| 摘要 |
An electron-emitting cathode (6) consists of an electrically conducting emitter layer (7) attached to a side wall (2) which consists of stainless steel and a gate (9) which is fixed at a mall distance inside a concave emitter surface of the emitter layer (7). The cathode (6) surrounds a reaction area (3) containing a cylindrical grid-like anode (5) and a central ion collector (4) which consists of a straight axial filament. An ion collector current (lie) reflecting the densitiy of the gas in the reaction region (3) is measured by a current meter (11) while a gate voltage (VG) is kept between the ground voltage of the emitter layer (7) and a higher anode voltage (VA) and is regulated in such a way that an anode current (IA) is kept constant. The emitter layer (7) may consists of carbon nanotubes, diamond-like carbon, a metal or a mixture of metals or a semiconductor material, e.g., silicon which may be coated, e.g., with carbide or molybdenum. The emitter surface can, however, also be a portion of the inside surface of the side wall roughened by, e.g., chemical etching. The gate (9) may be a grid or it may be made up of patches of metal film covering spacers distributed over the emitter area or a metal film covering an electron permeable layer placed on the emitter surface. |
