We report on an in situ observation of reassembly and oxidation of a self-assembled silver nanoparticle bilayer due to an UV/ozone treatment and removal of the nanoparticle surfactant molecules. Such ...arrays of metal oxide nanoparticles are designated for sensor applications. To follow simultaneously the temporal evolution of particular processes taking place at different length scales, we employed the small- and wide-angle X-ray scattering in situ. In this way, all relevant transformation stages were identified: removal of the nanoparticle surfactant shell accompanied by a loss of the nanoparticle position correlations, oxidation of the nanoparticle crystalline core, and final reassembly of the silver oxide nanoparticles into agglomerates. Study of these processes on a common timeline provides a detailed insight into the kinetics of the UV/ozone treatment which represents a simple and effective method for preparation of metal oxide nanoparticle arrays for sensors.
The avoiding of the hole transport layer (HTL) by an UV/ozone treatment of the indium tin oxide (ITO) electrode was successfully tested on the P3HT:PC61BM and PBDTTT‐CF:PC71BM organic solar cells ...with plasmonic gold nanoparticles and gold nanorods spincoated on ITO, respectively. Reference device on bare UV‐ozone treated ITO and the one with HTL were also prepared for comparison. It was found that the UV/ozone treatment of the bare ITO and plasmon‐enhanced ITO electrode allowed an effective alignment of the electrode work function with the polymer in the active layer at the saturated values of 5.5 eV and 5.6 eV, respectively. This result is well explained by the integer charge transfer model. The power conversion efficiency (PCE) of the device on bare UV/ozone treated ITO was comparable to that of the conventional device with HTL. Application of two types of 30 nm gold nanoparticles and 40 nm long gold nanorods on ITO before the subsequent UV/ozone treatment improved the PCE by up to 20% and 10%, respectively. These results suggest feasibility of a simple and cost‐effective preparation of OSCs.
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Self-assembled metal oxide nanoparticle layers have attracted much attention recently due to potential applications in sensors. Here we report on a UV/ozone-driven re-assembly and ...oxidation of a self-assembled silver nanoparticle bilayer deposited by a modified Langmuir-Schaefer technique that was probed in-situ by simultaneous measurements of the small- and wide-angle X-ray scattering at grazing incidence (GISAXS, GIWAXS). The experiments were performed at BL23A endstation of NSRRC, Taiwan. Four distinct stages of the system response to the UV/ozone treatment were identified. In the first stage 0-120 s, a gradual extinction of Bragg rods and the nanoparticle short-range order due to a gradual surfactant removal is observed in GISAXS that is connected with an array densification and order improvement obeying the paracrystal model in the shrinking self-assembled regions. In the second stage 120-360 s, the original self-assembly goes to a total extinction while the integral intensity of Ag 111 diffraction in GIWAXS starts to decrease, suggesting the total surfactant removal. No nanoparticle short-range order is observed in stage III 360-730 s where AgO monoclinic phase due to the nanoparticle surface oxidation appears and pure Ag phase disappears. The initial AgO unit cell volume corresponding to the unstrained phase gradually expands by 4.6 % to the end of stage III. In stage IV 730-2000 s (end of measurements), new Bragg rods appear in GISAXS, suggesting a nanoparticle agglomeration with a typical correlation length of approximately 240 nm that was confirmed by ex-situ atomic force microscopy. The agglomeration does not reach saturation even after 2000 s while the AgO phase remains stable. These results have direct implications for tailored preparation of advanced sensors based on metal oxide nanoparticles. The work was supported by the projects APVV-0308-11, VEGA 2/0041/11, SAS-NSC JRP 2011/05, SAS-TUBITAK JRP 2013/6, COST MP1203 and COST CM1101.
Real-time reassembly of an ordered nanoparticle monolayer due to UV-photolysis of the surfactant shell of nanoparticles was observed. The technique of grazing-incidence small-angle X-ray scattering ...provided the possibility to track in situ the nanoparticle pair correlation function of the sample processed in a UV-ozone reactor. The analysis revealed a total shift of ∼1 nm of the nanoparticle nearest-neighbor distance. The temporal evolution of the interparticle distance proved to be the first-order process governed by the UV-photolysis and described by a single-exponential decay function. The nanoparticles tend to agglomerate into a labyrinth-like structure with a typical length scale of some 30 nm.
A high-performance W/B
4
C multilayer mirror with 80 periods of nominally 1.37 nm was measured by grazing-incidence small-angle X ray scattering (GISAXS) in order to analyse the lateral and vertical ...correlations of the interface roughness within the framework of a scaling concept of multilayer growth. A dynamic growth exponent
z
= 2.19 (7) was derived, which is close to the value predicted by the Edwards–Wilkinson growth model. The effective number of correlated periods indicates a partial replication of the low interface roughness frequencies. A simulation of the GISAXS pattern based on the Born approximation suggests a zero Hurst fractal parameter
H
and a logarithmic type of autocorrelation function. The as-deposited mirror layers are amorphous and exhibit excellent thermal stability up to 1248 K in a 120 s rapid thermal vacuum annealing process. At higher temperatures, the B
4
C layers decompose and poorly developed crystallites of a boron-rich W–B hexagonal phase are formed, and yet multilayer collapse is not complete even at 1273 K. Ozone treatment for 3000 s in a reactor with an ozone concentration of 150 mg m
−3
results in the formation of an oxidized near-surface region of a thickness approaching ∼10% of the total multilayer thickness, with a tendency to saturation.
Two-dimensional (2D) transition metal dichalcogenides are potential candidates for ultrathin solid-state lubricants in low-dimensional systems owing to their flatness, high in-plane mechanical ...strength, and low shear interlayer strength. Yet, the effects of surface topography and surface chemistry on the tribological properties of 2D layers are still unclear. In this work, we performed a comparative investigation of nanoscale tribological properties of ultra-thin highly-ordered PtSe2 layers deposited on the sapphire substrates with the in-plane and out-of-plane crystallographic orientation of the PtSe2 c-axis flakes, and epitaxial PtSe2 layers. PtSe2 c-axis orientation was found to has an impact on the nanotribological, morphological and electrical properties of PtSe2, in particular the change in the alignment of the PtSe2 flakes from vertical (VA) to horizontal (HA) led to the lowering of the coefficient of friction from 0.21 to 0.16. This observation was accompanied by an increase in the root-mean-square surface roughness from 1.0 to 1.7 nm for the HA and VA films, respectively. The epitaxial films showed lower friction caused by lowering adhesion when compared to other investigated films, whereas the friction coefficient was similar to films with HA flakes. The observed trends in nanoscale friction is attributed to a different distribution of PtSe2 structure.
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 100ppm in mixture with the dry air. Best response values Igas/Iair were obtained with CoFe2O4 device being 3 for 100ppm of CO and with Fe2O3 device being (38)-1 for 0.5ppm of NO2.
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