A.V. Khomich

Electrochemical behaviour of a-C:N:H films

Abstract Electrochemical impedance in H2SO4 solutions and the kinetics of redox reactions in the Fe(CN)63−/4− system were studied in amorphous nitrogenated diamond-like carbon thin-film electrodes. The films were fabricated on p- and i-type silicon and quartz substrates, using direct ion beam deposition from an RF inductively coupled N2+CH4 plasma source. The films were characterized by optical and electrical measurements. Parameters of point defects (trapping centres) were measured by deep level transient spectroscopy techniques. The increase in the N2/CH4 ratio in the gas mixture leads to a decrease in the electrical resistivity and optical bandgap of the films from 3×1010 to 5×106 Ωxa0cm and from 1.3 to 0.6 eV, respectively. Simultaneously, the concentration of electrically active point defects increased and the charge transfer at the a-C:N:H filmxa0∣xa0redox electrolyte interface was significantly facilitated.

Effect of crystal structure on the electrochemical behaviour of synthetic semiconductor diamond: Comparison of growth and a nucleation surfaces of a coarse-grained polycrystalline film

Comparative studies of the electrochemical behaviour of the growth and nucleation surfaces of a free-standing boron-doped polycrystalline diamond film grown in a microwave plasma CVD reactor are performed. The uncompensated acceptor concentration in diamond is determined from the electrochemical impedance (Mott–Schottky plots), uncompensated boron acceptor concentration from infrared absorption measurements, and the total boron concentration, by the SIMS method. In the diamond bulk adjacent to the nucleation surface, constituted from submicrometre-sized crystallites, both the boron concentration and the total acceptor concentration are found to be significantly higher than near the growth surface, where the film crystallinity is more perfect. This difference is tentatively attributed to the increased concentration of crystal lattice defects near the nucleation surface. These defects, in addition to boron atoms, play the role of acceptors in diamond.

Electrochemical properties of undoped CVD diamond films vacuum- annealed at 1775-1915 K

Abstract Electrochemical behavior of vacuum-annealed undoped polycrystalline diamond films is studied. The film annealed at 1775 K appeared to be practically not conducting. With further increase in the annealing temperature above 1825 K, the film effective resistivity decreased from initial value of 10 11 –10 12 Ω cm down to less than 0.1 Ω cm; the differential capacitance increased from ∼10 -3 to ∼50 μF per 1 cm 2 of geometrical surface; the transfer coefficients for electrochemical reactions in the [Fe(CN) 6 ] 3−/4− redox solution increased from ∼0.2 to 0.5; and the degree of reversibility of the electrochemical reaction increased. The observed changes of the electrode properties can be attributed to gradual change of the thickness and/or properties (first and foremost, conductivity) of the non-diamond carbon phase formed along the intercrystallite boundaries upon the annealing and outcropping at the film surface as ‘active sites’.

Vacuum-annealed undoped polycrystalline diamond: a new electrode material

Electrochemical behavior of undoped polycrystalline diamond films annealed in a vacuum at 1775 to 1915 K is studied. The annealing at temperatures over 1825 K imparts conductance to initially insulating films, which permits using them as electrode material. With further increase in the annealing temperature to above 1915 K, the effective resistivity decreases from initial value of 1011 to 1012 Ω cm down to less than 0.1 Ω cm, the differential capacitance increases from ∼10–3 to ∼50 μF per cm2 of geometrical surface, the transfer coefficients for electrochemical reactions in the Fe(CN)63–/4– redox solution increase from ∼0.2 to 0.5, and the degree of reversibility of the electrochemical reaction increases. The observed changes in the electrode properties are caused by the formation, upon the annealing, of a nondiamond phase at the intercrystallite boundaries and defect areas in the crystallites; the outcroppings of the conducting phase play the role of active sites at the electrode surface. With increasing annealing temperature, both the amount of this phase and its conductivity increase.

Synthetic Semiconductor Diamond Electrodes: Comparison of Electrochemical Impedance at the Growth and Nucleation Surfaces of a Coarse-Grained Polycrystalline Film

A comparative study of the impedance of the growth and nucleation surfaces of a free-standing film of polycrystalline diamond deposited from RF-plasma and moderately doped with boron is performed. Using Mott–Schottky plots, the acceptor concentration is determined. It is shown that in the diamond bulk adjacent to the film growth side, which has more perfect crystal structure, this concentration is much lower than that near the nucleation side, where the film consists of submicron-sized grains.

Electrochemical properties of amorphous nitrogen-containing hydrogenated diamondlike-carbon films

The electrochemical impedance of thin-film electrodes made of amorphous nitrogen-containing diamondlike carbon (a-C:N:H) in H2SO4 solutions and the kinetics of redox reactions on these electrodes in the Fe(CN)63-/4- system are studied. The amorphous diamondlike carbon films with an admixture of nitrogen are grown by a directed deposition from inductively coupled methane-nitrogen plasma. The films’ resistivity values determined from the ac impedance of a-C:N:H/electrolyte contact practically coincided with those determined from the current-vol.tage curves taken at the a-C:N:H/metal contact. With an increase in the nitrogen : methane ratio in the gas phase, both the electrical resistance and optical bandgap decrease from 3 x 1010 to 5 x 106 ohm cm and from 1.3 to 0.6 eV, respectively. Simultaneously, the concentration of electrically active point-defect centers in a-C:N:H increases significantly and the reaction in the Fe(CN)63-/4- system is facilitated.

Electrical and Electrochemical Properties of a-C:N:H Films

Electrochemical impedance in H 2 SO 4 solutions and kinetics of redox reactions in the Fe(CN) 6 3-/4- system were studied on amorphous nitrogenated diamond-like carbon (a-C:N:H) thin-film electrodes. Parameters of point defects (trapping centers) were also measured by the Deep Level Transient Spectroscopy techniques. The films have been fabricated on p - and i -type silicon and quartz substrates, using direct ion beam deposition from an RF inductively coupled N 2 + CH 4 plasma source. The increase in N 2 /CH 4 ratio in the gas mixture lead to a decrease in the electrical resistivity and optical bandgap of the films from 3×10 10 to 5×10 6 Ω cm and from 1.3 to 0.6 eV, respectively. Simultaneously, the concentration of electrically active point defects increased significantly and the charge transfer at the a-C:N:H film/redox electrolyte interface was facilitated