M. Sawczak

Novel nitrogen precursors for electrochemically driven doping of titania nanotubes exhibiting enhanced photoactivity

Nitrogen doped titania nanotubes were successfully sensitized by the electrochemical method, i.e. as-anodized titania was immersed in different amine (diethylenetriamine – DETA, triethylamine – TEA, and ethylenediamine – EDA) and urea (U) solutions and a constant potential was applied. The highly ordered morphology of fabricated N-TiO2 was investigated by scanning electron microscopy. Spectroscopic techniques, i.e. UV-Vis spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy, were utilized to characterize absorbance capability and the crystalline phase, to confirm the presence of nitrogen atoms and to study charge recombination, respectively. The highest photocurrent under both UV-Vis and visible illumination (λ > 420 nm) was registered for the N-TiO2 sample obtained from diethylenetriamine solution, used as a nitrogen precursor. The photocurrent density exhibited during UV-Vis irradiation by the most active nitrogen doped titania was 2.83 times higher compared to pure TiO2 nanotubes. The photocatalytic activity studies demonstrated a significant improvement when N-TiO2–DETA (52%) and N-TiO2–U samples (49%) where used instead of undoped TiO2 (27%). The presented results show that electrochemical doping with 0.5 M amine or urea solutions is a simple, cheap and effective strategy to introduce nitrogen atoms into the titania structure without affecting its morphology.

Enhanced photoelectrochemical and photocatalytic performance of iodine-doped titania nanotube arrays

The paper discusses the synthesis and performance of iodine doped titania nanotube arrays exhibited under irradiation. The doping procedure was performed as an additional, electrochemical process carried out after formation of nanotube arrays via anodization of the Ti substrate. The optical and structural properties were characterized using Raman, UV-vis, photoluminescence and X-ray photoelectron spectroscopy. The surface morphology and cross-section studies performed by means of scanning electron microscopy show that the ordered tubular architecture is not influenced by the doping method. However, iodine doping causes a reduction of bandgap energy and photoluminescence intensity. The nanotubular TiO2 electrodes have been monitored by electrochemical (using cyclic voltammetry and electrochemical impedance spectroscopy) and in situ UV-vis spectroelectrochemical measurements in contact with an aqueous electrolyte. Collected results show significant differences in electrochemical activity between pure and doped titania exhibited as i.e. change of Mott–Schottky relation or shift in the onset potential when a decrease in reflectance is initiated. The photocurrent density reached 155.2 and 142.2 μA cm−2 for iodine doped materials when KI and HIO4 were used as iodine precursors whereas only 25.6 μA cm−2 was registered for pure titania nanotubes under UV-vis illumination. Moreover, doped samples are far more efficient for the photodegradation progress than undoped material leading to decomposition of over 70% of methylene blue used as a model organic pollutant. The reported studies demonstrate for the first time the detailed optical, electrochemical and photoelectrochemical studies of iodine doped nanotube arrays.

Use of optical skin phantoms for preclinical evaluation of laser efficiency for skin lesion therapy

Abstract. Skin lesions are commonly treated using laser heating. However, the introduction of new devices into clinical practice requires evaluation of their performance. This study presents the application of optical phantoms for assessment of a newly developed 975-nm pulsed diode laser system for dermatological purposes. Such phantoms closely mimic the absorption and scattering of real human skin (although not precisely in relation to thermal conductivity and capacitance); thus, they can be used as substitutes for human skin for approximate evaluation of laser heating efficiency in an almost real environment. Thermographic imaging was applied to measure the spatial and temporal temperature distributions on the surface of laser-irradiated phantoms. The study yielded results of heating with regard to phantom thickness and absorption, as well as laser settings. The methodology developed can be used in practice for preclinical evaluations of laser treatment for dermatology.

High-performance method of carbon nanotubes modification by microwave plasma for thin composite films preparation

In this work we present a simple and efficient method of nitrogen plasma modification of carbon nanotubes (CNTs). The process allows for treatment of the nanotubes in the form of powder with quite a high yield (65 mg of CNTs per hour). The modified carbon nanotubes contain approx. 3.8% nitrogen, mostly in the pyridinic form. Plasma treated CNTs exhibit better dispersibility in water and higher electric capacitance than pristine CNTs. Modified CNTs are a proper component of novel nanocomposites based on the conducting polymer poly(3,4-ethyleneidoxythiophene). Electrodeposited thin layers of the nanocomposite exhibit improved electrochemical properties (higher capacitance, better stability, lower resistance, faster diffusion) compared to the pure polymer layers.

Diagnostic instrument for measurements of a high power CO2 laser beam

A measuring device based on a rotating pinhole method was designed and developed at IF-FM for recording the spatial structure of high power cs CO2 laser beams in the near and far field region. The main performance parameters of the device are presented together with the measurement results concerning the beam propagation characteristics of the 1.2 kW technological laser.

Fs-laser processing of polydimethylsiloxane

We present an experimental analysis on surface structuring of polydimethylsiloxane films with UV (263 nm) femtosecond laser pulses, in air. Laser processed areas are analyzed by optical microscopy, SEM, and μ-Raman spectroscopy. The laser-treated sample shows the formation of a randomly nanostructured surface morphology. μ-Raman spectra, carried out at both 514 and 785 nm excitation wavelengths, prior and after laser treatment allow evidencing the changes in the sample structure. The influence of the laser fluence on the surface morphology is studied. Finally, successful electro-less metallization of the laser-processed sample is achieved, even after several months from the laser-treatment contrary to previous observation with nanosecond pulses. Our findings address the effectiveness of fs-laser treatment and chemical metallization of polydimethylsiloxane films with perspective technological interest in micro-fabrication devices for MEMS and nano-electromechanical systems.

The effect of wavelength and fluence on the cellulose degradation of laser-cleaned paper

The effect of a Q-switched Nd:YAG laser irradiation applied for ablative cleaning of the surface contaminants on cellulose samples and aimed on conservation of historical paper documents is investigated. The removal effectiveness of an artificial graphite contamination from model samples is investigated in dependence on the laser wavelength (532, 355 and 266 nm) and fluence (0.3 to 0.9J/cm2) and also the surface color changes are measured. Damages of cellulose fibers due to laser interaction are examined by means of the SEM technique. For irradiation at 266 nm only partial removal of the contamination and a distinct cellulose degradation, and also the yellowing of paper surface are observed. For the 355 nm wavelength and energy fluence below 0.6 J/cm2 the degradation of cellulose fibers does not occur. However, a slight yellowness of the surface is observed. The optimal cleaning wavelength of 532 nm and safe energy fluence below 0.6 J/cm2 found experimentally agree with literature.

Interfacial Properties of Organic Semiconductor-Inorganic Magnetic Oxide Hybrid Spintronic Systems Fabricated Using Pulsed Laser Deposition.

We report fabrication of a hybrid organic semiconductor-inorganic complex oxide interface of rubrene and La0.67Sr0.33MnO3 (LSMO) for spintronic devices using pulsed laser deposition (PLD) and investigate the interface structure and chemical bonding-dependent magnetic properties. Our results demonstrate that with proper control of growth parameters, thin films of organic semiconductor rubrene can be deposited without any damage to the molecular structure. Rubrene, a widely used organic semiconductor with high charge-carrier mobility and spin diffusion length, when grown as thin films on amorphous and crystalline substrates such as SiO2-glass, indium-tin oxide (ITO), and LSMO by PLD at room temperature and a laser fluence of 0.19 J/cm2, reveals amorphous structure. The Raman spectra verify the signatures of both Ag and Bg Raman active modes of rubrene molecules. X-ray reflectivity measurements indicate a well-defined interface formation between surface-treated LSMO and rubrene, whereas X-ray photoelectron spectra indicate the signature of hybridization of the electronic states at this interface. Magnetic measurements show that the ferromagnetic property of the rubrene-LSMO interface improves by >230% compared to the pristine LSMO surface due to this proposed hybridization. Intentional disruption of the direct contact between LSMO and rubrene by insertion of a dielectric AlOx layer results in an observably decreased ferromagnetism. These experimental results demonstrate that by controlling the interface formation between organic semiconductor and half-metallic oxide thin films, it is possible to engineer the interface spin polarization properties. Results also confirm that by using PLD for consecutive growth of different layers, contamination-free interfaces can be obtained, and this finding is significant for the well-controlled and reproducible design of spin-polarized interfaces for future hybrid spintronics devices.

Characterisation of CFRP surface contamination by laser induced fluorescence

The application of Carbon Fibre Reinforced Polymers (CFRP) in aeronautics has been increasing. The CFRP elements are joint using rivets and adhesive bonding. The reliability of the bonding limits the use of adhesive bonding for primary aircraft structures, therefore it is important to assess the bond quality. The performance of adhesive bonds depends on the physico-chemical properties of the adhered surfaces. This research is focused on characterization of surfaces before bonding. In-situ examination of large surface materials, determine the group of methods that are preferred. The analytical methods should be non-destructive, enabling large surface analysis in relatively short time. In this work a spectroscopic method was tested that can be potentially applied for surface analysis. Four cases of surface condition were investigated that can be encountered either in the manufacturing process or during aircraft service. The first case is related to contamination of CFRP surface with hydraulic fluid. This fluid reacts with water forming a phosphoric acid that can etch the CFRP. Second considered case was related to silicone-based release agent contamination. These agents are used during the moulding process of composite panels. Third case involved moisture content in CFRP. Moisture content lowers the adhesion quality and leads to reduced performance of CFRP resulting in reduced performance of the adhesive bond. The last case concentrated on heat damage of CFRP. It was shown that laser induced fluorescence method can be useful for non-destructive evaluation of CFRP surface and some of the investigated contaminants can be easily detected.

A rapid-response ultrasensitive biosensor for influenza virus detection using antibody modified boron-doped diamond

According to the World Health Organization (WHO), almost 2 billion people each year are infected worldwide with flu-like pathogens including influenza. This is a contagious disease caused by viruses belonging to the family Orthomyxoviridae. Employee absenteeism caused by flu infection costs hundreds of millions of dollars every year. To successfully treat influenza virus infections, detection of the virus during the initial development phase of the infection is critical, when tens to hundreds of virus-associated molecules are present in the patient’s pharynx. In this study, we describe a novel universal diamond biosensor, which enables the specific detection of the virus at ultralow concentrations, even before any clinical symptoms arise. A diamond electrode is surface-functionalized with polyclonal anti-M1 antibodies, which then serve to identify the universal biomarker for the influenza virus, M1 protein. The absorption of the M1 protein onto anti-M1 sites of the electrode change its electrochemical impedance spectra. We achieved a limit of detection of 1 fg/ml in saliva buffer for the M1 biomarker, which corresponds to 5–10 viruses per sample in 5 minutes. Furthermore, the universality of the assay was confirmed by analyzing different strains of influenza A virus.