[en] The variation of secondary ion intensity with target current was found to be linear and parabolic for low and medium current densities, respectively. A semi-empirical formula was proposed earlier to correlate these two effects. With further increase of target current density, it is found that the secondary ion yield varies approximately as cube of the primary current density. This enhanced ion emission has been attributed to the chemical enhancement effect caused by reactive ion bombardment. The semi-empirical formula has accordingly been modified in order to take into consideration the above effect. The combinations Cd⁺-Mo, Cd⁺-Ti, Cd⁺-Al and Cd⁺-Cu have been studied and the results are explained in terms of the modified semi-empirical formula. Our observations have further been supported by ion yield versus bombarding energy studies for the combinations: Cd⁺-Mg, Cd⁺-Ti and Cd⁺-Zr. (orig.)

[en] A comparative study of the secondary ion signals (Iⁿ⁺, n=1,2) for the N₂⁺-Ge and N₂⁺-Si ion-target combinations under varying bombardment conditions has been undertaken. Only the former reveals anomalous Ge²⁺ emission I²⁺/I⁺(Ge>1) over a wide range of primary energy (E) and target current densities (J_p). A possible explanation has been sought. This work is actually a follow-up of our previous work carried out in search of anomalous emission of multicharged ions for various ion-target combinations. (author)

[en] The current density effects for fcc, bcc and hcp lattice structures like Al, Ta and Zr bombarded by 3-9 keV Cd⁺ ions have been studied. Our observations support the idea that ionization takes place in vacuum outside the target surface. A semi-empirical formula is also proposed which takes into effect both the low and high current density effects and the results of the measurements have been explained in terms of the formula. (orig.)

[en] In this paper we present the results of the variation of secondary Mg⁺ ion yield as a function of Cd⁺ ion current, focussed on the Mg target, at different fixed values of bombarding ion energies. We then try to explain qualitatively the phenomena observed and formulate underlying mechanism. (orig./RK)

[en] Secondary emission of doubly-charged positive ions from 3-15keV Cd⁺ ion-bombarded polycrystalline Nb and V samples at target current densities (J_p) in the range 0-1.4 mA cm^-2 has been studied in detail. For each target the ratio of doubly-charged to singly-charged ion currents (I_s⁺⁺/I_s⁺) has been found to be 0.01 at low beam current densities and does not vary appreciably with primary ion energy (E). However, with increase in the primary ion current (I_p), there is a rapid increase in the value of I_s⁺⁺ as compared to I_s⁺ such that at J_p∼15μA cm^-2, the ratio I_s⁺⁺/I_s⁺ increases by 10 to 300 times depending upon the target and bombarding conditions. The values of J_p at which maximum enhancement of I_s⁺⁺ is observed often corresponds to the saturation region in the current density variation curve, observed in case of singly-charged ion emission. This region possibly corresponds to the formation of an intermetallic compound layer of a definite stochiometric composition due to the action of reactive Cd⁺ ions at the metallic target surface under energetic ion bombardment. By monitoring the doubly-charged ion intensity, it has become possible, to some extent, to characterize the layer. Reactive Cd⁺ ion bombardment of metal (M) surfaces at high beam current densities leads to the formation of a MCd₂-like structure and consequently, doubly-charged secondary ion emission occurs via breaking of chemical bonds corresponding to that particular structure. (author)

[en] Secondary emission of singly and multiply charged positive atomic ions (I_sⁿ⁺) from 3-10 keV Ar⁺ -bombarded Si and Ge targets at target current densities (J_p) in the range 0-820 μA cm^-2 has been studied in detail, both as functions of primary ion energy (E) and target current density J_p = I_p/A (A constant). While I_s⁺/I_s⁺ (Si) at a fixed value of E is found to correspond to the usual experimental results (∼ 1%), I_s²⁺/I_s⁺(Ge) is observed to be > I, which is rather anomalous at such low bombarding energies. The I_s²⁺ vs I_p curves, however, clearly indicate that, in both cases, the charge transfer process in vacuum (ionization of neutrally sputtered particles by projectile ions) plays a dominant part in the secondary ionization phenomena, especially at increased target current densities. The excessive yield for Ge²⁺ ions is attributed to near-resonance conditions for the charge-transfer process, that are satisfied for the Ge²⁺ ions only, at such low kiloelectronvolt energies. Again, a surprisingly high fraction of Ge³⁺ ions is also observed in the SIMS spectra. In this case, it is however, suggested that there probably exists an excited state into which electron capture can occur with nearly exact resonance so that at the energies concerned, the near-adiabatic region is attained. Both I_s³⁺ (Ge) vs I_p and l_s³⁺ (Ge) vs E curves support this idea. (Author)

[en] Resonance enhanced multiphoton ionization of the X₁²Π₁ at _∼sol∼ at ₂ state of lead monofluoride (²⁰⁸Pb¹⁹F) via the B ²Σ₁ at _∼sol∼ at ₂ state is demonstrated. The ionization potential is observed to be 7.54(1) eV. Limits on the lifetime of the B state are found to be consistent with that reported by Chen et al. The transition dipole moment for the X₁→B transition is found to be 0.005(1) a.u. Limits on the ionization cross section of the B state are found

[en] A time-of-flight coincidence detector is demonstrated. This detector is optimized for use in a pseudocontinuous resonance enhanced multiphoton ionization scheme that requires photoelectrons and photoions to be detected in coincidence. The detector utilizes two simultaneously operating charged particle detectors, one for the detection of electrons and the other for the detection of ions. In order to allow for field reversal, the detectors are physically identical, differing only by the value of applied voltages. Particular attention is given to the implementation of a charge-to-voltage transducer that allows for subnanosecond detection of both electrons and ions.

[en] We study charge transport in molecular organic semiconductors using two terminal and three terminal field effect transistor devices. Using phthalocyanines as examples, we achieve unification of carrier mobility between the different configurations in a Gaussian density of states. We find that the current density–voltage characteristics for two terminal devices can be understood by introducing a concentration dependence of the carrier mobility, as described by Oelerich et al (2012 Phys. Rev. Lett . 108 226403, 2010 Appl. Phys. Lett . 97 143302). Studying the evolution of the activation energy with the carrier density, we find results consistent with a percolation picture and a density dependent transport energy. (paper)

[en] SIMS signals of embedded primary atoms, I⁺(Ar) and I⁺(Ne), generated from Si and Ge surfaces have been monitored as a function of bombarding energy (E) as well as target current density (J_p). I⁺(Ar) data supports the predominence of resonance charge transfer phenomenon above the target surface. Under Ne⁺ bombardment, however, it is more likely that in addition to the charge transfer phenomenon, a significant fraction of secondary Ne⁺ ions is produced in close binary encounters between Ne-Si and Ne-Ne atoms within the solid by molecular orbital electron promotion - a phenomenon which is possible in the low keV region only for light ions. Our results might have some importance in the study of plasma confinement time in nuclear reactors where only light ions are used as initiating fuels. (orig.)