Anisotropic angular distribution of sputtered atoms

The sputtering yield angular distributions have been calculated on the basis of the ion energy dependence of total sputtering yields for Ni and Mo targets bombarded by low-energy Hg⁺ ions. The calculated curves show excellent agreement with the corresponding Wehner's experimental results of sputtering yield angular distributions. This fact clearly demonstrates the intrinsic relation between the ion energy dependence of total sputtering yields and the sputtering yield angular distribution. This intrinsic relation had been ignored in Yamamura's papers [Yamamura, Y. (1982). Theory of sputtering and comparison to experimental data, Nucl. Instr. and Meth., 194, 515–522; Yamamura, Y. (1981). Contribution of anisotropic velocity distribution of recoil atoms to sputtering yields and angular distributions of sputtered atoms, Rad. Eff., 55, 49–55.] due to some obvious mistakes.     

Secondary ion emission. Part II: Testing of the thermodynamic non-equilibrium model of surface ionization

Abstract

Using experimental values of the relative yields of positive and negative secondary ions for 31 pure elements and 9 compounds bombarded with 13.5 keV Cs⁺ ions temperatures of sputtering centers, T _sc , have been determined. Similarly, the degrees of ionization of sputtered atoms, α₊ and α_?, have been determined from M ₊ and M _? yields and as assumed secondary ion transmission efficiency of 1%. Two non-equilibrium equations of surface ionization (NESI) were used to determine T _sc . The calculated temperatures, as well as the degrees of ionization, have periodic dependence on the atomic number of the target, Z ₂. Most of the calculated temperatures are lower than the boiling temperatures, T _b , of bombarded targets and for refractory elements T _sc values are even lower than the melting temperatures, T _m . However, T _sc for most of the amphoteric and non-metallic elements are higher than T _b but lower than their critical temperatures, T _c .     

Stability of subatomic carbon films on metal surfaces against low-energy gas ion bombardment

The earlier developed original experimental technique for measuring and analyzing the parameters of low-frequency fluctuations of the field-emission current in metal film systems is used to measure the sputtering yield Y _f of carbon films (with a coverage Θ ranging from 1 to 4) applied on Fe, Nb, Ta, and U substrates. The value of Y _f is calculated by an expression derived within a theoretical model developed. The sputtering ratios were measured for the case when the carbon films are sputtered by H⁺ and He⁺ ions with an energy E _i between 2 and 10 keV. With Θ fixed, the energy dependences of Y _f are obtained for each of the ions. In addition, for each of the ions, the Θ dependences of Y _f are found for several values of E _i. In all the cases, the measured values of Y _f far exceed those for pure carbon. With another original technique that combines field-ion microscopy (FIM) and precise measurement of current and/or luminous properties of local regions in FIM images, the energy thresholds E _th of sputtering carbon films applied on the metal surfaces are found. The energy distributions of Y _f in the near-threshold energy range for various Θ are obtained.     

Magnetic properties of erbium iron garnet in high magnetic fields up to 150kOe

The magnetic properties of single crystals of erbium iron garnet (ErIG) were studied in applied fields up to 150kOe between 1.4 and 300K. At low temperature, the macroscopic easy direction of the bulk magnetization is [100]; below the compensation temperature (80±2K), the magnetization presents non-linear field evolution. On the assumption of an isolated ground doublet, the anisotropy constantsK _i (i=1,2) of ErIG are given byK _i (Er)+K _i (YIG); theK _i are calculated as a function of theG andg tensor components. It is worthwhile noting that theK _i (Er) are strongly temperature dependent; so at low temperature the anisotropy of the garnet is determined by the rare earth ions, while in the 50 K regionK ₁(Er) becomes comparable toK ₁(YIG) with the opposite sign which results in a very weak anisotropy of the garnet. Above 50 K,K ₁(YIG) is predominant and the Fe³⁺ ions determine the garnet anisotropy.     

Rotational Analysis of the 1–4 Band of the B 2Σ+–X 2Σ+ System of 14C16O+

ABSTRACT

High-resolution emission spectrum of the 1–4 band of the B ²Σ⁺–X ²Σ⁺ transition of ¹⁴C¹⁶O⁺ was observed for the first time by conventional emission spectroscopy. The band spectrum was excited in a water-cooled Geissler lamp filled with commercial gaseous carbon monoxide enriched in about 80% of the radiocarbon ¹⁴C. A rotational analysis has been carried out and obtained molecular constants have been merged with previously published data for the B ²Σ⁺–A ²Π_i and A ²Π_i–X ²Σ⁺ transitions. The principal equilibrium constants for the ground X ²Σ⁺ state obtained from this work are ω_e = 2121.7726(98), ω_e x _e = 13.9055(27), B _e = 1.815290(30), α_e = 1.6594(33) × 10^?2, and γ_e = ? 0.377(73) × 10^?4 cm^?1. Also, presently known experimental equilibrium molecular constants of the X ²Σ⁺ states of the CO⁺ isotopic molecules are summarized and isotopic dependence of the B _e and ω _e constants is discussed.     

Reactive scattering of alkali dimers: chemi-ionization

Measurements of total cross sections Q_i for chemi-ionization in scattering of a K₂ dimer beam by a range of halogen containing molecules, at translational energies E ～ 7–11 kcal mol^-1, are reported. Substantial cross sections, Q_i ～ 2–10 Ų are exhibited by the halogen molecules Br₂, ICl, IBr, I₂. Distinctly lower values Q_i ～ 0·1–0.2 Ų are exhibited by BrCN and the mercuric and stannic halides, HgX₂, SnX₄. The results show a close correlation with the chemi-ionization exoergicities, particularly for formation of a K⁺,X^- ion pair. These chemi-ionization data and results from previous reactive scattering studies are compared, in order to estimate relative reaction yields for different reaction paths. The reaction dynamics for K₂ with halogen molecules and cyanohalides are rationalized in terms of the electronic structure of the potential surface, where the orientation of the K₂ dimer plays a crucial role.     

Laser Desorption Mass Spectrometry of Some Organic Acids

Abstract

Positive and negative ion laser desorption (LD) mass spectra of organic acids are characterized by the emission of the quasimolecular ions (M+H)⁺ and (M-H)^?. Generation of (M+H)⁺ ions is interpreted as evidence for the occurence of high pressure proton transfer reactions in LD. Fragment ions can be rationalized by loss of stable neutral molecules from quasimolecular ions although decomposition may also be occuring prior to ionization. Features unique to LD, including the detection of pyrolysis products along with ions characteristic of the sample, are discussed in terms of the internal energy distribution in the irradiated microvolume. Negative ion mass spectra of acids are dominated by (M-H)^?, while positive ion spectra contain abundant fragment ions, underlining the utility of detecting negative ions for acidic compounds.     

Swift heavy ions-induced degradation on the electrical characteristics of silicon NPN power transistors

ABSTRACT

The pre- and post-irradiation effects on the DC electrical characteristics of 100?MeV Phosphorous (P⁷⁺) and 80?MeV Nitrogen (N⁶⁺) ion-irradiated NPN transistors were studied in the dose range from 600?krad (Si) to 100?Mrad (Si). The different electrical characteristics, such as Gummel characteristics, excess base current (ΔI_B?=?I_B-Post?–?I_B-Pre), current gain (h_FE), damage constant (K) and output characteristics, were measured in situ after ion irradiation. The considerable increase in the base current (I_B) at lower V_BE and slight decrease in the collector current (I_C) at higher V_BE were observed after ion irradiation. The C–V measurements revealed that the doping concentration (N_d) was found decreased, while the built-in potential (V_bi) increased after irradiation. The ion-irradiated results are compared with ⁶⁰Co gamma-irradiated results in the same dose range. The SRIM simulation was performed to understand the range of ions and energy loss in the transistor structure. The SRIM simulation showed that 100?MeV P⁷⁺ and 80?MeV N⁶⁺ ions can easily pass through the active region of transistors by creating ionization and displacement damages in the device structure. The irradiation results showed that ions induce more degradation in the electrical characteristics when compared to ⁶⁰Co gamma radiation at the same dose range.     

Sodium profiles in β″-alumina crystals: Modifications induced by argon bombardment

Abstract

Sodium depth profiles in implanted sodium β″-alumina single crystals have been measured by the nuclear resonance technique. A systematic investigation of the depth profile modifications as function of the implanted ion energy has been done using argon-ion (E = 50–600 keV) irradiation at fixed dose (Φ = 4 × 10¹⁶ions/cm²) and beam current (I = 1 μA/cm²). Argon doses were checked by Rutherford backscattering spectrometry. The changes in the sodium profiles are discussed in terms of transport equations which include three main processes: radiation enhanced transport, electric field assisted migration, and preferential surface sputtering of the alkali element. Special attention is devoted to the discussion of sputtering processes.     

Sputtering yields of PMMA films bombarded by keV C60 ions

A quartz crystal microbalance (QCM) has been used to determine total-mass sputtering yields of PMMA films by 1-16 keV C₆₀^+,2+ ion beams. Quantitative sputtering yields for PMMA are presented as mass loss per incident ion Y_m. Mass-lost rate QCM data show that a 13 keV C₆₀ cluster leads to emission equivalent to 800 PMMA molecules per ion. The power law obtained for the increase in sputtering yield with primary ion energy is in good agreement those predicted by “thermal spike” regime and MD models, when crater sizes are used to estimate sputtering.     

Temperature dependence of ion-induced auger electron emission from (111) silicon: I. Experiments

Abstract

Measurements of both secondary electron emission coefficient γ and SiL₂₃ Auger yield ρ_A obtained from (111) Si target bombarded by high fluence of noble gas ions were performed. For Si irradiated at room temperature at doses more than 10¹⁷ ions per cm², monotonous increasing variation of γ and ρ_A versus incidence angle i was observed. For Si irradiated at a temperature more than a critical value, γ(i) and ρ_A(i) curves exhibited, superimposed to monotonous variation, some minima when the ion beam penetrates the crystal along low index directions. In the range 20–650°C, the Auger yield temperature dependence showed a sharp variation around a critical value depending on the ion mass for a given incident energy. These results are linked to an amorphous-crystalline phase transition.     

Threshold energy electron impact excitation of carbon dioxide and carbon disulphide

The threshold energy electron impact excitation spectra of CO₂ and CS₂ have been studied using the sulfur hexafluoride scavenger technique. The main results are triplet state excitation and autoionisation of negative ions associated with resonant excited states of the molecules. This confirms previous data concerning diatomic molecules. Furthermore, transitions such as ¹Π_g?X¹Σ_g⁺ and ¹Π_u?X ¹Σ_g⁺ are only weakly induced by low energy electrons, while the corresponding triplet excitations are probably more easily produced. Structures at 5.6, 6.1 and 6.6 eV observed in CS₂ are due to negative ions and/or to ³Π_u, ³Π_g excitation.The autoionisation of CO₂^?(X²Π_u) proceeds also by ejection of a thermal energy electron and leads to highly excited vibrational levels (3–5 eV) of the ground electronic state of CO₂.     

Anomalous enhancement of negative sputtered ion emission by oxygen

Enhancement of negative sputtered ion yields by oxygen (either O⁺₂ bombardment or O₂ gas with Ar⁺ bombardment) is demonstrated for Si^?, As^?, P^?, Ga^?, Cu^? and Au^?, sputtered from a variety of matrices. Because oxygen also enhances positive ion yields of the same species, this effect cannot be simply explained on the basis of existing sputtered ion emission models. To rationalize these phenomena, a surface polarization model is developed which invokes localized electron emissive or electron retentive sites associated with differently oriented surface dipoles in the oxygenated surface. Such sites are considered to dominate the emission of negative and positive ions respectively. The model is shown to correctly predict that Au⁺ and Au^? ion yields are much more strongly enhanced by oxygen in dilute Au-Al alloys than in pure gold.     

Photophysics and Fluorimetric Titrations of Fluorescent Ion Indicators

A test based on time-resolved fluorescence experiments (Anal. Biochem. 245, 28–37, 1997) allows one to assess the interference of the excited-state association with the fluorimetric determination of the ground-state dissociation constant K _d of fluorescent ion:indicator complexes. If an inflection point occurs in the plot of the fluorescence signal vs – log[ion] in the ion concentration range where both decay times are invariant, this inflection point can be associated with the correct K _d. Here we apply this test to the fluorescent ion indicators SBFO (for Na⁺), Mag-fura-2 (for Mg²⁺), and APTRA-BTC (for Ca²⁺). In all three cases the decay times are invariant in the concentration ranges of the respective ions where the fluorescence titrations show unique inflection points, indicating that the fluorimetrically determined K _d values are the true K _d values.     

A new theoretical development of the limiting electric conductivity of ions in solution

The physical interpretation of the limiting equivalent conductivity of binary electrolytes in solution, Λ⁰ (=Σ_i?=?+,– λ⁰_i), has been a challenge for almost a century. Here, as a follow-up on a preliminary communication [D. Fraenkel, Mol. Phys. 115, 2944 (2017)], a quantitative theoretical treatment is offered and fully developed for the limiting ionic equivalent conductivity, λ⁰_i, based on assuming that around any singled-out ion i in solution, there is an electrostatic atmosphere that includes oriented solvent dipoles and the counterion as ‘charge density’. This leads to a simple mathematical expression for λ⁰_i as the result of the tandem operation of the dipole viscosity and dipole relaxation forces on the drifting ion. Contrary to literature teaching, λ⁰_i is found proportional to the effective ionic radius, r_i. An ‘electric ion-radius scale’ derived from experimental λ⁰_i’s for aqueous solutions, compares reasonably well with known ion-size scales. A newly defined solvent-specific dipole random-walk correction factor, ξ, is used for nonaqueous solvents as an adjustable parameter, to attain a parallel electric ion-size scale. The new theory provides overall a comprehensive view of the limiting ion mobility in solution, based on the ionic properties, solvent variables and universal constants.     

Study of the mechanism of the negative secondary ionic emission by selective superficial oxidation and adsorption

With the aid of a speed analyser mass spectrograph able to function in an ultra vacuum, it was shown in previous work by conducting a study of the speed of ejection of secondary ions O^? emitted under the impact of ions K⁺ by copper target, that under certain experimental conditions at least two different origins of this emission could be demonstrated. The hypothesis that we thus adopted was that the O^? ions having the greatest ejection speed could originate from the layer adsorbed on the surface, whereas the O^? ions having the weakest ejection speed could originate from the oxide. In order to confirm this hypothesis, we conducted the following experiments.We oxidized a copper target with a natural isotope ¹⁸₈O of oxygen. The spectrogram of the negative secondary emission involved then, in addition to the ions of the adsorbed layers (H^?, C^?, CH^?, ¹⁶₈O^?, ¹⁶₈O^?,...) the ion ¹⁶₈OH^?, which could only originate from a chemical compound formed at the time of the reaction of the oxidation.In a second series of experiments, we introduced molecular oxygen ¹⁸₈O₂ into the system, beginning with an initial pressure of 10^?8 torr up to a pressure of 10^?5 torr. The mass spectrogram again contained, over and above the aforementioned ions, the ion ¹⁸₈O^?. Here this ion could only originate from the adsorbed layers, since the experimental conditions favored the chemical and physical adsorptions.In addition, the energy analysis of the ions ¹⁸₈O^? obtained in the two instances allows us to say that the ion O^? originating from the rupture of the chemical junction Cu₂O has a weaker speed of ejection than the ion O^? originating from the adsorbed layer of gas. In conclusion, the experiment shows that the energy transfer from the incident particle to the ejected particle, by means of the atoms in the target, leads to a speed of ejection which is discrete but weak, in the case of the particle originating from the rupture of a chemical junction; whereas in the case of particles originating from the adsorbed layers of gas, the speeds of ejection are greater and have a widespread distribution.     

Transformations of radicals and ions in irradiated sodium sulfate doped with nitrate ions

The structure and properties of the paramagnetic centers formed by γ-irradiation at 77 K in sodium sulfate doped with nitrate ions have been investigated by the EPR method. The NO^2? ₃, NO₂ and SO^? ₄ radicals have been identified. The orientation of NO^2? ₃ relation to crystallographic axes is determined. In the 77-400 K temperature range the transformations of observable radicals have been studied. The mechanisms of their formation and thermal annealing have been discussed. The symmetry of nitrate ions in sodium sulfate was investigated by diffuse reflectance infrared Fourier transform spectroscopy. At the concentration of NO^? ₃ up to 5.5 × 10¹⁸ g^?1 the nitrate ion was supposed to have a planar or pyramidal configuration of the D_3h or C_3V symmetries. At the concentration of the dopant higher than 5.5 × 10¹⁸ g^?1 the nitrate ions with the C_2V symmetry were observed.     

A Study of the Phase Transition in the System [Ag1−x(Na)x]NO3 by Infrared Spectroscopy

A complete infrared study of the mixed crystal system of AgNO₃ and NaNO₃ is carried out in the region 400–4000 cm^?1. The study includes internal fundamental normal vibrations of the NO^?₃ ion in the ordered and disordered phases of AgNO₃ at different values of the sodium concentration, the I.R. spectra, spectral band shape intensities, and frequencies of the internal modes as functions of the sodium ion concentration. Special attention is paid to bending mode, combination mode, asymmetric stretching mode, and over-tone. The rotational energy barrier is determined at different concentrations of the sodium ions in the system.     

New Bands in the Shock Excited NbO Blue/Visible and Near Infrared Systems

Abstract

Band systems of the astrophysically important molecule Niobium Oxide (NbO) have been excited in helium-driven shock waves through argon containing powdered Nb₂O₅. Of the 25 bands of the Δv = +3, +2, +1,0, -1, -2 and -3 sequences of the C ⁴Σ^? – X ⁴Σ^? blue/visible system which were excited between 4220Å and 5608Å, 16 are newly reported here. The Δv = +3 and -3 sequences are completely new. 12 new bands were also excited in the near infrared region 7952Å - 8450Å.     

Sputtering of AlxGa1−x As semiconductor targets by Ar+ ions with energies of 2–14 keV

Investigations of the sputtering of Al_xGa_1−x As semiconductor solid solutions by Ar⁺ ions with energies of 2–14 keV are performed. The dependence of the sputtering yield on the energy and angle of incidence of the ions are determined and the character of the surface relief formed during the sputtering is investigated. A comparison with theory shows that the best agreement between theory and experiment is achieved when the Haff-Switkowski formula is used together with Yudin’s stopping cross section. It is shown that the surface binding energies obtained differ from the atomization energies by an amount approximately equal to the amorphization energy. Zh. Tekh. Fiz. 67, 113–117 (June 1997)