A two-step liquid phase exfoliation method for synthesizing MoTe2 quantum dot ink and a preparation method of a near-infrared detector thereof

Abstract

The application relates to a preparation method of high-quality MoTe2 quantum dot (QD) ink and a thin film device, and particularly relates to the technical field of MoTe2 QD ink and near-infrared detector preparation, which comprises the following steps: MoTe2 powder is weighed and added into a N-methyl-pyrrolidone solvent, after ultrasonic treatment for 30 hours, the precipitate is reserved by centrifugation; the cleaned MoTe2 nanosheet is obtained after vacuum drying; N,N-dimethylformamide is added into the cleaned MoTe2 nanosheet powder, ultrasonic treatment is carried out for 30 hours, the mixed solution after ultrasonic treatment is centrifuged at 1000 r / min to obtain supernatant, the supernatant is centrifuged at 8000 r / min to obtain a precipitate, and acetone solution is added into the MoTe2 QD precipitate, then the MoTe2 QD precipitate is washed, centrifuged and dried to obtain the final MoTe2 QD powder; in the MSM structure device, quantum dots are used as a photosensitive layer, gold electrodes at two ends are responsible for transmitting electrons and holes, and the planar device structure enables the device to absorb incident light to a greater extent, compared with a vertical structure device, the attenuation effect of a functional layer on incident light is avoided.

Description

Technical Field

[0001] This invention relates to a method for fabricating high-quality MoTe2 quantum dot (QDs) ink and thin-film devices, specifically relating to the field of MoTe2 QDs ink and near-infrared detector fabrication technology. Background Technology

[0002] Infrared detectors are widely used in night vision imaging, communication, and gas sensing. Molybdenum ditelluride (MoTe2) belongs to the transition metal dichalcogenides (TMDs) family and is a material with a narrow band gap and high electron mobility. However, due to its van der Waals structure, research on quantum dot devices based on this material is currently limited. Therefore, the fabrication and performance study of devices based on this material are of great significance for the development of photoelectric detection devices.

[0003] MoTe2 is a popular low-toxicity two-dimensional semiconductor material in the field of near-infrared detectors, and thin films made from it are often the most critical component of the detector. However, there are no reports on near-infrared detectors using MoTe2 quantum dots (QDs). Fabricating MoTe2 into quantum dot ink using a top-down method and then spin-coating it into a thin film as the photosensitive layer of a near-infrared detector would be beneficial for expanding the application of MoTe2 quantum dots in optoelectronic fields.

[0004] Spin-coating MoTe2 ink to prepare MoTe2 QDs thin films can introduce interfacial defects, causing carrier recombination during transport. This reduces carrier migration rates and degrades device performance. Therefore, fabricating thin films with smooth, dense, and uniform surfaces is crucial. Summary of the Invention

[0005] The main objective of this invention is to provide a two-step liquid-phase exfoliation method for synthesizing MoTe2 quantum dot ink and its near-infrared detector, thereby addressing the problems existing in the background art. Specifically, this invention provides the following technical solution:

[0006] This invention provides a method for preparing MoTe2 quantum dot (QDs) ink, comprising the following steps:

[0007] S1: Weigh MoTe2 powder and add it to a condenser beaker containing N-methyl-pyrrolidone solvent. Sonicate the mixture for 30 hours using an ultrasonic instrument at 300W power, then centrifuge and retain the precipitate. Wash the precipitate several times with acetone and vacuum dry it to obtain cleaned MoTe2 nanosheets.

[0008] S2: Add N,N-dimethylformamide to the cleaned MoTe2 nanosheet powder, sonicate at 300W for 30h, centrifuge the ultrasonicated mixture at 1000r / min to collect the supernatant, then centrifuge the supernatant at 8000r / min to collect the precipitate, add acetone solution to the MoTe2 QDs precipitate, wash 2-3 times to obtain MoTe2 QDs solution, centrifuge and discard the supernatant, dry the precipitate to obtain the final MoTe2 QDs powder;

[0009] S3: Add isopropanol solvent to the final MoTe2 QDs powder and shake to dissolve it, thus obtaining MoTe2QDs ink.

[0010] Furthermore, in step S1, the mass-to-volume ratio of MoTe2 powder to N-methylpyrrolidone solvent is 2:50.

[0011] Furthermore, in step S2, the mass-to-volume ratio of MoTe2 nanosheets to N,N-dimethylformamide solvent is 2:50.

[0012] The present invention also provides a method for preparing MoTe2 QDs thin films, wherein the method comprises obtaining MoTe2 QDs thin films by spin coating of any of the preparation methods described herein.

[0013] Furthermore, the application of MoTe2 QDs ink obtained by any of the preparation methods described in this invention in the preparation of near-infrared detectors.

[0014] In one embodiment, the present invention provides a method for fabricating a near-infrared detector, wherein a near-infrared detector with a Si-SiO2-Au structure is fabricated by magnetron sputtering. During the fabrication process, a thin film of MoTe2 QDs ink obtained by any fabrication method is spin-coated onto the gold electrode to form an Au-MoTe2-Au structure.

[0015] The technical effects achieved by this invention are as follows:

[0016] This invention utilizes quantum dots as the photosensitive layer in an MSM (Metal-Semiconductor-Metal) structure device, with gold electrodes at both ends responsible for electron and hole transport. The planar device structure allows for greater absorption of incident light, avoiding the attenuation effect of the functional layer on incident light compared to vertical structures. Under 850nm light illumination, this quantum dot device exhibits a maximum responsivity of 0.13 A / W and a detectivity of 2.4 × 10⁻⁶. 10 Jones; 0.05 A / W and 8 × 10⁻⁶ under 940 nm illumination. 9 Jones, this result provides a strategy for applying MoTe2 quantum dots to optoelectronic devices. Attached Figure Description

[0017] Figure 1 Preparation and TEM images of MoTe2: (a) Flowchart of MoTe2 QDs preparation; (b) Flowchart of MoTe2 QDS device preparation; (cf) TEM image of MoTe2 nanosheets prepared by NMP ultrasonication; (gh) TEM image of MoTe2 QDs prepared by DMF ultrasonication;

[0018] Figure 2 Optical testing and device structure characterization of MoTe2 quantum dots. (a) Relationship between diameter and band gap of MoTe2 quantum dots, (b) UV-Vis-NIR absorption spectrum of quantum dots, (c) AFM image of MoTe2 quantum dot layer, (d) Device structure diagram, (e) Cross-sectional SEM image of device, (f) Planar SEM image of device.

[0019] Figure 3 The photoelectric performance test results of MoTe2 are shown in the figure: (a) IV diagram of the photodetector of MoTe2 device under 850nm and 940nm LED light source; (bd) EQE, R and D* of MoTe2 device are respectively. Specific Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0022] Example 1: Preparation of MoTe2 quantum dot ink

[0023] Figure 1 (a) is a flowchart of the preparation process of MoTe2 quantum dots by liquid phase exfoliation, and the specific steps are as follows:

[0024] S1: Weigh 2g of MoTe2 powder and add it to a condenser beaker containing 50mL of N-methyl-pyrrolidone solvent. Sonicate the mixture for 30h using a probe-type ultrasonic instrument at 300W. Centrifuge the ultrasonically treated mixture at 8000r / min for 20min and retain the precipitate. Wash the precipitate 2-3 times with acetone and vacuum dry it to obtain cleaned MoTe2 nanosheets.

[0025] S2: Add 50 mL of N,N-dimethylformamide to 2 g of cleaned MoTe2 nanosheet powder, and then sonicate for 30 h using a probe-type ultrasonic instrument at 300 W to obtain a mixture of MoTe2 quantum dots and nanosheets. After ultrasonic treatment, centrifuge the mixture at 1000 r / min to collect the supernatant, thereby removing the unbroken MoTe2 nanosheets. Then centrifuge the supernatant at 8000 r / min to collect the precipitate. Add acetone solution to the MoTe2 QDs precipitate and wash 2-3 times to obtain the MoTe2 QDs solution. Centrifuge and discard the supernatant. After drying, obtain the final MoTe2 QDs powder.

[0026] S3: Add isopropanol solvent to the final MoTe2 QDs powder and shake to dissolve it, thus obtaining MoTe2QDs ink;

[0027] S4: Obtain MoTe2 QDs thin films by spin coating MoTe2 QDs ink solution.

[0028] Example 2: Fabrication of MoTe2 quantum dot devices

[0029] The obtained MoTe2 quantum dot powder was mixed with isopropanol as a dispersant to prepare 80 mg / mL MoTe2 quantum dot ink for later use. Then, a near-infrared detector with a Si-SiO2-Au structure was prepared by magnetron sputtering. A thin film of MoTe2 quantum dot ink was spin-coated in the middle of a gold electrode.

[0030] The specific steps are as follows:

[0031] S1: Ultrasonic cleaning of silicon wafers in acetone and deionized water for 30 minutes each;

[0032] S2: A 300nm thick SiO2 thin film is deposited on the front side of the silicon wafer using magnetron sputtering technology;

[0033] S3: Place the mask on the deposited SiO2 film, and then use magnetron sputtering technology to sputter a 50nm gold electrode on the SiO2 surface;

[0034] S4: Spin-coat the MoTe2 QDs solution onto the center of the gold electrode;

[0035] S5: The spin-coated electrodes are attached to the circuit board, and gold wires are drawn out from the two electrodes on the sample surface using silver paste. The other end of the gold wires is soldered to the circuit board. Then, the load circuit is connected from the corresponding pins to test its response characteristics.

[0036] Effect

[0037] Figure 1(a) is a schematic diagram of the liquid-phase exfoliation method for preparing quantum dots. NMP (N-methylpyrrolidone) is mainly used to break the van der Waals forces between the layers of MoTe2 material during the ultrasonic process, thereby preparing MoTe2 few-layer nanosheets with a lateral size of 100-200 nm. Then, DMF (N,N-dimethylformamide) is used to break the covalent bonds between Te and Mo in the MoTe2 nanosheets during the ultrasonic process. The entire process is carried out in a cooling circulating water cup to ensure a constant experimental temperature. Finally, MoTe2 quantum dots with an average particle size of 3.5 nm are obtained. Finally, the quantum dot powder is dried at 50 degrees Celsius in a vacuum drying oven, and MoTe2 quantum dot ink with a concentration of 80 mg / mL is prepared using isopropanol solvent as a dispersant. Figure 1 (b) SiO2 and Au are sputtered layer by layer on a silicon wafer by magnetron sputtering, and finally MoTe2 quantum dot ink is spin-coated onto the interdigitated electrodes of the Si-SiO2-Au structure. Figure 1 (cf) is a TEM image of MoTe2 nanosheets obtained by sonicating MoTe2 powder under NMP for 30 hours. Figure 1 As can be seen in (c), the lateral size of the nanosheets is between 100-300 nm, indicating that NMP has a high efficiency in ultrasonic ablation. Figure 1 (d) is the TEM diffraction pattern of the nanosheet. The diffraction points marked in the figure correspond to the four crystal planes (0 0 8), (1 0 0), (1 0 8), and (2 0 8) of the MoTe2 material. The arrows from the transmission center to the diffraction spots can also represent vectors, which satisfy the geometric properties of vectors in the diffraction space. The geometric vector formed by (0 0 8) and (1 0 0) corresponds to the (1 0 8) crystal plane, and the geometric vector formed by (1 0 0) and (1 0 8) corresponds to the (2 0 8) crystal plane. Figure 1 (e) shows the van der Waals layers on the side of a relatively thick MoTe2 nanosheet as scanned by TEM, with an interlayer spacing of 0.7 nm. Each layer is composed of alternating Te and Mo atomic structures. Figure 1 (e) shows the relatively thick MoTe2 nanosheet plane as scanned by TEM. The plane is composed of alternating hexagonal structures of Te and Mo atoms. Figure 1 (f) is a TEM image of MoTe2 quantum dots obtained by DMF sonication. The inserted particle size distribution map shows an average particle size (Xc) of 3.5 nm and a full width at half maximum (FWHM) of 1.3 nm, indicating that this method is feasible for preparing MoTe2 quantum dots. Figure 1 (d) is a high-resolution transmission electron microscope (HRTEM) image of the quantum dots, which clearly shows that they have high crystallinity and have (0 0 8) and (1 0 5) crystal planes, indicating that the ultrasonic process did not damage the crystal structure of MoTe2.

[0038] The relationship between the band gap and size of MoTe2 QDs can be calculated using the following formula:

[0039]

[0040] E in formula 1 g The bulk band gap of MoTe2 material is 0.88 eV, m e It is the effective mass of electrons (m) e =0.34m0), m h The effective mass of holes (m) h =0.48m0), m o =9.11×10 -34 F / m, ε0 is the vacuum permittivity (8.854 × 10⁻⁶). -12 F / m), ε r is the relative permittivity of MoTe2 (13), e is the electron charge, and R is the radius of the quantum dot;

[0041] Figure 2 (a) The particle size and band gap variation curves of MoTe2 quantum dots obtained by Equation 1 show that the bulk band gap of MoTe2 is 0.88 eV (marked by the red dashed line in the figure). The band gap of the quantum dots is very large, exceeding 3 eV, when their size is very small. This is because the quantum effect is extremely large due to the small size of the quantum dots. The band gap decreases with increasing radius until it exceeds the exciton Bohr radius, after which this quantum effect is almost negligible. This results in the quantum dot band gap having almost no size correlation after the quantum dot size exceeds 4 nm, approaching the bulk band gap. This means that when the diameter varies within 4 nm, the material exhibits a strong quantum size effect, further demonstrating that experimentally prepared 3.5 nm MoTe2 quantum dots produce unique quantum effects. Figure 2 (b) is the UV-Vis-NIR absorption spectrum of MoTe2 quantum dots spin-coated on quartz. It can be seen from the figure that its absorption covers the visible and near-infrared bands. The bulk band gap of this material is 0.88 eV. When it becomes a quantum dot structure, the band gap will increase. From the exciton peak at 1150 nm in the figure, it can be roughly concluded that the band gap of the MoTe2 quantum dot structure is 1.10 eV. Figure 2 (c) is an atomic force microscope (AFM) image of the quantum dot film, which shows that the surface roughness of the film is 12 nm and the surface is relatively smooth. Figure 2 (d) is a physical image of the MoTe2 quantum dot device; Figure 2 (e) is a cross-sectional scanning electron microscope (SEM) image of the interdigitated electrode, which shows Si, SiO2 and MoTe2 quantum dot layers from bottom to top. The MoTe2 quantum dot layer serves as the photosensitive layer and has a thickness of about 260 nm. The film thickness is flat. Figure 2(f) is a planar SEM image of the near-infrared detector without spin-coated MoTe2 quantum dots. The gold part represents the gold electrode, and the black area in the middle represents the channel, which has a width of 1 μm.

[0042] Figure 3 (a) shows the IV diagrams of the MoTe2 near-infrared detector under LED light sources at 850nm and 940nm. It can be seen that the device has a certain response to near-infrared light, and has a greater response to 850nm light, which is related to the optical absorption of the material. Figure 3 (bd) shows the EQE, R, and D* of the device within a bias range of -1V to 1V, calculated using the IV curve. When illuminated with light at wavelengths of 940nm and 850nm, respectively, EQE reaches its maximum value at -1V, at 0.18 and 0.50, respectively; R is 0.05A / W and 0.14A / W at -1V, respectively; and D* reaches 8×10⁻⁶ at -1V. 9 Jones and 2.4×10 10 Jones

[0043] In summary, this invention prepared MoTe2 quantum dots with an average size of 3.5 nm using a stepwise ultrasonic liquid-phase exfoliation method with NMP and DMF solvents, and dispersed them in isopropanol to prepare quantum dot ink. MoTe2 was then spin-coated as the photosensitive layer material for an Au-MoTe2-Au near-infrared detector. I-V curves of the device under different wavelengths of light showed that the maximum responsivity and detectivity of the quantum dot device under 850 nm light illumination were 0.13 A / W and 2.4 × 10⁻⁶, respectively. 10 Jones; 0.05 A / W and 8 × 10⁻⁶ under 940 nm illumination. 9 Jones's work indicates that MoTe2 has great application potential in the field of photoconductive near-infrared detectors. In future research, improving the surface smoothness of MoTe2 thin films may enable this quantum thin film to be applied to vertical junction detectors.

Claims

1. A method for preparing a MoTe2 quantum dot (QDs) ink, and an application of the MoTe2 QDs ink in preparing a near-infrared detector, characterized in that, Comprising the following steps: S1: MoTe2 powder is weighed and added to a condensing beaker containing N-methyl-pyrrolidone solvent, after 30 hours of ultrasonic treatment at a power of 300W, the precipitate is centrifuged and reserved; the precipitate is washed with acetone multiple times, and after vacuum drying, clean MoTe2 nanosheets are obtained; S2: N,N-dimethylformamide is added to the clean MoTe2 nanosheet powder, and the mixture is ultrasonically treated for 30 hours at a power of 300W; the treated mixture is centrifuged at 1000 r / min to obtain the supernatant, and the supernatant is then centrifuged at 8000 r / min to obtain the precipitate; acetone solution is added to the MoTe2 QDs precipitate, and the mixture is washed 2-3 times to obtain a MoTe2 QDs solution; the solution is centrifuged and the supernatant is discarded, and the precipitate is dried to obtain the final MoTe2 QDs powder; S3: Isopropyl alcohol solvent is added to the final MoTe2 QDs powder and shaken to dissolve, obtaining MoTe2 QDs ink; In step S1, the mass-volume ratio of MoTe2 powder to N-methyl-pyrrolidone solvent is 2:50; In step S2, the mass-volume ratio of MoTe2 nanosheet to N,N-dimethylformamide solvent is 2:

50.

2. A method for preparing a near-infrared detector, the near-infrared detector with a Si-SiO2-Au structure is prepared by magnetron sputtering, characterized in that, During the preparation process, the MoTe2 QDs ink obtained by the preparation method of claim 1 is spin-coated to form a thin film in the middle of the gold electrode to form an Au-MoTe2-Au structure.

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