A method for preparing PbI2 single nanosheets, a PbI2 single nanosheet, and a spin laser.

Abstract

This invention discloses a method for preparing PbI2 single nanosheets, a PbI2 single nanosheet, and a spin laser. The preparation method includes: S1, depositing and growing a multilayer transition metal chalcogenide film on a substrate as a substrate, and rapidly transferring the substrate to the downstream region of a tube furnace; S2, placing PbI2 powder in the central region of the tube furnace; S3, rapidly heating the central region of the tube furnace to 380-420°C and holding it at that temperature for a period of time, while simultaneously heating the downstream region of the tube furnace to 210-240°C, and obtaining PbI2 single nanosheets after cooling. This invention utilizes the atomically flat surface of a multilayer transition metal chalcogenide as a substrate for epitaxial growth of PbI2 material, enabling the preparation of highly flat PbI2 single nanosheets. Based on the atomically flat surface of the PbI2 single nanosheet as a microcavity, a low-threshold micro-sized spin laser is realized.

Description

Technical Field

[0001] This application relates to the field of single nanosheet spin laser technology, and in particular to a method for preparing a PbI2 single nanosheet, a PbI2 single nanosheet, and a spin laser. Background Technology

[0002] Spin lasers have attracted considerable interest due to their immense potential applications in quantum communication, optical information processing, and other fields. Traditional spin lasers require the integration of photonic microcavity structures to achieve spin gain and thus spin lasing. This results in traditional spin lasers having large dimensions (typically on the order of millimeters) and necessitating a series of complex fabrication processes. Furthermore, traditional spin gain materials possess non-degenerate multiple spin levels, leading to non-unique spin excitation and a decrease in spin rate.

[0003] Recently, lead iodide (PbI2) nanosheets have been reported to exhibit excellent lasing performance and good spin characteristics, making them ideal candidate materials for microcavity-free spin lasers. However, the layered structure of PbI2 is extremely sensitive to the growth environment, thus affecting its direct growth process. PbI2 nanosheets prepared by conventional methods exhibit many structural defects (such as adsorption structures and lattice defects), resulting in surface roughness fluctuations >4.96 nm. Such large fluctuations demonstrate that conventional PbI2 nanosheets themselves do not possess a good optical microcavity, thus severely limiting their lasing performance. Summary of the Invention

[0004] This invention provides a method for preparing PbI2 single nanosheets, a PbI2 single nanosheet, and a spin laser, enabling the preparation of smooth-surfaced PbI2 single nanosheets using a simple process.

[0005] To achieve the above objectives, this invention proposes a method for preparing PbI2 single nanosheets, comprising the following steps:

[0006] S1. A multilayer transition metal chalcogenide film is deposited and grown on a substrate as a substrate, and the substrate is rapidly transferred to the downstream region of a tube furnace; wherein, multilayer refers to 6-10 layers;

[0007] S2. Place the PbI2 powder in the central area of ​​the tube furnace;

[0008] S3. Rapidly heat the central region of the tube furnace to 380-420℃ and hold it at that temperature for a period of time, while simultaneously heating the downstream region of the tube furnace to 230-250℃. After cooling, PbI2 single nanosheets are obtained. Here, rapid heating refers to a heating rate of 38-40℃ / min.

[0009] To achieve the above objectives, the present invention also proposes a PbI2 single nanosheet, which is prepared by the preparation method described above.

[0010] To achieve the above objectives, the present invention also proposes a spin laser that uses the aforementioned PbI2 single nanosheet as a microcavity structure.

[0011] The advantage of this invention over the prior art lies in:

[0012] 1. This invention uses a multilayer transition metal chalcogenide film as the direct substrate for depositing PbI2. Based on the atomically flat surface of the multilayer transition metal chalcogenide as the substrate, PbI2 material is epitaxially grown, which initially ensures that the epitaxially grown PbI2 also has atomic-level flatness.

[0013] 2. In the process of preparing PbI2 single nanosheets, the present invention rapidly heats the central region of the tube furnace in which PbI2 powder is placed, and combined with an atomically flat substrate, it is possible to finally prepare PbI2 single nanosheets with high flatness.

[0014] 3. The preparation method of the present invention uses widely available raw materials and has a simple manufacturing process, making it suitable for industrialization.

[0015] 4. The thickness of the PbI2 single nanosheets prepared by this method is 450–600 nm. Since PbI2 is a semiconductor, its band gap corresponds to an emission wavelength of approximately 510 nm. Therefore, a smaller thickness cannot confine light at this wavelength, thus preventing lasing resonance. A larger thickness, close to one or two times half the emission wavelength, can effectively confine light emission, thereby forming resonance and lowering the lasing threshold.

[0016] 5. The PbI2 single nanosheets prepared by this method have a smooth surface, thus forming an excellent microcavity structure, and can achieve a threshold below 10 μJ / cm at a low temperature of 20 K. 2 A single-nanosheet ultra-low threshold laser. This threshold is an order of magnitude lower than that of ordinary lead iodide (PbI₂) single nanosheets (reported as 250 μJ / cm²). 2 and 126.2 μJ / cm 2 Near the threshold, due to the low exciton density, the exciton spin relaxation effect decreases significantly, resulting in a spin polarization of up to 68% at the lasing wavelength. This polarization is much greater than the fluorescence spin polarization of ordinary PbI₂ single nanosheets (approximately 10%), and much greater than the spin lasing polarization of ordinary lead iodide PbI₂ single nanosheets (approximately 0%). Figure 9 As shown.

[0017] 6. The spin laser of this invention achieves spin lasing solely through a nanosheet-sized microcavity, representing the first realization of a micro-spin laser. Previously reported spin lasers required the integration of optical microcavities, resulting in typical millimeter-scale dimensions, and their fabrication processes were complex. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 The test results are for the multilayer WS2; where: a is the optical image, b is the atomic force microscopy image of the surface, and c is the atomic force microscopy line scan image. The scale bar is 5 μm. It can be seen that the thickness of the multilayer WS2 is 4.2 nm and the roughness is less than 0.3 nm.

[0020] Figure 2 The image shows the test results of the optimized PbI2 single nanosheets obtained in Example 1; where: i is an optical image with a thickness of approximately 511 nm, ii is a surface atomic force microscopy image (range 2 μm × 2 μm), and iii is an atomic force microscopy line scan image with a roughness < 0.5 nm. The scale bar is 5 μm.

[0021] Figure 3 For σ at 300K temperature - Photoexcited σ + and σ - Fluorescence polarization spectroscopy;

[0022] Figure 4 Spin polarization at temperatures of 20K-300K;

[0023] Figure 5 σ fluorescence emission in the wavelength range of 488-508 nm - and σ + Light decay curve over time;

[0024] Figure 6 The excitation energy is 16.3 μJ / cm. 2 Optimized polarization spectra and spin polarizability of lead iodide (PbI2) single nanosheets at a temperature of 20K and a wavelength range of 488-508nm.

[0025] Figure 7 The fluorescence spectra of the optimized PbI2 single nanosheets immediately after preparation and the optimized lead iodide PbI2 single nanosheets after one month of deposition are shown, along with the corresponding normalized fluorescence intensity diagrams.

[0026] Figure 8 The results are for testing ordinary PbI2 nanosheets, where: a is an optical image, b is an atomic force microscopy image of the surface (range 2μm×2μm), and c is an atomic force microscopy line scan; the scale bar is 5μm.

[0027] Figure 9 The spin lasing polarization of a typical PbI2 single nanosheet;

[0028] Figure 10 The results are as follows: (a) Raman spectra collected from ordinary and optimized lead iodide PbI2 single nanosheets, and (b) normalized Raman spectra of ordinary and optimized lead iodide PbI2 single nanosheets.

[0029] Figure 11 The results are from the fluorescence spectrum study;

[0030] Figure 12 The graphs show the fluorescence intensity as a function of the reciprocal of temperature, 1 / T; where: (a) is the fluorescence intensity of ordinary lead iodide PbI2 single nanosheets as a function of 1 / T, and (b) is the fluorescence intensity of optimized lead iodide PbI2 single nanosheets as a function of 1 / T.

[0031] Figure 13 The graph shows the relationship between fluorescence intensity and excitation power.

[0032] Figure 14 To optimize the laser threshold performance of lead iodide (PbI2) single nanosheets;

[0033] Figure 15 The results show the laser threshold performance of ordinary lead iodide (PbI2) single nanosheets. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0036] This invention proposes a method for preparing PbI2 single nanosheets, comprising the following steps:

[0037] S1. A multilayer transition metal chalcogenide film is deposited and grown on a substrate as a substrate, and the substrate is rapidly transferred to the downstream region of a tube furnace; wherein, multilayer refers to 6-10 layers;

[0038] S2. Place the PbI2 powder in the central area of ​​the tube furnace;

[0039] S3. Rapidly heat the central region of the tube furnace to 380-420℃ and hold it at that temperature for a period of time, while simultaneously heating the downstream region of the tube furnace to 230-250℃. After cooling, PbI2 single nanosheets are obtained.

[0040] Among them, a single nanosheet refers to a single-layer nanosheet.

[0041] Rapid heating refers to a heating rate of 38-40℃ / min. The purpose of rapid heating is to ensure that the source evaporates as quickly as possible to form an atmosphere.

[0042] The central region of the tube furnace used to prepare PbI2 single nanosheets is a high-temperature evaporation zone, while the downstream region is a low-temperature deposition zone.

[0043] Preferably, in step S1, the specific steps for depositing and growing a multilayer transition metal chalcogenide film are as follows: a multilayer transition metal chalcogenide film is prepared by physical vapor deposition.

[0044] Preferably, in step S1, the transition metal chalcogenide is one or more of tungsten disulfide, tungsten diselenide, molybdenum disulfide, molybdenum diselenide, or molybdenum ditelluride. Among these, PbI2 single nanosheets prepared using disulfide as a substrate have the smoothest surface.

[0045] If the transition metal chalcogenide is tungsten disulfide, when a multilayer transition metal chalcogenide film is deposited and grown in a tube furnace using physical vapor deposition, the growth temperature is 1120-1170℃ and the deposition temperature is 750-770℃.

[0046] If the transition metal chalcogenide is tungsten diselenide, when a multilayer transition metal chalcogenide film is deposited and grown in a tube furnace using physical vapor deposition, the growth temperature is 1070-1100℃ and the deposition temperature is 750-770℃.

[0047] This scheme requires two tube furnaces. The first tube furnace is used to prepare multilayer transition metal chalcogenides, and the second tube furnace is used for epitaxial growth of PbI2 on the multilayer transition metal chalcogenides. The two materials require different growth temperatures, and the two tube furnaces ensure that the growth sources of the two materials do not contaminate each other, thus avoiding defects in the materials.

[0048] Preferably, the substrate in step S1 is a silicon substrate with a silicon oxide thin film.

[0049] Preferably, step S2 further includes:

[0050] The pressure of the tube furnace system is reduced to less than 20 mtorr using a vacuum pump, while maintaining an argon flow rate of 38-40 sccm. Using argon as the carrier gas helps to obtain a smooth surface.

[0051] The present invention also proposes a PbI2 single nanosheet, which is prepared by the above preparation method. The thickness of the PbI2 single nanosheet is 450-600 nm and the roughness is less than 0.5 nm.

[0052] The present invention also proposes a spin laser that uses the above-mentioned PbI2 single nanosheet as a microcavity structure.

[0053] Example 1:

[0054] High-quality lead iodide (PbI2) single nanosheets were prepared on a 7-layer tungsten disulfide (WS2) substrate.

[0055] Step 1: Preparation of 7-layer tungsten disulfide (WS2) film.

[0056] 1. Seven tungsten disulfide (WS2) films were grown on a silicon substrate with a silicon oxide film by physical vapor deposition.

[0057] The specific preparation control conditions are as follows: the center temperature of the tube furnace is 1170℃, the downstream deposition temperature is 770℃, the atmosphere is argon, and the gas flow rate is 40 sccm.

[0058] Among them, the multilayered nature of transition metal chalcogenides gives them atomic-scale flatness. For example... Figure 1 As shown, the test results of multilayer WS2 are provided, where: a is an optical image, b is an atomic force microscopy image of the surface, and c is an atomic force microscopy line scan image. The scale bar is 5 μm. It can be seen that the thickness of multilayer WS2 is 4.2 nm (corresponding to 7 layers), and the roughness is less than 0.3 nm.

[0059] Step 2: Preparation of lead iodide (PbI2) single nanosheets.

[0060] 1. The substrate with 7 layers of tungsten disulfide (WS2) film is rapidly transferred to the downstream area of ​​another tube furnace.

[0061] 2. Place PbI2 powder in the center of a tube furnace and use carrier gas to guide a steam source to prepare high-quality lead iodide PbI2 single nanosheets.

[0062] The specific preparation control conditions are as follows: the system pressure is reduced to less than 20 mtorr by a vacuum pump; an argon flow rate of 40 sccm is maintained at the same time; the temperature is rapidly increased to 400℃ and held at this temperature for 20 minutes; after optimizing the deposition temperature to 235℃, lead iodide PbI2 single nanosheets with a thickness of 511 nm can be successfully obtained.

[0063] The optimized test results for lead iodide (PbI₂) single nanosheets are shown below. Figure 2 As shown, where: i is the optical image with a thickness of approximately 511 nm, ii is the surface atomic force microscopy image (range 2 μm × 2 μm), and iii is the atomic force microscopy line scan image with a roughness < 0.5 nm. The scale bar is 5 μm.

[0064] Taking the optimized lead iodide (PbI₂) single nanosheets from Example 1 as an example, corresponding performance tests were performed.

[0065] Test 1: Spin Property Test (Circular Polarization Experiment)

[0066] Test steps:

[0067] Step 1, place I σ+ and I σ- Defined as the detected σ + and σ - Polarized emission intensity. At σ + and σ - Under polarized excitation light, the spin polarizability can be defined as ρ = (I σ- / σ+ -Ι σ+ / σ- ) / (Ι σ+ +Ι σ- ).

[0068] Step 2: Draw the optimized lead iodide (PbI₂) single nanosheets at 300K using σ - Photoexcited σ + and σ - Polarization spectrum.

[0069] Step 3: Investigate the change in spin polarization as the temperature decreases.

[0070] Test results:

[0071] 1, σ - The main emission (black) has a measured spin polarization of ~22.1%, as shown below. Figure 3 As shown.

[0072] 2. A spin polarization of 36.3% is obtained at 20K, such as... Figure 4 As shown.

[0073] Test 2: Spin-Turning Lifetime Test

[0074] Test steps:

[0075] Step 1, such as Figure 5 As shown, the σo of fluorescence emission in the wavelength range of 488-508 nm was measured using a streak camera. - (Black) and σ + (Red) Attenuation curve. The gray dashed line represents the instrument response function (IRF) obtained from the excitation light.

[0076] Step 2: Based on these two spin polarization curves, plot the spin polarizability as a function of decay time.

[0077] Step 3: Fit the curve using a single exponential decay equation: I(t)=exp(-t / τ) F Where I(t) is the emission intensity at decay time t, and τ F It is the time constant of spin flipping.

[0078] Test results: By fitting the above curve, τ is obtained. F The time constant is 48.2 ps.

[0079] Conclusion: τ F The time constant of 48.2 ps is significantly longer than the 15 ps previously reported in ordinary lead iodide PbI₂ single nanosheets. This implies that the spin-flipping process is greatly suppressed, while optimizing the spin-flipping rate (1 / τ) of lead iodide PbI₂ single nanosheets... F The concentration of lead iodide (PbI2) nanosheets is lower than that of ordinary lead iodide (PbI2) nanosheets.

[0080] Test 3: Spin Laser Polarizability Test

[0081] Test environment: Spontaneous emission wavelength: 498.9 nm, excitation light energy: 16.3 μJ / cm² 2 Temperature: 20K

[0082] Test results: such as Figure 6 As shown, the laser wavelength is 498.9 nm, the temperature is 20 K, and the excitation light energy is 16.3 μJ / cm². 2 Under these conditions, a spin polarization of up to 62.8% can be obtained.

[0083] Taking the optimized lead iodide (PbI2) single nanosheets in Example 1 as an example, the optical stability of the optimized lead iodide (PbI2) single nanosheets during preparation was compared with that of the optimized lead iodide (PbI2) single nanosheets after deposition for one month.

[0084] The fluorescence emission spectra of the optimized lead iodide PbI2 single nanosheets during preparation and after deposition for 1 month were plotted, along with the corresponding normalized spectrum and normalized fluorescence emission intensity plot.

[0085] like Figure 7 As shown, (a) is the fluorescence emission spectrum during preparation and one month after deposition; the inset in (a) is the corresponding normalized spectrum. (b) is the normalized fluorescence emission intensity under photoexcitation.

[0086] The two fluorescence emission spectra show almost no change in peak shape and similar intensity, indicating that the optimized PbI₂ single nanosheets have good atmospheric stability. With prolonged time, the optimized lead iodide (PbI₂) single nanosheets exhibit almost constant fluorescence emission intensity, demonstrating good photoexcitation stability.

[0087] Comparative testing results: The stability study of the optimized lead iodide (PbI2) single nanosheets demonstrates the higher quality of optimized PbI2, and the deposition and photoexcitation stability of the optimized lead iodide (PbI2) single nanosheets are improved. This improvement in the quality of lead iodide (PbI2) single nanosheets will bring significant physical and photonic characteristics.

[0088] Comparative Example 1

[0089] PbI2 was directly deposited on a silicon substrate with a silicon oxide thin film using a tube furnace. PbI2 was placed at the center of the tube furnace as the source, with a center temperature of 400°C and a deposition temperature of 280°C. The center was rapidly heated to 400°C and held for 20 minutes before naturally cooling to room temperature to obtain ordinary PbI2 single nanosheets.

[0090] Test results of ordinary PbI2 single nanosheets are as follows Figure 8 As shown, (a) is an optical image with a thickness of approximately 524 nm, (b) is an atomic force microscopy image of the surface (range 2 μm × 2 μm), and (c) is an atomic force microscopy line scan image with a roughness > 4.9 nm and a scale bar of 5 μm.

[0091] The spin lasing polarization of ordinary lead iodide (PbI₂) single nanosheets (approximately 0%), such as Figure 9 As shown.

[0092] To verify the performance of the optimized lead iodide (PbI2) single nanosheets, the following tests were conducted on the optimized lead iodide (PbI2) single nanosheets in Example 1 and ordinary lead iodide (PbI2) single nanosheets, and the comparison results are as follows:

[0093] Comparative Test 1: Raman Spectroscopy Study

[0094] Raman spectra of ordinary and optimized lead iodide (PbI2) single nanosheets were plotted.

[0095] Figure 10 (a) Raman spectra collected from ordinary and optimized lead iodide (PbI₂) single nanosheets. (b) Normalized Raman spectra of ordinary and optimized lead iodide (PbI₂) single nanosheets.

[0096] E was detected in ordinary lead iodide (PbI2) single nanosheets. g (74.7cm -1 A) 1g (97.5cm -1 ) and A 2u (113.8cm -1 Three typical vibrational modes were detected. In addition to the three modes of PbI2, two vibrational modes (at 351.0 cm⁻¹) of seven-layer tungsten disulfide (WS₂) nanosheets were also detected in the optimized lead iodide (PbI₂) single nanosheets. -1 E at the location 2g and 421.8cm -1 A 1g ).

[0097] In addition, it can be observed that, compared with ordinary lead iodide PbI2 single nanosheets, the optimized lead iodide PbI2 single nanosheets show a significant blue shift in pattern, E g The peak is located at 71.8cm. -1 A 1g The peak is located at 95.5cm. -1 and A 2u The peak is located at 110.8 cm. -1 .

[0098] Comparative Test 2: PL Spectroscopy Test

[0099] Plot the fluorescence emission spectrum, such as... Figure 11 As shown.

[0100] Compared to ordinary lead iodide (PbI₂) single nanosheets, the optimized lead iodide (PbI₂) single nanosheets exhibit significantly enhanced fluorescence intensity, with a multiplication factor of approximately 6.4 times.

[0101] The full width at half maximum (FWHM) of optimized lead iodide (PbI2) nanosheets was significantly reduced from 25.1 nm (for ordinary lead iodide (PbI2) nanosheets) to 12.7 nm. Meanwhile, the fluorescence emission peak of the optimized PbI2 was blue-shifted from 515.1 nm (for ordinary PbI2) to 504.8 nm.

[0102] Comparative Test 3: Temperature-Related Experiment

[0103] like Figure 12 The figure shows a temperature-related experiment.

[0104] (a) Ordinary lead iodide PbI2 single nanosheets and (b) optimized lead iodide PbI2 single nanosheets have fluorescence intensity as a function of 1 / T, where T is the measurement temperature.

[0105] According to the equation: Where E b It is the exciton binding energy, K B It is the Boltzmann constant, and we fit the data using the Arrhenius relation.

[0106] The binding energy of ordinary PbI2 was fitted to be ~27.4 meV, which is close to the activation energy at room temperature.

[0107] The optimized PbI2 has an exciton binding energy of ~42.8 meV, which is significantly higher than the activation energy at room temperature.

[0108] Comparative Test 4: Power-Related Experiment

[0109] like Figure 13 As shown: Power-related experiment.

[0110] Double logarithmic curves of fluorescence intensity versus excitation power for ordinary lead iodide (PbI2) single nanosheets and optimized lead iodide (PbI2) single nanosheets.

[0111] The superlinear / quasi-linear power-law exponents of ordinary lead iodide (PbI2) single nanosheets and optimized lead iodide (PbI2) single nanosheets are ~1.588 and ~1.173, respectively, indicating that their quasiparticle types are free carriers / excitons.

[0112] Comparative Test 5: Laser Properties of Lead Iodide (PbI2) Single Nanosheets at 20K

[0113] The threshold power of the laser process was tested by excitation with linearly polarized pulsed laser.

[0114] Testing revealed that, at a low temperature of 20K, the threshold power of optimized lead iodide (PbI₂) single nanosheets during the laser process was 15.1 μJ / cm². 2 The half-width at half maximum (FWHM) decreased from ~2.5 nm to ~1.2 nm, while the emission intensity increased rapidly, such as... Figure 14 As shown.

[0115] In contrast, ordinary lead iodide (PbI₂) single nanosheets showed a strength of 112.4 μJ / cm² at a low temperature of 20 K. 2 The high threshold value results in a laser peak FWHM of approximately 2.4 nm. Figure 15 As shown.

[0116] Comparative test conclusions:

[0117] 1. Raman spectroscopy experiments revealed a blue-shifted Raman mode in the optimized lead iodide (PbI₂) nanosheets, suggesting that their lattice quality may be superior to that of ordinary lead iodide (PbI₂) nanosheets, since defect doping always leads to a red-shift in the Raman spectrum. Further analysis showed that the background scattering in the optimized PbI₂ Raman spectrum was lighter than that of ordinary PbI₂, indicating that the optimized lead iodide (PbI₂) nanosheets possess a higher lattice quality than ordinary lead iodide (PbI₂) nanosheets.

[0118] 2. Based on the fluorescence intensity spectrum, the radiative recombination of optimized lead iodide PbI2 single nanosheets is enhanced compared with that of ordinary lead iodide PbI2 single nanosheets.

[0119] 3. Temperature-related spectroscopy experiment ( Figure 11 The results show that the exciton characteristics in lead iodide PbI2 single nanosheets are enhanced due to the increase in exciton binding energy from 27.4 meV (ordinary PbI2) to 42.8 meV (optimized PbI2).

[0120] 4. Power-related spectroscopy experiment ( Figure 12 This indicates that, at room temperature, the dominant quasi-particle species shifts from free carriers in ordinary lead iodide PbI2 single nanosheets to excitons in optimized lead iodide PbI2 single nanosheets.

[0121] 5. The optimized lead iodide (PbI₂) single nanosheets achieved a low threshold of 15.1 μJ / cm². 2 High-performance laser.

[0122] Test equipment and parameters:

[0123] Optical properties. Raman spectroscopy was performed using a confocal microscope (WITec, alpha-300) with a 532 nm continuous-wave laser (incident power 200 μW). Steady-state fluorescence spectroscopy experiments were conducted using the same system, but with a 400 nm continuous-wave laser as the excitation light (excitation power 4 μW). Fluorescence intensity experiments were performed at different excitation powers. Temperature-dependent fluorescence spectroscopy experiments were conducted using an additional microscope cryostat system (C01-001-122, LINKPHYSICS).

[0124] Laser experiments were conducted using a confocal microscope (WITec, alpha-300). An 800 nm (80 fs pulse width, 80 MHz repetition rate) mode-locked Ti:sapphire laser (Tsunami) was amplified by a regenerative amplifier laser (Spitfire Ace100, 1 kHz) and then introduced into an optical parametric amplifier (OPA, TOPAS Prime). The 470 nm wavelength output laser from the OPA was used as the light source for the laser experiments.

[0125] TRPL experiments were conducted using a streak camera (C10910, Hamamatsu) and the same excitation light as the laser experiments. The attenuation curves are centered in the wavelength range of 488-508 nm. The excitation light was a 400 nm pulsed laser, derived from the mode-locked Ti:sapphire laser described above, which passed through a barium borate crystal to generate a second harmonic.

[0126] Circular polarization experiment. A linear polarizer and a quarter-wave plate are used in the incident beam to produce high-quality circularly polarized light. The PL signal is checked by a quarter-wave plate and a polarizer that rotates through the polarizer. The main system is the same as described above. All circular polarization experiments are performed by σ... - Optical pumping.

[0127] Example 2:

[0128] High-quality lead iodide (PbI2) single nanosheets were prepared on a 7-layer tungsten disulfide (WS2) substrate.

[0129] Step 1: Preparation of 7-layer tungsten disulfide (WS2) film.

[0130] 1. A 7-layer tungsten disulfide (WS2) film was grown by physical vapor deposition.

[0131] The specific preparation control conditions are as follows: the center temperature of the tube furnace is 1170℃, the downstream deposition temperature is 750℃, the atmosphere is argon, and the gas flow rate is 40 sccm.

[0132] Step 2: Preparation of lead iodide (PbI2) single nanosheets.

[0133] 1. The substrate with 7 layers of tungsten disulfide (WS2) film is rapidly transferred to the downstream area of ​​another tube furnace.

[0134] 2. Place PbI2 powder in the center of a tube furnace and use carrier gas to guide a steam source to prepare high-quality lead iodide PbI2 single nanosheets.

[0135] The specific preparation control conditions were as follows: the system pressure was reduced to less than 18 mtorr by a vacuum pump; an argon flow rate of 60 sccm was maintained at the same time; the temperature was rapidly increased to 390℃ and held at this temperature for 20 minutes; after optimizing the deposition temperature to 245℃, we were able to successfully obtain lead iodide PbI2 single nanosheets with a thickness of 480 nm and a roughness of <0.5 nm.

[0136] Based on Example 1, the roughness of PbI2 single nanosheets corresponding to 1 to 5 layers of WS2 is provided in Table 1.

[0137] Table 1. Roughness of PbI2 single nanosheets corresponding to WS2 layers 1–5

[0138] <![CDATA[Number of WS2 layers]]> <![CDATA[Roughness of PbI2 single nanosheet / nm]]> 1 >8.3 2 >6.6 3 >2.7 4 >2.9 5 >1.4

[0139] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing PbI2 single nanosheets, characterized in that, Includes the following steps: S1. A multilayer transition metal chalcogenide film is deposited and grown on a substrate as a substrate, and the substrate is rapidly transferred to the downstream region of a tube furnace; wherein, multilayer refers to 6-10 layers; S2. Place the PbI2 powder in the central area of ​​the tube furnace; S3. Rapidly heat the central region of the tube furnace to 380-420℃ and hold it at that temperature for a period of time, while simultaneously heating the downstream region of the tube furnace to 230-250℃. After cooling, PbI2 single nanosheets are obtained. Here, rapid heating refers to a heating rate of 38-40℃ / min.

2. The preparation method according to claim 1, characterized in that, In step S1, the specific steps for depositing and growing a multilayer transition metal chalcogenide film are as follows: a multilayer transition metal chalcogenide film is prepared by physical vapor deposition.

3. The preparation method according to claim 1, characterized in that, In step S1, the transition metal chalcogenide is one or more of tungsten disulfide, tungsten diselenide, molybdenum disulfide, molybdenum diselenide, or molybdenum ditelluride.

4. The preparation method according to claim 3, characterized in that, If the transition metal chalcogenide is tungsten disulfide, when a multilayer transition metal chalcogenide film is deposited and grown in a tube furnace using physical vapor deposition, the growth temperature is 1120-1170℃ and the deposition temperature is 750-770℃.

5. The preparation method according to claim 3, characterized in that, If the transition metal chalcogenide is tungsten diselenide, when a multilayer transition metal chalcogenide film is deposited and grown in a tube furnace using physical vapor deposition, the growth temperature is 1070-1100℃ and the deposition temperature is 750-770℃.

6. The preparation method according to claim 1, characterized in that, Step S2 also includes: The pressure of the tube furnace system is reduced to less than 20 mtorr by a vacuum pump, while maintaining an argon flow rate of 38-40 sccm.

7. The preparation method according to claim 1, characterized in that, The substrate in step S1 is a silicon substrate with a silicon oxide thin film.

8. A PbI2 single nanosheet, characterized in that, The PbI2 single nanosheets are prepared by the preparation method described in any one of claims 1 to 7; the thickness of the single nanosheets is 450 to 600 nm, and the roughness is less than 0.5 nm.

9. A spin laser, characterized in that, The PbI2 single nanosheets prepared by any one of the preparation methods described in claims 1 to 7, or the PbI2 single nanosheets as described in claim 8, are used as microcavity structures.

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