Materials with combined ferroelectric and ferromagnetic properties or magneto-electric coupling effects are promising candidates for information technology, photosensoring, and device fabrication. Preparation and characterization of multiferroic materials in which ferroelectricity and ferromagnetism coexist attracted much interest in research for functionalized materials and devices. They present a possibility to electrically control magnetic memory devices and, conversely, magnetically manipulate electric devices. In this work we considered Fe3O4 magnetic nanoparticles with and without a protective SiO2/TiO2 double-layer coating embedded into the carbazole-based, namely, polyepoxypropylcarbazole (PEPC) thin (500 nm) film. Optical characterization of the PEPC films was performed using light irradiation in the UV/VIS and NIR ranges. A shift in the optical absorption edge toward a higher wavelength region of the spectrum took place for all irradiated samples: the polymer film, as well as for the samples with Fe3O4 and Fe3O4/SiO2/TiO2 nanoparticles inside of the polymer matrix. We suggest that changes in the UV/VIS/NIR spectra took place as a function of the degree of structural changes and stabilizing of the atomic matrix, as well as due to change in the values of the refractive index following irradiation, calculated from the spectral data. In such a way photo-structural modifications induced by the UV irradiation and the implantation of the magnetic nanoparticles make these materials perspective for optical recording media. We conclude, therefore, that Fe3O4 and Fe3O4/SiO2/TiO2 nanoparticles considerably affect the optical properties of the PEPC thin film, and result in the enhancement of the photodarkening effect following the UV irradiation.
Experimental results on some physical and optical properties of (As2Se3)1-x:Snx and (As4S3Se3)1-x:Snx (x = 0-10 at %) glasses and amorphous films (d~2.0 μm) are presented. The bulk chalcogenide glasses are studied by X-ray diffraction spectroscopy and nanoindentation methods. It is established that the addition of these amounts of tin (x = 0-10 at %) does not lead to significant changes in the physical properties of the glass, such as values of stress and Young’s modulus related to the modification of the density and compactness. It has been found that the addition of these amounts of tin in (As4S3Se3)1-x:Snx does not lead to significant changes in the glass physical properties, such as values of stress and Young’s modulus related to the modification of the density and compactness. The study of the photoplastic effect is performed in situ, with illumination of the bulk and thin film samples during indentation as well as their indentation after illumination with a green laser (λ = 532 nm) at a power of P = 50 mV/cm2. The hardness is calculated from load-displacement curves by the Oliver-Pharr method. A sharp increase in hardness is registered if the tin concentration exceeds a value of 34% Sn. The hardness H of (As2Se3)1-x:Snx films varies between 115 and 130 kg/mm2. It is found that the hardness H of amorphous thin films is generally higher than the hardness of bulk samples with the same chemical composition. In this study, we are focused on the mechanical characteristics of high-purity As2Se3: Snx thin films. Keyword: Chalcogenide glasses, hardness,
Phase-change memory materials are promising for the next generation of non-volatile flash memory that will serve in
new mobile computing entertainment and other handheld electronics. Among them are chalcogenide glasses Ge-Sb-Te (GST) which can exist in two separate structural states – amorphous and crystalline. Switching of the material from one to another state can be done by heating applying an electrical pulse or by exposure to intense laser beam. In the present work we report the changes of optical parameters of amorphous Ge1Sb2Te4, Ge1Sb4Te7, and Ge2Sb2Te5 thin films under heat treatment and light exposure. The illumination with white during 1 hour does not change the transmission spectra of the as-deposited amorphous film. The spot of phase change transformation of the amorphous material was observed when the film was illuminated with UV laser pulses. From the transmission spectra T=f(λ) the optical constants (Absorption coefficient α, optical band gap Eg, refractive index n, the average electronic energy gap E0 and the dielectric oscillator strength Ed were calculated. For Ge1Sb2Te4 the value of E0 is smaller than optical band gap Eg=1.08 eV obtained from the Tauc plot. Large values of the refractive index n are obtained for smaller E0=0.931 eV and for large Ed=7.448 eV. The anealing of the amorphous Ge2Sb2Te5 thin film at T=100 oC during t=4 min shifts the transmission spectra in the low frequency region. The anealing at higher temperatures makes the thin film non-transparent, e.g. take place the process of crystalization.
Transparent thin films of polyepoxypropylcarbazole polymer were produced using spin-coating technique. Optical
materials constants such as refractive index of thin films and thickness were determined by optical spectroscopy. It was
shown the possibility of variation of film thickness by polymer concentration in solution. It was shown that film
thickness dependence on the concentration of solution is linear. Therefore this linear dependence can be used to predict the film thickness of spin-coated polymers if the solvent is known. The thickness can be varied from 170 nm up to 940 nm for the solution with concentration from 2.5% up to 12.5%. To confirm the validity of our method, we also carried out the interferometric thickness measurements and analysis with a thin film of polyepoxypropylcarbazole. The
difference of obtained results of two methods averaged not more than 5%.
The measured film thickness by transmission spectra of the polymer film was found to be well correlated to the
results of interferometric thickness measurement. The refractive index of the polyepoxypropylcarbazole was 1.62,
which was well above the refractive index of 1.49 for polymethylmethacrylate. It was found that the inclusion of even a
small amount of a photosensitizer, such as CHI3, was effective in producing of high refractive index material with
refractive index 1.64.
The transmission spectra of bulk and thin films of (As2S1.5Se1.5)1-x:Snx in the visible and near infrared (IR) regions were investigated. Doping of As2S1.5Se1.5 chalcogenide glass with tin impurities essentially reduce the absorption bands of SH (Se-H) and H2O located at ν = 5190 cm-1 and ν = 3617 cm-1, respectively. The amorphous As2Se3:Snx and (As2S1.5Se1.5)1-x:Snx thin films exhibit photoinduced effects under the light irradiation with photon energy above the optical band gap (hν≥Eg), that make its perspective materials for registration of optical and holographic information. The modification of optical parameters (optical band gap Eg, absorption coefficient α, refractive index n) under light irradiation and heat treatment of the amorphous thin films with different amount of Sn was studied. The shift of the absorption edge after light exposure to lower energy region was observed, i.e. the effect of photodarkening take place. The dispersions curves n=f(λ) show a modification of the refractive index n under light exposure. For the glass composition (As2S1.5Se1.5)0.96:Sn0.04 the change of the optical band gap Egopt under light exposure was determined from 1.92±0.02 eV to 1.86±0.02 eV. The similar calculations of the optical constants were done for the amorphous films of glass compositions x=0.03 and x=0.05. The relaxation of photodarkening in amorphous As2Se3:Snx and (As2S1.5Se1.5)1-x:Snx thin films, which is described by the stretch exponential function T(t)/T(0) = A0+Aexp[-(t-t0)/τ](1-α)also wasinvestigated. The experimental results are interpreted in framework of the model of molecular structure of chalcogenide glasses doped with tin impurities.
The optical and photoelectrical characteristics of amorphous As2Se3:Sn and Sb2Se3:Sn prepared by vacuum evaporation on glass substrates are investigated. From the transmission spectra the changes of the refractive index under the light irradiation and heat treatment are calculated. The band gap for amorphous Sb2Se3 was found to be Eg=1.30 eV and decrease with increasing of the tin concentration up to Eg=1.0 eV for Sb2Se3:Sn10.0. The kinetics of photoinduced absorption in the investigated thin films was studied. The relaxation of the photocurrent has been recorded in the wide times scale (from 0.05 up to 25 s) and was determined by capture on the deep acceptor-like traps. The photoconductivity spectra of amorphous Sb2Se3 and Sb2Se3:Sn films in the photon energy range 1.0÷2.5 eV show the band connected with the presence of the defect states with the maximum located at 1.46 eV. The intensity of this band increases in the samples with tin impurity. The experimental data are discussed in framework of the model of the charged defects and non-equilibrium dielectric polarization in amorphous semiconductors.
Photostructural transformations in amorphous films of chalcogenide glasses (ChG) under light irradiation present
scientific and practical interests. From scientific point of view, because the composition of ChG determine the kind of
structural units and the mean coordination number, in the present work the amorphous films of the chalcogenide systems
As100-xSex (x=40÷98) and As40Se60:Sny (y=0÷5.0 at.% Sn) were studied. The changes of the refractive index under light
irradiation and heat treatment are calculated from the transmission spectra. The more sensitive to light irradiation are the
amorphous films of As60Se40 and As50Se50, which exhibit big modifications of the refractive index ((Δn/n)=0.394).
Photostructural transformations in amorphous films of chalcogenide glasses (ChG) under light irradiation present scientific
and practical interests. From scientific point of view, because the composition ofChG determine the kind of structural units
and the mean coordination number, in the present work the amorphous films of the chalcogenide systems As1ooSe
(x40÷98) and As40Se60:Sny (As50Se50:Sny) (y=O÷1O.O at.% Sn) were studied. The changes of the refractive index under
light irradiation and heat treatment are calculated from the transmission spectra. The more sensitive to light irradiation are
the amorphous films of As60Se40 and As50Se50, which exhibit big modifications of the refractive index ((delta-n/n) = 0.394).
Relaxation of pulsed photocurrents under optical bias is studied in amorphous films of glassy alloys As2Se3:Snx (x=0 to 3.5 at. %) by the time-of-flight technique and steepness band-to-band light illumination. In frame of multiple-trapping model it is shown that by adding tin to the glass former As2Se3, the hole drift mobility is strongly increased and hamper the recombination. The kinetics of the long-term photocurrent decay can be described by stretched exponential hction. The dispersion parameter a, which can be deduced from the time dependence of the photocurrent Iph(t) -infinity- exp[-(τ/τ)α] and, is about 0.47 for undoped samples, and 0.35 for tin-containing samples. The obtained results indicate the variation in occupation of deep localized centers. For the investigated samples, the width of distribution of the deep traps is approximately kT/α~50-70 meV.
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