Electronic and morphological properties of the electrochemically prepared step bunched silicon (111) surface

Abstract

8062 42434Topographical and electronic and properties of step bunched Si(111), prepared by electrochemical processing in alkaline solution, are analyzed. Tapping mode atomic force microscopy (TM AFM) analysis shows that one bunched step consists of about 15 atomic steps (each 0.314 nm in height) and that the (111) oriented terraces have widths that range from 150 to 250 nm. Scanning tunneling microscopy (STM) experiments show a corrugation of the (111) terraces with an rms roughness of 0.5-0.8 nm, correlated with etch pits in alkaline solution. Low energy electron diffraction (LEED) data show a splitting of the (10) and (01) spot from which a minimum terrace width of 4.8 nm have been calculated in good agreement with the TM AFM data. Kelvin probe force microscopy (KPFM) experiments show a decrease of the contact potential difference (CPD) at and near the edges of steps indicating a more negatively charged surface area. Synchrotron radiation photoelectron spectroscopy (SRPES) on electrochemically and purely chemically prepared step bunched surfaces is compared. From the Si 2p core level shift, and, in particular, from the onset of the valence band emission, an accumulation layer-type shift is observed on the electrochemically prepared sample that is absent for chemical preparation. The move of the Fermi level toward the conduction band minimum of the electrochemically conditioned samples is interpreted by H incorporation and discussed by a doping model that involves the mechanism of hydrogen evolution.

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“…In synchrotron radiation photoelectron spectroscopy (SRPES) it was shown that these surfaces are in an accumulation condition where the Fermi level is located only 0.06 eV below the conduction band edge whereas from the bulk doping, this energetic difference amounts to 0.26 eV [29]. In separate Kelvin probe AFM measurements, it has been found that the negative charge associated with the accumulation condition is located at the step edges of the nanostructure [35] as schematically indicated in Fig. 1.…”

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“…Such work is in progress. SRPES valence band measurements show a shift of the Fermi level that can be due to degenerately doped n + Si or to the formation of an accumulation layer [14]. Kelvin probe force microscopy reveals the anisotropic lateral distribution of the electrostatic potential, thus providing sites with different charge [14].…”

“…This modified surface is characterized by extended rather smooth terraces and steps that are between 5 and 15 atomic bilayers (BL) in height. It has been shown by synchrotron radiation photoelectron spectroscopy (SRPES) [12,13], and Kelvin probe microscopy (KPM) [14] that an n-Si surface is in an accumulation condition where a two dimensional electron system is formed on the surface. KPM data show that the electrostatic (or Galvani) potential near step-edges of the nanostructure surface decreases corresponding to a localized increase of negative electronic charge [14].…”

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“…Electrodeposition of Pt from PtCl 2À 6 complexes onto n-Si yielded different sizes for H-terminated (1 1 1) surfaces and for the step bunched Si surface where the major terraces are (1 1 1) oriented and the bunched steps are likely to show (1 1 0) orientation [19,20]. At step bunched surfaces, the Pt NPs had an average width of 30 nm and a height of 3 nm.…”