Valence band gaps and plasma energies for galena, sphalerite, and chalcopyrite natural minerals using differential optical reflectance spectroscopy

Todoran, Radu; Todoran, Daniela; Szakacs, Zs.

doi:10.1134/s0036024415130361

Cited by 5 publications

(3 citation statements)

References 8 publications

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“…The spectral dependences of the refractive index n(ωħ) and extinction coefficient k(ωħ) for the deposited thin films were obtained from the reflection spectra in the Kramers-Krönig framework [ 4 , 18 – 21 ]. Knowing that this formalism works best when the spectral data covers a wide domain, we proceeded to extrapolate R(λ) in the UV region down to λ = 125 nm using an 1 /a υ -type law.…”

Section: Methodsmentioning

confidence: 99%

Electrical and Optical Properties of CeNi5 Nanoscale Films

Todoran

Racolta

et al. 2016

Nanoscale Res Lett

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Rare earth compounds are interesting from both a theoretical point of view and for their applications. That is the reason why determining their optical and electrical properties deserves special attention. In this article, we present the conditions we obtained homogenous CeNi5 thin films of nanometer thicknesses. To achieve this goal, our method of choice was laser-induced vaporization, using short and modulated impulses, with electro-optical tuning for the quality factor. The layers that were deposited at a single laser burst had thicknesses between 1.5 and 2.5 nm, depending on the geometry of the experimental setup.Structural and compositional studies of the nanoscale films were made using XRD. The temperature dependence of electrical conductivity was also determined. The following optical properties of the specimens were computed using the Kramers-Krönig framework and discussed: absolute reflection and transmission coefficients for a single wavelength and relative ones for the wide UV-VIS-IR spectra, spectral dependence of the refractive index, and extinction coefficient as real and imaginary parts of the complex refractive index. The valence band studies were made with X-ray photoelectron spectroscopy. All these determinations were well correlated and permitted the evaluation of the energy densities of states in the deeper bands, near the Fermi energy, and at the surface states.

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Section: Methodsmentioning

confidence: 99%

Electrical and Optical Properties of CeNi5 Nanoscale Films

Todoran

Racolta

et al. 2016

Nanoscale Res Lett

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“…These data were processed to compute the refractive index n and the extinction coefficient k using the Kramers-Krönig formalism [46,47]. Variations of the above-mentioned method were previously applied by us and gave good results on natural mineral semiconductors [48], solid–liquid interfaces [49,50], and other intermetallic nanoscale films [35,36]. …”

Section: Methodsmentioning

confidence: 99%

Electrical Conductivity and Optical Properties of Pulsed Laser Deposited LaNi5 Nanoscale Films

Todoran

Szakács

et al. 2018

Materials

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This work presents pulsed laser deposition as a method to obtain unoxidized LaNi5 nanoscale films and describes their temperature and thickness dependent electrical conductivity and the spectral dispersions of some optical properties. AB5-type rare earth element (REE)-nickel compounds are currently studied from both theoretical and practical points of view. Special challenges are posed during the preparation of these nanomaterials, which can be overcome using finely tuned parameters in a preparation process that always involves the use of high energies. Film deposition was made by laser—induced vaporization, with short and modulated impulses and electro–optical tuning of the quality factor, mainly on glass and one SiO2 substrate. Deposition geometry dependent linear thickness increase, between 1.5–2.5 nm per laser burst, was achieved. Film structures and phase compositions were determined using XRD and discussed in comparison with films obtained by similar deposition procedures. Temperature and scale dependent properties were determined by studying electrical conductivity and optical properties. Electrical conductivity was measured using the four-probe method. The observed semiconductor-like conductivity for film thicknesses up to 110 nm can be explained by thermal activation of electrons followed by inter-insular hopping or quantum tunneling, which, on the other hand, modulates the material’s native metallic conductance. Films with thicknesses above this value can be considered essentially metallic and bulk-like. The spectral behaviors of the refractive index and absorption coefficient were deduced from differential reflectance spectroscopy data acquired on a broad ultraviolet, visible, near- and mid-infrared (UV-VIS-NIR-MIR) domain, processed using the Kramers-Krönig formalism. Their study led to the identification of the allowed interband transitions. Electronic behavior in the energy bands near the Fermi level and in the surface and interface-states was described, discussing the differences between experimental data and the classical free-electron theoretical model applied for the bulk intermetallic alloy, in correlation with theoretical optical properties or experimental X-ray photoelectron spectroscopy (XPS) results from references. However, the dielectric-like shape of the reflectance of the thinnest film was in accordance with the Lorentz–Drude model.

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“…The spectral dependences of the refractive index n(ωħ) and extinction coefficient k(ωħ) for the deposited thin films were obtained from the reflection spectra in the Kramers-Krönig framework [4,[18][19][20][21]. Knowing that this formalism works best when the spectral data covers a wide domain, we proceeded to extrapolate R(λ) in the UV region down to λ = 125 nm using an 1/a υ -type law.…”

Section: Methodsmentioning

confidence: 99%

Electrical and Optical Properties of CeNi 5 Nanoscale Films

Todoran¹,

Todoran²,

Racolta³

et al. 2017

Nano Online

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Rare earth compounds are interesting from both a theoretical point of view and for their applications. That is the reason why determining their optical and electrical properties deserves special attention. In this article, we present the conditions we obtained homogenous CeNi 5 thin films of nanometer thicknesses. To achieve this goal, our method of choice was laser-induced vaporization, using short and modulated impulses, with electro-optical tuning for the quality factor. The layers that were deposited at a single laser burst had thicknesses between 1.5 and 2.5 nm, depending on the geometry of the experimental setup. Structural and compositional studies of the nanoscale films were made using XRD. The temperature dependence of electrical conductivity was also determined. The following optical properties of the specimens were computed using the Kramers-Krönig framework and discussed: absolute reflection and transmission coefficients for a single wavelength and relative ones for the wide UV-VIS-IR spectra, spectral dependence of the refractive index, and extinction coefficient as real and imaginary parts of the complex refractive index. The valence band studies were made with X-ray photoelectron spectroscopy. All these determinations were well correlated and permitted the evaluation of the energy densities of states in the deeper bands, near the Fermi energy, and at the surface states.

show abstract

Valence band gaps and plasma energies for galena, sphalerite, and chalcopyrite natural minerals using differential optical reflectance spectroscopy

Cited by 5 publications

References 8 publications

Electrical and Optical Properties of CeNi5 Nanoscale Films

Electrical and Optical Properties of CeNi5 Nanoscale Films

Electrical Conductivity and Optical Properties of Pulsed Laser Deposited LaNi5 Nanoscale Films

Electrical and Optical Properties of CeNi 5 Nanoscale Films

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