Experimental electronic structure of In2O3and Ga2O3

Janowitz, C.; Scherer, V.; Mohamed, Mansour; Krapf, A.; Dwelk, H.; Manzke, R.; Galazka, Zbigniew; Uecker, R.; Irmscher, K.; Fornari, R.; Michling, Marcel; Schmeißer, Dieter; Weber, J. R.; Varley, Joel B.; Walle, Chris G. Van de

doi:10.1088/1367-2630/13/8/085014

Cited by 299 publications

(161 citation statements)

References 14 publications

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“…The main portion of the peak is centered around 530 eV and is associated with indium oxide. The shoulder peak at higher binding energies, which decreases with decreasing calcination temperature, is commonly attributed to a combination of defects with contribution from both oxygen vacancies, with a peak centered around 531 eV, and hydroxides, with a peak centered around 532 eV (35,41). The light-gray curves in Fig.…”

Section: Resultsmentioning

confidence: 98%

“…Although the optoelectronic properties of indium oxide have been widely studied in relation to its use as a transparent conductive oxide material (29,35,36), to our knowledge only Tsokkou et al have looked at these processes in detail using TA spectroscopy (37,38). They investigated excited-state lifetimes in In 2 O 3 nanoparticles (37) and gold-decorated In 2 O 3 nanorods (38) and their dependence on the pump fluence, and indicated that both shallow and deep trap states played a significant role in the carrier dynamics.…”

Section: Significancementioning

confidence: 99%

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Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO ₂ reduction

Hoch

Szymanski

Ghuman

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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In 2 O 3-x (OH) y nanoparticles have been shown to function as an effective gas-phase photocatalyst for the reduction of CO 2 to CO via the reverse water-gas shift reaction. Their photocatalytic activity is strongly correlated to the number of oxygen vacancy and hydroxide defects present in the system. To better understand how such defects interact with photogenerated electrons and holes in these materials, we have studied the relaxation dynamics of In 2 O 3-x (OH) y nanoparticles with varying concentration of defects using two different excitation energies corresponding to above-band-gap (318-nm) and near-band-gap (405-nm) excitations. Our results demonstrate that defects play a significant role in the excited-state, charge relaxation pathways. Higher defect concentrations result in longer excited-state lifetimes, which are attributed to improved charge separation. This correlates well with the observed trends in the photocatalytic activity. These results are further supported by density-functional theory calculations, which confirm the positions of oxygen vacancy and hydroxide defect states within the optical band gap of indium oxide. This enhanced understanding of the role these defects play in determining the optoelectronic properties and charge carrier dynamics can provide valuable insight toward the rational development of more efficient photocatalytic materials for CO 2 reduction.indium oxide | solar fuels | CO 2 hydrogenation | transient absorption | surface defects C oncerns over climate change and the projected rise in global energy demand have motivated researchers to develop alternative, more sustainable ways to generate energy from naturally abundant and renewable sources (1-3). An important challenge associated with using renewable energy sources, such as solar, is their inherent intermittent nature (4-6). The emerging field of solar fuels seeks to address this issue by storing radiant solar energy in chemical bonds, which can then be released on demand and act as a drop-in replacement for traditional fossil fuels (7-11). By using the greenhouse gas, CO 2 , currently regarded as a waste product, as a feedstock and converting it into valuable products such as solar fuels or platform chemicals, we could simultaneously address concerns over climate change and energy security while creating significant economic benefits (12)(13)(14). However, despite recent advances in the development of active materials that can drive the photocatalytic reduction of CO 2 into useful chemical species, much remains unknown about the fundamental physical properties that control the activity of a photocatalyst. To facilitate the rational development and improvement of photocatalytic materials, a detailed understanding of the complex interplay between chemical, optical, and electronic processes is needed.Indium oxide has many favorable optical, electronic, and surface properties that make it a compelling choice as a photocatalyst for CO 2 reduction. It has a relatively high conduction band, and common defects such as oxyge...

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Section: Resultsmentioning

confidence: 98%

Section: Significancementioning

confidence: 99%

Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO ₂ reduction

Hoch

Szymanski

Ghuman

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…3.4 [29] Interpolation [54] 6.0 [55] Multiple 4.9 [56] 6.4 [57] 5.5 [58] Multiple ( 4.9 [59,60] (measured baseline) Varies non-uniformly by composition [61] 15.4 [60] 2.6 (reported) 10.3 [60] 17.5 [60] 13.0 [60] Depends on insulator [63] /2013 [64] (4) Electron drift mobility (cm 2…”

Section: Materials/device Types and Propertiesmentioning

confidence: 99%

“…[55] Ga 2 O 3 has both a direct and an indirect bandgap with nearly identical values, [56] and cubic BN and diamond both have indirect gaps.…”

Section: Materials/device Properties (mentioning

confidence: 99%

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

Tsao

Chowdhury

Hollis

et al. 2017

Adv Elect Materials

976

463

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“…• Oxide layer: Both experiments 44 and DFT calculations 44 show that for the oxide layer the bandwidth of the valence band is about 7 eV. The parameters chosen for the top and the bottom of the band of the oxide layer are therefore ε Oxt = −4.5 eV and ε Ox b = −11.5 eV respectively.…”

Section: Supporting Informationmentioning

confidence: 99%

Charge Transport Across Insulating Self-Assembled Monolayers: Non-equilibrium Approaches and Modeling To Relate Current and Molecular Structure

et al. 2014

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This paper examines charge transport by tunneling across a series of electrically (insulating molecules with the structure HS(CH 2 ) 4 CONH(CH 2 ) 2 R) in the form of selfassembled monolayers (SAMs), supported on silver. The molecules examined were studied experimentally by Yoon et al. (Angew. Chem. Int. Ed., 51, 4658−4661, 2012), using junctions of the structure AgS(CH 2 ) 4 CONH(CH 2 ) 2 R//Ga 2 O 3 /EGaIn. The tail group R had approximately the same length for all molecules, but a range of different structures. Changing the R entity over a range of different structures (aliphatic to aromatic) does not influence the conductance significantly. To rationalize this surprising result, we investigate transport through these SAMs theoretically, using both full quantum methods and a generic, independent-electron tight-binding toy model. We find that the frontier orbitals HOMO, HOMO-1, HOMO-2 and HOMO-3, have similar structures for all of the different R-groups, and that the HOMO, which is largely responsible for the transport in these molecules, is always strongly localized on the thiol group. The relative insensitivity of the current density to the structure of the R group is due not only to these similar frontier orbitals but also to a combination of energy levels (ε) and tunneling amplitudes (t), which lead to similar conductance for different tail groups, i.e. the large difference between ε's in conjugated and saturated groups is compensated by tunneling amplitudes inside the tail group. In addition, the coupling of the tail group to the alkane chain is much weaker for conjugated groups than for saturated ones. Conductance change in these molecules is not influenced by the broadening of the molecular levels connected to the left and right electrodes, since in all these molecules the effective coupling to the silver substrate is the same, whereas the other effective couplings are determined by the weak connection to the oxide Ga 2 O 3 layer. All these factors combine to produce currents largely insensitive to the R group.An estimation of the attenuation constant, β, of the simplified Simmons equation obtained using these methods is β = 1.1 per CH 2 group, in good agreement with observed results. Our analysis sketches the potential landscapes across which tunneling occurs, and suggests that it will be difficult to change rates of tunneling by simple changes 2 in molecular structure. This work indicates that significant control over SAMs largely composed of nominally insulating groups may be possible when tail groups are used that are significantly larger than those used in the experiments of Yoon et al. 13

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Experimental electronic structure of In₂O₃and Ga₂O₃

Cited by 299 publications

References 14 publications

Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO ₂ reduction

Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO ₂ reduction

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

Charge Transport Across Insulating Self-Assembled Monolayers: Non-equilibrium Approaches and Modeling To Relate Current and Molecular Structure

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Experimental electronic structure of In2O3and Ga2O3

Cited by 299 publications

References 14 publications

Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO 2 reduction

Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO 2 reduction

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

Charge Transport Across Insulating Self-Assembled Monolayers: Non-equilibrium Approaches and Modeling To Relate Current and Molecular Structure

Contact Info

Product

Resources

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Experimental electronic structure of In₂O₃and Ga₂O₃

Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO ₂ reduction

Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO ₂ reduction