keV Argon Ions Research Articles

Using ion beams to tune the nanostructure and optical response of co-deposited Ag : BN thin films

The present study is devoted to co-deposited Ag : BN nanocermet thin films and is focused on the influence of ion irradiation conditions on their structural and linear optical properties. Ion irradiation was performed in situ during the growth of the nanocermets using a 50 eV assistance beam (nitrogen/argon or nitrogen-ion assistance) and ex situ on as-grown films using a 120 keV argon-ion beam (post-irradiation). Grazing incidence small-angle x-ray scattering measurements show that (i) as-grown N-assisted films contain prolate spheroidal clusters (height-to-diameter ratio H/D ≈ 1.8), (ii) N/Ar-ion assistance leads to the formation of more elongated clusters (H/D ≈ 2.1) and (iii) post-irradiation leads to a decrease of H/D to a value close to 1. These results are discussed on the basis of atomic diffusion processes involved during the growth of the nanocermets and during the post-irradiation. The optical transmittance spectra of these films measured at normal incidence display one absorption band, due to the excitation of the (1,1) plasmon mode of the clusters. In the case of the as-grown films, an additional band appears at oblique incidence for P-polarized light, as a consequence of the excitation of the (1,0) plasmon mode of the clusters. Our results show that the spectral position of the absorption bands (which can be tuned in the 400–600 nm range) depends on the H/D ratio of the clusters, in good agreement with calculations of optical transmittance considering the nanocomposite layer as a uniaxial anisotropic medium whose dielectric tensor is described by an anisotropic Maxwell–Garnett model.

Effects induced by keV low-energy ion irradiation in the nematode Caenorhabditis elegans

The nematode Caenorhabditis elegans is an excellent model organism with which to study the biological effects and mechanisms of ionizing irradiation. In this study, using C. elegans as a model, the effects of keV low-energy argon ion irradiation were investigated, by examining cuticle damage, worm survival, brood size, life span, and germ cell death. The surface etching of worm cuticle after ion impact was investigated by trypan blue staining and SEM microscopy. The degree of damage increased with ion fluence (2 x 10(14) to 7 x 10(14) ions cm(-2)) and energy (5-25 keV). The survival rates, as compared to vacuum control, of ion-bombarded worm larvae at different developmental stages (L1-L4) decreased with increasing ion fluence. L1 larvae were found to be more sensitive to ion bombardment than larvae at other stages. The mean brood size in ion-bombarded groups decreased with increasing ion fluence and energy. Furthermore, keV argon ions caused a significant increase in the number of apoptotic germ cells. However, average lifespan was not significantly affected.

Observation of the emission of positive and negative ions in triple and quadruple collisions in a solid under bombardment with keV argon ions

Particles that leave a solid as a result of several consecutive binary collisions are detected in the energy spectra of positive and negative ions emitted upon the irradiation of C, Si, Ge, and In targets with 2-to 5-keV Ar+ ions. The appearance of a spectral structure due to the sequence of three and four collisions in the solid can be attributed to the selective role of the surface, which is similar to the channeling effect in crystals.

Investigations on the effect of argon ion bombardment on the structural and optical properties of crystalline gallium antimonide

The effects of bombardment of 250 keV argon ions in n-type GaSb at fluences 2×1015 and 5×1015 ions cm−2 were investigated by high-resolution X-ray diffraction (HRXRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). HRXRD studies revealed the presence of radiation-damaged layer (strained) peak in addition to the substrate peak. The variation in the lattice constant indicates the strain in the bombarded region. The out-of-plane (ϵ⊥) and in-plane strains (ϵ|) determined from the profiles of several symmetric and asymmetric Bragg reflections, respectively, were found to change with the ion fluence. Simulations of XRD patterns using dynamical theory of X-ray scattering (single-layer model) for the damaged layer yielded good fits to the recorded profiles. FTIR transmission studies showed that the optical density (α·d) of GaSb bombarded with different fluences increases near the band edge with increase in ion fluence, indicating the increase in the defect concentration. The density of the defects in the samples bombarded with different fluences was in the range of 3.20×1021–3.80×1021 cm−3. The tailing energy estimated from the transmission spectra was found to change from 12.0 to 58.0 meV with increasing ion fluences, indicating the decrease of crystallinity at higher fluences. SEM micrographs showed the swelling of the bombarded surface of about 0.33 μm for the fluence of 2×1015 ions cm−2, which increased to 0.57 μm for the fluence of 5×1015 ions cm−2.

RuO 2/SiO 2/Si and SiO 2/porous Si/Si interfaces analysed by SIMS

Compared are interfaces between thin silicon oxide layers and two substrates bulk silicon and porous silicon. About 2 μm thick porous silicon was prepared by an electrochemical etching of Si in HF solution. Oxide layers were formed by thermal oxidation. Part of SiO 2/Si samples were covered with 50 nm RuO 2 oxide. SIMS depth profiles of these interfaces were performed using ultra-low energy (880 eV) and low energy (5 keV) argon ion beams at several incidence angles. Positive and negative secondary ions were analysed by quadrupole mass spectrometer QMA 410 Balzers during Ar + bombardment with the use of 06-350E Physical Electronics ion gun. Charge build-up effects during positive secondary ion detection were observed dependent of the thickness of silicon oxide layer. The SiO 2/Si interface regions characterised by SIMS show differences related to the kind of a substrate used. In case of 50 nm SiO 2/porous Si interface, characteristic oxygen depletion region (20 nm thick) is present on the porous silicon side. The observed depletion was confirmed also by Auger depth profiling. The depletion formation mechanism is explained on the basis of ion beam induced redeposition of oxygen inside the pores.

XPS depth profiling of oxide scales of stainless steels formed in high‐temperature aqueous conditions

AbstractIn this work, we studied the oxide scales of AISI 304 and AISI 316 stainless steels formed under high‐temperature aqueous conditions using X‐ray photoelectron spectroscopy (XPS) together with sputter depth profiling. Two samples of SS 304 and 316 were prepared by exposing them to water at 300 °C containing 100 ppm boric acid and 7 ppm lithium hydroxide in an autoclave.In the case of sputtering with 3 keV argon ions, the elemental distribution as a function of the sputtering time was obtained. The formation of two oxide layers was observed—one mainly iron‐based on top, and a second at a greater depth, consisting mainly of chromium‐iron oxides. The depth scale of the profiles was calibrated by measuring the oxygen profile using Rutherford backscattering spectroscopy (RBS). On the basis of the distribution of the three oxidised alloying constituents (Fe, Cr, Ni) with respect to depth and elemental state, a relative increase of Fe2+ at the surface was found, while the chromium was depleted at the surface and Cr3+ tended to increase at the oxide/substrate interface. In order to estimate possible ion‐beam‐induced effects due to the ion sputtering, the profiles were compared to the computer‐simulated ones obtained by a dynamic TRIM computer code. The simulations included only collisional effects during the sputtering process. Copyright © 2006 John Wiley & Sons, Ltd.

Ion implantation induced phase transformation in carbon and boron nitride thin films

The mechanism behind energetic ion impact induced stress reduction in highly stressed tetrahedral amorphous carbon and cubic boron nitride thin films is investigated by real time in situ spectroscopic ellipsometry and ex situ electron microscopy. Highly stressed carbon and boron nitride films were grown by filtered cathodic vacuum arc and RF magnetron sputtering, respectively. The films were then implanted by 5–10 keV argon ions and the film optical properties and thickness monitored in situ by spectroscopic ellipsometry. In both cases the films were observed to expand due to a reduction in the density of the ion-modified layer. Cross-sectional transmission electron microscopy and electron energy loss spectroscopy of the carbon films showed that this reduction in density is associated with a conversion of diamond-like bonding to graphite-like bonding. In situ stress measurements performed on the boron nitride films revealed a simultaneous reduction in stress with expansion of the material.

An accurate semi‐empirical equation for sputtering yields I: for argon ions

AbstractAn analysis has been made of the historical data for argon ion sputtering yields of 28 mono‐elemental solids in the energy range 250–10 000 eV to develop an improved semi‐empirical formula based on Matsunami et al.'s and Yamamura and Tawara's formulations. The best result is found if an essential component involving the target density is included in Matsunami et al.'s approach. The scatter between the predictions and the experimental data is reduced to 9.0% by generating an analytical expression for the term Q that requires none of the target‐specific numbers from special look‐up tables of the type used by Matsunami et al. and Yamamura and Tawara. For elements other than the 34 elements for which Q values are tabulated, the new Q values range up to a factor of 5 from the default value that they recommend.The predictions are tested by a new method for determining sputtering yields using atomic force microscopy to measure very small crater volumes sputtered in ultrahigh vacuum. Here, 26 mono‐elemental targets were studied using a 5 keV argon ion beam set at 45° to the surface normal. The effect of the angle of incidence is evaluated best using Yamamura et al.'s angular equations for this contribution. Results for Sb, Te and Bi indicate a significantly higher sputtering yield than expected. This is thought to arise from the high content of polyatomic groups associated with the low sublimation energies for such clusters in the pure elements of groups V‐B and VI‐B of the Periodic Table. These 5 keV sputtering yield data, excluding Sb, Te and Bi, fit the new equations with a scatter of 20%. Results using SRIM‐2003 exhibit a poorer scatter of 27%. © Crown Copyright 2005. Reproduced with the permission of Her Majesty's Stationary Office. Published by John Wiley & Sons, Ltd.

Glow-discharge-driven bucket ion source

A two-stage source of broad beams of gaseous ions employing a glow-discharge plasma cathode and an anode chamber with a peripheral multicusp magnetic field has been studied. A grid, whose potential approached the potential of the screen grid of the ion source, separated the cathode and anode stages. The effect of the energy (0–300 eV), the current of injected electrons (0.2–0.8 A), and the gas pressure (argon) on the plasma parameters and the efficiency of ions extraction from the plasma have been analyzed. The current density of the ions extracted from the magnetic-field-free plasma had a nearly homogeneous distribution (∼10%). The beam of 3 keV argon ions was generated using a two-electrode ion optical system with the area of ∼50 cm2. The beam current was 60 mA at the electron current of the plasma cathode equal to 0.2 A.

Mass analysis of sputtered particles induced by Ar bombardment of two iced targets, H 2O and CO 2

A focused 15 keV argon ion beam was used to bombard iced targets, CO 2 and H 2O (at temperature (27 K). The sputtered particles were analyzed by a quadrupole mass spectrometer (QMS). The purpose of the experiment was to measure the percentage of the sputtered particles that originated from the impact sites on the iced targets. Some of the particles that were not induced from ion–iced-CO 2 interaction include, for instance, CO, O and C; these were produced during the disintegration by the QMS of pure CO 2, which is copiously sputtered in ion–iced-CO 2 interaction. The analyzed data will be useful for understanding the chemical reaction in ion–molecule interactions.

Angular distribution of sputtered particles induced by ion bombardment

Using a 15 keV argon ion beam to impact a polycrystalline aluminum target, the intensities of the sputtered Al particles and the backscattered projectiles in different angle of incidence were measured. The data showed that the angular distributions of Ar and Al particles were quite different. Due to the intensity of sputtered target atoms are strongly correlated to the sputtering yields of the target atoms. The SRIM-simulation program was employed to obtain the sputtering yields of Al atoms. The angular distributions of sputtered Al particles and sputtering yields were compared each other and revealed that both of them were in a fairly good agreement. From the results of simulated sputtering yields and backscattered Ar particles, we conclude that the structure of the target and a linear collision cascade processes determine the angular distribution of the sputtered target atoms in this measurement.

Modification of Electronic Structure of Mesoscopic Perchlorate-Doped Polypyrrole Films by Ion Irradiation

The effects of low-energy (1−3 keV) argon ion irradiation on a 100 nm thick polypyrrole film deposited potentiostatically in an aqueous perchlorate solution have been studied by X-ray photoelectron spectroscopy (XPS). Dramatic spectral changes in the valence band structure and Cl 2p region with increasing ion impact energy and total ion dose have been observed for the perchlorate-doped conductive polymer surface. Higher impact energy (3 keV) is found to be more effective in modifying the polymer backbone, particularly in the breakage and formation of terminal bonding units, while higher ion flux (for impact energy above 1 keV) appears to produce complete dissociation of the perchlorate counterions, leaving behind only Cl atoms. These observations are also consistent with the spectral changes in the C 1s, N 1s, and O 1s regions observed under different ion irradiation conditions.

Easy Release of Mold in Imprint Lithography Using Ion-Beam-Irradiated Photoresist Surface

We demonstrate the successful release of a mold from an ion-beam-irradiated photoresist film without pattern destruction in nano-imprint lithography. A stripe-patterned V-shaped groove was used as a mold for the imprinting. The photoresist containing mainly novolac resin was used. The surface of the photoresist was modified by irradiating it with 100 keV argon ions with varying ion doses. It is found that the success rate of release increases with the increase of ion dose without any deformation of the transferred structure. It is also found that the modification of the photoresist surface can shorten the imprinting time. These improvements of the release and imprinting characteristics are caused by the existence of a stiffened layer at the photoresist surface produced by the ion-beam irradiation. We also demonstrate step-and-repeat imprinting using this technique.

Characterisation of defects in LiF implanted with Ar + using variable energy positron beam

Slow positron implantation spectroscopy has been used to determine the surface and near surface defect profile in LiF after implantation with 100 keV argon ions for a range of fluences from 10 13 to 10 16 cm −2. The measured S-parameter is used to characterise the radiation damage as a function of depth. The spatial extent of the defect distributions was estimated by employing the computer program VEPFIT. Maximum lattice damage is shown to occur at incident positron energy of 4.0 keV for low doses and 5.0 keV for the high dose. This energy corresponds to a sample depth of about 200 nm. The positron annihilation spectroscopy results are correlated with optical absorption measurements on the crystals.

Radiation damage in polyvinyltoluene (PVT)

Polyvinyltoluene (PVT) is an organic polymer which is luminescent when it is irradiated by ionizing radiation. The luminescence yield is proportional to the radiation stopping power and to the absorbed dose. High stopping power radiations, such as ion beams, induce radiation damage in PVT with the production of CH bond break, dehydrogenation and free radical formation, as investigated by the mass quadrupole spectrometry. The damage reduces the luminescence yield significantly. A reduction of about 50% is obtained with 300 keV proton and argon ions, having 300 keV energy, at a dose of about 10 14 and 10 13 ions/cm 2, respectively.

Artifacts in sample preparation of transmission electron microscopy

Two types of typical artifacts induced by ion milling, damage on the surface and temperature elevation, were investigated. The ion-induced damage layer on the surface reached as high as 3.46 nm when 5 keV argon ions were bombarded at 75 degrees of incidence from the surface normal of Si(001). Cleaning up the surface using 250 eV argon ions could minimize the surface damage close to the level of natural oxide thickness. The local temperature was measured from samples with thermocouples mounted in two different ways. The temperature reached 296°C when a single ion gun was used to mill the sample at 5 keV with 80 degrees of incidence angle, while the sample with thick substrate was heated up to 198°C. A gold thin film was investigated to confirm the ion beam-induced annealing as an artifact. Possible ways to reduce the thermal load in the sample are suggested.

Pyramid formation on a high index copper bicrystal during bombardment with 10 keV argon and krypton ions

Pyramid formation on high index Cu (7 5 5) and Cu (13 3 2) crystal planes has been studied during ion beam sputtering with 10 keV argon and krypton ions. Thin sputter-deposited layers of Ti and redeposited layers of Cu–Ti–C on the crystal planes were used to generate dense pyramid arrangements. Ion bombardment at normal incidence leads to a microtopography depending on the crystal orientation. Changing the ion beam direction, it is shown that the high index surface orientations and/or special angles of ion incidence are not decisive for pyramids to arise. Experimental evidence is provided that surfaces covered by pyramids result from simultaneous action of both ion beam direction relative to the target lattice and surface covering with foreign atoms. The formation of the observed microtopography shapes is related to anisotropic sputtering of the crystalline copper target.

Oxidation, Diffusion and Segregation in CuNi(Mn) Films Studied by AES

The surface and in-depth compositions of sputter-deposited Cu0.57Ni0.42Mn0.01 thin films were studied by Auger electron depth profiling after thermal treatment. The samples were thermally cycled to maximum temperatures of 300 °C to 550 °C in air, argon and forming gas (N2, 5 vol. % H2). Linear least-squares fit to standard spectra and factor analysis were applied to separate the overlapping Auger transitions of Cu and Ni. Under bombardment by 4 keV argon ions, CuNi(Mn) layers display bombardment-induced surface enrichment of Ni in the same extent as binary CuNi alloys. At sufficiently high oxygen partial pressures, a duplex oxide layer is formed and a thick surface copper oxide overgrows the initial nickel oxide. In reducing atmosphere selective oxidation of manganese takes place. A capping NiCr layer prevents CuNi(Mn) from being oxidized, but the film configuration is degraded with increasing annealing temperature due to formation of a surface chromium oxide and diffusion of Ni from the CuNi(Mn) layer into the NiCr/CuNi(Mn) interface.

Determination of time-of-flight distributions of sputtered oxygen and carbon atoms by resonant multi-photon ionization

In this contribution measurements of time-of-flight (TOF) distributions of sputtered oxygen and carbon atoms obtained at a recently completed set-up are reported. Carbon atoms are released by bombardment of a graphite target by 6 keV argon ions. Atomic oxygen is sputtered from an oxidized titanium foil. In the case of sputtering of the titanium foil also titanium atoms and TiO molecules are detected. For resonant ionization of oxygen and carbon atoms a (2+1) single-color resonant ionization scheme is applied. TOF distributions are measured by delaying the ionizing laser pulse with respect to the ion pulse. The atomic oxygen density is estimated by a comparative measurement with a spectral close two-photon transition of xenon.

The transformation of β-FeSi2 under Ar ion bombardment studied by XPS, AES and Mössbauer spectroscopy

Irradiation effects on iron disilicide layers were induced by 3.5 keV argon ion bombardment and studied by XPS, AES and the Mössbauer spectroscopy. The use of these electron spectroscopies enables the investigation of different depth regions of the altered layer. Iron enrichment is found in a surface-near region by surface-sensitive XPS and shown to influence the electronic structure evaluated by factor analysis. For deeper regions a phase transformation of the stoichiometric β-FeSi2 into the iron-depleted α-FeSi2 is proved by non-destructive Mössbauer spectroscopy (CEMS). Applying depth-selective CEMS it turns out that the transformation to α-FeSi2 reaches up to a depth of 25 nm as evaluated by a model calculation. Simulations of preferential sputtering and atomic mixing processes by the TRIDYN Monte Carlo program agree very well with the experimental results. From these simulations, Si preferential recoil implantation appears to trigger the phase transformation for the structurally favoured α-phase under the sputtering conditions used.