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Method and Detector to Identify Chemical Elements with Bright-Field Scanning Transmission Electron Microscopy

IP.com Disclosure Number: IPCOM000033282D
Original Publication Date: 2004-Dec-03
Included in the Prior Art Database: 2004-Dec-03
Document File: 6 page(s) / 358K

Publishing Venue

National Institute of Standards and Technology

Related People

Zachary H. Levine: INVENTOR

Abstract

A multi-channel annular detector is proposed for bright-field imaging in the scanning transmission electron microscope. The detector consists of a plurality of nested annular arcs (approximately 90°120° each). Tens to hundreds of channels are envisioned. Too few, and the method described below will not work; too many and the method will not be superior to the existing charge-couple device (CCD) detectors. The sample is restricted to a partially amorphous material, or incoherent operation must be obtained. Maps of classes of chemical elements may be obtained by performing tomographic reconstructions of a particular transform of the radial distribution function of the electrons passing through the sample. Keywords: STEM; Scanning transmission electron microscopy; bright-field imaging; multi-channel detection; annular detector; tomography; chemical element identification °

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Method and Detector to Identify Chemical Elements with

. Bright-Field Scanning Transmission Electron Microscopy Using

Tomography

Zachary H. Levine

National Institute of Standards and Technology, Gaithersburg, MD 20899-8410

(Dated: October 28, 2003)

Abstract

A multi-channel annular detector is proposed for bright-field imaging in the scanning transmis­sion electron microscope. The detector consists of a plurality of nested annular arcs (approximately 90o120o each). Tens to hundreds of channels are envisioned. Too few, and the method described below will not work; too many and the method will not be superior to the existing charge-couple device (CCD) detectors.

The sample is restricted to a partially amorphous material, or incoherent operation must be obtained. Maps of classes of chemical elements may be obtained by performing tomographic reconstructions of a particular transform of the radial distribution function of the electrons passing through the sample.

Keywords: STEM; Scanning transmission electron microscopy; bright-field imaging; multi-channel detection; annular detector; tomography; chemical element identification

1

I.

OBJECT OF THE INVENTION

The object of the invention is to obtain 2D or 3D reconstructed images of samples includ­ing limited information on their chemical composition. The method purports to offer more

speed than existing methods for chemical element identification and more differentiation of elements than an existing faster method.

II.

DESCRIPTION OF THE INVENTION IN DETAIL

There are two parts to the invention. This first is a specialized detector. The detector is intended to replace standard bright-field / dark-field detector pair found in existing scan­

ning transmission electron microscopes. The key feature of the detector is that it averages the bright-field signal radially while providing good discrimination as a function of radius.

However, to achieve the radial geometry, the detector must be centered, and to achieve cen­tering, it must be segmented into three or four angular ranges. It is not necessary for every

annular segment to be segmented.

The second part is a mathematical procedure for processing the information from the detector. The procedure is somewhat involved, so I refer to sections IIA, lID, IlIA, and Appendix B of the attached manuscript "Theory of Bright-Field Scanning Transmission Electron Microscopy for Tomography". Also see section IIIB for a demonstration of the technique within computer simulation. The summary is that integral transforms of the

bright-field signal as a function of polar deflection angle (but not azimuthal deflection angle) may be used to perform independent tomographic reconstructions of the sample. These

reconstruction may be used to identify chemical elements within the sample. One way to do this is to perform three independent reconstructions and to overlay the result in a color

map. Then each element appears as a separate color in the image.

III.

INVENTIONS AS DEVICE

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