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Journal ArticleDOI

An X-ray photoelectron study of the dependence of HF concentration on an etched silicon surface

01 Jun 1992-Journal of Electron Spectroscopy and Related Phenomena (Elsevier)-Vol. 58, Iss: 4, pp 261-270

AbstractUsing X-ray photoelectron spectroscopy, the chemical state of a silicon surface treated with hydrofluoric acid and the resulting contaminant species (fluorine, carbon and oxygen) were studied as a function of the etchant concentration (2–48%). The surface contamination was quantified as a function of the etchant concentration using a submonolayer coverage theory. It was seen that the carbon level had a minimum value (≈ 4.5×10 13 atoms cm −2 ) for 5% HF concentration, whereas the oxygen level was almost constant (i.e. the variation was from 2×10 13 -4×10 13 atoms cm −2 ), and the fluorine level showed a steady increase (2×10 13 -12×10 13 atoms cm −2 ) with the concentration of the etchant. So, by selecting a suitable concentration of the etchant it is possible to create a silicon surface which is relatively free from contamination. Also one can modulate the amount of fluorine incorporation on the silicon surface. more

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Abstract: Carboxylic acids are found to adsorb weakly to the native oxide surface of aluminum. Under heat exchange conditions, synergistic carboxylate combinations provide superior high-temperature aluminum corrosion protection and show excellent heat-transfer characteristics. The surface films formed under these dynamic heat-transfer conditions are characterized with the use of X-ray photoelectron spectroscopy (XPS). Fourier transform infrared (FT-IR) is also used for the study and characterization of the surface films formed. The results are compared with the FT-IR data of the pure Al-carboxylate complexes. The combination of these results reveals that, under heat transfer conditions, carboxylates are chemically bonded to the aluminum surface. This molecular film shows excellent inhibition properties for aluminum.

35 citations

11 Sep 1984
Abstract: Olefins are converted into other olefins having different numbers of carbon atoms by contact with a catalyst comprising an inorganic refractory oxide support containing at least one of tungsten oxide and molybdenum oxide and a promoting amount of at least one methylating agent under conditions suitable for the methylating agent compounds to promote the activity of tungsten and molybdenum oxides for the disproportionation reaction.

25 citations

Journal ArticleDOI
Abstract: Supports consisting of a thin layer of SiO 2 on a silicon single crystal have been used to study the NbO x /SiO 2 /Si(100) model catalyst, obtained by a controlled surface reaction between Nb(OC 2 H 5 ) 5 and silanol groups on the SiO 2 support. Characterization of the niobic acid monolayer has been performed by a combination of conventional, angle-resolved and depth profiling X-ray photoelectron spectroscopy (XPS). Compared to the powder analogues, a drastic increase in spectral resolution and detailed band structure is observed in the XPS spectra. The number of attached Nb atoms on the silicagel (specific surface, S BET = 345 m 2 g −1 ; pore diameter, 20 nm) has been determined as 6.86 × 10 4 mol g −1 with a surface density of 1.25 atoms nm −2 .

20 citations

Journal ArticleDOI
Abstract: Scanning tunneling spectroscopy and microscopy investigations have been carried out in air on thermally evaporated tungsten oxide thin films deposited onto silicon substrates. The films have been submitted to thermal annealing at different temperatures and for different times. The microscopy images show strong effects of recrystallization and different grain sizes depending on the thermal treatment. The spectroscopic data exhibit a rectifying characteristics and the comparison between the topographic and current images allows a better understanding of the sample morphology in relation to the electrical behavior. X-ray photoelectron spectroscopy valence band measurements have evidenced a structure near the Fermi level, which has been assigned to a structural oxygen deficiency of the deposited films, which is also observed in the conductance curve of some samples.

11 citations

Journal ArticleDOI
Abstract: Model supports consisting of a thin layer of SiO2 on a Silicon single crystal have been used to study the [W]n+/SiO2/Si (100) model catalyst precursor prepared by a controlled reaction of π-C5H5W(CO)3Cl with the SiO2 surface. Characterization of the tungsten surface species has been performed by combination of conventional, angle-resolved and depth-profiling X-ray photoelectron spectroscopy (XPS). The silica surface consists of highly dispersed W-oxide units linked by two Si–O–W bonds. Further, compared with the powder analogues, a drastic increase in spectral resolution and detailed band structure is observed in the XPS spectra.

10 citations

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Abstract: High-resolution gold-valence-band photoemission spectra were obtained by the use of monochromatized $\mathrm{Al} K\ensuremath{\alpha}$ radiation and a single-crystal specimen. After background and scattering corrections were made, the results were compared directly with broadened theoretical density-of-states functions. The following conclusions were drawn: (i) Relativistic band-structure calculations are required to fit the spectrum. (ii) Both the Korringa-Kohn-Rostoker calculation of Connolly and Johnson and the relativistic-augmented-plane-wave calculation by Christensen and Seraphin give density-of-states results that (after broadening) follow the experimental curve closely. (iii) Of the theoretical functions available to date, those with full Slater exchange agree best with experiment (perhaps because of a cancellation of errors). Fractional ($\frac{2}{3} or \frac{5}{6}$) exchange gives $d$ bands that are too wide. (iv) Eastman's 40.8-eV ultraviolet photoemission spectrum is similar to the x-ray spectrum, suggesting little dependence on photon energy above 40 eV. (v) Both (ii) and (iv) imply an absence of strong matrix-element modulation in the photoemission spectrum of gold.

4,896 citations

Journal ArticleDOI
Abstract: The results of calculations of photoelectric cross-sections for the Kα lines of magnesium at 1254 eV and of aluminum at 1487 eV are presented. All of the subshell cross-sections are given for Z values up to 96. The calculations were carried out relativistically using the single-potential Hartree-Slater atomic model.

4,639 citations

Journal ArticleDOI
Abstract: A low temperature thermal cleaning method for Si molecular beam epitaxy (MBE) is proposed. This method consists of wet chemical treatment to eliminate carbon contaminants on Si substrates, thin oxide film formation to protect the clean Si surface from contamination during processing before MBE growth, and desorption of the thin oxide film under UHV. The passivative oxide can be removed at temperatures below 800°C. It is confirmed that Si epitaxial growth can take place on substrates cleaned by this method and that high quality Si layers with dislocations of fewer than 100/cm2 and high mobility comparable to good bulk materials are formed. Surface cleanliness, the nature of thin passivative oxide films, and cleaning processes are also studied by using such surface analytic methods as Auger electron spectroscopy, reflection high energy electron diffraction, and x‐ray photoelectron spectroscopy.

1,324 citations

Journal ArticleDOI
TL;DR: It is found that a standard, widespread, chemical-preparation method for silicon, oxidation followed by an HF etch, results in a surface which from an electronic point of view is remarkably inactive, which has implications for the ultimate efficiency of silicon solar cells.
Abstract: We have found that a standard, widespread, chemical-preparation method for silicon, oxidation followed by an HF etch, results in a surface which from an electronic point of view is remarkably inactive. With preparation in this manner, the surface-recombination velocity on Si111g is only 0.25 cm/sec, which is the lowest value ever reported for any semiconductor. Multiple-internal-reflection infrared spectroscopy shows that the surface appears to be covered by covalent Si-H bonds, leaving virtually no surface dangling bonds to act as recombinatiuon centers. These results have implications for the ultimate efficiency of silicon solar cells.

886 citations

Journal ArticleDOI
Abstract: Polarized internal reflection spectroscopy has been used to characterize HF‐treated Si(111) surfaces. The silicon‐hydrogen stretching vibrations indicate that the surface is well ordered, but is microscopically rough, with coupled monohydride, dihydride, and trihydride termination.

406 citations