Showing papers on "Charged particle published in 1989"

Dusty plasmas in the solar system

Abstract: The processes that lead to charging of dust grains in a plasma are briefly reviewed. Whereas for single grains the results have been long known, the reduction of the average charge on a grain by 'Debye screening' has only recently been discovered. This reduction can be important in the Jovian ring and in the rings of Uranus. The emerging field of gravitoelectrodynamics which deals with the motion of charged grains in a planetary magnetosphere is then reviewed. Important mechanisms for distributing grains in radial distance are due to stochastic fluctuations of the grain charge and a systematic variation due to motion through plasma gradients. The electrostatic levitation model for the formation of spokes is discussed, and it is shown that the radial transport of dust contained in the spokes may be responsible for the rich radial structure in Saturn's rings. Finally, collective effects in dusty plasmas are discussed which affect various waves, such as density waves in planetary rings and low-frequency plasma waves. The possibility of charged grains forming a Coulomb lattice is briefly described.

Regular and chaotic charged particle motion in magnetotaillike field reversals: 1. Basic theory of trapped motion

Abstract: We give a systematic theoretical analysis of trapped nonadiabatic charged particle motion in two-dimensional taillike magnetic field reversals. Particle dynamics is shown to be controlled by the curvature parameter κ, i.e., the ratio κ² = Rmin/ρmax between the minimum radius of curvature of the magnetic field and the maximum Larmor radius in it for a particle of given energy. κ≫1 corresponds to the usual adiabatic case with the magnetic moment μ as a first-order invariant of motion. As κ decreases toward unity, the particle motion becomes stochastic due to deterministic chaos, caused by the overlapping of nonlinear resonances between the bounce- and the gyro-motion. We determine the threshold of deterministic chaos and derive the related pitch angle diffusion coefficient which describes statistically the particle behavior in the limit κ → 1. Such behavior, which for κ ≅ 1 becomes strongly chaotic, applies, e.g., to thermal electrons in Earth's magnetotail and makes its collisionless tearing mode instability possible. We also show that in sharply curved field reversals, i.e., for κ 1. Both types of trapped particle motion in sharply curved magnetic field reversals κ<1 are closely connected with fast oscillations perpendicular to the reversal plane. However, the trajectories are adiabatic only in the case that they permanently remain crossing the reversal plane. The adiabatic are of a ring type, i.e., they resemble rings in phase space and also in real physical space. For ring-type orbits the action integral over the fast oscillations is an adiabatic invariant in the usual sense. On the other hand, the most common particle trajectories in a sharply curved field reversal with κ<1 are essentially of a cucumberlike quasi-adiabatic type. For quasi-adiabatic cucumberlike orbits the action integral over the fast oscillations is an adiabatic invariant only in a piecemeal way between successive traversals in the phase space of the fast motion of a separatrix between orbits which do and those, which do not cross the reversal plane. Due to the effect of separatrix traversals the slow motion shifts between different cucumber orbits with a conservation of the action integral on average but with its chaotic phase space diffusion even for very small perturbation parameters κ. The case κ<1 is applicable, e.g., to thermal ions and high-energy electrons in Earth's magnetotail. Our findings lead to a systematic interpretation of particle observations in Earth's magnetotail and of numerous numerical calculations, carried out in the past. They also explain rather well, e.g., the pitch angle diffusion of plasma sheet particles, the isotropization of the plasma sheet electron distribution immediately before a substorm and provide with the transition to chaos a mechanism for the onset of a large-scale tail instability and the explosion of isolated substorms. Further implications for magnetotail physics, such as acceleration processes and the influence of the particle escape from the field reversal will be discussed in a second related paper.

Spectral characteristics of plasma sheet ion and electron populations during undisturbed geomagnetic conditions

Abstract: The spectral characteristics of plasma-sheet ion and electron populations during periods of low geomagnetic activity were determined from the analysis of 127 one-hour average samples of central plasma sheet ions and electrons. Particle data from the ISEE-1 low-energy proton and electron differential energy analyzer and medium-energy particle instrument were combined to obtain differential energy spectra in the plasma sheet at geocentric radial distances above 12 earth radii. The relationships between the ion and electron spectral shapes and between the spectral shapes and the geomagnetic activity index were statistically investigated. It was found that the presence of interplanetary particle fluxes does not affect the plasma sheet particle spectral shape.

Cosmic-ray transport and acceleration. I - Derivation of the kinetic equation and application to cosmic rays in static cold media. II - Cosmic rays in moving cold media with application to diffusive shock wave acceleration

Abstract: The propagation of energetic charged particles in a zero electric field and an ordered uniform magnetic field (B0) in a cold background medium is investigated theoretically, with a focus on the case where Alfven waves propagating parallel or antiparallel to B0 are superposed. The derivations of the governing equations of a quasi-linear theory for pitch-angle and momentum diffusion and for its applications to cosmic-ray protons in a cold medium at rest or in nonrelativistic motion parallel to B0 are given in great detail; numerical predictions are presented in tables and graphs and discussed with reference to published observational data. 83 references.

Particle bombardment effects on thin‐film deposition: A review

Abstract: In many atomistic film deposition processes, concurrent energetic particle bombardment (ions, atoms, molecules, atom clusters) may occur inadvertently and uncontrollably or bombardment may be used to deliberately modify film properties. These energetic particles can arise from (i) the acceleration of charged particles, (ii) high‐energy neutrals from reflection from bombarded surfaces, or (iii) charge exchange processes. Particle bombardment effects that can affect film formation and growth include (a) modifying the substrate surface (cleaning, defect formation), (b) momentum transfer processes in the surface region (sputtering, desorption, recoil implantation, defect formation), (c) addition of heat to the surface region, and (d) formation of secondary elelctrons that can affect chemical reactions. These in turn affect film properties such as adhesion, residual film stress, film morphology, density, grain size and orientation, surface coverage, pinhole density, and surface area. The understanding of these effects and how to use them advantageously is important to those utilizing processes where concurrent energetic particle bombardment is occurring or can be made to occur.

Complete phase diagram of a charged colloidal system: A synchro- tron x-ray scattering study.

Abstract: High-resolution, small-angle, synchrotron x-ray-scattering techniques were used to determine the phase diagram, structure factor, and pair distribution function for a charged colloidal suspension from 6% to 30% volume fraction. The expected correlated liquid and fcc and bcc solid phases were observed along with a glass phase at high concentration with structure similar to metallic glasses. At high volume fractions the finite core size leads to substantial deviation from predictions resulting from a screened Coulomb interaction.

Charged particle multiplicity distributions at 200 and 900 GeV c.m. energy

Abstract: Multiplicity distributions of charged particles produced in non single-diffractive collisions between protons and antiprotons at centre of mass energies of 200 and 900 GeV are presented. The data were recorded in the UA5 streamer chambers at the CERN Collider, which was operated in a pulsed mode between the two energies. A new method to correct for acceptance limitations and inefficiencies based on the principle of maximum entropy has been used. Multiplicity distributions in full phase space and in intervals of pseudorapidity are presented in tabular form. The violation of KNO scaling in full phase space found by the UA5 group at an energy of 546 GeV is confirmed also at 200 and 900 GeV. The shape of the 900 GeV distribution in full phase space is narrower in the peak region than at 200 GeV but exhibits a pronounced high multiplicity tail. The negative binomial distribution fits data at 200 GeV in all pseudorapidity intervals and in small intervals at 900 GeV. In large intervals at 900 GeV, however, the negative binomial distribution. Fits to the partially coherent laser distribution are also presented as well as comparisons with predictions of the Dual Parton, the Fritiof and the Pythia models.

Multifragmentation, fragment flow, and the nuclear equation of state

Abstract: The quantum molecular dynamic method is used to study multifragmentation and fragment flow and their dependence on in-medium cross sections, momentum dependent interactions, and the nuclear equation of state, for collisions of $^{197}\mathrm{Au}$${+}^{197}$Au and $^{93}\mathrm{Nb}$${+}^{93}$Nb in the bombarding energy regime from 100 to 800A MeV. Time and impact parameter dependence of the fragment formation and their implications for the conjectured liquid-vapor phase transition are investigated. We find that the inclusive fragment mass distribution is independent of the equation of state and exhibits a power-law behavior Y(A)\ensuremath{\sim}${A}^{\mathrm{\ensuremath{-}}\ensuremath{\tau}}$ with an exponent \ensuremath{\tau}\ensuremath{\approxeq}-2.3. True multifragmentation events are found in central collisions for energies ${E}_{\mathrm{lab}\mathrm{\ensuremath{\sim}}30--200}$ MeV/nucleon. The associated light fragment (d,t,\ensuremath{\alpha}) to proton ratios increase with the multiplicity of charged particles and decrease with energy, in agreement with recent experiments. The calculated absolute charged particle multiplicities, the multiplicities of intermediate mass (Ag4) fragments, and their respective rapidity distributions do compare well with recent 4\ensuremath{\pi} data, but are quite insensitive to the equation of state.On the other hand, these quantities depend sensitively on the nucleon-nucleon scattering cross section, and can be used to determine \ensuremath{\sigma} experimentally. The transverse momentum flow of the complex fragments increases with the stiffness of the equation of state. Reduced (in-medium) n-n scattering cross sections reduce the fragment flow. Momentum dependent interactions increase the fragment flow. It is shown that the measured fragment flow at 200A MeV can be reproduced in the model. We find that also the increase of the ${p}_{x}$/A values with the fragment mass is in agreement with experiments. The calculated fragment flow is too small as compared to the plastic ball data, if a soft equation of state with in-medium corrections (momentum dependent interactions plus reduced cross sections) is employed. An alternative, most intriguing resolution of the puzzle about the stiffness of the equation of state could be an increase of the scattering cross sections due to precritical scattering in the vicinity of a phase transition.

Argus: A universal detector at DORIS II

Abstract: The detector ARGUS has been designed as a universal tool to investigate final states from e + e − annihilation processes in the energy range of the ϒ resonances. ARGUS started operation in October 1982 and has since successfully taken data at the ϒ(1S), ϒ(2S) and ϒ(4S) energies, and in the nearby continuum. The detector combines excellent charged particle identification and good photon energy resolution over more than 90% of the full solid angle. A particle originating from the interaction vertex and leaving the beam tube traverses the following components: the vertex drift chamber, the main drift chamber which determines its momentum and specific ionization, the time-of-flight system through which its velocity is determined, and the electromagnetic calorimeter. Muons pass through the magnet coils and the flux return yoke and finally hit the muon chamber system which surrounds the detector. The momentum resolution of ARGUS is σ (p T ) P T = (0.01 2 + (0.009p T [ GeV /c]) 2 ) 1 2 , the photon energy resolution in the barrel shower counters is σ (E) E = ( 0.072 2 +0.065 2 E[ GeV ] ) 1 2 . Combining the information from all p devices, more than 80% of all charged hadrons can be recognized unambiguously. The electron-hadron and muon-hadron rejection rates are 1:200 and 1:50 respectively.

Radiolytic production and properties of ultrasmall CdS particles

Abstract: The radiolytic production of CdS particles from solutions containing cadmium ions and a thiol (3-mercapto-1,2-propanediol, RSH) is described The production of the colloids is initiated by the reaction of solvated electron with the thiol to release HS{sup {minus}} ions The polynuclear complexes of cadmium with the thiolate form of RSH act as moderators to the growth of the particles and allow reproducible production of practically any predetermined size particles The complexes at the surface of the particles also stabilize the particles for long periods of time The particles are strongly fluorescent from size of ca 8 {angstrom} in radius Excess electrons in these particles lead to bleaching of the exciton band due to Coulomb screening effects At higher doses, formation of cadmium atoms leads to increased absorption in the visible range

Atomic collisions : electron and photon projectiles

Abstract: Fundamental concepts background information from the kinetic theory of gases collision theory: elastic scattering of electrons by neural atoms and molecules excitation and de-excitation of neutrals by electron impact ionization of neutrals by electron impact collisions of electrons with charged particles photon processes. Appendices: the distinction between a plasma and an ordinary ionized gas general references and sources of data.

Multiple-ionization collision dynamics

Abstract: The 1.4-MeV/u U/sup 32 +/+Ne collision system is studied in detail in order to elucidate the dynamics of multiple ionization in energetic, heavy-ion--atom collisions. Differential cross sections versus recoil-ion charge state, calculated by the /ital n/-body classical-trajectory Monte Carlo method, are presented for the theta and /ital cphi/ angle dependences of the projectile, recoil ion, and ejected electrons. The calculations show a high degree of ejected-electron asymmetry towards the projectile side of the target nucleus which strongly effects the transverse-momentum balance between the heavy particles. Experimental and calculated cross sections differential in the recoil-ion charge state and transverse momentum are found to differ by orders of magnitude from those for the projectile, providing evidence for the importance of explicitly considering the ejected electrons' momenta in the determination of the heavy-particle (both the projectile and the recoil-ion) angular differential cross sections. Polarization of the target electrons and screening of the recoil ion by the ejected electrons lead to /similar to/10/sup /minus/6/-rad negative-angle deflections of the projectile for recoil-ion charge states up to 4+. The angular scattering of the recoil ion departs significantly from that predicted for a two-body collision, and is found to be nearly isotropic for low recoil-ion charge statesmore » and peaked to angles theta/gt/90/degree/ for high recoil-ion charge states. A stopping-power calculation for this system is in good agreement with the experimental value. Stopping powers differential in impact parameter and for energy deposition to delta electrons and multiple ionization are given to further describe the projectile energy loss.« less

Device for accelerating and storing charged particles

Abstract: A device for accelerating and storing charged particles of the present invention comprises a vacuum duct which has two opposite linear portions and two opposite curved portions respectively connected to the linear portions and which functions to maintain the orbit of revolution of the charged particles in a vacuum; an accelerating device for accelerating charged particles which is disposed on the orbit of the charged particles; a pair of bending magnets which are respectively disposed on the curved portions of the vacuum duct; and a pair of quadrupole electromagnets which are respectively disposed on the linear portions of the vacuum duct and at least one of which is disposed at a position at a given distance from the center of the corresponding linear portion.

Post-collision interaction in atomic processes

Abstract: The review examines the interaction of several charged particles in the final state of processes in the case when the reaction proceeds in two stages through an intermediate resonance. In an inelastic collision of arbitrary atomic particles X and Y a particle D is formed in a quasistationary state along with particle A: X + Y → A + D. As a result of the breakup D → B + C charged particles A, B, and C are formed in the final state. The Coulomb interaction of these particles (the post-collision interaction—PCI) exerts a strong influence on the cross section for the process. Reactions in which the effects of PCI are manifested are the excitation of atomic autoionized states by ions and electrons and the ionization of inner shells of atoms by collisions with ions, electrons or photons followed by Auger decay. Under the influence of PCI the spectra of the products of these reactions are distorted: the lines in the autoionization spectrum are broadened, shifted, and become asymmetric. A survey is given of the available theoretical concepts concerning PCI and of the accumulated experimental data providing evidence of its manifestation. The kinematic region in which the problem has a parametrically exact analytic solution is investigated thoroughly. Post-collision interaction in more complex processes in the final state of which four charged particles are involved is also examined. Experiments are discussed that make it possible to observe new manifestations of PCI. Various interference effects in PCI are examined.

Hot Plasma and Energetic Particles in Neptune's Magnetosphere

Abstract: Voyager 2's low energy charged particle instrument employed an array of solid-state detectors in various configurations to measure energetic electrons and ions within the Neptune magnetosphere in several energy channels. Various features of the intensity, spectral, and anisotropic data obtained suggest that the Triton satellite exerts an important controlling influence over the outer regions of the Neptunian magnetosphere. Composition measurements have indicated the presence of H, H2, and He-4 at 1300:1:0.1 relative abundances, respectively, suggesting a Neptunian ionospheric source for the trapped particle population.

Massless Point Particle With Rigidity

Abstract: The model of relativistic particle with rigidity whose action A=−α∫ kds depends on the curvature of particle world trajectory k, is studied. The classical motion of the particle is shown to go along a helical line at superrelativistic velocity and its translational motion along the momentum direction—at the velocity of light (c). After quantization, the parameter a becomes integer, α=n, n>0. The quantum states of the system are massless states of helicities λ=n and λ=−n in which the evolution of gauge-invariant coordinate occurs at velocity c.

Fully relativistic and quasirelativistic distorted-wave methods for calculating collision strengths for highly charged ions.

Abstract: A rapid fully relativistic distorted-wave method for calculating collision strengths for highly charged ions is described. A more rapid quasirelativistic approximation in which the average over j value -1 is used for the relativistic quantum number \ensuremath{\kappa} for the free electrons is also discussed. Very rapid, but accurate, procedures for obtaining results for a given class of transitions for a large portion of an isoelectronic sequence by using fits to Z after making detailed calculations for only a few values of Z are described. Results by the present methods are compared with more elaborate relativistic distorted-wave calculations by other workers, principally for neonlike and nickel-like ions, but also comparisons for He-like, Li-like, and Na-like ions are discussed. In addition, comparisons with a few experimental results for neonlike barium could be made. Generally very good agreement is obtained with all these data.

Kinetic energy distributions of ionic fragments produced by subpicosecond multiphoton ionization of N 2

Abstract: A study of the kinetic energy distributions of ionic fragments produced by subpicosecond irradiation of ${\mathrm{N}}_{2}$ with 248-nm radiation at an intensity of \ensuremath{\sim}${10}^{16}$ W/${\mathrm{cm}}^{2}$ is reported. These measurements, in comparison to other findings involving molecular excitation with charged particles and soft x rays, reveal several important features of the nonlinear coupling. Four ionic dissociative channels are identified from the data on the multiphoton process. They are ${\mathrm{N}}_{2}^{2+}$\ensuremath{\rightarrow}${\mathrm{N}}^{+}$+${\mathrm{N}}^{+}$, ${\mathrm{N}}_{2}^{2+}$\ensuremath{\rightarrow}N+${\mathrm{N}}^{2+}$, ${\mathrm{N}}_{2}^{3+}$\ensuremath{\rightarrow}${\mathrm{N}}^{+}$+${\mathrm{N}}^{2+}$, and ${\mathrm{N}}_{2}^{4+}$\ensuremath{\rightarrow}${\mathrm{N}}^{+}$+${\mathrm{N}}^{3+}$, three of which are charge asymmetric. The data for the energy distributions are found to be in approximate conformance with a simple picture involving ionizing transitions occurring within a time of a few cycles of the ultraviolet wave at an internuclear separation close to that of the ground-state (X $^{1}\mathrm{\ensuremath{\Sigma}}_{\mathit{g}}^{+}$) molecule. The implication follows that a strong nonlinear mode of coupling is present which causes a high rate of energy transfer. A simple hypothesis is presented which unites the ability for rapid energy transfer with the observed tendency to produce charge-asymmetric dissociation.

Industrial applications of pulse power and particle beams

Abstract: An overview is given of recent progress in the industrial applications of intense pulse power and associated particle beams, except for activities in inertial confinement fusion. In particular, several topics are discussed which relate to the applications in the R&D of materials, the excitation of short wavelength lasers, the generation of charged particle beams, and the development of plasma X-ray sources. I. Applications in material processing. If intense pulsed charged particle beams are directed onto materials, only their surfaces where the beam energy is deposited are quickly heated up to very high temperatures. Using the pulsed beam in this way, we might expect to apply them in R&D of materials. Several novel attempts have been made, e.g., on the preparation of thin films by use of a high-density high-temperature plasma, surface modification by surface heating, and ion-beam mixing of multi-layers by use of the focused electron or ion beams, and so on. Furthermore, experimental studies have been done on the surface modification by ion implantation and the evaluation of the damage due to the irradiation by ion beams. II. Applications in the excitation of short wavelength lasers. Activities in the excitation of high-power, short wavelength lasers by using electron beams or ion beams have increased considerably. III. Applications in the generation of charged particle beams, and the development of plasma X-ray source. With regard to new accelerator technologies, several attempts are underway on the application of the modified betatron or the development of a convergent electron beam accelerator with a plasma cathode.

Particle behavior in thermal plasmas

Abstract: In this overview, effects exerted on the motion and on heat and mass transfer of particulates injected into a thermal plasma are discussed, including an assessment of their relative importance in the context of thermal plasma processing of materials. Results of computer experiments are shown for particle sizes ranging from 5–50 μm, and for alumina and tungsten as sample materials. The results indicate that (i) the correction terms required for the viscous drag and the convective heat transfer due to strongly varying properties are the most important factors; (ii) noncontinuum effects are important for particle sizes <10 μm at atmospheric pressure, and these effects will be enhanced for smaller particles and/or reduced pressures; (iii) the Basset history term is negligible, unless relatively large and light particles are considered over long processing distances; (iv) thermophoresis is not crucial for the injection of particles into thermal plasmas; (v) turbulent dispersion becomes important for particle <10 μm in diameter; and (vi) vaporization describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas.

Charged multiplicity distributions and correlations in e + e − annihilation at PETRA energies

Abstract: We report on an analysis of the multiplicity distributions of charged particles produced ine+e− annihilation into hadrons at c.m. energies between 14 and 46.8 GeV. The charged multiplicity distributions of the whole event and single hemisphere deviate significantly from the Poisson distribution but follow approximate KNO scaling. We have also studied the multiplicity distributions in various rapidity intervals and found that they can be well described by the negative binomial distribution only for small central intervals. We have also analysed forward-backward multiplicity correlations for different energies and selections of particle charge and shown that they can be understood in terms of the fragmentation properties of the different quark flavours and by the production and decay of resonances. These correlations are well reproduced by the Lund string model.

Angular and polarization correlations in photoionization and radiative recombination

Abstract: The relativistic formulation is given for the angular distribution of the electrons produced in the photoionization by linearly polarized photons and the distribution of photons of a particular polarization produced in the inverse process of radiative recombination. The electrons are treated as moving in a self-consistent Hartree-Slater central potential. Results are given for the radiative recombination onto heliumlike nickel and neonlike barium for electrons in the energy range below 100 keV.

Effect of particle-induced displacements on the critical temperature of YBa2Cu3O7−δ

Abstract: The particle‐induced depression of the superconducting critical temperature Tc of YBa2Cu3O7−δ is shown to be directly proportional, over seven orders of magnitude, to the nonionizing energy deposited in the lattice by primary knock‐on atoms displaced by incident electrons, protons, and heavy ions. It is concluded that ΔTc is proportional only to the average number of defects produced and can therefore be predicted for any particle, energy, and fluence from a calculation of the nonionizing energy loss.

Dispersion properties of dusty plasmas

Abstract: The presence of charged dust particles in a plasma can change its dispersion properties. From the linear response of an equilibrium dusty plasma to the propagation of small perturbations, we find an average dielectric function є(ω, k) for the system in the case when the grain space distribution is random, and ensemble averages are taken over the random variables. For the case of high-frequency plasma waves, when e ≈ 1-ω2p/ω2 for the unperturbed case (cold plasma), we find that є becomes complex in the presence of the dust, leading to possible damping in a domain where Landau damping is usually negligible (ω » kVT).

Temperatures and excitation energies of hot nuclei in the reactions of 32S+Ag and 16O+Ag at 30 MeV/nucleon.

Abstract: For the reactions of 30 MeV/nucleon /sup 16/O and /sup 32/S with Ag, singles and coincidence measurements have been made for heavy residues, fragments (3less than or equal tozless than or equal to14), and light charged particles (zless than or equal to2). Mass-velocity correlations for the residues and fragment-residue coincidences indicate that increasing residue velocities do correspond to increasing excitation energy. Excitation energies as high as 90% of those which would result from complete fusion are reached. The spectra of light particles detected in coincidence with residue groups having different average velocities are analyzed with a moving source fit. When recoil effects are properly taken into account, excellent fits to the data are obtained. From the energy spectra and multiplicities of particles emitted from a fusion-like source the initial temperatures of the primary composite nuclei are determined. The results suggest that a plateau temperature near 6.5 MeV is reached above excitation energies of 3 MeV/nucleon. The temperatures are compared to those resulting from various model calculations.

Electrostatic ion‐cyclotron waves in a plasma with negative ions

Abstract: Electrostatic ion‐cyclotron (EIC) waves have been investigated in plasmas containing K+ positive ions, electrons, and SF−6 negative ions Two EIC wave modes are generally present, the K+ and SF−6 modes Their frequencies increase with increasing e, the percentage of negative ions, while the critical electron drift velocities for excitation of either mode decrease with increasing e The observations are discussed on the basis of available theories

Investigation of the performance of CsI(Tl) for charged particle identification by pulse-shape analysis

Abstract: We have studied the possibility of particle discrimination by pulse-shape analysis in CsI(Tl) scintillator. In order to investigate the limitations of that process we have analysed the time response of the scintillator for different ions at various energies. It is found that for energies lower than 200 MeV the identification is limited to charges Z < 4. This work also gives an understanding of these limitations.

Energetic particle bombardment of films during magnetron sputtering

Abstract: The flux of energetic, neutral particles bombarding the sample location during magnetron sputtering has been measured for several cathode–gas systems of general interest. The technique used a differentially pumped detector placed at the sample location, from 5 to 9 cm from the cathode. The detector screens out charged particles, and measures the secondary electrons produced by energetic neutral bombardment of a collector coated with a thin film of cathode material. The energetic neutral flux has been measured as a function of chamber pressure over a range of 5 to 30 mTorr, as a function of discharge power, and as a function of angle (up to 30°) for cathodes of Ti, Cu, Al, Mo, T, and W, in Ar, Ne, and Kr gases. The deposition rate of the film was measured by means of a quartz‐crystal oscillator adjacent to the detector. The magnitude of the arriving, energetic neutral flux increased with decreasing gas mass or increasing cathode mass, as expected. The energetic neutral flux was found to increase with decreasing pressure, but the ratio of energetic neutrals to condensing films atoms was found to decrease slightly with decreasing pressure. The arrival rate of energetic neutrals ranged from 2–4% of the depositing atom flux for Ar+→Cu to 12%–20% for Ar+→Ti to 27%–50% for Ne+→Ta. At high discharge powers, the relative arrival rates were higher, due to gas rarefaction in the near cathode region.