Development of a surface ionization type dual-ion source applicable to ionic crystalline samples

A surface ionization type dual-ion source (DIS) developed for ionic crystalline samples such as alkali halides (MX) consists of (1) a sample plate (F₁, ∼0.02 cm²) heated up to ∼1000 K to produce primary ion (M⁺ or X^-) by dissociative self-surface ionization of MX deposited on F₁, (2) a second filament (F₂) kept at 1260 K to produce secondary ion (M⁺) by molecular beam surface ionization of the neutral molecule (MX⁰) desorbing from F₁ and (3) a grid (G) mounted between F₁ and F₂ to retard the primary and secondary ions. These ions are independently extracted efficiently and collected separately without using any separator other than G. Our DIS is free from background ions due to residual gases, easy in operation, simple in structure and small in size (∼2 cm³) but quite useful for kinetic studies of ionic and neutral desorption from MX and also for generating monochromatic and stable dual-ion beams (∼1 pA) from MX (∼1 μg) deposited on F₁.