Observation of the transition from image-potential states to resonances on argon-covered Cu(111) and Ag(111) by time-resolved two-photon photoemission
Observation of the transition from image-potential states to resonances on argon-covered Cu(111) and Ag(111) by time-resolved two-photon photoemission
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通过时间分辨双光子光电发射观察氩覆盖的 Cu(111) 和 Ag(111) 从像势态到共振的转变
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
U. Höfer
中科院分区：
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作者：
A. Damm;K. Schubert;J. Güdde;U. Höfer
用时间分辨双光子光电子能谱研究了Ar的有序吸附层对Cu（111）和Ag（111）的像势态和共振态的结合能和非弹性寿命的影响。Ar层在金属上的吸附导致强去耦的图像势态，沿着的非弹性寿命的指数增加和它们的结合能的降低。后者使第一个$（n=1）$像势态移动到Cu（111）上未被占据的投影体能带的最小值之上，从而引起从像势态到共振态的转变。这导致一个显着不同的依赖性的非弹性寿命的$n=1$状态上的Ar层厚度的两个表面。在Ag（111）上，寿命随层厚呈指数增长，从清洁表面的32 fs到Ar覆盖4个单层（ML）的约6 ps。在Cu（111）上，当$n=1$态成为共振态时，指数增长大大降低。在10 ML的Ar下，Cu（111）的寿命不超过3 ps。这种相当出乎意料的行为既不能解释一个简单的隧道图片的隧道通过薄Ar膜，也不是由模型计算使用的一维模型的潜力，占最重要的电子性质的金属基板以及Ar层。
The influence of well-ordered adlayers of Argon on binding energies and inelastic lifetimes of image-potential states and resonances on Cu(111) and Ag(111) has been investigated by means of time-resolved two-photon photoemission spectroscopy. The adsorption of Ar layers on metals results in a strong decoupling of the image-potential states that goes along with an exponential increase in their inelastic lifetimes and a lowering of their binding energies. The latter shifts the first $(n=1)$ image-potential state above the minimum of unoccupied projected bulk bands on Cu(111) and thereby induces a transition from an image-potential state to a resonance. This leads to a strikingly different dependence of the inelastic lifetime of the $n=1$ state on Ar layer thickness for the two surfaces. On Ag(111) the lifetime shows a continuous exponential increase with layer thickness from 32 fs on the clean surface to about 6 ps for an Ar coverage of four monolayers (ML). On Cu(111) the exponential increase is considerably reduced when the $n=1$ state becomes a resonance. Up to 10 ML of Ar the lifetime on Cu(111) does not exceed 3 ps. This rather unexpected behavior can neither be explained by a simple tunneling picture of the tunneling through thin Ar films nor by model calculations using a one-dimensional model potential that accounts for the most important electronic properties of both the metal substrate as well as of the Ar layers.