Organic Surface Contamination Research Articles

Surface microstructure regulation of a novel N-CQDs /C3N4/Bi2WO6 self-cleaning synergistic photocatalytic degradation of NO coating

As well known, the apparent structure and chemical composition of self-cleaning photocatalytic coatings are crucial for their application. In this study, C3N4 with a large specific surface area was introduced into N-CQDs/Bi2WO6 to construct a highly catalytic active catalyst (CBW-0.5), which continuously degraded 57.7 % of NO. A robust self-cleaning photocatalytic coating (CCBW-B) was prepared by firmly bonding CBW-0.5 to the substrate through a layered spraying process. CBW-0.5 endowed CCBW-B with high catalytic activity, maintaining a degradation rate of 64.9 % for NO, and most of the surface organic dye contamination was degraded after 36 h. Due to the appropriate arrangement of low surface energy substances and micro/nano particles on the surface, CCBW-B with a graded cross network on the surface has contact angles (CA) of 156°/145° for water/olive oil, respectively. The influence of each component of CCBW-B on its photocatalytic and liquid repellent ability was studied, and the patterns for the differences in coating performance due to the changes in surface roughness structure caused by different layer distributions was discussed. In addition, the mechanism for the excellent performance of CCBW-B was explored using SEM, specific surface area, and the theory of the generation and distribution of air pockets. Finally, the durability and self-cleaning ability of CCBW-B were tested, and the synergistic mechanism of self-cleaning and photocatalysis was also provided.

Effects of Organic Surface Contamination on the Mass Accommodation Coefficient of Water: A Molecular Dynamics Study.

The mass accommodation coefficient (MAC), a parameter that quantifies the possibility of a phase change to occur at a liquid-vapor interface, can strongly affect the evaporation and condensation rates at a liquid surface. Due to the various challenges in experimental determination of the MAC, molecular dynamics (MD) simulations have been widely used to study the MAC on liquid surfaces with no impurities or contaminations. However, experimental studies show that airborne hydrocarbons from various sources can adsorb on liquid surfaces and alter the liquid surface properties. In this work, therefore, we study the effects of organic surface contamination, which is immiscible with water, on the MAC of water by equilibrium and nonequilibrium MD simulations. The equilibrium MD simulation results show that the MAC decreases almost linearly with increasing surface coverage of the organic contaminants. With the MAC determined from EMD simulations, the nonequilibrium MD simulation results show that the Schrage equation, which has been proven to be accurate in predicting the evaporation/condensation rates on clean liquid surfaces, is also accurate in predicting the condensation rate at contaminated water surfaces. The key assumption about the molecular velocity distribution in the Schrage analysis is still valid for condensing vapor molecules near contaminated water surfaces. We also find that under nonequilibrium conditions the adsorption of the water vapor molecules on the organic surface results in an adsorption vapor flux near the contaminated water surface. When the water surface is almost fully covered by the model organic contaminants, the adsorption flux dominates over the water condensation flux and leads to a false prediction of the MAC from the Schrage equation.

Control the Mechanochemical Energy of Ball Milling To Remove Surface Organic Contamination without Damaging the Integrity of the Glass

Control the Mechanochemical Energy of Ball Milling To Remove Surface Organic Contamination without Damaging the Integrity of the Glass

Development of an environmentally safe non-mechanized technology of the polluted forest areas reclamation

The inaccessibility of forest areas dictates the need to optimize the ways of their reclamation in case of pollution. The northern regions are highly vulnerable. To determine the degree of pollution, a variant of mapping the site with the determination of the degree of pollution was considered. Water sampling in the contaminated zone indicates intensive processes of decomposition organically exceeding the MPC. The penetration depth of contaminants is up to 95 cm. With prolonged exposure to organo-fat contaminants covering surfaces, death of vegetation and forest stands is noted. With distance from the source of pollution, the projective cover of some types of vegetation increases. 2 variants of reclamation are considered: mechanized and two-stage treatment directly at the site of pollution, carried out using additional aeration. Accelerated decomposition of contaminants up to 9 days at a dose of 15 g/l was confirmed. The results of the treatment is an increase in the pH of the medium from acidic to neutral. The height of the layer of organic surface contamination is reduced by 88% in 9 days when the mixture is aerated. The second stage is also confirmed by a decrease in the nitrogen concentration by 1.5–2 times, while the transparency of the solution increases by 2–2.5 times. The peculiarity of the revealed method of reclamation is a two-stage biodegradation, implemented directly in the natural environment without the use of machines and mechanisms. According to the results of a technical and economic comparison of the costs of the two reclamation options, the use of the new technology turned out to be 9 times cheaper, and the time costs are reduced by 2 times and can be 14 days, which is acceptable for the northern territories.

Visible-Light-Driven Photocatalysts for Self-Cleaning Transparent Surfaces.

Highly transparent photocatalytic self-cleaning surfaces capable of harvesting near-visible (365-430 nm) photons were synthesized and characterized. This helps to address a current research gap in self-cleaning surfaces, in which photocatalytic coatings that exhibit activity at wavelengths longer than ultraviolet (UV) generally have poor optical transparency, because of broadband scattering and the attenuation of visible light. In this work, the wavelength-dependent photocatalytic activity of Pt-modified TiO2 (Pt-TiO2) particles was characterized, which exhibited activity for wavelengths up to 430 nm. Pt-TiO2 nanoparticles were embedded in a mesoporous SiO2 sol-gel matrix, forming a superhydrophilic surface that allowed for water adsorption and formation of reactive oxide species upon illumination, resulting in the removal of organic surface contaminants. These self-cleaning surfaces only interact strongly with near-visible light (∼365-430 nm), as characterized by photocatalytic self-cleaning tests. Broadband visible transparency was preserved by generating a morphology composed of small clusters of Pt-TiO2 surrounded by a matrix of SiO2, which limited diffuse visible light scattering and attenuation. The wavelength-dependent self-cleaning rate by the films was quantified using stearic acid degradation under both monochromatic and AM1.5G spectral illumination. By varying the film morphology, the average transmittance relative to bare glass can be tuned from ∼93%-99%, and the self-cleaning rate can be adjusted by more than an order of magnitude. Overall, the ability to utilize photocatalysts with tunable visible light activity, while maintaining broadband transparency, can enable the use of photocatalytic self-cleaning surfaces for applications where UV illumination is limited, such as touchscreen displays.

Robust multifunctional superhydrophobic, photocatalytic and conductive fabrics with electro-/photo-thermal self-healing ability

The fabrication of superhydrophobic and conductive fabrics that can conveniently and repeatedly restore the lost superhydrophobicity, caused by either the surface accumulation of trace organic contaminants or the chemical damage to surface components, remains challenging. Herein, we report a multifunctional superhydrophobic and conductive cotton fabric that integrates not only the photocatalytic activity for cleaning organic contaminants, but also the self-healing ability enabled by either electro-thermal or photo-thermal heating besides convection oven heating. The fabric was fabricated through the polydopamine (PDA)-assisted deposition of photocatalyst Ag/CdS and the subsequent thiol-Ag self-assembly. Either UV or visible light irradiation is able to decompose the surface organic contaminants, and the photocatalysis-induced slight damage on super water-repellency is curable by heating. The Ag layer endows the fabric with antibacterial property and conductivity along with the electro-/photo-thermal conversion ability, which offers relatively convenient ways of heating for curing the surface chemical damages caused by O2 plasma etching or accelerated washing. Of particular importance is that the fabric still shows super water-repellency even after 18 cycles of accelerated washing, which equals to 90 normal home laundering cycles. The combination of these multiple functions makes this fabric very promising for a wide range of wearable applications.

Generation of a Highly Efficient Electrode for Ethanol Oxidation by Simply Electrodepositing Palladium on the Oxygen Plasma-Treated Carbon Fiber Paper

In this study, a highly efficient carbon-supported Pd catalyst for the direct ethanol fuel cell was developed by electrodepositing nanostructured Pd on oxygen plasma-treated carbon fiber paper (Pd/pCFP). The oxygen plasma treatment has been shown to effectively remove the surface organic contaminants and add oxygen species onto the CFP to facilitate the deposition of nano-structured Pd on the surface of carbon fibers. Under the optimized and controllable electrodeposition method, nanostructured Pd of ~10 nm can be easily and evenly deposited onto the CFP. The prepared Pd/pCFP electrode exhibited an extraordinarily high electrocatalytic activity towards ethanol oxidation, with a current density of 222.8 mA mg−1 Pd. Interestingly, the electrode also exhibited a high tolerance to poisoning species and long-term stability, with a high ratio of the forward anodic peak current density to the backward anodic peak current density. These results suggest that the Pd/pCFP catalyst may be a promising anodic material for the development of highly efficient direct alcohol fuel cells.

РЕСТАВРАЦІЯ ТА ХІМІКО-ТЕХНОЛОГІЧНІ ДОСЛІДЖЕННЯ КАМ’ЯНОЇ СКУЛЬПТУРИ СВ. ЯНА НЕПОМУЦЬКОГО З СЕЛА ЧАБАРІВКА ВАСИЛЬКІВСЬКОГО Р-НУ ТЕРНОПІЛЬСЬКОЇ ОБЛ.

The sculptural composition originates from the village of Chabarivka, Vasylkiv district, Ternopil region (since 2015). On the map of 1779-1783 by Friedrich von Mieg, the sculpture of St. John of Nepomuk is marked with a red cross, located in the eastern part of the village stretched along the road, opposite the manor. The road from Kopychyntsi to Husiatyn passed to the north of the settlement. On the map of the late nineteenth century the figure of St. John of Nepomuk is recorded on the south side of the street, in the eastern part of Chabarivka. Instead, the manor no longer exists, and the existing church does not yet exist. It is probable that in the first half of the 19th century the village community changed the location of the roadside sculptural composition. Since there is a carved coat of arms of Pilava on the stone pedestal of the figure, it is logical to say that the founder of the composition was a representative of the Potocki magnate family. Since the owner of Husiatyn and its environs during 1729-1732 was Stanislav Vladyslav Potocki, we can assume that it was at this time that the sculptural composition of St. John of Nepomuk was made. As a result of thermal studies, it was found that the samples taken from the surface of the figure and the pedestal contain organic surface contaminants. A sample taken from the surface of the pedestal revealed a significant amount of clay contaminants introduced to the surface of the stone by dust deposits. The results of thermal analysis are confirmed by X-ray fluorescence analysis. In the samples taken from the surface layer of the pedestal and the figure, the presence of elements Si, Al, Mg, K, Fe, which are part of the structure of layered silicates, was detected. The relative content of elements present in the structure of clay minerals is determined by the ratio of the areas of the bands of electronic transitions, which are manifested on the spectrum of samples at the corresponding characteristic energies. Based on these data, it can be argued that the surface layer of the pedestal contains more clay contaminants. Based on chemical and technological research, it can be argued that the surface layer of the pedestal contains more clay contaminants than the sculpture. Taking into account the results of historical, art and chemical-technological research, a program of restoration of the monument has been developed: Carrying out a visual and field inspection of the work; Execution of photofixation before completion of restoration works; Study of analogues of the image of St. John of Nepomuk; Execution of mechanical clearing; Extraction of salts from the structure of the stone by applying a compress of cellulose and distilled water; Carrying out of structural strengthening of a stone by the KSE300 Remmers preparation; Production of the lost lower part of a plinth from limestone, its installation on stainless steel cores and epoxy glue; Gluing of the reflected and saved parts to a sculpture on proper places. Gluing the saved left hand with epoxy glue; Making a plasticine model of the saint's head according to the proportions and collected analogues. Execution of a lump plaster form and formation of a head from an artificial stone; Mounting the head using a stainless steel anchor and polyester glue; Gradual addition of lost elements on the sculpture and pedestal with mineral restoration solution with the addition of pigments; Modeling of the neck and collar of St. John of Nepomuk with mineral solution; Execution of structural strengthening of a stone by an alcoholic solution of nanovap; Execution of structural strengthening of a stone by the KSE300 Remmers preparation; Coating the monument with a long-acting biocidal solution from Remmers; Double plastering of the monument with a solution of historical translucent azure and water water repellent by Remmers with the addition of pigments for stone tinting; Execution of final photofixation of a monument after the carried-out restoration actions. Chemical-technological studies confirm what was revealed by visual examination and microscope. During the restoration, a full range of measures was taken to stabilize the material structure of the sculptural composition. Remains of blue and red paints were found during the work. According to the results of X-ray fluorescence analysis, it was found that the staining was done in the XIX century. Instead, the primary staining was not detected. The performed chemical-technological researches have formulated a restoration map, will allow in the following works to define more precisely mineral composition of a stone and the author's color decision of a work of art. After the completion of the restoration works, the sculptural composition acquired artistic integrity and received a sacred meaning. Similar works of art located on the territory of Ukraine need to be preserved and restored, as they form a valuable cultural landscape of historical settlements.

Impact of an Amino-Alcohol Organic Molecule on SiO2 and Si Bonding Energy

Direct bonding energy relates to the well-known “strength” or “toughness” of direct bonding interfaces. It is the energy needed to separate two bonded surfaces. Its evolution with the post bonding annealing temperature is an important parameter closely linked to the fundamental direct bonding mechanism [1]. There are different ways of modifying the bonding energy and especially to increase it at low annealing temperatures. Plasma activation, chemical mechanical polishing (CMP) are for instance well known surface preparations that enhance the bonding energy at temperatures below 500°C [2].Usually, for hydrophilic direct bonding, surfaces have to meet various specifications. A small high frequency roughness, a low nanotopology amplitude, a small wafer deformation, no particle contamination and a good hydrophilicity are mandatory to obtain spontaneous bonding at room temperature without any pressure [3, 4]. Moreover, the surface cleanliness in terms of hydrocarbon contamination is also very important to avoid bonding interface defectivity during the post bonding annealing. However, in this study, an intentional organic surface contamination will be shown to have a positive impact on direct bonding energy. An amino-alcohol molecule (N,N-diéthyléthanolamine also called DEAE) is sent vapor deposited on the surface of 200 mm silicon oxide or silicon. In an airtight reactor, 100 ml of water with different DEAE concentrations yield different DEAE saturated atmospheres in equilibrium with the liquid phase. As fast as possible, two wafers are loaded in the reactor and left there for different exposure times. Then, wafers covered with 145 nm of thermal silicon oxide surfaces are bonded just out of the reactor and annealed at different temperatures, for direct bonding energy measurements in an anhydrous atmosphere. As shown in figure 1a, different exposure times from 15 s up to 5 min to pure DEAE saturating vapor give almost the same bonding energy values. To have surfaces in good equilibrium with the reactor atmosphere, 5 min. of exposure time is selected to test various liquid DEAE concentrations. As shown on figure 1b, with the smallest tested concentration (2%) in the liquid phase, the direct bonding energy increases by more than 70% at 300°C compared to a reference bonding. Moreover, no bonding defect could be detected by acoustic microscopy. A positive impact of DEAE on silicon to silicon oxide bonding will also be shown.As silicon oxide direct bonding involves water oxide hydrolysis [1], a mechanism could be proposed to explain the beneficial impact of DEAE. Indeed, it is known that a high pH solution can enhance the silicon oxide hydrolysis [5]. As this molecule is very hydrophilic due to its alcoholic group, this molecule can be chemically adsorbed on a hydrophilic surface and can then be trapped at the bonding interface. After bonding, this molecule can increase the trapped water pH, enhancing the silica hydrolysis at the direct bonding interface and yielding higher bonding energies at low temperatures. As organic contamination is known to be detrimental for direct bonding, high concentration on the surface might be an issue. This should be the reason why a low concentration is more interesting. REFERENCES [1] F. Fournel, C. Martin-Cocher, D. Radisson, V. Larrey, E. Beche, C. Morales, P.A. Delean, F. Rieutord, and H. Moriceau, ECS J. Solid State Sci. Technol. 4, P124 (2015).[2] F. Fournel, H. Moriceau, C. Ventosa, L. Libralesso, Y.L. Tiec, T. Signamarcheix, and F. Rieutord, ECS Trans. 16, 475 (2008).[3] V. Larrey, G. Mauguen, F. Fournel, D. Radisson, F. Rieutord, C. Morales, C. Bridoux, and H. Moriceau, ECS Trans. 75, 145 (2016).[4] K.T. Turner, Wafer Bonding: Mechanics-Based Models and Experiments, Massachusetts Institute of Technology, 2004.[5] B.C. Bunker, Journal of Non-Crystalline Solids 179, 300 (1994). Figure 1

Simple and effective cleaning method for RuO2 nanosheet films for flexible transparent conducting electrodes

A critical and practical issue in employing low dimensional nanomaterials as transparent conducting electrodes (TCEs) is the simple and effectual cleaning of the nanomaterials; the presence of contaminants increases the contact resistance at the interface region in practical applications. In this study, various cleaning methods are examined to remove surface contaminants on RuO2 nanosheets (NSs), which are the promising materials for TCEs. The Ar gas cluster ion beam (GCIB) sputtering technique can effectively remove organic surface contaminants, although it has critical drawbacks in the mass production. The simple deionized water treatment can provide satisfactory cleaning performance, which is comparable with that of the Ar GCIB sputtering method. Other methods such as solution-based treatments that use ethanol and chloroform and the heating method do not provide a comparable cleaning performance. The conductive atomic force microscopy demonstrates highly increased conductivity of water-cleaned RuO2 NS films at the nanoscale. This study proposes a practical method for the cleaning of RuO2-based nanomaterials for their application as TCEs and emphasizes their significance of the cleaning process to achieve a higher performance for TCEs based on low dimensional nanomaterials.

Durable Superamphiphobic and Photocatalytic Fabrics: Tackling the Loss of Super-Non-Wettability Due to Surface Organic Contamination.

Superamphiphobic surfaces are self-cleaning against various liquids and dirt particles but they are not resistant to trace organic contaminants, the accumulation of which on surface would cause a decline in the liquid repellency. In this work, superamphiphobic and photocatalytic fabrics are developed that allow the elimination of various organic substances from surface by using photocatalytic decomposition. The fabrics have a contact angle of 163, 156, and 158° to water, hexadecane, and sunflower oil, respectively. They are also demonstrated to be able to decompose methylene blue, oleic acid and sodium dodecyl sulfate (SDS) under UV light. The removal of human body grease or laundry detergent from surface to recover the super-non-wettability was demonstrated through the natural sunlight exposure. The slight damage on superamphiphobicity caused by the photocatalytic activity can be cured with simple heat treatment. In addition, the superamphiphobic fabrics show excellent durability against abrasion and repeated washing. The photocatalytic and heat-curing strategy reported here may bring superamphiphobic fabrics one step closer to practical application in various fields.

Graphene transfer by surface activated bonding with poly(methyl glutarimide)

In this study, we investigated the use of surface activated bonding at room temperature for layer transfer to improve the quality of the transferred material. Surface organic contaminants and the crystal quality of graphene transferred by surface activated bonding were compared with those in the case of thermal compression bonding at 250 °C. The physical and chemical surface characteristics of the transferred graphene indicate that the amount of organic contaminants derived from the poly(methyl glutarimide) sacrificial layer was significantly decreased by surface activated bonding at room temperature in comparison with the case of by thermal compression bonding at 250 °C. Furthermore, Raman spectra revealed a lower level of disorder in the graphene transferred by the surface activated bonding. Thus, surface activated bonding can provide a platform for a layer transfer process suitable for the integration of two-dimensional materials.

Facile fabrication of electrolyte-gated single-crystalline cuprous oxide nanowire field-effect transistors

Oxide semiconductors are considered to be one of the forefront candidates for the new generation, high-performance electronics. However, one of the major limitations for oxide electronics is the scarcity of an equally good hole-conducting semiconductor, which can provide identical performance for the p-type metal oxide semiconductor field-effect transistors as compared to their electron conducting counterparts. In this quest, here we present a bulk synthesis method for single crystalline cuprous oxide (Cu2O) nanowires, their chemical and morphological characterization and suitability as active channel material in electrolyte-gated, low-power, field-effect transistors (FETs) for portable and flexible logic circuits. The bulk synthesis method used in the present study includes two steps: namely hydrothermal synthesis of the nanowires and the removal of the surface organic contaminants. The surface treated nanowires are then dispersed on a receiver substrate where the passive electrodes are structured, followed by printing of a composite solid polymer electrolyte (CSPE), chosen as the gate insulator. The characteristic electrical properties of individual nanowire FETs are found to be quite interesting including accumulation-mode operation and field-effect mobility of 0.15 cm2 V−1 s−1.

Communication—In-Line Detection of Silicon Surface Quality Variation Using Surface Photovoltage and Room Temperature Photoluminescence Measurements

Occasionally, in volume device manufacturing, a large number of particles may be generated on cleaned Si wafers. Surface (ionic, organic and/or metallic) contamination is generally suspected. However, conventional chemical analysis techniques for contamination are generally not able to distinguish between Si wafers with good and poor particle performance. No suspicious chemicals and elements were detected from any wafers regardless of characterization techniques. Surface photovoltage (SPV) measurement barely showed the differences between wafers with good and poor particle performance. Multiwavelength room temperature photoluminescence (RTPL) showed significant differences in intensity between them, indicating the presence of surface quality variations.

Removal of Organic Contamination from Graphene with a Controllable Mass-Selected Argon Gas Cluster Ion Beam

Since the discovery of graphene, organic surface contamination has posed difficulties both for accurate characterization of the material’s intrinsic properties and for development of graphene devices. In this study, we investigate the use of a mass-selected argon gas cluster ion beam for removing organic contaminants, such as residual poly(methyl methacrylate) (PMMA), from single-layer graphene. The influence of cluster ion size, energy, and ion dose has been investigated to identify the important factors for minimizing damage to the graphene layer during the cleaning process. Raman spectroscopy was used to analyze the variation in the D-peak and G-peak intensity ratio, an indicator of damage to the graphene lattice, as a function of ion beam dose and kinetic energy per atom (E/n) in the cluster ions. Using a mass-selected 5 keV Ar5000 beam with a dose of 5.0 ions/nm2, we were able to demonstrate removal of polymer residue and other carbonaceous material from single-layer chemical vapor deposition (CVD)-g...

Intrinsic wettability of graphitic carbon

The wettability of graphitic carbon can impact the behavior of many carbonaceous materials in a variety of systems involving water, for example, the carbon aerosols–cloud interaction that affects the climate and the penetration of micropores by aqueous solution in activated carbons. Previous studies on this topic have been limited to the basal surface of graphite. Apparent water-contact angle (WCA) values reported in the literature for the basal surface of graphite or graphene sheet vary from 35° to 126°, due to factors such as surface contamination and roughness. The intrinsic wettability of graphitic carbon remains uncertain. Here we report the first experimental attempt of quantifying the intrinsic wettability of the edge surface of graphite. We show that the basal surface is intrinsically hydrophilic with a WCA of about 61°; the edge surface is more hydrophilic than the basal surface and has an intrinsic WCA likely less than 40°. We also show that the apparent WCA is highly sensitive to sample preparation procedures. Annealing, a commonly used method for removing surface organic contaminants, could result in an underestimated WCA due to oxidation by the trace O2 in the inert gases.

Atmospheric Pressure Plasma Jet in Ar and O2/Ar Mixtures: Properties and High Performance for Surface Cleaning

An atmospheric pressure plasma jet generated in Ar and O2/Ar mixtures has been investigated by specially designed equipment with double power electrodes at 20∼32 kHz, and their effects on the cleaning of surfaces have been studied. Properties of the jet discharge are studied by electrical diagnostics, including the waveform of discharge voltage, discharge current and the Q-V Lissajous figures. The optical emission spectroscopy is used to measure the plasma parameters, such as the excitation temperature and the gas temperature. It is found that the consumed power and the excitation temperature increase with increase of the discharge frequency. On the other hand, at the same discharge frequency, these parameters in O2/Ar mixture plasma are found to be much larger. The effect on surface cleaning is studied from the changes in the contact angle. For Ar plasma jet, the contact angle decreases with increase of the discharge frequency. For O2/Ar mixture plasma jet, the contact angle decreases with increase of discharge frequency up to 26 kHz, however, further increase of discharge frequency does not show further decrease in the contact angle. At the same discharge frequency, the contact angle after O2/Ar mixture plasma cleaning is found to be much lower compared to the case of pure Ar. From the results of quadrupole mass-spectrum analysis, we can identify more fragment molecules of CO and H2O in the emitted gases after O2/Ar plasma jet treatment compared with Ar plasma jet treatment, which are produced by the decomposition of surface organic contaminants during the cleaning process.

Thermal annealing effects on multi-walled carbon nanotube yarns probed by Raman spectroscopy

The realized mechanical properties of CNT macrostructures such as webs and yarns remain significantly lower than those of the individual CNTs. Structural changes induced by thermal annealing under inert atmosphere were assessed using Raman spectroscopy. Annealing above 1000°C resulted in a marked decrease in the D/G ratio which can be attributed to an increase in the crystallite size or the distance between defects. The band component parameters obtained by spectral deconvolution reveal that the D band peak maximum shifts to slightly higher energy with increased annealing temperature. In contrast, the energy of the G band did not change. The full widths at half height (FWHH) of the D and G bands are seen to decrease with increasing annealing temperature. The tensile properties of the yarns have been investigated and it was found that the yarn tenacity did not improve with these structural changes. The effect of impurities in the annealing system such as oxygen, adsorbed water or organic surface contamination was also investigated.

Synthesis and characterization of single- and few-layer mica nanosheets by the microwave-assisted solvothermal approach

We have successfully fabricated single- and few-layer mica nanosheets, by means of using a solvothermal method in conjunction with a microwave irradiated expansion process. In the solvothermal process, dissolved potassium ions were intercalated onto the interlayer space of the mica. Following this, microwave irradiation facilitates the exfoliation of individual nanosheets. The synthesized products were characterized by field emission scanning electron microscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray diffraction, x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy measurements. AFM and TEM studies claimed the existence of single-layer mica. High-resolution TEM (HR-TEM) investigations revealed that the exfoliated product corresponded to a crystalline mica structure, being comprised of Si, Al, O, and K elements. XPS spectra exhibited the major constituent peaks, including O 1s, Si 2p, Al 2p, and K 2p. In addition, C atomic concentration has been slightly increased by the contamination during exfoliation, presumably due to the increase of the exposed mica surface. The C 1s XPS spectra revealed that the C–C bonding in organic surface contaminants was broken, whereas the Si–C bonding was enhanced, by the exfoliation process. The O 1s XPS spectra revealed that the Si–O bonding in mica was broken, generating the O–Si–C bonding. This study paves the way towards the fabrication of single- or few-layer inorganic nanosheets of desired materials, via a convenient and efficient route.

Comparative measurements on atomic layer deposited Al2O3 thin films using ex situ table top and mapping ellipsometry, as well as X-ray and VUV reflectometry

In this study we compare the thicknesses and optical properties of atomic layer deposited (ALD) Al2O3 films measured using table top and mapping ellipsometry as well as X-ray and optical reflectometry. The thickness of the films is varied in the range of 1–50nm. ALD samples are used as references with well-controlled composition and thickness, as well as with a good lateral homogeneity. The homogeneity is checked using mapping ellipsometry. Optical models of increasing complexity were developed to take into account both the top (surface roughness on the nanometer scale) and bottom interfaces (buried silicon oxide and interface roughness). The best ellipsometric model was the one using a single interface roughness layer. Since the techniques applied in this work do not measure in vacuum, organic surface contamination even in the sub-nanometer thickness range may cause an offset in the measured layer thicknesses that result in significant systematic errors. The amount of surface contamination is estimated by in situ reflectometry measurement during removal by UV radiation. Taking into account the surface contamination the total thicknesses determined by the different methods were consistent. The linearity of the total thickness with the number of atomic layer deposition cycles was good, with an offset of 1.5nm, which is in good agreement with the sum of thicknesses of the interface layer, surface nanoroughness, and contamination layer.