Abstract

Density functional theory simulations are used to predict ground state crystal structures, electronic properties, and thermodynamic stability of a new class of Si1-xGexN2O oxynitride materials with potential applications as tunable dielectrics. Thermochemical simulations are also used to explore their possible synthetic routes via reactions of ammonia with (a) mixtures of (SiH3)2O and (GeH3) 2O, and (b) a singlesource heteronuclear analogue SiH 3OGeH3.To obtain quantitative values for the above reaction energieswe implement a consistent computationalmethodology to simulate the structural and thermochemical properties of both molecular and solid state reactants and products at finite-temperature. In the case of the wellknown (SiH3)2O and (GeH3)2O compounds our calculatedmolecular structures and vibrational spectra are in excellent agreement with experiment. The hypothetical SiH3OGeH3 molecule is predicted to possess an intermediate molecular structure and energy, with stability differences on the order of 1-2 kcal/mol between SiH 3OGeH3 and mixtures of (SiH3) 2O/(GeH3)2O. For the solids we predict two new ordered structures: (i) an α-SiGeN2O phase composed of a uniform distribution of SiN3O and GeN3O tetrahedra, and (ii) a "pseudo-lamellar" form β-SiGeN2O in which the SiN3O and GeN3O units occupy alternating layers. The structural, electronic, and thermoelastic properties of the latter are then systematically compared to those of Si2N2O and Ge 2N2O. Here again, small energy differences comparable to those in the molecular case are found between the SiGeN2O polytypes and their Si2N2O/Ge2N2O analogues. The enthalpy of formation of α-SiGeN2O, β-SiGeN 2O, and a random SiGeN2O alloy are predicted to be comparable, indicating that mixing entropy should favor the disordered solid at high temperatures. Collectively, a remarkable consistency is found for the bond-lengths and bond-angles across molecular and solid-state forms. From an experimental perspective, the recent development of industrial scale synthesis for (SiH3)2O suggests that theGe-based analogues proposed here might be accessed using similar approaches, opening the door to new chemically compatible Si-Ge-O-Nhigh-k gate materials for high mobility Si-Ge based applications.

Original languageEnglish (US)
Pages (from-to)3884-3899
Number of pages16
JournalChemistry of Materials
Volume22
Issue number13
DOIs
StatePublished - Jul 13 2010

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Molecules
Bond length
Vibrational spectra
Ammonia
Electronic properties
Ground state
Molecular structure
Density functional theory
Enthalpy
Thermodynamic stability
Entropy
Crystal structure
Temperature
Experiments

ASJC Scopus subject areas

  • Materials Chemistry
  • Chemical Engineering(all)
  • Chemistry(all)

Cite this

Si-Ge-based oxynitrides : From molecules to solids. / Weng, C.; Kouvetakis, John; Chizmeshya, Andrew.

In: Chemistry of Materials, Vol. 22, No. 13, 13.07.2010, p. 3884-3899.

Research output: Contribution to journalArticle

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title = "Si-Ge-based oxynitrides: From molecules to solids",
abstract = "Density functional theory simulations are used to predict ground state crystal structures, electronic properties, and thermodynamic stability of a new class of Si1-xGexN2O oxynitride materials with potential applications as tunable dielectrics. Thermochemical simulations are also used to explore their possible synthetic routes via reactions of ammonia with (a) mixtures of (SiH3)2O and (GeH3) 2O, and (b) a singlesource heteronuclear analogue SiH 3OGeH3.To obtain quantitative values for the above reaction energieswe implement a consistent computationalmethodology to simulate the structural and thermochemical properties of both molecular and solid state reactants and products at finite-temperature. In the case of the wellknown (SiH3)2O and (GeH3)2O compounds our calculatedmolecular structures and vibrational spectra are in excellent agreement with experiment. The hypothetical SiH3OGeH3 molecule is predicted to possess an intermediate molecular structure and energy, with stability differences on the order of 1-2 kcal/mol between SiH 3OGeH3 and mixtures of (SiH3) 2O/(GeH3)2O. For the solids we predict two new ordered structures: (i) an α-SiGeN2O phase composed of a uniform distribution of SiN3O and GeN3O tetrahedra, and (ii) a {"}pseudo-lamellar{"} form β-SiGeN2O in which the SiN3O and GeN3O units occupy alternating layers. The structural, electronic, and thermoelastic properties of the latter are then systematically compared to those of Si2N2O and Ge 2N2O. Here again, small energy differences comparable to those in the molecular case are found between the SiGeN2O polytypes and their Si2N2O/Ge2N2O analogues. The enthalpy of formation of α-SiGeN2O, β-SiGeN 2O, and a random SiGeN2O alloy are predicted to be comparable, indicating that mixing entropy should favor the disordered solid at high temperatures. Collectively, a remarkable consistency is found for the bond-lengths and bond-angles across molecular and solid-state forms. From an experimental perspective, the recent development of industrial scale synthesis for (SiH3)2O suggests that theGe-based analogues proposed here might be accessed using similar approaches, opening the door to new chemically compatible Si-Ge-O-Nhigh-k gate materials for high mobility Si-Ge based applications.",
author = "C. Weng and John Kouvetakis and Andrew Chizmeshya",
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T1 - Si-Ge-based oxynitrides

T2 - From molecules to solids

AU - Weng, C.

AU - Kouvetakis, John

AU - Chizmeshya, Andrew

PY - 2010/7/13

Y1 - 2010/7/13

N2 - Density functional theory simulations are used to predict ground state crystal structures, electronic properties, and thermodynamic stability of a new class of Si1-xGexN2O oxynitride materials with potential applications as tunable dielectrics. Thermochemical simulations are also used to explore their possible synthetic routes via reactions of ammonia with (a) mixtures of (SiH3)2O and (GeH3) 2O, and (b) a singlesource heteronuclear analogue SiH 3OGeH3.To obtain quantitative values for the above reaction energieswe implement a consistent computationalmethodology to simulate the structural and thermochemical properties of both molecular and solid state reactants and products at finite-temperature. In the case of the wellknown (SiH3)2O and (GeH3)2O compounds our calculatedmolecular structures and vibrational spectra are in excellent agreement with experiment. The hypothetical SiH3OGeH3 molecule is predicted to possess an intermediate molecular structure and energy, with stability differences on the order of 1-2 kcal/mol between SiH 3OGeH3 and mixtures of (SiH3) 2O/(GeH3)2O. For the solids we predict two new ordered structures: (i) an α-SiGeN2O phase composed of a uniform distribution of SiN3O and GeN3O tetrahedra, and (ii) a "pseudo-lamellar" form β-SiGeN2O in which the SiN3O and GeN3O units occupy alternating layers. The structural, electronic, and thermoelastic properties of the latter are then systematically compared to those of Si2N2O and Ge 2N2O. Here again, small energy differences comparable to those in the molecular case are found between the SiGeN2O polytypes and their Si2N2O/Ge2N2O analogues. The enthalpy of formation of α-SiGeN2O, β-SiGeN 2O, and a random SiGeN2O alloy are predicted to be comparable, indicating that mixing entropy should favor the disordered solid at high temperatures. Collectively, a remarkable consistency is found for the bond-lengths and bond-angles across molecular and solid-state forms. From an experimental perspective, the recent development of industrial scale synthesis for (SiH3)2O suggests that theGe-based analogues proposed here might be accessed using similar approaches, opening the door to new chemically compatible Si-Ge-O-Nhigh-k gate materials for high mobility Si-Ge based applications.

AB - Density functional theory simulations are used to predict ground state crystal structures, electronic properties, and thermodynamic stability of a new class of Si1-xGexN2O oxynitride materials with potential applications as tunable dielectrics. Thermochemical simulations are also used to explore their possible synthetic routes via reactions of ammonia with (a) mixtures of (SiH3)2O and (GeH3) 2O, and (b) a singlesource heteronuclear analogue SiH 3OGeH3.To obtain quantitative values for the above reaction energieswe implement a consistent computationalmethodology to simulate the structural and thermochemical properties of both molecular and solid state reactants and products at finite-temperature. In the case of the wellknown (SiH3)2O and (GeH3)2O compounds our calculatedmolecular structures and vibrational spectra are in excellent agreement with experiment. The hypothetical SiH3OGeH3 molecule is predicted to possess an intermediate molecular structure and energy, with stability differences on the order of 1-2 kcal/mol between SiH 3OGeH3 and mixtures of (SiH3) 2O/(GeH3)2O. For the solids we predict two new ordered structures: (i) an α-SiGeN2O phase composed of a uniform distribution of SiN3O and GeN3O tetrahedra, and (ii) a "pseudo-lamellar" form β-SiGeN2O in which the SiN3O and GeN3O units occupy alternating layers. The structural, electronic, and thermoelastic properties of the latter are then systematically compared to those of Si2N2O and Ge 2N2O. Here again, small energy differences comparable to those in the molecular case are found between the SiGeN2O polytypes and their Si2N2O/Ge2N2O analogues. The enthalpy of formation of α-SiGeN2O, β-SiGeN 2O, and a random SiGeN2O alloy are predicted to be comparable, indicating that mixing entropy should favor the disordered solid at high temperatures. Collectively, a remarkable consistency is found for the bond-lengths and bond-angles across molecular and solid-state forms. From an experimental perspective, the recent development of industrial scale synthesis for (SiH3)2O suggests that theGe-based analogues proposed here might be accessed using similar approaches, opening the door to new chemically compatible Si-Ge-O-Nhigh-k gate materials for high mobility Si-Ge based applications.

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