Swift Heavy Ion Bombardment Research Articles

Suspended nanoporous graphene produced by swift heavy ion bombardment

In the present work, Raman spectroscopy measurements and molecular dynamics simulations were used to investigate damage production in suspended single-layer graphene when irradiated by 23 MeV I, 3 MeV Cu and 18 MeV Cu beams. Despite the high energies of the used swift heavy ion beams, we found no evidence of ion track formation, i.e. all damage imparted to graphene was due to elastic collisions between ions and carbon atoms. Comparing experimental results with simulations, we conclude that a significant amount of energy (at least 40 % in the case of 23 MeV I irradiation) is dissipated away from graphene following the ion impact, and is a likely reason for the absence of ion tracks.

Secondary ion formation on indium under nuclear and electronic sputtering conditions

The electronic sputtering of indium under swift heavy ion bombardment is investigated using time of flight secondary ion mass spectrometry in combination with 157 nm laser postionization. Secondary ion and neutral mass spectra generated under the impact of 4.8 MeV/u 48Ca10+ ions are analyzed in order to determine the ionization probability of the emitted indium atoms, and the results are compared to those measured under nuclear sputtering conditions via bombardment by 5 keV Ar+ primary ions. The influence of surface contamination on the ionization probability is studied by comparing (1) a pristine surface covered by a native oxide layer, (2) a kilo-electron-volt sputter-cleaned surface, and (3) a controlled oxygen coverage established by dosing the precleaned surface with O2. It is found that the native oxide layer increases the ionization probability for both kilo-electron-volt and mega-electron-volt primary ions. In contrast, oxygen deposited on a sputter-cleaned surface results in the well-known matrix effect for kilo-electron-volt ions, but has no influence on the ionization probability for the mega-electron-volt ions. In the case of a thoroughly sputter-cleaned surface a four- to sevenfold higher ionization probability for indium atoms is found for 4.8 MeV/u 48Ca10+ as compared to 5 keV Ar+ bombardment.

Swift heavy ion shaping of oxide-structures at (sub)-micrometer scales

100 nm thin NiO-films on oxidized Si-substrates were pre-structured into small platelets of 100–5000 nm side-lengths utilizing the focused ion beam technique. The development of the individual platelets under grazing angle swift heavy ion irradiation was monitored using our “High Resolution In Situ Scanning Electron Microscope” installed in the beam line of the UNILAC ion accelerator at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt/Germany. This instrument allows us to in situ investigate the structural and compositional development of individual objects in the μm- and nm-range under swift heavy ion bombardment, from the very first ion impact up to fluences of some 1015 ions/cm−2. The sample is irradiated in small fluence steps and in between SEM-images (and EDX-scans) of one-and-the-same surface area are taken. Swift heavy ion irradiation at grazing incidence (tilt angle ≥80°) and continuous azimuthal sample rotation results in lateral shrinking and vertical growth of the platelets. At intermediate fluences additional rounding of edges and corners can be observed. At high fluences the deformation finally saturates. The deformation of the platelets is accompanied by huge sputtering of the exposed SiO2-layer, which due to the retracting edges of the platelets results in a pyramidal-like base underneath of the NiO-structures. In our presentation we will illustrate and discuss the reshaping mechanisms and underlying driving forces.

Mass spectrometric investigation of material sputtered under swift heavy ion bombardment

Abstract The flux of particles emitted from a solid surface under electronic sputtering conditions induced by irradiation with Swift Heavy Ions (SHI) was investigated using time-of-flight mass spectrometry in connection with laser post-ionization. While secondary ions emitted from the irradiated surface were directly detected using a reflectron ToF spectrometer, the corresponding neutral particles were post-ionized after their emission using single photon ionization in a pulsed VUV laser beam. The ToF spectrometer was operated in delayed extraction mode, thereby ensuring that secondary ions and post-ionized neutrals were detected under otherwise identical experimental conditions. For comparison with a purely nuclear sputtering process, spectra taken under irradiation with 4.8 MeV/u 197Au26+ and 48Ca10+ ions were compared to those measured in situ under bombardment with 5 keV Ar+ ions. Most importantly, we find that in most cases the vast majority of the sputtered material is emitted in the neutral state, with the flux of sputtered particles mainly consisting of single atoms and small (mostly diatomic) clusters. For metallic targets, we find a significant electronic sputtering effect for In and Bi, while other metals like Mo or Ag do not appear to sputter very efficiently under SHI irradiation. As an example for a semiconductor target, (amorphous) Ge is found to exhibit a large electronic sputtering yield under irradiation with Au projectiles, while practically no effect is observed with the Ca ions, thereby clearly indicating a stopping power threshold for this material. KBr as an example for an ionic crystal exhibits the expected large yield, with the sputtered material mainly consisting of atomic species and neutral KBr and K2Br clusters. We find about equal signals of neutral and ionized K atoms and K2Br clusters, while KBr is exclusively detected as a neutral molecule. Besides these major species, we find a progression of [KBr]nK+ and – with much smaller intensity – [KBr]nBr− clusters, which exhibits a similar size distribution as observed by others for [LiF]nLi+ clusters emitted from LiF. Interestingly, no negative halogen ions are observed under SHI irradiation, while they are clearly detected under nuclear sputtering conditions with similar intensity as the corresponding positive alkali ions.

Amorphization of Indium Phosphide Single Crystals by Swift Heavy Ion Bombardment

Journal Article Amorphization of Indium Phosphide Single Crystals by Swift Heavy Ion Bombardment Get access AS Khalil AS Khalil Mining and Metallurgy Department, Tabbin Institute for Metallurgical Studies (TIMS), Helwan, POB 109, Cairo, Egypt Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 21, Issue S3, 1 August 2015, Pages 1011–1012, https://doi.org/10.1017/S1431927615005851 Published: 23 September 2015

Photoelectrochemical Ion Pumping with Dye-Functionalized Polymer Membranes

Artificial photosynthesis could be a cost-effective and sustainable means of converting sunlight energy into usable energy. Most artificial photosynthetic systems mimic nature’s properties of light absorption, electronic charge separation, and electronic charge collection, where ultimately electrons make and break chemical bonds. However, nature also transduces photon energy into proton gradients whose electric potential also drives chemical-bond formation. In my presentation I will report on my research group’s progress toward mimicking nature in function, by using light to drive endergonic proton transfer, ultimately converting photon energy into ionic current. The applicability and practicality of this material as a membrane in solar fuels devices and as a separate ionic photoelectrochemical device will also be discussed. My research group’s near-term goal is to provide a proof-of-concept demonstration of an artificial proton pump where light-driven ion transport results in photovoltaic action. For an initial model system we utilized a conical nanopore etched in a polyethylene terephthalate plastic sheet. This pore was formed via swift heavy ion bombardment followed by alkaline chemical etching which resulted in a pore lined with fixed anionic functional groups. Then, using peptide coupling chemistries, the pore was asymmetrically functionalized with novel photoacids to generate a region containing fixed cationic dyes. This ordered distribution of interfacial charge was intended to mimic a solid-state semiconductor pn-junction and be used to separate photogenerated charges. We demonstrated that under visible-light illumination and a small reverse bias, excitation of the photoacid molecules resulted in an ionic photocurrent. We are currently expanding this initial research and successful demonstration of an artificial light-driven ion pump to other polymeric materials with hopes of generating ionic power through sunlight absorption and incorporating these materials as ion-exchange membranes in solar fuels devices.

Transition metal oxides in etched ion tracks: Surface morphological studies

Transition metal oxide (TMO) nanoparticles comprising of different magnetic properties, have been inserted in ion tracks which have been created by swift heavy ion bombardment of the SiO2/Si substrate and further etched by hydrofluoric acid. To study the surface morphology of the system, pore structure (diameter, shape, size and depth), pore volume and surface area before and after filling of TMOs, atomic force microscopy (AFM) and Brunauer–Emmett–Teller (BET) techniques have been used. These TMO filled structures have been subjected to perpendicular magnetic field to study the alignment of the metal oxide particles. In this paper, the surface morphology of TMO based nanostructures is being reported corroborating the findings with vibrating sample magnetometer (VSM) and transmission electron microscopy (TEM) studies.

Functionalization of nanochannels by radio-induced grafting polymerization on PET track-etched membranes

The application of swift-heavy ion bombardment to polymers is a well-established technique to manufacture micro- and nanopores onto polymeric films to obtain porous membranes. A few years ago, it was realized that, during ion bombardment, the high energy deposition along the ion path through the polymer reached cylindrical damage regions corresponding to the core trace and the penumbra. After the etching procedure, there are still enough active sites left in the penumbra that can be used to initiate a polymerization process selectively inside the membrane pores.In this study, we report the grafting polymerization of glycidyl methacrylate onto etched PET foils to obtain functionalized nanochannels. Grafted polymers were labeled with a fluorescent tag and analyzed by different fluorescence techniques such as direct fluorescence, fluorescence microscopy and confocal microscopy. These techniques allowed identifying and quantifying the grafted regions on the polymeric foils.

Study of ion beam synthesized nanostructured PbTe surface

Vertically protruding out nano structures of PbTe are synthesized by ion beam mixing of Te/PbO bilayer using 100MeV Ag ions. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) of pristine and irradiated samples are performed to study surface structures. Power spectral density (PSD) spectra of the structures at different fluences have been determined from AFM micrograph. The values of roughness and growth exponent, deduced from PSD, are far from any universality classes. Results distinctly indicate the unstable growth and rapid roughening of surface under swift heavy ion (SHI) bombardment.

Swift heavy ion induced surface modification for tailoring coercivity in Fe–Ni based amorphous thin films

Fe–Ni based amorphous thin films were prepared by thermal evaporation. These films were irradiated by 108 MeV Ag8+ ions at room temperature with fluences ranging from 1×1012 to 3×1013 ions/cm2 using a 15 UD Pelletron accelerator. Glancing angle x-ray diffraction studies showed that the irradiated films retain their amorphous nature. The topographical evolution of the films under swift heavy ion (SHI) bombardment was probed using atomic force microscope and it was noticed that surface roughening was taking place with ion beam irradiation. Magnetic measurements using a vibrating sample magnetometer showed that the coercivity of the films increases with an increase in the ion fluence. The observed coercivity changes are correlated with topographical evolution of the films under SHI irradiation. The ability to modify the magnetic properties via SHI irradiation could be utilized for applications in thin film magnetism.

Effects of low-fluence swift iodine ion bombardment on the crystallization of ion-beam-synthesized silicon carbide

Ion beam synthesis using high-fluence carbon ion implantation in silicon in combination with subsequent or in situ thermal annealing has been shown to be able to form nanocrystalline cubic SiC (3C-SiC) layers in silicon. In this study, a silicon carbide layer was synthesized by 40-keV C12+ implantation of a p-type (100) Si wafer at a fluence of 6.5×1017 ions∕cm2 at an elevated temperature. The existence of the implanted carbon in Si substrate was investigated by time-of-flight energy elastic recoil detection analysis. The SiC layer was subsequently irradiated by 10–30 MeV I127 ions to a very low fluence of 1012 ions∕cm2 at temperatures from 80 to 800 °C to study the effect on the crystallization of the SiC layer. Infrared spectroscopy and Raman scattering measurement were used to monitor the formation of SiC and detailed information about the SiC film properties was obtained by analyzing the peak shape of the Si-C stretching mode absorption. The change in crystallinity of the synthesized layer was probed by glancing incidence x-ray diffraction measurement and transmission electron microscopy was also used to confirm the results and to model the crystallization process. The results from all these measurements showed in a coherent way that the synthesized structure was a polycrystalline layer with nanometer sized SiC crystals buried in a-Si matrix. The crystallinity of the SiC layer was enhanced by the low-fluence swift heavy ion bombardment and also favored by higher energy, higher fluence, and higher substrate temperature. It is suggested that electronic stopping plays a dominant role in the enhancement.

Fabrication of Well-Ordered High-Aspect-Ratio Nanopore Arrays in TiO2 Single Crystals

In this work a successful method for producing high-aspect-ratio nanopatterned single-crystal TiO2 is presented. The method used is based on nanolithography involving swift heavy ion bombardment through a porous anodic alumina mask. Nanopatterning of large areas allows for fabrication of new devices, for example, photonic crystals and electrodes for energy storage and conversion. Crystalline TiO2 also presents optimal characteristics for optical and catalysis applications. Samples were irradiated by MeV Br7+ ions with fluencies ranging from 7.9 × 1013 to 1.2 × 1015 cm-2. The high-energy Br7+ ions induce latent tracks of amorphous material into the TiO2 crystal suitable for selective etching by hydrofluoric acid. High-aspect-ratio (16) nanopatterned areas, up to 4 mm2, were obtained in a single radiation spot onto single-crystalline TiO2.

Smoothing of Fe/Au and Fe/Ag multilayers by swift heavy ion bombardment

We have investigated the influence of swift heavy ion (SHI) irradiation as well as thermal annealing on the interface roughness in thermally immiscible Fe/Au and Fe/Ag multilayers. The 5-fold multilayers consisted of 20–25nm Fe-, 10nm Ag- and 7–21nm Au-layers and were partly irradiated at liquid nitrogen temperature with 80–350MeV Ar, Ni, Kr, Xe ions at fluences between 1012cm−2 and 1015cm−2. The irradiated as well as the unirradiated parts of the samples were analyzed by means of Rutherford backscattering spectrometry (RBS) using 1MeV He+ ions. In the case of Fe/Ag, no change in the RBS spectra due to the ion irradiation could be detected, while in the case of Fe/Au, a clear increase of the steepness of the high energy edge of the Au signal was observed. A detailed analysis of the RBS Au profiles in comparison with RBS simulations for different shapes of the Au-layers allowed us to conclude that SHI irradiation results in smoothing of the Fe–Au interfaces, which can be understood in terms of a local minimization of the interface energy. In the Fe/Ag case, the symmetry of the RBS profiles of the Ag layers indicated that the interfaces became already smooth during the layer deposition. Heating of the Fe/Au multilayers resulted in broadening of the Au profiles and finally a complete destruction of the multilayer structure was observed. Here the whole sample is at high temperature and therefore interface energy minimization now occurs by the formation of spherical Au particles, which destroys the layered structure.

Surface studies on 100 MeV Ag7+ ions and 150 MeV Ni11+ ions irradiated nanocrystalline ferrite thin films

We have systematically studied the effect of swift heavy ion bombardment on surface morphologies of nanocrystalline ferrite thin films using atomic force microscopy (AFM) technique. From TRIM calculation, 150MeV Ni11+ ions and 100MeV Ag7+ ions have been selected to suffice the two irradiation conditions namely Se<Seth and Se∼Seth, respectively. Nanocrystalline films of Li0.5Mn0.1Fe2.4O4 have been grown on Si(100) substrate by using rf magnetron sputtering technique. Implementation of the first condition (150MeV Ni11+ ions) resulted in irradiation induced growth in the grain volumes at the fluence of 2.5×1012ions/cm2. The results of the second experimental condition (100MeV Ag7+ions) are entirely different showing deep ditches (holes) and channels on the surfaces. Online elastic recoil detection analysis (ERDA) has been performed to observe the effects on preferential loss of the elements in the films.

Self-organised nano-structuring of thin oxide-films under swift heavy ion bombardment

Surface instabilities and the resulting self-organisation processes play an important role in nano-technology since they allow for large-array nano-structuring. We have recently found that the occurrence of such instabilities in thin film systems can be triggered by energetic ion bombardment and the subsequent self-assembly of the surface can be nicely controlled by fine-tuning of the irradiation conditions. The role of the ion in such processes is of double nature: If the instability is latently present already in the virgin sample, but self-assembly cannot take place because of kinetic barriers, the ion impact may just supply the necessary atomic mobility. On the other hand, the surface may become instable due to the ion beam induced material modifications and further irradiation then results in its reorganisation. In the present paper, we will review recently observed nano-scale self-organisation processes in thin oxide-films induced by the irradiation with swift heavy ions (SHI) at some MeV/amu energies. The first example is about SHI induced dewetting, which is driven by capillary forces already present in the as-deposited samples. The achieved dewetting pattern show an amazing similarity to those observed for liquid polymer films on Si, although in the present case the samples were kept at 80K and hence have never reached their melting point. The second example is about self-organised lamellae formation driven by planar stresses, which are induced by SHI bombardment under grazing incidence and result in a surface instability and anisotropic plastic deformation (hammering effect). Taking advantage of these effects and modifying the irradiation procedure, we were able to generate more complex structures like NiO-“nano-towers” of 2μm height and 200nm in diameter.

Effects of swift heavy ion bombardment on magnetic tunnel junction functional properties

In this article, we report on recent irradiation experiments on magnetic tunnel junctions (MTJ) using either light (C, O) or heavy (Ni) ion beams with energies in the range of 10 MeV/A. For all ions, albeit with different fluence thresholds, the tunnel magnetoresistance decreases irreversibly with increasing ion fluence, with conversely little or no impact on overall resistance. This can only be explained by a modification of the alumina barrier stoechiometry, rather than by interdiffusion. Measurements on irradiated so-called “spin-mirrors” sheet films show that AlOx/metal interface is altered by radiations. Finally, it is shown that MTJs are not a fortiori insensible to swift heavy ion bombardment.

Mechanical properties of Sialon glass after swift heavy-ion bombardment

Mechanical properties of Sialon glass after swift heavy-ion bombardment

Desorption of nitrogen from amorphous carbon under electron and swift heavy ion bombardment

Desorption of nitrogen adsorbates from amorphous carbon (a-C) surfaces due to swift ion ( Z=6–73, q=6–54, energy 6–13 MeV/u) and electron impact (5 keV) was studied by secondary electron emission (SEE) measurements. The fluence dependence of ion induced electron emission obeys an exponential decay law as the coverage rate is in the sub-mono-layer range. The desorption yield σ varies approximately as σ∼(d E/d x) 3/2 or σ∼ q 3 as a function of the electronic energy loss d E/d x and the projectile charge q, respectively. We discuss the possible desorption mechanisms connected to electronic excitation. Furthermore, we present an ESCA investigation on the mechanism for the influence of nitrogen adsorbates on SEE yields. The mechanism for the SEE enhancement effect is connected to the surface termination: nitrogen adsorbates are believed to provide surface states which generate a downwards energy band bending, which on relative scale pushes up the Fermi level towards the conduction band minimum, reducing the work function.

Influence of adsorbates on electron emission from amorphous carbon under electron and swift heavy ion bombardment

Secondary Electron Emission (SEE) yield measurements have been used to investigate the desorption of nitrogen adsorbates from amorphous carbon (a-C) surfaces due to swift heavy ion impact. The fluence dependence of ion induced electron emission obeys an exponential decay law when the coverage rate is in the sub-mono-layer range. This reveals the relative contribution of the both emitting zones, the “clean” one (having the SEE properties of carbon) and the covered one (with a higher SEE coefficient) to the total measured yield. The mechanism for the SEE enhancement effect is connected to the surface termination. Nitrogen adsorbates are believed to provide surface states which generate a downwards energy band bending, which on relative scale pushes up the Fermi level towards the conduction band minimum, reducing the work function and increasing the SEE yield subsequently. A shoulder observed on the rising edge of the peak of the true SE peak is ascribe to the fraction of hydrogenated termination of a-C which exhibits a lower electron affinity.

Formation of Individual Holes in Amorphous SiO2 by Swift Heavy-Ion Bombardment Followed by Wet and Dry Etching

Individual holes in amorphous SiO2 were formed from latent tracks which were introduced by bombardment with swift iodine ions. Hole contours strongly depend on the etching method used. Conic holes with the highest aspect ratio were obtained by etching with 48% hydrofluoric acid. The aspect ratio of the holes increased with the acidity of the hydrofluoric acid. Selective etching of the latent tracks was not observed with reactive ion etching, yet 48% hydrofluoric acid etching followed by reactive ion etching formed columnar holes. The etching mechanism is briefly discussed.