Electroluminescent device based on hexagonal boron nitride and preparation method thereof

Abstract

The invention relates to an electroluminescent device based on hexagonal boron nitride and a preparation method thereof, and belongs to the technical field of electroluminescent devices. The electroluminescent device based on hexagonal boron nitride comprises: a metal substrate; the silver nanowire layer is arranged on the surface of the metal substrate; the hexagonal boron nitride layer is arranged on the surface of the silver nanowire layer; the graphene layer is arranged on the surface of the hexagonal boron nitride layer and is in contact with the metal substrate; the silver nanowire layer, the hexagonal boron nitride layer and the graphene layer form a tunnel junction structure, the limitation of a large band gap of hexagonal boron nitride is overcome, the electroluminescent device based on the hexagonal boron nitride is achieved in an electrical excitation mode, and fluorescence emission from visible light to a near-infrared band is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of electroluminescent devices, and in particular relates to an electroluminescent device based on hexagonal boron nitride and a preparation method thereof. Background Art

[0002] Defects within the hexagonal boron nitride lattice, such as boron or nitrogen vacancies, have high photon emission efficiency at room temperature. Hexagonal boron nitride has a wide band gap (~6eV), and its lattice defects have different band structures, so that the luminescence wavelength of hexagonal boron nitride defects covers the range from ultraviolet to visible light and near-infrared. At the same time, defect-based luminescence in hexagonal boron nitride has been shown to have single-photon luminescence characteristics and can be activated at selected locations through stress engineering. These luminescence characteristics of defects in hexagonal boron nitride make it have the potential to be a room-temperature single-photon light source.

[0003] However, currently almost all hBN-based defect emission has been studied under photoexcitation, while electrically driven light sources based on hBN defect emission remain quite challenging considering the wide bandgap of hBN. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an electroluminescent device based on hexagonal boron nitride and a preparation method thereof, which overcomes the limitation of the large band gap of hexagonal boron nitride and realizes an electroluminescent device based on hexagonal boron nitride through electrical excitation, which has fluorescence emission in the visible light to near-infrared band.

[0005] The first object of the present invention is to provide an electroluminescent device based on hexagonal boron nitride, comprising: Metal substrate; A silver nanowire layer is disposed on the surface of the metal substrate; A hexagonal boron nitride layer is disposed on the surface of the silver nanowire layer; A graphene layer is disposed on the surface of the hexagonal boron nitride layer and is in contact with the metal substrate; The silver nanowire layer, the hexagonal boron nitride layer and the graphene layer form a tunnel junction structure.

[0006] In one embodiment of the present invention, the diameter of the silver nanowire is 280nm-320nm and the length is 10μm-50μm. The silver nanowire has a relatively sharp cross section, which is easier to activate the hexagonal boron nitride defects; in addition, the silver nanowire acts as a bottom electrode and a local stress source, which is used to inject charge carriers and activate defects in the hexagonal boron nitride layer to achieve electrically driven defect emission.

[0007] In one embodiment of the present invention, the thickness of the hexagonal boron nitride layer is 2nm-6nm. Hexagonal boron nitride is a wide bandgap material, and the fluorescence emission wavelength covers ultraviolet, visible and infrared, so the electrically excited hexagonal boron nitride defect luminescence has a larger wavelength range, so the bias voltage-induced electroluminescence (EL) emission based on the tunnel junction of hexagonal boron nitride has the opportunity to be a highly integrated electrically driven light source operating at room temperature.

[0008] In one embodiment of the present invention, the thickness of the graphene layer is 5nm-15nm. Graphene has excellent conductivity and very high light transmittance. Because the present invention is about electroluminescence, the light transmittance of the upper electrode is required to be high, otherwise it will affect its luminous efficiency and the collection of the luminous spectrum.

[0009] In one embodiment of the present invention, the metal substrate is selected from gold, silver, copper, nickel, ITO, FTO or PEDOT:PSS.

[0010] In one embodiment of the present invention, the electroluminescent device based on hexagonal boron nitride, under external bias, has a tunnel junction structure that allows quantum tunneling to occur preferentially in the local stress region of the hexagonal boron nitride layer, resulting in sub-band transition or defect emission of the hexagonal boron nitride.

[0011] In one embodiment of the present invention, the light emitting band of the hexagonal boron nitride based electroluminescent device is visible light or near infrared light.

[0012] The second object of the present invention is to provide a method for preparing the electroluminescent device based on hexagonal boron nitride, comprising the following steps: S1, preparing a silver nanowire layer on the surface of a metal substrate; S2, preparing a hexagonal boron nitride layer on the surface of the silver nanowire layer; S3. Prepare a graphene layer on the surface of the hexagonal boron nitride layer and contact it with the metal substrate.

[0013] In one embodiment of the present invention, in S1, the method for preparing the silver nanowire layer is selected from chemical synthesis combined with dry transfer, and photolithography combined with metal evaporation.

[0014] In one embodiment of the present invention, in S2, the preparation method of the hexagonal boron nitride layer is selected from mechanical stripping combined with dry transfer and chemical synthesis combined with wet transfer.

[0015] In one embodiment of the present invention, in S3, the graphene layer is prepared by a method selected from mechanical exfoliation combined with dry transfer and chemical synthesis combined with wet transfer.

[0016] The technical solution of the present invention has the following advantages over the prior art: The silver nanowires in the hexagonal boron nitride-based electroluminescent device described in the present invention not only serve as the bottom electrode for injecting charge carriers, but also can introduce local strain to activate atomic-level defects in thin-layer hexagonal boron nitride. Under the action of an external bias voltage, quantum tunneling occurs preferentially in the defect region of the thin-layer hexagonal boron nitride, i.e., a local conduction channel, thereby leading to sub-band transitions or defect emission of the thin-layer hexagonal boron nitride. In addition, the defect luminescence of hexagonal boron nitride is single-photon emission, and the bias voltage-induced electroluminescence (EL) spatially overlaps with the laser-excited photoluminescence (PL) emission with a bias-independent spectrum, indicating that both luminescences originate from the same defect in the thin-layer hexagonal boron nitride, and the device has the potential to be an electrically driven single-photon light source at room temperature.

[0017] Defects in the hexagonal boron nitride lattice in the hexagonal boron nitride-based electroluminescent device of the present invention change its local electrical properties. The current-voltage characteristics of the hexagonal boron nitride tunnel junction show step-like behavior, and the defects dominate the charge transport and can serve as an electrical switching center.

[0018] The electroluminescent device based on hexagonal boron nitride of the present invention is designed with a tunnel junction structure of silver nanowires / hexagonal boron nitride / graphene, which allows quantum tunneling to occur preferentially in the defective region of the hexagonal boron nitride layer, resulting in sub-band transition or defect emission of the hexagonal boron nitride, thereby realizing electrically driven fluorescence emission of thin-layer hexagonal boron nitride. The limitation of the large band gap of hexagonal boron nitride is overcome, and fluorescence emission from the visible light to the near-infrared band is realized by electrical excitation, paving the way for the further development of electrically driven light sources based on thin-layer hexagonal boron nitride, which has important scientific significance and application prospects.

[0019] The hexagonal boron nitride-based electroluminescent device described in the present invention extends the defect-based emission research in hexagonal boron nitride materials from light excitation to electrical excitation, provides a new electrically excited defect emission mechanism, and provides a new approach to preparing high-performance optoelectronic devices.

[0020] The hexagonal boron nitride-based electroluminescent device of the present invention can be used as a highly integrated nanoscale electrically driven light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein: Figure 1 This is a process flow chart of an electroluminescent device based on hexagonal boron nitride according to Example 1 of the present invention; Figure 2 1 is a characterization diagram of the thickness of hexagonal boron nitride in Example 1 of the present invention; wherein a is an atomic force microscope characterization diagram, and b is a data diagram; Figure 3 It is a characterization diagram of the thickness of hexagonal boron nitride in comparative example 1 of the present invention; wherein a is an atomic force microscope characterization diagram, and b is a data diagram; Figure 4 This is an atomic force microscope characterization image of the morphology of hexagonal boron nitride according to Example 1 of the present invention; Figure 5 This is a scanning electron microscope characterization image of the morphology of hexagonal boron nitride according to Example 1 of the present invention; Figure 6 The photoluminescence images of defects in hexagonal boron nitride layers of different thicknesses activated by stress in Test Example 2 of the present invention are shown; wherein a is 3 nm, b is 4 nm, c is 5 nm, and d is 6 nm; Figure 7 Statistical diagram of peak positions of defects in the hexagonal boron nitride layer in Test Example 3 of the present invention, wherein a is a representative photoluminescence spectrum of defect emission, b is a histogram of zero phonon lines emitted by the defect, and c is a histogram of photon sidebands emitted by the defect; Figure 8 This is an electric drive characterization diagram of the hexagonal boron nitride-based electroluminescent device of Example 1 in Test Example 4 of the present invention; wherein a is a current-voltage curve diagram, b is a photoluminescence imaging diagram, and c is an electroluminescence imaging diagram; Fig. 9 This is an electric drive characterization diagram of the hexagonal boron nitride-based electroluminescent device of Comparative Example 1 in Test Example 4 of the present invention; wherein a is a current-voltage curve diagram, b is a photoluminescence imaging diagram, and c is an electroluminescence imaging diagram; Fig.10 This is an analysis diagram of the electrically driven luminescence spectrum of the hexagonal boron nitride-based electroluminescent device of Example 1 in Test Example 5 of the present invention; wherein a is the electroluminescence spectrum and multi-peak fitting diagram, b is a curve diagram of the change of electroluminescence peak wavelength with voltage, and c is a half-peak width diagram of the electroluminescence peak; Fig.11 It is the three-dimensional finite difference time domain simulation result based on the structure of Example 1 in Test Example 5 of the present invention; wherein a is the scattering spectrum diagram, and b is the field intensity distribution diagram. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0023] In the present invention, unless otherwise explained, technical and scientific terms used in the present invention have the same meanings as commonly understood by those skilled in the art to which the present invention belongs.

[0024] In the present invention, unless otherwise stated, the term "and / or" used in the present invention includes any and all combinations of one or more of the associated listed items.

[0025] In the present invention, unless otherwise stated, the experimental methods used in the embodiments of the present invention are conventional methods unless otherwise stated, and the materials, reagents, etc. used are all commercially available unless otherwise stated.

[0026] In the present invention, unless otherwise specified, the silver nanowires used in the embodiments of the present invention have a diameter of about 300 nm and a length of about 30 μm. Example 1

[0027] Reference Figure 1 As shown, the electroluminescent device based on hexagonal boron nitride and the preparation method thereof of the present invention specifically include the following steps: S1. Expose the gold counter electrode to ultraviolet light for 15 min; S2, dissolving the silver nanowires in alcohol to prepare a silver nanowire solution, dropping the silver nanowire solution on the polydimethylsiloxane, waiting for the alcohol to evaporate naturally, and transferring the silver nanowires to the gold counter electrode by dry transfer technology; S3, transferring the hexagonal boron nitride layer with a thickness of about 4 nm obtained by mechanical exfoliation to the silver nanowires through a two-dimensional material transfer platform; S4. The graphene layer with a thickness of about 15 nm obtained by mechanical peeling is transferred to the hexagonal boron nitride layer through a two-dimensional material transfer platform and contacted with a gold counter electrode. A DC bias is applied to the graphene layer side and the silver nanowire side is grounded. Comparative Example 1

[0028] It is basically the same as Example 1, except that the thickness of the hexagonal boron nitride layer is 7 nm. Test Example 1

[0029] Based on Example 1 and Comparative Example 1, the thickness of the hexagonal boron nitride layer after transfer was characterized using an atomic force microscope. The results are as follows: Figure 2-Figure 3 As shown. Figure 2 It can be seen that the thickness of the hexagonal boron nitride layer of Example 1 is about 4 nm. Figure 3 It can be seen that the thickness of the hexagonal boron nitride layer of Comparative Example 1 is about 7 nm.

[0030] Based on Example 1, the morphology of the transferred hexagonal boron nitride layer was characterized using an atomic force microscope. The results are as follows Figure 4 As shown. Figure 4 It can be seen that the three-dimensional contours of the silver nanowires are intact, thus ensuring the stress-induced local strain in the hBN lattice.

[0031] Based on Example 1, the morphology of the transferred hexagonal boron nitride layer was characterized using a scanning electron microscope. The results are as follows Figure 5 As shown. Figure 5 It can be seen that the local strain in the hBN layer. Test Example 2

[0032] Based on Example 1, it was tested whether stress could activate the photoluminescence of defects in hexagonal boron nitride layers of different thicknesses (3nm, 4nm, 5nm, and 6nm). Through a confocal Raman system, a continuous laser excitation with a power of 1mW and a wavelength of 532nm was used, and the integration time was 0.1s. The photoluminescence images of defects in hexagonal boron nitride layers of different thicknesses activated by stress were as follows: Figure 6 As shown. Figure 6 It can be seen that each sample has an obvious fluorescent luminescence center, and the luminescence center is distributed along the direction of the silver nanowires. In the area without nanowires, that is, the area without stress, there is no photoluminescence phenomenon in hexagonal boron nitride. In addition, even under conditions of different thicknesses, the defects in hexagonal boron nitride can still be effectively activated by the silver nanowires, and its fluorescence emission is still distributed along the direction of the silver nanowires, and is not significantly affected by the change in the thickness of the hexagonal boron nitride. This shows that stress can activate the photoluminescence of hexagonal boron nitride defects, and this stress-activated defect luminescence is not affected by the change in the thickness of the hexagonal boron nitride, and has strong universality. It can be seen that hexagonal boron nitride defects can be used as a luminescence center, providing a luminescence source for subsequent electroluminescence experiments. Test Example 3

[0033] Based on Example 1, it was tested whether stress can activate the photoluminescence spectrum of defects in hexagonal boron nitride layers of different thicknesses (3nm-6nm). Through a confocal Raman system, a continuous laser with a power of 1mW and a wavelength of 532nm was used for excitation, and an integration time of 0.1s. The photoluminescence spectrum was collected by a spectrometer. The results are as follows: Figure 7 As shown, from Figure 7 It can be seen that a is a typical spectrum of hexagonal boron nitride defect photoluminescence, which consists of a zero phonon line and a photon sideband. The energy difference between the two is ~160meV, showing a typical single-photon emission spectrum of hexagonal boron nitride defects; b and c respectively count the peak positions of the zero phonon line and photon sideband of many samples, and find that the defect type of this type of hexagonal boron nitride is substitutional carbon defect; through the analysis of its spectrum, it is further proved that stress can activate the luminescence of hexagonal boron nitride defects, and it is single-photon emission at room temperature, providing conditions for its electrically induced single-photon emission. Test Example 4

[0034] Based on Example 1 and Comparative Example 1, by applying an electrical bias between the bottom electrode of the silver nanowire and the top electrode of the graphene, the current-voltage of the electroluminescent device based on hexagonal boron nitride was measured using a Keithley 4200 ultrafast high-precision digital source meter system. The results are as follows: Figure 8 a and Fig. 9 As shown in a. Figure 8 a and Fig. 9 It can be seen from a in that the current-voltage curve of the sample of Example 1 is nonlinear and similar to the curve form of the natural exponential function, and has the typical characteristics of the electron tunneling curve. Since the hexagonal boron nitride layer (tunneling layer) has a relatively thin thickness, the current can reach the microampere level under low bias, which will enhance the intensity of electroluminescence to a certain extent; the current-voltage curve of the sample of Comparative Example 1 is an obvious electron tunneling curve. Under low bias, the current increases linearly, and under high bias, it shows a superlinear increase. However, in Comparative Example 1, due to the large thickness of the hexagonal boron nitride, even at a voltage of 10V, the current value only reaches more than 80 nanoamperes, and the current density is far from meeting the requirements of electroluminescence. It shows that the thicker tunneling layer significantly increases the difficulty of electrons to tunnel across the barrier, thereby greatly reducing the possibility of exciting plasmon emission through inelastic tunneling. Therefore, in the electroluminescent device, the thickness of the hexagonal boron nitride layer needs to be thinned to enhance its luminescence intensity.

[0035] Based on Example 1 and Comparative Example 1, a confocal Raman system was used to collect spatial imaging of the photoluminescence of hexagonal boron nitride defects using continuous laser excitation with a power of 1 mW and a wavelength of 532 nm, such as Figure 8 b and Fig. 9 As shown in b. Figure 8 b and Fig. 9 As can be seen from b, the samples of Example 1 and Comparative Example 1 both have obvious photoluminescent centers, and the luminescent centers are distributed along the silver nanowires, which indicates that despite the different thicknesses of hexagonal boron nitride, the defects in hexagonal boron nitride can still be effectively activated by the silver nanowires. Hexagonal boron nitride defects can be used as a luminescent center, providing a luminescent source for subsequent electroluminescent experiments, and also providing a direct comparison object for subsequent electroluminescent experiments.

[0036] Based on Example 1 and Comparative Example 1, an external DC bias was applied to the electroluminescent device based on hexagonal boron nitride using a waveform generator through a microscopic imaging system, and spatial imaging of hexagonal boron nitride defect electroluminescence under different voltages was collected (each integration time was 120 s). The results are as follows: Figure 8 c and Fig. 9 As shown in c. Figure 8 c and Fig. 9It can be seen from c that most of the samples in Example 1 have two different electroluminescent centers, and the luminescent centers are also distributed along the silver nanowires, which is consistent with their corresponding photoluminescent images; in particular, at 4.0V and 5.5V, there is only one electroluminescent center in the electroluminescent image. This is because the other luminescent center changes from a bright state to a dark state, which is a luminescent flickering phenomenon. This luminescent flickering phenomenon is a common behavior of single-photon light sources. When the voltage of the sample in Comparative Example 1 reaches 8V, an obvious luminescent center appears near the tip of the silver nanowire, which also corresponds to the photoluminescent center. As the voltage continues to increase, at 9V, the position of the luminescent center changes; when the voltage reaches 10V, the luminescent center increases significantly. This is because as the voltage increases, the electric field can also activate the defects of the hexagonal boron nitride itself, resulting in an increase in the number of electroluminescent centers. However, due to the weak electroluminescent intensity of the sample in Comparative Example 1, the spectrum was not successfully collected.

[0037] In addition, by comparing the photoluminescence imaging and electroluminescence imaging of Example 1, it is found that the photoluminescence center and the electroluminescence center overlap in space. Therefore, the electroluminescence imaging shown is likely to be dominated by the emission of hexagonal boron nitride defects, preliminarily proving that the emission of hexagonal boron nitride defects is extended from light excitation to electrical excitation. Test Example 5

[0038] Based on Example 1, the defect luminescence spectra of the hexagonal boron nitride layer at different voltages were collected by a microscopic imaging system, and Lorentz fitting was performed on them. The peak wavelengths of multiple Lorentz fittings were plotted as a function of the applied bias. Five peaks marked as P1 to P5 were determined using the peak wavelengths that were almost independent of the deviation. The half-peak widths of these five peaks were analyzed from multiple Lorentz fittings, and the results are as follows: Fig.10 As shown. Fig.10 It can be seen that P1 has the highest half-peak width, which is over 150 nm, while the half-peak widths of the other four peaks (P2 to P5) are similar, which are about 60 nm-80 nm.

[0039] In order to identify the resonance peak position of plasmons in hexagonal boron nitride defect electroluminescence, the local plasmon resonance of hexagonal boron nitride-based electroluminescent devices was simulated by the three-dimensional finite difference time domain (3D-FDTD) method. In the simulation, the silver nanowire was defined as a circular pentagon (300nm in diameter and 10nm in radius), and a 1.5nm thick PVP surfactant layer outside the silver nanowire. The silver nanowire was covered by a 4nm thick hexagonal boron nitride layer and a 15nm thick graphene layer. Perfectly matched layers were used as boundary conditions, and a full-field scattered field (TFSF) light source was used as the light source. The simulation results are shown in Figure 2. Fig.11 As shown. Fig.11As can be seen from a in the figure, the scattering spectrum has a localized plasmon resonance peak centered at 780nm, which is consistent with Fig.10 P1 in is very close, so P1 is assigned to the surface plasmon excited by the tunneling electrons. Fig.11 As can be seen from b in the figure, P1 is almost unaffected by the applied bias due to the local plasma resonance of the hexagonal boron nitride-based electroluminescent device. At the same time, the other four peaks have a smaller half-peak width. Therefore, these peaks are understood to be defect luminescence determined by subband transitions in hexagonal boron nitride (related to the defect type), which also do not change when a bias is applied. In this case, using a hexagonal boron nitride-based tunnel junction, the defect luminescence of hexagonal boron nitride is successfully excited electrically and dominates at higher biases. In addition, under the action of an electric field, the hexagonal boron nitride defects in the hexagonal boron nitride-based electroluminescent device will be activated to emit, and it is expected to become a single-photon source of hexagonal boron nitride under electrical drive at room temperature, and thanks to its rich emission characteristics, it has potential huge application prospects in the field of quantum optical chips in the future.

[0040] In summary, the electrically driven fluorescence emission of thin-layer hexagonal boron nitride defects was achieved by using the silver nanowire / hexagonal boron nitride / graphene tunnel junction. Among them, the silver nanowire not only plays the role of electrical contact, but also induces a strain field to activate local defects in hexagonal boron nitride. The local defects in hexagonal boron nitride show bright emission in both photoluminescence and electroluminescence images, with typical ZPL and PSB characteristics in the spectrum. This electroluminescent emission based on the hexagonal boron nitride tunnel junction is expected to work as a highly integrated electrically driven light source operating at room temperature, and thus this hexagonal boron nitride-based tunnel junction also has the potential to be an electrically driven single-photon light source at room temperature.

[0041] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. An electroluminescent device based on hexagonal boron nitride, characterized in that: include: Metal substrate; A silver nanowire layer is disposed on the surface of the metal substrate; A hexagonal boron nitride layer is disposed on the surface of the silver nanowire layer; A graphene layer is disposed on the surface of the hexagonal boron nitride layer and is in contact with the metal substrate; The silver nanowire layer, the hexagonal boron nitride layer and the graphene layer form a tunnel junction structure.

2. The hexagonal boron nitride-based electroluminescent device according to claim 1, characterized in that: The silver nanowire has a diameter of 280nm-320nm and a length of 10μm-50μm.

3. The hexagonal boron nitride-based electroluminescent device according to claim 1, characterized in that: The thickness of the hexagonal boron nitride layer is 2nm-6nm.

4. The hexagonal boron nitride-based electroluminescent device according to claim 1, characterized in that: The thickness of the graphene layer is 5nm-15nm.

5. The hexagonal boron nitride-based electroluminescent device according to claim 1, characterized in that: The metal substrate is selected from gold, silver, copper, nickel, ITO, FTO or PEDOT:PSS.

6. The hexagonal boron nitride based electroluminescent device according to claim 1, characterized in that: The light-emitting band of the hexagonal boron nitride-based electroluminescent device is visible light or near-infrared light.

7. A method for preparing an electroluminescent device based on hexagonal boron nitride according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, preparing a silver nanowire layer on the surface of a metal substrate; S2, preparing a hexagonal boron nitride layer on the surface of the silver nanowire layer; S3. Prepare a graphene layer on the surface of the hexagonal boron nitride layer and contact it with the metal substrate.

8. The method for preparing an electroluminescent device based on hexagonal boron nitride according to claim 7, characterized in that: In S1, the preparation method of the silver nanowire layer is selected from chemical synthesis combined with dry transfer, and photolithography combined with metal evaporation.

9. The method for preparing an electroluminescent device based on hexagonal boron nitride according to claim 7, characterized in that: In S2, the preparation method of the hexagonal boron nitride layer is selected from mechanical stripping combined with dry transfer and chemical synthesis combined with wet transfer.

10. The method for preparing an electroluminescent device based on hexagonal boron nitride according to claim 7, characterized in that: In S3, the preparation method of the graphene layer is selected from mechanical exfoliation combined with dry transfer and chemical synthesis combined with wet transfer.

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