Study of the useful yield of the Storing Matter technique using Ge(1 0 0) as a sputter target

Storing Matter is a new analytical technique for organic and inorganic materials, which tries to circumvent the well-known matrix effect in SIMS. This technique consists of separating the sputtering of the sample from the subsequent analysis steps. Thus, the sample to be analysed is sputtered with a focused ion beam produced by a floating low-energy ion gun (FLIG) and the particles emitted under the ion impacts are deposited at a sub-monolayer level on a well-known collector. The collector with the deposited material is then analysed in a second step by SIMS (dynamic and static mode). The main advantage of this new technique is to improve the sensitivity and the quantification of the SIMS analysis. All the processes, including all the sample and collector transfers, are performed in UHV conditions. This paper presents preliminary results obtained on the Storing Matter prototype instrument developed in our laboratory. The sputtering of a (1 0 0) Ge wafer by ions was used as a model system to study the influence of using different collector surfaces (W, Ta and Al) on the Storing Matter useful yield.     

380 keV proton irradiation effects on photoluminescence of Eu-doped GaN

The effect of 380 keV proton irradiation on the photoluminescence (PL) properties has been investigated for undoped and Eu-doped GaN. As the proton irradiation exceeds , a drastic decrease of PL intensity of the near band-edge emission of undoped GaN was observed. On the other hand, for Eu-doped GaN, the PL emission corresponding to the ⁵D₀→⁷F₂ transition in Eu³⁺ kept the initial PL intensity after the proton irradiation up to . Present results, together with our previous report on electron irradiation results, suggest that Eu-doped GaN is a strong candidate for light emitting devices in high irradiation environment.     

Density effects on the guided transmission of 3 keV Ne ions through PET nanocapillaries

Experiments for guided transmission of 3 keV Ne⁷⁺ ions through nanocapillaries in insulating PET polymers are reported. The ion guiding was studied for a two types of PET samples which consist of 200 nm capillaries with densities of and . The width of the emission profile and the fraction of transmitted ions were measured as a function of the capillary tilt angle. For the high capillary density the profile width of the transmitted ions is independent of the tilt angle in agreement previous studies. However, for the low-density sample the profile width was found to increase by a factor of 2 as the tilt angle increases from 0° to 8°. The results for the fraction of transmitted ions are used to evaluate the guiding angle, which specifies the guiding power of the material. The guiding powers were found to be equal for the two samples. The present results are discussed in terms of scaling laws, which have recently been established.     

Morphology and interface structure of α-Fe2O3 islands grown on sapphire by ion-implantation and annealing

The morphology and interface structure of α-Fe₂O₃ islands grown on α-Al₂O₃ single crystals (sapphire) by Fe-ion-implantation and annealing in an oxidizing atmosphere have been studied using transmission electron microscopy. The α-Fe₂O₃ islands have the orientation relationship of and with sapphire. The typical outline of α-Fe₂O₃ islands consists of two (0 0 0 1) and six planes. The interfaces between α-Fe₂O₃ islands and sapphire are semicoherent, that is coherent regions separated by misfit dislocations at the interfaces. When imaged along the direction, the projected Burgers vector is determined to be . When imaged along the direction, the projected Burgers vector is determined to be . These misfit dislocations form a network structure at the interface to accommodate the mismatch between the lattices of the α-Fe₂O₃ and the α-Al₂O₃.     

Comparison of secondary ion emission yields for poly-tyrosine between cluster and heavy ion impacts

Emission yields of secondary ions necessary for the identification of poly-tyrosine were compared for incident ion impacts of energetic cluster ions (0.8 MeV , 2.4 MeV , and 4.0 MeV ) and swift heavy monoatomic molybdenum ions (4.0 MeV Mo⁺ and 14 MeV Mo⁴⁺) with similar mass to that of the cluster by time-of-flight secondary ion mass analysis combined with secondary ion electric current measurements. The comparison revealed that (1) secondary ion emission yields per impact increase with increasing incident energy within the energy range examined, (2) the 4.0 MeV impact provides higher emission yields than the impact of the monoatomic Mo ion with the same incident energy (4.0 MeV Mo⁺), and (3) the 2.4 MeV impact exhibits comparable emission yields to that for the Mo ion impact with higher incident energy (14 MeV Mo⁴⁺). Energetic cluster ion impacts effectively produce the characteristic secondary ions for poly-tyrosine, which is advantageous for highly sensitive amino acid detection in proteins using time-of-flight secondary ion mass analysis.     

First-principles study on electronic structures and absorption spectra for BaWO4 crystal containing barium vacancy

The electronic structures, dielectric function and absorption spectra for the perfect BaWO₄ (BWO) crystal and the BWO crystal containing barium vacancy () have been studied using density functional theory code CASTEP with the lattice structure optimized. The results indicate that the optical properties of the BWO crystal exhibit anisotropy and its optical symmetry coincide with lattice structure geometry of the BWO crystal. For the BWO crystal containing , there exhibit four absorption bands peaking at 0.71 eV (1751 nm), 1.85 eV (672 nm), 3.43 eV (362 nm) and 3.85 eV (322 nm), respectively. The origins of the 370 nm absorption band should be related to the .     

The interaction of antihydrogen with simple atoms and molecules

In this paper, we describe calculations that we have carried out of cross sections for rearrangement processes in very low-energy helium + antihydrogen scattering that result in or or . A significantly more accurate method from that used previously [E.A.G. Armour, S. Jonsell, Y. Liu, A.C. Todd, Nucl. Instr. and Meth. B 247 (2006) 127] is used to calculate the entrance channel wave function. Results are presented for the first two processes. Mention is made of the use of the method in calculations of low-energy e⁺H₂ scattering.     

Preparation of Ne, Mg, Si, S, and Ar targets by ion implantation into thin carbon foils

The preparation of isotopically pure targets of ²⁰Ne, ²⁴Mg, ²⁸Si, ³²S, and ³⁶Ar by the implantation of 25-70 keV ions into carbon foils is described.     

Fabrication and nuclear analysis of isotopic N and N ion-implanted silicon standards

The fabrication of reliable isotopic nitrogen standards is achieved in Si through ¹⁴N and ¹⁵N ion implantation. 60 keV and ions were implanted at 400 °C up to ∼60% peak atomic concentration, yielding nitrogen-saturated silicon layers as measured using resonant nuclear reaction analysis. No isotopic effect has been observed. The nitrogen standards are validated by measurements of stability under ion irradiation. No significant desorption of nitrogen is observed either under a ⁴He⁺ ion fluence of 3.36 × 10¹⁶ cm⁻² or under a ¹H⁺ ion fluence of 8.60 × 10¹⁷ cm⁻², giving strong evidence that isotopic nitrogen standards can be achieved.     

Ion implantation in 4H-SiC

Silicon carbide offers unique applications as a wide bandgap semiconductor. This paper reviews various aspects of ion implantation in 4H-SiC studied with a view to optimise ion implantation in silicon carbide. Al, P and Si ions with keV energies were used. Channelling effects were studied in both a-axis and c-axis crystals as a function of tilts along major orthogonal planes and off the major orthogonal planes. Major axes such as [0 0 0 1] and the and minor axis like the showed long channelling tails and optimum tilts for minimising channelling are recommended. TEM analyses of the samples showed the formation of (0 0 0 1) prismatic loops and the loops as well,in both a and c-cut crystals. We also note the presence of voids only in P implanted samples implanted with amorphising doses. The competing process between damage accumulation and dynamic annealing was studied by determining the critical temperature for the transition between crystalline and amorphous SiC and an activation energy of 1.3 eV is extracted.     

Stability and delayed fragmentation of highly charged C60 trapped in a conic-electrode electrostatic ion resonator (ConeTrap)

We employed a conic-electrode electrostatic ion resonator (ConeTrap) to store the recoil ions resulting from collision between 56 keV Ar⁸⁺ ions and C₆₀ in order to study their stability over a long time range (several milliseconds). The originality of our method, based on the trapping of a single ion to preserve the detection in coincidence of all the products of the collision, is presented in detail. Our results show that C₆₀ ions produced in such collisions are stable in the considered observation time. By employing the ConeTrap as a secondary mass spectrometer in order to let the ions oscillate only for a single period, we have been able to observe delayed evaporation of cold ions 20 μs after the collision. We interpret quantitatively the relative yields of daughter ions with a cascade model in which the transition rates are estimated via the commonly used Arrhenius law, taking into account the contribution of the radiative decay.     

Development of secondary ion mass spectroscopy using medium energy C60 ion impact

In this paper, we report time-of-flight (TOF) secondary ion mass spectroscopy using primary C₆₀ ions with an energy range from several tens of keV to several hundreds of keV. Application of the spectroscopy to the analysis of a poly(amino acid) film revealed that characteristic peaks, necessary for identification of the amino acid in proteins, show higher intensities for medium energy C₆₀ (120 keV and 540 keV ) impacts than those for low energy C₆₀ (30 keV ) impacts. This finding demonstrates that medium energy C₆₀ ion impacts are useful for highly sensitive characterization of amino acids.     

Radiation induced defects in BaBPO5:Ce and their role in thermally stimulated luminescence reactions: EPR and TSL investigations

Defect centers induced by gamma irradiation in Ce doped BaBPO₅ were investigated using EPR spectroscopy. From EPR studies, three phosphorous centered radicals were characterized on the basis of observed ³¹P hyperfine splitting and g values as , and radicals. In addition to this, two types of boron oxygen hole centers (BOHC) and O⁻ were also formed at room temperature. An intense broad signal in sample annealed in argon (g_⊥ = 1.9258 and g_‖ = 1.8839) was assigned to Ce³⁺ ions associated with the electron trapped at anion vacancy or nearby lattice defect. TSL studies showed two glow peaks, a relatively weaker one at 425 K and an intense one at 575 K. Spectral studies of the TSL glow peaks have shown that Ce³⁺ ion acts as emission center. From the temperature dependence of the EPR spectra of gamma irradiated samples, the glow peaks at 425 K and 575 K were attributed to thermal destruction of /O⁻ and BOHC, respectively, by trapping of electrons from elsewhere. The energy released in electron hole recombination process is used for the excitation of Ce³⁺ ions resulting in these glow peaks at 425 K and 575 K. The spectral studies of the TSL glow peaks have shown emission at 330 nm indicating Ce³⁺ acts as the luminescent centre. The trap depth and the frequency factor for the 425 K and 575 K peaks were determined using different heating rates method.     

SIMS analysis of xenon and krypton in uranium dioxide: A comparison of two models of gas-phase ionisation

Reasonable detection limits in secondary ion mass spectrometry (SIMS) analysis of inert gases in solids may be achieved by gas-phase ionisation. For Xe in UO₂ Desgranges and Pasquet (D&P) have recently reported that the ion intensity can be enhanced significantly using ion bombardment in combination with an oxygen jet directed at the sputtered area. A similar effect was reported by Portier et al. for Kr in UO₂. The enhancement was attributed to ionisation by an interaction with oxygen atoms and molecules (D&P model). The proposed mechanism is at variance with a recently outlined model of gas-phase ionisation involving charge transfer between the ejected atoms and the incoming primary ions. The purpose of this study was to clarify these contradictory views by a reanalysis of the original data. Access to all relevant original data was kindly provided by L. Desgranges. In contrast to expectation based on the D&P model, step-wise increases in the flow rate of the oxygen jet did not result in an immediate response of . Instead, transient yield changes were observed, with characteristic rise times that were even longer for Xe⁺ than for uranium specific signals. This observation invalidates the idea that ionisation of Xe atoms is due to interaction with oxygen molecules of the jet. Recalling well known transient phenomena in ion-bombardment induced photon emission, it is argued that the enhancement effect may be associated with the increase in the oxidation state of the sample, as a result of which the fraction of Xe (or Kr) atoms leaving the sample in an electronically excited state is presumably increasing, thus enlarging the effective cross section for charge transfer. Alternatively, the enhancement may be due to a lowering of the ejection velocity of rare gas atoms, possibly caused by the increase in near-surface sample oxidation. A second problem with the D&P study is the use of as a reference signal. Literature data as well as new results reveal that and UO⁺ secondary ions dominate the SIMS spectrum of oxidised uranium at energies <60 eV, the U⁺ fraction amounting to only 1% or less. Other issues are (i) the significant variation of the sample erosion rate that occurred upon deliberate changes of the mean primary ion current density, (ii) the associated bombardment induced, progressive oxygen depletion of the sample, (iii) the presence of a background superimposed on the Xe⁺ signals, a significant effect at low current densities and (iv) the space-charge broadening of the primary ion beam at high beam currents. Eliminating all these interfering factors, the (reduced) ionisation probabilities of Xe⁺ were found to be in accordance with gas-phase ionisation by charge exchange, even in the pressure of excessive oxygen flooding.