were obtained using new materials that do not inter-diffuse. Focusing and imaging with 8.4 × 6.4 nm resolution has been demonstrated. The larger NA and higher efficiency of these lenses allow rapid imaging of thick samples, as needed for tomographic imaging.

Imaging with hard X-rays offers advantages for the study of whole biological cells and of devices such as batteries under operating conditions. The increased penetration of the X-rays can image thicker objects. Even with improved NA, by operating at short X-ray wavelengths, a depth of field larger than the thickness of such objects is achieved, enabling high-resolution three-dimensional tomographic imaging. Shorter wavelengths also reduce the dose to the specimen and allow chemical analysis by X-ray fluorescence of all elements in the periodic table.

Phase Retrieval from the Differential Phase Contrast Signal

HREM Research, Inc .

Developers: Akimitsu Ishizuka, Masaaki Oka, and Kazuo Ishizuka

Differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM) was proposed by Dekker and de Lang in 1974. A few years later Waddell and Chapman showed that the center of mass (COM) of the diffraction pattern

is proportional to the gradient of the phase distribution of a phase object and that a split semicircular electron detector will give an approximate estimate of the COM perpendicular to a bisector of the detector. Recently, the possibility of DPC imaging at atomic resolution was demonstrated using a quadrant detector from which two perpendicular DPC signals may be obtained.

Since the DPC signal is proportional to the gradient of the phase distribution, the phase distribution of the sample can be retrieved by integrating the DPC signal. The new method here uses numerical procedures to obtain the object phase from the two DPC signals. Before the present method, procedures to retrieve a phase distribution from the DPC signal used the Fast Fourier Transform (FFT), which inevitably introduced periodic continuation at the boundaries of its solution (creating an image artifact). The present method uses the discrete cosine transform (DCT) to integrate the DPC signal since the Neumann boundary condition can be directly specified by the DPC signals. Recently a high-speed camera (a pixel detector) became available, and a diffraction pattern now can be obtained at each scan position.

Previous methods to retrieve the phase distribution by integrating the DPC signal used the FFT, which inevitably

2018 September •

Integrated Dynamic Electron Solutions, Inc. Developer: Bryan Reed

electrostatic deflector system that deflects transmission electron microscope (TEM) beams into sub-regions of the TEM camera with a 20 ns inter-frame switching time. This multiplexed image acquisition allows kHz-level frame rates, with nanosecond- precise single-frame exposure times, even using conventional TEM cameras. Each sub-image

Relativity ® is a post-specimen

contains image data to reconstruct a video of the experiment. The deflector provides true compressive sensing of TEM video with effective frame rates 100× faster than the base camera frame rate. The sophisticated temporal sequencing software of Relativity

introduces a slowly varying background (artifact) due to its implicit assumption of the periodic continuation at the image boundaries. The new method uses the Neumann boundary condition, which does not introduce such an artifact.

For many applications, STEM recently has become more popular than conventional transmission electron microscopy because of its versatility. Using STEM we can acquire chemical information simultaneously with structural information from an image. DPC imaging adds to STEM another capability: observation of a phase object using a segmented detector or a pixel detector. The new method gives a boundary-artifact-free phase distribution retrieved from the DPC signal. A DigitalMicrograph plug-in is in development, called qDPC (quantitative DPC), based on the above method.

Relativity ® Compressive Sensing and Multiplexed TEM Video

the timing and duration of beam blanking, multiplexing of exposure patterns, and detailed nanosecond-precise control of up to 8 auxiliary devices including sample holders, lasers, and detectors. The deflector system projects images, diffraction patterns, or EELS spectra onto the camera. Relativity

® provides a high degree of control over

wide range of operating modes and gives users the ability to precisely define where, when, and how long the electron dose is delivered to each sub-region of the detector over the duration of an experiment. Combined with Acuity

® has been designed to be configurable over a

of an integrated high-speed data acquisition and analysis tool. Relativity

camera port and requires no significant modifications to the TEM.

analysis software (IDES, Inc.), Relativity ® acts as the core ® can be installed into any standard 35 mm

™ data 35

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