9 nm) and the long-wavelength limit of the refractive index (n ∞ ~ 2.663) were obtained. The thicknesses of the films are
in good agreement with the values directly measured by the step profilometer as listed in Table 1. And the long-wavelength limit of the refractive index n ∞ is an important optical parameter associated with the mass density and atomic structure of nc-Si:H thin films, which together with the X C obtained from the Raman measurement can be used to calculate the respective volume fractions of the three components, namely c-Si, a-Si, and voids in the films. Table 1 summarizes the structural and optical properties of the nc-Si:H thin BIBW2992 films under various R H. Finally, room-temperature IR transmission measurements were conducted to obtain both the oxygen content and hydrogen content in these films. Figure 2a shows the IR absorption spectra of the samples prepared under different R H, with four major absorption peaks appearing at around 630 cm-1 (Si-H rocking-wagging mode), 880 cm-1 (Si-H bending mode), 1,030 cm-1 (Si-O stretching mode), and 2,090 cm-1 (Si-H stretching mode) [21–24]. In the calculation of the absorption
coefficient, the transmittance was normalized to eliminate the interference fringes due to the small index of refraction difference between the c-Si substrate and the films. The bonded oxygen content C O can be yielded by numerical integration of the peak around 1,000 to 1,200 cm-1, which is click here related to the Si-O-Si stretching mode through the equation C O (at.%) = 1/N Si × A W × ∫(α(ν)/ν)dν, where α(υ) 4-Aminobutyrate aminotransferase is the absorption
coefficient of the film at wavenumber υ, N Si = 5 × 1022 cm-3 is the atomic density of pure silicon, and the proportionality constant A W is fixed to be 2.8 × 1019 cm-2[22, 23]. The bonded hydrogen content C H can also be calculated from the Si-H rocking mode at around 630 cm-1 with A W = 2.1 × 1019 cm-2[25]. The calculated C O and C H for all these nc-Si:H films are listed in Table 1. Figure 2 IR absorption spectra and oxygen content and volume fraction of voids. (a) IR absorption spectra of the nc-Si:H thin films prepared under different R H. (b) Oxygen content and volume fraction of voids as a function of R H. As a mixed-phase material with nanocrystallites embedded in an amorphous matrix, nc-Si:H contains a certain volume fraction of nanometer-sized voids, which should not be neglected when characterizing the microstructure of the films [26]. The volume fraction of voids P V in these nc-Si:H thin films was calculated based on Bruggeman’s effective media approximation [27] using the crystalline fraction X C from the Raman analysis and the refractive index n ∞ from the transmission calculation.