Ultrathin undoped tetrahedral amorphous carbon films: The role of the underlying titanium layer on the electronic structure

Protopopova, Vera; Iyer, Ajai; Kondrateva, Anastasia; Sainio, Sami; Palomäki, Tommi; Laurila, Tomi; Mishin, M. V.

doi:10.1016/j.diamond.2015.06.009

Cited by 21 publications

(19 citation statements)

References 57 publications

(78 reference statements)

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“…The influence of this geometric asymmetries can be seen in the difference in the energy position of the QB states, their energy width, and localization degree. Although the localized states at each side of the barrier are not at the same energy (due to the wells' asymmetry), there is a considerable tail overlapping that is responsible for the resonance in T(E), thus, evidencing RT transport as reported by Bhattacharyya et al 1,12 Our results can also be contrasted with the experimental results from Protopopova et al 61 They studied the thickness dependence of the conductivity in a-C ultra-thin films, and proposed that for thinner films ( 4 nm) the conduction decreases due to the filling of exponentially distributed traps. On the contrary, we propose that conduction in high-density ultra-thin films decreases due to the reduction in the number of charge traps (localized electronic states) induced by the atomic reconfiguration.…”

Section: Fig 10 Pdos On Spcontrasting

confidence: 57%

Density and localized states' impact on amorphous carbon electron transport mechanisms

Caicedo‐Dávila

Lopez-Acevedo

Velasco-Medina

et al. 2016

Journal of Applied Physics

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This work discusses the electron transport mechanisms that we obtained as a function of the density of amorphous carbon (a-C) ultra-thin films. We calculated the density of states (total and projected), degree of electronic states' localization, and transmission function using the density functional theory and nonequilibrium Green's functions method. We generated 25 sample a-C structures using ab-initio molecular dynamics within the isothermal-isobaric ensemble. We identified three transport regimes as a function of the density, varying from semimetallic in low-density samples (≤2.4 g/cm3) to thermally activated in high-density (≥2.9 g/cm3) tetrahedral a-C. The middle-range densities (2.4 g/cm3 ≤ρ≤ 2.9 g/cm3) are characterized by resonant tunneling and hopping transport. Our findings offer a different perspective from the tight-binding model proposed by Katkov and Bhattacharyya [J. Appl. Phys. 113, 183712 (2013)], and agree with experimental observations in low-dimensional carbon systems [see S. Bhattacharyya, Appl. Phys. Lett. 91, 21 (2007)]. Identifying transport regimes is crucial to the process of understanding and applying a-C thin film in electronic devices and electrode coating in biosensors.

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Section: Fig 10 Pdos On Spcontrasting

confidence: 57%

Density and localized states' impact on amorphous carbon electron transport mechanisms

Caicedo‐Dávila

Lopez-Acevedo

Velasco-Medina

et al. 2016

Journal of Applied Physics

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“…The electronic properties of ta-C depend strongly on the film thickness because it affects the fraction of sp 2 and sp 3 bonded carbon. [78,79] We observed in publication III, that the fraction of sp 2 increases with decreasing ta-C film thickness from 100 to 7 nm. This correlated with a decrease in mobility gap and an increase in the current flow through the films.…”

Section: Electrical Propertiesmentioning

confidence: 83%

Corrigendum to “Unmodified and multi-walled carbon nanotube modified tetrahedral amorphous carbon (ta-C) films as in vivo sensor materials for sensitive and selective detection of dopamine” [Bios. Bioelectron. 118 (2018) 23–30]

Palomäki

Peltola

Sainio

et al. 2019

Biosensors and Bioelectronics

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“…The reference sample was a planar silicon wafer coated with ta-C. The filtered cathodic vacuum arc (FCVA) deposited ta-C films are typically ultrasmooth [44] and atomic force microscope (AFM) measurements have shown that ta-C films deposited with the same equipment produces coatings with root mean square (RMS) surface roughness of 0.1–0.2 nm [23] and this coating copies the roughness of underlying substrate in few nm roughness range [24].…”

Section: Resultsmentioning

confidence: 99%

“…DLC is not a specific single material, but a group of amorphous carbonaceous materials with different atomic bond structures and properties. Among DLC materials, tetrahedral amorphous carbon (ta-C) is a form with high sp 3 bonding and low hydrogen content, and it is considered the hardest and most wear resistant [21], but it also possesses beneficial properties for sensor material: it is electrochemically active [13,15,22], it has a wide water window [23], it is transparent, and its deposition is possible at low temperatures [24].…”

Section: Introductionmentioning

confidence: 99%

Fabrication of Micro- and Nanopillars from Pyrolytic Carbon and Tetrahedral Amorphous Carbon

et al. 2019

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Pattern formation of pyrolyzed carbon (PyC) and tetrahedral amorphous carbon (ta-C) thin films were investigated at micro- and nanoscale. Micro- and nanopillars were fabricated from both materials, and their biocompatibility was studied with cell viability tests. Carbon materials are known to be very challenging to pattern. Here we demonstrate two approaches to create biocompatible carbon features. The microtopographies were 2 μ m or 20 μ m pillars (1:1 aspect ratio) with three different pillar layouts (square-grid, hexa-grid, or random-grid orientation). The nanoscale topography consisted of random nanopillars fabricated by maskless anisotropic etching. The PyC structures were fabricated with photolithography and embossing techniques in SU-8 photopolymer which was pyrolyzed in an inert atmosphere. The ta-C is a thin film coating, and the structures for it were fabricated on silicon substrates. Despite different fabrication methods, both materials were formed into comparable micro- and nanostructures. Mouse neural stem cells were cultured on the samples (without any coatings) and their viability was evaluated with colorimetric viability assay. All samples expressed good biocompatibility, but the topography has only a minor effect on viability. Two μ m pillars in ta-C shows increased cell count and aggregation compared to planar ta-C reference sample. The presented materials and fabrication techniques are well suited for applications that require carbon chemistry and benefit from large surface area and topography, such as electrophysiological and -chemical sensors for in vivo and in vitro measurements.

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Ultrathin undoped tetrahedral amorphous carbon films: The role of the underlying titanium layer on the electronic structure

Cited by 21 publications

References 57 publications

Density and localized states' impact on amorphous carbon electron transport mechanisms

Density and localized states' impact on amorphous carbon electron transport mechanisms

Corrigendum to “Unmodified and multi-walled carbon nanotube modified tetrahedral amorphous carbon (ta-C) films as in vivo sensor materials for sensitive and selective detection of dopamine” [Bios. Bioelectron. 118 (2018) 23–30]

Fabrication of Micro- and Nanopillars from Pyrolytic Carbon and Tetrahedral Amorphous Carbon

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