14N Ions Research Articles

Characteristics of low energy atom and molecule beams generated by the charge exchange reaction

A low energy NB source, which consisted of a surface wave plasma (SWP) source and two large diameter carbon electrodes, was developed for damageless etching of ultralarge-scale integrated devices. Ion beams were extracted from the SWP using two carbon electrodes, accelerated and injected to the process chamber, and then neutralized without energy loss by a charge exchange reaction. The energy distribution functions of an Ar ion beam and an Ar atom beam was observed using a quadrupole mass spectroscope equipped with an energy analyzer. The energy of the Ar ion beam and the Ar atom beam was controlled by the acceleration voltage. N2 ion and N ion beams were also extracted from a nitrogen plasma source. The intensity ratio of the N ion beam to the N2 ion beam was 5:9, indicating that N ions were efficiently generated in the nitrogen SWP. The N2 ion and N ion beams were changed to N2 molecule and N atom beams, respectively, through a charge exchange reaction without energy loss. The energy of these beams was controlled by the acceleration voltage and was in the region less of than 100eV. When the acceleration voltage is higher than 40V, not only the primary peaks due to the N2 ion beam or N ion beam were observed but also a low energy second peak was observed in the energy distribution. The energy of the low energy second peak was controlled by the acceleration voltage. It was concluded that the low energy second peak corresponds to the N2 molecule ion beam and the N ion beam, which is extracted from the second plasma generated in the space between the two carbon electrodes.

Nitrogen Atom Densities in Rare Gas Diluted N2 Plasmas with Capacitive and Inductive Coupling

Nitrogen atom densities in rare-gas diluted N2 plasmas are diagnosed by using Vacuum Ultra Violet Absorption Spectroscopy (VUVAS). The influence of rare-gas dilution for low pressure (20 mTorr) inductively coupled plasma is that N atom density shows a peak around 3 % of N2 fraction due to the increase of the high energy electrons. The N2 ion density, another precursor for nitridation, did not show a peak even for the high rare-gas fraction. On the other hand, capacitively coupled plasma operated at 0.5 Torr range showed no steep increase of N atom density. The optical diagnostics shows that rare-gas dilution of N2 plasma leads to the change of reactant flux ratio between neutral atoms and ions.

Low energy N2 ion bombardment for removal of (HfO2)x(SiON)1−x in dilute HF

The ion assisted wet removal of (HfO2)x(SiON)1−x high dielectric constant (k) materials and its effect on electrical properties were investigated. Crystallization temperature of (HfO2)x(SiON)1−x increased as the percentage of SiON increased. The crystallized (HfO2)0.6(SiON)0.4 was damaged and turned to an amorphous film via incorporation of N species into the film by N2 plasma treatment. In addition, the structure of (HfO2)0.6(SiON)0.4 was disintegrated into HfO2, SiO(N), and ON after N2 plasma treatment. N2 plasmas using low bias power were applied for wet removal of high-k films and the mechanism of the ion assisted wet removal process was explored. When high bias power was applied, the surface of source and drain regions was nitrided via the reaction between N and Si substrates. Feasibility of the low bias power assisted wet removal process was demonstrated for short channel high-k metal oxide semiconductor device fabrication by the smaller shift of threshold voltage, compared to the high bias power as...

Photocatalytic degradation of azo dye Metanil Yellow: Optimization and kinetic modeling using a chemometric approach

The photocatalytic degradation of an azo dye Metanil Yellow was carried out in aqueous solution using TiO2 as photocatalyst under UV irradiation. The decolorization and degradation kinetics were investigated and both followed a pseudo first order kinetic according to Langmuir–Hinshelwood model. Using HPLC/DAD and GC/MS analyses, more than 10 major reaction intermediates were identified and a tentative degradation pathway was proposed. Furthermore, ion chromatography (IC) and TOC measurements revealed a complete mineralization of Metanil Yellow into CO2, N2, H2O and inorganic ions (NH4+, NO3− and SO42−).On the other hand, an experimental design based on the surface response methodology was applied to assess the individual and interaction effects of several operating parameters (dye concentration, TiO2 concentration, pH, light flux, etc.) on the treatment efficiency (dye removal time). Based on the experimental design data, a semi-empirical expression was obtained, permitting to predict and optimize the dye removal time. This model was very consistent with experiment results (correlation factor: 99.5%). Moreover, additional experimental results obtained under near optimal conditions were found to be very close to the predicted values.This work demonstrates well the utility and benefits of the experimental design approach for screening and modeling the reaction parameters. Furthermore, it contributes significantly to the improvement and better understanding of photocatalytic processes.

Anaerobic ammonium oxidation in the Peruvian oxygen minimum zone

We investigated the microbial pathways of nitrogen (N) loss in an April 2005 transect through the Peruvian oxygen minimum zone (OMZ) at 12°S latitude using short anaerobic incubations with 15N‐labeled substrates and molecular‐ecological and lipid‐biomarker studies. In incubations with 15NH4+, immediate production of 14N15N, but not 15N15N, indicated that N2 was produced by the pairing of labeled 15NH4+ with in situ 14NO2− via anaerobic ammonium oxidation (anammox). Supporting this finding, we also found anammox‐related 16S ribosomal ribonucleic acid gene sequences similar to those previously known from other marine water columns in which anammox activity was measured. We identified and enumerated anammox bacteria via fluorescence in situ hybridization and quantitative polymerase chain reaction and found ladderane membrane lipids specific to anammox bacteria wherever anammox activity was measured by our isotope tracer method. However, in incubations with 15NO3− or 15NO2−, in which denitrification would have been expected to produce 15N15N by pairing of oxidized 15N ions, 15N15N production was not detected before 24 h, showing that denitrification of fixed N to N2 was not taking place in our samples. At the time and locality of our study, anammox, rather than denitrification, was responsible for N2 production in the Peruvian OMZ waters.

Energy loss in polycarbonate and polyethylene terephthalate by 2.0–6.5 MeV 14N, 31P and 75As ions

Energy loss for 2.0–6.0MeV 14N ions, 3.0–6.5MeV 31P ions and 3.0–6.5MeV 75As ions in thin foils of polycarbonate and polyethylene terephthalate were measured by means of a transmission technique using a half-covered silicon surface barrier detector. During the measurement, the charged particle count rates were kept below 100cps in order to minimize dead time and radiation damage in the system. The obtained data are compared with the SRIM 2003 calculation and the ICRU Report 73. Most of the measurement results compare quite favorably with the ICRU Report 73.

Dissociative double photoionization of N2 using synchrotron radiation: Appearance energy of the N2+ dication

Photoionization cross sections for the production of the doubly charged ion N2+ from N2 have been measured by means of synchrotron radiation in the photon energy range from 50 to 110 eV. The appearance energy for N2+ has been determined as 55.2+/-0.2 eV, i.e., about 1.3 eV higher than the spectroscopic dissociation limit leading to the charge asymmetric dissociation channel N2+(2P)+N(4S) at 53.9 eV. The onset of a second threshold at 59.9+/-0.2 eV is detected and the energy dependence of photoion intensities near the threshold regions is interpreted in terms of the Wannier theory. The production of the N2+ dication is discussed in terms of direct and indirect mechanisms for dissociative charge asymmetric photoionization and by comparison with the potential energy curves of the intermediate N(2)2+ dication. Experimental evidences for the opening of the Coulomb explosion channel N2++N+ at high photon energies are provided by measuring the kinetic energy release spectra of N2+ fragments at selected photon energies.

Formation of carbon nitride nanospheres by ion implantation

Carbon nitride nanospheres have been synthesized into copper by simultaneous high fluence (10 18 at. cm −2) implantations of 12C and 15N ions. The composition of the implanted region has been measured using 12C(d,p 0) 13C and 15N(d,α 0) 13C nuclear reactions induced by a 1.05 MeV deuteron beam. The 12C and 15N depth profiles are very close and the retained doses into copper are relatively high, which indicates that carbon and nitrogen diffusion processes are likely limited during implantation. High resolution transmission electron microscopy (HRTEM) observations and electron diffraction (ED) analyses have been carried out to determine the structure of the nanospheres formed during implantation. Some consist in small hollow amorphous nanocapsules with sizes ranging from 30 to 100 nm. Large gas bubbles with diameters up to 300 nm have also been observed in the copper matrix. Electron energy-loss spectroscopy (EELS) measurements performed on the small nanocapsules indicate that their shells are composed of carbon and nitrogen.

Radiocarbon detection by ion charge exchange mass spectrometry

A method for detection of radiocarbon at low levels is described and the results of tests are presented. We refer to this method as ion charge exchange mass spectrometry (ICE-MS). The ICE-MS instrument is a two stage mass spectrometer. In the first stage, molecular interferences which would otherwise affect radiocarbon detection at mass 14 are eliminated by producing high charge state ions directly in the ion source (charge state ⩾2). 14N interference is eliminated in the second stage by converting the beam to negative ions in a charge exchange cell. The beam is mass-analysed at each stage. We have built a test apparatus consisting of an electron cyclotron resonance ion source and a pair of analysing magnets with a charge exchange cell in between, followed by an electrostatic analyser to improve the signal to background ratio. With this apparatus we have measured charge exchange probabilities for (Cn+→C−) from 4.5 to 40.5keV (n=1–3). We have studied the sources of background including assessment of limits for nitrogen interference by searching for negative ions from charge exchange of 14N ions. Our system has been used to detect 14C in enriched samples of CO2 gas with 14C/12C isotopic ratio down to the 10−9 level. Combined with a measured sample consumption rate of 4ng/s, this corresponds to a capability to detect transient signals containing only a few μBq of 14C activity, such as may be obtained from chromatographic separation. The method will require further development to match the sensitivity of AMS with a gas ion source; however, even in its present state its sensitivity is well suited to tracer studies in biomedical research and drug development.

水素観察のためのマイクロ・ビーム核反応法装置の開発と応用

A microscope for hydrogen has been developed by means of micro-beam nuclear reaction analysis. The resonance nuclear reaction between proton and 15N accelerated up to ~6 MeV is used. The micro-beam of 15N ion was made by a glass capillary, which has a taper shape. Against this focused 15N ion beam, samples are scanned perpendicularly to the beam direction by stepping motors. As an application of the microscope, a patterned Y thin film covered by Pd thin film was prepared, and the sample was exposed to 1 atm hydrogen atmosphere over a night. The hydrogen distribution in this sample was investigated by using a glass capillary, which has an exit with the 50 μm diameter. As a result, a profile of nuclear reaction analysis, indicating that the hydrogen atoms are concentrated in the patterned Y thin films, was taken.

Dielectric Constants on Mixture Thin Films of Barium Carbide and Barium Nitrate Deposited on Silicon Wafers by Barium Carbonate Electron Beam Evaporation Using Nitrogen Molecular and Ion Beams

Thin barium carbide (BaC6) films were deposited on Si substrates by the electron beam evaporation of barium carbonate (BaCO3). Mixture films of BaC6 and barium nitrate (BaN2O4) were deposited on Si substrates using N2 molecules and ion beams during the evaporation of BaCO3 by electron beams. The fraction of BaN2O4 in the mixture films increased with increasing intensity of N2 molecular and nitrogen ion beams. The prepared films had a large number of C–O bonds, because the BaCO3 used was a source material. Highly O-doped BaC6 films had very low dielectric constants of (1–2)ε0. However, the dielectric constants of the mixture films varied from 1.3 to 5.8ε0 with increasing proportion of BaN2O4.

Analysis of ion mobility and diffusion in atmospheric gaseous mixtures from Monte Carlo simulation and macroscopic laws

The reduced mobility and diffusion coefficients of and O− are calculated with a Monte Carlo simulation for the gas mixtures N2–H2O (50%, 50%) and O2–N2 (80%N2, 20%O2), respectively, from measured and calculated elastic and inelastic cross sections. These mobility and longitudinal diffusion coefficients have been compared with the standard Blanc's law and with the common mean energy (CME) procedure. Good agreement between these three calculation methods was found for the mobility and diffusion of in the N2–H2O mixture at high reduced fields where inelastic processes are relatively uninfluential. However, a strong deviation between Blanc's law and both CME procedure and our Monte Carlo calculations for the reduced mobility and the diffusion coefficient of in this gas mixture N2–H2O was observed at low reduced fields, because inelastic processes are significant. On the contrary, for the case of the N2–O2 mixture, where inelastic processes are small over the reduced electric field range 1–8000 Td, the three calculation methods led to similar results. The elastic collision cross sections used were determined from a semi-classical JWKB approximation by using a rigid core potential model for both symmetric and asymmetric , O−/O2 and O−/N2 ion–neutral systems. Moreover, the inelastic cross sections were extended to low energies from appropriate approximations. These cross section sets were validated from the good agreement between our Monte Carlo calculated reduced mobilities in N2 and H2O, O− in O2 and N2 and either measured values for the systems and O−/O2 or physical properties of the systems and O−/N2.

Measurements of the stopping forces for heavy ions in Ge, Ag and Au using novel ‘polka-dot’ detectors

Measurements of the stopping forces for 14C, 14N and 16O ions in Ge and Au, for 14N and 19F ions in Ag, as well as for 19F ions in Au have been made, respectively. A novel technique, reported recently, using PIN diodes coated directly with the stopping medium in a polka dot pattern was used. This provided a set of precise, self-consistent measurements on the same stopping medium. Results show small but significant deviations from SRIM stopping predictions and are also compared to a recently-developed empirical stopping force predictor.

Projectile electron loss in nitrogen

The projectile electron loss channel plays an important role in modeling several processes connected to the penetration of swift ions in gases, such as radiation damage, energy loss, upper atmosphere studies, storage lifetimes of low-charge state heavy ions, etc. In this paper we have used recent measurements of projectile electron loss of He+ ions in N2 together with previous data for higher charged ions in order to shed light on the role played by the projectile electron loss in the heating and ionization of Titan's atmosphere.

Depth profiling of carbon and nitrogen in copper using nuclear reactions

Simultaneous implantations of 12C and 15N were performed into copper using the non-deviated beam line of a 2MV Tandetron accelerator. The atomic composition of the implanted layer was measured using appropriate nuclear reactions with a 1.05MeV deuteron beam. 12C(d,p0)13C and 15N(d,α0)13C nuclear reactions were used to depth profile simultaneously 12C and 15N and to determine the relative contribution of multi-ionised 12C and 15N ions to the carbon and nitrogen distribution. We also used the narrow resonance at 429keV of the 15N(p,αγ)12C nuclear reaction to check the validity of our results. The depth distributions obtained with this resonant nuclear reaction confirmed that (d,p) and (d,α) reactions are well suited to profile both carbon and nitrogen elements with a quite good resolution. Moreover, using these reactions makes possible to profile 12C and 15N atoms with a single and relatively rapid measurement.

Absolute differential and total cross sections for charge transfer of O+ ground and mixed states ions in N2

We report measurements of the total and absolute differential cross sections for charge transfer of ground- and excited-states O+ ions at 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5 keV in collisions with N2 at scattering angles −5.2° ⩽ Θ ⩽ +5.2° in the laboratory frame. Total cross sections for ground- and mixed state ions are compared with previous measurements. The behaviour of the absolute differential cross sections display an expected decreasing behaviour with increasing angle. The mixed state ions cross sections are considerably higher than those measured for the ground state ions.

Reaction of Implanted N Isotope with SiO2 Near Si3N4-Film and SiO2-Substrate Interface

We have investigated 100 keV 15N (90% enriched) implantation effects on Si3N4 films on SiO2-glass-substrate. The Si3N4 films were prepared by using reactive RF-magnetron-sputter-deposition method in N2 (natural isotope abundance) gas at room temperature. The composition and film thickness were measured by Rutherford backscattering spectroscopy (RBS) and optical absorption spectroscopy. The RBS and optical absorption spectroscopy show increase in the film thickness with the stoichiometric composition, by 15N ion implantation. These results and depth distribution of the implanted 15N, which is obtained by nuclear reaction analysis (NRA), lead to formation of Si3 15N4 film (embedded isotope rich nitride film). Enrichment of 15N in the grown silicon-nitride film is estimated to be ∼70%.

Reaction of Implanted N Isotope with SiO2 Near Si3N4-Film and SiO2-Substrate Interface

We have investigated 100 keV 15N (90% enriched) implantation effects on Si3N4 films on SiO2-glass-substrate. The Si3N4 films were prepared by using reactive RF-magnetron-sputter-deposition method in N2 (natural isotope abundance) gas at room temperature. The composition and film thickness were measured by Rutherford backscattering spectroscopy (RBS) and optical absorption spectroscopy. The RBS and optical absorption spectroscopy show increase in the film thickness with the stoichiometric composition, by 15N ion implantation. These results and depth distribution of the implanted 15N, which is obtained by nuclear reaction analysis (NRA), lead to formation of Si3 15N4 film (embedded isotope rich nitride film). Enrichment of 15N in the grown silicon-nitride film is estimated to be ∼70%.

Low-thermal-budget and selective relaxation of stress gradients in gold micro-cantilever beams using ion implantation

The stress gradient of gold micro-cantilever beams induced during dry-release in oxygen plasma is quantitatively studied, and the relaxation of the stress gradient by He and N2 ion implantation is investigated. An analytic model considering the finite anchor stiffness of a step-up anchor and the geometry of the beam cross-section is constructed to evaluate the induced stress gradient. Various measurements are carried out to verify the effectiveness of ion implantation in relaxing the stress gradient.

Effect of N2 ion flux on the photocatalysis of nitrogen-doped titanium oxide films by electron-beam evaporation

Abstract Nitrogen-doped titanium oxide (TiOxNy) films were prepared with ion-assisted electron-beam evaporation. The nitrogen (N) incorporated in the film is influenced by the N2 flux modulated by the N2 flow rate through an ion gun. The TiOxNy films have the absorption edge of TiO2 red-shifted to 500 nm and exhibit visible light-induced photocatalytic properties in the surface hydrophilicity and the degradation of methylene blue. The structures and states of nitrogen in the films are investigated by X-ray diffraction patterns (XRD), and X-ray photoelectron spectroscopy (XPS) and related to their visible light-induced photocatalytic properties. The results indicate that the substitutional N in anatase TiO2 can induce visible light photocatalysis. The substitutional N is readily doped by the energetic nitrogen ions from the ion gun. The best photocatalytic activity is obtained at the largest N loading about 5.6 at.%, corresponding to the most substitutional N in anatase TiO2. The film exhibits the degradation of methylene blue with a rate-constant (k) about 0.065 h−1 and retaining 7° water contact angle on the surface under visible light illumination.