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Abstract
The defects in the host lattice play a major role in tuning the surface roughness, optical band gap and the room temperature ferromagnetism (RTFM) of ZnO thin films. Herein, we report a novel approach to tailor the band gap and RTFM of a ZnO nanostructure by varying the angle of implantation of 60 keV N ions keeping the ion fluence of 1 × 1016 ions per cm2 and the beam size of 3 mm constant. The implantation was performed by changing the thin films' orientations at 30°, 60° and 90° with respect to the incident beams. Remarkably, an enhancement of ∼6 times in RTFM, tuning in band gap from 3.27 to 3.21 eV and ∼60% reduction in surface roughness were noticed when the ion implantation was done at 60° to the normal. This novel technique may be suitable for tuning the physical properties of nanostructures for their application in the spintronics, semiconductor and solar cell industries.
Highlights
The ion beam implantation technique has been widely used for the last two decades to tune material properties by generating defects in a very controlled and reproducible manner.[1,2,3,4,5] In order to alter the physical properties, mainly the magnetic and optical properties of nanostructures by nonmagnetic ion implantation in metal oxides like ZnO, TiO2, SnO2, MgO, etc., various research groups have extensively investigated varying the ion beam parameters such as current, energy, uence and ion species.[6,7,8,9,10] ZnO is selected due to its high exciton binding energy (60 meV), better resistance to radiation damage, high optical gain (320 cmÀ1) and wide band gap of $3.37 eV at room temperature.[11,12] N ion beam implantation has an advantage over other dopants in producing shallow accepter levels with higher hole binding energy ($400 meV) by replacing O ions in the ZnO nanostructure due to its ionic radius ($1.46 A) being comparable to oxygen ($1.38 A).[13,14,15] In general, the room temperature ferromagnetism (RTFM) evolves in ZnO due to increase in the oxygen vacancies (Vo) induced by the various defects like substitutions, interstitials, local structure transformations, etc.[16,17,18,19,20] The defects induce the lattice distortion which results in the mechanical stress near dislocations and this leads to increase in band gap (compressional stress) or reduction (tensile stress) due to the forming of the bands and accumulating the defects
We report for the rst time to control the ferromagnetism, band gap energy, surface roughness and grain size in N implanted ZnO nanostructured thin lms by changing the implantation angles only and keeping other ion beam parameters such as current, energy, uence and beam size constant
The pristine ZnO thin lms and N ion beam implanted thin lms at 30, 60 and 90 herea er will be referred to as ZnO and ZnO:N30, ZnO:N60 and ZnO:N90, respectively. These three angles were selected for the N ion implantations due to various considerations
Summary
The ion beam implantation technique has been widely used for the last two decades to tune material properties by generating defects in a very controlled and reproducible manner.[1,2,3,4,5] In order to alter the physical properties, mainly the magnetic and optical properties of nanostructures by nonmagnetic ion implantation in metal oxides like ZnO, TiO2, SnO2, MgO, etc., various research groups have extensively investigated varying the ion beam parameters such as current, energy, uence and ion species.[6,7,8,9,10] ZnO is selected due to its high exciton binding energy (60 meV), better resistance to radiation damage, high optical gain (320 cmÀ1) and wide band gap of $3.37 eV at room temperature.[11,12] N ion beam implantation has an advantage over other dopants in producing shallow accepter levels with higher hole binding energy ($400 meV) by replacing O ions in the ZnO nanostructure due to its ionic radius ($1.46 A) being comparable to oxygen ($1.38 A).[13,14,15] In general, the room temperature ferromagnetism (RTFM) evolves in ZnO due to increase in the oxygen vacancies (Vo) induced by the various defects like substitutions, interstitials, local structure transformations, etc.[16,17,18,19,20] The defects induce the lattice distortion which results in the mechanical stress near dislocations and this leads to increase in band gap (compressional stress) or reduction (tensile stress) due to the forming of the bands and accumulating the defects. It is evident that the energy transferred from N ion to ZnO is maximum in case of the normal incidence and when the beam has a longer projected range ($127 nm) but it leads to the lowest sputtering yield.
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