A high-pressure mass spectrometric study of ion-molecule reactions in a mixture of CF4 and He

Gas phase ion-molecule reactions of positive He⁺ ions produced from helium with neutral carbon tetrafluoride have been studied. The measurements were made with a quadrupole mass spectrometer with a high-pressure ion source. The fractional abundance I_i/∑I_i of dominant ions CF₃⁺, CF₂⁺ and helium ions has been determined as a function of the (1% CF₄ and 99% He) gas mixture pressure (in the range 1.33-31.92 Pa) and of the repeller electrode potential (ranging from 3 to 10 V).     

Helium ion bombardment induced amorphization of silicon crystals

The possibility of amorphization of a silicon crystal bombarded at room temperature with helium ions is studied by monitoring structural changes in the target crystal by means of transmission electron microscopy. Thin free-standing Si(100) plates were irradiated from the plane edge ({011} face) with 17-keV He⁺ ions in a dose range from 3×10¹⁶ to 3×10¹⁷ cm⁻². It was established that amorphization of the silicon crystal takes place for a total fluence exceeding 10¹⁷ cm⁻², provided that the ratio of the point defect production rate to the rate of helium introduction into silicon exceeds 90 displacements per He atom.     

Rare-Gas Implantation and Damage of Fullerene at High Fluence

Abstract

100 keV Ar⁺and Kr⁺ ions were implanted into fullerene films up to fluences which exceed the fullerene destruction threshold. The depth profiles of implanted atoms were measured using conventional RBS techniques. The depth profile parameters differ significantly from theoretical estimates and with increasing ion fluence the depth profiles move to the sample surface. This suggests a high degree of fullerene sputtering. In annealing experiments at temperatures up to 375 °C no significant changes of the depth profiles were observed.     

Precision Measurement of the 2

Abstract

The 4f¹³ 6s^{2 2}F_7/2–4f¹⁴ 5d ²D_5/2 3·43 μm infrared transition in ¹⁷²Yb⁺ has been driven for the first time and measured to be 87 360 087(4) MHz. The frequency was determined by probing a cloud of ¹⁷²Yb⁺ ions held in a radiofrequency trap in the presence of helium buffer gas. The infrared radiation was generated by difference frequency mixing in LiNbO₃. The frequency measurement is part of a programme to locate the 4f¹⁴ 6s ²S_1/2–4f¹³ 6s^{2 2}F_7/2 467 nm ultra-narrow transition in laser-cooled Yb⁺.     

Copper diffusivity in boron-doped silicon wafer measured by dynamic secondary ion mass spectrometry

The effective copper diffusivity (D_eff) in boron-doped silicon wafer was measured using a Dynamic Secondary Ion Mass Spectrometry (D-SIMS) that was incorporated with an out-drift technique. By this technique, positive interstitial copper ions (Cu_I⁺) migrated to the surface region when a continuous charge of electrons showered on the oxidized silicon wafer, which was also bombarded by primary O₂⁺ ions. The Cu_I⁺ ions at the surface region diffused back to the bulk when the electron showering stopped. The D-SIMS recorded the real-time distribution of Cu_I⁺ ions, generating depth profiles for in-diffusion of copper for silicon-wafer samples with different boron concentrations. These were curve-fitted using the standard diffusion expressions to obtain different D_eff values, and compared with other measurement techniques.     

Single crystal ZnSr:Mn prepared by ion implantation

Single crystal ZnS was implanted with 100 keV Mn⁺ ions. Low-temperature ZnS:Mn emission spectra were obtained using 5 keV electrons for excitation. Phonon structure was observed in thermally annealed material, and Mn diffusion was measured using a depth-selective emission profile.     

Optical emission spectroscopy study for nitrogen-acetylene-argon and nitrogen-acetylene-helium 100 kHz and dc discharges

The optical emission spectroscopy was applied to investigate the middle frequency (100 kHz) and dc low pressure discharges, generated in the nitrogen-acetylene-argon and nitrogen-acetylene-helium mixtures, commonly used for deposits of carbon nitride thin layers. Changes in the emission intensities of the selected species: CN, CH, C, H, N₂, N₂⁺ as well as Ar, Ar⁺ and He, were studied as a function of the discharge current. Excitation processes occurring in the presence of argon and helium were compared and discussed. The N₂-C₂H₂-Ar and N₂-C₂H₂-He plasmas generated in the 100 kHz and dc glow discharges were characterized by the excitation (Ar, He, H), vibrational (CN, N₂) and rotational (CN, N₂⁺) temperatures. A significant deviation from the equilibrium state was observed for the plasma containing argon as well as helium.     

Planar optical waveguides formed in β-BBO by MeV O+ implantation

The planar waveguides have been fabricated in z-cut β-BaB₂O₄ crystal by 2.8 MeV O⁺ ion implantation with the doses of 8 × 10¹⁴ and 2 × 10¹⁵ ions/cm² at room temperature. The waveguides were characterized by the prism-coupling method. The dark modes are measured before and after the annealing at 300°C for 20 and 40 min in air. The refractive index profile is reconstructed using the reflectivity calculation method. It is found that relatively large positive changes of extraordinary refractive indices happen in the guiding regions, and a slight change increases with the doses, which are different from most of the observed ion-implanted waveguides.     

Study of iron-ion implantation in rutile single crystals

TiO₂ crystals implanted with 100 keV ⁵⁷Fe⁺ ions at doses ranging from 10¹⁶ to 10¹⁷ ions.cm^?2 have been investigated with the conversion electron Mössbauer spectroscopy (CEMS), Rutherford backscattering (RBS) and transmission electron microscopy (TEM). Implanted samples of iron ions are mostly in a Fe²⁺ state and small precipitates of FeTi₂O₅ are observed using TEM. The migration of iron ions in a Fe³⁺ state occurs at about 600°C. Such a low temperature diffusion is thought to go along extended defects.     

Effect of Ga irradiation on the magneto-optic spectra of Pt/Co/Pt sandwiches

Interfacial changes in rf sputtered Pt/Co(2.6 nm)/Pt sandwiches grown onto sapphire (Al₂O₃) substrates induced by irradiation of 30 keV Ga⁺ ions at low dose (10¹⁴ ions/cm²) have been investigated by magneto-optic polar Kerr rotation (PKR) spectroscopy between 1 and 5 eV. The irradiation resulted in an increase of PKR over the whole spectral range. The measured PKR spectra were compared with those computed from the transfer matrix formalism using known polar Kerr rotation and ellipticity spectra for Co and five Co_xPt_1 − x alloys. The comparison between measured and computed PKR spectra provided an in-depth profile of Co and Pt ion distributions across the sandwich and confirmed that irradiation favors alloying in the vicinity of the two interfaces. These results are in a good agreement with the profile evaluated independently by TRIDYN simulations. Our results evidence an asymmetry in the irradiation effect due to an excess of Pt-Co alloying at the upper interface. Moreover, the observation of a negative PKR peak around 3.2 eV states definitively the presence of a chemically ordered Co_0.75Pt_0.25 alloy phase inside the irradiated film structure.     

Longitudinal and lateral distributions of medium energy heavy ions in some semiconductor films

The depth distributions of Bi⁺ and Fe⁺ ions implanted into SiN_1.375H_0.603, α-Si, Si₃N₄ and SiO₂ films at different angles were measured by Rutherford backscattering technique. The results show that: (1) the experimental mean projected range R_p is in agreement with the calculated value by TRIM'98 within 9% for SiN_1.375H_0.603, Si₃N₄ α-Si cases; (2) the experimental range straggling ΔR_p is larger than the calculated value by TRIM'98, the reason is not known; and (3) the depth distributions of implanted ions at different angles in all cases exhibit nearly Gaussian behaviour; the agreement of the extracted lateral spread with the calculated value is best for the case of Bi⁺ ions implanted into SiO₂.     

Ion–molecule reactions in mixtures of ethane with carbon tetrafluoride

Ion–molecule reactions have been measured for the ethane–carbon tetrafluoride mixtures of different compositions using a quadrupole mass spectrometer with a high-pressure ion source. Concentration of ethane in these mixtures ranged from 10% to 90% (at 10% increment). The following primary and secondary ions: CH₃⁺, F⁺, C₂H₃⁺, C₂H₄⁺, C₂H₅⁺, C₂H₆⁺, C₃H₅⁺, C₃H₇⁺, C₄H₇⁺, C₄H₉⁺, C₄H₁₀⁺, C₄H₁₁⁺ and CF₃⁺ were observed. Relative ion current intensities for primary and secondary ions are presented as a function both of total mixture pressure and concentration of carbon tetrafluoride in the mixture. Primary ions were produced by electrons with the energy of 300 eV. Potential of repeller electrode inside the ion source collision chamber was fixed at 5 V for all measurements. The total mixture pressure was changed from 0.7 to 26.6 Pa. Schemes of ion–molecule reactions were proposed.     

Mass Spectrometric Observations of Enhanced Rates of Association Reactions: nLiF = Li n F n (n = 2, 3) at LiF Single Crystal Surfaces

A mass spectrometric method was used to study the kinetics of lithium fluoride single-crystal sublimation. In electron impact ionization mass spectra, Li⁺, LiF⁺, Li₂F⁺, and Li₃ F ₂ ⁺ ions originating from monomer (LiF), dimer (Li₂F₂), and trimer (Li₃F₃) molecular precursors were detected in the temperature range 970–1070 K. The dimer-to-monomer and trimer-to-monomer flux ratios were found to increase progressively with increasing temperature and also in comparison with those measured under equilibrium of crystalline LiF with its saturated vapor. The temperature dependence of the ion current ratio I(Li₂F⁺)/I(Li⁺) measured over the interval 916–1087 K was shown to pass reproducibly through a minimum at about 975 K. The enhancement of the rate of association reactions at LiF crystal surfaces is discussed in light of the terrace-ledge-kink model of vaporization and surface charge concept.     

Collisional Population Trapping and Optical Deexcitation of Ytterbium Ions in a Radiofrequency Trap

Abstract

We describe and discuss experiments related to the phenomenon of population trapping of ytterbium ions in the extremely long-lived 4f¹³ 6s^{2 2}F_7/2 level. Ion clouds are confined in a radiofrequency trap in the presence of helium buffer gas. The experimental set-up permits electronic ion detection, the observation of resonance fluorescence, and optical excitation at alternating wavelengths to excite either the ²S_1/2–²P_1/2 resonance transition, or transitions of similar wavelength which provide optical deexcitation of ions from the ²F_7/2 level to the ground state. The observed dependence of the population trapping rates on helium pressure is attributed to the effect of fine structure mixing collisions. The transitions which deexcite ions from the ²F_7/2 state show Lorentzian lineshapes with widths of 6–10 GHz and resonance wavelengths which are in significant disagreement with tabulated level positions.     

Stabilizing Perovskite Light-Emitting Diodes by Incorporation of Binary Alkali Cations

The poor stability of perovskite light-emitting diodes (PeLEDs) is a key bottleneck that hinders commercialization of this technology. Here, the degradation process of formamidinium lead iodide (FAPbI₃)-based PeLEDs is carefully investigated and the device stability is improved through binary-alkalication incorporation. Using time-of-flight secondary-ion mass spectrometry, it is found that the degradation of FAPbI₃-based PeLEDs during operation is directly associated with ion migration, and incorporation of binary alkali cations, i.e., Cs⁺ and Rb⁺, in FAPbI₃ can suppress ion migration and significantly enhance the lifetime of PeLEDs. Combining experimental and theoretical approaches, it is further revealed that Cs⁺ and Rb⁺ ions stabilize the perovskite films by locating at different lattice positions, with Cs⁺ ions present relatively uniformly throughout the bulk perovskite, while Rb⁺ ions are found preferentially on the surface and grain boundaries. Further chemical bonding analysis shows that both Cs⁺ and Rb⁺ ions raise the net atomic charge of the surrounding I anions, leading to stronger Coulomb interactions between the cations and the inorganic framework. As a result, the Cs⁺–Rb⁺-incorporated PeLEDs exhibit an external quantum efficiency of 15.84%, the highest among alkali cation-incorporated FAPbI₃ devices. More importantly, the PeLEDs show significantly enhanced operation stability, achieving a half-lifetime over 3600 min.     

CF3 etching silicon surface: A molecular dynamics study

In this study, a molecular dynamics simulation method has been employed to investigate CF₃⁺ ions bombarding Si surface with the energy of 100, 200, 300 and 400 eV and an incident angle of 45° with respect to the normal. The simulation results show that when CF₃⁺ ions approach the Si surface they are broken up into small fragments. Some fragments deposit on the surface to form a “fluorocarbosilyl” layer. The erosion of Si is dominated by formation of SiF₃ followed by SiF₂ species and in minority species SiF.     

Influence of repeller potential on ion-molecule reactions in methane and carbon tetrafluoride mixtures

Investigations of ion-molecule reactions were performed for methane-carbon tetrafluoride mixtures of different compositions. Concentration of methane in these mixtures ranged from 10% to 90% (at 10% increment) and total mixture pressure was fixed at 13.3 Pa. Measurements were made using a quadrupole mass spectrometer with a high-pressure ion source. Primary ions CH₄⁺, F⁺, CF⁺ and CF₃⁺ were produced by electrons with energy of 300 eV. Secondary ions CH₅⁺, C₂H₃⁺, C₂H₄⁺, C₂H₅⁺, C₂H₇⁺ and CF₃⁺ were observed as the result of ion-molecule reactions.The influence of repeller potential on ion-molecule reactions efficiency was examined.     

Molar extinction coefficients of the cupric ion in silicate glasses

The absorption characteristics of Cu²⁺ ions in binary alkali silicate and ternary silicate glasses were investigated. The molar extinction coefficients of the Cu²⁺ ion were determined in a series of binary alkali silicate and a ternary soda-lime-silica glasses for the actual intensities of the observed bands at their wavelength maxima. The absorption maxima due to Cu²⁺ ions were found to shift towards the longer wavelengths with increasing ionic radii of the alkali ions, in the present series of glasses. The base glass compositions were selected as30R₂O·70SiO₂ and 20Na₂O·10CaO·70SiO₂ where R⁺=Li⁺, Na⁺ and K⁺ ions. The results obtained are discussed in the light of a ligand field approach.     

The effect of Li intercalation on different sized TiO2 nanoparticles and the performance of dye-sensitized solar cells

The effect of Li⁺ insertion into different sized TiO₂ nanoparticles and their influences on the photoconversion efficiency of dye-sensitized solar cells (DSSC) were investigated. TiO₂ nanoparticles with different particle sizes (22 nm, 14 nm and 6 nm) doped with Li⁺ were employed to form thin film electrodes and their properties were characterized by X-ray diffraction (XRD) and electrochemical impedance spectroscopy analysis. XRD evidenced the presence of anatase as the main phase. From the XRD analysis, it was observed that the Li⁺ ions could be inserted into both the surface and bulk of the TiO₂ nanoparticles. In the larger particle size, the Li⁺ ions are inserted into the bulk anatase where as Li⁺ ions bounded on the TiO₂ surface for the smaller crystallite size. The photovoltaic properties were measured by a current-voltage meter under AM1.5 simulated light radiation. It exhibited that the overall photoconversion efficiency of DSSC was decreased in the larger particles while it was enhanced in the smaller nanoparticles when Li⁺ was doped into the TiO₂ nanoparticles. A nearly 40% decrease in the efficiency (η) of DSSC was observed upon intercalation of Li⁺ ions into 22 nm sized TiO₂ nanoparticles (P25). The 14 nm sized TiO₂ nanoparticles (P90) showed slightly less efficiency (η) upon Li⁺ doping than that of the undoped sample. However, the smallest sized TiO₂ nanoparticles (6 nm) showed higher efficiency than that of the undoped one. This phenomenon is explained based on electron trapping and charge recombination due to lithium doping.     

The role of sputter etching and annealing processes on the formation of β-FeSi2 thin films

For formation of β-FeSi₂ using ion beam sputter deposition (IBSD) method, sputter etching (SE) followed by thermal annealing is effective substrate treatment to obtain highly (100)-oriented β-FeSi₂ on Si(100). However, the best condition of these treatments are not yet known. In this work, the effect of SE together with annealing process on the orientation of the film is investigated. Prior to the deposition of Fe, the substrate is irradiated by Ne⁺ ions with various energy and fluence followed by thermal annealing at 1073 K for 60 min. The overall results show the most suitable SE condition using Ne⁺ ion on IBSD method is the energy of 1 keV with the fluence of 3.0×10¹⁹ ions /m².