An evaluation method for the energy level of the valence band (VB) top from the vacuum level (VL) for metals, dielectrics, and semiconductors from the results of X-ray photoelectron spectroscopy (XPS) is presented for the accurate determination of the energy band diagram for materials of interest. In this method, the VB top can be determined by the energy difference between the onset of VB signals and the cut-off energy for secondary photoelectrons by considering the X-ray excitation energy (hν). The energy level of the VB top for three kinds of Si-based materials (H-terminated Si, wet-cleaned 4H-SiC, and thermally grown SiO2) has been investigated by XPS under monochromatized Al Kα radiation (hν = 1486.6 eV). We have also demonstrated the determination of the electron affinity for the samples by this measurement technique in combination with the measured and reported energy bandgaps (E
g).
We fabricated nanometer-scale Ni dots and NiSi dots on an ultrathin SiO 2 layer using remote H 2 plasma and demonstrated the feasibility of remote H 2 plasma treatment for controlling the areal density of the dots. 1.8-nm-thick-Ni/SiO 2 and Ni/Siquantum dots (QDs)/SiO 2 layer were treated with remote H 2 plasma generated by the inductive coupling between an external single-turn antenna and a 60 MHz generator. When a Ni/SiO 2 was treated with remote H 2 plasma at room temperature, Ni nanodot density could be controlled in the range of 10 9 to 10 12 cm À2 by adjusting the plasma conditions. After the remote H 2 plasma treatment of the Ni/Si-QDs, the formation of electrically isolated NiSi dots with an areal density of $10 11 cm À2 was confirmed. These results imply that hydrogen radicals generated in H 2 plasma play an important role in improving surface diffusion caused by energy reduction at the Ni/SiO 2 interface. The surface potential of the Ni nanodots changes stepwise with the tip bias. This is due to the multistep electron injection into and extraction of Ni nanodots. The minimum tip biases for electron injection into Ni nanodots, NiSi dots and Si-QDs were À0:2, À0:7, and À1:0 V, respectively. This reflected the difference in electron affinity among Ni, NiSi and Si.
Two-dimensional (2D) crystals of Si and Ge atoms such as silicene and germanene are currently receiving much attention because of their exceptional electronic properties. We have studied the growth of ultrathin Si and Ge layers by the segregation of Si and Ge atoms on the Ag surface from the substrate by annealing the Ag/Si(111), Ag/Ge(111), and Ag/Si 0.5 Ge 0.5 (111) structures. After the epitaxial growth of the Ag(111) layer on the substrate by thermal evaporation, the stability of the Ag surface was also investigated for use as the template of ultrathin Si and Ge crystals. After annealing a >90-nm-thick Ag(111)/Ge(111) structure at 450 °C in N 2 ambience for 2 h, the surface segregation of Ge and a flat Ag surface were demonstrated.
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