WO2021240434A1 - Method for patterning a thin film of a solid material - Google Patents

Abstract

A method for patterning a thin film of (a) solid material(s), comprising the steps of providing a thin film of said solid material(s) onto a substrate, said substrate being deformable by heat and indentation; and performing a thermo-mechanical indentation of said thin film of solid material(s), comprising the steps of thermally deforming the deformable substrate and patterning by indentation the thin film of solid material(s), thereby obtaining patterning features on the thin film of (a) solid material(s).

Description

Method for patterning a thin film of a solid material

Technical Field

[0001] The present invention belongs to the fields of nano-/microfabrication and device manufacturing. In particular, the invention pertains to a method for nanostructuration and patterning of thin films, such as two-dimensional layers, of a solid material, as well as items obtainable therefrom.

Background Art

[0002] Atomically thin, two-dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDC) continue to be considered viable key components for diverse nanoelectronics applications and future applications in micro/nano devices and systems. This is mainly due to their atomically thin structures and extraordinary properties beyond bulk counterparts, enabling applications where for instance flexibility and stretchability are important.

[0003] The capability of producing high-quality 2D material nanostructures with well- defined geometries at high resolution is a critical requirement for fostering 2D material-based applications. For instance, patterning thin film materials into finite structures with nanometer-scale confinement is important for tuning their electronic transport properties, but remains a major challenge. Scaling of electronic devices to smaller dimensions also increases the device density and reduces power consumption.

[0004] As a way of example, developing a controllable and reproducible strain engineering method, enabling the tailored design of the bandgap of 2D materials, is of significant importance for electronic and optoelectronic devices. Straining thin 2D materials (2DMs) can create new artificial materials with broader electronic and optoelectronic properties, as well as for practical applications of high- performance strain engineered 2D devices and flexible electronics. Existing methods of straining 2DMs mainly include stretching/compressing the supporting substrate or transferring the 2DM on a topographically patterned surface. However, with weak van der Waals (vdW) force in between, the strain applied on the substrate may not be effectively transferred to the lattice of 2D materials where the decoupling (between substrate and 2D materials) and interlayer slippage are unavoidable, leading to insufficient bandgap modulation. Though various types of strategies have been proposed to strain 2DMs, more versatile approaches for modulating the magnitude and spatial distribution of the strain would be valuable for further fundamental studies and applications.

[0005] Besides pushing the magnitude of the strain, the ability to apply a spatially controllable strain at nanoscale is crucial to precisely manipulate the local properties of 2DMs. The challenge of substrate-induced approaches is that the amount of transferred strain, as well as its crystallographic orientation are not easily controlled.

[0006] To produce nanostructures of 2D materials, top-down techniques such as photolithography, electron beam lithography (EBL), and ion beam lithography (IBL) are typically used. It has been recently observed that the lithographic techniques using electrons or ions may induce structural damage in 2D materials, or add resist contaminations that need to be removed by plasma cleaning. Laser ablation is a resist-free, one-step alternative, but the optical diffraction limit prevents its use where sub-micrometer resolution is required. Bottom-up techniques, like chemical vapor deposition and site-selective growth, allow for scalability and high resolution. However, reproducible fabrication of complex device structures and device integration is still unsolved.

[0007] A probe-based indentation technique combines the ability to indent strain profiles with the possibility to control the crystallographic orientation of the strain. For example, an AFM tip can create strain in a suspended 2D material, although the strain cannot be remained after tip removal. When the tip indents the 2DM on the substrate with conformal contact, limited strain magnitude can be achieved since the substrate tends to recover the original geometry.

[0008] Scanning probe lithography (SPL) embraces a set of nanolithographic techniques that enable unique applications requiring ultrahigh resolution. The working principle of SPL is based on various physical and chemical interactions between a nanoprobe and the surface and has also been applied to 2D materials for mechanical scratching, local oxidation, and dip-pen processes. Specifically, thermal scanning probe lithography (t-SPL) is an emerging direct-write method that uses a heated nanotip for 2D and 3D subtractive/additive manufacturing. The creation of patterns by t-SPL is accomplished by consecutive indentation of the sample with the heated nanotip while simultaneously scanning the sample. In addition to ultra-fast writing, the sample can be imaged with the cold tip similar to conventional AFM, enabling closed-loop lithography and pattern overlay.

[0009] Though various types of patterning engineering methods have been proposed for 2DMs, the patterned features obtainable are far from being controlled with nanometre-scale resolution.

Summary of invention

[0010] In order to address and overcome at least some of the above-mentioned drawbacks of the prior art solutions, the present inventors developed a new method for patterning nanometre-scale features onto thin films or layers of solid materials having improved features and capabilities.

[0011] The purpose of the present invention is therefore that of providing an improved and tailored patterning method for thin films or layers, such as atomically thin layers, of solid materials that overcomes or at least reduces the above- summarized drawbacks affecting known solutions according to the prior art.

[0012] In particular, a first purpose of the present invention is that of providing a versatile, rapid and cost-effective method for patterning a few nanometers thick layer of (a) solid material(s), such as a covalent network solid, including graphene and transition metal dichalcogenides such as molybdenum ditelluride (MoTe2), molybdenum disulfide (M0S2), and molybdenum diselenide (MoSe2).

[0013] A further purpose of the present invention is that of providing a new method for the direct nanocutting of 2D materials for precisely tailoring nanostructures with foreseen applications in the fabrication of electronic and photonic nanodevices.

[0014] Still a further purpose of the present invention is that of providing a method for strain nanopatterning to manipulate the local bandgap of 2D materials with nanometer-scale resolution for ultrathin semiconductor applications.

[0015] All those aims have been accomplished with the present invention, as described herein and in the appended claims.

[0016] In view of the above-summarized drawbacks and/or problems affecting the prior art, according to the present invention there is provided a method for patterning a two-dimensional layer of (a) covalent network solid(s) according to claim 1.

[0017] Another object of the present invention relates to an article of manufacture obtainable by the method of the invention, according to claim 14. [0018] Still another object of the present invention relates to a device comprising an article of manufacture of the invention, according to claim 15.

[0019] Further embodiments of the present invention are defined by the appended claims.

[0020] The above and other objects, features and advantages of the herein presented subject matter will become more apparent from a study of the following description with reference to the attached figures showing some preferred aspects of said subject matter.

Brief description of drawings

[0021] Figure 1. Thermo-mechanical indentation technique for 2D materials and fabrication results a) Conceptual schematic of the t-SPL applied to 2D materials which can be cut and locally removed at nanoscale. For clarity, the size of the tip is not to scale b) Cross-sectional view of 2D material cutting using t-SPL. c) A monolayer/multilayer (1L/ML) MoTe2 flake is dry transferred on a 50-nm thick PPA layer spin coated on a Si02/Si substrate d) AFM topography of the fabricated MoTe2 nanosquare structures with 50 nm side (top right and bottom left) and 70 nm (top left and bottom right) e) Magnified 3D topography of the selected area in d. f) Depth profile of the selected line in d. The cutting depth is around 20 nm. g) Pattern used to create the 2D material labyrinth. The feature size is 50 nm. h) AFM topography of the MoTe2 labyrinth nanostructure showing the capability of on-demand cutting. The feature size of the fabricated labyrinth structure is around 55 nm. i) The corresponding 3D topography of h. j) Depth profiles of the selected cross-sections in h.

[0022] Figure 2. Versatility of the t-SPL nanocutting technique a) AFM topography of nanosquare arrays in 1L MoTe2 with feature sizes in the range from 20 to 200 nm and corresponding profile (Line 1). b) AFM topography of 1L & 2L MoTe2 nanoribbon array with a linewidth of 50 nm (above) and the profiles corresponding to 1L-2L boundary (Line 2) and the selected cut area (Line 3) (below) c) AFM topography of 2L & 3L MoTe2 nanoribbon array with a linewidth of 70 nm (above) and the profiles of 2L-3L boundary (Line 4) and a selected patterned area (Line 5) (below). d,e,f,g) Evaluation of effects of indentation voltage and temperature on the nanostructure generation on the same 1L MoTe2: (d) 500 °C and 4.5 V; (e) 500 °C and 8.5 V; (f) 900 °C and 4.5 V, and (g) 900 °C and 8.5 V. The indicated temperature refers to the heater temperature. The temperature of the tip is a monotonic function of the heater temperature but difficult to estimate accurately.

[0023] Figure 3. Raman spectra of 1L MoTe2 micro/nanostructures fabricated using t- SPL. a) Raman signals for MoTe2 at different regions. The insets show AFM topography of the structures for measurement b) Ai_g and c) E¹2g peak positions and intensities in MoTe2 for pristine, edge, and cut areas d) Raman signals for MoTe2 nanopatterns fabricated using different indentation force. The insets show AFM topographies for measurement e) Ai_g and f) E¹2_g peak positions and intensities in MoTe2 with different indentation forces g) AFM topography of MoTe2 hexagonal microstructures. h,i) Raman intensity mapping of Ai_g band (169 cm^-1) and E¹2g band (235 cm^-1), respectively. The circles in a and d indicate the regions illuminated with the laser of the Raman spectroscopy.

[0024] Figure 4. Nanocutting process of MoTe2 micro/nanoribbon devices and their electrical characterization a) Fabrication of Au microelectrodes on the S1O2 substrate by standard photolithography b) PPA layer is spin coated on top of the substrate. The inset is the optical stereomicroscopy image of the device with PPA. c) Direct laser removal of the PPA on top of Au electrodes d) Dry transfer of the 2D material e) The 2D layer is cut by the hot tip of the t-SPL and the PPA polymer film partially sublimates when the 2D layer is broken f) 3D scheme of the patterned 2D device. g,h) False-colored optical stereomicroscopy images of the devices used in i and k, respectively i) AFM topographies of the flake on the substrate and after the 1^st, 2^nd, 3^rd, and final cutting processes. The highlighted is the 3D profile of the cutting track j) Measured sheet resistances ( R_s ) of the microribbon flake at the pristine condition, after 1^st, 2^nd, 3^rd, and final cut. k) AFM topographies of the device in h, after separation from the bulk flake and after successive cutting processes. I) Corresponding measured sheet resistances of the nanoribbons in k.

[0025] Figure 5. The generation of strain nanopatterning in 2D materials (2DMs). a) Conceptual illustration of the thermo-mechanical nanoindentation process for strain nanopatterning in hexagonal-structure 2DM, such as graphene or TMDCs. For clarity, the size of the tip is not to scale b) Cross-section scheme showing details on the heated nanotip indenting monolayer TMDC on a PPA layer. The sizes of the atoms are not to scale c) AFM topography of the fabricated M0S2 ripple nanostructures d) Magnified 3D topography of the selected nanoripples in c. e) Depth profile of the selected line in c. The nanoindentation depth is around 4 nm and the pileup height is around 1.5 nm.

[0026] Figure 6. Versatility of the method and application to different 2D materials a) AFM topography of nanostripe arrays in 1L M0S2 with designed feature sizes in the range from 2 to 100 nm and corresponding profile b) AFM topography of nanopatterns produced with a heater temperature from 200 to 1200 °C and corresponding depth profile. The indicated temperature refers to the heater temperature. The temperature of the tip is a monotonic function of the heater temperature but difficult to estimate accurately c) Topography of 2L MoTe2 nanoripples with uniaxial strain d) Topography of 1L graphene nanowell arrays with biaxial strain e) Topography of 1L MoSe2 with arbitrary strain distribution (the EPFL logo is given as an example).

[0027] Figure 7. Raman characterization of the patterned 1L M0S2. a) Topography image of the strained M0S2 nanopattern created by the t-SPL. b) Raman spectra of the strained M0S2 and unstrained M0S2. Inset: schematic atomic vibration of the in-plane E¹2g and out-of-plane Ai_g modes c), d) Scanning Raman spectroscopic maps of (c) E¹2g peak Raman shift and (d) Ai_g Raman shift of the uniaxially strained M0S2. The laser scanning step in x-axis is 0.2 pm and that in y-axis is 0.1 pm. The peaks of the measured spectra are selected after processing Lorenz fitting.

[0028] Figure 8. Schematics of a first implementation embodiment of the method according to the invention.

[0029] Figure 9. Schematics of a second implementation embodiment of the method according to the invention.

Detailed description of the invention

[0030] The subject matter described in the following will be clarified by means of a description of those aspects that are depicted in the drawings. It is however to be understood that the scope of protection of the invention is not limited to those aspects described in the following and depicted in the drawings; to the contrary, the scope of protection of the invention is defined by the claims. Moreover, it is to be understood that the specific conditions or parameters described and/or shown in the following are not limiting of the scope of protection of the invention, and that the terminology used herein is for the purpose of describing particular aspects by way of example only and is not intended to be limiting.

[0031] Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, unless otherwise required by the context, singular terms shall include pluralities and plural terms shall include the singular. The methods and techniques of the present disclosure are generally performed according to conventional methods well known in the art and as described in various general and more specific references that are cited and discussed throughout the present specification unless otherwise indicated.

[0032] Non-limiting aspects of the subject matter of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. For purposes of clarity, not every component is labelled in every figure, nor is every component of each aspect of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.

[0033] The following description will be better understood by means of the following definitions.

[0034] As used in the following and in the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Also, the use of "or" means "and/or" unless stated otherwise. Similarly, "comprise", "comprises", "comprising", "include", "includes" and "including" are interchangeable and not intended to be limiting. It is to be further understood that where for the description of various embodiments use is made of the term "comprising", those skilled in the art will understand that in some specific instances, an embodiment can be alternatively described using language "consisting essentially of or "consisting of."

[0035] The expression “thin film” relates to the thin form factor of a layer, sheet, membrane or film according to the invention. Generally speaking, a “thin film” as used herein relates to a layer of a material having a thickness much smaller than the other dimensions, e.g. at least one fifth compared to the other dimensions, and a thickness generally comprised between 0.3 nm and 500 pm, depending on the needs and circumstances, e.g. the manufacturing steps used to produce it. Typically, a thin film is a sheet-like structure having an upper surface and a bottom surface, with any suitable shape. In some embodiments, thin films according to the invention may have a thickness comprised between 0.3 nm and 500 pm, such as between 0.3 and 10 nm, between 1 and 50 nm, between 20 and 100 nm, between 200 and 500 nm, between 50 nm and 1 pm, between 1 and 50 pm, between 50 pm and 150 pm, 100 pm and 500 pm or between 200 pm and 500 pm.

[0036] As used herein, a “two-dimensional” or “2D” layer, sheet, polymer, film, membrane and the like is a sheet-like, macromolecule of elements or crystal having a thickness in the order of a single molecule (monomolecular) layer, i.e. of a few nanometres or less, and are therefore not retrievable in nature as free-standing structures. The most known example of a two-dimensional crystal is graphene, an individual, atomically thin layer or sheet of graphite. However, in a broader sense, a 2D structure may comprise more than one monolayer, such as two or three stacked monomolecular layers, and still be considered as two-dimensional in nature. Two-dimensional materials, sometimes also referred to as layered materials, may comprise laterally connected repeat units (monomers) or may be composed of a single or few atomic elements. These materials have found use in applications such as photovoltaics, semiconductors, electrodes and water purification, to cite a few. Layered combinations of different 2D materials are generally called van der Waals heterostructures, and are contemplated in the frame of the present invention.

[0037] A “covalent network solid” is crystalline solid in which atoms of similar or dissimilar elements are held together in a network of single bonds. The atoms of a covalent network solid are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal or amorphous solid may be considered a macromolecule. Examples of network solids include diamond with a continuous network of carbon atoms and silicon dioxide or quartz with a continuous three-dimensional network of S1O2 units. Graphite and the mica group of silicate minerals structurally consist of continuous two-dimensional sheets covalently bonded within the layer, with other bond types holding the layers together. Examples of 2D covalent network solids include graphene, boron nitride, and transition metal dichalcogenides such as molybdenum ditelluride (MoTe2), molybdenum disulfide (M0S2) and molybdenum diselenide (MoSe2), as well as heterostructures such as MoS2/MoTe2 sheets.

[0038] As used herein, “3D surface feature” or “surface feature” are terms used to refer to any structure, shape, void, cavity, etc., such as but not limited to dots, protrusions, depressions, channels (trenches), etc., having any dimensions. Although preferred but non-limiting embodiments herein are described as including substrates with 3D surface features thereon having at least one nanoscale dimension of 20 nanometers or less, it is within the scope of the present disclosure that the 3D surface features may have all or some dimensions greater than 100 nanometers, for instance comprised between 100 nm and 100 pm. As a non-limiting example, 3D surface features could have dimensions in the range of 10 nm to a 500 nm or even more, including specific non-limiting examples of 20 to 50 nm, 1 to 10 nm, 1 to 20 nm and 1 to 100 pm. Preferably, the aspect ratio (i.e. , ratio of its sizes in different dimensions; e.g., width to depth of a channel) of the 3D surface features is in the range of about five to eighty percent, depending on the materials and application. The term “structured” or “patterned” is used to describe a surface or area in which one or more 3D surface features have been created.

[0039] According to a first aspect, the invention features a method for patterning a thin film of (a) solid material(s), comprising the steps of:

[0040] - Providing a thin film of said solid material(s) onto a substrate, said substrate being deformable by heat and indentation; and

[0041] - Performing a thermo-mechanical indentation of said thin film of solid material(s), said thermo-mechanical indentation comprising the steps of:

[0042] - thermally deforming the deformable substrate and

[0043] - patterning by indentation the thin film of solid material(s)

[0044] thereby obtaining patterning surface features on the thin film of (a) solid material(s).

[0045] The invention is based at least in part on the surprising evidence that a direct and extremely tunable nanocut or nanopattern processing of a thin film, such as 2D films, of a solid material can be achieved by performing a thermal deformation of a polymeric substrate while indenting at the same time the solid thin film, which has been previously coupled via its bottom surface to the upper surface of the polymeric substrate. The indentation process is such that both the solid thin film and the polymeric substrate are patterned.

[0046] The method according to the invention can be employed to perform various forming approaches, including but not limited to conformal shaping, uniform bending, cutting, and lateral compression, preferably without unintentionally fracturing or cracking the nanomaterials. Such a capability can also be used to tunably change various properties of nanomaterials, for example, electrical and optical properties, which may provide opportunities for developing miniature devices, for example, for use in electronics. According to a non-limiting aspect of the invention, local strains may be induced in nanomaterials to increase the band gap of the material (energy range in a solid where no electron states exist). An additional non-limiting aspect of the invention is the capability of inducing local strains in 2D nanomaterials to generate and produce 3D nanomaterials or otherwise increase the nanoscale dimension of the 2D nanomaterials.

[0047] Contrary to the common implementation of the so-called thermo-mechanical indentation technique, that is typically applied to patterning sublimable polymers, the present invention provides for a thermo-mechanical indentation technique for patterning surface features on solid materials films by acting on the below-placed deformable polymer. Depending on the conditions used, the method according to the invention permits in turn a direct cutting of solid thin film materials (by thermo- mechanically cleaving the chemical bonds and by rapid sublimation of the polymer layer underneath the 2D material layer), or a strain nanopatterning of the solid thin films (by inducing an out-of-plane deformation of the thermally sensitive supporting polymer). Arbitrarily shaped cuts with a resolution down to 20 nm are obtained even in monolayer 2D materials, and versatile strain categories can be established by designing different patterns on the thin film.

[0048] Without wishing to be bound to any theory, it is considered that this high versatility is provided by the combined action of the heating process and the indentation process on the substrates at stake, a combination never been tested and validated before up to the inventors’ knowledge. As a way of example, the thermal deformation of the deformable polymeric substrate followed by indentation patterning of the thin film of solid material(s) and the deformable polymeric substrate permits to “design” arbitrary shapes onto the thin film by displacement of an indentation tip or probe on its surface, as well as the use of heated stamps such as those exploited in nanoimprint lithography for rapid and high-throughput patterning.

[0049] Advantageously, the method can be performed under ambient pressure and temperature conditions, thereby facilitating the manufacturing process of items for use in diverse applications, including electronics, semiconductor industry and optoelectronic devices, as will be detailed later on. In embodiments envisaging the implementation of the method for strain nanopatterning of solid thin films, the thermo-mechanical nanoindentation technique allows to manipulate the local bandgap of 2D materials, which can be spatially controlled at nanoscale and tunable up to 200 meV in magnitude. In parallel, in embodiments envisaging the implementation of the method for the direct nanocutting of solid thin films, the proposed technique does not require high vacuum and avoids electron-induced damage typical of EBL, and can be therefore readily implemented in a very cost- effective manner to prototype and fabricate high-quality 2D nanostructures. Additional advantages compared to processes for engineering thin films, particularly two-dimensional layers of solid materials, include the possibility to induce a uniform strain, obtaining a conformal contact with the underlying deformable substrate as well as the avoidance of any slippage between 2D materials and the below polymeric substrate.

[0050] The method according to the present disclosure is particularly suitable for patterning surface features on thin films of covalent network solids. Possible materials include, but are not limited to: graphene; black phosphorus; GaS; GaSe; GaTe; MX2type of dichalcogenides where M=Mo, Nb, Ni, Sn, Ti, Ta, Pt, V, W, or Hf and X=S, Se, or Te; M2X3 type of trichalcogenides where M=As, Bi, or Sb and X=S, Se, orTe; M PX3 where X=S or Se; MAX3 where A=Si or Ge and X=S, Se, or Te; and alloy sheets like M_xMVxS2,as well as combinations of any of the foregoing. Accordingly, suitable materials include molybdenum disulfide (M0S2), molybdenum diselenide (MoSe2), molybdenum ditelluride (MoTe2), tungsten disulfide (WS2), tungsten diselenide (WSe2), tungsten ditelluride (WTe2), chromium disulfide (CrS2), chromium diselenide (CrSe2), chromium ditelluride (CrTe2), gallium arsenide, germanium, boron nitride (hBN) and gallium indium phosphide. These materials typically have been shown their ability to support sufficient elastic strain and accordingly a significant change in the band gap, therefore exhibiting desirable optoelectronic properties. Other optoelectronic materials may also include more conventional materials capable of supporting sufficient elastic strain. For example, a crystalline, polycrystalline, and/or amorphous silicon nanosheet can sustain tensile strain of a few percent which is sufficient to induce a smaller though still significant change in the band gap.

[0051] In embodiments of the invention, the thin film of (a) solid material(s) is a two- dimensional layer of (a) solid material(s), such as a monolayer, a bilayer or a multilayer of (a) solid material(s). In preferred embodiments, moreover, the thin film of (a) solid material(s) is linked or otherwise coupled to the below deformable polymeric substrate by van der Waals interactions. Two-dimensional layers of (a) solid material(s), such as graphene or transition metal dichalcogenides, are known for their unusual and intriguing mechanical, electronic and optoelectronic properties that make them promising for a wide range of applications, and is therefore highly desirable to pattern surface features thereon for engineering the same.

[0052] The deformable substrate used according to preferred aspects of the invention include thermally deformable polymeric materials, and particularly one or more thermoplastic materials and/or one or more elastomeric materials. A non exhaustive list of suitable materials includes thermoplastics such as a polycarbonate, polyetherimide (PEI), polyamide, polyimide, polysulfone, poly ether sulfone (PES), poly phenylene oxide (PPO), poly ether ketones, polyphenyl sulfides (PPS), polyhydroxyethers, styrene-butadiene, polyacrylates, polyacetal, polybutyleneterephthalate, polyamide-imide, poly ether ether sulfone (PEES), blends thereof, or a copolymer thereof, such as PES/PEES with various repeat unit ratios, PES homopolymers or PEES homopolymers, elastomeric materials such as silicone rubber (e.g. polydimethylsiloxane PDMS) orfluorosilicone rubber, thermoplastic elastomers such as styrenic block copolymer (SBC), ethylene propylene diene monomer (EDPM) rubber, butyl rubber, nitrile rubber, acrylonitrile butadiene styrene (ABS), polystyrene (PS), polyethylene (PE), polypropylene (PP), polyphthalaldehyde (PPA), polymethyl methacrylate (PMMA) and the like, as well as combinations of the foregoing.

[0053] With reference to Figure 8, in a first implementation embodiment of the method according to the invention, a thin film such as a two dimensional layer of (a) solid material(s) is firstly transferred onto a polymeric, thermally deformable substrate by method known by a skilled in the art such as stamp-assisted dry transfer, wet transfer, physical vapour deposition including thermal evaporation or sputtering, chemical vapour deposition, spray coating, lamination, screen printing, inkjet printing, doctor blading and the like. The thermally deformable substrate may be previously placed onto a rigid substrate such as a silicon wafer by e.g. spin coating. At the end of this first step, a substantially planar starting structure is obtained, having a substantially flat and planar thin film of one or more solid material located on top of a thicker polymeric substrate.

[0054] In a subsequent step according to the embodiment, a thermo-mechanical indentation of said solid material thin film is performed by a heated indentation probe or stamp. To this aim, preferably thermal scanning probe lithography and/or thermal nanoimprint lithography is used, according to procedures as known in literature and described for instance in Howell, S.T., et al. (Microsyst Nanoeng 6, 21 (2020). https://doi.org/10.1038/s41378-019-0124-8), incorporated herein in its entirety by reference. The thermo-mechanical indentation is performed in such a way to thermally deform the deformable polymeric substrate, while indenting directly the thin film of (a) solid material(s) in a way to also deform the below- located polymeric substrate to obtain patterning surface features. Advantageously, this procedure does not expose the materials to charged particles such as electrons or ions, thereby avoiding unwanted creation or scission of covalent bonds, lattice defects, vacancies or trapped charges, is fast and reliable, performs at high resolution and is accurately controllable.

[0055] In an alternative embodiment, as shown in Figure 9, the starting planar structure comprising a thin film of a solid material placed on top of a polymeric deformable substrate undergoes a heating process via heat diffusion or a thermal trigger such as IR light, laser light, UV light, and exposed to an indenting force applied on the solid thin film in a way to also deform the below-located polymeric substrate, to obtain patterning surface features. The indenting force can be provided by suitable tools such as AFM cantilevers or otherwise indenting probes, as well as by nanoimprint stamps or similar devices.

[0056] In any of the embodiments of the invention, the thermal trigger can be provided before, during or immediately after the application of the indenting force, depending on the needs and circumstances, and can vary over time and/or along the surface(s) of the material(s), typically in a time window comprised between 1 ps and 1 hour. In turn, the indenting force can also vary over time and/or along the surface(s) of the material(s).

[0057] The heating process may be carried out at a temperature Tg ± 0.2Tg, where Tg is the glass transition temperature of the thermally deformable polymer. In one example, the heating may occur at a temperature in the range of from about Tg-10° C to about Tg+20° C. Glass transition temperatures of suitable polymeric substrates are readily available to a skilled person, or can be measured for instance through differential scanning calorimetry or differential thermal analysis, if needed.

[0058] The thermal trigger inducing the heating process may be provided for a time duration of from about 1 ps to 100 minutes, such as for instance between 1 ps and 1 ms, between 1 ms and 1 second, between 500 ms and 10 seconds, or between 1 and 100 minutes. Similarly, the application of an indentation force upon the solid thin film may be carried out for a time duration from about 1 ps to 100 minutes, such as for instance between 1 ps and 1 ms, between 1 ms and 1 second, between 500 ms and 10 seconds, or between 1 and 100 minutes, and with a pressure range spanning from 10⁷ to 10¹¹ Pascal depending on the needs and the foreseen applications.

[0059] In fact, in embodiments envisaging the engineering of a thin film strain, the force applied by the thermo-mechanical indentation on the thin film of (a) solid material(s) is lower than the breaking strength of the thin film of (a) solid material(s), and the heat and force transferred by the thermo-mechanical indentation to the deformable substrate plastically deforms, and/or increases the density of, said deformable substrate. In this way, non-destructive and plastically deforming surface features such as waves, trenches or ripples can be formed on the solid thin film. Preferably, this embodiment comprises a step of cooling down the deformable substrate following the thermo-mechanical indentation to fix and stabilize the obtained surface features.

[0060] In additional or alternative embodiments, the force applied by the thermo mechanical indentation on the thin film of (a) solid material(s) is higher than the breaking strength of the thin film of (a) solid material(s), and the heat and force transferred by the thermo-mechanical indentation to the deformable substrate sublimates said deformable substrate, thereby producing nanocut features on both the deformable polymer and the solid thin film on top. The breaking strength of the thin film can be measured for instance through methods available to a skilled person, such as those described in Lee C. et al. (Science, 2008; 321 (5887) :385-388) .

[0061] For integration of the thin films into an article of manufacture or a device, in embodiments of the invention it is desirable at the end of the method to decouple the thin film of (a) solid material(s) from the below-located deformable polymeric substrate. Accordingly, in some embodiments the method of the invention further comprises a step d) of decoupling the thin film of (a) solid material(s) from the deformable substrate.

[0062] For both the nanocut and the nanodeformation surface features achievable on a solid thin film by the method of the invention, these can span from point indentation to complex structures such as paths with any suitable design. Advantageously, the method according to the invention allows to 1) combine both nanocut and nanodeformation surface features on a single thin film and 2) arbitrarily design any features with high resolution and in a deterministic fashion. In fact, as will be shown in the below example section, complex, non-random surface features such as spirals, ripples, waves, concentric shapes and many more can be easily obtained, thanks to the combined action of heating of the deformable polymeric substrate and the movement of an indentation probe on the thin film. The surface features can have for instance a depth spanning from 0.1 nm to 100 pm, such as from 0.1 to 10 nm, and a width comprised between 2 and 100 nm, 100 and 500 nm, 500 and 1000 nm, 1 pm and 10 pm, 10 pm and 100 pm. Additionally or alternatively, the surface features can have a depth spanning from 1 to 500 pm, such as from 10 to 100 pm, and a width comprised between 100 and 500 pm. The surface features can be evenly disposed along all or part of the thin film.

[0063] As it will be apparent, another object according of the invention relates to an article of manufacture obtainable by the method of the invention, as well as a device comprising an article of manufacture according to the invention. The article of manufacture may comprise or consist of a patterned thin film of (a) solid material(s) or a patterned thin film of (a) solid material(s) placed on a patterned polymeric substrate. In this latter case, the patterned thin film of (a) solid material(s) is linked or otherwise connected to the below polymeric substrate via van der Waals interactions. [0064] The article of manufacture of the invention may combine both nanocut and nanodeformation surface features on a single thin film such as non-random surface features including spirals, ripples, waves, concentric shapes and the like. The surface features can have for instance a depth spanning from 0.1 to 100 nm, such as from 0.1 to 10 nm, and a width comprised between 2 and 100 nm, 100 and 500 nm, 500 and 1000 nm, 1 pm and 10 pm, 10 pm and 100 pm. Additionally or alternatively, the surface features can have a depth spanning from 1 to 500 pm, such as from 10 to 100 pm, and a width comprised between 100 and 500 pm. The surface features can be evenly disposed along all or part of the thin film of the article of manufacture.

[0065] The thin film of the article of manufacture can be a two-dimensional layer of (a) solid material(s), such as a monolayer, a bilayer or a multilayer of (a) solid material(s). In embodiments of the invention, said solid material(s) is (are) (a) covalent network solid(s), selected for instance from a non-limiting list comprising graphene; boron nitride; black phosphorus; GaS; GaSe; GaTe; MX2 type of dichalcogenides where M=Mo, Nb, Ni, Sn, Ti, Ta, Pt, V, W, or Hf and X=S, Se, or Te; M2X3 type of trichalcogenides where M=As, Bi, or Sb and X=S, Se, or Te; MPX3 where X=S or Se; MAX3 where A=Si orGe andX=S, Se, orTe; alloy sheets like MxM'1-xS2, as well as combinations of any of the foregoing. In the embodiments of an article of manufacture comprising a polymeric substrate, this can be one or more thermoplastic materials and/or one or more elastomeric materials.

[0066] A device of the invention can be a next-generation device characterized by the need of some components to have a nanometric or micrometric scale and/or nanometric or micrometric 3D surface features. In embodiments of the invention, such a device can be for instance a light emitting device, an optoelectronic device, a semiconductor electronic component or device, chemical sensors, strain sensors, mechanical sensors, magnetic field sensors, Hall sensors, biosensors, quantum computing devices, single electron devices, memory and storage devices, and component or device for micro/nano systems. [0067] EXAMPLES

[0068] Example 1 - direct nanocutting of 2D materials

[0069] For most applications, functional nanostructures of 2D materials have to be patterned by lithography techniques. In this example, the inventors developed a one-step lithography technique, also named direct nanocutting, for monolayer 2D materials using a thermo-mechanical indentation method, as illustrated in Figure 1a. To do so, a 2D material flake was transferred directly onto a 50-nm-thick sublimable polymer layer, which was spin coated on a SiC /silicon substrate. The cutting is performed by approaching a heated nanotip to the 2D material surface and by applying a sufficiently high force (or pressure) such that the chemical bonds in the 2D layer are broken.

[0070] The resulting cut exposes the underlying polymer to the heat emitted by the nanotip, which results in sublimation of the polymer and thereby creating a deeper indent (Figure 1b). The sublimation of the polymer in fact facilitates the tip to physically break the chemical bonds. This is very different with respect to earlier work describing the mechanical scratching of 2D material on an inelastic S1O2 surface using an AFM tip. The polymer used is polyphthalaldehyde (PPA) with a glass transition temperature of -150 °C. Above this temperature, the PPA polymer chains break and simultaneously unzip into small volatile molecules. Consequently, PPA does not melt, but directly sublimates and thus enables the localized depolymerization at sub-10 nm scale and at high speed. Without being bound to any theory, it is considered that the combination of both the heat and the force is central for the cutting of 2D materials. Indeed, the thermo-mechanical indentation enables the tip to displace the 2D layer sufficiently deep into the PPA layer until the chemical bonds of the 2D layer break, allowing the PPA to sublimate. Thus, the scanning nanotip creates nanocuts in the order of the tip diameter and thereby produces any required layout in the 2D layer to yield ribbons with variable geometries.

[0071] The cutting capability of the technique was systematically studied on several 2D materials (MoTe2, M0S2, MoSe2, and graphene), having different number of layers, in particular, monolayer (1L), two layers (2L), and three layers (3L). These 2D materials have breaking strengths ranging from 3 to 42 N/m. Depending on this value, the cutting can be performed, or not, at a given writing temperature and indentation force. It was first designed a test pattern consisting of nanosquare arrays and a labyrinth pattern in a 1L MoTe2 flake (Figure 1c). Figure 1d shows nanosquare arrays in the 1L MoTe2 flake with side lengths of 50 nm and 70 nm. The number of layers is identified by Raman Spectroscopy. The patterning speed of the probe is 0.5 mm/s and the total time of writing and imaging spent on the 2.5 x 2.5 pm² area in Figure 1d is 45 s. The three-dimensional (3D) topography, as measured by AFM (Dimension FastScan AFM system, Bruker), shows that the PPA polymer has well-defined 3D nanopatterns (Figure 1e). Figure 1f shows the cross-section profile of the selected area in Figure 1d with nanosquares having an average width of 50 nm and a uniform depth of 20 nm. The indentation depth of these structures corresponds to straining the 2D layer twice as high as the calculated breaking strength. Although it is difficult to experimentally determine the strain at which the 2D material breaks, these results clearly show that a cut has been achieved. Nanocutting of continuous lines in 1L MoTe2 is also successfully conducted in a labyrinth pattern (Figure 1g) with a linewidth of 50 nm as shown in Figure 1 h, 1 i and 1j.

[0072] To investigate the patterning capability at various scales the inventors performed nanocutting experiments to create square patterns that have feature sizes ranging from 20 to 200 nm (Figure 2). The smallest feature the inventors were able to cut is about 20 nm, which is the smallest reported for a direct cutting method and is similar to the resolution in EBL. The direct nanofabrication technique is not limited to monolayer MoTe2 but can be also used to cut other 2D materials, certain multilayers and, most interestingly, also heterostructures. To break the 2D layer apart, the indenting tip has to induce sufficient deformation to reach the failure strain of about 10% for MoTe2, 10% for M0S2, 2.6% for MoSe2, and 12% for graphene, respectively, as confirmed by our experiments. For instance, a 1 L M0S2 concentric nanostructure and a 1L MoSe2 nanoribbon array are also readily fabricated. Besides these, 1L M0S2/IL MoTe2 heterostructures were successfully cut with the highest indentation force that the used t-SPL system can provide.

[0073] Monolayer and bilayer MoTe2 flakes have been readily cut (Figure 2b) into nanoribbon array. As expected, increasing the number of layers renders the cutting increasingly difficult, or impossible. For instance, the out-of-plane deformation of a 3L MoTe2 flake is only about 4 nm, which is less than the breaking limit (Figure 2c). This can be overcome by a t-SPL system with a higher indentation force. To further elucidate the detailed and combined effect of the tip- induced indentation force and the tip temperature, a series of patterns in a 1L MoTe2 flake (Figure 2d, 2e, 2f and 2g) was written, varying both values. The indentation force is F„ = F_ei - k_{ca Zo}nset = k_ca (Az - Zoftset), where F_ei is the electrostatic force between the cantilever and the 2D layer, k_ca is the spring constant of the cantilever, Z_oftset is the height offset of the cantilever, and Az is the deflection of the cantilever due to the combined effect of heating (bimorph effect) and applied voltage (electrostatic force).

[0074] Figure 2d shows the topography of the patterned 2D layer at 500 °C and 4.5 V. In these conditions, the 2D layer is not broken and the PPA layer underneath cannot sublimate. When the voltage is increased to 8.5 V, the 2D layer deforms downwards out of plane by 5 nm for 70 nm wide patterns (Figure 2e). When the temperature is increased to 900 °C at 4.5 V, a similar out-of-plane strain occurs, which does not reach the failure strain (Figure 2f). Successful cutting of the 2D layer is achieved when the indentation voltage and the temperature are respectively increased to 8.5 V and 900 °C, (Figure 2g). This experiment demonstrates that high indentation force and high temperature are concurrently necessary to cleave the chemical bonds of the 2D material. During the cutting, the temperature at the 2D layer is less than the heater but over 150 °C, the sublimation temperature of PPA. In the experiments performed here, the indentation force was estimated to be up to -310 nN for a heater temperature of 900 °C and an electrostatic potential between cantilever and substrate of 8.5 V.

[0075] To determine the pressure exerted on the 2D material during the process, one has to take into account the contact area. If one assumes a tip diameter of 30 ± 20 nm a pressure up to about 3.9 GPa can be reached, which is in the order of the required pressure for cutting 2D materials.

[0076] To characterize the physical properties of the 2D material nanostructures before and after the t-SPL cutting, the Raman spectra of the nanostructured MoTe2 flake patterned under different parameters was compared. Figure 3a shows the three Raman spectra of the pristine, edge and cut areas, respectively. The Raman spectra of the edge area has the same peak positions at around 169 cnr¹ and 235 cnr¹ as the pristine area, but with 1/3 less intensity as expected from the ratio of patterned and pristine area within the observation spot (Figure 3b and 3c). The discriminative Raman peaks of MoTe2 disappear after cutting, indicating the complete removal of the 2D material. Figure 3d shows the Raman spectra of a 1L MoTq2 flake patterned at different indentation voltages. There is no peak position shift between the pristine material and the nanoribbon array, while there is a small but noticeable shift of 0.4 cnr¹ between pristine and strained area. This indicates that an indentation-induced strain is generated in the 2D material already at the low indentation force and no oxidation of MoTe2 was observed as analyzed in wide-range Raman spectra. The Raman mapping of a MoTe2 hexagonal microstructure (Figure 3g) shows that the intensities of the Ai_g- (Figure 3h) and E¹2g-band (Figure 3i) signals are clearly different in the cut areas (blue regions), edge areas (white regions), and pristine areas (red regions), further confirming the successful removal of the 2D material.

[0077] In the following, it is described the fabrication of two test devices to observe the evolution of the electrical characterization when the 2D material is progressively cut (Figure 4). First, a 30-nm-thick PPA layer is spin coated on a SiC>2/Si substrate with prefabricated 30-nm-thick Au microelectrodes as shown in Figure 4b. Then, the laser direct-write head is used to remove the PPA polymer from the top of the electrodes (Figure 4c). A 1L MoTe2 flake is dry transferred on this area resulting in electrical contact with the electrodes (Figure 4d). The t-SPL is then used to cut the 2D material at nanoscale as described earlier (Figure 4e). A schematic of the 2D material nanocutting is shown in Figure 4f. Figure 4g and 4h present optical stereomicroscopy images of the devices corresponding to the step in Figure 4d, including the Au electrodes without PPA on top and the 1L MoTe2 across the electrodes. Two-terminal resistive tracks have been created by successively cutting the side bands away to decrease the width of the conduction paths. Figure 4i presents topographies of the 2D layer on the substrate respectively before cutting and successively after the 1^st, 2^nd, 3^rd and final separation cut.

[0078] Material preparation: PPA (polyphthalaldehyde, Allresist) solution (3 wt% in anisole) is spin coated on S1O2 (200 nm thick)/Si (500 pm thick) substrate (conditions: 100 rpm for 5 s and then 6000 rpm for 60 s). MoTe2 flakes are exfoliated from 2H-MoTe2 bulk crystal onto PDMS substrates then are transferred on the PPA substrate. The M0S2, MoSe2, and graphene flakes are obtained and processed with the same procedure. MoTe2, M0S2 and graphene crystals are purchased from HQ Graphene. MoSe2 crystal is purchased from 2D Semiconductor. [0079] Nanostructure cutting: Cutting 2D materials is performed using a commercial t- SPL (NanoFrazor, SwissLitho AG, Switzerland). The cantilever is made of n- doped silicon. The spring constant of the tip is around 0.9 N/m.^[241 During the writing process, the tip is heated to reach a temperature above 150 °C at the 2D/PPA surface. The NanoFrazor has also an integrated 405 nm laser which is used to remove PPA on areas larger than a few square micrometers at a much higher speed than the hot tip.

[0080] Material and structure characterizations: AFM is performed to collect the topographies of the nanostructured or nanostrained 2D materials. AFM is also used to verify the thickness of the nanoflakes. Images are collected using Bruker’s Dimension FastScan AFM system. The FastScan AFM scanner mode (contact mode) is used. Raman spectroscopy is performed to confirm the layer number of all the exfoliated MoTe2 flakes and to characterize the properties of the fabricated nanostructures. Raman spectra are collected using a confocal Raman microscope system (inVia Qontor, Renishaw) coupled with an Olympus inverted optical microscope, and using a laser source with an excitation wavelength of 532 nm. The laser power (84 pW) is adjusted to avoid sample damage. Raman spectra are acquired in the range from 0 to 1800 cm-1 with a 30 s exposure time and an average of three measurements. The peak at 520.7 cm-1 from the silicon substrate is used as a reference.

[0081] Example 2 - strain nanocatterning for local bandgac modulation in 2D materials

[0082] The concept of the thermo-mechanical strain nanopatterning process is illustrated in Figure 5a. A monolayer hexagonal-structure 2DM, such as graphene or TMDCs, is transferred onto the polyphthalaldehyde (PPA) layer that serves as a deformable substrate, linked to the 2DM layer by van der Waals interactions. With the indentation force from the heated nanotip, the underlying polymer is spatio- temporarily plastically deformed and remains entrapped under the intact 2D film, thereby creating surface ripples after re-solidification. The ripples induce local strain in the 2D layer, providing a new method for strain nanoengineering of 2DMs. When the nanotip approaches and indents the 2D layer, two effects contribute to the creation of strained structures, as illustrated in Figure 5b. On the one hand, a portion of PPA under the 2DM decomposes when locally heated but remains trapped underneath the layer. On the other hand, the thermoplastic deformation of the 2DM displaces some polymer to the side, which results in tensile strain buildup in the 2D layer. When the tip is removed, the indented area rapidly cools down whereby the van der Waals interaction between the polymer and the 2D layer prevents the 2D layer from relaxing back to its original geometry. As a result, a permanent strain can be applied to the 2D layer, in a very different manner compared to earlier work describing the mechanical scratching of 2D material on an inelastic S1O2 surface using an AFM tip.

[0083] To illustrate this approach, we first designed a test pattern consisting of ripple arrays in parallel and vertically on a 1L M0S2 flake. The number of layers is identified by Raman Spectroscopy. Figure 5c shows the topography of the nanoripples with the stripes designed to be 60 nm wide. The patterning speed of the probe is 0.5 mm/s and the total time of writing and imaging spent on the 1.5 ^c 1.2 pm² area in Figure 5c is 38 s. The topography was also imaged by AFM (Dimension FastScan AFM system, Bruker). The three-dimensional (3D) topography shows that the PPA polymer has well-defined 3D nanopatterns (Fig. 1d). Figure 5e shows the cross-section profile of the selected area in Figure 5c with nanoripples consisting of uniform valleys with a 4 nm in depth and pileups of 1.5 nm in height.

[0084] To investigate the patterning capabilities of this approach, inventors designed patterns ranging from 2 to 100 nm resulting in visible indents with feature sizes down to 20 nm (Figure 6a), which is the smallest reported for strain engineering methods. Large-area strain pattern in the 20-nm resolution have been also successfully demonstrated in 1L M0S2. The indentation depth can be quantitatively manipulated by changing the indentation temperature and force. With gradient linear increase in the heater temperature from 200 to 1200 °C, the indentation depth reaches 2.8 nm when the heater temperature is over 700 °C, as shown in Figure 6b.

[0085] Another determinative parameter, the indentation force is F,_n = F_ei - k_ca z₀nset = k_ca (Az - Zoftset), where F_ei is the electrostatic force between the cantilever and the 2D layer, k_ca is the spring constant of the cantilever, Zo_ftset is the height offset of the cantilever, and Az is the deflection of the cantilever due to the combined effect of heating (bimorph effect) and applied voltage (electrostatic force). By varying the voltage, the inventors wrote a series of nanopatterns in a 1L M0S2 flake, defining a linear dependence of the nanoindentation process on the indentation force. In the experiments performed here, the indentation force was estimated to be up to -310 nN fora heater temperature of 900 °C and an indentation tip-sample voltage of 7.5 V. To determine the pressure exerted on the 2D material during the process, one has to take into account the contact area. Assuming a tip diameter of 15 ± 5 nm, a pressure up to about 3.9 GPa can be achieved.

[0086] More importantly, the 2DM/polymer system and subsequent nanotip indentation to produce strain can be extended to other 2DMs. Versatile strain categories can be established by designing the patterns of tip indentation, including uniaxial strain, biaxial strain, radial strain and others, demonstrating the high variability of the strain and bandgap modulation in the terms of magnitude and distribution. Nanoripples were written in 2L MoTe2 with uniaxial strain (Figure 6c). Figure 6d shows the topography of 1 L graphene nanowells with biaxial strain distribution. On-demand strain nanopatterning is also precisely demonstrated by writing the EPFL logo in 1L MoSe2 (Figure 6e). In addition, under the same parameters described in Figure 6a, nanoindentation experiments were performed on polymethyl methacrylate (PMMA). Similar to the case of PPA, the PMMA as supporting polymer layer also deforms and local strain is created in the 1L M0S2 layer. The ability to apply strain with nanometer-scale resolution to 2DM and van der Waals heterostructures offers possibilities for tuning the electronic and optoelectronic behaviors of these materials.

[0087] The spatially varying strain distribution over the nanopatterned monolayer M0S2 is verified by micro-Raman spectroscopy. Figure 7a shows the topography of nanopatterned 1L M0S2 created by t-SPL with a temperature of 900 °C and a voltage of 7.5 V. The depth of the strained area is about 8 nm. There are two columns of strained stripes with a valley pitch of 60 nm. Figure 7b shows the Raman spectra of unstrained M0S2 (flat region) and the strained M0S2 (patterned region). The unstrained M0S2 presents the typical Raman spectrum of a M0S2 monolayer with two dominant peaks at 385.7 cnr¹ (E¹2g) and 405.3 cnr¹ (Ai_g)²⁵. The Ai_g mode is assigned to the out-of-plane vibration of S atoms in M0S2, and the E¹2g mode is assigned to the in-plane opposite vibration of two S atoms with respect to the Mo atom. Figure 7b and 7c shows significant redshifts for both E¹2g and Ai_g peaks: 2.4 and 1 cnr¹ respectively for the strained M0S2. This indicates that an indentation-induced strain is generated in the 2D material at the nanoscale and no oxidation of the MoTe2 is observed in wide-range Raman spectra. The mappings of the E¹2g and Ai_g peaks show that the strain is uniform through the entire nanopatterned region. The blue (lower Raman shift peak) and red (higher Raman shift peak) colours indicate that tensile strain is higher on the nanopatterned region. From an overall fit to the redshift magnitudes and the unstrained values, it was estimated that an averaged 1.94% uniaxial tensile strain of the patterned M0S2 is achieved. Due to the laser spot diameter (about 0.5-1 pm), Raman spectrum is an optical average of the most-strained valleys and less- strained pileups.

[0088] Material preparation. PPA (polyphthalaldehyde, Allresist) solution (3 wt% in anisole) was spin coated on S1O2 (200 nm thick)/Si (500 pm thick) substrate (conditions: 100 rpm for 5 s and then 6000 rpm for 60 s). M0S2 flakes were exfoliated from M0S2 bulk crystal onto PDMS stamps then are transferred on the PPA substrate. The MoTe2, MoSe2 and graphene flakes were obtained and processed with the same procedure. MoTe2, M0S2, MoSe2, and graphene crystals were purchased from HQ Graphene.

[0089] Nanostrain engineering. The strain nanopatterning of 2D materials was performed using a commercial t-SPL (NanoFrazor, Heidelberg Instruments, Switzerland). The cantilever is made of n-doped silicon. The spring constant of the cantilever is around 0.9 N/m. the apex diameter is 15 ± 5 nm. During the writing process, the tip was heated at a temperature in the range of 200-1200 °C. The indentation tip- sample voltage was in the range of 4.5 to 7.5 V. 1L M0S2, 2L MoTe2, 1L MoSe2 and 1L graphene samples were patterned at nanoscale.

[0090] Material and structure characterizations. AFM was performed to collect the topographies of the nanostrained 2D materials. AFM was also used to verify the thickness of the nanoflakes. Images were collected using Bruker’s Dimension FastScan AFM system. The FastScan AFM scanner mode (contact mode) was used. Raman spectroscopy was performed to confirm the monolayer nature of all the exfoliated MoTe2 flakes and to characterize the properties of the fabricated nanostructures. Raman spectra were collected using a confocal Raman microscope system (inVia Qontor, Renishaw) coupled with an Olympus inverted optical microscope, and using a laser source with an excitation wavelength of 532 nm. The laser power (84 pW) was adjusted to avoid sample damage. Raman spectra were acquired in the range from 79 to 1843 cm^-1 with a 15 s exposure time and an average of three measurements. Gratings of 3000 and 1800 gr/mm were used for Raman mapping and wide-range Raman measurements, respectively.

[0091] While the invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments, and equivalents thereof, are possible without departing from the sphere and scope of the invention. Accordingly, it is intended that the invention not be limited to the described embodiments, and be given the broadest reasonable interpretation in accordance with the language of the appended claims.

Claims

Claims

1. A method for patterning a thin film of (a) solid material(s), comprising the steps of:

- Providing a thin film of said solid material(s) onto a substrate, said substrate being deformable by heat and indentation; and

- Performing a thermo-mechanical indentation of said thin film of solid material(s), comprising the steps of: thermally deforming the deformable substrate and patterning by indentation the thin film of solid material(s) thereby obtaining patterning features on the thin film of (a) solid material(s).

2. The method of claim 1, wherein the thermo-mechanical indentation step is performed by a heated indentation probe or stamp.

3. The method of claim 2, wherein the thermo-mechanical indentation step is performed by thermal scanning probe lithography and/or thermal nanoimprint lithography.

4. The method of any one of the previous claims, wherein said thin film of (a) solid material(s) is a two-dimensional layer of (a) solid material(s).

5. The method of any one of the previous claims, wherein said solid material(s) is (are) (a) covalent network solid(s).

6. The method of any one of the previous claims, wherein the thin film of (a) solid material(s) is linked to the below deformable substrate by van der Waals interactions.

7. The method of any one of claims 4 to 6, wherein said two-dimensional layer consists of a monolayer, a bilayer or a multilayer of (a) solid material(s).

8. The method of any one of claims 5 to 7, wherein the covalent network solid(s) is (are) selected from a list comprising graphene; boron nitride; black phosphorus; GaS; GaSe; GaTe; MX2 type of dichalcogenides where M=Mo, Nb, Ni, Sn, Ti, Ta, Pt, V, W, or Hf and X=S, Se, or Te; IV Xstype of trichalcogenides where M=As, Bi, or Sb and X=S, Se, or Te; MPX3 where X=S or Se; MAX3 where A=Si or Ge and X=S, Se, or Te; alloy sheets like M_xMVxS2, as well as combinations of any of the foregoing.

9. The method of any one of the previous claims, wherein the substrate being deformable by heat and indentation is one or more thermoplastic materials and/or one or more elastomeric materials.

10. The method of any one of the previous claims, further comprising a step c) of cooling down the deformable substrate.

11. The method of any one of the previous claims, wherein the force applied by the thermo-mechanical indentation on the thin film of (a) solid material(s) is lower than the breaking strength of the thin film of (a) solid material(s), and the heat and force transferred by the thermo-mechanical indentation to the deformable substrate plastically deforms, and/or increases the density of, said deformable substrate.

12. The method of claims 1 to 9, wherein the force applied by the thermo-mechanical indentation on the thin film of (a) solid material(s) is higher than the breaking strength of the thin film of (a) solid material(s), and the heat and force transferred by the thermo-mechanical indentation to the deformable substrate sublimates said deformable substrate.

13. The method of any one of the previous claims, further comprising a step d) of decoupling the thin film of (a) solid material(s) from the deformable substrate.

14. An article of manufacture obtainable by the method of claims 1 to 13.

15. A device comprising an article of manufacture of claim 14.