Toplinska stabilnost W1−xSix/Si višeslojeva za rendgensku optiku

The thermal stability of multilayers (MLs) for X-ray mirrors can be increased by using a pair of materials in thermodynamic equilibrium. This was achieved by doping the W-layer by Si to decrease the driving force of interdiffusion. The W0.66Si0.33/Si, W0.5Si0.5/Si, W0.33Si0.66/Si and, for comparison, W/Si MLs with ten bilayers were fabricated by electron-beam deposition in UHV onto oxidized Si substrates. The nominal thickness was 5.5 nm for Si and 2.5 nm for W or W1-xSix layers. The samples were heat treated by halogen-lamp rapid thermal annealing and by standard annealing in vacuum up to 1000 °C for 30 s and 25 min, respectively. Samples were analyzed by X-ray reflectivity and large angle X-ray diffraction measurements. From the results follows an increased stability of W1-xSix/Si MLs in comparison with the W/Si ones. The temperature which the sample can withstand without a serious damage increased from 500 to 850 °C with x increasing from 0 to 0.66 . As-deposited, MLs were amorphous. The crystalline bcc W or WSi2 phases appeared at 500 °C for x Ł 0.5. For x = 0.66, a well developed WSi2 was obtained only after annealing at 1000 °C. Hence, Si helps to keep W in the amorphous state.Primjenom parova materijala, koji se stavljaju u termodinamičku ravnotežu, može se povećati toplinska stabilnost višeslojeva za zrcala rendgenskog zračenja. Sloj volframa dopunjen je silicijem da bi se smanjila difuzija medu slojevima. Istraženi su višeslojevi W1−x Six sa x = 0.66, 0.5, 0.33 i x = 0.0 radi usporedivanja. W/Si višeslojevi sa deset dvoslojeva pripremljeni su nanošenjem uz pomoć elektronskog snopa na oksidirane Si podloge u ultravakuumu. Nominalna debljina slojeva Si bila je 5.5 nm, a W odnosno W1−xSix 2.5 nm. Višeslojevi su toplinski otpuštani. Uzorci su istraživani mjerenjem refleksivnosti i difrakcijom rendgenskog zračenja. Povećanjem x od 0 na 0.66, povisila se granična temperatura bez većeg oštećenja sa 500 na 800 ◦C

Intrinsic anomalous surface roughening of TiN films deposited by reactive sputtering

7 pages, 7 figures.-- PACS nrs.: 68.55.−a, 81.15.Cd, 81.15.Aa, 68.35.Ct.Final publisher version available Open Access at: http://gisc.uc3m.es/~cuerno/publ_list.htmlWe study surface kinetic roughening of TiN films grown on Si(100) substrates by dc reactive sputtering. The surface morphology of films deposited for different growth times under the same experimental conditions were analyzed by atomic force microscopy. The TiN films exhibit intrinsic anomalous scaling and multiscaling. The film kinetic roughening is characterized by a set of local exponent values α(loc)=1.0 and β(loc)=0.39, and global exponent values α=1.7 and β=0.67, with a coarsening exponent of 1/z=0.39. These properties are correlated to the local height-difference distribution function obeying power-law statistics. We associate this intrinsic anomalous scaling with the instability due to nonlocal shadowing effects that take place during thin-film growth by sputtering.Financial support is acknowledged from Spanish MCyT Grants No. MAT 2002-04037-C03-03 and No. BFM 2003-07749-C05-01, -02, and -05; Comunidad Autónoma de Madrid, Grant No. GR/MAT/0431/2004, European Community Grant No. G5RD-CT-2000-00333, Centre of Excellence CE PI SAS, Contract No. I/2/2005, and Slovak Grant Agency for Science VEGA, Grant No. 2/6030/26.Publicad

Nanoparticle Langmuir-Blodgett Arrays for Sensing of CO and NO2 Gases

Metal oxide sensors with active Fe2O3 and CoFe2O4 nanoparticle arrays were studied. Sensing nanoparticle films from 1, 2, 4 or 7 monolayers were deposited by Langmuir-Blodgett technique. Sensors are formed on the alumina substrates equipped with heating meander. Langmuir-Blodgett layers were heated or UV irradiated to remove the insulating surfactant. Sensing properties were studied towards CO or NO2 gases in concentrations between 0.5 and 100 ppm in mixture with the dry air. Best response values Igas/Iair were obtained with CoFe2O4 device being 3 for 100 ppm of CO and with Fe2O3 device being (38)-1 for 0.5 ppm of NO2

Graphene Langmuir-Schaefer films Decorated by Pd Nanoparticles for NO2 and H2 Gas Sensors

NO2 and H2 gas sensing by few-layer graphene (FLG) were studied in dependence on the annealing and decoration of graphene by palladium nanoparticles (NPs). Graphene was deposited onto SiO2 (500 nm)/Si substrates by a modified Langmuir-Schaefer technique. A solution of FLG flakes in 1-methyl-2-pyrrolidone was obtained by a mild sonication of the expanded milled graphite. FLG films were characterized by atomic force microscopy, X-ray diffraction, Raman spectroscopy, and the Brunnauer-Emmett-Teller method. Average FLG flake thickness and lateral dimension were 5 nm and 300 nm, respectively. Drop casting of Pd NP (6–7 nm) solution onto FLG film was applied to decorate graphene by Pd. The room temperature (RT) resistance of the samples was stabilized at 15 kΩ by vacuum annealing. Heating cycles of FLG film revealed its semiconducting character. The gas sensing was tested in the mixtures of dry air with H2 gas (10 to 10 000 ppm) and NO2 gas (2 to 200 ppm) between RT and 200 °C. The response of 26 % to H2 was achieved by FLG with Pd decoration at 70 °C and 10 000 ppm of H2 in the mixture. Pure FLG film did not show any response to H2. The response of FLG with Pd to 6 ppm of NO2 at RT was ≥ 23 %. It is 2 times larger than that of the pure FLG sample. Long term stability of sensors was studied

Effect of crystallinity on UV degradability of poly[methyl(phenyl)silane] by energy-resolved electrochemical impedance spectroscopy

Low stability and degradability of polymers by ambient air, UV irradiation or charge transport are major problems of molecular electronics devices. Recent research tentatively suggests that the presence of a crystalline phase may increase polymer stability due to an intensive energy trapping in the ordered phase. Using the UV degradability, we demonstrate this effect on an archetypal model σ bonded polymer - poly[methyl(phenyl)silane] (PMPSi) - with partially crystalline and amorphous-like layers. UV degradation with 345 nm, derived from the branching state generation rate, was inversely proportional to the crystalline phase content, changing from 4.8x1011 s-1 (partially crystalline phase) to 1.8x1013 s-1 (amorphous-like phase). A model is proposed where crystallites formed by molecular packing act as effective excitation energy traps with a suppressed nonradiative recombination improving thus PMPSi film stability. The molecular packing and higher crystalline phase proportion may be a general approach for stability and degradability improvement of polymers in molecular electronics. © 2017 Author(s).0096-11, APVV, Agentúra na Podporu Výskumu a Vývoja; 1/0501/15, VEGA, Vedecká Grantová Agentúra MŠVVaŠ SR a SAV; 2/0163/17, VEGA, Vedecká Grantová Agentúra MŠVVaŠ SR a SAVSlovak Research and Development Agency [APVV-0096-11]; Scientific Grant Agency (VEGA) [1/0501/15, 2/0163/17

Thickness effect on structural defect-related density of states and crystallinity in P3HT thin films on ITO substrates

We report on a study of thickness effect on the formation of structural defect-related density of states (DOS) in the band gap of poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films spincoated on ITO substrates. The energy-resolved electrochemical impedance spectroscopy and grazing-incidence wide-angle X-ray scattering were used to correlate the DOS with the degree of crystallinity in P3HT thin films. We found an exponential increase of the defect DOS in the band gap with increasing fraction of the amorphous phase when decreasing the film thickness. The exponent increases abruptly when reducing the thickness down to 30 nm, which indicates two thickness regions with different dynamics of the defect DOS formation driven by increasing the fraction of the amorphous phase. Moreover, we observed the co-existence of two P3HT polymorphic crystalline phases with different backbone spacings, which results in the appearance of a peculiar DOS satellite peak above the highest occupied molecular orbital. The volume of the minor, more dense, crystalline phase exhibits a thickness dependence with a maximum plateau around 40 nm. These results suggest an important effect of the substrate roughness on the crystallinity and polymorphism of P3HT thin films depending on the film thickness with general implications for polymer thin films. © 2018 American Chemical Society.P3HT, SAS Institute; COFORD, Programme of Competitive Forestry Research for Development; APVV-0096-11, APVV, Agentúra na Podporu Výskumu a Vývoja; 2/0092/18; 1/0501/15; 2/0163/17; 26240220047; FEDER, European Regional Development FundSlovak Research and Development Agency [APVV-0096-11]; Scientific Grant Agency VEGA [1/0501/15, 2/0163/17, 2/0092/18]; Research and Development Operational Programme - ERDF [26240220047

A Non-Equilibrium Transient Phase Revealed by in Situ GISAXS Tracking of the Solvent-Assisted Nanoparticle Self-Assembly

We report on a time-resolved study of the colloidal nanoparticle self-assembly into a high-quality nanoparticle crystal with the face-centered cubic crystallographic symmetry. In particular, the grazing-incidence small-angle X-ray scattering technique was employed to track kinetics of the solvent evaporation driven self-assembly on casting a drop of plasmonic Ag nanoparticles on a silicon substrate. The short-range (cumulative) disorder typical for paracrystal structures before the complete solvent evaporation at 300–350 s from the drop casting was found with the exception of the time window of 125–150 s where a highly regular transient phase with the long-range order was observed. This temporary improvement of the nanoparticle crystal perfection occurring shortly before the complete solvent evaporation is the main message of the paper. It is attributed to interaction between the surfactant shells of the neighboring nanoparticles getting into contact in the presence of solvent residua to the end of the solvent evaporation which results in a larger nanoparticle hydrodynamic diameter with a smaller dispersion and improvement of the crystallization. This process has direct impact on the quality of the resulting nanoparticle crystal and tailoring its properties

Kinetics of Polymer–Fullerene Phase Separation during Solvent Annealing Studied by Table-Top X‑ray Scattering

Solvent annealing is an efficient way of phase separation in polymer–fullerene blends to optimize bulk heterojunction morphology of active layer in polymer solar cells. To track the process in real time across all relevant stages of solvent evaporation, laboratory-based in situ small- and wide-angle X-ray scattering measurements were applied simultaneously to a model P3HT:PCBM blend dissolved in dichlorobenzene. The PCBM molecule agglomeration starts at ∼7 wt % concentration of solid content of the blend in solvent. Although PCBM agglomeration is slowed-down at ∼10 wt % of solid content, the rate constant of phase separation is not changed, suggesting agglomeration and reordering of P3HT molecular chains. Having the longest duration, this stage most affects BHJ morphology. Phase separation is accelerated rapidly at concentration of ∼25 wt %, having the same rate constant as the growth of P3HT crystals. P3HT crystallization is driving force for phase separation at final stages before a complete solvent evaporation, having no visible temporal overlap with PCBM agglomeration. For the first time, such a study was done in laboratory demonstrating potential of the latest generation table-top high-brilliance X-ray source as a viable alternative before more sophisticated X-ray scattering experiments at synchrotron facilities are performed