Single Positive Ions Research Articles

Analysis of the plasma meniscus in a hydrogen electronegative plasma

The emitting surface of an ion beam (plasma meniscus) in the vicinity of the extraction aperture is theoretically investigated. In the present study, the electrons, H+ ions and volume produced H− ions are contained in the electronegative plasma. By solving the one-dimensional Poisson equation, an analytical formula is obtained from the balance between the current reaching a wall and the space charge limited current of negatively charged particles. The analytical formula indicates that the distance, d eff, between the plasma meniscus and the extraction grid includes the ratio of masses of the negative ions and electrons, which is different from that for a plasma containing electrons and single positive ions, and depends on the ratio of the negative ion density to the electron density, α. With increase in the value of α, the distance d eff becomes shorter, and thus the penetration of the electric field for negative ion extraction into the source plasma becomes smaller. This tendency is confirmed by using a three-dimensional particle-in-cell simulation from the results of the contour map of the electrostatic potential near the plasma grid and the location of the plasma meniscus. The reasons why the distance d eff becomes shorter with increase in the value of α are considered to be the larger space charge effect of the negative ions compared with that of the electrons and the decrease in the plasma potential.

Solitary waves in a dusty adiabatic electronegative plasma

AbstractThe dust ion-acoustic solitary waves (SWs) in an unmagnetized dusty adiabatic electronegative plasma containing inertialess adiabatic electrons, inertial single charged adiabatic positive and negative ions, and stationary arbitrarily (positively and negatively) charged dust have been theoretically studied. The reductive perturbation method has been employed to derive the Korteweg-de Vries equation which admits an SW solution. The combined effects of the adiabaticity of plasma particles, inertia of positive or negative ions, and presence of positively or negatively charged dust, which are found to significantly modify the basic features of small but finite-amplitude dust-ion-acoustic SWs, are explicitly examined. The implications of our results in space and laboratory dusty electronegative plasmas are briefly discussed.

Plasma diagnostic of ion and plasma PVD processes

The aim of this work was to compare different plasma PVD processes in respect to their plasma properties in dependence on the process parameters. The processes under investigation were reactive d.c. pulsed magnetron sputtering magnetically assisted, arc source ion plating, reactive multi plasma supported d.c. magnetron sputtering and reactive low voltage ion plating. The experiments were carried out in specially designed plants under variable vacuum and plasma conditions. The plasma properties, like ion mass, ion energy distribution, ion and electron densities of the different processes were investigated by mass spectroscopy with additional energy distribution analysis (PPM421-Inficon) and a Langmuir probe system (Smart Probe-Scientific Systems). The magnetically forced and medium frequency pulsed biased d.c. magnetron sputter deposition variants, showed a relatively large amount of single and double charged positive ions with kinetic energies up to 55 and 95 eV, as consequence of the applied modifications. The arc source process, even when performed at high pressures of approximately 10 −1 mbar, showed a remarkable amount of ions with energies up to 75 eV.

Hydrogen Atom or Proton Transfer in Neutral and Single Positive Ions of Salicylic Acid and Related Compounds

The nature of the process “hydrogen atom” or “proton” transfer reaction in neutral and single positive ions of salicylic acid, o-hydroxybenzaldehyde, and salicylaldimine has been studied using the B3LYP density functional method. Single-point calculations at the CCSD(T) level have also been performed. For neutral systems, the reaction corresponds to a proton transfer process coupled with an important electronic transfer, which leads to a compound with nonzwitterionic character. A similar behavior is observed for ionized π radical cations. In ionized σ states, however, the process is that of a hydrogen transfer. In all cases, π ionization strengthens the initial H-bond and favors the reaction. For some of the systems the proton transfer occurs spontaneously.

Quantitative secondary ion mass spectrometry analysis of impurities in GaN and Al xGa 1− xN films using molecular ions MCs + and MCs 2+

In SIMS analysis of GaN and Al x Ga 1− x N films, MCs + and MCs 2 + ion detection (M is the element to be analyzed) was investigated under Cs + bombardment. The MCs 2 + ions have a larger ion yield than the MCs + ions when M is one of electronegative ions. Application of these molecular ions to SIMS analysis has made it possible to detect electropositive and electronegative elements in a single analysis run. Further, these molecular ions are useful to minimize the matrix effect in Al x Ga 1− x N films, with x ranging from 0 to 0.17. The formation mechanism of the MCs + and MCs 2 + ions can also be postulated by comparing the useful yield of these molecular ions and that of single (negative and/or positive) ions. These molecular ions are assumed to be produced mainly by recombination processes in which sputtered neutral species (M and/or MCs) combine with Cs + ions.

Nonlinear fluid equations for low-frequency phenomena in partially ionized dusty magnetoplasmas

A set of five coupled field equations governing the nonlinear dynamics of low-frequency (in comparison with the ion gyrofrequency) phenomena in partially ionized collisional dusty magnetoplasmas has been derived. These are the continuity and the momentum transfer equations for the neutral and dust fluids as well as an appropriate Ampère's law for partially ionized dusty gases. The presented set of nonlinear magnetohydrodynamic (MHD) equations should be useful for a self-consistent description of linear and nonlinear wave and instability phenomena in dusty magnetoplasmas whose constituents are negatively charged dust grains, single charged positive ions, as well as neutral atoms.

Pulsed Laser Ablation as a Source of Energetic Reactants: Synthesis of Superconducting High to Thin Films

ABSTRACTPulsed KrF (248 nm) excimer laser ablation of targets can provide a source of atomic particles with energies in the range of 40 – 850 eV with beam-like characteristics. Optical intensities above about 109 W/cm2 lead mainly to single and multiply charged ground state positive atomic ions plus electrons with a pronounced angular energy dependence, the highest energies peaked in the direction normal to the target. A wide mass range of metallic and non-metallic targets were studied to determine the effects of atomic weights and other physical properties on the distribution of ion energies. Analysis of the energetics indicates that ablation mechanisms are non-equilibrium in nature. We have explored the use of very energetic (200–400 eV) Y, Ba and Cu ions to form very thin YBa2Cu3O7-x superconducting films grown on flat gold surfaces. SQUID magnetometry is used to study the temperature and field dependence of magnetization in these materials.

Detection of single atoms by resonance ionization spectroscopy

Rutherford’s idea for counting individual atoms can, in principle, be implemented for nearly any type of atom, whether stable or radioactive, by using methods of resonance ionization. With the technique of resonance ionization spectroscopy (ris), a laser is tuned to a wavelength that will promote a valence electron in a Z-selected atom to an excited level. Additional resonance or non-resonance photoabsorption steps are used to achieve nearly 100% ionization efficiencies. Hence, the ris process can be saturated for the Z-selected atoms: and because detectors are available for counting either single electrons or positive ions, one-atom detection is possible. Some examples of one-atom detection are given, including that of the noble gases, to show complementarity with accelerator mass spectrometry ams methods. For instance, the detection of 81 Kr by using ris has interesting applications for solar-neutrino research, ice-cap dating, and groundwater dating.

Energy distribution of secondary ions emitted from pure elements and amorphous alloys

The energy distribution of mono-atomic single charged positive ions emitted from pure metals and amorphous alloys of Fe 80B 17X 3 type was measured. The effect of matrix and bombarding ion was studied. Amorphous alloys are suitable model materials for studies of multicomponent systems being homogeneous without crystal effects. The effect of Ar + and O + 2 primary ions were compared in the presence of oxygen flooding. The sensitive comparison of energy distribution curves was made by functions M(E) and X(E) defined here. Both the nature of the ion and the emitting surroundings determine the energy distribution, for some elements, however, the nature of the emitted element is dominant. The present results also contribute to the development of quantification of secondary ion mass spectrometry.

New Method for the Measurement of Electron Yield from Ion Bombardment

A new technique is described for measuring directly the statistical distribution of electrons produced by single positive ions striking a surface. This method complements present techniques and permits the determination of the electron emission coefficient γ due to ion impact on semiconductors or insulators. Previous measurements of this type have been difficult or impossible owing to charge buildup on the target. In this new experimental approach, a beam of mass- and energy-resolved positive ions is focused on the surface being studied. Electrons ejected by individual ions are then accelerated through from 10 to 30 keV and focused into a silicon surface barrier detector. The magnitude of the detector output pulse produced corresponds to the number of electrons striking the detector simultaneously thus giving the electron yield. Preliminary results for the secondary electron yield coefficient γ are reported for aluminum oxide and titanium oxide surfaces bombarded by cesium, barium, lithium, and strontium ions having incident kinetic energies in the range of 10–40 keV.

The Detection of Single Atoms and Molecules†

ABSTRACT A technique based on the field emitting properties of a heavily contaminated tungsten point cathode is used to detect the existence of single positive ions. Those are formed by electron impact in the residual gas atmosphere in which the field currents are produced. The emitter thus acts as collector for the single ions, each of which, on impact with it, produces abrupt variations of some (10-30)% in the value of the emission current; the ensuing disturbance on the surface lasts for times of the order of 1 msec. In comparison, the ‘ shot ’ and ‘ flicker ’ effects are negligible. A schedule of thermal annealing is described by which the point can be ‘ conditioned ’. to give reproducible results. The field characteristic differs markedly from that for clean points in that it consists of two lines of very different slopes, similar in fact to that given by gas covered semiconducting points; it is suggested that the electrons come from the conduction band of an ‘ n ’ type semiconductor at ’the tungsten...

The Detection of Single Positive Ions, Electrons and Photons by a Secondary Electron Multiplier

A secondary electron multiplier tube has been developed and used successfully for counting single positive ions, electrons and photons. This tube has twelve electrodes covered with a thin layer of beryllium. Tests have shown that with 330 volts per stage this tube will multiply the primary current by a factor of ${10}^{5}$. The use of guard ring insulation and electrostatic shielding for the final collecting electrode has reduced the background current to an extremely low value. The last electrode was connected to the grid of the first tube in a linear amplifier. In order to count single positive ions or electrons the tube was waxed to the end of a simple magnetic spectrograph. Ions having energies from 50 to 20,000 electron volts and masses from one to 32 were detected. By increasing the gain of the thermionic amplifier electrons could be counted. With still more gain single photons were counted. The multiplier tube has an extremely low background counting rate. Because a pressure of ${10}^{\ensuremath{-}6}$ mm of Hg is maintained in the counter, it can be connected directly to the vacuum system through which the electrons or positive ions are accelerated. The absence of a thin window between the counter and the vacuum system should be a great advantage in experiments dealing with low energy positive ions or electrons.