Tailoring of Multisource Deposition Conditions towards Required Chemical Composition of Thin Films.

The model to tailor the required chemical composition of thin films fabricated via multisource deposition, exploiting basic physicochemical constants of source materials, is developed. The model is experimentally verified for the two-source depositions of chalcogenide thin films from Ga-Sb-Te system (tie-lines GaSb-GaTe and GaSb-Te). The thin films are deposited by radiofrequency magnetron sputtering using GaSb, GaTe, and Te targets. Prepared thin films are characterized by means of energy dispersive X-ray analysis coupled with a scanning electron microscope to determine the chemical composition and by variable angle spectroscopic ellipsometry to establish film thickness. Good agreement between results of calculations and experimentally determined compositions of the co-deposited thin films is achieved for both the above-mentioned tie-lines. Moreover, in spite of all the applied simplifications, the proposed model is robust to be generally used for studies where the influence of thin film composition on their properties is investigated.

Linear and nonlinear optical properties of co-sputtered Ge-Sb-Se amorphous thin films.

Amorphous Ge-Sb-Se thin films were co-sputtered from ${{\rm GeSe}_4}$GeSe4 and ${{\rm Sb}_2}{{\rm Se}_3}$Sb2Se3 targets. Depending on the film composition, linear optical properties were studied by ellipsometry. The Kerr coefficient and two-photon absorption coefficient were estimated using Sheik-Bahae's formalism for co-sputtered films of ${{\rm GeSe}_4} {\text -} {\rm Sb}_2{{\rm Se}_3}$GeSe4-Sb2Se3 compared to ${{\rm GeSe}_2}{\text -}{\rm Sb}_2{{\rm Se}_3}$GeSe2-Sb2Se3 pseudo-binary system and ${{\rm As}_2}{{\rm Se}_3}$As2Se3 as reference. The Kerr coefficient was found within the range of $4.9 {\unicode {x2013}}- 21 \times {10^{ - 18}}$4.9--21×10-18. Quantitatively by means of a figure of merit at 1.55 µm, thin films with compositions of ${{\rm Ge}_7}{\rm Sb}_{25}{\rm Se}_{68}$Ge7Sb25Se68 and ${{\rm Ge}_9}{\rm Sb}_{20}{\rm Se}_{71}$Ge9Sb20Se71 having an estimated Kerr coefficient of about ${10.1} \times {10^{ - 18}}\;{{\rm m}^2}{{\rm W}^{ - 1}}$10.1×10-18m2W-1 and ${13.4} \times {10^{ - 18}}\;{{\rm m}^2}{{\rm W}^{ - 1}}$13.4×10-18m2W-1 should be considered for the future nonlinear optical integrated platforms. Such compositions being close to ${({{\rm GeSe}_4})_{50}}{({{\rm Sb}_2}{{\rm Se}_3})_{50}}$(GeSe4)50(Sb2Se3)50 pseudo-binary (i.e., ${\rm Ge}_{7.5}{\rm Sb}_{25.0}{\rm Se}_{67.5}$Ge7.5Sb25.0Se67.5) provides just the trade-off between a high Kerr coefficient and low optical losses related to two-photon absorption.

GaTe-Sb2Te3 thin-films phase change characteristics.

A radio frequency magnetron co-sputtering technique exploiting GaTe and ${\rm Sb}_2 {\rm Te}_3$Sb2Te3 targets was used for the fabrication of Ga-Sb-Te thin films. Prepared layers cover broad region of chemical composition (${\sim}{10.0 {-} 26.3}\,\, {\rm at.}$∼10.0-26.3at. % of Ga, ${\sim}{19.9 {-} 34.4}\,\, {\rm at.}$∼19.9-34.4at. % of Sb) while keeping Te content fairly constant (53.8-55.6 at. % of Te). Upon crystallization induced by annealing, large variations in electrical contrast were found, reaching a sheet resistance ratio of ${{R}_{\rm annealed}}/{{R}_{\rm as - deposited}}\;\sim{2.2} \times {{10}^{ - 8}}$Rannealed/Ras-deposited∼2.2×10-8 for the ${{\rm Ga}_{26.3}}{{\rm Sb}_{19.9}}{{\rm Te}_{53.8}}$Ga26.3Sb19.9Te53.8 layer. Phase transition from the amorphous to crystalline state further leads to huge changes of optical functions demonstrated by optical contrast values up to $|\Delta n| + |\Delta k| = {4.20}$|Δn|+|Δk|=4.20 for ${{\rm Ga}_{26.3}}{{\rm Sb}_{19.9}}{{\rm Te}_{53.8}}$Ga26.3Sb19.9Te53.8 composition.

Mass spectrometric investigation of amorphous Ga-Sb-Se thin films.

Amorphous chalcogenide thin films are widely studied due to their enhanced properties and extensive applications. Here, we have studied amorphous Ga-Sb-Se chalcogenide thin films prepared by magnetron co-sputtering, via laser ablation quadrupole ion trap time-of-flight mass spectrometry. Furthermore, the stoichiometry of the generated clusters was determined which gives information about individual species present in the plasma plume originating from the interaction of amorphous chalcogenides with high energy laser pulses. Seven different compositions of thin films (Ga content 7.6-31.7 at. %, Sb content 5.2-31.2 at. %, Se content 61.2-63.3 at. %) were studied and in each case about ~50 different clusters were identified in positive and ~20-30 clusters in negative ion mode. Assuming that polymers can influence the laser desorption (laser ablation) process, we have used parafilm as a material to reduce the destruction of the amorphous network structure and/or promote the laser ablation synthesis of heavier species from those of lower mass. In this case, many new and higher mass clusters were identified. The maximum number of (40) new clusters was detected for the Ga-Sb-Se thin film containing the highest amount of antimony (31.2 at. %). This approach opens new possibilities for laser desorption ionization/laser ablation study of other materials. Finally, for selected binary and ternary clusters, their structure was calculated by using density functional theory optimization procedure.

Intensity mediated change in the sign of ultrafast third-order nonlinear optical response in As2S2 thin films.

We study experimentally and theoretically the intensity-dependent off-resonant ultrafast third-order nonlinear optical response of As2S2 thin films. At low intensity, we observed saturable absorption with a negative (self-defocusing) nonlinear refractive index (n2) which at higher intensity switched over to reverse saturable absorption with a change in the sign of n2 to positive (self-focusing). Our findings constitute compelling evidence on how to dynamically tune the optical response with the intensity that has its origin in the combined effect of two-photon absorption and Pauli blocking. The results were explained with the help of time-resolved measurements and rigorous theoretical and numerical simulations.

Laser Desorption Ionization of As2Ch3 (Ch = S, Se, and Te) Chalcogenides Using Quadrupole Ion Trap Time-of-Flight Mass Spectrometry: A Comparative Study.

Laser desorption ionization using time-of-flight mass spectrometer afforded with quadrupole ion trap was used to study As2Ch3 (Ch = S, Se, and Te) bulk chalcogenide materials. The main goal of the study is the identification of species present in the plasma originating from the interaction of laser pulses with solid state material. The generated clusters in both positive and negative ion mode are identified as 10 unary (S p+/- and As m+/- ) and 34 binary (As m S p+/- ) species for As2S3 glass, 2 unary (Se q+/- ) and 26 binary (As m Se q+/- ) species for As2Se3 glass, 7 unary (Te r+/- ) and 23 binary (As m Te r+/- ) species for As2Te3 material. The fragmentation of chalcogenide materials was diminished using some polymers and in this way 45 new, higher mass clusters have been detected. This novel approach opens a new possibility for laser desorption ionization mass spectrometry analysis of chalcogenides as well as other materials. Graphical abstract ᅟ.