METHOD AND APPARATUS FOR OXIDATION OF TWO-DIMENSIONAL MATERIALS

Abstract

In accordance with an example embodiment of the present invention, a method is disclosed. The method comprises providing a two-dimensional object comprising a lll-V group material, e.g. Boron nitride (BN), Boron carbon nitride (BCN), Aluminium nitride (AIN), Gallium nitride (GaN), Indium Nitride (InN), Indium phosphide (InP), Indium arsenide (InAs), Boron phosphide (BP), Boron arsenide (BAs), and Gallium phosphide (GaP) and/or a Transition Metal Dichalcogenides (TMD) group material, e.g Molybdenum sulfide (MoS2), Molybdenum diselenide (MoSe2), Tungsten sulfide (WS2), Tungsten diselenide (WSe2), Niobium sulfide (NbS2), Vanadium sulfide (VS2,), and Tantalum sulfide (TaS2) into an environment comprising oxygen; and exposing at least one part of the two-dimensional object to photonic irradiation in said environment, thereby oxidizing at least part of the material of the exposed part of the two-dimensional object.

Claims

1-20. (canceled)

21. A method, comprising: providing a two-dimensional object comprising a III-V group material and/or a Transition Metal Dichalcogenides (TMD) group material into an environment comprising oxygen; and exposing at least one part of the two-dimensional object to photonic irradiation in said environment, thereby oxidizing at least part of the material of the exposed part of the two-dimensional object.

22. The method of claim 21, further comprising: providing a substrate, and prior to providing the two-dimensional object into an environment comprising oxygen, depositing the III-V group material and/or the TMD group material onto the substrate, thereby forming the two-dimensional object comprising the III-V group material and/or the Transition Metal Dichalcogenides (TMD) group material.

23. The method of claim 22, wherein depositing the III-V group material and/or the TMD group material onto the substrate is performed by at least one of the following techniques: spray coating, spin-coating, drop-coating, thin film transfer and inkjet printing.

24. The method of claim 22, wherein the substrate comprises a plastic substrate.

25. The method of claim 22, wherein the substrate comprises a rigid glass substrate.

26. The method of claim 21, wherein the III-V group material comprises at least one of: Boron nitride (BN), Boron carbon nitride (BCN), Aluminium nitride (AlN), Gallium nitride (GaN), Indium Nitride (InN), Indium phosphide (InP), Indium arsenide (InAs), Boron phosphide (BP), Boron arsenide (BAs), and Gallium phosphide (GaP).

27. The method of claim 21, wherein the TMD group material comprises at least one of: Molybdenum sulfide (MoS.sub.2), Molybdenum diselenide (MoSe.sub.2), Tungsten sulfide (WS.sub.2), Tungsten diselenide (WSe.sub.2), Niobium sulfide (NbS.sub.2), Vanadium sulfide (VS.sub.2,), and Tantalum sulfide (TaS.sub.2).

28. The method of claim 21, wherein the photonic irradiation comprises a wavelength spectrum between 200 nanometers to 900 nanometers by a xenon flash lamp.

29. The method of claim 21, wherein exposing at least one part of the two-dimensional object to photonic irradiation comprises exposing the at least one part of the two-dimensional object to pulsed photonic irradiation.

30. The method of claim 29, wherein an individual pulse duration of the pulsed photonic irradiation is between 10 microseconds and 5 milliseconds, with a pulse frequency between 1 Hertz and 300 Hertz.

31. The method of claim 21, wherein exposing at least one part of the two-dimensional object to photonic irradiation is performed for a period of time between 1 second and 60 minutes.

32. The method of claim 21, wherein exposing at least one part of the two-dimensional object to photonic irradiation comprises exposing the at least one part of the two-dimensional object to photonic irradiation using a photomask.

33. The method of claim 32, wherein exposing at least one part of the two-dimensional object to photonic irradiation using a photomask comprises selectively exposing to photonic irradiation at least one part of the two-dimensional object that is not covered by the photomask, thereby oxidizing at least part of the material of the two-dimensional object not covered by the photomask.

34. The method of claim 22, wherein exposing at least one part of the two-dimensional object to photonic irradiation comprises exposing the at least one part of the two-dimensional object to photonic irradiation from a source that is positioned, at a predetermined distance, on the side of the substrate on which the III-V group material and/or the TMD group material was deposited.

35. A device comprising: a reactor and a flash lamp, wherein the reactor comprises an environment comprising oxygen, and wherein the device further comprises: a space at least partially inside the environment for receiving a two-dimensional object comprising a III-V group material and/or a Transition Metal Dichalcogenides (TMD) group material, wherein the flash lamp is caused to irradiate at least one part of the two-dimensional object when the two-dimensional object is in the space, thus causing oxidation of at least part of the material in the irradiated part of the two-dimensional object.

36. The device of claim 35, further comprising a reflector for directing the photonic irradiation of the flash lamp toward the two-dimensional object.

37. The device of claim 35, further comprising a discharge module for providing electrical power to the flash lamp at a predetermined frequency and duration.

38. The device of claim 35, wherein the flash lamp is a xenon flash lamp with an emission spectrum between 200 nanometers and 900 nanometers, and wherein the flash lamp is caused to irradiate at least one part of the two-dimensional object in pulses.

39. The device of claim 38, wherein individual pulse duration is between 10 microseconds and 5 milliseconds and a pulse frequency is between 1 Hertz and 300 Hertz.

40. An apparatus comprising at least one processor; at least one memory coupled to the at least one processor, the at least one memory comprising program code instructions which, when executed by the at least one processor, cause the apparatus to: provide a two-dimensional object comprising a III-V group material and/or a Transition Metal Dichalcogenides (TMD) group material into an environment comprising oxygen; and expose at least one part of the two-dimensional object to photonic irradiation in said environment, thereby oxidizing at least part of the material of the exposed part of the two-dimensional object.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] For a more complete understanding of example embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:

[0039] FIG. 1 shows a method according to an embodiment of the present invention;

[0040] FIG. 2a is a graph of the static Water Contact Angle (WCA) against irradiation time for two-dimensional hexagonal Boron Nitride (2D h-BN);

[0041] FIG. 2b is a graph of the static Water Contact Angle (WCA) against irradiation time for 2D MoS.sub.2;

[0042] FIG. 2c is graph of the static Water Contact Angle (WCA) against irradiation time for 2D WS.sub.2

[0043] FIG. 3a is a graph illustrating the bandgap difference of 2D h-BN before and after oxidation;

[0044] FIG. 3b is a graph illustrating the bandgap difference of 2D MoS.sub.2 before and after oxidation;

[0045] FIG. 4 shows an apparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] Exemplary embodiments of the present invention and its potential advantages are understood by referring to FIGS. 1 through 5 of the drawings.

[0047] Conventional thermal oxidation of 2D objects comprising TMDs and III-V materials can be challenging due to the costs and complexity, as well as high temperature which may be destructive for plastic substrates and thin films; while plasma-induced oxidation is hardly scalable due to very slow process and lack of uniformity. A fast and efficient oxidation of III-V materials and TMDs which would be compatible with low-temperature and high-throughput roll-to-roll processes is desirable. In one embodiment of the present invention, a new technique for photo-thermal oxidation of 2D III-V materials and 2D TMD materials is disclosed. The oxidation takes place upon exposure to photonic irradiation (for example, by pulsed xenon light) in an environment comprising Oxygen. In an embodiment, the oxidation may take place at ambient conditions.

[0048] For the purposes of this specification, two-dimensional objects such as 2D films, 2D single crystals, 2D flakes etc. are provided for exemplary purposes only. In these examples, the materials used are also substantially two-dimensional for exemplary purposes.

[0049] FIG. 1 shows an exemplary embodiment of the present invention. Normal lines show required steps of the method according to this embodiment, while optional steps and positions are shown by dashed lines. As a first optional step, a substrate 101 can be provided. The substrate may be e.g. a low melting temperature plastic substrate or a rigid glass substrate. A material 102 is then optionally deposited onto the substrate, forming a 2D object 103. The material 102 comprises a TMD group material and/or a III-V group material. It may be deposited, for example, by spray coating, spin-coating, drop-coating, thin film transfer or inkjet printing. The thickness (i.e. the smallest dimension) of the deposited material may vary between 1 nanometer and 1 micrometer. A TMD group material may be, for example, Molybdenum sulfide (MoS.sub.2), Molybdenum diselenide (MoSe.sub.2), Tungsten sulfide (WS.sub.2), Tungsten diselenide (WSe.sub.2), Niobium sulfide (NbS.sub.2), Vanadium sulfide (VS.sub.2,), or Tantalum sulfide (TaS.sub.2), or a combination thereof. A III-V group material may be, for example, Boron nitride (BN), Boron carbon nitride (BCN), Aluminium nitride (AlN), Gallium nitride (GaN), Indium Nitride (InN), Indium phosphide (InP), Indium arsenide (InAs), Boron phosphide (BP), Boron arsenide (BAs), or Gallium phosphide (GaP), or a combination thereof.

[0050] The 2D object 103 is then provided into an environment comprising Oxygen. The environment may be, for example, air at ambient conditions, oxygen, oxygen mixed with the inert gas or ozone.

[0051] In the environment comprising Oxygen, at least one part of the 2D object is exposed to photonic irradiation. A source of photonic irradiation 104 is schematically shown as a circle on FIG. 1; however, a skilled person would assume that the source 104 may be of any shape or form. A xenon flash lamp may be used as a source of photonic irradiation 104 to irradiate the object 103 for a predetermined amount of time. The wavelength of the photonic irradiation may be between 200 nm and 900 nm. The materials used absorb the light in Ultraviolet-visible (UV-vis) region, which is well matched with a xenon flash lamp emission spectrum. The xenon flash lamp or another source of irradiation may be positioned above the substrate, or in any other suitable position at a predetermined distance. The flash lamp power may vary from 100 to 3000 Watts. If pulsed photonic irradiation is used, the pulse frequency may be from 1 to 300 Hertz. The individual pulse duration may be in the range from 10 microseconds to 5 milliseconds. The overall exposure time may vary from 1 second to 60 minutes. A photomask may be applied to the 2D object prior to the photonic irradiation. Alternatively, a photomask may be used at a distance from the 2D object during the irradiation. Using the photomask allows selective exposure of at least one part of the 2D object that is not covered by the photomask to photonic irradiation.

[0052] The photonic irradiation oxidizes at least part of the material 102 of the exposed part of the 2D object 103. In other words, if a part of the 2D object 103 exposed to irradiation comprises a III-V group material or a TMD group material, at least part of this material will be oxidized by the irradiation. The resulting partially or fully oxidized material is indicated by position 105 on FIG. 1. In case of partial oxidation, multiple layers along the thickness of the resulting material 105 may be produced. For example, a top layer may be oxidized, while the bottom layer may remain unoxidized, which creates a vertical oxidation pattern in the material, i.e. a pattern of different levels of oxidations along the thickness of the material. Intermediate oxidation may also occur in one or more layers of the resulting material 105. If a photomask is used, areas or parts of the material film that are not covered by the photomask are oxidized. This can create a horizontal oxidation pattern in the material, i.e. a pattern of different levels of oxidations along the greater dimensions (width and length) of the material. The resulting object may be nearly transparent.

[0053] The oxidation of material can be used to create surface wettability contrast in the material, to tune the bandgap of the material and for various other purposes. Examples of such applications of the method according to the present invention are described with reference to FIGS. 2-3. The resulting 2D objects with fully or partially oxidized material 105 can be used in photoluminescence, photochromics devices, solar cells, lasers, heterotransistors, Schottky diodes, photocatalysis, Field Effect Transistors; low-work and high-work function transparent electrodes in transistors, OLEDs, solar cells; chemical and gas sensors and various other applications.

[0054] The methods according to the present invention are easy to scale up and use e.g. in mass production; the invention does not rely on the use of a mask; use of any chemicals which result in hazardous waste is not necessary; and compatibility with low-melting-point substrates, flexible substrates and Roll-to-Roll manufacture is possible.

[0055] For better understanding of the mechanisms underlying embodiments of the present invention in more detail, an example of the oxidation process for two-dimensional hexagonal Boron Nitride (2D h-BN) can be provided. Photothermally induced oxidation of 2D h-BN is most likely to occur through breaking the BN bonds and substitution of nitrogen atoms in the BN plane by O atoms. The formation of epoxide groups on the surface is also possible. In the case of TMD materials, the photonic oxidation causes the substitution of chalcogen atoms by oxygen atoms aligned with the metal valence change from four to higher values. In case of exemplary TMD materials such as 2D MoS.sub.2 and WS.sub.2, oxidation using a xenon flash lamp in the presence of oxygen is also performed. It has been observed by the inventors that the 2D MoS.sub.2 thin film oxidizes more readily than the WS.sub.2 thin film. The resulting oxides MoO.sub.x and WO.sub.x have been obtained most likely through the step of formation of sub-oxides MoS.sub.xO.sub.y and WS.sub.xO.sub.y. Due to the fact that the xenon flash irradiation induces a local heat generation in the 2D thin films, the flash oxidation is considered to be a substantially thermal process. Thus, photothermal flash oxidation in the presence of oxygen from the air leads to the formation of oxygen groups on the surface of 2D layered materials.

[0056] In general, the abovementioned 2D materials appear to be more reactive than bulk materials due to a larger surface area and defects at the edge of flakes which cause electron/hole accumulation. That is one of the reasons why 2D thin films can be oxidized relatively quickly while the bulk materials are usually more stable. The morphology of 2D thin films changes with irradiation time most likely because of restructuring and rapid degassing which leads to exfoliated and disorderly packed 2D flakes. When oxidizing a 2D single crystal, the light intensity possibly needs to be controlled in order to prevent the etching of the layer.

[0057] One possible implementation of embodiments of the present invention is control of surface wettability of the materials and consequently 2D objects. This is exemplified by the 2D hexagonal Boron Nitride (h-BN) for the III-V group materials and by 2D MoS.sub.2 and WS.sub.2 for TDM group materials, illustrated through FIGS. 2a-2c. As it is clear to a skilled person, this implementation is suitable for any other material of these groups.

[0058] In case of 2D h-BN, the surface wettability can be effectively controlled by creating a combination of hydrophilic BNO regions and relatively hydrophobic h-BN regions using selective oxidation by photonic irradiation with a photomask. Hydrophilic material refers to a solid polar material that naturally has an affinity for water. Hydrophobic material is a solid non-polar substance with relatively low surface free energy, which naturally repels water. As a result of oxidation, the water contact angle (WCA) of the material becomes lower, showing an increase in surface energythis is demonstrated by the graph of WCA against irradiation time in seconds on FIG. 2a. The polar component of the surface energy increases during oxidation.

[0059] In case of 2D MoS.sub.2 and WS.sub.2, the water contact angle evolution with irradiation time is shown on FIGS. 2b and 2c. A wettability contrast approaching 60 can be obtained by oxidation of MoS.sub.2 to MoO.sub.x and WS.sub.2 to WO.sub.x, which is a significant contrast that may have different applications. The surface energy increases from approximately 32.2 to 69.5 mN/m for MoS.sub.2 and from approximately 35.8 to 68.6 mN/m for WS.sub.2, with the polar component of the surface energy increasing predominantly.

[0060] Using a mask in this implementation can result in a pattern with high surface energy contrast, which can be utilized advantageously for improved inkjet printing or advanced microfluidics.

[0061] Another possible implementation of embodiments of the present invention is tuning an electronic property of 2D materials by changing the bandgap width by oxidation via photonic irradiation. This is exemplified by the 2D h-BN for the III-V group materials and by 2D MoS.sub.2 for TDM group materials, illustrated through FIGS. 3a and 3b. As it is clear to a skilled person, this implementation is suitable for any other material of these groups.

[0062] The bandgap of the 2D BNO material decreases from 5.80 to 5.25 eV with increase in oxygen composition, leading to a change of the electrical conductivity. FIG. 3a is a graph of the square of the production absorption coefficient and photon energy against photon energy, illustrating the change in the bandgap of the material. BN and BNO are insulators, which can be advantageous for example when using the material as a heat spreader in direct contact with high-power density semiconductor nanodevices.

[0063] The bandgap of oxidized MoS.sub.2 (2.90 eV) appeared to be close to that of bulk MoO.sub.3 (2.7-3.0 eV) and the bandgap of oxidized WS.sub.2 (2.85 eV) is also similar to that of bulk WO.sub.3 (2.8-3.1 eV). In contrast, pristine 2D MoS.sub.2 and WS.sub.2 have 1.5-1.9 eV and 1.3-1.8 eV bandgap, respectively. This increase can be seen on FIG. 3b which is a graph similar to FIG. 3a but for the TMD material MoS.sub.2, and the behavior is similar for WS.sub.2 (not illustrated).

[0064] Tunable bandgap between 1 and 3 eV can be advantageous in photoluminescence, photochromic devices, solar cells, optical devices and for various other applications.

[0065] According to an aspect of the present invention, a device for oxidation of two-dimensional materials is disclosed. The device is configured to provide an environment comprising oxygen in the reactor, i.e. create conditions in the reactor suitable for the oxidation; hold a two-dimensional object comprising a III-V group material and/or a Transition Metal Dichalcogenides (TMD) group material inside the reactor; expose at least one part of the two-dimensional object to photonic irradiation of the flash lamp in the reactor; and oxidize at least part of the material in the exposed at least one part of the two-dimensional object.

[0066] FIG. 4 is a schematic illustration of the device according to an embodiment of the present invention. The illustrated embodiment includes a two-dimensional object 401 comprising a III-V group material or a TMD group material to be oxidized by the device. The device may comprise a substrate holder. The 2D object 401 may be stationary relative to the device, or the 2D object 401 may be conveyed relative to the device, for example between rolls in a roll-to-roll process. The device may include a lamp, such as a xenon flash lamp 402, which may have an emission spectrum ranging from 200 nanometers to 900 nanometers. The lamp 402 may be selected based on the absorption spectrum of the material. The lamp 402 may be partially surrounded by a reflector 403 which may be elliptical or parabolic in shape and which may serve to direct the emitted irradiation of the lamp 402 toward the 2D object 401. The lamp 402 may be driven by a discharge module 404 which may be configured to provide the necessary electrical power to the lamp 402 at a predetermined frequency and duration. The device may further comprise a power supply 405 to provide power to the discharge module 404, and a controller 406 which controls the frequency, pulse duration and irradiation time of the lamp 402 by controlling the discharge module 404.

[0067] The device may further include a mask disposed between the flash lamp and the substrate, the mask serving to obstruct or block at least a portion of irradiation from the flash lamp 402 to the 2D object 401.

[0068] Without in any way limiting the scope, interpretation, or application of the claims appearing below, a technical effect of one or more of the example embodiments disclosed herein is compatibility with flexible and/or low-melting-temperature substrates and Roll-to-Roll manufacturing. Another technical effect of one or more of the example embodiments disclosed herein is clean production of 2D objects comprising oxidized materials without the output of chemical waste. Another technical effect of one or more of the example embodiments disclosed herein is that Xenon flash method can be easily coupled to mass production in a printing method for the III-V and TMD materials and their derivatives. The wettability and bandgap may be tailored in situ for the described processes.

[0069] Among the various technical application of one or more of the example embodiments disclosed herein, production of the following structures can be mentioned: TMO-TMD heterojunctions which can be utilized in heterotransistors, Schottky diodes, photocatalysis; High-k TMO dielectrics to be used in Field Effect Transistors; Conductive TMO low-work and high-work function transparent electrodes for transistors, OLEDs, solar cells; TMO-TMD based chemical and gas sensors.

[0070] An apparatus in accordance with the invention may include at least one processor in communication with a memory or memories. The processor may be configured to store, control, add and/or read information from the memory. The memory may comprise one or more computer programs which can be executed by the processor. The processor may also be configured to control the functioning of the apparatus. The processor may be configured to control other elements of the apparatus by effecting control signaling. The processor may, for example, be embodied as various means including circuitry, at least one processing core, one or more microprocessors with accompanying digital signal processor(s), one or more processor(s) without an accompanying digital signal processor, one or more coprocessors, one or more multi-core processors, one or more controllers, processing circuitry, one or more computers, various other processing elements including integrated circuits such as, for example, an application specific integrated circuit (ASIC), or field programmable gate array (FPGA), or some combination thereof. Signals sent and received by the processor may include any number of different wireline or wireless networking techniques.

[0071] The memory can include, for example, volatile memory, non-volatile memory, and/or the like. For example, volatile memory may include Random Access Memory (RAM), including dynamic and/or static RAM, on-chip or off-chip cache memory, and/or the like. Non-volatile memory, which may be embedded and/or removable, may include, for example, read-only memory, flash memory, magnetic storage devices, for example, hard disks, floppy disk drives, magnetic tape, etc., optical disc drives and/or media, non-volatile random access memory (NVRAM), and/or the like.

[0072] If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined.

[0073] Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims.

[0074] It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.