JP3971090B2 - Method for producing diamond having needle-like surface and method for producing carbon-based material having cilia-like surface - Google Patents

Description

【００４５】
また、水素ガス又は水素ガス中に、窒素ガス、Ｈｅガス、Ａｒガス、酸素ガス、ＣＯ₂ガス、Ｈ₂Ｏガス、及び炭化水素ガスからなる群から選択された１種以上のガスを混合比が１０体積％以下で混合した混合ガスを使用し、ガス圧及び基板の温度を本発明範囲内にある条件、即ち、圧力６６．５乃至６６５Ｐａ、基板の温度−５０乃至８００℃の範囲でバイアス電圧を−１００乃至−５００Ｖ、エッチング時間を０．２乃至１０時間の範囲で適当に選択してダイヤモンド膜をプラズマ処理しても、図４に示すような針状構造が表面に形成されたダイヤモンドが得られる。なお、プラズマ処理するダイヤモンドが天然及び人工の単結晶、粉末並びに焼結体のいずれのダイヤモンドであっても、表面に針状構造を形成することができる。
【００４６】
また、図４は、図３に示す針状ダイヤモンド膜上に、更に気相合成によりダイヤモンド膜を積層したダイヤモンド膜表面のＳＥＭ写真である。図３に示す針状ダイヤモンド膜を形成した後、同一のマイクロ波プラズマ発生装置により、形成した針状ダイヤモンド膜上に、０．３体積％ＣＨ₄＋９９．７体積％Ｈ₂の混合ガスを使用し、ガス圧６６５０Ｐａ、基板の温度を８００℃、処理時間１時間で、周波数２．４５ＧＨｚのマイクロ波を使用してプラズマを発生させ、気相合成によりダイヤモンド膜を成長させた。図４に示すように、針状ダイヤモンド膜上に更にダイヤモンド膜を成長させても、表面の針状の構造を維持したままダイヤモンド膜が成長しているのがわかる。
【００４７】
次に、本発明の第２の実施例について説明する。第２の実施例においては、針状表面を有するダイヤモンド膜を電気分解用の電極として使用する。電気分解用の電極としては、例えば金属又は低抵抗シリコン基板にマイクロ波ＣＶＤ装置により、ｐ型半導体ダイヤモンド膜を形成後、所定の条件でプラズマ処理を行って、ｐ型半導体ダイヤモンド膜表面に、針状構造を形成したものを使用することができる。
【００４８】
本実施例においては、プラズマ処理して表面に針状構造が形成されているため、ダイヤモンド膜表面の面積が広く、且つエッチングによりダイヤモンド膜が薄くなるため、発熱及び界面抵抗等によるエネルギ損失を低減することができる。従って、表面に針状構造を形成したダイヤモンド膜を使用した電気分解用電極は、電気抵抗が低減され、接触面積が広くなるため、電気分解効率を著しく向上させることができ、電気分解に必要とする時間を極めて短時間にすることができる。
【００４９】
なお、本実施例では、ｐ型ダイヤモンド膜を形成した後プラズマ処理したものを使用したが、ｎ型ダイヤモンド膜としても同様の効果が得られる。
【００５０】
また、電気分解用電極と同様に、針状表面を有するダイヤモンド膜を化学センサ用の電極に使用することもできる。針状表面を有するダイヤモンド膜を使用することにより、表面積が増大するので、感度を著しく向上させることができる。
【００５１】
更に、燃料電池用電極に使用することもできる。針状表面を有するダイヤモンド膜を使用することにより、金属触媒量が増加するので、燃料分解効率が飛躍的に高くなり、従って高効率の燃料電池を得ることができる。
【００５２】
次に、本発明の第３の実施例について説明する。第３の実施例は、針状ダイヤモンド膜をグルコースセンサ等のバイオセンサのトランスデューサ部（信号変換回路）の電極として使用したものである。図５は、本実施例の針状ダイヤモンド膜を使用したバイオセンサのトランスジューサ部を示す断面図である。図５に示すように、本実施例のバイオセンサにおいては、基板３０の上に下地層としてアンドープダイヤモンド膜３１が形成されている。そして、このアンドープダイヤモンド膜３１上に半導体ダイヤモンドからなる作用電極３４が形成され、この作用電極３４の両側のアンドープダイヤモンド膜３１上には白金対向電極３３及び白金参照電極３２が形成されている。作用電極３４は、生体識別物質３５により被覆され、更にこの生体識別物質３５は生体膜３６により被覆されている。例えばグルコースセンサの場合は生体識別物質３５としてグルコースオキシダーゼ等を使用することができる。これらの作用電極３４、対向電極３３及び参照電極３２は、半導体ダイヤモンドヒータ３７により取り囲まれており、このヒータ３７はアンドープダイヤモンド膜３８により被覆されている。
【００５３】
バイオセンサが、例えばグルコースセンサの場合においては、試料中のグルコースがグルコースオキシダーゼと触媒反応してグルコノラクトンに変化するときの電子移動を電極で検出してグルコース濃度を測定することができる。バイオセンサの長寿命化には、繰り返し測定又は長時間測定に対して識別物質の流出を防ぐことが必要である。本実施例においては、ダイヤモンド作用電極３４の表面に針状構造が形成されているため、生体識別物質３５の固定期間が極めて長く、その活性も極めて長時間失われない。
【００５４】
次に、本発明の第４の実施例について説明する。本実施例においては、針状ダイヤモンド膜をキャリア（電子又は正孔）輸送層に使用した有機発光素子である。
【００５５】
本実施例においては、正孔注入電極と、電子注入電極との間に電圧を印加すると、正孔輸送層として形成したダイヤモンド膜の表面には針状構造が形成されているため、針状構造からの正孔注入効率が高くなり、極めて発光強度が高い有機発光素子を得ることができる。従って、微細加工技術を使用して、この素子を平面パネル上に規則的に配列することにより本実施例の有機発光素子を平面パネルに適用すると、高効率の平面パネルディスプレイを得ることができる。
【００５６】
次に、本発明の第５の実施例について説明する。本実施例においては、針状構造を有するダイヤモンド膜を使用した電子放出素子である。
【００５７】
図６は、本実施例の電子放出素子を示す模式的断面図である。図６に示すように、本実施例の電子放出素子は、基体４０上に下部電極４１が形成され、その上に表面に針状構造が形成されたダイヤモンド層４２が形成されている。更に、この針状ダイヤモンド層４２がら離隔して、下部電極４１に対向する透明な上部電極４４が形成され、これらが真空中に配置されている。そして、上部電極４４及び下部電極４１は電源４８に接続されている。
【００５８】
本実施例においては、上部電極４４に正、下部電極４１に負の電圧を印加するが、ダイヤモンド層４２の表面に針状構造が形成されているため、ダイヤモンド層４２からの電子４５の放出量が大きい。従って、電子放出電圧のしきい値が低下し、電流値を著しく増大させることができる。このような電子放出素子は、光電管、平面パネルディスプレイ、マイクロ波発振源、及び高耐圧スイッチング素子等へ適用することができ、これらのデバイス特性を飛躍的に向上させることができる。
【００５９】
次に、本発明の第６の実施例について説明する。本実施例においては、表面に針状構造を有するダイヤモンド膜を使用した紫外線発光素子である。本実施例の紫外線発光素子においては、低抵抗シリコン等からなる基板上に例えば表面に針状構造が形成されたｐ型ダイヤモンド膜形成されている。更に、この針状表面を有するダイヤモンド膜上にアンドープダイヤモンド薄膜が積層され、更にこの上に金等を蒸着した極薄膜からなる上部電極が形成されている。
【００６０】
本実施例においては、基板側に正、上部電極に負の電圧を印加すると、上部電極中のフェルミレベルにある電子がトンネリング等の機構を経てアンドープダイヤモンド薄膜を通過し、針状ダイヤモンド膜へ注入される。そして、この電子が価電子帯に存在する正孔と再結合して光を放出する。このとき、本実施例の紫外線発光素子は表面に針状構造を有しているため、針状構造の先端付近で電界が強まると共に電流密度が増大する。従って、発光強度が極めて高い。
【００６１】
次に、本発明の第７の実施例について説明する。図７は、本実施例の可視光発光素子を示す断面図である。図７に示すように、本実施例の可視光発光素子においては、シリコン等の基体４０上に下部電極４１が形成され、その上にダイヤモンド層４２が形成されている。このダイヤモンド層４２は、所定の条件でプラズマ処理され表面に針状構造が形成されている。更に、その上面にアンドープダイヤモンド薄膜４３が積層されている。更に、このアンドープダイヤモンド薄膜４３上には蛍光薄膜４６及び透明な上部電極４４が順次積層されている。そして、上部電極４４の表面には、選択的に配線用電極４７が形成されている。更に、配線用電極４７及び下部電極４１は電源４８に接続されている。
【００６２】
本実施例においては、配線用電極４７に正、下部電極４１に負の電圧を印加すると、下部電極４１からダイヤモンド膜４２にキャリアとしての電子４５が注入される。そして、この電子４５はダイヤモンド膜４２及びアンドープダイヤモンド薄膜４３中において加速され、蛍光薄膜４６を励起して蛍光を発し、更に、上部電極（透明電極）４４から配線用電極４７に移動する。この際、高濃度のボロンを含有した針状ダイヤモンド薄膜４２により、針状構造の先端付近で電界が強まると共に、電子４５の放出密度が高いため、電流密度が増大し、極めて高い発光強度を得ることができる。また、本実施例の可視光発光素子を使用することにより、高輝度の平面パネルディスプレイを得ることができる。
【００６３】
次に、本発明の第８の実施例について説明する。図８は本実施例のガスセンサを示す模式的断面図である。本実施例のガスセンサにおいては、針状表面を有するダイヤモンド膜を使用したガスセンサである。
【００６４】
図８に示すように、本実施例のガスセンサにおいては、母材５２上にシリコン等からなる基板５３が接着され、この上に、アンドープダイヤモンド層５４と、表面に針状構造が形成された半導体ダイヤモンド層５５が順次積層されている。このダイヤモンド２層膜はセンサ部となっており、マイクロ波プラズマＣＶＤ装置によりダイヤモンドの連続膜として形成することができる。針状表面構造を有するｐ型半導体ダイヤモンド層５５上には、１対の例えば白金からなる電極５６が、微細加工により適長間隔をおいて形成されている。これらの電極５６には夫々白金等からなる配線５７が金等からなるペースト（図示せず）により被覆されて接着されている。また、母材５２の裏面には、白金等の抵抗材料を薄膜でパターン形成することにより、ヒータ５１が設けられている。
【００６５】
母材５２は、シリコン、窒化シリコン、酸化珪素、アルミナ、炭化珪素、チタン酸ストロンチウム及び酸化マグネシウムからなる群から選択された材料の単結晶、多結晶、非晶質、焼結体又は薄膜であることが好ましい。特に、母材５２の材料としては、シリコン、窒化シリコン、酸化珪素、アルミナ又は炭化珪素が好ましい。これは、ダイヤモンド気相合成の最適な基板の温度が７００〜１０００℃であり、しかも気相合成が化学的に活性な水素プラズマ雰囲気中で行われるので、基板材料としてはこのような条件に耐える必要があるからである。また、基板裏面には白金ヒータを形成するので、基板材料は電気絶縁性でなければならない。上述の材料はこれらの条件を満たしている。これらの材料はバルク材料を加工することにより基板に成形してもよいが、母材上に薄膜をコーティングしたものであってもよい。
【００６６】
本実施例においては、ヒータ５１によりセンサ部を所定温度に加熱しておき、センサ部が動作状態にあるときに、センサ部表面にガス種が吸着すると、ｐ型半導体ダイヤモンド層５５に空乏層が拡がり、電気抵抗が変化する。この電気抵抗の変化を電極５６間に電圧を印加することにより検知する。これにより、ガスの存在がｐ型半導体ダイヤモンド層５５における電気抵抗値の変化として検出されるが、ｐ型半導体ダイヤモンド層５５の表面には針状構造が形成されているため、ガス種の吸着率が高く、従って、ガスセンサの検出感度が極めて高くなる。また、この電気抵抗値と、ガス濃度との関係を予め求めておけば、その関係をもとに、検出電気抵抗値からガス濃度を検知することができる。
【００６７】
次に、本発明の第９の実施例について説明する。本実施例においては、針状表面を有するダイヤモンド膜を使用した短波長センサである。
【００６８】
シリコン、窒化シリコン、酸化珪素、アルミナ、炭化珪素又は金属等からなる基板上に表面に針状構造が形成されたアンドープダイヤモンド膜が形成されている。そして、針状アンドープダイヤモンド膜上に微細加工技術により、白金等からなる一対の電極が形成されている。
【００６９】
本実施例においては、電極間に数乃至数十ボルトの電圧を印加しつつ、紫外線を照射すると、ダイヤモンド膜内で電子及びホールの対が生成し、電流が流れ、紫外線を検知することができるが、本実施例の短波長センサのダイヤモンド膜は表面に針状構造が形成されているため、紫外線の吸収率が高く、極めて感度が高い。
【００７０】
次に、本発明の第１０の実施例について説明する。図９は、本実施例の光増倍管用電子放出板を示す模式的断面図である。本実施例の光増倍管用電子放出板においては、図９に示すように、導電性の低抵抗シリコン基板６１上に、マイクロ波ＣＶＤ法により、表面に針状構造が形成された電子放出板であるＢドープ多結晶ダイヤモンド膜６２が形成され、反射型光電面６３が形成されている。反射型光電面６３のＢドープ多結晶ダイヤモンド膜６２は、その表面が水素プラズマ処理されて針状構造が形成され、また、シリコン基板６１の裏面はインジウム等（図示せず）を介して、金属電極（金属板）６４が接着されている。更に、この金属電極６４の裏面は、導電性の支持部材６７ａに接続され、これにより、反射光電面６３が支えられている。そして、光電面６３の上方には、光電面６３と対向して配置されるメッシュ状の金属受電面６５を有し、その一端は導電性の支持部材６７ｂに接続され、これにより受電面６５が支えられている。そして、これらの光電面６３及び金属受電面６５は、夫々支持部材６７ａ、６７ｂを介して、リードピン６８及び６９に接続され、光電面６３及びこの光電面６３の上方にて対向して配置された金属受電面６５が内部を真空にした石英ガラス等からなる封着ガラス管７０内に封入されている。この封着ガラス管７０の金属受電面６５と対向する位置には、例えばフッ化カルシウム等からなる窓７２が形成されている。
【００７１】
本実施例においては、受電面６５に対して光電面６３に負電圧を印加しつつ、波長が例えば２００ｎｍ程度の紫外線を窓７２から金属受電面６５を透過して光電面６３に照射すると、光電面６３のＢドープ多結晶ダイヤモンド膜６２から電子が放出される。この際、電子放出板であるＢドープ多結晶ダイヤモンド膜６２の表面には針状構造が形成されているため、表面の凹凸が大きいので紫外線吸収量が大きくなり、光電面６３からの電子放出が極めて多くなり、従って極めて大きい電流を得ることができる。
【００７２】
次に、本発明の第１１の実施例について説明する。図１０は、本実施例の放電電極を示す側面図である。図１０に示すように、本実施例の放電電極においては、放電電極（陰極）８０は細長い棒状の支持部８１の先端に円柱部８２を有し、更にこの円柱部８２の先端には、電子放出を効率的に行うべく円錐状の円錐部８３が形成され電極基材８４が構成されている。この電極基材８４は、例えば緻密な構造を有するタングステン等からなる電極母材からなる。電極基材８４の円錐部８３上には、例えば０．１乃至１０μｍ厚のダイヤモンド薄膜８５がコーティングされている。このダイヤモンド薄膜８５は、不純物としてＩＩＩ族の元素である例えばボロン（Ｂ）等がドープされたｐ型の不純物半導体であり、このダイヤモンド薄膜８５の表面は、所定の条件で水素プラズマで処理され、針状構造が形成されている。
【００７３】
本実施例においては、電極基材８４表面が針状表面を有する半導体ダイヤモンド薄膜８５によりコーティングされているので、陰極８０と陽極（図示せず）との間に適当な電圧を印加した状態でダイヤモンド薄膜８５中から電子が放出されやすく、充填してあるＸｅ等のガスによりアーク放電が生成されやすくなる。この結果、出力安定性の改善は高い再現性が要求される装置等の応用分野において特に有効である。
【００７４】
なお、本発明の放電管は、例えばパルス点灯型のフラッシュランプ又は直流点灯型の放電管に適用することが可能である。
【００７５】
次に、本発明に係る繊毛状表面を有する炭素系材料の実施例について説明する。本願発明者等は、炭素系材料において、表面積が大きい繊毛状構造を低コストで形成するため、鋭意実験研究した結果、プラズマ発生装置を使用し、炭素系材料に負電圧を印加し、基板の温度を−５０乃至１０００℃の範囲に維持し、プラズマ処理ガスとしてガス圧を１３３０Ｐａ以下とし、水素ガス又は水素ガスを主成分とする混合ガスによるプラズマを発生させ、炭素系材料を処理することにより、炭素系材料表面に高密度の繊毛状構造を形成することができることを見出した。
【００７６】
また、本願発明者等は、表面を繊毛状化した炭素系材料上に、更にダイヤモンド薄膜を気相合成して積層すると、表面の繊毛状構造を維持したままダイヤモンド薄膜が均一にコーティングことができることを見出した。ダイヤモンドは不純物をドープすることにより半導体化が可能であり、機能性の高い繊毛状構造の炭素系材料を得ることができる。
【００７７】
本発明は、水素又は水素を主成分とする混合ガスのプラズマ中で炭素系材料を処理することにより、炭素系材料表面に繊毛状構造を形成することを特徴としている。しかし、ガス圧が１３３０Ｐａを超えると、プラズマが均一に広がらなくなり、しかも、炭素系材料の表面に均一な繊毛状構造を形成することができないことが本願発明者らの研究で判明した。従って、繊毛状構造を形成するための水素ガス又は水素を主成分とする混合ガスの圧力は１３３０Ｐａ以下とする。
【００７８】
また、本願発明者等はプラズマ処理する際の基板の温度は、−５０乃至１０００℃と広い範囲で繊毛状構造が形成されることを知見した。しかし、１０００℃を超えると基板に熱歪が生じやすくなる。一方、基板の温度を−５０℃より低くするためには基板温度制御のために装置構造が複雑化すると共に、プラズマ処理速度が低下するので処理時間が長くなる。従って、基板の温度は−５０乃至１０００℃とする。
【００７９】
基板に印加する負電圧については、特に制限があるわけではないが、高周波及びマイクロ波によりプラズマを発生させる場合では、電圧が０乃至−１００Ｖでは繊毛状構造の形成速度が遅く、−５００Ｖ以下では異常放電が生じるので、−１００乃至−５００Ｖが適当である。
【００８０】
また、プラズマ処理に用いるガスは、水素ガスに加えて、窒素ガス、Ｈｅガス、Ａｒガス、酸素ガス、ＣＯ₂ガス、Ｈ₂Ｏガス及び炭化水素ガス（アルコール及びアセトン等のガスも含む）からなる群から選択された１種以上のガスを、水素ガス中に、混合比１０体積％以下で添加することができる。
【００８１】
水素に混合するガスとして、不活性な窒素ガス、Ｈｅガス、又はＡｒガス等の添加すると、炭素系材料表面の繊毛状構造の形成速度を抑制することができる。また、酸素ガス、ＣＯ₂ガス及びＨ₂Ｏガス等の添加すると、酸化効果により繊毛状構造の尖鋭性が低下するが、機械強度がより優れた円錐状の繊毛状構造が形成できる。
【００８２】
これに対し、炭化水素ガスを添加すると、炭素の均一な蒸着が進行するため、繊毛状構造の形成速度が遅くなるが、表面欠陥の抑制、含有水素量の制御等が可能になり、望ましい電気的特性が得られる。
【００８３】
図１１は、上述のごとくして製造した本発明の第１２実施例に係る繊毛状表面を有する炭素系材料（グラファイト）を示す図である。即ち、図１１は、鏡面研磨したグラファイトの表面をプラズマ処理し、その表面に繊毛状構造を形成したグラファイトの表面を示す走査型電子顕微鏡（Scanning electron microscope（ＳＥＭ））写真である。図１１に示すように、プラズマ処理には、水素ガスを用いてマイクロ波プラズマ発生装置（周波数２．４５ＧＨｚ）でプラズマを発生させ、ガス圧１．５Ｔｏｒｒ、基板温度４００ ℃、処理時間１時間とした結果、グラファイトの表面に高密度の繊毛状構造が形成されている。そして、上述した如く、本発明の繊毛状構造は、典型的には先端の直径が数乃至数十ｎｍでその長さが数百乃至数μｍとなっている。
【００８４】
図１２は、図１１に示す繊毛状炭素系材料上に、更に気相合成によりダイヤモンド膜を積層した炭素系材料表面のＳＥＭ写真である。図１１に示す繊毛状構造を有する炭素系材料を形成した後、同一のマイクロ波プラズマ発生装置により、形成した繊毛状炭素系材料上に、０．３体積％ＣＨ₄＋９９．７体積％Ｈ₂の混合ガスを使用し、ガス圧６６５０Ｐａ、基板の温度を１０００℃、処理時間３０分で、周波数２．４５ＧＨｚのマイクロ波を使用してプラズマを発生させ、気相合成によりダイヤモンド薄膜を成長させたものである。図１２に示すように、繊毛状炭素系材料上に更にダイヤモンド薄膜を成長させても、表面の繊毛状の構造を維持したまま炭素系材料が成長しているのがわかる。このように、ダイヤモンド薄膜がコーティングされた繊毛状構造では、先端の直径が数十ｎｍ乃至数μｍとなる。
【００８５】
従来、ダイヤモンドを除く炭素系材料上にダイヤモンド薄膜を成長させることは困難であったが、本発明によれば、どのような炭素系材料にもダイヤモンド薄膜を成長させることができるという極めて優れた効果が得られる。
【００８６】
本第１２実施例によれば、水素ガス又は水素ガス中に、窒素ガス、Ｈｅガス、Ａｒガス、酸素ガス、ＣＯ₂ガス、Ｈ₂Ｏガス、及び炭化水素ガスからなる群から選択された１種以上のガスを混合比が１０体積％以下で混合した混合ガスを使用し、ガス圧及び基板の温度を本発明範囲内にある条件、即ち、圧力１３３０Ｐａ以下、基板の温度−５０乃至１０００℃の範囲で印加電圧を−１００乃至−５００Ｖ、プラズマ処理時間を０．２乃至１０時間の範囲で適当に選択して炭素系材料をプラズマ処理することにより、図１１に示すような繊毛状構造が表面に形成された炭素系材料が得られ、またプラズマ処理する炭素系材料がバルク、薄膜、粉末及びに焼結体のいずれの形態であっても、その表面に繊毛状構造を形成することができる。
【００８７】
次に、本発明の第１３実施例について説明する。この第１３実施例においては、第１２実施例の繊毛状表面を有する炭素系材料を電気分解用の電極として使用する。
【００８８】
本実施例においては、プラズマ処理して表面に繊毛状構造が形成されているため、炭素系材料表面の面積が広くなるため、電気分解効率を著しく向上させることができ、電気分解に必要とする時間を極めて短時間にすることができる。
【００８９】
また、電気分解用電極と同様に、繊毛状表面を有する炭素系材料を化学センサ用の電極に使用することもできる。繊毛状表面を有する炭素系材料を使用することにより、表面積が増大するので、感度を著しく向上させることができる。
【００９０】
更に、この繊毛状表面を有する炭素系材料は、燃料電池用電極に使用することもできる。繊毛状表面を有する炭素系材料を使用することにより、金属触媒量が増加するので、燃料分解効率が飛躍的に高くなり、従って高効率の燃料電池を得ることができる。
【００９１】
次に、本発明の第１４実施例について説明する。この第１４実施例は、繊毛状構造を有する炭素系材料の薄膜を電子放出素子に使用したものである。
【００９２】
図１３は、この第１４実施例の電子放出素子を示す模式的断面図である。図１３に示すように、本実施例の電子放出素子は、基体９０上に下部電極９１が形成され、その上に表面に繊毛状構造が形成された炭素系材料層９２が形成されている。更に、この繊毛状炭素系材料層９２から離隔した位置に下部電極９１に対向する透明な上部電極９４が形成され、これらが真空中に配置されている。そして、上部電極９４及び下部電極９１は電源９８に接続されている。
【００９３】
本実施例においては、上部電極９４に正、下部電極９１に負電圧を印加するが、炭素系材料層９２の表面に繊毛状構造が形成されているため、炭素系材料層９２からの電子９５の放出量が大きい。従って、電子放出電圧のしきい値が低下し、電流値を著しく増大させることができる。このような電子放出素子は、光電管、平面パネルディスプレイ、マイクロ波発振源、及び高耐圧スイッチング素子等へ適用することができ、これらのデバイス特性を飛躍的に向上させることができる。
【００９４】
【実施例】
次に、本発明のダイヤモンド膜の製造方法により作製したダイヤモンド膜、並びにこれを使用した化学電極及び電子デバイスを実際に製造した実施例について、その特性を比較例と比較した結果について説明する。
【００９５】
実施例１
先ず、シリコン基板上に、基板の温度を８００℃、ガス圧が６６５０Ｐａとし、０．５体積％ＣＨ₄＋９９．５体積％Ｈ₂の混合ガスにより、周波数２．４５ＧＨｚのマイクロ波プラズマを発生させ、１４時間の気相合成によりダイヤモンド膜を形成した。その後、このダイヤモンド膜を下記表２に示す条件で、ダイヤモンド膜表面をプラズマ処理した。なお、表２のＲＴは室温（room temperature）を示す。プラズマ処理については、工業用周波数として認可されている２．４５ＧＨｚ又は９１５ＭＨｚのマイクロ波でプラズマを発生させた。処理後のダイヤモンド表面を観察し、針状構造が形成されているものについては、走査型電子顕微鏡（Scanning electron microscope（ＳＥＭ））により、その針密度を測定した。その結果も下記表２に示す。
【００９６】
【表２】

【００９７】
実施例１乃至１１では、ダイヤモンド膜の表面には、針密度が１０⁹乃至１０¹⁰と高い針状構造が形成された。
【００９８】
比較例１３及び１４は、ガス圧が本発明範囲から外れるため、また、比較例１５及び１６は基板温度が本発明範囲から外れるため、ダイヤモンド表面に針状構造が形成されなかった。
【００９９】
実施例２（電気分解用電極）
電気分解用電極を作製し、その特性を評価するため、塩化ナトリウム水溶液の電気分解を行った。なお、比較のため、プラズマ処理を行わず、表面に針状構造を形成していないダイヤモンド膜（以下、未処理のダイヤモンド膜という。）を使用したものについても同様に電気分解を行った。電気分解用電極としては、先ず、１辺が１０ｍｍの正方形の低抵抗シリコン基板を２枚用意し、マイクロ波ＣＶＤ装置により、メタン１体積％及び水素希釈したジボラン（Ｂ₂Ｈ６）（原料ガス中のジボラン濃度は１００体積ｐｐｍ）を原料ガスとして、２０時間の合成を行い、膜厚が５μｍのｐ型半導体ダイヤモンド膜を前記シリコン基板上に形成した。
【０１００】
ダイヤモンド膜を合成後、一方のダイヤモンド膜には、表１の針状ダイヤモンド膜のプラズマ処理条件と同一の処理条件にて、水素プラズマ処理をして、ダイヤモンド膜表面に針状構造を形成した（以下、処理試料という。）。また、他方のダイヤモンド膜は、参照試料とするため、未処理のダイヤモンド膜とした。これらの処理試料及び参照試料について、シリコン基板の裏面に銀ペーストで銅配線を接着し、ダイヤモンド膜表面に、１辺が８ｍｍの正方形の領域を残し、その他全体をエポキシ樹脂によりシールして、電気分解用電極を得た。
【０１０１】
測定には、ビーカに０．１Ｍ％の塩化ナトリウム水溶液を入れ、アノードに本実施例の電気分解用電極である処理試料を、カソードに白金電極を使用した場合と、アノードに参照試料、カソードに白金電極を使用した場合とを、夫々同一電圧で、同一の電気料を通電し、発生する水素量及び塩素量を測定して比較した。
【０１０２】
測定した結果は、未処理のダイヤモンド膜を使用した参照試料に対して、本実施例の電気分解用電極である処理試料の方が電気抵抗が約６０％小さく、電気分解効率が約４０％優れていた。このため、電気分解が参照試料より処理試料の方が短時間に完了した。これは、処理試料の表面積が参照試料よりも大きく、また処理試料の膜厚が参照試料よりも薄いため、発熱及び界面抵抗等によるエネルギ損失が小さくなったためである。
【０１０３】
実施例３（化学センサ用電極）
実施例２で作製した電極を化学センサ用電極として使用した場合の特性について評価した。実施例２の処理試料及び参照試料を電極として使用して、１ｍＭＦｅ（ＣＮ）₆／１ＭＫＣｌの溶液中においてサイクリック・ボルタンメトリー測定を行った。図１４は、サイクリック・ボルトメトリー測定の結果を示すグラフ図である。図１４において、破線１０は処理試料、実線１５は参照試料の測定結果を示している。対向電極には白金、参照電極として、Ａｇ／ＡｇＣｌ電極を使用した。参照試料と比べると、処理試料を使用した電極は、表面に針状構造が形成されているため、極めて感度が高く、バックグラウンド電流が小さくなり、化学センサ用電極として使用すれば化学センサの感度が１０倍以上向上する。
【０１０４】
実施例４（燃料電池用電極）
燃料電池用電極を作製し、その特性を評価するため、メタノール中のサイクック・ボルタンメトリー測定を行った。燃料電池用電極は、先ず、高濃度にＢをドーピングした導電性の膜厚２μｍのダイヤモンド膜を表１の条件２に示す針状ダイヤモンド膜形成条件でプラズマ処理して針状表面を有するダイヤモンド膜を得た。次いで、この表面にスパッタ法により、白金微粒子を分散蒸着し、更に１時間ダイヤモンド気相合成を行って白金微粒子を固定し燃料電池用電極を得た。また、比較のためプラズマ処理を行わず、ダイヤモンド膜表面が針状化されていない未処理のダイヤモンド膜及び白金を電極として使用した燃料電池用電極も夫々作製した。そしてこれらの燃料電池用電極のサイクリック・ボルタンメトリー測定を行った。測定は、参照電極にＡｇ／ＡｇＣｌを使用した。
【０１０５】
図１５は、サイクリック・ボルタンメトリー測定の結果を示すグラフ図である。図１５において、本実施例の燃料電池用電極を破線１１で、未処理のダイヤモンド膜を電極として使用したものを実線１６ａで、白金を電極としたものを一点鎖線１６ｂで示す。図１５に示すように、本実施例の燃料電池用電極は、メタノール分解効率が極めて高いことがわかる。
【０１０６】
実施例５（グルコースセンサ）
図５と同様の構造を有するグルコースセンサを作製した。針状構造が形成されたダイヤモンド作用電極３４を有する本実施例のグルコースセンサと、針状構造を形成していない未処理のダイヤモンド膜を作用電極３４として有するグルコースセンサと比較した結果、生体識別物質３５が約５倍長い期間固定され、活性が約５倍長い期間失われなかった。
【０１０７】
実施例６（有機発光素子）
有機発光素子を作製し、その発光強度を測定した。先ず、２個の窒化シリコン基板を用意し、このシリコン基板上に正孔注入電極として白金膜を蒸着し、マイクロ波プラズマＣＶＤ法により、正孔注入用電極上に正孔輸送層として高濃度にＢをドーピングしたダイヤモンド膜を約１μｍの厚さで形成した。そして、一方のダイヤモンド膜には、表１の条件２に示す針状ダイヤモンド膜形成条件で水素プラズマ処理をして、針状表面を有するダイヤモンド膜を形成した。他方は未処理のダイヤモンド膜とした。次いで、これらの２種類のダイヤモンド膜上に、有機発光層として、ＭＤＤＯ−ＰＰＶ（Poly(2-methoxy5-dodecyloxy-1,4-phenylene vinylene)）膜をスピンコートした。更に、有機発光層上に電子注入用電極として、アルミニウム薄膜を真空蒸着した。
【０１０８】
このようにして作製した本実施例の有機発光素子及び未処理のダイヤモンド膜を使用した有機発光素子の正孔注入電極と、電子注入電極との間に電圧を印加して各素子の発光強度を測定した。図１６は縦軸に発光強度をとり、横軸に波長をとって、実施例６の有機発光素子の発光強度を示すグラフ図である。図１６において、破線１２及び実線１７で示すのは夫々本実施例の有機発光素子及び未処理のダイヤモンド膜を使用した有機発光素子に夫々２５Ｖの電圧を印加した場合の発光スペクトルを示す。図１６に示すように、本実施例の有機発光素子の方が、針状構造からの正孔注入効率が高いため、発光強度が約２０％増大した。
【０１０９】
実施例７（電子放出素子）
図６に示した構造を有する電子放出素子を作製し、その電流電圧特性を測定した。電流電圧素子は、図６に示す電子放出素子のダイヤモンド層４２に実施例２と同様の処理試料を使用したものと、表面に針状構造を形成していない未処理のダイヤモンド膜をダイヤモンド層４２に使用したものとを用意し、夫々真空中で２００μｍ離して上部電極を配置した。作製したこれらの電子放出素子の電流電圧測定を行った。
【０１１０】
図１７は、縦軸に電流密度とり、横軸に印加電圧をとって、実施例７の電子放出素子の電流電圧測定の結果を示すグラフ図である。図１７において、破線１３は本実施例の電子放出素子、実線１８は未処理のダイヤモンド膜を使用した電子放出素子の測定結果を示す。図１７に示すように、本実施例の電子放出素子の立ち上がり電圧が、未処理のダイヤモンド膜を使用した電子放出素子と比較すると、１／３００に低下し、電流値が大幅に増大することがわかった。
【０１１１】
実施例８（紫外線発光素子）
実施例２の処理試料及び参照試料を使用し、紫外線素子を作製して、その発光強度を測定した。実施例２の処理試料及び参照試料上に、膜厚が０．４μｍのアンドープダイヤモンド膜を形成した後、金の極薄膜を蒸着して上部電極を形成し、本実施例の紫外線発光素子及び未処理のダイヤモンド膜を使用した紫外線発光素子を得た。いずれの紫外線発光素子についても、ダイヤモンド膜に正電圧、金極薄膜に負の電圧を印加したところ、５．０ｅＶの発光が観察されたが、針状構造を形成した本実施例の紫外線発光素子の発光強度は参照試料を使用した紫外線発光素子の約２．６倍大きかった。
【０１１２】
実施例９（可視光発光素子）
図７に示した構造を有する可視光発光素子を作製し、その発光強度を測定した。実施例２と同様の試料、即ち、下部電極となる低抵抗シリコン基板上にｐ型ダイヤモンド膜を５μｍ形成したダイヤモンド膜に対して、表１の条件２に示す針状ダイヤモンド膜形成条件でプラズマ処理し、針状表面を有するダイヤモンド膜としたものと、未処理のダイヤモンド膜とを基板とし、これらのダイヤモンド膜上にマイクロ波ＣＶＤ法により膜厚が約２μｍのアンドープダイヤモンド薄膜を積層することにより、ほぼ平坦な表面を形成した。次いで、この上に、蛍光薄膜及びＩＴＯからなる透明な上部電極を順次積層し、微細加工により可視光発光素子を作製した。そして、下部電極と上部電極との間に電圧５００Ｖを印加したところ、蛍光薄膜から発光が生じた。本実施例の針状表面を有するダイヤモンド膜を使用した可視光発光素子の発光強度は、未処理のダイヤモンド膜を使用した可視光発光素子の発光強度より約５倍程度大きかった。
【０１１３】
実施例１０（ガスセンサ）
図８に示した構造を有するガスセンサを作製し、その感度応答特性について評価した。先ず、縦が２ｍｍ、横が１ｍｍのピッチで溝を形成した２．５４ｃｍ径の窒化珪素焼結体を基板として熱フィラメント気相合成装置を使用して膜厚５μｍの多結晶アンドープダイヤモンド薄膜を成膜した。続いて、マイクロ波プラズマ装置を使用してプラズマ処理を行って表面に針状構造を形成し、更に、感ガス層であるＢドープした半導体ダイヤモンド層（膜厚１０００Å）をアンドープダイヤモンド層上に積層した。半導体ダイヤモンド層内のＢの原子密度は２×１０¹⁸／ｃｍ³であった。次に、試料を２００℃のクロム酸及び硫酸の混合液で２０分間、次いで１００℃の王水で１０分間洗浄した。この後、スパッタ蒸着法によりダイヤモンド薄膜表面には１対の白金電極を形成した。白金電極の膜厚は３０００Åとし、白金電極の面積は、１ｍｍ×０．５ｍｍ、電極間隔は０．５ｍｍとした。電極形成後、２ｍｍ×１ｍｍのセンサユニットに分割した。また、アルミナからなる母材裏面に、スパッタ蒸着法により白金ヒータを形成した。白金ヒータの膜厚は３０００Åとした。そして、アルミナ母材の白金ヒータが形成されていない側に、分割したセンサユニットを接着した。続いて、１００μｍ径の白金リード線を使用してスポット溶接により、白金ヒータ及び白金電極と、センサ・マウントユニットの端子とを夫々接続した。最後に白金電極と白金リード線との接続部を金ペーストで被覆し、大気中６００乃至７００℃で３０分間の熱処理を行いガスセンサを作製した。
【０１１４】
作製したガスセンサのホスフィンガスに対する応答を評価するため、ホスフィンガスに対するガスセンサの電気抵抗値を測定した。図１８は、縦軸にガスセンサの出力（電気抵抗）をとり、横軸に時間をとって、実施例１０のガスセンサのホスフィンに対する感度測定結果を示すグラフ図である。測定は、大気中で、白金ヒータにより、温度を３００乃至４５０℃に保ち、０．１、０．２、０．５体積ｐｐｍのホスフィン（ＰＨ₃）ガスを順次曝露させ、ガスセンサの出力（抵抗値）変化を観測した。図１８に示すように、０．１体積ｐｐｍのホスフィンガスに対して８０乃至１００％の出力変化が観測できた。この値は、未処理のダイヤモンド薄膜を使用したガスセンサより、感度が２０乃至２００％程度大きいことを示し、本実施例のガスセンサのように、針状構造を形成したダイヤモンド膜をセンサ部に使用することにより、センサ感度が大幅に向上することが分かった。
【０１１５】
実施例１１（短波長センサ）
短波長センサを作製し、その特性について評価した。基板上に形成したアンドープダイヤモンド膜を表１の条件２に示す針状ダイヤモンド膜形成条件で水素プラズマ処理し、表面に針状構造を形成した試料と、これと比較するためにプラズマ処理しない参照試料とを形成し、これらのダイヤモンド膜上に微細加工技術を使用して、白金により、電極が相互に噛み合った１対の櫛形電極を形成した。そして、この電極間に数ボルトの電圧を印加し、これらの素子に紫外線を照射すると、電極間に流れる電流を測定した。測定の結果、本実施例の短波長センサは、表面に針状構造を形成していない未処理のダイヤモンド膜を使用した短波長センサと比較すると、同一の印加電圧、紫外線照射量において、電極間に流れる電流が約１桁大きくなり、本実施例の短波長センサは、極めて紫外線吸収が大きい、即ち高感度であることが分かった。
【０１１６】
実施例１２（光増倍管）
図９に示した構造を有する光増倍管を作製し、受電面と光電面との間に流れる電流を測定した。
【０１１７】
先ず、導電性の低抵抗のシリコン基板上に、マイクロ波ＣＶＤ法により、Ｂドープ多結晶ダイヤモンド膜を合成し、表１の条件２に示す条件で水素プラズマ処理を行って針状表面を有するダイヤモンド膜を形成した反射型光電面を作製した。次に、高温に熱した金属板上でインジウム溶解し、この上にＢドープ多結晶ダイヤモンド膜を形成したシリコン基板を配置することにより、シリコン基板裏面に金属板を接着した。この光電面に対向してメッシュ状の金属受電面を配置し、これらを石英ガラス管に挿入した後、管内を１０^-7Ｔｏｒｒ以下の真空にして封止し、光増倍管を作製した。
【０１１８】
作製した光増倍管の受電面に対して光電面に１０乃至２００Ｖの負電圧を印加しつつ、波長が２００ｎｍの紫外線を光電面に照射したところ、光電面から電子放出を確認した。本実施例の針状表面を有するダイヤモンド膜を光電面の電子放出板に使用した光増倍管と、表面に針状構造を形成していない未処理のダイヤモンド膜を使用した光増倍管とを同様の電圧を印加しつつ、紫外線を照射して比較したところ、針状表面を有するダイヤモンド膜を使用した光増倍管の方が電流量が約１桁大きかった。
【０１１９】
実施例１３（放電電極）
図１０に示した構造を有するフラッシュランプ用の放電電極を作製して安定性の評価を行った。先ず、電極基材８４の円錐部８３上に形成した針状のダイヤモンド薄膜８５は、膜厚を０．１乃至１０μｍとし、Ｂをドープしたｐ型の半導体ダイヤモンドとした。この放電電極を陰極とし、陽極との間に適当な電圧を印加したところ、充填したＸｅガスから生じたアーク放電の光出力の安定性は、ダイヤモンド薄膜をコーティングいていないフラッシュランプが約１．５％、また、ダイヤモンド薄膜をコーティングしているがプラズマ処理をせず、表面に針状構造を形成していない未処理のダイヤモンド膜を形成した放電電極を使用したフラッシュランプでは、約０．７５％となったのに対し、本実施例の放電電極では、光出力の安定性が０．５％以下となった。
【０１２０】
次に、繊毛状表面を有する炭素系材料を製造してその特性を評価した結果について説明する。
【０１２１】
実施例１４（電気分解用電極）
電気分解用電極を作製し、その特性を評価するため、塩化ナトリウム水溶液の電気分解を行った。なお、比較のため、プラズマ処理を行わず、表面に繊毛状構造を形成していない炭素系材料を使用したものについても同様に電気分解を行った。
【０１２２】
電気分解用電極として、シリコン基板上に形成した１辺が２０ｍｍの正方形のグラファイトを使用した。そして、実施例１４のグラファイト電極として、図１１に示す繊毛状炭素系材料の製造条件と同一の条件で処理したものを使用した。即ち、プラズマ処理条件は、水素ガスを用いてマイクロ波プラズマ発生装置（周波数２．４５ＧＨｚ）によりプラズマを発生させ、ガス圧１．５Ｔｏｒｒ、基板温度４００ ℃、処理時間１時間として、グラファイトの表面に高密度の繊毛状構造を形成したものである（実施例１４）。比較例のグラファイトとして、プラズマ処理を行わなかったものも用意した（比較例１４）。なお、実施例１４及び比較例１４の電気分解用電極について、シリコン基板の裏面に銀ペーストで銅配線を接着し、炭素系材料表面に、１辺が１２ｍｍの正方形の表面領域を残し、その他全体をエポキシ樹脂によりシールして、電気分解に供した。
【０１２３】
ビーカに０．１Ｍ％の塩化ナトリウム水溶液を入れ、アノードに本実施例１４の電気分解用電極を使用し、カソードに白金電極を使用した場合と、アノードに比較例１４の電気分解用電極を使用し、カソードに白金電極を使用した場合とについて、夫々同一電圧及び同一の電気量で通電し、発生する水素量及び塩素量を測定して、実施例１４と比較例１４における電気分解効率を比較した。
【０１２４】
その結果、未処理のグラファイトを使用した比較例１４に比して、本発明の範囲に入る実施例１４の電気分解用電極の方が、電気分解効率が約３５％優れていた。このため、電気分解が比較例１４より実施例１４の方が短時間に完了した。これは、実施例１４の表面積が比較例１４よりも大きいためである。
【０１２５】
実施例１５（電子放出素子）
図１３に示した構造を有する電子放出素子（第１４実施例）を作製し、その電流電圧特性を測定した。電子放出素子は、図１３に示す電子放出素子の炭素系材料層９２にプラズマ処理して繊毛状構造を形成した試料（実施例１５）を使用したものと、表面に繊毛状構造を形成していない未処理の炭素系材料を炭素系材料層９２に使用したもの（比較例１５）とを用意し、夫々真空中で１７０μｍ離して上部電極を配置した。作製したこれらの電子放出素子の電流電圧測定を行った。なお、炭素系材料層として、グラファイト層を使用した。
【０１２６】
図１９は、縦軸に電流密度をとり、横軸に印加電圧をとって、実施例１５の電子放出素子の電流−電圧特性の測定結果を示すグラフ図である。図１９において、破線１４は実施例１５の電子放出素子、実線１９は未処理の炭素系材料である比較例１５を使用した電子放出素子の測定結果を示す。図１９に示すように、実施例１５の電子放出素子の立ち上がり電圧が、比較例１５の電子放出素子に比して、１／３００に低下し、電流値が大幅に増大することがわかる。
【０１２７】
【発明の効果】
以上詳述したように、本発明によれば、ダイヤモンド又は炭素系材料に負のバイアス電圧を印加し、適切な基板温度で、低いガス圧の水素ガス又は水素を主成分とする混合ガスによるマイクロ波プラズマを発生させてダイヤモンド又は炭素系材料の表面を処理することにより、ダイヤモンドの表面に針状構造を形成し、又は炭素系材料の表面に繊毛状構造を形成することができる。この針状構造又は繊毛状構造は、ダイヤモンド又は炭素系材料の表面の面積を１０倍以上増大させ、物質の吸着量を増加させ、電子放出量が増大するため、電気分解用電極、化学センサ用電極、燃料電池用電極及びバイオセンサ用電極等の化学電極、電子放出素子、紫外線発光素子、可視光発光素子、ガスセンサ、短波長センサ、光電子放出板及び放電電極等の電子デバイス全般の性能を飛躍的に向上させることができる。
【０１２８】
また、ダイヤモンド膜をマイクロ波プラズマＣＶＤ装置により製造すると、ダイヤモンド膜の合成及び表面処理をいずれも同一チャンバ内で行うことが可能となり、製造が更に容易になると共に製造コストを極めて低減することができる。
【図面の簡単な説明】
【図１】本発明のプラズマ処理条件と、従来例１及び従来例２のプラズマ条件との比較を示すグラフ図である。
【図２】プラズマ処理前のダイヤモンド薄膜の表面の図面代用写真である（走査型電子顕微鏡（Scanning electron microscope（ＳＥＭ））、倍率：１００００倍）。
【図３】図２に示すダイヤモンド薄膜にプラズマ処理をし、表面に針状構造を形成したダイヤモンド薄膜の表面の図面代用写真である（ＳＥＭ写真、倍率６００００倍）。
【図４】図３に示す針状ダイヤモンド膜上に更に気相合成によりダイヤモンド膜を積層したダイヤモンド膜表面の図面代用写真である（ＳＥＭ写真、倍率６００００倍）。
【図５】本発明の第２実施例の針状ダイヤモンド膜を使用したバイオセンサ（グルコースセンサ等）のトランスジューサ部を示す断面図である。
【図６】本発明の第４実施例の電子放出素子を示す模式的断面図である。
【図７】本発明の第６実施例の可視光発光素子を示す断面図である。
【図８】本発明の第７実施例のガスセンサを示す模式的断面図である。
【図９】本発明の第９実施例の光増倍管用電子放出板を示す模式的断面図である。
【図１０】本発明の第１０実施例の放電電極を示す側面図である。
【図１１】鏡面研磨したグラファイトに水素プラズマ処理をし、その表面に繊毛状構造を形成したグラファイトの表面の図面代用写真である（ＳＥＭ写真、倍率６００００倍）。
【図１２】図１１に示す繊毛状炭素系材料上に更に気相合成によりダイヤモンド薄膜を積層した炭素系材料表面の図面代用写真である（ＳＥＭ写真、倍率６００００倍）。
【図１３】本発明の第１４実施例の電子放出素子を示す模式的断面図である。
【図１４】実施例３のサイクリック・ボルトメトリー測定の結果を示すグラフ図である。
【図１５】実施例４のサイクリック・ボルタンメトリー測定の結果を示すグラフ図である。
【図１６】縦軸に発光強度をとり、横軸に波長をとって、実施例６の有機発光素子の発光強度を示すグラフ図である。
【図１７】縦軸に電流密度、横軸に印加電圧をとって、実施例７の電子放出素子の電流電圧素子の測定結果を示すグラフ図である。
【図１８】縦軸にガスセンサの出力（電気抵抗）、横軸に時間をとって、実施例１０のガスセンサのホスフィンに対する感度測定結果を示すグラフ図である。
【図１９】縦軸に電流密度をとり、横軸に印加電圧をとって、実施例１５の電子放出素子の電流−電圧特性の測定結果を示すグラフ図である。
【符号の説明】
３０、４０、５３、６１；基板
３１、３８、５４；アンドープダイヤモンド膜
３２；白金参照電極
３３；白金対向電極
３４；作用電極
３５；生体識別物質
３６；生体膜
３７；ヒータ
４１；下部電極
４２；ダイヤモンド層
４３；アンドープダイヤモンド薄膜
４６；蛍光薄膜
４４；上部電極
４７；配線用電極
４５；電子
５２；母材
５５；ｐ型半導体ダイヤモンド層
５６；電極
５１；ヒータ
６２；Ｂドープ多結晶ダイヤモンド膜
６３；光電面
６４、６７；金属電極
６５受電面
６８、６９；リードピン
７０；管
７１；封着ガラス
７２；窓
８０；放電電極（陰極）
８１；支持部
８２；円柱部
８３；円錐部
８４；電極基材
８５；ダイヤモンド薄膜
９２；炭素系材料層
９３；炭素系材料薄膜[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diamond- or cilia-like carbon having a needle-like surface, a method for producing the same, an electrode using the same, and an electronic device, and in particular, diamond or cilia having a needle-like surface suitable as an electron-emitting material. The present invention relates to a carbon-based material having a surface having a shape. In the present invention, the “carbon-based material” refers to graphite, amorphous carbon (aC), and hydrogenated amorphous carbon (aC: H), which are often used in the past, It is defined as including diamond, a B—C—N compound, and a composite material containing Si or a metal in carbon, which is being studied recently. Examples of the carbon-based material include bulk, powder, sintered body, and carbon-based material particles or carbon-based material thin films synthesized by physical and chemical vapor deposition.
[0002]
[Prior art]
Carbon-based materials are expected to be applied to highly functional and highly valued elements or devices such as chemical electrodes, electrodes for electronic devices, and elements for electron emission. For this purpose, ciliary structures with a large surface area are expected. Or it is necessary to make it a needle-like structure. Among these carbon-based materials, diamond has the highest practicality.
[0003]
Diamond that does not contain an impurity element is an electrical insulator, but can be made into a p-type or n-type semiconductor by doping with an element such as B, P, or S. Semiconductor diamond is known to have superior electrical characteristics compared to Si, GaAs, SiC, and the like, and research and development of semiconductor sensor devices are underway.
[0004]
Recently, due to the negative electron affinity (NEA) of the hydrogen-terminated diamond surface, the electron emission voltage from diamond is low and the electron emission is high. That is, it is found that electron emission occurs with high efficiency, and application to a flat panel display using electron emission is considered.
[0005]
Further, it has been shown that semiconductor diamond can be used as a chemical electrode because it has excellent characteristics such as high overvoltage, low noise, and chemical resistance.
[0006]
Diamond types include natural and artificial single crystals, powders and sintered bodies. Further, diamond particles or a diamond thin film can be synthesized by gas phase synthesis using hydrocarbon gas as a raw material. As a vapor phase synthesis method of this diamond thin film, a microwave chemical vapor deposition (CVD) method (for example, Japanese Patent Publication Nos. 59-27754 and 61-3320) is known. By such a gas phase synthesis method, a film-like diamond can be produced at a low cost and in a large area.
[0007]
Usually, the diamond film is a polycrystalline film in which particles are aggregated randomly. However, by adjusting the synthesis conditions, it is possible to synthesize a uniaxially oriented diamond film in which most regions of the surface are composed of diamond (111) crystal planes or (100) crystal planes. In addition, when (100) -oriented single crystal Si, SiC, or the like is used for the substrate, a diamond film (hereinafter referred to as a highly oriented film) in which the diamond (100) crystal plane is oriented in-plane can be synthesized. Furthermore, when single crystal Pt (111) or Ir (100) is used for the substrate, diamonds in which the (111) or (100) crystal planes of diamond are oriented in-plane and the adjacent crystal planes are fused (coalescence), respectively. A membrane (hereinafter referred to as a fusion membrane) can be synthesized.
[0008]
For etching a diamond film, oxygen and Ar mixed gas or H₂A gas containing oxygen such as O gas is used, and the surface of the diamond film is treated with plasma of these gases. As described above, conventionally, etching of a carbon-based material is performed by high-temperature treatment using oxygen and plasma. However, with this method, the surface of the carbon-based material is uniformly etched, or some unevenness is generated. Therefore, it is not possible to obtain a large surface area of the cilia-like structure or the needle-like structure.
[0009]
Further, as a carbon ciliary structure having a large surface area, recently discovered carbon nanotubes are well known, but there is a problem that the yield during production is low and the cost is high.
[0010]
Therefore, there is a method for uniformly etching a diamond film by treating the surface of the diamond film while applying a negative bias voltage to the polycrystalline diamond film using hydrogen plasma excited by a microwave of 2.45 GHz. (BR Stoner, GJ Tessmer, and DL Dreifus, Applied Physics Letters, Vol. 62, No. 15, pp1803-1805, 12 April 1993: Conventional Example 1). In this case, the gas pressure of hydrogen gas is 1.33 × 10^ThreeTo 1.995 × 10^ThreeThe substrate temperature is maintained at about 500 ° C ..
[0011]
On the other hand, hydrogen (gas pressure 5.3 to 9.3 × 10^-2The surface of the diamond film is needle-shaped by treating the polycrystalline diamond thin film or single crystal diamond with an ECR (electron cyclotron resonance) plasma generated by a microwave of 2.45 GHz. The technology has also been disclosed (Yamamoto et al., Abstracts of the 13th Diamond Forum Symposium, p. 220 (New Diamond Forum, published in November 1999): Conventional Example 2). In the method of Conventional Example 2, the surface of the diamond film can be formed into a needle shape only when hydrogen plasma is used. Further, as a result of evaluating the electron field emission, a low electric field is obtained by forming a needle-like structure. High electron emission density is obtained.
[0012]
[Problems to be solved by the invention]
However, since the gas pressure is high in the method of Conventional Example 1, it is difficult to generate a uniformly expanded plasma, and a diamond film having a large area cannot be uniformly etched. Further, since the gas pressure is high, the diamond film is uniformly etched when processing is performed under such conditions.
[0013]
Further, the technique of Conventional Example 2 has a problem that an ECR plasma generator having a large magnetic field coil for generating a uniform magnetic field in the reaction chamber is necessary.
[0014]
The present invention has been made in view of such problems, and diamond or carbon-based material having a needle-like or ciliary structure surface by treating the surface with microwave plasma in a simpler manner, and its production It is an object to provide a method, an electrode using the method, and an electronic device.
[0015]
[Means for Solving the Problems]
The diamond having a needle-like surface according to the present invention is subjected to surface treatment by microwave plasma with hydrogen gas by applying a negative voltage, maintaining the temperature of the substrate at −50 to 800 ° C., and pressure of 66.5 to 665 Pa. And a needle-like structure is formed on the surface.
[0016]
In the present invention, since a needle-like structure is formed on the surface, the surface area is 10 times or more wider than that of normal diamond, and thus has excellent electrode characteristics. Further, since the tip is sharp, it has excellent electron emission characteristics.
[0017]
The method for producing a diamond having a needle-like surface according to the present invention comprises synthesizing a first diamond on a substrate, applying a negative voltage to the first diamond, and adjusting the temperature of the substrate to −50 to 800. A process of forming a needle-like structure on the surface of the first diamond by maintaining the temperature of the first diamond and treating the surface of the first diamond by generating microwave plasma using hydrogen gas having a pressure of 66.5 to 665 Pa. It is characterized by having.
[0018]
In the present invention, a needle-like structure can be formed on the surface of the first diamond by processing in a low gas pressure plasma generated by a microwave plasma generator without a large coil. It is possible to obtain a diamond which can be processed in area and has excellent electron emission characteristics at an extremely low cost.
[0019]
Further, in the hydrogen gas, nitrogen gas, He gas, Ar gas, oxygen gas, CO₂Gas, H₂One or more gases selected from the group consisting of O gas and hydrocarbon gas may be mixed at a mixing ratio of 10% by volume or less. By mixing these gases with hydrogen gas, the processing speed and surface shape of diamond can be controlled.
[0020]
Further, after the step of forming the needle-like structure, a step of synthesizing diamond to form a second diamond on the first diamond may be included. By forming the second diamond, it is possible to repair the damage received on the surface of the first diamond by the plasma treatment and to obtain a diamond having a needle-like surface with higher crystallinity.
[0021]
Furthermore, the first diamond and / or the second diamond may be semiconductor diamond doped with impurities. A semiconductor can be formed by doping impurities into diamond.
[0022]
The first diamond formation step and the plasma treatment step can be continuously performed in the same chamber. As a result, the synthesized diamond can be plasma-treated as it is, so that the diamond surface can be prevented from being exposed to the atmosphere and contaminated, and the diamond synthesis and plasma treatment can be further performed continuously. It can be manufactured at low cost and the manufacturing time is shortened.
[0023]
The carbonaceous material having a ciliary surface according to the present invention is mainly composed of hydrogen or hydrogen having a substrate temperature of −50 to 1000 ° C. and a pressure of 1330 Pa or less while applying a negative voltage to the carbonaceous material. A cilia-like structure is formed on the surface by surface treatment with plasma of a mixed gas as a component.
[0024]
In the present invention, the cilia-like structure can be formed only on the surface of the carbon-based material that requires functionality, so that treatment of a large area is possible, and the cilia-like shape having excellent characteristics at an extremely low cost. A carbon-based material having a structure can be obtained. The plasma of hydrogen and a mixed gas containing hydrogen as a main component of the present invention can be generated by high frequency, microwave, direct current discharge, arc discharge or the like. Further, the definition of the ciliary structure in the present invention is not particularly limited, but the cilia-like structure of the carbon-based material typically has a tip diameter of several to several tens of nm and a length of several hundreds. To several μm.
[0025]
Furthermore, the method for producing a carbon-based material having a ciliary surface according to the present invention includes a step of depositing a carbon-based material on a substrate to form a thin film, a negative voltage is applied to the thin film, and the temperature of the substrate is adjusted. A ciliary structure is formed on the surface of the thin film by treating the surface of the thin film by generating a plasma of hydrogen or a mixed gas containing hydrogen as a main component at a pressure of 1330 Pa or less, maintained at −50 to 1000 ° C. And a step of performing.
[0026]
In the method for producing a carbon-based material having a cilia-like surface, a step of forming diamond on the thin film by gas-phase synthesis of diamond can be provided after the step of forming the ciliary structure.
[0027]
The electrode according to the present invention is made of diamond having a needle-like surface as described above or a carbon-based material having a cilia-like surface.
[0028]
Since the surface of the electrode of the present invention is formed of diamond or carbon-based material having a needle-like or cilia-like surface whose surface is subjected to plasma treatment, the electrode surface area is diamond or carbon obtained by ordinary vapor phase synthesis or the like. Since it is about 10 times wider than the system material and has a high substance adsorbing power, it can be suitably used as an electrode for electrolysis, chemical sensor, fuel cell, biosensor, or carrier injection.
[0029]
The electronic device according to the present invention is characterized in that the above-described diamond-based surface having a needle-like surface or a carbon-based material having a cilia-like surface is a constituent element.
[0030]
In the present invention, since the surface has a needle-like structure, it has excellent electron emission characteristics. Therefore, when used in an electronic device, its performance can be dramatically improved. The electronic device of the present invention uses an organic light-emitting element, an electron-emitting element, an ultraviolet light-emitting element, a visible light-emitting element, a flat panel display, a gas sensor, a short-wave dimming sensor, or a photoelectron-emitting plate having excellent performance by utilizing its shape. can do. The same applies to an electronic device having a carbon-based material having a ciliated surface as a constituent element.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples of the present invention will be described in more detail. First, a diamond having a needle-like surface according to the first embodiment of the present invention will be described. As a result of earnest experiment research to solve the above-mentioned problems, the inventors of the present application used a microwave plasma apparatus for diamond vapor phase synthesis using microwaves, applied a negative bias voltage to diamond, By maintaining the temperature in the range of −50 to 800 ° C., setting the gas pressure to 66.5 to 665 Pa as an etching process gas, generating plasma by hydrogen gas or a mixed gas mainly containing hydrogen gas, and processing diamond. The inventors have found that a high-density needle-like structure can be formed on the diamond surface.
[0032]
Further, the inventors of the present application have found that a diamond film can be formed while maintaining a needle-like structure on the surface by further synthesizing and laminating a diamond film on the diamond having a needle-like surface. After the surface is needle-shaped by plasma treatment, a diamond film is newly deposited to repair the diamond surface damage caused by the plasma treatment and obtain a diamond with a needle-like structure with better crystallinity. it can. Furthermore, it has been found that the shape of the acicular structure can be controlled by controlling the gas phase synthesis conditions of the diamond film to be laminated. That is, by controlling the temperature, pressure, etc. of the substrate during vapor phase synthesis, the diamond film is preferentially grown in the longitudinal direction of the needle of the needle-like structure formed on the surface of the diamond, or in the lateral direction. It is possible to control the needle shape by, for example, preferentially growing a diamond film. Furthermore, a p-type or n-type semiconductor diamond film can be obtained by adding impurities to the diamond film to be laminated.
[0033]
In addition, the inventors of the present application also provide a highly oriented film in which the diamond (100) crystal plane is aligned in-plane, or a fusion in which the (111) or (100) crystal plane of diamond is aligned in-plane and adjacent crystal planes are fused. It has been found that by performing the plasma treatment of the present invention using a film, the crystal orientation of the formed needle-like structure can be aligned. By aligning the crystal orientation of the acicular structure, for example, the electron emission characteristics and the luminance distribution of the light emitting element can be made uniform.
[0034]
FIG. 1 is a graph showing a comparison between the plasma processing conditions for forming the needle-like structure of the present invention and the plasma conditions of Conventional Example 1 and Conventional Example 2. FIG.
[0035]
In the present invention, as shown in FIG. 1, a diamond-like structure is formed on a diamond surface by treating diamond in a plasma generated at a gas pressure lower than that of the gas pressure of Conventional Example 1. It is a feature. However, when the diamond structure is etched to form a needle-like structure, if the gas pressure is less than 66.5 Pa, plasma cannot be generated stably and the etching rate becomes slow, which requires a long time for processing. On the other hand, when the gas pressure exceeds 665 Pa, the plasma cannot be spread uniformly, and a uniform needle-like structure cannot be formed on the surface of the diamond film. Thus, the inventors of the present application can form a needle-like structure by using a microwave plasma generator without a large coil and treating diamond with plasma generated at a pressure lower than that of Conventional Example 1. I found. Accordingly, the pressure of the hydrogen gas or the mixed gas containing hydrogen as a main component for forming the needle-like structure is 66.5 to 665 Pa.
[0036]
Further, the inventors of the present application have found that the needle-like structure is formed in a wide range of the temperature of the substrate at the time of the plasma treatment of −50 to 800 ° C. However, when the temperature exceeds 800 ° C., thermal strain tends to occur. On the other hand, in order to make the temperature of the substrate lower than −50 ° C., the structure of the apparatus becomes complicated for controlling the substrate temperature, and the etching rate is lowered, so that the processing time becomes longer. Therefore, the substrate temperature is set to -50 to 800 ° C.
[0037]
Etching gas is nitrogen gas, He gas, Ar gas, oxygen gas, CO2 in addition to hydrogen gas.₂Gas, H₂One or more gases selected from the group consisting of O gas and hydrocarbon gas (including gases such as alcohol and acetone) can be added to hydrogen gas at a mixing ratio of 10% by volume or less.
[0038]
When an inert nitrogen gas, He gas, Ar gas, or the like is added as a gas mixed with hydrogen, graphitization of the diamond surface proceeds, so that the etching rate can be increased.
[0039]
Also, oxygen gas, CO₂Gas and H₂When O gas or the like is added, the oxidation of diamond progresses, and the etching rate increases. In this case, the sharpness of the needle-like structure is lowered.
[0040]
On the other hand, when a hydrocarbon gas is added, the vapor deposition of carbon proceeds, so that the etching rate becomes slow.
[0041]
The practical frequency range is 2.45 GHz or 915 MHz, but the frequency is not limited to this.
[0042]
FIG. 2 is a scanning electron microscope (SEM) photograph of the surface of the diamond thin film before the plasma treatment. This diamond film is formed by vapor phase synthesis by generating plasma using a microwave with a frequency of 2.45 GHz under the diamond vapor phase synthesis conditions shown in Table 1 below. As shown in FIG. 2, it can be seen that a diamond thin film synthesized by vapor phase is usually an aggregate (polycrystalline film) of diamond particles having a clear self-shaped surface.
[0043]
FIG. 3 is an SEM photograph of the surface of the diamond thin film obtained by subjecting the diamond thin film shown in FIG. 2 to plasma processing and forming a needle-like structure on the surface. By using the same microwave plasma generator (frequency 2.45 GHz) for the diamond thin film shown in FIG. 2 and performing plasma treatment under the condition 2 shown in Table 1 below, as shown in FIG. The surface of the diamond thin film is etched to form high-density needle-like structures.
[0044]
[Table 1]

[0045]
Further, in hydrogen gas or hydrogen gas, nitrogen gas, He gas, Ar gas, oxygen gas, CO₂Gas, H₂A condition in which the gas pressure and the substrate temperature are within the scope of the present invention using a mixed gas in which one or more gases selected from the group consisting of O gas and hydrocarbon gas are mixed at a mixing ratio of 10% by volume or less. That is, the diamond film is formed by appropriately selecting the bias voltage from −100 to −500 V and the etching time from 0.2 to 10 hours in the range of pressure 66.5 to 665 Pa, substrate temperature −50 to 800 ° C. Even with the plasma treatment, diamond having a needle-like structure as shown in FIG. 4 is obtained. In addition, even if the diamond to be plasma-treated is a natural or artificial single crystal, powder, or sintered diamond, a needle-like structure can be formed on the surface.
[0046]
FIG. 4 is an SEM photograph of the surface of the diamond film in which a diamond film is further laminated by vapor phase synthesis on the acicular diamond film shown in FIG. After the acicular diamond film shown in FIG. 3 is formed, 0.3 vol% CH is formed on the acicular diamond film formed by the same microwave plasma generator._Four+ 99.7% by volume H₂A diamond film was grown by vapor phase synthesis using a gas of 6450 Pa, a gas pressure of 6650 Pa, a substrate temperature of 800 ° C., a processing time of 1 hour, using a microwave with a frequency of 2.45 GHz. . As shown in FIG. 4, even when a diamond film is further grown on the acicular diamond film, it can be seen that the diamond film is grown while maintaining the acicular structure on the surface.
[0047]
Next, a second embodiment of the present invention will be described. In the second embodiment, a diamond film having a needle-like surface is used as an electrode for electrolysis. As an electrode for electrolysis, for example, after forming a p-type semiconductor diamond film on a metal or low-resistance silicon substrate by a microwave CVD apparatus, plasma treatment is performed under predetermined conditions, and a needle is formed on the surface of the p-type semiconductor diamond film. What formed the shape structure can be used.
[0048]
In this embodiment, since a needle-like structure is formed on the surface by plasma treatment, the diamond film surface has a large area and the diamond film becomes thin by etching, thereby reducing energy loss due to heat generation and interface resistance. can do. Therefore, an electrode for electrolysis using a diamond film having a needle-like structure on the surface can reduce the electrical resistance and increase the contact area, so that the electrolysis efficiency can be remarkably improved and is necessary for electrolysis. The time to do can be made extremely short.
[0049]
In this embodiment, a p-type diamond film that has been subjected to plasma treatment is used, but the same effect can be obtained with an n-type diamond film.
[0050]
Similarly to the electrode for electrolysis, a diamond film having a needle-like surface can be used as an electrode for a chemical sensor. By using a diamond film having a needle-like surface, the surface area is increased, so that the sensitivity can be remarkably improved.
[0051]
Furthermore, it can also be used for a fuel cell electrode. By using a diamond film having an acicular surface, the amount of metal catalyst is increased, so that the fuel decomposition efficiency is remarkably increased, and thus a highly efficient fuel cell can be obtained.
[0052]
Next, a third embodiment of the present invention will be described. In the third embodiment, a needle-like diamond film is used as an electrode of a transducer part (signal conversion circuit) of a biosensor such as a glucose sensor. FIG. 5 is a cross-sectional view showing a transducer part of a biosensor using the needle-like diamond film of this example. As shown in FIG. 5, in the biosensor of this embodiment, an undoped diamond film 31 is formed on the substrate 30 as a base layer. A working electrode 34 made of semiconductor diamond is formed on the undoped diamond film 31, and a platinum counter electrode 33 and a platinum reference electrode 32 are formed on the undoped diamond film 31 on both sides of the working electrode 34. The working electrode 34 is covered with a bio-identification substance 35, and this bio-identification substance 35 is further covered with a biofilm 36. For example, in the case of a glucose sensor, glucose oxidase or the like can be used as the biometric substance 35. These working electrode 34, counter electrode 33, and reference electrode 32 are surrounded by a semiconductor diamond heater 37, and this heater 37 is covered with an undoped diamond film 38.
[0053]
In the case where the biosensor is a glucose sensor, for example, the glucose concentration can be measured by detecting the electron transfer when glucose in the sample is catalytically reacted with glucose oxidase to change to gluconolactone with an electrode. In order to extend the life of a biosensor, it is necessary to prevent the identification substance from flowing out during repeated measurement or long-time measurement. In this embodiment, since the needle-like structure is formed on the surface of the diamond working electrode 34, the fixing period of the biometric substance 35 is extremely long, and its activity is not lost for a very long time.
[0054]
Next, a fourth embodiment of the present invention will be described. In this example, the organic light-emitting device uses a needle-like diamond film as a carrier (electron or hole) transport layer.
[0055]
In this example, when a voltage is applied between the hole injection electrode and the electron injection electrode, a needle-like structure is formed on the surface of the diamond film formed as the hole transport layer. The hole injecting efficiency of the organic light emitting device can be increased, and an organic light emitting device with extremely high emission intensity can be obtained. Therefore, when the organic light-emitting device of this embodiment is applied to a flat panel by regularly arranging the devices on the flat panel using a fine processing technique, a highly efficient flat panel display can be obtained.
[0056]
Next, a fifth embodiment of the present invention will be described. In this embodiment, the electron-emitting device uses a diamond film having a needle-like structure.
[0057]
FIG. 6 is a schematic cross-sectional view showing the electron-emitting device of this example. As shown in FIG. 6, in the electron-emitting device of this example, a lower electrode 41 is formed on a base 40, and a diamond layer 42 having a needle-like structure formed on the surface is formed thereon. Further, the needle-like diamond layer 42 is spaced apart to form a transparent upper electrode 44 facing the lower electrode 41, and these are arranged in a vacuum. The upper electrode 44 and the lower electrode 41 are connected to a power source 48.
[0058]
In the present embodiment, a positive voltage is applied to the upper electrode 44 and a negative voltage is applied to the lower electrode 41, but since the needle-like structure is formed on the surface of the diamond layer 42, the amount of electrons 45 emitted from the diamond layer 42 is Is big. Therefore, the threshold value of the electron emission voltage is lowered, and the current value can be significantly increased. Such an electron-emitting device can be applied to a phototube, a flat panel display, a microwave oscillation source, a high-breakdown-voltage switching device, and the like, and these device characteristics can be dramatically improved.
[0059]
Next, a sixth embodiment of the present invention will be described. In this embodiment, the ultraviolet light emitting element uses a diamond film having a needle-like structure on the surface. In the ultraviolet light emitting device of this embodiment, a p-type diamond film having a needle-like structure formed on the surface is formed on a substrate made of low resistance silicon or the like. Further, an undoped diamond thin film is laminated on the diamond film having the needle-like surface, and an upper electrode made of an ultrathin film obtained by depositing gold or the like is further formed thereon.
[0060]
In this example, when a positive voltage is applied to the substrate side and a negative voltage is applied to the upper electrode, electrons at the Fermi level in the upper electrode pass through the undoped diamond thin film via a mechanism such as tunneling and are injected into the needle-like diamond film. Is done. These electrons recombine with holes present in the valence band to emit light. At this time, since the ultraviolet light-emitting element of this example has a needle-like structure on the surface, the electric field increases and the current density increases near the tip of the needle-like structure. Therefore, the emission intensity is extremely high.
[0061]
Next, a seventh embodiment of the present invention will be described. FIG. 7 is a cross-sectional view showing the visible light emitting device of this example. As shown in FIG. 7, in the visible light emitting device of this embodiment, a lower electrode 41 is formed on a substrate 40 such as silicon, and a diamond layer 42 is formed thereon. The diamond layer 42 is plasma-treated under a predetermined condition, and a needle-like structure is formed on the surface. Further, an undoped diamond thin film 43 is laminated on the upper surface. Further, a fluorescent thin film 46 and a transparent upper electrode 44 are sequentially laminated on the undoped diamond thin film 43. A wiring electrode 47 is selectively formed on the surface of the upper electrode 44. Further, the wiring electrode 47 and the lower electrode 41 are connected to a power source 48.
[0062]
In this embodiment, when a positive voltage is applied to the wiring electrode 47 and a negative voltage is applied to the lower electrode 41, electrons 45 as carriers are injected from the lower electrode 41 into the diamond film 42. The electrons 45 are accelerated in the diamond film 42 and the undoped diamond thin film 43 to excite the fluorescent thin film 46 to emit fluorescence, and further move from the upper electrode (transparent electrode) 44 to the wiring electrode 47. At this time, the acicular diamond thin film 42 containing a high concentration of boron enhances the electric field in the vicinity of the tip of the acicular structure and increases the emission density of the electrons 45, thereby increasing the current density and obtaining an extremely high emission intensity. be able to. Moreover, a high-intensity flat panel display can be obtained by using the visible light emitting element of the present embodiment.
[0063]
Next, an eighth embodiment of the present invention will be described. FIG. 8 is a schematic cross-sectional view showing the gas sensor of this example. The gas sensor of the present embodiment is a gas sensor using a diamond film having a needle-like surface.
[0064]
As shown in FIG. 8, in the gas sensor of this embodiment, a substrate 53 made of silicon or the like is bonded on a base material 52, and an undoped diamond layer 54 and a semiconductor in which a needle-like structure is formed on the substrate 53 are formed. Diamond layers 55 are sequentially stacked. This diamond double-layer film is a sensor part, and can be formed as a continuous diamond film by a microwave plasma CVD apparatus. On the p-type semiconductor diamond layer 55 having a needle-like surface structure, a pair of electrodes 56 made of platinum, for example, are formed at appropriate intervals by fine processing. A wiring 57 made of platinum or the like is covered with and adhered to these electrodes 56 by a paste (not shown) made of gold or the like. A heater 51 is provided on the back surface of the base material 52 by patterning a resistance material such as platinum with a thin film.
[0065]
Base material 52 is a single crystal, polycrystal, amorphous, sintered body or thin film of a material selected from the group consisting of silicon, silicon nitride, silicon oxide, alumina, silicon carbide, strontium titanate and magnesium oxide. It is preferable. In particular, the material of the base material 52 is preferably silicon, silicon nitride, silicon oxide, alumina, or silicon carbide. This is because the optimum substrate temperature for diamond vapor phase synthesis is 700 to 1000 ° C., and the vapor phase synthesis is performed in a chemically active hydrogen plasma atmosphere, so that the substrate material can withstand such conditions. It is necessary. In addition, since a platinum heater is formed on the back surface of the substrate, the substrate material must be electrically insulating. The materials described above meet these conditions. These materials may be formed into a substrate by processing a bulk material, or may be a thin film coated on a base material.
[0066]
In this embodiment, when the sensor unit is heated to a predetermined temperature by the heater 51 and a gas species is adsorbed on the surface of the sensor unit when the sensor unit is in an operating state, a depletion layer is formed on the p-type semiconductor diamond layer 55. It spreads and the electrical resistance changes. This change in electrical resistance is detected by applying a voltage between the electrodes 56. As a result, the presence of gas is detected as a change in the electrical resistance value in the p-type semiconductor diamond layer 55, but since a needle-like structure is formed on the surface of the p-type semiconductor diamond layer 55, the adsorption rate of the gas species Therefore, the detection sensitivity of the gas sensor is extremely high. If the relationship between the electrical resistance value and the gas concentration is obtained in advance, the gas concentration can be detected from the detected electrical resistance value based on the relationship.
[0067]
Next, a ninth embodiment of the present invention will be described. In this embodiment, the short wavelength sensor uses a diamond film having a needle-like surface.
[0068]
An undoped diamond film having a needle-like structure formed on the surface is formed on a substrate made of silicon, silicon nitride, silicon oxide, alumina, silicon carbide, metal, or the like. A pair of electrodes made of platinum or the like is formed on the needle-like undoped diamond film by a fine processing technique.
[0069]
In this embodiment, when an ultraviolet ray is applied while applying a voltage of several to several tens of volts between the electrodes, a pair of electrons and holes is generated in the diamond film, an electric current flows, and the ultraviolet ray can be detected. However, since the diamond film of the short wavelength sensor of the present example has a needle-like structure on the surface, the absorption rate of ultraviolet rays is high and the sensitivity is extremely high.
[0070]
Next, a tenth embodiment of the present invention will be described. FIG. 9 is a schematic cross-sectional view showing an electron emission plate for a photomultiplier tube of this example. In the photomultiplier tube electron emission plate of the present embodiment, as shown in FIG. 9, an electron emission plate having a needle-like structure formed on the surface of a conductive low-resistance silicon substrate 61 by microwave CVD. A B-doped polycrystalline diamond film 62 is formed, and a reflective photocathode 63 is formed. The B-doped polycrystalline diamond film 62 on the reflective photocathode 63 is treated with hydrogen plasma to form a needle-like structure, and the back surface of the silicon substrate 61 is made of metal via indium (not shown). An electrode (metal plate) 64 is bonded. Further, the back surface of the metal electrode 64 is connected to a conductive support member 67a, thereby supporting the reflective photocathode 63. And above the photocathode 63, it has the mesh-shaped metal power receiving surface 65 arrange | positioned facing the photocathode 63, the one end is connected to the electroconductive support member 67b, and, thereby, the power receiving surface 65 is It is supported. The photocathode 63 and the metal power receiving surface 65 are connected to lead pins 68 and 69 via support members 67a and 67b, respectively, and are arranged to face the photocathode 63 and the photocathode 63 above. A metal power receiving surface 65 is sealed in a sealed glass tube 70 made of quartz glass or the like whose inside is evacuated. A window 72 made of, for example, calcium fluoride is formed at a position facing the metal power receiving surface 65 of the sealing glass tube 70.
[0071]
In the present embodiment, when a negative voltage is applied to the photoelectric surface 63 with respect to the power receiving surface 65 and ultraviolet light having a wavelength of, for example, about 200 nm is transmitted from the window 72 through the metal power receiving surface 65 and irradiated to the photoelectric surface 63, Electrons are emitted from the B-doped polycrystalline diamond film 62 on the surface 63. At this time, since a needle-like structure is formed on the surface of the B-doped polycrystalline diamond film 62 which is an electron emission plate, the surface unevenness is large, so that the amount of ultraviolet absorption increases, and electron emission from the photocathode 63 is prevented. It becomes very large and therefore a very large current can be obtained.
[0072]
Next, an eleventh embodiment of the present invention will be described. FIG. 10 is a side view showing the discharge electrode of this example. As shown in FIG. 10, in the discharge electrode of this embodiment, the discharge electrode (cathode) 80 has a cylindrical portion 82 at the tip of an elongated rod-like support portion 81, and further, at the tip of this cylindrical portion 82, an electron A conical conical portion 83 is formed to efficiently discharge, and an electrode base 84 is configured. The electrode base 84 is made of an electrode base material made of tungsten or the like having a dense structure, for example. On the conical portion 83 of the electrode substrate 84, for example, a diamond thin film 85 having a thickness of 0.1 to 10 μm is coated. The diamond thin film 85 is a p-type impurity semiconductor doped with a group III element such as boron (B) as an impurity, and the surface of the diamond thin film 85 is treated with hydrogen plasma under predetermined conditions. A needle-like structure is formed.
[0073]
In this embodiment, since the surface of the electrode substrate 84 is coated with a semiconductor diamond thin film 85 having a needle-like surface, diamond is applied with an appropriate voltage applied between the cathode 80 and the anode (not shown). Electrons are easily emitted from the thin film 85, and arc discharge is easily generated by the filled gas such as Xe. As a result, the improvement in output stability is particularly effective in application fields such as devices that require high reproducibility.
[0074]
The discharge tube of the present invention can be applied to, for example, a pulse lighting type flash lamp or a DC lighting type discharge tube.
[0075]
Next, examples of the carbon-based material having a cilia-like surface according to the present invention will be described. Inventors of the present application have made extensive experimental research to form a ciliary structure having a large surface area at low cost in a carbon-based material, and as a result of using a plasma generator, applying a negative voltage to the carbon-based material, By maintaining the temperature in the range of −50 to 1000 ° C., setting the gas pressure as a plasma processing gas to 1330 Pa or less, generating plasma by hydrogen gas or a mixed gas mainly containing hydrogen gas, and processing the carbon-based material The present inventors have found that a high-density ciliary structure can be formed on the surface of a carbon-based material.
[0076]
In addition, the inventors of the present application can uniformly coat a diamond thin film while maintaining a ciliary structure on the surface by further synthesizing and laminating a diamond thin film on a carbonaceous material having a ciliated surface. I found. Diamond can be made into a semiconductor by doping impurities, and a carbon-based material having a highly functional ciliated structure can be obtained.
[0077]
The present invention is characterized in that a ciliary structure is formed on the surface of a carbon-based material by treating the carbon-based material in plasma of hydrogen or a mixed gas containing hydrogen as a main component. However, when the gas pressure exceeds 1330 Pa, the present inventors have found that the plasma does not spread uniformly and a uniform ciliary structure cannot be formed on the surface of the carbon-based material. Therefore, the pressure of hydrogen gas or a mixed gas containing hydrogen as a main component for forming the ciliary structure is 1330 Pa or less.
[0078]
Further, the inventors of the present application have found that the ciliary structure is formed in a wide range of the temperature of the substrate during the plasma treatment of −50 to 1000 ° C. However, when the temperature exceeds 1000 ° C., thermal distortion tends to occur in the substrate. On the other hand, in order to make the temperature of the substrate lower than −50 ° C., the structure of the apparatus is complicated for controlling the substrate temperature, and the plasma processing speed is lowered, so that the processing time becomes longer. Therefore, the substrate temperature is set to -50 to 1000 ° C.
[0079]
The negative voltage applied to the substrate is not particularly limited, but when plasma is generated by high frequency and microwave, the ciliary structure formation rate is slow when the voltage is 0 to −100V, and when −500V or less. Since abnormal discharge occurs, −100 to −500 V is appropriate.
[0080]
In addition to hydrogen gas, the gas used for plasma treatment is nitrogen gas, He gas, Ar gas, oxygen gas, CO 2₂Gas, H₂One or more gases selected from the group consisting of O gas and hydrocarbon gas (including gases such as alcohol and acetone) can be added to hydrogen gas at a mixing ratio of 10% by volume or less.
[0081]
When an inert nitrogen gas, He gas, Ar gas, or the like is added as a gas mixed with hydrogen, the formation speed of the cilia-like structure on the surface of the carbon-based material can be suppressed. Also, oxygen gas, CO₂Gas and H₂When O gas or the like is added, the sharpness of the ciliated structure is lowered due to the oxidation effect, but a conical ciliated structure with better mechanical strength can be formed.
[0082]
On the other hand, when hydrocarbon gas is added, since uniform vapor deposition of carbon proceeds, the formation speed of ciliary structure is slowed, but it becomes possible to suppress surface defects, control the amount of hydrogen contained, etc. Characteristics are obtained.
[0083]
FIG. 11 is a view showing a carbon-based material (graphite) having a cilia-like surface according to a twelfth embodiment of the present invention manufactured as described above. That is, FIG. 11 is a scanning electron microscope (SEM) photograph showing the surface of graphite having a ciliated structure formed on the surface of the mirror-polished graphite by plasma treatment. As shown in FIG. 11, in plasma processing, plasma is generated with a microwave plasma generator (frequency: 2.45 GHz) using hydrogen gas, gas pressure is 1.5 Torr, substrate temperature is 400 ° C., and processing time is 1 hour. As a result, a high-density cilia-like structure is formed on the surface of the graphite. As described above, the ciliary structure of the present invention typically has a tip diameter of several to several tens of nm and a length of several hundred to several μm.
[0084]
FIG. 12 is an SEM photograph of the surface of a carbon-based material obtained by further laminating a diamond film on the ciliary carbon-based material shown in FIG. 11 by vapor phase synthesis. After forming the carbon-based material having the ciliary structure shown in FIG. 11, 0.3 vol% CH is formed on the formed ciliated carbon-based material by the same microwave plasma generator._Four+ 99.7% by volume H₂A diamond thin film was grown by vapor-phase synthesis using a gas mixture of 6650 Pa, a gas pressure of 6650 Pa, a substrate temperature of 1000 ° C., a processing time of 30 minutes, a plasma generated using a microwave with a frequency of 2.45 GHz. Is. As shown in FIG. 12, even when a diamond thin film is further grown on the ciliated carbon-based material, it can be seen that the carbon-based material is grown while maintaining the ciliated structure on the surface. Thus, in the cilia-like structure coated with a diamond thin film, the diameter of the tip is several tens nm to several μm.
[0085]
Conventionally, it has been difficult to grow a diamond thin film on a carbon-based material other than diamond. However, according to the present invention, the diamond thin film can be grown on any carbon-based material. Is obtained.
[0086]
According to the twelfth embodiment, in hydrogen gas or hydrogen gas, nitrogen gas, He gas, Ar gas, oxygen gas, CO₂Gas, H₂A condition in which the gas pressure and the substrate temperature are within the scope of the present invention using a mixed gas in which one or more gases selected from the group consisting of O gas and hydrocarbon gas are mixed at a mixing ratio of 10% by volume or less. That is, the pressure is not higher than 1330 Pa, the substrate temperature is in the range of −50 to 1000 ° C., the applied voltage is −100 to −500 V, the plasma treatment time is appropriately selected in the range of 0.2 to 10 hours, and the carbon-based material is plasma. By processing, a carbon-based material having a cilia-like structure formed on the surface as shown in FIG. 11 is obtained, and the carbon-based material to be plasma-processed is in any form of bulk, thin film, powder and sintered body. Even if it exists, a cilia-like structure can be formed on the surface.
[0087]
Next, a thirteenth embodiment of the present invention will be described. In the thirteenth embodiment, the carbon-based material having the ciliated surface of the twelfth embodiment is used as an electrode for electrolysis.
[0088]
In this example, the cilia-like structure is formed on the surface by plasma treatment, so the area of the surface of the carbon-based material is widened, so that the electrolysis efficiency can be remarkably improved and required for electrolysis. The time can be extremely short.
[0089]
Similarly to the electrode for electrolysis, a carbon-based material having a cilia-like surface can also be used for the electrode for a chemical sensor. By using a carbon-based material having a cilia-like surface, the surface area is increased, so that the sensitivity can be remarkably improved.
[0090]
Further, the carbon-based material having the cilia-like surface can be used for a fuel cell electrode. By using a carbon-based material having a cilia-like surface, the amount of the metal catalyst is increased, so that the fuel decomposition efficiency is remarkably increased, and thus a highly efficient fuel cell can be obtained.
[0091]
Next, a fourteenth embodiment of the present invention will be described. In the fourteenth embodiment, a thin film of a carbon-based material having a ciliary structure is used for an electron-emitting device.
[0092]
FIG. 13 is a schematic sectional view showing the electron-emitting device according to the fourteenth embodiment. As shown in FIG. 13, in the electron-emitting device of this example, a lower electrode 91 is formed on a substrate 90, and a carbon-based material layer 92 having a cilia-like structure formed on the surface is formed thereon. Further, a transparent upper electrode 94 facing the lower electrode 91 is formed at a position separated from the ciliary carbon-based material layer 92, and these are arranged in a vacuum. The upper electrode 94 and the lower electrode 91 are connected to a power source 98.
[0093]
In this embodiment, a positive voltage is applied to the upper electrode 94 and a negative voltage is applied to the lower electrode 91. However, since a ciliary structure is formed on the surface of the carbon-based material layer 92, electrons 95 from the carbon-based material layer 92 are formed. The amount of release is large. Therefore, the threshold value of the electron emission voltage is lowered, and the current value can be significantly increased. Such an electron-emitting device can be applied to a phototube, a flat panel display, a microwave oscillation source, a high-breakdown-voltage switching device, and the like, and these device characteristics can be dramatically improved.
[0094]
【Example】
Next, the results of comparing the characteristics of the diamond film produced by the method for producing the diamond film of the present invention and the chemical electrode and the electronic device using the diamond film with the comparative example will be described.
[0095]
Example 1
First, on a silicon substrate, the substrate temperature is 800 ° C., the gas pressure is 6650 Pa, and 0.5 vol% CH_Four+ 99.5% by volume H₂A microwave plasma having a frequency of 2.45 GHz was generated from the mixed gas, and a diamond film was formed by gas phase synthesis for 14 hours. Thereafter, the diamond film surface was plasma-treated under the conditions shown in Table 2 below. In Table 2, RT represents room temperature. For the plasma treatment, plasma was generated with a microwave of 2.45 GHz or 915 MHz, which is approved as an industrial frequency. The diamond surface after the treatment was observed, and the needle density was measured with a scanning electron microscope (SEM) for those having a needle-like structure. The results are also shown in Table 2 below.
[0096]
[Table 2]

[0097]
In Examples 1 to 11, the needle density is 10 on the surface of the diamond film.⁹Thru 10^TenA high needle-like structure was formed.
[0098]
In Comparative Examples 13 and 14, the gas pressure was out of the range of the present invention, and in Comparative Examples 15 and 16, the substrate temperature was out of the range of the present invention, so that no needle-like structure was formed on the diamond surface.
[0099]
Example 2(Electrode for electrolysis)
In order to produce an electrode for electrolysis and evaluate the characteristics, an aqueous solution of sodium chloride was electrolyzed. For comparison, electrolysis was performed in the same manner for a sample using a diamond film (hereinafter referred to as an untreated diamond film) in which the plasma treatment was not performed and the needle-like structure was not formed on the surface. As an electrode for electrolysis, first, two square low-resistance silicon substrates having a side of 10 mm were prepared, and diborane (B₂H6) (diborane concentration in the source gas is 100 ppm by volume) was used as a source gas, and synthesis was performed for 20 hours to form a p-type semiconductor diamond film having a thickness of 5 μm on the silicon substrate.
[0100]
After synthesizing the diamond film, one diamond film was subjected to hydrogen plasma treatment under the same processing conditions as those of the acicular diamond film in Table 1 to form a needle-like structure on the surface of the diamond film ( Hereinafter referred to as a treated sample). The other diamond film was an untreated diamond film to serve as a reference sample. For these treated samples and reference samples, copper wiring was bonded to the back surface of the silicon substrate with silver paste, a square region with a side of 8 mm was left on the surface of the diamond film, and the rest were sealed with epoxy resin, A decomposition electrode was obtained.
[0101]
For the measurement, a 0.1 M% aqueous sodium chloride solution was placed in a beaker, a treatment sample as an electrode for electrolysis of this example was used for the anode, a platinum electrode was used for the cathode, a reference sample for the anode, and a cathode for the cathode. The case of using a platinum electrode was compared by measuring the amount of hydrogen and chlorine generated by applying the same electric charge at the same voltage.
[0102]
As a result of the measurement, the treated sample which is the electrode for electrolysis of this example has an electric resistance of about 60% smaller and the electrolysis efficiency is about 40% better than the reference sample using the untreated diamond film. It was. For this reason, electrolysis was completed in a shorter time for the treated sample than for the reference sample. This is because the surface area of the processed sample is larger than that of the reference sample and the film thickness of the processed sample is thinner than that of the reference sample, so that energy loss due to heat generation and interface resistance is reduced.
[0103]
Example 3(Chemical sensor electrode)
The characteristics when the electrode produced in Example 2 was used as an electrode for a chemical sensor were evaluated. Using the treated sample and the reference sample of Example 2 as electrodes, 1 mM Fe (CN)₆Cyclic voltammetry measurement was performed in a solution of / 1 MKCl. FIG. 14 is a graph showing the results of cyclic voltmetry measurement. In FIG. 14, the broken line 10 indicates the measurement result of the processed sample, and the solid line 15 indicates the measurement result of the reference sample. Platinum was used as the counter electrode, and an Ag / AgCl electrode was used as the reference electrode. Compared to the reference sample, the electrode using the treated sample has a needle-like structure on the surface, so the sensitivity is extremely high and the background current is small. If used as a chemical sensor electrode, the sensitivity of the chemical sensor Is improved 10 times or more.
[0104]
Example 4(Fuel cell electrode)
In order to fabricate an electrode for a fuel cell and evaluate its characteristics, a cyclic voltammetry measurement in methanol was performed. The electrode for a fuel cell is a diamond film having a needle-like surface by first plasma-treating a conductive diamond film doped with B at a high concentration and having a thickness of 2 μm under the conditions for forming a needle-like diamond film shown in Condition 2 in Table 1. Got. Next, platinum fine particles were dispersed and deposited on this surface by sputtering, and diamond vapor phase synthesis was further performed for 1 hour to fix the platinum fine particles to obtain a fuel cell electrode. For comparison, plasma treatment was not performed, and an untreated diamond film whose surface was not formed into needles and a fuel cell electrode using platinum as electrodes were also produced. Then, cyclic voltammetry measurement of these fuel cell electrodes was performed. In the measurement, Ag / AgCl was used as a reference electrode.
[0105]
FIG. 15 is a graph showing the results of cyclic voltammetry measurement. In FIG. 15, the fuel cell electrode of this example is indicated by a broken line 11, the untreated diamond film used as an electrode is indicated by a solid line 16a, and the one using platinum as an electrode is indicated by a one-dot chain line 16b. As shown in FIG. 15, it can be seen that the fuel cell electrode of this example has extremely high methanol decomposition efficiency.
[0106]
Example 5(Glucose sensor)
A glucose sensor having the same structure as in FIG. 5 was produced. As a result of comparing the glucose sensor of the present example having the diamond working electrode 34 formed with the needle-like structure and the glucose sensor having an untreated diamond film not forming the needle-like structure as the working electrode 34, the biometric substance 35 was fixed for about 5 times longer and activity was not lost for about 5 times longer.
[0107]
Example 6(Organic light emitting device)
An organic light emitting device was produced and the light emission intensity was measured. First, two silicon nitride substrates are prepared, a platinum film is deposited on the silicon substrate as a hole injection electrode, and a high concentration is formed on the hole injection electrode as a hole transport layer by microwave plasma CVD. A diamond film doped with B was formed to a thickness of about 1 μm. One diamond film was subjected to hydrogen plasma treatment under the conditions for forming a needle-like diamond film shown in Condition 2 in Table 1 to form a diamond film having a needle-like surface. The other was an untreated diamond film. Next, an MDDO-PPV (Poly (2-methoxy5-dodecyloxy-1,4-phenylene vinylene)) film was spin-coated as an organic light emitting layer on these two kinds of diamond films. Further, an aluminum thin film was vacuum deposited on the organic light emitting layer as an electron injection electrode.
[0108]
A voltage is applied between the hole injection electrode and the electron injection electrode of the organic light-emitting device of this example and the organic light-emitting device using the untreated diamond film thus prepared to increase the light emission intensity of each device. It was measured. FIG. 16 is a graph showing the light emission intensity of the organic light-emitting device of Example 6, with the light emission intensity on the vertical axis and the wavelength on the horizontal axis. In FIG. 16, the broken line 12 and the solid line 17 indicate the emission spectra when a voltage of 25 V is applied to the organic light emitting device of this example and the organic light emitting device using the untreated diamond film, respectively. As shown in FIG. 16, the organic light emitting device of this example has a higher efficiency of hole injection from the needle-like structure, and therefore the emission intensity increased by about 20%.
[0109]
Example 7(Electron emitting device)
An electron-emitting device having the structure shown in FIG. 6 was fabricated, and the current-voltage characteristics were measured. As the current-voltage device, the diamond layer 42 of the electron-emitting device shown in FIG. 6 uses a treated sample similar to that of Example 2, and an untreated diamond film having no needle-like structure formed on the surface is used as the diamond layer 42. The upper electrodes were arranged at 200 μm apart in vacuum. The current and voltage of these fabricated electron-emitting devices were measured.
[0110]
FIG. 17 is a graph showing the results of current-voltage measurement of the electron-emitting device of Example 7, with the current density on the vertical axis and the applied voltage on the horizontal axis. In FIG. 17, the broken line 13 shows the measurement result of the electron-emitting device of this example, and the solid line 18 shows the measurement result of the electron-emitting device using an untreated diamond film. As shown in FIG. 17, the rising voltage of the electron-emitting device of this example is reduced to 1/300 compared with the electron-emitting device using an untreated diamond film, and the current value is greatly increased. all right.
[0111]
Example 8(UV light emitting device)
Using the processed sample and the reference sample of Example 2, an ultraviolet device was prepared, and the light emission intensity was measured. After forming an undoped diamond film having a film thickness of 0.4 μm on the treated sample and the reference sample of Example 2, an ultrathin gold film was deposited to form an upper electrode. An ultraviolet light emitting element using the treated diamond film was obtained. In any ultraviolet light emitting element, when a positive voltage was applied to the diamond film and a negative voltage was applied to the gold ultrathin film, light emission of 5.0 eV was observed, but the ultraviolet light emitting element of this example in which a needle-like structure was formed Was about 2.6 times greater than the ultraviolet light emitting device using the reference sample.
[0112]
Example 9(Visible light emitting device)
A visible light emitting device having the structure shown in FIG. 7 was prepared, and the light emission intensity was measured. A sample similar to Example 2, that is, a diamond film having a p-type diamond film of 5 μm formed on a low-resistance silicon substrate serving as a lower electrode, is subjected to a plasma treatment under the needle-like diamond film formation conditions shown in Condition 2 in Table 1. Then, a diamond film having a needle-like surface and an untreated diamond film are used as substrates, and an undoped diamond thin film having a thickness of about 2 μm is laminated on these diamond films by a microwave CVD method. A substantially flat surface was formed. Next, a transparent upper electrode made of a fluorescent thin film and ITO was sequentially laminated thereon, and a visible light emitting device was produced by fine processing. When a voltage of 500 V was applied between the lower electrode and the upper electrode, light was emitted from the fluorescent thin film. The emission intensity of the visible light emitting device using the diamond film having the needle-like surface of this example was about 5 times larger than the emission intensity of the visible light emitting device using the untreated diamond film.
[0113]
Example 10(Gas sensor)
A gas sensor having the structure shown in FIG. 8 was fabricated and its sensitivity response characteristic was evaluated. First, a polycrystalline undoped diamond thin film having a thickness of 5 μm is formed using a 2.54 cm diameter silicon nitride sintered body with grooves formed at a pitch of 2 mm in length and 1 mm in width using a hot filament vapor phase synthesis apparatus. Filmed. Subsequently, a plasma treatment is performed using a microwave plasma apparatus to form a needle-like structure on the surface, and a B-doped semiconductor diamond layer (thickness 1000 mm) as a gas-sensitive layer is laminated on the undoped diamond layer. did. The atomic density of B in the semiconductor diamond layer is 2 × 10¹⁸/ Cm^ThreeMet. Next, the sample was washed with a mixture of chromic acid and sulfuric acid at 200 ° C. for 20 minutes and then with aqua regia at 100 ° C. for 10 minutes. Thereafter, a pair of platinum electrodes was formed on the surface of the diamond thin film by sputtering deposition. The film thickness of the platinum electrode was 3000 mm, the area of the platinum electrode was 1 mm × 0.5 mm, and the electrode interval was 0.5 mm. After forming the electrode, it was divided into 2 mm × 1 mm sensor units. Further, a platinum heater was formed on the back surface of the base material made of alumina by a sputtering vapor deposition method. The film thickness of the platinum heater was 3000 mm. And the divided | segmented sensor unit was adhere | attached on the side in which the platinum heater of the alumina base material is not formed. Subsequently, a platinum heater and a platinum electrode were connected to the terminals of the sensor / mount unit by spot welding using a platinum lead wire having a diameter of 100 μm. Finally, the connection part between the platinum electrode and the platinum lead wire was covered with a gold paste, and heat treatment was performed in the atmosphere at 600 to 700 ° C. for 30 minutes to produce a gas sensor.
[0114]
In order to evaluate the response of the produced gas sensor to phosphine gas, the electrical resistance value of the gas sensor to phosphine gas was measured. FIG. 18 is a graph showing the sensitivity measurement results for the phosphine of the gas sensor of Example 10 with the output (electrical resistance) of the gas sensor on the vertical axis and the time on the horizontal axis. The measurement was carried out by maintaining the temperature at 300 to 450 ° C. with a platinum heater in the atmosphere, and 0.1, 0.2, 0.5 volume ppm of phosphine (PH_Three) Gas was sequentially exposed, and changes in the output (resistance value) of the gas sensor were observed. As shown in FIG. 18, an output change of 80 to 100% was observed with respect to 0.1 volume ppm of phosphine gas. This value indicates that the sensitivity is about 20 to 200% higher than that of a gas sensor using an untreated diamond thin film, and a diamond film having a needle-like structure is used for the sensor portion as in the gas sensor of this example. As a result, it was found that the sensor sensitivity was greatly improved.
[0115]
Example 11(Short wavelength sensor)
A short wavelength sensor was fabricated and its characteristics were evaluated. A sample in which an undoped diamond film formed on a substrate was subjected to hydrogen plasma treatment under the needle diamond film formation conditions shown in Condition 2 in Table 1 to form a needle-like structure on the surface, and a reference sample not subjected to plasma treatment for comparison with this sample A pair of comb-shaped electrodes in which the electrodes are meshed with each other were formed of platinum on these diamond films by using a microfabrication technique. A voltage of several volts was applied between the electrodes, and when these elements were irradiated with ultraviolet rays, the current flowing between the electrodes was measured. As a result of the measurement, the short wavelength sensor of the present example was compared between the electrodes at the same applied voltage and ultraviolet irradiation amount as compared with the short wavelength sensor using an untreated diamond film having no needle-like structure on the surface. It has been found that the short-wavelength sensor of this example has extremely large ultraviolet absorption, that is, high sensitivity.
[0116]
Example 12(Photomultiplier tube)
A photomultiplier having the structure shown in FIG. 9 was prepared, and the current flowing between the power receiving surface and the photocathode was measured.
[0117]
First, a B-doped polycrystalline diamond film is synthesized on a conductive low-resistance silicon substrate by microwave CVD, and subjected to hydrogen plasma treatment under the conditions shown in Condition 2 in Table 1 to obtain diamonds having a needle-like surface. A reflective photocathode having a film formed thereon was prepared. Next, indium was dissolved on a metal plate heated to a high temperature, and a silicon substrate on which a B-doped polycrystalline diamond film was formed was disposed thereon, thereby bonding the metal plate to the back surface of the silicon substrate. A mesh-shaped metal power receiving surface is arranged facing this photocathode, and after inserting these into a quartz glass tube, the inside of the tube is filled with 10^-7A photomultiplier tube was prepared by sealing with a vacuum below Torr.
[0118]
While applying a negative voltage of 10 to 200 V to the photocathode with respect to the power receiving surface of the produced photomultiplier tube, the photocathode was irradiated with ultraviolet light having a wavelength of 200 nm, and electron emission was confirmed from the photocathode. A photomultiplier tube using the diamond film having a needle-like surface of this example for the electron emission plate of the photocathode, and a photomultiplier tube using an untreated diamond film having no needle-like structure formed on the surface, When a similar voltage was applied and irradiated with ultraviolet rays, the photomultiplier tube using a diamond film having a needle-like surface was about one digit larger in current.
[0119]
Example 13(Discharge electrode)
A discharge electrode for a flash lamp having the structure shown in FIG. 10 was produced and stability was evaluated. First, the acicular diamond thin film 85 formed on the conical portion 83 of the electrode base material 84 is a p-type semiconductor diamond having a thickness of 0.1 to 10 μm and doped with B. When an appropriate voltage was applied between the discharge electrode and the anode, the light output stability of the arc discharge generated from the filled Xe gas was about 1.5% for a flash lamp not coated with a diamond thin film. In a flash lamp using a discharge electrode coated with a diamond thin film but not subjected to plasma treatment and having an untreated diamond film having no needle-like structure formed on the surface, about 0.75% In contrast, in the discharge electrode of this example, the light output stability was 0.5% or less.
[0120]
Next, the result of producing a carbon-based material having a cilia-like surface and evaluating its characteristics will be described.
[0121]
Example 14(Electrode for electrolysis)
In order to produce an electrode for electrolysis and evaluate the characteristics, an aqueous solution of sodium chloride was electrolyzed. For comparison, electrolysis was performed in the same manner for a carbon-based material that was not subjected to plasma treatment and had no ciliary structure formed on the surface.
[0122]
As an electrode for electrolysis, square graphite having a side of 20 mm formed on a silicon substrate was used. And as a graphite electrode of Example 14, what was processed on the conditions same as the manufacturing conditions of the ciliary carbonaceous material shown in FIG. 11 was used. That is, the plasma treatment conditions are as follows: plasma is generated by a microwave plasma generator (frequency 2.45 GHz) using hydrogen gas, gas pressure 1.5 Torr, substrate temperature 400 ° C., treatment time 1 hour, A high-density cilia-like structure is formed (Example 14). A graphite not subjected to plasma treatment was also prepared as a comparative graphite (Comparative Example 14). In addition, about the electrode for electrolysis of Example 14 and the comparative example 14, copper wiring is adhere | attached on the back surface of a silicon substrate with a silver paste, and the surface area of a square whose one side is 12 mm is left on the surface of the carbon-based material. Was sealed with an epoxy resin and subjected to electrolysis.
[0123]
A 0.1 M% aqueous sodium chloride solution was placed in a beaker, the electrode for electrolysis of Example 14 was used for the anode, the platinum electrode was used for the cathode, and the electrode for electrolysis of Comparative Example 14 was used for the anode. In the case where a platinum electrode is used for the cathode, the electrolysis efficiency in Example 14 and Comparative Example 14 is compared by energizing at the same voltage and the same amount of electricity and measuring the amount of hydrogen and chlorine generated. did.
[0124]
As a result, compared with Comparative Example 14 using untreated graphite, the electrolysis electrode of Example 14 that falls within the scope of the present invention was superior in electrolysis efficiency by about 35%. For this reason, electrolysis was completed in Example 14 in a shorter time than Comparative Example 14. This is because the surface area of Example 14 is larger than that of Comparative Example 14.
[0125]
Example 15(Electron emitting device)
An electron-emitting device (fourteenth example) having the structure shown in FIG. 13 was produced and its current-voltage characteristics were measured. The electron-emitting device uses a sample (Example 15) in which the carbon-based material layer 92 of the electron-emitting device shown in FIG. 13 is subjected to plasma treatment to form a cilia-like structure, and a cilia-like structure is formed on the surface. An untreated carbon-based material using the carbon-based material layer 92 (Comparative Example 15) was prepared, and the upper electrodes were arranged 170 μm apart in vacuum. The current and voltage of these fabricated electron-emitting devices were measured. Note that a graphite layer was used as the carbon-based material layer.
[0126]
FIG. 19 is a graph showing the measurement results of the current-voltage characteristics of the electron-emitting device of Example 15 with the current density on the vertical axis and the applied voltage on the horizontal axis. In FIG. 19, the broken line 14 shows the measurement result of the electron-emitting device of Example 15, and the solid line 19 shows the measurement result of the electron-emitting device using Comparative Example 15 which is an untreated carbon-based material. As shown in FIG. 19, it can be seen that the rising voltage of the electron-emitting device of Example 15 is reduced to 1/300 as compared with the electron-emitting device of Comparative Example 15, and the current value is greatly increased.
[0127]
【The invention's effect】
As described above in detail, according to the present invention, a negative bias voltage is applied to diamond or a carbon-based material, and a hydrogen gas with a low gas pressure or a mixed gas containing hydrogen as a main component at an appropriate substrate temperature is used. By generating a wave plasma to treat the surface of the diamond or carbon-based material, a needle-like structure can be formed on the surface of the diamond, or a cilia-like structure can be formed on the surface of the carbon-based material. This needle-like structure or cilia-like structure increases the surface area of diamond or carbon-based material by 10 times or more, increases the amount of adsorbed substances, and increases the amount of emitted electrons. Advances in the performance of electronic devices such as electrodes, chemical electrodes such as fuel cell electrodes and biosensor electrodes, electron-emitting devices, ultraviolet light-emitting devices, visible light-emitting devices, gas sensors, short-wavelength sensors, photoelectron emission plates, and discharge electrodes Can be improved.
[0128]
In addition, when a diamond film is manufactured by a microwave plasma CVD apparatus, it is possible to perform synthesis and surface treatment of the diamond film in the same chamber, which further facilitates the manufacturing and significantly reduces the manufacturing cost. .
[Brief description of the drawings]
FIG. 1 is a graph showing a comparison between plasma processing conditions of the present invention and plasma conditions of Conventional Example 1 and Conventional Example 2. FIG.
FIG. 2 is a drawing-substituting photograph of the surface of the diamond thin film before the plasma treatment (Scanning electron microscope (SEM), magnification: 10,000 times).
FIG. 3 is a drawing-substituting photograph of the surface of a diamond thin film obtained by subjecting the diamond thin film shown in FIG. 2 to plasma treatment and forming a needle-like structure on the surface (SEM photograph, magnification 60000 times).
4 is a drawing-substituting photograph of a diamond film surface obtained by further laminating a diamond film by vapor phase synthesis on the needle-like diamond film shown in FIG. 3 (SEM photograph, magnification 60000 times).
FIG. 5 is a cross-sectional view showing a transducer portion of a biosensor (such as a glucose sensor) using a needle-like diamond film according to a second embodiment of the present invention.
FIG. 6 is a schematic sectional view showing an electron-emitting device according to a fourth embodiment of the present invention.
FIG. 7 is a sectional view showing a visible light emitting device according to a sixth embodiment of the present invention.
FIG. 8 is a schematic cross-sectional view showing a gas sensor according to a seventh embodiment of the present invention.
FIG. 9 is a schematic sectional view showing an electron emission plate for a photomultiplier tube according to a ninth embodiment of the present invention.
FIG. 10 is a side view showing a discharge electrode according to a tenth embodiment of the present invention.
FIG. 11 is a drawing-substituting photograph (SEM photograph, magnification 60000 times) of the surface of graphite obtained by subjecting mirror-polished graphite to hydrogen plasma treatment and forming a cilia-like structure on its surface.
12 is a drawing-substituting photograph of the surface of a carbon-based material obtained by further laminating a diamond thin film by vapor-phase synthesis on the ciliated carbon-based material shown in FIG. 11 (SEM photograph, magnification 60000 times).
FIG. 13 is a schematic cross-sectional view showing an electron-emitting device according to a fourteenth embodiment of the present invention.
14 is a graph showing the results of cyclic voltmetry measurement in Example 3. FIG.
15 is a graph showing the results of cyclic voltammetry measurement in Example 4. FIG.
FIG. 16 is a graph showing the light emission intensity of the organic light-emitting device of Example 6 with the light emission intensity on the vertical axis and the wavelength on the horizontal axis.
FIG. 17 is a graph showing the measurement results of the current-voltage element of the electron-emitting device of Example 7, with the current density on the vertical axis and the applied voltage on the horizontal axis.
FIG. 18 is a graph showing the sensitivity measurement results for the phosphine of the gas sensor of Example 10 with the vertical axis representing the output (electric resistance) of the gas sensor and the horizontal axis representing time.
19 is a graph showing measurement results of current-voltage characteristics of the electron-emitting device of Example 15 with current density on the vertical axis and applied voltage on the horizontal axis. FIG.
[Explanation of symbols]
30, 40, 53, 61; substrate
31, 38, 54; undoped diamond film
32; Platinum reference electrode
33; Platinum counter electrode
34; working electrode
35; Biometric substance
36; biological membrane
37; Heater
41; lower electrode
42; diamond layer
43; Undoped diamond thin film
46; fluorescent thin film
44; upper electrode
47; Wiring electrode
45; Electronics
52; Base material
55; p-type semiconductor diamond layer
56; Electrode
51; heater
62; B-doped polycrystalline diamond film
63; Photocathode
64, 67; metal electrodes
65 power receiving surface
68, 69; lead pins
70; tube
71; sealing glass
72; Window
80; discharge electrode (cathode)
81; support part
82; cylindrical portion
83; Conical part
84; Electrode substrate
85; Diamond thin film
92: Carbon material layer
93; Carbon material thin film

Claims (7)

Synthesizing a first diamond on a substrate, applying a negative bias voltage of −100 to −500 V to the first diamond, maintaining the temperature of the substrate at −50 to 800 ° C., and a pressure of 66. Generating a needle-like structure on the surface of the first diamond by generating microwave plasma using hydrogen gas of 5 to 665 Pa to etch the surface of the first diamond in an etching time of 0.2 to 10 hours; A method for producing diamond having a needle-like surface, characterized by comprising: In the hydrogen gas, one or more gases selected from the group consisting of nitrogen gas, He gas, Ar gas, oxygen gas, CO ₂ gas, H ₂ O gas, and hydrocarbon gas are mixed at a volume ratio of 10% by volume. The method for producing diamond having a needle-like surface according to claim 1, wherein mixing is performed in the following manner. 3. The acicular surface according to claim 1 or 2, further comprising a step of synthesizing diamond to form a second diamond on the first diamond after the step of forming the acicular structure. The manufacturing method of the diamond which has. The method for producing diamond having a needle-like surface according to any one of claims 1 to 3, wherein the first diamond and / or the second diamond is a semiconductor diamond to which an impurity is added. 5. The production of diamond having a needle-like surface according to claim 1, wherein the first diamond formation step and the plasma treatment step are continuously performed in the same chamber. Method. A step of depositing a carbon-based material on the substrate to form a thin film; a negative bias voltage of −100 to −500 V is applied to the thin film; the temperature of the substrate is maintained at −50 to 1000 ° C .; and the pressure is 1330 Pa. Generating a ciliary structure on the surface of the thin film by generating plasma of hydrogen or a mixed gas containing hydrogen as a main component and etching the surface of the thin film in an etching time of 0.2 to 10 hours; A method for producing a carbon-based material having a cilia-like surface, characterized by comprising: The method for producing a carbon-based material having a cilia-like surface according to claim 6 , further comprising a step of forming diamond on the thin film by vapor-phase synthesis of diamond after the step of forming the ciliary structure. Method.

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