201223862 六、發’明說明： 【發明所屬之技術領域】 本發明係有關於一種奈米碳管及其製作方法，特別是 有關於一種具有高表面積之奈米碳管及其製作方法。 【先前技術】 奈米碳管於1991年被日本飯島教授發現至今已將近 20年，由於奈米碳管有質量輕、高強度、高韌性、可撓區、 參 高表面積、表面曲度大、高導熱度及具金屬或半導體特性 等優點，因此可作為各種電池、電容器、或感測器之電極 材料。目前有關奈米碳管應用與研究仍快速的成長中。B.C. Satishkumar及L.P. Biro等人是利用碳原子在觸媒不同晶面 的成長速度不同，製作出Y型奈米碳管，然而，此方法無 法控制奈米碳管之數量和長度。Hao Yu及Y. Chai等人在 氣態中列解觸媒二絡鐵(ferrocene)成長過程中合成分支狀 奈米碳管，藉由氣態中裂解之觸媒附著於奈米碳管之管壁 鲁 上，形成奈米碳管之二次成長。然而，此方法仍難以控制 奈米碳管之密度和長度。X.Sim等人在奈米碳管之管壁上 鑛一層觸媒，以兩次成長之方式製作分支狀碳管，然而， 其對於奈米碳管之成長無法做精確的控制。 奈米碳管的表面積與其長度和直徑成正比，若用在需 要高表面積的奈米元件上，過長及直徑過大的奈米碳管不 適用於奈米尺度的元件。因此，需要一種奈米碳管及其製 作方法，能在固定碳管長度及直徑的條件下，控制奈米碳 201223862 管的表面積。 【發明内容】 本發明提供一種奈米碳管結構之製作方法，包括：提 供一基板；形成一金屬觸媒層於基板上；於一反應室中通 入反應氣體，並施加負偏壓，以於基板上成長複數個奈米 碳管；及於反應室中施加正偏壓，以於上述奈米碳管上成 長奈米碳薄片。 本發明提供一種奈米碳管結構，包括：一基板；複數 個奈米碳管，位於基板上；及複數個奈米碳薄片，位於各 奈米碳管上。 為了讓本發明之上述目的、特徵及優點能更明顯易 懂，下文特舉一較佳實施例，並配合所附圖式，作詳細說 明如下： 【實施方式】 以下提供許多不同實施例或範例，以實行本發明各種 不同實施例的特徵。以下將針對特定實施例的構成與製作 方法作簡要描述，當然，下列之描述僅是範例，非用來限 定本發明。 本發明係利用改變電壓之方式，在不需鍍第二次觸媒 的條件下，於奈米碳管側壁形成奈米碳薄片，其薄片大小 及密度及密度可以由電壓大小及氣體流量調整，藉以控制 201223862 奈米碳管結構的表面積。 第1圖顯示本發明一實施例奈米碳管之製作方法的流 程圖。第2A圖-第2C圖顯示本發明一實施例奈米碳管之 製作方法各階段的剖面圖。首先，請參照第1圖和第2A 圖，進行步驟S102，提供一基板202，於基板202上形成 金屬觸媒層203。基板202的材料視產品的應用來決定。 在本發明一實施例中，基板202可以為矽或碳布。金屬觸 媒層203可以為鐵、鈷或鎳。形成金屬觸媒層203的方法 • 可以為濺鍍、蒸鍍、電鍍或化學還原法。接著，執行步驟 S104，進行電漿還原處理，使金屬觸媒層變成顆粒狀的結 構（未繪示）。在本發明一實施例中，電漿還原處理可以為 氫電漿還原處理。後續，進行步驟S106，將基板202置入 微波產生電漿化學氣相沉積系統，於反應室中通入反應氣 體，準備進行電漿化學氣相沉積形成奈米碳管。在本發明 一實施例中，反應氣體可以為含碳氣體，例如烷類、烯類 或炔類。接著，請參照第1圖和第2B圖，進行步驟S108， ® 於製程室中施加負偏壓，並調整電壓，於基板202上成長 奈米礙管204。在本發明一實施例中，此步驟施加之負偏 壓為0〜-300V，工作壓力為1〜30Torr，微波能量(micro wave)為50〜500W，製程時間為1〜3600秒。後續，請參 照第1圖和第2C圖，進行步驟S110，於製程室中施加正 偏壓，並調整電壓，於奈米碳管204側壁形成奈米碳薄片 206,其薄片大小及密度及密度可以由電壓大小及氣體流量 調整，藉以控制奈米碳管204結構的表面積。在本發明一 201223862 實施例中，此步驟施加之正偏壓為0〜300V，工作壓力為1 ~ 30Torr，微波能量（micro wave)為50〜500W，製程時間 為1〜3600秒，反應氣體曱烷(CH4)之流量為0〜100 seem， 反應氣體氫氣(H2)之流量為0〜100 seem。 根據上述，本發明形成一種奈米碳管結構，包括一基 板、複數個奈米碳管，位於該基板上，及複數個奈米碳薄 片，位於各奈米礙管上。在本發明一實施例中，奈米碳薄 片為一片狀結構。 【實施範例】 首先，提供一矽晶片，濺鍍鐵觸媒於矽晶片上，通入 反應氣體曱烧(CH4)和氫氣(H2)，基礎壓力（base pressure)為 10_3Torr，工作壓力為lOTorr，微波能量（micro wave)為 300W，施加偏壓（additive bias)為-150V，於石夕晶片上成長 奈米碳管（本範例奈米碳管之掃描式電子顯微鏡照片請參 照附件一），成長時間（growth time)為20分鐘。 接著，將施加偏壓（additive bias)切換為正偏壓+ 150V， 其它製程條件則維持相同：反應氣體為甲烷(CH4)和氫氣 (H2)，基礎壓力（base pressure)為l(T3Torr，工作壓力為 lOTorr，微波能量（micro wave)為300W，於奈米碳管上成 長奈米碳薄片（本範例奈米碳薄片之掃描式電子顯微鏡照 片請參照附件二）。 相較於習知技術，本發明實施例奈米碳管及其製作方 法具有以下優點：1.本發明在不需鍍第二次觸媒的條件 6 201223862 下，於奈米碳管側壁形成奈米碳薄片，形成高表面積的奈 米碳管結構。2.本發明能在固定碳管長度及直徑的條件 下，控制奈米碳管的表面積。3.本發明可調整電壓大小及 氣體流量，控制奈米碳薄片之大小及密度，藉以控制奈米 碳管結構之表面積。4.本發明奈米碳管及其製作方法可應 用於燃料電池（fuel cell)、敏化太陽能電池（dye sensitized solar cell，簡稱 DSSC)、感應器（sensor)、超級電容器（super capacitor)、場發射顯示器（field emission display)等需高表 鲁 面積材料之領域。 雖然本發明已揭露較佳實施例如上，然其並非用以限 定本發明，任何熟悉此項技藝者，在不脫離本發明之精神 和範圍内，當可做些許更動與潤飾。另外，本發明不特別 限定於特定說明書中描述之實施例的裝置和結構。熟悉本 領域的人士可根據本發明說明書之揭示，進一步發展出與 本發明大體上具有相同功能，或大體上可達成相同結果之 裝置和結構。因此，本發明之保護範圍當視後附之申請專 *利範圍所界定為準。 201223862 【圖式簡單說明】 第1圖顯示本發明一實施例奈米碳管之製作方法的流 程圖。 第2A圖-第2C圖顯示本發明一實施例奈米碳管之製作 方法各階段的剖面圖。 【主要元件符號說明】 202〜基板； 203〜金屬觸媒層； 204〜奈米碳管； 206〜奈米碳薄片。201223862 VI. STATEMENT: TECHNICAL FIELD OF THE INVENTION The present invention relates to a carbon nanotube and a method of fabricating the same, and more particularly to a carbon nanotube having a high surface area and a method of fabricating the same. [Prior Art] The carbon nanotubes were discovered by Professor Iijima in 1991 for nearly 20 years. Because of the light weight, high strength, high toughness, flexible area, high surface area and large surface curvature of the carbon nanotubes, It has high thermal conductivity and metal or semiconductor characteristics, so it can be used as an electrode material for various batteries, capacitors, or sensors. At present, the application and research on carbon nanotubes is still growing rapidly. B.C. Satishkumar and L.P. Biro et al. produced Y-type carbon nanotubes by using carbon atoms at different growth rates of different crystal planes. However, this method cannot control the number and length of carbon nanotubes. Hao Yu and Y. Chai et al. synthesize branched carbon nanotubes during the growth of the ferrocene in the gaseous state, and adhere to the wall of the carbon nanotubes by the catalyst of the crack in the gaseous state. On the top, the second growth of the carbon nanotubes is formed. However, this method still has difficulty controlling the density and length of the carbon nanotubes. X.Sim et al. made a layer of carbon nanotubes on the wall of the carbon nanotubes to make a branched carbon tube in two ways. However, it could not precisely control the growth of the carbon nanotubes. The surface area of a carbon nanotube is proportional to its length and diameter. For use on nanocomponents that require high surface area, too long and too large diameter carbon nanotubes are not suitable for nanoscale components. Therefore, there is a need for a carbon nanotube and a method for producing the same that can control the surface area of the nanocarbon 201223862 tube under the condition of fixing the length and diameter of the carbon tube. SUMMARY OF THE INVENTION The present invention provides a method for fabricating a carbon nanotube structure, comprising: providing a substrate; forming a metal catalyst layer on the substrate; introducing a reactive gas into a reaction chamber, and applying a negative bias to A plurality of carbon nanotubes are grown on the substrate; and a positive bias is applied to the reaction chamber to grow the nanocarbon sheets on the carbon nanotubes. The invention provides a carbon nanotube structure comprising: a substrate; a plurality of carbon nanotubes on the substrate; and a plurality of nano-carbon sheets on each of the carbon nanotubes. The above described objects, features, and advantages of the present invention will become more apparent and understood. To carry out the features of various embodiments of the invention. The following is a brief description of the construction and method of the specific embodiments. The following description is merely exemplary and is not intended to limit the invention. The invention utilizes a method of changing the voltage to form a nano-carbon sheet on the sidewall of the carbon nanotube without plating a second catalyst, and the sheet size, density and density can be adjusted by the voltage magnitude and the gas flow rate. In order to control the surface area of the 201223862 carbon nanotube structure. Fig. 1 is a flow chart showing a method of fabricating a carbon nanotube according to an embodiment of the present invention. 2A to 2C are cross-sectional views showing respective stages of a method of fabricating a carbon nanotube according to an embodiment of the present invention. First, referring to Fig. 1 and Fig. 2A, step S102 is performed to provide a substrate 202 on which a metal catalyst layer 203 is formed. The material of the substrate 202 is determined by the application of the product. In an embodiment of the invention, the substrate 202 may be a crucible or a carbon cloth. The metal catalyst layer 203 may be iron, cobalt or nickel. Method of Forming Metal Catalyst Layer 203 • It may be sputtering, evaporation, electroplating or chemical reduction. Next, in step S104, a plasma reduction treatment is performed to change the metal catalyst layer into a granular structure (not shown). In an embodiment of the invention, the plasma reduction treatment may be a hydrogen plasma reduction treatment. Subsequently, in step S106, the substrate 202 is placed in a microwave-generated plasma chemical vapor deposition system, and a reaction gas is introduced into the reaction chamber to prepare a plasma chemical vapor deposition to form a carbon nanotube. In an embodiment of the invention, the reaction gas may be a carbon-containing gas such as an alkane, an alkene or an alkyne. Next, referring to Fig. 1 and Fig. 2B, step S108 is performed, and a negative bias voltage is applied to the process chamber, and the voltage is adjusted to grow the nano tube 204 on the substrate 202. In an embodiment of the invention, the negative bias applied in this step is 0 to -300 V, the working pressure is 1 to 30 Torr, the microwave energy is 50 to 500 W, and the process time is 1 to 3600 seconds. Subsequently, referring to FIG. 1 and FIG. 2C, step S110 is performed to apply a positive bias voltage in the process chamber and adjust the voltage to form a nano-carbon sheet 206 on the sidewall of the carbon nanotube 204, the sheet size, density and density. The surface area of the nanocarbon tube 204 structure can be controlled by voltage magnitude and gas flow rate adjustment. In the embodiment of the present invention 201223862, the positive bias applied in this step is 0 to 300 V, the working pressure is 1 to 30 Torr, the microwave energy is 50 to 500 W, and the processing time is 1 to 3600 seconds. The flow rate of the alkane (CH4) is 0 to 100 seem, and the flow rate of the reaction gas hydrogen (H2) is 0 to 100 seem. In accordance with the above, the present invention forms a carbon nanotube structure comprising a substrate, a plurality of carbon nanotubes, on the substrate, and a plurality of nanocarbon sheets on each of the nanotubes. In an embodiment of the invention, the nanocarbon sheet is in the form of a sheet. [Examples] First, a germanium wafer is provided, and a tin-plated catalyst is sputtered on a germanium wafer, and a reaction gas calcination (CH4) and hydrogen gas (H2) are introduced, a base pressure is 10_3 Torr, and a working pressure is 10 Torr. Microwave energy (microwave) is 300W, and the applied bias is -150V. The carbon nanotubes are grown on the Shixi wafer (see the attached electron micrograph of the sample carbon nanotubes in this example). The growth time is 20 minutes. Next, the applied bias is switched to a positive bias + 150V, and the other process conditions remain the same: the reactive gases are methane (CH4) and hydrogen (H2), and the base pressure is l (T3Torr, working). The pressure is lOTorr, the microwave energy is 300W, and the nano-carbon flakes are grown on the carbon nanotubes. (For the scanning electron micrograph of the carbon nanosheets of this example, please refer to Appendix II). Compared with the prior art, The carbon nanotube of the embodiment of the invention and the manufacturing method thereof have the following advantages: 1. The invention forms a nano-carbon sheet on the sidewall of the carbon nanotube to form a high surface area under the condition 6 201223862 without plating the second catalyst. Nano carbon tube structure. 2. The invention can control the surface area of the carbon nanotube under the condition of fixing the length and diameter of the carbon tube. 3. The invention can adjust the voltage and gas flow rate and control the size of the nano carbon sheet. And density, thereby controlling the surface area of the carbon nanotube structure. 4. The carbon nanotube of the present invention and the manufacturing method thereof can be applied to a fuel cell, a sensitized solar cell (D) SSC), sensors, super capacitors, field emission displays, etc., which require high surface area materials. Although the present invention has been disclosed as a preferred embodiment, it is not used It is to be understood that the invention may be modified and modified without departing from the spirit and scope of the invention. The invention is not particularly limited to the apparatus and structure of the embodiments described in the specific specification. Those skilled in the art can further develop devices and structures that have substantially the same function as the present invention, or substantially achieve the same results, in accordance with the disclosure of the present specification. Therefore, the scope of protection of the present invention is attached to the application. 201223862 [Simplified Schematic Description] Fig. 1 is a flow chart showing a method of fabricating a carbon nanotube according to an embodiment of the present invention. Fig. 2A - Fig. 2C show an embodiment of the present invention. Cross-sectional view of each stage of the production method of the carbon tube. [Description of main components] 202~substrate; 203~metal catalyst layer; 204~奈Carbon tubes; 206~ carbon nano sheet.