A method and system for improving the resolution of three-dimensional atom probe mass spectrometry of metal materials based on laser polarization and field enhancement effect

Abstract

The present invention discloses a method and system for improving the three-dimensional atomic probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect. The method first prepares the metal material to be tested into a nano-scale needle tip sample, places it on a three-dimensional atomic probe sample stage, and then uses a linearly polarized laser as an excitation source, adjusts its polarization direction to be consistent with the axis of the sample needle tip, and then uses a three-dimensional mobile platform to gradually adjust the distance between the sample needle tip and the focused spot of the laser for detection. In order to realize the above method, the present invention also provides a related system, which includes a linearly polarized laser source, an optical polarization adjustment module, a three-dimensional mobile platform, a three-dimensional atomic probe body and a data acquisition and processing device. The method uses the laser field enhancement effect to replace the traditional thermal effect driving mechanism through laser polarization direction adjustment, near-field positioning and parameter optimization, effectively solving the technical problem of low resolution caused by thermal effect, and greatly improving the resolution of three-dimensional atomic probe mass spectrometry.

Description

Technical Field

[0001] The present invention relates to a three-dimensional atom probe mass spectrometry resolution method, and in particular to a method and system for improving the three-dimensional atom probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect, belonging to the field of three-dimensional atom probe analysis. Background Art

[0002] Three-dimensional atom probe (3DAP) is a powerful technique capable of atomic-scale compositional analysis and three-dimensional atomic imaging of materials. In metallic materials research, 3DAP can provide key information such as the distribution of alloying elements and the composition and size of precipitated phases, which is of great significance for understanding material properties and developing new materials.

[0003] Traditional three-dimensional atom probe technology primarily utilizes electric-field evaporation, which involves applying a high DC voltage to the sample and superimposing a voltage pulse. This uses the strong electric field at the tip to evaporate atoms from the sample surface one by one. However, this method has several limitations: the pulse voltage (on the order of kilovolts) must have a minimum width of approximately 100 nanoseconds. Excessively long pulse durations lead to time-of-flight dispersion (uncertainty about the moment of atomic evaporation), which reduces mass spectrometric resolution. Furthermore, to achieve a high mass spectrometry signal-to-noise ratio, the pulse voltage is typically set to approximately 20%. However, excessively high voltages can cause excessive random evaporation events, further reducing the signal-to-noise ratio.

[0004] With technological advancements, three-dimensional atom probes using laser-assisted atomic evaporation have emerged. Their principle is to apply a high DC voltage to the tip while simultaneously irradiating the sample tip with short laser pulses (pulse width approximately 10 ps). The heating effect of the laser on the sample reduces the electric field intensity required for atomic evaporation at the tip, achieving the goal of evaporating atoms one by one. This method is called laser mode. The advantages of laser mode are that the laser pulse width is significantly shorter than that of voltage pulses, reducing uncertainty in the moment of atomic evaporation, making time-of-flight measurements more accurate, and improving mass spectrometry accuracy. However, the laser irradiation causes the instantaneous temperature at the sample tip to rise to hundreds or even thousands of K. Although the high temperature lasts only briefly, as the temperature rises, factors such as thermal migration of atoms on the sample surface, thermal deformation of the sample, and localized thermal damage directly affect not only mass spectral resolution but also spatial resolution.

[0005] Currently, the latest three-dimensional atom probe evaporation technology uses a voltage and laser synergistic mode. This involves applying a high DC voltage to the sample and superimposing a lower voltage pulse to ensure that no atoms evaporate. Then, during the duration of the high-voltage pulse, a picosecond laser is used to illuminate the sample tip, further lowering the atomic evaporation barrier and promoting atomic evaporation. Although this method significantly improves mass spectral resolution compared to the previous two methods, it still suffers from the shortcomings of the laser mode, such as poor mass spectral resolution caused by laser heating of the sample, poor spatial resolution caused by thermal deformation of the sample, and localized thermal damage. Summary of the Invention

[0006] To address the challenges of the existing technology, the first objective of the present invention is to provide a method for improving the resolution of three-dimensional atom probe mass spectrometry of metallic materials based on laser polarization and field enhancement effects. This method utilizes the field enhancement effect of the laser field at the nanoscale tip, replacing the traditional thermal drive mechanism, by adjusting the laser polarization direction, performing near-field positioning, and optimizing parameters. This method effectively addresses the long-standing technical issue of low resolution caused by thermal effects in three-dimensional atom probe technology, providing a new approach for atomic-scale material analysis and possessing significant value for materials science research and industrial applications.

[0007] A second objective of the present invention is to provide a system for improving the three-dimensional atom probe mass spectrometry resolution of metallic materials based on laser polarization and field enhancement effects. This system utilizes a linearly polarized laser source, with an optical polarization adjustment module adjusting the laser's polarization direction to align with the sample tip's axial direction. A three-dimensional mobile platform then adjusts the distance between the sample tip and the laser spot. Ion extraction efficiency and sample heating are simultaneously monitored to determine optimal positioning parameters. Data acquisition and processing further enhance the accuracy and reliability of data analysis.

[0008] In order to realize the above technical solution, the present invention provides a method for improving the three-dimensional atomic probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect, comprising: preparing the metal material to be tested as a nanoscale needle tip sample, placing it on a three-dimensional atom probe sample stage, and then using a linearly polarized laser as an excitation source, adjusting its polarization direction to be consistent with the axial direction of the sample needle tip, and then gradually adjusting the distance between the sample needle tip and the focused spot of the laser through a three-dimensional moving platform for detection.

[0009] Existing technologies, such as the laser-assisted mode and the voltage-laser synergistic mode, rely on the thermal effect of the laser to reduce the atomic evaporation barrier. However, instantaneous high temperature can cause thermal migration, deformation and damage to the sample, which in turn seriously affects the resolution. The technical solution provided by the present invention utilizes the laser field enhancement effect of the linearly polarized laser, whose polarization direction is consistent with the axis of the needle tip, to achieve a significant enhancement of the electric field strength through the localized plasma resonance and optical antenna effect of the nanotip. Atoms can be efficiently evaporated without heating the sample, fundamentally avoiding the negative impact of thermal effects on mass spectrometry resolution.

[0010] As a preferred solution, the sample needle tip is located in the near field area of ​​the laser field, 50 to 200 nm away from the center of the laser spot.

[0011] The present invention places the sample tip in the near-field area of ​​the laser field rather than the direct irradiation area, which not only utilizes the near-field enhancement effect but also avoids direct laser heating. It optimizes the distance between the sample and the laser spot through experiments and numerical simulations, greatly reducing the thermal effect while ensuring the field enhancement effect.

[0012] As a preferred solution, the metal material is a metal element or an alloy.

[0013] As a preferred solution, the laser pulse width is 1-20 ps, ​​and the single pulse energy is 10-100 nJ.

[0014] The present invention optimizes parameters such as laser wavelength, pulse width, and energy through theoretical calculations and experiments to balance the field enhancement effect with the thermal effect. Within the above range, the pulse width effectively shortens the evaporation time and dispersion, while the pulse energy ensures that the inherent electric field strength of the laser is sufficiently high.

[0015] As a preferred solution, the calculation process of the electric field intensity of the laser is:

[0016] Formula 1: ;

[0017] Formula 2: ;

[0018] In Equation 1 and Equation 2: is the peak intensity of the laser, is the single pulse energy, is the laser spot size, is the pulse width, is the vacuum permittivity, is the amplitude of the laser electric field intensity, is the polarization axis angle, The polarization axis angle is The electric field strength at .

[0019] The present invention can achieve the electric field strength required for evaporation without relying on high laser energy. It mainly meets actual needs through field enhancement at the needle tip, significantly reducing the power requirement for the laser, while reducing random evaporation events and improving the signal-to-noise ratio.

[0020] As a preferred solution, the size of the laser spot is less than 5 μm, and the enhancement factor η of the electric field is greater than or equal to 50.

[0021] As a preferred solution, the mass spectrometry resolution is 300-1000, the spatial resolution is 0.18-0.22 nm in the lateral direction, and 0.08-0.12 nm in the depth.

[0022] The present invention also provides a system for improving the three-dimensional atom probe mass spectrometry resolution based on laser polarization and field enhancement effect, which is used to implement any of the methods described above, and includes a linearly polarized laser source, an optical polarization adjustment module, a three-dimensional mobile platform, a three-dimensional atom probe body and a data acquisition and processing device.

[0023] As a preferred solution, the optical polarization adjustment module includes a half-wave plate and a polarizer for adjusting the polarization direction of the laser.

[0024] As a preferred solution, the three-dimensional moving platform is used to accurately control the relative position of the sample needle tip and the laser spot.

[0025] The present invention utilizes a high-precision three-dimensional mobile platform to adjust the relative position of the needle tip and the laser spot to ensure that it is in the near-field enhancement region. Then, by real-time monitoring of the ion signal and heating conditions, the position parameters are optimized to maximize the field enhancement efficiency, minimize the thermal effect, and improve the stability and repeatability of data acquisition.

[0026] As a preferred solution, the data acquisition and processing device is used to collect ion signals generated by samples, perform statistical analysis and remove noise, and its processing methods include filtering, noise reduction and peak fitting.

[0027] The present invention uses filtering, noise reduction, peak fitting and other algorithms to process ion signals and remove noise interference, which can further improve the signal-to-noise ratio and peak resolution of the mass spectrometer. In particular, in trace element analysis, it can more accurately identify low-abundance ion signals.

[0028] Compared with the prior art, the present invention provides the following beneficial technical effects:

[0029] 1) The mass spectrometry resolution method provided by this invention utilizes the laser field enhancement effect to replace the traditional thermal effect driving mechanism through laser polarization direction adjustment, near-field positioning and parameter optimization. This effectively solves the long-standing technical problem of low resolution caused by thermal effects in three-dimensional atom probe technology, providing a new method for atomic-scale material analysis and having important value for materials science research and industrial applications.

[0030] 2) The system provided by the present invention uses a linearly polarized laser source, and adjusts the polarization direction of the laser through an optical polarization adjustment module so that it is along the axial direction of the sample needle tip. Then, the distance between the sample needle tip and the laser spot is adjusted by a three-dimensional mobile platform, and the ion extraction efficiency and sample heating conditions are simultaneously monitored to determine the optimal position parameters. The accuracy and reliability of data analysis are further improved through a data acquisition and processing device.

[0031] 3) In the technical solution provided by the present invention, the field enhancement effect is used to improve the ion extraction efficiency, reduce the evaporation time dispersion, significantly reduce the half-height width of the mass spectrum peak, and enhance the isotope resolution capability. This solution effectively avoids sample deformation and atomic migration caused by laser heating, and the low laser energy can greatly reduce random evaporation events. Combined with the data processing algorithm, the noise level is significantly reduced, further improving the detection limit of the three-dimensional atom probe. DETAILED DESCRIPTION

[0032] For ease of understanding of the present invention, the present invention will be described more fully below with reference to specific implementation examples. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0033] Example 1

[0034] This embodiment provides a method for improving the resolution of three-dimensional atom probe mass spectrometry of metal materials based on laser polarization and field enhancement effect, specifically:

[0035] 1) Laser system commissioning: Select a pulsed laser with a wavelength of 355 nm, a pulse width of 10 ps, ​​a repetition rate of 500 kHz, and a single pulse energy of 10 nJ. Using optical components such as focusing lenses and polarizers, adjust the laser's focused spot size to less than 5 μm. Adjust the laser's polarization direction to align with the needle tip's axial direction. Use devices such as photodetectors and polarization analyzers to precisely measure and adjust the laser's parameters.

[0036] 2) Calculation and analysis of laser electric field intensity: Calculated using Equation 1 and Equation 2:

[0037] Formula 1: ;

[0038] Formula 2: ;

[0039] In Equation 1 and Equation 2: = 10 nJ, = 5μm, = 10 ps, =8.854×10 −12 F / m, =3×10 8 m / s, substitute the above parameters and calculate the peak intensity of the laser :

[0040] ;

[0041] Then we can solve :

[0042] ;

[0043] Considering the polarization of the laser, assuming the laser's polarization direction is along the sample's axial direction, the electric field intensity at an angle θ with the polarization axis is expressed as Equation 2. This shows that the electric field intensity is strongest along the laser's polarization axis. Therefore, adjusting the laser's polarization direction to be along the sample's tip's axial direction maximizes the laser's electric field intensity.

[0044] 3) Adjustment of sample and laser position: The prepared sample is mounted on the sample stage of the three-dimensional atom probe. The relative position of the sample tip and the laser spot is adjusted using a high-precision three-dimensional mobile platform. The positional relationship between the sample tip and the laser spot is observed using a laser detector and other equipment to ensure that the sample tip is in the near-field area of ​​the laser field. During the adjustment process, the distance between the sample tip and the laser spot can be gradually changed while monitoring the ion extraction efficiency and sample heating conditions. The optimal position parameters are determined through optimization.

[0045] 4) Data acquisition and analysis: Turn on the three-dimensional atom probe device and data acquisition system. Under laser excitation, collect the ion signals generated by the sample. Perform statistical analysis on the large number of collected ion signals, remove noise signals, and obtain high-quality mass spectra and three-dimensional atomic distribution information. Advanced data processing algorithms such as filtering, noise reduction, peak fitting, etc. can be used to further improve the accuracy and reliability of data analysis.

[0046] It should be noted that although the maximum electric field strength of the selected laser is only 0.2 V / nm, it does not seem to be very helpful for atomic evaporation (usually tens of V / nm are required, for example, to evaporate Al + Requires 19 V / nm, Fe 2+ 33 V / nm is required). However, the sample tip used in a 3D atom probe typically needs to be processed to tens of nanoseconds. At the nanoscale, the laser field can achieve an electric field enhancement effect of tens or even hundreds of times due to factors such as localized plasmon resonance and optical antenna effects. Therefore, the laser electric field strength does not need to reach tens of V / nm, which greatly reduces the requirements for the laser.

[0047] The present invention also provides a system for improving the three-dimensional atom probe mass spectrometry resolution based on laser polarization and field enhancement effect, which is used to implement the above method. The system includes a linearly polarized laser source, an optical polarization adjustment module, a three-dimensional mobile platform, a three-dimensional atom probe body, and a data acquisition and processing device.

[0048] The optical polarization adjustment module includes a half-wave plate and a polarizer for adjusting the polarization direction of the laser; the three-dimensional moving platform is used to accurately control the relative position of the sample needle tip and the laser spot;

[0049] The present invention uses a high-precision three-dimensional mobile platform to adjust the relative position of the needle tip and the laser spot to ensure that it is in the near-field enhancement region. Then, by real-time monitoring of ion signals and heating conditions, the position parameters are optimized to maximize the field enhancement efficiency, minimize thermal effects, and improve the stability and repeatability of data acquisition.

[0050] The data acquisition and processing device is used to collect ion signals generated by samples, perform statistical analysis and remove noise, and its processing methods include filtering, noise reduction and peak fitting.

[0051] The present invention uses filtering, noise reduction, peak fitting and other algorithms to process ion signals and remove noise interference, which can further improve the signal-to-noise ratio and peak resolution of the mass spectrometer. In particular, in trace element analysis, it can more accurately identify low-abundance ion signals.

[0052] To further illustrate the advantages of the technical solution provided by the embodiments of the present invention, the above method and system are used to detect aluminum metal. The half-width mass resolution in the above system is 300-1000, and no energy compensator is provided. The mass resolving power (MRP) calculation process is as follows:

[0053] Time-of-flight error of three-dimensional atom probe equipment There are three sources: physical time error , Electronics Timing Error and ion evaporation time error , satisfying the following relationship:

[0054] Formula 3: ;

[0055] Among them, the physical time error It is determined by physical parameters and The time error caused by the error in , can be obtained from the following equation by energy conservation:

[0056] Formula 4: ;

[0057] In formula 4, is the initial energy of the ion when it leaves the sample, is the charge state of the ion, is the electron charge, is the potential difference between the sample and the detector, is the mass of the ion, is the velocity of the ion, is the flight distance of the ion, is the flight time of the ion; therefore, the flight time of the ion can be calculated from Equation 4 as:

[0058] Formula 5: ;

[0059] Furthermore, for Al ions, 、 、 are all constants, then and The resulting time-of-flight error is:

[0060] Formula 6: ;

[0061] Formula 7: ;

[0062] Electronics timing error is the time uncertainty caused by electronics and is a fixed value for a given experimental setup. In this embodiment, its value is 100 ps.

[0063] Further, by The relationship between time error and mass resolving power (MRP) can be deduced:

[0064] Formula 8: ;

[0065] For pure aluminum samples, press Al + Ion calculation, the values ​​are as follows: , C, kg, mm, mm, kV, V, p.s. p.s. eV, after calculation, .

[0066] Comparative Example 1

[0067] This comparative example uses laser heating evaporation method to perform three-dimensional atomic probe testing on metal aluminum. In this comparative example, for pure aluminum samples, according to Al + The values ​​calculated for ions are exactly the same as those in Example 1, except that: p.s. eV.

[0068] In the case of laser heating evaporation, the sample partially absorbs the laser energy, the temperature rises sharply, and it takes a long time to cool down. During this period of temperature rise, there is a certain probability that atoms will be evaporated, which leads to the error of ion evaporation time. In addition, the smaller the laser beam spot, the smaller the heated area and the shorter the cooling time required.

[0069] Furthermore, the maximum temperature of laser-heated metal samples is about 300 K. The value of is positively correlated with temperature. At 300K, its value is 0.025eV. Therefore, for this comparative example, .

[0070] In addition, for the method provided in Example 1 of the present invention, It only depends on the duration of the laser field (~ 10ps), so the value is greatly reduced, and this method is carried out at low temperature, with basically no thermal effect. It can be ignored and calculated as 0. Therefore, the mass resolution of the method in the embodiment of the present invention is greatly improved compared with the laser heating solution.

[0071] It can be seen from the above-mentioned Example 1 and Comparative Example 1 that by reasonably selecting laser parameters and adjusting the polarization direction of the laser, the present invention can utilize the near-field enhancement effect of the laser field without heating the sample to significantly improve the resolution capability and signal-to-noise ratio of the mass spectrometer, thereby achieving more accurate atomic-scale analysis of metal materials.

Claims

1. A method for improving the three-dimensional atomic probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect, characterized in that: include: The metal material to be tested is prepared as a nanoscale needle tip sample and placed on a three-dimensional atom probe sample stage. Then, a linearly polarized laser is used as the excitation source, and its polarization direction is adjusted to be consistent with the axial direction of the sample needle tip. Then, the three-dimensional moving platform is used to gradually adjust the distance between the sample needle tip and the focused spot of the laser for detection. The sample needle tip is located in the near-field area of ​​the laser field, 50~200nm away from the center of the laser spot.

2. The method of claim 1 for improving the three-dimensional atom probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect, characterized in that: The metal material is a single metal or an alloy.

3. The method of claim 1 for improving the three-dimensional atom probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect, characterized in that: The laser has a pulse width of 1-20 ps and a single pulse energy of 10-100 nJ.

4. The method of claim 1 for improving the three-dimensional atom probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect, characterized in that: The calculation process of the electric field intensity of the laser is: Formula 1: ; Formula 2: ; In Equation 1 and Equation 2: is the peak intensity of the laser, is the single pulse energy, is the laser spot size, is the pulse width, is the vacuum permittivity, is the amplitude of the laser electric field intensity, is the polarization axis angle, The polarization axis angle is The electric field strength at .

5. The method of improving the three-dimensional atom probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect according to claim 4, characterized in that: The size of the laser spot is less than 5 μm, and the enhancement factor η of the electric field is greater than or equal to 50.

6. The method for improving the three-dimensional atom probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect according to any one of claims 1 to 5, characterized in that: The mass spectrometry resolution is 300-1000, the spatial resolution is 0.18-0.22 nm in the horizontal direction, and 0.08-0.12 nm in the depth.

7. The method of claim 1 for improving the three-dimensional atom probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect, characterized in that: The implementation system of the method includes a linearly polarized laser source, an optical polarization adjustment module, a three-dimensional moving platform, a three-dimensional atom probe body and a data acquisition and processing device.

8. The method for improving the three-dimensional atom probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect according to claim 7, characterized in that: The optical polarization adjustment module includes a half-wave plate and a polarizer, and is used to adjust the polarization direction of the laser.

9. The method of claim 7, wherein: The three-dimensional moving platform is used to accurately control the relative position of the sample needle tip and the laser spot.

10. The method for improving the three-dimensional atom probe mass spectrometry resolution of metal materials based on laser polarization and field enhancement effect according to claim 7, characterized in that: The data acquisition and processing device is used to collect ion signals generated by samples, perform statistical analysis and remove noise, and its processing methods include filtering, noise reduction and peak fitting.