scholarly journals Local Band Gap Measurements by VEELS of Thin Film Solar Cells

2014 ◽  
Vol 20 (4) ◽  
pp. 1246-1253 ◽  
Author(s):  
Debora Keller ◽  
Stephan Buecheler ◽  
Patrick Reinhard ◽  
Fabian Pianezzi ◽  
Darius Pohl ◽  
...  
Keyword(s):  
Band Gap ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Band Gap Energy ◽  
Radiation Losses ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Compositional Gradients ◽  
Future Work ◽  
The Impact

AbstractThis work presents a systematic study that evaluates the feasibility and reliability of local band gap measurements of Cu(In,Ga)Se2 thin films by valence electron energy-loss spectroscopy (VEELS). The compositional gradients across the Cu(In,Ga)Se2 layer cause variations in the band gap energy, which are experimentally determined using a monochromated scanning transmission electron microscope (STEM). The results reveal the expected band gap variation across the Cu(In,Ga)Se2 layer and therefore confirm the feasibility of local band gap measurements of Cu(In,Ga)Se2 by VEELS. The precision and accuracy of the results are discussed based on the analysis of individual error sources, which leads to the conclusion that the precision of our measurements is most limited by the acquisition reproducibility, if the signal-to-noise ratio of the spectrum is high enough. Furthermore, we simulate the impact of radiation losses on the measured band gap value and propose a thickness-dependent correction. In future work, localized band gap variations will be measured on a more localized length scale to investigate, e.g., the influence of chemical inhomogeneities and dopant accumulations at grain boundaries.

Resolution in the Scanning Transmission Electron Microscope

1972 ◽  
Vol 30 ◽  
pp. 454-455
Author(s):  
M. G. R. Thomson
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Spherical Aberration ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Objective Lens ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission

The variation of contrast and signal to noise ratio with change in detector solid angle in the high resolution scanning transmission electron microscope was discussed in an earlier paper. In that paper the conclusions were that the most favourable conditions for the imaging of isolated single heavy atoms were, using the notation in figure 1, either bright field phase contrast with β0⋍0.5 α0, or dark field with an annular detector subtending an angle between ao and effectively π/2.The microscope is represented simply by the model illustrated in figure 1, and the objective lens is characterised by its coefficient of spherical aberration Cs. All the results for the Scanning Transmission Electron Microscope (STEM) may with care be applied to the Conventional Electron Microscope (CEM). The object atom is represented as detailed in reference 2, except that ϕ(θ) is taken to be the constant ϕ(0) to simplify the integration. This is reasonable for θ ≤ 0.1 θ0, where 60 is the screening angle.

Background subtraction in STEM energy-loss mapping

1984 ◽  
Vol 42 ◽  
pp. 568-569
Author(s):  
R.D. Leapman ◽  
K.E. Gorlen ◽  
C.R. Swyt
Keyword(s):  
Energy Loss ◽  
Signal To Noise Ratio ◽  
Statistical Error ◽  
Scanning Transmission Electron Microscope ◽  
Reference Image ◽  
Inverse Power Law ◽  
Transmission Electron ◽  
Least Squares Fit ◽  
Scanning Transmission ◽  
Single Number

The determination of elemental distributions by electron energy loss spectroscopy necessitates removal of the non-characteristic spectral background from a core-edge at each point in the image. In the scanning transmission electron microscope this is made possible by computer controlled data acquisition. Data may be processed by fitting the pre-edge counts, at two or more channels, to an inverse power law, AE-r, where A and r are parameters and E is energy loss. Processing may be performed in real-time so a single number is saved at each pixel. Detailed analysis, shows that the largest contribution to noise comes from statistical error in the least squares fit to the background. If the background shape remains constant over the entire image, the signal-to-noise ratio can be improved by fitting only one parameter. Such an assumption is generally implicit in subtraction of the “reference image” in energy selected micrographs recorded in the CTEM with a Castaing-Henry spectrometer.

Some Quantification Problems in Parallel EELS Images

1990 ◽  
Vol 48 (2) ◽  
pp. 36-37
Author(s):  
G. Botton ◽  
G. L’Espérance ◽  
M.D. Ball ◽  
C.E. Gallerneault
Keyword(s):  
Electron Microscope ◽  
Imaging System ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Acquisition Time ◽  
Thickness Variation ◽  
Transmission Electron ◽  
Distribution Of Elements ◽  
Scanning Transmission ◽  
Present Distribution

The recently developed parallel electron energy loss spectrometers (PEELS) have led to a significant reduction in spectrum acquisition time making EELS more useful in many applications in material science. Dwell times as short as 50 msec per spectrum with a PEELS coupled to a scanning transmission electron microscope (STEM), can make quantitative EEL images accessible. These images would present distribution of elements with the high spatial resolution inherent to EELS. The aim of this paper is to briefly investigate the effect of acquisition time per pixel on the signal to noise ratio (SNR), the effect of thickness variation and crystallography and finally the energy stability of spectra when acquired in the scanning mode during long periods of time.The configuration of the imaging system is the following: a Gatan PEELS is coupled to a CM30 (TEM/STEM) electron microscope, the control of the spectrometer and microscope is performed through a LINK AN10-85S MCA which is interfaced to a IBM RT 125 (running under AIX) via a DR11W line.

Identifying and Correcting Scan Noise and Drift in the Scanning Transmission Electron Microscope

2013 ◽  
Vol 19 (4) ◽  
pp. 1050-1060 ◽  
Author(s):  
Lewys Jones ◽  
Peter D. Nellist
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Electromagnetic Interference ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Great Sensitivity ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Recorded Data

AbstractThe aberration-corrected scanning transmission electron microscope has great sensitivity to environmental or instrumental disturbances such as acoustic, mechanical, or electromagnetic interference. This interference can introduce distortions to the images recorded and degrade both signal noise and resolution performance. In addition, sample or stage drift can cause the images to appear warped and leads to unreliable lattice parameters being exhibited. Here a detailed study of the sources, natures, and effects of imaging distortions is presented, and from this analysis a piece of image reconstruction code has been developed that can restore the majority of the effects of these detrimental image distortions for atomic-resolution data. Example data are presented, and the performance of the restored images is compared quantitatively against the as-recorded data. An improvement in apparent resolution of 16% and an improvement in signal-to-noise ratio of 30% were achieved, as well as correction of the drift up to the precision to which it can be measured.

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.

scholarly journals Increasing Spatial Fidelity and SNR of 4D-STEM Using Multi-Frame Data Fusion

2021 ◽  
pp. 1-11 ◽  
Author(s):  
Colum M. O'Leary ◽  
Benedikt Haas ◽  
Christoph T. Koch ◽  
Peter D. Nellist ◽  
Lewys Jones
Keyword(s):  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Distortion Correction ◽  
Environmental Scanning ◽  
Data Series ◽  
Signal To Noise ◽  
Diffraction Plane ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Overall Performance

4D-STEM, in which the 2D diffraction plane is captured for each 2D scan position in the scanning transmission electron microscope (STEM) using a pixelated detector, is complementing, and increasingly replacing existing imaging approaches. However, at present the speed of those detectors, although having drastically improved in the recent years, is still 100 to 1,000 times slower than the current PMT technology operators are used to. Regrettably, this means environmental scanning-distortion often limits the overall performance of the recorded 4D data. Here, we present an extension of existing STEM distortion correction techniques for the treatment of 4D data series. Although applicable to 4D data in general, we use electron ptychography and electric-field mapping as model cases and demonstrate an improvement in spatial fidelity, signal-to-noise ratio (SNR), phase precision, and spatial resolution.

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.

Improvements in the X-Ray Analytical Capabilities of a Scanning Transmission Electron Microscope by Spherical-Aberration Correction

2006 ◽  
Vol 12 (6) ◽  
pp. 515-526 ◽  
Author(s):  
M. Watanabe ◽  
D.W. Ackland ◽  
A. Burrows ◽  
C.J. Kiely ◽  
D.B. Williams ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Spherical Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Analytical Sensitivity ◽  
X Ray ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
The Impact

A Nion spherical-aberration (Cs) corrector was recently installed on Lehigh University's 300-keV cold field-emission gun (FEG) Vacuum Generators HB 603 dedicated scanning transmission electron microscope (STEM), optimized for X-ray analysis of thin specimens. In this article, the impact of the Cs-corrector on X-ray analysis is theoretically evaluated, in terms of expected improvements in spatial resolution and analytical sensitivity, and the calculations are compared with initial experimental results. Finally, the possibilities of atomic-column X-ray analysis in a Cs-corrected STEM are discussed.

The High Resolution Scanning Transmission Electron Microscope

1974 ◽  
Vol 32 ◽  
pp. 316-317
Author(s):  
A. V. Crewe
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
High Vacuum ◽  
Scanning Transmission Electron Microscope ◽  
Ultra High Vacuum ◽  
Resolving Power ◽  
Imaging Characteristics ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
The Moment

The high resolution STEM is now a fact of life. I think that we have, in the last few years, demonstrated that this instrument is capable of the same resolving power as a CEM but is sufficiently different in its imaging characteristics to offer some real advantages.It seems possible to prove in a quite general way that only a field emission source can give adequate intensity for the highest resolution^ and at the moment this means operating at ultra high vacuum levels. Our experience, however, is that neither the source nor the vacuum are difficult to manage and indeed are simpler than many other systems and substantially trouble-free.

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