scholarly journals Direct Observations Of Atomic Structures Of Defects In Gan By High Resolution Z-Contrast Stem

1997 ◽  
Vol 482 ◽  
Author(s):  
Y. Xin ◽  
S.J. Pennycook ◽  
N.D. Browning ◽  
P. D. Nellist ◽  
S. Sivananthan ◽  
...  
Keyword(s):  
High Resolution ◽  
Direct Observation ◽  
Stacking Fault ◽  
Threading Dislocation ◽  
Contrast Imaging ◽  
Atomic Core ◽  
Atomic Structures ◽  
Direct Observations ◽  
Z Contrast ◽  
Contrast Image

AbstractGaN/(0001)Sapphire grown by low pressure MOVPE is studied by high resolution Z-contrast imaging using STEM. First direct observation of the threading dislocation with edge character shows the atomic core structure, which appears to have a similar configuration to the {10–10} surface. The surfaces of the nanopipe walls are on {10–10} with the terminating layer between the atoms with one bond per pair. In addition, the high resolution Z-contrast image of the prismatic stacking fault confirms the results by conventional HRTEM.

scholarly journals Direct observation of threading dislocations in GaN by high-resolution Z-contrast imaging

1998 ◽  
Author(s):  
Y. Xin ◽  
N.D. Browning ◽  
S. Sivananthan ◽  
S.J. Pennycook ◽  
P.D. Nellist ◽  
...  
Keyword(s):  
High Resolution ◽  
Direct Observation ◽  
Threading Dislocations ◽  
Contrast Imaging ◽  
Z Contrast

Z-Contrast Imaging of Ordered Structures in Pb(Mg1/3Nb2/3)O3 and Ba(Mg1/3Nb2/3)O3

1998 ◽  
Vol 4 (S2) ◽  
pp. 554-555
Author(s):  
Y. Yan ◽  
Z. Xu ◽  
D. Viehland ◽  
S. J. Pennycook
Keyword(s):  
Relaxor Ferroelectrics ◽  
Charge Balance ◽  
Contrast Imaging ◽  
Ordered Structures ◽  
Net Charge ◽  
Order And Disorder ◽  
Direct Observations ◽  
Z Contrast ◽  
La Doped ◽  
Contrast Image

Lead-based cubic perovskites such as Pb(B2+1/3B5+2/3)O3 (B2+ = Mg, Co, Ni, Zn; B5+ = Nb, Ta) are relaxor ferroelectrics. Localized order and disorder often occur in materials of this type. In the Pb(Mg1/3Nb2/3)O3 (PMN) family, previous studies have proposed two models, space-charge and charge-balance models. In the first model, the ordered regions carry a net negative charge [Pb(Mg1/2Nb,/2)03], while in the second model it does not carry a net charge [Pb((Mg2/3Nb1/3)1/2Nb1/2)03]. However, no direct evidence for these two models has appeared in the literature yet. In this paper we report the first direct observations of local ordering in undoped and La-doped Pb(Mg1/3Nb2/3)03, using high-resolution Z-contrast imaging.Because the ordered structure in Ba(Mg1/3Nb2/3)03 is well known, the Z-contrast image from an ordered domain is used as a reference for this study. Fig. 1(a) shows the projection of the supercell of fully ordered Ba(Mg1/3Nb2/3)03 along the [110] direction.

Atomic-resolution characterization of an SrTiO3 grain boundary in the STEM

1994 ◽  
Vol 52 ◽  
pp. 972-973
Author(s):  
M. M. McGibbon ◽  
N. D. Browning ◽  
M. F. Chisholm ◽  
A. J. McGibbon ◽  
S. J. Pennycook ◽  
...  
Keyword(s):  
High Resolution ◽  
Atomic Structure ◽  
Scanning Transmission Electron Microscope ◽  
Tilt Boundary ◽  
Atomic Scale ◽  
Chemical Information ◽  
Contrast Imaging ◽  
Scanning Transmission ◽  
Z Contrast ◽  
Contrast Image

High-resolution Z-contrast imaging in the scanning transmission electron microscope (STEM) forms an incoherent image in which changes in atomic structure and composition across an interface can be interpreted intuitively without the need for preconcieved atomic structure models. Since the Z-contrast image is formed by electrons scattered through high angles, parallel detection electron energy loss spectroscopy (PEELS) can be used simultaneously to provide complementary chemical information on an atomic scale. The fine structure in the PEEL spectra can be used to investigate the local electronic structure and the nature of the bonding across the interface. In this paper we use the complimentary techniques of high resolution Z-contrast imaging and PEELS to investigate the atomic structure and chemistry of a 25 degree symmetric tilt boundary in a bicrystal of the electroceramic SrTiO3.Figure 1(a) shows a Z-contrast image of a symmetric region of the tilt boundary. The brightest spots in the image correspond to the increased scattering power of the Sr atomic columns (Z=38) with theless bright spots corresponding to the Ti atomic columns (Z=22). The lighter O atomic columns are notvisible in a Z-contrast image.

scholarly journals Direct observations of atomic structures of defects in GaN by high-resolution Z-contrast STEM

1997 ◽  
Author(s):  
Y. Xin ◽  
S.J. Pennycook ◽  
N.D. Browning ◽  
S. Sivananthan ◽  
P.D. Nellist ◽  
...  
Keyword(s):  
High Resolution ◽  
Atomic Structures ◽  
Direct Observations ◽  
Z Contrast

High-resolution z-contrast imaging of semiconductor interfaces

1989 ◽  
Vol 47 ◽  
pp. 468-469
Author(s):  
S. J. Pennycook
Keyword(s):  
High Resolution ◽  
Phase Contrast ◽  
Contrast Imaging ◽  
Compositional Modulation ◽  
Semiconductor Interfaces ◽  
Complex Figure ◽  
Thin Region ◽  
Stem Image ◽  
Annular Detector ◽  
Z Contrast

Using a high-angle annular detector on a high-resolution STEM it is possible to form incoherent images of a crystal lattice characterized by strong atomic number or Z contrast. Figure 1 shows an epitaxial Ge film on Si(100) grown by oxidation of Ge-implanted Si. The image was obtained using a VG Microscopes' HB501 STEM equipped with an ultrahigh resolution polepiece (Cs ∽1.2 mm, demonstrated probe FWHM intensity ∽0.22 nm). In both crystals the lattice is resolved but that of Ge shows much brighter allowing the interface to be located exactly and interface steps to be resolved (arrowed). The interface was indistinguishable in the phase-contrast STEM image from the same region, and even at higher resolution the location of the interface is complex. Figure 2 shows a thin region of an MBE-grown ultrathin super-lattice (Si8Ge2)100. The expected compositional modulation would show as one bright row of dots from the 2 Ge monolayers separated by 4 rows of lighter Si columns. The image shows clearly that strain-induced interdiffusion has occurred on the monolayer scale.

Quantitative structure determination of interfaces through Z-contrast imaging and electron energy loss spectroscopy

1996 ◽  
Vol 54 ◽  
pp. 104-105
Author(s):  
S. J. Pennycook ◽  
P. D. Nellist ◽  
N. D. Browning ◽  
P. A. Langjahr ◽  
M. Rühle
Keyword(s):  
Grain Boundaries ◽  
Cuprate Superconductors ◽  
Structure Refinement ◽  
3D Structure ◽  
Real Space ◽  
Contrast Imaging ◽  
Coordination Polyhedra ◽  
Burgers Vector ◽  
Z Contrast ◽  
Contrast Image

The simultaneous use of Z-contrast imaging with parallel detection EELS in the STEM provides a powerful means for determining the atomic structure of grain boundaries. The incoherent Z-contrast image of the high atomic number columns can be directly inverted to their real space arrangement, without the use of preconceived structure models. Positions and intensities may be accurately quantified through a maximum entropy analysis. Light elements that are not visible in the Z-contrast image can be studied through EELS; their coordination polyhedra determined from the spectral fine structure. It even appears feasible to contemplate 3D structure refinement through multiple scattering calculations.The power of this approach is illustrated by the recent study of a series of SrTiC>3 bicrystals, which has provided significant insight into some of the basic issues of grain boundaries in ceramics. Figure 1 shows the structural units deduced from a set of 24°, 36° and 65° symmetric boundaries, and 24° and 45° asymmetric boundaries. It can be seen that apart from unit cells and fragments from the perfect crystal, only three units are needed to construct any arbitrary tilt boundary. For symmetric boundaries, only two units are required, each having the same Burgers, vector of a<100>. Both units are pentagons, on either the Sr or Ti sublattice, and both contain two columns of the other sublattice, imaging in positions too close for the atoms in each column to be coplanar. Each column was therefore assumed to be half full, with the pair forming a single zig-zag column. For asymmetric boundaries, crystal geometry requires two types of dislocations; the additional unit was found to have a Burgers’ vector of a<110>. Such a unit is a larger source of strain, and is especially important to the transport characteristics of cuprate superconductors. These zig-zag columns avoid the problem of like-ion repulsion; they have also been seen in TiO2 and YBa2Cu3O7-x and may be a general feature of ionic materials.

Towards Z-Contrast Imaging in an Aberration-Corrected STEM

2000 ◽  
Vol 6 (S2) ◽  
pp. 106-107
Author(s):  
S. J. Pennycook ◽  
B. Rafferty ◽  
P. D. Nellist
Keyword(s):  
Information Transfer ◽  
Signal To Noise Ratio ◽  
Image Resolution ◽  
Contrast Imaging ◽  
Atomic Column ◽  
Potential Benefits ◽  
Potential Factor ◽  
Incoherent Imaging ◽  
Z Contrast ◽  
Contrast Image

The demonstration of an aberration corrector for the STEM promises enormous improvements in the contrast and signal to noise ratio of Z-contrast images, with similar benefits for atomic column EELS. Here we show that the limiting resolution for a zone axis crystal will become not the probe, as in the case of isolated atoms, but the Is Bloch states. In fact, the Z-contrast image becomes a direct image of the Is Bloch states with limiting intensities for large thicknesses roughly proportional to Z The potential benefits for the (STEM) appear to far exceed those for the conventional TEM. Some of these benefits are intrinsic to incoherent imaging: the lack of interference artifacts and the potential factor of two improvement in image resolution were first pointed out by Lord Rayleigh. This improved resolution has been demonstrated by the achievement of sub-ingstrom information transfer in the VG Microscopes HB603U, and the resolution advantage will still apply after aberration correction.

Evaluation of high-quality image reconstruction techniques applied to high-resolution Z-contrast imaging

2017 ◽  
Vol 182 ◽  
pp. 283-291 ◽  
Author(s):  
G. Bárcena-González ◽  
M.P. Guerrero-Lebrero ◽  
E. Guerrero ◽  
A. Yañez ◽  
D. Fernández-Reyes ◽  
...  
Keyword(s):  
High Resolution ◽  
Image Reconstruction ◽  
Contrast Imaging ◽  
High Quality ◽  
Image Reconstruction Techniques ◽  
High Quality Image ◽  
Quality Image ◽  
Z Contrast

Atomic Structures of Oxygen-associated Defects in Sintered Aluminum Nitride Ceramics

1999 ◽  
Vol 5 (5) ◽  
pp. 352-357 ◽  
Author(s):  
Yanfa Yan ◽  
S. J. Pennycook ◽  
M. Terauchi ◽  
M. Tanaka
Keyword(s):  
Stacking Sequence ◽  
Contrast Imaging ◽  
Octahedral Layer ◽  
Atomic Structures ◽  
Inversion Domain ◽  
Sintered Aluminum ◽  
Domain Boundaries ◽  
Convergent Beam ◽  
Z Contrast ◽  
Inversion Domain Boundaries

Convergent-beam electron diffraction and Z-contrast imaging are used to study oxygen-associated defects, flat inversion domain boundaries, dislocations, and interfaces in sintered AlN ceramics. The structures of these defects are directly derived from atomic-resolution Z-contrast images. The flat inversion domain boundaries contain a single Al-O octahedral layer and have a stacking sequence of . . .bAaB-bAc-CaAc. . , where -cAb- indicates the single octahedral layer. The expansion at the flat inversion domain boundaries is measured to be 0.06 (±0.02) nm. The interfaces between 2H- and polytypoid-AlN are found to be also inversion domain boundaries but their stacking sequence differs from that of the flat inversion domain boundaries.

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