Aging and crystallization of evaporated amorphous selenium films

Grenet, J.; Larmagnac, J.P.; Michon, P.

doi:10.1016/0040-6090(80)90309-0

Cited by 20 publications

(3 citation statements)

References 10 publications

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“…In comparison to a-Se, a-PbO structural stability is much higher: the first a-PbO layers deposited two years ago and stored in air did not degrade and do not show any changes in both Raman and XRD spectra. This is an advantage over a-Se, since the later requires special doping for stabilization against recrystallization at ambient conditions, while un-stabilized pure a-Se structurally degrades in approximately one month after the deposition [29,30].…”

Section: Xrd Spectroscopymentioning

confidence: 99%

Ion-assisted deposition of amorphous PbO layers

et al. 2017

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Lead oxide (PbO) is one of the most promising materials for application in direct conversion medical imaging X-ray detectors. Despite its high potential, conventional polycrystalline PbO layers deposited with the basic thermal evaporation method are not yet mature for practical use in x-ray imaging; indeed, they are highly porous, unstable at ambient conditions, and sub-stoichiometric. In order to combat the above issues with PbO, we advance the basic evaporation process with simultaneous energetic ion bombardment of the growing film. We show that tuning the ion-assisted thermal deposition not only solves the structural problems of poly-PbO, but also enables the growth of a new non-crystalline polymorphic form of the material-amorphous PbO (a-PbO). In contrast to poly-PbO, novel a-PbO layers grown by ion-assisted thermal deposition are stable at ambient conditions. Structural and morphological analysis confirms that a-PbO is stoichiometric and free of detectable voids, which suggests higher bulk X-ray stopping power than porous poly-PbO.

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Section: Xrd Spectroscopymentioning

confidence: 99%

Ion-assisted deposition of amorphous PbO layers

et al. 2017

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“…However, it is quite important not to hide this phenomenon by the shift to the lower temperatures of the crystallization peak with the age of the samples ( fig. 3b) [14].…”

Section: Analysis Proceduresmentioning

confidence: 98%

Non-isothermal crystallization in amorphous selenium films

Grenet

Larmagnac

Michon

1982

Journal of Thermal Analysis

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The usual determination of kinetic parameters of crystallization of amorphous products is based on isothermal measurements. In general the crystallization of amorphous selenium thin films is studied by non-isothermal experiments (DTA). The adaptation to non-isothermal crystallization of the Avrami transformation rate equation allows us to determine different types of crystallization. These different regions enable one to determine the variations of the growth rate and of the nucleation rate versus temperature. The influence of the wavelength of illumination during the crystallization time on these parameters is also investigated.The last decades have seen a strong theoretical and experimental interest in the non-isothermal analysis techniques for the study of phase transformations. These non-isothermal techniques have several advantages: rapidity of experiment and facilities to extend the temperature range beyond that accessible to isothermal experiments. Also, many phase transformations depend on non-isothermal kinetics.Thus it is not surprising for the study of systems in which the temperature of the interface (amorphous-crystal for example) is well defined by the temperature of the system (i.e. the difference of temperature between the interface and the system is negligible), to see differential thermal analysis (DTA)and differential scanning calorimetry (DSC) as techniques which are applicable, in particular to the study of crystallization kinetics. Isothermal crystallization Avrami equationThe crystallized fraction x of the system at time t, is defined as follows:The volume V0 is the total volume of the sample and Ve(t) is the "extended crystallized volume", i.e. the volume which includes all the crystalline regions, assumed to be independent without taking into account possible overlapping, Vc(t ) is the real crystallized volume at time t. This notion of "extended crystallized volume" 20* J. Thermal Anal. 25 1982

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“…Thin selenium films also found a booming way in the fabrication of other solid-state devices such as Schottky diodes, solar cells and photovoltaic junctions (Ito et al, 1982;Touihri et al, 1997;Bernede et al, 1998;Lakshmi, 2001;Mukolu, 2004;Iyayi & Oberafo, 2005;Joshi & Lokhande, 2006;El-Nahass et al, 2006). Undoped a-Se is a typical p-type semiconducting chalcogenide glassy material with a high dc dark electrical resistivity (10 Ω cm at 300 K) (Mott & Davis, 1979;Kolobov, 1996;Abdul-Gader et al, 1998;El-Zawawi & Abd-Alla, 1999); however, its glass-transformation temperature T is low (below 50 , depending on its definition and experimental procedure used to define it (Grenet et al, 1980;Larmagnac et al, 1981;Kasap & Juhasz, 1986;Kasap et al, 1990;Pejova & Grozdanov, 2001;Tonchev & Kasap, 2002)). Thus, it is only possible to exploit inherent physical properties of as-deposited undoped a-Se films at low ambient temperatures, after ageing them in dark and humidity-free environment to reach structural relaxation.…”

Section: Introductionmentioning

confidence: 99%

Determination of Optical Properties of Undoped Amorphous Selenium (a-Se) Films by Dielectric Modeling of Their Normal-Incidence Transmittance Spectra

Saleh¹,

Jafar²,

Bulos³

et al. 2014

APR

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Normal-incidence specular transmittance of undoped amorphous selenium (a-Se) films of several thicknesses ( 0.25 1 μm ) thermally evaporated on thick microscopic glass-slide substrates upheld at temperatures near 30 (below glass transition temperature of undoped Se) has been measured at room temperature in the spectral wavelength range 300 1100 nm. Above a threshold wavelength (~ 600 nm), their as-measured curves display transmittance values near that of glass substrates and exhibit well-resolved interference-fringe maxima and minima, signifying good uniformity of fabricated a-Se films. Below , the curves decline progressively to zero transmittance, preceded by a tailing-like trend of possible structural disorder origin. The spectral dependencies of optical constants and of the studied a-Se films on were retrieved from iterative curve-fitting of their -data to theoretical -formulations of an air-supported {thin film/thick substrate}-stack using the O'Leary-Johnson-Lim (OJL) interband-transition dielectric model, combined with a dielectric constant , representing the dielectric background at very high photon energies (at spectral wavelengths much smaller than measured). Regardless of the number of observed interference fringes, reliable simulation to the as-measured normal-incidence -spectra has been achieved, but were remarkably curve-fitted if we presume that a thin roughness layer ( 5 nm) of selenium was formed on top of the fabricated undoped a-Se films. The retrieved spectra display a broad peak around ≅ 0.52 μm, below which was found to vary with wavelength in accordance with a Sellmeier-like (Wemple-DiDominco) single-oscillator (normal) dispersion formula, with a static index of refraction 0 ≅ 2.42, where is the static dielectric constant of the material at zero photon energy , and an oscillator "average" bandgap energy of ≅ 3.93 eV ≅ 2 , the optical (Tauc) bandgap energy. The values of of studied undoped a-Se films deduced from Tauc-like plots were around 1.92 eV ( 0.02 eV) and the retrieved values of OJL band-tailing energy parameter (Urbach-tail parameter Γ ) was found to be in the range 40 50 meV, slightly dependent on film thickness.

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Aging and crystallization of evaporated amorphous selenium films

Cited by 20 publications

References 10 publications

Ion-assisted deposition of amorphous PbO layers

Ion-assisted deposition of amorphous PbO layers

Non-isothermal crystallization in amorphous selenium films

Determination of Optical Properties of Undoped Amorphous Selenium (a-Se) Films by Dielectric Modeling of Their Normal-Incidence Transmittance Spectra

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