Crisan Alina Daniela, Crisan Ovidiu
National Institute for Materials Physics, P.O. Box MG-7, 077125 Magurele, Romania.
Nanomaterials (Basel). 2022 Sep 16;12(18):3225. doi: 10.3390/nano12183225.
Intermetallic Cr-Al-C thin films from the 211 class of MAX phases were fabricated via ion beam deposition and structural investigations were undertaken to obtain information about morpho-structural effects propelled by carbon excess in the stoichiometry of the films. In order to promote the occurrence of the CrAlC MAX phase, the stoichiometric thin films were subsequently annealed at two temperature values: 650 °C and 700 °C in UHV conditions for 30 min. The morpho-structural effects in both as-deposited and annealed films were monitored using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. XRD analysis showed that the as-deposited sample was almost completely crystallized in the hexagonal CrAlC structure, with a remaining amorphous fraction of about 17%, most probably rich in carbon. Raman analysis allowed the identification of three spectral regions, two of them encompassing the Raman optical modes belonging to the CrAlC 211 MAX phase, while the third one gave strong evidence of highly intense and large D- and G-bands of carbon. Structural parameters such as the crystal lattice parameters as well as the volume of the crystal unit cell were found to decrease upon annealing; this decrease is attributed to the grain growth. The average crystallite dimension was proven to increase after annealing, while the lattice micro-strain lowered to approximately 63% in the annealed thin film compared to the as-deposited one. Well-formed and intense Raman peaks attributed to D- and G-bands of carbon were also observed and, corroborated with the structural data, seemed to indicate an overall increased level of crystal ordering as well as potential carbon nanoclustering after thermal treatments with thin CrAlC films. This observed phenomenon concords with previously documented reports on ab initio modelling of possible CrAlC structures with carbon excess.
通过离子束沉积制备了211类MAX相的金属间Cr-Al-C薄膜，并进行了结构研究，以获取有关薄膜化学计量中碳过量所推动的形态结构效应的信息。为了促进CrAlC MAX相的出现，随后将化学计量薄膜在超高真空条件下于650℃和700℃两个温度值下退火30分钟。使用扫描电子显微镜、X射线衍射和拉曼光谱监测沉积态和退火态薄膜中的形态结构效应。XRD分析表明，沉积态样品几乎完全结晶为六方CrAlC结构，剩余非晶部分约为17%，很可能富含碳。拉曼分析确定了三个光谱区域，其中两个区域包含属于CrAlC 211 MAX相的拉曼光学模式，而第三个区域则有力地证明了碳的高强度和大D带及G带。发现晶格参数以及晶体单元胞体积等结构参数在退火后减小；这种减小归因于晶粒生长。经证明，退火后平均微晶尺寸增大，而与沉积态薄膜相比，退火态薄膜中的晶格微应变降低至约63%。还观察到了归因于碳的D带和G带的形态良好且强烈的拉曼峰，与结构数据相互印证，似乎表明经过CrAlC薄膜热处理后，晶体有序度总体提高以及可能存在碳纳米团簇。这一观察到的现象与先前关于碳过量的可能CrAlC结构的从头算建模的文献报道一致。
