Method and apparatus for mechanical cleaning of 2D material surfaces

Abstract

A method and apparatus for cleaning a two-dimensional, or 2D, material placed on a substrate, wherein the first surface of the 2D material faces away from the substrate and the second surface of the 2D material faces the substrate, and the cleaning is carried out by providing a plurality of force-applying elements, each having an outer end; positioning them substantially equidistant from the first surface using the outer ends of the plurality of force-applying elements; and applying a shear force to the first surface, particularly at the interface between the first surface and any residue present on the first surface, by moving the plurality of force-applying elements and the substrate relative to each other.

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for mechanically cleaning the surface of two-dimensional or 2D materials. The method and apparatus are particularly suitable for cleaning carbonaceous contaminants and residues from the graphene surface.

Background Art

[0002] Two-dimensional or 2D materials refer to materials that have a thickness of only one or at most a few atoms in the third dimension while having macroscopic dimensions in two dimensions. Graphene is a well-known example of a 2D material and has recently attracted much scientific and technological interest. Other examples include graphene-based materials, materials containing graphene, chemically modified graphene, hexagonal boron nitride (h-BN), and TMDC materials such as MoS2, WS2, WSe2, etc.

[0003] Such 2D materials have been found to have certain properties, for example, regarding their electrical and / or chemical properties. The specific properties of 2D materials such as graphene or graphene-containing materials make them very interesting for a wide range of applications including electronics, lasers, biosensors, photonic switches, light-emitting diodes (LEDs), infrared sensors, protective coatings, hydrogen storage, and energy storage.

[0004] 2D materials such as graphene are generally grown on a growth substrate, finally processed, and then transferred to a target substrate.

[0005] During fabrication for applications as described above, graphene is processed by several different techniques including deposition of different materials onto its surface, lithography processes for forming patterns related to different components on the graphene surface, etc. During processing, various materials, typically polymer materials, can be applied to one or both surfaces of the 2D material. In lithography processes, a resist, for example, a photoresist layer, is applied onto the surface, and this resist must be removed after patterning the surface.

[0006] Such resist layers are typically removed by application to or immersion in a solvent, heating in a gas atmosphere, plasma cleaning, etc.

[0007] These methods are considered successful in conventional semiconductor processing involving conventional three-dimensional (3D) materials such as silicon. Furthermore, mechanical methods, including scrubbing or brushing, may be used.

[0008] However, it has been found that such resist materials containing carbon compounds are generally difficult to completely remove from 2D material surfaces. This is especially true for 2D materials such as graphene, which also contains carbon, but is also observed for other types of 2D materials mentioned above. Some cleaning methods, such as heating in a gas atmosphere or plasma cleaning, do partially remove the resist, but can lead to the formation of aggregates of resist residue remaining on the surface, (partial) oxidation of the surface and / or other damage to the surface.

[0009] When transferring 2D materials, such as graphene, from a growth substrate to a target substrate, polymers (such as PMMA) are commonly used to support the graphene during the process. After the graphene is transferred, the polymer is dissolved in a suitable solvent. After this cleaning step, a layer of residue less than 5 nm thick may often remain on the surface. Additional solvent cleaning does not help remove this layer. Typically, cleaning methods rely on reactive oxygen plasma, UV ozone, or heat treatment to remove this residue layer. The problem with these methods is that they do not clean the graphene without damaging it; in other words, they are not 100% selective. Since graphene is made of carbon atoms and the residue is also partially made of carbon atoms, plasma or ozone removes the residue but also damages the graphene, and may even etch it away. Heat treatment does not remove all of the residue (some of the residue will volatilize, but some will become amorphous carbon, which is even more difficult to remove).

[0010] Similarly, after patterning graphene with photoresist and developing and stripping the resist, carbon-containing residues (e.g., phenolic resins such as novolac from the resist) may remain on the surface even after the application of a resist stripper.

[0011] Furthermore, by leaving exposed graphene in the atmosphere, it is exposed to various types of volatile organic compounds present. These contaminate the graphene over time and need to be removed if atomically clean graphene is required. This can be partially done by the thermal, plasma, and melting methods described above. However, a better and more selective method that works on a wafer scale is needed.

[0012] Therefore, cleaning 2D material surfaces presents specific problems or challenges, as carbonaceous contaminants must be removed from the 2D material surface while avoiding damage to the 2D material itself.

[0013] Known methods for cleaning or removing contaminants from 2D materials such as graphene include atomic force microscopy, i.e., AFM; mechanical cleaning using sharp tips within an electron microscope, such as using a lintroller with activated carbon; or using an electrostatic brush.

[0014] However, these known methods are not suitable for scaling up to wafer-scale applications or for cleaning 2D materials on an industrial scale. [Overview of the project] [Problems that the invention aims to solve]

[0015] The objective of the present invention is to provide a method for cleaning the surface of a 2D material while avoiding damage to the 2D material.

[0016] In particular, an object of the present invention is to provide selective cleaning of 2D materials, in which contaminants are cleaned from 2D materials while avoiding damage to the 2D materials. [Means for solving the problem]

[0017] This is achieved by the method described in claim 1 and the apparatus described in claim 12.

[0018] Embodiments of the present invention are claimed in the dependent claims.

[0019] The present invention relates to a system and method for cleaning wafer-scale substrates having a 2D material on their surface or having their surface coated with a 2D material, and covers both wafers that are completely coated with a 2D material and wafers that have already been processed into devices in which the 2D material is included as one of the top layers. These devices may be sensors, such as magnetic Hall sensors, biosensors, or photonic devices.

[0020] As a general concept, the present invention uses a force applicator such as a brush, pad, or cloth to move or remove a layer of residue from a 2D material, e.g., a device. This is done by locally applying a shear force in / on the residue layer present on the surface.

[0021] The methods and apparatuses disclosed herein are easy to scale up and, in contrast to the known methods described in the background section, provide a method for selectively removing carbon residues from a 2D material or other surface, and in some cases even completely selectively, when thermal, chemical, or plasma cleaning is not an option.

[0022] The methods and systems disclosed herein have advantages in a plurality of applications including biosensors and photonics. For example, reducing the amount of contaminants in a biosensor leads to improved performance, i.e., improved sensitivity of the biosensor. In photonics devices such as photonic modulators, using graphene with improved cleanliness also leads to improved performance, e.g., improved switching speed due to improved electron / hole mobility in graphene.

[0023] In a first aspect, a method of cleaning a two-dimensional or 2D material disposed on a substrate is provided, wherein a first surface of the 2D material faces away from the substrate and a second surface of the 2D material faces the substrate, - providing a plurality of force application elements each having an outer end, the front outer ends thereof being disposed substantially equidistant from the first surface, - applying a shear force to the first surface, particularly at the interface between the first surface and the residue present on the first surface, by moving the plurality of force application elements and the substrate relative to each other, comprising a method.

[0024] According to the concept of the present invention, a shearing force is provided to the residue layer. The shearing force should be applied locally, i.e., not simultaneously across the entire wafer, but through small contact points such as the ends of the force application elements. The ends of the force application elements may be filaments of a hair-like body or brush, a pad or cloth, beads or balls, etc. that are fixed or attached to a body such as a wire, net or cloth. Thereby, the surface of the wafer, especially the surface of the 2D material, can be selectively cleaned. That is, unnecessary contaminant species are removed while preventing or even avoiding damage to the 2D material such as graphene. By using a plurality of force application elements such as hair-like bodies, beads or the like in parallel, the surface can be cleaned relatively quickly, i.e., more quickly than known methods of mechanically cleaning the residue or contaminant layer from the 2D material surface. Thereby, the present invention facilitates the application of selective cleaning at the wafer scale level.

[0025] A plurality of force application elements such as hair-like bodies or beads may form part of a component or feature such as a brush, cloth or pad. The outer ends of the force application elements form individual contact points with the surface of the 2D material, and in particular with the interface between the residue layer and / or other contaminants present on the surface of the 2D material. Through these individual contact points, a shearing force is applied, thereby moving and / or removing the residue or other contaminants from the surface. By using a plurality of contact points, especially a large number of contact points, the surface can be effectively cleaned on the wafer scale dimensions while enabling the applied shearing force to be controlled by the design of the system and passive control of the force. As further explained below in this specification, the elastic properties of the force application elements such as hair-like bodies or beads and the force applicators such as brushes, pads or cloths can absorb surface irregularities, thereby avoiding applying excessive shearing forces that could damage the 2D material.

[0026] The plurality of force application elements can be realized or formed by a plurality of hair-like bodies each having an outer end, and the outer ends thereof are arranged at substantially equal distances from the first surface.

[0027] Alternatively, multiple force-applying elements may be realized or formed by multiple beads attached to the body of a force-applying device, with each of their outer peripheries positioned to form an outer end. For example, force-applying elements may be realized by multiple beads or balls attached to or fixed to a body such as a wire, net, cloth, etc., which can be dragged, slid, or otherwise moved on a 2D material surface in particular to interact with the 2D material surface by their own weight.

[0028] The outer ends of multiple force-applying elements can be favorably positioned relative to the first surface by passive force control, and the outer ends of the force-applying elements are brought into contact with the first surface by one or more forces, including gravity and spring action. This avoids unnecessary complexity in the system.

[0029] The 2D material can be supported on a substrate by van der Waals forces between the second surface of the 2D material and the support surface of the substrate facing the second surface. This allows the 2D material to maintain its properties.

[0030] The method may involve moving multiple force-applying elements relative to a first surface in one or more passes of multiple brushes over a portion of the first surface. The specific arrangement of the force-applying elements, such as the number of bristles or beads and the total contact area achieved by their outer ends, may be selected as a trade-off between the area that can be cleaned during a single pass of the elements and the control of the contact force, so that the contact force remains within the cleaning range and damage to the 2D material is avoided. Because the surface of a 2D material generally has varying heights across the surface, it can be difficult to provide multiple bristles or beads at substantially uniform or equal distances relative to the surface, for example, while providing passive force control to the multiple bristles or beads.

[0031] Multiple force-applying elements may be included in the force-applying device, and moving multiple force-applying elements and the substrate relative to each other is possible. - Rotating the substrate relative to the force application device, - To move the force-applying device and the substrate relative to each other, - Rotating the substrate in a second rotational direction with respect to a second axis while applying a force in a first rotational direction with respect to a first axis, wherein the first axis and the second axis do not coincide, and the first rotational direction is opposite to the second rotational direction. This may include one or more of the following:

[0032] This method can be carried out at a controlled temperature. For example, it can be carried out at a temperature higher than room temperature. The temperature can be chosen such that the properties of the 2D material are substantially unaffected by the temperature, while the mechanical and / or chemical properties of the residue layer or other contaminant particles are altered. This allows the substrate to be brought to a temperature that may facilitate the removal of the residue layer.

[0033] The method may further include applying electrostatic forces between multiple force-applying elements and a 2D material. This may cause residue layers and / or contaminant components to adhere to the force-applying elements. Alternatively and / or further, the force-applying elements may be formed of a material to which residue particles, residues and / or contaminant components tend to adhere or stick. Thereafter, the residue or contaminant may not only move across the surface of the 2D material but also be removed from it.

[0034] The method may further include arranging a plurality of force-applying elements at least partially in a liquid containing, for example, an organic solvent, an aqueous solution, or a solvent containing dissolved molecules. Furthermore, the method may include exciting a plurality of bristles to perform vibrational motion, such as ultrasonic vibration or megasonic vibration. This allows residues and / or contaminants adhering to the bristles to be removed from the bristles as they pass over the surface of the 2D material. This may be done at predetermined or periodic intervals, for example, between two passes of the bristles over the surface, to avoid the re-accumulation of contaminants on the surface. Alternatively, the solvent or liquid may be applied directly to the surface of the 2D material and / or the substrate. This allows residues and / or contaminants at the interface between the 2D material surface and the liquid / solvent to be dissolved.

[0035] In a second embodiment, an apparatus is provided for cleaning a two-dimensional, or 2D, material disposed on a substrate, wherein the first surface of the 2D material faces away from the substrate, and the second surface of the 2D material faces the substrate. This apparatus is - A force applying device comprising a plurality of force applying elements, each having an outer end, wherein the force applying device and the substrate are arranged such that each of the outer ends of the plurality of force applying elements is substantially equidistant from a first surface, -Includes an actuator configured to move a substrate and a force-applying device relative to each other such that a shear force is applied to a first surface of a 2D material while the force-applying device and the substrate move relative to each other.

[0036] This apparatus may, advantageously, be used to carry out the method of the first embodiment.

[0037] The multiple force-applying elements may include multiple hair-like bodies, each having an outer end, the outer ends of which are positioned substantially equidistant from the first surface.

[0038] Alternatively, the multiple force-applying elements may include multiple beads, which are attached to the force-applying device body and arranged such that the outer circumference of each bead forms an outer end.

[0039] The device may be configured such that the contact force between the outer ends of multiple force-applying elements and the first surface is achieved by the weight of the force-applying device and / or a spring acting on the force-applying device. This allows for passive force control and provides a device with relatively low complexity, avoiding complex feedback and control systems for applying force to a surface via force-applying elements to achieve, for example, shear force.

[0040] Brush / pad designs can be made so that the pressure applied to each contact point is approximately equal. If force-applying elements such as bristles or beads have different lengths or end shapes (e.g., conical vs. round), the local contact pressure at the ends of the force-applying elements can be expected to vary considerably. High pressure can cause damage, while low pressure will not clean. Force-applying device designs can be expected to ensure that the local contact pressure is within a narrow range by using a soft material with a lower modulus of elasticity than the pad or brush material, and by combining passive pressure distribution on the back of the force-applying device, e.g., brush / pad, with active or passive force control on the back of the pad.

[0041] A force-applying device may include a force-applying device body, with multiple force-applying elements extending from the surface of the force-applying device body. Advantageously, the force-applying device may include a first body having a first elasticity and a second body having a second elasticity, the first and second bodies being attached to each other, with multiple force-applying elements extending from the second body, and the first elasticity being lower than the second elasticity. The force-applying elements may be formed from the same material as the second body, or from a different material than the second body. Due to the difference in elasticity between the first and second bodies, the first body may be more rigid than the second body, and the second body may exhibit a specific deformability. The elasticity of the second body and the elastic properties of force-applying elements such as bristles, which can be set by the design and selection of materials, such as their bending properties, can enable the force-applying device to absorb height changes across the surface of a 2D material, thereby contributing to passive force control.

[0042] Alternatively, the force application device may be designed so that the force application elements, by their properties, provide the ability to deform to absorb height changes, thereby facilitating passive force control. In such embodiments, the second body may be omitted, and instead, the force application elements extend from the first body.

[0043] The device may further include a spring that acts on the first body, thereby providing a force to the first body in a direction toward the substrate. This allows a force controlled by the properties of the spring, such as its spring constant, to be simultaneously supplied to multiple bristles. This can contribute to passive force control of the system.

[0044] For example, force-applying elements formed by bristles or beads may contain or be formed from materials to which residue particles, residues, and / or contaminant components tend to adhere or stick. Residual particles, residues, and / or contaminant components may adhere to the bristles by chemical forces, physical (e.g., mechanical) forces, or a combination thereof. This allows the residue or contaminant to not only move across the 2D material surface but also be removed from the 2D material surface.

[0045] The apparatus may further include a reservoir for containing a solvent, and multiple force-applying elements may be at least partially immersed in the solvent to clean residue and / or contaminants from the bristles.

[0046] Therefore, according to the present invention, a pad or bristles may be used to mechanically remove thin (0-20 nm, usually less than 5 nm) carbonaceous material from a 2D material or other surface that cannot be properly cleaned by conventional methods without damaging the underlying surface.

[0047] For example, by using multiple contact points in the form of brushes or pads, a shear force is provided to move or remove the residue layer with damaging the graphene or the rest of the device. The distance between the brush / pad and the surface can be controlled by passive force control so that it is within the cleaning range. Such passive force control can be achieved by the design of the system, in particular by the geometric dimensions and material selection of the force applicator and its multiple bristles.

[0048] Alternative methods for providing shear force to clean 2D material surfaces may include jetting a pellet of residue-adsorbing material onto the wafer at a glazing angle, or using a glazing-incident CO2 ice particle jet, solvent jet, gas jet, or something similar to a vibrating tumbler used for cleaning / polishing metal parts, or by sonic treatment with a suitable solvent and excitation frequency and amplitude.

[0049] In this application, the term “2D material” is used, according to a generally accepted definition, to mean a material that has a thickness of, for example, only one or at most a few atoms in a third dimension, while having a macroscopic extent in two dimensions. Well-known examples include graphene and chemically modified graphene, as well as hexagonal boron nitride (h-BN) and TMDC materials, such as MoS2, WS2, and WSe2.

[0050] A pilus is defined as comprising strands, filaments, or fibers extending from a surface, substantially flexible and / or elastic, and deformable or bendable under the action of a force applied thereto. Thus, the pilus can facilitate or contribute to passive force control as described herein.

[0051] As mentioned herein, beads, balls, or other (hemi)spherical features or features having rounded outer ends may be used in a similar manner and with similar effects to those of the hair-like structures described herein.

[0052] The "cleaning range" is defined as the range of shear forces, contact forces, or contact pressures generated by multiple bristles as they move against a 2D material surface, within which the force is large enough to move contaminants or residue particles or compounds against the surface, but small enough not to damage the 2D material. In other words, the force may be greater than the adhesion or bonding force of residue particles or contaminants to the surface, but less than the interatomic forces within the 2D material.

[0053] Further features and advantages of the present invention will become apparent from the description of the invention by non-limiting and non-exclusive embodiments. These embodiments should not be construed as limiting the scope of protection. Those skilled in the art will recognize that other alternative and equivalent embodiments of the invention can be devised and implemented without departing from the scope of the invention. Embodiments of the present invention are described with reference to the drawings of the accompanying drawings, where the same or similar reference numerals indicate the same, identical or corresponding parts. [Brief explanation of the drawing]

[0054] [Figure 1] A schematic diagram of an apparatus for cleaning 2D materials according to an embodiment of the present invention is shown. [Figure 2a-2c] An embodiment of the present invention for cleaning a 2D material is shown, schematically illustrating the relative motion between the 2D material and the force-applying device in the apparatus of Figure 1. [Figure 3] A schematic diagram of a force-applying device that may be used in the apparatus shown in Figure 1 is provided. [Figure 4] The principle relating to the present invention is outlined below. [Figure 5] A schematic diagram of an apparatus for cleaning 2D materials according to an alternative embodiment of the present invention is shown. [Modes for carrying out the invention]

[0055] Figure 1 shows a non-limiting embodiment of an apparatus 1 for cleaning a 2D material 2 according to an embodiment of the present invention.

[0056] To illustrate and explain the cleaning apparatus and methods that may be implemented, the apparatus and the 2D material to be cleaned are shown schematically and not to a specific scale. 2D materials are materials in which strong bonding forces exist between atoms in the plane of the 2D material. However, 2D materials can be susceptible to damage caused by forces acting perpendicular to the plane of the material.

[0057] A 2D material is a two-dimensional material as defined above in this specification, such as graphene. A 2D material has a first surface 2-1 and a second surface 2-2 that extend parallel to each other in two dimensions. The thickness of the 2D material can be as thin as one atom or several atoms. Therefore, a 2D material may be a single 2D material, or it may include a laminate of 2D materials stacked on top of each other.

[0058] 2D materials, such as graphene layers, typically have a thickness of 0-2 nm.

[0059] The first surface 2-1 of the 2D material is at least partially covered by a residue or contaminant layer 10. This layer may be uniform or non-uniform, and may contain particles on the layer and / or aggregates of contaminant or residue material present on the first surface 2-1. As described in the introduction, the residue and contaminants may be formed from photoresists and / or transfer polymers and may contain carbonaceous, i.e., carbon species.

[0060] The residue layer is typically 0–5 nm thick, and sometimes contains larger particles.

[0061] The 2D material 2 is placed on the substrate 4, with its second surface 2-2 facing the surface 4-1 of the substrate 4, and its first surface 4-1 facing away from the substrate 4.

[0062] The 2D material is positioned or supported in a manner that maintains its two-dimensional properties. This can be achieved by positioning the 2D material on the support surface 4-1 of the substrate 4 using van der Waals forces.

[0063] In other words, the 2D material whose first surface 2-1 is being cleaned behaves differently from 3D materials, such as a silicon wafer or a thin film deposited on a silicon wafer. For example, a 2D material can generally withstand a pure shear force or a force component parallel to the spread of the 2D material applied to its surface and will not be damaged by this force component, but it has low strength in a direction perpendicular to its spread and can therefore be easily damaged by peeling forces and / or compressive forces having a component substantially perpendicular to the spread of the 2D material.

[0064] The substrate 4 may be a semiconductor wafer, such as a silicon wafer, such as a conventional semiconductor wafer. The wafer may be 100 to 1000 microns thick. The wafer 4 may be supported by a chuck 6, such as a conventional vacuum chuck that holds the wafer and clamps it on using vacuum. The chuck 6 may be advantageously a rotary and / or translational chuck. This facilitates integration into a semiconductor fab using conventional wafer handling equipment.

[0065] The apparatus 1 further includes a force applicator 8, which applies a shear force to the first surface 2-1 when the substrate 4 moves relative to the force applicator 8.

[0066] The force applicator includes a force applicator body 12, from which a plurality of force applicators extend, shown in the form of bristles 14 in the embodiment of Figure 1. Each of the bristles 14 has an outer end, and a shear force is applied to the 2D material by the interaction of the outer end with the first surface 2-1.

[0067] The main body 12 is attached to or otherwise connected to a force application fixture 16. The force application fixture 16 may be in a fixed position, or may be configured to be fixed relative to, for example, the housing of the device (not shown). The fixture 16 may be movably arranged, for example, so that the main body 12 holding the bristles 14 moves toward and away from the 2D material 2 and substrate 4. This may be by linear dimensions and / or by swivel arrangement.

[0068] In the embodiment shown in Figure 1, the force applicator includes a brush. Alternatively, the force applicator may include a pad or cloth similar to, for example, a microfiber cloth, having bristles, filaments, or fibers extending from its surface to contact, for example, a 2D material surface. Alternatively, the force applicator may include a wire or net to which a plurality of beads are attached. One embodiment of the force applicator 8 is shown in more detail in Figure 3.

[0069] Subsequently, cleaning may be achieved by passing or swiping a force-applying tool, such as a brush, pad, cloth, wire, or net, over the surface of the 2D material, thereby dislodging and removing contaminants.

[0070] The apparatus further includes one or more actuators 18, 20 arranged to produce relative motion between a substrate 4 holding a 2D material 2 and a force application 8, particularly a plurality of bristles 14. The actuator 18 may be realized by a rotational and / or translational chuck 6, i.e., by an actuator for moving the chuck 6 translationally or linearly and / or rotating the chuck 6 with respect to a vertical axis. A second actuator 20 may be arranged to rotate the force application body 12, shown herein in the form of a brush, with respect to its central vertical axis. Alternatively, the second actuator 20 may be arranged to move or displace the force application 8 translationally.

[0071] As can be seen from the schematic diagram in Figure 1, a shear force is applied to the first surface 2-1 via the outer ends 15 of the bristles 14 by the relative motion between the force-applying device 8, for example, the main body 12 having a plurality of bristles 14, and the 2D material 2.

[0072] The force actuator is arranged and configured such that the outer ends 15 of the multiple hair-like bodies 14 are all substantially equidistant from the first surface 2-1, in order to provide a substantially uniform shear force to the surface. This will be explained in more detail below.

[0073] The force applicator 8 may be configured such that the contact force between the bristles 14 having their outer ends 15 and the first surface 2-1 of the 2D material is provided by the weight of the force applicator, i.e., by gravity. Alternatively, one or more springs (not shown) may be provided to apply a spring load to the force applicator body 12 in the direction toward the substrate 4. This allows for passive control of the contact force between the bristles 14 and the first surface 2-1.

[0074] A force gauge or force sensor (not shown) for measuring the force applied to the 2D material surface 2-1 via the mounting fixture 16 may be provided on the brush mounting fixture 16. Subsequently, as described in the previous paragraph, the applied force may be adjusted, for example, by adding or removing the weight of the force applicator and / or by adjusting the spring load acting on the mounting fixture.

[0075] The apparatus 1 may further include one or more heaters and one or more temperature sensors (not shown). For example, a heater placed in the chuck 6 to heat the substrate 4 and the 2D material 2. This heater can be controlled to heat the substrate having the 2D material 2 including a residue layer 10 provided thereon. Thus, the cleaning method can be carried out at a temperature higher than room temperature and / or repeated at several different temperatures.

[0076] Although not shown in Figure 1, the apparatus 1 may be located within a housing and provide a controlled atmosphere in which cleaning is performed. For example, the pressure may be reduced so as to provide a certain degree of vacuum on, for example, a 2D material surface and / or so that a specific gas can be introduced.

[0077] Furthermore, a solvent reservoir may be provided in which residual particles or other contaminants adhering to the bristles can be cleaned.

[0078] Figures 2a, 2b, and 2c show different alternative forms of relative motion between the force applicator 8 and the 2D material according to the method of the present invention, for example, as implemented in the apparatus of Figure 1. Figures 2a to 2c show a top view. In Figures 2a and 2b, the contact area between the force applicator body and the effective bristles is shown as having a rectangular cross-section, and in Figure 2c, it is shown as having a circular cross-section, but other mounting configurations are also possible.

[0079] Furthermore, it should be noted that the force applicator and substrate are not shown to a fixed scale, but are drawn to illustrate the principle. Figures 2a and 2c may appear to suggest that the force applicator may extend approximately over the radius of the substrate 4, and Figure 2b may appear to suggest that the force applicator may extend over the diameter of the substrate 4, but these are merely examples, and the dimensions of the force actuator relative to the substrate 4 may generally be smaller. Therefore, areas of the 2D material surface are generally cleaned by making several passes with a brush, for example, to clean a portion of the surface.

[0080] However, in all figures, the effective fibrous contact area formed by the multiple outer edges 15 is smaller than the area of ​​the first surface 2-1, and such a cleaning method is usually performed by making multiple passes on the substrate using a force actuator. One or more passes may be made along the same path on the first surface. Furthermore, multiple passes may be made along different paths on the first surface to clean the entire surface 2-1.

[0081] As shown in Figure 2a, while the force application device 8 is maintained in a fixed position, the substrate 4 may be rotated around or relative to its central axis a2. The substrate may be rotated at a constant or non-constant substrate angular velocity w2. This results in the relative velocity between the individual bristles 14 and the surface 2-1 becoming non-uniform in the radial direction across the entire brush. The rotation direction and number of passes of the brush on the surface can be controlled and may be preset.

[0082] As shown in Figure 2b, the substrate 4 may be subjected to translational motion relative to the force applicator 8. For example, the substrate 4, and therefore the 2D material 2, may reciprocate linearly relative to the force applicator. Alternatively, a shear force may be applied only during movement in one direction, and the force applicator may be lifted during movement in the other direction so that the bristles no longer come into contact with the first surface 2-1. The direction, speed, and number of passes can be controlled and may be preset.

[0083] As shown in Figure 2c, the multiple hair-like structures 15 and the substrate 4 may be controlled to form a planetary motion relative to each other. Here, the force actuator 8, i.e., the force-applying device body 12, may be controlled to rotate around its central axis a1, and the substrate 4 may be controlled to rotate around its central axis a2, where the central axes a1 and a2 generally do not coincide. The body 12 and the substrate 4 may be controlled to rotate in the same or different directions, and their respective angular velocities w1 and w2 may be different.

[0084] Figure 3 schematically shows a force applicator according to an embodiment of the present invention that may be used in the device shown in Figure 1. In the embodiment of Figure 3, the force applicator body 12 includes a first force applicator body 22 and a second force applicator body 24 fixed to each other. The first body 22 is connected to or fixed to a force applicator mount 16. For example, the first body 22 may be formed as a single part with the force applicator mount 16. The first body 22 is at least substantially rigid compared to the deformable second body 24. For example, the second body 24 may be more elastic by being formed of a material that has higher elasticity than, for example, the first body 22. A plurality of bristles 15 extend from the second body 24. The plurality of bristles 15 may be formed of the same material as the second body 24, for example, they may be formed integrally with the second body 24. Alternatively, the bristles 15 may be formed of a different material.

[0085] The multiple hair-like structures 14 are preferably all substantially equal in length and thickness, and their outer ends 15 are preferably substantially equal in geometric shape.

[0086] Advantageously and preferably, the force F applied by passive force control as described herein is introduced through the rigid first body 22. In order to achieve efficient cleaning of the surface while avoiding surface damage, the contact force between each bristles 14 and the surface 2-1 must be within the cleaning range. That is, the contact force must be low enough not to damage the 2D material 2, but high enough to provide a shear force that moves the contaminant 10 against the first surface 2-1.

[0087] Contact forces F1, F2, ..., F generated between the outer end 15 of each pilosa and the first surface 2-1 n These should be substantially equal. This can be facilitated by the embodiment in Figure 3, in which the rigid body 22 facilitates the equal distribution of force F across the multiple bristles 14, while the second body 24, by its elastic properties, can absorb or compensate for differences in the height of the 2D material surface over which the brush passes when it moves across the surface.

[0088] The multiple bristles 14 may be substantially equal in length so that, during use in the apparatus 1, i.e., while cleaning the 2D material surface 2-1, the distance between each of the outer ends 15 and the 2D material surface, i.e., the first surface 2-1, is substantially equal. As described above, the forces F1, ..., F at each outer end n Since the bristles are equal and all outer ends 15 have the same geometric shape, the contact areas A1, ... An between each bristles and the surface are also substantially equal, and the contact pressure P between each bristles and the surface is substantially equal. c , n They should be essentially equal.

[0089] Figure 4 shows the shear force F of one of the bristles 14, such as a brush, shown in Figure 3, during contact with the surface of the 2D material 2 and the residue layer 10 when the substrate 4 is moved relative to the bristles 14. s This illustrates the principle of cleaning 2D material 2 by applying a certain force.

[0090] P is applied via each hair-like body 15 c =F i / A i The contact pressure, as defined, should be within a cleaning range where the contact pressure between the bristles and the 2D material leads to surface cleaning, i.e., displacement of residues or contaminants 10 present on surface 2-1, without causing damage to the 2D material 2.

[0091] As can be seen from the diagram, in 2D materials, there is a relatively narrow window, called the cleaning range or cleaning window, where the contact pressure Pc leads to surface cleaning while avoiding damage to the surface. If the contact pressure is too low, cleaning does not occur, and if the contact pressure is too high, damage occurs to the surface, and therefore to the 2D material. It has been observed that this is more easily achieved with a smaller contact area, i.e., a brush that does not cover the entire area to be cleaned.

[0092] Figure 5 schematically shows an apparatus 61 for cleaning 2D material 2 according to an alternative embodiment of the present invention. Apparatus 61 operates on the same principles and concepts as apparatus 1 described with reference to Figure 1. Therefore, for details, please refer to the embodiment described with reference to Figure 1.

[0093] In the embodiment shown in Figure 5, the force-applying device 68 is formed like a roller and is positioned to rotate at an angular velocity w3 around its cylindrical axis c, which is shown to extend within the plane of the paper.

[0094] The force-applying device body 612 may be formed by a first body 622 and a second body 624, the first body 622 being coaxially arranged within the second body 624. The first body 622 and the second body 624 may correspond to and have similar functions to the first body 22 and the second body 24 shown in Figure 3 and described with reference to Figure 3. Multiple bristles 614 extend from the outer surface of the second body 624 and come into contact with the surface 2-1 of the 2D material 2 as the force-applying device body 612 rotates, thereby moving the outer ends 615 of the bristles 614 relative to the surface of the 2D material.

[0095] As mentioned above, the material of the bristles may be such that contaminants or residue particles tend to adhere to the bristles and / or that contaminants or residue particles can adhere when an electrostatic force is applied between the bristles and the 2D material. These can be removed from the bristles, for example, by cleaning them with a solvent.

[0096] The force-applying device body 612 can be partially immersed in a fluid solvent 632 placed in a container 630. When the bristles 614 are placed in the solvent 632, any residue or contaminant particles that may be stuck in the bristles 614 can be cleaned off the bristles 614 as the bristles 614 come into contact with the 2D material surface, for example, the interface between the residue or contaminant layer 10 and the first surface 2-1.

[0097] To be understood, the method for cleaning 2D material surfaces described herein can be carried out using apparatus 1, 61 according to the embodiments described herein.

[0098] Those skilled in the art will see that the scope of the present invention is not limited to the examples discussed above, and that several modifications and changes to the examples discussed above are possible without departing from the scope of the invention as defined in the appended claims. Although the present invention is illustrated and described in detail in the figures and specification, such illustrations and descriptions should be considered illustrative or illustrative only and not limiting. The present invention is not limited to the disclosed embodiments and includes any combination of disclosed embodiments that may provide advantages.

[0099] Variations of the disclosed embodiments are understandable and implementable by a person skilled in carrying out the claimed invention by examining the drawings, specification, and appended claims. In the specification and claims, the word “comprising” does not exclude other elements, and the indefinite article “a” or “an” does not exclude plurals. In fact, it should be interpreted as meaning “at least one.” The mere fact that certain features are described in different dependent claims does not mean that combinations of these features cannot be used to produce an advantage. Any reference numerals in the claims should not be interpreted as limiting the scope of the invention. The features of the embodiments and aspects described above can be combined insofar as combining them does not result in an obvious technical contradiction.

Claims

1. A method for cleaning a two-dimensional, or 2D, material placed on a substrate, wherein the first surface of the 2D material faces away from the substrate, and the second surface of the 2D material faces the substrate. - To provide a plurality of force-applying elements, each having an outer end, wherein the outer ends of the plurality of force-applying elements are arranged substantially equidistant from the first surface. - By moving the plurality of force-applying elements and the substrate relative to each other, a shear force is applied to the first surface, particularly to the interface between the first surface and the residue present on the first surface, Methods that include...

2. The method according to claim 1, wherein the plurality of force-applying elements each include a plurality of hair-like bodies having an outer end, and the outer ends of the plurality of force-applying elements are arranged substantially equidistant from the first surface.

3. The method according to claim 1, wherein the plurality of force-applying elements include a plurality of beads, the plurality of beads are attached to the force-applying device body, and the outer circumference of each of the plurality of beads is arranged to form the outer end.

4. The method according to any one of claims 1 to 3, wherein the outer ends of the plurality of force-applying elements are positioned relative to the first surface by passive force control, and the outer ends are brought into contact with the first surface by gravity, the action of a spring, or fluid pressure.

5. The method according to any one of claims 1 to 4, wherein the 2D material is supported by the substrate by van der Waals forces between the second surface of the 2D material and the surface of the substrate facing the second surface.

6. The method according to any one of claims 1 to 5, comprising moving the plurality of force-applying elements relative to the first surface by having the plurality of force-applying elements pass over a portion of the first surface one or more times.

7. The plurality of force-applying elements are included in the force-applying device, and moving the plurality of force-applying elements and the substrate relative to each other is, - Rotating the substrate with respect to the force applying device, - To move the force-applying device and the substrate relative to each other, - Rotating the substrate in a second rotational direction with respect to a second axis while rotating the applied force in a first rotational direction with respect to a first axis, wherein the first axis and the second axis do not coincide, and the first rotational direction is opposite to the second rotational direction, The method according to any one of claims 1 to 6, comprising one or more of the above.

8. The method according to any one of claims 1 to 7, further comprising applying an electrostatic force between the plurality of force-applying elements and the 2D material.

9. The method according to any one of claims 1 to 8, carried out at a controlled temperature.

10. The method according to any one of claims 1 to 9, further comprising arranging the plurality of force-applying elements which are at least partially disposed in a solvent.

11. The method according to claim 10, further comprising exciting the plurality of force-applying elements in order to perform vibration motion.

12. An apparatus for cleaning a two-dimensional, or 2D, material placed on a substrate, wherein the first surface of the 2D material faces away from the substrate, and the second surface of the 2D material faces the substrate. - A force applying device comprising a plurality of force applying elements, each having an outer end, wherein the force applying device and the substrate are arranged such that each of the outer ends of the plurality of force applying elements is substantially equidistant from the first surface, - An actuator configured to move the substrate and the force-applying device relative to each other such that a shear force is applied to the first surface of the 2D material while the force-applying device and the substrate move relative to each other, A device including a device.

13. The apparatus according to claim 12, wherein the plurality of force-applying elements each include a plurality of hair-like bodies having an outer end, the outer ends thereof being arranged substantially equidistant from the first surface.

14. The apparatus according to claim 12, wherein the plurality of force-applying elements include a plurality of beads, which are attached to the force-applying device body, and which are arranged such that the outer circumference of each of the plurality of beads forms the outer end.

15. The apparatus according to any one of claims 12 to 14, wherein the contact force between the outer ends of the plurality of force-applying elements and the first surface is achieved by the weight of the force-applying device and / or a spring acting on the force-applying device.

16. The apparatus according to any one of claims 12 to 15, wherein the force applying device includes a force applying device body, and the plurality of force applying elements extend from the surface of the force applying device body.

17. The force applying device is - A first body having first elasticity, - A second body having second elasticity, wherein the plurality of force-applying elements extend from the second body, Includes, The first body and the second body are attached to each other, and the elasticity of the first body is lower than that of the second body. The apparatus according to any one of claims 12 to 16.

18. The apparatus according to claim 17, wherein the plurality of force-applying elements are formed from the same material as the second body.

19. The apparatus according to any one of claims 17 or 18, further comprising a spring acting toward the substrate relative to the first body.

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