A method for preparing a piezoresistive sensor based on a PN junction type carbon-based material

Abstract

The present application relates to the technical field of piezoresistive sensor, and provides a preparation method of piezoresistive sensor based on PN junction type of carbon-based material.The present application mixes reduced graphene oxide and graphene oxide suspension to obtain a mixed solution, coats the mixed solution on a substrate and dries to obtain the piezoresistive sensor based on PN junction type of carbon-based material.Through the mixing method, the present application adopts the reduced graphene oxide to simply dope the graphene oxide, and then obtains the piezoresistive sensor based on PN junction type of carbon-based material through coating and drying.The present application does not need to carry out complex chemical vapor deposition, nor needs to adopt wet spinning, heat annealing and other steps, and the preparation method is very simple and easy to operate, and the obtained piezoresistive sensor based on PN junction type has good piezoresistive effect and rectification characteristics, and has wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of piezoresistive sensors, and particularly relates to a preparation method of a PN junction type piezoresistive sensor based on carbon-based materials. BACKGROUND

[0002] In 1954, C.S. Smith studied the piezoresistive effect of silicon in detail, and then began to study the piezoresistive sensor made of silicon. Since then, piezoresistive sensors have been widely used in sensing, power machinery, meteorology and geology, and have attracted widespread attention.

[0003] In semiconductor devices, PN junctions are the basis. Through the difference of the material, the doping distribution, the geometric structure and the bias condition of the PN junction, the device can have the function of rectification. According to the difference of the dopant, P-type or N-type semiconductor can be formed, so as to prepare the PN junction. The PN junction is applied to the field of sensors to form a functional application device. There are many studies on piezoresistive sensors with different dopants, such as wearable piezoresistive sensors with layered microspikes made of reduced graphene oxide (rGO) and Mxene (ACSAppl. Mater. Interfaces 2022, 14, 27262-27273) and three-dimensional mixed porous piezoresistive sensors made of Mxene and sponge (Nano Energy 50 (2018) 79-87).

[0004] At present, there are precedents for piezoresistive sensors of PN junction type based on graphene full carbon materials. Weiquan Yao et al. (Carbon 2020, 158, 418-425) published a piezoresistive sensor formed by graphene carbon nanotube aerogel balls, which is a piezoresistive sensor of full carbon material. Carbon nanotubes and graphene oxide doped spherical hydrogel are prepared by using wet spinning technology, and then graphene carbon nanotube aerogel balls are obtained through pre-reduction, drying and heat annealing. The preparation method is very complicated, and the preparation steps are complex. In the traditional method, chemical vapor deposition is also used for doping in graphene to construct a PN junction type piezoresistive sensor. However, chemical vapor deposition requires high temperature, high cost and poor safety.

[0005] Therefore, there is an urgent need to provide a method for simply preparing a PN junction type piezoresistive sensor. SUMMARY

[0006] Therefore, the present application provides a preparation method of a PN junction type piezoresistive sensor based on carbon-based materials. The preparation method provided by the present application has simple steps and is easy to operate. Only the graphene oxide needs to be doped by simple mixing, and the obtained piezoresistive sensor has good piezoresistive sensing performance.

[0007] To achieve the above object, the present application provides the following technical solutions.

[0008] A preparation method of a PN junction type piezoresistive sensor based on carbon-based material, comprising the following steps:

[0009] Mixing a reduced graphene oxide and an oxidized graphene oxide suspension to obtain a mixed solution;

[0010] After coating the mixed solution on a substrate and drying, a PN junction type piezoresistive sensor based on carbon-based material is obtained.

[0011] Preferably, the concentration of the oxidized graphene oxide suspension is 0.1-10 mg / mL; and the solvent of the oxidized graphene oxide suspension is one or several of water, ethanol, acetone and dimethyl sulfoxide.

[0012] Preferably, the mass ratio of the oxidized graphene oxide in the oxidized graphene oxide suspension to the reduced graphene oxide is 10:1-3.

[0013] Preferably, the purity of the reduced graphene oxide is >95 wt%.

[0014] Preferably, the mixing comprises ultrasonic and stirring in sequence, the ultrasonic time is 2-4 h, the ultrasonic power is 200-400 W, the stirring time is 1-2 h, and the stirring speed is 450-650 r / min.

[0015] Preferably, the coating method is drop coating, and the drop coating is performed by using a pipette gun.

[0016] Preferably, the coating and drying are performed 2-10 times alternately.

[0017] Preferably, the substrate is a Pt electrode, and after drying, the obtained reduced graphene oxide-oxidized graphene oxide composite film is peeled off from the substrate.

[0018] The present application also provides a PN junction type piezoresistive sensor based on carbon-based material prepared by the preparation method described in the above scheme, wherein the PN junction type piezoresistive sensor based on carbon-based material is a reduced graphene oxide-oxidized graphene oxide composite film.

[0019] Preferably, the thickness of the reduced graphene oxide-oxidized graphene oxide composite film is 0.2-1 μm.

[0020] The application provides a preparation method of a PN junction type piezoresistive sensor based on carbon-based materials, and comprises the following steps: mixing a reduced graphene oxide and an oxidized graphene oxide suspension to obtain a mixed solution; and coating the mixed solution on a substrate and drying to obtain the PN junction type piezoresistive sensor based on carbon-based materials. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A real object diagram of the reduced graphene oxide-oxidized graphene oxide composite film prepared in the embodiment 1 of the application;

[0022] Figure 2 A schematic diagram of an electrical performance measurement device of the reduced graphene oxide-oxidized graphene oxide composite film prepared in the embodiment 1 of the application;

[0023] Figure 3 An I-V curve diagram of the reduced graphene oxide-oxidized graphene oxide composite film prepared in the embodiment 1 of the application under full pressing;

[0024] Figure 4 An I-V curve diagram of the reduced graphene oxide-oxidized graphene oxide composite film prepared in the embodiment 1 of the application under two-side pressing;

[0025] Figure 5 An R-T curve diagram of the reduced graphene oxide-oxidized graphene oxide composite film prepared in the embodiment 1 of the application under pressing, Figure 5 The upper right corner is a local enlarged view. DETAILED DESCRIPTION

[0026] The application provides a preparation method of a PN junction type piezoresistive sensor based on carbon-based materials, and comprises the following steps:

[0027] Mixing a reduced graphene oxide and an oxidized graphene oxide suspension to obtain a mixed solution;

[0028] Coating the mixed solution on a substrate and drying to obtain the PN junction type piezoresistive sensor based on carbon-based materials.

[0029] The present application mixes reduced graphene oxide powder and graphene oxide suspension to obtain a mixed solution. In the present application, the concentration of the graphene oxide suspension is preferably 1-10 mg / mL, more preferably 5 mg / mL; the solvent of the graphene oxide suspension is preferably one or more of water, ethanol, acetone and dimethyl sulfoxide; the graphene oxide is obtained by four steps of pre-oxidation, oxidation, centrifugation and washing using a modified "Hummers" method, which is a method well known to those skilled in the art, and the present application does not make specific limitations.

[0030] In the present application, the purity of the reduced graphene oxide is preferably > 95 wt%; the reduced graphene oxide is preferably in powder form, the thickness of the reduced graphene oxide is preferably 3-8 nm, and the flake diameter is preferably 10-50 μm; the mass ratio of graphene oxide in the graphene oxide suspension to the reduced graphene oxide is preferably 10:1-3, and more preferably 10:1, 10:2 or 10:3.

[0031] In the present application, the mixing preferably includes ultrasonic and stirring in sequence, the time of the ultrasonic is preferably 2-4 h; the power of the ultrasonic is preferably 200-400 W, more preferably 300 W; the time of the stirring is preferably 1-2 h, and the stirring speed is preferably 450-650 r / min, more preferably 500 r / min.

[0032] After obtaining the mixed solution, the present application coats the mixed solution on a substrate and then dries to obtain a PN junction type piezoresistive sensor based on carbon-based materials. In the present application, the substrate is preferably a Pt electrode, and the present application does not have special limitations on the Pt electrode, which can be selected from Pt electrodes well known to those skilled in the art, and specifically commercially available platinum pieces.

[0033] In the present application, the method of coating is preferably drop coating, which is preferably performed using a pipette gun; the specification of the pipette gun is preferably 20-200 μL, more preferably 200 μL; in a specific embodiment of the present application, the Pt electrode is preferably placed on a glass sheet, and then drop coating is performed on the surface of the Pt electrode.

[0034] The present application does not have special limitations on the operation and specific conditions of the drying, which can be selected from drying methods well known to those skilled in the art that do not damage the properties and structure of the film, and is more preferably oven drying, the temperature of the oven drying is preferably 60-80 °C, more preferably 60 °C, and the total time of the oven drying is preferably 3-5 h, more preferably 4 h.

[0035] In the present application, the number of coating and drying is preferably 2-10 times, preferably 5 times, and the coating and drying are alternately performed, that is, the first time of dripping is followed by the first time of drying, and then the second time of dripping and the second time of drying are performed on the dried film, and so on until 5 times of dripping and drying are completed. The present application removes the solvent through the drying process to obtain a reduced graphene oxide-graphene oxide composite film, wherein the graphene oxide is P type, the reduced graphene oxide is N type, and the two are doped to form a PN junction, and the reduced graphene oxide-graphene oxide composite film is the PN junction type piezoresistive sensor based on carbon-based material; the reduced graphene oxide-graphene oxide composite film can be stored for a long time at room temperature and pressure, in an oven at-100-100 DEG C or other environment without destroying the film structure.

[0036] In the present application, after the last time of coating and drying is completed, the substrate with the reduced graphene oxide-graphene oxide composite film attached is preferably cooled, and then the reduced graphene oxide-graphene oxide composite film is peeled off from the substrate. The present application does not have special limitation on the cooling condition, and any cooling condition known to those skilled in the art can be selected as long as the structure of the material is not destroyed; in the embodiments of the present application, the cooling is specifically natural cooling.

[0037] In the present application, the process of preparing the PN junction type piezoresistive sensor based on carbon-based material does not need traditional chemical vapor deposition treatment, and only needs to be doped by mixing, which is very simple to operate.

[0038] The present application also provides the PN junction type piezoresistive sensor based on carbon-based material prepared by the preparation method described in the above scheme, and the PN junction type piezoresistive sensor based on carbon-based material is a reduced graphene oxide-graphene oxide composite film. In the present application, the mass ratio of graphene oxide and reduced graphene oxide in the composite film is preferably 10:1-3, more preferably 5:1; the thickness of the reduced graphene oxide-graphene oxide composite film is preferably 0.2-1 μm; the surface flatness, thickness and size of the reduced graphene oxide-graphene oxide composite film do not affect its sensing performance, and the thickness of the material is limited to ensure that the resistance value of the material is within the detection range of the instrument when the resistance performance is measured, and the resistance performance detection is realized.

[0039] In the present application, when applied specifically, the reduced graphene oxide-graphene oxide composite film is preferably connected with wires at both ends and then encapsulated, so as to be used as a piezoresistive sensor.

[0040] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments but not all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative effort belong to the protection scope of the present application.

[0041] Embodiment 1

[0042] 10 mg of reduced graphene oxide powder with a purity of > 95 wt% was doped into 10 mL of graphene oxide suspension with a mass concentration of 5 mg / mL (solvent: water), and after ultrasonic treatment at 300 W for 3 h and stirring at a speed of 500 r / min for 1 h, a reduced graphene oxide-graphene oxide mixed solution was obtained;

[0043] A Pt electrode was placed on a glass sheet, and 200 μL of the obtained mixed solution was drop-coated onto the Pt electrode. After drop-coating, the Pt electrode was placed in a 60°C oven for drying for 15 min. The process of drop-coating and drying was repeated 5 times, and a reduced graphene oxide-graphene oxide composite film with a thickness of 0.2 μm was obtained on the surface of the Pt electrode. After natural cooling at room temperature, the composite film was peeled off from the Pt electrode, and then electrical performance test was carried out.

[0044] Figure 1 A physical map of the reduced graphene oxide-graphene oxide composite film prepared in Embodiment 1; according to Figure 1 It can be seen that there are some reduced graphene oxide powder dots on the surface of the composite film, which proves that the composite film is well prepared. Moreover, the present application does not use traditional chemical vapor deposition for doping treatment, but obtains a carbon-based material composite film prepared by simple mixing and doping.

[0045] Figure 2 A schematic diagram of a measuring device for electrical performance test of the reduced graphene oxide-graphene oxide composite film prepared in Embodiment 1; wherein the PI substrate is polyimide, the GO / rGO sample is the reduced graphene oxide-graphene oxide composite film prepared in the present application, and the upper and lower of the composite film are both Pt electrodes during the test; Figure 2 It can be seen that the electrical characteristics of the sample are measured in a vertical structure. The specific test method and test results are as follows:

[0046] (1) I-V test: a keithley 6487 picoammeter was used to test the current-voltage curve of the reduced graphene oxide-graphene oxide composite film prepared in Embodiment 1 under the conditions of no applied pressure and full-range applied pressure, and the test results are shown in Figure 3 . From the results, it can be seen that the reduced graphene oxide-graphene oxide composite film has a good ohmic contact with the Pt electrode, and the current increases with the increase of the voltage. Figure 3It can be seen that when opposite voltages are applied to both sides of the composite film, there is a large difference in the current through the composite film under the conditions of no applied pressure and full-range applied pressure, which indicates that there is a clear PN junction between the composite films.

[0047] The current-voltage curve of the reduced graphene oxide-graphene oxide composite film prepared in Example 1 under the positive and negative pressing conditions of the press was tested by using a Keithley 6487-type picoammeter, and the test results are shown in Figure 4 . It can be seen that when the measurement is run to the negative voltage and the positive voltage, pressing the composite film will produce a clear peak, and the peak obtained by pressing under the negative voltage is larger than that obtained by pressing under the positive voltage. The above results can also prove the PN junction characteristics of the sample. Figure 4

[0048] (2) R-T test: The reduced graphene oxide-graphene oxide composite film was placed between two Pt electrodes, and the process of pressing and stopping applying pressure was cycled by pressing for 5 s and then stopping applying pressure for 5 s. The voltage of the whole process was 0.5 V. The resistance-time curve of the reduced graphene oxide-graphene oxide composite film was tested by using a Keithley 6487-type picoammeter, and the test results are shown in Figure 5 . According to Figure 5 it can be seen that under the conditions of pressing and no pressing, the resistance value of the composite film differs by about 300 times, proving that the device has a good piezoresistive effect.

[0049] Example 2

[0050] 5 mg of reduced graphene oxide powder with a purity of >95wt% was doped into 10 mL of graphene oxide suspension with a mass concentration of 5 mg / mL (solvent: water). After ultrasonic treatment at 300 W for 3 h and stirring at a speed of 500 r / min for 1 h, a reduced graphene oxide-graphene oxide mixed solution was obtained.

[0051] Pt electrodes were placed on glass sheets, and 200 μL of the mixed solution was dropped onto the Pt electrodes using a 200 μL pipette. After dropping, the Pt electrodes were placed in a 60°C oven for drying for 15 min. The process of dropping and drying was repeated 5 times to obtain a reduced graphene oxide-graphene oxide composite film with a thickness of 0.2 μm. After natural cooling at room temperature, the composite film was peeled off from the Pt electrodes.

[0052] Example 3

[0053] 15 mg of reduced graphene oxide powder with a purity of >95wt% was doped into 10 mL of graphene oxide suspension with a mass concentration of 5 mg / mL (solvent: water). After ultrasonic treatment at 300 W for 3 h and stirring at a speed of 500 r / min for 1 h, a reduced graphene oxide-graphene oxide mixed solution was obtained.​

[0054] Pt electrode was placed on a glass sheet, 200 μL of the mixed solution was dropped on the Pt electrode, and the Pt electrode was dried in an oven at 60°C for 15 min after dropping. The dropping and drying process was repeated 5 times to obtain a reduced graphene oxide-graphene oxide composite film with a thickness of 0.2 μm. The obtained composite film was naturally cooled at room temperature and then peeled off from the Pt electrode.

[0055] The reduced graphene oxide-graphene oxide composite films prepared in Examples 2-3 were subjected to I-V and R-T tests according to the method of Example 1. The results showed that the composite films prepared in Examples 2-3 also had good rectification effect and piezoresistive characteristics.

[0056] The above only describes the preferred embodiments of the present application. It should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of the present application.

Claims

1. A method for fabricating a PN junction piezoresistive sensor based on carbon-based materials, characterized in that, Includes the following steps: Reduced graphene oxide and a graphene oxide suspension are mixed to obtain a mixture; the mass ratio of graphene oxide to reduced graphene oxide in the graphene oxide suspension is 10:1~3. The mixture is coated onto a substrate and then dried to obtain a reduced graphene oxide-graphene oxide composite film. The two ends of the reduced graphene oxide-graphene oxide composite film are connected with wires and then encapsulated to obtain a PN junction piezoresistive sensor based on carbon-based materials. The coating and drying are performed 2 to 10 times, and the coating and drying are performed alternately. The substrate is a Pt electrode.

2. The preparation method according to claim 1, characterized in that, The concentration of the graphene oxide suspension is 0.1~10 mg / mL; the solvent of the graphene oxide suspension is one or more of water, ethanol, acetone and dimethyl sulfoxide.

3. The preparation method according to claim 1, characterized in that, The purity of the reduced graphene oxide is >95 wt%.

4. The preparation method according to claim 1, characterized in that, The mixing process includes sequential ultrasonication and stirring. The ultrasonication time is 2-4 hours, the ultrasonic power is 200-400W, the stirring time is 1-2 hours, and the stirring speed is 450-650 r / min.

5. The preparation method according to claim 1, characterized in that, The coating method is drop coating; the drop coating is performed using a pipette.

6. The preparation method according to claim 1, characterized in that, After drying, the process also includes peeling the resulting reduced graphene oxide-graphene oxide composite film off the substrate.

7. The PN junction piezoresistive sensor based on carbon-based materials prepared by the preparation method according to any one of claims 1 to 6, wherein the PN junction piezoresistive sensor based on carbon-based materials is a reduced graphene oxide-graphene oxide composite film.

8. The PN junction piezoresistive sensor based on carbon-based materials according to claim 7, characterized in that, The thickness of the reduced graphene oxide-graphene oxide composite film is 0.2~1μm.

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