JP3652313B2 - Method for producing vapor grown carbon fiber - Google Patents
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【０００１】
【産業上の利用分野】
本発明は、気相成長炭素繊維の製造方法、特に生産技術上、より容易な工程を用い、かつ大量生産可能な気相成長炭素繊維の製造方法を提供するものである。
【０００２】
【従来の技術】
従来、炭素原子６０個から構成され、サッカーボール状の構造をもつＣ６０の大量合成法が報告（Ｋｒａｔｓｃｈｍｅｒ，ｅｔ．ａｌ．：Ｎａｔｕｒｅ ３４７（１９９０）３５４）されて以来、炭素のクラスターであるフラーレンの一族や、これを一方向に引き伸ばした構造を持つカーボンナノチューブの様々な性質に興味がもたれ、数多くの研究が行われている。
【０００３】
とりわけ、アルカリ金属原子をドープしたＣ６０の結晶が高い臨界温度をもつ超伝導性を示すことは注目を集めた。このほかにも、これら炭素クラスターは新規な電子素子や、固体潤滑材などとしての応用が期待されており、様々な観点からの応用を目指して、旺盛な研究が進められている。
【０００４】
気相成長炭素繊維は、カーボンナノチューブよりやや大きなクラスターであるが、炭化水素樹脂繊維を高温で炭化した炭素繊維と比較して、良好な結晶性をもち、特徴ある用途が期待されている。
【０００５】
現在、この気相成長炭素繊維を製造する代表的な方法はベンゼンの熱分解による気相成長法である。この方法は、酸化鉄などの鉄化合物を基板とし、９５０〜１０００℃程度で、高純度の水素をキャリアガスとしたベンゼンの蒸気に接触させる。まず、基板の一部が還元されＦｅ微粒子を形成する。この微粒子表面の触媒能により、表面に炭素が析出しはじめる。この炭素がＦｅ微粒子の後方に繊維状に成長し、微粒子を持ち上げながら成長を続ける。
【０００６】
この方法では、Ｆｅ微粒子の存在が不可欠であり、また金属Ｆｅ微粒子を基板に噴霧したものを用いる方法も行われている。（稲垣道夫：「炭素材料工学」７２頁、日刊工業新聞社発行 １９８５年）
【０００７】
【発明が解決しようとする課題】
上記の方法は、工業的に利用可能ではあるが、いくつかの問題点がある。第１に、工程中に、１０００℃程度の高温のプロセスが必要であり、装置が大掛かりになり、電力の消費が大きいなどコスト上昇を招く恐れがある。第２に、高純度の水素を用いるため、爆発事故防止の対策が必要となる。とりわけ上記の高温のプロセスに用いることから、特に厳重な対策が求められ、これもコスト上昇の要因となる恐れがある。
【０００８】
また、基板にＦｅの微粒子を噴霧したものを用いる方法は、収量も多くすることが可能で、工業的には好ましいが、金属Ｆｅの微粒子は反応性が高く、大気中で扱うことは出来ない。また、粉塵爆発の危険も無視できず、やはり対策が必要である。
【０００９】
一方、気相成長法には、ＣＯを熱分解する方法もあるが、ＣＯは爆発性のほかに、極めて強い毒性があり、許容濃度は５０ｐｐｍと非常に厳しいものであって、安全対策がコスト上昇要因になることは明白である。
【００１０】
したがった、工業的生産に適し、低温のプロセスで、安全対策が容易で、大気中で扱えるプロセスによって構成された気相成長炭素繊維の製造方法が求められている。
【００１１】
本発明は、これらの問題点を解決する新規の製造方法を検討した結果到達したものであり、炭化水素ガスの熱分解によって炭素を気相成長することにより、工業的生産に適用可能で、高温のプロセスや、特別な安全対策など困難なプロセスを必要としない気相成長炭素繊維の製造方法を提供することを目的とするものである。
【００１２】
【課題を解決するための手段】
即ち、本発明は、Ｐｄ微粒子を分散してなる基板を不活性ガスで希釈したＣ2Ｈ4ガスに曝露して熱処理し、該Ｃ2Ｈ4ガスの熱分解を行う工程を有する気相成長炭素繊維の製造方法において、前記不活性ガスで希釈したＣ2Ｈ4の濃度が２．７ｖｏｌ％未満であることを特徴とする気相成長炭素繊維の製造方法である。
【００１３】
また、本発明は、基体上のＰｄＯを不活性ガスで希釈した還元性ガスで熱処理することによりＰｄ微粒子を分散してなる基板を形成する工程と、前記Ｐｄ微粒子を分散してなる基板を不活性ガスで希釈したＣ2Ｈ4ガスに曝露して熱処理し、該Ｃ2Ｈ4ガスの熱分解を行う工程とを有する気相成長炭素繊維の製造方法において、前記不活性ガスで希釈したＣ2Ｈ4の濃度が２．７ｖｏｌ％未満であることを特徴とする気相成長炭素繊維の製造方法である。
【００１４】
本発明において、前記不活性ガスで希釈したＣ2Ｈ4の濃度が０．１ｖｏｌ％以上２．７ｖｏｌ％未満であることが好ましい。
前記不活性ガスが窒素ガス、ヘリウムガスおよびアルゴンガスから選ばれる少なくとも１種であることが好ましい。
前記Ｃ2Ｈ4ガスの熱分解工程の熱処理温度が４５０℃以上であることが好ましい。
前記Ｃ2Ｈ4ガスの熱分解工程の熱処理温度が５００〜９００℃であることが好ましい。
【００１５】
【発明の実施の形態】
以下、本発明を詳細に説明する。
本発明は、Ｃ2Ｈ4ガスの熱分解によって気相成長炭素繊維を得る方法である。Ｃ2Ｈ4ガスは可燃性であるが、不活性ガスで希釈することにより安全に取り扱うことが出来、特別な防爆設備を必要としない。また、毒性は、ガス種により異なるが、普通深刻な危険性はなく、希釈された状態では、酸欠防止のため十分な換気を行うことで十分である。
【００１６】
基板としては、耐熱性の基体上に触媒微粒子を分散してなる基板を用いる。触媒微粒子としては、金属Ｐｄ微粒子を分散配置したものが好ましい。Ｐｄ表面は、Ｃ2Ｈ4の分解反応に顕著な触媒能を有し、低温での反応が可能である。また、後述するように、微粒子の形成工程は非常に容易に実現できる。
【００１７】
また、基板上に金属Ｐｄ微粒子を形成する方法は、絶縁性基体に有機Ｐｄ錯体溶液を塗布する工程と、該有機Ｐｄ錯体溶液を塗布した基体を大気中または酸化雰囲気中で熱処理しＰｄＯとする工程と、該ＰｄＯを不活性ガスで希釈した還元性ガス中で熱処理して金属Ｐｄとする工程を有する方法により行なうことができる。
【００１８】
絶縁性基体に塗布する有機Ｐｄ錯体溶液としては、例えば酢酸Ｐｄのアミン錯体を酢酸ブチルに溶かした溶液が挙げられる。
【００１９】
前記ＰｄＯを不活性ガスで希釈した還元性ガスで熱処理する工程において、該還元性ガスとしては、Ｈ2 ガス、ＣＯガス、Ｃ2Ｈ4ガス等が挙げられるが、その中でＨ2 ガスが好ましい。還元性ガスの濃度は、該ガス種の爆発範囲下限未満、Ｈ2ガスの場合４ｖｏｌ％未満、特に１〜３ｖｏｌ％が好ましい。
【００２０】
また、ＰｄＯを不活性ガスで希釈した還元性ガスで熱処理して金属Ｐｄとする工程において、該還元性ガスとして炭化水素ガスを用いることができる。この炭化水素ガスは気相成長炭素繊維の製造方法に用いるものと同一の炭化水素ガスを用いると、ＰｄＯの金属Ｐｄへの還元反応と炭素繊維の気相成長を同時に行うことができるので好ましい。
【００２１】
また本発明において、不活性ガスで希釈した炭化水素ガスを用いる還元及び熱分解の工程において、炭化水素ガスとしては、例えばＣ2 Ｈ4 、Ｃ3Ｈ6、Ｃ2Ｈ6、ＣＨ4等が挙げられ、特にＣ2 Ｈ4 が好ましい。また、不活性ガスで希釈した炭化水素ガスの濃度は、該ガス種の爆発範囲下限未満、Ｃ2Ｈ4ガスの場合通常は２．７ｖｏｌ％未満であり、好ましくは０．１〜２ｖｏｌ％が望ましい。２．７ｖｏｌ％を越えると、防爆のための処置が必要で好ましくない。
【００２２】
不活性ガスとしては、特に制限することはないが、例えば窒素ガス、ヘリウムガス、アルゴンガスが用いられる。
【００２３】
また、Ｃ2Ｈ4ガスの熱分解工程の熱処理温度は、４５０℃以上、好ましくは５００〜９００℃が望ましい。４５０℃未満では、Ｐｄ微粒子表面での熱分解が生じなくなるので好ましくない。
【００２４】
【実施例】
以下実施例に基づき本発明を説明する。
【００２５】
実施例１
表面酸化膜を形成したシリコン基板を有機溶剤で洗浄した後、有機Ｐｄ錯体溶液をスピンナーコートした。有機Ｐｄ錯体溶液は、奥野製薬（株）製：ｃｃｐ４２３０を酢酸ブチルで５倍に希釈したものを用いた。スピンナーコートの条件は、８００ｒｐｍ、３０秒である。
【００２６】
これを大気中で、３００℃で１２分間熱処理した。同じ条件で作製した試料をＸ線回折で調べたところ、酸化Ｐｄ（ＰｄＯ）になっており、他の相は存在しなかった。
【００２７】
続いて、Ｎ2 （９８ｖｏｌ％）＋Ｈ2 （２ｖｏｌ％）の混合ガス気流中で、１８５℃、１０分間の熱処理を行った。これを、走査電子顕微鏡で観察したところ、シリコン基板上にφ５ｎｍ程度の微粒子が分散していることが確かめられた。同じ条件で作製した試料のＸ線回折によると、金属Ｐｄに変化しており、他の相は見られなかった。
【００２８】
続いて、Ａｒ（９９ｖｏｌ％）＋Ｃ2 Ｈ4 （１ｖｏｌ％）の混合ガスと、Ｎ2 を１：９で混合した（したがって、Ｃ2 Ｈ4 ：０．１ｖｏｌ％）気流中で、７００℃、１０分間の熱処理を行った。
【００２９】
これを走査電子顕微鏡で観察したところ、図１の走査電子顕微鏡写真（倍率 ×１００，０００）に示すように、φ１０ｎｍ程度の繊維状のものが形成されていることがわかった。ラマン分光分析、およびＸ線光電子分光分析（ＸＰＳ）の結果から、これが炭素であることが確認された。
【００３０】
目視では、基板上に黒色の粉体が堆積しているように見え、刷毛で軽く擦ると容易に剥離する。剥離した粉体を集め、透過電子顕微鏡で観察したところ、図２の透過電子顕微鏡写真（倍率×２，０００，０００）に示す様に、気相成長炭素繊維に特徴的な外周部の格子像が見られた。また、中心部には格子像が見えないことから内部は中空になっていると思われる。
【００３１】
実施例２
実施例１と同様に、表面酸化膜を有するシリコン基板に有機Ｐｄ錯体溶液をスピンナーコートし、３００℃の熱処理によりＰｄＯを形成した後、２５℃で６０分間Ｎ2 （９８ｖｏｌ％）＋Ｈ2 （２ｖｏｌ％）混合ガス気流に曝露した。これを走査電子顕微鏡で観察したところ、形がやや不規則であるが、実施例１と同様に微粒子が形成されていることがわかった。Ｘ線回折により、金属Ｐｄになっていることも確認された。
【００３２】
これを実施例１と同様に、Ｃ2 Ｈ4 ：０．１ｖｏｌ％気流中で７００℃、１０分間の熱処理を行った。これを走査電子顕微鏡により観察したところ、実施例１と同様にφ１０ｎｍ程度の気相成長炭素繊維が形成されていた。
【００３３】
実施例３
実施例１と同様に、表面酸化膜を形成したシリコン基板上に、Ｐｄ微粒子の分散膜を形成し、これをＣ2 Ｈ4 ：０．１ｖｏｌ％気流中で４５０℃、１０分間の熱処理を行った。これを走査電子顕微鏡で観察したところ、φ７ｎｍ程度のチューブが形成されていた。ラマン分光分析によりこれが炭素であることが確認された。
【００３４】
実施例４
実施例１と同様に、表面酸化膜を形成したシリコン基板上に、ＰｄＯ膜を形成した後、Ｎ2 −Ｈ2 気流中で還元する工程を省いて、Ｃ2 Ｈ4 ：０．１ｖｏｌ％気流中で７００℃、１０分間の熱処理を行った。これをラマン分光分析、走査電子顕微鏡観察により調べたところ、実施例１と同様の結果が得られた。
【００３５】
比較例１
実施例１と同様に、表面酸化膜を形成したシリコン基板上に、Ｐｄ微粒子の分散膜を形成し、これをＣ2 Ｈ4 ：０．１ｖｏｌ％気流中で、４００℃、１０分間の熱処理を行った。これをラマン分光分析により調べたところ、炭素の信号は、通常大気中に放置した際に生ずる汚染によるもの程度の大きさで、熱分解による炭素は形成されていないことがわかった。
【００３６】
比較例２
石英基板を中性洗剤と有機溶剤により洗浄し、真空蒸着法により、厚さ３００ｎｍのＰｄ薄膜を成膜した。これをＣ2 Ｈ4 ：０．１ｖｏｌ％気流中で、７００℃、１０分間の熱処理を行った。ラマン分光分析の結果、炭素が堆積していることがわかった。しかし走査電子顕微鏡観察により、気相成長炭素繊維は形成されておらず、網目状に切れ目の入った炭素の膜が形成されていることが判明した。
【００３７】
実施例４については、本発明者らはここで用いたのと同じ雰囲気中で、ＰｄＯを熱処理することにより、１８０℃以上で還元され金属Ｐｄとなることを確かめた。熱分解が起こるのは比較例１に示した様に４００℃より高温であるから、熱分解がはじまる前にＰｄ微粒子が形成され実施例１と同様の結果が得られたものと思われる。
【００３８】
上記実施例においては、Ｐｄ微粒子形成方法として、有機錯体溶液塗布、酸化、還元という工程を用いたが、これに限定されるものではなく、ガス中蒸着法その他により微粒子形成を行った場合でも同様の効果が得られる。
【００３９】
基板は、シリコンに限定されることなく、耐熱性で、炭化水素の熱分解の触媒能が無いか、小さい物質、たとえば石英基板など、ならば使用可能である。
Ｈ2 およびＣ2 Ｈ4 の濃度は実施例に限定されるものではなく、爆発限界以下の濃度であれば、特別な防爆設備を必要としない。ちなみにＨ2 の爆発範囲下限は４ｖｏｌ％、Ｃ2 Ｈ4 は２．７ｖｏｌ％である。
【００４０】
また、本発明を用い、有機Ｐｄ錯体溶液をスクリーン印刷などの手法で適当なパターンに形成すれば、基板上の所望の位置にのみ気相成長炭素繊維を形成することが可能となる。これにより、気相成長炭素繊維を量子細線として用いる電子素子など新規な素子の製造が可能になる。
【００４１】
【発明の効果】
以上説明した様に、本発明により、工業的生産に適用可能で、高温のプロセスや、特別な安全対策など困難なプロセスを必要としない気相成長炭素繊維の製造方法を実現することが可能となった。
【図面の簡単な説明】
【図１】実施例１により、シリコン基板上に形成された気相成長炭素繊維の形状を示す走査電子顕微鏡写真（倍率×１００，０００）である。
【図２】実施例１により形成された気相成長炭素繊維の形状を示す透過電子顕微鏡写真（倍率×２，０００，０００）である。[0001]
[Industrial application fields]
The present invention provides a method for producing a vapor-grown carbon fiber, particularly a method for producing a vapor-grown carbon fiber that can be mass-produced using an easier process in terms of production technology.
[0002]
[Prior art]
Conventionally, since a large-scale synthesis method of C60 composed of 60 carbon atoms and having a soccerball-like structure has been reported (Kratschmer, et.al .: Nature 347 (1990) 354), fullerenes, which are carbon clusters, have been reported. Numerous studies have been conducted on the various properties of the carbon nanotubes, which have a structure that stretches them in one direction.
[0003]
In particular, it has attracted attention that C60 crystals doped with alkali metal atoms exhibit superconductivity with a high critical temperature. In addition, these carbon clusters are expected to be used as new electronic devices and solid lubricants, and vigorous research is being conducted with the aim of applying them from various viewpoints.
[0004]
Vapor-grown carbon fiber is a slightly larger cluster than carbon nanotubes, but has better crystallinity and is expected to have a characteristic use as compared with carbon fiber obtained by carbonizing hydrocarbon resin fiber at high temperature.
[0005]
At present, a typical method for producing the vapor growth carbon fiber is a vapor growth method by thermal decomposition of benzene. In this method, an iron compound such as iron oxide is used as a substrate, and is brought into contact with benzene vapor at a temperature of about 950 to 1000 ° C. using high-purity hydrogen as a carrier gas. First, a part of the substrate is reduced to form Fe fine particles. Due to the catalytic ability of the fine particle surface, carbon begins to precipitate on the surface. This carbon grows in the form of fibers behind the Fe fine particles, and continues to grow while lifting the fine particles.
[0006]
In this method, the presence of Fe fine particles is indispensable, and a method in which metal Fe fine particles are sprayed on a substrate is also used. (Michio Inagaki: “Carbon Materials Engineering”, p. 72, published by Nikkan Kogyo Shimbun, 1985)
[0007]
[Problems to be solved by the invention]
Although the above method is industrially applicable, there are some problems. First, a high-temperature process of about 1000 ° C. is required during the process, which may increase the cost of the apparatus due to large equipment and high power consumption. Secondly, since high-purity hydrogen is used, it is necessary to take measures to prevent explosion accidents. In particular, since it is used in the above-described high-temperature process, particularly strict measures are required, which may also cause a cost increase.
[0008]
In addition, the method using a substrate sprayed with Fe fine particles can increase the yield and is industrially preferable, but the metal Fe fine particles are highly reactive and cannot be handled in the atmosphere. . In addition, the danger of dust explosion cannot be ignored, so it is necessary to take countermeasures.
[0009]
On the other hand, the vapor phase growth method also has a method of thermally decomposing CO, but CO is extremely toxic in addition to explosiveness, and the allowable concentration is very severe, 50 ppm, and safety measures are costly. It is clear that it will be an uplift factor.
[0010]
Therefore, there is a need for a method for producing vapor-grown carbon fiber that is suitable for industrial production, is a low-temperature process, is easy to take safety measures, and is configured by a process that can be handled in the atmosphere.
[0011]
The present invention has been achieved as a result of studying a novel manufacturing method that solves these problems, and is applicable to industrial production by vapor-phase growth of carbon by pyrolysis of hydrocarbon gas. It is an object of the present invention to provide a method for producing a vapor-grown carbon fiber that does not require a difficult process such as this process or special safety measures.
[0012]
[Means for Solving the Problems]
That is, the present invention is a vapor phase growth method including a step of exposing a substrate formed by dispersing Pd fine particles to a C 2 H 4 gas diluted with an inert gas and subjecting it to heat treatment, and thermally decomposing the C 2 H 4 gas. In the carbon fiber production method, the concentration of C 2 H 4 diluted with the inert gas is less than 2.7 vol%.
[0013]
The present invention also includes a step of forming a substrate in which Pd fine particles are dispersed by heat-treating PdO on the substrate with a reducing gas diluted with an inert gas, and a substrate in which the Pd fine particles are dispersed is not treated. In a method for producing a vapor-grown carbon fiber, the method includes a step of exposing to C 2 H 4 gas diluted with an active gas, heat-treating, and thermally decomposing the C 2 H 4 gas. A method for producing vapor-grown carbon fiber, characterized in that the concentration of 2 H 4 is less than 2.7 vol%.
[0014]
In the present invention, it is preferable that the concentration of C 2 H 4 diluted with an inert gas is less than 0.1 vol% or more 2.7vol%.
The inert gas is preferably at least one selected from nitrogen gas, helium gas and argon gas.
It is preferable that the heat treatment temperature in the thermal decomposition step of the C 2 H 4 gas is 450 ° C. or higher.
It is preferable that the heat treatment temperature in the thermal decomposition step of the C 2 H 4 gas is 500 to 900 ° C.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The present invention is a method for obtaining vapor-grown carbon fibers by thermal decomposition of C 2 H 4 gas. C 2 H 4 gas is flammable, but can be handled safely by diluting with an inert gas and does not require special explosion-proof equipment. In addition, although toxicity varies depending on the gas species, there is usually no serious danger. In a diluted state, sufficient ventilation is sufficient to prevent lack of oxygen.
[0016]
As the substrate, a substrate obtained by dispersing catalyst fine particles on a heat-resistant substrate is used. As the catalyst fine particles, those in which metal Pd fine particles are dispersedly arranged are preferable. The Pd surface has a remarkable catalytic ability for the decomposition reaction of C 2 H 4 and can be reacted at a low temperature. Further, as will be described later, the fine particle forming step can be realized very easily.
[0017]
Further, the method of forming metal Pd fine particles on a substrate includes a step of applying an organic Pd complex solution to an insulating substrate, and heat-treating the substrate coated with the organic Pd complex solution in the atmosphere or in an oxidizing atmosphere to form PdO. The method can include a step and a step of heat-treating the PdO in a reducing gas diluted with an inert gas to form metal Pd.
[0018]
Examples of the organic Pd complex solution applied to the insulating substrate include a solution in which an amine complex of Pd acetate is dissolved in butyl acetate.
[0019]
In the step of heat-treating in a reducing gas diluted with the PdO with an inert gas, as the reducing gas, H 2 gas, CO gas, although C 2 H 4 gas, and the like, are H 2 gas therein preferable. The concentration of the reducing gas is preferably less than the lower limit of the explosion range of the gas species, less than 4 vol%, particularly 1 to 3 vol% in the case of H 2 gas.
[0020]
In the step of heat-treating with a reducing gas diluted with an inert gas to form metal Pd, a hydrocarbon gas can be used as the reducing gas. It is preferable to use the same hydrocarbon gas as that used in the method for producing vapor-grown carbon fiber because the reduction reaction of PdO to metal Pd and the vapor growth of carbon fiber can be performed simultaneously.
[0021]
In the present invention, in the reduction and pyrolysis process using a hydrocarbon gas diluted with an inert gas, examples of the hydrocarbon gas include C 2 H 4 , C 3 H 6 , C 2 H 6 , and CH 4. C 2 H 4 is particularly preferable. The concentration of the hydrocarbon gas diluted with an inert gas is less than the lower limit of the explosion range of the gas species, and in the case of C 2 H 4 gas, it is usually less than 2.7 vol%, preferably 0.1 to 2 vol%. desirable. If it exceeds 2.7 vol%, an explosion-proof treatment is required, which is not preferable.
[0022]
The inert gas is not particularly limited, and for example, nitrogen gas, helium gas, or argon gas is used.
[0023]
The heat treatment temperature in the thermal decomposition step of C 2 H 4 gas is 450 ° C. or higher, preferably 500 to 900 ° C. If it is less than 450 ° C., thermal decomposition on the surface of the Pd fine particles does not occur, which is not preferable.
[0024]
【Example】
Hereinafter, the present invention will be described based on examples.
[0025]
Example 1
The silicon substrate on which the surface oxide film was formed was washed with an organic solvent, and then an organic Pd complex solution was spinner coated. As the organic Pd complex solution, an Okuno Pharmaceutical Co., Ltd. product: ccp4230 diluted 5 times with butyl acetate was used. The spinner coating conditions are 800 rpm and 30 seconds.
[0026]
This was heat-treated in the atmosphere at 300 ° C. for 12 minutes. When a sample prepared under the same conditions was examined by X-ray diffraction, it was oxidized Pd (PdO) and no other phase was present.
[0027]
Subsequently, heat treatment was performed at 185 ° C. for 10 minutes in a mixed gas stream of N 2 (98 vol%) + H 2 ( 2 vol%). When this was observed with a scanning electron microscope, it was confirmed that fine particles having a diameter of about 5 nm were dispersed on the silicon substrate. According to the X-ray diffraction of the sample prepared under the same conditions, it was changed to metal Pd, and no other phase was observed.
[0028]
Subsequently, a mixed gas of Ar (99 vol%) + C 2 H 4 (1 vol%) and N 2 were mixed at 1: 9 (hence, C 2 H 4 : 0.1 vol%) in an air stream at 700 ° C. Heat treatment was performed for 10 minutes.
[0029]
When this was observed with a scanning electron microscope, as shown in the scanning electron micrograph (magnification × 100,000) in FIG. 1, it was found that a fibrous material having a diameter of about φ10 nm was formed. From the results of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), it was confirmed that this was carbon.
[0030]
Visually, it appears that black powder is deposited on the substrate, and is easily peeled off when rubbed lightly with a brush. The peeled powder was collected and observed with a transmission electron microscope, and as shown in the transmission electron micrograph (magnification × 2,000,000) in FIG. It was observed. Also, since the lattice image is not visible at the center, the inside seems to be hollow.
[0031]
Example 2
As in Example 1, an organic Pd complex solution was spinner-coated on a silicon substrate having a surface oxide film, PdO was formed by heat treatment at 300 ° C., and then N 2 (98 vol%) + H 2 ( 2 vol) at 25 ° C. for 60 minutes. %) Exposed to a mixed gas stream. When this was observed with a scanning electron microscope, it was found that fine particles were formed as in Example 1, although the shape was somewhat irregular. It was also confirmed by X-ray diffraction that the metal was Pd.
[0032]
In the same manner as in Example 1, this was heat-treated at 700 ° C. for 10 minutes in a C 2 H 4 : 0.1 vol% stream. When this was observed with a scanning electron microscope, a vapor-grown carbon fiber having a diameter of about 10 nm was formed as in Example 1.
[0033]
Example 3
Similarly to Example 1, a dispersion film of Pd fine particles was formed on a silicon substrate on which a surface oxide film was formed, and this was heat-treated at 450 ° C. for 10 minutes in a C 2 H 4 : 0.1 vol% air flow. It was. When this was observed with a scanning electron microscope, a tube of about φ7 nm was formed. Raman spectroscopy confirmed that this was carbon.
[0034]
Example 4
Similarly to Example 1, after forming a PdO film on a silicon substrate on which a surface oxide film was formed, a step of reducing in a N 2 —H 2 air current was omitted, and a C 2 H 4 : 0.1 vol% air current was omitted. Heat treatment was performed at 700 ° C. for 10 minutes. When this was examined by Raman spectroscopic analysis and scanning electron microscope observation, the same results as in Example 1 were obtained.
[0035]
Comparative Example 1
As in Example 1, a dispersion film of Pd fine particles was formed on a silicon substrate on which a surface oxide film was formed, and this was subjected to heat treatment at 400 ° C. for 10 minutes in a C 2 H 4 : 0.1 vol% air flow. went. When this was examined by Raman spectroscopic analysis, it was found that the carbon signal was as large as that caused by contamination that would normally occur when left in the atmosphere, and no carbon was formed by pyrolysis.
[0036]
Comparative Example 2
The quartz substrate was washed with a neutral detergent and an organic solvent, and a 300 nm thick Pd thin film was formed by vacuum deposition. This was heat-treated at 700 ° C. for 10 minutes in a C 2 H 4 : 0.1 vol% stream. As a result of Raman spectroscopic analysis, it was found that carbon was deposited. However, it was found by scanning electron microscope observation that vapor-grown carbon fibers were not formed, and a carbon film having slits was formed.
[0037]
For Example 4, the present inventors confirmed that PdO was reduced to 180 ° C. or more to become metal Pd by heat-treating PdO in the same atmosphere as used here. As shown in Comparative Example 1, the thermal decomposition occurs at a temperature higher than 400 ° C. Therefore, it seems that Pd fine particles were formed before the thermal decomposition started and the same result as in Example 1 was obtained.
[0038]
In the above embodiment, the organic complex solution coating, oxidation, and reduction steps were used as the Pd fine particle formation method, but the present invention is not limited to this, and the same applies even when fine particle formation is performed by gas evaporation method or the like. The effect is obtained.
[0039]
The substrate is not limited to silicon and can be used if it is heat resistant and does not have catalytic ability for thermal decomposition of hydrocarbons, or is a small substance such as a quartz substrate.
The concentration of H 2 and C 2 H 4 is not limited to the examples, and no special explosion-proof equipment is required as long as the concentration is below the explosion limit. Incidentally, the lower limit of the explosion range of H 2 is 4 vol%, and C 2 H 4 is 2.7 vol%.
[0040]
If the organic Pd complex solution is formed into an appropriate pattern by a method such as screen printing using the present invention, it is possible to form vapor grown carbon fibers only at desired positions on the substrate. This makes it possible to manufacture novel devices such as electronic devices that use vapor-grown carbon fibers as quantum wires.
[0041]
【The invention's effect】
As described above, according to the present invention, it is possible to realize a method for producing vapor-grown carbon fiber that is applicable to industrial production and does not require difficult processes such as high-temperature processes and special safety measures. became.
[Brief description of the drawings]
1 is a scanning electron micrograph (magnification × 100,000) showing the shape of vapor-grown carbon fibers formed on a silicon substrate according to Example 1. FIG.
FIG. 2 is a transmission electron micrograph (magnification × 2,000,000) showing the shape of a vapor-grown carbon fiber formed in Example 1.
Claims (14)
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| JP2002016463A JP3652313B2 (en) | 2002-01-25 | 2002-01-25 | Method for producing vapor grown carbon fiber |
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| JP2002016463A JP3652313B2 (en) | 2002-01-25 | 2002-01-25 | Method for producing vapor grown carbon fiber |
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| JP25903094A Division JP3285284B2 (en) | 1994-09-29 | 1994-09-29 | Method for producing vapor grown carbon fiber |
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