Quantitative comparison of high resolution TEM images with image simulations

Hÿtch, Martin; Stobbs, W. M.

doi:10.1016/0304-3991(94)90034-5

Cited by 195 publications

(93 citation statements)

References 10 publications

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“…The resulting information limit g il % 1=ð Þ does not depend on the numerical aperture and scales proportional to the electron wavelength (i.e., like a magnetic force) for different beam energies. Hence, we were faced with a coherence loss of unknown reason in the process of image formation.There is a long record of detailed experimental and theoretical investigations of decoherence phenomena in transmission electron microscopy due to inelastic scattering in the specimen and also due to aloof beam excitations [15,16] since theoretically expected and observed contrast in TEM were often reported to disagree also in the past [17][18][19]. Unfortunately, none of the described effects proved strong enough to explain the limitation of the contrast transfer we observed.…”

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confidence: 73%

What Are the Resolution Limits in Electron Microscopes?

Marks¹

2013

Physics

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The resolving power of an electron microscope is determined by the optics and the stability of the instrument. Recently, progress has been obtained towards subångström resolution at beam energies of 80 kV and below but a discrepancy between the expected and achieved instrumental information limit has been observed. Here we show that magnetic field noise from thermally driven currents in the conductive parts of the instrument is the root cause for this hitherto unexplained decoherence phenomenon. We demonstrate that the deleterious effect depends on temperature and at least weakly on the type of material. DOI: 10.1103/PhysRevLett.111.046101 PACS numbers: 68.37.Og, 05.40.Ca, 41.85.Gy During the last 15 years after the introduction of aberration-corrected transmission electron microscopy (TEM) [1,2] the resolving power of the electron microscope could be improved from the Scherzer resolution [3] $100 set by the previously unavoidable spherical aberration of the objective lens C s and the wave length of the electron down to about 25 for beam energies of 60-300 kV [2,[4][5][6][7]. Recently, with the simultaneous correction of the spherical and the chromatic aberration C c , linear contrast transfer for spacings of 80 pm at a beam energy of 80 kV ( ¼ 4:2 pm) could be achieved [8]. The further improvement of the information limit of the TEM has exceptional importance as a driver for atomic-resolution imaging in materials science [9,10] and at even lower energies for light-atom materials sensitive to knock-on damage [11][12][13].The results obtained for the latest C c -and C s -corrected instruments are very convincing. Beyond that it could be demonstrated that the lateral incoherence and focus spread due to residual aberrations and instabilities are so small that a significant better instrumental information limit should be achievable than the one actually observed [8]. Therefore, during the development of new instrumentation we thoroughly analyzed this discrepancy and excluded possible parasitic effects like electronics noise, ac stray fields, higher-order aberrations, Coulomb interaction in the beam, and nonperfect vacuum conditions. However, the observed mismatch did not disappear. Also for the information limit achieved in aberration-corrected Lorentz microscopy [14] with the specimen in the field-free region, we discovered an unexplained discrepancy. By careful measurements of the contrast transfer as a function of the spatial frequency g we found that the mismatch can be described very well by an isotropic contrast envelope function of the form exp½À2ð jgjÞ 2 where is a characteristic image spread [8]. The resulting information limit g il % 1=ð Þ does not depend on the numerical aperture and scales proportional to the electron wavelength (i.e., like a magnetic force) for different beam energies. Hence, we were faced with a coherence loss of unknown reason in the process of image formation.There is a long record of detailed experimental and theoretical investigations of decoherence phenomena in transmission el...

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confidence: 73%

What Are the Resolution Limits in Electron Microscopes?

Marks¹

2013

Physics

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“…Questions on the sensitivity [17] and quantum efficiency [18] have been explored for pixel direct detection cameras, but their use for absolute-scale quantitative imaging in STEM has received less attention. Contrast mismatch or "Stobbs factor" issues in TEM have been discussed since the 1990s [19]. Recently, different imaging modes have been achieved on an absolute intensity scale in high-resolution TEM [20], and both HAADF [21] and BF [22] STEM.…”

Section: Quantitative Imaging From 4d Datasetsmentioning

confidence: 99%

Practical aspects of diffractive imaging using an atomic-scale coherent electron probe

et al. 2016

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a b s t r a c tFour-dimensional scanning transmission electron microscopy (4D-STEM) is a technique where a full twodimensional convergent beam electron diffraction (CBED) pattern is acquired at every STEM pixel scanned. Capturing the full diffraction pattern provides a rich dataset that potentially contains more information about the specimen than is contained in conventional imaging modes using conventional integrating detectors. Using 4D datasets in STEM from two specimens, monolayer MoS 2 and bulk SrTiO 3 , we demonstrate multiple STEM imaging modes on a quantitative absolute intensity scale, including phase reconstruction of the transmission function via differential phase contrast imaging. Practical issues about sampling (i.e. number of detector pixels), signal-to-noise enhancement and data reduction of large 4D-STEM datasets are emphasized.

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“…In this context, we propose the use of an iterative method which can simultaneously minimise the uncertainty in six parameters these being the thickness, defocus, beam tilt (in the two directions) and astigmatism (in the two directions). This scheme has been used successfully for an experimental focal series of [001] Al03Ga07As images [7] and a similar iterative scheme has been shown to work experimentally for determinations of thickness and defocus [5]. This approach to determining the experimental parameters and, more importantly, the exit wavefunction, is an alternative to the wavefunction reconstruction methods [14,15] as it deals more directly with the experimental problems such as microscope misalignment, specimen misorientation and the presence of noise due to amorphous layers of contamination.…”

Section: The Effects Of Crystalmentioning

confidence: 99%

“…Equally importantly, it is that effects of beam tilt and astigmatism are fairly independent of the thickness and defocus which allows them to be dealt with successively, the thickness and defocus having been optimised simultaneously because of their strong interaction. 7. The possibility of measuring the aluminium concentration in AlxGa1-xAs.…”

Section: The Effects Of Crystalmentioning

confidence: 99%