Triboemission is defined as the emission of electrons, ions, photons and neutral particles during tribological surface damage. Triboemission of negatively and positively charged particles and photons by the wearing of solid surfaces of metals, ceramics, glass, anodic aluminium oxide films (Al2O3), polymers and mica were studied using a special triboemission measuring apparatus which permits the simultaneous measurement of negatively and positively charged particles, photons and friction coefficients in a vacuum and in various atmospheres. The emission characteristics of the triboemission depended on the type of solid. Both charged particles and photons were emitted simultaneously in bursts during the scratching of the solid surfaces of semiconductors and insulators. In contrast, no photon emission was observed using conductors. With conductors and semiconductors, the particles emitted were mainly negatively charged particles, while with insulators both negatively and positively charged particles were emitted at the same level but with a slightly higher intensity of negative particles in air. The emission of the charged particles and the photons increased at higher loads and speeds as well as at greater thickness of Al2O3 films. The charge intensity from the insulators decreased with higher Vickers hardnesses. The intensity of the negatively and the positively charged particles was well correlated with that of photons. The mechanism of triboemission is discussed.

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PACS 85.60.HaWe have designed and fabricated new photo-tubes and photomultiplier tubes (PMTs) using In x Ga 1-x N films as photocathodes. Longer spectral cutoffs were controlled with Indium compositions x, from 365 nm to 430 nm. The calibrated maximum quantum efficiency (QE) of 56% at 200 nm was achieved for x = 0.11 Indium composition in the photo-tubes. Sharp cutoffs at around 160 nms were determined by window materials and those at around 400 nms were determined by the band gaps of the photocathodes. Gain and input/output linearity properties were confirmed to be very good for the PMTs. 1 Introduction In these days, photocathode devices detecting in UV and blue spectral region are important for detection of scintillation and Cherenkov radiation in high-energy physics, like Kamiokande, and astrophysics experiments. Besides, researchers in space UV astrophysics and planetary require advanced detectors [1][2][3]. A high quantum efficiency (QE), a sharp cutoff, a low dark current, and large formats are important for these detectors. Because of a wide dynamic range, a low dark current, and being able to operate in single photon counting mode, GaN-based photocathodes are suitable for UV space missions.GaN-based photocathodes are being studied since 70's, some good results have been reported [4][5][6][7]. Recently, we have realized extremely high QE for GaN-based photocathodes [8]. The spectral shapes of the response and the QE strongly depend on the Mg-doping concentration. The calibrated QE of the GaN-based photocathode is maximized to be 71.9% at 230 nm by a Mg-doping concentration of 3.0 x 10 19 cm -3 . Within the frame work of the Spicer's three step model [9], the diffusion length and the escape probability were identified to be 150 nm, and 0.8, respectively.Recently, InGaN photocathodes are reported [1,10,11]. However, the relationship between the In composition of the InGaN films and the sharp cutoff or the QE is not clear. Then, we have designed and fabricated the InGaN photocathodes with high QEs, and have incorporated them into photomultiplier tubes (PMTs) with high gain and wide dynamic ranges.

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