Thermodynamic conditions of ta-C formation at implantation of noble-gas ions in carbon

Relationship between nanoscale roughness and ion-damaged layer in argon plasma exposed polystyrene films

“…The relationship between amorphous carbon film density and the compressive stress intrinsic to the film produced by this mechanism, , has been reported in a number of publications. 42,44 Using the experimental relationship from Schwan et al, 42 for the modified layer film densities are shown in Table I.…”

Modeling of ta-C growth: Influence of the technological parameters

“…Both effects, sp³ formation and sp³ relaxation, are favored by higher ion energies, but to a different degree: At lower energies the formation is dominating, at high energies the relaxation, thus resulting in an energy optimum for maximal sp³ bonds. In the newer approaches of Hofsäss [7] and of Kalinichenko [24] the collision cascade determines only the initial energy concentration, whereas their transformation into the ta-C structure occurs inside the thermal spike. According to the Hofsäss model the sp³ bonds are formed by the intense thermally activated atomic restructurization within the excited thermal spike region.…”

“…The analytical approaches of Robertson [21,22], Davis [23], the Hofsäss group [7] and of Kalinichenko et al [24] use for the collisional stage the results of Monte-Carlo calculations within the TRIM program. The widely used SRIM program package (= Stopping and Range of Ions in Matter) with its core TRIM program (TRansport of Ions in Matter, www.srim.org) assumes binary collisions within an amorphous target, where the impact parameters of the subsequent collisions are randomly selected [25,26].…”

“…But for higher ion energies this trend is reversed: 1) an increasing part of the ion energy is transferred to electronic excitations, which in the short available time are not converted into thermal energy, 2) due to the increasing number of recoiled target atoms, the energy is spread over a larger cascade volume leading to a reduced energy concentration and corresponding to less redistribution. In [24] the additional effect of high pressure p(t, ε) in the overheated nano-region is considered by replacing q′ by q′ − p(t, ε) · Δv, where Δv represents the reduction of the atomic volume in the transition from sp² bonding to sp³ states. Again the non-monotonic energy dependence of the rearrangements in the thermoelastic peak reflects the corresponding course of the initial energy distribution (or initial temperature) due to the increasing excitation volume in combination with the reduced fraction of thermal energy.…”

“…The widely used SRIM program package (= Stopping and Range of Ions in Matter) with its core TRIM program (TRansport of Ions in Matter, www.srim.org) assumes binary collisions within an amorphous target, where the impact parameters of the subsequent collisions are randomly selected [25,26]. The subsequent thermalization is treated by the thermal spike model, where the local excitation of the atomic lattice is described within the framework of a continuum model by the transient temperature field in the surrounding of a point source [21][22][23] or a line source [7,24]. According to the early concepts of Robertson and Davis, the structures with high sp³ content (reflected by increased density or high compressive stress) are created during the collisional stage and then partially transformed to sp² bonds by structural relaxation in the thermal spike.…”