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

在2 Pa左右的Ar气氛中，用磁控溅射法制备了200 nm厚的MgO薄膜，用ESCA PHI 1600测量了薄膜的X射线激发光电子发射谱（XPS），发现MgO薄膜产生了能量高于入射光子能量的外逸电子，将MgO膜置于XPS装置中，通过以15 mA/cm ^2的速率轰击3 keV Ar离子约20秒来清洁表面，直到完全去除污染物，然后在室温下在10^ Pa的真空下退火48小时<-8>。可以在以下过程中观察到外生电子：首先，以15 mA/cm ^2的速率在样品表面上照射3 keV的Ar离子。然后将X射线光子照射到表面，并以每次扫描15秒的速率重复测量能量范围为1154至1554 eV的光子激发电子。辐照开始后，出现了能谱均匀的外逸电子，但强度随时间单调下降。超过100秒没有观察到任何外逸电子，但它们在光子照射的静止（约10分钟）后再次出现。这种现象的出现，衰减和恢复观察到的几个重复的照射和静止后的离子束照射。当我们将离子辐照时间从30秒增加到2分钟时，外逸电子的强度增加。认为离子轰击后的薄膜表面的原子被激活，在准稳定位置上被固定，在高能光子的照射下弛豫到更稳定的位置。然而，还没有清楚地理解，一些外逸电子的能量太高，并且并非所有样品都必然显示出外逸电子发射特性。

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.