WO2017158235A1

WO2017158235A1 - Composite film comprising an electrically conductive layer

Info

Publication number: WO2017158235A1
Application number: PCT/FI2017/050166
Authority: WO
Inventors: Juha RIIKONEN; Maria GRIGORYEVA; Ali Shah; Changfeng LI; Harri LIPSANEN
Original assignee: Aalto University Foundation
Priority date: 2016-03-15
Filing date: 2017-03-14
Publication date: 2017-09-21
Also published as: FI127535B; FI20165212A

Abstract

A composite film (CMP1) comprises graphene (GRF1) and a conformal layer (POLY1) of a polymer deposited on the graphene (GRF1). The composite film (CMP1) is produced by a method, which comprises: - depositing graphene (GRF1) on a substrate (S0), - forming a first polymer layer (POLY1) on the graphene (GRF1) by bringing a monomer (M1) into contact with the graphene (GRF1) such that the monomer (M1) polymerizes on the surface (SRF1) of the graphene (GRF1), and - removing the substrate (S0) from the graphene (GRF1), wherein the monolayer (GRF1) comprises a plurality of microscopic convex regions (CNX1), which are fully supported by the conformal polymer layer (POLY1).

Description

COMPOSITE FILM COMPRISING AN ELECTRICALLY CONDUCTIVE LAYER

FIELD

The present invention relates to a method for producing a film, which comprises graphene.

BACKGROUND

Referring to Figs. 1 a to 1 c, it is known that graphene layer GRF1 may be deposited on a first substrate SO, and that the graphene layer may be transferred from the first substrate SO to a second substrate S2 e.g. by using an adhesive tape. The adhesive tape may comprise an adhesive layer LAQ1 and a transfer film TF1 . The graphene layer GRF1 may be releasably attached to the transfer film TF1 by the adhesive layer LAQ1 . The adhesive layer LAQ1 may comprise polymer chains and/or semi-crystals BLC1 , which may form a bond with the graphene layer GRF1 . The transfer film TF1 may provide temporary mechanical support for the graphene layer GRF1 when the graphene layer GRF1 is separated from the first substrate SO. The transfer film TF1 may provide temporary mechanical support for the graphene layer GRF1 also when the graphene layer GRF1 is transferred to the second substrate S2.

SUMMARY Some versions may relate to a method for producing a composite, which comprises graphene. Some versions may relate to a composite, which comprises graphene. Some versions may relate to a device, which comprises said composite. Some versions may relate to a method for producing said device. According to an aspect, there is provided a method according to claim 1 . According to an aspect, there is provided a composite according to claim 8. According to an aspect, there is provided a device according to claim 12. Further aspects are defined in the other claims.

The composite may be a composite film, which comprises a graphene layer and a conformal layer attached to the graphene layer. The composite may be formed by depositing graphene on a substrate, by bringing a monomer into contact with the graphene such that a conformal layer is formed on the graphene by polymerization of the monomer, and by removing the substrate from the graphene.

The conformal layer may form a bond with the graphene layer and the conformal layer may also provide mechanical support for the graphene. The conformal layer may support the graphene when the substrate is removed from the graphene. The conformal layer may support substantially each point of the graphene layer in order to reduce the risk of damaging the graphene layer during separation and/or during subsequent manufacturing steps. Each point of the graphene may remain attached the conformal layer when the substrate is removed from the graphene. Substantially the whole area of the graphene may remain attached to the conformal layer when the substrate is removed from the graphene.

In an embodiment, the conformal layer may provide sufficient mechanical support for the graphene such that it is not necessary to transfer the graphene to a second substrate.

In an embodiment, the graphene layer of the composite film may further comprise a plurality of microscopic convex portions, which are fully supported by the conformal layer. The convex portions supported by the conformal layer may further reduce the risk of damaging the graphene layer when the composite film is stretched and/or bent. The composite film may be separated from the substrate e.g. by peeling. The peeling operation may cause local stretching and/or bending of the composite film. Thanks to the convex portions supported by the conformal layer, the risk of damaging the graphene layer may be reduced when the composite film is peeled away from the substrate.

In an embodiment, the sheet resistance Rs of the graphene layer may be e.g. in the range of 30-40Q/sq even after the composite film has been separated from the substrate by peeling.

In an embodiment, the sheet resistance Rs of the graphene layer may be increased e.g. by less than 1 % when the interface between the graphene layer and the conformal layer is stretched by 2 %. The graphene layer of the composite film may be arranged to operate e.g. as a transparent electrode. The absorbance of the graphene layer may be e.g. smaller than 3% at the wavelength 550 nm of green light. The optical transmittance of the composite film may be e.g. higher than 90% at the wavelength of 550 nm.

The graphene of the composite film may be arranged to operate as a flexible electrode. The graphene of the composite film may be arranged to operate as a transparent flexible electrode. In an embodiment, the composite film may be arranged to operate e.g. as a part of a display screen, wherein the graphene layer may be arranged to operate as a visually transparent electrically conductive electrode. The graphene layer may be used e.g. instead of an indium tin oxide (ITO) layer. The manufacturing costs of the composite film may be lower than the manufacturing costs of a layer of indium tin oxide. The use of the composite film may be more environmentally friendly than the use of indium tin oxide.

In an embodiment, the composite film may be used to implement a flexible electric circuit. The composite film may be used to implement a flexible electronic circuit In an embodiment, the composite film may be used e.g. as a part of a capacitor.

In an embodiment, the composite film may be used e.g. as a part of a battery.

In an embodiment, the composite film may be used e.g. as a part of a field effect transistor. In an embodiment, the composite film may be used e.g. to implement a biocompatible sensor electrode or an implant.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following examples, several versions will be described in more detail with reference to the appended drawings, in which

Fig. 1 a shows, in a cross sectional view, graphene deposited on a first substrate, and a transfer film which is temporarily attached to the graphene by an adhesive layer,

Fig. 1 b shows, in a cross sectional view, separating the graphene from the substrate by using the transfer film, shows, in a cross sectional view, a graphene layer which has been transferred to a second substrate by using the transfer film,

Fig. 2a shows, by way of example, in a cross sectional view, depositing graphene on a substrate,

Fig. 2b shows, by way of example, in a cross sectional view, forming a composite film by depositing monomer on the graphene, Fig. 2c shows, by way of example, in a cross sectional view, removing the substrate from the composite film,

Fig. 2d shows, by way of example, in a cross sectional view, a free standing composite film obtained by removing the substrate,

Fig. 3a shows, by way of example, in a cross sectional view, a substrate which comprises a plurality of microscopic concave portions, Fig. 3b shows, by way of example, in a cross sectional view, depositing graphene on the substrate,

Fig. 3c shows, by way of example, in a cross sectional view, forming a composite film by depositing monomer on the graphene,

Fig. 3d shows, by way of example, in a cross sectional view, a free standing composite film obtained by removing the substrate,

Fig. 4a shows, by way of example, a measured surface profile of graphene deposited on a substrate,

Fig. 4b shows, by way of example, a measured surface profile of graphene deposited on a substrate, Fig. 5a shows, in a cross sectional view, a comparative example where graphene is deposited on a substrate, and a transfer film is temporarily attached to the graphene by an adhesive layer,

Fig. 5b shows, in a cross sectional view, a comparative example where the graphene of Fig. 5a is separated from the substrate by using the transfer film,

Fig. 6a shows, by way of example, in a three dimensional view, a substrate which comprises a plurality of microscopic concave portions, shows, by way of example, in a three dimensional view, depositing graphene on the substrate, shows, by way of example, in a three dimensional view, forming a composite film by depositing a monomer on the graphene such that the monomer polymerizes on the surface of the graphene and forms a conformal layer, shows, by way of example, in a three dimensional view, removing the substrate from the composite film, shows, by way of example, in a three dimensional view, a free-standing composite film obtained by removing the substrate from the composite film, shows, by way of example, in a side view, the composite film, which comprises graphene and a conformal layer, shows, by way of example, in a three dimensional view, a convex portion of the composite film, shows, by way of example, in a cross sectional side view, a concave portion of a substrate, shows, by way of example, in a cross sectional side view, depositing graphene on the substrate, shows, in a cross sectional side view, depositing parylene on the graphene by bringing a monomer to the surface of the graphene, shows, in a cross sectional side view, depositing parylene on an underlying monolayer of parylene by bringing a monomer to the surface of the parylene, shows, by way of example, in a cross sectional side view, a conformal layer of parylene deposited on the surface of the graphene, shows, by way of example, in a cross sectional side view, the composite film, which comprises graphene and a conformal layer of parylene, shows, by way of example, forming a composite film by forming a conformal layer, and by removing the substrate from the composite film, shows, by way of example, method steps for forming the composite film, and method steps for producing a device, which comprises the composite film, shows, by way of example, obtaining dimer gas from a source material, shows, by way of example, forming monomer gas from the dimer gas, shows, by way of example, polymerization of the monomer on the surface of the graphene, shows by way of example, an apparatus for forming a conformal layer of parylene on the graphene, shows, by way of example, in cross sectional a side view, separating the composite film from the substrate by peeling,

Fig. 12b shows, by way of example, in cross sectional a side view, separating the composite from the substrate by using a liquid, shows, by way of example, in a three dimensional view, a composite, which comprises graphene and a conformal layer, shows, by way of example, in cross sectional a side view, measuring the resistance of the graphene as the function of stretching of the conformal layer, shows, by way of example, in cross sectional a side view, a set-up measuring the resistance of the graphene as the function of bending radius, shows, by way of example, in a three dimensional view, a composite, which comprises two or more regions of graphene separated by a gap, shows, by way of example, in a three dimensional view, a composite, wherein the first side of the graphene is attached to the conformal polymer layer, and the second side of the graphene is protected by a protective layer, shows, by way of example, in a three dimensional view, a composite, which comprises graphene, a conformal layer, and an additional layer, shows, by way of example, in a three dimensional view, a device which comprises composite film and one or more contact elements, wherein the contact elements are in contact with the graphene of the composite, shows, by way of example, in a three dimensional exploded view, a sensor electrode device,

Fig. 17b shows, by way of example, in a three dimensional view, the sensor electrode device of Fig. 17a arranged to monitor an object, Fig. 18a shows by way of example, in a cross sectional side view, a semimanufactured field effect transistor, which comprises graphene,

Fig. 18b shows by way of example, in a cross sectional side view, a field effect transistor, which comprises graphene,

Fig. 19a shows by way of example, in a cross sectional side view, a first conformal polymer layer formed on a first side of a substrate and a second conformal polymer layer formed on a second side of the substrate, and

Fig. 19b shows by way of example, in a cross sectional side view, a pair of composite films obtained by removing the substrate of Fig. 19a.

DETAILED DESCRIPTION

Referring to Fig. 2a, the graphene layer GRF1 may be formed on the surface SRFO of a substrate SO. The substrate SO may have a deposition surface SRFO, and the graphene layer GRF1 may be formed on the surface SRFO by deposition. The method may comprise forming a graphene GRF1 on the substrate SO such that the graphene consists essentially of a single monolayer. The method may comprise forming graphene GRF1 on the substrate SO such that the graphene consists essentially of a bilayer. The number of atomic layers of the graphene GRF1 may be e.g. in the range of 1 to 5. The substrate SO may e.g. consist of copper (Cu).

Referring to Fig. 2b, a conformal polymer layer POLY1 may be formed on the surface SRF1 of the graphene GRF1 by bringing a monomer into contact with the graphene such that a conformal layer is formed on the graphene by polymerization of the monomer. The conformal layer POLY1 may be formed e.g. by depositing parylene on the graphene GRF1 by chemical vapor deposition. The conformal layer POLY1 and the graphene layer GRF1 may together form a composite film CMP1 . Referring to Fig. 2c, the substrate SO may be removed from the graphene layer GRF1 . The substrate SO may be separated from the composite film CMP1 e.g. by peeling. Referring to Fig. 2d, the method may comprise producing a composite film CMP1 , which comprises the graphene layer GRF1 , which is permanently bonded to the conformal layer POLY1 . A free standing composite film CMP1 may be obtained by removing the substrate SO from the composite film CMP1 e.g. as shown in Fig. 2c.

The conformal layer POLY1 may support the graphene layer GRF1 such that the risk of damaging the graphene layer GRF1 may be reduced when the composite film CMP1 is stretched and/or bent. The conformal layer POLY1 may provide full mechanical support for the graphene layer GRF1 even at the molecular level. Each point of the graphene layer GRF1 may be attached to the conformal layer POLY1 . The conformal layer POLY1 may be substantially non-porous. The interface between the conformal layer POLY1 and the graphene layer GRF1 may be substantially free from pores. The conformal layer POLY1 may be substantially pinhole-free.

Referring to Fig. 3a, the substrate SO may further comprise a plurality of microscopic concave portions PORO₁, PORO₂, PORO_k, ... in order to provide an undulated composite film CMP1 . The undulated composite film CMP1 may comprise a plurality of microscopic protrusions CNX1 (Fig. 3d).

Referring to Fig. 3b, the graphene layer GRF1 may be deposited on the substrate SO. The graphene layer GRF1 may comprise a plurality of microscopic concave portions PORI 1, PORI2, POR1 k, ... corresponding to the concave portions PORO1, POR0₂, POR0_k, ... of the substrate SO. The symbol h₂ denotes the depth or height of a portion at a position where the width of said portion is equal to L2. Each concave portion may have a minimum radius of curvature Γ_ΜΙΝ- For example, a portion POR1 _k may have a minimum radius of curvature ΓΜΙΝ,Ι<- The maximum size of a monomer which can be brought into contact with the bottom of the concave portions may depend on the minimum radius of curvature Γ_ΜΙΝ- The atomic mass of the monomer may be smaller than e.g. 200 amu (atomic mass units) in order to ensure that the monomer which can be brought into contact with the bottom of the concave portions.

The graphene GRF1 may comprise microscopic concave portions POR1 . In particular, the graphene GRF1 may comprise a group GRP1 of microscopic concave portions POR1 such that height h₂ of each portion CNX1 of said group is higher than 0.3 nm at the width L2 of 10 nm.

Referring to Fig. 3c, the conformal polymer layer POLY1 may be formed on the surface SRF1 of the graphene GRF1 . The conformal layer POLY1 may provide full mechanical support for the graphene layer GRF1 also at the concave portions POR1 i, POR1₂, POR1 _k, ...

Referring to Fig. 3d, the substrate SO may be removed from the graphene layer GRF1 . The substrate SO may be separated from the composite film CMP1 e.g. by peeling. The composite film CMP1 may comprise a plurality of microscopic protrusions CNXI ₁, CNX1₂, CNX1 _k, ... corresponding to the concave portions PORI 1, POR1₂, POR1 k, ... The microscopic protrusions CNX1 of the graphene layer GRF1 may be fully supported by the conformal layer POLY1 . The microscopic protrusions CNX1 , when supported by the conformal layer, may further reduce the risk of damaging the graphene layer GRF1 when the composite film CMP1 is stretched and/or bent. The height of the protrusions may be substantially equal to the depth of the concave portions, which are on the other side of the graphene.

The composite film CMP1 may comprise microscopic convex portions CNX1 . In particular, the composite film CMP1 may comprise a group GRP2 of microscopic convex portions CNX1 such that height h₂ of each portion CNX1 of said group is higher than 0.3 nm at the width L2 of 10 nm.

Figs. 4a and 4b show, by way of example, surface profiles of a graphene layer GRF1 deposited on the substrate SO. The surface profile of a surface is defined by the intersection of the surface with a plane perpendicular to the surface. The position of the plane may be indicated e.g. by a sampling path LIN1 (see Fig. 6e). The surface profile may be measured e.g. by moving a sharp needle along the sampling path LIN1 . The sampling path LIN1 may be substantially linear when viewed in a direction perpendicular to the surface. The surface profile may be measured e.g. by atomic force microscopy (AFM), by scanning probe microscopy (SPM) and/or by tunneling electron microscopy (scanning tunneling microscopy, STM). The microscopy may comprise moving a sharp needle along the sampling path LIN1 .

Referring to Fig. 4a, the graphene layer GRF1 may comprise a concave portion POR1 , which has a depth h₂ at a width L2. In other words, the depth (or height) h₂ of the portion may mean the distance between a line segment CRD1 and the bottom (or peak) of the portion POR1 in a situation where the length of said line segment is equal to L2 and both ends P_a, P_b of said line segment CRD1 meet the surface of said portion. Said line segment CRD1 may also be called e.g. as a chord.

In particular, the depth h₂ of the portion may be greater than 0.3 nm (3- 10^"10 m) at a position where the width L2 of said portion is equal to 10 nm (1 - 10^"8 m). The distance h2 between the line segment CRD1 and the bottom of the portion POR1 may be greater than 0.3 nm when the ends P_a, P_b of said line segment CRD1 meet the surface of said portion and the length of the line segment CRD1 is equal to 10 nm. According to a circular approximation, the minimum radius Γ_ΜΙΝ corresponding to said dimensions h₂ and L2 may be e.g. equal to 40 nm (=0.04 μηη). The minimum radius Γ_ΜΙΝ 40 nm may be calculated by assuming that the width of a circular arc is equal to 10 nm and that the height of the circular arc is equal to 0.3 nm. In other words, a circle having a radius Γ_ΜΙΝ comprises a circular arc such that the width of a circular arc is equal to 10 nm and that the height of the circular arc is equal to 0.3 nm.

Small monomer molecules M1 may be brought into contact with the graphene surface of the concave portion POR1 also at the position where the concave portion POR1 has the minimum radius Γ_ΜΙΝ - On the other hand, it may be difficult or impossible to completely fill the concave portion POR1 of the graphene layer BLC1 in a situation where long polymer chains and/or semi-crystals BLC1 are brought into contact with the graphene and the minimum radius Γ_ΜΙΝ of the concave portion POR1 is small (see Fig. 5a).

Referring to Fig. 4b, the graphene layer may comprise a group of concave portions POR1 such that the minimum radius Γ_ΜΙΝ of concave portions POR1 of said group is smaller than 40 nm. The graphene layer may comprise a group of concave portions POR1 such that the depth h₂ of each portion of said group is greater than 0.3 nm at the width of 10 nm. L_SMP may denote a sampling length. A portion of the graphene along the sampling path LIN1 may comprise e.g. more than five concave portions POR1 of said group in a situation where the length of said portion is equal to 500 nm. A portion of the graphene along the sampling path LIN1 may comprise e.g. more than five concave portions POR1 of said group in a situation where the length of said portion is equal to 1000 nm.

The graphene GRF1 may comprise a first group GRP1 of concave portions POR1 such that the depth h₂ of each convex portion POR1 of the first group GRP1 is greater than 0.3 nm at a width of 10 nm, and wherein the number density of the concave portions (POR0) of the first group (GRP1 ) along a linear sampling path (LIN1 ) is greater than 5/1000 nm. Figs. 5a and 5b show a comparative example where a graphene layer GRF1 has been coated with a coating layer LAQ1 by bringing polymer chains and/or semi-crystals BLC1 into contact with the graphene layer GRF1 . A large fraction of the polymer chains may be formed before they are brought into contact with the graphene. The coating layer LAQ1 may be applied e.g. by brushing or spraying droplets of an adhesive or resin on the graphene GRF1 . The size of the polymer chains and/or semi-crystals BLC1 may be so large that microscopic voids VOIDO may remain between the coating layer LAQ1 and the graphene GRF1 . The graphene layer GRF1 may also comprise convex regions which have a small minimum radius. The size of the polymer chains and/or semi-crystals BLC1 may be so large that they cannot fill the convex regions completely. The size of the polymer chains and/or semi-crystals BLC1 may limit the capability of the polymer chains and/or semi-crystals BLC1 to penetrate into the steep concave portions POR1 of the graphene. The capability of the polymer chains and/or semi-crystals BLC1 to penetrate into the concave portions may be limited e.g. by cohesive interaction. Surface tension effects may also limit the capability to penetrate into the concave portions. Thus, the coating layer LAQ1 is not attached to each point of the graphene layer GRF1 , and the graphene layer may be easily damaged when the substrate is separated from the graphene. The coating layer LAQ1 of Fig. 5a does not conform to the surface of graphene. The structure may comprise a plurality of microscopic void spaces VOID0, which a located between the graphene GRF1 and the coating layer LAQ1 . The regions which are not supported by the coating layer LAQ1 may be brittle. The graphene layer GRF1 may be fractured easily at those regions, which coincide with the void spaces VOID0.

Fig. 5b shows a comparative example where the graphene layer GRF1 has been locally fractured at the locations of the voids VOID0. The graphene layer GRF1 may be fractured e.g. when the substrate SO is removed from the graphene layer GRF1 . Stretching and/or bending of the structure of the comparative example of Fig. 5a may damage the graphene layer and may degrade electrical properties of the graphene layer. Separating the substrate from the graphene layer GRF1 may cause damage to the graphene layer at the locations of the voids VOID0. The graphene layer shown in Fig. 5b may comprise a plurality of fractured regions. The fractured regions may significantly reduce the electrical conductivity of the graphene layer.

Figs. 6a-6e illustrate producing a composite film CMP1 such that the graphene layer is fully supported by a conformal polymer layer POLY1 .

Referring to Fig. 6a, a graphene layer may be deposited on a surface SRFO of a substrate SO. The macroscopic shape of deposition surface SRFO may be e.g. a planar, cylindrical or spherical. The surface SRFO may further comprise a plurality of structural features DF1 so as to form concave portions POR0. The structural features DF1 may be e.g. microscopic protrusions, steps and/or grooves. The height or depth hi of the structural features DF1 may be e.g. greater than 0.3 nm, greater than 1 .0 nm, or even greater than 10 nm. The height and/or depth of the microscopic structural features DF1 may be large when compared with the thickness of the graphene.

The substrate SO may comprise or consist essentially of e.g. copper (Cu), nickel (Ni), ruthenium (Ru), iridium (Ir), or silicon carbide (SiC). The upper material layer of the substrate SO may e.g. comprise or consist essentially of copper, nickel, ruthenium, iridium, or silicon carbide. The surface of said upper material layer may be used as the deposition surface SRF0.

The surface SRF0 may optionally comprise a first region which enables formation of graphene, and a second region which prevents formation of graphene. The second region may be used e.g. to form an electrically insulating layer between a first region of graphene and a second region of graphene.

SX, SY and SZ denote orthogonal directions. The (macroscopic) surface normal of the surface SRF1 may be parallel with the direction SZ.

Referring to Fig. 6b, graphene GRF1 may be formed on the surface SRF0 of the substrate SO. The graphene GRF1 may be formed by a deposition process DEPO1 . The graphene GRF1 may be formed on the surface SRF0 e.g. by chemical vapor deposition (CVD). The graphene GRF1 may be formed e.g. by plasma enhanced chemical vapor deposition (PECVD). The graphene GRF1 may be formed e.g. from methane and hydrogen e.g. by using plasma excitation. The graphene GRF1 may be formed e.g. by atomic layer deposition (ALD). The graphene GRF1 may be formed e.g. by chemical reduction of graphene oxide.

The temperature of the surface SRF0 of the substrate SO during the deposition DEPO1 may be e.g. in the range of 800 to 1200°C. The temperature of the surface SRF0 of the substrate SO during the deposition DEPO1 may be e.g. in the range of 900 to 1 100°C. The graphene GRF1 deposited on the surface SRFO may consist essentially of an array of carbon atoms arranged in a repeating hexagonal lattice. The graphene GRF1 formed on the surface SRFO may consist of a single monolayer. The thickness of the graphene may be equal to the thickness of one atom layer. Graphene consisting of single monolayer may be used e.g. as an optically transparent electrical conductor. The method may comprise depositing a single monolayer of graphene on the substrate SO, and depositing a conformal polymer layer on the single monolayer.

The graphene GRF1 formed on the surface SRFO may also comprise more than one atomic layer. For example, the graphene GRF1 formed on the surface SRFO may consist of two atomic layers, i.e. bilayer graphene may be formed on the surface SRFO. The method may comprise depositing bilayer graphene on the substrate SO, and depositing a conformal polymer layer on the bilayer. Bilayer graphene may exhibit e.g. anomalous quantum Hall effect, and/or a tunable band gap. Bilayer graphene may be used e.g. for an electronic or optoelectronic application. Bilayer graphene may be used e.g. to implement a field-effect transistor.

Multilayer graphene may be formed on the surface SRFO. The graphene GRF1 formed on the surface SRFO may consist essentially of one or more layers of carbon atoms. The number of atomic layers of the graphene GRF1 may be e.g. in the range of 1 to 5.

The graphene GRF1 may conform to the three-dimensional shape of the surface SRFO, i.e. the three-dimensional shape of the graphene layer GRF1 may match with the three-dimensional shape of the deposition surface SRFO. The graphene GRF1 may cover the structural features DF1 and the concave portions POR0 of the surface SRFO. Consequently, the graphene layer GRF1 may have a plurality of concave portions POR1 , which overlap the concave portions POR0 of the surface SRFO. The surface profile of the graphene layer GRF1 may be measured e.g. along a sampling path LIN1 .

Referring to Fig. 6c, a polymer layer POLY1 may be deposited on the graphene GRF1 such that the conformal layer POLY1 conforms to the three- dimensional shape of the graphene GRF1 and to the (optional) exposed portions of the surface SRFO. The polymer layer POLY1 may be formed by bringing monomer molecules M1 into contact with the graphene GRF1 such that the monomer molecules M1 polymerize when they are physisorbed and/or chemisorbed on the surface SRF1 of the graphene GRF1 . The polymer layer POLY1 may conform to the three-dimensional shape of the graphene GRF1 and (optional) exposed portions of the surface SRFO. The polymerization of the monomer M1 may form a conformal layer POLY1 on the graphene GRF1 . The three-dimensional shape of the conformal layer POLY1 may match with the three-dimensional shape of the graphene GRF1 and optionally also exposed parts of the surface SRFO. The conformal polymer layer POLY1 may be permanently attached to the graphene layer GRF1 so as to form a composite film CMP1 . The conformal layer POLY1 may be electrically insulating. The conformal layer POLY1 may consist of a dielectric material. The conformal layer POLY1 may consist essentially of a polymer. The conformal layer may be formed on the graphene by a deposition process DEPO2. Referring to Fig. 6d, a separated composite film CMP1 may be provided by removing the substrate SO from the composite film CMP1 . The composite film CMP1 may comprise the graphene GRF1 and the conformal layer POLY1 . The composite film CMP1 may consist of the graphene GRF1 and the conformal layer POLY1 . The composite film CMP1 may be a free- standing film. At an intermediate manufacturing stage, the composite film CMP1 may be a free-standing film.

The substrate SO may be removed from the composite film CMP1 e.g. by peeling, intercalation, and/or etching. Referring to Fig. 6e, the composite film CMP1 comprises graphene GRF1 and a conformal layer of the polymer POLY1 . The produced composite film CMP1 may further comprise microscopic protrusions CNX1 , which correspond to the concave portions PORO and the structural features DF1 of the deposition substrate SO. The graphene GRF1 supported by the conformal layer POLY1 may have a plurality of convex portions CNX1 , which correspond to the concave portions PORO of the substrate SO. The concave portions PORO may be fully supported by the conformal layer. The presence of the supported convex portions CNX1 may further improve the mechanical and/or electrical properties of the composite film CMP1 .

The surface profile of the graphene layer GRF1 of the composite film CMP1 may be measured e.g. along a sampling path LIN1 . Fig. 7a shows, in a side view, the composite film CMP1 where the convex portions CNX1 are fully supported by the conformal layer POLY1 . The conformal layer POLY1 may completely fill the space beneath the convex portions CNX1 , thereby improving the mechanical strength of the graphene layer. The conformal layer POLY1 may be attached to the graphene also at the locations of the microscopic convex portions CNX1 . The conformal layer POLY1 may be attached to substantially each point of the (one side of) the graphene layer GRF1 . The conformal layer of polymer POLY1 may provide strong mechanical support for each point of the graphene layer GRF1 . Fig. 7b shows, in a three dimensional view, a convex portion CNX1 of the composite film CMP1 . The height of the h₂ of the convex portion CNX1 may be e.g. higher than 0.3 nm when the width L2 of the convex portion CNX1 is equal to 10 nm. Γ_ΜΙΝ denotes the minimum radius of curvature of the convex portion CNX1 . The minimum radius of curvature of the convex portion CNX1 may be substantially equal to the radius of curvature of the concave portion of the graphene which is located on the other side of the graphene layer and which is now completely filled with the polymer layer POLY1 . The composite film CMP1 may comprise a group of convex portions CNX1 such that the minimum radius of curvature of the convex portions CNX1 of said group is smaller than 40 nm. The number density of said convex portions CNX1 may be e.g. higher than 5/1000 nm along a linear sampling path LIN1 . hcMPi denotes the thickness of the composite film CMP1 . The thickness hcMPi may be e.g. in the range of 0.1 μηη to 100 μηη.

The convex portions CNX1 may also be called e.g. as protrusions. The composite film CMP1 may comprise a plurality of microscopic protrusions CNX1 . The composite film CMP1 may comprise an undulated surface, which comprises a plurality of protrusions CNX1 . Substantially each convex portion CNX1 of the graphene layer may be fully supported by the polymer layer POLY1 .

The presence of the microscopic convex portions of the composite CMP1 may e.g. improve the tolerance to stretching and/or bending. Thanks to the convex portions the electrical properties of the graphene layer GRF1 are not significantly degraded when the composite CMP1 is stretched and/or bent. Thanks to the convex portions, the electrical properties of the graphene layer GRF1 are not significantly degraded when the substrate SO is removed from the composite CMP1 .

Referring to Fig. 8a, the surface SRFO of the substrate SO may have a plurality of microscopic structural features DF1 . The substrate SO may comprise e.g. a plurality of protrusions DF1 . The structural features DF1 may define a plurality of concave portions POR0.

Referring to Fig. 8b, the graphene layer GRF1 may be deposited on the surface SRFO by the deposition process DEPO1 . Substantially each point of the graphene layer GRF1 may be in contact with the surface SRFO. For example, at least 99.9% of the area of the graphene layer may be in contact with the surface SRFO. The graphene layer may conform to the three dimensional shape of the surface SRFO.

The graphene layer is very thin. The depth of the concave portions POR0 may be greater than the thickness of the graphene layer GRF1 . The surface SRF1 of the graphene GRF1 may comprise a plurality of concave portions POR1 corresponding to the convex portions PORO of the surface SRFO of the substrate SO. Referring to Figs. 8c and 8d monomer molecules M1 may be brought into contact with the graphene GRF1 so that the monomer molecules M1 polymerize on the surface SRF1 of the graphene GRF1 . Polymerization of the monomer molecules M1 on the surface SRF1 may provide a polymer layer POLY1 , which conforms to the surface SRF1 of the graphene. The concave regions POR1 of the graphene may be completely filled with the material of the conformal layer POLY1 . Substantially each point of the polymer layer POLY1 may be in contact with the surface SRF1 . For example, at least 99.9% of the area of the graphene layer GRF1 may be in contact with the polymer layer. The polymer layer POLY1 may conform to the three dimensional shape of the surface SRF1 .

Monomer molecules M1 may be brought into contact with the graphene GRF1 so that the monomer molecules M1 polymerize only on the solid-gas interface (SRF1 ). The contact with the surface SRF1 may catalyze the polymerization. The monomer molecules M1 may be physisorbed and/or chemisorbed to the solid-gas interface SRF1 , and the physisorbed monomer molecules M1 may subsequently form polymer chains on the solid-gas interface SRF1 . The monomer molecules M1 may be brought into contact with the graphene GRF1 such that a negligible fraction of the monomer molecules M1 polymerize before contact with the solid-gas interface SRF1 . For example, less than 0.1 % of the monomer molecules M1 may polymerize before contact with the solid-gas interface SRF1 . Consequently, the capability of the monomer molecules M1 to penetrate even the smallest cavities and concave portions POR1 is not limited by premature polymerization. The number density of the monomer molecules M1 may be kept below a predetermined limit in order to prevent premature polymerization. The partial pressure of the monomer molecules M1 may be kept below a predetermined limit in order to prevent premature polymerization. The partial pressure of the monomer molecules M1 above the surface SRF1 may be e.g. smaller than 0.2 Pa. The low partial pressure may minimize premature clustering of the monomer molecules M1 before they penetrate into the concave portions POR1 of the graphene.

The temperature of the graphene GRF1 during the polymerization may be e.g. in the range of -100°C to +100°C. The temperature of the graphene GRF1 during the polymerization may be e.g. in the range of -50°C to +50°C. The temperature of the graphene GRF1 during the polymerization may be e.g. in the range of 0°C to +50°C. The temperature of the graphene GRF1 during the polymerization may be near the room temperature 25°C, e.g. in order to reduce internal stress. The temperature of the graphene GRF1 during the polymerization may be near the final operating temperature of a device 100 in order to reduce internal stress.

The monomer may be physisorbed and/or chemisorbed on the surface of the graphene in order to initiate polymerization. The partial pressure of the monomer M1 above the graphene may be kept below a predetermined limit in order to prevent premature polymerization.

The monomer M1 may be e.g. p-xylylene. The conformal layer POLY1 may be formed e.g. by depositing poly-para-xylylene on the surface of the graphene. The poly-para-xylylene is also known as the "parylene". The partial pressure of the monomer may be kept below a predetermined limit in order to minimize premature polymerization of the monomer. The partial pressure of the monomer may be kept below a predetermined limit in order to maximize the capability of the monomer to penetrate into convex portions of the surface of the graphene. In particular, the conformal layer POLY1 may be formed e.g. by depositing poly-chloro-para-xylylene (parylene C) on the graphene GRF1 .

The parylene film may be formed e.g. by chemical vapor deposition such that it is not necessary e.g. to remove a solvent from the parylene layer. Deposing parylene on the graphene may provide a substantially non-porous pinhole- free parylene film.

The parylene monomer M1 is so small that it can penetrate into the microscopic concave portions of the graphene. The parylene film may be substantially free from internal stress. The dimensional changes of the parylene film may be small during the polymerization such that compressive and/or tensile stress of the graphene layer may be reduced. The parylene film may be chemically pure such that release of harmful substances from the parylene film may be minimized during subsequent use. The composite film may be biocompatible.

Polymerization of the monomer molecules M1 may take place on the surface SRF1 of the graphene GRF1 and/or on the solid-gas interface between the polymer layer POLY1 and the gas.

Fig. 8e shows the composite film CMP1 when the graphene layer GRF1 is still attached to the substrate SO.

Fig. 8f shows the composite film CMP1 after the substrate SO has been removed. The graphene layer GRF1 of the composite CMP1 may comprise a group of convex regions CNX1 , which correspond to the concave portions POR0 of the original substrate SO. The rear side of substantially each convex region CNX1 may be fully supported by the conformal layer POLY1 . Substantially each point of the graphene layer GRF1 may be in contact with the conformal polymer layer POLY1 .

A microscopic convex portion CNX1 may be classified as a "sharp" portion e.g. when the height h₂ of said portion is higher than 0.3 nm at the width L2 of 10 nm. The minimum radius of curvature of the "sharp" portions may be e.g. smaller than 40 nm. The graphene layer GRF1 may comprise a group GRP2 of the "sharp" convex regions CNX1 . The substrate SO may be selected e.g. such that the number density of the "sharp" portions CNX1 may be e.g. higher than 5/1000 nm along a linear sampling path. A sampling length of 1 mm of the graphene may comprise e.g. more than 5-10³ "sharp" portions CNX1 . An area of 1 mm² of the graphene may comprise e.g. more than 10⁶ "sharp" portions CNX1 . The number density of the "sharp" portions CNX1 along a linear path of the graphene may be e.g. higher than 5- 10³/mm. The number density of the "sharp" portions CNX1 in an area of the graphene may be e.g. higher than 10⁶/mm. The term "number density" means the number of said regions CNX1 per unit area or per unit length of the graphene surface. The other side of each concave region of the graphene layer forms a convex region of the composite film. The rear side of the each "sharp" portion CNX1 of the graphene is a concave portion POR1 , which is fully in contact with the conformal layer POLY1 because the individual monomer molecules M1 may penetrate into the concave portions POR1 of the graphene layer before the polymerzation. The concave regions may be completely filled with the material of the conformal layer such that the convex portions of the resulting composite film are fully supported by the conformal layer. Substantially each point of the convex portions may be in contact with the underlying supporting layer. Consequently, the risk of fracturing the graphene layer at the convex portions may be reduced.

The number density and the dimensions of the convex regions CNX1 may be determined e.g. by measuring a surface profile of the graphene layer of the composite CMP1 .

Fig. 9a shows forming a free-standing composite film CMP1 by depositing the conformal layer POLY1 on the graphene GRF1 , and by removing the substrate SO from the composite CMP1 . Fig. 9b shows method steps for forming the composite film CMP1 , and for forming a device 100, which comprises the composite film CMP1 .

Graphene GRF1 may be deposited on the surface SRF0 of a substrate SO in step 810. The graphene GRF1 may be deposited e.g. by chemical vapor deposition (DEPO1 ). In step 820, the conformal layer POLY1 may be formed on the graphene GRF1 e.g. by bringing monomers M1 to the surface SRF1 of the graphene GRF1 such that the monomers M1 polymerize on the surface SRF1 of the graphene GRF1 . The conformal polymer layer POLY1 may be formed e.g. by chemical vapor deposition (DEPO2). The conformal polymer layer POLY1 may be formed e.g. by forming parylene by chemical vapor deposition. The deposited conformal polymer layer POLY1 and the graphene GRF1 may together form a composite film CMP1 . The substrate SO may be removed from the composite film CMP1 in step 830. At an intermediate step or after the final step, the composite film CMP1 may be a free-standing film.

The substrate SO may have a predetermined length and a predetermined width. The substrate SO may be e.g. a disk whose diameter is in the range of 10 mm to 500 mm. The step 810, 820, and/or 830 may be performed e.g. as a batch process.

The step 810, 820, and/or 830 may also be performed as a roll-to-roll process. The substrate SO may be e.g. long sheet which may be moved from a first roll to a second roll. The substrate SO may also be an endless metal belt.

In an optional step 840, one or more electrical contact elements MC1 , MC2 may be implemented on the graphene GRF1 . One or more electrical contact elements may be in galvanic contact with the graphene. One or more electrical contact elements may be deposited on the graphene. One or more electrical contact elements may be attached to the graphene e.g. by an adhesive. One or more electrical contact elements may be clamped against the graphene by a clamping force.

In an optional step 850, a protective coating (e.g. CVR2 shown in Fig. 15b or POLY2 shown in Fig. 18b) may be applied to cover an exposed side of the graphene GRF1 , so that a first side of the graphene is protected by the conformal layer POLY1 , and a second side of the graphene is protected by the protective coating. The protective coating may be e.g. a second layer of parylene deposited on the graphene. The protective coating may also be applied e.g. by spraying resin on top of the composite CMP1 . The protective coating may protect the graphene e.g. from abrasion and/or corrosion.

Figs. 10a to 10c illustrate forming a conformal layer POLY1 of parylene by chemical vapor deposition.

Referring to Fig. 10a, dimer gas may be formed from a source material MAT1 e.g. by sublimation. The dimer may be e.g. [2.2]paracyclophane, dichloro[2.2]paracyclophane, or octafluoro[2.2]paracyclophane. The sublimation may take place at a temperature, which is e.g. lower than 200°C.

Referring to Fig. 10b, monomer gas M1 may be obtained from the dimer gas by cracking. The monomer gas M1 may be e.g. p-xylylene. The monomer may be e.g. tetrafluoro-p-xylylene monomer. The cracking temperature may be e.g. in the range of 500°C to 800°C, depending on the type of the dimer.

Referring to Fig. 10c, the monomer gas M1 may be brought into contact with the surface SRF1 of the graphene GRF1 or in contact with a solid-gas interface SRF1 so that the monomer gas M1 may polymerize on the surface SRF1 . The conformal layer may consist of e.g. parylene N, parylene C, parylene D, or parylene F. The partial pressure of the monomer above the surface SRF1 may be kept below a predetermined limit in order to prevent premature polymerization. The partial pressure of the monomer above the surface SRF1 may be kept below a predetermined limit in order to maximize capability of the monomer M1 to penetrate to the concave portions of the surface SRF1 . The partial pressure of the monomer may be e.g. lower than 0.2 Pa. The monomer may be carried by a carrier gas. The pressure of the carrier gas may be e.g. in the range of 1 Pa to 200 Pa. The partial pressure of the monomer may be e.g. lower than 0.2 Pa. The total pressure in the vicinity of the graphene GRF during the deposition DEPO2 may be e.g. in the range of 1 Pa to 200 Pa. The temperature of composite CMP1 may be e.g. in the range of 0°C to 40°C during the deposition. The composite CMP1 may be substantially at the normal room temperature during the deposition. The term parylene means poly-para-xylylene polymer. Parylene N means poly(para-xylylene). Parylene C means poly-chloro-para-xylylene. Parylene D means poly-dichloro-para-xylylene. Parylene-F means poly-tetrafluoro-para- xylylene. The poly(p-xylylene) polymer is obtained by polymerization of p- xylylene. A film of parylene may be produced from the p-xylylene intermediate by chemical vapor deposition. The p-xylylene intermediate may be derived e.g. from [2.2]paracyclophane by heating the [2.2]paracyclophane at a low pressure. The pressure may be e.g. in the range of 1 Pa to 200 Pa, and the precursor may be heated to a cracking temperature, which may be e.g. in the range of 450°C to 700°C. The p-xylylene may polymerize when physisorbed on a target surface. The intermediate p-xylylene has a low reactivity and therefore a small sticking coefficient for physisorption on the surface SRF1 of the graphene GRF1 . Consequently, chemical vapor deposition of p-xylylene on graphene GRF1 may provide a highly conformal coating also when deposited on the surface SRF1 which has microscopic structural features DF1 . The intermediate p-xylylene has an ability to form thin films that can conform to a microstructure, which has protrusions and/or recessed portions. Parylene is suitable for forming a conformal coating. Parylene may exhibit stable dielectric properties over a wide temperature range. Parylene may have a low dielectric constant. Parylene may be electrically insulating, i.e. a dielectric material. The parylene may protect at least one side of the graphene GRF1 from abrasion, wear and/or corrosion. The composite CMP1 may be biocompatible. For example, a medical implant may comprise the composite CMP1 . The aromatic ring of the polymer chain of the parylene may be oriented parallel to the surface SRF1 during the deposition DEPO2.

The p-xylylene may have a relatively low sticking coefficient to the surface SRF1 . Thanks to the low sticking coefficient of the monomer, the reflected monomers may dominate deposition on the inclined portions of the surface SRF1 . Thus the low sticking coefficient of the p-xylylene may result in a highly conformal coating.

Referring to Fig. 1 1 , a parylene coating apparatus 500 may comprise e.g. three chambers. In the vaporization chamber, parylene may vaporize and form a dimeric gas. The dimeric gas may subsequently enter into a pyrolysis chamber where the dimeric gas may be cracked to form monomer gas. The monomer gas may be subsequently deposited onto the graphene GRF1 in a deposition chamber. The parylene coating apparatus 500 may be arranged to produce e.g. parylene N, parylene C, parylene D, or parylene F.

Referring to Fig. 12a, the substrate SO may be separated from the composite film CMP1 e.g. by peeling. The conformal layer POLY1 may fully support the graphene layer GRF1 so that the risk of damaging the graphene layer GRF1 may be reduced. The composite film CMP1 may be bent during the peeling. The graphene layer GRF1 may have a minimum bending radius RMIN during the peeling. The composite film CMP1 may be pulled by a force F_SEP during the peeling. The bending and/or pulling of the composite film CMP1 may cause local stretching of the graphene layer GRF1 . The conformal layer POLY1 and the microscopic convex portions of the composite film CMP1 may improve the tolerance of the graphene layer GRF1 against the stretching caused by the bending and pulling.

The peeling may be performed as a dry process, i.e. in a gas or in vacuum. The substrate SO may be separated from the composite CMP1 by dry delamination. Consequently, the need for processing the composite after removal of the substrate SO may be reduced. For example, it is not necessary to wash or dry the composite, which has been separated from the substrate in a dry environment.

Alternatively, the peeling may be assisted e.g. by immersing the substrate SO and the composite CMP1 in a liquid before the peeling or during the peeling. The peeling operation may cause temporary bending of the composite film CMP1 . The bending may cause local stretching of graphene layer GRF1 and local compression of the conformal layer POLY1 . Referring to Fig. 12b, the substrate SO may be separated from the composite film CMP1 e.g. by immersing the combination of the composite film CMP1 and the substrate SO into a liquid LIQ1 . In particular, the liquid may be water, and the substrate SO may be separated from the composite film CMP1 by intercalation. The liquid LIQ1 may penetrate into a gap between the composite film CMP1 and the substrate SO so as to facilitate separation.

The substrate SO may be separated from the composite film CMP1 e.g. by electrochemical delamination. Fig. 13 shows, by way of example, a composite film CMP1 , which comprises graphene GRF1 supported by the conformal polymer layer POLY1 . The composite film CMP1 may comprise a plurality of microscopic protrusions and recesses. The composite film CMP1 may be an undulated sheet. The graphene layer GRF1 may have a plurality of convex portions CNX1 .

The sheet resistance Rs of an (undulated) graphene monolayer GRF1 supported by the conformal layer POLY1 may be e.g. lower than 60Q/sq, lower than 50Q/sq, or even lower than 40Q/sq. The sheet resistance Rs of the graphene monolayer GRF1 may be e.g. in the range of 30 to 60Q/sq. sq denotes a dimensionless unit, which may be called e.g. as the "square". Thanks to the conformal layer POLY1 , the sheet resistance Rs of the graphene monolayer GRF1 may remain at the low value also when the composite CMP1 is stretched and/or bent. The composite film CMP1 may comprise a group GRP2 of microscopic convex portions CNX1 such that height h₂ of each portion CNX1 of said group is higher than 0.3 nm at the width L2 of 10 nm. The number density of the convex portions CNX1 of the group GRP2 along a linear sampling path (LIN1 ) may be e.g. greater than 5/1000 nm. The sheet resistance Rs of the graphene layer GRF1 may remain lower than e.g. 50Q/sq after a test where the composite film CMP1 is stretched by 2%. For example, a strip having an initial length l_i₂ may be temporarily stretched to a length 1 .02 l_i₂ during said test.

The undulated graphene layer of the composite film may have self-healing properties. The sheet resistance Rs of the graphene layer GRF1 may be temporarily increased due to stretching, but the sheet resistance Rs may return close to the initial value after the stretching force has been reduced to zero.

One or more contact elements MC1 , MC2 may be implemented on the graphene GRF1 after the conformal layer POLY1 has been deposited on the graphene GRF1 , and after the substrate SO has been removed.

Referring to Fig. 14a, the composite film CMP12 may be stretched e.g. by using a force F_P such that the distance l_i₂ between points P1 and P2 is increased. Fig. 14b shows a set-up for testing the effect of bending on the sheet resistance Rs of the graphene layer GRF1 . The graphene layer GRF1 may be stretched by bending the composite film CMP12 around an auxiliary bar BAR1 . The relative stretching of the surface SRF1 of the graphene layer may be determined from the radius R0 of the auxiliary bar BAR1 and from the thickness h_CMPi of the film CMP1 . To the first approximation, the relative stretching of the graphene layer GRF1 may be equal to 0.5- h cMPi /R0. For example, the relative stretching of the graphene layer GRF1 may be approximately equal to 2.5% in a situation where R0=250 μηη and h_CMPi = 25 μηη.

The bending test of Fig. 14b was performed for a composite film CMP1 , where the conformal layer POLY1 was formed by depositing parylene C on the graphene layer GRF1 . The bending test indicated that the sheet resistance Rs of the graphene layer GRF1 increased less than 2% when the graphene layer GRF1 was stretched by 2.5%. Referring to Fig. 15a, two or more regions GPOR1 , GPOR2 of graphene GRF1 may be formed on the substrate SO e.g. by using a mask during the deposition DEPO1 and/or by locally removing graphene from selected regions (GAP1 ) e.g. by using a laser ablation. The regions GPOR1 , GPOR2 may be separated by a gap GAP1 . The region GPOR2 may be galvanically separated from the region GPOR1 by the gap GAP1 . The regions GPOR1 , GPOR2 may form the (undulated) composite CMP1 together with the conformal layer POLY1 . Referring to Fig. 15b, one or more further layers CVR2 may be optionally formed on the (undulated) composite film CMP1 . For example the conformal layer POLY1 may be attached to a first side of the graphene GRF1 , and a layer CVR2 may be implemented on a second side of the graphene GRF1 . For example, a device 100 may comprise the composite film CMP1 and optionally one or more structural layers CVR2. The layer CVR2 may e.g. protect the graphene GRF1 from abrasion. The layer CVR2 may e.g. operate as an electrically insulating layer. The layer CVR2 may e.g. provide support for one or more additional structures of the device 100.

The layer CVR2 may comprise e.g. parylene, PET (Polyethylene terephthalate), PMMA (Polymethyl methacrylate), or Kapton (polyimide).

Referring to Fig. 15c, the conformal layer POLY1 may be optionally attached to an additional material S3. The additional material S3 may be e.g. parylene, PET (Polyethylene terephthalate), PMMA (Polymethyl methacrylate), or Kapton (polyimide). The additional material S3 may also be e.g. metal, silicon or gallium arsenide. Referring to Fig. 16, the device 100 may comprise one or more contact elements MC1 , MC2 for coupling an electric current to and/or from the (undulated) graphene GRF1 supported by the conformal layer POLY1 . The contact element MC1 , MC2 may be in contact with the graphene GRF1 . The contact element MC1 , MC2 may comprise e.g. metal, graphite, and/or electrically conductive polymer. In an embodiment, one or more contact elements MC1 , MC2 may also be implemented on the graphene GRF1 before depositing the conformal layer POLY1 on the graphene GRF1 . The device 100 may be e.g. a display, a touch screen, a flexible electronic circuit, a biocompatible sensor, a field effect transistor, a capacitor or a resistor.

Referring to Figs. 17a and 17b, an electrical device 100 may comprise the composite CMP1 , one or more electrical contact elements MC1 , MC2, and a cover layer POLY2. The cover layer POLY2 may comprise one or more openings APE1 so as to provide an exposed portion of the graphene GRF1 . The cover layer POLY2 may comprise one or more openings APE2 so as to provide an exposed portion of a contact element MC1 , MC2.

Referring to Fig. 17b, the exposed portions of the graphene may be brought in contact with an object OBJ1 e.g. in order to monitor electric signals generated by the object OBJ1 . The contact elements MC1 , MC2 may be connected e.g. to a voltage sensing unit or to a current sensing unit.

The device 100 may be e.g. a biocompatible sensor for monitoring electric activity of living biological tissue. The object OBJ1 may be e.g. a muscle, a nerve, a brain, or a heart of a human. The object OBJ1 may be e.g. a muscle, a nerve, a brain, or a heart of an animal. The device 100 may be e.g. a sensor for monitoring e.g. EEG, EKG, or EMG. EEG means Electroencephalography, EKG means Electrocardiography, and EMG means Electromyography.

The conformal parylene layer POLY1 and the graphene GRF1 may be biocompatible. The cover layer POLY2 may also comprise biocompatible material, e.g. a second layer of parylene. The contact elements MC1 , MC2 may comprise biocompatible conductive material, e.g. gold and/or platinum. Referring to Figs. 18a and 18b, a device 100 may comprise a field effect transistor implemented by using graphene GRF1 supported by the conformal layer POLY1 . The symbol 100' denotes a semi-manufactured device 100. Referring to Fig. 18a, graphene GRF1 may be deposited on the substrate SO. Contact elements MC1 , MC2 may be subsequently formed on the graphene layer GRF1 . The conformal layer POLY1 may be subsequently formed on the graphene layer GRF1 and on the contact elements MC1 , MC2. A gate electrode GATE1 may be subsequently formed on the conformal layer POLY1 . The gate electrode GATE1 may be subsequently protected by a cover layer POLY2.

Referring to Fig. 18b, the substrate SO may be removed, and the graphene layer GRF1 may be subsequently protected by a protective layer POLY3. The produced device 100 may be arranged to operate as a field effect transistor. The contact element MC1 may be arranged to operate as the source terminal of the transistor 100, and the contact element MC2 may be arranged to operate as the drain terminal of the transistor 100. Referring to Fig. 19a, graphene layers GRF1 a, GRF1 b may be deposited on both sides of a substrate SO. Conformal layers POLYl a, POLYI b may be subsequently deposited on the graphene layers GRF1 a, GRF1 b. Referring to Fig. 19b, the substrate SO may be removed in order to provide a pair of graphene composite films.

The graphene layer GRF1 may be arranged to operate as a substantially transparent electrode. The graphene layer GRF1 supported by the conformal layer may be arranged to operate as a transparent flexible electrode. For example, a display screen may comprise one or more substantially transparent electrodes. The device 100 may be e.g. a display screen, which comprises a substantially transparent layer of graphene GRF1 supported by the conformal layer POLY1 . The device 100 may be e.g. a touch screen, which comprises a substantially transparent layer of graphene GRF1 supported by the conformal layer POLY1 . In an embodiment, a plurality of microscopic protrusions DF1 may be intentionally produced on the surface SRFO of the substrate SO prior to depositing the graphene GRF1 . The microscopic protrusions DF1 may be produced e.g. by etching, by laser machining, and/or by electron beam lithography. In an embodiment, the surface SRFO of the substrate SO may also comprise macroscopic protrusions in addition to the microscopic protrusions.

In an embodiment, a composite film CMP1 may also comprise a graphene layer GRF1 , and a self-assembled monolayer formed on the graphene layer GRF1 . The self-assembled monolayer may be formed e.g. by chemisorption of molecules onto the graphene GRF1 from a vapor phase or from a liquid phase. One end of the molecules may comprise a head group, which may be attracted by the surface SRF1 of the graphene GRF1 . Also in this case the partial pressure of the molecules may be kept low so as to minimize premature formation of molecular clusters before the molecules are brought into contact with the graphene GRF1 .

Various embodiments are illustrated by the following examples:

Example 1 . A method, comprising:

- depositing graphene (GRF1 ) on a substrate (SO),

- forming a first polymer layer (POLY1 ) on the graphene (GRF1 ) by bringing a monomer (M1 ) into contact with the graphene (GRF1 ) such that the monomer (M1 ) polymerizes on the surface (SRF1 ) of the graphene (GRF1 ), and

- removing the substrate (SO) from the graphene (GRF1 ).

Example 2. The method of example 1 wherein the partial pressure of the monomer (M1 ) above the graphene (GRF1 ) is lower than 0.2 Pa.

Example 3. The method of example 1 or 2 wherein the first polymer layer (POLY1 ) is formed by chemical vapor deposition (CVD). Example 4. The method according to any of the examples 1 to 3 wherein the first polymer layer (POLY1 ) comprises Poly-Para-Xylylene, preferably Poly- Monochloro-Para-Xylylene. Example 5. The method according to any of the examples 1 to 4, wherein the surface (SRF1 ) of the graphene (GRF1 ) comprises a plurality of microscopic concave portions (PORO), and wherein the first polymer layer (POLY1 ) conforms to the concave portions (PORO) of the graphene (GRF1 ). Example 6. The method according to any of the examples 1 to 5 wherein the graphene (GRF1 ) comprises a first group (GRP1 ) of concave portions (POR1 ) such that the depth (h₂) of each convex portion (POR1 ) of the first group (GRP1 ) is greater than 0.3 nm at a width of 10 nm, and wherein the number density of the concave portions (PORO) of the first group (GRP1 ) along a linear sampling path (LIN1 ) is greater than 5/1000 nm.

Example 7. The method according to any of the examples 1 to 6, wherein the substrate (SO) is removed from the graphene (GRF1 ) by peeling, by intercalation and/or by etching.

Example 8. A composite (CMP1 ) comprising graphene (GRF1 ) and a conformal layer (POLY1 ) of a polymer deposited on the graphene (GRF1 ), wherein the graphene (GRF1 ) comprises a plurality of microscopic convex regions (CNX1 ) which are fully supported by the conformal layer (POLY1 ).

Example 9. The composite of example 8 wherein the graphene (GRF1 ) comprises a group (GRP2) of convex regions (CNX1 ) such that the height (h₂) of each convex region (CNX1 ) of the group (GRP2) is greater than 0.3 nm at a width of 10 nm, and wherein the number density of the convex regions (CNX1 ) along a linear sampling path (LIN 1 ) is greater than 5/1000 nm.

Example 10. The composite (CMP1 ) of example 8 or 9 wherein the conformal layer (POLY1 ) comprises poly-para-xylylene. Example 1 1 . The composite (CMP1 ) according to any of the examples 8 to 10, wherein the sheet resistance (Rs) of the graphene layer is lower than 50Q/sq after a test where the interface between the graphene (GRF1 ) and the conformal layer (POLY1 ) has been stretched by 2%.

Example 12. A device (100) comprising:

- a composite (CMP1 ) comprising graphene (GRF1 ) and a conformal layer (POLY1 ) of a polymer deposited on the graphene (GRF1 ), wherein the graphene (GRF1 ) comprises a plurality of microscopic convex regions (CNX1 ) which are fully supported by the conformal layer (POLY1 ), and

- one or more electrical contact elements (MC1 , MC2), which are in galvanic contact with the graphene (GRF1 ).

For the person skilled in the art, it will be clear that modifications and variations of the devices and the methods according to the present invention are perceivable. The figures are schematic. The particular embodiments described above with reference to the accompanying drawings are illustrative only and not meant to limit the scope of the invention, which is defined by the appended claims.

Claims

1 . A method, comprising:

- depositing a monolayer of graphene (GRF1 ) on a substrate (SO),

- forming a first polymer layer (POLY1 ) on the monolayer (GRF1 ) by bringing a monomer (M1 ) into contact with the monolayer (GRF1 ) such that the monomer (M1 ) polymerizes on the surface (SRF1 ) of the monolayer (GRF1 ), and

- removing the substrate (SO) from the monolayer (GRF1 ),

wherein the monolayer (GRF1 ) comprises a plurality of microscopic convex regions (CNX1 ), which are fully supported by the conformal polymer layer (POLY1 ).

2. The method of claim 1 wherein the partial pressure of the monomer (M1 ) above the monolayer (GRF1 ) is lower than 0.2 Pa.

3. The method of claim 1 or 2 wherein the first polymer layer (POLY1 ) is formed by chemical vapor deposition (CVD).

4. The method according to any of the claims 1 to 3 wherein the first polymer layer (POLY1 ) comprises Poly-Para-Xylylene, preferably Poly-Monochloro- Para-Xylylene.

5. The method according to any of the claims 1 to 4, wherein the surface (SRF1 ) of the monolayer (GRF1 ) comprises a plurality of microscopic concave portions (PORO), and wherein the first polymer layer (POLY1 ) conforms to the concave portions (PORO) of the monolayer (GRF1 ).

6. The method according to any of the claims 1 to 5 wherein the monolayer (GRF1 ) comprises a first group (GRP1 ) of concave portions (POR1 ) such that the depth (h₂) of each concave portion (POR1 ) of the first group (GRP1 ) is greater than 0.3 nm at a width of 10 nm, and wherein the number density of the concave portions (PORO) of the first group (GRP1 ) along a linear sampling path (LIN1 ) is greater than 5/1000 nm.

7. The method according to any of the claims 1 to 6, wherein the substrate (SO) is removed from the monolayer (GRF1 ) by peeling, by intercalation and/or by etching.

8. A composite (CMP1 ) comprising a monolayer of graphene (GRF1 ) and a conformal layer (POLY1 ) of a polymer deposited on the monolayer (GRF1 ), wherein the monolayer (GRF1 ) comprises a plurality of microscopic convex regions (CNX1 ), which are fully supported by the conformal layer (POLY1 ).

9. The composite of claim 8 wherein the monolayer (GRF1 ) comprises a group (GRP2) of convex regions (CNX1 ) such that the height (h₂) of each convex region (CNX1 ) of the group (GRP2) is greater than 0.3 nm at a width of 10 nm, and wherein the number density of the convex regions (CNX1 ) along a linear sampling path (LIN1 ) is greater than 5/1000 nm.

10. The composite (CMP1 ) of claim 8 or 9 wherein the conformal layer (POLY1 ) comprises poly-para-xylylene.

1 1 . The composite (CMP1 ) according to any of the claims 8 to 10, wherein the sheet resistance (Rs) of the monolayer layer is lower than 50Q/sq after a test where the interface between the monolayer (GRF1 ) and the conformal layer (POLY1 ) has been stretched by 2%.

12. A device (100) comprising:

- a composite (CMP1 ) comprising a monolayer of graphene (GRF1 ) and a conformal layer (POLY1 ) of a polymer deposited on the monolayer (GRF1 ), wherein the monolayer (GRF1 ) comprises a plurality of microscopic convex regions (CNX1 ), which are fully supported by the conformal layer (POLY1 ), and

- one or more electrical contact elements (MC1 , MC2), which are in galvanic contact with the monolayer (GRF1 ).