Removal Of SiO2 Research Articles

Preparation of an O/N/P/S co-doped hierarchical porous carbon material derived from snake skin for supercapacitors

An O/N/P/S co-doped carbon material with hierarchical porous structure for supercapacitors is prepared from snake skin by a simple calcination method, which exploits its own scaffold silica (SiO2) as the self-sacrifice template combining with the activated agent potassium hydroxide (KOH). The KOH acts not only as activator to create micropores, but also as etching agent to remove the nonconductive SiO2 in situ, leading to better conductivity, as well as forming mesopores and macropores. The influences of calcination temperature and SiO2 etching on the electrochemical performances are discussed. Under the synergistic effects of the hierarchical pores in its structure and the existing of multiple hetero atoms, as well as the removal of SiO2, the obtained carbon material (C-KOH) displays outstanding specific capacitance (717.6 F g− 1 at 1 A g− 1) and excellent stability (120% capacitance retention rate after 40,000 cycles).

(Invited) Titania Inverse-Opal Photonic Crystals Incorporating Gold Nanoparticles in Void Spaces for Photoabsorption Enhancement

Designing of three-dimensional (3D) materials such as inverse-opal (IO) photonic crystals (PCs) has been identified as an effective pathway to enhance light harvesting to longer electromagnetic absorption regions such as visible and infrared [1]. IO PCs exhibit photonic band gap (PBG) and this band structure predicts the translation of photons with reduced velocity, namely as slow photons at certain crystallographic directions. The photonic effect from titania (TiO2)-IO structure was reported to enhance light-material interactions thus allowing better absorption of light at the wavelength at which the materials absorb poorly [2]. On the other hand, utilization of gold-nanoparticles (Au-NPs) on TiO2 could aid in charge separation and play its role as an amplifier for visible-light absorption due to its effects originating from localized surface plasmon resonance (LSPR) [3]. In this study, TiO2-IO PC with incorporated gold nanoparticles (Au-NPs) per void space was developed by implementing five important steps to achieve a good quality of TiO2-IO structure. Both photonic effects due to the slow photons in TiO2-IO structure and LSPR effects contributed by Au-NPs were expected to give visible-light absorption by the photocatalyst materialThe experimental procedure consists of five steps as shown in Scheme 1 starting from (i) synthesis of Au-NPs, (ii) silica (SiO2) coating on Au-NP to form Au/SiO2 core-shells, (iii) self-assembly of Au/SiO2 to form high-quality opal structure, (iv) infiltration of TiO2 precursor via forced impregnation method and (v) selective etching of SiO2 to obtain the final TiO2-IO structure. Photodegradation of acetic acid was carried out in the presence of the photocatalyst material by using blue LED light (450 nm) with optical power of 0.3 W.SiO2 containing Au-NP (Au/SiO2) was used as the opal template for the 3D macroporous TiO2-IO containing Au-NP per void space (TiO2(Au)-IO). Figures 1a and 1b are images observed for Au/SiO2 opal structure exhibiting face-centered cubic (FCC) arrangement. As is observed, the closely packed opal structure could be obtained as the minimum variation among each particle was less than 5 %. However, extra precautions should be taken to avoid cracking on the opal structure to sustain the quality of the final desired material. Figures 1c and 1d are images of TiO2(Au)-IO which was successfully obtained after TiO2 infiltration via forced impregnation method followed by the removal of SiO2 to form the nanovoids. The strategy that has been implemented to enhance the light harvesting process was by designing the TiO2-IO structure with different diameter of nanovoids, which can be controlled by altering the SiO2 shell thickness in the second step of the synthesis process.Photocatalytic activities of those samples were evaluated by measuring the amount of carbon-dioxide (CO2) generated from acetic acid by TiO2(Au)-IO with different diameter of nanovoid diameters (Au-NP size: 44 nm) under LED light irradiation (4 h). Enhanced CO2 evolution was detected with TiO2(Au)-IO with nanovoid diameter of 215 nm suggesting the successful matching of photonic and LSPR effects in TiO2(Au)-IO.

Atomic layer etching of SiO2 for surface cleaning using ammonium fluorosilicate with CF4/NH3 plasma

In this study, an atomic layer etching (ALE) process was developed and investigated for the removal of SiO2 with CF4/NH3. An ammonium fluorosilicate [AFS, (NH4)2SiF6] layer was successfully formed on SiO2 with CF4/NH3 plasma and removed by subsequent thermal treatment above 100 °C using a lamp. An oxide removal rate of 2.7 nm/cycle was achieved with CF4/NH3 chemistry, and the self-limiting characteristic of the ALE process was demonstrated by the removal rates. After the ALE process of SiO2 with CF4/NH3 plasma, no carbon residue was observed on the SiO2 surface. The reaction characteristics of the CF4/NH3 plasma were compared with those of the NF3/NH3 plasma. The removal rate with NF3/NH3 was 9.1 nm/cycle, which is three times higher than that with CF4/NH3 without saturation at 600 s. The lower removal rate with the CF4/NH3 plasma is attributed to the stronger C–F bonding in CF4 compared to the N–F bonding in NF3. Moreover, the stronger bonding generates fewer fluorine radicals required to form HF and NH4F reactants. This work demonstrates that CF4 is suitable for the ALE process for the removal of oxide layers at the nanometer-scale; in addition, it provides an effective process for the nanoscale removal of oxides in three-dimensional devices.

Tribological, Thermal and Kinetic Characterization of SiO2 and Si3N4 Polishing for STI CMP on Blanket and Patterned Wafers

We investigated the tribological, thermal and kinetic aspects of SiO2 and Si3N4 polishing on blanket and patterned wafers for STI CMP. Results showed the absence of anomalous tribological vibrational behaviors thanks to synergies between the colloidal CeO2-based slurry and application-specific conditioner. Removal rates for the two processes showed non-Prestonian behavior as both mechanical and chemical factors were at work. However, Si3N4 was much more non-Prestonian than SiO2. As expected, Si3N4 polishing resulted in COFvalues that were approximately one-half of their SiO2 counterparts resulting in high SiO2-Si3N4 removal rate selectivity. A modified Langmuir-Hinshelwood model was used to simulate removal rates allowing us to conclude that the process was mechanically-limited for SiO2 and highly chemically-limited for Si3N4. Patterned wafer polishing time traces showed that COFcould be utilized as a real-time indicator for end-point detection and that, after 6 min of polishing, we observed the total removal of SiO2 with a hard stop on Si3N4. End-points reached were also consistent with our blanket wafer polishing data. Regardless of pattern density and pitch, SiO2 removed was not proportional to polish time. This was a result of the low colloidal ceria nano-particle content in the slurry which was explained via a phenomenological model.

Mineralogical and Geochemical Evidence for Granite Metasomatism in Dikes in the North of the Berezovskoe Ore Field (Middle Urals)

Abstract —We present results of petrographic, geochemical, and mineralogical studies of apogranite metasomatites associated with sulfide–quartz gold ore veins. The studies show a predominance of muscovite and quartz–muscovite metasomatites. Formation of muscovite metasomatites was accompanied by the accumulation of W, Sc, Zr, Hf, Ga, REE, U, Th, Ta, and Nb and the genesis of new accessory minerals: monazite-(Ce), apatite, zircon, scheelite, W-containing rutile, uraninite, thorianite, cassiterite, etc. Compared with the primary granites, quartz–muscovite metasomatites are richer in Pb, Bi, As, Sb, Co, Ni, Ba, In, Cd, Mo, Te, Ag, and Au (elements of the gold ore assemblage). The high contents of these trace elements are due to abundant galena, fahlores, chalcopyrite, and pyrite among the accessory minerals. Metasomatism of granites was followed by the removal of SiO2, which was then spent for the formation of quartz veins. We have revealed that the distribution of metasomatites of different types within a dike body affects directly the distribution of sulfide–quartz veins and thus determines the ore content of the dike body fragments.

Silica depleted rice hull ash (SDRHA), an agricultural waste, as a high-performance hybrid lithium-ion capacitor

The partial removal of SiO2from rice hull ash (RHA, an agricultural waste) is a simple, low cost, eco-friendly method of producing high-performance electrode material for hybrid-lithium ion capacitors.

On the Mechanisms of Silica (SiO2) Recovery in Magnetite Ore Low-Magnetic-Drum Concentration

Magnetite (Fe3O4) ore is concentrated by low-magnetic-field drums to recover a magnetite concentrate that is low in silica (SiO2). The presence of SiO2 in the magnetite concentrate for steel production increases the steel processing costs, so a major challenge in magnetic concentration is to lower the SiO2 grade in the Fe concentrate. This work presents studies that were carried out on the removal of SiO2 from the magnetite concentration at the plant scale. Studies were performed with a three 36 × 96″ drum unit processing 46 ton/h of rougher magnetite concentrate. These studies showed that silica appears in the magnetite concentrate by three mechanisms, namely SiO2 entrainment in Fe3O4 chains, heterocoagulation between Fe3O4 and SiO2 particles, and mineral locking of SiO2 to Fe3O4. The SiO2 entrainment mechanism had the highest contribution (75%) to the SiO2 recovered in the Fe concentrate. Electrokinetic studies on Fe3O4 and SiO2 showed that heterocoagulation occurs because of the low negative zeta potential of the minerals at the pH of the plant slurry. This study also showed that a high percentage of ultrafine size SiO2 particles trapped in Fe3O4 agglomerates was not removed by the dilution water for the slurry fed to the drum. To lower the SiO2 recovery in the drum magnetic concentration process, work should be directed towards the removal of trapped SiO2 in Fe3O4 agglomerates.

Oxidation response of a SiCf/SiC CMC with a HfB2-based coating in an arc jet test

ABSTRACTThe behaviour of a SiC-fibre-reinforced composite with a graded matrix was investigated in an arc jet facility. The graded matrix was comprised of several layers of silicon carbide that transition to a mixed SiC-HfB2 top layer and was sealed with an HfB2-SiC coating. Samples were exposed to maximum specific total enthalpy hypersonic flow between 14 and 17 MJ kg−1 under stagnation pressures between 2700 and 3050 Pa for hold times of between 137 and 395 s. The resulting sample surface temperatures ranged between 1600 and 1950°C. Spectral emissivity at about 1 μm was calculated using a pyrometer capable of switching between one and two color modes and was shown to decrease with oxidation and removal of SiO2 from the surface. The impacts of the surface chemistry changes during oxidation and of active oxidation were investigated.

Minimization of SiO2/4H-SiC (0001) Interface State Density by Low-Temperature Post-Oxidation-Annealing in Wet Ambient after Nitrogen Passivation

4H-SiC has attractive properties for power devices of high voltage applications, however, the performance of MOSFETs is often severely limited by the poor SiO2/SiC interface quality. One of the common techniques to passivate the interface defects is the nitrogen introduction by NO annealing [1] while introduction of wide variety of impurity elements have also been studied [2]. Recently we have demonstrated the benefit of post-oxidation annealing in wet ambient at low-temperature as an alternative way to improve the SiO2/4H-SiC (0001) interface quality, which effectively works with only < 1nm additional growth of oxide at the interface [3]. In this study we investigated the validity of the combined passivation process of the NO annealing and the low-temperature H2O-annealing after the dry oxidation of 4H-SiC, to take the advantages of both the nitrogen passivation and the good quality interface formation by H2O-oxidation [4]. After HF cleaning of 4º off-axis 4H-SiC (0001) wafers covered with 5 μm-thick n-type epitaxial layers (ND ~ 1×1016 cm-3), ~30 nm-thick SiO2 layers were thermally-grown in dry oxygen at 1300ºC. As the post-oxidation annealing techniques, the annealing in NO:N2 =1:2 ambient at 1150ºC for 2hrs (NO-POA) and the additional annealing in H2O:O2=9:1 ambient at 800ºC (LT-H2O-POA) for various duration time, were sequentially conducted. Finally Au electrode was deposited to form a MOS capacitor. For the NO-POA process of SiC after thermal growth of SiO2, it has been clarified that nitrogen atoms are introduced mostly in the first few monolayers of SiC, and remains even after removal of SiO2 by chemical etching completely [5]. We evaluated the effects of our NO-POA and LT-H2O-POA on the amount of nitrogen introduced at the interface, from the relative change of core level XPS intensity ratio of N1s to the substrate component of Si2p, after the complete removal of SiO2 layer. It was found that the long-time LT-H2O-POA results in a significant reduction of nitrogen density at the interface after the growth of several MLs of SiO2, due to the consumption of nitrogen-introduced SiC surface layers for the oxidation by H2O. However, it would be noteworthy that most of the nitrogen still remains at the interface after a short-time LT-H2O-POA to cause the growth of limited amount of SiO2 around 1 ML. Next we evaluated the interface state density (Dit) of SiO2/SiC MOS capacitors fabricated with different duration time of LT-H2O-POA after NO-POA, by using conductance method. We found Dit was significantly reduced by short-time LT-H2O-POA, and minimized when only 1 ML of SiO2 was grown during the H2O-POA. The Dit value at the energy level at 0.2 eV below the conduction band edge of SiC was reduced below 5×1010 cm-2eV-1, which is less than half of the value observed just after the NO-POA (without H2O-POA). This would be the minimum Dit ever reported for 4H-SiC (0001) MOS capacitor at this energy level. On the other hand, LT-H2O-POA with excess duration time resulted in an increase of Dit. After the long-time LT-H2O-POA to cause ~1 nm SiO2 growth, the Dit value became even larger than the one just after the NO-POA. This deterioration would be caused by the partial lost of passivating nitrogen at the interface by the growth of new oxide layers, as indicated by the XPS analysis. One of the methods to evaluate the density of such slow traps in SiC MOS capacitors is the characterization of the hysteresis of CV curve observed for a voltage sweep just after the ejection of trapped charges by UV irradiation [6]. We observed that the slow trap density also significantly decreased by short-time LT-H2O-POA when the additional growth of SiO2 was limited to ~1 ML, but gradually increased by a long-time one, which is a quite similar behavior as Dit change by H2O-POA. These results show that the roles of nitrogen introduction and oxidation by H2O on SiO2/SiC interface defect annihilation are different from each other, and the interface with minimized Dit and less near-interface oxide traps is achievable by the sequential combination of those two POA processes, when the amount of additional oxidation by H2O is limited to ~ 1ML of SiO2.

Stabilization of Pt at the inner wall of hollow spherical SiO2 generated from Pt/hollow spherical SiC for sulfuric acid decomposition

Catalysts for sulfuric acid (SA) decomposition, one of three reactions in Sulfur-Iodine (SI) cycle to produce hydrogen, should be active and stable up to 800–900 °C. Here, a SiC hollow sphere supported Pt catalyst (1 wt% Pt/hSiC) is prepared, and its catalytic activity and stability are monitored in SA decomposition at 850 °C. The initial SA conversion with the Pt/hSiC catalyst is ca. 80% at 850 °C and a GHSV of 76,000 mL/gcat/h. For comparison, a core-shell SiO2 supported Pt catalyst (1 wt% Pt/SiO2@mSiO2) is prepared and tested for the reaction. The core-shell SiO2 support has the structure of a dense core and a mesoporous shell. The initial SA conversion with the Pt/SiO2@mSiO2 catalyst is ca. 54% at 850 °C and a GHSV of 76,000 mL/gcat/h. The Pt/hSiC catalyst is transformed to the SiO2 hollow sphere supported Pt catalyst (Pt/hSiO2) within 6 h reaction. CO chemisorption and TEM analysis exhibit that Pt particles on the pristine and spent catalysts, pretreated at 850 °C, are encapsulated by SiC or SiO2 on the surfaces of SiC and SiO2 supports. When the encapsulated Pt particles are in contact with sulfuric acid vapor, the Pt particles are exposed to the reactants by the removal of SiO2 encapsulating Pt during the reaction. Pt particles at the outer wall of the pristine hSiC are partly lost via PtOx evaporation, while Pt particles at the inner wall of the hollow sphere supports are stabilized without the severe Pt loss and Pt sintering. In contrast, the Pt particles on SiO2@mSiO2 with the dense SiO2 core are severely lost via PtOx evaporation during the reaction resulting in severe Pt sintering. The high stability of Pt particles at the inner wall of the hollow support is attributed to the Pt encapsulation and Pt anchoring of the small Pt particles at the inner walls and the diffusion barrier role of the shell for the migration of Pt at the inner wall to the outer wall.

Powder chemistry effects on the sintering of MgO‐doped specialty Al2O3

AbstractIn this work, we investigate the effects of powder chemistry on the sintering of MgO‐doped specialty alumina. The stages at which MgO influences densification of Al2O3 were identified by comparing dilatometry measurements and the sintering kinetics of MgO‐free and MgO‐doped specialty alumina powders. MgO is observed to reduce the grain boundary thickness during densification using TEM. We show that MgO increases the solubility of SiO2 in alumina grains near the boundaries using EDS. First‐principles DFT calculations demonstrate that the co‐dissolution of MgO and SiO2 in alumina is thermodynamically favored over the dissolution of MgO or SiO2 individually in alumina. This study experimentally demonstrates for the first time that removal of SiO2 from the grain boundaries is a key process by which MgO enhances the sintering of alumina.

Wet-chemical etching of atom probe tips for artefact free analyses of nanoscaled semiconductor structures

We introduce an innovative specimen preparation method employing the selectivity of a wet-chemical etching step to improve data quality and success rates in the atom probe analysis of contemporary semiconductor devices. Firstly, on the example of an SiGe fin embedded in SiO2 we demonstrate how the selective removal of SiO2 from the final APT specimen significantly improves accuracy and reliability of the reconstructed data. With the oxide removal, we eliminate the origin of shape artefacts, i.e. the formation of a non-hemispherical tip shape, that are typically observed in the reconstructed volume of complex systems. Secondly, using the same approach, we increase success rates to ∼90% for the damage-free, 3D site-specific localization of short (250 nm), vertical Si nanowires at the specimen apex. The impact of the abrupt emitter radius change that is introduced by this specimen preparation method is evaluated as being minor using field evaporation simulation and comparison of different reconstruction schemes. The Ge content within the SiGe fin as well as the 3D boron distribution in the Si NW as resolved by atom probe analysis are in good agreement with TEM/EDS and ToF-SIMS analysis, respectively.

Corundum formation by metasomatic reactions in Archean metapelite, SW Greenland: Exploration vectors for ruby deposits within high-grade greenstone belts

Corundum (ruby-sapphire) is known to have formed in situ within Archean metamorphic rocks at several localities in the North Atlantic Craton of Greenland. Here we present two case studies for such occurrences: (1) Maniitsoq region (Kangerdluarssuk), where kyanite paragneiss hosts ruby corundum, and (2) Nuuk region (Storø), where sillimanite gneiss hosts ruby corundum. At both occurrences, ultramafic rocks (amphibole-peridotite) are in direct contact with the ruby-bearing zones, which have been transformed to mica schist by metasomatic reactions. The bulk-rock geochemistry of the ruby-bearing rocks is consistent with significant depletion of SiO2 in combination with addition of Al2O3, MgO, K2O, Th and Sr relative to an assumed aluminous precursor metapelite. Phase equilibria modelling supports ruby genesis from the breakdown of sillimanite and kyanite at elevated temperatures due to the removal of SiO2. The juxtaposition of relatively silica- and aluminum-rich metasedimentary rocks with low silica ultramafic rocks established a chemical potential gradient that leached/mobilized SiO2 allowing corundum to stabilize in the former rocks. Furthermore, addition of Al2O3 via a metasomatic reaction is required, because Al/Ti is fractionated between the aluminous precursor metapelites and the resulting corundum-bearing mica schist. We propose that Al was mobilized either by complexation with hydroxide at alkaline conditions, or that Al was transported as K-Al-Si-O polymers at deep crustal levels. The three main exploration vectors for corundum within Archean greenstone belts are: (1) amphibolite- to granulite-facies metamorphic conditions, (2) the juxtaposition of ultramafic rocks and aluminous metapelite, and (3) mica-rich reactions zones at their interface.

Microwave Resistivity of Thermally Oxidized High Resistivity Silicon Wafers

We used a microwave dielectric resonator to study how the process of thermal oxidation of high resistivity silicon wafers reduces the wafer microwave resistivity. Measurements were performed before surface thermal oxidation, after the oxidation, and after wet oxide removal. We show that the process of oxide growth decreases the microwave resistivity of the wafer from approximately 20 kΩ cm to as low as 400 Ω cm (typically to 1–2 kΩ cm), depending on the dielectric layer thickness and the growth process conditions. After the wet removal of SiO2, the resistivity of the wafers increased, but it did not reach the initial value.

Improved thermal conductivity of sintered reaction-bonded silicon nitride using a BN/graphite powder bed

Sintered reaction-bonded silicon nitride (SRBSN) with improved thermal conductivity was achieved after the green compact of submicron Si powder containing 4.22wt% impurity oxygen and Y2O3-MgO additives was nitrided at 1400°C for 6h and then post-sintered at 1900°C for 12h using a BN/graphite powder bed. During nitridation, the BN/10wt%C powder bed altered the chemistry of secondary phase by promoting the removal of SiO2, which led to the formation of larger, purer and more elongated Si3N4 grains in RBSN sample. Moreover, it also enhanced the elimination of SiO2 and residual Y2Si3O3N4 secondary phase during post-sintering, and thus induced larger elongated grains, decreased lattice oxygen content and increased Si3N4-Si3N4 contiguity in final SRBSN product. These characteristics enabled SRBSN to obtain significant increase (∼40.7%) in thermal conductivity from 86 to 121 W∙m−1∙K−1 without obvious decrease in electrical resistivity after the use of BN/graphite instead of BN as powder bed.

Comprehensive understanding of chamber conditioning effects on plasma characteristics in an advanced capacitively coupled plasma etcher

An advanced capacitively coupled plasma etcher with two frequencies and additional direct current is characterized with complementary sensors. Due to the restrictive boundary conditions of the manufacturing environment, which the authors had to take into account, applicable plasma sensors are limited. Thus, the plasma parameters depending on the center, wall, sheath, and cathode regions are extracted separately based on the tool parameters, optical emission spectroscopy, and self-excited electron spectroscopy. One main target of this investigation is a cross verification of complementary sensor data and a deeper understanding. Due to the complex chamber setup, the authors use a chemically simple system of an Ar plasma with a blank Si wafer as the substrate. It is found that the removal of SiO2 and sputtering Si from the cathode and wafer changes the chamber condition and thus causes changes in the plasma characteristics. The established plasma process model comprises a change in secondary electron emission caused by changing the surface condition and a subsequent change in collisionless electron heating, in particular, in the case of applied low frequency power. Current electron heating models and conditioning models are used for cross verification of the plasma process model. It indicates that both chemical and electrical aspects to chamber conditioning should be considered in multiple frequency driven plasma etchers. The results presented in this paper are expected to contribute to the understanding of the interaction of the chamber conditioning effects and plasma parameters in advanced plasma etchers for sub-20 nm devices.

Order-of-magnitude differences in retention of low-energy Ar implanted in Si and SiO2

The retention of 1 and 5 keV Ar implanted at 45° in Si and 4.3 nm SiO2 on Si was studied at fluences between 3 × 1014 and 1.5 × 1016 cm−2. X-ray photoelectron spectroscopy (XPS) served to monitor the accumulation of Ar as well as the removal of SiO2. Bombardment induced changes in oxygen chemistry caused the O 1s peak position to move toward lower binding energies by as much as 2.2 eV. Plotted versus depth of erosion, the fluence dependent changes in oxygen content, and peak position were similar at 1 and 5 keV. The Ar content of Si increased with increasing exposure, saturating at fluences of ∼2 × 1015 cm−2 (1 keV) and ∼6 × 1015 cm−2 (5 keV). Much less Ar was retained in the SiO2/Si sample, notably at 1 keV, in which case the low-fluence Ar signal amounted to only 8% of the Si reference. The results imply that essentially no Ar was trapped in undamaged SiO2, i.e., the Ar atoms initially observed by XPS were located underneath the oxide. At the lowest fluence of 5 keV Ar, the retention ratio was much higher (43%) because the oxide was already highly damaged, with an associated loss of oxygen. The interpretation was assisted by TRIM(SRIM) calculations of damage production. Partial maloperation of the ion beam raster unit, identified only at a late stage of this work, enforced a study on the uniformity of bombardment. The desired information could be obtained by determining x,y line scan profiles of O 1s across partially eroded SiO2/Si samples. Fluence dependent Ar retention in Si was described using an extended version of the rapid relocation model which takes into account that insoluble implanted rare-gas atoms tend to migrate to the surface readily under ongoing bombardment. The range parameters required for the modeling were determined using TRIM(SRIM); sputtering yields were derived from the literature. The other three parameters determining the Ar signal, i.e., (1) the thickness w of the near-surface Si region devoid of Ar, (2) the relocation efficiency Ψrlc, and (3) the effective attenuation length L in XPS analysis were varied within reasonable limits until the calculated retention curves for 1 and 5 keV Ar in Si agreed with experimental data to better than 8%, using the same XPS sensitivity factor throughout. Results: w = 1.4 ± 0.1 nm, Ψrlc = 6.6 ± 0.5, and L = 2.7 ± 0.2 nm. Combining experimental and calculated data, it was found that the Ar trapping efficiency of the damaged oxide is intimately correlated with the loss of oxygen. The calculated stationary areal densities of all retained Ar are compared with results obtained by high-resolution medium-energy ion scattering spectrometry. Attractive areas of future research in rare gas retention and nanobubble formation are sketched briefly.

Evaluating femtosecond laser ablation of graphene on SiO2/Si substrate

We demonstrate a uniform single layer micropattern of graphene on 300 nm thick SiO2 on a Si substrate using a 1030 nm, 280 fs laser. The cutting process was conducted in air, the pattern defined through the motion of a high-precision translation stage. Approximately 1.6 μm wide graphene microchannels were cut with uniform widths and well defined edges. The ablation threshold of graphene was determined to be 66–120 mJ/cm2, at which the selective removal of graphene was achieved without damage to the SiO2/Si substrate. Scanning electron microscopy images revealed high quality cuts (standard deviation 40 nm) with little damage or re-deposition. Raman maps showed no discernible laser induced damage in the graphene within the ablation zone. Atomic force microscopy revealed an edge step height ranging from less than 2 to 10 nm, suggesting little removal of SiO2 and no damage to the silicon (the central path showed sub ablation threshold swelling). The effect of the ultrafast laser on the surface potential at the cut edge has been measured and it showed a distinguishable boundary.

Enhanced water flux through ultrafiltration polysulfone membrane via addition‐removal of silica nano‐particles: Synthesis and characterization

ABSTRACTIn the present paper, hierarchically structured ultrafiltration polysulfone (PSf) membrane was prepared to explore the effect of addition and subsequent removal of SiO2 nano‐particles on the membrane morphology, hydrophilicity, and separation properties. The PSf based membranes namely PSf, PSf/SiO2 and PSf/WSiO2 (i.e. SiO2 nano‐particles was acid‐washed and removed from PSf/SiO2), were synthesized and characterized by different characterization methods. Pure water flux through the membranes was determined using a filtration unit operating at a continuous dead‐end flow mode. The modification enhanced the morphology, hydrophobicity, porosity and transport properties of the modified membranes, although the molecular weight cut‐off (MWCO) of the membranes was not changed considerably. In comparison, PSf/WSiO2 membrane exhibited excellent pure water flux (about 4.5 times the flux of PSf, and 17 times the flux of PSf/SiO2), although antifouling property of PSf/SiO2 in separation of bovine serum albumin (BSA) was better than that of PSf and PSf/WSiO2 membranes. The results suggested that the addition/removal of sacrificial solid fillers within/from a membrane matrix may provide a promising strategy to enhance PSf membrane transport property. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43556.

Fabrication of sandwich nanostructure graphene/polyaniline hollow spheres composite and its applications as electrode materials for supercapacitor

A novel three-dimensional (3D) reduced graphene oxide/polyaniline hollow spheres (RGO/PANI-HS) composite, in which PANI-HS were inserted between RGO layers, has been fabricated as electrode materials for supercapacitor applications. This 3D nanostructure was constructed by electrostatic interaction between SiO2@polyaniline core–shell spheres and graphene oxide, reduction of graphene oxide and removal of SiO2 in sequence. Due to its tailored nanostructure and over-all conductive network, RGO/PANI-HS electrode exhibits a high specific capacitance of 529Fg−1 at 0.5Ag−1 and excellent rate capability (remains 72% even at 10Ag−1), which is much higher than that of PANI-HS electrode (424Fg−1 at 0.5Ag−1, 62% retention at 10Ag−1) in 1M H2SO4 aqueous solution. More importantly, RGO/PANI-HS composite can maintain 85% of its initial specific capacitance well above 51% for PANI-HS after 1000 cycles, suggesting a superior electrochemical cyclic stability.