JP5218958B2 - Carbon nanotube synthesis using quasicrystalline catalyst - Google Patents
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- 239000002041 carbon nanotube Substances 0.000 title claims description 52
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims description 31
- 229910021393 carbon nanotube Inorganic materials 0.000 title claims description 29
- 239000003054 catalyst Substances 0.000 title claims description 20
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- 238000005229 chemical vapour deposition Methods 0.000 claims description 9
- 239000010949 copper Substances 0.000 claims description 9
- 230000002194 synthesizing effect Effects 0.000 claims description 8
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- 229910052707 ruthenium Inorganic materials 0.000 claims description 7
- 229910052742 iron Inorganic materials 0.000 claims description 6
- 229910052751 metal Inorganic materials 0.000 claims description 6
- 239000002184 metal Substances 0.000 claims description 6
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 5
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 claims description 5
- 229910052782 aluminium Inorganic materials 0.000 claims description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 5
- SYQBFIAQOQZEGI-UHFFFAOYSA-N osmium atom Chemical compound [Os] SYQBFIAQOQZEGI-UHFFFAOYSA-N 0.000 claims description 5
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- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
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Description
本発明は、所定の電子的性質を有するカーボンナノチューブ（ＣＮＴ）の選択的合成法に関わり、具体的には金属的特性を有するＣＮＴ、特にアームチェア型ＣＮＴを、基板上に選択的に合成するために用いる合金触媒種に関わる。 The present invention relates to a method for selectively synthesizing carbon nanotubes (CNT) having predetermined electronic properties, and specifically, CNTs having metallic characteristics, particularly armchair CNTs, are selectively synthesized on a substrate. It relates to the alloy catalyst species used for this purpose.
ＣＮＴを薄型平面ディスプレイや大規模集積回路など、電子デバイス分野に応用する試みが国内および海外で活発に行われている。このようなＣＮＴの電子デバイスへの応用に際しては、ガラスやシリコン等の基板上に、所定の特性を有するＣＮＴを所定の場所に所定の長さだけ合成する方法が必須である。ＣＮＴの代表的応用例として、電界放出型表示装置(Field Emission Display：ＦＥＤ)用陰極、次世代大規模集積回路(Large Scale
Integration：ＬＳＩ)用層間配線材、走査トンネル顕微鏡／原子間力顕微鏡用探針、Micro Electro
Mechanical Systems (ＭＥＭＳ)デバイス、リチウムイオン電池用負極材、燃料電池、塗料用導電性フィラー等がある。
Attempts to apply CNTs to the field of electronic devices such as thin flat displays and large-scale integrated circuits have been actively conducted in Japan and overseas. When such CNTs are applied to electronic devices, a method of synthesizing CNTs having predetermined characteristics on a substrate such as glass or silicon in a predetermined place for a predetermined length is essential. Typical applications of CNT include cathodes for field emission display (FED), next generation large scale integrated circuits (Large Scale)
Integration: Interlayer wiring materials for LSI), scanning tunneling microscope / atomic force microscope probe, Micro Electro
There are mechanical systems (MEMS) devices, anode materials for lithium ion batteries, fuel cells, conductive fillers for paints, and the like.
現在、ＣＮＴ合成法には、アーク放電法、レーザーアブレーション法、触媒を用いた化学気相成長(Chemical Vapor Deposition：ＣＶＤ)法、の何れかが使われている。しかし、一般にデバイス用途に応じて最適なＣＮＴの仕様は異なり、したがってＣＮＴのデバイス特性を支配する、a) 直径、b) 長さ、c) カイラリティ(螺旋度)の、３要素を制御したＣＮＴ合成法を確立することが要求される。 Currently, any one of an arc discharge method, a laser ablation method, and a chemical vapor deposition (CVD) method using a catalyst is used for the CNT synthesis method. However, in general, the optimal CNT specifications differ depending on the device application, and therefore CNT synthesis is controlled by three elements: a) diameter, b) length, and c) chirality (helicality), which govern the device characteristics of CNT. It is required to establish a law.
現在、ＣＮＴの直径に関しては、用いる触媒金属微粒子の直径や反応炉内温度を制御することにより、人為的に直径分布を制御することが可能である。長さに関しても、ＣＮＴの成長速度を制御することで、長さ分布を制御することが可能である。しかし、ＣＮＴが金属的であるか半導体的であるかという電子的特性の最も支配的な要因であるカイラリティについては、その制御を試みたいくつかの報告がなされているのみであり、一般にその制御は困難であることが知られている。 At present, regarding the diameter of the CNT, it is possible to artificially control the diameter distribution by controlling the diameter of the catalyst metal fine particles to be used and the temperature in the reaction furnace. Regarding the length, it is possible to control the length distribution by controlling the growth rate of the CNTs. However, regarding the chirality, which is the most dominant factor in the electronic properties of whether CNTs are metallic or semiconducting, there are only a few reports that have attempted to control them. Is known to be difficult.
ＣＮＴ構造を示すカイラリティは、カイラルベクトル
C = n a1
+ m a2 の指数 (n, m) で表され、(n, n) をアームチェア型、 (n, 0) をジグザグ型、それ以外の (n, m) をカイラル型の、３種類に分類されている。ここで、a1, a2はグラフェンシートの単位格子ベクトルを表している。また、それぞれのカイラリティに応じて、金属的または半導体的性質を示すことが、理論的にも実験的にも証明されている (非特許文献１)。
The chirality indicating the CNT structure is a chiral vector
C = na 1
+ Ma 2 index (n, m), (n, n) is an armchair type, (n, 0) is a zigzag type, and other (n, m) is a chiral type. Has been. Here, a 1 and a 2 represent unit cell vectors of the graphene sheet. In addition, it has been proved theoretically and experimentally that it exhibits metallic or semiconducting properties depending on the chirality (Non-patent Document 1).
現在のところ、ジグザク型ＣＮＴの合成に関しては、楠らによるSiC表面分解法により２層ないし３層のジグザグ型ＣＮＴが、SiC単結晶基板上に選択的に形成されると報告されている (非特許文献２)。しかし、ジグザグ型ＣＮＴは、その３分の１が金属的、３分の２が半導体的であるので、所定の電子的特性を有するＣＮＴを得ることは困難であり、また、ガラスやシリコン等の任意の基板上に形成することは不可能である。さらにロジウム／パラジウム合金触媒を用いたレーザーアブレーション法(非特許文献３)や白金触媒を用いたアルコール触媒ＣＶＤ法によるＣＮＴのカイラリティ選択性が議論されている(非特許文献４)が、いずれもカイラル型について述べられており、ジグザグ型と同様にその３分の１が金属的、３分の２が半導体的であり、その特性制御には至っていない。 At present, regarding the synthesis of zigzag CNTs, it has been reported that 2 to 3 zigzag CNTs are selectively formed on a SiC single crystal substrate by the SiC surface decomposition method (1). Patent Document 2). However, zigzag CNTs are one-third metallic and two-third semiconducting, making it difficult to obtain CNTs with predetermined electronic properties, such as glass and silicon. It is impossible to form on an arbitrary substrate. Furthermore, the chirality selectivity of CNTs by the laser ablation method using a rhodium / palladium alloy catalyst (Non-patent Document 3) and the alcohol-catalyzed CVD method using a platinum catalyst has been discussed (Non-Patent Document 4). As with the zigzag type, one third is metallic and two third is semiconducting, and its characteristic control has not been achieved.
上述のようにＣＮＴを基板上に直接合成する触媒ＣＶＤ法で、ＣＮＴのカイラリティを制御すること、特に金属的性質を示すアームチェア型ＣＮＴを選択的に合成することは極めて困難である。そこで、本発明の目的は、ガラスやシリコン基板上に、電界放出用陰極材およびＬＳＩ用層間配線材などの用途として最適な金属的性質を有する、アームチェア型（本発明では金属的性質を有するニアアームチェア型を含める）ＣＮＴを選択的に合成する方法を提供することにある。 As described above, it is extremely difficult to control the chirality of CNTs, particularly to selectively synthesize armchair CNTs exhibiting metallic properties, by the catalytic CVD method in which CNTs are directly synthesized on the substrate. Therefore, an object of the present invention is to provide an armchair type (which has metallic properties in the present invention) having optimum metallic properties for applications such as field emission cathode materials and LSI interlayer wiring materials on a glass or silicon substrate. It is to provide a method for selectively synthesizing CNTs (including a near armchair type).
本発明者らは上記の課題を解決するため、準結晶組成を有するアルミニウム合金微粒子を触媒として用いる触媒ＣＶＤ法を考案し、本発明に至った。 In order to solve the above-mentioned problems, the present inventors have devised a catalytic CVD method using aluminum alloy fine particles having a quasicrystalline composition as a catalyst, and have reached the present invention.
本発明は、前記触媒用合金が、５回対称性を有する正２０面体構造の準結晶組成から成る、アルミニウムと銅及び、鉄、ルテニウム、オスミウムの３種のうち何れか１種からなる金属を構成成分とする３元アルミニウム合金である。ここで、準結晶組成を有するアルミニウム合金としては、Al 62 Cu 25.5 TM 12.5 (TM=Fe, Ru, Os), Al70Pd20TM10
(TM=V, Cr, Mn, Fe,Co, Mo, Ru, W, Re, Os) の何れを選択してもよいが、Al 62 Cu 25.5 TM 12.5 が、実用的には最も望ましい。５回対称性を有する正２０面体構造の準結晶合金を触媒とする目的は、準結晶合金微粒子がＣＮＴキャップ部の５員環合成のシーズとして作用し、アームチェア型ＣＮＴの合成を優先的に促進する効果をもたらすためである。
In the present invention, the catalyst alloy comprises a metal composed of any one of three types of aluminum, copper, iron, ruthenium, and osmium, having a quasicrystalline composition having a icosahedral structure having fivefold symmetry. It is a ternary aluminum alloy as a constituent component. Here, as an aluminum alloy having a quasicrystalline composition, Al 62 Cu 25.5 TM 12.5 (TM = Fe, Ru, Os), Al 70 Pd 20 TM 10
Any of (TM = V, Cr, Mn, Fe, Co, Mo, Ru, W, Re, Os) may be selected, but Al 62 Cu 25.5 TM 12.5 is most preferable in practical use. The purpose of catalyzing the icosahedral quasicrystal alloy with 5-fold symmetry is that the quasicrystalline alloy particles act as seeds for the 5-membered ring synthesis of the CNT cap part, giving priority to synthesis of armchair CNTs This is to bring about a promoting effect.
すなわち本発明は、ＣＮＴ合成時に触媒として作用する金属種として準結晶組成から成るアルミニウム合金薄膜を基板上に堆積し、それを熱処理することにより正２０面体構造の準結晶相を有する合金微粒子を形成して、その合金微粒子を触媒として用いる触媒ＣＶＤ法により、アームチェア型ＣＮＴを選択的に基板上に合成する方法である。 That is, according to the present invention, an aluminum alloy thin film having a quasicrystalline composition is deposited on a substrate as a metal species that acts as a catalyst at the time of CNT synthesis, and alloy fine particles having a quasicrystalline phase having a icosahedral structure are formed by heat treatment. Then, the armchair type CNT is selectively synthesized on the substrate by the catalytic CVD method using the alloy fine particles as a catalyst.
アルミニウム合金薄膜を得るには、予め準結晶組成のアルミニウム合金ターゲットを作製し、それを蒸着源として基板上に蒸着するか、又は、それぞれの単体金属を蒸着源として順次蒸着した後に、熱処理を加えて合金化してもよい。 In order to obtain an aluminum alloy thin film, an aluminum alloy target having a quasicrystalline composition is prepared in advance and vapor-deposited on a substrate as a vapor deposition source, or after each single metal is vapor-deposited sequentially as a vapor deposition source, heat treatment is applied. And may be alloyed.
また、基板上に準結晶合金薄膜を予めリソグラフィー法を用いてパターニングしておくことにより、基板上の所定の位置に、触媒ＣＶＤ法により、アームチェア型ＣＮＴを選択的に基板上に合成することが出来る。 Further, by patterning a quasicrystalline alloy thin film on the substrate in advance using a lithography method, an armchair CNT can be selectively synthesized on the substrate by a catalytic CVD method at a predetermined position on the substrate. I can do it.
本発明により、ガラスやシリコン基板上の所定の場所に、優れた金属的特性を有するアームチェア型から成るＣＮＴを選択的に合成することを可能にして、該ＣＮＴを応用したＦＥＤ用陰極、次世代ＬＳＩ用層間配線材等の電子的特性を向上させ、再現性の良い優れたデバイス特性を得ることが期待できる。 According to the present invention, it is possible to selectively synthesize an CNT made of an armchair type having excellent metallic characteristics at a predetermined place on a glass or silicon substrate, and to apply an FED cathode using the CNT, It can be expected to improve electronic characteristics of interlayer wiring materials for generation LSIs and to obtain excellent device characteristics with good reproducibility.
以下に本発明の実施形態を具体的に説明する。
ＣＮＴを直接合成させる基板としては、一般に平滑なガラス基板やシリコン単結晶を用いることが好ましい。
Embodiments of the present invention will be specifically described below.
As a substrate for directly synthesizing CNTs, it is generally preferable to use a smooth glass substrate or a silicon single crystal.
次に、上記基板上にSiO2やAl2O3等を、電子ビーム蒸着法やスパッタリング法等によってその膜厚が5 nm〜500 nmとなるように堆積し、下地層を形成する。この目的は、次工程で堆積する準結晶合金薄膜と基板とのアロイ化反応を防止するためである。 Next, SiO 2 , Al 2 O 3 or the like is deposited on the substrate by an electron beam evaporation method, a sputtering method, or the like so as to have a film thickness of 5 nm to 500 nm, thereby forming a base layer. The purpose is to prevent an alloying reaction between the quasicrystalline alloy thin film deposited in the next step and the substrate.
次工程として、正２０面体構造の準結晶組成比から成る、アルミニウムに銅及び、鉄、ルテニウム、オスミウムの何れか１種からなる金属を添加したアルミニウム３元合金薄膜を、電子ビーム蒸着法やスパッタリング法等により、その膜厚が1 nm〜100 nmとなるように堆積する。 As the next step, an aluminum ternary alloy thin film composed of a quasicrystal composition ratio of an icosahedral structure and made by adding copper and a metal of any one of iron, ruthenium, and osmium to an electron beam evaporation method or sputtering. It deposits so that the film thickness may become 1 nm-100 nm by a method etc.
次に、上記基板を350〜550℃で熱処理し、堆積した合金薄膜を、安定な準結晶相から成る微粒子構造に変える。合金薄膜を微粒子化する目的は、準結晶合金に触媒活性を付与するためと、次工程で合成されるＣＮＴの直径分布を触媒微粒子の直径により制御するためである。 Next, the substrate is heat treated at 350 to 550 ° C., and the deposited alloy thin film is changed to a fine particle structure composed of a stable quasicrystalline phase. The purpose of making the alloy thin film fine is to impart catalytic activity to the quasicrystalline alloy and to control the diameter distribution of the CNT synthesized in the next step by the diameter of the catalyst fine particles.
以上のように、安定な準結晶相から成る合金微粒子を形成した基板上に、ＣＮＴを合成する。ＣＮＴの合成方法として、一般にアーク放電法、レーザーアブレーション法、触媒ＣＶＤ法等が用いられ、本発明においては基板上に直接合成できる触媒ＣＶＤ法が最適である。触媒ＣＶＤ法として、熱ＣＶＤ法、光ＣＶＤ法、プラズマＣＶＤ法等が用いられるが、本発明においては結晶性の比較的優れたＣＮＴの得られる熱ＣＶＤ法が最適である。 As described above, CNTs are synthesized on the substrate on which alloy fine particles composed of a stable quasicrystalline phase are formed. Generally, an arc discharge method, a laser ablation method, a catalytic CVD method or the like is used as a CNT synthesis method. In the present invention, a catalytic CVD method that can be directly synthesized on a substrate is optimal. As the catalytic CVD method, a thermal CVD method, a photo CVD method, a plasma CVD method, or the like is used. In the present invention, a thermal CVD method capable of obtaining a CNT having relatively excellent crystallinity is optimal.
以下に本発明の好適な一実施の形態を実施例によって説明するが、本発明の技術的範囲は下記の実施形態によって限定されるものでなく、その要旨を変更することなく様々に改変して実施することができる。 Preferred embodiments of the present invention will be described below by way of examples. However, the technical scope of the present invention is not limited by the following embodiments, and various modifications can be made without changing the gist thereof. Can be implemented.
１）基板として10 mm×10 mm×0.5 mmtの形状のシリコン単結晶
(100) ウェーハを用いた。
２）上記基板上に、下地膜としてSiO2をスパッタリング法により、Ar 圧力 4.2×10-1 Pa、放電電力 300 Wの条件下で膜厚 50 nmの薄膜を堆積した。
３）次に、上記SiO2下地膜を付けた基板上に、完全な準結晶組成比になるようにAl (2.1 nm)/ Cu (0.6 nm)/Fe (0.3
nm)を、それぞれの膜厚を±0.01
nmの精度で、順々に電子ビーム蒸着法により、全膜厚3
nmの積層薄膜を堆積した。
４）次に、触媒活性工程として、ＣＮＴ合成に用いる反応炉内で、温度
450℃、時間 30分、Ar雰囲気の条件下で熱処理を施した。この熱処理で、正２０面体構造の準結晶組成から成るAl62Cu25.5Fe12.5合金微粒子を形成させた。
1) 10 mm x 10 mm x 0.5 mm t- shaped silicon single crystal as substrate
(100) A wafer was used.
2) A thin film having a thickness of 50 nm was deposited on the above substrate by sputtering using SiO 2 as an underlying film under the conditions of Ar pressure 4.2 × 10 −1 Pa and discharge power 300 W.
3) Next, Al (2.1 nm) / Cu (0.6 nm) / Fe (0.3 (0.3 nm)) is formed on the substrate with the SiO 2 base film so as to obtain a complete quasicrystalline composition ratio.
nm) for each film thickness ± 0.01
Thickness of 3 nm by electron beam evaporation in order with accuracy of nm
A laminated thin film of nm was deposited.
4) Next, in the reactor used for CNT synthesis as a catalyst activation step, the temperature
Heat treatment was performed at 450 ° C. for 30 minutes under Ar atmosphere. By this heat treatment, Al 62 Cu 25.5 Fe 12.5 alloy fine particles having a quasicrystalline composition having a regular icosahedron structure were formed.
ＣＮＴの合成方法としてアルコール触媒ＣＶＤ法を用い、温度 700℃、保持時間 5分、供給ガス C2H5OH、流量
200 sccm、圧力 5.3×103 Pa の条件下でＣＮＴを合成した。
Alcohol-catalyzed CVD is used as the synthesis method of CNT, temperature is 700 ° C, holding time is 5 minutes, supply gas C 2 H 5 OH, flow
CNTs were synthesized under the conditions of 200 sccm and pressure 5.3 × 10 3 Pa.
上記の条件で合成したＣＮＴは、基板上に垂直方向に配列した、長さL =〜2.6 μmのＣＮＴ膜が得られた。Si/SiO2基板上に垂直方向に配列して合成したＣＮＴ膜の断面走査電子顕微鏡像を図１に示す。また、層数は単層〜３層、直径
1 nm〜5 nmに広く分布を持ったＣＮＴが得られた。合成したＣＮＴ膜から採取したＣＮＴバンドルの高分解能透過電子顕微鏡像を図２に示す。
The CNT synthesized under the above conditions yielded a CNT film having a length L = ˜2.6 μm arranged in the vertical direction on the substrate. FIG. 1 shows a cross-sectional scanning electron microscope image of a CNT film synthesized by arranging in a vertical direction on a Si / SiO 2 substrate. Also, the number of layers is single to 3 layers, diameter
CNTs with a wide distribution from 1 nm to 5 nm were obtained. A high-resolution transmission electron microscope image of the CNT bundle collected from the synthesized CNT film is shown in FIG.
現在、カイラリティの指数付けに関しては、共鳴ラマン散乱(Resonance
Raman Scattering:ＲＲＳ)法、蛍光分光法、走査トンネル顕微鏡法等が用いられる。本発明においては、金属的および半導体的性質を有する、合成したすべてのＣＮＴのカイラリティ分布を判定するために、基板上に合成したＣＮＴを直接測定可能なＲＲＳ法が最適である（非特許文献５）。
Currently, regarding the indexing of chirality, resonance Raman scattering (Resonance
Raman Scattering (RRS) method, fluorescence spectroscopy, scanning tunneling microscopy, etc. are used. In the present invention, in order to determine the chirality distribution of all synthesized CNTs having metallic and semiconducting properties, the RRS method capable of directly measuring the synthesized CNTs on the substrate is optimal (Non-Patent Document 5). ).
次に、ＲＲＳ法により、上記の条件で合成したＣＮＴのラジアルブリージングモードのラマンスペクトルと、そのカイラリティを指数付けした結果を図３に示す。比較のために、アルコール触媒ＣＶＤ法で一般に触媒として用いられる下地層Al (2 nm)/触媒層Co (1 nm)により合成したＣＮＴ膜について、同様にそのカイラリティを指数付けした結果を図４に示す。ここで測定条件は、He-Neレーザーによる励起波長 632.8 nm、出力 0.06 mW、レーザービーム径 〜1 μmφとした。 Next, FIG. 3 shows the result of indexing the Raman spectrum of the radial breathing mode of CNT synthesized under the above conditions and its chirality by the RRS method. For comparison, FIG. 4 shows the result of indexing the chirality of a CNT film synthesized with an underlayer Al (2 nm) / catalyst layer Co (1 nm) generally used as a catalyst in an alcohol catalyst CVD method. Show. The measurement conditions here were an excitation wavelength of 632.8 nm with a He-Ne laser, an output of 0.06 mW, and a laser beam diameter of 1 μmφ.
図３より、本発明における準結晶を触媒とした場合、金属的なナノチューブが分布の８０％を超えており、中でも金属的なEM 11遷移エネルギーを有する(9, 9), (10, 10),
(11, 11)等のアームチェア型、および(11,
8), (12, 9)等のニアアームチェア型のカイラリティが極めて選択的に得られた。これに対して、図４より、通常用いられる遷移金属の一種であるコバルトを触媒とした場合、全体の３分の１が金属的、３分の２が半導体的なランダムなカイラリティ分布を示しており、特に金属的なEM 11遷移エネルギーを有するスペクトルの中にアームチェア型は全く検出されず、逆に(18, 0)のジグザク型や(12, 1)等のニアジグザク型が得られた。これらの実験事実より、本発明の有効性が実証された。
From FIG. 3, when the quasicrystal in the present invention is used as a catalyst, the metallic nanotubes exceed 80% of the distribution, and among them, (9, 9), (10, 10) having metallic E M 11 transition energy. ),
Armchair type such as (11, 11), and (11,
Near armchair-type chirality such as 8), (12, 9) was obtained very selectively. On the other hand, FIG. 4 shows that when cobalt, which is a kind of transition metal that is normally used, is used as a catalyst, one-third of the total is metallic and two-thirds is a semiconductor-like random chirality distribution. In particular, no armchair type was detected in the spectrum having metallic E M 11 transition energy, and a zigzag type of (18, 0) or a near zigzag type of (12, 1) was obtained. . These experimental facts proved the effectiveness of the present invention.
Claims (4)
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