Modification of structure and surface morphology in various ZnO facets via low fluence gold swift heavy ion irradiation

Abstract

The influence of low fluence high‐energy ion irradiation on the modification of the ZnO surface structure and optical properties has been studied. ZnO samples of various orientations, namely, c‐plane (0001), a‐plane (11–20) and m‐plane (10–10), have been implanted with 30‐MeV Au ions with fluences ranging from 5 × 109 to 5 × 1011 cm−2. Rutherford backscattering spectrometry in the channelling mode (RBS‐C) and Raman spectroscopy has shown the distinct damage accumulation in the irradiated surface layer about 1 μm depending on the ZnO facet being to larger extent evidenced in the m‐plane ZnO. Contrary, the a‐plane ZnO has been exhibited the lowest Zn disorder. Using atomic force microscopy (AFM), a complex morphology was detected on the irradiated samples containing grains and exhibiting increased roughness, both growing with the Au implantation fluence mainly in m‐plane ZnO. Positron annihilation spectroscopy (PAS) has shown distinct defect accumulation at the Au‐ion fluence of 5 × 1011 cm−2, where RBS‐C and Raman spectroscopy indicated sudden disorder increase in the irradiated layers, probably the creation of more complex clusters of Zn and O vacancies 4VZn + 8VO initiated in connection with an overlap of individual ion impacts. Photoluminescence measurements have shown a distinct near‐band‐edge (NBE) luminescence, developing with the increasing Au‐ion fluence in various ZnO orientations. The m‐plane ZnO had the most progressively suppressed NBE in comparison with the other orientations.

Surface modification by high-energy heavy-ion irradiation in various crystalline ZnO facets

“…Channelling in a depth is influenced by additional effects such as multiscattering, thus dechannelling effect in the higher depths is more pronounced, so the normalized yields for the pristine samples evaluated in the whole region of interest are higher than generally reported values around 3 -4 % [30,31] determined in a region just beyond the surface peak. The χmin analysis confirmed the lowest increase of Zn-sublattice disorder in aplane ZnO crystals observed also in [26]. For lower irradiation fluences the χmin values stay nearly the same as for pristine sample and the change is in a range of the measurement uncertainty.…”

“…Simultaneously, the surface morphology is different for m-plane ZnO facet and for the lower fluences represent more sponge-like networks with nuclei of emerging grains (Figure 6b) which is converted to the fully grainy pattern for the sample irradiated with the highest fluence (Figure 6c). This m-plane ZnO morphology is much progressively modified by ion bombardment as was already observed in [26]. The specific mplane structure can be result of aggregation of smaller defects supported by energy transfer from highly energetic W ions and therefore it can form sponge-like network or grain clusters.…”

“…After the W-ion irradiation with the higher fluences, the PL intensities rapidly drop down for all facets and in case of the m-plane ZnO, the irradiation with fluence 5x10 The above mentioned phenomena can be correlated to the distinct radiation damage in various ZnO facets caused by the energetic W-ion irradiation. also in [26]. The radiation defects mostly result in creation of Frenkel's pairs, interstitial and vacancy pairs of lattice atoms dislocated from its original position as a result of elastic collisions.…”

“…[23][24][25] The effect of ZnO crystallographic facet influence on the synthesis of surface nanostructures was simultaneously observed in case of SHI Au-ion surface nanostructuring. [26] To follow defect creation caused by SHI in the low ion fluence regime, where individual ion impact is expected, the surfaces of polar and non-polar ZnO crystallographic facets were modified by high-energy ion irradiation with heavy transition metals (W). Further, the focus should be given to the understanding to the connection between prepared nanostructures and its optical properties.…”

Energetic Au ion beam implantation of ZnO nanopillars for optical response modulation

“…For the single crystalline ZnO, the DLE band appeared around 550 nm -a green emission (GE) -whose origin is assigned to transitions including oxygen-vacancy VO defects in the ZnO structure [11,55]. The red centred DLE around 1.8 eV (650 nm) is ascribed to O and Zn vacancies [43].…”