A method for preparing a surface plasmon resonance chip using aluminum as an evaporation material

Abstract

The application belongs to the technical field of surface plasmon resonance sensing, and discloses a method for preparing a surface plasmon resonance chip by taking aluminum as an evaporation material, which comprises the following steps: a) selecting ultraviolet fused quartz as a substrate, cleaning and blowing dry; b) installing an evaporation boat on an evaporation source frame of a resistance type evaporation film coating instrument, adding 2-4 aluminum particles with a diameter of 3*3 mm on the evaporation boat, placing the substrate on a tray, and closing a vacuum chamber and starting cooling water; c) vacuumizing to 1*10 ‑4 The aluminum film is evaporated on the ultraviolet fused quartz substrate at a current of 150 A, a deposition speed of 1.5-2.0 nm / s, and a deposition time of 10-15 seconds. The evaporation mode adopted by the application is the simplest resistance evaporation, which is simple to operate, easy to control in process parameters, strong in repeatability, and low in cost. The aluminum film prepared has a dense and smooth surface and good adhesion, and can be used for surface plasmon resonance chips.

Description

Technical Field

[0001] This invention belongs to the field of surface plasmon resonance sensing technology, and particularly relates to a method for preparing a surface plasmon resonance chip using aluminum as the evaporation material. Background Technology

[0002] Surface plasmon resonance (SPR) works by using light waves to excite free electron density waves at the metal / dielectric interface. When the wave vectors of the two components match, resonance occurs, converting all incident light energy into the density wave energy of the free electrons, resulting in a reflection valley. The surface free electron density wave propagates along the metal-dielectric interface, generating an evanescent wave that decays exponentially in the vertical direction within the metal film and dielectric. Its effective depth in the dielectric is approximately 100–200 nm, forming a nanometer-sized optically enhanced near-field on the metal film surface. When the wave vectors do not match, SPR cannot be excited, resulting in high light reflectivity.

[0003] Angle modulation (SPR) involves incident excitation light at different angles. At the resonance angle satisfying the wave vector matching condition, a deep valley appears in the reflection angle spectrum. The intensity of the lowest point of this valley, the resonance angle, and the full width at half maximum (FWHM) are characteristic parameters of the SPR angle spectrum. The complex refractive index, thickness, and optical properties of the surface dielectric of the metal thin film, especially the dielectric within the effective depth, significantly influence the wave vector matching condition; that is, the resonance angle changes with the dielectric material at the metal thin film interface. SPR sensing technology typically studies the type and concentration of trace or even ultra-trace substances on the surface of SPR sensing chips by real-time monitoring the resonance angle changes caused by minute changes or the presence or absence of the dielectric material in contact with the metal thin film.

[0004] Metal thin films are one of the core components of SPR sensor chips, determining the sensitivity, resolution, and detection range of the sensing instrument. Currently, commercially available SPR sensor chips are based on precious metals such as gold and silver, making them extremely expensive. Gold SPR sensor chips often use other metals like chromium to improve adhesion to the glass substrate, which compromises the chip's sensitivity. Silver, on the other hand, has extremely poor chemical stability and easily forms a black oxide layer, rendering the SPR sensor completely unusable. Furthermore, commonly used surface plasmon resonance (SPR) materials like gold and silver undergo interband electron transitions in the blue light band, thus failing to support SPR resonance in this band. Current SPR sensor chips are limited to using red excitation light for refractive index sensing, requiring surface treatment on the chip to achieve selective detection of target molecules. These reasons severely limit the widespread adoption of SPR sensing technology based on precious metal materials. Expanding the operating frequency band of SPR sensor chips is essential, as many biomolecules have electronic transition frequencies in the blue light band. Different light-matter interactions can be used to perform multi-parameter sensing and detection of biomolecules based on the nano-optical near-field provided by SPR.

[0005] Aluminum, due to its higher electron density, possesses a higher plasma frequency than precious metals such as gold and silver, enabling it to support surface plasmon resonance in the blue light and even ultraviolet bands. Furthermore, its high quality factor results in aluminum thin-film SPR sensor chips exhibiting high sensitivity and resolution. Additionally, aluminum naturally possesses an oxide layer, resulting in extremely high optical transmittance and providing damage protection for the aluminum thin film. Notably, aluminum is inexpensive, abundant, and its processing methods are compatible with traditional CMOS, significantly reducing the cost of SPR sensing instruments.

[0006] The performance of SPR chips depends not only on the inherent properties of the materials but also on the influence of the fabrication process on the characteristic parameters of the metal thin film. When aluminum thin films are deposited using resistive evaporation, different vacuum levels and deposition rates affect the surface roughness and dielectric constant of the prepared aluminum thin films, thus influencing their sensitivity and resolution as SPR sensing chips. Therefore, exploring suitable evaporation parameters to achieve a high-sensitivity aluminum SPR sensing chip in the blue light band is of significant research importance. Summary of the Invention

[0007] The technical problem solved by this invention is to provide a method for preparing a surface plasmon resonance (SPR) chip using aluminum as the evaporation material. The aluminum thin film SPR chip obtained by this method has good surface roughness, good SPR reflection curve in the blue light band, and a characteristic thickness of 20-25 nm.

[0008] The technical solution of the present invention:

[0009] A method for preparing a surface plasmon resonance chip using aluminum as the evaporation material includes:

[0010] Step a) Select a UV-grade fused silica material that does not absorb blue light as a substrate, and clean and dry it;

[0011] Step b) Install the evaporation boat on the evaporation source rack of the resistive evaporation coating instrument, add 2 to 4 Ф3*3mm aluminum particles on it, place the substrate on the tray, close the vacuum chamber and turn on the cooling water;

[0012] Step c) Evacuate to 1×10 -4 Below Pa, the evaporation current corresponding to the aluminum particles is adjusted to 150A, so that the aluminum evaporates and is deposited on the substrate. The deposition time is controlled to be 10-15 seconds, thus obtaining an aluminum thin film on the substrate.

[0013] In step b), the evaporation boat material is selected as tungsten, which does not react with aluminum.

[0014] In step b), the purity of the aluminum particles should be no less than 99.999%, and the number of particles should be proportional to the thickness of the aluminum film, with approximately 0.8 nm corresponding to one aluminum particle.

[0015] In step c), the evaporation current is 150A and the evaporation rate is 1.5–2.0 nm / s. The thickness of the formed aluminum film is controlled by adjusting the deposition time.

[0016] It also includes substrate pretreatment, specifically:

[0017] The UV-grade fused silica substrate was ultrasonically cleaned in acetone and ultrapure water for 10 minutes in sequence, and then dried with nitrogen.

[0018] The beneficial effects of this invention are:

[0019] The aluminum SPR sensor chip prepared by this invention is fabricated using the simplest resistive evaporation coating technique, which is simple to operate, easy to control process parameters, highly repeatable, and low in cost.

[0020] The aluminum SPR sensor chip prepared by this invention has a dense and smooth surface, good adhesion, and a narrow half-wave width of its SPR spectrum. Under resonance conditions, the intensity of the reflection valley is very close to zero.

[0021] The aluminum SPR sensor chip prepared by this invention has high stability, and the natural aluminum oxide layer formed on the surface can effectively protect the internal aluminum film.

[0022] The aluminum SPR sensing chip prepared by this invention can perform sensing based on other light-matter interaction principles, and has low requirements for excitation light source. Attached Figure Description

[0023] Figure 1This is a schematic diagram of the surface roughness measured by AFM of the aluminum thin film prepared in Example 1.

[0024] Figure 2 The image shows the thickness curve of the aluminum film prepared in Example 1 as determined by AFM; (a) is an atomic force microscope scan image, and (b) is the thickness curve of the aluminum film as determined by AFM.

[0025] Figure 3 The image shows the complex refractive index data of the aluminum thin film prepared in Example 1, measured by ellipsometer.

[0026] Figure 4 The SPR measured reflection angle spectrum of the aluminum thin film prepared in Example 1 is shown.

[0027] Figure 5 This is a schematic diagram of the surface roughness measured by AFM for the aluminum thin film prepared in Example 4;

[0028] Figure 6 The image shows the thickness curve of the aluminum film prepared in Example 4, measured by AFM. (a) is an atomic force microscope scan image, and (b) is the thickness curve of the aluminum film measured by AFM.

[0029] Figure 7 The graph shows the complex refractive index data of the aluminum thin film prepared in Example 4, measured by ellipsometer.

[0030] Figure 8 The SPR measured reflection angle spectrum of the aluminum thin film prepared in Example 4 is shown. Detailed Implementation

[0031] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0032] Example 1:

[0033] Step a) Select UV-grade fused silica as the substrate, and ultrasonically clean the substrate in acetone and ultrapure water for 10 minutes in sequence, and then dry it with nitrogen.

[0034] Step b) Select a tungsten evaporation boat and install it on the evaporation source rack of the resistive evaporation coating instrument, add 3 aluminum particles with a purity of not less than 99.999% on it, fix the substrate on the tray, close the vacuum chamber and turn on the cooling water;

[0035] Step c) Turn on the main power of the coating equipment, turn on the power of the mechanical pump, open the fore-stage valve, and open the vacuum gauge. When the vacuum degree is less than 5 Pa, turn on the power of the molecular pump. When the vacuum degree is lower than 1 × 10⁻⁶ Pa, turn on the power of the molecular pump. -4At Pa, which falls within the high vacuum range, turn on the evaporation power supply and adjust the evaporation current corresponding to the aluminum particles to 80A. Increase the current by 10A every minute until it reaches 110A, at which point all the aluminum particles will melt. At this point, open the baffle, turn on the rotating tray, and quickly adjust the evaporation current to 150A. The deposition rate is approximately 1.7nm / s, which falls within the high-rate range, and the deposition time is approximately 13 seconds. After the coating is completed, return the evaporation power supply current to zero, wait for the evaporation boat to cool down, turn off the evaporation power supply, wait 10 minutes, and then turn off the molecular pump, the fore-stage valve, and the mechanical pump in sequence. Open the vacuum chamber and remove the sample.

[0036] Step d) Use AFM to detect the surface roughness of the sample prepared in step c) above, such as... Figure 1 As shown, the film surface is composed of some continuous micro-particles with good bonding. The film surface is flat and dense, and its root mean square roughness (RMS) is 0.49 nm, indicating that the film surface roughness is small.

[0037] Step e) Use AFM to detect the thickness of the sample prepared in step c) above, such as... Figure 2 As shown, the thickness of the aluminum film is approximately 22 nm.

[0038] Step f) Use a spectroscopic ellipsometry to detect the real and imaginary parts of the refractive index of the sample prepared in step c) above, such as... Figure 3 As shown, the measurement wavelength range is 370–1000 nm.

[0039] Step g) The SPR reflection angle spectrum of the sample prepared in step c) above is detected by angle modulation, such as... Figure 4 As shown, its half-width is relatively narrow and its resonant angle reflectivity is close to zero.

[0040] Comparative Example 1

[0041] Step c) Turn on the main power of the coating equipment, turn on the power of the mechanical pump, open the fore-stage valve, and open the vacuum gauge. When the vacuum degree is less than 5 Pa, turn on the power of the molecular pump. When the vacuum degree reaches 7 × 10 Pa... -4 At Pa, which falls within the low vacuum range, turn on the evaporation power supply and adjust the evaporation current corresponding to the aluminum particles to 80A. Increase the current by 10A every minute until it reaches 110A, at which point all the aluminum particles will melt. At this point, open the baffle, turn on the rotating tray, and quickly adjust the evaporation current to 150A. The deposition rate is approximately 1.7nm / s, which falls within the high-rate range, and the deposition time is approximately 13 seconds. After the coating is completed, return the evaporation power supply current to zero, wait for the evaporation boat to cool down, turn off the evaporation power supply, wait 10 minutes, and then turn off the molecular pump, the fore-stage valve, and the mechanical pump in sequence. Open the vacuum chamber and remove the sample.

[0042] The remaining steps are the same as in Example 1. The aluminum film obtained thus has a significantly different refractive index and a larger half-width compared to Example 1, which is not conducive to sensing and detecting minute changes in the refractive index on the surface of the aluminum film.

[0043] Comparative Example 2

[0044] Step c) Turn on the main power of the coating equipment, turn on the power of the mechanical pump, open the fore-stage valve, and open the vacuum gauge. When the vacuum degree is less than 5 Pa, turn on the power of the molecular pump. When the vacuum degree is lower than 1 × 10⁻⁶ Pa, turn on the power of the molecular pump. -4 At Pa, which falls within the high vacuum range, turn on the evaporation power supply and adjust the evaporation current corresponding to the aluminum particles to 80A. Increase the current by 10A every minute until it reaches 110A, at which point all the aluminum particles will melt. At this point, open the baffle, turn on the rotating tray, and adjust the evaporation current to 120A. The deposition rate is approximately 0.1nm / s, which is in the low rate range, and the deposition time is approximately 13 seconds. Wait for the coating to finish and for the evaporation power supply current to return to zero. Wait for the evaporation boat to cool down, turn off the evaporation power supply, and wait for 10 minutes. Then, turn off the molecular pump, the fore-stage valve, and the mechanical pump in sequence, open the vacuum chamber, and remove the sample.

[0045] The remaining steps are the same as in Example 1. The resulting aluminum film has a larger surface roughness and poorer overall quality compared to Example 1.

[0046] Comparative Example 3

[0047] Step a) Select UV-grade fused silica as the substrate, and ultrasonically clean the substrate in acetone and ultrapure water for 10 minutes in sequence, and then dry it with nitrogen.

[0048] Step b) Select a tungsten evaporation boat and install it on the evaporation source rack of the resistive evaporation coating instrument, add 3 aluminum particles with a purity of not less than 99.999% on it, place the substrate on the tray, close the vacuum chamber and turn on the cooling water;

[0049] Step c) Turn on the main power of the coating equipment, turn on the power of the mechanical pump, open the fore-stage valve, and open the vacuum gauge. When the vacuum degree is less than 5 Pa, turn on the power of the molecular pump. When the vacuum degree reaches 7 × 10 Pa... -4 At Pa, which falls within the low vacuum range, turn on the evaporation power supply and adjust the evaporation current corresponding to the aluminum particles to 80A. Increase the current by 10A every minute until it reaches 110A, at which point all the aluminum particles will melt. At this point, open the baffle, turn on the rotating tray, and adjust the evaporation current to 120A. The deposition rate is approximately 0.1nm / s, which is in the low rate range. The deposition time is approximately 220 seconds. Wait for the coating to finish and for the evaporation power supply current to return to zero. Wait for the evaporation boat to cool down, turn off the evaporation power supply, and wait for 10 minutes. Then, turn off the molecular pump, the fore-stage valve, and the mechanical pump in sequence, open the vacuum chamber, and remove the sample.

[0050] Step d) Use AFM to detect the surface roughness of the sample prepared in step c) above, such as... Figure 5As shown, the micro-particles on the film surface are uneven and well bonded, but the film surface has poor flatness. Its root mean square roughness (RMS) is 1.35 nm, which is about 3 times larger than the surface roughness of Example 1.

[0051] Step e) Use AFM to detect the thickness of the sample prepared in step c) above, such as... Figure 6 As shown, the thickness of the film is approximately 22 nm.

[0052] Step f) Use a spectroscopic ellipsometry to detect the real and imaginary parts of the refractive index of the sample prepared in step c) above, such as... Figure 7 As shown, the measurement wavelength range is 370–1000 nm.

[0053] Step g) The SPR reflection angle spectrum of the sample prepared in step c) above is detected by angle modulation, such as... Figure 8 As shown, compared to Example 1, its half-wavelength is wider, which is not conducive to sensing and detecting minute refractive index changes on the surface of aluminum thin films.

Claims

1. A method for preparing a surface plasmon resonance chip using aluminum as an evaporation material, characterized by, The application comprises the following steps: Step a) selecting ultraviolet grade fused quartz material which does not absorb blue light as the substrate, cleaning and blowing dry; Step b) installing the evaporation boat on the evaporation source frame of the resistance type evaporation coating instrument, adding 2-4 aluminum particles with a diameter of 3*3 mm on the evaporation boat, placing the substrate on the tray, and closing the vacuum chamber and starting the cooling water; Step c) vacuumed to 1 x 10 -4 Pa, the evaporation current of the aluminum particles was adjusted to 150 A, the aluminum was evaporated and deposited on the above substrate, the deposition time was controlled to 10-15 seconds, i.e. an aluminum thin film was obtained on the substrate.

2. The method of claim 1, wherein, The material of the evaporation boat in step b) is tungsten.

3. The method of claim 1, wherein, The number of aluminum particles placed in step b) is proportional to the thickness of the aluminum film, and 0.8 nm corresponds to one aluminum particle.

4. The method of claim 1, wherein, The evaporation speed in step c) is 1.5-2.0 nm / s, and the thickness of the aluminum film formed is controlled by adjusting the deposition time.

5. The method of claim 1, wherein, The application also comprises pretreatment of the substrate, specifically: ultraviolet grade fused quartz substrate is sequentially ultrasonically cleaned in acetone and ultrapure water for 10 minutes, and then dried with nitrogen.

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