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.

Z-contrast Imaging in an Aberration-corrected Scanning Transmission Electron Microscope

2000 ◽  
Vol 6 (4) ◽  
pp. 343-352 ◽  
Author(s):  
S.J. Pennycook ◽  
B. Rafferty ◽  
P.D. Nellist
Keyword(s):  
Spherical Aberration ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Zone Axis ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Z Contrast ◽  
Contrast Image ◽  
Aberration Corrected

AbstractWe show that in the limit of a large objective (probe-forming) aperture, relevant to a spherical aberration corrected microscope, the Z-contrast image of a zone-axis crystal becomes an image of the 1s Bloch states. The limiting resolution is therefore the width of the Bloch states, which may be greater than that of the free probe. Nevertheless, enormous gains in image quality are expected from the improved contrast and signal-to-noise ratio. We present an analytical channeling model for the thickness dependence of the Z-contrast image in a zone-axis crystal, and show that, at large thicknesses, columnar intensities become proportional to the mean square atomic number, Z2.

Z-contrast Imaging in an Aberration-corrected Scanning Transmission Electron Microscope

2000 ◽  
Vol 6 (4) ◽  
pp. 343-352 ◽  
Author(s):  
S.J. Pennycook ◽  
B. Rafferty ◽  
P.D. Nellist
Keyword(s):  
Spherical Aberration ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Zone Axis ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Z Contrast ◽  
Contrast Image ◽  
Aberration Corrected

Abstract We show that in the limit of a large objective (probe-forming) aperture, relevant to a spherical aberration corrected microscope, the Z-contrast image of a zone-axis crystal becomes an image of the 1s Bloch states. The limiting resolution is therefore the width of the Bloch states, which may be greater than that of the free probe. Nevertheless, enormous gains in image quality are expected from the improved contrast and signal-to-noise ratio. We present an analytical channeling model for the thickness dependence of the Z-contrast image in a zone-axis crystal, and show that, at large thicknesses, columnar intensities become proportional to the mean square atomic number, Z2.

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.

Quantification of Compositional Modulations in Self-Assembled Multisheet (Cd, Zn, Mn)Se Quantum Dot Structures

2001 ◽  
Vol 7 (S2) ◽  
pp. 202-203
Author(s):  
T. Topuria ◽  
P. Möck ◽  
N.D. Browning ◽  
L.V. Titova ◽  
M. Dobrowolska ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Imaging Technique ◽  
Optoelectronic Device ◽  
Scanning Transmission Electron Microscope ◽  
Contrast Imaging ◽  
Cdse Qds ◽  
Scanning Transmission ◽  
Device Applications ◽  
Incoherent Imaging ◽  
Z Contrast

CdSe/ZnSe based semiconductor quantum dot (Q D) structures are a promising candidate for optoelectronic device applications. However, key to the luminescence properties is the cation distribution and ordering on the atomic level within the CdSe QDs/agglomerates. Here the Z contrast imaging technique in the scanning transmission electron microscope (STEM) is employed to study multisheet (Cd,Zn,Mn)Se QD structures. Since Z-contrast is an incoherent imaging technique, problems associated with strain contrast in conventional TEM are avoided an accurate size and composition determinations can be made.For this work we used a JEOL JEM 201 OF field emission STEM/TEM. The sample was grown by molecular beam epitaxy in order to achieve vertical self-ordering of Cd rich quasi-2D platelet This sample comprises 8 sequences of 10 ML (2.83 nm)Zn0.9Mn0.1Se cladding layer and 0.3 ML (0.09 nm) CdSe sheet, a further 10 ML of Zn0.9Mn0.1Se, and a 50 nm ZnSe capping layer.

Incoherent Imaging by Z-Contrast Stem: Towards 1Å Resolution

1994 ◽  
Vol 332 ◽  
Author(s):  
S. J. Pennycook ◽  
D. E. Jesson ◽  
A. J. Mcgibbon
Keyword(s):  
Phonon Scattering ◽  
Scanning Transmission Electron Microscope ◽  
Complex Materials ◽  
Intrinsic Resolution ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Detector Geometry ◽  
Incoherent Imaging ◽  
Z Contrast ◽  
Contrast Image

ABSTRACTBy averaging phase correlations between scattered electrons a high angle detector in the scanning transmission electron microscope (STEM) can provide an incoherent, Z-contrast image at atomic resolution. Phase coherence is effectively destroyed through a combination of detector geometry (transverse incoherence) and phonon scattering (longitudinal incoherence). Besides having a higher intrinsic resolution, incoherent imaging offers the possibility of robust reconstruction to higher resolutions, provided that some lower frequency information is present in the image. This should have value for complex materials and regions of complex atomic arrangements such as grain boundaries. Direct resolution of the GaAs sublattice with a 300kV is demonstrated.

scholarly journals The Atomic-Scale Origins of Grain Boundary Superconducting Properties

1998 ◽  
Vol 4 (S2) ◽  
pp. 688-689
Author(s):  
S. J. Pennycook ◽  
J. Buban ◽  
C. Prouteau ◽  
M. F. Chisholm ◽  
P. D. Nellist ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Atomic Scale ◽  
Contrast Imaging ◽  
Qualitative Understanding ◽  
Quantitative Understanding ◽  
Bond Valence Sum ◽  
Z Contrast ◽  
Coherence Lengths ◽  
Contrast Image

Due to the extemely short coherence lengths of the high-Tc superconductors (around 30 Å in the a-b plane), defects such as grain boundaries are obvious barriers to the flow of supercurrent. Within a few months of the discovery of these materials, it was shown how the critical current dropped four orders of magnitude as the grain boundary misorientaion increased from zero to 45°. Even today, there is no quantitative understanding of this behavior. A qualitative understanding is however possible through atomic resolution Z-contrast imaging on YBa2cu3O7-δ and SrTiO3 bicrystal grain boundaries, combined with bond-valence-sum analysis.The Z-contrast image of a YBa2cu3O7-δ low angle grain boundary in Fig. 1 shows the same kind of reconstructed dislocation cores as seen in SrTiO3, containing reconstructions on both the Cu and Y/Ba sublattices.

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.

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 STEM in the Aberration-Corrected JEOL JEM2200FS

2008 ◽  
Vol 14 (1) ◽  
pp. 104-112 ◽  
Author(s):  
Robert F. Klie ◽  
Craig Johnson ◽  
Yimei Zhu
Keyword(s):  
Objective Lens ◽  
Contrast Imaging ◽  
Fringe Analysis ◽  
Strain Mapping ◽  
Atomic Column ◽  
Probe Size ◽  
Tem Mode ◽  
Materials Research ◽  
Z Contrast ◽  
Aberration Corrected

We report on the performance of our aberration-corrected JEOL-JEM2200FS electron microscope. This high-resolution field-mission TEM/STEM is equipped with a Schottky field-emission gun operated at 200 kV, a CEOS probe corrector, and an in-column energy filter. We focus on the performance of the probe corrector and show that the Si [110] dumbbell structure can be routinely resolved in STEM mode with the power spectrum indicating a probe size of ~1 Å. Ronchigram analysis suggests that the constant phase area is extended from 15 mrad to 35 mrad after corrector tuning. We also report the performance of our newly installed JEOL-JEM2200MCO, an upgraded version of the JEM2200FS, equipped with two CEOS aberration correctors (and a monochromator), one for the probe-forming lens and the other for the postspecimen objective lens. Based on Young's fringe analysis of Au particles on amorphous Ge, initial results show that the information limit in TEM mode with the aberration correction (Cs= −3.8 μm) is ~0.12 nm. Materials research applications using these two instruments are described including atomic-column-resolved Z-contrast imaging and electron energy-loss spectroscopy of oxide hetero-interfaces and strain mapping of a SrTiO3tilt-grain boundary. The requirements for a high-precision TEM laboratory to house an aberration-corrected microscope are also discussed.

Suppression of Amplitude Effects In Bright-Field Stem Phase Contrast Imaging

1985 ◽  
Vol 43 ◽  
pp. 72-73
Author(s):  
J. H. Butler
Keyword(s):  
Phase Contrast ◽  
Signal To Noise Ratio ◽  
Phase Contrast Imaging ◽  
Bright Field Image ◽  
Contrast Effects ◽  
Contrast Imaging ◽  
Bright Field ◽  
Strong Phase ◽  
Pure Phase ◽  
Contrast Image

Nearly all past Investigations Into the nature of the bright field Image in the STEM as a function of detector aperture size are based on the Scherzer conditions for optimum Imaging. Consequently, they are of limited use when applied to any but the thinnest of specimens. Here we examine Image contrast and resolution as the Scherzer conditions are relaxed in conjunction with detector size, and show that Image quality for strong phase objects can be significantly Improved because, in a certain configuration, amplitude contrast effects can be eliminated, while the phase contrast signal to noise ratio assumes a relative maximum. Thus, if the user is willing to make small sacrifices (≅5%) in resolution and contrast, it should be possible to obtain an amplitude effect free, pure phase contrast Image even for slightly thicker specimens.

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