Qimin Yan - Academia.edu (original) (raw)
Papers by Qimin Yan
Bulletin of the American Physical Society, Mar 5, 2015
First-principles study of MnNiO 3 as an alkaline oxygen-evolution photocatalyst JIE YU,tory -We p... more First-principles study of MnNiO 3 as an alkaline oxygen-evolution photocatalyst JIE YU,tory -We present a first-principles study of MnNiO 3 , a promising oxygen-evolution photocatalyst. Using density functional theory with the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we compute and analyze the ground-state geometry and electronic structure. We find that MnNiO 3 is a ferrimagnetic semiconductor with an indirect band gap, consistent with experimental observations. We also predict that MnNiO 3 has promising band edge positions relative to the vacuum, with potential to straddle the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) redox potentials in aqueous solution. A detailed analysis of the band structure and density of states provides a clear explanation why MnNiO 3 is promising for OER. Pourbaix diagram calculations suggest that MnNiO 3 is stable in alkaline solution at potentials relevant for oxygen evolution.
Physical chemistry chemical physics : PCCP, Jan 14, 2016
Deployment of solar fuels technology requires photoanodes with long term stability, which can be ... more Deployment of solar fuels technology requires photoanodes with long term stability, which can be accomplished using light absorbers that self-passivate under operational conditions. Several copper vanadates have been recently reported as promising photoanode materials, and their stability and self-passivation is demonstrated through a combination of Pourbaix calculations and combinatorial experimentation.
Walsh/Computational, 2013
The Journal of Chemical Physics, 2011
Band gaps and band alignments for AlN, GaN, InN, and InGaN alloys are investigated using density ... more Band gaps and band alignments for AlN, GaN, InN, and InGaN alloys are investigated using density functional theory with the with the Heyd-Scuseria-Ernzerhof {HSE06 [J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 134, 8207 (2003); 124, 219906 (2006)]} XC functional. The band gap of InGaN alloys as a function of In content is calculated and a strong bowing at low In content is found, described by bowing parameters 2.29 eV at 6.25% and 1.79 eV at 12.5%, indicating the band gap cannot be described by a single composition-independent bowing parameter. Valence-band maxima (VBM) and conduction-band minima (CBM) are aligned by combining bulk calculations with surface calculations for nonpolar surfaces. The influence of surface termination [(1100) mplane or (1120) a-plane] is thoroughly investigated. We find that for the relaxed surfaces of the binary nitrides the difference in electron affinities between m-and a-plane is less than 0.1 eV. The absolute electron affinities are found to strongly depend on the choice of XC functional. However, we find that relative alignments are less sensitive to the choice of XC functional. In particular, we find that relative alignments may be calculated based on Perdew-Becke-Ernzerhof [J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 134, 3865 (1996)] surface calculations with the HSE06 lattice parameters. For InGaN we find that the VBM is a linear function of In content and that the majority of the band-gap bowing is located in the CBM. Based on the calculated electron affinities we predict that InGaN will be suited for water splitting up to 50% In content.
Applied Physics Letters, Nov 1, 2010
The effect of strain on the valence-band structure of (112¯2) semipolar InGaN grown on GaN substr... more The effect of strain on the valence-band structure of (112¯2) semipolar InGaN grown on GaN substrates is studied. A kṡp analysis reveals that anisotropic strain in the c-plane and shear strain are crucial for deciding the ordering of the two topmost valence bands. The shear-strain deformation potential D6 is calculated for GaN and InN using density functional theory with the Heyd-Scuseria-Ernzerhof hybrid functional [J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 124, 219906 (2006)]. Using our deformation potentials and assuming a pseudomorphically strained structure, no polarization switching is observed. We investigate the role of partial strain relaxation in the observed polarization switching.
Strain plays a crucial role in group-III nitride semiconductor based devices since it affects the... more Strain plays a crucial role in group-III nitride semiconductor based devices since it affects the band structure near the valence- and conduction-band edges and thus the optical properties and the device characteristics. However, the deformation potentials that describe the change in band structure under strain have not yet been reliably determined. We present a systematic study of the strain effects
Group-II oxide semiconductors (MgO, ZnO, and CdO) are excellent candidates for use in solid state... more Group-II oxide semiconductors (MgO, ZnO, and CdO) are excellent candidates for use in solid state lighting. Due to the lattice mismatch between oxide epilayers and substrates, strain effects (described by deformation potential parameters) play a crucial role in the band structure. On the other hand, the band dispersion in the vicinity of the band extrema (described by effective masses and
Group-II oxide semiconductors (MgO, ZnO, and CdO) are excellent candidates for use in solid state... more Group-II oxide semiconductors (MgO, ZnO, and CdO) are excellent candidates for use in solid state lighting. Due to the lattice mismatch between oxide epilayers and substrates, strain effects (described by deformation potential parameters) play a crucial role in the band structure. On the other hand, the band dispersion in the vicinity of the band extrema (described by effective masses and
Advanced Energy Materials, 2015
InGaN alloys are successfully being used in optical, electronic, and photovoltaic devices; a nove... more InGaN alloys are successfully being used in optical, electronic, and photovoltaic devices; a novel application is for photochemical water splitting. In order to further improve InGaN-based devices a detailed understanding of the materials properties as a function of alloy composition is needed. To obtain such insight we have investigated the band bowing of InGaN alloys and the strain effects in GaN and InN in the wurtzite phase using density functional theory. The HSE exchange correlation functional has been used in order to accurately calculate the electronic band structure [1]. We will discuss bowing effects in InGaN alloys based on accurate calculation of band gaps of InGaN alloys and on a analysis of experimental results using our calculated deformation potentials to disentangle the effect of strain and alloying on the band gap. [4pt] [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003)
Optics express, Jan 14, 2013
Linear polarized electroluminescence was investigated for semipolar (3031) and (3031) InGaN light... more Linear polarized electroluminescence was investigated for semipolar (3031) and (3031) InGaN light-emitting diodes (LEDs) with various indium compositions. A high degree of optical polarization was observed for devices on both planes, ranging from 0.37 at 438 nm to 0.79 at 519 nm. The extracted valence band energy separation was consistent with the optical polarization ratios. The effect of anisotropic strain on the valance band structure was studied using k?p method for the above two planes. The theoretical calculations are consistent with the experimental results.
Chemical communications (Cambridge, England), Jan 3, 2015
We present a first-principles study of MnNiO3, a promising oxygen-evolution photocatalyst. Using ... more We present a first-principles study of MnNiO3, a promising oxygen-evolution photocatalyst. Using density functional theory with the PBE + U functional and the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we compute and analyze the ground-state geometry and electronic structure. We find that MnNiO3 is a ferrimagnetic semiconductor with an indirect band gap, consistent with experimental observations. We also predict that MnNiO3 has promising band edge positions relative to the vacuum, with potential to straddle the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) redox potentials in aqueous solution. A detailed analysis of the band structure and density of states provides a clear explanation for why MnNiO3 has appropriate electronic properties for OER. Furthermore, comprehensive calculations of its Pourbaix diagram suggest that MnNiO3 is stable in alkaline solution at potentials relevant for oxygen evolution.
First-principles study of MnNiO 3 as an alkaline oxygen-evolution photocatalyst JIE YU,tory -We p... more First-principles study of MnNiO 3 as an alkaline oxygen-evolution photocatalyst JIE YU,tory -We present a first-principles study of MnNiO 3 , a promising oxygen-evolution photocatalyst. Using density functional theory with the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we compute and analyze the ground-state geometry and electronic structure. We find that MnNiO 3 is a ferrimagnetic semiconductor with an indirect band gap, consistent with experimental observations. We also predict that MnNiO 3 has promising band edge positions relative to the vacuum, with potential to straddle the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) redox potentials in aqueous solution. A detailed analysis of the band structure and density of states provides a clear explanation why MnNiO 3 is promising for OER. Pourbaix diagram calculations suggest that MnNiO 3 is stable in alkaline solution at potentials relevant for oxygen evolution.
Applied Physics Letters, 2014
ABSTRACT To aid the development of AlN-based optoelectronics, it is essential to identify the def... more ABSTRACT To aid the development of AlN-based optoelectronics, it is essential to identify the defects that cause unwanted light absorption and to minimize their impact. Using hybrid functional calculations, we investigate the role of native defects and their complexes with oxygen, a common impurity in AlN. We find that Al vacancies are the source of the absorption peak at 3.4 eV observed in irradiated samples and of the luminescence signals at 2.78 eV. The absorption peak at similar to 4.0 eV and higher, and luminescence signals around 3.2 and 3.6 eV observed in AlN samples with high oxygen concentrations are attributed to complexes of Al vacancies and oxygen impurities. We also propose a transition involving Al and N vacancies and oxygen impurities that may be a cause of the absorption band peaked at 2.9 eV. (C) 2014 AIP Publishing LLC.
Physical Review B, 2014
We present a systematic study of strain effects on the electronic band structure of the group-III... more We present a systematic study of strain effects on the electronic band structure of the group-III-nitrides (AlN, GaN and InN) in the wurtzite phase. The calculations are based on density functional theory with band-gapcorrected approaches including the Heyd-Scuseria-Ernzerhof hybrid functional (HSE) and quasiparticle G 0 W 0 methods. We study strain effects under realistic strain conditions, hydrostatic pressure, and biaxial stress. The strain-induced modification of the band structures is found to be nonlinear; transition energies and crystal-field splittings show a strong nonlinear behavior under biaxial stress. For the linear regime around the experimental lattice parameters, we present a complete set of deformation potentials (a cz , a ct , D 1 , D 2 , D 3 , D 4 , D 5 , D 6 ) that allows us to predict the band positions of group-III nitrides and their alloys (InGaN and AlGaN) under realistic strain conditions. The benchmarking G 0 W 0 results for GaN agree well with the HSE data and indicate that HSE provides an appropriate description for the band structures of nitrides. We present a systematic study of strain effects on the electronic band structure of the group-III nitrides (AlN, GaN, and InN). We quantify the nonlinearity of strain effects by introducing a set of bowing parameters. We apply the calculated deformation potentials to the prediction of strain effects on transition energies and valence-band structures of InGaN alloys and quantum wells (QWs) grown on GaN, in various orientations (including c-plane, m-plane, and semipolar). The calculated band gap bowing parameters, including the strain effect for c-plane InGaN, agree well with the results obtained by hybrid functional alloy calculations. For semipolar InGaN QWs grown in , and (3031) orientations, our calculated deformation potentials have provided results for polarization ratios in good agreement with the experimental observations, providing further confidence in the accuracy of our values.
Frontiers of Physics in China, 2009
The successful fabrication of single layer graphene has greatly stimulated the progress of the re... more The successful fabrication of single layer graphene has greatly stimulated the progress of the research on graphene. In this article, focusing on the basic electronic and transport properties of graphene nanoribbons (GNRs), we review the recent progress of experimental fabrication of GNRs, and the theoretical and experimental investigations of physical properties and device applications of GNRs. We also briefly discuss the research efforts on the spin polarization of GNRs in relation to the edge states.
Advanced Energy Materials, 2015
Bulletin of the American Physical Society, Mar 5, 2015
First-principles study of MnNiO 3 as an alkaline oxygen-evolution photocatalyst JIE YU,tory -We p... more First-principles study of MnNiO 3 as an alkaline oxygen-evolution photocatalyst JIE YU,tory -We present a first-principles study of MnNiO 3 , a promising oxygen-evolution photocatalyst. Using density functional theory with the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we compute and analyze the ground-state geometry and electronic structure. We find that MnNiO 3 is a ferrimagnetic semiconductor with an indirect band gap, consistent with experimental observations. We also predict that MnNiO 3 has promising band edge positions relative to the vacuum, with potential to straddle the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) redox potentials in aqueous solution. A detailed analysis of the band structure and density of states provides a clear explanation why MnNiO 3 is promising for OER. Pourbaix diagram calculations suggest that MnNiO 3 is stable in alkaline solution at potentials relevant for oxygen evolution.
Physical chemistry chemical physics : PCCP, Jan 14, 2016
Deployment of solar fuels technology requires photoanodes with long term stability, which can be ... more Deployment of solar fuels technology requires photoanodes with long term stability, which can be accomplished using light absorbers that self-passivate under operational conditions. Several copper vanadates have been recently reported as promising photoanode materials, and their stability and self-passivation is demonstrated through a combination of Pourbaix calculations and combinatorial experimentation.
Walsh/Computational, 2013
The Journal of Chemical Physics, 2011
Band gaps and band alignments for AlN, GaN, InN, and InGaN alloys are investigated using density ... more Band gaps and band alignments for AlN, GaN, InN, and InGaN alloys are investigated using density functional theory with the with the Heyd-Scuseria-Ernzerhof {HSE06 [J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 134, 8207 (2003); 124, 219906 (2006)]} XC functional. The band gap of InGaN alloys as a function of In content is calculated and a strong bowing at low In content is found, described by bowing parameters 2.29 eV at 6.25% and 1.79 eV at 12.5%, indicating the band gap cannot be described by a single composition-independent bowing parameter. Valence-band maxima (VBM) and conduction-band minima (CBM) are aligned by combining bulk calculations with surface calculations for nonpolar surfaces. The influence of surface termination [(1100) mplane or (1120) a-plane] is thoroughly investigated. We find that for the relaxed surfaces of the binary nitrides the difference in electron affinities between m-and a-plane is less than 0.1 eV. The absolute electron affinities are found to strongly depend on the choice of XC functional. However, we find that relative alignments are less sensitive to the choice of XC functional. In particular, we find that relative alignments may be calculated based on Perdew-Becke-Ernzerhof [J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 134, 3865 (1996)] surface calculations with the HSE06 lattice parameters. For InGaN we find that the VBM is a linear function of In content and that the majority of the band-gap bowing is located in the CBM. Based on the calculated electron affinities we predict that InGaN will be suited for water splitting up to 50% In content.
Applied Physics Letters, Nov 1, 2010
The effect of strain on the valence-band structure of (112¯2) semipolar InGaN grown on GaN substr... more The effect of strain on the valence-band structure of (112¯2) semipolar InGaN grown on GaN substrates is studied. A kṡp analysis reveals that anisotropic strain in the c-plane and shear strain are crucial for deciding the ordering of the two topmost valence bands. The shear-strain deformation potential D6 is calculated for GaN and InN using density functional theory with the Heyd-Scuseria-Ernzerhof hybrid functional [J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 124, 219906 (2006)]. Using our deformation potentials and assuming a pseudomorphically strained structure, no polarization switching is observed. We investigate the role of partial strain relaxation in the observed polarization switching.
Strain plays a crucial role in group-III nitride semiconductor based devices since it affects the... more Strain plays a crucial role in group-III nitride semiconductor based devices since it affects the band structure near the valence- and conduction-band edges and thus the optical properties and the device characteristics. However, the deformation potentials that describe the change in band structure under strain have not yet been reliably determined. We present a systematic study of the strain effects
Group-II oxide semiconductors (MgO, ZnO, and CdO) are excellent candidates for use in solid state... more Group-II oxide semiconductors (MgO, ZnO, and CdO) are excellent candidates for use in solid state lighting. Due to the lattice mismatch between oxide epilayers and substrates, strain effects (described by deformation potential parameters) play a crucial role in the band structure. On the other hand, the band dispersion in the vicinity of the band extrema (described by effective masses and
Group-II oxide semiconductors (MgO, ZnO, and CdO) are excellent candidates for use in solid state... more Group-II oxide semiconductors (MgO, ZnO, and CdO) are excellent candidates for use in solid state lighting. Due to the lattice mismatch between oxide epilayers and substrates, strain effects (described by deformation potential parameters) play a crucial role in the band structure. On the other hand, the band dispersion in the vicinity of the band extrema (described by effective masses and
Advanced Energy Materials, 2015
InGaN alloys are successfully being used in optical, electronic, and photovoltaic devices; a nove... more InGaN alloys are successfully being used in optical, electronic, and photovoltaic devices; a novel application is for photochemical water splitting. In order to further improve InGaN-based devices a detailed understanding of the materials properties as a function of alloy composition is needed. To obtain such insight we have investigated the band bowing of InGaN alloys and the strain effects in GaN and InN in the wurtzite phase using density functional theory. The HSE exchange correlation functional has been used in order to accurately calculate the electronic band structure [1]. We will discuss bowing effects in InGaN alloys based on accurate calculation of band gaps of InGaN alloys and on a analysis of experimental results using our calculated deformation potentials to disentangle the effect of strain and alloying on the band gap. [4pt] [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003)
Optics express, Jan 14, 2013
Linear polarized electroluminescence was investigated for semipolar (3031) and (3031) InGaN light... more Linear polarized electroluminescence was investigated for semipolar (3031) and (3031) InGaN light-emitting diodes (LEDs) with various indium compositions. A high degree of optical polarization was observed for devices on both planes, ranging from 0.37 at 438 nm to 0.79 at 519 nm. The extracted valence band energy separation was consistent with the optical polarization ratios. The effect of anisotropic strain on the valance band structure was studied using k?p method for the above two planes. The theoretical calculations are consistent with the experimental results.
Chemical communications (Cambridge, England), Jan 3, 2015
We present a first-principles study of MnNiO3, a promising oxygen-evolution photocatalyst. Using ... more We present a first-principles study of MnNiO3, a promising oxygen-evolution photocatalyst. Using density functional theory with the PBE + U functional and the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we compute and analyze the ground-state geometry and electronic structure. We find that MnNiO3 is a ferrimagnetic semiconductor with an indirect band gap, consistent with experimental observations. We also predict that MnNiO3 has promising band edge positions relative to the vacuum, with potential to straddle the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) redox potentials in aqueous solution. A detailed analysis of the band structure and density of states provides a clear explanation for why MnNiO3 has appropriate electronic properties for OER. Furthermore, comprehensive calculations of its Pourbaix diagram suggest that MnNiO3 is stable in alkaline solution at potentials relevant for oxygen evolution.
First-principles study of MnNiO 3 as an alkaline oxygen-evolution photocatalyst JIE YU,tory -We p... more First-principles study of MnNiO 3 as an alkaline oxygen-evolution photocatalyst JIE YU,tory -We present a first-principles study of MnNiO 3 , a promising oxygen-evolution photocatalyst. Using density functional theory with the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we compute and analyze the ground-state geometry and electronic structure. We find that MnNiO 3 is a ferrimagnetic semiconductor with an indirect band gap, consistent with experimental observations. We also predict that MnNiO 3 has promising band edge positions relative to the vacuum, with potential to straddle the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) redox potentials in aqueous solution. A detailed analysis of the band structure and density of states provides a clear explanation why MnNiO 3 is promising for OER. Pourbaix diagram calculations suggest that MnNiO 3 is stable in alkaline solution at potentials relevant for oxygen evolution.
Applied Physics Letters, 2014
ABSTRACT To aid the development of AlN-based optoelectronics, it is essential to identify the def... more ABSTRACT To aid the development of AlN-based optoelectronics, it is essential to identify the defects that cause unwanted light absorption and to minimize their impact. Using hybrid functional calculations, we investigate the role of native defects and their complexes with oxygen, a common impurity in AlN. We find that Al vacancies are the source of the absorption peak at 3.4 eV observed in irradiated samples and of the luminescence signals at 2.78 eV. The absorption peak at similar to 4.0 eV and higher, and luminescence signals around 3.2 and 3.6 eV observed in AlN samples with high oxygen concentrations are attributed to complexes of Al vacancies and oxygen impurities. We also propose a transition involving Al and N vacancies and oxygen impurities that may be a cause of the absorption band peaked at 2.9 eV. (C) 2014 AIP Publishing LLC.
Physical Review B, 2014
We present a systematic study of strain effects on the electronic band structure of the group-III... more We present a systematic study of strain effects on the electronic band structure of the group-III-nitrides (AlN, GaN and InN) in the wurtzite phase. The calculations are based on density functional theory with band-gapcorrected approaches including the Heyd-Scuseria-Ernzerhof hybrid functional (HSE) and quasiparticle G 0 W 0 methods. We study strain effects under realistic strain conditions, hydrostatic pressure, and biaxial stress. The strain-induced modification of the band structures is found to be nonlinear; transition energies and crystal-field splittings show a strong nonlinear behavior under biaxial stress. For the linear regime around the experimental lattice parameters, we present a complete set of deformation potentials (a cz , a ct , D 1 , D 2 , D 3 , D 4 , D 5 , D 6 ) that allows us to predict the band positions of group-III nitrides and their alloys (InGaN and AlGaN) under realistic strain conditions. The benchmarking G 0 W 0 results for GaN agree well with the HSE data and indicate that HSE provides an appropriate description for the band structures of nitrides. We present a systematic study of strain effects on the electronic band structure of the group-III nitrides (AlN, GaN, and InN). We quantify the nonlinearity of strain effects by introducing a set of bowing parameters. We apply the calculated deformation potentials to the prediction of strain effects on transition energies and valence-band structures of InGaN alloys and quantum wells (QWs) grown on GaN, in various orientations (including c-plane, m-plane, and semipolar). The calculated band gap bowing parameters, including the strain effect for c-plane InGaN, agree well with the results obtained by hybrid functional alloy calculations. For semipolar InGaN QWs grown in , and (3031) orientations, our calculated deformation potentials have provided results for polarization ratios in good agreement with the experimental observations, providing further confidence in the accuracy of our values.
Frontiers of Physics in China, 2009
The successful fabrication of single layer graphene has greatly stimulated the progress of the re... more The successful fabrication of single layer graphene has greatly stimulated the progress of the research on graphene. In this article, focusing on the basic electronic and transport properties of graphene nanoribbons (GNRs), we review the recent progress of experimental fabrication of GNRs, and the theoretical and experimental investigations of physical properties and device applications of GNRs. We also briefly discuss the research efforts on the spin polarization of GNRs in relation to the edge states.
Advanced Energy Materials, 2015