A light detection method based on scanning probe light-induced mechanical response reading

Abstract

This invention relates to a photodetection method based on the readout of the photoinduced mechanical response of a scanning probe, belonging to the fields of photodetection and scanning probe microscopy. When light irradiates a quantum dot film, it generates photogenerated carriers, changes in surface potential, and thermal expansion, causing a change in the distance between the probe and the quantum dot film. When the illumination stops, the influencing factors disappear, and the probe returns to its original position. In this invention, periodic illumination causes the probe to vibrate, and a power-frequency-response model is established by analyzing the probe vibration signal. When photodetection is required, only the frequency and average power density of the incident light can be obtained by analyzing the probe vibration signal, eliminating the need for traditional current collection and complex optoelectronic device structures, effectively reducing detection costs.

Description

Technical Field

[0001] This invention belongs to the field of optical detection and scanning probe microscopy technology, and specifically relates to an optical detection method based on the readout of the photoinduced mechanical response of a scanning probe. Background Technology

[0002] Optical detection technology is a class of technologies that convert incident light signals into measurable output signals. It is widely used in optical communication, image sensing, environmental monitoring, biomedical detection, automatic control, and national defense security. Existing photodetectors typically convert light signals based on the photoconductive, photovoltaic, photothermal, or pyroelectric effects generated by semiconductor materials, quantum dot materials, two-dimensional materials, or organic photosensitive materials under illumination, and then read them out through changes in current, voltage, resistance, or temperature.

[0003] To achieve high detection performance, traditional photodetectors typically require device design that considers the absorption characteristics, band structure, carrier transport properties, and interfacial contact characteristics of the photosensitive material. For example, this necessitates designing structures such as metal electrodes, carrier transport layers, heterojunctions, Schottky barriers, field-effect structures, or micro / nano optics to facilitate the separation, transport, and collection of photogenerated carriers and reduce dark current and noise. While these structural designs can improve device performance to some extent, they also place high demands on material preparation, interface manipulation, micro / nano fabrication, and process optimization, making the device fabrication process relatively complex. For the verification of novel photosensitive materials, complex device structures may also introduce additional interface and transport effects, making it difficult for the measured signal to independently reflect the intrinsic response process of the material under illumination.

[0004] In the field of nanochemical imaging technology, one technique involves setting up an incident light source and a probe. During operation, the object to be measured is placed below the probe as a substrate. Specific light emitted from the incident light source illuminates the object, generating a photoinduced dipole force between the object and the probe, causing the probe to vibrate. The material properties of the object can then be calculated using the probe's vibration frequency and the relevant information of the incident light. Patent CN112513648A, "Scanning Probe Microscope Using Sensor Molecules to Improve Light Transmittance of Samples," describes this type of method. This method improves upon this technique, providing a light detection method that does not rely on traditional current collection and complex optoelectronic device structures. Summary of the Invention

[0005] The purpose of this invention is to provide a photodetector system based on the photoinduced mechanical response of a scanning probe, which can detect the average power density of incident light without relying on complex optoelectronic device structures.

[0006] To achieve the above objectives, the present invention employs a photodetection method based on the photoinduced mechanical response readout of a scanning probe, which is carried out according to the following steps:

[0007] Step 1: Position the probe above the substrate material;

[0008] Step 2: Use the fundamental frequency as The basic average power density is Incident light is irradiated onto the substrate material, while the on / off state of the incident light source is periodically changed, and the corresponding probe vibration signals are recorded. ;

[0009] Step 3: Change the average power density of the incident light Maintain the base frequency Repeat step 2 without changing the input method to obtain several sets of average power densities. and the corresponding probe vibration signal The power response relationship was obtained by fitting:

[0010]

[0011] in, For net response, This is the proportionality coefficient. It is a power coefficient;

[0012] Step 4: Change the modulation frequency of the incident light Maintaining the baseline average power density Repeat step 2 again to obtain several sets of modulation frequencies. and the corresponding probe vibration signal The probe vibration signal is transmitted using a lock-in amplifier. Converted into frequency response And calculate different modulation frequencies Normalized frequency transfer factor ;

[0013] Step 5: Combine with the proportional coefficient Power index and normalized frequency transfer factor Establish the power-frequency-response relationship between the probe and the substrate material:

[0014]

[0015] in, The average power density is The frequency is The net power response of the probe when light shines on the substrate material;

[0016] Step 6: Irradiate the substrate material with the incident light to be tested, and determine the modulation frequency of the incident light using a lock-in amplifier. According to the modulation frequency Determine the corresponding normalized frequency transfer factor The average power density of the incident light to be measured is obtained by substituting the values ​​into the formula obtained in step 5. .

[0017] The probe is made of single-crystal silicon with a gold coating on its surface. The substrate is a quantum dot film, and the distance between the probe and the substrate is 40 nm to 60 nm.

[0018] Step 3, obtaining the power response relationship through fitting, is specifically carried out according to the following steps:

[0019] Step 3.1: Change the average power density of the incident light Maintaining the modulation frequency Repeat step 2 without changing the input, to obtain several sets of average power densities. and the corresponding probe vibration signal ;

[0020] Step 3.2: Modulate the frequency with a square wave Based on the probe vibration signal Perform synchronous demodulation to obtain in-phase components. and orthogonal components :

[0021]

[0022]

[0023] Where T is the integration time. , The starting time of integration, For reference phase;

[0024] Step 3.3: Based on the in-phase component and orthogonal components Calculate the net response amplitude ;

[0025] Step 3.4: Obtain the power response relationship through fitting:

[0026]

[0027] in, This is the proportionality coefficient. It is a power coefficient.

[0028] Net response amplitude in step 3.3 The calculation method is as follows:

[0029]

[0030] in, For net in-phase components, The net orthogonal component is calculated as follows:

[0031]

[0032]

[0033] The voltage decay recovery coefficient is... , These represent the in-phase components of the incident light source under both on and off states within a single period. and These are the orthogonal components of the incident light source in the on and off states within a single period.

[0034] In step 3.4, the proportionality coefficient is obtained by fitting a nonlinear least squares power function. Power index :

[0035]

[0036] in, The average power density of different incident lights in step 3.1 This refers to the net response amplitude under different incident light illuminations in step 3.3.

[0037] Normalized frequency transfer factor in step 4 The calculation method is as follows:

[0038]

[0039] in, Based on power density at different modulation frequencies The frequency response measured below, Based on power density at modulation frequency The frequency response at that point, This is high-frequency residual background;

[0040] The frequency response plot is nonlinearly fitted using a generalized low-pass empirical function.

[0041]

[0042] in, For low-frequency platform amplitude, The cutoff frequency, The shape index is obtained after estimation. , , and Substituting the value of into the above formula yields the specific frequency. Lower normalized frequency transfer factor The calculation formula.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] The photodetector method provided by this invention uses incident light to irradiate a quantum dot film, causing the interaction between the film and the probe to vibrate. By analyzing the probe vibration, a power-frequency-response model is constructed, which can quantitatively calculate the average power density of the incident light to be measured.

[0045] The detection method provided by this invention does not rely on the complex structures required by traditional photodetectors, such as metal electrodes, carrier transport layers, heterojunctions, and Schottky barriers, thus avoiding complex material preparation, interface control, and micro / nano fabrication processes. This reduces the overall detection difficulty and cost. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the detection structure adopted in this invention;

[0047] Figure 2 This is a graph showing the change in net light response signal in Example 1;

[0048] Figure 3 This is the frequency response diagram from Example 1. Detailed Implementation

[0049] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0050] Example 1:

[0051] The test structure used in this embodiment is as follows: Figure 1 As shown, the signal generator is used to modulate the incident light, providing incident light of different frequencies or average power densities during the calibration process. Simultaneously, the signal generator also sends relevant information about the incident light to a lock-in amplifier to obtain relevant data.

[0052] The probe consists of two parts: a lever arm and a tip. The tip interacts with the quantum dot film, while the lever arm interacts with the feedback laser. When the lever arm is stationary, the feedback laser shines on it and is reflected onto a four-quadrant photodetector. When the tip interacts with the quantum dot film, the lever arm vibrates. This changes the position of the point on the lever arm where the feedback laser shines, and consequently, the position of the laser reflected onto the four-quadrant photodetector also changes. The movement of the position of the laser reflected onto the four-quadrant photodetector reflects the vibration state of the probe.

[0053] When incident light shines on a quantum dot film, the film absorbs the light, generating photogenerated carriers, changing the surface potential, and undergoing thermal expansion. These changes further alter the electrostatic interaction, dipole interaction, or surface displacement between the probe tip and the sample, thus causing changes in the probe's vibrational state. Since the materials of the quantum dot and the probe remain unchanged, their interaction is constant. By establishing the relationship between the probe's vibrational state and the incident light, relevant information about the incident light can be determined from the probe's vibrational state.

[0054] The probe is primarily made of silicon, with a gold layer on its surface and a chromium layer between the silicon and gold. The quantum dot film uses cadmium selenide quantum dots. The spacing between the probe and the substrate is 50 nm.

[0055] The wavelength of the incident light is set to 532 nm, the initial frequency to 100 Hz, and the initial average power density to 0.007. The duty cycle of the incident light source is 50% for periodic opening and closing, and the duration of a single opening and closing cycle is 40 s.

[0056] Keeping the wavelength, frequency, duty cycle, and switching period of the incident light constant, change the average power density of the incident light. Record each average power density After the change, the probe vibration signal output by the four-quadrant photodetector The average power density is 0.007. Up to 2.462 Select from the range. Among them, 0.007 up to 0.154 For the low-power region, set 15 sets of parameters; 0.231 Up to 2.462 For the high-power region, 22 sets of parameters were set. A total of 37 sets of power density parameters were set, each set of parameters was held for 20 seconds, and the needle vibration signal was collected simultaneously. .

[0057] probe vibration signal The in-phase components of the incident light when it is in the on state are obtained through processing. and orthogonal components and the in-phase component of the incident light when it is in the off state. and orthogonal components The calculation method for a certain set is as follows:

[0058]

[0059]

[0060]

[0061]

[0062] In this embodiment, T=17 s, =0°.

[0063] The net response amplitude is calculated based on the obtained in-phase and quadrature components. The calculation method is as follows:

[0064]

[0065]

[0066]

[0067] With net response amplitude The vertical axis represents the average power density. Plot the net light response signal variation curve with the x-axis as the horizontal axis, as shown below. Figure 2 As shown.

[0068] The power response relationship is obtained by fitting the image:

[0069]

[0070] in, and The proportionality coefficient is obtained by fitting a nonlinear least squares power function. power exponent .

[0071] Final net response amplitude With average power density The relationship between them is:

[0072] .

[0073] Then, keeping the wavelength, average power density, duty cycle, and switching period of the incident light constant, the modulation frequency of the incident light is changed. Record each modulation frequency After the change, the probe vibration signal output by the four-quadrant photodetector The modulation frequency of the incident light The frequency range was selected from 5 Hz to 30 kHz, with 5 Hz to 1.5 kHz being the low-frequency region and 17 sets of parameters set; the high-frequency region was 1.7 kHz to 30 kHz, with 17 sets of parameters set there as well. A total of 34 sets of modulation frequency parameters were set, each set held for 20 seconds, and the needle vibration signal was acquired simultaneously. .

[0074] Different frequencies The corresponding probe vibration signal output by the four-quadrant photodetector The signal is fed into a lock-in amplifier to obtain different frequencies. Corresponding frequency response And plot the corresponding frequency response diagram, such as Figure 3 As shown.

[0075] The frequency response plot is nonlinearly fitted using a generalized low-pass empirical function.

[0076]

[0077] in, , , Hz, Substituting the parameters into the above equation, we obtain the frequency response. With the frequency of incident light Relationship between them:

[0078] .

[0079] The above frequency response With the frequency of incident light Substituting the relational expression into the calculation formula, we get:

[0080]

[0081] Part Substituting into the above equation, we obtain the normalized frequency transfer factor at different frequencies:

[0082]

[0083] Combining the normalized frequency transfer factor and the power response relationship, the power-frequency-response relationship between the probe and the substrate material is obtained:

[0084]

[0085] Substituting the specific parameters into the above formula, we get:

[0086]

[0087] For the unknown average power density of the incident light Then we have:

[0088] .

[0089] When incident light of unknown frequency and average power density periodically irradiates cadmium selenide, the interaction between cadmium selenide and the probe causes the probe to vibrate, and the related vibration signal... The incident light frequency is collected by a four-quadrant photodetector and transmitted to a lock-in amplifier. The lock-in amplifier uses a reference frequency sweep method to determine the frequency of the incident light. Simultaneously through vibration signals Calculate the net response amplitude at this time. Based on the frequency of the incident light. Determine the corresponding normalized frequency transfer factor Then the net response and the corresponding normalized frequency transfer factor Substituting, the above average power density The average power density of the incident light is obtained from the solution formula. .

[0090] To verify the consistency of the power response relationship established in this embodiment within the calibration range, 10 sets of average power densities and their corresponding measured net response amplitudes were randomly selected from the power response experimental data. The measured net response amplitudes were substituted into the power density inversion formula to calculate the inverted power density, which was then compared with the actual set average power density. The test results are as follows:

[0091]

[0092] As shown in the table above, the method provided in this application exhibits relatively small errors when detecting the average power density of unknown light. The method provided in this application avoids the need for complex substrate structures while ensuring detection accuracy, effectively reducing detection costs.

Claims

1. A photodetection method based on the readout of a scanning probe's photoinduced mechanical response, characterized in that, Follow these steps: Step 1: Position the probe above the substrate material; Step 2: Use the fundamental frequency as The basic average power density is Incident light is irradiated onto the substrate material, while the on / off state of the incident light source is periodically changed, and the corresponding probe vibration signals are recorded. ; Step 3: Change the average power density of the incident light Maintain the base frequency Repeat step 2 without changing the input method to obtain several sets of average power densities. and the corresponding probe vibration signal The power response relationship was obtained by fitting: in, For net response, This is the proportionality coefficient. It is a power coefficient; Step 4: Change the modulation frequency of the incident light Maintaining the baseline average power density Repeat step 2 again to obtain several sets of modulation frequencies. and the corresponding probe vibration signal The probe vibration signal is transmitted using a lock-in amplifier. Converted into frequency response And calculate different modulation frequencies Normalized frequency transfer factor ; Step 5: Combine with the proportional coefficient Power index and normalized frequency transfer factor Establish the power-frequency-response relationship between the probe and the substrate material: in, The average power density is The frequency is The net power response of the probe when light shines on the substrate material; Step 6: Irradiate the substrate material with the incident light to be tested, and determine the modulation frequency of the incident light using a lock-in amplifier. According to the modulation frequency Determine the corresponding normalized frequency transfer factor The average power density of the incident light to be measured is obtained by substituting the values ​​into the formula obtained in step 5. .

2. The photodetection method based on the photoinduced mechanical response readout of a scanning probe according to claim 1, characterized in that, The probe is made of single-crystal silicon with a gold coating on its surface. The substrate is a quantum dot film, and the distance between the probe and the substrate is 40 nm to 60 nm.

3. The photodetection method based on the photoinduced mechanical response readout of a scanning probe according to claim 1, characterized in that, Step 3, obtaining the power response relationship through fitting, is specifically carried out according to the following steps: Step 3.1: Change the average power density of the incident light Maintaining the modulation frequency Repeat step 2 without changing the input, to obtain several sets of average power densities. and the corresponding probe vibration signal ; Step 3.2: Modulate the frequency with a square wave Based on the probe vibration signal Perform synchronous demodulation to obtain in-phase components. and orthogonal components : Where T is the integration time. , The starting time of integration, For reference phase; Step 3.3: Based on the in-phase component and orthogonal components Calculate the net response amplitude ; Step 3.4: Obtain the power response relationship through fitting: in, This is the proportionality coefficient. It is a power coefficient.

4. The photodetection method based on the photoinduced mechanical response readout of a scanning probe according to claim 3, characterized in that, Net response amplitude in step 3.3 The calculation method is as follows: in, For net in-phase components, The net orthogonal component is calculated as follows: The voltage decay recovery coefficient is... , These represent the in-phase components of the incident light source under both on and off states within a single period. and These are the orthogonal components of the incident light source in the on and off states within a single period.

5. The photodetection method based on scanned probe photoinduced mechanical response readout according to claim 3, characterized in that, In step 3.4, the proportionality coefficient is obtained by fitting a nonlinear least squares power function. Power index : in, The average power density of different incident lights in step 3.1 This refers to the net response amplitude under different incident light illuminations in step 3.

3.

6. The photodetection method based on the photoinduced mechanical response readout of a scanning probe according to claim 1, characterized in that, Normalized frequency transfer factor in step 4 The calculation method is as follows: in, Based on power density at different modulation frequencies The frequency response measured below, Based on power density at modulation frequency The frequency response at that point, This is high-frequency residual background; The frequency response plot is nonlinearly fitted using a generalized low-pass empirical function. in, For low-frequency platform amplitude, The cutoff frequency, The shape index is obtained after estimation. , , and Substituting the value of into the above formula yields the specific frequency. Lower normalized frequency transfer factor The calculation formula.

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