Abstract
Quantitative analysis of materials from Heavy Ion PIXE spectra remains impeded by the lack of reliable X-ray production cross section (XPCS) data. Although efforts at experimental Heavy Ion ...induced XPCS measurements still continue, Multiple Ionisation (MI) effects, which are not fully described by theory, render simulations of heavy ion PIXE data unreliable for large Z
1
/Z
2
collisions, especially at low energies. This is also exacerbated by the random selection of projectile-target combinations for measured and reported experimental data available to validate theory. This study explored heavy ion induced X-ray production cross section deviations from those induced by protons at the same ion velocity. This enabled evaluations of the degree to which cross sections are enhanced through MI effects, with the aim of predicting XPCS due to heavy ion impact. The evaluation was carried out through the scaling of experimental heavy ion to theoretical proton cross section ratios (
R
), which were then used for the interpolation of XPCS in the same target element for ‘missing’ projectiles within the range of evaluation. Here we present measurements of heavy ion induced total L-shell XPCS in Bi, carried out to determine HI/p MI induced deviations due to C, F, Cl and Ti projectiles at an ion velocity range of (0.2–1.0) MeV/nucleon.
•Determination of the elastic constants of Tb-MnO thin films on Si.•Surface phonons exhibit a softening effect and present a classic case of a soft on hard configuration.•Weak or soft ferromagnetism ...of Tb-MnO thin films at T⩽150 K.•Incommensurate magnetic ordering and spin-glass behaviors of Tb-MnO.
We report on the elastic and magnetic properties of multiferroic Tb0.3Mn20.9O78.8 thin films. The films were deposited on (001) Si using radio frequency magnetron (RF) sputtering at 50 W and ambient temperature. The elastic properties have been established by surface Brillouin scattering (SBS) after fitting the discrete phonon dispersion in the k||d range of 0 – 5 by surface Elastodynamic Green’s function. The uncertainties in elastic constants values were obtained from Taylor series expansion of the phonon phase velocity as a function of C11 and C44 values and subsequently fitted by the least-squares method. The optimum primary elastic constants and their uncertainties were determined as C11 = 180 ± 4.9 GPa and C44 = 43.0 ± 0.89 GPa. The derived elastic constants show that the films are ductile. Using a vibrating sample magnetometer (VSM), the films have been noted to behave like soft ferromagnetic materials at T⩽150 K. Incommensurate magnetic ordering and spin-glass behaviors have also been observed.
A bi-layers stack consisting of a semiconductor thin film of a varied thickness and a very thin Pd layer (SiC/Pd/c-Si).was deposited onto c-Si by e-beam evaporation at room temperature. The ...multi-layers structure was subjected to a thermal annealing process at near eutectic temperature of the Si – Pd phase. It is noticed, through top view SEM and cross-section STEM analyses, that the sandwiched Pd metal layer dewets from the interface with the c-Si substrate in well dispersed nanoparticles and it diffuses inward onto the top few monolayers of the substrate; at times it permeates shallowly through the SiC semiconductor top layer. The size distribution of the nanoparticles was found to be closely linked to the thickness of the top semiconductor layer. On the other hand, the top SiC layer was found to form islands protruding above the surface, when the film was very thin. When thicker, the semiconductor SiC layer retained its integrity and remained unaffected. An optical model of the resulting metal-dielectric mixed layer is proposed.
Experimental heavy ion induced X–ray production cross sections in matter continue to be of importance for both fundamental ion-atom collision studies as well as practical applications such as in ...nuclear analytical techniques. This work presents results of L-shell X-ray production cross section measurements in 89Y, 158Gd and 209Bi due to 4 MeV–12 MeV 12Cq + projectile ions. Experimental data are compared with theoretical calculations based on the ECPSSR, ECPSSR + EC and ECPSSR-UA models. Data show fairly good, albeit energy dependent agreement with the different models for yttrium and gadolinium cross sections. For bismuth, all three models overestimate data by an almost constant factor of two. The effect of multiple ionization on the l-line intensity ratios is also presented for gadolinium and bismuth targets.
•Measured L-shell X-ray production cross sections in 89Y, 158Gd and 209Bi due to 0.3 MeV/u – 1.0 MeV/u12C ions are reported.•Experimental data are compared with ECPSSR, ECPSSR + EC and ECPSSR-UA theoretical models.•Data show fairly good, agreement with the different models for yttrium and gadolinium cross sections. For bismuth, all three models overestimate experimental data by a factor of two.
Experimental X-ray production cross sections in matter are key to fundamental ion-atom interaction studies. They also find practical applications such as in the advancement of ion beam materials ...analysis techniques like Particle Induced X-ray Emission (PIXE) spectroscopy. Experimental work shows that heavy ion probes induce higher X-ray yields in target atoms compared to light ions of the same velocity. This, in principle, implies higher sensitivity for PIXE analyses performed using heavy ions (Heavy Ion PIXE). There is therefore need for substantial experimental data to improve existing theoretical models that describe X-ray production due to heavy ion-atom collisions. This article presents measurements carried out to determine K-shell X-ray production cross sections in vanadium (V) due to 12Cq+ ions, and L-shell X-ray production cross sections in zirconium (Zr) and tin (Sn) due to 12Cq+ (q = 2, 3) and 35Clq+ (q = 3, 5, 6, 7) MeV ion beams within a velocity range of 0.1 MeV/u - 1.0 MeV/u. Measured cross sections are compared with predictions by the modified Plane Wave Born Approximation (PWBA) and the ECPSSR theory. Observed agreements and discrepancies between experiment and theory are discussed in terms of the underlying ionisation mechanisms.
•New X-ray production cross section data for 12C and 35Cl ions in V, Zr and Sn.•ECPSSR theory (DI plus EC) describes 12Cq+ induced L-shell cross sections well.•ECPSSR theory grossly underestimates 35Clq+ induced cross sections.
In this work, Chemical Vapour Deposition (CVD) has been used to synthesize boron nitride (BN) nanostructures, particularly nanotubes, and selectively introduce defects into the lattice of the ...synthesized BN nanostructures through ion implantation. Scanning electron microscopy (SEM) images show clear evidence of BN nanostructures and BN nanotubes (BNNTs), with the latter appearing as long, thin structures with diameters ranging from ⁓30–80 nm. Raman analysis show an E2g mode of vibration assigned to hexagonal BN (h-BN) at 1366 cm−1 after ion implantation, with increased intensity. Grazing incidence X-ray diffraction (GIXRD) spectra revealed a prominent peak between 54 and 56°, corresponding to the (004) h-BN reflection, which was used to determine the average lattice parameter c⁓0.662 nm representing the stacking direction of the BN layers. The majority of the samples had broad peaks, indicative of a nanocrystalline material. The only exception was the sample grown at 1200 °C, which was found to have a Scherrer crystallite size >100 nm. In contrast, the rest of the samples had an average size of 3.5 nm. Notable observations in this study include a significant rise in the size of the Raman derived crystallite domains in the nanostructures synthesized at 1100 and 1200 °C after ion implantation with boron ions at fluence 5 × 1014 ions/cm2.
Previously, it has been shown that the implantation of hexagonal boron nitride with light ions (e.g. He+, Li+, B+) produces a surface layer containing nanoparticles of the much harder cubic form, as ...revealed by Raman spectroscopy, X-ray diffraction and electron microscopy. The present study shows that the irradiated layer is measurably harder when interrogated by micro-indentation which probes a layer comparable to the ion range. The hardness value increases reproducibly with the ion fluence, confirming that the latter is responsible for it. There are possible implications for the surface hardening of BN components after they have been configured in the easily machinable hexagonal form. Some aspects of the hardening mechanism are discussed.
•Implantation of light ions in h-BN induces a thin-layer transformation into c-BN.•An increase in micro-hardness can be clearly measured by micro-indentation.•The hardness increases up to an optimum ion fluence which depends on the ion.•The temperature of the substrate needs to be controlled during these implantations.
An inhibiting factor in the implementation of heavy ion PIXE is that heavy ion X-ray production cross sections are not well known for many materials. This contribution reports on work carried out at ...iThemba LABS to measure X-ray production cross-sections in Ti thin films irradiated with 12C and 28Si ions within the 0.3–1.0MeV/u energy range. Experimental data are compared to predictions by the PWBA, SCA-UA and ECPSSR theories. For the C–Ti asymmetric collision, ECPSSR theory describes experiment fairly well, but fails for the nearly symmetric Si–Ti collision, even after correction for multiple ionisation effects. The SCA-UA calculations tend to agree with data only at low (<0.5MeV/u) energies for the lighter 12C incident ions, but like ECPSSR, fail in the case of 28Si projectiles. The PWBA predictions grossly overestimate experiment in both cases.
The presence of radiation-induced defects and the high temperature of implantation are breeding grounds for helium (He) to accumulate and form He-induced defects (bubbles, blisters, craters, and ...cavities) in silicon carbide (SiC). In this work, the influence of He-induced defects on the migration of strontium (Sr) implanted into SiC was investigated. Sr-ions of 360 keV were implanted into polycrystalline SiC to a fluence of 2 × 10
16
Sr-ions/cm
2
at 600°C (Sr-SiC). Some of the Sr-SiC samples were then co-implanted with He-ions of 21.5 keV to a fluence of 1 × 10
17
He-ions/cm
2
at 350°C (Sr + He-SiC). The Sr-SiC and Sr + He-SiC samples were annealed for 5 h at 1,000°C. The as-implanted and annealed samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and Rutherford backscattered spectrometry (RBS). Implantation of Sr retained some defects in SiC, while co-implantation of He resulted in the formation of He-bubbles, blisters, and craters (exfoliated blisters). Blisters close to the critical height and size were the first to exfoliate after annealing. He-bubbles grew larger after annealing owing to the capture of more vacancies. In the co-implanted samples, Sr was located in three regions: the crystalline region (near the surface), the bubble region (where the projected range of Sr was located), and the damage region toward the bulk. Annealing the Sr + He-SiC caused the migration of Sr towards the bulk, while no migration was observed in the Sr-SiC samples. The migration was governed by “vacancy migration driven by strain fileds.”
In this report, random nickel nanowires (Ni-NWs) meshes are fabricated by ions beam irradiation-induced nanoscale welding of NWs on intersecting positions. Ni-NWs are exposed to beam of 50 KeV Argon ...(Ar+) ions at various fluencies in the range ~1015 ions cm−2 to 1016 ions cm−2 at room temperature. Ni-NWs are welded due to accumulation of Ar+ ions beam irradiation-induced sputtered atoms on crossing positions. Ar+ ions irradiated Ni-NWs meshes are optically transparent and optical transparency is enhanced with increase in beam fluence of Ar+ ions. Ar+ ions beam irradiation-induced welded and optically transparent mesh is then exposed to 2.75 MeV hydrogen (H+) ions at fluencies 1 × 1015 ions cm−2, 3 × 1015 ions cm−2 and 1 × 1016 ions cm−2 at room temperature. MeV H+ ions irradiation-induced local heat cause melting and fusion of NWs on intersecting points and eventually lead to reduce contact resistance between Ni-NWs. Electrical conductivity is enhanced with increase in beam fluence of H+ ions. These welded highly transparent and electrically conductive Ni-NWs meshes can be employed as transparent conducting electrodes in optoelectronic devices.
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