JP2010271144A - Background correction method in epma analysis - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a background correction method in EPMA (Electron Probe Micro-Analysis) analysis causing no sample damage, measuring by once electron beam scanning. <P>SOLUTION: This method comprises the first step wherein a portion in which an object element does not exist is put into a mapping domain; the second step wherein one of two dispersive crystals of the same kind is set at a characteristic X-ray wavelength λ<SB>A</SB>of the object element, and the other is set at a background wavelength λ<SB>B</SB>in the vicinity, and X-ray count data I<SB>A</SB>, I<SB>B</SB>are acquired by performing mapping measurement; and the third step of determining a correction coefficient α from the equation: α=I<SB>A</SB>/I<SB>B</SB>from the X-ray count data I<SB>A</SB>, I<SB>B</SB>. The background correction coefficient α of the EPMA analysis is determined via the first to third steps, and a value acquired by using an expression: I<SB>A</SB>-I<SB>B</SB>×α is used as an X-ray signal of the object element, relative to the X-ray count data I<SB>A</SB>pertaining to the characteristic X-ray wavelength λ<SB>A</SB>of the object element in the whole mapping domain, and further, mapping data of a concentration of the object element are acquired by using a calibration curve measured separately, from data of the X-ray signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a background correction method in EPMA (Electron Probe Micro-Analysis) analysis for examining a two-dimensional element distribution on a solid surface.

  EPMA analysis is performed by squeezing the electron probe emitted from the filament and irradiating the sample, diffracting the X-rays excited by the incident electrons with a spectroscopic crystal, and guiding the X-ray intensity to a counter for measurement. This is a method for qualitative and quantitative determination of elements contained in

  In the EPMA analysis, when the constituent elements are different at each measurement point, the background intensity (BG intensity) changes at each measurement point, so it is necessary to perform background correction (BG correction).

  Regarding BG correction, Patent Document 1 irradiates a sample with a finely focused electron beam, detects X-rays excited by incident electrons, and performs spectroscopic analysis to move the spectroscope by an appropriate distance from the peak position. The background is measured on both sides of the peak and the background intensity (BG intensity) at the peak position is obtained by linear approximation, and the relationship between the average atomic number and the background intensity using a plurality of standard samples is measured at least two times. A method has been proposed in which only the peak intensity is measured in the measurement of an unknown sample, and the background is estimated by calculating the average atomic number from the measured value in the correction calculation.

JP-A-63-313043

  The conventional method described in Patent Document 1 has a problem that the BG intensity cannot be accurately estimated by linear approximation when the background is curved, or when a disturbance line exists at the background position. In addition to the problem of measuring other X-rays that are not BG, the method proposed in Patent Document 1 also requires a plurality of standard samples, and in addition, when there are many constituent elements, many measurements are performed. Since data is required, there is a problem that the measurement time becomes long, the sample is damaged due to an increase in the number of electron beam scans, and the reliability of the data is lowered. In particular, when the amount of the target element is very small, it is necessary to integrate a small amount of characteristic X-ray signals to improve the S / N ratio, so that sample damage has a more serious effect on the reliability of measurement.

  An example of measuring the Pt distribution in the monolith catalyst will be described below. For measurement BG correction, the concentration distribution of elements such as Al, Ce, Zr, etc., which are carrier components, is measured, and the BG intensity distribution for each point is obtained by approximate calculation from the concentration of the constituent elements of the carrier. . However, when the carrier contains many elements such as La, Ba, and Nd, it is necessary to measure the concentration distribution of these elements in order to accurately calculate the BG intensity distribution.

  Since the number of elements that can be measured by one electron beam scan is limited, when there are many constituent elements as described above, the scan is divided into a plurality of times. In the case of a catalyst sample, multiple scans cause cracking or peeling of the coating layer and misalignment of the support secondary particles. Therefore, calculating the BG intensity from the element distribution measured by multiple scans causes an error. There is a problem that the accuracy of measurement is lowered.

  An object of the present invention is to solve the above-described problems of the conventional example.

In order to solve the above-mentioned problem, the method for obtaining the background correction coefficient α of the EPMA analysis according to the present invention includes a first step in which a site where the target element does not exist in the mapping region is included in the EPMA analysis Second step of obtaining X-ray count data I _A and I _B by setting one of the spectral crystals to the characteristic X-ray wavelength λ _A of the target element and the other to the nearby background wavelength λ _B and performing mapping measurement. If, from the X-ray count data I _a and I _B, alpha = and a third step of obtaining the I formula from the correction coefficient _a / I _B alpha, through the third step from the first 1, EPMA analysis The background correction coefficient α is obtained.

In addition, the background correction method for EPMA analysis according to the present invention uses the background correction coefficient α obtained by the above method, and X-ray count data for the characteristic X-ray wavelength λ _A of the target element in all mapping regions. For I _A , the value obtained using the formula of I _A -I _B × α is used as the X-ray signal of the target element.

  In addition, the method for obtaining the concentration data of the target element in the EPMA analysis according to the present invention is the mapping data of the element concentration using the calibration curve measured separately from the X-ray signal data of the target element obtained by the above correction method. Is calculated.

  According to the present invention, since the X-ray signal and BG signal of the target element can be measured simultaneously by one electron beam scan, the measurement time can be shortened and the sample can be prevented from being damaged. This reduces the reliability of the measurement data based on the damage of the sensor and can provide accurate data in a short time.

2 shows a characteristic X-ray spectrum (eg, RhLα) according to the present invention. It is a measurement result before correction | amendment of K-11580 shown in Table 1, and shows each mapping area | region at the time of using the spectral crystal of (a) Pt-L (alpha), (b) Pt-BG, (c) SiK (alpha). The Pt signal mapping image after BG correction and a line analysis result are shown. The Pt signal mapping image after BG correction (less than 20 counts are not displayed) is shown. The Pt concentration distribution calculated | required from Pt signal mapping after BG correction | amendment is shown. The lower layer Pt average density | concentration measurement result in the sample from which Pt carrying amount differs is shown.

When the target element is, for example, rhodium (Rh) and a part where the target element does not exist in the mapping region is put and EPMA analysis is applied, the characteristic X-ray spectrum shown in FIG. 1 is obtained. Here, the X-ray count of the characteristic X-ray wavelength (λ _A ) of the target element that appears as a peak is I _A, and the X-ray count of the nearby BG wavelength (λ _B ) is I _B. From this I _A and I _B, we obtain the background correction coefficients and used to correct the background EPMA analysis, and is to obtain a density data of interest element. Hereinafter, this will be described with reference to specific examples.

(Example)
The examples relate to the measurement of trace Pt distribution of monolith catalysts.
[EPMA measurement (setting of sample conditions and measurement conditions)]
As a sample, a two-layer coat model catalyst carrying rhodium (Rh) in the upper layer and platinum (Pt) in the lower layer was cut out, embedded in a resin, polished, and polished, and EPMA measurement was performed. In order to calculate the BG correction coefficient α in the base material without Pt, the mapping elements were Pt and Si. The specifications of the two-layer coat model catalyst are as shown in Table 1.

The measurement conditions are as follows.
・ Setting of detector (manufactured by Shimadzu Corporation) LIF: PtLα, LIF: BG wavelength of PtLα, ADP: SiKα
・ Other analysis conditions Acceleration voltage: 20kV
Current: 500nA
Sampling time: 50msec / point

[Analysis of measurement data]
2A to 2C show the measurement results before correction of K-11580 shown in Table 1. FIG. From the upper left of each mapping region shown in FIG. 2, a base material 1, a Pt-supported coat layer (lower layer) 2, an Rh-supported coat layer (upper layer) 3, and an embedding resin 4 are shown.

Using a spreadsheet software or the like, the Pt BG correction coefficient α was obtained by the following procedure.
(1) From the Pt-Lα count (I _Pt-Lα ) and (I _Pt-BG ) at each point, α is provisionally set to 1, and the count number (I _Pt ) of only the Pt signal is obtained by the following equation 1. It was.
I _Pt = I _Pt−Lα −I _Pt−BG × α (Formula 1)

(2) The total value (or average value) of the values of Formula 1 was calculated for all points where the Si concentration was a certain value (here, 5 wt%).

(3) An α value is calculated such that the total value (or average value) obtained in step (2) is zero. In the case of Excel, this calculation is easily obtained by using a solver.

(4) For all mapping regions, the count number (I _Pt ) of only the Pt signal was obtained by substituting α obtained in step (3) into Equation 1.

  From the above measurement result of K-11580, the α value obtained by the above procedure (3) was 0.899.

FIG. 3 shows a mapping image and a line analysis result of the Pt signal obtained in the procedure (4).
According to the line profile of FIG. 3, Pt is distributed mainly in the lower layer, and shows a distribution in a state where the base material, the upper layer, and the resin are centered on 0 count.

  FIG. 4 shows a mapping image in the case of setting not to display less than 20 counts during mapping display.

[Concentration conversion]
From the above-described Pt signal mapping corrected for BG, element concentration mapping data is calculated using a separately measured X-ray count and element concentration calibration curve or the like.
FIG. 5 shows the results for K-11580. When calculating the average Pt concentration for the upper layer and the lower layer, the upper layer was 0.02 wt% and the lower layer was 0.37 wt%.

  FIG. 6 shows the average Pt concentration of the lower layer obtained by measuring catalyst samples having different Pt loadings using this method. Since the carrying amount and the average concentration show a proportional relationship, it can be understood that the BG correction is correctly performed in the sample with a small amount of Pt.

1: base material,
2: Pt-supported coat layer (lower layer),
3: Rh-supported coat layer (upper layer),
4: Embedded resin

Claims (3)

In EPMA analysis,
A first step of adding a region where the target element does not exist in the mapping region;
Of the two same types of spectral crystals, one is set to the characteristic X-ray wavelength λ _A of the target element and the other is set to the nearby background wavelength λ _B , and mapping measurement is performed to obtain X-ray count data I _A and I _B. A second step;
From the X-ray count data I _A and I _B, and a third step of obtaining a correction coefficient alpha from the equation α = I _A / I _B,
A method of obtaining a background correction coefficient α of EPMA analysis through the first to third steps. Using the background correction coefficient α obtained by the method described in claim 1,
With respect to the X-ray count data I _A for the characteristic X-ray wavelength λ _A of the target element in all mapping regions, the value obtained using the formula I _A −I _B × α is used as the X-ray signal of the target element. EPMA analysis background correction method. From the X-ray signal data of the target element obtained by the correction method according to claim 2,
A method of obtaining concentration data of a target element in EPMA analysis in which element concentration mapping data is calculated using a separately measured calibration curve.

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