Orientation of fluorophenols on Si(111) by near edge x-ray absorption fine structure spectroscopy

Abstract

The adsorption of phenol, 4-fluorophenol, and 2,3,4-trifluorophenol on the Si͑111͒7 ϫ 7 surface is investigated by near edge x-ray absorption fine structure spectroscopy ͑NEXAFS͒. A strong polarization dependence of the * transitions is observed for fluorinated phenols, while phenol itself is more isotropic. A quantitative method is developed to convert polarization-dependent NEXAFS data into orientational information for such a situation. The model includes two angular degrees of freedom, the tilt angle ␥ of the end group and its rotation angle ␤ around the phenyl-to-oxygen bond. The tilt is fixed by the geometry of the free molecule, while the rotation is characterized by an average angle ␤ 0 with a Gaussian distribution due to thermal fluctuations. The model is applicable to a variety of self-assembled monolayers with tailored end groups that are used in molecular electronics and biosensors.

Chemical manipulation of multifunctional hydrocarbons on silicon surfaces

“…Only phenol exhibits similar behavior on both clean silicon surfaces, as phenol shows dissociative adsorption via O-H scission at temperatures as low as 50 K on Si(111)-7×7 [287]. Polarization dependence of the π* transitions in phenol, 4-fluorophenol, and 2,3,4-trifluorophenol on Si(111)-7×7 investigated by NEX-AFS confirms the generality of phenol derivatives' attachment to this substrate [382].…”

First‐principles study on the concentrations of native point defects in high‐dielectric‐constant binary oxide materials

“…The origin of these imperfections has been attributed to oxygen defects [3][4][5][6][7][8]. In the present article, we extend our previous work [9,10] to investigate the dominant point defects under the constraint of charge neutrality in bulk hafnium oxide (HfO 2 ), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ) and lanthanum oxide (La 2 O 3 ). By calculating the defect concentrations, our results support the speculation that oxygen-related defects are the dominant point defects in these binary high-k oxides.…”

“…The values for the image charge corrections for different charge states in HfO 2 and ZrO 2 were reported in Ref. [10]. The image charge corrections in Y 2 O 3 (k = 16) and La 2 O 3 (k = 25) are 0.12 eV and 0.07 eV, respectively for ±1 charge defects and they scale proportionally with q 2 for ± q charge defects.…”

“…The detailed computational procedure to obtain defect formation energies can be found in Refs. [9] and [10]. In these studies, the stable point defects were determined as a function of Fermi level and oxygen chemical potential without a local electroneutrality constraint as would be applicable to the interfacial regions between the high-k oxide and silicon.…”

“…The formation energies for native point defects are a function of Fermi level and chemical potentials, and their values for HfO 2 , ZrO 2 and Y 2 O 3 have been reported in Refs. [9] and [10]. It is noted that although a thermodynamic equilibrium condition is assumed, the formation energies can serve as a good indicator as to which defects are more likely to form and which material is more prone to the formation of certain type of defects, even when the equilibrium condition is not completely reached.…”