Sigitas Tamulevičius

Stress and strain in the vacuum deposited thin films

Abstract Thin films deposited by physical vapor deposition, chemical vapor deposition or electrodeposition processes all have a residual stress in the film which may be manifested by cracking or peeling of the film or by bending of a thin film substrate or can induce shifts in bandgap of semiconductors, transition temperatures for superconducting films or expected magnetic anisotropy. Paper presents a short survey concerning the stress and strain kinetics in thin film starting from the definitions and covering most interesting recent experimental facts as well as theoretical models describing ion induced processes that define stress sign and level.

SILAR deposition of CdxZn1-xS thin films

Abstract Cd x Zn 1− x S thin films were grown on (100)GaAs by the successive ionic layer adsorption and reaction (SILAR) technique from dilute aqueous precursor solutions. Crystallinity, refractive index and morphology of the thin films were studied as a function of composition and thickness of the films. The Cd x Zn 1− x S films were polycrystalline and cubic. The crystallite size and refractive index of the films increased when the film thickness and Cd concentration in the Cd x Zn 1− x S thin films increased. It was found that tensile stress dominates in thin films when Cd concentration is lower than x ≤0.54 and the change of the residual stress to the compressive one takes place after that. Correlation between the growth mode and residual stress is demonstrated.

Growth of PbS thin films on silicon substrate by SILAR technique

Lead sulfide thin films were grown on (100)Si and (111)Si crystalline substrates by successive ionic layer adsorption and reaction, (SILAR), technique from solution phase at room temperature and normal pressure. The stress development, crystallinity and crystallite size, morphology and roughness and composition of the films were characterized as a function of the film thickness. The PbS thin films were polycrystalline and cubic. The residual stress in PbS was tensile and changed depending on the growth mode and thickness of the PbS films.

A single emitting layer white OLED based on exciplex interface emission

A new triaryl molecule based on a benzene–benzothiadiazole–benzene core has been applied in a WOLED device. This very simple molecule emits from a combination of emissive states (exciton/electromer/exciplex/electroplex) to give white light with CIE coordinates of (0.38, 0.45) and a colour temperature of 4500 K.

Spectroellipsometric characterization and modeling of plasmonic diamond-like carbon nanocomposite films with embedded Ag nanoparticles

Diamond-like carbon nanocomposite films with embedded silver nanoparticles are considered experimentally (spectroellipsometric characterization) and theoretically (modeling of optical properties). Metallic nanocomposite films were synthesized by reactive magnetron sputtering and were studied by transmission electron microscope (TEM) and atomic force microscope (AFM). The optical constants of the films were determined from spectroscopic ellipsometry measurements and were modeled using the Maxwell-Garnett approximations. Comparison between the extended and renormalized Maxwell-Garnett theory was conducted. Surface plasmon resonance peak have been found to be strongly dependent on the shape of nanoparticles and interaction between them.

Ion beam synthesis of α-CNx:H films

Hydrogenated amorphous carbon nitride (α-CN x :H) films (100-200 nm) were grown by direct ion beam deposition on Si( 100) substrates. Ion beams have been produced by electrostatic ion sources from C 6 H 14 +H 2 +N 2 gas mixtures. The influence of N 2 / C 6 H 14 +H 2 +N 2 gas ratio (N 2 concentration) on structure and properties of α-CN x :H films was investigated. The increase of N 2 concentration in the gas mixture resulted in decrease of sp 3 bonding and formation of the more graphite-like α-CN x :H films. Growth rate and refractive index of formed α-CN x :H films decreased with increasing N 2 concentration. A slight decrease of wear resistance (<20%) of the formed films with higher nitrogen ratio was also observed.

Stress and surface studies of SILAR grown ZnS thin films on (100)GaAs substrates

Zinc sulfide thin films were grown on (100)GaAs by the successive ionic layer adsorption and reaction (SILAR) technique from dilute aqueous precursor solutions. The stress of thin films was characterized by means of laser interferometry, crystallinity by X-ray diffraction, refractive index by ellipsometry and by fitting the reflectance spectrum, composition by electron spectroscopy and morphology by atomic force microscopy. A clear correlation between the growth mode and the residual stress level is demonstrated. The changes from three-dimensional to two-dimensional growth of the film results in the change of the residual stress from tensile to compressive. The films were polycrystalline and cubic with rather low crystallinity. The crystallite size and the refractive index of the films increased when the film thickness increased.

Stress and surface studies of SILAR grown CdS thin films on GaAs(100)

Abstract Cadmium sulfide thin films were grown on GaAs (100) by the successive ionic layer adsorption and reaction (SILAR) technique from aqueous precursor solutions. The purpose of this work was to analyze and find stress dependence of CdS thin films thickness and growth mode. The stress of the thin films was characterized by means of laser interferometry, composition and morphology by electron spectroscopy for chemical analysis (ESCA) and by atomic force microscopy (AFM). Correlation between the growth mode and the residual stress level is demonstrated. The changes from three-dimensional to two-dimensional growth of the film results in the change from tensile to compressive residual stress (from 1.39 to −2.50)×109 N/m2.

Synthesis and characterization of silver nanoparticles

Silver nanoparticles have received considerable attention due to their attractive physical and chemical properties. The surface plasmon resonance and large effective scattering cross section of individual silver nanoparticles make them ideal candidates for molecular labeling, where phenomena such as surface enhance Raman scattering (SERS) can be exploited. In addition, silver nanoparticles have recently been shown to be a promising antimicrobial material. In the present research silver colloid was produced by sodium citrate reduction. The colloidal silver was incorporated by dip-coating to the polymer substrate. X-Ray Fluorescence Spectroscopy (XRF), Atomic force microscopy (AFM), ultraviolet-visible spectroscopy (UV-VIS ) and SERS indicate that the produced structures include metallic crystalline silver nanoparticles. The surface plasmon resonance peak in absorption spectra of silver particles showed an absorption maximum at 420-500 nm. The silver - polymer nanocomposites structures with selective light properties as a result of plasmon resonance shifting in the UV-VIS wavelength region were produced.

Nine-ring angular fused biscarbazoloanthracene displaying a solid state based excimer emission suitable for OLED application

A new biscarbazoloanthracene consisting of nine fused aromatic rings, including two pyrrole units, has been obtained in a straightforward and convergent synthesis. Computational chemistry and conformational analysis revealed that the semiconductors molecule is not planar, the two carbazole moieties being helical twisted from the plane of the anthracene unit. Photophysical and electrochemical measurements showed that this angular fused heteroacene has a low lying HOMO energy level with a wide band gap despite its extended π-conjugated molecular framework. Based on its relatively low-lying HOMO level, the semiconductor promises a high environmental stability in comparison to other related linear fused acenes and heteroacenes. The biscarbazoloanthracene has been applied as the light emitting layer in a white light emitting diode (WOLED). It is proposed that the white OLED feature is due to dual light emission properties from the active semiconductor layer being based on both the molecular luminescence of the small molecule and a discrete excimer emission made possible by suitable aggregates in the solid state. Noteworthy, this is the first reported example of such a behavior observed in a small molecule heteroacene rather than an oligomer or a polymer.