Andrius Vasiliauskas

Antimicrobial Properties of Diamond-Like Carbon/Silver Nanocomposite Thin Films Deposited on Textiles: Towards Smart Bandages

In the current work, a new antibacterial bandage was proposed where diamond-like carbon with silver nanoparticle (DLC:Ag)-coated synthetic silk tissue was used as a building block. The DLC:Ag structure, the dimensions of nanoparticles, the silver concentration and the silver ion release were studied systematically employing scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic absorption spectroscopy, respectively. Antimicrobial properties were investigated using microbiological tests (disk diffusion method and spread-plate technique). The DLC:Ag layer was stabilized on the surface of the bandage using a thin layer of medical grade gelatin and cellulose. Four different strains of Staphylococcus aureus extracted from humans’ and animals’ infected wounds were used. It is demonstrated that the efficiency of the Ag+ ion release to the aqueous media can be increased by further RF oxygen plasma etching of the nanocomposite. It was obtained that the best antibacterial properties were demonstrated by the plasma-processed DLC:Ag layer having a 3.12 at % Ag surface concentration with the dominating linear dimensions of nanoparticles being 23.7 nm. An extra protective layer made from cellulose and gelatin with agar contributed to the accumulation and efficient release of silver ions to the aqueous media, increasing bandage antimicrobial efficiency up to 50% as compared to the single DLC:Ag layer on textile.

Dynamic optical properties of amorphous diamond-like carbon nanocomposite films doped with Cu and Ag nanoparticles

The investigation of relaxation processes in noble metal nanoparticles upon ultrafast excitations by femtosecond laser pulses is useful to understand the origin and the enhancement mechanism of the nonlinear optical properties for metaldielectric nanocomposites. In the current work we analyze diamond like carbon (DLC) film based copper and silver nanocomposites with different metal content synthesized employing unbalanced magnetron sputtering of metal targets with argon ions in acetylene gas atmosphere. Surface morphology and nanoparticle sizes were analyzed employing scanning electron and atomic force microscopy. Optical properties of the nanocomposite films were analyzed employing UV-VIS-NIR spectrometry. Transient absorption measurements were obtained employing Yb:KGW femtosecond laser spectroscopic system (HARPIA, Light Conversion Ltd.). Energy relaxation dynamics in Cu nanoparticles showed some significant differences from Ag nanoparticles. The increase of excitation intensity hasn’t show additional nonlinear effects for the excited state relaxation dynamics for both kinds of samples.

Photovoltaic Properties and Ultrafast Plasmon Relaxation Dynamics of Diamond-Like Carbon Nanocomposite Films with Embedded Ag Nanoparticles

Ultrafast relaxation dynamics of diamond-like carbon (DLC) films with embedded Ag nanoparticles (DLC:Ag) and photovoltaic properties of heterojunctions consisting of DLC:Ag and crystalline silicon (DLC:Ag/Si) were investigated by means of transient absorption (TAS) spectroscopy and photovoltaic measurements. The heterojunctions using both p type and n type silicon were studied. It was found that TAS spectra of DLC:Ag films were dependent on the used excitation wavelength. At wavelengths where Ag nanoparticles absorbed light most intensively, only DLC signal was registered. This result is in good accordance with an increase of the DLC:Ag/Si heterojunction short circuit current and open circuit voltage with the excitation wavelength in the photovoltaic measurements. The dependence of the TAS spectra of DLC:Ag films and photovoltaic properties of DLC:Ag/Si heterostructures on the excitation wavelength was explained as a result of trapping of the photoexcited hot charge carriers in DLC matrix. The negative photovoltaic effect was observed for DLC:Ag/p-Si heterostructures and positive (“conventional”) for DLC:Ag/n-Si ones. It was explained by the excitation of hot plasmonic holes in the Ag nanoparticles embedded into DLC matrix. Some decrease of DLC:Ag/Si heterostructures photovoltage as well as photocurrent with DLC:Ag film thickness was observed, indicating role of the interface in the charge transfer process of photocarriers excited in Ag nanoparticles.

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.