Synchrotron radiation x-ray photoelectron spectroscopy of Si nanocrystals grown onto Al2O3∕Si surfaces

Abstract

Synchrotron radiation x-ray photoelectron spectroscopy is used for the study of 5 nm Si nanocrystals (NCs) for applications in nonvolatile memory devices. A detailed peak shape analysis of the high-resolution Si2p core-level spectra reveals average chemical shifts for the oxidized components consistent with those observed for planar oxidation. However, a much larger Gaussian width is found for each spectral component, reflecting the important level of structural disorder in the NCs, arising from stress produced during the kinetics of the oxide shell growth. Final state contributions to the core-level spectra are also discussed.

Characterization of Si Nanocrystals

“…The peak positions of oxidization states Si 2 O, SiO, Si 2 O 3 , SiO 2 shift from this value approximately by 0.93, 1.73, 2.56, 3.88 eV, respectively, and their FWHM increase with the same order for thin film of SiO 2 formed on Si [45,46,48]. According to an outstanding research from Renault et al [46], although the peak positions of Si þ n stated does not change noticeably, their FWHMs for Si nanocrystals on Al 2 O 3 are larger than thin films of SiO 2 on Si as shown in Figure 21.11. They attributed this broadening to the stress due to the variations of the SiÀO bond lengths and SiÀOÀSi bond angles in oxides on Si nanocrystals.…”

“…Shirley [43] and Tougaard [44] developed two methods that are widely used for background subtraction. Moreover, Voigt function is commonly applied to fit the XPS lines [45][46][47].…”

“…This shift was explained by pinning of the Fermi level close to the conduction band maximum of Si and can be observed with photons of 160 eV thanks to enhanced surface sensitivity [46]. XPS is employed in nanostructure analysis to find the relative concentrations of elements, to monitor the SiÀSiO 2 phase separation of Si nanocrystals with SiO 2 host matrix, and to investigate the chemical states of their interfaces [45][46][47]50]. In 1996, Min et al [50] investigated the effect of Si concentration, annealing temperature, and time on PL spectra of Si nanocrystals.…”

“…The different chemical regions of the samples with their corresponding contribution to the spectrum are given in the inset schematics. Pure Si, pure SiO 2 , and suboxides SiO x are represented by white, dark gray, and gray, respectively[46].…”

Effect of hydrofluoric acid concentration on the evolution of photoluminescence characteristics in porous silicon nanowires prepared by Ag-assisted electroless etching method

“…The XPS spectra was fitted using 1 doublet (Si 2p 3/2 -Si 2p 1/2 ) (with a fixed area ratio equal to 2:1 and doublet separation of 0. [41][42][43][44] indicating the absence of þ2 Si oxidation state. The SiO 2 peak was relatively broad compared to the Si peak due to phonon broadening.…”