Investigation of the composition-structure-property relationship of AsxTe100-x films prepared by plasma deposition

Further Increasing the Accuracy of Characterization of a Thin Dielectric or Semiconductor Film on a Substrate from Its Interference Transmittance Spectrum

Three means are investigated for further increasing the accuracy of the characterization of a thin film on a substrate, from the transmittance spectrum T(λ) of the specimen, based on the envelope method. Firstly, it is demonstrated that the accuracy of characterization, of the average film thickness d¯ and the thickness non-uniformity ∆d over the illuminated area, increases, employing a simple dual transformation utilizing the product T(λ)xs(λ), where Tsm(λ) is the smoothed spectrum of T(λ) and xs(λ) is the substrate absorbance. Secondly, an approach is proposed for selecting an interval of wavelengths, so that using envelope points only from this interval provides the most accurate characterization of d¯ and ∆d, as this approach is applicable no matter whether the substrate is transparent or non-transparent. Thirdly, the refractive index n(λ) and the extinction coefficient k(λ) are computed, employing curve fitting by polynomials of the optimized degree of 1/λ, instead of by previously used either polynomial of the optimized degree of λ or a two-term exponential of λ. An algorithm is developed, applying these three means, and implemented, to characterize a-Si and As98Te2 thin films. Record high accuracy within 0.1% is achieved in the computation of d¯ and n(λ) of these films.

Optical Characterization of AsxTe100-x Films Grown by Plasma Deposition Based on the Advanced Optimizing Envelope Method

Three As_xTe_100−x films with different x and dissimilar average thickness d¯ are characterized mainly from one interference transmittance spectrum T(λ = 300 to 3000 nm) of such film on a substrate based on the advanced optimizing envelope method (AOEM). A simple dual transformation of T(λ) is proposed and used for increasing the accuracy of computation of its envelopes T₊(λ) and T₋(λ) accounting for the significant glass substrate absorption especially for λ > 2500 nm. The refractive index n(λ) of As₄₀Te₆₀ and As₉₈Te₂ films is determined with a relative error <0.30%. As far as we know, the As₈₀Te₂₀ film is the only one with anomalous dispersion and the thickest, with estimated d¯ = 1.1446 nm, ever characterized by an envelope method. It is also shown and explained why the extinction coefficient k(λ) of any of the three As_xTe_100−x films is computed more accurately from the quantity T_i(λ) = [T₊(λ)T₋(λ)]^0.5 compared to its commonly employed computation from T₊(λ). The obtained results strengthen our conviction that the AOEM has a capacity for providing most accurate optical characterization of almost every dielectric or semiconductor film with d¯ > 300 nm on a substrate, compared to all the other methods for characterization of such films only from T(λ).

Monolayer AsTe2 : Stable Robust Metal in 2D, 1D and 0D

The structural, phononic, and electronic properties of the monolayer structures of AsTe₂ are characterized by performing density functional theory (DFT) calculations. Total energy optimization and phonon calculations reveal that single layers of the 2H-AsTe₂ and 1T-AsTe₂ phases form dynamically stable crystal structures. Electronic structure analysis also shows that both 2H and 1T phases have nonmagnetic metallic character. It is also predicted that the metallic nature of the ultra-thin both 2H-AsTe₂ and 1T-AsTe₂ structures remain unchanged even under high biaxial strain values. For further examination of the dimensionality effect in the robust metallicity in 2D AsTe₂ phases, electronic characteristics of 1D nanoribbons and 0D quantum dots are also investigated. It is found that independent from the dimension and crystallographic orientations 0D and 1D structures of 2H- and 1T-AsTe₂ structures have metallic behavior. It is found that single layers of AsTe₂ are quite promising materials for nanodevice applications owing to the robust metallic character.