Patent Application
20150114456
1. Field of the Invention
The present invention provides a method for the preparation of low-dimensional materials. Suitable materials comprise transition metal dichalcogenides (TMD), metal oxides, and carbonaceous materials. The low-dimensional materials obtained via the method can be applied in various uses, among which the low-dimensional materials of TMD materials have metallic, semi-metallic, or semiconducting properties and can be applied in super lubricants, optical-electronic devices, gas sensors, hydrogen evolution catalysts, and optical sensors.
2. Description of the Related Art
Low-dimensional materials are integrated materials of lattice structures in the shape of a nanosheet (two-dimensional), nanorod (one-dimensional), or nanoparticle (zero-dimensional). According to the concept of quantum effect, the physical properties of low-dimensional materials and bulk materials are completely different. Generally, low-dimensional materials have unique properties and can therefore be widely used to improve functionality in applications compared to bulk materials. Among all the low-dimensional materials, graphene has become the most widely studied two-dimensional (2D) material because of its excellent thermal, electronic, optical and mechanical properties. However, the absence of an energy gap has retarded its application in logic electronics. Therefore, it has become necessary to synthesize graphene analogues of layered inorganic materials that have a finite band gap for the development of next generation nanoelectronics. In recent years, it has been found that the transition metal dichalcogenides (TMD), which are formed by the combination of metals and Group VIA elements and can be of metallic, semi-metallic, and semiconducting materials, are extremely promising building blocks for the development of next generation nanoelectronics. Moreover, unlike the poor mobility of other organic semiconductors, semiconducting TMD materials are well-suited to applications where mobility is important.
TMD materials have the stoichiometry MX2, wherein M refers to a transition metal, such as tungsten (W), molybdenum (Mo), titanium (Ti), niobium (Nb), and tantalum (Ta), and X refers to sulfur (S), selenium (Se), and tellurium (Te). When the size of the material is changed from bulk (such as powder) to a mono-atomic layer, the band gap changes from indirect band gap to direct band gap, so TMD compounds can be used in various applications, such as super lubricants, super capacitors, batteries, thin film transistors (TFTs), field effect transistors (FETs, enhancement and depletion mode transistors, light emitting diodes (LEDs), gas sensors, hydrogen evolution catalysts, Schocky-barrier solar cells, optical sensors, displays, and transparent electrodes, wherein a new lattice structure of WS2 can be used as an ideal catalyst in hydrogen evolution reactions (HER) and is a potential replacement of the expensive platinum-based catalyst currently used in polymer thin film electrodes of a fuel cell.
In past studies, many methods for preparing low-dimensional TMD materials were developed, including Scotch tape-assisted micromechanical exfoliation, liquid exfoliation, intercalation-assisted exfoliation, atomic layer deposition, physical vapor deposition, sputtering, atomic layer with chemical vapor deposition, sol gel method, and electrochemical synthesis.
Of these methods, the most well-known method for the preparation of nanoparticle and nanorod materials is the sol gel method. However, the method must be carried out under high pressure and temperature. Moreover, a large amount of materials are consumed during the condensation process, followed by the generation of side products, such as hydroxyls and undesired pores. The sol gel method is complex and time-consuming, causes high consumption of energy and is dangerous. The most commonly seen method for preparation of nanosheet materials is liquid exfoliation carried out by using ionic liquid for the exfoliation and dispersion of materials.
Low-dimensional TMD materials having desirable properties can be prepared by the aforementioned method. However, the method has many drawbacks, such as: it must be carried out in a glove box; the lateral dimension of the products is typically small; the operation conditions must be controlled in high vacuum and under high temperature of 200 to 1200° C. or must involve a long reaction time. Moreover, the semiconducting properties of the TMD materials obtained according to the aforementioned method are variable (H. S, Matte, A. Gomathi, A. L. Manna, D. J. Late, R. Datta, S. K. Pati and C. N. Rao, Angew. Chem. Int, Ed., 2010, 49, 4059-4062; Z. Zeng, T. Sun, J. Zhu, X. Huang, Z. Yin, G. Lu, Z. Fan, O. Yan, H. H. Hng and H. Zhang, Angew. Chem. Int. Ed., 2012, 51, 9052-9056; and X. Rocquefelte, F. Boucher, P. Gressier, G. Ouvrard, P. Blaha and K. Schwarz, phys. Rev. B: Condens. Matter, 2000, 62, 2397-2400). In addition, a third phase surfactant is frequently used in the process of the prior art. However, the use of a surfactant affects the purity of the materials and therefore affects the electrical and optical properties of the final products. On the other hand, most TMD materials are of low solubility, and are only soluble in solvents that are highly toxic and have high boiling points, such as octadecylamine, which makes it difficult for large-scale production of the TMD materials and limits the utility of deposition of the TMD materials to form a film by solution processing.
To solve the technical problems in the existing technology, the applicant provides a method for the preparation of low-dimensional materials by a mechanical milling process. The mechanical power exfoliates the layered TMD materials without affecting their electrical properties. The pristine TMD materials are effectively exfoliated to obtain two-dimensional nanosheet materials. Further, one-dimensional nanorod materials and zero-dimensional nanoparticles are obtained as well. With the selection of suitable solvents, abrading environment and conditions, large amount of nanomaterials can be prepared by a simple process. Nevertheless, the method disclosed in the present application increases the process yield. Compared to the prior art, the method of the present invention is faster, simpler, and cheaper and can fulfill less stringent requirements in terms of ambient environment for preparation, which helps to save energy. The low-dimensional TMD materials obtained according to the method of the present invention can be widely used in materials of various properties and systems of various functionality. The applicant surprisingly found that the method of the present invention is also suitable for use in the preparation of low-dimensional metal oxides and carbonaceous materials.
The present invention provides a method for the preparation of a low-dimensional material, comprising:
(i) mixing a pristine material to be abraded with an organic solvent to form a mixture;
(ii) abrading the material to be abraded in the mixture by bead-milling,
(iii) obtaining a suspension comprising the material of low dimension and the organic solvent; and
(iv) removing the organic solvent from the suspension to obtain the low-dimensional material.
The present invention further provides a low-dimensional material suspension, characterized in that the suspension is obtained by mixing a pristine material to be abraded with an organic solvent followed by abrading the material to be abraded in the mixture by bead-milling. Moreover, the low-dimensional material suspension obtained according to the aforementioned method maintains good suspension stability and remains in a suspended state for six months. Such good suspension stability allows the low-dimensional material to be stably stored in the form of a suspension and able to be coated on a substrate by various common liquid processing methods such as spin-coating and ink-jetting for further preparation of low-dimensional material films and electronic devices comprising the low-dimensional materials.
The present invention further provides a method for the preparation of a low-dimensional material film, comprising forming a mixture by mixing a pristine material to be abraded with an organic solvent, abrading the material to be abraded in the mixture by bead-milling to obtain a suspension, coating the suspension on a substrate, and removing the organic solvent from the suspension to obtain the low-dimensional material film. The present invention further provides a low-dimensional material film prepared by the aforementioned method.
The present invention further provides a solar cell comprising the aforementioned low-dimensional TMD material film, wherein the film is used as an electron-extraction film.
a) and (b) are Powder XRD patterns and Raman spectra of pristine NbSe2 and the nanosheets and nanorods of NbSe2 (λexcitation=514 nm).
a) shows magnetic susceptibility plotted with respect to temperature for the pristine NbSe2, the NbSe2 nanosheets, the NbSe2 nanorods and the NbSe2 nanoparticles. Inset: magnified view of the superconductivity transition for the NbSe2 nanorods (left) and nanoparticles (right).
b) shows the conductivity of a thin film of NbSe2 nanosheets, nanorods, and nanoparticles plotted with respect to the bending angle.
c) shows the transmission spectra of films of NbSe2 nanosheets, nanorods, and nanoparticles measured by Jasco V-670 UV-Vis-NIR spectrometer. Inset: photograph of the (1) bare PET substrate, (2) film of NbSe2 nanoparticles on PET, (3) film of NbSe2 nanorods on PET, and (4) film of NbSe2 nanosheets on PET.
d) and (e) are resistance measurements of a flexible electrode coated with NbSe2 nanosheets subjected to bending, wherein the PET film in
a) shows XRD patterns of the pristine WS2 and WS2 nanosheets.
b) shows XRD patterns of the pristine MoS2 and MoS2 nanosheets.
a) shows the current density-voltage (J-V) characteristics of the solar cell devices prepared in Example 5. Inset is a dark J-V curves plot.
b) shows the stability of solar cell devices featuring WS2 and MoS2 as electron extraction layers, respectively, measured in terms of the PCE over time. Inset is the inverted device structure.
a) and (b) are the UV absorption spectra of (a) a WS2 thin film and (b) a MoS2 thin film tested on an ITO substrate.
a), (b) and (c) are SEM images of NbSe2 bulk, nanosheets, and nanorods, respectively.
a), (b) and (c) are the SEM images of (a) pristine graphene, (b) graphene nanosheets and (c) graphene nanorods.
a), (b), (c) and (d) are the SEM images of (a) pristine MoO3, (b) MoO3 nanosheets, (c) MoO3 nanorods, and (d) MoO3 nanoparticles.
a) and (b) are Raman spectra of pristine WS2 and MoS2 and WS2 and MoS2 nanosheets (λexcitation=473 nm).
The present invention provides a method for the preparation of low-dimensional materials, comprising:
(i) mixing a pristine material to be abraded with an organic solvent to form a mixture;
(ii) abrading the material to be abraded in the mixture by bead-milling,
(iii) obtaining a suspension comprising the material of low dimension and the organic solvent; and
(iv) removing the organic solvent from the suspension to obtain the low-dimensional material.
In one specific embodiment, the material to be abraded comprises transition metal dichalcogenides, in which the chalcogen comprises sulfur (S), selenium (Se), and tellurium (Te); metal oxides; and carbonaceous materials.
In another specific embodiment, in step (i), the concentration of the material to be abraded in the mixture is 0.01% to 1%, preferably 0.05% to 0.8%, and more preferably 0.2% to 0.5% by total weight of the mixture.
In another specific embodiment, in step (ii), the bead-milling is carried out by feeding the mixture into a wet-milling machine (as shown in
In another specific embodiment, the abrading beads are zirconia particles with a density of 5.95 g/cm3.
In another specific embodiment, in step (ii), when abrasion is carried out by utilizing the wet-milling machine, the speed of the rotating blades in the wet-milling machine is from 10 rpm to 6000 rpm, preferably 1000 rpm to 4000 rpm, and more preferably 1500 rpm to 3000 rpm. A double water-cooled jacket used in the wet-milling machine allows the temperature to be controlled during the abrasion process.
In another specific embodiment, the low-dimensional materials obtained by abrasion are two-dimensional nanosheets, one-dimensional nanorods, or zero-dimensional nanoparticles.
In another specific embodiment, the material to be abraded is NbSe2. It can be known by using SEM to examine the morphology of NbSe2 before abrasion and after different abrasion time periods that the pristine NbSe2 is a bulky structure with a thickness of >100 μm, and the bulky structure is constructed by random networking lamination of two-dimensional sheets. The abraded materials are very thin and separated nanosheets, nanorods, and nanoparticles, as shown in
Different abrasion time periods lead to materials of different dimensions. Moreover, the time periods required for producing different kinds of materials of different dimensions vary in light of the different characteristics of the materials. Taking NbSe2 as an example, the pristine materials become two-dimensional nanosheets after 4 hours of abrasion, become one-dimensional nanorods after 10 hours of abrasion, and become zero-dimensional nanoparticles after 14 hours of abrasion.
In another specific embodiment, in step (i), the weight ratio of the abrading beads and the organic solvent is from 5:1 to 1:1; preferably 4:1 to 3:1; and more preferably 4:1. In step (ii), the abrasion time period is 30 to 840 minutes; preferably 60 to 600 minutes; and more preferably 120 to 480 minutes.
The organic solvent in the mixture fed into the wet-milling machine comprising the abrading beads is selected from the group consisting of ethylene glycol, N-methylpyrrolidinone (NMP), isopropanol, and combinations thereof. In the case of TMD materials, the solvent is preferably isopropanol or N-methylpyrrolidinone. In the case of metal oxides, the solvent is preferably isopropanol. In the case of carbonaceous materials, the solvent is preferably N-methylpyrrolidinone.
The method of the present invention is easy and fast, and can be reproduced in any lab. In addition, the method of the present invention is not sensitive to ambient gas conditions and therefore does not need to be carried out in a glove box or equipment that controls ambient gas. Moreover, the method of the present invention does not require the use of highly toxic solvents as adopted in the prior art technologies to dissolve the materials to be abraded and does not require the use of flammable substances. Therefore, the method is relatively safe. Besides the aforementioned advantages, the operation power of the wet-milling machine for use in the method of the present invention is only 120 W; that is, the method of the present invention is a low-energy consumption process. The method of the present invention does not require the use of a third phase dispersant (such as a surfactant). The product itself has good suspension ability. Only a little deposition is found after six months of storage time. The low-dimensional TMD materials prepared according to the method of the present invention, based on their intrinsic properties, can be effectively used in the manufacturing processes of various kinds of electronic devices. The method of the present invention has the potential for rapid, large-scale production for obtaining low-dimensional material suspension in high concentration for use in the development of nanotechnology.
More importantly, the method of the present invention uses shear force to abrade the materials to be abraded. In accordance with yet another aspect of the present invention, where the material to be abraded is a TMD material, in which the pristine bulky material is formed by two-dimensional sheets stack through van der Waals interactions (as shown in
The present invention further provides a low-dimensional material suspension, characterized in that the suspension is obtained by mixing a pristine material to be abraded with an organic solvent followed by abrading the material to be abraded in the mixture by bead-milling. Moreover, the low-dimensional material suspension obtained according to the aforementioned method maintains good suspension stability and remains in a suspension state for six months. Such good suspension stability allows the low-dimensional material to be stably stored in the form of a suspension and able to be coated on a substrate by various common liquid processing methods such as spin-coating and ink-jetting for further preparation of low-dimensional material film and electronic devices comprising the low-dimensional materials.
The present invention further provides a method for the preparation of a low-dimensional material film, comprising forming a mixture by mixing a pristine material to be abraded with an organic solvent, abrading the material to be abraded in the mixture by bead-milling to obtain a suspension, coating the suspension on a substrate, and removing the organic solvent from the suspension to obtain the low-dimensional material film. The present invention further provides a low-dimensional material film prepared by the aforementioned method.
The present invention further provides a solar cell comprising the aforementioned low-dimensional TMD material film, wherein the film is used as an electron-extraction film
The following examples are to further describe the present invention. However, these examples should not be interpreted as limiting the scope of the present invention.
Material Preparation:
The wet-milling machine for use is shown in
A double water-cooled jacket in the wet-milling machine allowed the temperature inside the wet-milling machine to be controlled during the abrasion process. The suspension obtained was purified without any contamination from the zirconia particles, due to the highly dense zirconia precipitating readily to the bottom of the chamber of the wet-milling machine after abrasion.
Characterization:
The abraded NbSe2 suspension was diluted ten-fold with isopropanol (IPA); drops of the solution were placed on a holey carbon-coated copper grid (Lacey Carbon Type-A 300 mesh copper grid; TED Pella) or Si/SiO2 surface and then dried in air at 70° C. prior to characterization using SEM (FEI Nova200) and Raman spectroscopy (NT-MDT confocal Raman microscopic system; exciting laser wavelength: 514 nm; laser spot size: 0.5 μm).
TMD powders before and after abrasion were characterized using XRD (PANalytical). The results are shown in
Conductivity Test:
The conductivity test was carried out by first preparing a thin film by spray-coating on a PET substrate the pristine NbSe2, NbSe2 nanosheet, nanorods, and nanoparticles dispersions diluted ten-fold with IPA and drying under ambient atmosphere at 70° C. for 10 min, followed by using the van der Pauw four-point probe technique with a Hall effect measurement system (Ecopia, HMS 5000). The thickness of the thin film can be changed by changing the time for spray-coating. The electrical measurement results are as shown in
WS2 (powder, 99%; Sigma-Aldrich) and MoS2 (powder, 99%; Sigma-Aldrich) were used for the preparation of pristine WS2 and MoS2 mixtures, respectively, according to the same method as described in Example 1, with the exception that the organic solvent used was ethylene glycol (J. T. Baker), and wherein the concentration of the pristine WS2 or MoS2 was 1 wt %. The mixtures were fed to the chamber of the wet-milling machine. The peripheral speed of the rotor was fixed at 2000 rpm and the pristine mixtures were abraded by the zirconia beads, wherein the weight ratio of the zirconia particles to the ethylene glycol was 4:1. Dark green suspensions were obtained after abrasion.
The abraded suspension of the WS2 suspension was diluted ten-fold with methanol (Aldrich); drops of the solution were placed on a holey carbon-coated copper grid (Lacey Carbon Type-A 300 mesh copper grid; TED Pella) or Si/SiO2 surface and then dried in air at 70° C. prior to characterization using SEM (FBI Nova200) and Raman spectroscopy (NT-MDT confocal Raman microscopic system; exciting laser wavelength: 514 nm; laser spot size: 0.5 μm).
TMD powders before and after abrasion were characterized using XRD (PANalytical). The results are shown in
a) and (b) show the Raman spectra of pristine WS2 and MoS2, and WS2 and MoS2 nanosheets, respectively (λexcitation=473 nm). The samples were prepared by placing drops of the aforementioned suspensions diluted ten-fold with methanol onto a Si/SiO2 surface and drying under ambient atmosphere at 70° C. for 10 min after which measurements were conducted.
This experiment is directed to the preparation of solar cell devices comprising WS2 and MoS2, respectively, and the electrical tests of the devices, wherein the WS2 and MoS2 layers serve as the electron extraction layers in the solar cell devices of this experiment.
Prior to spin-coating a thin WS2 or MoS2 film, ITO substrates (<10 Ωsq−1; RiTdisplay) were cleaned through sonication in detergent-containing water and twice with deionized water (15 min each), dried in an oven overnight, and then treated with UV/ozone for 15 min. An ethylene glycol suspension of WS2 (MoS2) was spun onto the ITO substrate at 2000 rpm for 60 s and then the sample was thermally annealed at 150° C. for 60 min in air on a hot plate. Poly(3-hexylthiophene) (P3HT, Rieke Specialty Polymer), PCBM (>99%; Solenne), V2O5 and aluminum (Al; 99.999%; Admat Midas) were used therewith to prepare a solar cell device to undergo electrical tests. The solar cell device featuring a WS2 (MoS2) interfacial layer was prepared in an inverted ITO-WS2 (MoS2)—P3HT:PCBM-V2O5—Al structure, wherein the active layer (P3HT:PCBM) of the device was spin-coated from a solution containing P3HT:PCBM (1:1, w/w) in 1,2-dichlorobenzene (DCB; Aldrich) on top of the WS2 (MoS2) film and dried for 30 min in a covered Petri glass dish (solvent evaporation); the films were then annealed at 130° C. for 30 minutes. The thickness of the active layer was about 200 nm. Layers of V2O5 (10 nm) and Al (100 nm) were thermally evaporated through a shadow mask under vacuum (<10−6 Torr). The active area of each device was 10 mm2. The control device was a solar cell device using ZnO as the electron extraction layer.
The electrical test of the solar cell prepared according to the aforementioned steps is shown in
b) shows the stability of solar cell devices featuring WS2 and MoS2 as electron extraction layers, measured in terms of PCE over time. Inset is the inverted device structure.
It can be seen from
Graphite (Bay Carbon Inc. SP-1) was used for the preparation of the pristine graphite mixture by the same method as that disclosed in Example 1, wherein the organic solvent used was pure N-methyl-2-pyrolidinone (NMP, Macron Chemical, USA) and the concentration of the pristine graphite was 0.25 wt %. Moreover, 60% of the inner space of the chamber of the wet-milling machine was filled with zirconia particles (having a particle size of 200 μm and a density>5.95 g/cm3). The mixture was fed to the chamber of the wet-milling machine. The peripheral speed of the rotor of the wet-milling machine was fixed at 2000 rpm and the pristine mixture was abraded by the zirconia particles, wherein the weight ratio of the zirconia particles to the pure N-methyl-2-pyrolidinone was 4:1.
A sample of the abraded graphene was prepared according to the same method described in Example 2. SEM (FEI Nova 2000) was used to observe its morphology changes.
a), (b) and (c) are SEM images of pristine graphite, graphene nanosheets and nanoparticles. The thickness of the pristine graphite is >100 m. The lateral dimension of the graphene nanosheets is from 1 to 5 μm. The average particle size of the graphene nanoparticles is 30 to 150 nm.
MoO3 (99.5%; Alfa Aesar) was used for the preparation of the pristine MoO3 mixture by the same method as that disclosed in Example 1, with the exception that the organic solvent used was pure IPA (Aldrich), and wherein the concentration of MoO3 was 5 wt %. Moreover, 60% of the inner space of the chamber of the wet-milling machine was filled with zirconia particles (having a size of 200 μm and a density>5.95 g/cm3). The mixture was fed to the chamber of the wet-milling machine. The peripheral speed of the rotor of the wet-milling machine was fixed at 2000 rpm and the pristine mixture was abraded by the zirconia particles, wherein the weight ratio of the zirconia particles to the pure IPA was 4:1.
A sample of the abraded MoO3 was prepared according to the same method described in Example 2. SEM (FEI Nova 2000) was used to observe its morphology changes.
a), (b), (c) and (d) are SEM images of pristine graphite, graphene nanosheets, nanorods and nanoparticles. The thickness of the pristine MoO3 is >50 μm. The lateral dimension of the MoO3 nanosheets is from 2 to 10 μm. The length of the MoO3 nanorods is up to 5 μm. The average particle size of the MoO3 nanoparticles is 100 to 500 nm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102138955 | Oct 2013 | TW | national |
