tan_2003#
G.-L. Tan, M. F. Lemon and R. H. French, “Optical properties and London dispersion forces of amorphous silica determined by vacuum ultraviolet spectroscopy and spectroscopic ellipsometry”, J. Am. Ceram. Soc. 86, 1885 (2003)
Source record · Catalogue · Review register
DOI: 10.1111/j.1151-2916.2003.tb03577.x
Source kind: measurement
Recorded technique: One bulk sample of Suprasil 1 (Heraeus; flame-fused synthetic silica, < 1 ppmw metallic impurities, 1200 ppmw OH), polished on both faces (p. 1886). Spectroscopic ellipsometry, 0.69-8.55 eV, at 60, 70 and 80 degrees (Woollam VUV-VASE, MgF2 polarizer, analyzer and autoretarder, nitrogen purged), fitted together with the UV/visible transmission of the same sample; vacuum-ultraviolet reflectance, 1.7-44 eV, with a laser-plasma source, monochromator and filters (resolution 0.2-0.6 nm: 16 meV at 10 eV, 200 meV at 35 eV) (p. 1886). The reflectance, scaled and joined to the ellipsometric results and extended with low- and high-energy wings, is Kramers-Kronig analysed for the reflected phase; n and k then follow algebraically from Eq. (4) (pp. 1887-1888).
Materials in structured entries: SiO2
Dataset quantities: band_gap
Contents: 4 datasets; 0 formulas.
Curation notes#
Journal pages 1885-1892 = pdf pages 1-8. Identity checked against the first page. The optical constants themselves (n and k, eps_1 and eps_2, the absorption coefficient, the interband transition strength Re[J_cv], n_eff, the energy-loss function and the London-dispersion spectrum) are in figures only; nothing tabulates them (they are not available in the library; see the curators’ notes on missing papers). What is tabulated is the band-gap fits (Table I, the datasets) and the Hamaker constants (Table II, notes).
RANGE. ‘over the range of 1.5 to 42 eV’ (abstract), ‘from 0.7 to 43 eV’ (conclusions); the ellipsometry and the Kramers-Kronig n and k ‘agree ... within the 0.7-8 eV energy range’, and both agree ‘very well’ with Philipp’s handbook values (philipp_1985) at 0.75-6 eV (Fig. 3; pp. 1886-1888).
FIGURES (not digitised): Fig. 1, ellipsometric Psi and Delta; Fig. 2, DUV transmission (cut-off near 7.87 eV); Fig. 3, n and k 0.7-8 eV with Philipp’s values; Fig. 4, reflectance 1.7-44 eV; Fig. 5, absorption coefficient 6.3-12 eV (VUV and ellipsometry); Fig. 6, n and k 0-44 eV; Fig. 7, eps_1 and eps_2 0-44 eV; Fig. 8, Re[J_cv]; Fig. 9, n_eff; Fig. 10, the energy-loss function; Fig. 11, the London-dispersion spectrum eps_2(i xi); Fig. 12, the geometry of the Hamaker calculation (extracted as a one-row table: not a table).
TEXT VALUES (no vocabulary quantity; notes only): - Reflectance peaks at 10.4, 11.6, 14.03 and 17.10 eV ‘as reported previously’ (p. 1889); new interband transitions in Re[J_cv] at 21.3 and 32 eV (the 32 eV one from O 2s, at -30.6 eV, to the conduction-band edge); the transitions are assigned on p. 1890 (14.03 eV: VB -14.3 to CB 0.27 eV; 17.4 eV: -16.9 to 0.5 eV; 21.3 eV: -20.1 to 1.2 eV). The text prints both 17.10 and 17.3/17.4 eV for the third feature. - The bulk plasmon: the energy-loss function peaks at 23.7 eV (p. 1890). - ‘The absorption is dramatically decreased below 9.2 eV’ (p. 1889). - n_eff: 9.8 electrons per SiO2 at or below 43 eV, 7.3 at 26 eV (‘very close to Philipp’s 7.7 electrons per SiO2 molecule near 26 eV’; philipp_1971’s text says ‘approaching 8 electrons’, so the 7.7 is presumably read from its Fig. 8); 16 expected in all (p. 1890). The formula-unit volume v_f = 45.3 A^3 (p. 1888); the prefactor m_0^2 e^-2 hbar^-2 = 8.289e-6 g cm^-3 eV^-2 in cgs, set to unity so that J_cv is in eV^2 (Eq. (5), p. 1888; the text calls it Eq. (2)). - Table II (p. 1891), the non-retarded Hamaker constants A_121^NR (zJ) from the interband transition spectrum, with wings Re[J_cv] ~ omega^-2 below and omega^-3 above the data, to 250 eV: [Suprasil SiO2 | vacuum | Suprasil SiO2] 71.6; | Al2O3 | 24.6; | water | 8.0; | MgO | 7.4; | SiO2 | 1.1; [Si3N4 | SiO3 (sic, SiO2 meant) | Si3N4] 38.2; [Suprasil SiO2 | water | air] -15.6. The extraction loses the minus sign of -15.6 and the vertical bars; the image and the text (‘the Hamaker constant becomes negative, approaching -15.6 zJ’) have them. The vacuum value is ‘larger than the previously reported value of 66 zJ’ (French 2000, ref. 52, pp. 1890-1891).
BAND GAPS (Table I, p. 1889; text pp. 1889-1890). A direct gap is fitted as a linear alpha^2 E^2 against E, an indirect gap as a linear alpha^(1/2) against E, in three ranges of alpha; ‘Formally direct and indirect band gap models do not apply to amorphous materials such as glass ... Here we are using the direct and indirect models only as a tool to characterize the complex absorption edge behavior of the sample’ (p. 1889). The low-absorption row (31-1436 and 13-1293 cm^-1) is ‘Calculated from ellipsometric spectroscopy’ (dagger note), the text says ‘from both VUV and ellipsometric spectra’; the others from the Kramers-Kronig absorption coefficient. The authors attribute the low 7.92 eV (against 9.0-9.3 eV from photoconductivity) to the OH content (Si-OH) and to defect and impurity absorption near 7.9 eV. No uncertainties are stated. The vocabulary has no direct/indirect kind: kind = ‘optical’ with parameters.transition (as ensley_2019).
The literature values quoted in the text are reproduced datasets. The DiStefano and Eastman reference is printed ‘Solid State Commun., 99, 2259-61 (1971)’ (ref. 42): volume 9 is meant (weinberg_1979 cites Solid State Commun. 9, 2259). Also quoted, notes only: Ching’s calculated gaps of crystalline polymorphs, 8.4-11 eV with the Si-O-Si geometry (ref. 6); the absorption edge ‘at around 9 eV’ by photoconductivity (ref. 11, Ikuta et al., which is a paper on laser-induced defects).
refractiveindex.info’s copies in data/external have no page for this paper.
Recorded bibliographic identity status: VALIDATED_WITH_WARNINGS. This concerns identification of the source; it does not establish the scientific correctness of its contents.
Datasets#
tan_2003/direct_gap#
{
"id": "direct_gap",
"material": "SiO2",
"file": "SiO2/tan_2003__direct_gap.csv",
"table": "tbl_1982492688af",
"quantity": "band_gap",
"unit": "eV",
"abscissa": "label",
"use": "primary",
"parameters": {
"kind": "optical",
"transition": "direct",
"grade": "Suprasil 1",
"form": "bulk",
"technique": "absorption-edge fit (alpha^2 E^2 linear in E)"
}
}
Table I, ‘Direct gap (eV)’, one row per absorption-coefficient fitting range (the row label): 7.92 eV at 31-1436 cm^-1 (ellipsometry; the dagger), 9.55 eV at 2.5e5-5.6e5 and 9.90 eV at 5.6e5-1.1e6 cm^-1 (VUV Kramers-Kronig). ‘The evaluated direct gap ... in the upper limit is about 9.9 eV corresponding to alpha = 5.6e5 cm^-1, which is similar to Ravindra’s result’ (p. 1889). The value depends on the range: a characterisation of the edge, not a unique gap.
tan_2003/indirect_gap#
{
"id": "indirect_gap",
"material": "SiO2",
"file": "SiO2/tan_2003__indirect_gap.csv",
"table": "tbl_1982492688af",
"quantity": "band_gap",
"unit": "eV",
"abscissa": "label",
"use": "primary",
"parameters": {
"kind": "optical",
"transition": "indirect",
"grade": "Suprasil 1",
"form": "bulk",
"technique": "absorption-edge fit (alpha^(1/2) linear in E)"
}
}
Table I, ‘Indirect gap (eV)’, one row per fitting range (the row label): 7.72 eV at 13-1293 cm^-1 (ellipsometry; the dagger), 8.30 eV at 2.4e4-1.7e5 and 8.90 eV at 1.3e5-1.1e6 cm^-1. As direct_gap.
tan_2003/literature_optical#
{
"id": "literature_optical",
"material": "SiO2",
"table": "text",
"quantity": "band_gap",
"unit": "eV",
"abscissa": "label",
"use": "reproduced",
"reproduced_from": [
"R. H. French, R. A. Rahme, D. J. Jones and L. E. McNeil, Ceram. Trans. 28, 63 (1992)",
"N. M. Ravindra and J. Narayan, J. Appl. Phys. 60, 1139 (1986)"
],
"parameters": {
"kind": "optical",
"transition": "direct"
}
}
2 inline points in the source record.
p. 1885: ‘The experimentally determined direct band gap energy of fused SiO2 ranges from 7.52 eV (alpha = 14 cm^-1) [7] to 9.6 eV (alpha = 4 x 10^5 cm^-1) [8]’; also ‘the direct band gap of Suprasil 1 SiO2 glass containing OH was reported to be 7.52 eV [7]’. Direct-gap fits at the stated absorption levels.
tan_2003/literature_photoconductivity#
{
"id": "literature_photoconductivity",
"material": "SiO2",
"table": "text",
"quantity": "band_gap",
"unit": "eV",
"abscissa": "label",
"use": "reproduced",
"reproduced_from": [
"weinberg_1979",
"T. H. DiStefano and D. E. Eastman, Solid State Commun. 9, 2259 (1971)"
],
"parameters": {
"kind": "photoconductivity"
}
}
2 inline points in the source record.
p. 1889: ‘Weinberg et al. [41] as well as DiStefano and Eastman [42] have reviewed other experimental determinations of the direct band gap of SiO2 and reported values of 9.3 and 9.0 eV, respectively, for the band gap of SiO2 from photoconductivity measurements.’ Both are in weinberg_1979 (its band_gap and literature_photoconductivity datasets); DiStefano and Eastman’s volume is misprinted 99 in ref. 42.
Formulas#
No formulas are recorded.
Corrections#
No dataset errata are recorded in this source record.
Formula corrections, where recorded, appear with their formulas above. Curation notes may also discuss corrections or unresolved interpretation. Consult the review register for the checks and decisions.