Low temperature electrical transport in thin carbon films deposited on SiO2/Si substrates by pulsed laser deposition

• Published in: Journal of physics. Conference series Vol. 2487; no. 1; pp. 012038 - 12043
• Main Authors: Valcheva, E, Kirilov, K, Dikovska, A, Milenov, T
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.05.2023
• Subjects: Carbon; Diamond-like carbon films; Electric contacts; Electrical resistivity; Graphene; Laser ablation; Lasers; Low temperature; Phase composition; Physics; Pulsed laser deposition; Pulsed lasers; Raman spectra; Raman spectroscopy; Room temperature; Silicon dioxide; Silicon substrates; Spectrum analysis; Temperature; Temperature dependence; Thermal conductivity; Thin films; X ray photoelectron spectroscopy
• ISSN: 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/2487/1/012038

In this paper electrical transport studies are performed on thin carbon films deposited on SiO2/Si substrates by pulsed laser deposition (PLD) applying laser ablation of micro-crystalline graphite target. Experiments were carried out on 320 - 420 nm thick SiO2 on Si substrates as well as on hydrogenated diamond-like carbon (DLC) films deposited on SiO2/Si. Structural studies by means of XPS, SEM and Raman spectroscopy revealed that the films can be characterized as nano-sized carbon phases possessing different phase composition (i.e. the ratio sp3/sp2 hybridized carbon, etc.). The electrical conductivity/resistivity of the films was measured in the temperature range 10 K < T < 300 K. Four-contact Van der Pauw method as well as two contact schemes have been applied. Some films have low room temperature resistivity in the range ρ = (0.1–1.5)×10-3 Ω.·m and consist predominantly of sp2 hybridized carbon with Raman spectra, which resemble that of nano-sized graphene depending on the deposition conditions and substrates used. The thinnest only 0.5 nm layer deposited directly on SiO2 exhibits relatively low specific resistance (~10-3 Ω. m), which can be taken as an indication of good deposition conditions of graphene-like layers. The current flow mechanism was explored at temperatures from 300 K down to 10K. The temperature dependence reveals non-metallic behavior - the conductivity decreases at decreasing temperature as opposed to typical metal behaviour. A model of variable range hopping (VRH) mechanism is applied to explain the low temperature conductivity drawn from transport in nanocrystalline disordered systems.