JP2009277618A - Magnetic domain structural image acquisition method and scanning transmission electron microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a magnetic domain structural image without using a division detector. <P>SOLUTION: An electron diffraction figure D<SB>xy</SB>is photographed by a CCD camera at each observation point on a sample. One magnetic domain structural image data M<SB>xy</SB>against one electron diffraction figure D<SB>xy</SB>is calculated by performing the following (a)-(c) processing on each obtained electron diffraction figure D<SB>xy</SB>. (a) An image in a designated zone on the electron diffraction figure is divided into a plurality of partial images S<SB>1</SB>-S<SB>4</SB>. (b) One image strength signal is calculated by adding a strength signal of each pixel forming the partial image on every partial images S<SB>1</SB>-S<SB>4</SB>. (c) One magnetic domain structural image datum M<SB>xy</SB>is calculated on the basis of the image strength signal I<SB>1</SB>-I<SB>4</SB>calculated for every partial image S<SB>1</SB>-S<SB>4</SB>. Thus, the magnetic domain structural image is obtained on the basis of the magnetic domain structural image data M<SB>xy</SB>calculated at each electron diffraction figure D<SB>xy</SB>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for acquiring a magnetic domain structure image of a magnetic material sample using a scanning transmission electron microscope, and the scanning transmission electron microscope.

  As a method for observing the magnetic domain structure of a magnetic sample, there is a DPC (Differential Phase Contrast) method using a scanning transmission electron microscope (STEM). When observing the magnetic domain structure of a magnetic material sample by this DPC method, an electron diffraction pattern is irradiated with a finely divided electron beam sequentially on the observation point on the sample, and the electron diffraction pattern is formed by a divided detector composed of four or multi-divided detection elements. Detection is performed for each observation point, and the output signal of each detection element is processed to obtain image data, and the obtained image data for each observation point is supplied to the display means to obtain a magnetic domain structure image of the magnetic sample. Yes. Japanese Patent Publication No. 6-24109 (Patent Document 1) is a patent document describing such a DPC method.

Japanese Patent Publication No. 6-24109

  As described above, conventionally, in order to obtain a magnetic domain structure image of a magnetic sample, a special division detector such as a quadrant is separately required. Such a split detector is expensive and requires extra space to place it.

  The present invention has been made in view of these points, and an object thereof is to provide a magnetic domain structure image acquisition method and a scanning transmission electron microscope capable of obtaining a magnetic domain structure image without using a split detector. It is in.

The magnetic domain structure image acquisition method of the present invention that achieves the above object obtains a magnetic domain structure image of a magnetic sample by the following procedures (1) to (4).
(1) Irradiate the focused electron beam to observation points P _xy (x = 1, 2,..., M, y = 1, 2,..., N) on the sample in order,
(2) The electron diffraction pattern formed in the latter part of the sample by the electron beam irradiation is imaged for each observation point P _xy ,
(3) The following processes (a) to (c) are performed for each _captured electron diffraction pattern D _xy (x = 1, 2,..., M, y = 1, 2,..., N). _Obtain one magnetic domain structure image data M _xy (x = 1, 2,..., M, y = 1, 2,..., N) for the electron diffraction pattern D _xy ,
An image of a predetermined range on the (a) electron diffraction pattern, a plurality of partial images _{S 1,} S 2, ..., is divided into _{S t} (b) partial images _{S 1,} S 2, ..., for each _{S t,} the One image intensity signal is obtained based on the intensity signal of each pixel constituting the partial image. (C) The image intensity signals I ₁ , I ₂ ,... _{Obtained for} each of the partial images S ₁ , S ₂ ,. to obtain a magnetic domain structure image based on one of said seek domain structure image data M _xy (4) the domain structure image data M _xy obtained in electron diffraction pattern D for each _xy based on I _t.

  Therefore, according to the present invention, it is possible to obtain a magnetic domain structure image without using a split detector.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a magnetic domain structure image acquisition method according to the present invention, and shows a STEM for performing the image acquisition.

  In FIG. 1, reference numeral 1 denotes a microscope barrel, the inside of which is evacuated to a high vacuum by an evacuation device not shown. An electron gun 2, a focusing lens 3, a scanning coil 4, an objective lens 5, an intermediate lens 6, a projection lens 7, and a CCD camera (two-dimensional detector) 8 are arranged inside the lens barrel 1 in this order from the upper side. Has been.

The CCD camera 8 is a two-dimensional detector composed of a large number of detection elements C _ij (i = 1, 2,..., E, j = 1, 2,..., F) arranged two-dimensionally. It is already arranged in the conventional STEM. The present invention is characterized in that an electron diffraction pattern is imaged by the existing CCD camera 8 and does not use the division detector.

  Reference numeral 9 denotes a magnetic sample, and the sample 9 is disposed between the front magnetic field 5 a and the rear magnetic field 5 b of the objective lens 5.

  Reference numeral 10 denotes a central controller, and an output signal of the CCD camera 8 is configured to be supplied to the central controller 10. The central controller 10 includes an image memory 11, a magnetic domain structure image data acquisition unit 12, and an image memory 13 therein. Further, the central control device 10 is electrically connected to the display means 14 and the scanning coil driving unit 15. In the figure, O indicates the optical axis.

  The apparatus configuration of the STEM in FIG. 1 has been described above. The operation will be described below.

When observing the magnetic domain structure of the magnetic sample 9, the central controller 10 sends a deflection signal for scanning the surface of the electron beam in the xy direction on the sample to the scanning coil driving unit 15. Upon receiving this deflection signal, the scanning coil driving unit 15 supplies a deflection current to the scanning coil 4. As a result, the electron beam e emitted from the electron gun 2 and finely focused on the sample 9 by the front magnetic field 5a of the focusing lens 3 and the objective lens 5 is deflected by the scanning coil 4, and the sample 9 is directed in the xy direction. Surface scan. That is, as shown in FIG. 2, the electron beam e sequentially irradiates observation points P _xy (x = 1, 2,..., M, y = 1, 2,..., N) on the sample 9.

Thus, when the electron beam e incident on each observation point on the magnetic material sample 9 passes through the sample 9, it receives a Lorentz force depending on the magnetization direction of the sample and is deflected in the xy direction. Therefore, each electron diffraction pattern D _xy (x = 1, 2,..., M, y = 1, 2,..., N) imaged on the rear focal plane H of the objective lens 5 by the back magnetic field 5b of the objective lens 5. ) Moves in the xy direction according to the magnetization direction of the sample at each observation point P _xy . Accordingly, each electron diffraction pattern D _xy enlarged and projected on the CCD camera 8 by the intermediate lens 6 and the projection lens 7 moves in the xy direction according to the magnetization direction of the sample at each observation point P _xy .

The CCD camera 8 images the electron diffraction pattern moving in this way for each observation point P _xy . The picked up m × n electron diffraction patterns D _xy are stored in a predetermined location in the image memory 11 corresponding to the observation point P _xy .

When the electron diffraction pattern D _xy is stored in the image memory 11 in this way, the magnetic domain structure image data acquisition unit 12 performs the magnetic domain structure image data M _xy (x = 1, 2,..., M, _{y) for} each electron diffraction pattern D _xy. = 1, 2, ..., n). That is, the magnetic domain structure image data acquisition unit 12 obtains one magnetic domain structure image data M _xy for one electron diffraction pattern D _xy . The method for obtaining it will be described in detail in the following steps (a) to (c).
(A) splitting of the electron diffraction pattern First, the magnetic domain structure image data acquisition means 12 reads the image data of the electron diffraction pattern D ₁₁ from the image memory 11. Then, the magnetic domain structure image data acquisition means 12, as shown in FIG. 3 (a), extracts the (image data i.e. image K) a part of the image K in a predetermined range from the electron diffraction pattern D _11. This image K is the image of the central portion of the electron diffraction pattern D _11, the center C of the image K coincides with the center C 'of the electron diffraction pattern D _11. In the image K is included transmission spot W is the electron diffraction pattern D _11.

Next, as shown in FIG. 3B, the magnetic domain structure image data acquisition unit 12 divides the image K into four equal parts by two orthogonal straight lines, and the partial images S _{1 to} S ₄ (that is, the partial image S _1). It extracts image data) to S _4. The partial images S _{1 to} S ₄ correspond to electron diffraction patterns detected by the detection elements of the quadrant detector. That is, in the present invention, the extraction function of the partial images S _{1 to} S _{4 in} the magnetic domain structure image data acquisition unit 12 is used instead of the quadrant detector.
(B) Obtain one image intensity signal for each of the partial images S _{1 to} S ₄ Next, the magnetic domain structure image data acquisition unit 12 performs the following for each of the partial images S _{1 to} S ₄ extracted from the electron diffraction pattern D ₁₁ . One image intensity signal is obtained based on the signal intensity of each pixel constituting the partial image. That is, the magnetic domain structure image data acquiring unit 12, based on image data read from the image memory 11, each pixel a constituting part image S _1, b, c, ... intensity signal (see FIG. 3 (b)) the addition (integration) were determined image intensity signals I ₁ and. Similarly, the image intensity signal _{I 2} to the portion image _{S 2} is the image intensity signal _{I 3} for the partial image _{S 3} is the image intensity signal _{I 4} is calculated respectively for the partial image _{S 4.}
(C) Obtaining one magnetic domain structure image data M ₁₁ based on I _{1 to} I ₄ Next, the magnetic domain structure image data acquisition means 12 calculates the partial images S _{1 to} S ₄ of the electron diffraction pattern D _11. Based on the image intensity signals I _{1 to} I ₄ , magnetic domain structure image data M ₁₁ is obtained for the electron diffraction pattern D ₁₁ . That is, obtains the domain structure image data _{M 11} with respect to the observation point _{P 11} on the sample. At that time, the magnetic domain structure image data acquisition unit 12 obtains the domain structure image data M ₁₁ performs the following calculation.

M ₁₁ = ((I ₁ + I ₂ ) − (I ₃ + I ₄ )) / (I ₁ + I ₂ + I ₃ + I ₄ )
This calculation method corresponds to the conventional method of calculating the magnetic domain structure image data by calculating the output signal of each detection element of the quadrant detector. Then, the magnetic domain structure image data M ₁₁ obtained in this way is stored in a predetermined location of the image memory 13 corresponding to the observation point P _11.

The method for obtaining the magnetic domain structure image data M ₁₁ related to the electron diffraction pattern D ₁₁ (observation point P ₁₁ ) has been described above, but the remaining electron diffraction patterns D _{21 to} D _mn (observation points P _{21 to} P _mn ) are described. The magnetic domain structure image data acquisition unit 12 performs the same process, and the magnetic domain structure image data M _{21 to} M _mn are obtained. And their domain structure image data _M 21 _{~M mn} is stored in a predetermined location of the image memory 13 corresponding to the observation point _P 21 _{to P mn.}

FIG. 4 shows, for example, the extraction process of the partial images S _{1 to} S ₄ with respect to the electron diffraction pattern D ₁₅ , corresponding to FIG. 3B. The size and position of the partial image _S 1 to S ₄ in FIG. 4 is the same as the state of FIG. 3 (b). However, the position of the transmission spot W in FIG. 4 is different from the position of FIG. This is because the direction of magnetization of the sample is different between the two observation points P ₁₅ and P ₁₁ .

When the magnetic domain structure image data M _xy is obtained for the electron diffraction pattern D _xy (observation point P _xy ) as in the above (a) to (c), the central controller 10 The magnetic domain structure image data M ₁₁ , M ₂₁ ,..., M _mn are read from the image memory 13 and sent to the display means 14. As a result, a magnetic domain structure image related to the observation points P ₁₁ , P ₂₁ ,..., P _{mn as} shown in FIG. On this image, the black and white contrast shows the difference between the magnetic domains, and the same magnetic domain is displayed with the same luminance.

  The example of the present invention has been described above with reference to FIGS. According to the present invention, a magnetic domain structure image of a sample can be obtained without using a special split detector. According to the present invention, after the acquisition of the image data of the electron diffraction pattern, the electron diffraction pattern can be analyzed at any time.

  The present invention is not limited to the above example. In the above example, the image K extracted from the electron diffraction pattern is divided into four equal parts, but the image K may be divided into two equal parts by one straight line, or may be equally divided into other numbers. Then, the above processing is performed on each partial image extracted by the division.

  In the above example, the image K extracted from the electron diffraction pattern is divided into four equal parts, but the electron diffraction pattern itself read from the image memory 11 is divided into four equal parts without extracting the image K from the electron diffraction pattern. A partial image may be obtained.

In the above example, the arithmetic expression M ₁₁ = ((I ₁ + I ₂ ) − (I ₃ + I ₄ )) / (I ₁ + I ₂ + I ₃ + I ₄ ) is used to obtain the magnetic domain structure image data. Instead of this, the following arithmetic expression may be used.

M ₁₁ = (− (I ₁ + I ₂ ) + (I ₃ + I ₄ )) / (I ₁ + I ₂ + I ₃ + I ₄ )
The arithmetic expression may be changed as needed according to the number of divisions of the image K and the purpose.

1 shows an example of a scanning transmission electron microscope of the present invention. It is shown in order to demonstrate operation | movement of the apparatus of FIG. It is shown in order to demonstrate operation | movement of the apparatus of FIG. It is shown in order to demonstrate operation | movement of the apparatus of FIG. A magnetic domain structure image is shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lens barrel, 2 ... Electron gun, 3 ... Focusing lens, 4 ... Scanning coil, 5 ... Objective lens, 5a ... Front magnetic field, 5b ... Back magnetic field, 6 ... Intermediate lens, 7 ... Projection lens, 8 ... CCD camera, DESCRIPTION OF SYMBOLS 9 ... Magnetic material sample, 10 ... Central control apparatus, 11 ... Image memory, 12 ... Magnetic domain structure image data acquisition means, 13 ... Image memory, 14 ... Display means

Claims (6)

Magnetic domain structure image acquisition method for obtaining a magnetic domain structure image of a magnetic material sample by the following procedures (1) to (4) (1) A focused electron beam is observed on a sample at an observation point P _xy (x = 1, 2,... m, y = 1, 2,..., n) in order,
(2) The electron diffraction pattern formed in the latter part of the sample by the electron beam irradiation is imaged for each observation point P _xy ,
(3) The following processes (a) to (c) are performed for each _captured electron diffraction pattern D _xy (x = 1, 2,..., M, y = 1, 2,..., N). _Obtain one magnetic domain structure image data M _xy (x = 1, 2,..., M, y = 1, 2,..., N) for the electron diffraction pattern D _xy ,
An image of a predetermined range on the (a) electron diffraction pattern, a plurality of partial images _{S 1,} S 2, ..., is divided into _{S t} (b) partial images _{S 1,} S 2, ..., for each _{S t,} the One image intensity signal is obtained based on the intensity signal of each pixel constituting the partial image. (C) The image intensity signals I ₁ , I ₂ ,... _{Obtained for} each of the partial images S ₁ , S ₂ ,. to obtain a magnetic domain structure image based on one of said seek domain structure image data M _xy (4) the domain structure image data M _xy obtained in electron diffraction pattern D for each _xy based on I _t. By equally dividing the image of a predetermined range on the electron diffraction pattern, a plurality of partial images S _1, S 2, _..., the magnetic domain structure image acquisition method according to claim 1, wherein the obtaining the S _t.   2. The magnetic domain structure image acquisition method according to claim 1, wherein the image intensity signal is obtained by adding the intensity signals of the pixels constituting the partial image. In a scanning transmission electron microscope having a function of sequentially irradiating a focused electron beam to observation points P _xy (x = 1, 2,..., M, y = 1, 2,..., N) on a sample,
A two-dimensional detector that images the electron diffraction pattern formed in the latter stage of the sample by the electron beam irradiation for each observation point P _xy ;
A memory for storing electron diffraction patterns D _xy (x = 1, 2,..., M, y = 1, 2,..., N) imaged by the two-dimensional detector;
The following processes (a) to (c) are performed for each electron diffraction pattern D _xy stored in the memory, and one magnetic domain structure image data M _xy (x = 1) for one electron diffraction pattern D _xy . , 2,..., M, y = 1, 2,..., N), and magnetic domain structure image data acquisition means;
An image of a predetermined range on the (a) electron diffraction pattern, a plurality of partial images _{S 1,} S 2, ..., is divided into _{S t} (b) partial images _{S 1,} S 2, ..., for each _{S t,} the One image intensity signal is obtained based on the intensity signal of each pixel constituting the partial image. (C) The image intensity signals I ₁ , I ₂ ,... _{Obtained for} each of the partial images S ₁ , S ₂ ,. , further comprising a display means for displaying the magnetic domain structure image based on the domain structure image data M _xy found for the electron diffraction pattern D _xy for obtaining a single magnetic domain structure image data M _xy based on I _t A scanning transmission electron microscope. The domain structure image data acquisition means, by equally dividing the image of the predetermined range on the electron diffraction pattern, a plurality of partial images S _1, S 2, _..., according to claim 4, wherein the obtaining the S _t Scanning transmission electron microscope.   5. The scanning transmission electron microscope according to claim 4, wherein the magnetic domain structure image data acquisition means obtains the image intensity signal by adding the intensity signals of the pixels constituting the partial image.

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