Imaging At the Timescale Of Micro- and Milliseconds With the pnCCD (S)TEM Camera

Ryll, H.; Simson, M.; Hertog, M. den; Dunin‐Borkowski, Rafal E.; Hajraoui, Khalil El; Hartmann, R.; Huth, Martin; Ihle, Sebastian; Migunov, Vadim; Schmidt, Julia; Soltau, H.; Striider, Lothar

doi:10.1017/s1431927615008703

Cited by 4 publications

(3 citation statements)

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“…There are several benefits of high readout rates: first, shorter integration times enable detailed imaging of dynamic processes (for example phase transitions or mechanical movement [23]). Second, the number of primary electrons that can be measured per unit time interval without exceeding the CHC is increased and thus the primary electron current.…”

Section: Time Resolutionmentioning

confidence: 99%

“…The use of the pnCCD as a 4D STEM imager presupposes the high speed and radiation hardness which is fulfilled. Moreover, the flexible configuration of the pnCCD readout schemes enables complex readout sequences with integration times down to 25 µs [23].…”

Section: Time Resolutionmentioning

confidence: 99%

“…This includes imaging in TEM mode of dynamic processes (e.g. imaging growth of a Pt-Si phase inside a nanowire, vibrations of a nanowire [23]), using sub-pixel resolution for electron holography imaging [26] and fast electron tomography [11].…”

Section: Applications Of the Pnccd (S)tem Cameramentioning

confidence: 99%

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A pnCCD-based, fast direct single electron imaging camera for TEM and STEM

et al. 2016

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We report on a new camera that is based on a pnCCD sensor for applications in scanning transmission electron microscopy. Emerging new microscopy techniques demand improved detectors with regards to readout rate, sensitivity and radiation hardness, especially in scanning mode. The pnCCD is a 2D imaging sensor that meets these requirements. Its intrinsic radiation hardness permits direct detection of electrons. The pnCCD is read out at a rate of 1,150 frames per second with an image area of 264 × 264 pixel. In binning or windowing modes, the readout rate is increased almost linearly, for example to 4,000 frames per second at 4× binning (264 × 66 pixel). Single electrons with energies from 300 keV down to 5 keV can be distinguished due to the high sensitivity of the detector. Three applications in scanning transmission electron microscopy are highlighted to demonstrate that the pnCCD satisfies experimental requirements, especially fast recording of 2D images. In the first application, 65,536 2D diffraction patterns were recorded in 70 s. STEM images corresponding to intensities of various diffraction peaks were reconstructed. For the second application, the microscope was operated in a Lorentz-like mode. Magnetic domains were imaged in an area of 256 × 256 sample points in less than 37 seconds for a total of 65,536 images each with 264 × 132 pixels. Due to information provided by the two-dimensional images, not only the amplitude but also the direction of the magnetic field could be determined. In the third application, millisecond images of a semiconductor nanostructure were recorded to determine the lattice strain in the sample. A speed-up in measurement time by a factor of 200 could be achieved compared to a previously used camera system.

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Section: Time Resolutionmentioning

confidence: 99%

Section: Time Resolutionmentioning

confidence: 99%

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A pnCCD-based, fast direct single electron imaging camera for TEM and STEM

et al. 2016

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Imaging of Electric Fields with the pnCCD ( S ) TEM Camera

Ritz¹,

Simson²,

Ihle³

et al. 2016

European Microscopy Congress 2016: Proceedings

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The imaging of electric fields on the nanometer scale is of great interest for modern materials research. Techniques providing a fast, direct and precise measurement of local fields are thus useful for materials science applications. We present microscopic measurements of electric fields with the 4D‐STEM technique using the pnCCD (S)TEM camera. In 4D‐STEM, a 2D camera image is recorded for each probe position of a 2D scan area, yielding a 4D dataset. With this technique, small shifts of the bright field disc (BFD) due to a deflection of the electron beam through electric and magnetic fields in the sample region can be detected. Hence, the magnitude and direction of the local field at each probe position can be determined. Given the large number of necessary probe positions, this technique requires a fast camera system providing short enough readout times so that instabilities in the microscope and sample drift or radiation damage do not deteriorate the final STEM image. Furthermore, a pixelated detector is required to record and account for the intensity distribution variations caused by interaction of the electron beam with the sample. The pnCCD (S)TEM camera allows fast acquisition of 2D camera images with a direct detecting, radiation hard pnCCD with 264×264 pixels [1]. Routinely, the readout speed is 1000 frames per second (fps) and can be further increased through binning and windowing. For example, with the pnCCD (S)TEM camera a 256x256 STEM image – where a camera image is recorded at each probe position – can be recorded in less than 70 s. The 264x264 pixel camera image allows precise determination of the BFD position, yielding information about electric and magnetic fields in the sample. For data analysis, image subsets can be selected freely to obtain virtual diffraction images or perform differential phase contrast (DPC) analysis. A major advantage over conventional segmented DPC detectors is that, with the pnCCD (S)TEM camera, movements of the BFD can be discriminated from intensity variations inside the BFD which is of particular importance for analysis of electromagnetic fields inside specimens. Further 4D‐STEM applications benefitting from the pnCCD (S)TEM camera include imaging on the micro‐ and millisecond timescale [2], strain analysis [3], magnetic domain mapping [1], and electron ptychography [4]. A demonstration of electric field mapping in vacuum with the pnCCD (S)TEM camera is shown in Figure 1. A voltage of 50 V was applied to a tungsten needle mounted in an FEI Titan G2 80‐200 ChemiSTEM microscope, operated at 80 keV. For each of the 256x256 probe positions, a 2D camera image was recorded (Fig. 1a). From these camera images an incoherent bright field STEM image (Fig. 1b, background) as well as the position in the x‐ and y‐directions of the BFD at each probe position was calculated. A comparison of the position of the BFD with and without an applied voltage yields information about the magnitude and direction of the local gradient of the projected electrostatic potential (Fig. 1b, indicated by coloring and arrows). In addition to this direct mapping of the electric field around a needle with rather well‐shaped BFDs, the large number of pixels of the pnCCD (S)TEM camera allows the precise determination of the BFD position, even in cases when the BFD is weak and deformed through the interaction of the electron beam with the sample (Fig. 1c). In conclusion, 4D‐STEM techniques like electromagnetic field mapping benefit significantly from the capabilities of the pnCCD (S)TEM camera. The readout speeds of 1000 fps and above allow the fast acquisition of 4D datasets with 2D camera images at each probe position. Through the large number of pixels, position and intensity variations of BFDs can be precisely determined.

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Prospects for quantitative and time-resolved double and continuous exposure off-axis electron holography

et al. 2017

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The technique of double exposure electron holography, which is based on the superposition of two off-axis electron holograms, was originally introduced before the availability of digital image processing to allow differences between electron-optical phases encoded in two electron holograms to be visualised directly without the need for holographic reconstruction. Here, we review the original method and show how it can now be extended to permit quantitative studies of phase shifts that oscillate in time. We begin with a description of the theory of off-axis electron hologram formation for a time-dependent electron wave that results from the excitation of a specimen using an external stimulus with a square, sinusoidal, triangular or other temporal dependence. We refer to the more general method as continuous exposure electron holography, present preliminary experimental measurements and discuss how the technique can be used to image electrostatic potentials and magnetic fields during high frequency switching experiments.

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Imaging At the Timescale Of Micro- and Milliseconds With the pnCCD (S)TEM Camera

Abstract: International audienc

Cited by 4 publications

References 3 publications

A pnCCD-based, fast direct single electron imaging camera for TEM and STEM

A pnCCD-based, fast direct single electron imaging camera for TEM and STEM

Imaging of Electric Fields with the pnCCD ( S ) TEM Camera

Prospects for quantitative and time-resolved double and continuous exposure off-axis electron holography

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