In Situ Observations of Phase Transitions in Metastable Nickel (Carbide)/Carbon Nanocomposites.
In Situ Observations of Phase Transitions in Metastable Nickel (Carbide)/Carbon Nanocomposites.
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DOI：
10.1021/acs.jpcc.6b01555
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发表时间：
2016-10-06
影响因子：
3.7
通讯作者：
Hofmann, Stephan
中科院分区：
文献类型：
--
作者：
Bayer, Bernhard C.;Bosworth, David A.;Michaelis, F. Benjamin;Blume, Raoul;Habler, Gerlinde;Abart, Rainer;Weatherup, Robert S.;Kidambi, Piran R.;Baumberg, Jeremy J.;Knop-Gericke, Axel;Schloegl, Robert;Baehtz, Carsten;Barber, Zoe H.;Meyer, Jannik C.;Hofmann, Stephan
由碳基体中的亚稳态金属碳化物组成的纳米复合薄膜具有广泛的应用，从硬质涂层到磁性材料以及能量存储和转换。虽然利用非平衡技术进行沉积已得到确立，但对于此类亚稳态纳米复合材料在加工过程以及器件运行过程中高温热平衡条件下的动态演变的理解仍然有限。在此，我们通过原位X射线衍射、原位拉曼光谱和原位X射线光电子能谱等互补方法，研究了热后沉积处理过程中，非晶碳（a - C）基体中亚稳态碳化镍（Ni₃C）纳米晶体的溅射沉积纳米复合材料。在低退火温度（300°C）下，我们观察到等温的Ni₃C分解为面心立方镍和非晶碳，但初始精细结构的纳米复合形态没有改变。只有在较高温度（400 - 800°C）时，非晶碳基体的镍催化等温石墨化才开始，我们将其与纳米复合材料通过体扩散介导的相分离为较粗的镍和石墨颗粒联系起来。自然冷却时，仅观察到从镍中析出极少量的碳，这表明即使对于高度碳饱和的体系，冷却时的析出在动力学上也可能被抑制。我们的研究结果表明，填充物的相变和纳米复合材料的形态改变可以解耦，从制造角度来看这是有利的。我们的原位研究还确定了在加工的所有阶段镍填充物微晶的高碳含量是此类金属 - 碳纳米复合材料的关键特征，它决定了其整个热演变过程。在更广泛的背景下，我们还就备受争议的亚稳态Ni₃C作为石墨烯和碳纳米管生长中的催化剂相的潜在作用讨论了我们的研究结果。
Nanocomposite thin films comprised of metastable metal carbides in a carbon matrix have a wide variety of applications ranging from hard coatings to magnetics and energy storage and conversion. While their deposition using nonequilibrium techniques is established, the understanding of the dynamic evolution of such metastable nanocomposites under thermal equilibrium conditions at elevated temperatures during processing and during device operation remains limited. Here, we investigate sputter-deposited nanocomposites of metastable nickel carbide (Ni3C) nanocrystals in an amorphous carbon (a-C) matrix during thermal postdeposition processing via complementary in situ X-ray diffractometry, in situ Raman spectroscopy, and in situ X-ray photoelectron spectroscopy. At low annealing temperatures (300 °C) we observe isothermal Ni3C decomposition into face-centered-cubic Ni and amorphous carbon, however, without changes to the initial finely structured nanocomposite morphology. Only for higher temperatures (400–800 °C) Ni-catalyzed isothermal graphitization of the amorphous carbon matrix sets in, which we link to bulk-diffusion-mediated phase separation of the nanocomposite into coarser Ni and graphite grains. Upon natural cooling, only minimal precipitation of additional carbon from the Ni is observed, showing that even for highly carbon saturated systems precipitation upon cooling can be kinetically quenched. Our findings demonstrate that phase transformations of the filler and morphology modifications of the nanocomposite can be decoupled, which is advantageous from a manufacturing perspective. Our in situ study also identifies the high carbon content of the Ni filler crystallites at all stages of processing as the key hallmark feature of such metal–carbon nanocomposites that governs their entire thermal evolution. In a wider context, we also discuss our findings with regard to the much debated potential role of metastable Ni3C as a catalyst phase in graphene and carbon nanotube growth.
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影响因子：
4.5
作者：
Blume, Raoul;Rosenthal, Dirk;Schloegl, Robert
通讯作者：
Schloegl, Robert
影响因子：
3.7
作者：
Bayer, Bernhard C.;Fouquet, Martin;Robertson, John
通讯作者：
Robertson, John
影响因子：
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作者：
Bayer, Bernhard C.;Baehtz, Carsten;Hofmann, Stephan
通讯作者：
Hofmann, Stephan
影响因子：
3.9
作者：
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Shieu, Fuh-Sheng
影响因子：
10.9
作者：
Anton, R.
通讯作者：
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