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Structural damage reduction in protected gold clusters by electron diffraction methods

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ABSTRACT

The present work explores electron diffraction methods for studying the structure of metallic clusters stabilized with thiol groups, which are susceptible to structural damage caused by electron beam irradiation. There is a compromise between the electron dose used and the size of the clusters since they have small interaction volume with electrons and as a consequence weak reflections in the diffraction patterns. The common approach of recording individual clusters using nanobeam diffraction has the problem of an increased current density. Dosage can be reduced with the use of a smaller condenser aperture and a higher condenser lens excitation, but even with those set ups collection times tend to be high. For that reason, the methods reported herein collects in a faster way diffraction patterns through the scanning across the clusters under nanobeam diffraction mode. In this way, we are able to collect a map of diffraction patterns, in areas with dispersed clusters, with short exposure times (milliseconds) using a high sensitive CMOS camera. When these maps are compared with their theoretical counterparts, oscillations of the clusters can be observed. The stability of the patterns acquired demonstrates that our methods provide a systematic and precise way to unveil the structure of atomic clusters without extensive detrimental damage of their crystallinity.

Electronic supplementary material: The online version of this article (doi:10.1186/s40679-016-0026-x) contains supplementary material, which is available to authorized users.

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Experimental setup of the S-NBD technique. a Schematic representation of the transmission electron microscope and the synchronized collection of electron diffraction patterns using a high sensitive CMOS camera. b Beam size used for the scanning diffraction method and c example of a nanobeam scanned area and its perimeter recorded at the CMOS camera
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Fig2: Experimental setup of the S-NBD technique. a Schematic representation of the transmission electron microscope and the synchronized collection of electron diffraction patterns using a high sensitive CMOS camera. b Beam size used for the scanning diffraction method and c example of a nanobeam scanned area and its perimeter recorded at the CMOS camera

Mentions: The electron diffraction was performed in a JEOL 2010F microscope operated at 200 kV. The scanning of the electron beam is possible using a precession electron diffraction-assisted automated crystal orientation mapping (PED ACOM-TEM) unit attached to the microscope [24]. In the ACOM-TEM technique, the electron beam is scanned across the sample and collects the electron diffraction patterns using an ultrafast charge-coupled device (CCD) camera attached to the viewing screen of the microscope. The CCD camera allows us to obtain an image of the scanned area. However, the CCD camera is not sensitive enough to collect the patterns due to the small volume of the clusters which produce weak reflections. In this way, we have synchronized the scanning and the acquisition of the patterns with an ultrafast TVIPS 16-mega pixel F416 CMOS camera with a dynamic range (max./noise) of 10,000:1. This CMOS camera eliminates streaking problem for high intensity reflections and transmitted beam in electron diffraction suffered in regular CCD cameras. A schematic representation of the experimental setup is illustrated in Fig. 2a, the probe size is about 2 nm as show in the surface plot image of the Fig. 2b. In scanning electron diffraction, the electron beam is tilted and subsequently de-scanned in a complementary way with the image shift coils, so that the diffraction pattern appears as a stationary spot pattern and the scanning is carried out line-by-line of the field of view selected using the external CCD camera in front of the screen of the microscope as show in Fig. 2c. The patterns are recorded with the CMOS camera in video mode which is capable to register patterns every 0.1 s by means of a line-by-line sweep and saved in individual images which are subsequently processed and compared with simulated patterns of the theoretical structure. The scanning NBD allows the collection of the patterns, before any irreversible change in the cluster structure may arise following electron beam irradiation of a static beam in conventional TEM.Fig. 2


Structural damage reduction in protected gold clusters by electron diffraction methods
Experimental setup of the S-NBD technique. a Schematic representation of the transmission electron microscope and the synchronized collection of electron diffraction patterns using a high sensitive CMOS camera. b Beam size used for the scanning diffraction method and c example of a nanobeam scanned area and its perimeter recorded at the CMOS camera
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5037159&req=5

Fig2: Experimental setup of the S-NBD technique. a Schematic representation of the transmission electron microscope and the synchronized collection of electron diffraction patterns using a high sensitive CMOS camera. b Beam size used for the scanning diffraction method and c example of a nanobeam scanned area and its perimeter recorded at the CMOS camera
Mentions: The electron diffraction was performed in a JEOL 2010F microscope operated at 200 kV. The scanning of the electron beam is possible using a precession electron diffraction-assisted automated crystal orientation mapping (PED ACOM-TEM) unit attached to the microscope [24]. In the ACOM-TEM technique, the electron beam is scanned across the sample and collects the electron diffraction patterns using an ultrafast charge-coupled device (CCD) camera attached to the viewing screen of the microscope. The CCD camera allows us to obtain an image of the scanned area. However, the CCD camera is not sensitive enough to collect the patterns due to the small volume of the clusters which produce weak reflections. In this way, we have synchronized the scanning and the acquisition of the patterns with an ultrafast TVIPS 16-mega pixel F416 CMOS camera with a dynamic range (max./noise) of 10,000:1. This CMOS camera eliminates streaking problem for high intensity reflections and transmitted beam in electron diffraction suffered in regular CCD cameras. A schematic representation of the experimental setup is illustrated in Fig. 2a, the probe size is about 2 nm as show in the surface plot image of the Fig. 2b. In scanning electron diffraction, the electron beam is tilted and subsequently de-scanned in a complementary way with the image shift coils, so that the diffraction pattern appears as a stationary spot pattern and the scanning is carried out line-by-line of the field of view selected using the external CCD camera in front of the screen of the microscope as show in Fig. 2c. The patterns are recorded with the CMOS camera in video mode which is capable to register patterns every 0.1 s by means of a line-by-line sweep and saved in individual images which are subsequently processed and compared with simulated patterns of the theoretical structure. The scanning NBD allows the collection of the patterns, before any irreversible change in the cluster structure may arise following electron beam irradiation of a static beam in conventional TEM.Fig. 2

View Article: PubMed Central - PubMed

ABSTRACT

The present work explores electron diffraction methods for studying the structure of metallic clusters stabilized with thiol groups, which are susceptible to structural damage caused by electron beam irradiation. There is a compromise between the electron dose used and the size of the clusters since they have small interaction volume with electrons and as a consequence weak reflections in the diffraction patterns. The common approach of recording individual clusters using nanobeam diffraction has the problem of an increased current density. Dosage can be reduced with the use of a smaller condenser aperture and a higher condenser lens excitation, but even with those set ups collection times tend to be high. For that reason, the methods reported herein collects in a faster way diffraction patterns through the scanning across the clusters under nanobeam diffraction mode. In this way, we are able to collect a map of diffraction patterns, in areas with dispersed clusters, with short exposure times (milliseconds) using a high sensitive CMOS camera. When these maps are compared with their theoretical counterparts, oscillations of the clusters can be observed. The stability of the patterns acquired demonstrates that our methods provide a systematic and precise way to unveil the structure of atomic clusters without extensive detrimental damage of their crystallinity.

Electronic supplementary material: The online version of this article (doi:10.1186/s40679-016-0026-x) contains supplementary material, which is available to authorized users.

No MeSH data available.


Related in: MedlinePlus