Tomas Wagner

Ag doped chalcogenide glasses and their applications

Ag-doped chalcogenide glasses and amorphous thin films, their preparation, properties, photodoping, photoinduced surface deposition and applications, are reviewed, expanding on the results obtained recently. The progress obtained is not only connected with better understanding of their structure, chemical bonding and properties but also in application of Ag-containing glasses and films in solid-state batteries, electrochemical sensors and optoelectronics (gratings, microlenses, waveguides, optical memories, non-linear effects).

Photoenhanced dissolution and lateral diffusion of Ag in amorphous AsS layers

Abstract The photoenhanced dissolution and lateral diffusion (PLD) of Ag in AsS layers was measured. It was found that the lateral diffusion depends on temperature, composition of the layers, intensity of illumination and also on electrical conductivity of the substrate. The diffusion edge has a step-like form. It is suggested that the sharp drop of Ag content in the vicinity of diffusion edge is a consequence of the existence of two glass-forming regions in AgAsS system. The incorporation of Ag into amorphous As2S3 is accompanied by an increase of AsAs bond densities in AsS matrix. The parabolic law of diffusion edge movement ( x ∼ t 1 2 ) on non-conductive substrate is controlled by bipolar diffusion of Ag+ ions and electrons in doped layers. The increased rates of Ag+ PLD in amorphous chalcogenides deposited on conductive substrates evidently result from a decrease of diffusion field (Nernst potential) created by more mobile Ag+ ions and slower electrons and holes. It is suggested that the linear dependence of diffusion edge movement (x ∼ t) on a conductive substrate is caused by processes on the doped/undoped interface part of the layer.

Embossing of chalcogenide glasses: monomode rib optical waveguides in evaporated thin films

Single-mode optical rib waveguides operating at telecommunication wavelengths are successfully patterned via a hot embossing technique in a thermally evaporated chalcogenide glass thin film on a chalcogenide glass substrate. Ellipsometry is used to measure the refractive index dispersion of the pressed film (As(40)Se(60)) and substrate (Ge(17)As(18)Se(65)).

Optically and thermally induced changes of structure, linear and non-linear optical properties of chalcogenides thin films

Abstract The spectral dependence of third-order non-linear susceptibilities, χ (3) , of amorphous As–S thin films was evaluated from changes of index of refraction using Miller’s rule. The exposure of thin fresh evaporated films and their annealing increases χ (3) , it increases also their homogeneity and level of their polymerization as can be judged from Raman spectra of the films. The large covalently bonded parts (‘molecules’) of the samples are apparently favorable for increase of χ (3) .

Optical properties and phase change transition in Ge2Sb2Te5 flash evaporated thin films studied by temperature dependent spectroscopic ellipsometry

We studied the optical properties of as-prepared (amorphous) and thermally crystallized (fcc) flash evaporated Ge2Sb2Te5 thin films using variable angle spectroscopic ellipsometry in the photon energy range 0.54–4.13 eV. We employed Tauc–Lorentz (TL) model and Cody–Lorentz (CL) model for amorphous phase and TL model with one additional Gaussian oscillator for fcc phase data analysis. The amorphous phase has optical bandgap energy Egopt=0.65 eV (TL) or 0.63 eV (CL) slightly dependent on used model. The Urbach edge of amorphous thin film was found to be ∼70 meV. Both models behave very similarly and accurately fit to the experimental data at energies above 1 eV. The CL model is more accurate in describing dielectric function in the absorption onset region. The thickness decreases ∼7% toward fcc phase. The bandgap energy of fcc phase is significantly lower than amorphous phase, Egopt=0.53 eV. The temperature dependent ellipsometry revealed crystallization in the range 130–150 °C. The bandgap energy of amorph...

Photoenhanced dissolution and diffusion of Ag in As2Sx layers

Abstract The photoenhanced dissolution and diffusion (PD) of Ag in AsS layers was studied. The time dependence of PD rate is of sigmoid type and is influenced by the intensity of illumination, wavelength of actinic light and by the composition of layers. The induction period is shortened when Ag2S or an Ag-doped interlayer is placed between silver and the undoped AsS layer. It is proposed that during the induction period a new photodoped amorphous phase II with high Ag content is formed. Sharp diffusion profile of Ag is caused by the existence of an immiscibility gap of Ag in the AsS system. The rate of PD in the linear part of the sigmoid curve is controlled by a diffusion field (Nernst potential) created by different mobilities of Ag+ ions and holes (electrons). The diffusion of mobile Ag+ is controlled by diffusion of low mobility holes (electrons). The illumination increases their density, decreases the diffusion potential and speeds up the diffusion rate of Ag+ ions.

Index of refraction of Ag-doped As33S67 films: Measurement and analysis of dispersion

Abstract We report data on the dispersion of the index of refraction of silver-doped As33S67 thin films in the visible and near-infrared regions. The measured data is analysed on the basis of a single-effective-oscillator model proposed by Wemple and DiDomenico. The silver content dependence of the oscillator energy Eo seems to vary in proportion to optical gap Eg opt of the sample, whereas the dispersion energy or oscillator strength Ed increases with increasing silver content. This latter fact indicates that the effective coordination of the cation increases as silver is incorporated into the chalcogenide host matrix.

Effect of cluster size of chalcogenide glass nanocolloidal solutions on the surface morphology of spin-coated amorphous films

Amorphous chalcogenide thin film deposition can be achieved by a spin-coating technique from proper solutions of the corresponding glass. Films produced in this way exhibit certain grain texture, which is presumably related to the cluster size in solution. This paper deals with the search of such a correlation between grain size of surface morphology of as-deposited spin-coated As33S67 chalcogenide thin films and cluster size of the glass in butylamine solutions. Optical absorption spectroscopy and dynamic light scattering were employed to study optical properties and cluster size distributions in the solutions at various glass concentrations. Atomic force microscopy is used to study the surface morphology of the surface of as-deposited and thermally stabilized spin-coated films. Dynamic light scattering revealed a concentration dependence of cluster size in solution. Spectral-dependence dynamic light scattering studies showed an interesting athermal photoaggregation effect in the liquid state.

Multifractal characterization of water soluble copper phthalocyanine based films surfaces

This paper presents a multifractal approach to characterize the structural complexity of 3D surface roughness of CuTsPc films on the glass and quartz substrate, obtained with atomic force microscopy (AFM) analysis. CuTsPc films prepared by drop cast method were investigated. CuTsPc films surface roughness was studied by AFM in tapping-mode™, in an aqueous environment, on square areas of 100 μm2 and 2500 μm2. A detailed methodology for CuTsPc films surface multifractal characterization, which may be applied for AFM data, was also presented. Analysis of surface roughness revealed that CuTsPc films have a multifractal geometry at various magnifications. The generalized dimension Dq and the singularity spectrum f(α) provided quantitative values that characterize the local scale properties of CuTsPc films surface morphology at nanometer scale. Multifractal analysis provides different yet complementary information to that offered by traditional surface statistical parameters.

Down-scaling of resistive switching to nanoscale using porous anodic alumina membranes

An advanced approach for resistive switching memory cells based on porous anodic alumina (Al2O3) membranes is reported. The effective resistive switching resulting in 6 orders of magnitude difference in resistivity between “on” and “off” states of the cell is achieved by specific electronic and ionic interaction between Ag nanowires filled in the membrane and an ionic conductor (AgxAsS2) deposited on the membrane by thermal evaporation. This easy and robust approach can be exploited for deposition of other ionic conductors for novel types of memories.