Ion Irradiation-induced Changes Research Articles

Surface and subsurface damage in 14 MeV Au ion-irradiated diamond

The effects of ion irradiation on the surface and the subsurface of synthetic diamonds were characterized by using optical microscopy, atomic force microscopy, Raman spectroscopy, x-ray reflectivity, electron backscatter diffraction, and resistivity measurements. Irradiation experiments with 14 MeV Au6+ ions with fluences up to 2.4×1015 ions/cm2 were carried out on synthetic single crystal diamonds, grown either at high pressure or by chemical vapor deposition, and on polycrystalline samples with high boron concentrations. We show that the ion irradiation-induced changes to the surface and subsurface of diamonds are rather complex and, especially in the first few nanometers, more severe than generally considered. We establish a model describing the changes in density, defect concentration, topology, crystallinity, and bonding from the surface down to the first few micrometers of the irradiated diamond.

Unravelling the ion-energy-dependent structure evolution and its implications for the elastic properties of (V,Al)N thin films

Ion irradiation-induced changes in the structure and mechanical properties of metastable cubic (V,Al)N deposited by reactive high power pulsed magnetron sputtering are systematically investigated by correlating experiments and theory in the ion kinetic energy (Ek) range from 4 to 154 eV. Increasing Ek results in film densification and the evolution from a columnar (111) oriented structure at Ek ≤ 24 eV to a fine-grained structure with (100) preferred orientation for Ek ≥ 104 eV. Furthermore, the compressive intrinsic stress increases by 336 % to -4.8 GPa as Ek is increased from 4 to 104 eV. Higher ion kinetic energy causes stress relaxation to -2.7 GPa at 154 eV. These ion irradiation-induced changes in the thin film stress state are in good agreement with density functional theory simulations. Furthermore, the measured elastic moduli of (V,Al)N thin films exhibit no significant dependence on Ek. The apparent independence of the elastic modulus on Ek can be rationalized by considering the concurrent and balancing effects of bombardment-induced formation of Frenkel pairs (causing a decrease in elastic modulus) and evolution of compressive intrinsic stress (causing an increase in elastic modulus). Hence, the evolution of the film stresses and mechanical properties can be understood based on the complex interplay of ion irradiation-induced defect generation and annihilation.

Irradiation-induced homogeneous plasticity in amorphous/amorphous nanolaminates

Achieving homogeneous plastic deformation in metallic glasses is a long-standing goal yet to be solved in materials science. Here we investigate the effect of ion irradiation on the plastic deformation behavior of ZrCu/ZrCuNiAlSi amorphous/amorphous nanolaminates (A/ANLs) via nanoindentation testing. The experimental results indicate a dramatic change in deformation mode from multiple shear banding events to homogeneous compressive deformation before and after ion irradiation on the A/ANLs in the areas underneath the indenter. Ion irradiation-induced changes of both fraction and distribution of free volume inside each constituent layer and interfacial state in the A/ANLs may be responsible for the unusual homogeneous deformation behavior. Our results suggest that the mechanical property of A/ANLs could be modified by tuning both the inner and interfacial structure via ion irradiation.

Synthesis of heterostructured SiC and C–SiC nanotubes by ion irradiation-induced changes in crystallinity

Amorphous SiC nanotubes are successfully synthesized for the first time by the irradiation of polycrystalline SiC nanotubes with 340 keV Si+ ions. A polycrystalline/amorphous heterostructured SiC nanotube, in which polycrystalline SiC and amorphous SiC coexist in the same nanotube, is also synthesized by ion irradiation with a mask in front of the polycrystalline SiC nanotube. According to evaluation by electron energy loss spectroscopy, the plasmon energies of the SiC nanotube change rapidly at the interface between the polycrystalline and amorphous regions. The volume swelling induced by amorphization, as evaluated from the differences in plasmon energies, is approximately 5.0%. This result reveals that more relaxed amorphous SiC nanotubes with higher densities can be produced. The graphitic shells in the carbon layer of C–SiC nanotubes are found to gradually bend to align with the radial directions of the nanotubes by ion irradiation. Since graphite (002) spots in the selected-area electron diffraction pattern are clearly observed even after ion irradiation, the carbon layer in the C–SiC nanotube maintains crystallinity. Moreover, a new multi-walled carbon nanotube with graphitic shells completely parallel to the radial direction of the nanotube is also produced inside the amorphous SiC tubular layer, in the case of large-caliber C–SiC nanotubes.

MeV carbon ion irradiation-induced changes in the electrical conductivity of silver nanowire networks

MeV carbon ion irradiation-induced changes in the electrical conductivity of Silver nanowire (Ag-NW) networks is demonstrated systematically at different C+ ion fluences ranging from 1 × 1012 to 1 × 1016 ions/cm2 at room temperature. At low C+ ion fluences, the electrical conductivity of Ag-NWs decreases and subsequently increases with increase fluence. Finally, at high C+ ion fluences, conductivity again decreases. The variation in the electrical conductivity of Ag NW network is discussed after analysis using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The observed increase in electrical conductivity is thought to be due to ion induced coalescence of Ag-NWs at contact position, which causes reduction of wire–wire contact resistance, while the decrease in electrical conductivity may be due to defect production by C+ ions into Ag-NWs. Ion beam technology is therefore a very promising technology that is capable of fabricating highly conductive Ag-NW networks for transparent electrodes. Moreover, a method for thinning, slicing and cutting of Ag-NWs using ion beam technology is also reported.

Argon ion irradiation induced morphological instability of bare and thiol-functionalized Au(111) surfaces.

Ar ion irradiation-induced changes in the morphology of bare and 1-dodecanethiol self-assembled monolayer (SAM) covered Au(111) surfaces have been investigated systematically. The changes were followed by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) measurements while varying the ion charge (Ar(+),Ar(4+)), energy (10-40 keV) and fluency (10(12)-10(13) ions per cm(2)). The impact of flame-annealing of the Au(111) surface on subsequent ion bombardment was considered and more prominent related surface morphology changes were noted. The irradiation of Au(111) surfaces generated Au vacancy and adatom islands and caused roughening of step edges. The size and abundance of these islands and the level of deformation on the step edges depended strongly on the ion energy and fluency. In case of the SAM functionalized surface, the gold vacancy islands present on the surface already from the SAM formation were modified, step edges roughened and gold adatom islands formed. Similarly to the bare surface, the level of surface deformation increased as a function of ion energy and fluency. The Ar(4+) irradiation caused on the average slightly larger vacancy islands on the SAM modified surfaces than the Ar(+) irradiation. Irradiation to fluency of 10(12) ions per cm(2) mostly maintained standing-up orientation of the thiolates whereas irradiation to higher fluency resulted in reduced surface coverage and flat-lying molecules. As a general trend the DDT covered surfaces were more susceptible for irradiation-induced surface morphology changes than the unmodified Au surfaces.

Ga+ion irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt thin film studied by X-ray magnetic circular dichroism

Ga+ ion irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt ultrathin film are investigated by means of the X-ray magnetic circular dichroism (XMCD) technique. A large difference in the Co orbital moment is observed between out-of-plane and in-plane directions of the film at moderate Ga+ fluences of ~1-2×1014 ions/cm2 , which corresponds to the perpendicular magnetic anisotropy (PMA), while further increased fluences reduce the orbital moment difference, resulting in in-plane magnetization. In contrast, at much higher Ga+ fluences of ~5×1015 ions/cm2 , at which PMA is observed again, no significant difference is found in the orbital moment of Co between out-of-plane and in-plane directions. Different origins are thus suggested for the appearance of PMA induced by the irradiation between moderate and high Ga+ fluences.

Perpendicular magnetic anisotropy in a Pt/Co/Pt ultrathin film arising from a lattice distortion induced by ion irradiation

Ga${}^{+}$ irradiation-induced changes in magnetic anisotropy and crystalline structure of a Pt/Co/Pt ultrathin film are investigated by means of x-ray magnetic circular dichroism (XMCD) and extended x-ray absorption fine structure (EXAFS) techniques. The XMCD analysis shows a large orbital moment difference between out-of-plane and in-plane directions, which corresponds to perpendicular magnetic anisotropy (PMA), at moderate Ga${}^{+}$ fluences, while further increased fluences reduce the orbital moment difference resulting in in-plane magnetization. From the EXAFS analysis, enhancement of PMA is directly related to an in-plane lattice expansion caused by ion irradiation and Co-Pt intermixing, which results in a large lattice distortion. Thus, the origin of the ion irradiation-induced changes in magnetic anisotropy is successfully explained.

Influence of thermal history and 50 MeV Li ion irradiation on the structural properties of Al3+–Cr3+ co-substituted CuFe2O4

50 MeV Li3+ ion irradiation-induced changes on the structural properties of slow-cooled (SC) and quenched (QC) CuFe2−2x Al x Cr x O4 (x=0.0, 0.2, 0.4 and 0.6) ferro-spinels have been studied. Polycrystalline samples were prepared by using a standard double-sintering ceramic technique and were characterized by energy-dispersive X-ray analysis, X-ray diffraction and infrared (IR) absorption spectroscopy. The investigations on the influence of thermal history of the spinel system CuFe2−2x Al x Cr x O4 showed that the SC and QC samples exhibit Jahn–Teller structural tetragonal deformation owing to the presence of Cu2+ and Cr3+ ions at octahedral sites of the spinel lattice. The study also showed that the distribution of cations is sensitive to the heat treatment and swift heavy ion irradiation (SHII) of the materials. The SHII reduces the tetragonal distortion in both the cases and significantly modifies the cation distribution in the case of the QC sample. The shifts observed in the IR frequency bands ν1 and ν2 for tetrahedral and octahedral sites are due to the perturbation taking place in the Fe3+–O2− bond caused by substitution of Al and Cr ions. The presence of Cu2+ and Fe2+ ions in a spinel ferrite lattice gives rise to a ‘shoulder’ or splitting of the IR absorption band. The IR spectra results show that the irradiation shifts ν1 and ν2 bands to higher frequencies, attributable to the transformation of Fe3+ to Fe2+ having larger Pauling radius by irradiation on both octahedral and tetrahedral sites.

Ion Irradiation-Induced Changes in Surface Morphology of InSb

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009