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Currently, graphene synthesis involves several key factors need to be improved: (i) lengthy high-temperature annealing processes to increase the grain size of the metal catalyst used to form graphene; (ii) utilization of purified and compressed gases to offer a homogenous and controlled delivery of carbon source materials; and (iii) the use of lengthy vacuum operation to avoid the presence of any detrimental reactive oxygen species from air2,4. To overcome these problems, we have designed a thermal CVD process to produce graphene in an ambient-air environment that is completely free of compressed or purified gases and requires minimum processing time. The process is schematically illustrated in Fig. 1a, in which the precursor for graphene growth and a metal catalyst (for example, Ni foil) are placed close together inside the heating zone of a furnace, before heating the quartz tube. The quartz tube is then sealed and the temperature is increased. During the ramping stage, air inside the quartz tube is released through a valve to maintain atmospheric pressure. Once the annealing stage is complete, the sample is removed from the heating zone for rapid cooling. Raman spectra of the samples grown at 800 °C in the ambient-air process indicated the presence of single-to-few layer graphene films covering the surface of the growth substrate (Fig. 1b). In the standard operation, the catalyst is low-cost polycrystalline Ni foil. Graphene growth occurs by thermal reforming of a natural precursor, soybean oil, in a closed ambient-air environment. Unlike conventional CVD methods or conventional natural precursor methods for growing graphene, the technique does not require any purified gases8,9. Moreover, expensive vacuum processing is avoided. The natural precursors substituted for purified gases are cheaper and safer. By restricting the air flow into the quartz tube, the transformation of solid-state carbon into carbon dioxide or other gaseous species is prevented. By controlling the temperature, cooling rate and precursor amount, the process enables the growth of homogenous graphene films of good quality. A comparison of the method with other CVD processes is provided in Supplementary Tables 1 and 2. The parameters observed to control the quality of graphene include temperature, processing time, precursor, substrate and the ambient-air environment. Nickel acted as a good catalyst for the breakdown of precursor material (in this case, the soybean-oil molecules) into smaller building units that are essential for the synthesis of graphene12. To investigate how the transformation occurred in the process, we have analysed the chemical composition of the annealed soybean oils at different temperatures (Supplementary Fig. 1). During the early stages of the annealing process, for instance at 300 °C, the long carbon chains in the soybean oil precursor were thermally dissociated into gaseous carbon building units such as methyl and ethyl species (Supplementary Fig. 1a). Other gaseous species were also generated, including hydrogen, water, hydroxyls and carbon dioxide, as confirmed by mass spectrometry (Supplementary Fig. 1b and c). Traces of heavier hydrocarbons such as propane were also observed. Most of the oil was vapourized by about 425 °C and a rapid mass reduction of the oil was observed by thermogravimetric analysis below 500 °C (Supplementary Fig. 1d). These building units present in the vapour can diffuse through the tube during the heating stage. As the temperature gradually increases to 800 °C, these carbon building units begin to dissociate into carbon atoms and dissolve into the Ni bulk. The sample was annealed for 3 min at 800 °C to promote dissolution of carbon atoms in the Ni substrate. Finally, following the rapid cooling stage, carbon segregates from the bulk and crystallizes on the Ni surface forming graphene12,13. At elevated temperatures, long hydrocarbons in the oil decompose in the presence of O2 to form water vapour. In particular, water vapour can promote the etching of amorphous carbon deposits on the Ni surface14. As such, we did not observe the formation of amorphous carbons in our sample. This also helps maintain the catalytic activity of the Ni surface in breaking down the precursor material15. Moreover, we have conducted a detailed analysis on the consumption of oxygen in the reactor during the growth process (Supplementary Note 1). We found that the precursor amount was critical for the consumption of reactive oxygen species. In the optimal growth condition, a slight carbon excessive environment is used to promote the growth of graphene and deter the formation of amorphous carbon. On the other hand, an over-excessive amount of precursor material led to an oversaturation of deposited carbon in the bulk of Ni, and subsequently, the crystallization of graphite on the Ni surface. This may explain the resulting formation of thick graphene sheets as observed in Supplementary Fig. 2a. Moreover, in the case of an insufficient amount of precursor, oxygen species can be present in the as-grown product in the form of C–O amorphous carbons (Supplementary Fig. 2b), consistent with the aforementioned calculations of oxygen consumption (Supplementary Note 1)16. These experiments indicate the critical role of the thermally dissociated precursor materials (that is, hydrocarbons) in consuming the reactive oxygen species present in the ambient-air environment, which has a profound effect in controlling the quality of the as-grown graphene films.We have also noticed that a slow cooling can promote excessive carbon segregation from the Ni bulk, which may account for the observed formation of a graphite-like film (Supplementary Fig. 2c). Another parameter that significantly influences the growth of graphene in the ambient air environment is the annealing temperature. At an annealing temperature of 500 °C, an incomplete formation of the graphene film was observed (Supplementary Fig. 2d). This may be attributed to an insufficient amount of energy to dissociate and reform the precursor material (that is, hydrocarbon species) required for graphene formation. Conversely, at a higher annealing temperature of 900 °C, thicker graphene sheets were observed (Supplementary Fig. 2e). This may arise from the increased rate of carbon diffusion, segregation and graphitization as a result of the elevated temperature. Importantly, these parameters allow us to obtain graphene films with tuneable average thickness and optical transmission, as characterized by Raman spectroscopy and optical transmission (Supplementary Fig. 3). It is worth mentioning that graphene did not form on other growth substrate materials with significantly lower carbon solubility than Ni, such as the commonly used Cu foil. Moreover, we did not observe graphene formation on graphitic surfaces such as woven carbon cloth (Supplementary Fig. 4). This suggests that the use of Ni (through, for example, carbon solubility, carbon segregation ability, catalytic effect, possibility of formation of oxide in air) and its interaction with the precursor material play a critical role in enabling the growth of graphene films. We also investigated the possibility of transforming other types of renewable oil groups. In particular, we were able to demonstrate the ambient-air growth of similar graphene films from other types of triglyceride (carbon)-containing precursors such as butter (Supplementary Fig. 5). As such, this method is versatile and may be tailored to transform other renewable carbon-containing natural precursors into graphene films. |
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【答案】应助回帖
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In the standard operation, the catalyst is low-cost polycrystalline Ni foil. Graphene growth occurs by thermal reforming of a natural precursor, soybean oil, in a closed ambient-air environment. Unlike conventional CVD methods or conventional natural precursor methods for growing graphene, the technique does not require any purified gases8,9. Moreover, expensive vacuum processing is avoided. The natural precursors substituted for purified gases are cheaper and safer. By restricting the air flow into the quartz tube, the transformation of solid-state carbon into carbon dioxide or other gaseous species is prevented. By controlling the temperature, cooling rate and precursor amount, the process enables the growth of homogenous graphene films of good quality. A comparison of the method with other CVD processes is provided in Supplementary Tables 1 and 2. 在标准操作中，催化剂是低成本多晶Ni箔。通过在密封周围空气环境中天然前体大豆油的热重整来开始石墨烯生长。与用于生长石墨烯的常规CVD方法或常规天然前体方法不同，这种技术部需要任何纯化的气体。此外，避免了昂贵的真空加工。取代纯化气体的天然前体更便宜且更安全。通过限制进入石英管的空气流动，阻止固态碳转变成二氧化碳或其它气体物质。通过控制温度、冷却速率和前体量，该热CVD工艺实现生长具有良好质量的均匀的石墨烯膜。在补充的表1和表2中，比较了该方法与其它CVD工艺。 The parameters observed to control the quality of graphene include temperature, processing time, precursor, substrate and the ambient-air environment. Nickel acted as a good catalyst for the breakdown of precursor material (in this case, the soybean-oil molecules) into smaller building units that are essential for the synthesis of graphene12. 观察到控制石墨烯质量的参数包括温度、加工时间、前体、衬底和周围空气环境。镍用作用于将前体材料（在这种情况下，大豆油分子）分解成对石墨烯的合成而言所必要的构成单元。 To investigate how the transformation occurred in the process, we have analysed the chemical composition of the annealed soybean oils at different temperatures (Supplementary Fig. 1). During the early stages of the annealing process, for instance at 300 °C, the long carbon chains in the soybean oil precursor were thermally dissociated into gaseous carbon building units such as methyl and ethyl species (Supplementary Fig. 1a). Other gaseous species were also generated, including hydrogen, water, hydroxyls and carbon dioxide, as confirmed by mass spectrometry (Supplementary Fig. 1b and c). Traces of heavier hydrocarbons such as propane were also observed. Most of the oil was vapourized by about 425 °C and a rapid mass reduction of the oil was observed by thermogravimetric analysis below 500 °C (Supplementary Fig. 1d). These building units present in the vapour can diffuse through the tube during the heating stage. As the temperature gradually increases to 800 °C, these carbon building units begin to dissociate into carbon atoms and dissolve into the Ni bulk. The sample was annealed for 3 min at 800 °C to promote dissolution of carbon atoms in the Ni substrate. Finally, following the rapid cooling stage, carbon segregates from the bulk and crystallizes on the Ni surface forming graphene12,13. 为了研究在这个工艺中转变是如何进行的，我们分析了在不同温度下的退火的大豆油的化学组成（补充图1）。在退火过程的早期阶段，例如在300℃下，大豆油前体的长碳链热解离成气态碳构成单元例如甲基和乙基物质（补充图1a）。还产生其他气态物质，包括氢气、水、羟基和二氧化碳，如通过质谱所确认（补充图1b和1c）。还观察到痕量的更重的烃，例如丙烷。大多数的油到约425℃时蒸发，通过热重分析在500℃以下观察到油的快速的质量下降（补充图1d）。在加热阶段过程中，在蒸气中存在的构成单元可扩散通过管。随着温度逐渐增加到800℃，这些碳构成单元开始解离成碳原子，并溶解进入Ni本体。将样品在800℃下退火3分钟，以促进碳原子在Ni衬底中的溶解。最后，在快速冷却阶段之后，碳从本体分离，且在Ni表面上结晶，这形成石墨烯。 |
4楼2017-02-10 21:48:37
2楼2017-02-06 21:25:26
【答案】应助回帖
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fjtony163: 翻译EPI+1, 代发 金币由区长代发 2017-03-08 09:17:28
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fjtony163: 翻译EPI+1, 代发 金币由区长代发 2017-03-08 09:17:28
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-09 03:14:47
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:21:42
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:22:24
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:22:32
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:22:53
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:23:03
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:23:11
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:23:19
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:23:28
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:24:02
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zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:25:27
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:25:56
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:26:03
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:26:12
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:26:49
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:27:36
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:28:05
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:28:34
zsgandy(fjtony163代发): 金币+50, 代发 2017-03-10 03:28:43
|
Currently, graphene synthesis involves several key factors need to be improved: (i) lengthy high-temperature annealing processes to increase the grain size of the metal catalyst used to form graphene; (ii) utilization of purified and compressed gases to offer a homogenous and controlled delivery of carbon source materials; and (iii) the use of lengthy vacuum operation to avoid the presence of any detrimental reactive oxygen species from air2,4. To overcome these problems, we have designed a thermal CVD process to produce graphene in an ambient-air environment that is completely free of compressed or purified gases and requires minimum processing time. 目前，石墨烯合成涉及多个需要改进的关键因素：（i）冗长的高温退火过程增加用来形成石墨烯的金属催化剂的晶粒尺寸；（ii）利用纯化和压缩气体来提供碳源材料的均匀和受控的递送；以及（iii）使用冗长的真空操作来避免存在来自空气的任何有害反应性氧物质。为了克服这些不足，我们设计了热CVD工艺来在完全不含压缩或纯化气体且需要极少加工时间的周围空气环境中制备石墨烯。 The process is schematically illustrated in Fig. 1a, in which the precursor for graphene growth and a metal catalyst (for example, Ni foil) are placed close together inside the heating zone of a furnace, before heating the quartz tube. The quartz tube is then sealed and the temperature is increased. During the ramping stage, air inside the quartz tube is released through a valve to maintain atmospheric pressure. Once the annealing stage is complete, the sample is removed from the heating zone for rapid cooling. Raman spectra of the samples grown at 800 °C in the ambient-air process indicated the presence of single-to-few layer graphene films covering the surface of the growth substrate (Fig. 1b). 这种热CVD工艺如图1a示意性显示，其中将用于石墨烯生长的前体和金属催化剂（例如，Ni箔）一起靠近设置在炉子的热区里面，然后加热石英管。然后，密封石英管，增加温度。在升温阶段，通过阀门来释放石英管里面的空气，以保持常压。一旦退火阶段完成，从热区取出样品用于快速冷却。在周围空气工艺中在800℃下生长的样品的拉曼光谱表明存在覆盖生长衬底的单层石墨烯膜-到-几层石墨烯膜（图1b）。 |
3楼2017-02-10 21:24:11
【答案】应助回帖
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At elevated temperatures, long hydrocarbons in the oil decompose in the presence of O2 to form water vapour. In particular, water vapour can promote the etching of amorphous carbon deposits on the Ni surface14. As such, we did not observe the formation of amorphous carbons in our sample. This also helps maintain the catalytic activity of the Ni surface in breaking down the precursor material15. Moreover, we have conducted a detailed analysis on the consumption of oxygen in the reactor during the growth process (Supplementary Note 1). We found that the precursor amount was critical for the consumption of reactive oxygen species. In the optimal growth condition, a slight carbon excessive environment is used to promote the growth of graphene and deter the formation of amorphous carbon. On the other hand, an over-excessive amount of precursor material led to an oversaturation of deposited carbon in the bulk of Ni, and subsequently, the crystallization of graphite on the Ni surface. This may explain the resulting formation of thick graphene sheets as observed in Supplementary Fig. 2a. 在升高的温度下，油中的长烃在O2的存在下分解，以形成水蒸汽。具体地，水蒸汽可促进沉积在Ni表面上的无定形碳的蚀刻。这样，在我们的样品中，我们没有观察到形成无定形碳。这也有助于保持Ni表面在分解前体材料时的催化活性。此外，我们还对生长过程指南反应器中氧气的消耗进行了详细的分析（补充注释1）。我们发现前体量对于反应性氧物质的消耗是关键的。在优化的生长条件下，使用稍微碳过量的环境来促进石墨烯的生长，且阻止形成无定形碳。另一方面，过度过量的前体材料导致Ni本体中沉积的碳的过饱和，且随后导致在Ni表面上石墨的结晶。这可解释导致形成如补充图2a中所观察到的较厚的石墨烯片。 明天继续吧！ |
5楼2017-02-10 22:01:46