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Li.qun：/* 49. pixelated STEM detector */

2017-10-31T07:30:13Z

‎49. pixelated STEM detector

Li.qun：/* 49. pixelated STEM detector */

2017-10-31T07:25:44Z

‎49. pixelated STEM detector

Li.qun：/* 48. Si(Li) detector */

2017-10-31T07:24:35Z

‎48. Si(Li) detector

Li.qun：/* 48. Si(Li) detector */

2017-10-31T07:23:43Z

‎48. Si(Li) detector

Li.qun：/* 49. pixelated STEM detector */

2017-10-31T07:22:43Z

‎49. pixelated STEM detector

Li.qun：/* 48. Si(Li) detector */

2017-10-31T07:20:52Z

‎48. Si(Li) detector

Li.qun：/* 48. Si(Li) detector */

2017-10-31T07:20:30Z

‎48. Si(Li) detector

Li.qun：/* 49. pixelated STEM detector */

2017-10-12T09:04:53Z

‎49. pixelated STEM detector

2017年10月12日 (四) 09:03 Li.qun

2017-10-12T09:03:46Z

2017年10月12日 (四) 09:02 Li.qun

2017-10-12T09:02:12Z

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 A conventional STEM detector and a pixelated STEM detector are compared in Fig. 1.
-[[文件:Pixelated STEM detector 1.png]]
+[[文件:Pixelated STEM detector 1-1.png]]
 Fig. 1 Conventional single-channel STEM detector and Pixelated STEM detector

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 A STEM detector that records a diffraction (CBED) pattern formed on the detector as a two-dimensional (2D) image with a high-speed frame rate in synchronism with the scan of the incident electron probe. To take a two dimensional CBED pattern during the stay time of the STEM probe at one pixel, a direct electron detector of CCD or CMOS, which has a very high-speed frame rate of a few thousands of fps or more, is required. At present, using such a direct electron detector, a synchronous STEM scan with taking a 256 x 256 pixel CBED pattern is achieved.
 A conventional STEM detector and a pixelated STEM detector are compared in Fig. 1.
 [[文件:Pixelated STEM detector 1.png]]

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 One of the energy-dispersive X-ray detector used for EDS. A lithium (Li)-doped silicon single-crystal semiconductor is used as a detector element. When X-rays enter the detector element, electron-hole pairs (their generation energy is approximately 3 eV) are generated in the detector element, whose number is proportional to the energies of the X-rays. The generated electrons are collected to the anode at the bottom of the detector element by applying an external electric field. That is, the X-ray energies are measured as electric voltage pulses. Detectable elements range from boron (B: 0.18 keV @K line) to uranium (U: 3.16 keV @M line). The energy resolution of the detector is approximately 140 eV (@Mn K line). Cooling of the detector by liquid nitrogen is required to prevent diffusion of doped Li and to reduce a dark current caused by thermal noise. Owing to the development of a silicon drift detector (SDD) which has a high count rate and can be used by Peltier cooling, the Si(Li)detector has less been used.
 <pre>Related Term
-EDS,  energy-dispersive X-ray spectroscopy,  silicon drift detector,  SDD
+EDS,  energy-dispersive X-ray spectroscopy,  silicon drift detector,  SDD</pre>
 ==49. pixelated STEM detector ==

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 <pre>Related Term
 EDS,  energy-dispersive X-ray spectroscopy,  silicon drift detector,  SDD
 ==49. pixelated STEM detector ==

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 EDS,  energy-dispersive X-ray spectroscopy,  silicon drift detector,  SDD
+*
 ==49. pixelated STEM detector ==

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 Fig. 2 shows five sort of STEM images created from the final 4D data of SrTiO3 [100] taken at an accelerating voltage of 200 kV. It is seen that different information can be obtained by changing the integration area of the CBED pattern.
 The other applications of the pixelated STEM detector include creation of an electric-magnetic field map utilizing positional shift of the CBED pattern, and reconstruction of a phase image of a specimen by utilizing ptychography image processing.
+[[文件:Pixelated STEM detector 2.jpg]]
 Fig. 2 Various STEM images of SrTiO3 [100] taken at an accelerating voltage of 200 kV, by changing the integration area of the CBED pattern. Those STEM images are created from the final 4D data.

←上一版本		2017年10月12日 (四) 09:02的版本
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	<pre>Related Term		<pre>Related Term
	EDS, energy-dispersive X-ray spectroscopy, silicon drift detector, SDD		EDS, energy-dispersive X-ray spectroscopy, silicon drift detector, SDD
		+	==49. pixelated STEM detector ==
		+	A STEM detector that records a diffraction (CBED) pattern formed on the detector as a two-dimensional (2D) image with a high-speed frame rate in synchronism with the scan of the incident electron probe. To take a two dimensional CBED pattern during the stay time of the STEM probe at one pixel, a direct electron detector of CCD or CMOS, which has a very high-speed frame rate of a few thousands of fps or more, is required. At present, using such a direct electron detector, a synchronous STEM scan with taking a 256 x 256 pixel CBED pattern is achieved.
		+	A conventional STEM detector and a pixelated STEM detector are compared in Fig. 1.
		+
		+	Fig. 1 Conventional single-channel STEM detector and Pixelated STEM detector
		+	(a) Conventional single-channel STEM detector. The electron beam is converted to light using the scintillator and the light is guided to PMT. Then, the light creates electrons in the PMT. Finally they are measured as the output voltage signal. It should be noted that the signal is obtained as an integrated value from a CBED pattern area determined by the shape of the scintillator.
		+	(b) Pixelated STEM detector. The electron beam enters the direct electron detector (CCD or CMOS) and converted to electric signals. The detector records a CBED pattern as a 2D image unlike the conventional single-channel STEM detector.
		+	In the conventional STEM detector, the electron beam is converted to light with a scintillator and the intensity of the obtained light is measured as the output voltage of a photomultiplier tube (PMT) (Fig. 1(a)). All or part of the light signals from a CBED pattern formed on the detector plane are detected with a single-channel PMT, and then a 2D STEM image is acquired by displaying the output voltage as the function of the incident probe position. By selecting the acquisition region of the scattered electrons with the use of a circular or annular scintillator (detector), BF-, ABF-, or HAADF-STEM image can be obtained. It is noted that angle-resolved information is not available because the detector is single-channeled, thus the intensity of the CBED pattern is integrated.
		+	In the pixelated STEM detector, the CBED pattern is recorded as a 2D image (Fig. 1(b)). Furthermore, the electron probe is two-dimensionally scanned, and then the acquired final data becomes 4D data. It is emphasized that, the angle-resolved information about the diffraction intensity, which is lost in the conventional STEM detector, can be effectively used. For example, a variety of STEM images are created by flexibly changing the integration area of the CBED pattern.
		+	Fig. 2 shows five sort of STEM images created from the final 4D data of SrTiO3 [100] taken at an accelerating voltage of 200 kV. It is seen that different information can be obtained by changing the integration area of the CBED pattern.
		+	The other applications of the pixelated STEM detector include creation of an electric-magnetic field map utilizing positional shift of the CBED pattern, and reconstruction of a phase image of a specimen by utilizing ptychography image processing.
		+
		+
		+	Fig. 2 Various STEM images of SrTiO3 [100] taken at an accelerating voltage of 200 kV, by changing the integration area of the CBED pattern. Those STEM images are created from the final 4D data.
		+	The integration area of each CBED pattern is shown in insets (lower right of each STEM image), indicated by translucent red and blue colors. Acquisition conditions are as follows: Number of pixels of the STEM image: 256 x 256 pixels, Frame rate of the pixelated STEM detector: 4,000 fps (dwell time 250 μs), Data acquisition time: approx. 16 s.
		+	(a) STEM image created by integrating the whole area of the CBED pattern. Sr columns and Ti+O columns are observed as dark. O columns are not seen.
		+	(b) BF-STEM image. Sr columns are observed as dark, but O columns as bright.
		+	(c) ABF-STEM image. All of Sr-, O-, and Ti+O columns are observed as dark. Compared with the BF image, the ABF image enables intuitive interpretation of the atomic columns.
		+	(d) e-ABF (enhanced ABF) image. The image is created by subtracting the intensity of the area B from that of C. O columns appear more clearly compared with those of the ABF-STEM image.
		+	(e) LAADF-STEM image created by integrating the area except for the transmitted wave disk. Sr columns and Ti+O columns are observed as bright. O columns are not seen.
		+	(f) Conventional HAADF-STEM image acquired using a circular single-channel STEM detector.