Formation of surface nanostructures on rutile (TiO₂): comparative study of low-energy cluster ion and high-energy monoatomic ion impact

Abstract

The formation of nanostructures on rutile (TiO2) surfaces formed after the implantation of kiloelectronvolt-energy cluster ions and megaelectronvolt- to gigaelectronvolt-energy multiply charged heavy ions (Iq+, Taq+ and Uq+) is studied. Despite the differences in stopping and energy transfer mechanisms between the kiloelectronvolt-energy cluster ions and megaelectronvolt-energy monoatomic ions, their impacts lead to a similar type of surface damage, namely craters. For the cluster ion implantation the craters are caused by the multiple-collision effect (dominated by nuclear stopping) and the high density of energy and momentum transferred to the target, while for the case of megaelectronvolt multiply charged ions the craters are probably formed due to the Coulomb explosion and fast energy transfer caused by the electronic stopping. At ion energies in the gigaelectronvolt range, nanosize protrusions, so-called hillocks, are observed on the surface. It is suggested that electronic stopping leads to the formation of continuous tracks and the transferred energy is high enough to melt the material along the whole projectile path. Elastic rebound of the tension between the molten and solid state phases leads to liquid flow, expansion and quenching of the melt, thus forming the hillocks. Atomic force microscopy measurements carried out under different environmental conditions (temperature and atmosphere) suggest that the damaged material at the nanosize impact spots has very different water affinity properties (higher hydrophilicity or water adsorption) compared with the non-irradiated rutile surface.

Response of GaN to energetic ion irradiation: conditions for ion track formation

“…Similar values for the threshold for ion tracks in the bulk and on the surface have often been observed [17,36,37], thus enabling to analyse the threshold with two complementary techniques. SHI irradiation under grazing incidence angles increases the nearsurface interaction volume and therefore induces even more dramatic changes on the material surface.…”

Selective binding of oligonucleotide on TiO 2 surfaces modified by swift heavy ion beam lithography

“…1 b) to describe the different zones of the patterned substrate. The depth of the micro-wells (or etching depth) resulting after the localized SHI irradiation and subsequent HF etching, is related to the ion energy and fluence, in addition to the fact that there is a certain chemical etching threshold for rutile TiO 2 [24][25][26][27][28]32]. For the present applied ion energy and fluence a characteristic depth of 2 µm is obtained [28], which is the maximum depth obtainable with the used ion.…”

“…Other authors proposed a different mechanism for rough amorphous TiO 2 films that consists of the generation of a Ti-O dangling bond on the TiO 2 surface [40]. The generation of Ti 3+ -O vacancy complexes [41] and the absorption of water or hydroxyl groups [32], due to the induced defects after ion irradiation of rutile single crystals, have also been reported. Finally, it has also been observed that the wettability of smooth hydrophilic surfaces improves by roughening them [42].…”

“…For the present applied ion energy and fluence a characteristic depth of 2 µm is obtained [28], which is the maximum depth obtainable with the used ion. It is important to note that only damaged and amorphous TiO 2 is affect by HF etching, crystalline (virgin) rutile TiO 2 is not [24][25][26]32]. Therefore, the surface between the microwells (or top of the walls) is still crystalline rutile as it has not been exposed to ion irradiation.…”

Near surface latent track morphology of SHI irradiated TiO2

“…. Prior to this report, surface hillocks were characterized mainly by AFM . This technique has a disadvantage due to artefacts induced by the physical size of the tip and is not capable of discerning between crystalline and amorphous hillocks.…”