Thermodynamics and phase stability in the Si–O system

We investigated thermal oxide layers of different thickness on (100) and (111) silicon substrates by STEM/EELS to determine the stoichiometry profiles and compared these with stoichiometry profiles of plate-like and octahedral oxide precipitates in silicon. It was found that the stoichiometry of SiO x (x = 2) cannot be reached if the oxide layer thickness is lower than 10 nm for thermal oxides grown at 900 • C. This is due to an interface layer of equal maximum slope of x for all oxide layers. The slope of x is the change in stoichiometry with position and was obtained from fitting by sigmoid functions. Similar results were found for the oxide precipitates in silicon. However, there are arguments which question the slope determined via the low loss EEL spectra and the maximum x value could be closer to 2 in reality. On a sample with an oxide layer of 13.9 nm thickness we compared stoichiometry profiles obtained from the plasmon region and the Si-K 2,3 and O-K ionization edges. The width of the interface measured on stoichiometry profiles decreases with increasing energy loss and is lowest for the O-K ionization edge with a width of 1. In a previous work, we found that both the interface between an oxide precipitate and the surrounding silicon matrix and the interface between a silicon substrate and a thermal oxide layer are of the same nature.1 In both cases, between SiO 2 existing in the center of the precipitate and in the oxide layer and Si of the matrix and the substrate a suboxide region of 2-3 nm was found. These results were obtained by electron energy loss spectrometry (EELS) carried out by scanning transmission electron microscopy (STEM). In the low loss region, it is possible to distinguish between Si, SiO, and SiO 2 which all exhibit different maxima of the plasmon loss energy. By deconvolution, the local composition of the phase can be determined with the help of reference spectra of the three components.The stoichiometry of the oxide precipitates (SiO x ) was debated for a long time and application of different methods on different samples containing oxygen precipitates resulted in different values for x ranging from 1 to 2. Recently, it was demonstrated by applying several direct and indirect methods that the oxide precipitates consist of SiO 2 .2 Inspired by the results in Ref. 1 and 2, a layer model was proposed explaining the different experimental values for x for oxide precipitates of different geometry.3 Especially, for plate-like precipitates with a small aspect ratio the lower x values could be explained assuming that they consist of SiO 2 surrounded by a 2 nm SiO shell. However, neither is it known until now if all oxide precipitates consist of SiO 2 in the center nor is it known how thick the suboxide region for oxide precipitates grown at different temperature and time is. It needs to be mentioned that the suboxide region is not a layer of SiO composition but a profile of x increasing from the silicon matrix to the SiO 2 core. The impression of a layer just stems from the analysis of ele...

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“…• C. We plotted these results into the Si-O phase diagram 21 showing only the metastable phase boundaries in Fig. 16.…”

Section: Resultsmentioning

confidence: 99%

Investigation of the Composition of the Si/SiO₂Interface in Oxide Precipitates and Oxide Layers on Silicon by STEM/EELS

Kissinger

Schubert

Kot

et al. 2017

ECS J. Solid State Sci. Technol.

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“…In this regard, the associate solution model [12e14] is found to be more suitable, and is therefore used in this study to describe the liquid phase. A comprehensive study was carried out by Schnurre et al [15] on the SieO system beyond the work of Hallstedt [9]. The authors [15] presented a thorough literature review, critical thermodynamic assessment, and experimental investigation of this system.…”

Section: Introductionmentioning

confidence: 99%

“…A comprehensive study was carried out by Schnurre et al [15] on the SieO system beyond the work of Hallstedt [9]. The authors [15] presented a thorough literature review, critical thermodynamic assessment, and experimental investigation of this system. In contrast to the published phase diagram by Hallstedt [9], SiO 2 with tridymite structure was not considered as a stable phase in their work.…”

Section: Introductionmentioning

confidence: 99%

“…This is because Florke [16] has claimed that the existence of tridymite SiO 2 is due to the alkaline impurities. In the work of Schnurre et al [15], Si-rich liquid phase was described by the substitutional solution model, while SiO 2 (L) including stable liquid silica, glass and supercooled liquid was modeled as a stoichiometric phase. The SieO system was reassessed in this study on the basis of Schnurre et al's work [15].…”

Section: Introductionmentioning

confidence: 99%

“…In the work of Schnurre et al [15], Si-rich liquid phase was described by the substitutional solution model, while SiO 2 (L) including stable liquid silica, glass and supercooled liquid was modeled as a stoichiometric phase. The SieO system was reassessed in this study on the basis of Schnurre et al's work [15]. The major difference is that the Si-rich liquid phase and SiO 2 (L) described as two separated phases in [15] were describes as one phase in this study using an associate solution model, and SiO 2 is treated as one of the associates in the liquid.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Thermodynamic modeling of the Al–Si–Sr–O quaternary system

Zhang

Cao

et al. 2010

Intermetallics

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Liquid‐vapor phase relations in the Si‐O system: A calorically constrained van der Waals‐type model

Connolly

2016

JGR Planets

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This work explores the use of several van der Waals (vW)‐type equations of state (EoS) for predicting vaporous phase relations and speciation in the Si‐O system, with emphasis on the azeotropic boiling curve of SiO2‐rich liquid. Comparison with the observed Rb and Hg boiling curves demonstrates that prediction accuracy is improved if the a‐parameter of the EoS, which characterizes vW forces, is constrained by ambient pressure heat capacities. All EoS considered accurately reproduce metal boiling curve trajectories, but absent knowledge of the true critical compressibility factor, critical temperatures remain uncertain by ~500 K. The EoS plausibly represent the termination of the azeotropic boiling curve of silica‐rich liquid by a critical point across which the dominant Si oxidation state changes abruptly from the tetravalent state characteristic of the liquid to the divalent state characteristic of the vapor. The azeotropic composition diverges from silica toward metal‐rich compositions with increasing temperature. Consequently, silica boiling is divariant and atmospheric loss after a giant impact would enrich residual silicate liquids in reduced silicon. Two major sources of uncertainty in the boiling curve prediction are the heat capacity of silica liquid, which may decay during depolymerization from the near‐Dulong‐Petit limit heat capacity of the ionic liquid to value characteristic of the molecular liquid, and the unknown liquid affinity of silicon monoxide. Extremal scenarios for these uncertainties yield critical temperatures and compositions of 5200–6200 K and Si1.1O2–Si1.4O2. The lowest critical temperatures are marginally consistent with shock experiments and are therefore considered more probable.

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Thermodynamics and phase stability in the Si–O system

Cited by 137 publications

References 141 publications

Investigation of the Composition of the Si/SiO₂Interface in Oxide Precipitates and Oxide Layers on Silicon by STEM/EELS

Investigation of the Composition of the Si/SiO₂Interface in Oxide Precipitates and Oxide Layers on Silicon by STEM/EELS

Thermodynamic modeling of the Al–Si–Sr–O quaternary system

Liquid‐vapor phase relations in the Si‐O system: A calorically constrained van der Waals‐type model

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Thermodynamics and phase stability in the Si–O system

Cited by 137 publications

References 141 publications

Investigation of the Composition of the Si/SiO2Interface in Oxide Precipitates and Oxide Layers on Silicon by STEM/EELS

Investigation of the Composition of the Si/SiO2Interface in Oxide Precipitates and Oxide Layers on Silicon by STEM/EELS

Thermodynamic modeling of the Al–Si–Sr–O quaternary system

Liquid‐vapor phase relations in the Si‐O system: A calorically constrained van der Waals‐type model

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Investigation of the Composition of the Si/SiO₂Interface in Oxide Precipitates and Oxide Layers on Silicon by STEM/EELS

Investigation of the Composition of the Si/SiO₂Interface in Oxide Precipitates and Oxide Layers on Silicon by STEM/EELS