Photoacoustic cell with enhanced photoacoustic spectral signal and manufacturing method thereof

Abstract

The invention relates to the technical field of photoacoustic spectrum gas detection, in particular to a photoacoustic cell with enhanced photoacoustic spectrum signals and a manufacturing method, and the photoacoustic cell is characterized in that a gold coating is deposited on the surface of an inner cavity of the photoacoustic cell; the gold coating is used for reducing thermal viscosity sound loss of gas. In order to solve the problem that the sensitivity of a sensor is reduced due to the fact that a cavity of a photoacoustic cell in the prior art has high thermal viscosity acoustic loss, in the scheme, a gold coating is added to the surface of an inner cavity of the photoacoustic cell, good roughness of the inner cavity of the photoacoustic cell is achieved through good thermal conductivity and smooth surface characteristics of gold, and the sensitivity of the sensor is improved. And meanwhile, heat dissipation is facilitated, so that thermal viscosity sound loss is effectively reduced, and the problems that relatively weak photoacoustic signals are attenuated too fast and the signal-to-noise ratio is low in a high-sensitivity scene are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photoacoustic spectroscopy gas detection, in particular to a photoacoustic cell for enhancing photoacoustic spectroscopy signal and a manufacturing method thereof. BACKGROUND

[0002] Photoacoustic spectroscopy (PAS) is a high-sensitivity analysis method based on the photoacoustic effect, widely used in gas analysis, environmental monitoring, pollutant detection and other fields. Its basic principle is that when light (usually laser) irradiates gas molecules or solid surfaces, light energy is absorbed and converted into heat energy, causing local temperature changes, further exciting sound waves. By detecting these sound waves, information related to the intensity, frequency, etc. of the light source can be obtained, thereby realizing the analysis of the sample.

[0003] For example, Chinese patent CN202122197036.1 discloses a photoacoustic cell, which comprises a photoacoustic cell body, a first buffer chamber, a second buffer chamber and a resonance cavity are arranged in the photoacoustic cell body, the first buffer chamber and the second buffer chamber are communicated through the resonance cavity, an air inlet and a first window are arranged on the first buffer chamber, an air outlet and a second window are arranged on the second buffer chamber, the first window is provided with a first window piece, the incident light through the first window piece passes through the first buffer chamber, the resonance cavity and the second buffer chamber in turn, and is reflected from the inner wall of the second window back to the inner wall of the resonance cavity and the second buffer chamber, or directly emitted from the second window; a microphone is arranged on the resonance cavity; the inside of the photoacoustic cell body is a sealed cavity; a pressure sensor is arranged at the first buffer chamber, and a thermocouple is arranged at the second buffer chamber. The photoacoustic cell structure provided by the utility model can ensure the same experimental conditions, monitor the pressure and temperature parameters in the photoacoustic cell in real time, and facilitate the analysis of the influence of pressure and temperature on the photoacoustic detection characteristics.

[0004] However, in the actual implementation process, the inventors found that the intensity of the photoacoustic spectroscopy signal and its signal-to-noise ratio (SNR) are affected by multiple factors, among which the thermal viscous sound loss is a key factor. The thermal viscous sound loss is caused by the interaction between gas molecules and the inner surface of the photoacoustic cell, resulting in energy attenuation of the sound wave during propagation. Traditional photoacoustic cells are mostly made of metal materials such as aluminum and brass, which have rough surfaces and are prone to form oxide films or impurities, further enhancing the interaction between gas molecules and the cell wall, resulting in serious sound loss and limiting the improvement of signal-to-noise ratio in high-sensitivity applications. SUMMARY

[0005] In view of the above problems existing in the prior art, the present application provides a photoacoustic cell for enhancing photoacoustic spectroscopy signal;

[0006] On the other hand, a manufacturing method for manufacturing the photoacoustic cell is also provided.

[0007] The specific technical solutions are as follows:

[0008] A photoacoustic cell for enhancing photoacoustic spectrum signals, wherein a gold coating is deposited on the inner cavity surface of the photoacoustic cell.

[0009] The gold coating is used to reduce the thermal viscous sound loss of the gas.

[0010] In another aspect, the thickness of the gold coating is between 50-200nm.

[0011] The gold coating has a nanocrystalline structure with (111) preferred orientation.

[0012] The average grain size of the gold coating is 20-50nm.

[0013] The grain boundary density of the gold coating is ≤3×104μm -2 .

[0014] In another aspect, the photoacoustic cell is a brass substrate.

[0015] A titanium transition layer is deposited on the brass substrate.

[0016] A gold coating is deposited on the titanium transition layer.

[0017] In another aspect, the photoacoustic cell is a brass substrate.

[0018] An aluminum oxide interface layer is formed on the surface of the brass substrate.

[0019] A graphene base layer is deposited above the aluminum oxide interface layer.

[0020] A gold coating is deposited above the graphene base layer.

[0021] A method for manufacturing a photoacoustic cell, used to manufacture the photoacoustic cell described above, comprising:

[0022] Step S1: polishing the inner surface of the photoacoustic cell substrate to make the surface roughness of the inner cavity of the photoacoustic cell substrate reach a predetermined roughness.

[0023] Step S2: vapor deposition is performed on the photoacoustic cell substrate to deposit a gold coating on the inner cavity surface of the photoacoustic cell substrate to form a photoacoustic cell.

[0024] In another aspect, step S1 comprises:

[0025] Step S11: cleaning the inner surface of the photoacoustic cell substrate to obtain a pre-cleaned substrate.

[0026] Step S12: polishing the inner surface of the photoacoustic cell substrate using a mechanical polishing method until the predetermined roughness is reached.

[0027] In another aspect, step S2 comprises:

[0028] Step S21: Put the photoacoustic cell substrate into the vacuum chamber and perform vacuuming;

[0029] Step S22: Electron beam heats the gold target to perform physical vapor deposition on the surface of the photoacoustic cell substrate to form a gold coating;

[0030] Step S23: Naturally cool the photoacoustic cell, restore the air pressure when the cooling is completed, and take it out.

[0031] On the other hand, after performing step S22, before performing step S23, it includes:

[0032] In-situ annealing treatment is performed on the gold coating;

[0033] The annealing temperature is between 200-250℃, the annealing time is 30 minutes, and the vacuum degree is maintained.

[0034] On the other hand, after performing step S1, before performing step S2, it includes:

[0035] Step A1: Depositing a titanium transition layer on the inner surface of the photoacoustic cell substrate.

[0036] On the other hand, after performing step S1, before performing step S2, it includes:

[0037] Step B1: Forming an alumina interface layer on the inner surface of the photoacoustic cell substrate;

[0038] Step B2: Forming a graphene base layer above the alumina interface layer.

[0039] On the other hand, in step S2, nano-particle gradient embedding gold coating is performed on the graphene base layer by electrochemical deposition method.

[0040] The above technical solution has the following advantages or beneficial effects:

[0041] In view of the problem that the chamber of the photoacoustic cell in the prior art has high thermal viscous sound loss, thereby causing the sensitivity of the sensor to decrease, in the present scheme, a gold coating is added to the surface of the inner cavity of the photoacoustic cell, and the good thermal conductivity and smooth surface characteristics of gold are used to achieve good roughness of the inner cavity of the photoacoustic cell, which is also beneficial to heat dissipation, thereby effectively reducing the thermal viscous sound loss, and avoiding the problem that the relatively weak photoacoustic signal attenuates too fast and the signal-to-noise ratio is low in the high-sensitivity scenario. BRIEF DESCRIPTION OF DRAWINGS

[0042] The embodiments of the present application are described more fully with reference to the accompanying drawings. However, the accompanying drawings are only used for illustration and explanation, and do not constitute a limitation on the scope of the present application.

[0043] Figure 1 Fig. 1 is a schematic diagram of the whole embodiment of the present application;

[0044] Figure 2 Fig. 2 is a schematic diagram of the method in the embodiment of the present application;

[0045] Figure 3 Fig. 3 is a schematic diagram of step S1 in the embodiment of the present application;

[0046] Figure 4 Fig. 4 is a schematic diagram of step S11 in the embodiment of the present application;

[0047] Figure 5 Fig. 5 is a schematic diagram of step S2 in the embodiment of the present application;

[0048] Figure 6 Fig. 6 is a schematic diagram of step A1 in the embodiment of the present application;

[0049] Figure 7 Fig. 7 is a schematic diagram of step B1 in the embodiment of the present application;

[0050] Figure 8 Fig. 8 is a schematic diagram of step S3 in the embodiment of the present application. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0052] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0053] The present application will be further described below with reference to the drawings and specific embodiments, but not as a limitation of the present application.

[0054] The present application includes:

[0055] A photoacoustic cell for enhancing photoacoustic spectrum signal, wherein a gold coating 3 is deposited on the inner cavity surface of the photoacoustic cell.

[0056] The gold coating 3 is used to reduce the thermal viscous sound loss of the gas.

[0057] Specifically, in order to solve the problem that the cavity of the photoacoustic cell in the prior art has high thermal viscous sound loss, thereby reducing the sensitivity of the sensor, a gold coating 3 is added to the surface of the inner cavity of the photoacoustic cell, the good thermal conductivity and smooth surface characteristics of gold are used to achieve good roughness of the inner cavity of the photoacoustic cell, which is beneficial to heat dissipation, thereby effectively reducing the thermal viscous sound loss, and avoiding the problem that the relatively weak photoacoustic signal is attenuated too fast and the signal-to-noise ratio is low in the high-sensitivity scenario.

[0058] Specifically, as shown in Figure 1 The photoacoustic cell includes a photoacoustic cell base 1, and a pair of buffer cavities 4 are machined at both ends of the photoacoustic cell base 1. The central regions of the two buffer cavities 4 are connected through a through resonant cavity 5.

[0059] The outer side of the buffer cavity 4 is also provided with an end cap 6.

[0060] Generally, a microphone or other equivalent device is arranged in the resonant cavity 5 of the photoacoustic cell for collecting sound signals generated by the photoacoustic effect;

[0061] The buffer cavity 4 and the resonant cavity 5 are used to introduce the gas to be detected.

[0062] The end cap 6 is usually used to set up a light source, and a laser beam reaches the opposite buffer cavity 4 through the buffer cavity 4 and the resonant cavity 5, and is emitted through the window reserved on the end cap 6 or is reflected in the buffer cavity 4.

[0063] The gas to be detected absorbs light energy and generates sound signals, which are amplified in the resonant cavity and collected by the microphone.

[0064] The inner cavity of the photoacoustic cell mainly refers to the buffer cavity 4 and the resonant cavity 5, which are usually machined from a metal base. Since the base material is composed of metal, the surface is easily oxidized after machining, thereby forming an uneven oxide layer. At the same time, due to the limitation of actual machining conditions, the inner cavity surface 3 is still rough to a certain extent after polishing.

[0065] When the gas to be detected is injected into the buffer cavity 4 and the resonant cavity 5, the part of the gas close to the inner surface of the buffer cavity 4 and the resonant cavity 5 will produce a viscous effect due to the roughness of the inner surface, thereby causing the part of the gas molecules to be delayed near the inner surface, forming a viscous boundary layer.

[0066] Since the gas in the viscous boundary layer and the thermal boundary layer has a tendency to keep the original position, the sound wave generated by the photoacoustic effect is more likely to attenuate near the boundary layer, thereby further weakening the signal intensity at the microphone, making the amplitude of the sound signal actually sampled by the microphone closer to the system noise, and causing the signal-to-noise ratio of the sound signal to decrease.

[0067] To solve the problem, a gold coating 3 is introduced on the inner cavity surface of the photoacoustic cell. Since the gold coating 3 has good surface properties, by controlling the thickness of the gold coating 3, the rough part on the inner cavity can be better filled;

[0068] Meanwhile, the gold coating 3 can avoid the formation of an oxide layer, further reducing the surface roughness;

[0069] Further, the gold coating 3 can achieve good thermal conductivity, thereby reducing the gradient of the thermal boundary layer.

[0070] Through the combination of the above three effects, the thermal boundary layer and viscous boundary layer effects are effectively weakened, the sound loss of this part is reduced, and the sound signal strength collected by the microphone is improved.

[0071] In one embodiment, the thickness of the gold coating is between 50-200nm.

[0072] Specifically, to achieve better surface smoothness, in the embodiment, through research on the surface processing technology of the inner cavity, it is determined that when the thickness of the gold coating 3 is between 50-200nm, the rough surface of the photoacoustic cell substrate caused by mechanical processing and oxidation can be better filled, and a continuous smooth surface is formed above the substrate, thereby effectively weakening the thermal boundary layer and viscous boundary layer effects, reducing the sound loss of this part, and improving the sound signal strength collected by the microphone.

[0073] In one embodiment, the photoacoustic cell is a brass substrate;

[0074] The gold coating is deposited on the surface of the brass substrate.

[0075] Specifically, to achieve good thermal conductivity and roughness, in the embodiment, brass is selected as the substrate material of the photoacoustic cell.

[0076] During processing, first, the buffer cavity 4 and the resonance cavity 5 are machined from the brass substrate material, and then the inner surfaces of the buffer cavity 4 and the resonance cavity 5 are polished to form relatively smooth inner surfaces.

[0077] Subsequently, before starting to deposit the coating, the oxide layer on the inner surface is removed in advance by acid washing or other methods to further reduce the surface roughness, and then a coating is formed on the inner surface by evaporation, vapor deposition or other equivalent processes, and the thickness is gradually increased to the predetermined thickness, thereby forming a continuous smooth gold coating 3, thereby effectively weakening the thermal boundary layer and viscous boundary layer effects, reducing the sound loss of this part, and improving the sound signal strength collected by the microphone.

[0078] In one embodiment, the gold coating is a nanocrystalline structure with (111) preferred orientation;

[0079] The average grain size of the gold coating is 20-50 nm;

[0080] The grain boundary density of the gold coating is ≤3×104μm -2 .

[0081] Specifically, to achieve a better smooth surface, in the embodiment, firstly, the average grain size and the grain boundary density of the gold coating are controlled to form a relatively dense gold coating, and the structure of the gold coating is controlled to be a nanocrystalline structure with (111) preferred orientation, thereby further improving the acoustic performance of the surface of the gold coating to achieve a good reflection effect.

[0082] In one embodiment, a titanium transition layer is also deposited on the brass substrate;

[0083] The gold coating is deposited on the titanium transition layer after the titanium transition layer is deposited.

[0084] Specifically, considering that the brass material substrate itself is prone to scratches during mechanical processing, and the adhesion of gold on the brass material is poor. Therefore, to achieve better coating smoothness and coating firmness, in the embodiment, a titanium transition layer with a certain thickness is also deposited on the brass substrate, the surface of the brass substrate is filled through the smooth surface of the titanium transition layer, and then the gold coating is deposited thereon to achieve better surface smoothness.

[0085] The thickness of the titanium transition layer is preferably about 5 nm.

[0086] In another embodiment, the photoacoustic cell is a brass substrate;

[0087] The surface of the brass substrate forms an aluminum oxide interface layer;

[0088] A graphene base layer is deposited on the aluminum oxide interface layer;

[0089] The gold coating is deposited on the graphene base layer.

[0090] The graphene base layer and the gold coating form a graphene-gold nanocomposite coating to replace the pure gold coating. The coating combines the ultrahigh thermal conductivity (theoretical value is more than 5000 W / mK) of graphene and the density of the gold layer, which can further reduce the surface roughness, improve the thermal conductivity efficiency and mechanical strength, and at the same time achieve better signal-to-noise ratio improvement and durability.

[0091] The graphene-gold nano-composite coating takes chemically reduced graphene (rGO) as a matrix, embeds gold nanoparticles to form a multi-layer heterostructure. Its advantages include: graphene provides ultra-high thermal conductivity (measured value >4000 W / mK), reduces thermal viscous acoustic loss more thoroughly; gold nanoparticles enhance the compactness and adhesion of the coating, and the surface roughness can be reduced to below 0.05 μm; the cost of graphene material is lower than that of pure gold, which is suitable for photoacoustic cell substrates (such as brass or aluminum alloy).

[0092] A method for manufacturing a photoacoustic cell, for manufacturing the photoacoustic cell as shown in Figure 2 , comprising:

[0093] Step S1: polishing the inner surface of the photoacoustic cell substrate to make the surface roughness of the inner cavity of the photoacoustic cell substrate reach a predetermined roughness;

[0094] Step S2: vapor deposition on the photoacoustic cell substrate to deposit a gold coating on the surface of the inner cavity of the photoacoustic cell substrate to form a photoacoustic cell.

[0095] Specifically, to achieve better preparation effect of the photoacoustic cell, in the embodiment, first, the copper workpiece is cut by a mechanical machining method, a pair of buffer cavities 4 are formed on the predetermined position of the workpiece, and then a resonance cavity 5 is obtained in the middle part of the buffer cavity 4.

[0096] For the buffer cavity 4 and the resonance cavity 5, the inner surface can be polished by grinding, sandblasting, etc. to make the surface roughness of the inner cavity of the photoacoustic cell substrate reach a predetermined roughness.

[0097] Generally, the roughness of the inner surface needs to be reduced to below 0.2 μm to provide a relatively uniform inner surface substrate for the subsequent deposition process.

[0098] Then, the photoacoustic cell substrate is subjected to vapor deposition to grow a gold coating on the surface of the inner cavity.

[0099] During the deposition process, the microstructure and surface flatness of the gold layer are controlled by adjusting the deposition temperature, power and deposition time to obtain a gold coating with smooth surface and good thermal conductivity.

[0100] When the gold coating reaches a predetermined thickness, the photoacoustic cell is taken out to achieve better preparation effect.

[0101] In one embodiment, as shown in Figure 3 , step S1 comprises:

[0102] Step S11: cleaning the inner surface of the photoacoustic cell substrate to obtain a pre-cleaned substrate;

[0103] Step S12: polishing the inner surface of the photoacoustic cell base by mechanical polishing until a predetermined roughness is reached.

[0104] Step S13: ultrasonic cleaning of the photoacoustic cell base.

[0105] Specifically, to achieve a better polishing effect, in the embodiment, for the photoacoustic cell base obtained by mechanical processing, the inner surface of the photoacoustic cell base is first cleaned to obtain a pre-cleaned base. The cleaning step is used to remove metal chips, impurities and oxides and the like remaining on the inner surface during processing.

[0106] Subsequently, the inner surface of the photoacoustic cell base is polished by mechanical polishing until a predetermined roughness is reached.

[0107] Finally, the photoacoustic cell base is ultrasonically cleaned to remove remaining contaminants and impurities, so that the coating can be firmly combined with the surface.

[0108] In one embodiment, the predetermined roughness is below 0.2 μm.

[0109] Specifically, to achieve better processing efficiency and facilitate subsequent deposition of a gold coating, in the embodiment, according to relevant process parameters, it is determined that setting the predetermined roughness to be below 0.2 μm during mechanical polishing can achieve a relatively smooth inner surface and facilitate uniform deposition of the subsequent gold layer.

[0110] In one embodiment, the predetermined roughness of the surface of the photoacoustic cell is 0.18 μm.

[0111] In one embodiment, as shown in FIG. 1, step S11 includes: Figure 4

[0112] Step S111: acid pickling of the photoacoustic cell base to remove the oxide layer;

[0113] Step S112: plasma cleaning of the photoacoustic cell base to remove oil and microparticles.

[0114] Specifically, to achieve a better cleaning effect, in the embodiment, for the photoacoustic cell base obtained by mechanical processing, the oxide layer is first removed by acid pickling. The acid solution is determined according to the alloy material of the base and the type of the oxide layer, and the acid pickling time is adjusted according to the thickness of the oxide layer, so as to remove the oxide layer and impurities on the surface of the brass base.

[0115] Subsequently, the photoacoustic cell base is plasma cleaned to remove oil and microparticles to obtain a pre-cleaned base. Specifically, the photoacoustic cell base is placed in a specific cleaning chamber, then gas is introduced and ionized to effectively remove oil and microparticle contaminants.

[0116] ​In one embodiment, as shown in FIG. 2, step S2 comprises: Figure 5

[0117] Step S21: Put the photoacoustic cell substrate into the vacuum chamber and perform vacuuming;

[0118] Step S22: Use an electron beam to heat the gold target to perform physical vapor deposition on the surface of the photoacoustic cell substrate to form a gold coating;

[0119] Step S23: Naturally cool the photoacoustic cell, restore the atmospheric pressure after the cooling is completed, and take out the photoacoustic cell.

[0120] Specifically, to achieve a more uniform deposition effect, in the present embodiment, the photoacoustic cell substrate is first put into the vacuum chamber of the physical vapor deposition device and vacuumed, and the vacuum degree should be in a high vacuum degree of 10-6 to 10-7 Torr.

[0121] Then, the gold target is heated using an electron beam source, so that it evaporates into metal vapor under the action of the electron beam and is uniformly deposited on the inner surface of the photoacoustic cell.

[0122] To control the deposition rate, the power of the electron beam and the metal vapor flow are adjusted to ensure that the deposition rate is 1 nm / s, thereby achieving a uniform deposition effect.

[0123] During the deposition process, the deposition time is controlled for about a few minutes to ensure that the thickness of the gold coating reaches the predetermined thickness, so as to achieve a good surface flatness.

[0124] During the deposition process, monitoring of the deposition process can also be introduced to ensure the uniformity of the formed coating.

[0125] When the deposition process is completed, the photoacoustic cell is cooled in a vacuum environment, and after the cooling is completed, the atmospheric pressure is gradually restored, and the photoacoustic cell on which the gold layer deposition has been completed is taken out.

[0126] In one embodiment, to achieve a better deposition effect, a gradient deposition process is also added during step S22 to form a specific gold coating.

[0127] Gradient deposition refers to a deposition process in which the deposition is performed in at least two stages, and the deposition rate is different in each stage. For example, in the first stage, a 50 nm thick gold layer is deposited at a high rate of 5 nm / s, and then in the second stage, the deposition rate is reduced to 0.5 nm / s to continue to deposit a 50 nm thick gold layer, thereby reducing the defects that may be caused on the surface of the gold coating by reducing the deposition rate.

[0128] In one embodiment, to achieve better coating stability, an in-situ annealing process is further included after step S22 is performed and before step S23 is performed. ​

[0129] The annealing temperature is between 200-250℃, the annealing time is 30 minutes, and the vacuum degree is maintained.

[0130] The better firmness of the gold coating is achieved by the in-situ annealing process.

[0131] In one embodiment, to achieve better coating smoothness and firmness, as shown, after performing step S1, before performing step S2, the following is included: Figure 5

[0132] Step A1: deposit a titanium transition layer on the inner surface of the photoacoustic cell substrate.

[0133] Specifically, considering that the brass material substrate itself is prone to scratches during machining, and the adhesion of gold on the brass material is poor. In order to achieve better coating smoothness and firmness, in this embodiment, a certain thickness of titanium transition layer is deposited on the brass substrate, and the smooth surface of the titanium transition layer fills the surface of the brass substrate, and then the gold coating is deposited on top, achieving better surface smoothness.

[0134] In another embodiment of the graphene-gold composite coating, as shown, after performing step S1, before performing step S2, the following is included: Figure 6

[0135] Step B1: form an aluminum oxide interface layer on the inner surface of the photoacoustic cell substrate.

[0136] Step B2: form a graphene base layer on top of the aluminum oxide interface layer.

[0137] Then in step S2, nano-particle gradient embedding gold coating is performed on the graphene base layer by electrochemical deposition method.

[0138] Specifically, in step B1, an atomic layer deposition (ALD) is used to generate a 1nm aluminum oxide interface layer on the polished surface to enhance the adhesion of the coating. Trimethylaluminum (TMA) and deionized water (H2O) are used to perform 50 deposition cycles (single cycle: TMA pulse 0.1s / purge 60s→H2O pulse 0.1s / purge 60s) at a vacuum degree ≤10 -6 Torr and a temperature of 150±5℃,

[0139] In step B2, for the graphene base layer, chemical vapor deposition (CVD) is used in a vacuum chamber (vacuum degree 10 -6 Torr) to introduce CH4 / H2 mixed gas (flow ratio 1:2) at 800℃ for 5 minutes to form a single-layer graphene (thickness 0.34nm);

[0140] ​​For gold coating, gold layer is deposited on the graphene surface by electrochemical deposition method, and the electrolyte is KAu(CN)2:

[0141] First stage: current density 20 mA / cm 2 , deposit 50 nm gold particle layer (rate 5 nm / s);

[0142] Second stage: current density 5 mA / cm 2 , deposit to a total thickness of 100 nm (rate 0.5 nm / s), grain size 10-30 nm.

[0143] Finally, two-step annealing is performed in a vacuum environment of 10 -6 Torr.

[0144] First step: annealing at 200°C for 10 minutes to eliminate stress;

[0145] Second step: annealing at 300°C for 20 minutes to form a (111) preferentially oriented composite structure.

[0146] In one embodiment, as Figure 7 shown, after performing step S2, further comprising:

[0147] Step S3: Assemble the optoacoustic cell and peripheral devices to obtain a sensor.

[0148] After preparation is completed, the optoacoustic cell is assembled with end caps, light sources, microphones, and peripheral circuits, etc. components to form a complete sensor.

[0149] Place the optoacoustic cell in a gas analysis environment and excite the optoacoustic signal by the photoacoustic effect. When performing the experiment, the laser light source is irradiated on the gas sample in the optoacoustic cell to excite the optoacoustic signal. The experimental results show that the signal intensity of the optoacoustic cell after gold coating treatment is significantly enhanced, and the thermal viscous sound loss is effectively reduced. Compared with the uncoated optoacoustic cell, the signal-to-noise ratio is increased by about 30%. This result shows that the deposition of the gold layer effectively improves the quality of the optoacoustic signal and the sensitivity of the detection system.

[0150] This embodiment 1 takes a resonant optoacoustic cell for a gas analysis sensor system as an example to describe in detail the basic process of gold layer deposition according to the method of the present application.

[0151] 1. Optoacoustic cell substrate pretreatment:

[0152] The optoacoustic cell is made of brass. The brass substrate has good structural strength and thermal conductivity, and serves as the main framework of the optoacoustic cell. The inner surface of the optoacoustic cell is rough after general mechanical processing, and the thermal viscous sound loss is large.

[0153] Before the gold layer deposition, the inner surface of the photoacoustic cell is first cleaned thoroughly to remove possible oil stains, oxides and other impurities. The specific operation steps include: using acid washing method to remove the oxide layer and impurities on the surface of the brass substrate; using plasma cleaning technology to further clean the inner surface of the photoacoustic cell to remove oil stains and small particles; using mechanical polishing method to polish the inner surface of the photoacoustic cell to remove small surface roughness. Through the polishing process, the roughness of the inner surface of the photoacoustic cell is reduced to 0.18 μm. The polishing step helps to smooth the small irregularities on the surface, providing an ideal substrate for uniform deposition of the gold layer; finally, through ultrasonic cleaning, further ensure that the surface is free of any contaminants, and ensure that the gold layer can be uniformly deposited and firmly combined with the inner surface of the photoacoustic cell.

[0154] 2. Evaporative deposition of gold coating:

[0155] The pre-processed photoacoustic cell substrate is placed in a physical vapor deposition (PVD) device for deposition of a gold thin film. First, the photoacoustic cell substrate is placed in a vacuum chamber and pumped to a high vacuum degree of 10-6 Torr. Then, the gold target is heated using an electron beam source to evaporate it into metal vapor under the action of the electron beam, which is uniformly deposited on the inner surface of the photoacoustic cell. The power of the electron beam and the metal vapor flow are adjusted to control the deposition rate to be 1 nm / s. The deposition is terminated when the thickness of the gold coating reaches about 100 nm, thereby ensuring that the gold layer has good thermal conductivity and surface flatness. The entire process is monitored by monitoring the deposition rate and total amount to ensure the uniformity of the gold coating and meet the design requirements.

[0156] 3. Cooling and restoring atmospheric pressure:

[0157] After the deposition process is completed, the photoacoustic cell is placed in a vacuum environment for natural cooling. After the cooling process is completed, the atmospheric pressure is gradually restored, and the photoacoustic cell with the deposited gold layer is taken out.

[0158] 4. Assembly of photoacoustic cell:

[0159] The inner surface of the photoacoustic cell after deposition of the gold layer has excellent thermal conductivity and surface smoothness. The photoacoustic cell is assembled into a complete photoacoustic sensor device, and the structure of the photoacoustic cell is shown in Figure 1 .

[0160] 5. Experimental verification:

[0161] The photoacoustic cell is placed in a gas analysis environment to excite photoacoustic signals by photoacoustic effect. In the experiment, the laser light source irradiates on the gas sample in the photoacoustic cell to excite photoacoustic signals. The experimental results show that the signal intensity of the photoacoustic cell after gold coating treatment is obviously enhanced, and the thermal viscous sound loss is effectively reduced. Compared with the uncoated photoacoustic cell, the signal-to-noise ratio is improved by about 30%. This result shows that the deposition of gold layer effectively improves the quality of photoacoustic signal and the sensitivity of detection system.

[0162] Embodiment 2 takes a resonant photoacoustic cell for a gas analysis sensor system as an example, and based on the gold layer deposition basic process of embodiment 1, the gold layer deposition optimization process with gradient deposition and annealing is described in detail.

[0163] 1. Titanium transition layer deposition:

[0164] A titanium transition layer is prepared on the pretreated photoacoustic cell substrate by using a magnetron sputtering technique. Under the conditions of 20 sccm argon flow and 100 W radio frequency power, the titanium target sputtering process is precisely controlled. Titanium atoms are deposited on the photoacoustic cell substrate at a uniform rate to form a dense transition layer with a thickness of 5 nm.

[0165] 2. Gradient deposition of gold layer:

[0166] The gold layer deposition adopts a phased power regulation strategy: in the first phase, the electron beam evaporation source is driven at a high power of 9 kW to quickly melt the gold target and deposit a 50 nm thick gold layer at a high rate of 5 nm / s to form a dense substrate structure; in the second phase, the power is switched to a low power of 4 kW to reduce the deposition rate to 0.5 nm / s, and continue to deposit a 50 nm gold layer.

[0167] 3. In-situ annealing:

[0168] The deposited gold layer is subjected to in-situ annealing at 230°C in a high vacuum environment of 10-6 Torr for 30 minutes.

[0169] 4. Performance verification:

[0170] Experimental verification shows that the surface roughness of the gold layer is reduced to 0.08 μm, the (111) crystal plane orientation ratio is 85%, the coating adhesion is 55 MPa, and the photoacoustic signal test shows that the signal-to-noise ratio of the system is improved by 45% compared with the uncoated substrate. The acoustic performance improvement effect of the photoacoustic cell under different coating processes and the properties of the gold film are shown in Table 1:

[0171] Table 1 Signal-to-noise ratio, gold film surface roughness and adhesion under different coating processes

[0172]

[0173] The experimental results show that compared with the basic process, the optimized process has better performance in improving signal-to-noise ratio, reducing surface roughness and enhancing adhesion, and is a more effective coating technology.

[0174] The embodiment details how to improve the performance of the photoacoustic cell through gold layer deposition technology, and provides a technical solution for effectively reducing thermal adhesion sound loss and improving signal-to-noise ratio based on titanium transition layer design, gradient deposition control and in-situ annealing process.

[0175] Example 3 uses the same resonant photoacoustic cell (brass substrate) and test conditions as Example 2, and the acoustic performance improvement effect of the graphene-gold composite coating of the photoacoustic cell and the coating properties are shown in Table 2:

[0176] Table 2 Signal-to-noise ratio, gold film surface roughness and adhesion under different coating types

[0177]

[0178] The experimental results show that compared with the pure gold coating, the graphene-gold nano composite coating has more significant signal-to-noise ratio, lower surface roughness and greater adhesion, and is a more effective coating technology.

[0179] The above is only the preferred embodiment of the present application, and does not limit the implementation and protection scope of the present application. For those skilled in the art, it should be realized that any equivalent replacement and obvious changes made by applying the contents of the present application and the drawings should be included in the protection scope of the present application.

[0180] Although the present application includes many specific implementation details, these should not be interpreted as limiting the scope or the claimed scope of any disclosure, but mainly for describing the features of the specific embodiments of the particular disclosure. Some features described in multiple embodiments within the present application can also be implemented in a single embodiment. On the other hand, various features described in a single embodiment can also be implemented separately in multiple embodiments or in any suitable sub-combination. In addition, although the features can function as in some combinations and even originally so claimed, one or more features from the claimed combination can be removed from the combination in some cases, and the claimed combination can be directed to a sub-combination or a variation of a sub-combination.

Claims

1. A photoacoustic cell for photoacoustic spectroscopy signal enhancement, characterized in that, A gold coating is deposited on the inner cavity surface of the photoacoustic cell; The gold coating is used to reduce the thermal viscous sound loss of the gas.

2. The photoacoustic cell of claim 1, wherein, The thickness of the gold coating is between 50-200nm; The gold coating is nanocrystalline structure with (111) preferred orientation; The average grain size of the gold coating is 20-50nm; The gold coating has a grain boundary density of < 3 x 104μm -2 .

3. The photoacoustic cell of claim 1, wherein, The photoacoustic cell is a brass substrate; A titanium transition layer is deposited on the brass substrate; The gold coating is deposited on the titanium transition layer.

4. The photoacoustic cell of claim 1, wherein, The photoacoustic cell is a brass substrate; An aluminum oxide interface layer is formed on the surface of the brass substrate; A graphene base layer is deposited above the aluminum oxide interface layer; The gold coating is deposited above the graphene base layer.

5. A method of fabricating a photoacoustic cell, the method comprising: A method for making the photoacoustic cell of any one of claims 1-4, comprising: Step S1: polishing the inner surface of the photoacoustic cell substrate so that the surface roughness of the inner cavity of the photoacoustic cell substrate reaches a predetermined roughness; Step S2: vapor depositing a gold coating on the inner cavity surface of the photoacoustic cell substrate to form the photoacoustic cell.

6. The method of manufacturing according to claim 5, wherein, The step S1 comprises: Step S11: cleaning the inner surface of the photoacoustic cell substrate to obtain a pre-cleaned substrate; Step S12: polishing the inner surface of the photoacoustic cell substrate using a mechanical polishing method until the predetermined roughness is reached.

7. The method of manufacturing according to claim 5, wherein, The step S2 comprises: Step S21: placing the photoacoustic cell substrate into a vacuum chamber and performing vacuum pumping; Step S22: heating a gold target using an electron beam to physically vapor deposit the gold coating on the surface of the photoacoustic cell substrate; Step S23: naturally cooling the photoacoustic cell, and when the cooling is completed, restoring the air pressure and taking out.

8. The method of manufacturing according to claim 6, wherein, After performing the step S22 and before performing the step S23, comprising: In-situ annealing treatment of the gold coating; The annealing temperature is between 200-250℃, the annealing time is 30 minutes, and the vacuum degree is maintained.

9. The method of manufacturing of claim 5, wherein, After performing the step S1 and before performing the step S2, comprising: Step A1: depositing a titanium transition layer on the inner surface of the photoacoustic cell substrate.

10. The method of manufacturing according to claim 5, wherein, After performing the step S1 and before performing the step S2, comprising: Step B1: forming an aluminum oxide interface layer on the inner surface of the photoacoustic cell substrate; Step B2: forming a graphene base layer above the aluminum oxide interface layer.

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