In situ TEM measurements of the mechanical properties and behavior of WS2 nanotubes

The mechanical properties of individual WS2 nanotubes were investigated and directly related to their atomic structure details by in situ transmission electron microscope measurements. A brittle mode deformation was observed in bending tests of short (ca. 1 μm in length) multilayer nanotubes. This mode can be related to the atomic structure of their shells. In addition, longer nanotubes (6-7μm in length) were deformed in situ scanning electron microscope, but no plastic deformation was detected. A “sword-in-sheath” fracture mechanism was revealed in tensile loading of a nanotube, and the sliding of inner shells inside the outermost shell was imaged “on-line”. Furthermore, bending modulus of 217 GPa was obtained from measurements of the electric-fieldinduced resonance of these nanotubes.     

TEM characterization of ALD layers in deep trenches using a dedicated FIB lamellae preparation method

Driven by the shrinking of microelectronic devices there is a demand for novel high-k insulators and electrode materials. Recently, atomic layer deposition was integrated into volume production to coat the extreme geometries of modern DRAM capacitors. In order to evaluate next generation materials for those applications we introduce a sophisticated, modified TEM lamellae preparation using H-bars and FIB technology that allows to uncover buried features not accessible by conventional preparation. This technique was used to study the film properties of HfO₂, AlN and TaN ALD layers in deep trench structures with aspect ratio up to 50:1. It was demonstrated that the method provides cross section lamellae with low FIB damage as deep as 7 µm below the original sample surface.     

Effect of growth orientation and diameter on the elasticity of GaN nanowires. A combined in situ TEM and atomistic modeling investigation

We characterized the elastic properties of GaN nanowires grown along different crystallographic orientations. In situ transmission electron microscopy tensile tests were conducted using a MEMS-based nanoscale testing system. Complementary atomistic simulations were performed using density functional theory and molecular dynamics. Our work establishes that elasticity size dependence is limited to nanowires with diameters smaller than 20 nm. For larger diameters, the elastic modulus converges to the bulk values of 300 GPa for c-axis and 267 GPa for a- and m-axis.     

Application of TEM and SNMS in the study of thermally grown alumina scales

Abstract

The oxidation behaviour of several alumina-forming alloys containing reactive elements was investigated at 1100°C in air under atmospheric pressure. Analytical techniques were applied to characterise the corrosion products and to understand the role of reactive elements on the alumina scale growth. Secondary neutral mass spectrometry was used to determine the in-depth compositional profile of the element composing the oxide scale, as well as the oxygen isotope, after sequential oxidation experiments using ¹⁶O₂ and ¹⁸O₂ enriched environments. Transmission electron microscopy revealed the microstructure of the oxide scale and located the reactive elements within the Al₂O₃ scale or at the metal–oxide interface. The combination of both techniques led to a better understanding of the oxide scale growth mechanism.     

TEM investigation of the oxide scales formed on a FeCrAlRE alloy (Kanthal AF) at 900°C in dry O2 and O2 with 40% H2O

Abstract

The base oxide scales on a commercial FeCrAl alloy oxidized isothermally at 900°C in dry O₂ or O₂ with 40% H₂O were studied in detail using analytical electron microscopy. Electron transparent cross-section foils prepared with a FIB/SEM in-situ lift-out technique were investigated using STEM/EDX and CBED. The oxide scales on the samples exposed to dry O₂ are slightly thinner than the scales formed in O₂+H₂O. The oxide scales exhibit a multilayered structure, with a Cr-rich layer in the middle, indicating the original metal/gas interface. An almost pure inner α-Al₂O₃ layer, containing columnar grains, was formed by inward oxygen diffusion, after exposures in both the dry and wet atmospheres. The outer oxide layer consisted of γ-Al₂O₃ in the wet case and of α-Al₂O₃/MgAl₂O₄ in the dry case. It is suggested that the α-Al₂O₃/MgAl₂O₄ phases resulted from a phase transformation of initially grown γ-Al₂O₃. The observations indicate that water vapour may stabilize the γ-Al₂O₃ phase.     

65Si2MnWA钢下贝氏体碳原子调幅分解及有序化的TEM研究

利用Ｓｉ元素阻碍碳化物析出的作用，对６５ＳｉＭｎＷＡ钢进行适当热处理，获得无碳化物析出的下贝氏体组织，通过透射电镜分析了贝氏体基体衍射花样特征，进而考察其碳含量，结果表明，该钢下贝氏体转变初期存在碳原子调幅分解及有序化过程，其碳原子行为与马氏体回火早期阶段碳原子行为相似，说明该钢下贝氏体基体含碳量是过饱和的。     

Accurate determination of the voltage of a transmission electron microscope (TEM) by 〈0 1 2〉 CBED-HOLZ analyses using GaAs crystal

Convergent beam electron diffraction (CBED) is a powerful technique to estimate lattice distortion and lattice strain in crystals. The positions of the higher-order Laue-zone (HOLZ) lines in the transmitted disc of CBED patterns are very sensitive to the lattice parameter, and can therefore be used to estimate changes in the lattice parameter. This offers the possibility to calculate lattice misfit and lattice strain. The positions of the HOLZ lines depend not only on the lattice parameter, but also on the operating voltage of the microscope. It is essential to know the actual voltage of the microscope. In the present work, (1 0 0) GaAs crystal has been used as a standard. Cross-sectional TEM specimens were prepared by argon ion beam thinning technique using a liquid nitrogen cold stage. 〈0 1 2〉 on-zone CBED technique has been used to estimate the actual voltage of the transmission electron microscope (Philips EM430T TEM), when the voltage was set at 250 kV. CBED-HOLZ simulation and analyses have been done, using JEMS software, to correlate with the experimental data. The methodologies adopted for estimating the actual voltage of TEM are discussed in this paper. The studies have also been cross-checked using 〈0 1 2〉 and 〈2 3 3〉 zone axes using (1 0 0) silicon standard. The techniques established are found to be suitable for TEMs operating at a setting voltage of about 250 kV. For the TEM studies, a regular double-tilt specimen holder is required in order to be able to get to the desired zone axes. When the experiments were repeated using a cryogenic double-tilt holder, an improvement in the sharpness of HOLZ lines was observed. Wherever possible, the use of the cryogenic double-tilt holder is recommended. Care must, however, be taken to ensure that effects such as lattice parameter changes (due to temperature changes), phase transformations etc can be properly accounted for.     

Quasi-TEM modes in rectangular waveguides: a study based on the properties of PMC and hard surfaces

Hard surfaces or magnetic surfaces can be used to propagate quasi-TEM modes inside closed waveguides. The interesting feature of these modes is an almost uniform field distribution inside the waveguide. But the mechanisms governing how these surfaces act, how they can be characterized, and further how the modes propagate are not detailed in the literature. In this paper, we try to answer these questions. We give some basic rules that govern the propagation of the quasi-TEM modes, and show that many of their characteristics (i.e. their dispersion curves) can be deduced from the simple analysis of the reflection properties of the involved surfaces.     

RTM成型复合材料中微观缺陷表征及分析

通过对RTM成型复合材料制件及其预成型体进行解剖,并采用光学显微镜及扫描电镜对制件缺陷及预成型体表征,结果显示预成型体中定型剂富集的铺层与缺陷位置一致;并分析了缺陷表观形貌,阐述了缺陷形成原因。     

In-situ TEM observation of the evolution of helium bubbles &dislocation loops and their interaction in Pd during He+ irradiation

The microstructural evolution of purity Pd under 30 keV He+ irradiation at 573 K was investigated by in-situ transmission electron microscopy.The nucleation,growth,merging,annihilation,size change,number density variation,and types of dislocation loops were analyzed under the influence of irradiation fluence and sample thickness.Both perfect dislocation loops with b =1/2 < 110> and faulted dislocation loops with b =1/3 < 111> were formed.However,at low irradiation fluence,most of the loops were 1/3< 111> loops.The thickness of TEM foil obviously affected the ratio of 1 /3 < 111 > loop variants,the size and number density of dislocation loops,and the characteristics of bubble-loop complexes.With the increase of irradiation fluence,the size of dislocation loops increased,but loop volume number density remained almost constant until dislocation loops merged and evolved into dislocation network.There was an obvious interaction between dislocation loops and bubbles,indicating that 1 /3 < 111 > loop was first formed at the initial stage of irradiation,and when the loop grew to a certain size,obvious helium bubbles appeared inside its region.     

Synthesis and investigation of the properties of a star-shaped polysilane

The intermediate monomer of a star-shaped polymer's cyclosiloxane core, was prepared from CH₃HSiCl₂ and 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane(D₄^vi) through the basic method of hydrosilylation reaction. Then, a star-shaped polysilane [poly(core-methylphenyl-diphenyl)silane] was synthesized by the classical Wurtz coupling reaction. Futhermore, UV absorption, fluorescent spectrum, UV-resistant stability and thermal properties of the star-shaped polysilane were investigated. Results reveal that star-shaped polysilane possesses good UV-resistant stability, favourable thermo-oxidative stability and strong fluorescence emitting near 400 nm.     

Ion-beam synthesis and characterization of narrow-gap AB nanocrystals in Si: Effect of implantation and annealing regimes

The process of InAs and GaSb nanoprecipitates creation in Si matrix using high-fluence ion implantation of species from groups V and III followed by thermal treatment has been investigated. We have studied in detail a complex system of defects and nanocrystals in implanted layers, have compared a damage level for both systems, evaluated the influence of implantation and annealing regimes on a size of A³B⁵ nanocrystals and on a defect distribution in implanted layers. The crystalline nature of precipitates was identified by observing Moiré fringe patterns in TEM images, the Moiré period showing a tendency to increase with increasing size of inclusion. A “glowing” effect was observed at the nanocrystal/Si interfaces in the dark-field TEM images of the implanted and annealed samples, this being ascribed to the presence of misfit dislocation networks at the InAs/Si and GaSb/Si interfaces generated as a result of strain relaxation in the highly mismatched A³B⁵/Si systems. Also we compared our results on structural characterization of “A³B⁵ nanocrystals–Si matrix” systems with other papers.     

Comparative MD simulation study on the mechanical properties of a zigzag single-walled carbon nanotube in the presence of Stone-Thrower-Wales defects

Using molecular dynamics simulation, we investigate the influence of Stone-Thrower-Wales defects in the mechanical behavior of a zigzag (5, 0) single-walled carbon nanotube considering two different interatomic potential functions, the Tersoff–Brenner bond order potential and the Tight-Binding potential. The nanotube is subjected to axial stretch and the potential energy is computed for gradually increasing values of strain. From the energy–strain curve the mechanical characteristics like Young’s modulus, tensile strength and ductility are computed using both the potentials, firstly with a perfect lattice and then by introducing an increasing number of Stone-Thrower-Wales defects. Significant reduction in the values of the mechanical properties is observed with changes in the plastic deformation pattern. Experimental data compares reasonably well with our calculated values of the mechanical constants. Such investigations will help designing carbon nanotube based composites.     

An investigation of the transport and sorption properties of xenon in ferrierite and zeolite-L using molecular dynamics

Summary Molecular dynamics has been used to study the diffusion of xenon in ferrierite and zeolite-L. It was found that at 298 K and a loading level of 1.33 atoms per unit cell, diffusion down the 10-ring channel in ferrierite is a more facile process than down the wider 12-ring channel in zeolite-L (D = 8.90 x 10^-9 m²/s for ferrierite vs. 1.78 x 10^-9 m²/s for zeolite-L). This effect can be rationalised by consideration of the effect of channel shape on the diffusion pathway. Under the same conditions, the heat of sorption was calculated to be more favourable for ferrierite (U_ads = -25.7 kJ/mol vs. -20.0 kJ/mol).     

An investigation on the dispersibility of carbon nanotube in the latex nanocomposites using rheological properties

This study focuses on the preparation and rheological investigations of carboxylated styrene butadiene rubber latex (XSBR) – multiwall carbon nanotube (CNT) nanocomposites. Two types of non-functionalized CNT and hydroxyl functionalized multiwall carbon nanotube (CNTOH) were used. A new approach based on concurrent ball milling of CNT and XSBR latex was applied to embed the nano material into the carboxylated latex. To do so, first of all, the effect of ball milling on the colloidal stability of the carboxylated latex was examined by the use of Dynamic Light Scattering (DLS) method. The results of DLS revealed that the particle size of the carboxylated latex did not seriously alter during ball milling, implying that the milling process had no significant impact on the aggregation of particles. The study of rheological properties of nanocomposites showed that the simultaneous milling of the latex and CNT can lead to a relatively better dispersion of CNT in the latex compared to the dispersion obtained by ultrasonication which provides a new opportunity to produce latex nanocomposites in large scales using industrial ball mills. The hydroxyl functionality of CNT led to an enhanced dispersion of CNTOH into the polymer matrix through reaction with carboxyl group of the latex. These findings were also confirmed by infrared spectroscopy. Finally, ZnO was proposed as a Lewis catalyst for the improvement of CNT dispersion in the carboxylated latex and an improved dispersion was gained.     

Determination of the optimal part orientation in layered manufacturing using a genetic algorithm

Several important factors must be taken into consideration to maximise the efficiency of rapid prototyping (RP) processes. The ability to select the optimal orientation of a build direction is one of the most critical factors in using RP processes, since it affects the quality of the prototyped part, the support structure and the build time. This study aims to determine the optimal part orientation that improves the average weighted surface roughness (AWSR) generated from the stair stepping effect. It also minimises the build time including the structure of the support in fabricating a completely freeform part. To avoid pre-selection operation, which is often troublesome and time-consuming, the genetic algorithm, that considers the fuzzy weight for surface roughness and build time, is used to determine the optimal orientation. The validity of the proposed algorithm is demonstrated by several examples using different RP systems and compared with previous works. The algorithm can help RP users select the best orientation of the part and carry out efficient process planning.     

Energy band alignment at interfaces of semiconducting oxides: A review of experimental determination using photoelectron spectroscopy and comparison with theoretical predictions by the electron affinity rule, charge neutrality levels, and the common anion rule

The energy band alignment at interfaces of semiconducting oxides is of direct relevance for the electrical function of electronic devices made with such materials. The most important quantities of the interface determined by band alignment are the barrier heights for charge transport given by the Fermi level position at the interface and the band discontinuities. Different models for predicting energy band alignment are available in literature. These include the vacuum level alignment (electron affinity rule), branch point or charge neutrality level alignment governed by induced gap states, and an alignment based on the orbital contributions to the density of states (common anion rule). The energy band alignment at interfaces of conducting oxides, which have been experimentally determined using photoelectron spectroscopy with in situ sample preparation, are presented. The materials considered include transparent conducting oxides like In₂O₃, SnO₂, ZnO, and Cu₂O, dielectric and ferroelectric perovskites like (Ba,Sr)TiO₃ and Pb(Zr,Ti)O₃, and insulators like Al₂O₃. Interface formation with different contact partners including metals, conducting and insulating oxides are addressed. The discussion focuses on the energy band alignment between different oxides. A good estimate of the band alignment is derived by considering the density of states of the materials involved.     

Micromechanics-based investigation of the elastic properties of polymer-modified cementitious materials using nanoindentation and semi-analytical modeling

Cementitious materials are modified by the addition of polymers in order to improve the durability and the adhesive strength. However, polymer-modified mortars and concretes exhibit lower elastic moduli in comparison to unmodified systems. The macroscopic properties are governed by microstructural changes in the binder matrix, which consists of both cementitious and polymer components. Herein, different polymer-modified cement pastes were characterized using nanoindentation to better understand the microscopic origin of the macroscopic elastic modulus. By means of the statistical nanoindentation technique, the existence of three micromechanical phases in plain and polymer-modified cement pastes with a water-to-cement mass ratio of 0.40 is evidenced, illustrating that the polymer modification does not induce the formation of additional reaction products. Instead, the polymers adsorb on the hydration products as well as on unhydrated clinker grains and decrease the indentation moduli of the micromechanical phases. The link between the microscopic and macroscopic mechanical properties is established by means of a continuum micromechanics approach. A multiscale model aimed at the prediction of the elastic moduli of polymer-modified cementitious materials is developed with input parameters that are partially obtained from the nanoindentation tests. The comparison of the modeling results with the experimentally determined elastic (macroscopic) moduli at the scales of cement paste, mortar, and concrete is satisfactorily good, underlining the predictive capability of the modeling approach. The improvement of prediction models is essential for the application of polymer-modified cementitious materials in construction and will encourage their integration into design guidelines.     

Features of the Experimental Results When Measuring the Charge Center Density Distribution in the Active Region of a <Emphasis Type="Italic">p-n</Emphasis>-Junction with a Latent Inverse Layer by the Dynamic Capacitance Method

A dynamic barrier capacitance method is described for measuring the distribution density of fixed electrically active centers in the relatively lightly doped region of barrier structures such as p-n-junctions, Schottky barriers and MOD-structures with averaging of the density over the depth of the profile up to 1 nm. It is shown that the presence of latent inverse layers in the active region of the barrier structures leads to an inadequate experimental result of the charge center distribution with respect to the true distribution. The proposed method enables the latent inverse layer in the active region of the barrier structures to be revealed. __________ Translated from Izmeritel'naya Tekhnika, No. 10, pp. 63–67, October, 2005.     

Integration of run-to-run control schemes and on-line experiment to deal with the changes in semiconducting dynamic processes

Recently, detailed investigations of various ‘run-to-run’ (R2R) control schemes for semiconductor manufacturing have been conducted. However, a pure R2R control scheme cannot ensure sufficient control quality when the process suddenly undergoes a larger change (herein, a larger change is defined when the output exceeds 2σ_ε ). In many semiconductor processes, sudden changes in the situation are often generated through the operation of different devices during the same process or changes in the control environment (e.g. process ageing or the influence of chemical concentrations). We propose an integrated R2R control system (IRCS) to alleviate this problem; the system includes an on-line experiment, R2R double exponentially weighted moving average (dEWMA) control, R2R triple EWMA (triEWMA) control and R2R self-tuning control. The IRCS initially employs a warning threshold to evaluate the process changes. When the process is changed, the system then uses the 2^k centre points design to amend the process model and selects a suitable R2R control scheme to execute the process control. We used polysilicon gate etching and chemical mechanical planarisation processes as case studies for verifying the proposed method. Based on the analysis results, the IRCS can reduce problems due to process changes. The IRCS is also an improvement in that R2R EWMA-like control does not deal with the problem of process changes in more complicated models.