Electrical conduction in nanostructured carbon and carbon-metal films grown by supersonic cluster beam deposition

Bruzzi, M.; Piseri, P.; Miglio, S.; Bongiorno, G.; Barborini, E.; Ducati, Caterina; Robertson, John; Milani, P.

doi:10.1140/epjb/e2003-00311-4

Cited by 22 publications

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“…The activation energy (~ 0.16-0.2eV, Fig. 2C) is always definitely lower than the value of 0.3eV as obtained for sp 2 cluster-assembled carbon films where cumulenes were absent [20]. [6,7].…”

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confidence: 60%

“…[19,20]; two parallel gold contacts were previously evaporated on the substrate (200 nm thick, 4 mm long and 0.8 mm separation). The electrical conductivity at various temperatures of films with a thickness of 400 nm (applying a constant bias of 100 V) was characterized in situ by a Keithley 6517A electrometer with a d.c. current sensitivity of about 0.1 pA.…”

Section: Introductionmentioning

confidence: 99%

“…different cumulene contents). To fit these curves we assume a conductivity typical of disordered semiconductors as observed in sp 2 amorphous carbon [1] and in cluster-assembled carbon films [20]. The presence of disorder induces the formation of an electronic density of states characterized by tail bands extending from conduction and valence band edges within a forbidden gap; these tails arise from π states with atypical coordination, while dangling bonds create deep states forming a narrow band close to midgap [1].…”

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Influence of Cumulenic Chains on the Vibrational and Electronic Properties ofsp−sp2Amorphous Carbon

et al. 2007

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We report the production and characterization of a form of amorphous carbon films with sp/sp 2 hybridization (atomic fraction of sp hybridized species ≥ 20%) where the predominant sp bonding appears to be (=C=C=) n cumulene. Vibrational and electronic properties have been studied by in situ Raman spectroscopy and electrical conductivity measurements. Cumulenic chains are substantially stable for temperatures lower than 250 K and they influence the electrical transport properties of the sp/sp 2 carbon through a self-doping mechanism by pinning the Fermi level closer to one of the mobility gap edges. Upon heating above 250 K the cumulenic species decay to form graphitic nanodomains embedded in the sp 2 amorphous matrix thus reducing the activation energy of the material. This is the first example of a pure carbon system where the sp hybridization influences bulk properties. Cumulenes are expected to tend to a metallic behavior, characterized by the homogeneous distribution of the π orbitals, as their length increases, while polyynes are expected to be semiconducing even for infinitely long chains, due to bond length alternation opening an energy gap at the edge of the Brilluoin zone [6,7].Sp chains can be stabilized by isolation in rare gas or inorganic matrices [8,5] or terminating the chain ends with suitable functional groups [6,9]. Calculations on infinite carbon chains indicate that polyynes are energetically more stable than cumulenes due to Peierls distortion [10], however for finite length chains the gain in energy is too low to be significant even a T = 0 K [11].Furthermore it has been shown that the electronic configuration of the chains is determined, regardless their length, by the group termination of the chain [6]. A conspicuous amount of experimental and theoretical results are available on the electronic structure and vibrational properties of isolated polyynes [12][13][14], whereas almost no experimental characterizations can be found on cumulenes.The possibility of stabilizing sp chains in cluster-assembled nanostructured carbon films Here we report on the production and characterization of amorphous sp/sp 2 carbon films where the dominant sp species are cumulenes. This is obtained by supersonic cluster beam deposition on a substrate kept at a temperature of 150 K. We show that cumulenes are stable up to a temperature of roughly 210 K and that they influence the electrical transport properties of the films acting as metallic doping species. By rising the film temperature to 325 K cumulenes undergo a reorganization inducing the formation of nanometric graphitic islands in the amorphous sp 2 matrix, while the amount of polyynes remains substantially constant in the investigated temperature range.Cluster-assembled films were grown in ultra high vacuum (~ 10 -9 mbar) by depositing on glass substrates a supersonic beam of carbon clusters produced by a pulsed microplasma cluster source as described in detail in refs. [19,20]; two parallel gold contacts were previously evaporated on the substrat...

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Influence of Cumulenic Chains on the Vibrational and Electronic Properties ofsp−sp2Amorphous Carbon

et al. 2007

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“…One possible route toward increasing their conductivity (and thus improving their sensing properties) is through alloying with metallic elements such as Mo, Co or Ni [1,9]. Preparation of carbon structures in which metallic elements are included during synthesis have been studied for many years [10][11][12], but there are few reports on the effect of incorporated metallic elements on the electrical properties of nanoclustered carbon films [7,9].…”

Section: Introductionmentioning

confidence: 99%

“…Preparation of carbon structures in which metallic elements are included during synthesis have been studied for many years [10][11][12], but there are few reports on the effect of incorporated metallic elements on the electrical properties of nanoclustered carbon films [7,9].…”

Section: Introductionmentioning

confidence: 99%