Combined channeling study of α-LiIO3 crystal in an electrostatic field

The combined channeling backscattering and channeling nuclear reaction analysis of the α-LiIO₃ monocrystal in an electrostatic field has been performed by proton beam at different energies to identify the behaviour of Li and I ions in the crystal. The thickness of the crystal was about 2 mm and has been cut perpendicular to C-direction. The channeling parameters like half angular width and minimum yield of 〈001〉 axial channeling have been measured precisely and the channeling behaviour of different ions in the crystal has been observed and measured quantitatively first time. The ionic d.c. conductivity can be calculated from the surface peak of the aligned channeling spectrum directly.     

An orientation-dependent defect in ion-implanted silicon

A new EPR spectrum is resolved in the N⁺-implanted silicon, and this center can be produced only by the 〈110〉 channeling ions in the region underneath the amorphous layer.     

Characterisation of human hair surfaces by means of static ToF-SIMS: A comparison between Ga and C60 primary ions

This study deals with the secondary ion yield improvement induced by using C₆₀⁺ primary ions instead of Ga⁺ ones to characterize human hair surfaces by ToF-SIMS. For that purpose, a bunch of hair fibres has been analysed with both ion sources. A high improvement is observed for the detection of amino acids with C₆₀⁺ primary ions as compared to Ga⁺ ions. As an example, a yield enhancement factor greater than 3000 is found for the CNO⁻ peak. A similar gain is observed for the positive secondary ions characteristic of the amino acids. Most of the atomic ions, such as Ca⁺, O⁻ and S⁻, constitute minor peaks with C₆₀⁺ ions while they often dominate the spectrum in the case of Ga⁺ ions. However, with the C₆₀⁺ source, a series of inorganic combination peaks with the elements Ca, S and O are observed in the positive spectra (i.e. HCaSO₄⁺), while they are marginal with the Ga⁺ source. For the mass range beyond 100 m/z and in both polarities, the hair fingerprints are similar with both sources. In average, for a comparable number of primary ions per spectrum, the C₆₀⁺ ion source gives intensities between two and three orders of magnitude higher than the Ga⁺ one.     

Depth profiling of cells and tissues by using C60 and SF5 as sputter ions

In the present study, SF₅⁺ and C₆₀⁺ were used as primary ions for sputtering and Bi₃⁺ was used as primary ions for analysis. The depth profiling procedure was utilized to make 3D images of the chemistry of single cultured cells and tissue samples of intact intestinal epithelium.The results show sputtering of organic material from cells and tissue with both SF₅⁺ and C₆₀⁺ sources. Cholesterol fragments were found in the superficial layers when sputtering with C₆₀⁺. Spectra were collected revealing the change in yield along the z-axis of the sample. 3D images of the localization of Na, K, phosphocholine and cholesterol were constructed with both ion sources for single cell cultures and the mouse intestine.Cryostate sections of mouse intestine were analysed in 2D and the results were compared with the 3D image of the intestine. The localization of cholesterol and phosphocholine was found to be similar in cryostate sections analysed in two dimensions and the sputtered, freeze-dried intestine analysed in 3D. The comparison of 2D and 3D images suggest that the phosphocholine signal faded with C₆₀⁺ sputtering. In conclusion, both C₆₀⁺ and SF₅⁺ can be used as primary ion sources for sputtering of organic material from cells and tissues. Consecutive analysis with a Bi₃⁺ source can be used to obtain image stacks that could be used for reconstruction of 3D images.     

Model multilayer structures for three-dimensional cell imaging

The prospects for SIMS three-dimensional analysis of biological materials were explored using model multilayer structures. The samples were analyzed in a ToF-SIMS spectrometer equipped with a 20 keV buckminsterfullerene (C₆₀⁺) ion source. Molecular depth information was acquired using a C₆₀⁺ ion beam to etch through the multilayer structures at specified time intervals. Subsequent to each individual erosion cycle, static SIMS spectra were recorded using a pulsed C₆₀⁺ ion probe. Molecular intensities in sequential mass spectra were monitored as a function of primary ion fluence. The resulting depth information was used to characterize C₆₀⁺ bombardment of biological materials. Specifically, molecular depth profile studies involving dehydrated dipalmitoyl-phosphatidylcholine (DPPC) organic films indicate that cell membrane lipid materials do not experience significant chemical damage when bombarded with C₆₀⁺ ion fluences greater than 10¹⁵ ions/cm². Moreover, depth profile analyses of DPPC-sucrose frozen multilayer structures suggest that biomolecule information can be uncovered after the C₆₀⁺ sputter removal of a 20 nm overlayer with no appreciable loss of underlying molecular signal. The experimental results support the potential for three-dimensional molecular mapping of biological materials using cluster SIMS.     

“Crystal fields” for magnetic ions in metals from itinerant electrons

The interaction of conduction electrons with host ions are shown to give rise to “crystal fields”, V_C, which act on the magnetic ion in some dilute magnetic alloys. Crystal fields, V_N, arising directly from ions neighbouring the magnetic ion have been compared with V_C to show that the overall crystal field splitting from all 3d magnetic ions in axial symmetries is enhanced by the p-like character of V_C. A⁰₄〈r⁴〉 from V_N is also increased by the d-component of V_C. The angular properties of itinerant electron states give rise to the above results. For all rare-earth ions in fcc symmetry the radial and angular components of conduction-electron states with mainly d, but also f character, are shown to give rise to a reversal in sign of A⁰₄〈r⁴〉 from V_N. A⁰₆〈r⁶〉 is enhanced by the f component of the conduction electrons.     

Molecular ion emission from single large cluster impacts

We investigated the emission of the secondary ions stimulated by single impacts of 136 keV Au₄₀₀⁴⁺ projectiles. The study was carried out on targets of glycine, phenylalanine, and C₆₀. In addition, a target of C₆₀ was examined with 18 keV C₆₀⁺ projectiles. The experiments were performed in the event-by-event bombardment/detection mode. The secondary ions were identified with linear time-of-flight mass spectrometer equipped with an 8-anode detector. The Au₄₀₀⁴⁺ projectile induces abundant multi-ion emission, for instance the average number of detected ions (atomic, fragment, molecular and cluster ions) emitted per event from glycine target is 12.5. The glycine intact molecular ion (Gly⁻) yield is 1.14. The bombardment of a C₆₀ target results in the efficient emission of multiple intact C₆₀⁻ (total yield is 0.15).     

Polyethylene terephthalate (PET) bulk film analysis using C60, Au3, and Au primary ion beams

The damage characteristics of polyethylene terephthalate (PET) have been studied under bombardment by C₆₀⁺, Au₃⁺ and Au⁺ primary ions. The observed damage cross-sections for the three ion beams are not dramatically different. The secondary ion yields however were significantly enhanced by the polyatomic primary ions where the secondary ion yield of the [M + H]⁺ is on average 5× higher for C₆₀⁺ than Au₃⁺ and 8× higher for Au₃⁺ than Au⁺. Damage accumulates under Au⁺ and Au₃⁺ bombardment while C₆₀⁺ bombardment shows a lack of damage accumulation throughout the depth profile of the PET thick film up to an ion dose of ∼1 × 10¹⁵ ions cm⁻². These properties of C₆₀⁺ bombardment suggest that the primary ion will be a useful molecular depth profiling tool.     

Analysis of TOF-SIMS spectra from fullerene compounds

We analyzed TOF-SIMS spectra obtained from three different size of fullerenes (C₆₀, C₇₀ and C₈₄) by using Ga⁺, Au⁺ and Au₃⁺ primary ion beams and investigated the fragmentation patterns, the enhancement of secondary ion yields and the restraint of fragmentation by using cluster primary ion beams compared with monoatomic primary ion beams. In the TOS-SIMS spectra from C₇₀ and C₈₄, it was found that a fragment ion, identified as C₆₀⁺ (m/z = 720), showed a relatively high intensity compared with that of other fragment ions related to C₂ depletion. It was also found that the Au₃⁺ bombardment caused intensity enhancement of intact molecules (C₆₀⁺, C₇₀⁺ and C₈₄⁺) and restrained the fragmentation due to C₂ depletion.     

Branching ratios of successive emission (up to three) of C2n + (n = 1–5) fragments in asymmetrical fission processes of C60 r+ ions (r = 4–6)

Highly charged C₆₀ molecules are produced in collisions between neutral C₆₀ and multiply charged ions within a large range of temperatures. Successive emission of one, two or three light monocharged fragments referred as one-, two- and three-step processes have been observed. The experimental mass branching ratios for the emission of one C_2n⁺ fragment from C₆₀⁶⁺, C₆₀⁵⁺ and C₆₀⁴⁺ ions are compared with the theoretical values using a statistical model. From hotter C₆₀⁶⁺ ions, branching ratios for three-step processes have been measured and the data are in good agreement with an estimation using the branching ratios in one-step process.     

Energy distributions of atomic and molecular ions sputtered by C60 projectiles

In the process of investigating the interaction of fullerene projectiles with adsorbed organic layers, we measured the kinetic energy distributions (KEDs) of fragment and parent ions sputtered from an overlayer of polystyrene (PS) oligomers cast on silver under 15 keV C₆₀⁺ bombardment. These measurements have been conducted using our TRIFT™ spectrometer, recently equipped with the C₆₀⁺ source developed by Ionoptika, Ltd. For atomic ions, the intensity corresponding to the high energy tail decreases in the following order: C⁺(E^−0.4) > H⁺(E^−1.5) > Ag⁺(E^−3.5). In particular, the distribution of Ag⁺ is not broader than those of Ag₂⁺ and Ag₃⁺ clusters, in sharp contrast with 15 keV Ga⁺ bombardment. On the other hand, molecular ions (fragments and parent-like species) exhibit a significantly wider distribution using C₆₀⁺ instead of Ga⁺ as primary ions. For instance, the KED of Ag-cationized PS oligomers resembles that of Ag⁺ and Ag_n⁺ clusters. A specific feature of fullerene projectiles is that they induce the direct desorption of positively charged oligomers, without the need of a cationizing metal atom. The energy spectrum of these PS⁺ ions is significantly narrower then that of Ag-cationized oligomers. For characteristic fragments of PS, such as C₇H₇⁺ and C₁₅H₁₃⁺ and polycyclic fragments, such as C₉H₇⁺ and C₁₄H₁₀⁺, the high energy decay is steep (E⁻⁴ − E⁻⁸). In addition, reorganized ions generally show more pronounced high energy tails than characteristic ions, similar to the case of monoatomic ion bombardment. This observation is consistent with the higher excitation energy needed for their formation. Finally, the fraction of hydrocarbon ions formed in the gas phase via unimolecular dissociation of larger species is slightly larger with gallium than with fullerene projectiles.     

Amino-acid derivatives of fullerene C60 behave as lipophilic ions penetrating through biomembranes

It was found using potential-sensitive probes that the water-soluble amino-acid derivatives of fullerene C₆₀, such as C₆₀-Pro, C₆₀-? aminocapronic acid, and C₆₀-Arg, possess a pronounced membranotropic activity. The first two cause concentration-dependent dissipation of the membrane potential (Δψ) of the symbiosomes of the nodules of the yellow lupine generated in the presence of ATP and Mg²⁺ ions. In contrast to the first two derivatives, C₆₀-Arg, which carries a strong positive charge at the physiological pH, has no effect on the dissipation of Δψ in this model. On the contrary, this derivative caused a noticeable dissipation of the K⁺ diffusion potential (“minus” inside) generated on the membrane of human erythrocytes with the help of the K⁺ ionophore of valinomycin. The regularities obtained indicate that the derivatives of C₆₀ are transported across biological membranes as lipophil ions, thus causing depolarization of the membranes.     

纳秒激光诱导C60分子碎裂中轻碎片离子C+n(n＜30)的产生机理研究

采用飞行时间质谱计测量了纳秒激光诱导C₆₀分子碎裂中轻碎片离子C⁺_n(n≤11)的初始平均动能,结果显示轻碎片离子具有相同的初始平均动能(约为0.34eV),并且该动能在一定范围内不随激光通量的变化而明显改变.结合前人的实验结果,对纳秒激光诱导C₆₀分子碎裂中轻碎片离子C⁺_n(n＜30)的主要产生模式作了新的阐述,即C< 关键词： 飞行时间质谱计 轻碎片离子 笼形结构塌陷 初始动能     

The Hd-center interaction with a Rb+ ion during irradiation and thermal annealing in kBr

The role of Rb⁺ ions on defect formation in KBr has been studied. The impurity suppresses colorability due to X-raying at 6 K, but does not result in the formation of any centers characteristic to Rb⁺ ions at this temperature. A new optical absorption band peaked at 3.19 eV is produced only by thermal annealing of irradiated KBr:Rb. This band is annealed in parallel to the annealing of the F band in a stage at 55 K, obeying second-order rate equation with an activation energy of 0.102 eV. This band is ascribed to the H_A(Rb⁺)-center. Calculation is made on the elastic interaction energy between the H-center and a Rb⁺ ion, to show that the interaction along 〈110〉 is repulsive, whereas that along 〈001〉 is attractive. Based on this result of calculation, the structure and the formation mechanism of the H_A(Rb⁺) center, and origin of suppression of colorability at 6 K are discussed. The difference in the interaction of the interstitial atom with Rb⁺ during its dynamical motion and thermal motion is emphasized.     

New bounds for dilepton production from heavy neutral leptons

Bounds on 〈E_?ⁿ〉/〈E₊ⁿ〈, 〉E₊E_?〈/〉E₂²〈 and 〈E₊E_?〉/〈E₊〉〈E_?〉 are direved for the processes ν_μN → μ^?μ⁺(e⁺) + X and μN → μ^?μ⁺ + X if dileptons are mediated by a $\text{spin}\text{-}\text{1}\text{2}$ heavy neutral lepton L₀. The bounds are shown to be independent of the production mechanism and mass of L₀. Useful conditional bounds are obtained relating the bounded quantities, which give information about the structure of the weak current responsible for L₀ decay.     

Isotopic mass effects for low-energy channeling in a silicon crystal

Monte Carlo (MC) simulations have been used to study the low-energy channeling of ¹⁰B and ¹¹B ions along the [100] axis in Si crystal. MC simulations show that the critical angle Ψ_C ≈ 15.3(keV/E)^1/2 (in degrees) for the channeling of isotopic ¹⁰B ions and Ψ_C=14.5(keV/E)^1/2 (in degrees) for the channeling of isotopic ¹¹B ions, where E is the incident energy. This means that (Ψ_{C for 10B ions}/Ψ_{C for 11B ions})≈ (15.3/14.5)≈ (11/10)^1/2.     

Unimolecular dissociation of singly- and multiply-charged fullerene ions

The formation of fragment ions from C₆₀ due to electron impact ionization leading to a bimodal fragmentation pattern with a minimum around the cluster size of 30 is investigated with help of mass spectrometric techniques. Based on a detailed analysis of the energetics and kinetics of the singly- and multiply-charged fragment ions by two-sector field mass spectrometry (MIKE-scans) we can conclude that on the one hand some of the dissociation reactions proceed via evaporation of an intact C₆ ⁺ or C₄ ⁺ unit (and not via the sequential loss of smaller molecular carbon units). On the other hand, measured appearance energies and the direct observation of sequential C₂-loss reactions confirm that the sequential loss of neutral C₂ units is the dominant production mechanism for C_n ^z+ fragment ions with sizes 40 < n < 60. This revised version was published online in August 2006 with corrections to the Cover Date.     

Trapping ions at high temperatures: thermal decay of C60 +

An ensemble of trapped C₆₀ ⁺ ions has been heated with a continuous CO₂ laser to a stationary state where, in time average, the same energy is emitted as absorbed. With 10 W laser power, equilibria have been reached, which correspond to temperatures between 1800 and 2000 K. The ions are confined in a radio frequency quadrupole field created by a set of ring electrodes (split ring electrode trap). The number of stored ions can be determined in two ways, on one side by extracting and counting them with a Daly detector, on the other side via imaging their thermal emission onto an intensified CCD camera. Single photon sensitivity and a spatial resolution of a few μm provide precise information on the geometrical distribution and the total number of the trapped C₆₀ ⁺ ions. The spectral distribution of the emitted photons or their total number provides information on the internal energy of the ions. Trapping times of many minutes make it possible to follow very slow thermal loss of C₂ from hot C₆₀ ⁺ resulting in fragmentation rates between 10^?1 and 10^?3 s^?1. Correlating them to the internal temperature leads to a curved Arrhenius plot. The resulting parameters are smaller than the values derived from nonequilibrium ensembles.     

Low energy boron and phosphorus implants in silicon (b) doping profiles

Silicon wafers were implanted in 〈111〉-and 〈110〉-direction with boron ions of 6 keV and phosphorus ions of 20 keV at room temperature. Doses of 10¹⁴ ions/cm² were applied. At four different temperatures, 300, 420, 600, and 900°C. a few samples of each type of implant were annealed. Standard electrical techniques combined with successive layer removals were used to determine the depth distribution of electrically active centers. Since the method of using non type inverting implanted layers was applied, the local annealing behavior over the whole penetration region could be measured.

For both Si(B)-and Si(P)-implants the part of the profile beyond approx. 0.15 μm, i.e. the deeper part of the channeling and the whole supertail region, is unaffected by going from 300 to 900°C. All additional annealing, with respect to the electrical yield, takes place in the amorphous range and the adjacent part of the channeling range. After raising the temperature from 600 to 900°C both B-and P-profiles undergo diffusion controlled changes in this latter region.     

implantation of Bi into GaP. II. channeling studies

The channeling technique has been used to investigate the properties of Bi-implanted Gap. Measurements of the crystal disorder for 100 keV room temperature implants indicate a damage vs dose curve corresponding to ～13000 displacements/ion in the linear region and saturation at ～1.5 × 10¹³ Bi ions/cm². Annealing of the radiation damage has been observed and indicates two annealing steps at ～450°C for light damage and ～750°C for implants in the 1 × 10¹⁴/cm² range. Difficulties associated with the thermal decomposition of the implanted area have been overcome with the use of SiO _x coatings. The experimental details associated with the use of the SiO _x layer and with the use of a C¹² beam to obtain better depth and mass resolution in the backscattering spectrum are discussed. The lattice location measurements of the Bi impurity show ～50 per cent of the Bi atoms to be along the 〈110〉 string after a 900°C anneal for a 7.5 × 10¹³/cm² implant. In addition, the spectra show ～25 per cent of the Bi atoms have diffused to the surface. Correlations of these lattice location results with measurements of the photoluminescent intensity of the GaP (Bi) isoelectronic trap show an agreement in trend with anneal temperature but indicate a factor of ～10 more substitutional ions in the channeling measurement as compared to the photoluminescence results.