Thin Films and Coatings

Pressure sensors are a key component in electronic skin (e-skin) sensing systems. Most reported resistive pressure sensors have a high sensitivity at low pressures (<5 kPa) to enable ultra-sensitive detection. However, the sensitivity drops significantly at high pressures (>5 kPa), which is inadequate for practical applications. For example, actions like a gentle touch and object manipulation have pressures below 10 kPa, and 10–100 kPa, respectively. Maintaining a high sensitivity in a wide pressure range is in great demand. Here, a flexible, wide range and ultra-sensitive resistive pressure sensor with a foam-like structure based on laser-scribed graphene (LSG) is demonstrated. Benefitting from the large spacing between graphene layers and the unique v-shaped microstructure of the LSG, the sensitivity of the pressure sensor is as high as 0.96 kPa−1 in a wide pressure range (0 ~ 50 kPa). Considering both sensitivity and pressure sensing range, the pressure sensor developed in this work is the best among all reported pressure sensors to date. A model of the LSG pressure sensor is also established, which agrees well with the experimental results. This work indicates that laser scribed flexible graphene pressure sensors could be widely used for artificial e-skin, medical-sensing, bio-sensing and many other areas.

During the last two decades, the industry (including scientists) has focused on diamond-like carbon (DLC) coating because of its wide range of application in various fields. This material has numerous applications in mechanical, electrical, tribological, biomedical, and optical fields. Severe friction and wear in some machine parts consumes high amount of energy, which makes the process energy inefficient. Thus, DLC coating can be an effective means to lower the friction and wear rate. Some important process variables that affect the tribological characteristics of DLC coating are adhesion promoter intermediate layer, substrate surface roughness, hydrogen incorporation or hydrogen non involvement, and coating deposition parameters (e.g., bias voltage, etching, current, precursor gas, time, and substrate temperature). Working condition of DLC-coated parts also affects the tribological characteristics, such as temperature, sliding speed and load, relative humidity, counter surface, and lubrication media (DLC additive interaction). Different types of lubricated oils and additives are used in engine parts to minimize friction and wear. DLC can be coated to the respective engine parts; however, DLC does not behave accordingly after coating because of lubricant oil and additive interaction with DLC. Some additive interacts positively and some behave negatively because of the tribochemical reactions between DLC coating and additives. Numerous conflicting views have been presented by several researchers regarding this coating additive interaction, resulting in unclear determination of true mechanism of such interaction. However, lubricant additive has been established to be more inert to DLC coating compared with uncoated metal surface because the additive is fabricated in such a way that it can react with metal surfaces. In this article, the tribological characteristics of different types of DLC coating in dry and lubricated conditions will be presented, and their behavior will be discussed in relation to working condition and processing parameters.

Increasingly precise control of polymer architectures generated by “Living” Anionic Ring-Opening Polymerization (Living AROP) is leading to a broad range of commercial ad-vanced material applications, particularly in the area of siloxane macromers. While academic reports on such materials remain sparse, a significant portion of the global population interacts with them on a daily basis—in applications including medical devices, microelectronics, food packaging, synthetic leather, release coatings, and pigment dispersions. The primary driver of this increased utilization of siloxane macromers is their ability to incorporate the properties of silicones into organic structures in a balanced manner. Compared to organic polymers, the differentiating properties of silicones—low Tg, hydrophobicity, low surface energy, and high free molal space—logically lend themselves to applications in which low modulus, release, permeability to oxygen and moisture, and tactile interaction are desired. However, their mechanical, structural and processing properties have until recently precluded practical applications. This review presents applications of “Living” AROP derived polymers from the perspective of historical technology development. Applications in which products are produced on a commercial scale—defined as not only offered for sale, but sold on a recurrent basis—are emphasized. Hybrid polymers with intriguing nanoscale morphology and potential applications in photoresist, microcontact printing, biomimetic soft materials, and liquid crystals are also discussed. Previously unreported work by the authors is provided in the context of this review. Keywords: Breathable Films; Block Polymers; Silicones; Double Gyroid; Self-Healing Polymers; Ultra-high Elongation Elastomers; Release Coatings; Photoresists; siloxanes

The results of studies on the regularities of structure formation and properties of high-entropy alloys prepared by different methods are analyzed and generalized. Specific features of the synthesis of nitride coatings based on multicomponent alloys are considered. Main physicomechanical properties of the coatings of different elemental composition deposited in different manner were compared.

High-entropy alloy and nitride coatings (TiHfZrVNb)N were prepared by the cathodic-arc-vapor-deposition method under various deposition conditions. The composition, crystal structure, strain-stress state, profiles of defects and atoms in-depth and at surfaces of the (TiHfZrVNb)N coatings were characterized by EDS and SEM analysis, X-ray diffraction with “α-sin2ψ” method of measurements and slow positron beam. The oxidation behavior of nitride films after annealing at 600 °C temperature was studied. The results indicate that nitride coatings show the face-centered cubic crystal structure. The redistributions of elements and defects, their arrangement (segregation) due to the thermally stimulated diffusion and termination of the spinodal segregation near the interfaces, around the grains and subgrains were found. The peak hardness and modulus of the nitride films were 44.3 and 384 GPa, respectively. The tribological properties of the (TiHfZrVNb)N coatings against AISI 1045 were evaluated by a ball-on-disc tribometer with a 3.0 N applied load.

Development of better diffusion barriers for Cu metallization is one of the key issues for the microelectronics industry. Although metallic diffusion barriers offer many advantages, their application is hindered due to their inferior thermal stability relative to ceramic barriers. Here we report on a metallic diffusion barrier, NbSiTaTiZr, which shows thermal stability comparable to ceramic barriers. The outstanding performance of NbSiTaTiZr is due to its better structural and chemical stability at high temperatures.

Tablet coating is a common pharmaceutical technique of applying a thin polymer-based film to a tablet or a granule containing active pharmaceutical ingredients (APIs). Inter-and intra-tablet variability of film coating is a critical issue in the production of solid oral dosage forms. In fact, inhomogeneity in the coating thickness can lead to significant variations in the delivery rate of active pharmaceutical ingredients and compromise the functional attributes of the tablet film. Although attempts have been made to use numerical approaches to analyze this complex problem, at present the uniformity of coating thickness is difficult to predict without expensive experimental work.

Surface contamination by microbes is a major public health concern. A damp environment is one of potential sources for microbe proliferation. Smart photocatalytic coatings on building surfaces using semiconductors like titania (TiO 2) can effectively curb this growing threat. Metal-doped titania in anatase phase has been proven as a promising candidate for energy and environmental applications. In this present work, the antimicrobial efficacy of copper (Cu)-doped TiO 2 (Cu-TiO 2) was evaluated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) under visible light irradiation. Doping of a minute fraction of Cu (0.5 mol %) in TiO 2 was carried out via sol-gel technique. Cu-TiO 2 further calcined at various temperatures (in the range of 500-700 • C) to evaluate the thermal stability of TiO 2 anatase phase. The physico-chemical properties of the samples were characterized through X-ray diffraction (XRD), Raman spectroscopy, X-ray photo-electron spectroscopy (XPS) and UV-visible spectroscopy techniques. XRD results revealed that the anatase phase of TiO 2 was maintained well, up to 650 • C, by the Cu dopant. UV-vis results suggested that the visible light absorption property of Cu-TiO 2 was enhanced and the band gap is reduced to 2.8 eV. Density functional theory (DFT) studies emphasize the introduction of Cu + and Cu 2+ ions by replacing Ti 4+ ions in the TiO 2 lattice, creating oxygen vacancies. These further promoted the photocatalytic efficiency. A significantly high bacterial inactivation (99.9999%) was attained in 30 min of visible light irradiation by Cu-TiO 2 .

The influence of polydopamine-and polydopamine-graft-poly(ethylene glycol)-coated feed spacers and membranes, copper-coated feed spacers, and commercially-available biostatic feed spacers on biofouling has been studied in membrane fouling simulators. Feed spacers and membranes applied in practical membrane filtration systems were used; biofouling development was monitored by feed channel pressure drop increase and biomass accumulation. Polydopamine and polydopamine-g-PEG are hydrophilic surface modification agents expected to resist protein and bacterial adhesion, while copper feed spacer coatings and biocides infused in feed spacers are expected to restrict biological growth. Our studies showed that polydo-pamine and polydopamine-g-PEG coatings on feed spacers and membranes, copper coatings on feed spacers, and a commercial biostatic feed spacer did not have a significant impact on feed channel pressure drop increase and biofilm accumulation as measured by ATP and TOC content. The studied spacer and membrane modifications were not effective for biofouling control; it is doubtful that feed spacer and membrane modification , in general, may be effective for biofouling control regardless of the type of applied coating.

Nickel doped zinc oxide (Ni/ZnO) nanostructures have the potential to improve the performance of electrochemical capacitors. This study investigates the preparation of Ni/ZnO nanomaterials by facile co-precipitation (CPM) and hydrothermal (HTM) methods. The effect of the synthesis methods on the optical, structural, chemical and morphological properties on ZnO products is investigated using ultra violet (UV)-visible spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray spectrometry (EDX), room temperature photoluminescence (PL), Fourier transform infrared (FTIR) and Raman spectroscopy. Finally, the electrochemical performance of the synthesized nanorods were examined by fabrication of a supercapacitor using standard three electrode cell configuration and tested with a cyclic voltammogram (CV) and galvanostatic charge-discharge (GCD) measurements. The results shown that the samples synthesized by HTM exhibited improved electrochemical capacitance performance with higher current density. The discharge curves are linear in the total range of potential with constant slopes, showing perfect capacitance. In conclusion, Ni/ZnO nanoparticles synthesized by this method with further optimization have the potential to lead to a high-efficiency supercapacitors.