Rubrene Thin Films with Viably Enhanced Charge Transport Fabricated by Cryo-Matrix-Assisted Laser Evaporation.

Among organic semiconductors, rubrene (RB; C42H28) is of rapidly growing interest for the development of organic and hybrid electronics due to exceptionally long spin diffusion length and carrier mobility up to 20 cm2V-1s-1 in single crystals. However, the fabrication of RB thin films resembling properties of the bulk remains challenging, mainly because of the RB molecule's twisted conformation. This hinders the formation of orthorhombic crystals with strong π-π interactions that support the band transport. In this work, RB films with a high crystalline content were fabricated by matrix-assisted laser evaporation and the associated structure, composition, and transport properties are investigated. Enhanced charge transport is ascribed to the crystalline content of the film. Spherulitic structures are observed on top of an amorphous RB layer formed in the initial deposition stage. In spherulites, orthorhombic crystals dominate, as confirmed by X-ray diffraction and the absorption and Raman spectra. Surprisingly, nanowires several microns in length are also detected. The desorption/ionization mass and X-ray photoelectron spectra consistently show minimal material decomposition and absence of RB peroxides. The observed carrier mobility up to 0.13 cm2V-1s-1, is close to the technologically accepted level, making these rubrene films attractive for spintronic and optoelectronic applications.

Anodic titania nanotubes decorated with gold nanoparticles produced by laser-induced dewetting of thin metallic films.

Herein, we combine titania layers with gold species in a laser-supported process and report a substantial change of properties of the resulting heterostructures depending on the major processing parameters. Electrodes were fabricated via an anodisation process complemented with calcination to ensure a crystalline phase, and followed by magnetron sputtering of metallic films. The obtained TiO2 nanotubes with deposited thin (5, 10 nm) Au films were treated with a UV laser (355 nm) to form Au nanoparticles on top of the nanotubes. It was proven that selected laser working parameters ensure not only the formation of Au nanoparticles, but also simultaneously provide preservation of the initial tubular architecture, while above-threshold laser fluences result in partial destruction (melting) of the top layer of the nanotubes. For almost all of the samples, the crystalline phase of the nanotubes observed in Raman spectra was maintained independently of the laser processing parameters. Enhanced photoresponse up to ca 6 mA/cm2 was demonstrated by photoelectrochemical measurements on samples obtained by laser annealing of the 10 nm Au coating on a titania support. Moreover, a Mott-Schottky analysis indicated the dramatically increased (two orders of magnitude) concentration of donor density in the case of a laser-treated Au-TiO2 heterojunction compared to reference electrodes.

Wear Resistance Enhancement of Al6061 Alloy Surface Layer by Laser Dispersed Carbide Powders.

In this paper, results of the experimental study on improving wear resistance in sliding friction of Al-based alloy are presented. The technique used involves the formation of a metal matrix composite (MMC) in the alloy surface layer by laser dispersion of carbide powders such as WC, TiC and SiC. For WC and TiC MMC surface coatings fabricated under conditions typical for most of the technologically relevant solid-state lasers (wavelength range of 0.8-1.1 µm), the nearly inversely proportional dependence of the required laser energy density on the powder mass density is observed. Highly homogenous distribution of powder particle content (up to 40%) in the MMC surface coatings of a thickness between 0.8 and 1.6 mm obtained by multiple scanning is observed in the cross-section of specimens processed within a rather narrow parameter window. Tribological tests and comparison to untreated material reveal wear resistance increases by five- and ten-fold, observed in samples with laser-dispersed TiC and WC powders, respectively. Results indicate that substantial modification and reinforcement of the surface layer can be achieved in Al alloy in a one-step process without substrate preheating.

Ordered titanium templates functionalized by gold films for biosensing applications - Towards non-enzymatic glucose detection.

Recently, metal nanostructures evoke much interest due to application potential in highly sensitive detectors in biochemistry and medical diagnostics. In this work we report on preparation and characteristics of thin (1-100nm) Au films deposited onto highly ordered structured titanium templates for SERS (Surface Enhanced Raman Spectroscopy) and electrochemical sensing. The Ti templates are formed by selective removal of TiO2 nanotubes out of as-anodized titanium substrate. The surface of the obtained material reproduce precisely the bottom layer of the nanotubes and consists of a uniformly distributed dimples with diameter of ~100nm. For all structures covered with Au films the measured average SERS signal is markedly higher than the one observed for bare Ti templates. This is due to strong electromagnetic field in the vicinity of the film grains. Moreover, such nanostructured gold surface exhibits also attractive electrochemical and electrocatalytic properties, which should be attributed to enhancement of the electron transfer at the Au-Ti interface formed without any linker molecules. It is shown that prepared material can be used as an enzyme-free sensor for glucose detection in air-saturated neutral media especially in case of low sugar concentrations present in human body liquids, such as saliva, sweat and interstitial fluid.

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.

Raman spectroscopic signatures of the yellow and ochre paints from artist palette of J. Matejko (1838-1893).

The Raman and complementary spectroscopic analyses were performed using the exceptional possibility of research on the XIX c. original paint materials of the artist palette of J. Matejko stored in the National Museum in Cracow. The yellow and ochre-based paints characteristic for Matejko's workshop and selected from the ensemble of 273 labelled tubes (brand of R. Ainé/Paris) supplied during the period of 1880-1893 were investigated. Highly specific Raman spectra were obtained for paints containing mixtures of the Zn- and Sn-modified Pb-Sb pigment, and also for the ochre-based ones. A clear pigment discrimination of the mixture of cadmium yellow (CdS), cinnabar (HgS) and lead white (2PbCO3⋅Pb(OH)2) was possible by means of Raman data collected under different excitations at 514 nm and 785 nm. It was shown that the Raman spectra complemented by the XRF, SEM-EDX and in some cases also by the LIPS and FTIR data ensure reliable pigment identification in multi-component paints containing secondary species and impurities. The reported spectral signatures will be used for non-destructive investigation of the collection of about 300 oil paintings of J. Matejko. In view of the comparative research on polish painting which point out that richness of modified Naples yellows clearly distinguish Matejko's artworks from other ones painted in the period of 1850-1883, the Raman data of these paints can provide support in the authentication studies.

Properties of plasmonic arrays produced by pulsed-laser nanostructuring of thin Au films.

A brief description of research advances in the area of short-pulse-laser nanostructuring of thin Au films is followed by examples of experimental data and a discussion of our results on the characterization of structural and optical properties of gold nanostructures. These consist of partially spherical or spheroidal nanoparticles (NPs) which have a size distribution (80 ± 42 nm) and self-organization characterized by a short-distance order (length scale ≈140 nm). For the NP shapes produced, an observably broader tuning range (of about 150 nm) of the surface plasmon resonance (SPR) band is obtained by renewal thin film deposition and laser annealing of the NP array. Despite the broadened SPR bands, which indicate damping confirmed by short dephasing times not exceeding 4 fs, the self-organized Au NP structures reveal quite a strong enhancement of the optical signal. This was consistent with the near-field modeling and micro-Raman measurements as well as a test of the electrochemical sensing capability.