Nonmetal–metal transition in carbon films embedded by nickel nanoparticles: absorption coefficients studies and Wemple–Didomenico dispersion parameters

Microscopy Res & Technique

Solaymani

2020

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In this article, the Ni-Cu nanoparticles (NPs) in the amorphous carbon hydrogenated thin films with different copper percentage by co-deposition of RF-plasma enhanced chemical vapor deposition were prepared using acetylene gas and Ni and Cu targets. The films deposited with 5% Cu have minimum value of the average diameter of Multi-walled Carbon Nanotubes, MWCNTs, in about of 100 nm. It can be seen that the lateral size values of the nanoparticles for films with 5% Cu have minimum value of 5.34 nm. Films deposited with 75% Cu have maximum value of optical density specially in high energy. The spectral density power of all films indicated the presence of fractal components in prominent topographies. Films deposited without Cu NPs have minimum value of fractal dimension in about of 2.96. The diagram of the bearing area versus the nanoparticles height has shown the percentage of cavities and single-layers. The single-layer contents of all films were about 95%.

Section: Resultsmentioning

confidence: 99%

The optical density and topography characterizations of MWCNTs on Ni‐Cu/ a‐C:H substrates with different copper percentage

Microscopy Res & Technique

Solaymani

2020

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“…The energy dependence of n ( E ) of amorphous materials can be fitted to the Wemple–DiDomenico (WDD) dispersion relationship; that is single‐oscillator model 28,29

n^{2} (E) - 1 = false(E_{0} E_{d} false) / false({E_{0}}^{2} - E^{2} false),

where E is the photon energy, E 0 is the oscillator energy and E d is the dispersion energy. The parameter E d , which measures the intensity of the inter band optical transition, does not depend on the band gap.…”

Section: Resultsmentioning

confidence: 99%

“…Obviously, this value is almost in agreement with that obtained from the Tauc extrapolation model. The static refractive index n 0 for the films is calculated incident photon energy equal zero and is given by 29

n_{0} = {((), 1 + E_{d} / E_{0})}^{1 / 2} .

…”

Section: Resultsmentioning

confidence: 99%

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The relation between the average diameter of CNTs on Ni–Cu @ a‐C:H catalyst with the optical absorption edge and the optical dispersion parameters

Solaymani

2020

Journal of Microscopy

Summary In this study, the average diameter of the grown CNTs on Ni–Cu NPs @ a‐C:H substrates were increased by increasing of Cu content. The obtained results indicated that by increase of Cu content, all films exhibited high‐absorption spectra; therefore, we were facing an increase in the energy gap of films. The values of dT/dλ and dR/dλ measurements for grown CNTs with 75% Cu shown that maximum values of optical band gap correspond to with values of 2.48 eV and 2.90 eV, respectively. It can be seen that with increase of average diameter of the grown CNTs, the values of Urbach energy of films were increased. The RBS and EDAX measurements were confirmed presence of Ni and Cu atoms into films. The films deposited with 75% Cu were more smooth. Films deposited with 75% Cu have more disordered. Films deposited with 75% Cu atoms have maximum values of the oscillator strength f and the dispersion energy Ed about of 0.108 eV2 and 0.0543 eV, respectively.

“…Specifically, this value is approximately the same as the values obtained from the Tauc extrapolation model. The static refractive index n for the thin films is calculated incident the photon energy equal zero and is given by 47 :…”

Section: Scanning Electron Microscope Images (Sem)mentioning

confidence: 99%

Influence of different Ni nanolayers thicknesses on single oscillator model parameters, optical band gap, and disordering energy in CNTs synthesized by Cu‐Ni @ a‐CH catalyst

Surface & Interface Analysis

2021

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co-deposition of RF-sputtering and RF-plasma enhanced chemical vapor deposition (RF-PECVD) were prepared using acetylene gas and Ni and Cu targets. The absorption edge and the optical dispersion parameters in CNTs synthesized by Cu-Ni @ a-C:H catalyst were studied. RBS measurements were performed, which confirmed the presence of Ni and Cu atoms in these films. Using Atomic Force Microscopy (AFM) system, the morphology of the films surface was investigated. The average diameter of the grown CNTs on Ni-Cu NPs @ a-C:H substrates were increased by increasing of Ni layers thickness. The values of dT/dλ and dR/dλ for grown CNTs without Ni show that the minimum value of the optical band gap corresponds to values of 2.55 and 2.56 eV, respectively. The absorption spectra peaks of films are about 400-600 nm. These peaks are quite sharp for carriers band to band transitions and with increasing Ni layers thickness, there is a small shift. It can be seen that the dispersion energy E d and the oscillator strength f of CNTs synthesized by Cu-Ni @ a-C:H catalyst had the lowest values of 2.21 eV and 9.39 eV 2 , respectively, compared to the other films.