Large-angle Convergent-beam Electron Research Articles

Nanoestructuras y su caracterización por medio de microscopía electrónica de transmisión; ciencia y arte

En el presente trabajo se describen de forma didáctica los alcances de la Microscopia Electrónica de Transmisión (TEM) para el estudio de nanosistemas. Para ilustrar el uso de las técnicas TEM, se utilizaron nanopartículas de Au y películas de Si adelgazadas con iones.Se describen técnicas de estudio convencional en TEM, como campo claro (BF), camp obscuro (DF), HAADF, SAED y EELS; además se mencionan las ventajas que ofrece el empleo de técnicas menos convencionales como CBED, LACBED y PED. También se brindan algunas sugerencias prácticas que permitirán describir y diferenciar de forma sencilla el contraste observado en las distintas técnicas disponibles en el TEM con el objetivo de ofrecer una visión, llamativa, clara y didáctica de los alcances actuales de la microscopia electrónica en México.

Structure refinement from ‘digital’ large angle convergent beam electron diffraction patterns

We use semi-automated data acquisition and processing to produce digital large angle CBED (D-LACBED) patterns. We demonstrate refinements of atomic coordinates and isotropic Debye–Waller factors for well-known materials using simulations produced with a neutral, spherical independent atom model. We find that atomic coordinate refinements in Al2O3 have sub-pm precision and accuracy. Isotropic DWFs are accurate for Cu, a simple fcc metal, but do not agree with X-ray measurements of GaAs or Al2O3. This lack of agreement is probably caused by bonding and change transfer between atoms. While it has long been appreciated that CBED is sensitive to bonding, examination of D-LACBED data shows that some regions exhibit large changes in diffracted intensity from small changes in the periodic crystal potential. Models of bonding will be essential to fully interpret D-LACBED data.

Peculiarities of plastic relaxation of (0001) InGaN epilayers and their consequences for pseudo-substrate application

In this paper, we study the plastic relaxation of InGaN layers deposited on (0001) GaN bulk substrates and (0001) GaN/sapphire templates by molecular beam epitaxy. We demonstrate that the InGaN layers relax by the formation of (a+c)-type misfit dislocations gliding on pyramidal planes in the slip system ⟨112¯3⟩{112¯2} down to the interface where they form a trigonal dislocation network. Combining diffraction contrast and large angle convergent beam electron diffraction analyses performed using a transmission electron microscope, we reveal that all (a+c)-type dislocations belonging to one subset of the network exhibit Burgers vectors with the same c-component. This relaxation mechanism leads to partially relaxed InGaN layers with smooth surfaces and threading dislocation densities below 109 cm−2. Such layers are of potential interest as pseudo-substrates for the growth of InGaN heterostructures.

The Art and Application of Large Angle Convergent Beam Electron Diffraction

The antiphase domain structure in Ni3Al and Al3Ti+Cu intermetallic alloys was recognized by conventional transmission electron microscopy and large angle convergent beam electron diffraction methods. In the case of antiphase boundary the superlattice excess line is split into two lines with equal intensity on bright and dark field LACBED pattern. This splitting can be considered as typical and used to identify APBs. The recognition between perfect structure of the defect-free matrix and the screw deviation around the nanopipes in GaN epilayers was performed with high accuracy using Zone Axis LACBED images.

Low-Cost and Highly Manufacturable Strained-Si Channel Technique for Strong Hole Mobility Enhancement on 35-nm Gate Length pMOSFETs

Local strained-silicon channel pMOSFETs with minimum gate length down to 22 nm have been fabricated by integrating Ge preamorphization implantation (PAI) for source/drain (S/D) extension, which induces a uniaxial compressive stress in the channel to attain an enhanced pMOSFET performance without additional masks. A 43 % improvement of hole effective mobility has been obtained for 35-nm gate length pMOSFETs with an optimized Ge PAI condition for S/D extension at 1.1-MV cm vertical effective field, and the hole mobility improvement is nearly maintained at higher vertical field. The corresponding enhancement of a saturated drive current is 25 % at 1.3-MV ldr cm vertical field. The scaling strengthens the enhancement of the hole mobility remarkably. No negative effect on electron effective mobility is observed. An analysis by using a zero-order Laue zone diffraction on large angle convergent beam electron diffraction patterns in a transmission electron microscopy confirms that the significant residual compressive strain up to -3.0 % in the channel region is induced for 60-nm gate length strained channel pMOSFETs with the same optimized Ge PAI condition as that of 35-nm gate length pMOSFETs. The depth profiles of the residual compressive strain and shear strain in the channel region are given, respectively. The possible mechanisms are discussed.

Lateral migration of dislocations in oxygen-doped GaN grown by molecular beam epitaxy

Threading dislocations in gallium nitride epilayers intermittently doped with oxygen were examined using transmission electron microscopy. Dislocations of all types were observed to incline away from the [0001] growth direction at the first introduction of oxygen, remaining inclined through subsequently doped layers. The type and the sign of the Burgers vector of inclined dislocations were characterized by large angle convergent beam electron diffraction, which revealed that the direction of inclination was not primarily driven by misfit stresses. In contrast, dislocations were observed to incline towards pronounced surface pits. It is concluded that the inclination is driven by surface roughening induced by oxygen doping, in contrast to previously published results.

Structural Defects in Laterally Overgrown GaN Layers Grown on Non-polar Substrates

ABSTRACTTransmission electron microscopy was used to study defects in lateral epitaxial layers of GaN which were overgrown on a template of a-plane (1120) GaN grown on (1102) r-plane Al2O3. A high density of basal stacking faults is formed in these layers because the c-planes of wurtzite structure are arranged along the growth direction. Density of these faults is decreasing at least by two orders of magnitude lower in the wings compared to the seed areas. Prismatic stacking faults and threading dislocations are also observed, but their densities drastically decrease in the wings. The wings grow with opposite polarities and the Ga-wing width is at least 6 times larger than N-wing and coalescence is rather difficult. Some tilt and twist was detected using Large Angle Convergent Beam Electron Diffraction.

(001) silicon surfacial grain boundaries obtained by direct wafer bonding process: accurate control of the structure before bonding

Ultra-thin (001) silicon films bonded onto (001) silicon wafers, which form ‘surfacial grain boundaries’, are analysed by transmission electron microscopy and X-ray diffraction. The aim of this study is to find a way of controlling precisely, before direct wafer bonding, the structure of the Si/Si (001) interface. Two kinds of dislocation networks are found at the bonded interface. A square array of screw dislocations accommodates the twist between the two crystals, whereas a linear network of mixed dislocations accommodates the tilt resulting from the residual vicinality of the initial surfaces. A theoretical study shows that knowing and choosing before bonding the characteristics of these interfacial dislocations depend on the control of the ‘twist’ angle during the hydrophobic molecular bonding process. Recently, a new bonding method allows us to obtain an accuracy of ± 0.005° for the ‘twist’ angle from patterned grooves without any crystallographic measurement. The precision of this technique is compared with three different measurement of the disorientation between the two grains taken after bonding. The first one is deduced from the periodicity of the dislocation networks located at the interface. The second one is calculated from large angle convergent beam electron diffraction patterns. The last one is obtained by synchrotron X-ray diffraction. The possibility of choosing precisely the characteristics of the Si (001) ‘surfacial grain boundaries’ before direct wafer bonding process is then discussed in light of an experimental study.

CBED study of grain misorientations in AlGaN epilayers

Large angle convergent beam electron diffraction (LACBED) has been used to examine AlGaN epilayers grown by facet-controlled epitaxial lateral overgrowth on GaN/(0 0 0 1) sapphire substrates in prototype UV laser structures. The substrates, defined by masks with seed openings along a 〈 1 0 - 1 0 〉 stripe direction, had GaN seed columns with { 1 1 - 2 2 } surfaces. Studies were carried out on cross-sectional samples cut perpendicular to the stripe axis. An LACBED analysis of the orientation of (0 0 0 2) planes, and of the ( 1 1 - 2 0 ) planes parallel to the stripe axis, revealed that the AlGaN wings were both rotated by angles of 1–2×10 −2 radians about the 〈 1 0 - 1 0 〉 stripe axis with respect to the underlying GaN, and distorted due to misfit strains. It is shown that the results are consistent with the observed structure of the AlGaN/GaN and the wing/wing boundaries, and with a new model for the generation of a-type misfit dislocations at the AlGaN/GaN interface.

TEM observation of nanopipes in heteroepitaxial GaN

Heteroepitaxial GaN layers grown on sapphire by metal organic vapour phase epitaxy (MOVPE) have been characterised by conventional transmission electron microscopy (TEM) on planar and cross-sectional samples, Large Angle Convergent Beam Electron Diffraction (LACBED) and by high-resolution transmission electron microscopy (HRTEM). Hollow tubes termed nanopipes were resolved on planar view and cross-sections of heteroepitaxial GaN. For advanced studies of the nature of nanopipes the LACBED method was employed. The recognition between perfect structure and screw distortion around nanopipes was performed with high accuracy using Zone Axis LACBED images.

Damage formation in high energy helium implanted 4H-SiC

He + ions were implanted in 4H-SiC at 1.6 MeV with fluences of 5 × 10 16 and 1 × 10 17 ions cm −2. The damage induced by the implantation was studied using different techniques of microscopy along the length of the ion path. Conventional transmission electron microscopy was used to observe the buried amorphous layer. No bubbles were detected in the amorphous area for the lowest dose while a high density of small bubbles was observed for the highest dose. Between the surface and the highly damaged region, the local distribution of strains was determined using large angle convergent beam electron diffraction. Results are correlated to the nuclear energy losses profile.

Transmission electron microscopy investigations of damage induced by high energy helium implantation in 4H–SiC

In 4H–SiC, damage created by helium implantation at high fluence (5×1016 ions cm−2) and high energy (1.6 MeV) was studied using different techniques of electron microscopy all along the ion path. Around the end of range, conventional transmission electron microscopy was used to observe the fine microstructure of defects in the as-implanted and 1500 °C annealed samples. No bubbles were found in the as-implanted sample while numerous cavities with different shape, size and density are present after annealing. The amorphous-crystalline (a/c) transition region was checked by high resolution transmission electron microscopy. The strain profile, determined using the large angle convergent beam electron diffraction, shows a strong correlation with the nuclear stopping curve given by SRIM simulation. The dilatation of the c axis measured all along the ion path is in agreement with the value of the observed swelling. Relaxation volumes for interstitial and vacancy do not cancel. After annealing the cavity parameters are found to be dependent on both the helium density and the as-implanted microstructure.

LACBED characterization of dislocations in Cu-Al-Ni shape memory alloys processed by powder metallurgy

Powder metallurgy Cu-Al-Ni shape memory alloys show excellent thermomechanical properties, being the fracture behavior close to the one observed in single crystals. However, the microstructural mechanisms responsible of such behavior are still under study. In this paper we present the characterization of the dislocations present in these alloys by Large Angle Convergent Beam Electron Diffraction (LACBED) in two different stages of the elaboration process: after HIP compaction and after hot rolling.

An analysis of elementary dislocations in icosahedral Al-Pd-Mn by Large Angle Convergent-Beam Electron Diffraction (LACBED)

Large Angle Convergent Beam Electron Diffraction (LACBED) experiments on dislocations located in the mirror planes of icosahedral AlPdMn single grains show that – as previously inferred from standard image contrast technique – the direction of the Burgers vector is perpendicular to the mirror plane of movement, thus confirming the fact that climb should be an important process for the plasticity mechanisms in icosahedral quasicrystals.

TEM characterisation of defects, strains and local electric fields in AlGaN/InGaN/GaN structures

This paper describes how transmission electron microscopy (TEM) can be used to study the structure and electronic properties of threading defects in GaN structures. A combination of TEM and large angle convergent beam electron diffraction (LACBED) is used to examine dislocations and nanopipes, and to show that migration of dislocations in epitaxially overgrown material is correlated to local shear strains and grain rotations. It is shown how electron holography (EH) can be used to examine in-plane electric fields, and, in particular, the charge on threading edge dislocations.

Dislocations and Slip Systems of Mantle Minerals

Research Article| January 01, 2002 Dislocations and Slip Systems of Mantle Minerals Patrick Cordier Patrick Cordier Laboratoire de Structure et Propriétés de l’Etat Solide (ESA CNRS 8008), Université des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq-Cedex, France Search for other works by this author on: GSW Google Scholar Author and Article Information Patrick Cordier Laboratoire de Structure et Propriétés de l’Etat Solide (ESA CNRS 8008), Université des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq-Cedex, France Publisher: Mineralogical Society of America First Online: 03 Mar 2017 © The Mineralogical Society Of America Reviews in Mineralogy and Geochemistry (2002) 51 (1): 137–179. https://doi.org/10.2138/gsrmg.51.1.137 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Patrick Cordier; Dislocations and Slip Systems of Mantle Minerals. Reviews in Mineralogy and Geochemistry 2002;; 51 (1): 137–179. doi: https://doi.org/10.2138/gsrmg.51.1.137 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search This chapter focuses on dislocations and slip systems that are responsible for the plastic flow of high-pressure mantle minerals. After briefly introducing some basic concepts on crystal plasticity, we describe some recent experimental advances of the last decade that have contributed to our understanding of the rheology of mantle minerals. Among them, we describe some progress in the achievement of deformation experiments under high pressure. A more detailed review is presented by Durham et al. (this volume). We present then a novel Transmission Electron Microscopy (TEM) technique: Large Angle Convergent Beam Electron Diffraction (LACBED), which is very well adapted to... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

LACBED measurement of the chemical composition of a thin In xGa 1− x As layer buried in a GaAs matrix

Large angle convergent beam electron diffraction (LACBED) observations are used to determine the x indium content of a thin In x Ga 1− x As quantum well buried in a GaAs matrix. The method consists in a quantitative analysis of the Bragg line intensities lying in the central disc of any LACBED pattern. This analysis makes it possible to determine the displacement vector R introduced, between the two parts of the GaAs matrix, by the deformation of the quantum well and consequently to determine the x indium content. This indium content is found to be consistent with the value expected from the molecular beam epitaxy growth conditions.

HOLZ line analysis of lattice parameters in magnesium alloys.

A method of refining lattice parameters from deficit higher-order Laue zone (HOLZ) line data from large angle convergent beam electron diffraction (LACBED) data is presented, relying on distances between nearest neighbour intersections alone in order to minimize effects of distortion over the field of view. Use is made of a dynamical correction deltak to the fast electron wavevector k for kinematic analysis. This correction term is shown to depend on the specific HOLZ beam under consideration, as well as the zone axis and eigenvalue associated with the branch index of the relevant dispersion surface. This method is applied to analysis of data from magnesium alloys, where momentum filtering induced by the LACBED method facilitates HOLZ contrast from a relatively low index zone axis (where contrast is not detectable with conventional CBED), and contrast is enhanced at elevated temperatures from a higher index zone axis. Although the accuracy of refined lattice parameters from these sets of data is shown to be no better than 0.1%, it is felt that issues arising out of the analysis may be of some interest, particularly since these are non-ideal specimens. Full eigen-state analysis of the fast electron wavefunction is presented, and issues related to the influence of the dispersion surface on deficit HOLZ line behaviour are discussed.

Anaysis of Lacbed Patterns from A Microtwin in Cobalt

Recently LACBED (Large Angle Convergent Beam Electron Diffraction) studies for identifying the nature of stacking faults has been reported in [1,2]. Here we report the LACBED study for a microtwin whose images are usually similar to those of an intrinsic or an extrinsic stacking faults (for this discussion, see [3]).Observations: Thin foils of cobalt with the thickness of about 180 nm (f.c.c phase, a=0.354 nm) were examined by a Philips CM200. Fig. 1 shows strong beam dark field images of microtwins or stacking faults. Fig. 2 shows the bright field LACBED pattern taken near the area marked as a circle in fig. 1. The specimen height, from the convergent point of beams, was about 0.0586 mm and the convergent angle was 0.615 degrees.Calculations and analysis: Analysis of fig. 1 alone indicates the encircled fault an extrinsic stacking fault.

AFM, SEM, EDX and HRTEM study of the crystalline growth rate anisotropy-induced internal stress and surface roughness of YBaCuO thin film

The influence of the anisotropy of the crystalline growth rate on the microstructure and morphology of YBaCuO thin film deposited by laser ablation has been studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM), atomic force microscopy (AFM) and energy dispersive X-ray (EDX) analysis. The results obtained from high resolution lattice imaging and large angle convergent beam electron diffraction (LACBED), together with the investigations of the thin film surface morphology, show the strong influence of the different crystalline growth rates on both the internal stress present in the YBaCuO film and the roughness of the outer surface. These results should be of prime importance for the superconducting properties. This is essential in tailoring these thin films for device applications.