Application of Aberration-Corrected TEM and Image Simulation to Nanoelectronics and Nanotechnology

The image quality in electron microscopy often suffers from lens aberration. As a result of lens aberrations, critical information appears distorted at the atomic scale in high-resolution transmission electron microscopy (HRTEM). In scanning TEM (STEM), the spatial resolution of images and the quality of spectroscopic data are greatly reduced. With the recent introduction of aberration-corrected lenses and monochromators, new and exciting images with sub-0.1-nm spatial resolution are now recorded routinely, and electron energy loss data has been used to determine the location of a single atom in an atomic column. As a result of the decreased focal depth of an aberration-corrected lens used in STEM, the dream of three-dimensional (3-D) atomic resolution is one step closer and for HRTEM it was shown that 3-D imaging with atomic resolution is feasible. However, understanding imaging and spectroscopy in HRTEM and STEM still requires refined modeling of the underlying electron scattering processes by multislice image simulation. Since research into the physics and technology of nanoelectronic devices has already moved into sub-10-nm transistor gate lengths, the need for well-understood imaging and spectroscopy at nanoscale dimensions is already upon us. Fortunately, nanowires and other nanotechnology materials serve as useful test samples as well as being potential materials for future nanoelectronics. This enables early development of microscopy methods that will be used to investigate future generations of integrated circuits     

电子显微镜的现状与展望

本文扼要介绍了电子显微镜的现状与展望，透射电子显微镜方面主要有：高分辨电子显微学及原子像的观察，像差校正电子显微镜，原子尺度电子全息学，表面的高分辨电子显微正面成像，超高压电子显微镜，中等电压电镜，１２０ｋＶ，１００ｋＶ分析电镜，场发射枪扫描透射电镜及能量选择电镜等，透射电镜将又一次面临新的重大突破，扫描电子显微镜方面主要有：分析扫描电镜和Ｘ射线能谱仪，Ｘ射线波谱仪和电子探针仪，场发射枪扫描电镜和     

Application of atomic scale STEM techniques to the study of interfaces and defects in materials

Incoherent imaging and analysis techniques in the scanning transmission electron microscope (STEM) provide the potential to map changes in structure, composition and bonding that occur at materials interfaces and defects on the fundamental atomic scale. Such comprehensive characterization capabilities permit a detailed analysis of the structure-property relationships of interfaces and defects to be performed. In this paper, we discuss the resolution limits of such techniques in the JEOL 2010F STEM/TEM operating both under standard conditions and at elevated temperatures. Examples of the use of such techniques to quantify the atomic scale defect chemistry at interfaces and defects in perovskite oxides, the growth and structure of II-VI and III-V quantum dots and the electronic structure of threading dislocations in GaN will also be presented.     

Single‐Crystalline Gallium Nitride Microspindles: Synthesis,Characterization, and Thermal Stability

This paper describes a facile procedure for synthesizing high‐quality gallium nitride microspindles on a large scale using a solid‐state reaction of GaI₃, NaNH₂, and NH₄Cl in a sealed system at 500 °C for 6 h. The structures, compositions, and morphologies of the as‐synthesized products are derived from X‐ray powder diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field‐emission scanning electron microscopy (FE‐SEM). The selected‐area electron diffraction (SAED) patterns and high‐resolution transmission electron microscopy (HRTEM) images show that the as‐synthesized GaN spindles are composed of many single‐crystalline platelets. The GaN microspindles show different optical properties depending on their shape (e.g., nanowires or nanoparticles) in photoluminescence (PL) emission spectroscopy and Raman spectroscopy. The possible growth mechanism of GaN microspindles is controlled by linear kinetics with a driving force proportional to the difference between a local supersaturation and an equilibrium chemical potential. Furthermore, the thermal stability of the GaN microspindles is investigated under various annealing conditions and discussed on the basis of additional TEM and XRD analyses.     

Synthesis of CeOx‐Decorated Pd/C Catalysts by Controlled Surface Reactions for Hydrogen Oxidation in Anion Exchange Membrane Fuel Cells

Due to the sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline electrolytes, the development of more efficient HOR catalysts is essential for the next generation of anion‐exchange membrane fuel cells (AEMFCs). In this work, CeO_x is selectively deposited onto carbon‐supported Pd nanoparticles by controlled surface reactions, aiming to enhance the homogenous distribution of CeO_x and its preferential attachment to Pd nanoparticles, to achieve highly active CeO_x‐Pd/C catalysts. The catalysts are characterized by inductively coupled plasma–atomic emission spectroscopy, X‐ray diffraction, high‐resolution transmission electron microscopy, scanning transmission electron microscopy (STEM), electron energy loss spectroscopy, and X‐ray photoelectron spectroscopy to confirm the bulk composition, phases present, morphology, elemental mapping, local oxidation, and surface chemical states, respectively. The intimate contact between Pd and CeO_x is shown through high‐resolution STEM maps. The oxophilic nature of CeO_x and its effect on Pd are probed by CO stripping. The interfacial contact area between CeO_x and Pd nanoparticles is calculated for the first time and correlated to the electrochemical performance of the CeO_x‐Pd/C catalysts. Highest recorded HOR specific exchange current (51.5 mA mg^?1_Pd) and H₂–O₂ AEMFC performance (peak power density of 1,169 mW cm^?2 mg_Pd^?1) are obtained with a CeO_x‐Pd/C catalyst with Ce_0.38/Pd bulk atomic ratio.     

Electron microscopy at a sub-50 pm resolution

An aberration-corrected electron microscope developed in CREST project has been applied for imaging atoms and clusters buried inside crystals. The resolution of the microscope in scanning transmission electron microscopy (STEM) has experimentally proved to be better than 47 pm by use of a cold-field emission gun at 300 kV. The high resolution has given an advantage for imaging light elements such as lithium atoms discriminating one by one. Moreover, a three-dimensional structure imaging has been demonstrated for dopant clusters by a sub-50 pm STEM, using its high depth resolution.     

Electrical,optical and visible light-photocatalytic properties of monoclinic BiVO4 nanoparticles synthesized hydrothermally at different pH

Monoclinic BiVO₄ nanoparticles were synthesized hydrothermally at pH 0.5, 2.0, 5.0 and 7.0. They were characterized by high resolution scanning electron microscopy or field emission scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, selected area electron diffraction, powder X-ray diffraction, Raman spectroscopy, solid state impedance spectroscopy, UV–visible diffuse reflectance spectroscopy and photoluminescence spectroscopy. While BiVO₄ nanoparticles synthesized at pH 0.5 and 2.0 provide perfect semicircular Nyquist plots the nanocrystals prepared at pH 5 show a semicircular arc. The nanocrystals obtained at pH 7 exhibit a quasi-linear dependence of Z_Im on Z_Re. The absorption edge of BiVO₄ nanoparticles is red-shifted on decrease of the pH of synthesis; BiVO₄ synthesized at pH 0.5 is an exception. The synthesized nanoparticles show band gap emission at 483 nm and defect emissions at 534 and 578 nm. The band gap emission of BiVO₄ nanocrystals synthesized at pH 0.5 is much less than those of others. The photocatalytic activity of BiVO₄ nanoparticles decreases with increase of the pH of synthesis and nanocrystalline BiVO₄ synthesized at pH 0.5 is an exception. The photocatalytic activities of BiVO₄ nanoparticles synthesized at different pH are explained in terms of the charge transfer resistance, band gap energy, photoluminescence due to charge carrier recombination and preferential orientation of 040-plane in BiVO₄ nanocrystals synthesized at pH 2.     

New views of materials through aberration-corrected scanning transmission electron microscopy

The successful correction of third-order and, more recently, fifth-order aberrations has enormously enhanced the capabilities of the scanning transmission electron microscope (STEM), by not only achieving record resolution, but also allowing near 100% efficiency for electron energy loss spectroscopy, and higher currents for two-dimensional spectrum imaging. These advances have meant that the intrinsic advantages of the STEM, incoherent imaging and simultaneous collection of multiple complementary images can now give new insights into many areas of materials physics. Here, we review a number of examples, mostly from the field of complex oxides, and look towards new directions for the future.     

Atomically resolved mapping of EELS fine structures

Over the past two or three decades, nanoscience and nanotechnology have clearly established themselves as prominent domains in research in physics, not only because of the innovative concepts and properties that they display but also for their capacity to generate many important applications and commercial developments. As many of these new devices exhibit a range of properties (transport, optical, magnetic, catalysis) which are governed by local structural and electronic configurations, such as coordination and bonding at the atomic level, it is no surprise that new tools of investigation are constantly being developed for imaging, analyzing, understanding and controlling at the relevant scale. Among them, electron microscopy has recently demonstrated its ability to meet many of these requirements. In particular, Å-sized probes are nowadays generated by aberration correctors in a scanning transmission electron microscope (STEM) and they can investigate the electron excitation spectrum of the specimen (through electron energy-loss spectroscopy, EELS) with a typical energy resolution of 0.1–0.3 eV over a broad spectral band from the IR to the X ray domain. In the high energy range, characteristic signals due to the excitation of atomic core levels are quite useful because they identify the atoms in the analyzed volume (which can itself be as small as a single atom) and can therefore deliver atomically-resolved elemental maps. But the pixel-by-pixel recording of the fine structures beyond the characteristic threshold is much more informative and tells us how the excited atom is surrounded by its neighbors, what is its exact structural environment and its charge population. The present review focuses on this particularly exciting field, with a special interest in the types of information accessible and their signature. After summarizing the ingredients required for successful experiments (instrumental as well as theoretical), examples encountered in different situations, in particular in single layers of 2D materials and at the interfaces in oxide heterostructures, will demonstrate the present capabilities of this STEM-EELS technique.     

One‐Step Synthesis and Optical Properties of Benzoate‐ and Biphenolate‐Capped ZrO2 Nanoparticles

A simple one‐pot approach based on the “benzyl alcohol route” is used for the preparation of benzoate‐ and biphenolate‐capped zirconia and, benzoate‐capped Eu‐doped zirconia nanoparticles. Powder X‐ray diffraction studies and high‐ resolution transmission electron microscopy (HR‐TEM) showed that the nanoparticles present high crystallinity and uniform particle sizes ranging from 3 to 4 nm. FT‐IR and solid state NMR (SS‐NMR) studies revealed that the nanoparticles are coated with a large amount of organic species when the reaction temperature is above 300 °C. It was found that the alcohol used as solvent is oxidized at the surface of the nanoparticles to the respective carboxylic acid which acts as a stabilizer, controlling the nanoparticles growth. The optical properties of these hybrid nanoparticles were studied by room and low (12K) temperature photoluminescence spectroscopy, time‐resolved spectroscopy and absolute emission quantum yield. The as‐synthesized benzoate‐ and biphenolate‐capped nanoparticles exhibit interesting emission properties in the UV and blue spectral regions together with values of emission quantum yields much higher than those reported for zirconia nanoparticles of similar size. The photoluminescent properties were attributed to a cooperative effect of the capping ligands and the defects associated to the ZrO₂ nanoparticles. Due to the overlapping of the various emission components involved (i.e., the emission of europium(III) intra‐4f⁶ transitions, defects in the zirconia and capping ligands) a tunable emission color ranging from purplish‐pink to greenish‐blue could be obtained for the europium‐doped zirconia nanoparticles by simply selecting different excitation wavelengths.     

Probing Functional Structures,Defects, and Interfaces of 2D Transition Metal Dichalcogenides by Electron Microscopy

2D transition metal dichalcogenides (TMDs) exhibit remarkable properties that are strongly influenced by their atomic structures, as well as by various types of defects and interfaces that can be precisely engineered and controlled. These features make 2D TMDs and TMD-based materials highly promising for a wide range of applications in electronics, optoelectronics, magnetism, spintronics, catalysis, energy, etc. By providing a comprehensive approach to understand the structure–property–functionality relationship in materials at the atomic scale, electron microscopy, and spectroscopy techniques have emerged as invaluable tools for studying both the static characteristics and dynamic evolutions of 2D TMDs. In this review, the primary focus lies in exploring intrinsic and artificial structures in TMDs and their heterostructures, along with their corresponding properties, through cutting-edge aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). Additionally, recent advancements in the field of in situ visualization and manipulation of 2D TMDs using electron beams are highlighted. It is anticipated that the up-to-date overview provided, along with a glimpse into the future development of STEM-based techniques, will make a substantial contribution to advancing research on 2D materials.     

Electron diffraction from laser-aligned beams of large hydrated molecules

We consider X-ray or electron diffraction from a molecular beam of hydrated proteins. These are aligned by the polarized field of a powerful continuous infrared laser. The laser power, temperature and molecular size needed to obtain sufficient alignment accuracy for sharp diffraction patterns is estimated using a thermal average, and the resulting Dawson integral compared with the estimate based on equipartition used in our previous work. The conditions determined allow sub-nanometer resolution charge-density maps to be reconstructed from phased diffraction patterns, so that the secondary structure of the proteins can be observed.     

Nanoscale Disorder and Deintercalation Evolution in K-Doped MoS2 Analysed Via In Situ TEM

Intercalation and deintercalation processes in van der Waals crystals underpin their use in nanoelectronics, energy storage, and catalysis but there remains significant uncertainty regarding these materials’ structural and chemical heterogeneity at the nanoscale. Deintercalation in particular often controls the robustness and cyclability of the involved processes. Here, a detailed analysis of potassium ordering and compositional variations in as-synthesised K intercalated MoS₂ as well an analysis of deintercalation induced changes in the structure and K/Mo elemental composition is presented. By combining 4D scanning transmission electron microscopy (4DSTEM), in situ atomic resolution STEM imaging, selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS) the formation of previously unknown intermediate superstructures during deintercalation is revealed. The results provide evidence supporting a new deintercalation mechanism that favors formation of local regions with thermodynamically stable ordering rather than isotropic release of K. Systematic time-temperature measurements demonstrate the deintercalation behavior to follow first-order kinetics, allowing compositional and superstructural changes to be predicted. It is expected that the in situ correlative STEM-EDS/SAED methodology developed in this work has the potential to determine optimal synthesis, processing and working conditions for a variety of intercalated or pillared materials.     

Spatially-resolved EELS analysis of multilayer using EFTEM and STEM

Spatially-resolved electron energy-loss spectroscopy (EELS) is applied to the multilayer (SiO2/Si3N4/SiOxNy/Si), a common semiconductor device structure. To observe depth profile at sub-nanometre spatial resolution, scanning transmission electron microscopy (STEM) and energy-filtering transmission electron microscopy (EFTEM)-based techniques are compared in practical application. STEM-based EELS is useful in simultaneously analysing plural elements. EFTEM-based EELS is suitable for analysing the chemical shift and core loss intensity of single element. The practical spatial resolution is of the same order for each technique, both involving beam damage, which can be reduced by decreasing current density in EFTEM and avoiding beam overlapping in STEM.     

Sandwiched Ruthenium/Carbon Nanostructures for Highly Active Heterogeneous Hydrogenation

The immobilization of metal nanoparticles in the framework of porous carbon for heterogeneous catalysis may avoid particle aggregation, movement, and leaching, thus leading to a high catalyst efficiency. In this Full Paper, an approach to prepare Ru nanoparticles incorporated into the pore walls of porous carbon to form a sandwiched Ru/C nanostructure for heterogeneous hydrogenation is demonstrated. Physical adsorption of nitrogen, X‐ray diffraction, thermogravimetric analysis, field‐emission transmission electron microscopy, field‐emission scanning electron microscopy, and energy dispersive X‐ray spectroscopy techniques are employed to study the structure and morphology of the catalysts. Catalytic results show that the Ru nanoparticles sandwiched in the pore walls of porous carbon display a remarkably high activity and stability in the hydrogenation of benzene. An enhanced hydrogen spillover effect is believed to play a significant role in the hydrogenation reaction because of the intimate interfacial contact between Ru nanoparticles and the carbon support. The catalyst system described in this work may offer a new concept for optimizing catalyst nanostructures.     

Atomic resolution Z-contrast imaging of semiconductors

The direct interpretability of atomic resolution Z-contrast images obtained from a scanning transmission electron microscope (STEM) makes this imaging technique particularly powerful for the analysis of interfaces and defects in semiconductor materials and devices. In this paper, the principles of the technique are outlined and representative examples of its use are presented. In particular, we show the use of Z-contrast imaging to determine the polarity of a CdTe film grown on a Si substrate, the atomic structures of stacking faults and threading dislocation cores in GaN, and the atomistic structure of an ohmic metal/semiconductor contact of Au/GaAs.     

球状微米金刚石的制备过程及其场发射性能的研究

在纯平的陶瓷衬底上面,利用磁控溅射方法镀上一层金属钛。对金属钛层进行表面缺陷处理后,放入微波等离子体化学气相沉积腔中,利用正交实验方法制备出场发射性能最优的薄膜,通过扫描电镜、X射线衍射仪、拉曼光谱仪等仪器,研究了薄膜的微观表面形态、结构组成等,得到了该薄膜是球状微米金刚石薄膜的结论。并进一步研究了最优场发射薄膜的发射机理。     

A specimen-drift-free EDX mapping system in a STEM for observing two-dimensional profiles of low dose elements in fine semiconductor devices

We developed a specimen-drift-free energy-dispersive X-ray (EDX) mapping system in a scanning transmission electron microscope (STEM) to improve the sensitivity and spatial resolution of EDX elemental mapping images. The amount of specimen drift was analysed from two STEM images before and after specimen drift by using the phase-correlation method, and was compensated for with an image-shift deflector of the STEM by the displacement of the scanning electron beam. We applied this system to observe the two-dimensional distribution of low dose arsenic in silicon semiconductor devices. The sensitivity of the elemental mapping was improved to several tenths atomic % for arsenic atoms while maintaining a spatial resolution of 2 nm.     

The development and characteristics of a high-speed EELS mapping system for a dedicated STEM

A new EELS (electron energy loss spectroscopy) real-time elemental mapping system has been developed for a dedicated scanning transmission electron microscope (STEM). The previous two-window-based jump-ratio system has been improved by a three-window-based system. It is shown here that the three-window imaging method has less artificial intensity in elemental maps than the two-window-based method. Using the new three-window system, the dependence of spatial resolution on the energy window width was studied experimentally and also compared with TEM-based EELS. Here it is shown experimentally that the spatial resolution of STEM-based EELS is independent of the energy window width in a range from 10 eV to 60 eV.     

Self‐Assembly and Metallization of Resorcinarene Microtubes in Water

Amphiphilic resorcinarene‐based multiwalled microtubes, millimetres in diameter and centimetres in length, are generated in water. The thickness of the tube wall approaches 300 nm. Their self‐assembly properties are investigated using transmission electron microscopy, scanning electron microscopy, atomic‐force microscopy, dynamic light scattering, X‐ray diffraction, UV‐vis spectra, and Fourier transform IR techniques. From these studies, the structures critical for the self‐assembly of resorcinarene into microtubes in aqueous media are determined. Furthermore, the study manifests a feasible method that aims to completely change the structure from a microtube to a sheet‐like morphology by selectively eliminating key groups. Subsequently, resorcinarene‐capped water‐soluble gold nanoparticles (AuNPs) are fabricated. By utilizing the obtained microtubes as a template, a gold/organic microtubular composite is successfully prepared.