JP5563500B2 - Synthesis method of graphene and carbon molecular thin film - Google Patents
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Description
本発明は、炭素原子が互いに二次元的に結合して成る一原子層シートであるグラフェン及び、当該グラフェンが積層された構造の炭素分子薄膜の合成方法に関する。 The present invention relates to a graphene that is a monolayer sheet in which carbon atoms are two-dimensionally bonded to each other, and a method for synthesizing a carbon molecular thin film having a structure in which the graphene is laminated.
グラフェンは、炭素原子のsp2結合により形成された六員環構造が二次元的に連続して結合したハニカムシート構造として表される一原子層シートである。グラフェンが複数積層されたものを、ここでは炭素分子薄膜と呼ぶこととする。近年、その電子・正孔移動度やスピン輸送特性等の特徴的な性質が注目され、デバイス等への応用が期待されるナノ材料である。 Graphene is a monoatomic layer sheet represented as a honeycomb sheet structure in which six-membered ring structures formed by sp 2 bonds of carbon atoms are continuously bonded two-dimensionally. Here, a stack of graphene is referred to as a carbon molecular thin film. In recent years, it has attracted attention for its characteristic properties such as electron / hole mobility and spin transport properties, and is a nanomaterial expected to be applied to devices and the like.
グラフェン及び炭素分子薄膜の合成方法としては、金属を触媒として合成する方法が広く知られている。この方法では、炭素原子の供給源となるガス等を触媒金属に供給し、ガス分子の分解と炭素原子の結合によるグラフェン構造の形成反応を経て、触媒金属表面にグラフェン及び炭素分子薄膜が形成される。 As a method of synthesizing graphene and a carbon molecular thin film, a method of synthesizing using a metal as a catalyst is widely known. In this method, a gas or the like as a carbon atom supply source is supplied to the catalyst metal, and a graphene and carbon molecule thin film is formed on the surface of the catalyst metal through a decomposition reaction of gas molecules and a graphene structure formation reaction by the combination of carbon atoms. The
グラフェンは二次元平面構造を有するため、グラフェンが合成される金属表面は、原子レベルで平坦であることが、欠陥の少ないグラフェンの合成には理想的と考えられる。そのため、当該金属表面が、金属結晶面であると理想的である。 Since graphene has a two-dimensional planar structure, it is considered ideal for the synthesis of graphene with few defects that the metal surface on which graphene is synthesized is flat at the atomic level. Therefore, it is ideal that the metal surface is a metal crystal plane.
また、グラフェンは、数十ナノメートル程度の微小な広さであっても、特徴となる構造と物性を有すると考えられるが、デバイス等への応用を考慮した場合には、均一な範囲がなるべく広くなるように製造することが望ましい。 In addition, graphene is considered to have a characteristic structure and physical properties even if it is as small as several tens of nanometers, but when considering application to devices, etc., a uniform range should be as much as possible. It is desirable to make it wide.
これらの要件を満たすために、触媒金属となるイリジウム（１１１）などの金属単結晶を基板として用い、その表面により均一なグラフェン、炭素分子薄膜を合成する手法等がこれまでに報告されている（例えば、非特許文献１参照）。 In order to satisfy these requirements, a method of synthesizing uniform graphene and carbon molecular thin films on the surface using a metal single crystal such as iridium (111) serving as a catalyst metal as a substrate has been reported ( For example, refer nonpatent literature 1).
しかしながら、上述した金属単結晶を基板とする場合、金属単結晶基板の作製は、超高真空下で、高温での触媒金属の塗布と高温加熱の繰り返し処理が必要になるなど手間がかかり、必要な条件が厳しく、作製に多大な困難が伴う。 However, when the above-described metal single crystal is used as the substrate, the production of the metal single crystal substrate is time-consuming and requires, for example, repeated application of high-temperature catalytic metal and high-temperature heating under ultrahigh vacuum. The conditions are severe and the production is very difficult.
例えば、上述した非特許文献１のイリジウム（１１１）の金属単結晶基板の作製では、１×１０-5Ｐａ程度の超高真空性能を持つチャンバー内で、１１２０Ｋに加熱した基板上にイリジウムをスパッタリングし、その後１５７０Ｋで加熱するという工程を繰り返すことで、数百ナノメーターの厚さを持つイリジウム（１１１）基板を作製している。 For example, in the production of the iridium (111) single-crystal substrate of Non-Patent Document 1 described above, iridium is sputtered onto a substrate heated to 1120 K in a chamber having an ultrahigh vacuum performance of about 1 × 10 −5 Pa. Then, by repeating the process of heating at 1570 K, an iridium (111) substrate having a thickness of several hundred nanometers is produced.
このような超高真空・超高温処理プロセスを実現する装置の作製には、高い技術と多くの費用が必要となり、実施できる事業者も限られる。また、市場でこのような金属単結晶基板を多量に調達しようとすると、コスト的負担が大きくなる。 Manufacturing an apparatus that realizes such an ultra-high vacuum / ultra-high temperature processing process requires high technology and a large amount of money, and the number of operators that can be implemented is limited. Further, if a large amount of such a metal single crystal substrate is procured in the market, a cost burden increases.
本発明は、上記の問題を解決するグラフェン及び炭素分子薄膜の合成法を提供するものであり、一般的な製膜法で作製された金属薄膜を用いて、触媒となる金属結晶を調製し、低コストにてより広い均一領域を有するグラフェン及び炭素分子薄膜を容易に合成する方法を提供することを目的とする。 The present invention provides a method for synthesizing graphene and carbon molecular thin film that solves the above problems, and using a metal thin film produced by a general film forming method, prepares a metal crystal as a catalyst, It is an object of the present invention to provide a method for easily synthesizing graphene and carbon molecular thin films having a wider uniform region at low cost.
本発明に係るグラフェン及び炭素分子薄膜の合成方法は、触媒金属の結晶粒を作製する第１工程と、グラフェン及び炭素分子薄膜を合成する第２工程とから成り、第１工程は、不活性ガスと水素ガス雰囲気下で触媒金属を加熱し、第１の所定温度まで昇温する工程と、昇温後、第１の所定温度のまま、第１の所定時間にわたって保持する工程と、触媒金属が再配列する温度範囲を含む範囲で一定となる第１の所定降温速度で降温する工程とを含む。 A method for synthesizing graphene and a carbon molecular thin film according to the present invention includes a first step for producing catalyst metal crystal grains and a second step for synthesizing graphene and a carbon molecular thin film. The first step is an inert gas. A step of heating the catalyst metal in a hydrogen gas atmosphere to raise the temperature to a first predetermined temperature, a step of maintaining the first predetermined temperature after the temperature increase for a first predetermined time, And a step of decreasing the temperature at a first predetermined temperature decrease rate that is constant within a range including a temperature range to be rearranged.
さらに、第２工程は、不活性ガスと水素ガス雰囲気下で触媒金属を加熱し、第２の所定温度まで昇温する工程と、第２の所定温度まで昇温後、第２の所定時間にわたって炭素原料ガスを更に供給する工程と、第２の所定温度から触媒金属が再配列する温度範囲を含む範囲で一定となる第２の所定降温速度で降温する工程とを含む。Furthermore, the second step includes a step of heating the catalyst metal in an inert gas and hydrogen gas atmosphere to raise the temperature to a second predetermined temperature, and after raising the temperature to the second predetermined temperature, over a second predetermined time. A step of further supplying a carbon source gas, and a step of lowering the temperature at a second predetermined temperature decrease rate that is constant within a range including a temperature range in which the catalyst metal is rearranged from the second predetermined temperature.
さらに、第１及び第２の所定温度、および第１及び第２の所定降温速度を制御することにより、触媒金属の多結晶面を作製して、当該多結晶面の各結晶粒の平均粒径を増大させるとともに、各結晶粒の結晶方位を揃える方向に制御して、当該多結晶面上にグラフェン及び炭素分子薄膜を合成する。これにより、欠陥の少ない質の高いグラフェン及び炭素分子薄膜を得ることができる。 Furthermore , by controlling the first and second predetermined temperatures and the first and second predetermined temperature-decreasing speeds, a polycrystalline surface of the catalyst metal is produced, and the average particle size of each crystal grain of the polycrystalline surface In addition, the graphene and the carbon molecular thin film are synthesized on the polycrystalline surface by controlling the crystal grains so that the crystal orientations of the crystal grains are aligned. Thereby, high-quality graphene and carbon molecular thin films with few defects can be obtained.
また、第２工程において、第２の所定温度まで昇温後、第２の所定温度に保持して、第２の所定時間にわたって炭素原料ガスを更に供給する工程と、炭素原料ガスを排気して、不活性ガスと水素ガス雰囲気下で、第２の所定降温速度で降温する工程とを含む。In the second step, after raising the temperature to the second predetermined temperature, maintaining the second predetermined temperature and further supplying the carbon source gas over a second predetermined time; and exhausting the carbon source gas And a step of lowering the temperature at a second predetermined temperature reduction rate in an inert gas and hydrogen gas atmosphere.
また、第１工程を複数回にわたって実行した後に、第２工程を実行する。その際、上記第１の所定温度と、第１の所定時間と、第１の所定降温速度、及び第２の所定温度と、第２の所定時間と、第２の所定降温速度とをそれぞれ独立に制御することで、触媒金属の結晶粒を作製し、当該結晶粒の結晶面上にグラフェン及び炭素分子薄膜を合成することができる。上記第１工程を複数回繰り返す場合は、それぞれの第１の所定温度、第１の所定時間、及び第１の所定降温速度をそれぞれ独立に制御してもよい。Moreover, after performing a 1st process in multiple times, a 2nd process is performed. At this time, the first predetermined temperature, the first predetermined time, the first predetermined temperature decrease rate, the second predetermined temperature, the second predetermined time, and the second predetermined temperature decrease rate are independent of each other. By controlling this, the crystal grains of the catalyst metal can be produced, and the graphene and the carbon molecular thin film can be synthesized on the crystal plane of the crystal grains. When the first step is repeated a plurality of times, the first predetermined temperature, the first predetermined time, and the first predetermined temperature decrease rate may be controlled independently.
また、本発明に係るグラフェン及び炭素分子薄膜の合成方法は、不活性ガスおよび水素ガス雰囲気下で触媒金属を加熱し、所定温度に至るまで昇温する工程と、昇温後、所定の時間にわたって炭素原料ガスを更に供給する工程と、触媒金属が再配列する温度範囲を含む範囲で一定となる所定の降温速度で降温する工程とを含み、所定温度および所定の降温速度を制御することにより、触媒金属の多結晶面を作製して、当該多結晶面の各結晶粒の平均粒径を増大させるとともに、各結晶粒の結晶方位を揃える方向に制御して、当該多結晶面上にグラフェン及び炭素分子薄膜を合成する。Further, the method for synthesizing graphene and carbon molecular thin film according to the present invention includes a step of heating a catalyst metal in an inert gas and hydrogen gas atmosphere to raise the temperature to a predetermined temperature, and after the temperature increase, for a predetermined time. A step of further supplying a carbon source gas, and a step of lowering the temperature at a predetermined temperature decrease rate that is constant in a range including a temperature range in which the catalyst metal is rearranged, and by controlling the predetermined temperature and the predetermined temperature decrease rate, A polycrystalline surface of the catalyst metal is produced, and the average grain size of each crystal grain of the polycrystalline surface is increased, and the crystal orientation of each crystal grain is controlled to be aligned, so that graphene and Synthesize carbon molecular thin film.
また、昇温後、所定温度に保持して、所定の時間にわたって炭素原料ガスを更に供給する工程と、炭素原料ガスを排気して、不活性ガスおよび水素ガス雰囲気下で、所定の降温速度で降温する工程とを含む。Further, after the temperature rise, the step of maintaining the predetermined temperature and further supplying the carbon raw material gas over a predetermined time; and exhausting the carbon raw material gas at a predetermined temperature decreasing rate in an inert gas and hydrogen gas atmosphere And a step of lowering the temperature.
以上説明した本発明によれば、一般的な製膜法で作製された金属薄膜を用いて触媒となる金属結晶を調製し、低コストにて、より広い均一領域を有するグラフェン及び炭素分子薄膜を容易に合成できるという優れた効果が得られる。 According to the present invention described above, a metal crystal serving as a catalyst is prepared using a metal thin film produced by a general film forming method, and graphene and carbon molecular thin films having a wider uniform region are prepared at a low cost. An excellent effect that it can be easily synthesized is obtained.
以下、本発明の実施の形態について図面に基づいて詳細に説明する。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
［実施の形態１］
図１は、本発明の実施の形態１に係るグラフェン及び炭素分子薄膜の合成方法を示すフローチャートである。
[Embodiment 1]
FIG. 1 is a flowchart showing a method for synthesizing graphene and a carbon molecular thin film according to Embodiment 1 of the present invention.
まず、基板に触媒金属を塗布する。基板としては、例えば、研磨したシリコンウェハを熱酸化して表面に二酸化ケイ素（ＳｉＯ2）を形成した平滑基板を使用する。基板はこれに限らず、平滑であり、グラフェンの合成温度において触媒金属と反応しない材料からなるものであればよい。例えば他に、酸化マグネシウム（ＭｇＯ）やサファイア（Ａｌ2Ｏ3）などが挙げられる。 First, a catalytic metal is applied to the substrate. As the substrate, for example, a smooth substrate in which a polished silicon wafer is thermally oxidized to form silicon dioxide (SiO 2 ) on the surface is used. The substrate is not limited to this, and may be any material that is smooth and made of a material that does not react with the catalyst metal at the graphene synthesis temperature. Other examples include magnesium oxide (MgO) and sapphire (Al 2 O 3 ).
上記基板の上に、例えば、ニッケル（Ｎｉ）などの触媒金属を３００ｎｍの厚さで塗布して触媒金属基板を作製する。ここで、触媒金属を塗布する方法としては、金属を融解、蒸発させて塗布する方法（蒸着）または、高速粒子によって当該触媒金属のターゲットから金属原子を弾き飛ばして塗布する方法（スパッタリング法）など一般的な製膜法を採用することができる。 On the substrate, for example, a catalytic metal such as nickel (Ni) is applied to a thickness of 300 nm to produce a catalytic metal substrate. Here, as a method of applying the catalytic metal, a method of applying the metal by melting and evaporating (vapor deposition), a method of applying metal atoms from the target of the catalytic metal by high-speed particles (sputtering method), etc. A general film forming method can be employed.
なお、触媒金属の厚さは、上述した３００ｎｍに限らず、任意の厚さで良いが、後述する昇温過程を経ることで触媒金属が凝集し、基板が露出することがないよう、後述する所定温度θ１１や、その所定温度θ１１での保持時間Ｔ１、触媒金属種、触媒金属と基板との親和性等も考慮して適宜選択すればよい。また、触媒金属としては、ニッケル（Ｎｉ）の他に、コバルト（Ｃｏ）、鉄（Ｆｅ）、銅（Ｃｕ）など、グラフェンの合成場として作用しうる金属種が使用可能で、基板と反応しないものを適宜選択すればよい。 The thickness of the catalyst metal is not limited to the above-described 300 nm, but may be any thickness, but will be described later so that the catalyst metal does not aggregate and the substrate is not exposed through a temperature rising process described later. The predetermined temperature θ11, the holding time T1 at the predetermined temperature θ11, the catalytic metal species, the affinity between the catalytic metal and the substrate, and the like may be selected as appropriate. In addition to nickel (Ni), catalytic metals such as cobalt (Co), iron (Fe), copper (Cu), and other metal species that can act as a synthesis field for graphene can be used and do not react with the substrate. What is necessary is just to select suitably.
図２は、触媒金属基板１０を処理する際に用いる電気炉２０を模式的に示した図である。図２に示すように、電気炉２０は、密閉容器２２と、密閉容器２２を加熱するヒータ２４とを備え、密閉容器２２の一端から各種ガスを供給するとともに、密閉容器２２の他端からポンプ（図示せず）によりガスを排気することができる構成となっている。 FIG. 2 is a diagram schematically showing the electric furnace 20 used when the catalytic metal substrate 10 is processed. As shown in FIG. 2, the electric furnace 20 includes a sealed container 22 and a heater 24 that heats the sealed container 22, supplies various gases from one end of the sealed container 22, and pumps from the other end of the sealed container 22. The gas can be exhausted by (not shown).
この電気炉２０を用いて触媒金属基板１０を加熱する処理は以下のとおりである。 The process of heating the catalytic metal substrate 10 using this electric furnace 20 is as follows.
まず、触媒金属基板１０を電気炉の内部に装填し、不活性ガス（例えば、アルゴンガスなど）及び水素ガス雰囲気下で、所定温度（例えば、９００℃など）に至るまで昇温する（ステップＳ１００）。こうして、触媒金属基板１０の温度が所定温度に達した後、その、所定時間にわたって、炭素原料ガスを更に供給する（ステップＳ１１０）。これは、所定温度に保持した状態で行えばよい。炭素原料ガスは、触媒金属の上にグラフェンや炭素分子薄膜を形成するための原料ガスである。次いで、触媒金属基板１０の温度を所定の降温速度（例えば、−１２．５℃／ｍｉｎなど）で降温させる（ステップＳ１２０）。この降温は、例えば、密閉容器２２内のガスを排気した後、不活性ガスと水素ガス雰囲気下で行えばよい。 First, the catalytic metal substrate 10 is loaded into the electric furnace, and the temperature is raised to a predetermined temperature (eg, 900 ° C.) in an inert gas (eg, argon gas) and hydrogen gas atmosphere (step S100). ). Thus, after the temperature of the catalytic metal substrate 10 reaches a predetermined temperature, the carbon source gas is further supplied over the predetermined time (step S110). This may be performed in a state where the temperature is maintained at a predetermined temperature. The carbon source gas is a source gas for forming graphene or a carbon molecular thin film on the catalyst metal. Next, the temperature of the catalyst metal substrate 10 is decreased at a predetermined temperature decrease rate (for example, −12.5 ° C./min) (step S120). This temperature decrease may be performed, for example, in an inert gas and hydrogen gas atmosphere after exhausting the gas in the sealed container 22.
以下、ステップＳ１００〜Ｓ１２０の各処理内容を詳細に説明する。 Hereafter, each processing content of step S100-S120 is demonstrated in detail.
まず、触媒金属基板１０を電気炉の内部に装填し、不活性ガス及び水素ガス雰囲気下で、所定温度（例えば、９００℃など）に至るまで昇温する（ステップＳ１００）。 First, the catalytic metal substrate 10 is loaded into the electric furnace, and the temperature is raised to a predetermined temperature (eg, 900 ° C.) in an inert gas and hydrogen gas atmosphere (step S100).
図２に示すように、触媒金属基板１０を密閉容器２２に装填したまま、密閉容器２２の内部にある気体をポンプにより排気した後、不活性ガスであるアルゴンガス１８０ｓｃｃｍと水素ガス２０ｓｃｃｍとを密閉容器２２の一端から供給するとともに、ポンプによって他端側で排気することによって密閉容器２２内の圧力を５×１０4Ｐａ程度に維持する。 As shown in FIG. 2, the gas inside the sealed container 22 is exhausted by a pump while the catalytic metal substrate 10 is loaded in the sealed container 22, and then the argon gas 180 sccm and the hydrogen gas 20 sccm, which are inert gases, are sealed. The pressure in the sealed container 22 is maintained at about 5 × 10 4 Pa by supplying from one end of the container 22 and exhausting the other end side by a pump.
密閉容器２２内の圧力は、数百Ｐａから、常圧（大気圧）付近までの任意の圧力でよく５×１０4Ｐａ程度では、実施上、安全で、高真空・高耐圧性を備えた高性能な容器を使用する必要がない。その他、ガスの拡散、均一性をより高めるに、５×１０3Ｐａ程度の低圧としても良い。また、アルゴンガスや水素ガスの流量は上記数値に限らず、密閉容器２２内の設定圧力を鑑みて適した流量とすればよい。水素ガスは、触媒金属表面の酸化物を還元する作用等を有する。不活性ガスであるアルゴンガスはキャリアガスであり、流量はゼロとしても良い。なお、ｓｃｃｍは流量の単位であり、０℃・１０１３ｈＰａの流体が１分間に１ｃｍ3流れることを示す。 The pressure in the sealed container 22 may be any pressure from several hundred Pa to around normal pressure (atmospheric pressure), and is about 5 × 10 4 Pa, which is safe in practice and has high vacuum and high pressure resistance. There is no need to use high performance containers. In addition, a low pressure of about 5 × 10 3 Pa may be used to further enhance gas diffusion and uniformity. Further, the flow rates of argon gas and hydrogen gas are not limited to the above values, and may be set to suitable flow rates in view of the set pressure in the sealed container 22. Hydrogen gas has the effect | action etc. which reduce | restore the oxide of the catalyst metal surface. Argon gas, which is an inert gas, is a carrier gas, and the flow rate may be zero. Note that sccm is a unit of flow rate, and indicates that a fluid at 0 ° C. and 1013 hPa flows 1 cm 3 per minute.
このような条件下で、ヒータ２４を稼働させ、触媒金属基板１０を所定温度θ１１に至るまで、例えば６０℃／ｍｉｎのペースで加熱する。 Under such conditions, the heater 24 is operated, and the catalytic metal substrate 10 is heated at a pace of, for example, 60 ° C./min until reaching the predetermined temperature θ11.
なお、所定温度θ１１は、触媒金属の沸点より低く、表面の触媒金属原子が再配列可能であり、かつ後述する処理でグラフェンを合成できる温度であればよい。所定温度θ１１が高いほど、より短い保持時間（ゼロを含む）で、表面からより深い位置にある触媒金属原子の再配列が可能になる。このため、所定温度θ１１は、触媒金属の種類、触媒金属の膜厚、保持時間などを考慮して適宜変更すればよい。また、昇温速度は、上述した６０℃／ｍｉｎという数値に限られず、速やかに所定温度θ１１へ到達する値であればよい。 The predetermined temperature θ11 may be any temperature as long as it is lower than the boiling point of the catalytic metal, the catalytic metal atoms on the surface can be rearranged, and graphene can be synthesized by the treatment described later. The higher the predetermined temperature θ11, the rearrangement of catalytic metal atoms at a deeper position from the surface is possible with a shorter holding time (including zero). For this reason, the predetermined temperature θ11 may be appropriately changed in consideration of the type of catalyst metal, the thickness of the catalyst metal, the holding time, and the like. Further, the rate of temperature increase is not limited to the above-described numerical value of 60 ° C./min, and may be a value that quickly reaches the predetermined temperature θ11.
続いて、触媒金属基板１０の温度が所定温度に達した後、その所定温度に保持して、所定時間Ｔ１１にわたって、炭素原料ガスを更に供給する（ステップＳ１１０）。具体的には、触媒金属基板１０の温度を所定温度θ１１に維持したまま、所定時間Ｔ１１（例えば、５分間など）にわたってメタンガス１０ｓｃｃｍをアルゴンガスと水素ガスに追加して流すことで、グラフェン及び炭素分子薄膜の構成材料となる炭素原子を供給する。なお、所定時間Ｔ１１は、所定温度に保持する時間と同じでもよく、また、これより短くても良い。 Subsequently, after the temperature of the catalytic metal substrate 10 reaches a predetermined temperature, the carbon source gas is further supplied over a predetermined time T11 while maintaining the predetermined temperature (step S110). Specifically, while maintaining the temperature of the catalytic metal substrate 10 at a predetermined temperature θ11, graphene and carbon are added by flowing 10 sccm of methane gas in addition to argon gas and hydrogen gas over a predetermined time T11 (for example, 5 minutes). Supply carbon atoms that will be the constituent material of the molecular thin film. The predetermined time T11 may be the same as the time for holding at the predetermined temperature, or may be shorter than this.
ここで、グラフェン及び炭素分子薄膜の構成材料となる炭素原料ガスとしては、メタンガスに限られず、他の飽和炭化水素ガス、エチレン（Ｃ2Ｈ4）などの不飽和炭化水素ガス、エタノール（Ｃ2Ｈ5ＯＨ）などアルコールの気化ガスを用いてもよい。 Here, the carbon source gas that is a constituent material of the graphene and the carbon molecular thin film is not limited to methane gas, but other saturated hydrocarbon gas, unsaturated hydrocarbon gas such as ethylene (C 2 H 4 ), ethanol (C 2 An alcohol vapor gas such as H 5 OH) may be used.
また、所定温度θ１１は炭素供給源となるガス分子が分解し、触媒金属の触媒作用により炭素原子からグラフェンが形成される反応が進む温度であればよい。したがって、使用するガス種や触媒金属種によって、所定温度θ１１を適宜選択可能である。メタンガスを流す時間は、少なくとも、グラフェンの形成が可能な量の炭素が触媒金属に供給されうる時間以上であれば良く、適宜変更することができる。一般的に、炭素源の供給量（流量）は、グラフェンの層数等に影響すると考えられるため、所望のグラフェン及び炭素分子薄膜の形態などを鑑みて適宜変更すればよい。 Further, the predetermined temperature θ11 may be a temperature at which a gas molecule serving as a carbon supply source decomposes and a reaction in which graphene is formed from carbon atoms by the catalytic action of the catalytic metal proceeds. Therefore, the predetermined temperature θ11 can be appropriately selected depending on the type of gas used and the type of catalytic metal. The time for flowing the methane gas may be at least as long as the amount of carbon capable of forming graphene can be supplied to the catalyst metal, and can be changed as appropriate. In general, the supply amount (flow rate) of the carbon source is considered to affect the number of graphene layers and the like, and may be appropriately changed in view of the desired graphene and the shape of the carbon molecular thin film.
次いで、密閉容器２２内のガスを排気した後、アルゴンガスと水素ガス雰囲気下で、触媒金属基板１０の温度を所定の降温速度（例えば、−１２．５℃／ｍｉｎなど）で降温させる（ステップＳ１２０）。 Next, after the gas in the sealed container 22 is exhausted, the temperature of the catalytic metal substrate 10 is decreased at a predetermined temperature decrease rate (for example, −12.5 ° C./min, etc.) in an atmosphere of argon gas and hydrogen gas (Step 1). S120).
具体的には、まず、密閉容器２２内のメタンガス、アルゴンガス、水素ガスを一旦すべて排気して炭素源となるガスを排除し、この後、再びアルゴンガス１８０ｓｃｃｍと水素ガス２０ｓｃｃｍを５×１０4Ｐａの圧力下で流す状態にする（はじめに５×１０3Ｐａ程度の低圧とした場合は、その圧力下で流す）。このような条件下で、触媒金属基板１０の温度を所定温度θ１１から所定温度θ１２（例えば、１００〜１５０℃など）まで、所定の降温速度Δθ１（例えば、１２．５℃／ｍｉｎ）で冷ます。なお、メタンガス、アルゴンガス、水素ガスを一旦すべて排気せずに、そのままメタンガス、アルゴンガス、水素ガスを流しながら、所定の降温速度で冷ましても良い。また、降温途中でメタンガスを停止して、アルゴンガス、水素ガスのみにしても良い。 Specifically, first, the methane gas, argon gas, and hydrogen gas in the sealed container 22 are all exhausted once to remove the gas serving as the carbon source, and then argon gas 180 sccm and hydrogen gas 20 sccm are again added to 5 × 10 4. It is made to flow under a pressure of Pa (when it is initially set to a low pressure of about 5 × 10 3 Pa, it is flowed under that pressure). Under such conditions, the temperature of the catalytic metal substrate 10 is cooled from a predetermined temperature θ11 to a predetermined temperature θ12 (for example, 100 to 150 ° C.) at a predetermined temperature decrease rate Δθ1 (for example, 12.5 ° C./min). . Note that the methane gas, the argon gas, and the hydrogen gas may be cooled at a predetermined temperature decrease rate while the methane gas, the argon gas, and the hydrogen gas are allowed to flow without being exhausted once. Further, the methane gas may be stopped in the middle of temperature lowering, and only argon gas and hydrogen gas may be used.
上記所定の降温速度Δθ１は、加熱を停止して制御せずに自然に冷ました場合に比較して、降温初期、つまり、温度が高い領域での冷却速度が遅くなるように設定する。所定の降温速度で冷ます温度範囲は、触媒金属原子が移動して再配列する温度範囲を含む範囲であれば良い。また、降温速度は上記値に限らず、結晶粒の形成がより促進される降温速度であればよく、触媒金属種の特性等により適宜選択すればよい。以上のように、本実施の形態によれば、到達する所定の温度、炭素原料ガスを更に供給する所定の時間、および所定の降温速度を制御することで、後述するように粒径などの結晶粒の形態を制御するところに特徴がある。 The predetermined temperature decrease rate Δθ1 is set so that the cooling rate in the initial temperature decrease period, that is, in the region where the temperature is high, is slower than that in the case where the temperature is naturally cooled without stopping and controlling. The temperature range for cooling at a predetermined temperature drop rate may be a range including a temperature range in which the catalyst metal atoms move and rearrange. The temperature lowering rate is not limited to the above value, and may be any temperature cooling rate that promotes the formation of crystal grains, and may be appropriately selected depending on the characteristics of the catalyst metal species. As described above, according to the present embodiment, by controlling the predetermined temperature to be reached, the predetermined time for further supplying the carbon source gas, and the predetermined temperature decrease rate, the crystal such as the grain size as will be described later. It is characterized by controlling the morphology of the grains.
図３は、本実施の形態に係るグラフェン及び炭素分子薄膜の合成方法において、触媒金属基板１０を所定の降温速度で降温するときの温度変化を実線で示し、降温速度を制御せずに自然に冷ました場合の温度変化を点線で示したタイムチャートである。縦軸は温度を示しており、横軸は降温を開始してからの経過時間を示している。所定の降温速度Δθ１は、制御せずに自然に冷ました場合に比べて、図３に示すように、降温開始初期の比較的高い温度領域での降温速度が遅く一定となるよう設定すればよい。 FIG. 3 shows, in a solid line, the temperature change when the catalytic metal substrate 10 is cooled at a predetermined temperature decrease rate in the method for synthesizing graphene and carbon molecular thin film according to the present embodiment, and naturally without controlling the temperature decrease rate. It is the time chart which showed the temperature change at the time of cooling with the dotted line. The vertical axis indicates the temperature, and the horizontal axis indicates the elapsed time since the start of the temperature decrease. The predetermined temperature decrease rate Δθ1 may be set so that the temperature decrease rate in the relatively high temperature region at the beginning of the temperature decrease is slow and constant, as shown in FIG. 3, as compared with the case where the temperature is naturally cooled without control. .
所定の降温速度で冷ます温度範囲は、触媒金属原子が移動して再配列する温度範囲を含む範囲であればよい。また、降温速度は上記値に限らず、結晶粒の形成がより促進される降温速度であればよく、触媒金属種の特性等により適宜選択すればよい。なお、前述したように、降温前の温度（所定温度θ１１）が、炭素供給源となるガス（炭素原料ガス）分子が分解し、触媒金属の触媒作用により炭素原子からグラフェンが形成される反応が進む温度であれば、金属原子は移動して再配列などが可能な状態となる。 The temperature range for cooling at a predetermined temperature decrease rate may be a range including a temperature range in which the catalyst metal atoms move and rearrange. The temperature lowering rate is not limited to the above value, and may be any temperature cooling rate that promotes the formation of crystal grains, and may be appropriately selected depending on the characteristics of the catalyst metal species. Note that, as described above, the temperature before the temperature decrease (predetermined temperature θ11) is such that the gas (carbon raw material gas) molecule serving as the carbon supply source is decomposed and graphene is formed from carbon atoms by the catalytic action of the catalytic metal. At advancing temperature, the metal atoms move and can be rearranged.
降温過程で触媒金属原子（ニッケル原子）が再配列して固定し、ニッケルの結晶粒が表面に形成される。図４は、降温速度を制御した場合としなかった場合の触媒金属基板の表面を比較した原子間力顕微鏡（ＡＦＭ：Atomic Force Microscope）像である。図４（ａ）は制御して降温速度Δθ１により降温して得られた触媒金属基板のＡＦＭ像であり、図４（ｂ）は制御せずに自然に冷まして得られた触媒金属基板のＡＦＭ像である。図４から、所定の降温速度に制御せずに自然に冷ました場合に比べると、制御して降温速度Δθ１で降温した場合に形成される触媒金属の結晶粒の粒径は、大きいものが増えることが分かる。 During the temperature lowering process, catalytic metal atoms (nickel atoms) are rearranged and fixed, and nickel crystal grains are formed on the surface. FIG. 4 is an atomic force microscope (AFM) image in which the surface of the catalytic metal substrate is compared with and without controlling the temperature drop rate. FIG. 4A is an AFM image of the catalytic metal substrate obtained by controlling and cooling at a temperature drop rate Δθ1, and FIG. 4B is an AFM image of the catalytic metal substrate obtained by natural cooling without control. It is a statue. From FIG. 4, compared with the case where it cools naturally without controlling to a predetermined temperature-decreasing rate, when the temperature is controlled and the temperature is decreased at a temperature-decreasing rate Δθ1, the crystal grain size of the catalyst metal formed increases. I understand that.
図５は、後方散乱電子回折（ＥＢＳＤ：Electron Back-Scatter Diffraction）により、降温速度を制御した場合（ａ）としなかった場合（ｂ）のニッケル結晶粒の結晶方位を解析した結果の一例である。また、図５の（ａ’）および図５の（ｂ’）は、それぞれ、走査電子顕微鏡の二次電子像（ＳＥＭ像）の破線で囲った部分に対応する領域にある各結晶粒の結晶方位を、濃淡で示したものである。同図では、結晶粒の結晶面方位が（１１１）に揃うほど、高い濃度で（より黒く）示されている。 FIG. 5 is an example of the result of analyzing the crystal orientation of nickel crystal grains when the temperature drop rate is controlled (a) or not (b) by backscattered electron diffraction (EBSD). . Further, (a ′) in FIG. 5 and (b ′) in FIG. 5 show the crystal of each crystal grain in the region corresponding to the portion surrounded by the broken line in the secondary electron image (SEM image) of the scanning electron microscope. The azimuth is shown by shading. In the same figure, the crystal grains are shown with a higher concentration (blacker) as the crystal plane orientation of the crystal grains becomes (111).
図５の（ａ）は、濃度が高く広い部分が多く、これは、結晶面方位が（１１１）に近く結晶粒が大きい部分が多く出現していることを示している。一方、図５の（ｂ）は、濃度が高く広い部分が少なく、濃度が高い部分は小さく分散しており、これは、結晶面方位が（１１１）に近く結晶粒が大きい部分が少ないことを示している。これらの観察結果から、上述した所定の降温速度に制御した触媒金属基板の場合には、表面に形成される触媒金属の結晶粒の結晶面方位が、（１１１）の方位に揃う傾向があることが分かる。また、結晶粒がより大きくなる方が、より（１１１）の方位に揃う傾向が見られる。 (A) of FIG. 5 has many parts with a high density | concentration, and this has shown that many parts with crystal plane orientation close | similar to (111) and a large crystal grain have appeared. On the other hand, (b) of FIG. 5 shows that the concentration is high and the wide portion is small, and the high concentration portion is small and dispersed. This means that the crystal plane orientation is close to (111) and there are few large crystal grains. Show. From these observation results, in the case of the catalytic metal substrate controlled to the above-described predetermined temperature drop rate, the crystal plane orientation of the crystal grains of the catalytic metal formed on the surface tends to be aligned with the (111) orientation. I understand. In addition, as the crystal grains become larger, a tendency to align in the (111) orientation is observed.
ニッケル（１１１）結晶面の格子定数は０．２４９７ｎｍであり、グラフェンの格子定数は０．２４６ｎｍであることから非常に適合性が良く、ニッケル（１１１）結晶面で合成されるグラフェンは、格子定数値の近い結晶面の影響を受けることが考えられ、質の高い均一な単結晶グラフェン及び炭素分子薄膜が形成されやすいと考えられる。よって、触媒金属の結晶面を大きくし、各結晶面の面方位を揃えるこの方法により、より大きな均一領域を有するグラフェン及び炭素分子薄膜を簡便に得ることができる。 Since the lattice constant of the nickel (111) crystal plane is 0.2497 nm and the lattice constant of graphene is 0.246 nm, the compatibility is very good. Graphene synthesized on the nickel (111) crystal plane has a lattice constant. It may be affected by the crystal planes with close numerical values, and it is considered that high-quality uniform single-crystal graphene and carbon molecular thin films are likely to be formed. Therefore, by this method of enlarging the crystal plane of the catalyst metal and aligning the plane orientation of each crystal plane, it is possible to easily obtain graphene and a carbon molecular thin film having a larger uniform region.
さらに、本発明による触媒金属面には、図４及び図５に示すとおり、多数の結晶面が存在している。このそれぞれの結晶面上に形成されるグラフェン及び炭素分子薄膜は、ひと続きで繋がっているものの、層数が変化する傾向がある。図６は、結晶粒と結晶粒の間である粒界部分で、グラフェンの層数が大きく変化している様子を観察した透過型電子顕微鏡像（ＴＥＭ像）である。このように、それぞれの結晶粒に対応する領域ごとに、形状、層数の異なるひと続きの炭素分子薄膜を得ることができる。それぞれの領域を、微細加工技術により切り離せば、所望の形状、層数の部分のみの利用も可能である。 Furthermore, as shown in FIGS. 4 and 5, the catalytic metal surface according to the present invention has a large number of crystal planes. Although the graphene and the carbon molecular thin film formed on each crystal plane are connected in a row, the number of layers tends to change. FIG. 6 is a transmission electron microscope image (TEM image) obtained by observing a state in which the number of graphene layers is greatly changed at a grain boundary portion between crystal grains. In this way, a series of carbon molecular thin films having different shapes and the number of layers can be obtained for each region corresponding to each crystal grain. If each region is separated by a microfabrication technique, only a portion having a desired shape and number of layers can be used.
また、本発明によりグラフェンが複数層形成された炭素分子薄膜は、それぞれ規則的に積み重なった（スタッキングした）構造をとる傾向がある。図７の（ａ）に平面ＴＥＭ像、図７の（ｂ）にその拡大像、図７の（ｃ）に電子回折像を示す。図７の（ｃ）は、図７の（ａ）において円で囲んだ領域の電子回折像である。図７の（ａ）では、ひと続きの炭素分子薄膜の中に、各結晶粒に対応した形状で区分された領域が見える。各区分の境界は、図７の（ｂ）に示すとおり、炭素分子薄膜にしわがより、垂直に立った状態になるため現れると考えられる。 In addition, the carbon molecular thin films in which a plurality of graphene layers are formed according to the present invention tend to have a structure in which they are regularly stacked (stacked). FIG. 7A shows a planar TEM image, FIG. 7B shows an enlarged image, and FIG. 7C shows an electron diffraction image. FIG. 7C is an electron diffraction image of a region surrounded by a circle in FIG. In (a) of FIG. 7, the area | region divided by the shape corresponding to each crystal grain can be seen in a continuous carbon molecule thin film. As shown in FIG. 7B, the boundary of each section is considered to appear because the wrinkles of the carbon molecular thin film stand more vertically.
図７の（ｃ）に示すように、グラフェンの六員環単位格子構造に起因する回折像が得られる。もし、各グラフェン層がランダムな回転角度で単に積み重なった乱層の炭素分子薄膜であれば、環状の回折像が観測されると予測できるが、図７の（ｃ）に示す結果から、炭素分子薄膜は乱層ではなく、スタッキングしていることが分かる。回転角度の異なるいくつかの成分が見られるのは、スタッキングした単結晶グラフェンが、測定領域内に複数存在することを示している。 As shown in FIG. 7 (c), a diffraction image resulting from the six-membered ring unit cell structure of graphene is obtained. If each graphene layer is a turbulent carbon molecular thin film simply stacked at a random rotation angle, it can be predicted that an annular diffraction image will be observed. From the results shown in FIG. It can be seen that the thin film is not a turbulent layer but is stacked. The presence of several components with different rotation angles indicates that there are a plurality of stacked single crystal graphenes in the measurement region.
グラフェンがスタッキングした場合、ランダムな回転角度で単に積み重なった乱層の場合とは異なる物性を示す。代表的な例として、バンド構造に与える影響が知られており、例えば、二層にスタッキングした炭素分子薄膜（二層グラフェン）は、その面に垂直方向に電界を印加することで、バンドギャップが形成される。このバンドギャップを利用することで、二層グラフェンをチャネルとした超高速電界効果トランジスタのオンオフ動作が可能になる。 When graphene stacks, it exhibits different physical properties than a turbulent layer simply stacked at random rotation angles. As a typical example, the effect on the band structure is known. For example, a carbon molecular thin film (double-layer graphene) stacked in two layers has a band gap that is applied by applying an electric field in a direction perpendicular to the surface. It is formed. By using this band gap, an on / off operation of an ultrafast field effect transistor using bilayer graphene as a channel becomes possible.
このように、本発明によれば、結晶粒に対応した大きさの均質なグラフェン及び炭素分子薄膜を得ることができ、また、炭素分子薄膜はスタッキングした構造として合成することができるため、微細加工技術などと組み合わせることで、その特徴を利用した応用が可能になる。 As described above, according to the present invention, it is possible to obtain a homogeneous graphene and carbon molecular thin film having a size corresponding to a crystal grain, and the carbon molecular thin film can be synthesized as a stacking structure. Combining with technology, etc. enables application using the features.
［実施の形態２］
次に、本発明の実施の形態２に係るグラフェン及び炭素分子薄膜の合成方法について説明する。実施の形態１で説明したもの（電気炉）と同一の構成要素については、同一の符号を付すとともに詳しい説明を省略することにする。以下、本発明の実施の形態１との相違点を中心に説明する。
[Embodiment 2]
Next, a method for synthesizing graphene and a carbon molecular thin film according to Embodiment 2 of the present invention will be described. The same components as those described in the first embodiment (electric furnace) are denoted by the same reference numerals and detailed description thereof is omitted. Hereinafter, the difference from Embodiment 1 of the present invention will be mainly described.
図８は、本発明の実施の形態２に係るグラフェン及び炭素分子薄膜の合成方法を示すフローチャートである。 FIG. 8 is a flowchart showing a method of synthesizing graphene and a carbon molecular thin film according to Embodiment 2 of the present invention.
ステップＳ２００の、触媒金属基板１０を昇温する処理については、実施の形態１で説明したステップＳ１００と同一なのでその説明を省略する。 The process for raising the temperature of the catalytic metal substrate 10 in step S200 is the same as that in step S100 described in the first embodiment, and thus the description thereof is omitted.
次に、触媒金属基板１０の温度を所定時間Ｔ２１にわたって所定温度θ２１に保持する（ステップＳ２１０）。実施の形態１では、触媒金属基板１０の温度が所定温度θ１１に至るまで加熱した後、所定時間Ｔ１１にわたってメタンガスをアルゴンガスと水素ガスに追加して流すのに対し（図１のステップＳ１１０）、実施の形態２では、触媒金属基板１０の温度が所定温度θ２１（例えば、９００℃など）に至るまで加熱した後、メタンガス１１０を流さずにアルゴンガス及び水素ガスのみを供給した状態で所定時間Ｔ２１（例えば、０〜６０分間など）にわたって触媒金属基板１０の温度を所定温度θ２１に保持する（ステップＳ２１０）。この処理は、触媒金属の結晶粒の形成を促すために行うものであり、所定温度θ２１が低いほど、長い時間に設定すればよい。逆に、所定温度θ２１が十分に高ければ、所定時間Ｔ２１はゼロであってもよい。 Next, the temperature of the catalytic metal substrate 10 is held at a predetermined temperature θ21 for a predetermined time T21 (step S210). In the first embodiment, after the catalyst metal substrate 10 is heated until the temperature reaches the predetermined temperature θ11, the methane gas is added to the argon gas and the hydrogen gas over a predetermined time T11 (step S110 in FIG. 1). In the second embodiment, after the catalyst metal substrate 10 is heated to a predetermined temperature θ21 (for example, 900 ° C. or the like), the argon gas and the hydrogen gas are supplied without flowing the methane gas 110 for a predetermined time T21. The temperature of the catalytic metal substrate 10 is maintained at the predetermined temperature θ21 over (for example, 0 to 60 minutes) (step S210). This treatment is performed to promote the formation of catalyst metal crystal grains. The lower the predetermined temperature θ21, the longer the time may be set. Conversely, if the predetermined temperature θ21 is sufficiently high, the predetermined time T21 may be zero.
この後、触媒金属基板１０を所定温度θ２１から所定温度θ２２（例えば、１００〜１５０℃など）まで、所定の降温速度Δθ２１（例えば、−１２．５℃／ｍｉｎなど）で制御して降温する（ステップＳ２２０）。所定温度θ２２は、触媒金属の金属原子が動いて再配列しなくなる程度の低い温度とすればよい。 Thereafter, the temperature of the catalytic metal substrate 10 is controlled from a predetermined temperature θ21 to a predetermined temperature θ22 (for example, 100 to 150 ° C., etc.) at a predetermined temperature decrease rate Δθ21 (for example, −12.5 ° C./min, etc.). Step S220). The predetermined temperature θ22 may be a low temperature that prevents the metal atoms of the catalyst metal from moving and rearranging.
このように実施の形態２では、メタンガスの供給を伴わない、昇温及び降温過程を経て予め触媒金属層に触媒金属の結晶粒を形成する触媒金属結晶粒作製工程を設ける。このため、グラフェン及び炭素分子薄膜合成工程の結果得られる結晶粒の大きさは、実施例１のように１回の昇温・保持・降温過程によるグラフェン合成と比較して、より大きな結晶面を有する結晶粒が形成される。このため、大きな結晶面に対応する均質なグラフェンをより簡便に合成することができる。 As described above, in the second embodiment, there is provided a catalyst metal crystal grain preparation step for forming catalyst metal crystal grains in the catalyst metal layer in advance through a temperature rising and temperature lowering process without supplying methane gas. For this reason, the size of the crystal grains obtained as a result of the graphene and carbon molecular thin film synthesis step is larger than that of the graphene synthesis by one heating / holding / cooling process as in Example 1. The crystal grain which has is formed. For this reason, homogeneous graphene corresponding to a large crystal plane can be synthesized more easily.
また、金属触媒のニッケルを基板に塗布した際、ニッケルは無定形状態となっており、実施の形態１のように触媒金属結晶粒作製工程を予め設けない場合、ニッケルが無定形状態から結晶化する過程と並行してグラフェンの合成も進む反応過程となる。このため、反応過程の進み具合により触媒金属表面に結晶面がうまく形成されない場合、グラフェンが形成できない、または、質が劣化する結果となりやすいと考えられる。これに対し実施の形態２では、予め触媒金属結晶粒作製工程により、触媒金属表面は既に結晶粒が並んでいる状態であるため、炭素原子の反応もよりスムーズに進行すると考えられ、欠陥の少ない質の高いグラフェンが得られやすい。 Further, when nickel of the metal catalyst is applied to the substrate, the nickel is in an amorphous state, and when the catalyst metal crystal grain preparation step is not provided in advance as in the first embodiment, the nickel is crystallized from the amorphous state. In parallel with this process, the synthesis of graphene proceeds. For this reason, it is considered that if the crystal plane is not well formed on the catalytic metal surface due to the progress of the reaction process, graphene cannot be formed or the quality is likely to deteriorate. On the other hand, in Embodiment 2, since the catalyst metal surface is already in a state where crystal grains are already aligned in the catalyst metal crystal grain preparation step, the reaction of carbon atoms is considered to proceed more smoothly, and there are few defects. It is easy to obtain high quality graphene.
所定温度θ２２に達した後、再び触媒金属基板１０を所定温度θ２３（例えば９００℃など）に至るまで昇温する（ステップＳ２３０）。昇温開始までの間に時間をおいてもよい（例えば１０分など）。 After reaching the predetermined temperature θ22, the catalytic metal substrate 10 is again heated to a predetermined temperature θ23 (for example, 900 ° C.) (step S230). There may be a period of time before the start of temperature increase (for example, 10 minutes).
次いで、実施の形態１で説明した図１のステップＳ１１０と同様に、触媒金属基板１０の温度を所定温度θ２３（例えば、９００℃など）に維持したまま、所定時間Ｔ２２（例えば、５分など）にわたってメタンガス（例えば１０ｓｃｃｍ）をアルゴンガスと水素ガスに追加して流した後（ステップＳ２４０）、密閉容器２２内のガスを排気し、アルゴンガスと水素ガス雰囲気下で、所定の降温速度Δθ２４（例えば、−１２．５℃／ｍｉｎなど）のペースで所定温度θ２４（例えば、１００〜１５０℃など）に至るまで降温した後（ステップＳ２５０）、触媒金属基板１０を密閉容器２２から取り出す。所定時間Ｔ２２は、所定温度θ２３に維持する時間と同じでもよいし、それより短くても良い。また、密閉容器２２内のガスを一旦すべて排気せずに、そのままメタンガス、アルゴンガス、水素ガスを流しながら降温しても良い。また、降温途中でメタンガスを停止して、アルゴンガス、水素ガスのみにしても良い。 Next, as in step S110 of FIG. 1 described in the first embodiment, the temperature of the catalytic metal substrate 10 is maintained at a predetermined temperature θ23 (for example, 900 ° C.), for a predetermined time T22 (for example, 5 minutes). Then, methane gas (for example, 10 sccm) is added to the argon gas and hydrogen gas to flow (step S240), the gas in the sealed container 22 is exhausted, and a predetermined temperature decrease rate Δθ24 (for example, under argon gas and hydrogen gas atmosphere) The temperature of the catalyst metal substrate 10 is taken out from the sealed container 22 after the temperature is lowered to a predetermined temperature θ24 (for example, 100 to 150 ° C.) at a pace of −12.5 ° C./min) (step S250). The predetermined time T22 may be the same as the time for maintaining the predetermined temperature θ23, or may be shorter than that. Alternatively, the temperature in the sealed container 22 may be lowered while flowing methane gas, argon gas, and hydrogen gas as they are without exhausting all of the gas in the sealed container 22 once. Further, the methane gas may be stopped in the middle of temperature lowering, and only argon gas and hydrogen gas may be used.
このような処理を経ることにより、触媒金属の結晶粒の上に形成された本実施の形態に係るグラフェン及び炭素分子薄膜を得ることができる。触媒金属層に結晶粒を形成する第１段階と、グラフェン及び炭素分子薄膜を形成する第２段階とに分けることにより、触媒金属の結晶粒の拡大をより促進し、この触媒金属の結晶粒の上に形成されるグラフェン及び炭素分子薄膜の低欠陥化と、均一領域の拡大を、容易にはかれる。 Through such treatment, the graphene and carbon molecular thin film according to the present embodiment formed on the crystal grains of the catalyst metal can be obtained. By dividing into the first stage of forming crystal grains in the catalyst metal layer and the second stage of forming graphene and carbon molecular thin films, the expansion of the catalyst metal crystal grains is further promoted. It is easy to reduce the defects of the graphene and carbon molecular thin films formed thereon and to enlarge the uniform region.
なお、上述した実施の形態２では、ステップＳ２００〜Ｓ２２０の触媒金属結晶粒作製工程と、ステップＳ２３０〜Ｓ２５０のグラフェン及び炭素分子薄膜合成工程とで、昇温時の所定温度θ２１、θ２３、降温時の所定の温度θ２２、θ２４、所定の保持時間Ｔ２１、Ｔ２２及び、所定の降温速度Δθ２２、Δθ２４は、それぞれ必ずしも同じ値にする必要はなく、適宜変更することができる。ステップＳ２００〜Ｓ２２０の触媒金属結晶粒作製工程では、触媒金属の原子が移動して再配列することが可能な程度の温度及び保持時間を選択すればよく、ステップＳ２３０〜Ｓ２５０のグラフェン及び炭素分子薄膜合成工程では、グラフェン及び炭素分子薄膜の合成が可能な程度の温度及び保持時間を選択すればよい。また、降温速度も結晶粒の形成がより促進される降温速度であればよく、触媒金属種の特性等により適宜選択し、それぞれの工程で適宜独立に制御すればよい。 In the above-described second embodiment, the catalyst metal crystal grain preparation process in steps S200 to S220 and the graphene and carbon molecular thin film synthesis process in steps S230 to S250 are performed at predetermined temperatures θ21 and θ23 at the time of temperature increase and at the time of temperature decrease. The predetermined temperatures θ22 and θ24, the predetermined holding times T21 and T22, and the predetermined temperature decrease rates Δθ22 and Δθ24 do not necessarily have the same value, and can be changed as appropriate. In the catalyst metal crystal grain preparation step of steps S200 to S220, a temperature and a holding time that can move and rearrange the atoms of the catalyst metal may be selected, and the graphene and carbon molecular thin film of steps S230 to S250 may be selected. In the synthesis step, a temperature and a holding time that can synthesize graphene and the carbon molecular thin film may be selected. The temperature lowering rate may be any temperature decreasing rate that promotes the formation of crystal grains, and may be appropriately selected depending on the characteristics of the catalyst metal species and the like, and may be appropriately controlled independently in each step.
［実施の形態３］
次に、本発明の実施の形態３に係るグラフェン及び炭素分子薄膜の合成方法について説明する。なお、実施の形態１で説明したものと同一の構成要素については、同一の符号を付すとともに詳しい説明を省略することにする。
[Embodiment 3]
Next, a method for synthesizing graphene and a carbon molecular thin film according to Embodiment 3 of the present invention will be described. Note that the same components as those described in the first embodiment are denoted by the same reference numerals and detailed description thereof is omitted.
図９は、本発明の実施の形態３に係るグラフェン及び炭素分子薄膜の合成方法を示すフローチャートである。以下、本発明の実施の形態１，２との相違点を中心に説明する。 FIG. 9 is a flowchart showing a method of synthesizing graphene and a carbon molecular thin film according to Embodiment 3 of the present invention. Hereinafter, the difference from the first and second embodiments of the present invention will be mainly described.
ステップＳ３００は、触媒金属層に触媒金属の結晶粒を形成する処理であり、具体的な処理内容は、実施の形態２で説明した、触媒金属基板１０を所定温度θ２１に至るまで加熱し（図８のステップＳ２００）、所定温度θ２１のまま触媒金属基板１０を所定時間Ｔ２１にわたって保持した後（図８のステップＳ２１０）、所定温度θ２２に至るまで所定の降温速度Δθ２１で冷却する（図８のステップＳ２２０）という一連の触媒金属結晶粒作製工程を、複数回（例えば、３回など）にわたって実行するものである。このようにすることによって、触媒金属層に形成される結晶粒の平均粒径を増大させ、結晶方位をそろえることができる。 Step S300 is a process of forming catalyst metal crystal grains in the catalyst metal layer, and the specific process is as follows. The catalyst metal substrate 10 described in the second embodiment is heated to a predetermined temperature θ21 (see FIG. 8 (step S200), the catalyst metal substrate 10 is held at the predetermined temperature θ21 for a predetermined time T21 (step S210 in FIG. 8), and then cooled at a predetermined temperature decrease rate Δθ21 until the predetermined temperature θ22 is reached (step in FIG. 8). A series of catalytic metal crystal grain production steps S220) are performed a plurality of times (for example, three times). By doing in this way, the average particle diameter of the crystal grain formed in a catalyst metal layer can be increased, and a crystal orientation can be aligned.
図１０に、触媒金属結晶粒作製工程を３回にわたって実行し、より大きな結晶面が形成されたニッケル表面の観察像（図１０（ａ））を、触媒金属結晶粒作製工程を行う前の無定形状態の表面像（図１０（ｂ））と併せて示す。 FIG. 10 shows the observation image (FIG. 10A) of the nickel surface on which a larger crystal plane is formed by performing the catalytic metal crystal grain preparation process three times before the catalytic metal crystal grain preparation process. It is shown together with a surface image in a fixed state (FIG. 10B).
なお、複数回の触媒金属結晶粒作製工程それぞれの到達温度、及び保持時間は同じに限らず、また、触媒金属結晶粒作製工程とグラフェン及び炭素分子薄膜合成工程との到達温度、及び保持時間も同じに限らない。触媒金属結晶粒作製工程では、触媒金属原子が移動して再配列することが可能な程度の温度及び時間を適宜選択すればよく、グラフェン及び炭素分子薄膜合成工程ではグラフェン合成反応が進む温度及び時間を適宜選択すれば良い。降温速度も結晶粒の形成がより促進される降温速度であればよく、触媒金属種の特性等により適宜選択し、それぞれの工程で適宜独立に制御すればよい。 In addition, the arrival temperature and the holding time of each of the catalyst metal crystal grain preparation processes of the plurality of times are not limited to the same, and the arrival temperature and the holding time of the catalyst metal crystal grain preparation process and the graphene and carbon molecule thin film synthesis process are also the same. It is not limited to the same. In the catalyst metal crystal grain preparation step, a temperature and a time at which the catalyst metal atoms can be moved and rearranged may be appropriately selected. In the graphene and carbon molecular thin film synthesis step, the temperature and time at which the graphene synthesis reaction proceeds. May be selected as appropriate. The temperature lowering rate may be any temperature decreasing rate that promotes the formation of crystal grains, and may be appropriately selected depending on the characteristics of the catalyst metal species and the like, and may be appropriately controlled independently in each step.
また、本発明では、金属原子の移動が無くなるのに十分な温度まで一旦降温する触媒金属結晶粒作製工程を複数回行っており、このようにすることで、降温せず長時間高温のまま保持する場合と比較して、より効率よく触媒金属の結晶粒の粒径の増大を行っている。 Further, in the present invention, the catalyst metal crystal grain preparation process is performed a plurality of times, once the temperature is lowered to a temperature sufficient to eliminate the movement of metal atoms. By doing so, the temperature remains high for a long time without lowering the temperature. Compared with the case where it does, the crystal grain diameter of the catalyst metal is increased more efficiently.
続いて、実施の形態２で説明した図８のステップＳ２３０〜Ｓ２５０の処理と同様に、触媒金属基板１０を所定温度θ２３に至るまで加熱し（ステップＳ３１０）、触媒金属基板１０の温度を所定温度θ２３（例えば、９００℃など）に維持したまま、所定時間Ｔ２２（例えば、５分など）にわたってメタンガス（例えば１０ｓｃｃｍ）をアルゴンガスと水素ガスに追加して流した後（ステップＳ３２０）、密閉容器２２内のガスを排気した後、アルゴンガスと水素ガス雰囲気下で、所定の降温速度Δθ２４（例えば、−１２．５℃／ｍｉｎなど）のペースで所定温度θ２４（例えば、１００〜１５０℃など）に至るまで降温する（ステップＳ３３０）。このような処理を経ることにより、触媒金属層表面の結晶粒の結晶面上にグラフェン及び炭素分子薄膜を得ることができる。なお、密閉容器２２内のガスを排気せずに、メタンガス、アルゴンガス、水素ガスの雰囲気下で降温しても良い。 Subsequently, similar to the processing in steps S230 to S250 of FIG. 8 described in the second embodiment, the catalytic metal substrate 10 is heated to the predetermined temperature θ23 (step S310), and the temperature of the catalytic metal substrate 10 is set to the predetermined temperature. Methane gas (for example, 10 sccm) is added to the argon gas and hydrogen gas for a predetermined time T22 (for example, 5 minutes) while maintaining θ23 (for example, 900 ° C.) (step S320), and then the sealed container 22 After exhausting the gas in the atmosphere, the temperature is set to a predetermined temperature θ24 (for example, 100 to 150 ° C.) at a predetermined temperature decrease rate Δθ24 (for example, −12.5 ° C./min) in an atmosphere of argon gas and hydrogen gas. (Step S330). Through such treatment, graphene and a carbon molecular thin film can be obtained on the crystal plane of the crystal grains on the surface of the catalyst metal layer. The temperature may be lowered in an atmosphere of methane gas, argon gas, or hydrogen gas without exhausting the gas in the sealed container 22.
触媒金属結晶粒作製工程の回数を制御することにより、金属結晶粒の粒径を制御することも可能である。このように金属結晶粒の粒径を制御することで、グラフェン及び炭素分子薄膜の形状、層数の異なる均一結晶領域の大きさを容易に制御することができ、所望の大きさ、層数を有するグラフェン及び炭素分子薄膜を得ることができる。 It is also possible to control the particle size of the metal crystal grains by controlling the number of catalyst metal crystal grain production steps. By controlling the particle size of the metal crystal grains in this way, the shape of the graphene and the carbon molecular thin film and the size of the uniform crystal region with different number of layers can be easily controlled. It is possible to obtain the graphene and carbon molecular thin film.
［変形例］
なお、上述した実施の形態１〜３における触媒金属基板は、触媒金属を塗布しないで、触媒金属の自立基板を用いてもよい。また、炭素の原料となるメタンガスを流す工程では、段階的に複数の到達温度に制御し、そのある段階でメタンガスを流すようにしても良い。例えば、９５０℃まで一旦昇温し、所定の時間保持した後、９００℃まで降温し、所定の時間保持している間にメタンガスを流すという段階的な温度制御を行う工程でも良い。また、触媒金属基板を加熱するゾーンのさらに上流側に、炭素原料ガスが分解する温度まで加熱したゾーンを設けても良い。
[Modification]
In addition, the catalyst metal board | substrate in Embodiment 1-3 mentioned above may use the catalyst metal self-supporting board | substrate, without apply | coating a catalyst metal. Further, in the process of flowing methane gas as a carbon raw material, the temperature may be controlled to a plurality of temperatures in stages, and the methane gas may be flowed at a certain stage. For example, the temperature may be raised to 950 ° C., held for a predetermined time, then lowered to 900 ° C., and stepwise temperature control may be performed in which methane gas is allowed to flow while holding for a predetermined time. Further, a zone heated to a temperature at which the carbon source gas is decomposed may be provided further upstream of the zone for heating the catalytic metal substrate.
［実施の形態４］
実施の形態１〜３に係る合成法により合成されたグラフェン及び炭素分子薄膜を利用するに際し、次のように剥離して利用することもできる。
[Embodiment 4]
When using the graphene and the carbon molecular thin film synthesized by the synthesis method according to the first to third embodiments, they can be peeled and used as follows.
グラフェン及び炭素分子薄膜が合成された触媒金属基板を、酸の水溶液（例えば塩酸と水を１：３の割合で混合した希塩酸）中に浸漬させる。触媒金属を平滑基板に例えば３００ナノメートルの厚さで塗布した形態の場合は、浸漬後しばらくすると、グラフェン及び炭素分子薄膜が合成された触媒金属層が、平滑基板から脱離して水溶液面に浮いてくる。 The catalytic metal substrate on which the graphene and the carbon molecular thin film are synthesized is immersed in an acid aqueous solution (for example, dilute hydrochloric acid in which hydrochloric acid and water are mixed at a ratio of 1: 3). In the case where the catalyst metal is applied to a smooth substrate with a thickness of 300 nanometers, for example, after a while, the catalyst metal layer synthesized with graphene and the carbon molecular thin film is detached from the smooth substrate and floats on the aqueous solution surface. Come.
このように脱離して浮上した状態で、今度はグラフェン及び炭素分子薄膜を転写したい任意の基板（例えばガラス基板）を、酸の水溶液中に入れ、グラフェン及び炭素分子薄膜が合成された触媒金属層の下に配置する。やがて触媒金属が酸によりエッチングされ、グラフェン及び炭素分子薄膜の層のみ、酸の水溶液面に浮かんだ状態となる。酸の水溶液を吸引して取り出し、代わりに水を入れることを繰り返すことで、酸の成分を洗い流すことができる。 In such a state where the graphene and the carbon molecular thin film are separated and then floated, an arbitrary substrate (for example, a glass substrate) to which the graphene and the carbon molecular thin film are transferred is placed in an acid aqueous solution, and the catalyst metal layer in which the graphene and the carbon molecular thin film are synthesized. Place below. Eventually, the catalytic metal is etched by the acid, and only the graphene and carbon molecular thin film layers float on the acid aqueous solution surface. The acid component can be washed away by repeatedly taking out the aqueous solution of the acid by suction and adding water instead.
このように酸成分を洗い流して十分中性になったところで、水を吸引して取り出し、グラフェン及び炭素分子薄膜を上記任意の基板上に着地させ、乾燥させる。このようにすることで、触媒金属からグラフェン及び炭素分子薄膜を剥離して利用することが可能になる。水溶液を入れる容器の大きさを、転写したい任意の基板と合わせることにより、放置しておけば、水が蒸発してそのまま転写が完了するようにすることもできる。 When the acid component is washed away and becomes sufficiently neutral as described above, water is sucked out and the graphene and the carbon molecular thin film are landed on the arbitrary substrate and dried. By doing in this way, it becomes possible to peel and utilize a graphene and a carbon molecule thin film from a catalyst metal. By matching the size of the container containing the aqueous solution with an arbitrary substrate to be transferred, if left unattended, water can be evaporated and transfer can be completed as it is.
以上に説明した本発明に係るグラフェン及び炭素分子薄膜の製造方法によれば、一般的な金属塗布法によって作製でき、入手が容易な無定形状態の触媒金属を用いて簡便な手法により、触媒金属層の結晶粒の大きさを制御し、その結晶面上に広い均一領域を有する質の良いグラフェン及び炭素分子薄膜を、低コストにて合成することができる。 According to the method for producing graphene and carbon molecular thin film according to the present invention described above, a catalyst metal can be produced by a simple method using a catalyst metal in an amorphous state that can be prepared by a general metal coating method and is easily available. By controlling the size of the crystal grains of the layer, high-quality graphene and carbon molecular thin films having a wide uniform region on the crystal plane can be synthesized at a low cost.
なお、本発明は以上に説明した実施の形態に限定されるものではなく、本発明の技術的思想内で、当分野において通常の知識を有する者により、多くの変形及び組み合わせが実施可能であることは明白である。 The present invention is not limited to the embodiment described above, and many variations and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.
本発明は、グラフェン及び炭素分子薄膜の製造業に利用可能である。 The present invention can be used in the manufacturing industry of graphene and carbon molecular thin films.
１０…触媒金属基板、２０…電気炉、２２…密閉容器、２４…ヒータ。 DESCRIPTION OF SYMBOLS 10 ... Catalytic metal substrate, 20 ... Electric furnace, 22 ... Sealed container, 24 ... Heater.
Claims (5)
第１工程は、
不活性ガスと水素ガス雰囲気下で触媒金属を加熱し、第１の所定温度まで昇温する工程と、
昇温後、前記第１の所定温度のまま、第１の所定時間にわたって保持する工程と、
前記触媒金属が再配列する温度範囲を含む範囲で一定となる第１の所定降温速度で降温する工程と
を含み、
第２工程は、
不活性ガスと水素ガス雰囲気下で触媒金属を加熱し、第２の所定温度まで昇温する工程と、
前記第２の所定温度まで昇温後、第２の所定時間にわたって炭素原料ガスを更に供給する工程と、
前記第２の所定温度から、触媒金属が再配列する温度範囲を含む範囲で一定となる第２の所定降温速度で降温する工程と
を含み、
前記第１及び前記第２の所定温度、および前記第１及び前記第２の所定降温速度を制御することにより、前記触媒金属の多結晶面を作製して、当該多結晶面の各結晶粒の平均粒径を増大させるとともに、各結晶粒の結晶方位を揃える方向に制御して、当該多結晶面上にグラフェン及び炭素分子薄膜を合成する
ことを特徴とするグラフェン及び炭素分子薄膜の合成方法。 It consists of a first step of producing catalyst metal crystal grains and a second step of synthesizing graphene and a carbon molecular thin film,
The first step is
Heating the catalyst metal under an inert gas and hydrogen gas atmosphere to raise the temperature to a first predetermined temperature;
Holding the first predetermined temperature for a first predetermined time after the temperature rise;
Lowering the temperature at a first predetermined temperature-decreasing rate that is constant in a range including a temperature range in which the catalytic metal is rearranged .
The second step is
Heating the catalyst metal under an inert gas and hydrogen gas atmosphere to raise the temperature to a second predetermined temperature;
A step of further supplying a carbon source gas over a second predetermined time after raising the temperature to the second predetermined temperature;
From the second predetermined temperature, see contains a step of cooling at a second predetermined descending rate of temperature becomes constant in a range including the temperature range in which the catalytic metal is rearranged,
By controlling the first and second predetermined temperatures and the first and second predetermined temperature-decreasing rates, a polycrystalline plane of the catalyst metal is produced, and each crystal grain of the polycrystalline plane is formed. A method of synthesizing graphene and a carbon molecular thin film , wherein the graphene and the carbon molecular thin film are synthesized on the polycrystal surface by increasing the average grain size and controlling the crystal grains in a direction in which the crystal orientations are aligned .
前記第２の所定温度まで昇温後、前記第２の所定温度に保持して、前記第２の所定時間にわたって炭素原料ガスを更に供給する工程と、
前記炭素原料ガスを排気して、不活性ガスと水素ガス雰囲気下で、前記第２の所定降温速度で降温する工程と
を含むことを特徴とする請求項１に記載のグラフェン及び炭素分子薄膜の合成方法。 In the second step,
Maintaining the second predetermined temperature after raising the temperature to the second predetermined temperature, and further supplying a carbon source gas over the second predetermined time;
And exhausting the carbon source gas, an inert gas and hydrogen gas atmosphere, a step of cooling by the second predetermined descending rate of temperature
The method for synthesizing graphene and carbon molecular thin film according to claim 1, comprising :
昇温後、所定の時間にわたって炭素原料ガスを更に供給する工程と、
前記所定温度から、前記触媒金属が再配列する温度範囲を含む範囲で一定となる降温速度で降温する工程と
を含み、
前記所定温度および前記所定の降温速度を制御することにより、前記触媒金属の多結晶面を作製して、当該多結晶面の各結晶粒の平均粒径を増大させるとともに、各結晶粒の結晶方位を揃える方向に制御して、当該多結晶面上にグラフェン及び炭素分子薄膜を合成する
ことを特徴とするグラフェン及び炭素分子薄膜の合成方法。 Heating the catalyst metal in an inert gas and hydrogen gas atmosphere and raising the temperature to a predetermined temperature;
A step of further supplying a carbon source gas over a predetermined time after the temperature rise;
A step of lowering the temperature from the predetermined temperature at a constant temperature lowering rate within a range including a temperature range in which the catalytic metal is rearranged .
By controlling the predetermined temperature and the predetermined temperature-decreasing rate, a polycrystalline surface of the catalytic metal is produced, and the average grain size of each crystal grain of the polycrystalline surface is increased, and the crystal orientation of each crystal grain The graphene and carbon molecular thin films are synthesized on the polycrystalline surface.
A method for synthesizing graphene and a carbon molecular thin film.
前記炭素原料ガスを排気して、不活性ガスおよび水素ガス雰囲気下で、前記所定の降温速度で降温する工程と
を含むことを特徴とする請求項４に記載のグラフェン及び炭素分子薄膜の合成方法。 Maintaining the predetermined temperature after the temperature rise, and further supplying a carbon source gas over the predetermined time;
Exhausting the carbon source gas and lowering the temperature at the predetermined temperature lowering rate in an inert gas and hydrogen gas atmosphere; and
The method for synthesizing graphene and carbon molecular thin film according to claim 4 , comprising :
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