Controllable preparation and application of porous / non-porous monolayer crystals

Abstract

The present invention discloses a controllable preparation and application of porous / non-porous monolayer crystals. The preparation method comprises the following steps: using organic small molecules as raw materials, regulating the surface energy of the substrate, and obtaining porous or non-porous monolayer crystals on the substrate by dripping; the solvent used in the dripping method is toluene, o-xylene, chlorobenzene or o-dichlorobenzene; the concentration of the solution used is 0.01-1 mg / mL; plasma cleaning, OTS, BCB, Cytop or PMMA are used to regulate the surface energy of the substrate. The present invention adopts a "bottom-up" assembly process to directly and controllably prepare porous and non-porous monolayer crystals, which can not only effectively reduce the thickness of the organic semiconductor layer, reduce the diffusion distance of the object to be detected to the minimum (monolayer thickness), and overcome the limitation of the semiconductor layer thickness on the sensor sensitivity, but also directly prepare porous monolayer crystals, providing a channel for the object to be detected to directly interact with the carrier, which can greatly improve its sensor sensitivity.

Description

Technical Field

[0001] The invention relates to the controllable preparation and application of a porous / non-porous monolayer crystal, and belongs to the field of material preparation. Background Art

[0002] In field effect transistors, the charge density and charge transport in the conductive channel are not only regulated by the gate voltage, but also affected by external stimuli, which provides the possibility for the application of field effect transistors in the field of sensing. At present, traditional field effect transistor-based sensors use semiconductor films or single crystals as active layers. However, the sensitivity and response speed of such sensors are severely limited by the diffusion rate of their stimuli in the semiconductor layer. In order to improve the sensing performance and alleviate this limitation, a large number of improvement works have been reported, such as reducing the thickness of the semiconductor layer to a few molecular layers or even a single molecular layer, or preparing a porous organic semiconductor layer. Whether the porous semiconductor layer is prepared by the template-assisted method or the thermal annealing method, it is prepared by a "top-down" method. Therefore, it is still challenging to directly prepare porous crystals using a "bottom-up" assembly process. Summary of the invention

[0003] The purpose of the present invention is to provide a controllable preparation method of porous or non-porous monolayer crystals (MMCs). The present invention adopts a "bottom-up" assembly process to directly and controllably prepare porous and non-porous monolayer crystals, which can not only effectively reduce the thickness of the organic semiconductor layer, reduce the diffusion distance of the object to be detected to the minimum (monolayer thickness), and overcome the limitation of the semiconductor layer thickness on the sensor sensitivity, but also directly prepare porous monolayer crystals, providing a channel for the object to be detected to directly interact with the carrier, which can greatly improve its sensor sensitivity. This controllably prepared monolayer crystal field effect transistor sensor has excellent performance and is expected to be widely used in practical sensing applications.

[0004] The method for preparing the porous / non-porous monolayer crystal provided by the present invention comprises the following steps:

[0005] With organic small molecules as raw materials, porous or non-porous monolayer crystals are obtained on the substrate by regulating the surface energy of the substrate using a dripping method.

[0006] In the above preparation method, the organic small molecule can be a compound represented by Formula I or Formula II,

[0007]

[0008] In the above-mentioned preparation method, the solvent used in the dripping method can be toluene, o-xylene, chlorobenzene or o-dichlorobenzene;

[0009] The concentration of the solution used can be 0.01-1 mg / mL. The concentration of the solution affects the thickness of the prepared monolayer crystals. For example, when the concentration is 0.08 mg / mL, the obtained crystals are monolayer crystals with regular morphology and uniform thickness. When the solution concentration is greater than 0.08 mg / mL, the obtained crystals are mainly multilayer crystals.

[0010] In the above preparation method, oxygen plasma (plasma) cleaning, octadecyltrichlorosilane (OTS), divinylsiloxane-bis-phenylcyclobutene (BCB), perfluoropolymer (Cytop) or polymethyl methacrylate (PMMA) can be used to regulate the surface energy of the substrate, so that the surface free energy of the solvent is close to or less than the surface free energy of the substrate;

[0011] Modification can be performed as follows:

[0012] The modification methods are as follows:

[0013] ① Place the substrate to be modified in an oxygen plasma cleaning machine and clean it at 200W for 5 minutes;

[0014] ② Place the substrate to be modified in a vacuum oven in an OTS atmosphere and let it stand at 120°C for 2 hours;

[0015] ③ The BCB mesitylene solution was placed at room temperature for 1 hour and filtered with a 0.45 μm filter membrane; in a glove box, the BCB solution was spin-coated on the substrate surface and annealed at 260°C for 1 hour;

[0016] ④ In a glove box, spin coat the Cytop solution on the surface of the substrate to be modified and anneal at 90°C for 30 min;

[0017] ⑤ In air, spin-coat the PMMA solution on the surface of the substrate to be modified and anneal at 90°C for 10 min;

[0018] The crystals grown on the surface of the substrate modified by method ① have a porous structure, while the crystals grown on the substrate modified by methods ②-⑤ have a non-porous structure.

[0019] In the above preparation method, the substrate can be a silicon substrate, polyethylene terephthalate (PET) with indium tin oxide (ITO) electrodes, ITO glass, etc.

[0020] The porous or non-porous monomolecular layer crystal prepared by the present invention can be used to prepare a sensor based on a field effect transistor, wherein the porous or non-porous monomolecular layer crystal serves as a semiconductor layer.

[0021] The sensor may be a solid phase sensor or a gas phase sensor.

[0022] The sensor can be prepared according to the following steps:

[0023] After cleaning the substrate with the gate electrode, the substrate (the insulating layer is actually modified) is modified to adjust its surface free energy to meet the growth requirements of different types of crystals; then the porous and non-porous monolayer crystals are prepared on the above substrate, and finally the source and drain electrodes are prepared by the physical transfer gold film method, and silicon or ITO is used as the gate electrode.

[0024] The present invention has the following beneficial effects:

[0025] 1. The preparation process is simple and fast (the drip method can complete crystal growth in one step, no transfer is required, and it can be prepared directly on any substrate at room temperature);

[0026] 2. The growth of crystals (such as crystal thickness, the presence or absence of pores, and the size of pores) can be strictly controlled by regulating the solution concentration and the substrate surface energy. For example, when the solution concentration is less than or equal to 0.08 mg / mL, the grown crystals are mainly monolayer crystals, and when the concentration is greater than this, the grown crystals are mainly multilayer crystals. For example, SiO2 washed with plasma 2 The crystals grown on the surface have a porous structure, while the crystals grown on the BCB-modified substrate have a non-porous structure;

[0027] 3. The sensor device is prepared by electrode transfer method, avoiding the metal evaporation process and the use of mask;

[0028] 4. The sensor device prepared by the present invention can not only realize gas phase sensing, but also solid phase sensing, and is even expected to realize liquid phase sensing, and has extremely broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the sensor test device.

[0030] Figure 2 Optical micrographs of porous and nonporous monolayer crystals prepared for NDI.

[0031] Figure 3 Polarized light micrographs of porous and nonporous monolayer crystals prepared for NDI.

[0032] Figure 4 AFM and HR-AFM images of porous and nonporous monolayer crystals prepared for NDI.

[0033] Figure 5 This is the XRD pattern of multilayer NDI crystal.

[0034] Figure 6 Transfer curves and output curves of porous and nonporous monolayer crystals prepared for NDI.

[0035] Figure 7 This is the performance test curve of the gas phase sensor.

[0036] Figure 8 This is the performance test curve of the solid phase sensor. DETAILED DESCRIPTION

[0037] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0038] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0039] Example 1: Controllable preparation of porous and non-porous monolayer crystals

[0040] (1) preparing a series of stock solutions of the compound represented by formula I (NDI), the solvent being toluene, and the concentration range being 0.01 to 1 mg / mL;

[0041] (2) cleaning and performing surface modification on the substrate to adjust its surface energy, wherein the modification method is any one of the following 1) and 2):

[0042] 1) Place the substrate to be modified in an oxygen plasma cleaning machine and clean it at 200W for 5 minutes;

[0043] 2) In a glove box, spin coat the BCB solution on the substrate surface and anneal at 260°C for 1 h.

[0044] (3) The solution obtained in step (1) is dripped onto the surface of the substrate obtained in step (2) to obtain porous monolayer crystals (method 1) and non-porous monolayer crystals (method 2).

[0045] The optical, polarizing microscope, AFM and HR-AFM images of the monolayer crystal prepared in this example are shown in Figure 1. Figure 2 , Figure 3 and Figure 4 shown.

[0046] Figure 2 (a) and Figure 2 (b) Optical microscope images of porous monolayer crystals and non-porous ones, respectively. It can be seen that the sample has relatively uniform size and regular morphology.

[0047] Figure 3 (a) and Figure 3 (b) is a polarizing microscope image of a porous monolayer crystal. Figure 3 (c) and Figure 3 (d) is a polarizing microscope image of a non-porous monolayer crystal. It can be seen that both samples have consistent orientation, proving that the samples are both crystalline.

[0048] Figure 4 (a) and Figure 4 (b) AFM image and high-resolution AFM image of porous monolayer crystal, respectively. Figure 4 (c) and Figure 4 (d) are the AFM image and high-resolution AFM image of the non-porous monolayer crystal, respectively. It can be seen that the thickness of the crystal is 2.0nm, and the two are porous crystals and non-porous crystals respectively. Its thickness is close to the length of the molecule, and its multilayer crystal XRD structure ( Figure 5 ) proved that the crystal grew in layers with a d-spacing of 2.08nm. Therefore, both samples were single-layer crystals.

[0049] The substrates were modified by the following methods: a) placing the substrate to be modified in a vacuum oven in an OTS atmosphere and standing at 120°C for 2 hours; b) in a glove box, spin coating the surface of the substrate to be modified with Cytop solution and annealing at 90°C for 30 minutes; c) in air, spin coating the surface of the substrate to be modified with PMMA solution and annealing at 90°C for 10 minutes. The above methods were tested to obtain non-porous monolayer crystals.

[0050] Example 2: Field effect transistor based on porous and non-porous monolayer crystals

[0051] (1) Cleaning of substrate with gate electrode

[0052] 1×1cm 2 The silicon wafer with a certain thickness of silicon dioxide layer (as an insulating layer and gate electrode) was first ultrasonically cleaned with deionized water and then cleaned with Piranha (H 2 O 2 :H 2 SO 4 =3:7) in a boiling water bath, followed by ultrasonic cleaning with deionized water and isopropanol, and drying with nitrogen.

[0053] (2) Preparation of organic field effect transistors

[0054] According to the method in Example 1, porous and non-porous monolayer crystals were prepared on the silicon wafer cleaned in step (1) (the surface energy of the substrate was regulated by oxygen plasma cleaning (plasma) and BCB modification, respectively), and the source and drain electrodes were prepared by transferring the gold film.

[0055] The transfer curve and output curve of the organic field effect transistor prepared in this embodiment are shown in FIG. Figure 6 As shown, Figure 6 (a) and Figure 6 (b) is the transfer curve and output curve of the porous monolayer crystal. Figure 6 (c) and Figure 6(d) is the transfer curve and output curve of the non-porous monolayer crystal. Figure 6 The illustration in (a) is a schematic diagram of the sensor structure based on field effect transistor, which includes silicon, silicon dioxide, monolayer crystal and source and drain electrodes from bottom to top. It adopts a bottom-gate top contact configuration. The monolayer crystal is the organic semiconductor layer (1.8-2.1nm), the 100nm gold film is the source and drain electrode, and the silicon substrate is the gate.

[0056] Depend on Figure 6 It can be seen that the mobility of the organic field effect transistor with porous monolayer crystal as the semiconductor layer is 1.33×10 -2 cm 2 V -1 s -1 The mobility of an organic field-effect transistor with a nonporous monolayer crystal as the semiconductor layer is 5.47×10 -2 cm 2 V -1 s -1 .

[0057] Example 3: Performance of field effect transistor sensors based on porous and non-porous monolayer crystals

[0058] 1) Preparation of gas phase and solid phase analytes

[0059] ① Purchase the NH 3 The standard gas is diluted with nitrogen to a series of concentrations:

[0060] 0.1ppb, 1ppb, 10ppb, 100ppb, 1ppm, 100ppm, 1% (v / v);

[0061] ② Grind dopamine into powder and disperse it in the ground silica gel powder to a mass ratio of 500 ppb;

[0062] 2) Testing of device sensing performance

[0063] ①Performance test of gas phase sensor:

[0064] use Figure 1 The device shown tests the gas sensing performance. In sampling mode, V G =V DS =50V, and then the prepared ammonia gas of different concentrations was introduced in turn. The results are as follows Figure 7 As shown in the figure, the non-porous monolayer crystal exhibits good sensing performance, with a response value of 72% for 1 ppb ammonia, and its response value increases with the increase of gas concentration.

[0065] The porous monolayer crystal further exposes the sites where the semiconductor interacts with ammonia due to its pore structure, and its sensing performance is further improved. The response value for 1 ppb ammonia reaches 190%, and its minimum detection limit is 0.1 ppb, which is the lowest value reported so far for field effect transistor sensors. Since the non-porous monolayer crystal has a wider detection range, it can detect ammonia from 1 ppb to 1%, and can be used as a supplement to the porous monolayer crystal sensor.

[0066] Since the semiconductor layer is a single molecular layer, the conductive channel can be directly exposed, and the object to be detected can directly interact with the carriers in the conductive channel, thus providing the possibility for solid-phase sensing.

[0067] ②Performance test of solid phase sensor:

[0068] In sampling mode, V G =V DS =50V, add different concentrations of solid powder to be tested in sequence. Figure 8 As shown. The sensor based on the non-porous monolayer crystal showed excellent performance and achieved the detection of solid substances at the ppb level. The response value for 500 ppb dopamine powder reached 7.58. This is the first field effect transistor solid phase sensor to date.

Claims

1. A method for preparing a porous or non-porous monolayer crystal, comprising the following steps: Using organic small molecules as raw materials, by regulating the surface energy of the substrate, a porous or non-porous monolayer crystal is obtained on the substrate using a dripping method; The organic small molecule is a compound represented by Formula I or Formula II: The solvent used in the dripping method is toluene, o-xylene, chlorobenzene or o-dichlorobenzene; The concentration of the solution used is 0.01 to 1 mg / mL; Using plasma cleaning, OTS, BCB, Cytop or PMMA to regulate the surface energy of the substrate; The control method is any one of the following 1)-5): 1) placing the substrate to be modified in an oxygen plasma cleaning machine for cleaning; 2) placing the substrate to be modified in a vacuum oven in an OTS atmosphere and leaving it to stand; 3) In a glove box, spin-coat the surface of the substrate to be modified with BCB solution and anneal; 4) In a glove box, spin-coat the surface of the substrate to be modified with a Cytop solution and anneal; 5) In air, spin-coat the PMMA solution on the surface of the modified substrate and anneal.

2. The preparation method according to claim 1, characterized in that: The substrate is a silicon substrate, PET with an ITO electrode or ITO glass.

3. A porous or non-porous monolayer crystal prepared by the method of claim 1 or 2.

4. Use of the porous or non-porous monolayer crystal according to claim 3 in preparing a sensor based on a field effect transistor; The porous or non-porous monomolecular layer crystal serves as a semiconductor layer.

5. The use according to claim 4, characterized in that: The sensor is a solid phase sensor or a gas phase sensor.

6. A sensor based on a field effect transistor, characterized in that: The porous or non-porous monolayer crystal according to claim 3 is used as a semiconductor layer.

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