Density, sp3 fraction, and cross-sectional structure of amorphous carbon films determined by x-ray reflectivity and electron energy-loss spectroscopy
Density, sp3 fraction, and cross-sectional structure of amorphous carbon films determined by x-ray reflectivity and electron energy-loss spectroscopy
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DOI：
10.1103/physrevb.62.11089
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发表时间：
2000-10-15
影响因子：
3.7
通讯作者：
Robertson, J
中科院分区：
文献类型：
--
作者：
Ferrari, AC;Li Bassi, A;Robertson, J
掠入角X射线反射率(XRR)被描述为一种有效的、无损的、无参数测量方法，可以测量各种类型的非晶态碳膜的质量密度，其厚度范围可达纳米级。它展示了XRR如何也可以检测到分层-如果它存在于胶片中，在这种情况下，必须对反射率分布进行建模以推导出密度。质量密度也可以通过电子能量损失谱(EELS)测量的等离子体激元能量由价电子密度得到。我们正式定义了一个带间有效电子质量m*，它解释了有限的带隙。XRR和EELS密度的比较使我们能够对碳系统拟合出平均m*=0.87m，m是自由电子质量。在光谱的Drude-Lorentz模型下，我们证明了m*=[1-n(0)(-2)]m，其中n(0)是零光频下的折射率。由碳K边EELS谱得到了sp(2)键的分数，并说明了选择扫描电子显微镜中的“魔术”入射和收集角度可以得到与样品取向或各向异性无关的sp(2)分数。从而给出了碳膜质量密度与Sp(3)含量之间的一般关系。
Grazing-angle x-ray reflectivity (XRR) is described as an efficient, nondestructive, parameter-free means to measure the mass density of various types of amorphous carbon films down to the nanometer thickness range. It is shown how XRR can also detect layering if it is present-in the films, in which case the reflectivity profile must be modeled to derive the density. The mass density can also be derived from the valence electron density via the plasmon energy, which is measured by electron energy-loss spectroscopy (EELS). We formally define an interband effective electron mass m*, which accounts for the finite band gap. Comparison of XRR and EELS densities allows us to fit an average m* = 0.87m for carbon systems, m being the free-electron mass. We show that, within the Drude-Lorentz model of the optical spectrum, m* = [1-n(0)(-2)]m, where n(0) is the refractive index at zero optical frequency. The fraction of sp(2) bonding is derived from the carbon K-edge EELS spectrum, and it is shown how a choice of "magic" incidence and collection angles in the scanning transmission electron microscope can give sp(2) fraction values that are independent of sample orientation or anisotropy. We thus give a general relationship between mass density and sp(3) content for carbon films.