| 摘要 |
<p>The atom probe, which is suitable for use as a scanning atom probe, has a two-part counter electrode (10) and a detector (20) positioned behind the counter electrode. Power supply means are also provided for applying a positive dc voltage to a specimen under study and for applying a negative voltage pulse to a first plate (11) of the counter electrode whilst a second plate (12) and the detector (20) are held to ground. The two plates (11, 12) of the counter electrode are electrically isolated from one another with the plate (11) nearest the specimen shaped so that the electric field generated between the specimen and the plate (11) is concentrated at an individual microtip (31a) on the surface of the specimen. In use, the voltage pulse Vp applied to the first plate is shaped such that there is a substantially constant maximum negative voltage for a period of time dependent upon the separation of the specimen from the first plate. In this way ions produced at the microtip coast from the first plate (11) to the detector (20). This results in a narrow spread of kinetic energies of ions reaching the detector (20) which in turn provides improved mass resolution.</p> |
