Detection of Exo-Electrons From a Scratch Damage of Thin Films

采用磁控溅射法制备了厚度为200 nm的MgO靶膜。在1253.6 eV的x射线激发下，用ESCA PHI 1600测量了薄膜的x射线激发光电子发射光谱（XPS）。结果表明，在离子轰击作用下，MgO薄膜产生的外逸电子的能量高于入射光子的能量。将MgO薄膜置于XPS装置中，用3kev氩离子以15 mA/cm^2的速度轰击清洁表面约20秒，直到污染完全清除，然后在10^<-8> Pa的真空下室温退火48小时。首先，以15ma /cm^2的速率辐照3kev的Ar离子到样品表面。然后将x射线光子照射到表面，以每扫描15秒的速率重复测量能量范围为1154 ~ 1554 eV的光子激发电子。辐照一开始，就出现了能谱均匀的外逸电子，但其强度随时间单调减小。在100秒后没有观察到任何外电子，但在光子照射的静止（约10分钟）后它们再次出现。经过几次辐照和离子束辐照后的静止，观察到这种出现、衰减和恢复的现象。当离子辐照时间从30秒增加到2分钟时，外逸电子的强度增加。认为离子轰击膜表面固定在准稳定位置的原子在高能光子照射下被激活松弛到更稳定的位置。然而，一些外电子的能量过高，并不是所有样品都显示出外电子发射特性，这一点还没有弄清楚。

MgO films of 200 nm thick were prepared by magnetron sputtering of MgO target in an Aratmosphere of about 2 Pa.X-ray excited photoelectron emission spectrum (XPS) of the films was measured with ESCA PHI 1600 by an excitation of x-rays of 1253.6 eV.It was found that the MgO film yielded exoelectrons, whose energy was higher than that of the incident photons, when it was subjected to the ion bombardment.The MgO film was set in an XPS apparatus, and the surface was cleaned by the bombardment of 3 keV Ar ions at a rate of 15 mA/cm^2 for about 20 seconds until the contamination was completely removed, followed by an annealing at room temperature for 48 hours under the vacuum of 10^<-8> Pa.Exoelectrons could be observed in the following procedure : First, Ar ions of 3 keV were irradiated on the sample surface at a rate of 15 mA/cm^2. Then the x-ray photons were irradiated to the surface and the photon excited electrons of the energy range from 1154 to 1554 eV were measured repeatedly at a rate of 15 seconds per a scan. As soon as the irradiation started, exoelectrons of uniform energy spectrum appeared but the intensity decreases monotonically with time. Any exoelectrons were not observed beyond 100 seconds, but they appeared again after quiescence (about 10 minutes) of the photon irradiation. This phenomenon of appearance, decay and recovery was observed for a few repetition of the irradiation and quiescence after the ion beam irradiation. When we increased the ion irradiation period from 30 seconds to 2 minutes, the intensity of exoelectrons increased. It is considered that atoms on the ion-bombarded film surface, which are get fixed at quasi-stable sites, are activated to relax to more stable positions with an irradiation of high energy photons. It has not been understood clearly, however, that the energy of some exoelectrons is too high and that all samples did not necessarily show the exoelectron emission characteristics.