K. Šlapikas

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.

Optical properties of the undoped and SiOx doped DLC films

In present study DLC films were deposited by direct ion beam deposition. Hexamethyldisiloxane vapor and hydrogen gas mixture, mixture of the hexamethyldisiloxane with acetylene as well as acetylene gas alone has been used as a source of the hydrocarbons. Optical properties of the synthesized films were investigated by spectroscopic ellipsometry. Structure of the DLC films has been studied by means of the Raman spectroscopy. Effects of the technological deposition parameters such as composition of the gas precursors, ion beam energy, ion beam current density were considered.

The Influence of Annealing on Current–Voltage Characteristics of H2SeO3 Treated Al–nGaAs Schottky Contact

This study the annealing effects on current-voltage and low-frequency noise characteristics of Al-nGaAs Schottky contact were investigated. Selenious acid treatment of GaAs surface prior Al deposition resulted in effective barrier height (φ * b ) reduction up to 0.36 eV and to the Ohmic contact formation after annealing above 450 °C. SEM analysis revealed that Se passivation affected both metallisation morphology and interface reaction kinetic during the Al-GaAs anneals. Observed changes of the Schottky contact barrier height, low-frequency noise and thermostability are explained by the interface Se reactions with both GaAs and Al.

Giant Negative Piezoresistive Effect in Diamond-like Carbon and Diamond-like Carbon-Based Nickel Nanocomposite Films Deposited by Reactive Magnetron Sputtering of Ni Target

Piezoresistive properties of hydrogenated diamond-like carbon (DLC) and DLC-based nickel nanocomposite (DLC:Ni) films were studied in the range of low concentration of nickel nanoparticles. The films were deposited by reactive high power pulsed magnetron sputtering (HIPIMS) of Ni target, and some samples were deposited by direct current (dc) reactive magnetron sputtering for comparison purposes. Raman scattering spectroscopy, energy-dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS) were used to study the structure and chemical composition of the films. A four-point bending test was applied to study piezoresistive properties of the films. For some samples containing less than 4 at. % Ni and for the samples containing no Ni (as defined by both EDS and XPS), a giant negative piezoresistive effect was observed. The giant negative piezoresistive effect in DLC films deposited by either reactive HIPIMS or dc magnetron sputtering of Ni target was explained by possible clustering of the sp2-bonded carbon and/or formation of areas with the decreased hydrogen content. It was suggested that the tensile stress-induced rearrangements of these conglomerations have resulted in the increased conductivity paths.

Optical Properties Nanocomposite Composed of Ag Nanoparticles Embedded in a DLC Film

The results of theoretical and experimental investigation of the optical absorption spectra of thin films of nanocomposite materials composed of silver nanoparticles embedded in a diamond like carbon (DLC) matrix are presented. The optical characteristics of DLC-Ag nanocomposite are considered within the framework of the effective medium approximation. Fundamental properties of nanostructured materials are currently excessively studied because of their potential application in numerous fields such as electronic devices, opto-electronics, optics, tribology, biotechnology, human medicine and others. The noble metal nanoparticles embedded in a matrix such as amorphous carbon have been studied intensively (Montiel-Gonzalez Z et al. Thin Solid Films 519:5924–5932, 2011), since such type of nanocomposites are expected to exhibit interesting optical property so called surface plasmon resonance and are promising materials for developing the elemental base of different physics devices. Amorphous hydrocarbon coatings, often called diamond-like carbon (DLC) coatings are nowadays used in many applications due to low friction coefficient and high hardness and also corrosion resistance, chemical inertness, high electrical resistivity, infrared-transparency, high refractive index (Robertson, Mater Sci Eng R Rep 37:129–281, 2002). In this work, the optical absorption of DLC-Ag films was experimentally and theoretically investigated. The experimental absorption spectra of DLC based silver nanocomposites deposited by reactive magnetron sputtering on fused silica were compared with the simulated ones. Role of the host matrix and silver nano-particles on the tunable effective refractive index of the films was analyzed. Using Mie theory it was researched that absorption of the nanocomposite thin films is sensitive to both refractive index and extinction coefficient parameters of the DLC host and in the evaluation of the absorption of the film it is necessary to take into account the spectral dependence of the complex refractive index of DLC. Reduction in size of the metal particles results in blue-shift of the surface plasmon resonance peak but spectral position of the absorption peak is more sensitive to the dielectric constant of DLC, than to the radius of nanoparticles. The absorption peaks related to the surface plasmon resonance are red-shifted with the increase in Ag volume fraction and this shift may be attributed to the increased electromagnetic interaction between the particles and change in the effective permittivity of the DLC-Ag nanocomposite (Yaremchuk et al. Physica Status Solidi (a) 211:329–335, 2014). In Fig. 71.1 experimental and calculated optical absorption spectra of DLC-Ag thin film with 20 % Ag concentration are depicted. The optical absorption peak due to the surface plasmon resonance of Ag particles centered at around 530 nm was observed. Strong absorption peak centered at around 480 nm we address to the nanoparticles with a radius of 8.5 nm (calculation 1, see Fig. 71.1) and peak at around 580 nm – to the nanoparticles with a radius of 30 nm (calculation 2, Fig. 71.1). The approximation curve consists of these two peaks and provides reasonable fit of the experimental curve. Application of the extended Maxwell–Garnett effective theory provides good fit of the experimental optical absorption spectra of the DLC-Ag films with the silver nanoparticle concentration up to 20 %. The difference between the Maxwell-Garnett theory prediction and the experimental results is that a surface plasmon resonance is broader than the computed one as a result of wide distribution of the particle size consequently resulting in the broadening of the experimental plasmon resonance peak.

In situ analysis of adsorption process from residual gases during thin film deposition

In this work we present the developed experimental technique as well as results of optical control of adsorption processes during thin film deposition. Different metallic films: (silver) as a model material and barium getter films were studied. Thermal evaporation method has been used to deposit thin metallic films and films of barium getter on glass substrates. Kinetics of the optical absorbance of the growing film was registered in situ measuring transmission of the film-substrate structure. These measurements were done in parallel to the ex-situ absorption (UV-VIS) and reflection spectra as well as XRD analysis. Such complex measurements enabled us to follow adsorption process from the residual gases during thermal evaporation as well to control adsorption process after the evaporation.

Al-nGaAs ohmic contact formation by H2SeO3 treatment and annealing

In this research the influence of annealing on current- voltage characteristics of selenious acid (H2SeO3) treated Al-nGaAs contacts was investigated. Linear Al-nGaAs contacts were obtained by combination of selenious acid treatment and annealing. Dependence of the annealing and selenious acid treatment effects on nGaAs substrate dopants concentration was observed. Specific resistivity of the Al- nGaAs ohmic contact as low as 7.3(DOT)10-6 (Omega) (DOT)cm2 was achieved. Formation of the Al-nGaAs ohmic contact was explained by the interface Se reactions with both GaAs and Al.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Influence of plasma spraying process parameters on properties of the deposited Ni-Al coatings

Plasma spraying technique was used for deposition of Al and Ni-Al coatings with special electrochemical characteristics. Influence of the plasma spraying process on characteristics of plasma stream and properties of the deposited coatings was investigated. Temperature field in the plasma torch, dependence of temperature of the probe placed in the plasma stream on the gas flux, pressure in the deposition chamber and arc discharge output power were measured experimentally. Surface morphology of th3 coatings by optical microscope and scanning electron microscope was investigated. It was found high dependence of the morphology on composition of the plasma gas. X-ray technique for investigation of chemical composition of the coatings was used. It was found that inter-diffusion of nickel and aluminum during deposition of the coatings takes part. This phenomenon influences chemical composition of the surface and electro-chemical characteristics of the coatings.

Influence of annealing on the morphology and phase composition of plasma-sprayed Ni/Al coatings

Thermal annealing of plasma sprayed Ni/Al coatings used as the catalyst was investigated. The coatings were plasma sprayed on Cu substrate at low vacuum conditions (approximately 1 Pa) and were heated at temperatures of 600 degree(s)C and 800 degree(s)C in Ar atmosphere for 5 hours. Scanning electron microscopy and X-ray diffraction were used to study influence of annealing on the morphology and phase transformation in the Ni/Al coatings. A change of morphology of the coatings to smoother and less porous during thermal treatment was observed. Grain size number changes from n equals 5.52 for annealed coatings to n equals 5.37 and n equals 5.26 for coatings annealed at 600 degree(s)C and 800 degree(s)C, respectively. At the same time phase transformation with appearance of new alloys took place. These changes greatly influence other properties of the Ni/Al coatings.