Density,sp3fraction, and cross-sectional structure of amorphous carbon films determined by x-ray reflectivity and electron energy-loss spectroscopy

Abstract

Grazing-angle x-ray reflectivity ͑XRR͒ 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 ͑EELS͒. 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*ϭ0.87m for carbon systems, m being the free-electron mass. We show that, within the Drude-Lorentz model of the optical spectrum, m*ϭ͓1Ϫn(0) Ϫ2 ͔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.

Plasma biasing to control the growth conditions of diamond-like carbon

“…The EELS data revealed that all films had a high sp 3 content, sp 3 /(sp 2 +sp 3 ), see fraction correlates with the plasmon-inferred densities and, with the exception of sample 4 , this trend follows that proposed by Ferrari et al [9] (albeit using m* = 0.87 m e ).…”

“…correlation between the plasmon-inferred density and the sp 3 content [9]. Experimental investigations [10] and theoretical considerations of ta-C [9] have shown that it is appropriate to use prescribe an effective mass m* ≅ 0.9 m e for the valence electrons when calculating the specimen density from the plasmon peak position, where m e is the rest mass of the electron.…”

“…Experimental investigations [10] and theoretical considerations of ta-C [9] have shown that it is appropriate to use prescribe an effective mass m* ≅ 0.9 m e for the valence electrons when calculating the specimen density from the plasmon peak position, where m e is the rest mass of the electron. However, for the sake of simplicity, the approximate densities in this paper are quoted using m* = m e .…”

Principles for designing sputtering-based strategies for high-rate synthesis of dense and hard hydrogenated amorphous carbon thin films

“…In a previous study we addressed this issue by conceiving and implementing a strategy [18] which entailed increase of the electron temperature in high electron density discharge (such as HiPIMS) by using higher ionization potential buffer gas, Ne, instead of Ar. The result was a substantial increase in the ionized fraction of C which facilitated an increase in mass densities of films to levels which are close to those obtained by CVA and PLD [8,10].…”

“…Bonding configuration and hydrogen content can be, in turn, tailored by controlling the energy and flux of the depositing species [5,6]. An efficient way to achieve this is by using ionized deposition fluxes which can be generated by high plasma density discharges, such as cathodic vacuum arc (CVA) [8,9], pulsed laser deposition (PLD) [10,11], inductively coupled plasma (ICP) [12] and electron cyclotron resonance (ECR) [13] based plasma enhanced chemical vapor deposition (PECVD). Synthesis of a-C using magnetron sputtering-based discharges may be more industrially relevant owing to their conceptual simplicity and scalability.…”