本文選題：計算流體力學(xué) + 有限體積法��； 參考：《中國科學(xué)技術(shù)大學(xué)》2015年碩士論文

【摘要】：石墨烯是碳材料家族中一種明星材料,因其獨特的電子結(jié)構(gòu)和優(yōu)異的物理特性一直備受關(guān)注。石墨烯有望在高性能納米電子器件、復(fù)合材料、場發(fā)射器、傳感器和能量儲存等領(lǐng)域獲得廣泛應(yīng)用�，F(xiàn)今主要制備石墨烯的方法有：微機械剝離法,外延生長法,氧化還原法和化學(xué)氣相沉積法。其中在金屬表面化學(xué)氣相沉積法有望成為一種理想的大規(guī)模制備大面積,價格低廉的,高質(zhì)量的石墨烯。銅金屬由于其具有低碳溶解度,是一種很優(yōu)良的生長襯底材料,而且在生長過程中比較容易控制石墨烯樣品的層數(shù)。近來,對于在銅襯底上制備石墨烯的生長機制由很多理論研究工作。但是研究主要集中在銅襯底上的生長反應(yīng)機制。關(guān)于氣相動作用也只是從熱力學(xué)角度進(jìn)行簡單分析。很少有關(guān)于氣相動力學(xué)因素對石墨烯在銅襯底上生長影響的研究。但是在實驗上已經(jīng)表明氣相動力學(xué)也是石果烯生長的一個很重要的影響因素。以甲烷作為碳源在銅襯底上CVD生長石墨烯實驗中,反應(yīng)室壓強是影響石墨烯樣品平整性的重要因素。理論淪分析甲烷的氣相熱分解反應(yīng)導(dǎo)致反應(yīng)室中各種活性組分處于非平衡狀態(tài),從氣體流動上游到下游方向,活性組分濃度逐漸升高,因此在實驗上觀察到銅襯底處于下游相比銅襯底處于上游獲得石墨烯樣品的厚度較厚。基于這些結(jié)果,我們利用計算流體力學(xué)方法來研究氣相動力學(xué)對在臥式管式爐中CVD生長石墨烯的影響。本工作利用計算流體力學(xué)軟件包FLUENT仿真模擬以甲烷作為碳源在銅襯底上CVD生長石墨烯過程。從模擬結(jié)果可以發(fā)現(xiàn),反應(yīng)室的壓強為低壓(83Pa)時,甲烷的組分輸運系數(shù)遠(yuǎn)大于表面化學(xué)反應(yīng)常數(shù),反應(yīng)面上縱向沒有濃度梯度,甲烷的表面濃度和主氣流濃度差不多,表面沉積速率隨溫度變大呈指數(shù)增長；反應(yīng)室的壓強為常壓(101325Pa)時,甲烷的化學(xué)反應(yīng)常數(shù)大于組分輸運系數(shù),反應(yīng)而上縱方向有明顯濃度梯度,表面濃度最低,表而沉積速率隨溫度變大只是稍微增長。因此分析推出,反應(yīng)室壓強為低壓時,石墨烯生長受限于表面化學(xué)反應(yīng)；反應(yīng)室壓強為常壓時,石墨烯生長受限于組分輸運過程程。在常壓(101325Pa)、中等壓強(2666Pa)和低壓(83Pa)三種不同壓強條件下,并且在沒有考慮甲烷氣相分解反應(yīng)情況下,我們模擬計算將銅襯底表面放置在加熱區(qū)不同位置時表面沉積速率的變化。模擬獲得的結(jié)果顯示表面沉積速率從氣體流動上游到下游方向是逐漸變小,與試驗結(jié)果不相符,因此側(cè)面說明了甲烷的熱分解反應(yīng)在整個石墨烯CVD生長過程中的重要性。
[Abstract]:Graphene is a kind of star material in carbon material family, which has attracted much attention because of its unique electronic structure and excellent physical properties. Graphene is expected to be widely used in high performance nanoelectronic devices, composites, field emitters, sensors and energy storage. At present, the main preparation methods of graphene are: micromechanical stripping, epitaxial growth, redox and chemical vapor deposition. Among them, chemical vapor deposition on metal surface is expected to be an ideal large-scale preparation of large area, low cost, high quality graphene. Because of its low carbon solubility, copper is a very good substrate material, and it is easy to control the layers of graphene samples during the growth process. Recently, there have been many theoretical studies on the growth mechanism of graphene on copper substrates. However, the mechanism of growth reaction is mainly focused on copper substrates. The use of gas phase action is also simply analyzed from the point of view of thermodynamics. There are few studies on the effect of gas kinetic factors on the growth of graphene on copper substrates. However, it has been shown experimentally that gas phase dynamics is also an important factor in the growth of iriodene. The pressure of the reaction chamber is an important factor affecting the flatness of graphene samples in the experiment of CVD growth of graphene on copper substrate with methane as the carbon source. It is theoretically analyzed that the gas phase thermal decomposition of methane results in the non-equilibrium of various active components in the reaction chamber, and the concentration of the active components increases gradually from the upstream to the downstream of the gas flow. Therefore, it is observed that the thickness of graphene sample is thicker than that of copper substrate downstream. Based on these results, the effect of gas dynamics on the growth of graphene in horizontal tube furnace is studied by computational fluid dynamics (CFD). In this work, the growth of graphene on copper substrate using methane as carbon source was simulated by computational fluid dynamics software package fluent. From the simulation results, it can be found that when the pressure of the reaction chamber is low pressure (83 Pa), the transport coefficient of methane component is much larger than the surface chemical reaction constant, there is no concentration gradient in the longitudinal direction of the reaction surface, and the surface concentration of methane is about the same as that of the main gas flow. The surface deposition rate increases exponentially with the increase of temperature, when the pressure of the reaction chamber is 101325Pa, the chemical reaction constant of methane is larger than the transport coefficient of the component, and there are obvious concentration gradients in the longitudinal direction of the reaction, and the surface concentration is the lowest. The deposition rate increases only slightly with the increase of temperature. Therefore, the growth of graphene is limited by the surface chemical reaction when the pressure of the reaction chamber is low, and the growth of graphene is limited by the transport process of the component when the pressure of the reaction chamber is normal. Under three different pressures: atmospheric pressure (101325Pa), moderate pressure (2666Pa) and low pressure (83Pa), and without considering the gas phase decomposition of methane, we simulated and calculated the surface deposition rate when copper substrate was placed in different positions in the heating region. The simulated results show that the surface deposition rate decreases gradually from upstream to downstream of the gas flow, which is inconsistent with the experimental results. Therefore, the importance of the thermal decomposition of methane in the whole growth process of graphene CVD is explained.
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TN304.05

【共引文獻(xiàn)】

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1 黃曉媛;熱等離子體裂解反應(yīng)機理的密度泛函理論及實驗研究[D];浙江大學(xué);2014年

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本文編號：2104863