Systematic row and zone axis STEM defect image simulations

Transmission electron microscopy (TEM) has been instrumental in advancing the field of crystalline defect analysis. Conventional TEM imaging techniques, such as bright field (BF), dark field (DF), and weak beam dark field (WBDF or g–3g) imaging, have been well-documented in the scientific literature, with simulation methods readily available for each. The present contribution highlights the use of a field-emission TEM, operated in scanning transmission electron microscopy mode, as a viable tool for defect analysis. Common techniques such as two-beam diffraction contrast and zone axis imaging are applied to defect analysis; both experimental and computational results are presented. Effects of experimental parameters such as camera length, beam divergence angle, and diffraction aperture placement are also discussed and illustrated by both experimental and computed micrographs of stacking faults.     

2D strain measurement in sub-10 nm SiGe layer with dark-field electron holography

In this paper, we carried out the two-dimensional (2D) strain measurement in sub-10 nm SiGe layer; images were obtained by dark-field electron holography (DFEH). This technique is based on transmission electron microscopy (TEM), in which dark-field holograms were obtained from a (400) diffraction spot. The measured results were compared to the X-ray diffraction (XRD) results in terms of the strain value and the depth of strain distribution in a very thin SiGe layer. Subsequently, we were able to successfully analyze the 2D strain maps along the [100] growth direction of the nanoscale SiGe region. The strain was measured and found to be in the range of 1.8–2.4%. The strain precision was estimated at 2.5 × 10⁻³. As a result, the DFEH technique is truly useful for measuring 2D strain maps in very thin SiGe layers with nanometer resolution and high precision.     

Comparison of off-axis and in-line electron holography as quantitative dopant-profiling techniques

Many different dopant-profiling techniques are available for semiconductor device characterization. However, with length scales shrinking rapidly, only transmission electron microscopy (TEM) techniques promise to fulfil the spatial resolution required for the characterization of future device generations. Here, we use three advanced TEM techniques, off-axis electron holography, Fresnel imaging (in-line electron holography) and Foucault imaging, to examine a focused ion beam-prepared silicon p–n junction device. Experiments are carried out on electrically unbiased samples and with an electrical bias applied in situ in the TEM. Simulations are matched to experimental data to allow quantitative conclusions to be drawn about the underlying electrostatic potential distributions. The off-axis electron holography and Fresnel results are compared to assess whether the techniques are consistent, and whether they can be used to provide complementary information about dopant potentials in semiconductor devices.     

Using transmission Kikuchi diffraction to study intergranular stress corrosion cracking in type 316 stainless steels

Transmission Kikuchi diffraction (TKD), also known as transmission-electron backscatter diffraction (t-EBSD) is a novel method for orientation mapping of electron transparent transmission electron microscopy specimen in the scanning electron microscope and has been utilized for stress corrosion cracking characterization of type 316 stainless steels. The main advantage of TKD is a significantly higher spatial resolution compared to the conventional EBSD due to the smaller interaction volume of the incident beam with the specimen.Two 316 stainless steel specimen, tested for stress corrosion cracking in hydrogenated and oxygenated pressurized water reactor chemistry, were characterized via TKD. The results include inverse pole figure (IPFZ) maps, image quality maps and misorientation maps, all acquired in very short time (<60 min) and with remarkable spatial resolution (up to 5 nm step size possible). They have been used in order to determine the location of the open crack with respect to the grain boundary, deformation bands, twinning and slip. Furthermore, TKD has been used to measure the grain boundary misorientation and establish a gauge for quantifying plastic deformation at the crack tip and other regions in the surrounding matrix. Both grain boundary migration and slip transfer have been detected as well.     

Sphere-shaped SiGe micro/nanostructures with tunable Ge composition and size formed by laser irradiation

SiGe spheres with different diameters are successfully fabricated on a virtual SiGe template using a laser irradiation method. The results from scanning electron microscopy and micro-Raman spectroscopy reveal that the diameter and Ge composition of the SiGe spheres can be well controlled by adjusting the laser energy density. In addition, the transmission electron microscopy results show that Ge composition inside the Si Ge spheres is almost uniform in a well-defined, nearly spherical outline. As a convenient method to prepare sphere-shaped SiGe micro/nanostructures with tunable Ge composition and size, this technique is expected to be useful for Si Ge-based material growth and micro/optoelectronic device fabrication.     

暗中空光束的产生及应用

综述了几何光学、模式变换、光学全息、计算全息、横模选择、中空光纤等几种产生暗中空光束的方法,并简单介绍了暗中空光束在原子光学及其他领域的应用。     

Deformation and annealing behavior. I. Polyethylene terephthalate films

The morphology and deformation behavior of uniaxially and biaxially oriented thin polyethylene terephthalate (PET) films was examined by bright field, diffraction and dark field electron microscopy. A large, 250-500 Å, nodule structure was observed under a variety of conditions, in addition to the smaller 75–100 Å nodules that have been reported previously. Dark field micrographs indicate that oriented PET, heat set at 180° to 240° C, is composed of small (140 Å) isometric crystallites, with a tendency to orient the 100 plane in the plane of the film. It is suggested that the nodular structure and small isometric crystallites may contribute to PET ductility at low temperatures.     

Deformation and annealing behavior. III. thin films of polycarbonate,isotactic polymethyl methacrylate,and isotactic polystyrene

The morphology of thin films of polycarbonate (PC), isotactic polymethyl methacrylate (i-PMMA), and isotactic polystyrene (i-PS) were studied by bright field, diffraction, and dark field transmission, electron microscopy. The films were thermally annealed both before and after uniaxial deformation. The undrawn i-PMMA did not develop a crystalline texture upon annealing whereas the undrawn i-PS developed a random arrangement of lamellae. Thermal crystallization of undrawn PC has been shown to occur through the growth and merging of a nodular structure into fibrillar spherulites. Deformation of gold-decorated samples indicated a nonhomogeneous structure in the amorphous polymer on the 200-500 A scale. Thermal annealing of drawn samples resulted in fibrillar lamellae arranged perpendicular to the draw direction for all three polymers, indicating the straining has a marked influence on the crystalline morphology. This morphology is compared to similar morphologies reported in the literature for crystallization from stressed melts. High-resolution dark field micrographs confirm this morphology and indicate variations in crystallite size, depending upon the polymer and deformation conditions.     

New directions in X-ray microscopy

The development of high brightness X-ray sources and high resolution X-ray optics has led to rapid advances in X-ray microscopy. Scanning microscopes and full-field instruments are in operation at synchrotron light sources worldwide, and provide spatial resolution routinely in the 25–50 nm range using zone plate focusing elements. X-ray microscopes can provide elemental maps and/or chemical sensitivity in samples that are too thick for electron microscopy. Lensless techniques, such as diffraction microscopy, holography and ptychography are also being developed. In high resolution imaging of radiation-sensitive material the effects of radiation damage needs to be carefully considered. This article is designed to provide an introduction to the current state and future prospects of X-ray microscopy for the non-expert.     

Correlative microscopy of a carbide-free bainitic steel

In this work a carbide-free bainitic steel was examined by a novel correlative microscopy approach using transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). The individual microstructural constituents could be identified by TKD based on their different crystal structure for bainitic ferrite and retained austenite and by image quality for the martensite–austenite (M–A) constituent. Subsequently, the same area was investigated in the TEM and a good match of these two techniques regarding the identification of the area position and crystal orientation could be proven. Additionally, the M–A constituent was examined in the TEM for the first time after preceded unambiguous identification using a correlative microscopy approach. The selected area diffraction pattern showed satellites around the main reflexes which might indicate a structural modulation.     

Characterization of solution-synthesized CdTe and HgTe

We report the characterization of solution-synthesized CdTe and HgTe nanocrystals by X-ray diffraction, transmission electron microscopy, and photoluminescence. Methanol solutions of sodium telluride and cadmium iodide or mercury iodide, respectively, are reacted to precipitate the nanocrystalline metal tellurides, while the sodium iodide byproduct remains in solution. The existence of crystalline CdTe, HgTe, and ternary HgCdTe compounds has been demonstrated by powder X-ray diffraction after a post-synthesis sintering process. Precipitated crystallites from this synthesis were analyzed by transmission electron microscopy, which revealed that crystal diameters can vary from approximately 1 nm to 100 nm and that crystals are stoichiometric within the detection limit of the electron microprobe technique. Narrow size ranges can be selected and investigated due to an in-situ separation process in the electron microscope. Photoluminescence is found at energies above the bulk exciton energy for CdTe and is attributed to near-band-gap recombination which is blue-shifted due to quantum confinement. Both low defect luminescence and dark field imaging suggest a high crystalline quality. A comparative characterization by photoluminescence, transmission electron microscopy, and X-ray diffraction evaluates the effects of heat treatments during and after synthesis.     

基于线性成像系统的光学超分辨显微术回顾

随着纳米科学技术的发展,如何打破光学衍射极限,将光学显微术的分辨本领推进到纳米尺度,已经成为光学领域的一个核心议题.在此背景下,过去的三十年间,发展了多种超分辨光学显微技术,并在生物、材料、化学领域取得了一系列令人瞩目的应用.本文以衍射理论为线索,回顾各类基于线性成像系统的超分辨光学显微技术;对以固浸物镜、结构光照明、扫描近场光学显微术、完美透镜以及超振荡透镜为代表的超分辨光学显微技术进行综述,讨论各种技术的原理,对其特点、应用与局限加以总结,并对该领域的未来发展予以展望.     

Effect of severe plastic deformation by torsion on the structure and properties of TiNi-based alloys with shape memory effects

The microstructure and properties of TiNi-based shape memory alloys subjected to severe plastic deformation by torsion have been studied using transmission electron microscopy, X-ray diffraction analysis, and mechanical measurements.     

FePt L10 ordering and grain growth using millisecond pulse laser processing

The structural and magnetic properties of ∼12 nm thick FePt thin films grown on Si substrates annealed using a 1064 nm wavelength laser with a 10 ms pulse have been examined. The A1 to L1₀ ordering phase transformation was confirmed by electron and X-ray diffraction. An order parameter near 50% and a maximum coercivity of 12 kOe were obtained with laser energy densities of 25-32 J/cm². Grain growth, quantified by dark field transmission electron microscopy, occurred during chemical ordering at the laser pulse widths studied.     

Elemental electron energy loss mapping of a precipitate in a multi-component aluminium alloy

The elemental distribution of a precipitate cross section, situated in a lean Al-Mg-Si-Cu-Ag-Ge alloy, has been investigated in detail by electron energy loss spectroscopy (EELS) and aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). A correlative analysis of the EELS data is connected to the results and discussed in detail. The energy loss maps for all relevant elements were recorded simultaneously. The good spatial resolution allows elemental distribution to be evaluated, such as by correlation functions, in addition to being compared with the HAADF image.The fcc-Al lattice and the hexagonal Si-network within the precipitates were resolved by EELS. The combination of EELS and HAADF-STEM demonstrated that some atomic columns consist of mixed elements, a result that would be very uncertain based on one of the techniques alone. EELS elemental mapping combined with a correlative analysis have great potential for identification and quantification of small amounts of elements at the atomic scale.     

全息术及其应用

全息术是一种用相干光干涉得到物体全部信息的2步成像技术。全息术的发展大约可分同轴全息术、离轴全息术、白光再现全息术、白光全息术等4个阶段。全息术具有三维、不可撕毁、再现像的缩放、信息容量大等特点。全息术是一门正在蓬勃发展的光学分支，近年来已渗透到社会生活的各个领域并被广泛地应用于近代科学研究和工业生产中，特别是在现代测试、生物工程、医学、艺术、商业、保安及现代存储技术等方面已显示出特殊的优势。随着全息技术的快速发展，全息技术的产品正越来越多地走向市场、应用于现代生活中。     

Precipitation in silicon wafers after high temperature preanneal studied by X-ray diffraction methods

We have investigated oxygen precipitation in Czochralski silicon wafers focusing on influence of nucleation temperature and high temperature pre-anneal during common three step treatment. Thick Si wafers were studied mainly by x-ray diffraction in Laue transmission geometry using Mo x-ray tube, but were also compared to reciprocal space maps obtained in Bragg reflection geometry. The analysis of measured diffraction scans in Laue geometry was performed by means of Takagi equations and statistical dynamical theory of diffraction. From the simulated Laue diffraction curves we find the size of the individual defect area and the fraction of strain area volume in the wafer. The results obtained from x-ray diffraction were compared to loss of interstitial oxygen according to infrared absorption spectroscopy and the size of SiO₂ precipitate core was estimated. These techniques are in agreement with transmission electron microscopy images.     

Analysis of precipitates in ultrafine-grained metallic materials

In the present work, new possibilities of the X-ray diffraction for investigations of the phase composition, size, shape and volume fraction of particles in ultrafine-grained ferritic/martensitic steel and the Cu-Cr-Zr alloy have been demonstrated. For the first time, the method of X-ray diffraction in the transmission mode was used to identify particles with a volume fraction of less than one percent in the ultrafine-grained materials studied. The small-angle X-ray scattering method was used to estimate the size and shape of dispersed particles. Specific features of the ultrafine-grained structure determined by the X-ray diffraction and transmission electron microscopy studies were used for estimation of dispersion hardening in the samples obtained by equal-channel angular pressing in comparison with the samples subjected to standard treatment.     

Establishing the microstructure-strengthening correlation in severely deformed surface of titanium

Surface nanostructuring of engineering materials can be utilised to enhance materials performance for various applications. The aim of this work was to investigate the evolution of microstructure and its correlation with strengthening mechanisms in nanocrystalline commercially pure titanium (cp-Ti) produced by surface mechanical attrition treatment (SMAT). The individual contributions of dislocation slip and twining as the deformation mechanisms during SMAT have been quantified using X-ray line profile analysis and corroborated with transmission electron microscopy and electron backscattered diffraction techniques. It is found that twining is operative only in the early stages of deformation. The absence of twin–twin intersections suggests that twining is not directly responsible for the initial refinement of grain size. Dislocation slip is the major deformation mode, which leads to the refinement of the microstructure by forming low-angle lamellar boundaries. Continuous dynamic recrystallisation is demonstrated to be the mechanism of nanocrystallisation in cp-Ti using detailed microscopic analysis. In contrast to previous studies, which have neglected the contribution of Taylor strengthening, it is observed that a combination of Hall–Petch and Taylor relationships can explain the strength only if separate set of parameters K (Hall–Petch constant) and α (geometrical factor in Taylor relationship) are used for the nanocrystalline surface and severely deformed sub-surface of cp-Ti. Taken together, this work provides new insights into the underlying mechanisms for engineering nanocrystalline materials.     

Electrosynthesis and characterization of CdSe thin films: Optimization of preparative parameters by photoelectrochemical technique

CdSe thin films have been electrodeposited potentiostatically onto stainless-steel and fluorine-doped tin oxide-coated glass substrates from an aqueous acidic bath using cadmium acetate ((CH₃COO)₂Cd·2H₂O) as a Cd ion source. Preparative parameters such as deposition potential, solution concentration, bath temperature, pH of the electrolytic bath and deposition time have been optimized by using photoelectrochemical (PEC) technique to obtain well adherent and uniform thin films. The electrodeposits were dark brown in colour. The films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical absorption techniques. XRD studies reveal that films are polycrystalline, with hexagonal crystal structure. SEM shows that the films are compact, with spherical grains. Optical absorption studies reveal that the material exhibits a direct optical transition having band gap energy ∼1.72 eV. PEC study shows that the films are photoactive.