Role Of Secondary Electrons Research Articles

Gas-phase chemistry and lasers characterize role of secondary electrons in DNA fragmentation

Gas-phase iodide-thymine clusters exhibit similar fragmentation properties to uracil, one of RNA’s four bases, but iodide-cytosine clusters behave differently over the complex’s photodetachment energy.

On the role of secondary electrons in beam plasma generation inside a dielectric flask by fore-vacuum plasma-cathode electron source

The paper presents the results of experimental research and numerical simulation, demonstrating a considerable influence of secondary electrons on parameters of the beam-produced plasma generated at a pressure range of 1–13 Pa by injection of a continuous (with current of tens mA) electron beam into a dielectric (quartz) flask. An electron beam was formed by a fore-vacuum plasma-cathode electron source based on a hollow cathode discharge. The secondary electrons were emitted as a result of high-energy (3–8 keV) electron beam bombardment mainly a bottom end of the flask. These electrons provide an additional contribution to the ionization of the gas and also affect on the longitudinal distribution of the plasma density along the flask.

The characteristic shape of emission profiles of plasma spokes in HiPIMS: the role of secondary electrons

A time-resolved analysis of the emission of high power impulse magnetron sputtering (HiPIMS) plasmas reveals inhomogeneities in the form of rotating spokes. The shape of these spokes is very characteristic depending on the target material. The localized enhanced light emission has been correlated with the ion production. Based on these data, the peculiar shape of the emission profiles can be explained by the localized generation of secondary electrons, resulting in an enhanced outward diffusion. This general picture is able to explain the observed emission profile for different target materials including gas rarefaction and second ionization potential of the sputtered elements.

Different modes of electron heating in dual-frequency capacitively coupled radio frequency discharges

A systematic study of different modes of electron heating in dual-frequency capacitively coupled radio frequency (CCRF) discharges is performed using a particle-in-cell simulation. Spatio-temporal distributions of the total excitation/ionization rates under variation of gas pressure, applied frequencies and gas species are discussed. Some results are compared qualitatively with an experiment (phase resolved optical emission spectroscopy) operated under conditions similar to a parameter set used in the simulation. Different modes of electron heating are identified and compared with α- and γ-mode operation of single-frequency CCRF discharges. In this context the frequency coupling and its relation to the ion density profile in the sheath are discussed and quantified. In light gases the ion density in the sheath is time modulated. This temporal modulation is well described by an analytical model and is found to affect the excitation dynamics via the frequency coupling. It is shown that the frequency coupling strongly affects the generation of beams of highly energetic electrons by the expanding sheath and field reversals caused by the collapsing sheath. The role of secondary electrons at intermediate and high pressures is clarified and the transition from α- to γ-mode operation is discussed. Depending on the gas and the corresponding cross sections for excitation/ionization the excitation does not generally probe the ionization as is usually assumed.

The Role of Secondary Electrons in Forming the Image of Electron Nanoprobe

Formation of a lithographic image (a pixel) of electron nano‐probe has been studied using fullerite C60 film as a negative electron beam resist. A mechanism of widening a pixel due to modification of the resist by secondary electrons has been revealed. Widening a pixel occurs due to diffusion of secondary electrons around the area filled by primary and scattered electrons. The mechanism manifests itself in formation of a large carbon cluster‐pixel on which small cluster‐pixel formed by primary electrons is superimposed. It was shown that the role of the revealed mechanism may be important in the case of formation of lithographic pictures and carbon nanostructures with high density of elements.

Self-sputtering runaway in high power impulse magnetron sputtering: The role of secondary electrons and multiply charged metal ions

Self-sputtering runaway in high power impulse magnetron sputtering is closely related to the appearance of multiply charged ions. This conclusion is based on the properties of potential emission of secondary electrons and energy balance considerations. The effect is especially strong for materials whose sputtering yield is marginally greater than unity. The absolute deposition rate increases ∼Q1∕2, whereas the rate normalized to the average power decreases ∼Q−1∕2, with Q being the mean ion charge state number.

Influence of substrate material on plasma in deposition/sputtering reactor: experiment and computer simulation

The aim of this work was to investigate the influence of the substrate material on the plasma enhanced chemical vapour deposition and the plasma sputtering of thin films in low pressure (3–20 Pa) parallel-plate radio frequency (rf) discharges. It was observed that the deposition or sputtering rates differed above different materials, e.g. above a substrate and substrate electrode. Moreover, the substrates placed on the bottom rf electrode seemed to be mirrored in the thickness of a thin film deposited or sputtered on the upper grounded electrode. The influence of the substrate material on the plasma parameters was studied via particle in cell/Monte Carlo computer simulation. According to our finding the mirroring of the substrate was caused by different secondary electron emission yields of the substrate material and material of the substrate electrode. This difference in the secondary electron yield affected plasma density above the substrate leading to higher or lower deposition or sputtering rates on the grounded electrode. Therefore, the role of secondary electrons in the discharge was studied. Spatial distributions of impact positions on the grounded electrode for electrons and ions emitted from the rf electrode and created in the ionization avalanche of the secondary electrons were calculated in order to simulate the mirroring of the substrates.

Role of secondary electrons and metastable atoms in the electron-beam activation of argon-silane mixtures

The energy and spatial degradation of the primary beam electrons and the production of high- energy secondary electrons in ionizing collisions are analyzed by solving the Boltzmann integral equation for the electron distribution function. The effect of the primary and secondary electrons on the direct ionization of an Ar- SiH 4 mixture, the production of metastable argon atoms, and the dissociation of monosilane molecules is investigated over a wide range of the beam electron energies, argon pressures, and monosilane concentra- tions. The influence of metastable Ar* atoms on the dissociation of SiH 4 is studied by using the balance equa- tion for metastable argon atoms and the equation for the ambipolar diffusion of ions and low-energy secondary (plasma) electrons in the beam plasma. It is shown that the main contribution to the activation of an Ar-SiH 4 mixture in an electron-beam plasma is provided by secondary electrons with energies higher than the excitation threshold for argon and the dissociation threshold for monosilane, whereas the contribution from metastable argon atoms, though potentially being comparable with that from secondary electrons, is less than in gas-dis- charge plasmas.

The role of secondary electrons in some experiments determining fluorescence emission from nitrogen [formula omitted] levels

The processes involved in fluorescence emission from C 3 Π u levels of N 2 molecule by electron impact are studied. Secondary electrons are shown to play an important role in typical experiments for the measurement of emission cross sections and fluorescence yields, dominating at high impact energies. A simple model is proposed which accounts for fluorescence measurements in a wide range of experimental conditions, and in particular for some recent results up to 1 GeV energies.

Role of secondary electrons in hot-electron femtochemistry at surfaces using tunnel junctions

A theory of resonance-assisted, hot-electron-induced femtochemical processing at surfaces using a tunnel junction device, which has previously been developed in terms of inelastic electron scattering via negative-molecular-ion shape resonances associated with molecules adsorbed on solid surfaces, is extended here to include the effects of secondary electron cascades produced within the device. The potential influence of the secondaries on the proposed control and selectivity of the device is demonstrated and assessed.

Author's response to the comment on the role of secondary electrons in liquid metal ion sources

This comment responds to the several criticisms of the paper on the role of secondary electrons in liquid metal ion sources raised by Mair. In particular, it is pointed out that the experimental evidence does not contradict the conclusions of that paper. In addition to the secondary electron experimental data quoted by Mair some more recent results are reviewed.

On the role of secondary electrons in liquid metal ion sources

In the context of liquid metal ion source operation, a recent paper suggested that secondary electrons released by ion-collecting surfaces might play a fundamental role in source behaviour, by causing emitter heating. The present note looks again at the role of secondary electrons. It confirms the long-established view that in all normal circumstances, the associated heating effects are not sufficient to modify ion source operating characteristics.

The role of secondary electrons in electron-assisted adsorption process

In an ultrahigh vacuum chamber in which the partial pressure of Cl containing residual gases was 10 −12 Torr, the entire surface of a Cu sample was found to be covered with Cl after a small area (0.1 mm diameter) of the sample surface was irradiated with an electron beam. This was shown to be caused by secondary electrons rather than by surface migration as was postulated to explain a previously observed similar phenomenon.

The role of secondary electrons in electron-assisted adsorption process

In an ultrahigh vacuum chamber in which the partial pressure of Cl containing residual gases was 10 −12 Torr, the entire surface of a Cu sample was found to be covered with Cl after a small area (0.1 mm diameter) of the sample surface was irradiated with an electron beam. This was shown to be caused by secondary electrons rather than by surface migration as was postulated to explain a previously observed similar phenomenon.

Evidence of multiple H+ ion desorption pathways with ESD of chemisorbed and multilayer water

Measurements have been initiated of H+ ion energy distributions from a water dosed Si(100) substrate at room temperature and with multilayer formation at ~ 100 K. The apparently wide energy distributions usually observed with electron stimulated desorption are attributed to desorption along multiple pathways. Increasing the beam energy from 170 to 200 eV causes a shift in the peak position from around 8.5 to 5.7 eV, and is assigned to the role of secondary electrons which increasingly dominate as the energy is increased (seemingly associated with the ionisation of the silicon 2p (L2,3) level). A further peak in the ion energy distribution is emphasised towards low electron energy (< 50 eV) with peak energy at around 3.6 eV. Overall the production of H+ is enhanced with multilayer growth, but similar features of the ion energy distribution are present also at room temperature.

Analytical Relationships of Nuclear Field and Microdosimetric Quantities for Target Fragmentation in Tissue Systems

A simple analytic formula for the nuclear fields formed by target fragmentation in tissue systems is derived using the continuous slowing down approximation (CSDA). The energy fluctuations in sensitive localized sites within the tissue system caused by these nuclear events are defined by microdosimetry. In that CSDA is used, the energy fluctuations exclude the role of secondary electrons. The relations also relate to the response of microdosimetric devices to nuclear fragmentation fields.

The Role of Secondary Electrons in Charged Particle Degradation

approach. In this paper, we review our work involving secondary electron distributions since 1963, beginning with the work of Green and Barth, largely in relation to applications but also in relation to the fitting of experimental data and the testing of theoretical models. In the latter context, we utilize the independent particle model of Green, Sellin, and Zachor in the Born approximation and in the Eikonal approximations. Our