Direct and indirect transitions in the region of the band gap using electron-energy-loss spectroscopy

Rafferty, B.; Brown, L. M.

doi:10.1103/physrevb.58.10326

Cited by 187 publications

(142 citation statements)

References 16 publications

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“…The possibility to detect both indirect and direct transitions is related to the electronic structure of the oxide, as discussed in ref. [62] for chemical vapour deposited diamond films. However, no theoretical studies are available on the influence of Ti 4+ on the electronic structure of zirconia, which could help in understanding the reason of the simultaneous presence of both indirect and direct optical transitions.…”

Section: Discussionmentioning

confidence: 99%

Influences of structure and composition on the photoelectrochemical behaviour of anodic films on Zr and Zr–20at.%Ti

Santamaria

Quarto

Habazaki

2008

Electrochimica Acta

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A photoelectrochemical investigation on anodic films of different thickness grown on sputter-deposited Zr and Zr-20 at.%Ti was carried out. The estimated optical band gap and flat band potential of thick (U F ≥ 50 V) anodic films were related to their crystalline structure and compared with those obtained for thinner (U F ≤ 8 V/SCE) anodic oxides having undetermined crystalline structure. The E g values obtained by photocurrent spectroscopy were also compared with the experimental band gap estimated by other optical ex situ techniques and with the available theoretical estimates of the zirconia electronic structures in an attempt to reconcile the wide range of band gap data reported in the literature. Finally, the optical band gap and flat band potential values obtained for tetragonal Zr 0.8 Ti 0.2 O 2 mixed oxide were compared with that expected on the basis of a correlation between E g and the film composition.

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Section: Discussionmentioning

confidence: 99%

Influences of structure and composition on the photoelectrochemical behaviour of anodic films on Zr and Zr–20at.%Ti

Santamaria

Quarto

Habazaki

2008

Electrochimica Acta

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“…Examples have shown that diamond has an indirect band gap [35] and GaAs has a direct band gap [36]. In arriving at this, Brown and Rafferty have shown that electronic excitation intensity is described as [35] I…”

Section: E Dimensionality Analysis Of Joint Density-of-states and Lamentioning

confidence: 99%

Layer-dependent anisotropic electronic structure of freestanding quasi-two-dimensionalMoS2

Hong

Jin

et al. 2016

Phys. Rev. B

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The anisotropy of the electronic transition is a well-known characteristic of low-dimensional transition-metal dichalcogenides, but their layer-thickness dependence has not been properly investigated experimentally until now. Yet, it not only determines the optical properties of these low-dimensional materials, but also holds the key in revealing the underlying character of the electronic states involved. Here we used both angle-resolved electron energy-loss spectroscopy and spectral analysis of angle-integrated spectra to study the evolution of the anisotropic electronic transition involving the low-energy valence electrons in the freestanding MoS 2 layers with different thicknesses. We are able to demonstrate that the well-known direct gap at 1.8 eV is only excited by the in-plane polarized field while the out-of-plane polarized optical gap is 2.4 ± 0.2 eV in monolayer MoS 2 . This contrasts with the much smaller anisotropic response found for the indirect gap in the few-layer MoS 2 systems. In addition, we determined that the joint density of states associated with the indirect gap transition in the multilayer systems and the corresponding indirect transition in the monolayer case has a characteristic three-dimensional-like character. We attribute this to the soft-edge behavior of the confining potential and it is an important factor when considering the dynamical screening of the electric field at the relevant excitation energies. Our result provides a logical explanation for the large sensitivity of the indirect transition to thickness variation compared with that for the direct transition, in terms of quantum confinement effect.

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“…A more reliable and accurate procedure was developed by Rafferty and Brown 28 without requiring a priori knowledge of the nature of the gap. Rafferty and Brown found that the experimental spectrum is fitted best by a function of the form ͑E − E g m ͒ n , if the trial band gap E g m is equal to the correct band gap E g .…”

Section: Band Gapmentioning

confidence: 99%

Crystal structure and band gap determination of HfO2 thin films

Cheynet¹,

Pokrant²,

Tichelaar³

et al. 2007

Journal of Applied Physics

142

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Valence electron energy loss spectroscopy ͑VEELS͒ and high resolution transmission electron microscopy ͑HRTEM͒ are performed on three different HfO 2 thin films grown on Si ͑001͒ by chemical vapor deposition ͑CVD͒ or atomic layer deposition ͑ALD͒. For each sample the band gap ͑E g ͒ is determined by low-loss EELS analysis. The E g values are then correlated with the crystal structure and the chemical properties of the films obtained by HRTEM images and VEELS line scans, respectively. They are discussed in comparison to both experimental and theoretical results published in literature. The HfO 2 ALD film capped with poly-Si exhibits the largest band gap ͑E g = 5.9± 0.5 eV͒, as a consequence of its nanocrystallized orthorhombic structure. The large grains with a monoclinic structure formed in the HfO 2 ALD film capped with Ge and the carbon contamination induced by the precursors in the HfO 2 CVD film capped with Al 2 O 3 are identified to be the main features responsible for lower band gap values ͑E g = 5.25± 0.5 and 4.3± 0.5 eV respectively͒.

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Direct and indirect transitions in the region of the band gap using electron-energy-loss spectroscopy

Cited by 187 publications

References 16 publications

Influences of structure and composition on the photoelectrochemical behaviour of anodic films on Zr and Zr–20at.%Ti

Influences of structure and composition on the photoelectrochemical behaviour of anodic films on Zr and Zr–20at.%Ti

Layer-dependent anisotropic electronic structure of freestanding quasi-two-dimensionalMoS2

Crystal structure and band gap determination of HfO2 thin films

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