Triboemission phenomena: electronic and photonic outputs from surface modification, and their use as novel probes
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Triboemission phenomena: electronic and photonic outputs from surface modification, and their use as novel probes Gustavo J. Molina1, and Czeslaw Kajdas2 1 Department of Mechanical Engineering, Georgia Southern University, Statesboro, GA 304588045, USA. Corresponding author e-mail: [email protected], 2Institute of Chemistry in Plock, Warsaw University of Technology, Plock, Poland. ABSTRACT Triboemission comprises the emission of low energy electrons and photons, the eventual formation of micro-triboplasmas, and the possible charge-initiated tribochemical reactions on the surfaces under contact. Electron triboemission is often seen as a case of electron exoemission, but such low-energy output may be just a fraction of the total electronic excitation on the surface, the majority of which may proceed as internal currents. The dynamics of these related surface phenomena have been investigated by different techniques, which are discussed in this work; in particular, the authors have obtained extensive data indicating that electrons and photons are produced from mechanical surface work, particularly from surface oxides and semiconductors under contact sliding in vacuum. This paper also discusses the existing body of work on triboemission, and the possible use of the developed measurement techniques as novel probes for surface processes. INTRODUCTION The emission of electrons, ions, neutral particles, photons, and acoustic emission under conditions of tribological contact and damage is called triboemission [1]. The authors have produced extensive results on triboemitted electrons from the scratching of ceramics (i.e., alumina, sapphire and silicon nitride) and semiconductors (i.e., Si and Ge) in vacuum; these charged-emissions are characteristically burst-type for low-energy electrons (e.g., up to 10 eV) [1-4]. Research works on charged-particle triboemission were also carried out by Nakayama et al. [5] and Dickinson et al. [6]. The possibility of thermionic emission is ruled out as the origin of this triboemission because of the very low load and velocities employed in experiments. The early work of Sujak and Gieroszynski [7,8] indicated a relationship between electron emission under tension and simultaneous external photostimulation , but they later realized, however, that no added excitation was needed for surface-oxidized Al and Ni to emit electrons under tension [9]. Research on triboemitted photons from the scratching of materials was started by Dickinson et al. [6] on electron and photon emissions from reciprocating scratching of MgO with diamond; they were respectively measured by a channel electron multiplier and a photomultiplier tube. They found significant burst-type electron and photon emissions as high as, respectively, 3x106 counts/sec and 2x104 counts/sec (for 0.1 N load, and 4 cm/sec of average sliding speed). Photon emission from this material system decayed on the millisecond scale after each burst, returning to near-zero between spikes (while electron emission from diamond-onMgO, however, show
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