Electron Diffraction Contrast Imaging Research Articles

Interfacial evolution and coordinated deformation mechanism of Ti/Al laminated metal composites prepared by diffusion bonding

Laminated metal composites (LMCs) of titanium and aluminum (Ti/Al), combining the high strength and thermal stability of titanium with the low density and corrosion resistance of aluminum, hold substantial promise for industrial applications. Utilizing diffusion bonding under optimal processing conditions—specifically a bonding temperature of 550 °C and a holding time of 120 min—an average interfacial shear strength of 68.7 MPa was achieved. Transmission electron microscopy (TEM) revealed a metallurgically bonded interface facilitated by the mutual atomic diffusion of titanium and aluminum; this diffusion layer predominantly comprises the TiAl3 phase. Detailed insights into the microstructural evolution at the interface, including dislocation configurations, were also obtained in this study. The Burgers vectors of these dislocations were determined using the two-beam electron diffraction contrast imaging method. Based on these results, it can be elucidated that the deformation mechanism of Ti layer was dominated by the dislocation slip (mainly prismatic and the basal slip), while the coordinated deformation of TiAl3/Al interface benefitted by the dislocations gliding across the interface.

Development and applications ofultrafast transmission electron microscopy.

We present a review on the development and applications of the ultrafast transmission electron microscopy (UTEM) at RIKEN. We introduce the UTEM system for the pump-probe TEM observation in a wide temporal range. By combining the UTEM and pixelated detector, we further develop five-dimansional scanning TEM (5D STEM) which provides the ultrafast nanoscale movie of physical quantities in nano-materials, such as crystal lattice information and electromagnetic field, by convergent-beam electron diffraction (CBED) and differential phase contrast (DPC) imaging technique. We show our recent results on the nanosecond-to-microsecond magnetic skyrmion dynamics observed by Lorentz TEM (LTEM) and photo-induced acoustic wave generation in picosecond regime by bright-field TEM and electron diffraction measurements by UTEM. We also show the demonstartion of the 5D STEM on the quantitative time (t)-dependent strain mapping by CBED with an accuracy of 4 ps and 8 nm, and the ultrafast demagnetization under zero magnetic field observed by DPC with 10 ns and 400 nm resolution.

Identification of (Tb,Eu)9.43(SiO4)6O2-δ Oxy-Apatite Structures as Nanometric Inclusions in Annealed (Eu,Tb)-Doped ZnO/Si Junctions: Combined Electron Diffraction and Chemical Contrast Imaging Studies.

(Tb,Eu)-doped ZnO-annealed films at 1100 °C showed intense photoluminescense (PL) emission from Eu and Tb ions. The high-temperature annealing led to a chemical segregation and a secondary Zn-free phase formation that is suspected to be responsible for the high PL intensity. Large faceted inclusions of rare-earth (RE) silicates of a size of few hundred nanometers were observed. Owing to various advanced electron microscopy techniques, a detailed microstructural study of these nanometric inclusions combining atomic Z contrast imaging (STEM) and precession electron diffraction tomography (PEDT) data was carried out and resulted in the determination of a hexagonal P63/m-type (Tb,Eu)9.43(SiO4)6O2-δ structure related to an oxy-apatite structure. Chemical analyses from spectroscopic data (energy-dispersive X-ray mapping and electron energy loss spectroscopy) at the atomic scale showed that both RE elements sitting on two independent (4f) and (6h) atomic sites have three-fold oxidation states, while refinements of their occupancy sites from PEDT data have evidenced preferential deficiency for the first one. The deduced RE-O distances and their corresponding bond valences are listed and discussed with the efficient energy transfer from Tb3+ toward Eu3+.

Structural characterization of electrodeposited boron

Structural characterization of electrodeposited boron was carried out by using transmission electron microscopy and Raman spectroscopy. Electron diffraction and phase contrast imaging were carried out by using transmission electron microscopy. Phase identification was done based on the analysis of electron diffraction patterns and the power spectrum calculated from the lattice images from thin regions of the sample. Raman spectroscopic examination was carried out to study the nature of bonding and the allotropic form of boron obtained after electrodeposition. The results obtained from transmission electron microscopy showed the presence of nanocrystallites embedded in an amorphous mass of boron. Raman microscopic studies showed that amorphous boron could be converted to its crystalline form at high temperatures.

TEM investigation of precipitates in VCz GaAs crystals

AbstractBulk GaAs crystals were grown from various Ga‐rich melts by the vapour‐pressure controlled Czochralski method in order to reduce As precipitates. The correlation of the melt composition with both, structural perfection and solid composition was examined by various methods of transmission electron microscopy (TEM). From transmission electron diffraction and diffraction contrast imaging a direct correlation between melt composition and sample properties is missing. High‐resolution TEM imaging hints to inhomogeneities only for the sample grown from a melt with a mole fraction of y = 0.492. Strain analysis of a selected defect reveals a strained crystal lattice in the surrounding of the defect. For the same sample, high angle annular dark‐field imaging and energy dispersive X‐ray spectroscopy verify the formation of precipitates. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

TEM investigations of (In,Ga)N/GaN quantum structures

AbstractThe paper reports on the influence of the growth temperature on the structural and chemical properties of (In,Ga)N quantum wells (QWs) on GaN. Two different samples A and B were fabricated. The QWs of the sample A were grown at a constant temperature of 600 °C. For the QWs of the sample B the temperature was 530 °C, while for the GaN barrier it was raised to 600 °C. The chemical and structural properties were studied by electron diffraction contrast imaging using the 0001 and 0002 reflection, respectively. Sample A exhibits homogeneous (In,Ga)N QWs. For sample B some undulated strain contrast of the QWs is visible hinting to the formation of quantum dots (QDs). The self‐organisation of (In,Ga)N QDs in sample B is also evidenced by composition sensitive STEM‐HAADF imaging, where the individual (In,Ga)N layers exhibit inhomogeneous intensity as well as varied thickness. Moreover, energy dispersive X‐ray spectroscopy yielded enrichment of indium at QD sites. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study of the Nanostructures Formed in 2024 Alloy during Thermomechanical Treatments

A study on the microstructures developed during artificial aging of the 2024 alloy in nondeformed and 8% pre-deformed specimens is presented. The microstructural characterization was carried out using transmission electron microscopy (TEM), specifically, diffraction contrast and highresolution imaging. The S phase was found to precipitate heterogeneously on dislocations in both nondeformed and pre-deformed alloys. After the same artificial aging time, a larger density of S phase precipitates was obtained in the pre-deformed specimens. In non-deformed specimens, a high density of small nanometer-sized aggregates was found, that was absent in the pre-deformed specimens, that were identified as GP zones. To further analyze the small sized aggregates, artificially aged specimens with no previous deformation were also studied with Coincidence Doppler Broadening (CDB) of positron annihilation radiation. With this technique, information on the chemical environment around vacancy sites contained in the GP zones was obtained. Specifically, a composition close to (AlCu)2Mg was derived.

Nanoscale stress analysis of strained-Si metal-oxide-semiconductor field-effect transistors by quantitative electron diffraction contrast imaging

A technique that uses quantitative electron diffraction contrast imaging (EDCI) to measure stress with a spatial resolution on the order of 10nm and sensitivity on the order of tens of MPa is applied to strained-Si metal-oxide-semiconductor field-effect transistors. This is accomplished by utilizing transmission electron microscopy and focused ion beam micromachining in conjunction with finite element modeling and electron diffraction contrast simulations. Our techniques enable quantitative interpretation of EDCI intensity, as a function of the magnitude of the local stress field. Analysis shows that the stress distribution in the strained-Si channel is very sensitive to the stress state of the surrounding materials, especially TiSi2, which can modify the stress distribution in the channel by well over 100MPa.

Microstructure of columnar crystallites in Ni80Fe20/Cu magnetic multilayers

We have used electron microscopy to investigate the microstructure of Ni80Fe20/Cu magnetic multilayers which were synthesized by dc magnetron sputtering. Columnar structure was found in the specimen with and without giant magnetoresistance (GMR). All the columnar crystallites (CCs) originate from the Fe buffer layer on silicon wafer or glass substrate and penetrate though all the multilayers up to the surface of the film. The lateral size of the CCs ranges from 10 to 30 nm. Cross-sectional high-resolution electron microscopy study shows that the CCs are single-crystal-like with fcc structure resulting from the epitaxial growth of NiFe and Cu sublayers. Electron diffraction contrast imaging and electron energy filtered elemental mapping confirmed that multilayer nature is maintained throughout the entire NiFe/Cu film. Grain boundaries between CCs can be the most likely place where NiFe or Cu bridging will occur. Columnar structure was also found in a Ta/NiFe/Cu/NiFe/FeMn/Ta spin valve film. The possible influence of the columnar crystalline structure on the GMR related problems is discussed. The microstructure results revealed in this article provide useful information for the GMR property investigation of NiFe/Cu based metallic multilayers.

Atomic Structures of Inversion Domain Boundaries and Dislocations in Sintered ALN

A1N is an attractive material because of its mechanical, thermal and electronic properties. However, these properties are often adversely altered by extended defects such as inversion domain boundaries (IDBs), and through impurities associated with the defects, especially oxygen. Thus to improve the properties of the material it is important to understand the structures of the defects. A number of studies have been carried out to characterize these defects using fringe contrast, weak-beam, convergent-beam electron diffraction and conventional high-resolution phase contrast imaging. These techniques all require the use of model structures for data interpretation. In this paper, we report a direct determination of the structures of IDBs and dislocation cores in A1N by highresolution Z-contrast imaging using a 300 kV VG HB603U scanning transmission electron microscope, with a probe size of 1.3 Å.

Assessment of the quantitative characterization of localized strain using electron diffraction contrast imaging

In state-of-the art development of more performant materials for advanced technologies often residual strain of submicrometer size plays an important role. Quantitative analysis of strain on such small scales is extremely difficult. In the present paper the use of electron diffraction contrast imaging for the quantitative analysis of localized strain is shown to be a feasible analysis method. Versatile image simulation software has been developed and numerical image comparison criteria are introduced. With these tools a case study is performed of a typical localized strain analysis problem: a coherent spheroidal particle. The results show that apart from the strain components themselves three parameters related to the diffraction conditions and specimen surface relaxation play an important role in quantifying the image interpretation procedure.

Precipitation in vapour quenched titanium-magnesium alloys

The effect of hot-pressing and annealing on precipitation in a Ti-9 wt% Mg alloy solid solution produced by quenching from the vapour phase is described. Precipitates about 20 nm diameter and over 100 nm diameter were found within the grains and at grain boundaries, respectively, after hot pressing at 500–600 °C. Using electron diffraction contrast imaging, selected area electron diffraction, Moire fringe analysis and energy dispersive X-ray spectroscopy, the particles were identified as Mg. The negligible solubility of Mg in Ti led to exceptional resistance to Mg particle coarsening at temperatures up to 960 °C in the Ti beta-phase field.

Characterization of strain in an advanced semiconductor laser structure with nanometer range resolution using a new algorithm for electron diffraction contrast imaging interpretation

In the present letter electron diffraction contrast imaging (EDCI) computations for strain characterization on the nanometer scale are presented. Using newly developed simulation software for EDCI image interpretation it is demonstrated how the technique can be used in the characterization, with submicron resolution, of localized strain fields in any crystalline material. Strain fields of arbitrary geometrical symmetry can be treated. As a case study, localized strain in an advanced semiconductor laser structure is investigated.

Strain analysis with nanometer resolution using a conventional transmission electron microsopy technique: electron diffraction contrast imaging revisited

There is a growing need for elastic strain characterization techniques with submicrometer resolution in several engineering technologies. In advanced material science and engineering the quantitative knowledge of elastic strain, e.g. at small particles or fibers in reinforced composite materials, can lead to a better understanding of the underlying physical mechanisms and thus to an optimization of material production processes. In advanced semiconductor processing and technology, the current size of micro-electronic devices requires an increasing effort in the analysis and characterization of localized strain. More than 30 years have passed since electron diffraction contrast imaging (EDCI) was used for the first time to analyse the local strain field in and around small coherent precipitates1. In later stages the same technique was used to identify straight dislocations by simulating the EDCI contrast resulting from the strain field of a dislocation and comparing it with experimental observations. Since then the technique was developed further by a small number of researchers, most of whom programmed their own dedicated algorithms to solve the problem of EDCI image simulation for the particular problem they were studying at the time.

A transmission electron microscopy study of tweed-like structures in Al62Cu17.5Co17.5Si3decagonal quasicrystals

Abstract A tweed-like structure with striated contrast has been observed in an Al62Cu17.5Co17.5Si3 decagonal quasicrystal, for the first time, by using conventional electron diffraction contrast imaging and high-resolution electron microscopy images. The contrast of these striations, as observed under two-beam conditions, is different from that resulting from dislocations, stacking faults and small-angle grain boundaries in quasicrystals, and it can be interpreted as being due to quasilattice distortions introduced by the lattice misfit between the decagonal quasicrystal matrix and the local ordering.

Localised strain characterisation in semiconductor structures using electron diffraction contrast imaging

Understanding and controlling localised strain in semiconductor devices is one of the critical challenges confronting the designer of new technologies. Due to continuous scaling down in very large and ultralarge scale integration there is a growing requirement for techniques with sujjicientcapacity to characterise localised strain quantitatively with a resolution in the micrometre to nanometre range. The present paper reports such a technique, namely, electron diffraction contrast imaging (EDCI) using transmission electron microscopy (TEM). As a case study the characterisation of localised strain in a semiconductor laser structure is presented. The strain in the structure is modelled using finite element calculations, and the EDCI results are simulated using the ‘Simeon’ software. The three-dimensional effects of TEM specimen preparation on the interpretation of EDCI results are also reported.MST/3250

Localised strain characterisation in semiconductor structures using electron diffraction contrast imaging

Understanding and controlling localised strain in semiconductor devices is one of the critical challenges confronting the designer of new technologies. Due to continuous scaling down in very large and ultralarge scale integration there is a growing requirement for techniques with sujjicientcapacity to characterise localised strain quantitatively with a resolution in the micrometre to nanometre range. The present paper reports such a technique, namely, electron diffraction contrast imaging (EDCI) using transmission electron microscopy (TEM). As a case study the characterisation of localised strain in a semiconductor laser structure is presented. The strain in the structure is modelled using finite element calculations, and the EDCI results are simulated using the ‘Simeon’ software. The three-dimensional effects of TEM specimen preparation on the interpretation of EDCI results are also reported.MST/3250

Transmission Electron Diffraction Techniques for Nm Scale Strain Measurement in Semiconductors

AbstractAn overview is given of transmission electron microscopy techniques to address strain with nm scale spatial resolution. In particular the possibilities and limitations of (large angle) convergent beam electron diffraction ((LA)CBED) and electron diffraction contrast imaging (EDCI) techniques are discussed in detail. It will be shown by a few case studies that unique and quantitative information on local strain distributions can be obtained by the combined use of both (LA)CBED and EDCI in correlation with three dimensional finite element simulations of the strain distributions in the thinned specimen.

Transmission Electron Diffraction Techniques for NM Scale Strain Measurement in Semiconductors

AbstractAn overview is given of transmission electron microscopy techniques to address strain with nm scale spatial resolution. In particular the possibilities and limitations of (large angle) convergent beam electron diffraction ((LA)CBED) and electron diffraction contrast imaging (EDCI) techniques are discussed in detail. It will be shown by a few case studies that unique and quantitative information on local strain distributions can be obtained by the combined use of both (LA)CBED and EDCI in correlation with three dimensional finite element simulations of the strain distributions in the thinned specimen.

On the determination of Burgers vectors of type B dislocations in an Al70Co15Ni15decagonal quasicrystal by convergent-beam electron diffraction

Abstract Type B dislocations with Burgers vectors parallel to the twofold axes of the Al70Co15Ni15 decagonal quasicrystal were studied by means of electron diffraction contrast imaging and defocus convergent-beam electron diffraction techniques. Two kinds of Burgers vector of the type B dislocations were determined, both being parallel to a twofold axis A2P of the decagonal quasicrystal. The components |b∥| of the Burgers vector b = 〈00 1 0 [sbnd] 1 0〉 in physical space and the component |bperp| of the Burgers vector in complementary space are 0.186 and 0:115 nm respectively, with a ratio T of 1.618. The components for b = 〈0 1 0 [sbnd]11〉 are 0.302 and 0.071 nm with a ratio τ3 of 4.235.