Table 2.

Comprehensive summary of ion energy effects on polymer film characteristics.

Deposition Rate	High ion energy generally increases the deposition rate, as demonstrated in the synthesis of polyterpenol thin films using terpinen-4-ol and Melaleuca alternifolia oil [129]. An increase in mean ion energy from 3 eV to 17 eV augments mass deposition rates from 5.6 to 42.3 µg·m−2·s−1. Conversely, a decrease in ion energy can hinder this rate, as adsorption and desorption processes become dominant factors.
Etching rate	Ion energy has a substantial impact on the etching rate of polymer films. This effect is evident in the case of photoresist coatings (consisting of a Novolak polymer with a photoactive compound) exposed to SF6 plasma. As shown in Figure 7a, the etching rate increases from 200 nm/min to 600 nm/min when the ion energy is increased from 30 eV to 200 eV [130]. Similar trends are observed with PET films exposed to Ar-O2 plasma, where higher ion energies not only improve etching, but result also in a heater load of the substrate [75].
Cross- linking	Nanoscratching experiments on plasma-modified LDPE show that increased ion energy fluence stimulates chain crosslinking, enhancing surface shear resistance [131]. Ion energy fluences of 0, 70 and 630 kJ·m−2 result in friction forces of 10, 30 and 100 µN, respectively. A similar trend is seen in PDMS during plasma immersion ion implantation, where elevated ion energies trigger a linear increase in wrinkle amplitude and wrinkle wavelength, two key indicators of crosslinking [132].
Film Density	In the DBD polymerization process, ion energy plays a key role in promoting surface interactions that contribute to film densification [133]. Specifically, when the ion energy is increased (by controlling the applied power from 30 W to 70 W), the synthesized hydrogenated amorphous carbon (a-C:H) films present densities rising from 1.1 g·cm−3 to 1.4 g·cm−3.
Surface Morpho-logy	Ion energy can influence the morphology or surface topography of polymer films such as PEEK, as ions with higher energy can affect the surface diffusion or mobility of polymer chains, leading to films with different surface textures [134].
Surface Composition	Plasma source ion implantation (PSII) is a technique where the control of ion energy is straightforward as it is directly correlated with the applied voltage. CF4 plasma generated in a PSII device can change the surface composition of LDPE films to improve their hydrophobicity. As reported in Figure 7b, maximum WCA are obtained at ion energies of −1 kV, with values peaking at 122° and 113°, respectively, 1 day and 28 days after plasma treatment. These improvements can be attributed to the substitution of hydrocarbon and oxygen groups by fluorocarbon bonds (CF2 and CF3) [135]. However, when ion energies are further reduced to −5 kV and −10 kV, Figure 7b shows that the process becomes less effective, with WCA values close to 95°. In plasma polymerization, ion energy has a significant impact on changes to surface composition, in particular on the effective integration of specific chemical functionalities. Analyzing the polymer coatings derived from an ethyl trimethylacetate (ETMA) monomer, Saboohi et al. identified two distinct scenarios: (i) under conditions of low ion energy and flux, ions gently interact with the surface, conserving the chemical integrity of groups and enhancing the overall film development; (ii) conversely, high-energy ions can cause the fragmentation of ETMA, a large molecular monomer, subsequently causing a deviation from the expected chemical functionalities [136].