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

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.

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Bonding, Defects, And Defect Dynamics In The Sic-SiO2 System

MRS Proceedings ◽

10.1557/proc-640-h3.3 ◽

2000 ◽

Vol 640 ◽

Cited By ~ 2

Author(s):

S. T. Pantelides ◽

R. Buczko ◽

M. Di Ventra ◽

S. Wang ◽

S.-G. Kim ◽

...

Keyword(s):

First Principles ◽

Oxidation Process ◽

Atomic Scale ◽

Contrast Imaging ◽

Interface Defects ◽

Device Applications ◽

Z Contrast ◽

And Control ◽

Electron Energy Loss ◽

Ultimate Purpose

ABSTRACTThis paper presents a review of new results obtained by a combination of first-principles theory, Z-contrast imaging, and electron-energy-loss spectroscopy in the context of a broader experimental/theoretical program to understand and control the atomic-scale structure of SiCSiO2 interfaces. The ultimate purpose is to achieve low interface trap densities for device applications. Results are given for global bonding arrangements in comparison with those of the Si-SiO2 interface, the mechanism of the oxidation process, the nature of possible interface defects and their passivation by N and H, and the formation and dissolution of C clusters in SiO2 during oxidation and reoxidation.

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The Atomic-Scale Origins of Grain Boundary Superconducting Properties

Microscopy and Microanalysis ◽

10.1017/s1431927600023564 ◽

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.

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

MRS Proceedings ◽

10.1557/proc-482-781 ◽

1997 ◽

Vol 482 ◽

Cited By ~ 3

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.

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

MRS Proceedings ◽

10.1557/proc-159-447 ◽

1989 ◽

Vol 159 ◽

Cited By ~ 3

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.

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First-Principles Mobility Calculations and Atomic-Scale Interface Roughness in Nanoscale Structures

Physical Review Letters ◽

10.1103/physrevlett.95.106802 ◽

2005 ◽

Vol 95 (10) ◽

Cited By ~ 54

Author(s):

M. H. Evans ◽

X.-G. Zhang ◽

J. D. Joannopoulos ◽

S. T. Pantelides

Keyword(s):

First Principles ◽

Interface Roughness ◽

Atomic Scale ◽

Nanoscale Structures

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

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100172590 ◽

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.

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Z-Contrast Scanning Transmission Electron Microscopy Of Nanometer-Scale Coated Particulate Materials

Microscopy and Microanalysis ◽

10.1017/s1431927600023904 ◽

1998 ◽

Vol 4 (S2) ◽

pp. 756-757

Author(s):

H.J. Gao ◽

Y. Yan ◽

J. Fitz-Gerald ◽

D. Kumar ◽

R.K. Singh ◽

...

Keyword(s):

Deep Understanding ◽

Scanning Transmission Electron Microscope ◽

Atomic Scale ◽

Particulate Materials ◽

Atomic Structures ◽

Scanning Transmission Electron ◽

Novel Structure ◽

Transmission Electron ◽

Scanning Transmission ◽

Z Contrast

Particulate materials with unique functional properties have been the focus of much attention in recent years. Of particular interest, due to their considerable scientific and technological importance, are particles coated with nanoparticles. These have greatly stimulated interest for their novel structure and properties. In these kinds of particulate materials, the interface structures between the support particle and the nanoparticle play a crucial role in controlling their properties. Consequently, imaging of the atomic structures at the interfaces can provide deep understanding of the relationship between the particulate and the corresponding properties. Z-contrast scanning transmission electron microscope (STEM) provides a new view of materials on the atomic scale, a direct image of atomic structure composition which can be interpreted without the need for any preconceived model structure. Therefore it is a powerful tool in the study of particulate materials. In this report, we will present the structures of 18 micron diameter alumina particles coated with Ag nanoparticles.

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Atomic Scale Analysis of Cubic Zirconia Grain Boundaries

MRS Proceedings ◽

10.1557/proc-589-323 ◽

1999 ◽

Vol 589 ◽

Author(s):

E.C. Dickey ◽

X. Fan ◽

M. Yong ◽

S.B. Sinnott ◽

S.J. Pennycook

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Mirror Symmetry ◽

Fluorite Structure ◽

Atomic Scale ◽

Contrast Imaging ◽

Cubic Zirconia ◽

Atomic Structures ◽

Periodic Arrays ◽

Z Contrast

AbstractThe core structures of two symmetric tilt [001” grain boundaries in yttria- stabilized cubic zirconia are determined by Z-contrast imaging microscopy. In particular, near-σ=13 (510) and σ=5 (310) boundaries are studied. Both grain boundaries are found to be composed of periodic arrays of basic grain-boundary structural units, whose atomic structures are determined from the Z-contrast images. While both grain boundaries maintain mirror symmetry across the boundary plane, the 36° boundary is found to have a more compact structural unit than the 24° boundary. Partially filled cation columns in the 24° boundary are believed to prevent cation crowding in the boundary core. The derived grain boundary structural models are the first developed for ionic crystals having the fluorite structure

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