Chapter 7 - Electron-Based Imaging Techniques

Exploring the structural, dynamical, mechanical, electronic, magnetic, and optical properties of Ta2AlN, Ti2AlN & Ti2GaN MAX phase compounds: First-principles study

No abstract is available for this article.

The thermal, mechanical, catalytic and adsorptive properties, etc. are the key factors dominating the applied field of precious metal materials. High temperature alloys doped by precious metal elements have high strength, excellent room temperature, high temperature oxidation resistance and corrosion resistance, excellent in fatigue resistance, good long-term stability, which applies in many fields, such as industrial catalyst, coating materials and medical biological etc. The structural, electronic, elastic, adsorptive, catalytic and magnetic properties of the precious metal materials are summarized systemically via first-principles calculations based on density functional theory. Moreover, the density functional theory has been introduced which provided theoretical support for subsequent analysis. In this review, recent advances of calculating the electronic and mechanical properties of pure, binary and ternary precious metal materials via first-principles calculations methods are concluded comprehensively. Lastly, conclusion and outlook are assessed briefly to further refine calculation of precious metal materials and provided guidance for experiment and its application.

Effect of electron beam irradiation on multi-walled carbon nanotubes

Electron beam induced deposition (EBID) is a promising technique for fabricating nanometre-sized structures in a position-controlled manner. In this technique, organometallic precursors are decomposed by focused electron beams. Then, the non-volatile part of the decomposed precursor deposits on the substrate. As electron beams can be focused to a subnanometre scale in modern electron microscopes, the resolution of EBID is now reaching down to subnanometres. However, the deposits generally contain a large amount of amorphous carbon. This carbon contamination may be the most serious drawback and is preventing practical uses of EBID in nanodevice technology. In this study, nanostructures, such as nanowires, were fabricated by EBID using methyl cyclopenta dienyl platinum trimethyl (MeCpPtMe3) and iron pentacarbonyl (Fe(CO)5) precursors in a scanning electron microscope with a custom-made gas introduction system. After the deposition, nanostructures were heated at 400°C in air for 30 min. to remove contaminated carbon. Then, the nanostructures were observed using a transmission electron microscope (TEM). TEM observation revealed that a post-deposition heat-treatment in air resulted in the removal of carbon. The nanostructures made from MeCpPtMe3 and Fe(CO)5 became pure Pt and a mixture of hematite and maghemite iron oxides, respectively.

A novel approach for the localization of weak points in thin transistor and capacitor oxides before electrical breakdown will be presented in this paper. The proposed approach utilizes Electron Beam Absorbed Current (EBAC) imaging based on Scanning Electron Microscopy (SEM). This technique uses the generation of additional charge carriers within the semiconductor substrate level by scanning with a focused electron beam. Over a thin transistor or capacitor oxide layer inside the interaction volume of the electron beam an increased tunnel current is visualized by EBAC and shows areas with different current intensities indicating weak points. These soft defect areas are investigated in comparison to references which were analyzed by using cross sectioning in a dual beam FIB/SEM system followed by a high resolution Transmission Electron Microscopy (TEM) investigation. The feasibility of this new technique is demonstrated on a defective transistor gate oxide test structure.

Vladimir P. Oleshko and James M. Howe University of Virginia, Department of Materials Science & Engineering, Charlottesville, VA 22904 Understanding physical principles for controlling the dynamic behavior of nanoparticles in inhomogeneous gas (liquid) – solid systems is becoming increasingly important for nanoscience and technology. Nondestructive trapping of micron- and nano-sized dielectric and metal particles in a liquid using a laser beam, which is refracted by the particle and transfers momentum to it, is known as a single-beam gradient force optical trap, or optical tweezers [1]. Recent experiments utilizing partially molten submicron-sized Al-Si alloy spheres and a focused electron beams in a medium-voltage TEM [2] and theoretical calculations of linear and angular momentum transfer from an electron beam to small particles [3] indicate that optical trapping of particles using electron beams may occur. Such thermally assisted “electron tweezers” potentially can be utilized for manipulation and processing of individual nanoobjects and fabrication of assembled nanodevices with up to atomic level sensitivity and lateral resolution provided by modern electron optical systems. In this work, we demonstrate electron-beam trapping of solid nanoparticles inside opaque submicron-sized Al-Si alloy spheres using energy filtering TEM (EFTEM) and parallel electron energy-loss spectroscopy (PEELS). Thermally assisted motion of crystalline Al nanospheres confined within the partially molten Al-Si particles was initiated by the electron beam, which was used to control and to observe the trapping in real-time by plasmon spectroscopic imaging (Fig. 1). Such approaches enable

A novel method for directly applying material on only a very small area of a substrate (selective deposition) at low temperature has been reported by applying a gas-substrate interface1-7). When an electron beam is irradiated onto a substrate in electron beam Chemical Vapor Deposition (CVD), source gas molecules, adsorbed on a substrate, are dissociated into nonvolatile and volatile materials. Nonvolatile materials are deposited on a substrate, which volatile materials are evacuated. Nanometer structures can be fabricated by electron beam CVD, using electron beam induced surface reaction, because beam diameters as small as 5 Å can be formed with conventional electron equipment8). Computer controlled direct writing also is possible for electron beam CVD. Metals, semiconductors, and inorganic materials can be deposited by this means. Thus, electron beam CVD has some excellent advantages over other CVD methods. Namely, processing methods in microelectronic devices can be simplified and new structure devices with nanometer dimensions can be realized. When source gas molecules adsorbed on a substrate are dissociated by electron beam irradiation, Auger electrons are emitted from deposited materials at the same time. Therefore, the deposited material growth process can be observed in situ by Auger electron spectroscopy (AES)3,7). Moreover, the deposited material growth process can be observed in situ by transmission electron microscopy (TEM), if source gas molecules are adsorbed on a TEM specimen5,6). This paper presents results obtained for AES and TEM W electron beam CVD observation in situ, using the WF6 source.

When 2205 duplex stainless steel (DSS) is immersed in simulated seawater under high hydrostatic pressure, or in an electrochemically hydrogen charged state, a spindle-shaped product is found in the ferrite phase that seriously deteriorates the mechanical properties of 2205 DSS. This paper systematically studied the composition, structure, and properties of the hydrogen charging product. The results of a slow strain rate tensile test show that the hydrogen charging product evidently reduces the elongation of 2205 DSS, and microcracks mainly initiate at the interface between the hydrogen charging product and the ferrite matrix at either a low or a high strain rate. However, the elongation recovers to that of the hydrogen free sample after heating the sample at 300 °C for 0.5 h. The nano-hardness and reduced modules of the product are higher than those of the ferrite and austenite phases. An element analysis by energy dispersive spectroscopy (EDS) and secondary ion mass spectrometry (SIMS) indicates that the Ni and H contents in the hydrogen charging product are higher than in the normal ferrite area, and X-ray diffraction shows the characteristic peak of iron hydride at 40.07°. Moreover, a differential scanning calorimeter (DSC) test demonstrated that the phase decomposition temperature of the product is 268 °C, which coincides with the fact that it dissolves at a high temperature caused by the focused electron beam during transmission electron microscopy (TEM) analysis. All experimental results indicate that the hydrogen charging product is a hydride of FeH or (Fe, Ni)H.

In this presentation, I show how advanced approaches within density functional theory, namely dispersive corrections and optimal tuning of range-separated hybrid functionals, can lead to quantitative predictive power for structural, electronic, and optical properties of organic electronic materials.

Experimental simulation of Edge Localised Modes using focused electron beams – features of a circular load pattern

The application prospects of ZnS stress luminescent materials cover many fields such as high‐precision structural monitoring, smart materials, biomedical imaging, and new sensor technologies, which bring broad application prospects and significance to them in the fields of engineering, medicine, and scientific research. In this article, the electronic structure and optical properties of ZnS materials are successfully regulated by applying pressure and doping rare earth metals (Re), and it is found that the regulation of the luminescence properties of ZnS is the result of stress and doping interactions. Specifically, when pressure is applied or Re metal doping, the lattice structure is deformed and the atomic spacing is adjusted, which affects the electronic energy level distribution and optical properties of ZnS materials. Computational analysis of density functional theory (DFT) reveals the microscopic mechanisms behind these changes, including changes in lattice parameters, adjustment of bond length, and changes in band structure. This study provides theoretical guidance for the design and synthesis of high‐performance and high‐stability ZnS light‐emitting materials, and is of great significance for expanding the application of ZnS in the field of lasers and sensors.

The recent progress in the studies of 2D materials placed in front many experimental and theoretical works on the interesting class of materials, the so-called transition metal phosphorus trichalcogenides with structural formula MPX3 (M: transition metal, X: chalcogen). Here, the diversity in the M/X combination opens the possibility to tune the electronic and magnetic properties of these materials in a very wide range, resulting in many interesting physical phenomena followed by the promoting their use in different application areas. This review gives a timely overview of the recent progress in the fundamental studies of electronic structure and magnetic properties of MPX3 materials (M: Mn, Fe, Co, Ni, X: S, Se) focusing on the results obtained by density functional theory, Raman spectroscopy and electron spectroscopy methods. We pay close attention to the large amount of theoretical and experimental data giving critical analysis of the previously obtained results. It is shown how the systematic fundamental studies of the electronic and magnetic properties of MPX3 can help to understand the functionality of these interesting 2D materials in different applications, ranging from optoelectronics to catalysis.

Measuring the physical properties of 2D materials and correlating the spatial variation of these physical properties to the structure provides a route to better understand these materials. A very powerful tool for probing the surface structure and local electronic properties is scanning tunneling microscopy. Scanning tunneling spectroscopy allows the observation of electronic spectral properties with a resolution down to the atomic scale. In this thesis, we mainly employed scanning tunneling microscopy and scanning tunneling spectroscopy to study the structure and electronic properties of different types of 2D materials. Such fundamental research can help us to understand the 2D materials at the nano-scale, and pave the way towards the application of these materials in future electronic devices. In this thesis, we have studied the structural and electronic properties of various 2D materials by using scanning tunneling microscopy and scanning tunneling spectroscopy techniques. Their intrinsic electronic properties are modified via varied ways, such as stacking, hydrogenation, defects and so on. The main points are as follows. In the twisted graphene with a twisted angle of 2o, we have revealed the Van Hove singularities and spatially mapped the electronic structure with the atomic resolution. With the help of dI/dz spectroscopy, we have proved the growth behavior of silicon on TMDs at room temperature. We propose that the silicon atoms prefer to intercalate in the TMDs at the beginning of the growth due to defects in TMDs. For the first time, we have successfully synthesized germanene on a bandgap material, which paves the way towards determining the intrinsic properties of this novel 2D buckled Dirac material. The existence of charge puddles in germanene on MoS2 substrate is resulted from the charge-donating impurities in MoS2. Hydrogenation of germanene, synthesized on Ge2Pt nanocrystals, results in the opening of a bandgap of about 0.5 eV, which means hydrogenated germanene is a promising material for applications of field-effect devices. The high density of defects in HfSe2 mainly degrade its electrical performance, thus the quality of HfSe2 crystal should be carefully evaluated before it is used to make devices.

Cu-based ternary oxides with delafossite structure have received considerable attention in recent years for their versatility in a wide range of applications, among which is the possibility to use them in heterostructure solar cells as hole transport layers, due to their promising behavior as p-type conducting oxides. Ab initio calculations have been performed with density functional theory to investigate the role of the trivalent metal within the CuMO2 structure and the dependence of structural and electronic properties with the species (M = Al, Ga, In, Fe, Cr, Co, Sc, Y) occupying the site of the metal. Generalized Gradient Approximation also including a Hubbard term and nonlocal Heyd–Scuseria–Enzerhof screened hybrid functional schemes were tested and their results were compared. Excellent agreement with experimental lattice parameters and measured gaps have been found. The use of hybrid functionals in HSE approximation considerably improves the bandgaps when compared with the experimental results but takes considerable time to converge, hence the need to explore less demanding methodologies. Trends in the geometry as well as in the electronic properties are discussed, and the effect of mixing different metals (CuMxN1−xO2, M, N being the aforementioned elements) in the geometry and electronic properties of these delafossite materials is investigated. Due to the high cost of HSE calculations, especially when supercells are needed to model several x concentrations, statistical models and techniques based on machine learning have also been explored to predict HSE bandgap values from GGA and structural information.