Abstract
Ag-Mg alloy is used as a dynode material in electron multiplier tubes due to the high secondary electron yields (δ) of the surface of MgO film. However, MgO film is readily degraded under strong electron or ion bombardment, which results in a decrease in the lifetime of devices. In this study, alumina-containing MgO films of ~50–150 nm were developed on a Ag-2Mg-2Al alloy (silver alloy containing 2 wt % Mg and 2 wt % Al) after a thermal activation process performed at 500–600 °C under low oxygen pressures of 5.0–20.0 Pa. Auger electron spectroscopy and X-ray photoelectron spectroscopy analyses reveal that the film consists of a thin layer of pure MgO and a relatively thicker layer of alumina-containing MgO located beneath the top MgO layer. The alumina-containing MgO film exhibits high δ value of 7.7 at a primary electron energy of 580 eV and a much better stability under energetic electron bombardment than pure MgO film on Ag-Mg alloy. Alumina has higher bond dissociation energy than MgO, and the presence of alumina in the film contributes to mitigating the dissociation of the MgO film under electron bombardment. The Ag-2Mg-2Al alloy with alumina-containing MgO film is a promising candidate as a dynode material for electron multiplier tubes.
Highlights
The secondary electron emission (SEE) process is important for various vacuum electronic devices, such as scanning electron microscopes, atomic clocks, alternating current plasma display panels, and electron/photomultipliers for mass spectroscopy, photoelectron spectrometers, magnetrons, and crossed-field amplifiers [1,2,3,4,5]
MgO films prepared through activation on Ag-Mg alloys and by various deposition methods are readily dissociated under constant bombardment from electron beam and ionized particles, which restricts their practical applications in vacuum electron devices
Unique round-shaped flakes of ~20–60 nm were developed on the surface after activation, which is similar to the surface morphology of activated Ag-3Mg alloy [15]
Summary
The secondary electron emission (SEE) process is important for various vacuum electronic devices, such as scanning electron microscopes, atomic clocks, alternating current plasma display panels, and electron/photomultipliers for mass spectroscopy, photoelectron spectrometers, magnetrons, and crossed-field amplifiers [1,2,3,4,5]. Materials with high δ and good stability under exposure to energetic electron beam and charged particles, such as BeO [8], MgO [9,10], Al2 O3 [11], and chemical vapor deposition (CVD) diamond films [12], are required for various electron multipliers. MgO films prepared through activation on Ag-Mg alloys and by various deposition methods are readily dissociated under constant bombardment from electron beam and ionized particles, which restricts their practical applications in vacuum electron devices. Pan studied the SEE properties of the Cu-Al-Mg alloy and found that MgO/Al2 O3 composite film is developed spontaneously at room temperature without activation, and the alloy emitter has excellent stability with δ values over 3 under constant electron bombardment [26]. Superior SEE properties, including high δ and better stability under electron bombardment, were found for the Ag-Mg-Al emitter with proper film thickness. The film composition and element distribution in the film are characterized and the effect of Al in the film on the SEE properties of the alloy is discussed
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