keV Xenon Ion Research Articles

Disclination loops observed in ion irradiated NiMo amorphous films and their fractal characteristics

Ni 65Mo 35 amorphous alloy films were obtained by 200 keV xenon ion mixing of multilayered NiMo films at room temperature with doses greater than 7 × 10 14 Xe/cm 2. When the dose was increased to 7 × 10 15 Xe/cm 2, corresponding to the amorphous-to-crystalline phase transition, many odd lines were observed, for the first time, in transmission electron micrographs of the ion mixed amorphous matrix. After excluding other possible explanations, these lines were attributed to disclination loops, which can be considered as an analogue of dislocations in crystalline materials. Scaling analysis showed that the loops featured self-similarity and had a common fractal dimension, D f, of 1.20 for a particular length scale.

Trapping of low-energy xenon ions in surfaces of transition metals

Trapping states of 5 keV xenon ions in surfaces have been investigated for nineteen kinds of transition-metal targets by means of X-ray photoelectron spectroscopy (XPS). The quasi-saturated values of the Xe/Me (Me = metal) ratio in the surface layer were found to be appreciably different among the metal targets. It ranges from nearly 0 for the gold target to 4.1 × 10 −2 for scandium and titanium targets. Since the rate of sputtering of the implanted layer becomes comparable to that of the implantation for such low energy bombardment, the real trapping efficiency in the surface detectable by XPS was obtained by correcting the effect of sputtering during the implantation. As a result of this correction, it was found that a relationship exists between the trapping efficiency and the position in the periodic table of the target metal. This finding is discussed in relation to the effect of the potential of metal d-electrons on the trapping states of implanted xenon.

Damage profiles in MgO after ion implantation

Damage depths in MgO 〈100〉 after implantation of 150 keV argon, krypton and xenon ions were analyzed by means of α-particle channeling in a backscattering geometry. Ion flucnces ranged between 4 × 1014 to 1 × 1016 at. cm2 and all implantations were performed at room temperature. Even at the highest ion dose only partial lattice disorder was observed, which is typical for ionic crystals. However, in all cases damage depths exceeded the projected ion ranges significantly. This effect becomes more pronounced with increasing ion mass.

Metastable phases formed in Fe–Cu–Si multilayered films by ion irradiation

Iron-rich Fe–Cu–Si multilayers were made by alternately depositing pure elements in a high vacuum system. The as-deposited films were then subjected to 200 keV xenon ion irradiation to doses ranging from 2 × 10 15 to 1.2 × 10 16 Xe/cm 2 at liquid nitrogen and room temperature. Transmission or scanning electron microscope and in situ energy dispersive spectroscopy were used to characterize the films. It was found that ion irradiation induced the formation of a new metastable phase in many irradiated films. The new phase was identified to be of fee structure with a lattice constant a = 0.423 nm. Strikingly, another phase reflecting sharp diffraction spots with 12-fold symmetry was also observed in a room temperature irradiated sample at a dose of 9 × 10 15 Xe/cm 2 . The distribution of the diffraction spots was shown to be incommensurate and bore a close relationship with the metastable fee phase. Furthermore, scanning electron microscope examination revealed that many clusters with 5-fold symmetry emerged in the corresponding film. The sharp incommensurate diffraction patterns may be ascribed to some incommensurate or quasicrystalline order appearing in the ion-induced structures.

Amorphization Induced by Ion Mixing in Some Y-Based Binary Metal Systems

Amorphization behavior is studied for several Y-based binary metal systems by room temperature 360 keV xenon ion mixing of multiple metal films to doses ranging from 7 × 1014 to 1 × 1016 Xe/cm2. In all systems studied, amorphization is achieved after ion mixing to the relevant doses. Interesting results are observed in the Ti-Y system, having rather positive heat of formation, i.e. 16 kJ/mol. A metastable crystalline Ti-Y phase is formed, for the first time, at medium dose ion mixing, and complete amorphous phase is formed in a narrow composition range, i.e. around Ti45Y55. Recrystallization temperatures of all formed amorphous alloys are determined by both, in-situ transmission electron microscopy annealing and confined furnace annealing. Possible interpretation is given to the observations by comparing with those proposed models for predicting glass forming ability. Bei Zimmertemperatur wird mittels Ionenmischung von 360 keV-Xenonionen von Metallmehrfach-schichten das Amorphisierungsverhalten für einige binüre Metallsysteme auf Y-Basis und Dosen zwischen 7 × 1014 und 1 × 1016 Xe/cm2 untersucht. In allen untersuchten Systemen wird Amorphisierung nach lonenmischung mit den relevanten Dosen erreicht. Interessante Ergebnisse werden im Ti-Y-System beobachtet, das eine positive Bildungswürme besitzt, d. h. 16kJ/Mol. Es wird erstmals eine metastabile kristalline Ti Y-Phase bei lonenmischung mittlerer Dosis gebildet und eine vollstündige amorphe Phase in einem schmalen Zusammensetzungsbereich, d. h. bei etwa Ti45Y55 gebildet. Die Rekristallisierungstemperaturen aller gebildeten amorphen Legierungen werden sowohl mittels In-situ-Transmissionselektronenmikroskopietemperung als auch begrenzter Ofentemperung bestimmt. Es wird eine mögliche Erklürung für die Beobachtungen durch Vergleich mit vorgeschlagenen Modellen für die Vorhersage von Glasbildungsfühigkeit angegeben.

Disclination loops in Ni-Mo amorphous alloy films induced by ion irradiation

Ni-Mo amorphous films were obtained by 200 keV xenon ion mixing at room temperature to dosages higher than 7*1014 ion cm-2. It was found, for the first time, that when the irradiation dose went up to 7*1015 ion cm-2, many odd lines appeared in the amorphous matrix. After excluding various possible explanations, the authors attribute the observed loops to line defects, i.e., disclinations in amorphous solids. Rich microstructures pertinent to disclination loops are described in detail. Scaling analysis showed that the observed disclinations shared a common fractal dimension in the small length scale. Moreover, approximation of gauge theory in the limit of elastic continuum media enables the authors to account for their anomalous properties successfully.

Xenon and argon irradiation of TiN films on Al-3wt.%Mg

The modifications of TiN films about 100 nm thick deposited via d.c. magnetron sputtering on Al-3wt.%Mg substrates and irradiated with 100–900 keV argon and xenon ions at fluences of (0.5–8) × 10 16 ions cm −2 were investigated. The effects of surface sputtering, interface mixing and segregation of the mixing ions at the interface were derived from Rutherford-backscattering spectra taken at 900 keV α particle energy. Sputtering and mixing rates were deduced and are compared with our recent findings for heavy ion-irradiated titanium and TiN films on stainless steel substrates.

The effect of Xe ion irradiation in [formula omitted] single-crystalline austenitic stainless steel

The dynamics of the irradiation-induced martensitic transformation in a single crystal of 17 13 austenitic stainless steel has been studied using the RBS channelling technique, conversion electron Mossbauer spectroscopy (CEMS), and glancing incidence X-ray diffraction (GXRD). 300 keV xenon ions were used to induce the martensitic α phase in the austenitic steel. It is shown that in the single-crystalline steel the martensitic phase occurs abruptly and covers almost all, i.e. the region near the surface of the specimen in a very short fluence increase, i.e. from 4 × 10 16 to 5 × 10 16ions/cm 2, which suggest an introduction of a critical transition, in contrast with the fluence dependence in polycrystalline 17 7 steel specimens; in the latter case the induced phase increases gradually to a saturated amount around a fluence of (5–7) × 10 16ions/cm 2.

Metastable Phase Formation in the Y-TI System by Ion Mixing

ABSTRACTAmorphization behavior was studied for the Y-Ti system, which has rather positive heat of formation being around + 22 kJ/mol, by room temperature 360 keV xenon ion mixing of YxTi100−xmultilayered films to various doses, ranging from 7×1014 to 1×1016 xe/cm2 Single and uniform amorphous phase was obtained in a narrow composition region, i.e. x=65 to 75, after ion mixing to the relevant doses. Moreover, a metastable fee crystalline Y-Ti phase was observed, for the first time, in this system. The crystalline lattice constant of the metastable phase was determined to be 4.012 Å. The re-crystallization temperature of the formed amorphous alloy was found out to be 600°C by in situ transmission electron microscope annealing as well as by vacuum furnace experiments. Possible interpretation is also discussed by comparing the experimental results with those proposed models for predicting glass forming ability.

Al-Yb Amorphous Alloys Produced by Ion Mixing or Solid State Reaction

ABSTRACTWe report, in this paper, three different ways of producing amorphous alloys in the Al-Yb system, (i) Al80Yb20multilayered films were readily amorphized by 180 keV xenon ion mixing at room temperature(RT) to a dose of 3×1015 Xe/cm2. (ii) When the dose went up to 1×1016 Xe/cm2 or higher, a metastable phase of hcp structure was formed. Interestingly, the hcp phase turned into amorphous after annealing at 500°C for about 10 minutes. (iii) Amorphous alloys were also formed by steady state thermal annealing of the Al-Yb multilayered films at about 450 °C for 20 minutes. The optimum amorphization range was found out by experiments to be 17 to 30 Yb at%, i.e., within this composition range, the multilayered films could entirely be amorphized by solid state reaction.The recrystallization behavior of the amorphous alloys formed by different methods was also studied and the difference in this aspect was thought to relate to the structures resulting from different processing methods.Possible explanation of the observed sequence of phase transition is also discussed.

FTMS Studies of Sputtered Metal Cluster Ions (III): The Chemistry of Ni+n, Co+n, V+n, Ag+n, Au+n and Fe+n with C2H4, C6H6 or NH3

AbstractAs previously described in greater detail, diverse transition metal cluster cations are produced in an external source by sputtering with 20 keV Xenon ions and transferred to the ICR cell of a home‐built Fourier transform mass spectrometer. There, they are thermalized by collisions with Neon atoms and stored for up to tens of seconds. They undergo a variety of reactions in the presence of ethene, benzene or ammonia, displaying different size‐specific effects. Depending upon the metal and the actual cluster size, mere physical adsorption or dehydrogenation is prevailing.

Sputter reduction of oxides by ion bombardment during Auger depth profile analysis

AbstractQuantification of the magnitude of preferential sputtering of oxygen from metallic oxides has been examined for a large number of 30 nm thick amorphous oxides deposited onto polished silicon substrates. The method of analysis was derivative‐mode Auger analysis carried out in a cleaner vacuum system and with cleaner initial surfaces than has been the case usually for data found in the literature. Ion sputtering was primarily with 3 keV xenon ions but the effect of ion energy (1, 3 and 4.5 keV), ion mass (argon or xenon) and sputter rate was also examined. The magnitude of preferential sputtering at 20°C was generally much less than has been reported previously and was not a function of ion energy, mass or sputter rate over the range studied. The results separate into two groups: oxides that reduce appreciably and those that do not. The results agree well with the predictions from the theoretical model of Kelly.1 It must be concluded from the work that most of the data reported in literature are primarily the result of unrecognized and therefore unreported variables. Likely candidates are contaminants within the ion beam and background environment that contribute chemical effects to the sputter process, ion beam and electron beam heating of poorly conducting samples, or redeposition of sputtered material into the analysis area.

Range profiles of 50 to 400 keV xenon ions in a silicate glass

The range profiles of Xe ions implanted in a silicate glass at energies from 50 to 400 keV have been studied by the Rutherford backscattering technique. The data obtained are compared with the calculated values based on Biersack's angular diffusion model (1981). The results show that the measured mean projected range is in good agreement with the calculated value, but a marked improvement in the range straggling fit is obtained after including the second-order energy loss.

A transmission electron microscopy study of xenon bubbles in ion-implanted tin

This paper describes a transmission electron microscopy (TEM) study of a body-centred-tetragonal metal (β tin) after room temperature implantation with 40 keV xenon ions. At low to medium doses, dark-field microscopy showed that a large fraction of the bubbles present (those with diameters less than 5 nm) contained solid xenon precipitates. From the inferred bubble pressures, it was demonstrated that these bubbles were in equilibrium, as expected from the high homologous implant temperature. At the highest dose, a large range of bubble sizes was found with strongly facetted bubbles having edge lengths in excess of 100 nm. Further results were obtained using a microscope cooling holder to follow the freezing of xenon in medium and large sized bubbles. The details of the gas adsorption on the bubble facets was deduced and the xenon content of the larger bubbles estimated. Of particular interest was that the xenon content of the larger bubbles suggested that they were grossly underpressurized, in contrast with the coexisting small equilibrium bubbles. The bimodal nature of the bubbles is discussed using the critical radius concept within the framework of bias-driven cavity growth.

Anomalous Hall effect in AlMn quasicrystals

We report resistivity, magnetoresistance and Hall effect measurements in a large temperature range (2 K ≲ T ≲ 300 K) on two Al 100-xMn x (x = 16 and 20) quasicrystalline samples obtained by ion-beam mixing of AlMn multilayers with 500 keV xenon ions. All these properties exhibit magnetic effects at low temperature, especially the anomalous Hall effect is in good agreement with the spin glass behaviour previously reported in AlMn and AlMnSi quasicrystalline alloys made by melt-spinning.

Damage production and retention in xenon and antimony implanted silicon

Abstract A comparison is made of damage production in silicon, by 30 keV antimony and xenon ion bombardment for both room temperature and elevated temperature substrates as a function of ion dose. The purpose of the study is to investigate the role of any chemical effects which might modify damage retention resulting from high concentration of implanted impurity.

Reactions of thin molybdenum films on silicon induced by argon and xenon irradiation

Irradiation of molybdenum films on silicon by 80 keV argon and xenon ions has been used to investigate the mechanisms involved in altering the interface and in the formation of molybdenum disilicide. The films were bombarded at room temperatures by Ar 2+ and Xe 2+ ions up to doses in the range 2 × 10 15 – 2 × 10 16 ions cm −2, and at temperatures ranging from room temperature to 350°C by 2 × 10 16 ions cm −2 Ar 2+ ions. Backscattering of 2 MeV helium was used to determine the degree of Mo-Si mixing and the composition of the resulting films. Interfacial mixing was shown to occur with Ar 2+ and Xe 2+ bombardment at all temperatures and exhibited a linear dependence on the dose. Below 150°C, the mixing showed no detectable dependence on temperature but, at irradiation temperatures above 150°C, there was a strong dependence of mixing on temperature. At temperatures above 250°C and for Ar 2+ doses in excess of 2 × 10 16 ions cm −2 a region, appearing to have the stoichiometric composition of MoSi 2, was formed at the interface and its formation was found to have a linear dependence on the dose. The thermally activated contribution of the mixing, derived from the temperature dependence of mixing, gives rise to an activation energy of 0.9 eV and the reaction kinetics appear to be very similar to those for the Nb/Si system. At the lowest irradiation temperatures the efficiency of mixing was found to be an order of magnitude higher than the theoretical collisional mixing predictions. This difference is attributed to the relaxation processes occurring immediately after the cascade. Subsequent annealing of films bombarded at room temperature did not lead to any detectable interfacial change.

Mössbauer study of amorphous thin Fe-Si films produced by ion mixing

Abstract Ion beam induced reactions of multilayered Fe/Si thin films have been studied by means of conversion electron Mossbauer spectroscopy (CEMS). A ferromagnetic amorphous layer is formed as a consequence of 300 keV xenon ion mixing of the multilayered films at room temperature. However, it is shown by the technique of depth profiling of CEMS that even in the case of coating films thicker than irradiating ion range a significant mixing occurs in the interface region between the overlayered films and the substrate. The interfacial mixing is found to lead to inhomogeneities in the distribution of Fe and Si elements and to non-uniform magnetic hyperfine field through in the mixed amorphous layer.

A Study of Grain Growth in Ion Irradiated Co-Cr Alloy Films

ABSTRACTExperiments concerning the behavior of grain size in Co80Cr20 alloy thin films upon ion irradiation were conducted. The alloy films of 80 nm thick were prepared by magnetron sputtering on cleaved NaCl crystal substrates, and then irradiated by 300 keV argon or xenon ions to a wide range of doses. The irradiated samples, before and after annealing, were examined by transmission electron microscope (TEM). It was found that the initial grain size with the dimension of 20 nm remained unchanged when the dose was less than 1×1016Ar/cm2, but rapidly reduced to the scale of 5 nm at a dose of 5×1016Ar/cm2. It is thought that this is due to a polymorphic transformation of an HCP to a BCC structure in the alloy films. After 30 min. anneals at 200° C, it was observed that the grain growth rate was a function of ion dose, and that there exists a critical fluence yielding a maximum grain growth rate. The possible mechanisms for the observations in this study are discussed.

From nuclear stopping to interatomic potential via the power law formalism

A general method for inverting the energy-dependent nuclear stopping cross sections S n(ϵ) to derive the interatomic potential V( x) is described. A correspondence between ϵ and x is derived for mapping S n(ϵ) to V( x) and vice versa. The method is illustrated by using the recent range-energy data of keV indium and xenon ions in amorphous silicon to self-consistently deduce the In-Si and Xe-Si potentials.