One-step metal electroplating and patterning on a plastic substrate using an electrically-conductive layer of few-layer graphene

Few-layer graphene (FLG) was investigated as an electrically-conductive interleaf layer for one-step electroplating and patterning of metal on nonconductive polymer substrates without using multiple and toxic pretreatment processes in traditional electroplating. An individual FLG (5–10 nm of thickness with 6.4% of oxygen content) was obtained by expanding graphite with microwave followed by exfoliating the expanded graphite with sonication in N-methyl-pyrrolidone. Stacking FLG in the in-plane direction, a robust FLG film was obtained by the vacuum-assisted filtering and drying methods, and transferred to a polyethylene terephthalate (PET) substrate via an intermediate transfer to the water surface. The sheet resistance of the FLG film on the PET substrate was 0.9 kΩ/sq with a thickness of 80 nm and the root-mean-square roughness of 29 nm. In the electroplating of nickel on the FLG film, hemisphere-shape metal seeds appeared in the early stage of electroplating and they subsequently grew up to 200–480 nm, which became connected to form a continuous nickel layer. The thickness of the continuous nickel layer increased linearly with electroplating time. The developed electroplating method demonstrated its capability of selective patterning on nonconductive substrates using a simple masking technique.     

Plasma-induced photoresponse in few-layer graphene

A device consisting of a few layers of graphene (FLG) sheets was exposed to atmospheric plasma, resulting in the generation of significant number of defects, oxygen absorption, and doping. The plasma-induced electrical transformation and photoconducting properties of pristine FLG and plasma-irradiated FLG (p-FLG) were compared under visible and ultraviolet (UV) light illumination. The visible light photoresponsivity of p-FLG was 0.47 AW⁻¹ at 535 nm, comparatively higher than that observed for pristine FLG (10 m AW⁻¹); this result was attributed to the formation of defect midgap states band by plasma irradiation. Photoinduced molecular desorption causes the responsivity of the higher energy (UV) photons. Our results suggest that plasma irradiation is a simple, novel way to tailor the optoelectronic properties of graphene layers.     

Few-layer graphene by assisted-exfoliation of graphite with layered silicate

Few-layer graphene has been achieved in liquid dispersion from graphite by the assistance of titanosilicate JDF-L1, using ultrasound and methanol as dispersive media. After a sedimentation step, both the dispersed and the sedimented phases were collected and then the titanosilicate was removed by alkaline hydrothermal dissolution from the mixed materials to obtain few-layer graphene (FLG) and sedimented material, respectively. The production of smaller particles was confirmed by means of N₂ adsorption and zeta-potential measurements, so that the BET specific surface area increased from 20 m²/g of the raw graphite to 333 ± 22 m²/g in FLG. Raman spectroscopy shows a decrease in the ratio of intensities of the peaks G and 2D from 3.8 in the raw material to 2.5 in FLG. Particles as fine as 1.3 nm, corresponding to 4-layered FLG, were observed by AFM, while high-resolution TEM showed defect-free regions of graphene.     

Excellent field emission characteristics from few-layer graphene–carbon nanotube hybrids synthesized using radio frequency hydrogen plasma sputtering deposition

The growth of few-layer graphene (FLG) on carbon nanotubes (CNTs) was realized by using radio frequency hydrogen plasma sputtering deposition. A defect nucleation mechanism and a two dimensional growth model of the FLG were proposed, and field emission characteristics of these FLG–CNT hybrids were studied. They show excellent field emission properties, with a low turn-on electric field (0.98 V/μm) and threshold field (1.51 V/μm), large field enhancement factor (～3980) and good stability behavior, which are much better than those of the as-grown CNT arrays. The sharp edges and the low work function of the hybrids are believed to be responsible for the improved field emission properties.     

Effects of second-phase particles and elemental distributions of ITO targets on the properties of deposited ITO films

As the key material of transparent electrodes in various optoelectronic devices, ITO targets with uniform microstructure and homogeneous elemental distributions are vital to obtain high-quality ITO films in industrial production. In this paper, the differences in the crystalline structure, sheet resistance and transmittance of ITO films with 40 nm, 70 nm and 100 nm thickness were studied between two ITO targets that were respectively sintered at 1580 °C for 10 h (target A) and 1600 °C for 5 h (target B). Surface morphology, surface roughness and thickness uniformity of ITO films with 100 nm thickness and etching property of ITO films with 40 nm and 70 nm thickness in mixed acids were further focused in the paper. The results indicate that target A, which owns homogeneous distributions of second-phase particles and elements, could be conductive to obtain the ITO films with low crystallinity that are easy to be etched leaving less and smaller residual particles. Based on the analysis, the change of sintering process has a great influence on the electrical and etching properties, but it has only a little influence on the optical property.     

The influence of a hierarchical porous carbon network on the coherent dynamics of a nanoconfined room temperature ionic liquid: A neutron spin echo and atomistic simulation investigation

The molecular-scale dynamic properties of the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, or [C₄mim⁺][Tf₂N⁻], confined in hierarchical microporous–mesoporous carbon, were investigated using neutron spin echo (NSE) and molecular dynamics (MD) simulations. Both NSE and MD reveal pronounced slowing of the overall collective dynamics, including the presence of an immobilized fraction of RTIL at the pore wall, on the time scales of these approaches. A fraction of the dynamics, corresponding to RTIL inside 0.75 nm micropores located along the mesopore surfaces, are faster than those of RTIL in direct contact with the walls of 5.8 nm and 7.8 nm cylindrical mesopores. This behavior is ascribed to the near-surface confined-ion density fluctuations resulting from the ion–ion and ion–wall interactions between the micropores and mesopores as well as their confinement geometries. Strong micropore–RTIL interactions result in less-coordinated RTIL within the micropores than in the bulk fluid. Increasing temperature from 296 K to 353 K reduces the immobilized RTIL fraction and results in nearly an order of magnitude increase in the RTIL dynamics. The observed interfacial phenomena underscore the importance of tailoring the surface properties of porous carbons to achieve desirable electrolyte dynamic behavior, since this impacts the performance in applications such as electrical energy storage devices.     

A comparative study on different aqueous-phase graphite exfoliation methods for few-layer graphene production and its application in alumina matrix composites

Four different methods (attrition milling, shear mixing, low-power bath sonication and tip sonication) used for the aqueous-phase, surfactant-assisted exfoliation of graphite were compared. Few-layer graphene (FLG) concentration, yield and production rate were measured for each method at different production times and the quality of the as produced FLG was determined using Raman spectroscopy and X-ray diffraction. It was inferred from the results that a combined method comprising tip sonication and shear exfoliation would offer the best balance between quality and quantity of FLG for relatively short processing times (<6 h). FLG dispersions produced with this method were used to fabricate 1 wt.% FLG/Al₂O₃ nanocomposites by ball milling and extrusion, followed by pressure-less sintering. The influence of the FLG addition on the microstructure and mechanical properties was studied, with observed increases of 26.4% and 67.6% in flexural strength and fracture toughness,respectively, and a 25.3% decrease in average grain size.     

Computational fluid dynamics simulations of submicrometer and micrometer particle deposition in the nasal passages of a Sprague-Dawley rat

Computational fluid dynamics (CFD) simulations were conducted in a model of the complete nasal passages of an adult male Sprague-Dawley rat to predict regional deposition patterns of inhaled particles in the size range of 1 nm to 10 μm. Steady-state inspiratory airflow rates of 185, 369, and 738 ml/min (equal to 50%, 100%, and 200% of the estimated minute volume during resting breathing) were simulated using Fluent?. The Lagrangian particle tracking method was used to calculate trajectories of individual particles that were passively released from the nostrils. Computational predictions of total nasal deposition compared well with experimental data from the literature when deposition fractions were plotted against the Stokes and Peclet numbers for micro- and nanoparticles, respectively. Regional deposition was assessed by computing deposition efficiency curves for major nasal epithelial cell types. For micrometer particles, maximum olfactory deposition was 27% and occurred at the lowest flow rate with a particle diameter of 7 μm. Maximum deposition on mucus-coated non-olfactory epithelium was 27% for 3.25 μm particles at the highest flow rate. For submicrometer particles, olfactory deposition reached a maximum of 20% with a particle size of 5 nm at the highest flow rate, whereas deposition on mucus-coated non-olfactory epithelium reached a peak of approximately 60% for 1–4 nm particles at all flow rates. These simulations show that regional particle deposition patterns are highly dependent on particle size and flow rate, indicating the importance of accurate quantification of deposition in the rat for extrapolation of results to humans.     

Synthesis of high-quality graphene films on nickel foils by rapid thermal chemical vapor deposition

We report the synthesis of high-quality graphene films on Ni foils using a cold-wall reactor by rapid thermal chemical vapor deposition (CVD). The graphene films were produced by shortening the growth time to 10 s, suggesting that a direct growth mechanism may play a larger role rather than a precipitation mechanism. A lower H₂ flow rate is favorable for the growth of high-quality graphene films. The graphene film prepared without the presence of H₂ has a sheet resistance as low as ～367 ohm/sq coupled with 97.3% optical transmittance at 550 nm wavelength, which is much better than for those grown by hot-wall CVD systems. These data suggest that the structural and electrical characteristics of these graphene films are comparable to those prepared by CVD on Cu.     

Effect of electrochemical surface area on electroless copper deposition: Pd nanocubes as new activators

In this study, the electrochemical surface area (ESA) and specific activity are used to obtain a fair comparison of various activators used for electroless copper deposition (ECD). Different sizes (i.e., 27, 48, and 63 nm) of Pd nanocubes (NCs) enclosed by {1 0 0} facets were successfully synthesized for use as new activators. The results of an analysis based on mixed potential theory indicated that the specific activities in terms of deposition current densities for the 27, 48, and 63 nm NCs and 9 nm nanoparticles (NPs) were 0.31, 1.06, 0.93, and 0.13 mA cm^?2_ESA, respectively. From the results of electrochemical quartz crystal microbalance measurements, the specific activities calculated from the mean deposition rates of the 27, 48, and 63 nm NCs and 9 nm NPs were 29.62, 68.72, 54.77, and 9.72 μg cm^?2 s^?1, respectively. A specific activity order of 48 nm NC > 63 nm NC > 27 nm NC > 9 nm NP was obtained. The 48 nm Pd NCs exhibited the maximum activity towards the activation of the ECD bath.     

Light-assisted adsorption processes in nanocrystalline diamond membranes studied by femtosecond laser spectroscopy

We report on femtosecond photoluminescence spectroscopy of nanocrystalline diamond membranes (thickness ～ 1000 nm) prepared by microwave plasma enhanced chemical vapour deposition (CVD) technique. The decay of photoluminescence excited by the blue femtosecond light pulses (405 nm) reflects the photoexcited charge carrier dynamics in the sub-band gap energy states. The photoluminescence is strongly influenced by ambient conditions and by the laser irradiation (405 nm, 70 fs pulses). Under lower ambient air pressure (5–300 Pa) the photoluminescence intensity increases and the photoluminescence decay gets faster. For higher air pressures (> 600 Pa) the photoluminescence intensity decreases and the photoluminescence decay rates do not evolve. We interpret the observed different behaviour of the photoluminescence in the two air pressure intervals in terms of a thin water layer condensed on the surface at higher air pressures. Due to a low coverage of the sample surface by water molecules under low pressure the air species can be adsorbed to NCD and influence the sub-band gap energy states.     

Influence of negative bias voltage on structural and mechanical properties of nanocrystalline TiNx thin films treated in hot cathode arc discharge plasma system

Ti thin films were grown by DC sputtering on a glass substrate and then nitrided in a hot cathode arc discharge plasma system, which is an effective approach to independently monitoring the plasma and nitriding parameters. The hardness of pristine Ti thin film is found to be ~3.06 GPa, which increases upto ~16.08 GPa with an increase in negative bias voltage to −140 V and then decreases to ~15.05 GPa for higher of −240 V bias voltage. Similar kind of variation has been observed in crystallite size and surface roughness. Crystallite size is found to increase from 11.1 nm (pristine Ti) to 14.8 nm (for −140 V) and then reduces to 11.9 nm for –240 V. Surface roughness increases from 2.78 nm (pristine) to 6.84 nm (for –140 V), which is found to be 4.14 nm for –240 V. Optical and electrical measurements also reveal the strong impact of negative bias voltage on the bandgap and resistivity of the films. Above results are understood on the basis of diffusion of nitrogen ions for lower voltages and saturation of nitrogen ions in the host lattice for high voltages.     

Direct formation of graphene layers on diamond by high-temperature annealing with a Cu catalyst

The formation of high-quality graphene layers on diamond was achieved based on a high-temperature annealing method using a Cu catalyst. Typical features of monolayer graphene were observed in the Raman spectra of layers formed by annealing of Cu/diamond heterostructures at 950 °C for 90 min. The coverage ratio of these graphene layers on diamond was estimated to be on the order of 85% by Raman mapping of the 2D peak. The sheet hole concentration and mobility values of the layers were estimated to be ~ 10¹³ cm^− 2 and ~ 670 cm²/Vs, respectively. These values are comparable to those previously observed for high-quality graphene layers on SiC.     

Controlled variation of the refractive index in ion-damaged diamond

A fine control of the variation of the refractive index as a function of structural damage is essential in the fabrication of diamond-based optical and photonic devices. We report here about the variation of the real part of the refractive index at λ = 632.8 nm in high-quality single-crystal diamond damaged with 2 and 3 MeV protons at low-medium fluences (10¹³–10¹⁷ ions cm^? 2). After implanting the samples in 125 × 125 μm² areas with a raster scanning ion microbeam, the variation of optical thickness of the implanted regions was measured with laser interferometric microscopy. The results were analyzed with a model based on the specific damage profile. The technique allows the direct fabrication of optical structures in bulk diamond based on the localized variation of the refractive index, which will be explored in future works.     

Technological capability of synthesis of inorganic oxides in water fluid in neighborhood of critical point

This technology is based on the use of water fluid as a reaction medium for synthesis of fine-crystalline oxides. The production of fine-crystalline oxides in a pilot plant using the industrial autoclaves has demonstrated the economical expediency and environmental safety of manufacturing of various fine-crystalline oxides by this method. The synthesis is performed at temperature in the range 380–410 °C and pressure of the water fluid 10–30 MPa in a high-pressure apparatus (reactor, autoclave or gasostat).Both the simple and mixed oxides with crystal sizes ranged from 100 nm to 400 μm were synthesized including quartz, corundum, zincite, aluminates of alkaline earth and rare earth elements, barium hexaferrite and yttrium-aluminum garnet.     

Strengthening behavior of few-layered graphene/aluminum composites

Strengthening behavior of composite containing discontinuous reinforcement is strongly related with load transfer at the reinforcement–matrix interface. We selected multi-walled carbon nanotube (MWCNT) and few-layer graphene (FLG) as a reinforcing agent. By varying a volume fraction of the reinforcement, aluminum (Al) matrix composites were produced by a powder metallurgy method. Uniform dispersion and uniaxial alignment of MWCNT and FLG in the Al matrix are evidenced by high-resolution transmission electron microscope analysis. Although the reinforcements have a similar molecular structure, FLG has a 12.8 times larger specific surface area per volume more than MWCNT due to geometric difference. Therefore an increment of a yield stress versus a reinforcement volume fraction for FLG shows 3.5 times higher than that of MWCNT Consequently, for both reinforcements, the composite strength proportionally increases with the specific surface area on the composite, and the composites containing 0.7 vol% FLG exhibit 440 MPa of tensile strength.     

High-performance diamond soft-X-ray detectors with internal amplification function

We have characterized the performance of soft-X-ray detectors fabricated with high-quality chemical-vapor-deposition (CVD) diamond layers which were homoepitaxially grown on high-pressure/high-temperature-synthesized Ib-type (100) substrates by means of a high-power microwave plasma CVD method. The soft-X-ray detectors with thin (≈ 15 nm) titanium-nitride interdigitated electrodes were fabricated using a standard photolithography process. We have found that the signal currents significantly increased at sufficiently higher voltages which were applied to the electrodes. The apparent room-temperature quantum efficiencies estimated at the applied voltage of 100 V from the signal currents attained by the diamond-based detector for a photon irradiation rate of ≈ 4 × 10⁶ photons/s ranged from 3.2 × 10⁵ to 3.1 × 10⁶ with photon energies ranging from 400 to 1800 eV. In addition, the diamond detector had signal-to-noise ratios larger than 6 orders of magnitudes. Thus, the present diamond detector has been verified to have excellently high sensitivities to soft-X-ray photons. The internally amplifying function of the diamond detector is discussed.     

Electrophotocatalytic decolorization of an azo dye on TiO2 self-organized nanotubes in a laboratory scale reactor

It was investigated the feasibility of decolorization of an azo dye (DG 26) using a large scale nanotubular TiO₂ structured electrode in a laboratory photoelectrochemical reactor (0.8 L). Catalyst was grown by anodic oxidation directly on Ti surface and its microstructure and crystalline structure were characterized with SEM and XRD. TiO₂/Ti photoactivity under different anodic polarization values was evaluated via photoelectrochemical tests. The nanostructured TiO₂ was used in a reactor as photo-anode under UV monochromatic irradiation (254 nm) and it was subjected to bias (+ 1.5 V vs. SCE). A comparison with photolysis and photocatalysis processes was carried out under the same operating conditions to evaluate the synergistic action of photocatalysis and TiO₂/Ti electrochemical polarization.Electrophotocatalysis was proven to be more effective than photocatalysis in DG 26 decolorization. Catalyst polarization resulted in synergistic effect on process yields. The complete decolorization of a 40 mg/L solution of DG 26 was achieved in 24 h, without adding chemical reagents, and catalyst durability was demonstrated over 360 h tests. Therefore, the work done is challenging to prove that the process (irradiation + catalyst + polarization) is feasible and effectively up-grading to pilot and demonstrative scale applications after a fluid dynamics optimization of the photoreactor.     

Facile corrosion synthesis and sintering of disperse pure tetragonal zirconia nanoparticles

Disperse pure tetragonal zirconia (t-ZrO₂) nanoparticles smaller than 10 nm are essential for preparation of structural and functional zirconia materials, but syntheses of t-ZrO₂ nanoparticles using inorganic zirconium salts usually result in severe agglomeration. In this paper, we report a hydrothermal corrosion approach for improving the dispersity of t-ZrO₂ nanoparticles synthesized by precipitation using zirconium oxychloride without any surfactants. Disperse pure t-ZrO₂ nanoparticles with average sizes of 4.5 and 6 nm and size distributions of 2–11 and 3–12 nm were obtained by calcining precipitates at 400 °C for 2 h and 500 °C for 0.5 h followed by HCl corrosion at 120 °C for 75 h, respectively. Disperse t-ZrO₂ nanoparticles with an average size of 6 nm and a size distribution of 3–12 nm were pressed into green compacts at 500 MPa and sintered by two-step sintering (heating to 1150 °C without hold and decreasing to 1000 °C with a 10 h hold). The sintered bodies are dense pure monoclinic ZrO₂ nanocrystalline ceramic with a relative density of 99.9% and an average grain size of 110 nm.