Disorder and optical properties of amorphous carbon

Mathioudakis, Christos; Kopidakis, Georgios; Patsalas, P.; Kelires, P. C.

doi:10.1016/j.diamond.2007.08.009

Cited by 28 publications

(28 citation statements)

References 17 publications

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“…7. The value we extract from the HSE calculation, 1.3 eV, is in good agreement with the recent tight-binding results of Mathioudakis et al 28 As expected, the PBE calculation severely underestimates this value. peak-center position of these levels, using a Gaussian fit, for the MD trajectory average in the explicit interfacial system, as shown in Fig.…”

Section: Bandgap Determination: Tauc Approachsupporting

confidence: 78%

“…The HSE results for the DOS in the energy gap region, together with a comparison with the results from a PBE calculation, are shown in the figure. The determination of the optical gap following the Tauc procedure, 27 described in detail in Appendix A, yields E 28 It can be clearly observed how the DOS profile of the bulk sample is shifted upward by over 500 meV compared to the DOS profile of the surface structure shown in Fig. 1(a).…”

Section: B A-c Surface In Aqueous Environmentmentioning

confidence: 99%

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Energy band alignment and electronic states of amorphous carbon surfaces in vacuo and in aqueous environment

Miguel

Määttä

Lopez-Acevedo

et al. 2015

Journal of Applied Physics

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In this paper, we obtain the energy band positions of amorphous carbon (a-C) surfaces in vacuum and in aqueous environment. The calculations are performed using a combination of (i) classical molecular dynamics (MD), (ii) Kohn-Sham density functional theory with the PerdewBurke-Ernzerhof (PBE) exchange-correlation functional, and (iii) the screened-exchange hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE). PBE allows an accurate generation of a-C and the evaluation of the local electrostatic potential in the a-C/water system, HSE yields an improved description of energetic positions which is critical in this case, and classical MD enables a computationally affordable description of water. Our explicit calculation shows that, both in vacuo and in aqueous environment, the a-C electronic states available in the region comprised between the H 2 /H 2 O and O 2 /H 2 O levels of water correspond to both occupied and unoccupied states within the a-C pseudogap region. These are localized states associated to sp 2 sites in a-C. The band realignment induces a shift of approximately 300 meV of the a-C energy band positions with respect to the redox levels of water. V C 2015 AIP Publishing LLC.

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Section: Bandgap Determination: Tauc Approachsupporting

confidence: 78%

Section: B A-c Surface In Aqueous Environmentmentioning

confidence: 99%

Energy band alignment and electronic states of amorphous carbon surfaces in vacuo and in aqueous environment

Miguel

Määttä

Lopez-Acevedo

et al. 2015

Journal of Applied Physics

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“…This is because the embedding of minority configurations into a host phase produces disorder, which is reflected in the π-π ⋆ subgap transitions. We also showed [38] that transitions between states localized on unpaired sp 2 sites (dangling bonds), or between such states and neighboring π or σ states, are negligible. This is in contrast to a-Si:H, where dangling bond defects are the main contributors to the Urbach edge.…”

Section: Optoelectronic Propertiesmentioning

confidence: 92%

“…We have recently shown [38], that E U is a good measure of disorder in a-C, as it reflects not only bond-length and bond-angle distortions (structural disorder), but also topological disorder related to the size distribution of chains and clusters of sp 2 and sp 3 atoms in the mixed phase [3]. Thus, it is a measure of the inhomogeneous disorder in the two-phase network.…”

Section: Optoelectronic Propertiesmentioning

confidence: 99%

Carbon-based nanostructured composite films: Elastic, mechanical and optoelectronic properties derived from computer simulations

Fyta¹,

Mathioudakis²,

Remediakis³

et al. 2011

Surface and Coatings Technology

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In this review, we present our recent computational work on carbon-based nanostructured composites. These materials consist of carbon crystallites embedded in an amorphous carbon matrix and are modeled here through classical and semi-empirical quantum-mechanical simulations. We investigate the energetics, mechano-elastic, and optoelectronic properties of these materials. Once the stability of the composites is discussed, we move on to the calculation of their elastic moduli and constants, their anisotropy and elastic recovery. At a next step, we focus on diamond composites, which were found to be the most stable among the composites studied, and went beyond the elastic regime to investigate their ideal fracture. Finally, for these materials, the electronic density of states, dielectric function, and optical response were calculated and linked to the disorder in the structures. Our findings unveil the high potential of these materials in nanotechnological applications, especially as ultlra-hard coatings.

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“…These bonding states classify several allotropes of carbon which significantly changes important properties such as electrical, thermal, optical, mechanical and tribological behavior. [5][6][7][8] Depending upon the chemical state of carbon atoms, several classes of tribologically important materials, exclusively in the form of micro/nano-crystalline diamond and diamond-like carbon (DLC) film can be formed. [9][10][11] The DLC film is unique in several critical applications due to the ease of merging the tribological and mechanical properties such as high wear resistance, low friction coefficient and high hardness.…”

Section: Introductionmentioning

confidence: 99%

Impact of laser power density on tribological properties of Pulsed Laser Deposited DLC films

et al. 2013

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Fabrication of wear resistant and low friction carbon films on the engineered substrates is considered as a challenging task for expanding the applications of diamond-like carbon (DLC) films. In this paper, pulsed laser deposition (PLD) technique is used to deposit DLC films on two different types of technologically important class of substrates such as silicon and AISI 304 stainless steel. Laser power density is one of the important parameter used to tailor the fraction of sp2 bonded amorphous carbon (a-C) and tetrahedral amorphous carbon (ta-C) made by sp3 domain in the DLC film. The I(D)/I(G) ratio decreases with the increasing laser power density which is associated with decrease in fraction of a-C/ta-C ratio. The fraction of these chemical components is quantitatively analyzed by EELS which is well supported to the data obtained from the Raman spectroscopy. Tribological properties of the DLC are associated with chemical structure of the film. However, the super low value of friction coefficient 0.003 is obtained when the film is predominantly constituted by a-C and sp2 fraction which is embedded within the clusters of ta-C. Such a particular film with super low friction coefficient is measured while it was deposited on steel at low laser power density of 2 GW/cm2. The super low friction mechanism is explained by low sliding resistance of a-C/sp2 and ta-C clusters. Combination of excellent physical and mechanical properties of wear resistance and super low friction coefficient of DLC films is desirable for engineering applications. Moreover, the high friction coefficient of DLC films deposited at 9GW/cm2 is related to widening of the intergrain distance caused by transformation from sp2 to sp3 hybridized structure.

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Disorder and optical properties of amorphous carbon

Cited by 28 publications

References 17 publications

Energy band alignment and electronic states of amorphous carbon surfaces in vacuo and in aqueous environment

Energy band alignment and electronic states of amorphous carbon surfaces in vacuo and in aqueous environment

Carbon-based nanostructured composite films: Elastic, mechanical and optoelectronic properties derived from computer simulations

Impact of laser power density on tribological properties of Pulsed Laser Deposited DLC films

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