CN116930234A - Digital positron annihilation Doppler broadening spectrometer for micron-sized film test and test method thereof - Google Patents
Digital positron annihilation Doppler broadening spectrometer for micron-sized film test and test method thereof Download PDFInfo
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- 229910052732 germanium Inorganic materials 0.000 claims abstract description 22
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 claims abstract description 22
- 239000010409 thin film Substances 0.000 claims abstract description 15
- 230000007547 defect Effects 0.000 claims abstract description 8
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- 239000004033 plastic Substances 0.000 claims description 46
- 238000012545 processing Methods 0.000 claims description 20
- 238000000034 method Methods 0.000 claims description 17
- 238000012216 screening Methods 0.000 claims description 9
- 230000002285 radioactive effect Effects 0.000 claims description 8
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- 239000002772 conduction electron Substances 0.000 claims description 4
- 230000008569 process Effects 0.000 claims description 3
- 238000007493 shaping process Methods 0.000 claims description 3
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- 238000005259 measurement Methods 0.000 abstract description 7
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- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 229920001721 polyimide Polymers 0.000 description 1
- 229920006254 polymer film Polymers 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
- G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/20—Measuring radiation intensity with scintillation detectors
- G01T1/203—Measuring radiation intensity with scintillation detectors the detector being made of plastics
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/20—Measuring radiation intensity with scintillation detectors
- G01T1/208—Circuits specially adapted for scintillation detectors, e.g. for the photo-multiplier section
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/24—Measuring radiation intensity with semiconductor detectors
- G01T1/248—Silicon photomultipliers [SiPM], e.g. an avalanche photodiode [APD] array on a common Si substrate
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Abstract
The invention relates to the technical field of Doppler spectrometers for positron annihilation Doppler broadening measurement, in particular to a digital positron annihilation Doppler broadening spectrometer for micrometer-scale film testing and a testing method thereof. The high-purity germanium detector is used for receiving annihilation photons generated by annihilation of positive and negative electrons and depositing energy; the amplifier amplifies and Gaussian-forms the negative index nuclear pulse signal to obtain a Gaussian pulse signal; one path of the high-speed digital oscilloscope collects anti-coincidence pulse signals, and the other path of the high-speed digital oscilloscope collects Gaussian pulse signals of the amplifier; and the computer obtains a dual-channel signal of the high-speed digital oscilloscope to perform anti-coincidence logic judgment, obtains Doppler broadening spectrum, calculates S-W parameters of the Doppler broadening spectrum and obtains defect information in the film sample. The invention adopts the anti-coincidence module to judge the annihilation photon position, thereby realizing the digital anti-coincidence Doppler spectrometer for the micrometer thin film test.
Description
Technical Field
The invention relates to the technical field of Doppler spectrometers for positron annihilation Doppler broadening measurement, in particular to anti-coincidence logic judgment and positron digital spectrometer technology, and specifically relates to a digital positron annihilation Doppler broadening spectrometer for micrometer-scale film testing and a testing method thereof.
Background
Positron annihilation doppler broadening measurement is an experimental means that uses more positrons to characterize. When positron annihilates inside a material, the total momentum of electron-positron annihilation pairs is not zero according to the principle of conservation of momentum because the momentum of electrons on the shell layers of atoms is not zero. Then, in laboratory coordinates, the Doppler spread occurs in the energy of the two 511keV annihilation photons, which becomes E=m 0 c 2 + - ΔE, doppler shift ΔE=cP obtained from frequency shift L /2，P L Is a momentum component of the annihilation gamma photon emission direction.
The Doppler broadening measurement reflects the change of the electron momentum, and then information of the internal defect concentration, defect type and change of chemical environment around the defect of the material is obtained. Doppler broadening is mostly measured by a high-energy-resolution high-purity germanium detector (1), resulting in annihilation gamma photon energy spectra with energy of 511 keV. The change of Doppler broadening is analyzed by a common S-W parameter method to obtain information of detected defects. Where S is defined as the ratio of the peak center count to the total count, reflecting low momentum electron information such as valence and conduction electrons. W is defined as the ratio of the counts on both sides of the peak to the total count, reflecting high momentum electron information, such as core electrons.
The output signal of the gamma detector of the analog spectrometer is amplified and formed and then input into a multi-channel analyzer, and the digital spectrometer directly samples the pulse by using high-speed digital acquisition equipment. In the test, byClamping two identical samples to be tested and packaging with polyimide film 22 Na radiation source, forming a sandwich-type radiation source structure. Due to the slave 22 Since positrons emitted from Na have a certain energy distribution (0 to 545 keV), the annihilation positions of positrons in a sample also have a certain depth distribution. In order to ensure that most of the positrons annihilate in the sample, there is a high requirement for the thickness of the sample (two identical samples, thickness>1mm)。
However, for testing specific samples, such as semiconductor films, polymer films and the like, the thickness is in the order of tens of micrometers, and it is difficult to perform positron characterization tests. On one hand, most positrons pass through the sample due to the fact that the sample is thinner, on the other hand, multiple layers of samples are required to be stacked to a thickness of 1mm during testing, however, the problems that the sample to be tested is damaged due to insufficient sample quantity, the backscattering probability is increased, thermalized positrons are diffused to the surface and the like can occur.
The use of a slow positron beam (comprising a beam current and an accelerator system) has traditionally been used to measure the doppler spread spectrum of samples on the order of microns in thickness, but this is more complex, more expensive and less maintenance than a conventional positron annihilation doppler spread spectrometer (no beam current and accelerator system).
Disclosure of Invention
The invention aims to provide a digital positron annihilation Doppler broadening spectrometer for micron-scale film testing and a testing method thereof, which realize annihilation radiation Doppler broadening measurement of a micron-scale film through anti-coincidence logic; the requirement on the quantity of the test sample is reduced, and the application range of positron characterization test is improved; the digital spectrometer has a simple structure and realizes data processing on line.
The specific technical scheme of the invention is as follows: a digital positron annihilation Doppler broadening spectrometer for micron-scale film testing,
comprises a high-purity germanium detector 1, an amplifier 2, an anti-coincidence module and a data acquisition and processing module,
the high-purity germanium detector 1 is used for receiving annihilation photons generated by annihilation of positive and negative electrons and depositing energy, and outputting negative index nuclear signal pulses, wherein the pulse height is related to the deposition energy;
the amplifier 2 amplifies and Gaussian-forms the negative index nuclear pulse signal to obtain a Gaussian pulse signal;
the anti-coincidence module comprises a first plastic scintillator 31, a second plastic scintillator 32, a film sample 33 and a photomultiplier 34, wherein the photomultiplier 34 is used for outputting anti-coincidence pulse signals; the first plastic scintillator 31 and the second plastic scintillator 32 clamp the micron-sized film sample 33 from two sides, a positron emission source is arranged in the middle of the film sample 33, the first plastic scintillator 31 is coupled with a photocathode window of the photomultiplier 34, and a reflecting layer is plated on the side surface of the second plastic scintillator 32 far away from the film sample 33;
the data acquisition processing module comprises a high-speed digital oscilloscope 41 and a computer 42, wherein one channel of the high-speed digital oscilloscope 41 acquires anti-coincidence pulse signals, and the other channel acquires Gaussian pulse signals of the amplifier 2; the computer 42 obtains the dual-channel signal of the high-speed digital oscilloscope 41 to perform anti-coincidence logic judgment, and processes the reserved data to obtain a corresponding Doppler broadening spectrum and calculate the S-W parameter of the Doppler broadening spectrum to obtain the defect information in the film sample 33.
The invention also comprises a testing method of the digital positron annihilation Doppler broadening spectrometer for testing the micron-sized film,
the method specifically comprises the following steps:
step (1): when positron emitted from a radioactive source passes through the film sample 33 and enters the first plastic scintillator 31 or the second plastic scintillator 32 to be annihilated, the positron deposits energy in the first plastic scintillator 31 or the second plastic scintillator 32 and emits light, and photons enter a photocathode of the photomultiplier 34 after being transmitted, and the photomultiplier 34 outputs an anti-coincidence pulse signal for anti-coincidence logic judgment;
step (2): when a positron emitted from a radiation source annihilates in the thin film sample 33 or the first plastic scintillator 31 or the second plastic scintillator 32, annihilation photons of energy 511keV are generated; the high-purity germanium detector 1 detects annihilation photons, and outputs negative index nuclear signal pulses, and Gaussian pulse signals with the pulse width of 10 mu s are output after the negative index nuclear signal pulses are formed and amplified by the main amplifier 2;
step (3): in order for the gaussian pulse signal to be fully acquired, the time window to be set should be greater than the gaussian pulse signal width, and since the photomultiplier 34 has a faster time response and has several anti-coincidence pulse signals within the time window, the anti-coincidence time window and the anti-coincidence threshold should be set for screening the anti-coincidence pulse signals obtained by positron instances related to annihilation photons detected by the high purity germanium detector 1;
step (4): one channel of the high-speed digital oscilloscope 41 collects anti-coincidence pulse signals, and the other channel collects Gaussian pulse signals of the amplifier 2; the anti-coincidence pulse signal and the Gaussian pulse signal are converted into digital pulse data and transmitted to a computer 42 terminal through USB3.0 for online processing;
step (5): processing of gaussian pulse signals by computer 42 terminals: the Gaussian pulse signal is subjected to digital pulse screening through a Gaussian shape screening device, and the Gaussian pulse signal is subjected to baseline removal processing to obtain the pulse amplitude of the Gaussian pulse signal; processing of the anti-coincidence pulse signal by the computer 42 terminal: an anti-coincidence pulse signal exceeding an anti-coincidence threshold value appears in the anti-coincidence time window, and the signal is false; if the anti-coincidence pulse signal exceeding the anti-coincidence threshold value does not appear, the signal is true, and a Boolean signal is output; if true, annihilating positrons emitted by the representative radioactive source in the film sample 33, and retaining corresponding Gaussian pulse signal amplitude information; if false, the positrons emitted by the representative radioactive source are annihilated in the first plastic scintillator 31 or the second plastic scintillator 32, and the corresponding Gaussian pulse signal amplitude information is not reserved;
step (6): the preserved Gaussian pulse signal amplitude information is a count, the annihilation photon energy spectrum is drawn through the Gaussian pulse signal amplitude information of enough counts, S and W parameters are calculated, S is defined as the ratio of the peak center count to the total count, and low momentum electron information such as valence electrons and conduction electrons is reflected. W is defined as the ratio of the counts on both sides of the peak to the total counts, reflecting high momentum electron information, such as core electrons;
further, when the setting method of the anti-coincidence time window in the step (3) is constant ratio: because the shaping time of the main amplifier 2 and the time response of the high-purity germanium detector 1 are slower than that of the photomultiplier 34, the Gaussian pulse signal lags behind the anti-coincidence pulse signal, the lag time is t, the time t is pushed forward from the moment when the signal amplitude of the high-purity germanium detector 1 rises by 10%, the midpoint of the anti-coincidence time window is obtained, and the anti-coincidence time window is set to be t-1 mu s-t+1 mu s;
further, in the step (3), setting of the anti-coincidence threshold value: and selecting a proper time window, ensuring that each window only contains one anti-coincidence pulse signal or no pulse signal, counting the pulse amplitude spectrum of the photomultiplier 34, obtaining the pulse baseline jitter amplitude of the photomultiplier 34 to be 3-4 mV, wherein the selected anti-coincidence threshold value is higher than the pulse baseline jitter amplitude, and the smaller the anti-coincidence threshold value is, the more accurate the result is.
The beneficial technical effects of the invention are as follows:
(1) According to the digital positron annihilation Doppler spread spectrum device for the micrometer thin film test and the testing method thereof, the digital anti-coincidence Doppler spread spectrum device for the micrometer thin film test is designed and built for the first time, the positron annihilation position is determined through the anti-coincidence pulse signal based on anti-coincidence logic judgment, namely, the thin film sample or the first plastic scintillator or the second plastic scintillator is tested under the condition that experimental precision is not affected, the annihilation photon position is judged by adopting the anti-coincidence module, the digital anti-coincidence Doppler spread spectrum device for the micrometer thin film test is realized, the performance of the Doppler spread spectrum device is excellent, the rigid requirements on the number and thickness of samples during positron annihilation Doppler spread measurement are relieved, and the digital positron annihilation Doppler spread spectrum device has important significance for application and popularization of positron annihilation technology.
(2) The invention relates to a digital positron annihilation Doppler spread spectrum instrument for a micrometer-scale film test and a test method thereof, wherein one channel of a high-speed digital oscilloscope collects anti-coincidence pulse signals, and the other channel collects Gaussian pulse signals of an amplifier; the high-speed digital oscilloscope digitizes the two-channel analog signal,
the computer obtains data and carries out inverse coincidence logic judgment and data processing, so that the digital nuclear spectrometer is realized, the digital nuclear spectrometer has the performance advantages of high sampling rate and high vertical resolution, the signal integrity design is fully considered, proper sampling points are selected, the realization of system indexes is ensured, the high energy resolution is realized, the digital nuclear spectrometer has a simple structure, is easy to maintain and upgrade and has the function expansion, the digital waveform processing brings convenience to data optimization and correction, and meanwhile, the error example rate and the system error caused by physical and electronic reasons are reduced.
Drawings
FIG. 1 is a schematic diagram of a digital positron annihilation Doppler broadening spectrometer for micrometer thin film testing according to the present invention.
Fig. 2 is a schematic diagram of a digital positron annihilation doppler broadening spectrometer for micrometer scale thin film testing in accordance with the present invention.
Fig. 3 is a graph of gaussian pulse signals output from a high purity germanium detector of the present invention via a main amplifier.
FIG. 4 is a graph of an anti-coincidence pulse signal output from a photomultiplier tube according to the present invention.
FIG. 5 is a pulse amplitude spectrum of a photomultiplier tube of the present invention.
FIG. 6 is a diagram of a Doppler spread spectrum and S-W parameter calculation region of an anti-coincidence discriminator of the present invention.
FIG. 7 is a graph of S-W parameters for testing micro-scale metal films according to the present invention.
Wherein: a high-purity germanium detector 1, an amplifier 2, a first plastic scintillator 31, a second plastic scintillator 32, a thin film sample 33, a photomultiplier 34, a high-speed digital oscilloscope 41, and a computer 42.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the detailed description is presented by way of example only and is not intended to limit the invention.
Example 1
Referring to fig. 1, a digital positron annihilation doppler broadening spectrometer for micrometer-scale thin film testing,
comprises a high-purity germanium detector 1, an amplifier 2, an anti-coincidence module and a data acquisition and processing module,
the high-purity germanium detector 1 is used for receiving annihilation gamma photons generated by annihilation of positive and negative electrons and depositing energy, and outputting negative index nuclear signal pulses, wherein the pulse height is related to the deposition energy;
the amplifier 2 amplifies and Gaussian-forms the negative index nuclear signal pulse to obtain Gaussian pulse signals;
the anti-coincidence module comprises a first plastic scintillator 31, a second plastic scintillator 32, a film sample 33 and a photomultiplier 34, wherein the photomultiplier 34 is used for outputting anti-coincidence pulse signals; the first plastic scintillator 31 and the second plastic scintillator 32 clamp the micron-sized film sample 33 from two sides, a positron emission source is arranged in the middle of the film sample 33, the first plastic scintillator 31 is coupled with a photocathode window of the photomultiplier 34, and a reflecting layer is plated on the side surface of the second plastic scintillator 32 far away from the film sample 33;
the data acquisition processing module comprises a high-speed digital oscilloscope 41 and a computer 42, wherein one channel of the high-speed digital oscilloscope 41 acquires anti-coincidence pulse signals, and the other channel acquires Gaussian pulse signals of the amplifier 2; the computer 42 obtains the dual-channel signal of the high-speed digital oscilloscope 41 to perform anti-coincidence logic judgment, and processes the reserved data to obtain a corresponding Doppler broadening spectrum and calculate the S-W parameter of the Doppler broadening spectrum to obtain the defect information in the film sample 33.
Example 2
Referring to fig. 2, the invention also includes a method for testing the digital positron annihilation doppler broadening spectrometer for testing the micron-sized film,
the method specifically comprises the following steps:
step (1): when positron emitted from a radioactive source passes through the film sample 33 and enters the first plastic scintillator 31 or the second plastic scintillator 32 to be annihilated, the positron deposits energy in the first plastic scintillator 31 or the second plastic scintillator 32 and emits light, and photons enter a photocathode of the photomultiplier 34 after being transmitted, and the photomultiplier 34 outputs an anti-coincidence pulse signal for anti-coincidence logic judgment;
step (2): when a positron emitted from a radiation source annihilates in the thin film sample 33 or the first plastic scintillator 31 or the second plastic scintillator 32, annihilation photons of energy 511keV are generated; the high-purity germanium detector 1 detects annihilation photons, and outputs negative index nuclear signal pulses, and Gaussian pulse signals with the pulse width of 10 mu s are output after the negative index nuclear signal pulses are formed and amplified by the main amplifier 2, as shown in figure 3;
step (3): for the gaussian pulse signal to be completely collected, the time window to be set should be larger than the gaussian pulse signal width, the time window is 20 μs, and since the photomultiplier 34 has a fast time response, the anti-coincidence pulse signal width is 3ns, and there are several anti-coincidence pulse signals in the 20 μs time window, the anti-coincidence time window and the anti-coincidence threshold should be set for screening the anti-coincidence pulse signals obtained by positron instances related to annihilation photons detected by the high-purity germanium detector 1, see fig. 4;
the setting method of the anti-coincidence time window is that when the constant ratio is:
because the shaping time of the main amplifier 2 and the time response of the high-purity germanium detector 1 are slower than that of the photomultiplier 34, the Gaussian pulse signal lags behind the anti-coincidence pulse signal, the lag time is t, the midpoint of an anti-coincidence time window is obtained by pushing t forwards from the moment that the signal amplitude of the high-purity germanium detector 1 rises by 10%, the anti-coincidence time window is set to be t-1 mu s-t+1 mu s, and the anti-coincidence pulse signal obtained by positron instance related to annihilation photons detected by the high-purity germanium detector 1 is ensured to be positioned in the anti-coincidence time window;
setting of anti-coincidence threshold:
and selecting a proper time window, ensuring that each window only contains one anti-coincidence pulse signal or no pulse signal, counting the pulse amplitude spectrum of the photomultiplier 34, and obtaining the pulse baseline jitter amplitude of the photomultiplier 34 as shown in fig. 5, wherein the selected anti-coincidence threshold value is higher than the pulse baseline jitter amplitude and can be set to be 5-20mV.
Step (4): one channel of the high-speed digital oscilloscope 41 collects anti-coincidence pulse signals, and the other channel collects Gaussian pulse signals of the amplifier 2; the anti-coincidence pulse signal and the Gaussian pulse signal are converted into digital pulse data and transmitted to a computer 42 terminal through USB3.0 for online processing;
step (5): processing of gaussian pulse signals by computer 42 terminals: the Gaussian pulse signal is subjected to digital pulse screening through a Gaussian shape screening device, and the Gaussian pulse signal is subjected to baseline removal processing to obtain the pulse amplitude of the Gaussian pulse signal; processing of the anti-coincidence pulse signal by the computer 42 terminal: an anti-coincidence pulse signal exceeding an anti-coincidence threshold value appears in the anti-coincidence time window, and the signal is false; if the anti-coincidence pulse signal exceeding the anti-coincidence threshold value does not appear, outputting a Boolean signal, if the anti-coincidence pulse signal exceeds the anti-coincidence threshold value, the anti-coincidence pulse signal represents that the positron emitted by the radioactive source is annihilated in the film sample 33, and the corresponding Gaussian pulse signal amplitude information is reserved; if false, the positrons emitted by the representative radioactive source are annihilated in the first plastic scintillator 31 or the second plastic scintillator 32, and the corresponding Gaussian pulse signal amplitude information is not reserved;
step (6): the remaining gaussian pulse signal amplitude information is a count, the annihilation photon energy spectrum is plotted by the gaussian pulse signal amplitude information of sufficient count, and the S and W parameters are calculated, see fig. 6, where S is defined as the ratio of the peak center count to the total count, reflecting low momentum electron information such as valence electrons and conduction electrons. W is defined as the ratio of the counts on both sides of the peak to the total count, reflecting high momentum electron information, such as core electrons.
Referring to fig. 7, the invention verifies the testing accuracy of the digital anti-coincidence positron annihilation Doppler broadening spectrometer for the micrometer-scale metal film aluminum, iron, nickel, copper and zinc testing results, wherein the S-W parameter method testing results are consistent with the metal element electron orbit distribution momentum information rule.
Therefore, the invention adopts the anti-coincidence module to judge the annihilation photon position, realizes the digital anti-coincidence Doppler spectrometer for the micron-scale film test, has excellent spectrometer performance, liberates the rigid requirements on the number and thickness of samples during positron Doppler measurement, and has important significance for the application and popularization of positron annihilation technology.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (4)
1. A digital positron annihilation Doppler broadening spectrometer for micron-scale film testing,
the method is characterized in that: the high-purity germanium detector (1) is used for receiving annihilation photons generated by annihilation of positive and negative electrons and depositing energy, and outputting negative index nuclear signal pulses, wherein the pulse height is related to the depositing energy;
the amplifier (2) amplifies and Gaussian-forms the negative index nuclear pulse signal to obtain a Gaussian pulse signal; the anti-coincidence module comprises a first plastic scintillator (31), a second plastic scintillator (32), a film sample (33) and a photomultiplier (34), wherein the photomultiplier (34) is used for outputting anti-coincidence pulse signals; the first plastic scintillator (31) and the second plastic scintillator (32) clamp the micron-sized film sample (33) from two sides, a positron emission source is arranged in the middle of the film sample (33), the first plastic scintillator (31) is coupled with a photocathode window of the photomultiplier (34), and the side surface of the second plastic scintillator (32) far away from the film sample (33) is plated with a reflecting layer;
the data acquisition processing module comprises a high-speed digital oscilloscope (41) and a computer (42), wherein one channel of the high-speed digital oscilloscope (41) acquires anti-coincidence pulse signals, and the other channel acquires Gaussian pulse signals of the amplifier (2); the computer (42) obtains the dual-channel signal of the high-speed digital oscilloscope (41) to carry out anti-coincidence logic judgment, and processes the reserved data to obtain a corresponding Doppler broadening spectrum and calculate S-W parameters thereof to obtain the defect information in the film sample (33).
2. The method for testing a digital positron annihilation Doppler broadening spectrometer for micrometer-scale thin film testing as claimed in claim 1,
the method is characterized in that: the method specifically comprises the following steps:
step (1): when positrons emitted from a radiation source pass through a film sample (33) and enter a first plastic scintillator (31) or a second plastic scintillator (32) to be annihilated, the positrons deposit energy in the first plastic scintillator (31) or the second plastic scintillator (32) and make the positrons emit light, photons enter a photocathode of a photomultiplier tube (34) after being transmitted, and the photomultiplier tube (34) outputs an anti-coincidence pulse signal for anti-coincidence logic judgment;
step (2): when a positron emitted from a radiation source annihilates in a thin film sample (33) or a first plastic scintillator (31) or a second plastic scintillator (32), annihilation photons of energy 511keV are generated; the high-purity germanium detector (1) detects annihilation photons, and outputs negative index nuclear signal pulses, and Gaussian pulse signals with the pulse width of 10 mu s are output after the negative index nuclear signal pulses are formed and amplified by the main amplifier (2);
step (3): in order for the gaussian pulse signal to be fully acquired, the time window to be set should be greater than the gaussian pulse signal width, and since the photomultiplier (34) has a faster time response and a plurality of anti-coincidence pulse signals are in the time window, an anti-coincidence time window and an anti-coincidence threshold should be set for screening the anti-coincidence pulse signals obtained by positron instances related to annihilation photons detected by the high-purity germanium detector (1);
step (4): one channel of the high-speed digital oscilloscope (41) collects anti-coincidence pulse signals, and the other channel collects Gaussian pulse signals of the amplifier (2); the anti-coincidence pulse signal and the Gaussian pulse signal are converted into digital pulse data and transmitted to a computer (42) terminal through USB3.0 for online processing;
step (5): processing of gaussian pulse signals by a computer (42) terminal: the Gaussian pulse signal is subjected to digital pulse screening through a Gaussian shape screening device, and the Gaussian pulse signal is subjected to baseline removal processing to obtain the pulse amplitude of the Gaussian pulse signal; processing of the anti-coincidence pulse signal by the computer (42) terminal: an anti-coincidence pulse signal exceeding an anti-coincidence threshold value appears in the anti-coincidence time window, and the signal is false; if the anti-coincidence pulse signal exceeding the anti-coincidence threshold value does not appear, the signal is true, and a Boolean signal is output; if true, annihilating positrons emitted by the representative radioactive source in the film sample (33), and retaining corresponding Gaussian pulse signal amplitude information; if the signal is false, the positrons emitted by the representative radioactive source are annihilated in the first plastic scintillator (31) or the second plastic scintillator (32), and the corresponding Gaussian pulse signal amplitude information is not reserved;
step (6): the preserved Gaussian pulse signal amplitude information is a count, the annihilation photon energy spectrum is drawn through the Gaussian pulse signal amplitude information of enough counts, S and W parameters are calculated, S is defined as the ratio of the peak center count to the total count and reflects low-momentum electron information such as valence electrons and conduction electrons, W is defined as the ratio of the peak two-side count to the total count and reflects high-momentum electron information such as core electrons.
3. The method for testing a digital positron annihilation doppler spread spectrum meter for micrometer-scale thin film testing according to claim 2, wherein: when the setting method of the anti-coincidence time window in the step (3) is constant ratio: because the shaping time of the main amplifier (2) and the time response of the high-purity germanium detector (1) are slower than that of the photomultiplier (34), the Gaussian pulse signal lags behind the anti-coincidence pulse signal, the lag time is t, the signal amplitude of the high-purity germanium detector (1) is increased by 10% and pushed forward by t to obtain the midpoint of the anti-coincidence time window, and the anti-coincidence time window is set to be t-1 mu s-t+1 mu s;
4. the method for testing a digital positron annihilation doppler spread spectrum meter for micrometer-scale thin film testing according to claim 2, wherein: setting of the anti-coincidence threshold in the step (3): and selecting a proper time window, ensuring that each window only contains one anti-coincidence pulse signal or no pulse signal, counting the pulse amplitude spectrum of the photomultiplier (34), and obtaining the pulse baseline jitter amplitude of the photomultiplier (34) to be 3-4 mV, wherein the selected anti-coincidence threshold value is higher than the amplitude of the pulse baseline jitter, and the smaller the anti-coincidence threshold value is, the more accurate the result is.
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