Ultrafast X-ray transient absorption spectrometer driven by double lasers

Abstract

The invention discloses a dual-laser-driven ultrafast X-ray transient absorption spectrometer, and relates to the technical field of X-ray material structure characterization. Pumping light is generated through a nanosecond ultraviolet-visible laser to excite the sample; detection is carried out through nanosecond X-ray detection light generated by interaction of a high-energy Nd: YAG near-infrared laser and a krypton gas target; dispersive detection and synchronous capture of the detection light with different wavelengths on the sample are realized through the grating polychromator and the high-speed spectrograph; the time-resolved transient X-ray absorption spectrum characterization of nanosecond-order time resolution is realized through a precise delay control circuit and an optical path design. According to the spectrometer, the measurement of miniaturized, off-line, wide-spectrum, element-resolved and nanosecond time-resolved transient X-ray absorption spectra is innovatively realized according to the excitation state measurement requirement of ultrahigh time resolution.

Description

Technical Field

[0001] The present invention relates to the technical field of X-ray material structure characterization, and in particular to a dual-laser driven ultrafast X-ray transient absorption spectrometer. Background Art

[0002] Semiconductor heterogeneous integration technology can achieve optimal configuration of functional modules through collaborative design across material systems, improving the performance of wide-bandgap semiconductor devices in diverse extreme application scenarios. This effectively overcomes the intrinsic performance limitations of single semiconductor materials, enabling revolutionary breakthroughs in exploration equipment for extreme environments such as deep sea, deep space, deep earth, nuclear power, and ultra-high voltage power grids. Defects are inevitably introduced during the growth of heterogeneous interfaces, thereby degrading device performance. For example, local lattice distortion caused by lattice mismatch and thermal mismatch can enhance phonon scattering, significantly reducing carrier mobility and affecting the device's saturation current density and switching speed. Furthermore, interface defects can form electric field concentration points, reducing the device's breakdown voltage and limiting its power density. Therefore, addressing heterogeneous interface defects is key to the development of wide-bandgap semiconductor devices. However, existing experimental methods are relatively limited, and in situ monitoring of defect evolution and mechanistic exploration remain relatively superficial. In situ measurement and tracking of microscopic processes across temporal and spatial scales are impossible, resulting in a lack of effective analysis and feedback control of the microscopic mechanisms of heterogeneous interface defect formation.

[0003] Ultrafast X-ray technology uses ultrashort X-ray pulses in the femtosecond to attosecond range to probe ultrafast dynamic processes in matter at the atomic and molecular scales (such as electron motion, chemical bond breaking, and lattice vibrations). X-ray absorption spectroscopy is a technique that uses X-rays to study specific elements in materials. By measuring how the sample's absorption of X-rays changes with energy, it can reveal the element's valence state, electronic structure, and the type, distance, and number of surrounding atoms. It is element-specific and does not require long-range order in the sample. Using ultrafast X-ray pump-probe technology for transient X-ray absorption testing, dynamic processes in materials (such as defect formation, phase transitions, and carrier transport) can be captured in real time at the atomic scale, enabling three-dimensional visualization of defect dynamics. This allows for the detection of coordination changes and defect states at heterogeneous interfaces, providing ultrafast time-resolved and in-situ defect dynamics analysis. Its core principle is to reconstruct the transient structural evolution of materials on femtosecond to nanosecond timescales by precisely controlling the time delay between optical pumping and X-ray detection. Currently, ultrafast X-ray light sources with continuously adjustable wavelengths can only be achieved by large scientific devices such as X-ray free electron lasers. They are expensive and available in small quantities, making them difficult to be widely used. This hinders the development of new materials and new technologies. There is an urgent need to develop in-situ monitoring and control methods for heterogeneous and heterogeneous interfaces.

[0004] Existing miniaturized time-resolved X-ray absorption spectrometers primarily use the same set of ultrafast lasers for beam splitting: one beam is used as pump light to excite the sample, and the other is used to excite X-rays to generate ultrafast X-ray probe light for absorption spectrum detection. This requires that the ultrafast laser light generated by the laser be able to both excite the sample and have sufficient intensity to excite the X-rays. However, the energy range of the X-rays excited by existing technology is below 600 eV, which can only detect the X-ray absorption spectra of elements in the water window band (C, N, O). This has limited application scenarios and is difficult to apply to defect research at semiconductor heterojunction interfaces. Therefore, it is necessary to design a dual-laser-driven ultrafast X-ray transient absorption spectrometer to expand the range of detectable elements. Summary of the Invention

[0005] In response to the problem that defects in existing semiconductor heterojunction interfaces are difficult to effectively analyze and feedback-control, the present invention discloses an integrated detection system that meets the needs of ultra-high time-resolved excited-state measurements and innovatively realizes miniaturized, off-line, multi-element and nanosecond time-resolved X-ray absorption spectroscopy (tr-XAS) measurements.

[0006] In order to solve the technical problem, the present invention adopts the following specific technical solutions:

[0007] A dual-laser driven ultrafast X-ray transient absorption spectrometer, comprising a time delay circuit, two sets of nanosecond lasers, a plasma source, a time delay line, a grating polychromator, a vacuum sample chamber and a high-speed spectrometer; wherein:

[0008] The delay circuit is used to synchronize the two sets of lasers to achieve synchronous start-up;

[0009] Two sets of nanosecond lasers, namely nanosecond UV-visible laser and nanosecond near-infrared laser. The UV-visible laser is used to generate ultrafast UV-visible pump light to excite samples, and the nanosecond near-infrared laser is used to excite X-rays and generate ultrafast detection X-rays to detect samples. The nanosecond near-infrared laser uses a high-energy Nd:YAG laser.

[0010] A time delay line, used to achieve different time delays of the detection light;

[0011] Plasma source, used to generate ultrafast X-rays. The present invention uses a krypton gas target. Ultrafast near-infrared laser excites the krypton gas target to generate plasma, which then radiates wide-spectrum ultrafast X-rays with an energy range of 200-1200 eV and a pulse width of 1-2 ns.

[0012] Grating polychromator, used to disperse the different wavelengths of detection light in the broadband ultrafast X-ray and focus it onto the sample surface. After being absorbed by the sample, it is then dispersed to obtain the transient changes in the sample's absorption rate at different wavelength bands;

[0013] High-speed spectrometers are used to achieve multi-channel parallel measurement of absorption spectra. They have extremely high time resolution and can obtain data from all channels within the entire preset spectral range at one time. Therefore, they can capture transient and rapidly changing X-ray transient absorption spectrum signals of different wavelengths, with a time resolution of nanoseconds.

[0014] Furthermore, the time delay caused by the delay circuit and the time delay line and the time jitter caused by the laser can be displayed and adjusted through a photodetector and an oscilloscope.

[0015] Furthermore, the time delay line is installed between the nanosecond near-infrared laser and the plasma source in the detection circuit rather than on the pump circuit, so as to avoid additional error introduced into the time delay by the wavelength-variable pump beam.

[0016] Furthermore, the vacuum sample chamber is used to provide a vacuum environment, or to couple in-situ control means, including but not limited to heating and ventilation devices, to achieve in-situ thermal and atmosphere control during testing.

[0017] Furthermore, the ultrafast X-rays radiated from the plasma source are not limited to the above methods and can be generated in directions other than the laser direction. Therefore, windows can also be opened in other directions to couple other X-ray testing equipment based on the spectrometer.

[0018] A method for implementing a dual-laser driven ultrafast X-ray transient absorption spectrometer utilizes the aforementioned dual-laser driven broadband ultrafast X-ray transient absorption spectrometer, generates pump light through a nanosecond ultraviolet-visible laser, excites a krypton gas target through a nanosecond near-infrared laser to generate broadband ultrafast X-ray detection light, ensures laser synchronization and different time delays of the detection light through a delay circuit and a time delay line, and finally achieves dispersed detection and synchronous capture of a sample with different wavelengths of detection light through a grating polychromator and a high-speed spectrometer, thereby obtaining a time- and element-resolved X-ray absorption spectrum of the sample.

[0019] The ultrafast UV-visible pump light generated by the nanosecond UV-visible laser of this invention has a wide wavelength tunability range, allowing for the selection of different test wavelengths based on the characteristics of different samples, thereby expanding the range of testable samples. The spectrometer can detect the carrier behavior of 17 elements, including F, Ne, Na, Mg, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ga, in addition to elements in the water window band. The water window band elements refer to C, H, and O.

[0020] The present invention has the following beneficial effects:

[0021] 1. The present invention utilizes two sets of laser sources for delay control, enabling nanosecond-scale dual-laser-driven ultrafast X-ray transient absorption testing. The variable-wavelength nanosecond X-ray detection light increases the variety of detectable elements, providing a feasible method for detecting and controlling defects at semiconductor heterogeneous interfaces.

[0022] 2. The present invention utilizes a grating polychromator and a high-speed spectrometer to achieve dispersed detection and synchronous capture of samples by ultrafast detection light of different wavelengths, obtaining the element-resolved X-ray transient absorption spectrum of the sample, and providing a feasible implementation method for the study of the transport behavior and transfer mechanism of carriers at semiconductor heterogeneous interfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be better understood through the following description, which will provide a specific embodiment in combination with relevant principles and will be explained with reference to the accompanying schematic diagrams, wherein:

[0024] Figure 1 This is a schematic diagram of the principle of X-ray absorption spectroscopy.

[0025] Figure 2 Schematic diagram of plasma-induced ultrafast X-rays.

[0026] Figure 3 This is a schematic diagram of the structure of a dual-laser driven ultrafast X-ray transient absorption spectrometer.

[0027] Figure 4 This is a schematic diagram of time- and element-resolved carrier transport behavior analysis.

[0028] Figure 5 This is a schematic diagram of a grating polychromator realizing transient absorption of X-rays of different wavelengths. DETAILED DESCRIPTION

[0029] The present invention will be described in further detail below with reference to the accompanying drawings.

[0030] Figure 1This is a schematic diagram of the principle of X-ray absorption spectroscopy. X-ray absorption spectroscopy (XAS) is an analytical technique that studies the elemental composition, electronic structure, and local atomic structure of a material by measuring its X-ray absorption characteristics. Its core principle is based on the photoelectric effect: when the incident X-ray energy reaches the binding energy of the inner-shell electrons of a specific atom, the electrons are excited to unoccupied bound states or continuous free states, generating absorption transitions (absorption edges) and forming a characteristic absorption spectrum. XAS spectra are generally divided into two key regions: near-edge structure (XANES) and extended-edge fine structure (EXAFS). The XANES region within ±50 eV of the absorption edge reflects electronic transitions. Its peak position, shape, and intensity are sensitive to the chemical valence state, coordination symmetry, and electron orbital hybridization of the element, allowing direct estimation of the redox state. The EXAFS region, 50-1000 eV after the absorption edge, originates from oscillations caused by photoelectrons scattered by neighboring atoms. Fourier transforms can be used to resolve the type, distance, number, and disorder of the coordinating atoms, providing local structural information with sub-angstrom precision. XAS has the advantages of element specificity and non-destructiveness, and is suitable for a variety of complex systems such as semiconductor heterogeneous interfaces and disordered materials, solutions, catalysts, etc.

[0031] Figure 2 This is a schematic diagram of plasma-induced ultrafast X-ray emission. A high-energy Nd:YAG laser generates near-infrared nanosecond laser pulses through an oscillator and amplifier. These pulses are then focused onto a krypton gas target, instantly ionizing it to form a high-temperature, high-density plasma. The laser energy is efficiently absorbed by electrons through mechanisms such as inverse bremsstrahlung heating, generating a large number of high-energy electrons with energies ranging from keV to MeV, which in turn stimulate collective oscillations in the plasma. These high-energy electrons undergo two primary emission mechanisms during their non-equilibrium evolution: first, the deflection of electrons by the ion Coulomb field produces a broadband bremsstrahlung continuum of X-rays; second, high-energy electron collisions excite inner-shell electrons to form holes, which are then filled by outer-shell electrons, releasing characteristic X-rays of specific energies (such as Kα rays). The ultrafast nature of the X-ray emission stems from the nanosecond laser pulse duration, which directly determines the timescales for initial plasma excitation and electron acceleration, enabling the X-ray pulse duration to be compressed to the nanosecond scale. Furthermore, the photon energy can be adjusted by adjusting the target material and laser parameters. Ultimately, ultrafast X-rays are emitted from a specific window for subsequent detection. This technology combines ultra-high time resolution and high throughput characteristics, providing an ideal light source for detecting ultrafast dynamic processes at the atomic scale.

[0032] Figure 3 This is a schematic diagram of the structure of a dual-laser driven ultrafast X-ray transient absorption spectrometer. A dual-laser driven ultrafast X-ray transient absorption spectrometer includes a delay circuit, two sets of nanosecond lasers, a plasma source, a time delay line, a grating polychromator, a vacuum sample chamber and a high-speed spectrometer;

[0033] The delay circuit is used to synchronize the two sets of nanosecond lasers to achieve synchronous start-up;

[0034] The two sets of nanosecond lasers are respectively a nanosecond ultraviolet-visible laser and a nanosecond near-infrared laser. The ultraviolet-visible laser is used to generate ultrafast ultraviolet-visible pump light to excite the sample, and the nanosecond near-infrared laser is used to excite X-rays to generate ultrafast detection X-rays to detect the sample;

[0035] The plasma source is used to radiate and generate 200-1200 eV wide-spectrum ultrafast X-rays;

[0036] The time delay line is used to achieve different time delays of the detection light;

[0037] The grating polychromator is used to disperse X-rays of different wavelengths in the horizontal direction, focus them on the sample, and then disperse them after being absorbed by the sample;

[0038] The vacuum sample chamber is used to place the sample to be tested;

[0039] The high-speed spectrometer is used to collect signals from all energy points at one time and simultaneously obtain X-ray transient absorption spectra of different wavelengths.

[0040] The time delay introduced by the delay circuit and time delay line, as well as the time jitter introduced by the laser, are displayed and adjusted via a photodetector and oscilloscope. The time delay line is installed in the detection circuit between the nanosecond near-infrared laser and the plasma source, rather than in the pump circuit, to prevent the variable-wavelength pump beam from introducing additional error into the time delay. The vacuum sample chamber is used to provide a vacuum environment or to couple in-situ control methods, including but not limited to heating and ventilation devices, to achieve in-situ thermal and atmosphere control during testing.

[0041] Figure 4This is a schematic diagram of time- and element-resolved carrier transport behavior analysis. When using this spectrometer to probe heterojunctions and heterostructured interfaces, the sample is first excited from the ground state to a non-equilibrium state using ultrafast UV-visible pump light generated by a UV-visible laser. This excites the sample, inducing physical or chemical processes such as electronic excitation, lattice vibrations, phase transitions, and chemical reaction intermediates. The pulsed X-ray probe light reaches the sample after a specific time delay following the pump pulse, and the XAS spectrum of the sample is measured. By precisely controlling the time delay between the pump and probe pulses, the evolution of the excited state at different moments in the evolution can be captured. By comparing the XAS spectra at different time delays with the ground state spectrum, the corresponding electronic dynamics can be tracked, revealing oxidation state changes, charge transfer, valence electron excitation and relaxation, and transient changes in the conduction band / valence band density of states between the substrate, interface, and heterojunction film. Structural dynamics such as bond length changes and coordination environment modifications, as well as ultrafast processes such as electron-phonon coupling and coherent phonon driving, can also be tracked. An example of tracking electronic dynamics is shown in the figure. The pump light excites the heterogeneous film to produce electron transitions. Then, the detection X-rays of different wavelengths are absorbed by the inner-layer electrons and transition to different energy levels in the film, interface defects, and even the substrate, generating corresponding XAS spectra. By comparing the changes in the XAS spectrum over time, the transition of electrons in the film can be characterized, and then information such as the defect type and defect density of the interface and its evolution over time can be obtained. At the same time, the detection of X-rays of different wavelengths also gives it elemental resolution, which can accurately analyze the defect situation.

[0042] Figure 5 This is a schematic diagram of a grating polychromator to achieve transient absorption of X-rays of different wavelengths. Conventional monochromators, such as crystal monochromators, use the principle of Bragg diffraction of X-rays in crystals to select monochromatic X-rays of specific energy. They can only obtain time-resolved X-ray absorption at a specific wavelength at a time. Precision crystal rotation is required to change the Bragg angle to obtain a continuous XAS spectrum. For shorter pulses, such as femtoseconds, multiple pulses need to be emitted and different energy points measured at different monochromator angles. It is difficult to ensure that the state of the sample is exactly the same after each pulse excitation, which introduces more errors. Using a grating polychromator, X-rays of different energies can be diffracted to different positions on the detector plane. In this way, after a single pulse irradiates the sample, different pixel positions on the detector correspond to different X-ray energies. A single pulse can obtain the entire energy spectrum and its changes over time, avoiding most of the photon loss caused by scanning monochromators. It is also more suitable for unstable or irreversible processes.

[0043] Based on the above description, the present invention uses two sets of lasers to generate pump light and probe light, respectively. The generated ultraviolet-visible laser has a time resolution of the nanosecond level and a wavelength range of 200-1000nm. The nanosecond near-infrared laser is a high-energy Nd:YAG laser with a time resolution of the nanosecond level and a wavelength of 1064nm. The plasma source is a krypton gas target. The high-energy Nd:YAG laser interacts with the krypton gas target to generate plasma, which in turn radiates broadband ultrafast X-rays with an energy range of 200-1200eV and a pulse width of 1-2ns. Through dual laser-driven beam splitting, the nanosecond ultraviolet-visible laser generates pump light to excite the sample, while the high-energy Nd:YAG near-infrared laser interacts with the krypton gas target to generate an ultrafast X-ray transient absorption spectrometer, expanding the range of detectable elements.

[0044] Based on the above implementations, the ultrafast UV-visible pump light generated by the nanosecond UV-visible laser of the present invention has a wide wavelength tunable range, allowing for the selection of different test wavelengths based on the characteristics of different samples, thereby expanding the range of testable samples. Broad-spectrum ultrafast X-rays can detect elements in the water window band, or the carrier behavior of any of the following elements: F, Ne, Na, Mg, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ga; the water window band elements refer to C, H, and O.

[0045] Based on the above implementations, the present invention utilizes a dual-laser-driven, broadband, ultrafast X-ray transient absorption spectrometer. This instrument uses a nanosecond UV-visible laser to generate ultrafast UV-visible pump light to excite the sample. This instrument uses nanosecond X-ray probe light generated by the interaction of a high-energy Nd:YAG near-infrared laser with a krypton gas target for detection. A grating polychromator and a high-speed spectrometer enable dispersed detection and synchronous capture of the sample using probe light of different wavelengths. Precision delay control circuitry and optical path design enable time-resolved transient X-ray absorption spectroscopy with nanosecond-scale time resolution. This spectrometer, designed for ultrahigh time-resolution excited-state measurements, innovatively achieves miniaturized, off-line, broadband, element-resolved, and nanosecond-time-resolved transient X-ray absorption spectroscopy.

[0046] It should be further noted that the above embodiments are intended only to facilitate understanding of the technical solution of the present invention and are not intended to limit the scope of protection of the present invention. Any obvious adjustments and modifications to the technical solution of the present invention that fall within the technical concept of the present invention shall also fall within the scope of protection of the present invention.

Claims

1. A dual-laser driven ultrafast X-ray transient absorption spectrometer, characterized in that: It includes a delay circuit, two sets of nanosecond lasers, a plasma source, a time delay line, a grating polychromator, a vacuum sample chamber and a high-speed spectrometer; among them, The delay circuit is used to synchronize the two sets of nanosecond lasers to achieve synchronous start-up; The two sets of nanosecond lasers are respectively a nanosecond ultraviolet-visible laser and a nanosecond near-infrared laser. The ultraviolet-visible laser is used to generate ultrafast ultraviolet-visible pump light to excite the sample, and the nanosecond near-infrared laser is used to excite X-rays and generate ultrafast detection X-rays to detect the sample; The plasma source is used to radiate and generate 200-1200 eV wide-spectrum ultrafast X-rays; The time delay line is used to achieve different time delays of the detection light; The grating polychromator is used to disperse ultrafast X-rays of different wavelengths in the horizontal direction, focus them on the sample, and then disperse them after being absorbed by the sample; The vacuum sample chamber is used to place the sample to be tested; The high-speed spectrometer is used to collect signals from all energy points at one time and simultaneously obtain X-ray transient absorption spectra of different wavelengths.

2. The dual-laser driven ultrafast X-ray transient absorption spectrometer according to claim 1, characterized in that: The pump light and probe light are generated by two sets of lasers respectively; the nanosecond UV-visible laser generates ultrafast UV-visible pump light to excite the sample; A nanosecond near-infrared laser excites a plasma source to generate ultrafast X-ray detection light to detect samples; the ultraviolet-visible laser has a time resolution of the nanosecond order and a wavelength range of 200-1000nm; the nanosecond near-infrared laser is a high-energy Nd:YAG laser with a time resolution of the nanosecond order and a wavelength of 1064nm; the plasma source is a krypton gas target, and the high-energy Nd:YAG laser interacts with the krypton gas target to generate plasma, which in turn radiates wide-spectrum ultrafast X-rays with an energy range of 200-1200eV and a pulse width of 1-2ns.

3. The dual-laser driven ultrafast X-ray transient absorption spectrometer according to claim 1, characterized in that: The time delay caused by the delay circuit and time delay line and the time jitter caused by the laser are displayed and adjusted through a photodetector and an oscilloscope; the time delay line is installed between the nanosecond near-infrared laser and the plasma source in the detection circuit rather than on the pump circuit to avoid additional errors introduced by the wavelength-variable pump beam on the time delay.

4. The dual-laser driven ultrafast X-ray transient absorption spectrometer according to claim 1, characterized in that: The vacuum sample chamber is used to provide a vacuum environment, or to couple in-situ control means, including but not limited to heating and ventilation devices to achieve in-situ thermal and atmosphere control during testing.

5. The dual-laser driven ultrafast X-ray transient absorption spectrometer according to claim 2, characterized in that: The ultrafast UV-visible pump light generated by the nanosecond UV-visible laser has a wide adjustable wavelength range. Different test wavelengths can be selected according to the characteristics of different samples to expand the types of testable samples.

6. The dual-laser driven ultrafast X-ray transient absorption spectrometer according to claim 2, characterized in that: Broad-spectrum ultrafast X-rays can detect elements in the water window band, or the carrier behavior of any one of the elements F, Ne, Na, Mg, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ga; the water window band elements refer to the three elements C, H, and O.

7. A method for implementing the dual-laser driven ultrafast X-ray transient absorption spectrometer according to any one of claims 1 to 6, comprising: using a dual-laser driven broadband ultrafast X-ray transient absorption spectrometer, generating pump light with a nanosecond ultraviolet-visible laser; exciting a krypton gas target with a nanosecond near-infrared laser to generate broadband ultrafast X-ray detection light; ensuring laser synchronization and different time delays of the detection light with a delay circuit and a time delay line; and finally, achieving dispersed detection and synchronous capture of a sample with different wavelengths of detection light with a grating polychromator and a high-speed spectrometer to obtain a time- and element-resolved X-ray absorption spectrum of the sample.

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