Quantum electronic stability and spectroscopy of ultrathin Pb films onSi(111)7×7

Abstract

The growth of Pb on Si(111)7ϫ7 has been studied with photoelectron spectroscopy. At low temperature ͑110 K͒, Pb grows in a quasi layer-by-layer mode that allows for the direct observation of discrete quantum well states. The quantum well states are analyzed in terms of the Bohr-Sommerfeld phase quantization model using a phenomenological phaseshift function and reduced quantum numbers. Fermi-level crossings occur when the film thickness Ndϭn(F /2), where d is the atomic layer spacing and F the bulk Fermi wavelength (N,n are integers͒. The photoemission intensity from the quantum well states shows a strong modulation with photon energy which can be interpreted on the basis of the matrix elements for direct transitions in bulk Pb͑111͒. The in-plane effective mass of the quantum well states is greatly enhanced in the vicinity of the substrate band edge. The present results provide important elements for understanding the growth morphology of Pb films in recent STM studies.

Experimental observation of quantum oscillation of surface chemical reactivities

“…In this case, the thickness-dependent adsorption behavior is much more obvious. All CoPc molecules diffuse long enough and are able to reach the energetically favorable regions (10,12,14,17 and 19 ML) where stronger oxygen adsorption and oxidation are always observed to form an ordered self-assembled monolayer, leaving other regions (11,13,15,16, and 18 ML) intact. With this experiment, the influence thickness-dependent diffusion can safely be ruled out.…”

“…For Pb, F ϭ 1.06 nm, which is nearly 4 times of the interplanar distance d 0 along the crystallographic [111] direction. This coincidence ( F Ϸ 4d 0 ) suggests that, when 1 ML of Pb is added or removed, electron interference will change from being constructive to destructive and vice versa, leading to a 2-ML modulation of the electronic structure (15)(16)(17)(18)(19). More accurate analysis indicates that the exact period should be 1.8 ML.…”

Quantum Size Effects Induced Novel Properties in Two-Dimensional Electronic Systems: Pb Thin Films on Si(111)

“…As a result, the quantum oscillations in superconducting transition temperature T c were observed, which correlate perfectly with the confined electronic structure. 36) Other novel properties induced by QWS, such as double-layer growth, [29][30][31]38) selective strip-flow growth and growth rate modulation, 39) oscillating perpendicular upper critical field, 40) thermal expansion, 41) adhesion force, 42) local work function (LWF), 43) and surface diffusion barrier, 44) have also been observed. In this article, we would mainly summarize these recent results on Pb/Si(111) by our group.…”

“…Several groups observed that the stability of Pb islands depends on the thickness, magic and preferential heights of the islands were identified by their STM/STS measurements. 27) In the case of flat Pb films, ARPES studies revealed the significance of QSE on DOS(E F ) 31) and thermal stability of the Pb films, 11,32) and the stability was explained in terms of the electronic structure modulation by QWS. Quantum beating patterns in the thickness-dependent surface energy 32,33) were also observed, which, according to the simple picture mentioned above, should be a manifestation of the slight deviation from the perfect matching F ¼ 4a 0 .…”

Controlling the effective mass of quantum well states in Pb/Si(111) by interface engineering

“…Examples of these observations are the strong dependence of the Schottky barrier on the exact atomic structure 6 , the formation of magic height islands 7 , anomalies in the superconductivity transition temperature [8][9][10] , oscillations of the work function and extremely long excited state life times 11,12 , and the observation of a Rashba-type spin splitting 13 . The origin of many of these phenomena lies in the peculiar electronic structure of Pb on Si(111) manifested in the high in-plane effective mass [14][15][16] . A control of this effective mass can thus also give control over many of the other physical properties which make Pb films on Si such a rich research subject.…”