Layer Coverage Research Articles

Fabrication of electrodes with ultralow platinum loading by RF plasma processing of self-assembled arrays of Au@Pt nanoparticles

Conductive, carbon-free, electrocatalytically active, nanostructured electrodes with ultra-low platinum loading were fabricated using self-assembly of octadecanethiol-coated Au@Pt nanoparticles followed by RF plasma treatment. Bilayer arrays of Au@Pt nanoparticles with platinum loadings of 0.50, 1.04, 1.44, and 1.75 μg cm−2 (corresponding to 0.5, 1, 1.5 and 2 atomic layer coverage of platinum on nominally 5 nm gold core) were subjected to RF argon plasma treatment for various durations and their electrical conductivity, morphological evolution, and electrocatalytic activity characterized. Samples with monolayer and above platinum coverages exhibit maximum electrochemically active surface areas values of ∼100 m2/gpt and specific activities that are ∼4× to 6× of a reference platinum nanoparticle bilayer array. The underlying gold core influences the structural evolution of the samples upon RF plasma treatment and leads to the formation of highly active Pt(110) facets on the surface at an optimal plasma treatment duration, which also corresponds to the onset of a sharp decline in lateral sheet resistance. The sample having a two atom thick platinum coating has the highest total mass activity of 48 ± 3 m2/g(pt+au), corresponding to 44% Pt atom utilization, while also exhibiting enhanced CO tolerance as well as high methanol oxidation reaction and oxygen reduction reaction activity.

Ultrathin and Uniform Carbon Coating on Active Materials Using Liquid CO2 As a Coating Solvent

Some of cathode and anode active materials (e.g., LiFePO4, Li4Ti5O12, Li2FeSiO4, TiO2, MoO2) exhibit inherently low electronic conductivities and low ionic conductivities; thus, these materials typically suffer from poor electrochemical performance. The reduction of particle size to a nanoscale dimension to enhance lithium ion diffusivity and carbon coating to increase electronic conductivity are the most widely used strategies to improve the performance of the potential active materials. Incorporation of too much carbon content, thick carbon layer coating, and non-uniform carbon coating on individual particles can also deteriorate energy density and battery performance. The complete, uniform, and thin carbon layer coverage ensures that the particles receive electrons from all directions and the electrons penetrate easily through the carbon layer, resulting in low polarization and high-rate performance. Herein, the use of liquid carbon dioxide (l-CO2) for uniform and ultrathin carbon layer coverage on highly porous LiFePO4 and MoO2 particles is discussed. The extremely low surface tension and the low viscosity associated with l-CO2 make it an excellent coating solvent for uniform and ultrathin carbon layer formation on the highly porous active materials. In addition, the carbon content in the range of 1-10 wt% can be easily controlled by adjusting process parameters such as solution concentration or evaporation velocity. The hierarchically porous MoO2 microspheres are synthesized in supercritical methanol without using any surfactants or structure-directing chemicals. The highly porous LiFePO4 particles are synthesized using a co-precipitation method. The MoO2 and LiFePO4 particles exhibits hierarchically porous nano/micro structure, in which primary particles with 30-65 mn size are loosely aggregated and form secondary spheres with 0.5-10 mm size. Owing to the low viscosity and low surface tension of l-CO2, the coating solution is penetrated into the pores of the particles and uniform and ultrathin carbon layer is covered on the primary particles. The thickness of carbon layers were in range of 0.8-2.0 nm by adjusting the carbon precursor concentration in l-CO2. The TEM analysis on the cross-sectional area of the particles shows that the uniform incorporation of the carbon layer on the whole surface of the micron-sized secondary particles. The carbon-coated LiFePO4 exhibits ~108.6 mAh g-1 at a high charge-discharge rate of 30 C. In addition, after 1000 cycles of 10 C, ~ 85% of an initial capacity is maintained. The carbon-coated MoO2 exhibits enhanced high-rate performance and cell stability. Figure 1

One-step dip-coating of uniform γ-Al2O3 layers on cordierite honeycombs and its environmental applications

Cordierite honeycomb with high loading and uniform coating of γ-Al2O3 was prepared by a facile one-step dip coating strategy. The γ-Al2O3 obtained loading, which was as high as 30%, could be calculated according to the different weight of bare and washcoated cordierite honeycomb. SEM micrographs showed that coarser surface and round channels were formed, demonstrating complete coverage of a γ-Al2O3 layer on cordierite. The coating thickness was 30µm, corresponding very well to the theoretical value, indicating a homogeneous coating of γ-Al2O3. Besides, no crack was observed on the surface or the corner of the channel wall. The washcoat exhibited excellent adherence with no significant weight loss after 3h ultrasonic treatment, attributing to the “nail-like” strong interaction between the support and the washcoat. The derived PdCl2-CuCl2 monolith catalyst showed excellent activity and stability for CO oxidation at room temperature in microreactor. The catalyst was also effective in pilot-scale test using the diesel exhaust as feed gas, presenting a great application prospect.

Study of the formation of a protective layer in a defect from lithium-leaching organic coatings

Abstract Lithium salts were investigated as leachable corrosion inhibitor and potential replacement for hexavalent chromium in organic coatings. Coatings loaded with lithium carbonate or lithium oxalate demonstrated active corrosion inhibition by the formation of a protective layer in a damaged area. The present paper provides more insight into the formation and composition of the protective layer in a damaged area generated from the lithium salt loaded coatings when exposed to neutral salt spray testing conditions (ASTM B-117). Lithium-ion leaching from the coating matrix was demonstrated with atomic absorption spectroscopy and the pH conditions in the damaged area were determined with a scanning ion-selective electrode technique. Additionally, the formation of the protective layer was studied with microscopic and surface analytical techniques. Scanning electron micrographs and Auger electron spectroscopy depth profiles revealed the process of coverage and growth of the protective layer in the damaged area. Furthermore, X-ray photoelectron spectroscopy analysis indicated that the protective layer likely consists of a hydrated oxide in the form of a (pseudo) boehmite with lithium distributed in its matrix.

Comparison of the cytotoxic effect of polystyrene latex nanoparticles on planktonic cells and bacterial biofilms

The cytotoxic effect of positively charged polystyrene latex nanoparticles (PSL NPs) was compared between planktonic bacterial cells and bacterial biofilms using confocal laser scanning microscopy, atomic force microscopy, and a colony counting method. Pseudomonas fluorescens, which is commonly used in biofilm studies, was employed as the model bacteria. We found that the negatively charged bacterial surface of the planktonic cells was almost completely covered with positively charged PSL NPs, leading to cell death, as indicated by the NP concentration being greater than that required to achieve single layer coverage. In addition, the relationship between surface coverage and cell viability of P. fluorescens cells correlated well with the findings in other bacterial cells (Escherichia coli and Lactococcuslactis). However, most of the bacterial cells that formed the biofilm were viable despite the positively charged PSL NPs being highly toxic to planktonic bacterial cells. This indicated that bacterial cells embedded in the biofilm were protected by self-produced extracellular polymeric substances (EPS) that provide resistance to antibacterial agents. In conclusion, mature biofilms covered with EPS exhibit resistance to NP toxicity as well as antibacterial agents.

Titanium dioxide/silver nanoparticle bilayers prepared in self-assembly processes

<p>A new method for the preparation of TiO<sub>2</sub>/Ag bilayers via colloid <br /> self-assembly process using well-characterized titanium dioxide and silver suspensions was developed. The titanium dioxide nanoparticles, forming a supporting layer, were 46 nm in diameter, exhibiting an isoelectric point at pH 6.4. The silver nanoparticles, forming an external layer of the diameter of 50 nm were prepared via a chemical reduction method with the presence inorganic phosphate salts. The electrophoretic mobility measurements revealed that the zeta potential of silver nanoparticles was highly negative for a broad range of pH and ionic strengths. By explaining this information, the optimum condition for the silver nanoparticle immobilization on TiO<sub>2</sub> supporting layers were selected. The coverage of the first layer was adjusted by ionic strength of the suspensions and by the deposition time. Afterward, the silver nanoparticle monolayers of controlled coverage were deposited under the diffusion-controlled transport. Their coverage was determined by a direct enumeration of deposited nanoparticles from AFM images and SEM micrographs. The experimental results showed that for extended deposition times, the coverage of silver nanoparticle layers significantly increases with ionic strength. Therefore, it was proven that the formation of bilayers is mainly controlled by electrostatic interactions and that it is feasible to produce uniform TiO<sub>2</sub>/Ag materials of desired coverage and structure.</p>

Ultrathin and uniform carbon-layer-coated hierarchically porous LiFePO4 microspheres and their electrochemical performance

Uniform and complete coverage of ultrathin carbon layer coatings on the surface of nano-sized LiFePO4 (LFP) particles prepared using a supercritical alcohol route was investigated. In the presence of oleylamine, nanosized oleylamine-modified LFP particles were synthesized in supercritical ethanol because particle growth was inhibited. When the oleylamine-modified LFP was calcined, uniform coverage of carbon layers with thicknesses of 1.5–2.0nm on individual LFP particles was achieved. The carbon-coated LFP (C-LFP) exhibited hierarchical porous nano/micro sphere morphology with a porosity of 45.6%. In comparison with bare LFP synthesized in the absence of oleylamine, C-LFP exhibited excellent Li ion uptake performance; C-LFP delivered a reversible discharge capacity of 158.4mAhg−1 after 100 cycles at 0.1C and a rate performance of 84.0mAhg−1 at 20C. In addition, after 700 continuous cycles at 10C, the C-LiFePO4 electrode exhibited a reversible discharge capacity of 84.0mAhg−1 with small capacity loss. Electrochemical impedance tests revealed that the uniform and ultrathin carbon coating improved charge transfer kinetics and lithium diffusion into the active material.

Surgical treatment of osteonecrosis of the jaw with the use of platelet-rich fibrin: a prospective study of 15 patients

The objective of this study was to evaluate the outcome of the surgical treatment of osteonecrosis of the jaw (ONJ) with the additional use of autologous membranes of platelet-rich fibrin (PRF). The study population consisted of 15 patients with ONJ lesions in the maxilla (n=3), mandible (n=11), or both (n=1). Eight patients had malignant disease and were treated with high-dose anti-resorptive medication; seven were treated with low-dose anti-resorptive drugs for osteoporosis. Thirteen patients had grade 2 ONJ lesions and two had grade 3 lesions. The following standardized surgical technique was applied: resection of necrotic bone, mobilization of mucoperiosteal flaps, and multiple layer coverage of bone with PRF membranes. At follow-up 7–20 months after surgery, complete mucosal healing and an absence of symptoms were found in 14 of the 15 patients (93%). The patient with persistent bone exposure had a grade 3 ONJ lesion before surgery. This study suggests that the use of PRF membranes in the surgical treatment of grade 2 ONJ may be a contributing factor to a successful outcome.

Controlling nucleation of monolayer WSe2 during metal-organic chemical vapor deposition growth

Tungsten diselenide (WSe2) is a semiconducting, two-dimensional (2D) material that has gained interest in the device community recently due to its electronic properties. The synthesis of atomically thin WSe2, however, is still in its infancy. In this work we elucidate the requirements for large selenium/tungsten precursor ratios and explain the effect of nucleation temperature on the synthesis of WSe2 via metal-organic chemical vapor deposition (MOCVD). The introduction of a nucleation-step prior to growth demonstrates that increasing nucleation temperature leads to a transition from a Volmer–Weber to Frank–van der Merwe growth mode. Additionally, the nucleation step prior to growth leads to an improvement of WSe2 layer coverage on the substrate. Finally, we note that the development of this two-step technique may allow for improved control and quality of 2D layers grown via CVD and MOCVD processes.

Chlorobenzene vapor assistant annealing method for fabricating high quality perovskite films

In this study, chlorobenzene (CB) vapor assistant annealing (VAA) method is employed to make high quality perovskite films and produce high efficiency CH3NH3PbI3-xClx perovskite solar cells. The perovskite films made by this method present several advantages such as increased crystallinity, large grain size and reduced crystal boundaries compared with those prepared by thermal annealing (TA) method, which is beneficial to charge dissociation and transport in hybrid photovoltaic device. In addition, it is found that the CB VAA method could improve the surface property of perovskite film, resulting in a preferable coverage of PCBM layer and a better interfacial contact between perovskite film and upper PCBM film. Consequently, the short circuit current density (Jsc) of the devices is significantly increased, yielding a high efficiency of 14.79% and an average efficiency of 13.40%, which is 13% higher than that of thermal annealed ones. This work not only put forward a simple and efficient approach to prepare highly efficient perovskite solar cells but also provide a new idea to improve the morphology and interfacial contact in one integration step.

Synthesis of lithium titanium oxide (Li4Ti5O12) with ultrathin carbon layer using supercritical fluids for anode materials in lithium batteries

Lithium titanium oxide (LTO: Li4Ti5O12) particles were produced via a continuous supercritical fluid process for use as anodes in lithium ion batteries. The synthesized LTO particles in supercritical water (scH2O) or in supercritical methanol (scMeOH) generate nanoparticles of 10–30 nm sizes, and the modified LTO particles using oleylamine in scMeOH affects the inhibition of particle growth. The modified LTO particle was coated by the usage of supercritical carbon dioxide (scCO2) and polyethylene glycol (PEG-400). The conformal coverage of the carbon layer on LTO particles with a thickness of 1.2 nm, and a uniform distribution of carbon on the entire surface of LTO particles are confirmed. The modified and carbon-coated LTO with a carbon content of 5.3 wt% exhibits a high discharge capacity of 175 mAh/g (which approaches the theoretical value of LTO) at 0.1 C and 83 mAh/g at 50 C. The carbon-coated LTO prepared using supercritical fluids delivered 160, 153, 123 mAh/g at 1 C and 60 °C, room temperature, and −25 °C, respectively.

Synthesis and characterization of polycaprolactone urethane hollow fiber membranes as small diameter vascular grafts

The design of bioresorbable synthetic small diameter (<6mm) vascular grafts (SDVGs) capable of sustaining long-term patency and endothelialization is a daunting challenge in vascular tissue engineering. Here, we synthesized a family of biocompatible and biodegradable polycaprolactone (PCL) urethane macromers to fabricate hollow fiber membranes (HFMs) as SDVG candidates, and characterized their mechanical properties, degradability, hemocompatibility, and endothelial development. The HFMs had smooth surfaces and porous internal structures. Their tensile stiffness ranged from 0.09 to 0.11N/mm and their maximum tensile force from 0.86 to 1.03N, with minimum failure strains of approximately 130%. Permeability varied from 1 to 14×10−6cm/s, burst pressures from 1158 to 1468mmHg, and compliance from 0.52 to 1.48%/100mmHg. The suture retention forces ranged from 0.55 to 0.81N. HFMs had slow degradation profiles, with 15 to 30% degradation after 8weeks. Human endothelial cells proliferated well on the HFMs, creating stable cell layer coverage. Hemocompatibility studies demonstrated low hemolysis (<2%), platelet activation, and protein adsorption. There were no significant differences in the hemocompatibility of HFMs in the absence and presence of endothelial layers. These encouraging results suggest great promise of our newly developed materials and biodegradable elastomeric HFMs as SDVG candidates.

Controlled functionalization of a double-junction n+/n−/n+ polysilicon nanobelt for hydrogen sensing application

In this paper, a double-junction n+/n−/n+ polysilicon nanobelt selectively functionalized with platinum has been studied for hydrogen sensing application. The selective modification of the devices is performed by the combination of localized ablation of a resist and a lift-off process of e-beam evaporation of a catalyst material. The coverage of a Pt layer on the n− region is precisely controlled by adjusting Joule heating bias and pulse length. The Pt-functionalized devices show a rapid response to hydrogen with a limit of detection of only 5 ppm. The device with fully Pt-covered n− region is optimum for obtaining the best response to hydrogen.

The role of ion exchange in the passivation of In(Zn)P nanocrystals with ZnS.

We have investigated the chemical state of In(Zn)P/ZnS core/shell nanocrystals (NCs) for color conversion applications using hard X-ray absorption spectroscopy (XAS) and photoluminescence excitation (PLE). Analyses of the edge energies as well as the X-ray absorption fine structure (XAFS) reveal that the Zn2+ ions from ZnS remain in the shell while the S2− ions penetrate into the core at an early stage of the ZnS deposition. It is further demonstrated that for short growth times, the ZnS shell coverage on the core was incomplete, whereas the coverage improved gradually as the shell deposition time increased. Together with evidence from PLE spectra, where there is a strong indication of the presence of P vacancies, this suggests that the core-shell interface in the In(Zn)P/ZnS NCs are subject to substantial atomic exchanges and detailed models for the shell structure beyond simple layer coverage are needed. This substantial atomic exchange is very likely to be the reason for the improved photoluminescence behavior of the core-shell particles compare to In(Zn)P-only NCs as S can passivate the NCs surfaces.

Scrotal-Septal Fasciocutaneous Flap Used as a Multifunctional Coverage for Prior Failed Hypospadias Repair

Objectives: The study aims to report the method and outcome of using scrotal-septal fasciocutaneous flap as a multifunctional coverage for prior failed hypospadias repair. Methods: From January 2014 to June 2015, 18 hypospadias patients who have undergone repeated failed surgeries were enrolled. Their penile skin, urethral plate and dartos fascia are not enough to reconstruct the urethra, but have well-developed scrota. We performed urethroplasty by buccal mucosa free grafting and tubularized anastomosis 6 months after the urethroplasty. Then, scrotal-septal fasciocutaneous flap was used to be a multifunctional coverage on the surface of anastomotic urethra, which was a waterproof layer and cutaneous coverage. Results: The skin flaps survived and the incisions healed in 18 patients. No fistula and stricture occurred. The scar of donor site seemed like a new scrotal raphe. The flap can slip slightly along with the preputial movement and retain the original sense of touch. All patients were followed up at 1 and 6 months by telephone or in person and gained good recoveries. Conclusion: Scrotal-septal fasciocutaneous flap, including sufficient fascia tissue, reliable blood supply and skin coverage, is a good choice for the coverage of anastomotic urethra as both the waterproof layer and skin coverage, especially for hypospadias patients who have undergone several failed operations.

Fine control of perovskite-layered morphology and composition via sequential deposition crystallization process towards improved perovskite solar cells

The ability to prepare high coverage and compact perovskite films via solution-based crystallization manipulation processes still represents a vital issue towards improving the ultimate photoelectric conversion efficiency of devices. In this work, we prepare the active perovskite layer by means of sequential deposition crystallization process i.e. dipping PbI2-infiltrated TiO2 film within CH3NH3I solution from 20s to 60s. The morphology and thickness of the as-prepared perovskite layer, and its overall performance superiority are investigated. X-ray diffraction (XRD) reveals that a maximum conversion of PbI2 to perovskite is completed upon applying a sequential deposition crystallization process of 40s. Field emission scanning electron microscope (FESEM) demonstrates that the coverage of the perovskite capping layer exhibits a trend from rise to decline in the whole dipping time from 20s to 60s. By fine control of the dipping time, a 620 nm-thickness compact perovskite active layer is obtained at the optimized dipping time of 40s and is verified to possess strong light absorption and high electron extraction efficiency, leading to a higher photocurrent. By further optimizing the mesoporous TiO2 film thickness, a high photocurrent of 23.98 mA cm−2 and an efficiency of 13.47% are achieved.

Capacitive sensing of local bond layer thickness and coverage in thermal interface materials

An instrumentation technique is developed using embedded capacitive sensors to measure the thickness and evenness of coverage of a thin layer of dielectric thermal interface material (TIM) between two substrates. The technique requires an array of sensors embedded into one substrate, with an electrically conductive opposing substrate. Local capacitance measurements are sensitive to both local bond layer thickness and local voiding. We propose a means for using an array of capacitance measurements to interpret both bond layer thickness and local voiding at every sensor location. An algorithm is developed which reveals both characteristics from a single set of capacitance measurements. Experiments are conducted with thermal grease layers of different bond layer thicknesses and void distributions using a prototype system constructed on printed circuit boards. The thickness and void distribution are successfully mapped across the bond layer using the algorithm developed. The technique offers a sensing approach for in situ instrumentation of layers of thermal grease in a thermal test vehicle.

Morphological analysis of pad–disc system during braking operations

A method has been developed for quantifying the percentage of friction layer coverage on a brake disc surface. The method is used to examine the relationship of layer coverage to the coefficient of friction and the morphology of the contact plateaus existing on the brake pad surface. Two kinds of brake pads, a non asbestos organic (NAO) and a semi-metallic (SM), were subjected to sliding against a gray cast iron disc in a laboratory-scaled tribometer. In order to observe the effect caused by the contact pressure on the measured parameters, tests were carried out with two normal forces (600N and 1200N). Micrographs of brake discs and pads were obtained as the tests progressed. MatLab (Mathworks®) scripts were developed to process the images of the brake disc and pad. Using these, the number and the area fraction of contact plateaus were investigated. Both the NAO and the SM materials formed a heterogeneous friction layer on the disc surface, but SM material produced a more uniform distribution of the friction layer. An increase in the normal force led to an increase in the friction layer deposited on the brake disc surface for the NAO; however, the opposite was observed for the SM material, that is, an increase in the normal force tended to remove the friction layer on the brake disc surface. Correlations among friction, friction layer coverage, temperature variation and morphology parameters are discussed.

Influence of Microscale Surface Modification on Impinging Flow Heat Transfer Performance

An experimental approach has been used to investigate the influence of a thin layer of carbon nanotubes (CNTs) on the convective heat transfer performance under impinging flow conditions. A successful synthesis of CNT layers was achieved using a thermal catalytic vapor deposition process (TCVD) on silicon sample substrates. Three different structural arrangements, with fully covered, inline, and staggered patterned layers of CNTs, were used to evaluate their heat transfer potential. Systematic surface characterizations were made using scanning electron microscope (SEM) and confocal microscopy. The external surface area ratio of fully covered, staggered, and inline arrangement was obtained to be 4.57, 2.80, and 2.89, respectively. The surface roughness of the fully covered, staggered, and inline arrangement was measured to be (Sa = 0.365 μm, Sq = 0.48 μm), (Sa = 0.969 μm, Sq = 1.291 μm), and (Sa = 1.668 μm, Sq = 1.957 μm), respectively. On average, heat transfer enhancements of 1.4% and − 2.1% were obtained for staggered and inline arrangement of the CNTs layer. This is attributed to the negligible improvement on the effective thermal resistance due to the small area coverage of the CNT layer. In contrast, the fully covered samples enhanced the heat transfer up to 20%. The deposited CNT layer plays a significant role in reducing the effective thermal resistance of the sample, which contributes to the enhancement of heat transfer.

Lateral gas phase diffusion length of boron atoms over Si/B surfaces during CVD of pure boron layers

The lateral gas phase diffusion length of boron atoms, LB, along silicon and boron surfaces during chemical vapor deposition (CVD) using diborane (B2H6) is reported. The value of LB is critical for reliable and uniform boron layer coverage. The presented information was obtained experimentally and confirmed analytically in the boron deposition temperature range from 700 °C down to 400 °C. For this temperature range the local loading effect of the boron deposition is investigated on the micro scale. A LB = 2.2 mm was determined for boron deposition at 700 °C, while a LB of less than 1 mm was observed at temperatures lower than 500 °C.