Atomic Structure and Chemistry of Si/Ge Interfaces Determined by Z-Contrast Stem

1989 ◽  
Vol 159 ◽  
Author(s):  
M. F. Chisholm ◽  
S. J. Pennycook ◽  
D. E. Jesson
Keyword(s):  
Critical Thickness ◽  
Film Formation ◽  
Film Surface ◽  
Atomic Scale ◽  
Layer By Layer ◽  
Si Substrate ◽  
Powerful Approach ◽  
Z Contrast ◽  
Contrast Image ◽  
Misfit Accommodation

ABSTRACTThe technique of Z-contrast STEM provides a fundamentally new and powerful approach to determining the atomic scale structure and chemistry of interfaces. The images produced do not show contrast reversals with defocus or sample thickness, there are no Fresnel fringe effects at interfaces, and no contrast from within an amorphous phase. Such images are unambiguous and intuitively interpretable. In this paper, the technique has been used to directly image subnanometer interdiffusion in ultrathin (SimGen)p superlattices. The Z-contrast image of a (Si8Ge2)p superlattice grown by MBE at 400°C clearly shows significant broadening of the Gerich layer. Also, film formation and misfit accommodation in epitaxial Ge films on (001)Si produced by implantation and oxidation of Si wafers was studied. It was found that the Ge films, which are constrained to grow layer-by-layer, remain completely coherent with the Si substrate to a thickness of 5–6 nm. This is 3 to 6 times thicker than the observed critical thickness for Ge films grown on Si by MBE. It is observed that misfit accommodating dislocations nucleate at the film surface as Shockley partials. The Z-contrast images show these partials can combine to form perfect dislocations whose cores are found to lie entirely in the elastically softer Ge film.

Misfit accommodation in epitaxial Ge films on Si

1990 ◽  
Vol 48 (4) ◽  
pp. 340-341
Author(s):  
M. F. Chisholm ◽  
S. J. Pennycook
Keyword(s):  
Misfit Dislocation ◽  
Critical Thickness ◽  
Film Formation ◽  
Dislocation Nucleation ◽  
Layer By Layer ◽  
Chemical Sensitivity ◽  
Contrast Imaging ◽  
Z Contrast ◽  
Misfit Accommodation ◽  
Si Wafer

Electron microscopy is well suited for the study of the initial stages of misfit dislocation nucleation and of dislocation reactions. High-resolution Z-contrast imaging has the added advantages of producing intuitively interpretable images with chemical sensitivity. This technique has been used to study film formation and misfit accommodation in epitaxial Ge films grown on Si. The epitaxial Ge films studied herein were produced by steam oxidation of Ge-implanted (001) Si. The implanted Ge is rejected by the growing SiO2 layer and has no time to diffuse into the Si. The partitioned Ge forms a distinct strained epitaxial layer on Si. With this growth process the Ge films are constrained to grow layer-by-layer instead of the normally observed island mode. The growth morphology in turn governs the interfacial misfit dislocation nucleation, location, and character.Figure 1 shows a cross-section view of a dislocation-free 5-nm thick Ge film on (001)Si produced by the oxidation of a Ge (2×l016 ions/cm2) implanted Si wafer. This is three to six times thicker than the observed critical thickness for Ge films grown on Si by more conventional growth processes. Ge normally grows as islands on Si and, after the equivalent of six monolayers of Ge is deposited, dislocations are introduced at the island parameters to relieve the misfit strains.

The Si/SiO2 Interface: Atomic Structures, Composition, Strain And Energetics

1999 ◽  
Vol 5 (S2) ◽  
pp. 122-123 ◽  
Author(s):  
S. J. Pennycook ◽  
G. Duscher ◽  
R. Buczko ◽  
S. T. Pantelides
Keyword(s):  
First Principles ◽  
Interface Roughness ◽  
Atomic Scale ◽  
Thickness Variation ◽  
Atomic Structures ◽  
Bright Contrast ◽  
Z Contrast ◽  
Impurity Sites ◽  
Contrast Image ◽  
Detector Angle

A number of recent studies of grain boundaries and heterophase interfaces have demonstrated the power of combining Z-contrast STEM imaging, EELS and first-principles theoretical modeling to give an essentially complete atomic scale description of structure, bonding and energetics. Impurity sites and valence can be determined experimentally and configurations determined through calculations.Here we present an investigation of the Si/SiO2 interface. The Z-contrast image in Fig. la, taken with the VG Microscopes HB603U STEM, shows that the atomic structure of Si is maintained up to the last layers visible. The decrease in intensity near the interface could originate from interfacial roughness of around one unit cell (∼0.5 nm), or may represent dechanneling in the slightly buckled columns induced by the oxide. Fig. lb, taken from a sample with ∼1 nm interface roughness, shows a band of bright contrast near the interface. This is not due to impurities or thickness variation since it disappears on increasing the detector angle from 25 mrad to 45 mrad (Fig. lc), and is therefore due to induced strain.

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.

The Si/SiO2 Interface: Atomic Structures, Composition, Strain and Energetics

2001 ◽  
Vol 7 (S2) ◽  
pp. 768-769
Author(s):  
S. J. Pennycook ◽  
G. Duscher ◽  
R. Buczko ◽  
S. T. Pantelides
Keyword(s):  
First Principles ◽  
Interface Roughness ◽  
Atomic Scale ◽  
Thickness Variation ◽  
Atomic Structures ◽  
Bright Contrast ◽  
Z Contrast ◽  
Impurity Sites ◽  
Contrast Image ◽  
Detector Angle

A number of recent studies of grain boundaries and heterophase interfaces have demonstrated the power of combining Z-contrast STEM imaging, EELS and first-principles theoretical modeling to give an essentially complete atomic scale description of structure, bonding and energetics. Impurity sites and valence can be determined experimentally and configurations determined through calculations.Here we present an investigation of the Si/SiO2 interface. The Z-contrast image in Fig. la, taken with the VG Microscopes HB603U STEM, shows that the atomic structure of Si is maintained up to the last layers visible. The decrease in intensity near the interface could originate from interfacial roughness of around one unit cell (∼0.5 nm), or may represent dechanneling in the slightly buckled columns induced by the oxide. Fig. lb, taken from a sample with ∼1 nm interface roughness, shows a band of bright contrast near the interface. This is not due to impurities or thickness variation since it disappears on increasing the detector angle from 25 mrad to 45 mrad (Fig. lc), and is therefore due to induced strain.

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.

Temperature Dependence of Critical Thickness for Two Dimensional Growth of GexSi1−x on Si Substrate

1991 ◽  
Vol 220 ◽  
Author(s):  
Xun Wang ◽  
G. L. Zhou ◽  
T. C. Zhou ◽  
C. Sheng ◽  
M. R. Yu
Keyword(s):  
Growth Temperature ◽  
Critical Thickness ◽  
Layer Growth ◽  
Layer By Layer ◽  
Two Dimensional ◽  
Si Substrate ◽  
Lower Growth ◽  
Germanium Content ◽  
Si Substrates ◽  
Molecular Beam Epitaxial

ABSTRACTFor obtaining good structural perfection, the molecular beam epitaxial (MBE) growth of GexSi1−x on Si substrate should not only be kept in the pseudomorphic form but also in layer-by-layer growth stage. We found that the two dimensional layer-by-layer growth of GexSi1−x on Si could persist to a certain deposition thickness, beyond that the transition to islanding growth occurs. The transition thickness is significantly dependent on the growth temperature and germanium content, and is always smaller than the critical thickness of pseudomorphic growth. In order to obtain good crystalline quality in growing GexSi1−x superlattices on Si substrates, the thickness of GexSi1−x layers should be controlled below the transition thickness and lower growth temperature is favorable.

Epitaxial growth manner and structure of superconducting oxide films

1990 ◽  
Vol 48 (4) ◽  
pp. 2-3
Author(s):  
Yoshichika Bando ◽  
Takahito Terashima ◽  
Kenji Iijima ◽  
Kazunuki Yamamoto ◽  
Kazuto Hirata ◽  
...  
Keyword(s):  
Ultrathin Films ◽  
Film Surface ◽  
High Energy ◽  
Epitaxial Films ◽  
Layer By Layer ◽  
Initial Growth ◽  
In Situ Growth ◽  
High Quality ◽  
Activated Reactive Evaporation

The high quality thin films of high-Tc superconducting oxide are necessary for elucidating the superconducting mechanism and for device application. The recent trend in the preparation of high-Tc films has been toward “in-situ” growth of the superconducting phase at relatively low temperatures. The purpose of “in-situ” growth is to attain surface smoothness suitable for fabricating film devices but also to obtain high quality film. We present the investigation on the initial growth manner of YBCO by in-situ reflective high energy electron diffraction (RHEED) technique and on the structural and superconducting properties of the resulting ultrathin films below 100Å. The epitaxial films have been grown on (100) plane of MgO and SrTiO, heated below 650°C by activated reactive evaporation. The in-situ RHEED observation and the intensity measurement was carried out during deposition of YBCO on the substrate at 650°C. The deposition rate was 0.8Å/s. Fig. 1 shows the RHEED patterns at every stage of deposition of YBCO on MgO(100). All the patterns exhibit the sharp streaks, indicating that the film surface is atomically smooth and the growth manner is layer-by-layer.

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.

scholarly journals Meso-Scale Transmission Electron Microscope Tomography Applied for Wax Distribution in Toner Particles

2013 ◽  
Vol 19 (S5) ◽  
pp. 58-61 ◽  
Author(s):  
Mino Yang ◽  
Jun-Ho Lee ◽  
Hee-Goo Kim ◽  
Euna Kim ◽  
Young-Nam Kwon ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Three Dimensional ◽  
Chromatic Aberration ◽  
Laser Printer ◽  
Medium Voltage ◽  
Transmission Electron ◽  
Z Contrast ◽  
Contrast Image

AbstractDistribution of wax in laser printer toner was observed using an ultra-high-voltage (UHV) and a medium-voltage transmission electron microscope (TEM). As the radius of the wax spans a hundred to greater than a thousand nanometers, its three-dimensional recognition via TEM requires large depth of focus (DOF) for a volumetric specimen. A tomogram with a series of the captured images would allow the determination of their spatial distribution. In this study, bright-field (BF) images acquired with UHV-TEM at a high tilt angle prevented the construction of the tomogram. Conversely, the Z-contrast images acquired by the medium-voltage TEM produced a successful tomogram. The spatial resolution for both is discussed, illustrating that the image degradation was primarily caused by beam divergence of the Z-contrast image and the combination of DOF and chromatic aberration of the BF image from the UHV-TEM.

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