Ca. Dimitriadis et al., Microstructure and its effect on the conductivity of magnetron sputtered carbon thin films, J APPL PHYS, 89(12), 2001, pp. 7954-7959
Carbon thin films were grown by magnetron sputtering at room temperature on
silicon substrates, with the substrate bias voltage varying from +10 to -2
00 V. Transmission electron microscopy analysis has shown that films deposi
ted at V-b = +10 and -40 V are amorphous (alpha -C), while films deposited
at V-b = -200 V are nanocrystalline (nc-C). Temperature dependent conductiv
ity measurements were carried out in the temperature range 300-77 K. With r
espect to conductivity, the results indicate that the investigated carbon f
ilms are classified in three groups: (i) In alpha -C films deposited at V-b
= +10 V (sp(2) rich bonds), the variable range hopping (VRH) conduction do
minates below 300 K. (ii) In alpha -C films deposited at negative V-b up to
-100 V (sp(3) rich bonds), VRH conduction dominates at low temperatures (T
< 150 K) and a thermally activated process satisfying the Meyer-Neldel rul
e at higher temperatures (T > 150 K). (iii) In nc-C film deposited at V-b =
-200 V, the conductivity is explained by a heteroquantum-dots model based
on a thermal-assisted tunneling process. The earlier differentiation in the
conductivity mechanisms may play a significant role in the field electron
emission properties of the films. (C) 2001 American Institute of Physics.