Nanometer-Scale Oxide Particles in Gesi Films Grown by Wet Oxidation

1993 ◽  
Vol 321 ◽  
Author(s):  
Tan-Chen Lee ◽  
Robert J. Soave ◽  
Yosi Y. Shacham-Diamand ◽  
John Silcox
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Nanometer Scale ◽  
Wet Oxidation ◽  
Random Nucleation ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Oxide Particles ◽  
Deposited Film

ABSTRACTAmorphous GeSi films with different thicknesses and oxygen contents were electron beam evaporated onto Si (KK)) wafers and wet oxidized at 900 °C for 30 Min. If there was no oxygen in the as-deposited film, an epitaxial GeSi film would be grown after wet oxidation. For the samples with oxygen, epitaxial growth broke down when the thickness of the epitaxy exceeded about 200 A and polycrystalline GeSi films were formed. A dedicated STEM (scanning transmission electron Microscope) was used to characterize the sample after oxidation. STEM BF (bright field), ADF (annular dark field), and energy filtered images revealed the presence of small oxide particles in the polycrystalline GeSi films. X-ray microprobe analysis with a windowless detector was employed to identify the oxide particles. The failure of the epitaxy is explained by the random nucleation and growth of GeSi grains on the oxide particles.

Design of a new objective lens for an HB-501A STEM

1991 ◽  
Vol 49 ◽  
pp. 416-417
Author(s):  
Earl J. Kirkland ◽  
Robert J. Keyse
Keyword(s):  
High Resolution ◽  
Spherical Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Objective Lens ◽  
Specimen Holder ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
High Resolution Microscopy

An ultra-high resolution pole piece with a coefficient of spherical aberration Cs=0.7mm. was previously designed for a Vacuum Generators HB-501A Scanning Transmission Electron Microscope (STEM). This lens was used to produce bright field (BF) and annular dark field (ADF) images of (111) silicon with a lattice spacing of 1.92 Å. In this microscope the specimen must be loaded into the lens through the top bore (or exit bore, electrons traveling from the bottom to the top). Thus the top bore must be rather large to accommodate the specimen holder. Unfortunately, a large bore is not ideal for producing low aberrations. The old lens was thus highly asymmetrical, with an upper bore of 8.0mm. Even with this large upper bore it has not been possible to produce a tilting stage, which hampers high resolution microscopy.

Incoherent High-Resolution Z-Contrast Imaging of Silicon and Gallium Arsenide Using HAADF-STEM

1999 ◽  
Vol 589 ◽  
Author(s):  
Y Kotaka ◽  
T. Yamazaki ◽  
Y Kikuchi ◽  
K. Watanabe
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Contrast Imaging ◽  
High Spatial Resolution Image ◽  
Transmission Electron ◽  
Eigen Value ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Convergent Beam ◽  
Z Contrast

AbstractThe high-angle annular dark-field (HAADF) technique in a dedicated scanning transmission electron microscope (STEM) provides strong compositional sensitivity dependent on atomic number (Z-contrast image). Furthermore, a high spatial resolution image is comparable to that of conventional coherent imaging (HRTEM). However, it is difficult to obtain a clear atomic structure HAADF image using a hybrid TEM/STEM. In this work, HAADF images were obtained with a JEOL JEM-2010F (with a thermal-Schottky field-emission) gun in probe-forming mode at 200 kV. We performed experiments using Si and GaAs in the [110] orientation. The electron-optical conditions were optimized. As a result, the dumbbell structure was observed in an image of [110] Si. Intensity profiles for GaAs along [001] showed differences for the two atomic sites. The experimental images were analyzed and compared with the calculated atomic positions and intensities obtained from Bethe's eigen-value method, which was modified to simulate HAADF-STEM based on Allen and Rossouw's method for convergent-beam electron diffraction (CBED). The experimental results showed a good agreement with the simulation results.

Direct observation ofB-site cation displacements in Pb-based complex perovskite relaxor oxides

2010 ◽  
Vol 44 (1) ◽  
pp. 111-121 ◽  
Author(s):  
K. Z. Baba-Kishi
Keyword(s):  
Long Range ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Unit Cells ◽  
Annular Dark Field ◽  
Pb Ions ◽  
Diffraction Patterns ◽  
Spatial Displacements

Electron diffraction patterns recorded using a scanning transmission electron microscope (STEM) from PbMg1/3Nb2/3O3(PMN) crystallites and PbZn1/3Nb2/3O3(PZN) crystals show weak and systematic continuous diffuse streaking along the 〈110〉 directions. Detailed high-angle annular dark-field (HAADF) images recordedviaan aberration-corrected STEM show that theB-site cations in PMN and PZN undergo correlated and long-range displacements towards the Pb2+ions on the (110) planes. The planarB-site displacement measured from the centres of the octahedra is about 0.3–0.5 Å in PMN and about 0.20–0.4 Å in PZN. In the HAADF images of the PMN crystallites and PZN crystals studied, there is insufficient evidence for systematic long-range planar displacements of the Pb2+ions. The observed Pb2+ion displacements in PMN and PZN appear randomly distributed, mostly displaced along 〈110〉 towards theB-site columns. There is also evidence of possible stress-related distortion in certain unit cells of PMN. In the relaxors studied, two distinct types of displacements were observed: one is the long-range planarB-site spatial displacement on the (110) planes, correlated with the Pb2+ions, possibly resulting in the observed diffuse streaking; the other is short-range Pb2+ion displacement on the (110) planes. The observed displacement status indicates a mutual attraction between the Pb ions and theB-site cations in which theBsites undergo the largest spatial displacements towards the Pb ions along 〈110〉.

High-angle annular dark-field STEM imaging of doped semiconductor layers

1991 ◽  
Vol 49 ◽  
pp. 704-705
Author(s):  
D.D. Perovic ◽  
J.H. Paterson
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
High Angle ◽  
Axis Orientation ◽  
Undoped Material ◽  
Transmission Electron ◽  
Ultrathin Layers ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
P Type

With the development of crystal growth techniques such as molecular beam epitaxy (MBE), it is now possible to fabricate modulation-doped superlattices consisting of alternating ultrathin layers of n-and/or p-type material abruptly separated by undoped material. At sufficiently high dopant concentrations these abrupt layers may be imaged in cross section by electron microscopy. Pennycook et al. and Treacy et al. have used high angle annular dark-field (HAAD) imaging in the scanning transmission electron microscope (STEM) to image low levels of dopants (∼1 at. %) in semiconductors. This work is concerned with imaging boron and arsenic doped layers in silicon at levels « 1 at.%.Fig. 1 shows a HAAD image of a B-Si superlattice at the <110> zone-axis orientation taken at 100 kV using a VG HB501UX STEM. The bright vertical layers are the B-doped regions, containing ∼4 x 1020 B/cm3. The horizontal lines are due to beam instability while the image was recorded. Fig.2 shows a line scan across the same superlattice, recorded by scanning the beam across the specimen in a direction perpendicular to the layers.

Single atom visibility on (111) silicon in simulated ADF STEM images

1988 ◽  
Vol 46 ◽  
pp. 820-821
Author(s):  
R. F. Loane
Keyword(s):  
Silicon Crystal ◽  
Gold Atom ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Single Atom ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Crystal Substrate ◽  
Annular Dark Field ◽  
Stem Image

The multislice method has been adapted to simulate annular dark field (ADF) scanning transmission electron microscope (STEM) images. In the STEM image simulation, a highly focused electron probe is scanned across a specimen and the scattered intensity, accumulated over an annular detector, is recorded as a function of probe position. Each pixel in the STEM image is determined by an entire multislice calculation for a particular position of the incident probe. This N4 process is very computationally expensive and currently requires the use of a supercomputer to achieve runtimes of less than a day.The simulated specimen consisted of a (111) silicon crystal substrate, which was a multiple of 94 Å (30 slices) thick, followed by an additional slice containing a single gold atom. Slice potentials were 38.4 Å x 39.9 Å (256 x 256 pixels) in size, which set the maximum included scattering angle to 79 mrad.

Multislice Simulation of Adf Stem Images

1987 ◽  
Vol 45 ◽  
pp. 188-191
Author(s):  
E. J. Kirkland ◽  
R. F. Loane ◽  
J. Silcox
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Scattering Amplitude ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Heavy Atoms ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

The multislice method (e.g. Goodman and Moodie) of simulating bright field conventional transmission electron microscope (BF-CTEM) images of crystalline specimens can be extended to simulation of scanning transmission electron microscope (STEM) images of similar specimens in the annular dark field (ADF) mode. According to the reciprocity theorem (Pogany and Turner and Cowley) BF-CTEM would be equivalent to BF STEM with a point detector. Such a detector (STEM) however would yield an exceedingly small signal to noise ratio. Thus, STEM has found more use in the ADF mode (e.g. Crewe et al.) exploiting the large contrast arising from heavy atoms. In BF imaging (CTEM and STEM) the constrast is roughly proportional to the scattering amplitude f α Z3/4 whereas in DF (CTEM and STEM) imaging it is roughly proportional to the scattering cross σ α Z3/2 where Z is atomic number, a form that is advantageous foatom discrimination.

Rapid and Semi-automated Method for Analysis of the Number of Atoms of Ultra-small Platinum Clusters on Carbon

2000 ◽  
Vol 6 (4) ◽  
pp. 353-357
Author(s):  
J.C. Yang ◽  
S. Bradley ◽  
J.M. Gibson
Keyword(s):  
Three Dimensional ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Spectroscopic Technique ◽  
Automated Method ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Dimensional Shape ◽  
Three Dimensional Shape

Abstract Very high angle (~100 mrad) annular dark-field (HAADF) images in a dedicated scanning transmission electron microscope (STEM) can be used to quantitatively measure the number of atoms in a cluster on a support material. We have developed a computer program which will automatically find the location of the particles and then integrate the intensity to find the number of atoms per cluster. We have examined ultra-small Pt clusters on a C substrate by this novel mass-spectroscopic technique. We discovered that the Pt clusters maintain their three-dimensional shape, and are probably spherical.

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