Experimental evidence for Na coordination to bridging oxygen in Na-silicate glasses: Implications for spectroscopic studies and for the modified random network model

Hard X-ray photoelectron spectra (HXPES) of bulk non-conductor vitreous SiO 2 : Minimum linewidths and surface chemical shifts

“…Second, using a thin metal films on the SiO 2 , we want to quantify the increase in escape depth for SiO 2 from 1486 eV to 5000 eV photon energies, and demonstrate that we can use the O 1s and Si 1s chemical shifts created by the interface Cr-subox to indirectly determine the unknown intensity of the expected [13,23,24], but not previously observed, surface peaks. Third, we will also show that the minimum Si 1s linewidths obtained are consistent with that expected from the final state vibrational broadening mechanism outlined previously for the Si 2p and O 1s linewidths [12][13][14][15][17][18][19]]. …”

“…For example, the present experimental and theoretical IMFP values show that the IMPF increases from 2.7 nm at 1486 eV to 16 nm at 10 keV [5,6,8] giving a so-called analysis depth increase (for 95% detection of photoelectrons) of ∼8 to ∼50 nm, respectively. We demonstrate here that the O 1s spectra of the silicate SiO 2 collected at 2.5 to 5 keV contain very weak surface signals; and such future high-energy spectra of bulk silicate glasses could confirm that these surface contributions are not generally important [12][13][14][15].…”

“…A high purity vitreous SiO 2 glass rod [12,13,15] was used as the test sample. The rod was fractured outside of the vacuum chamber and a thin, flat piece was selected and loaded immediately into the transfer chamber of the XPS endstation.…”

“…Bulk analysis can be obtained because the XPS escape depth or inelastic mean free path (IMFP) at 10,000 eV photon energy is >10 nm compared to a 2-3 nm escape depth at the "normal" laboratory photon energy [11], it is easy to quantify the three types of O present in these bulk glasses: (1) bridging oxygen (Si O Si, so-called BO), (2) nonbridging oxygen (Si O M, so-called NBO), and (3) so-called "free oxide" (M O M) after showing that possible surface effects (from radiation decomposition, surface chemical shifts, and adsorbed OH [12][13][14][15]) are either unimportant or can be compensated for [10][11][12][13]. The much larger IMFP's provided by HXPES provide us with the opportunity of obtaining bulk O analyses directly because the surface contributions will be greatly minimized.…”

“…For example, the O 1s linewidths from one O species on non-conducting silicate minerals and glasses using the Kratos XPS are 1.25 ± 0.1 eV (the minimum expected from theoretical considerations [17][18][19]), compared to O 1s linewidths of closer to 2 eV for instruments using conventional electron flood guns for charge compensation [13,16]. These much better linewidths are critical for optimum resolution of the BO and NBO peaks in silicates, and for accurate analysis of the BO, NBO and free oxide content of these glasses [12][13][14][15].…”