NL2008533C2

NL2008533C2 - Graphene synthesis.

Info

Publication number: NL2008533C2
Application number: NL2008533A
Authority: NL
Inventors: Shou-En Zhu; Guido Cornelis Antonius Maria Janssen
Original assignee: Univ Delft Tech
Priority date: 2012-03-23
Filing date: 2012-03-23
Publication date: 2013-09-25

Description

Graphene Synthesis

DESCRIPTION

FIELD OF THE INVENTION

5 The present invention is in the field of structured graphene synthesis.

BACKGROUND OF THE INVENTION Graphene is carbon comprising material. Its structure relates to one-atom-thick planar sheets of sp2-bonded carbon 10 atoms that are crystallographically densely packed in a honeycomb crystal lattice. The crystalline or "flake" form of graphite consists of many graphene sheets stacked together. It can be a basic building block for graphitic materials of all other dimensionalities. It can be wrapped up into fullerene, 15 rolled into ID carbon nanotubes or stacked into 3D graphite. Graphene has attracted a lot of research interest because of its promising electronic applications related to its superior electron mobility, mechanical strength and thermal conductivity. It may have wide range of applications, for 20 instance, field-effect transistors, photonic or optoelectronic device, sequencing DNA through nano-holes in graphene etc. Graphene macroscopic samples have unusual properties such as a bipolar-transistor effect, ballistic transport of charges, large quantum oscillations, etc.

25 Various production methods of graphene are reported.

Graphene or ultra-thin graphitic layers can be epitaxially grown on various substrates. Graphene produced by exfoliation was a very expensive material. Since then, exfoliation procedures have been scaled up. It is noted that the price of 30 epitaxial grown graphene on e.g. SiC is dominated by the substrate price. Graphene has been produced by transfer from nickel, copper, gold, iridium, etc., and alloys thereof, though graphene on iridium is slightly rippled.

Epitaxial graphene on SiC can be patterned using standard 35 microelectronics methods, providing a 2D-structure. The possibility of large integrated electronics on SiC-epitaxial graphene was proposed.

Various documents recite graphene synthesis.

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Zhangcheng Li et al, in "Low-temperature growth of graphene by chemical vapor deposition using solid and liquid carbon sources", ACS Nano, 2011, 5, 3385-3390, use benzene as carbon source and a quartz tube hot wall furnace to synthesize 5 graphene at low temperature. Therein a copper foil (25 (am) was used as a synthesis substrate, providing only microscale graphene flakes at 500 °C. The method does not provide large scale graphene, nor high quality, nor graphene that can be harvested easily.

10 Y. Kim et al, in "Low-temperature synthesis of graphene on nickel foil by microwave plasma chemical vapor deposition", Appl. Phys. Lett., 2011, 98, 263106, use a cold wall type microwave plasma chemical vapor deposition to synthesize centimeter scale graphene at low temperature. Therein as feed 15 stock methane and hydrogen are used, as substrate material a polycrystalline nickel foil (50 pm) is used, within a temperature range from 450 °C to 750 °C. Thereto a microwave with a power of as much as 1400 W was used to generate a plasma, which attributes to a high energy consumption.

20 Gopichand Nadamuri et al, in "Remote plasma assisted growth of graphene films", Appl. Phys. Lett., 2010, 96, 154101 use a horizontal oven with a quartz tube (3 cm diameter) which is surrounded by a copper RF-coil on one side. Graphene is grown on a 300 nm nickel film, nickel foil, and nickel single 25 crystal. The RF-coil with 250 W power can induce a plasma 25 cm from the substrate. Graphene was synthesized with methane and hydrogen as feed stock at 650 - 700 °C with a base pressure of 1 mTorr.

Jaeho Kim et al, in "Low-temperature synthesis of large-30 area graphene-based transparent conductive films using surface wave plasma chemical vapor deposition", Appl. Phys. Lett., 2011, 98, 091502 employ a 3 - 4.5 kW surface wave plasma chemical vapor deposition to grow graphene on a 23 cm x 22 cm copper foil (30 jam) and an aluminum foil (12 |am) at 300 - 400 35 °C with a gas pressure of 3 - 5 Pa. Methane, argon and hydrogen were used as feed stock. A sheet resistance ranged from 2.2 kQ to 45 kQ per square with a transmittance of 78% to 94%.

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It is noted that various methods relating to synthesizing other carbon comprising molecules, such as carbon nanotubes, are known. These methods typically are not applicable for obtaining graphene.

5 A drawback of prior art methods is that the guality of the graphene is not very good, e.g. it may contain many dislocations. Further it is difficult to grow a large area of graphene layers, especially of good guality. Typically when obtaining graphene after growth thereof it is cumbersome to 10 separate graphene, such as by removing a supporting layer. It is noted that various technigues, e.g. PECVD, result in poor quality graphene. It is also a drawback that prior art systems are not very costs effective, e.g. as synthesis consumes relatively large amounts of energy, are performed at relative 15 high temperatures (1000 °C or higher), etc. As a consequence also characteristics of a graphene layer are not very good, e.g. in terms of being impermeable to gas and liquid, in terms of homogeneity, in terms of conductivity, etc.

Manufacturing a structured graphene layer has not been 20 reported to the knowledge of inventors, specially a 30-structure .

The present invention therefore relates to method of forming a structured graphene layer, a structured graphene layer, and a device comprising said layer, which overcomes one 25 or more of the above disadvantages, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

The present invention relates in a first aspect to a 30 method for a low temperature synthesis of structured graphene e.g. on a flat and pre-patterned surface, e.g. comprising a trench, such as in a sputter deposition system. It is noted that the structure within the graphene layer is intentional, e.g. in view of further use of the layer, such as in a device. 35 Even further, it is now possible to release a more or less complex (2D- or 3D-) structured graphene layer from a support, e.g. as required by an application thereof. As such the present invention does not relate to an arbitrary structured 4 graphene layer, such as a repetitive pattern, the arbitrary structure being provided e.g. in order to improve release of graphene from a support. The surface typically is a metal catalyst surface. Therewith a method with low power 5 consumption and simplicity is provided.

It is noted that in principle other monolayers such as boron nitride, molybdenum disulfide, mica, dichalcogenides and complex oxides can be obtained likewise.

The synthesis comprises providing a carbon source, making 10 the carbon available, and forming graphene. A structure to the graphene is provided by a surface layer of a support on which the graphene is synthesized. Typically the structure is adapted in view of further use, e.g. in a present device.

The support may comprise one or more materials, e.g.

15 stacked as (multi)layers .

The support further functions as a sorbent for carbon atoms. As such the sorbent "absorbs" the carbon atoms, e.g. into its structure. An amount of carbon atoms to be absorbed is limited e.g. by a volume of the sorbent and by saturation. 20 As a consequence provision of the carbon source needs to be sufficiently long, e.g. up to saturation of a sorbent.

Typically decomposition of the carbon source takes place at certain process conditions, e.g. temperature, pressure, time, power, etc., whereas synthesis of graphene takes place 25 at other process conditions, e.g. at a lower temperature. As mentioned above synthesis is typically supported by presence of a catalytic material, such as a metal.

It has been found experimentally that graphene can be formed as a conformal layer, i.e. forming a more or less 30 uniform layer with respect to thickness. It is noted that during formation of a crystallographic material, such as graphene, a growth process may involve defects, dislocations and topographical effects, such as a slope. In other words, on a microscopic scale some non-uniformity may exist.

35 As such decomposition and synthesizing preferably take place in a well-conditioned environment, the environment being adaptable in view of required process conditions, and the environment being extremely clean. Even more preferable the 5 environment can be used for all or many of the present (optional) method steps. The environment preferably is a vacuum chamber, such as a CVD chamber, a PVD chamber, and combinations thereof.

5 The present 3D-structure comprises microscopic and/or nanoscopic features. These features are copied from the support into the graphene layer.

The present invention provides amongst others the advantage that in principle any microscopic or nanoscopic 3D-10 structure can be formed, by conformal growth. Therein graphene uniformly covers the surface, such as a flat or pre-patterned surface, e.g. a trench on a nickel surface. Thickness variations are in the order of one or a few layers, which is very acceptable. It is noted that a conformal grown graphene 15 layer is preferred, though a less conformal grown (e.g. directional) may be adequate for specific purposes.

It is noted that hydrogen can be added as active gas precursor in order to improve deposition of carbon. In general cooling between a step of providing carbon and a step of 20 synthesizing graphene takes place at a certain rate, such as 10-50 °C/minute. The plasma can be used to further reduce the synthesis temperature to 500-700 °C. Thereby a well controllable graphene layer is provided of excellent quality, e.g. in terms of integrity, dislocation density, electrical 25 properties, gas and liquid (im)permeability, etc. Further the layer can be removed well from the support.

Typically decomposition takes place during a time of 1-600 seconds, such as 5-200 seconds, e.g. 10-50 seconds. Typically synthesis of graphene takes place during a time of 1-500 30 minutes, such as 2-200 minutes, e.g. 10-30 minutes. Such is considered rather quick and efficient.

Thereby the present invention provides a solution to one or more of the above mentioned problems.

Advantages of the present description are detailed 35 throughout the description.

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DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to a method for synthesizing structured graphene according to claim 1.

5 In an example a relatively low temperature of 300 °C - 1100 °C, such as 650 °C, is used to decompose the carbon source. In a further example a 100 mm or 200 mm (diameter) (Si-)wafer support is used, having a thickness of 150-1500 pm, preferably 250-750 pm. It has been found that graphene 10 grows uniformly and covers structures well through conformal growth, such as a trench and a flat surface. It has been found that also larger layers can be made, such as with a 300 mm Si-wafer, the layers typically being continuous. In principle size of the graphene layer of the invention is 15 limited by the size of a chamber. Typical dimensions of the present graphene layers are 1-300 mm long, e.g. 2-150 mm, such as 5-50 mm, 1-300 mm wide, e.g. 2-150 mm, such as 5-50 mm, and 1-10 layers thick, e.g. 2-5 layers. The number of layers depends amongst others on a time of synthesizing and 20 a thickness of the sorbent. More sorbent (volume) provides an opportunity of growing thicker graphene. Typically the layer obtained is of good quality and homogeneous. Such relatively large layers can be applied as such in e.g. a device, or in parts thereof, e.g. a repetition of structures 25 may be grown.

In principle the graphene structure could also be formed directly on a polymer support, the polymer support being stable at higher processing temperatures. The support would likewise comprise a carbon sorbens/catalyst, such as a 30 nickel layer. A disadvantage hereof is that the e.g. nickel layer remains present in a final structure or device. An advantage is that various characteristics are improved, such as a higher current carrier density, a longer life time, limited corrosion, a higher electrical conductivity, a 35 higher heat conductivity, a lower stiction and lower friction of metal surface.

In an example the present invention relates to a method wherein after step f) 7 g) the one or more conformal graphene layers are transferred to a release layer, such as by applying a release layer on the one or more conformal graphene layers, and/or h) removing one or more of 5 the sacrificial layer, such as by a chemical etch process, removing the catalyst comprising surface, such as by a chemical etch process, and the carbon sorbent, and/or 10 z) forming prior to step a) on the catalyst comprising surface the one or more of a predefined 3D- microscopic and 3D-nanoscopic structure, such as by applying a mask, such as a lithographic mask, thereafter removing part of the catalyst comprising surface, and removing the mask, such as by etching, 15 wherein steps a)-h) may be performed in the same conditioned environment, and step z) is performed in the same or another conditioned environment.

By introducing the carbon source such as benzene gas into a sputter chamber as feed stock there is no need for breaking 20 vacuum. Further there is no need to provide a solvent. Thus a physical vapor deposition system can be combined with a chemical vapor deposition to achieve unique results. By directly synthesizing graphene after a metal, such as nickel, sputter deposition without breaking the vacuum the quality of 25 graphene is improved significantly, the contamination is reduced, and the efficiency of synthesis is improved. A further advantage is that the present sputter deposition produces a uniform nickel film on e.g. a flat and prepatterned surface, e.g. comprising one or more 3D-structures 30 such as a trench, a chamber, a channel, a pump, a valve, an outlet, an inlet, a connector, a sensor, and a heater. Typical sizes of these structures are such that they have required microfluidic properties, e.g. from 10 nm to 5mm, such as 100 nm to 1000 (xm.

35 In an example the present invention relates to a method wherein the release layer is applied as a fluid and is allowed to solidify, and/or wherein the release layer comprises one or more of an organo silicon compound, such as 8 CH3 [Si (CH3) 2O] nSi (CH3) 3 (PDMS) , a polymer, such as PMMA, polyimide, polyamide, and epoxy, such as SU-8, and a rubber. The rubber may be a natural and synthetic rubber. As such a wide range of release layers may be applied, having various 5 characteristics, thereby providing various applications, which can be tuned with ease, e.g. in view of intended use.

In an example the present invention relates to a method wherein the catalyst comprising surface comprises one or more of a Group 3-12 element, preferably of Period 4 or 5, such as 10 nickel, copper, cobalt, iron, and alloys thereof, and/or wherein the catalyst surface is from 50-500 nm thick, preferably 100-300 nm. It is preferred to use a somewhat thicker layer, e.g. of 300 nm, if a lower decomposition temperature, e.g. 650 °C, is used. Likewise it is preferred 15 to use a somewhat thinner layer, e.g. of 100 nm, if a higher decomposition temperature, e.g. 1000 °C, is used.

In an example nickel is sputtered onto a flat or prepatterned 100 mm wafer surface as catalyst metal, the surface comprising one or more trenches. Subsequently benzene is used 20 as feed stock gas, and a heating stage with a lamp as heat source are used. As a result a uniform and controllable multilayer graphene film was deposited on the nickel surface. The present method therefore relates to an economic and convenient synthesis.

25 In an example a 300 nm nickel film was sputter deposited on a 100 mm Si-wafer. The wafer comprises a channel pattern and one or more chambers and further a SiC>2 sacrificial layer on the Si and underneath the nickel layer. A heating stage was used to raise the temperature to about 650 °C. A benzene gas 30 was introduced into chamber during about 5 hours. In a further example the benzene was introduced during 10 minutes.

Typically time, flow and temperature are adjusted such that sufficient carbon is being formed for a required layer. Such can be determined by standard tests.

35 In an example the present invention relates to a method wherein the carbon source is selected from (poly)aromatic compounds, such as benzene, naphthalene, and toluene, and a hydrocarbon preferably having one or more double bonds, such 9 as Ci-18 alkene, and Ci-ie alkane, preferably a (poly) aromatic compound, such as benzene, optionally having a functional group attached thereto, such as halogenated benzene, such as fluorinated benzene, e.g. hexafluorobenzene, and wherein the 5 carbon source is provided at a partial pressure of 10-6 - 2*10+4 Pa, such as 53-108 * 102 Pa(mbar) at ambient temperature. It is preferred to use benzene, as less energy is needed to decompose benzene. Having an optional functional group present may improve formation of graphene.

10 In an example a hydrocarbon precursor is used, such as methane. The precursor is cracked at low temperature with assistance of a high energy plasma. The plasma may be a surface wave plasma, a microwave plasma, a remote plasma, an inductive coupled plasma, and a combination thereof.

15 Benzene can be used as well. It has a partial pressure of 53 - 108 * 102 Pa (mbar) at 5 - 20 °C, which is proven to be sufficient for feed stock in the present sputter system.

Therein a base pressure ranged from about 10"6 to 2*10+4 Pa. Benzene is a very cheap feed stock. Addition of benzene is 20 controlled with high accuracy by using a needle valve to adjust the gas flow rate precisely. A needle valve typically has a relatively small orifice with a long, tapered seat, and a needle-shaped plunger, on the end of a screw, which exactly fits this seat. As the screw may be turned and the plunger 25 retracted, flow between the seat and the plunger is possible; however, until the plunger is completely retracted the fluid flow is significantly impeded. Since it takes many turns of the fine-threaded screw to retract the plunger, precise regulation of the flow rate is possible.

30 In an example the present invention relates to a method wherein the heating stage is made from one or more of stainless steel, tungsten, titanium, and/or wherein the heat source is a radiation source, such as a halogen lamp, or resistor, such as molybdenum/tungsten, with a power of 200-35 5000 W. The present heating stage is stable over time, does not give much contaminations, can be heated well, etc.

In an example the present invention relates to a method wherein support is a silicon support, and/or wherein the 10 sacrificial layer comprises SiC>2, and/or wherein the carbon sorbent and catalyst comprising layer are the same. The present sacrificial layer can be removed easily, without giving rise to noticeable contamination. It is preferred to 5 have a limited number of layers, while maintaining functionality; therefore the sorbent and catalyst are preferably the same.

The present invention relates in a second aspect to a method for making a microfluidic device according to claim 9. 10 In an example the present invention relates to a method wherein one or more layers are applied to a release layer side comprising structured graphene, such as by adhesive tape, and/or wherein the release layer preferably forms a support for the 15 device, and/or wherein the microfluidic device comprises one or more of a conditioned environment, such as a reaction conditioned environment, a transfer conditioned environment, a channel for fluidic connecting conditioned environments and/or channels, a 20 pump for transferring a fluid, a valve, an inlet, an outlet, a reservoir, such as a reservoir comprising reaction chemical(s), medicament, a physiological fluid, a heater, and a sensor.

It is noted that graphene can also be patterned through 25 lithography into a shape of e.g. a micro resistor heater or a micro sensor.

The present invention relates in a third aspect to a device according to claim 11.

In an example the present invention relates to a device 30 comprising one or more for gas and liquid impermeable structured graphene layers integrated therein, wherein the graphene layers are obtainable by a method according to the invention.

The device may be used for characterizing a fluid, 35 comprising the present microfluidic device and a measurement device. Typically the present device comprises at least one body, wherein the body has at least one surface, wherein the at least one surface has at least a part of the recess for 11 containing the fluid in the microfluidic device and/or transporting the fluid in the microfluidic device through at least a part of the microfluidic device, wherein the body has at least one provision for an inlet and at least one provision 5 for an outlet, wherein at least a part of said recess is a reaction chamber, which reaction chamber comprises a moiety that binds to the at least one component that is suspected to be present and that is to be characterized or analyzed, which reaction chamber is arranged for characterizing or analyzing 10 the at least one component, wherein at least a part of said recess is a fluid connection between the at least one provision for an inlet and the at least one provision for an outlet, wherein at least a part of said recess is a pump chamber through which fluids can move by cyclic pumping, 15 wherein at least the reaction chamber, pump chamber and fluid connection are sealed from the environment by at least one cover layer.

Recesses may be formed on both sides of the body. In an example the fluid to be characterized or measured is then 20 brought into the provision for an inlet. Then, it flows to the reaction chamber. In the reaction chamber, a component that is suspected to be present can e.g. bind to a moiety, present in the reaction chamber. It may further contain a pump chamber, which can be arranged to a pump. The pump forces the fluid to 25 flow from the pump chamber to the reaction chamber or vice versa.

A component may bind to a label or a moiety present in the microfluidic device, or to a chemical part of that component, of which at least one part binds to a label or a moiety 30 present, or to a component which is labeled in the microfluidic device, which labeled component binds to the moiety present in the microfluidic device, or to a component that causes a detectable signal by itself, by a chemical reaction with another component, or by a component formed here 35 out, whereby the detectable signal may be chemiluminescent flash or flow, colorimetric, fluorescent and time-resolved fluorescent.

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The term "fluid" as used herein refers to liquid compositions that flow at operating pressure and temperature.

The pump may relate to a combination of an actuator, a displacement volume and at least one means for transferring 5 the variation in pressure of the actuator towards the displacement volume. The means for transferring the variation can be a membrane. The displacement volume is referred to as pump chamber. The pump further comprises means for controlling the actuator. The pump chamber typically has a volume of 1-10 1000 \il, preferably of 10-100 (4.1.

A recess is typically sealed by a cover layer. It is to be interpreted in a broad sense. Thus, it is not intended to be restricted to elongated configurations where the transverse or longitudinal dimension greatly exceeds the diameter or cross-15 sectional dimension. Rather, recesses are meant to comprise cavities and/or tunnels of any desired shape or configuration through which fluids may be directed. A cavity may, for example, comprise a flow-through cell where fluid is to be continuously passed or, alternatively, a chamber for holding a 20 specified, discrete amount of fluid for a specified amount of time .

A volume of the present device is preferably from 1 to 10000 (il, more preferably from 10-1000 |iil.

Typically one or more of dimensions of the present device 25 is less than 500 |im.

It is noted that implants, chips, etc. can be coated with graphene, wherein graphene is a compound being biocompatible for a human or animal body. Further graphene is impermeable to gas and liquid. This offers e.g. the advantage that impurities 30 can not pass the present graphene layer and that chemical can be stored/maintained much longer without degradation. Also the layer has a relatively low friction. Thus, e.g. a device, a chamber, a reservoir, a fluid channel, a chip implant are biocompatible for use in an animal or human body. Further a 35 for water and gas impermeable device or layer can be made, e.g. for medicine, such as a container. It is at present possible to form a conformal, flexible, shape changeable, graphene surface. The surface can also be functionalized or 13 passivated, e.g. to switch between a hydrophobic and hydrophilic surface status, to allow gas and water to be selectively permeable, etc.

Further applications relate e.g. to a micro resistor 5 heater. Such a heater can be used e.g. in a polymerase chain reaction to amplify a single or a few copies of a piece of DNA by several orders of magnitude, or by generating thousands to millions of copies of a particular DNA sequence. As such an increase of a chemical reaction rate and an increase of a 10 sensor sensibility are provided. The present heater can be provided with an appropriate resistance, e.g. from about 100 -100 kQ, can be varied in size, e.g. length, can be integrated easy, e.g. in existing structures, has a low power consumption (1 mW-100 mW), can be controlled accurately over a broad 15 range, e.g. from 0 - 500 °C, being limited by a melting temperature and/or temperature budget of other components being present, e.g. a semiconductor device.

Further a graphene valve is provided. Such can e.g. be used as a pressure sensor, in order to e.g. minimize stiction 20 and friction force. Multi-valves also can be integrated to micro pump. Such a valve provides a relatively low stiction, a high switching frequency, etc.

Further a sensor wire is provided. Such can e.g. be used as a pressure sensor, flow rate sensor, calorimeter, DNA 25 sequencing, charge and molecular detection, and fluid temperature sensor. Any device comprising graphene, such as the sensor, can be integrated with ease. Further the present sensor can be functionalized easy, e.g. for sensing various chemicals and/or liquids.

30 The present invention further provides a large scale integration of e.g. independent microfluidic channels.

EXAMPLES

The invention is further detailed by the accompanying figures, which are exemplary and explanatory of nature and 35 are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

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FIGURES

Figures la-g, 2a-b and 3a-c show details of a present layer configuration.

Figure 4 shows a microscopic picture of a present layer 5 configuration.

DETAILED DESCRIPTION OF THE DRAWINGS / FIGURES

It is noted that the present invention in an example relates to a device, e.g. a microfluidic device, of which 10 figures provide further details. Various parts of the present device, e.g. a chamber, a channel, etc. are typically in fluidic connection with one and another, e.g. in order to allow passage of a fluid.

In figure la a cross section of a sequence of layers is 15 shown. Therein a Si-wafer (100) having a diameter of 200 mm is provided. The Si-wafer functions as a support for further layers. On the Si a Si02 layer (110) with a thickness of 50 nm is provided. The thickness of this layer may be from 10-500 nm, preferably from 20-250 nm. The Si wafer can be 20 oxidized, e.g. by dry- or wet etch. Likewise the Si wafer can be obtained from a supplier, comprising a Si02 layer.

On the Si02 layer a nickel layer (120) is sputtered by PVD. The thickness of the nickel layer is 100 nm. The thickness of this layer may be from 10-500 nm, preferably 25 from 20-250 nm. The nickel layer functions first as a sorbent (120) for the carbon atoms, and subsequently as a catalyst (130) for the formation of graphene. The nickel layer functioning as sorbent and catalyst may be the same.

In the latter case the thickness mentioned before relates to 30 the thickness of a combined layer (120) and (130).

In figure lb a cross section of a sequence of layers is shown. Therein a structure is provided, e.g. by etching. Typically a lithographic process is used to define the structures, such as by applying a mask, forming an image, 35 removing part of the mask, etching, and removing a remainder of the mask. In figure lb various trenches (131) are shown. Of course other structures may be provided likewise.

In figure lc a top view of the nickel layer (130) is 15 shown. Therein an outlet (138), an inlet (139), various chambers (135), e.g. for reacting, mixing, heating, cooling, etc. are shown. Also various connector channels (137) are shown. Further elements may be present as well, such as a 5 micro heater and a micro sensor.

In figure Id the top nickel layer (130) is provided with a conformal grown graphene layer (140).

In figure le a cross section of a sequence of layers is shown. Therein the sacrificial SiC>2 layer (110) is 10 chemically etched and thereby removed. An example is an etch with diluted HF, mixtures (5% to 49 %) of HF/HCl, HF/Glycerin, HF/isoproponal, or BOE (buffered oxide etch). BOE is e.g. a mixture of a buffering agent, such as ammonium fluoride (NH4F) , and hydrofluoric acid (HF) . The mixture 15 used in an example comprises a 6:1 volume ratio of 40% NH4F in water to 49% HF in water. This solution etches thermally grown oxide at approximately 2 nanometers per second at 25 °C.

In figure If a cross section of a sequence of layers is 20 shown. Therein a release layer (180) is provided. The release layer may be a liquid polymer, being set by a further treatment, e.g. by temperature, such as PDMS, e.g. at about 60 °C for about 60 minutes.

In figure lg a cross section of a sequence of layers is 25 shown. Therein the support layer (130) is removed, e.g. by a chemical etch. Thereto e.g. 30% FeCl3 or a combination of FeCl3 and HC1 in water (1:4:5) is used, e.g. at about 35 °C for about 5 minutes.

In figure 2a 3D- graphene channels (237) are shown.

30 Further a chamber (235) is shown, the chamber also being suited as a reservoir.

In figure 2b further a graphene valve (232), a micro heater (233), e.g. a graphene micro heater (233), and a micro sensor (234). As graphene is electrically conductive, graphene 35 may be used as a (micro) heater by using an electrical current. The figure provides further examples, not limiting, of applications of a structured graphene layer.

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It is noted that two structures according to e.g. figure 1 or 2 may put together, e.g. face to face, in order to provide a by graphene fully covered 3D-structure, now being enclosed by the two structures. In such a case special care was taken 5 to avoid a short circuit, such as by removing parts of graphene being present by photolithography, or by growing graphene after removing parts of a catalyst surface.

Figure 3a shows a schematic configuration of a channel (337) and a graphene valve (332) located therein. Figure 3b shows 10 that the graphene valve can be in an open state, i.e. allowing passage of a fluid through the channel, or in a closed state (figure 3b) preventing passage of the fluid. The valve can e.g. be manipulated by an external force, such as fluid pressure, an electro-magnetic field, an actuator, etc.

15 Figure 4 shows an AFM microscopic picture of a graphene surface according to the invention.

Claims

A method for synthesizing structured graphene, comprising the steps of: a) providing a support, wherein the support is provided with a first material, a surface comprising a catalyst, optionally one sacrificial layer between the first material and the catalyst surface, and a carbon sorbent, wherein the catalyst-comprising surface comprises one or more of a predefined 3D microscopic and 3D-nanoscopic structure and a carbon source followed by b) introducing the metal-catalyst-containing surface into a conditioned environment, and c) the introducing the carbon source into the conditioned environment, d) decomposing the carbon source into at least carbon, e) absorbing the carbon into the carbon sorbent 20 for a period of time and f) synthesizing graphene from carbon by activation with the catalyst for a predetermined period of time with formation of one or more conformel e graphene layers on the catalyst surface.

Method according to claim 1, wherein the 3D structure is for a micro-liquid device and / or wherein the carbon source is benzene and / or wherein decomposition takes place by raising the temperature in the conditioned room, preferably to 400 to 1100 ° C, such as 500-850 ° C, and / or wherein synthesizing graphene takes place by cooling the conditioned space.

3. Method as claimed in claim 1 or 2, wherein after step f) g) the one or more conformal graphene layers are transferred to a release layer, such as by applying a release layer to the one or more conformal graphene layers, and / or h) the removing one or more of the sacrificial layer, such as by a chemical etching process, the surface comprising the catalyst, such as by a chemical etching process, and the carbon sorbent, and / or 5 z) prior to step a) forming surface on the catalyst comprising the one or more of a predefined 3D microscopic and 3D nanoscopic structure, such as by applying a mask, for example a lithographic mask, subsequently removing part of the catalyst surface, removing the mask, for example by etching, wherein steps a) -h) can be performed in the same conditioned environment and step z) is performed in the same or a different conditioned space.

The method of claim 3, wherein the release layer is used as a liquid and can solidify and / or wherein the release layer comprises one or more of an organic silicon compound, such as CH 3 [Si (CH 3) 20] n Si (CH 3) 3 (PDMS) , a polymer, such as PMMA, polyimide, polyamide, and epoxy, and a rubber.

5. A method according to any one of the preceding claims, wherein the catalyst comprising surface comprises one or more of nickel, copper, cobalt, iron and alloys thereof, and / or wherein the catalyst surface is 50-500 nm thick, preferably 100-300 nm .

6. A method according to any one of the preceding claims, wherein the carbon source is selected from (poly) aromatic compounds, such as benzene, naphthalene and toluene, and a hydrocarbon preferably with one or more double bonds, such as C 1-8 alkene, and C 1-8 alkane , preferably a (poly) aromatic compound, such as benzene, and wherein the carbon source is provided at a partial pressure of 10-6 -2 * 10 + 4 Pa, such as 53-108 * 102 Pa (mbar) at room temperature.

7. Method as claimed in any of the foregoing claims, wherein the heating container is made from one or more of stainless steel, tungsten, titanium and / or wherein the heat source is a radiation source, such as a halogen lamp, or resistor, such as molybdenum / tungsten, with a power of 200-5000 W.

A method according to any one of the preceding claims, wherein the carrier is a silicon carrier or wherein the carrier is a heat-stable polymeric carrier and / or wherein the sacrificial layer comprises SiO 2, and / or wherein the carbon sorbent and catalyst comprising layer are the same.

9. A method for making a microfluidic device, comprising i) synthesizing structured graphene, ii) transferring the structured graphene to a release layer, and iii) forming a microfluidic device.

10. Method as claimed in claim 9, wherein one or more layers are transferred to a release layer side comprising structured graphene, such as by adhesive tape, and / or wherein the release layer preferably forms a support for the device, and / or wherein the microfluidic device is one or more more of a conditioned environment, such as a conditioned reaction vessel environment, a conditioned transfer environment, a conditioned channel for fluid communication between spaces and / or channels, a pump for transferring a liquid, a valve, an inlet, an outlet, a reservoir such as a reservoir include reaction chemicals, medicament, a physiological fluid, a heater, and a sensor.

Device comprising one or more gas and liquid non-permeable structured graphene layers integrated therein, the graphene layers being obtainable by a method according to any one of claims 1-8.

12. Device as claimed in claim 11, such as a microfluidic device, an implant, and a chip.