage materials.  相似文献   

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