Luminal Surface Plasma Treatment of Closed Cylindrical Microchannels: A Tool toward the Creation of On-Chip Vascular Endothelium

On-chip vascular microfluidic models provide a great tool to study aspects of cardiovascular diseases in vitro. To produce such models, polydimethylsiloxane (PDMS) has been the most widely used material. For biological applications, its hydrophobic surface has to be modified. The major approach has been plasma-based surface oxidation, which has been very challenging in the case of channels enclosed within a microfluidic chip. The preparation of the chip combined a 3D-printed mold with soft lithography and commonly available materials. We have introduced the high-frequency low-pressure air-plasma surface modification of seamless channels enclosed within a PDMS microfluidic chip. The plasma treatment modified the luminal surface more uniformly than in previous works. Such a setup enabled a higher degree of design freedom and a possibility of rapid prototyping. Further, plasma treatment in combination with collagen IV coating created a biomimetic surface for efficient adhesion of vascular endothelial cells as well as promoted long-term cell culture stability under flow. The cells within the channels were highly viable and showed physiological behavior, confirming the benefit of the presented surface modification.

Multifaceted Structurally Coloured Materials: Diffraction and Total Internal Reflection (TIR) from Nanoscale Surface Wrinkling

We investigate the combined effects of surface diffraction and total internal reflection (TIR) in the design of 3-dimensional materials exhibiting distinct structural colour on various facets. We employ mechanical wrinkling to introduce surface diffraction gratings (from the nano to the micron scales) on one face of an elastomeric rectangular parallelepiped-shaped slab and explore the roles, in the perceived colours, of wrinkling pattern, wavelength, the directionality of incident light and observation angles. We propose a simple model that satisfactorily accounts for all experimental observations. Employing polydimethylsiloxane (PDMS), which readily swells in the presence of various liquids and gases, we demonstrate that such multifaceted colours can respond to their environment. By coupling a right angle triangular prism with a surface grating, we demonstrate the straightforward fabrication of a so-called GRISM (GRating + prISM). Finally, using a range of examples, we outline possibilities for a predictive material design using multi-axial wrinkling patterns and more complex polyhedra.

Speciation of Oxygen Functional Groups on the Carbon Support Controls the Electrocatalytic Activity of Cobalt Oxide Nanoparticles in the Oxygen Evolution Reaction

The effective use of the active phase is the main goal of the optimization of supported catalysts. However, carbon supports do not interact strongly with metal oxides, thus, oxidative treatment is often used to enhance the number of anchoring sites for deposited particles. In this study, we set out to investigate whether the oxidation pretreatment of mesoporous carbon allows the depositing of a higher loading and a more dispersed cobalt active phase. We used graphitic ordered mesoporous carbon obtained by a hard-template method as active phase support. To obtain different surface concentrations and speciation of oxygen functional groups, we used a low-temperature oxygen plasma. The main methods used to characterize the studied materials were X-ray photoelectron spectroscopy, transmission electron microscopy, and electrocatalytic tests in the oxygen evolution reaction. We have found that the oxidative pretreatment of mesoporous carbon influences the speciation of the deposited cobalt oxide phase. Moreover, the activity of the electrocatalysts in oxygen evolution is positively correlated with the relative content of the COO-type groups and negatively correlated with the C═O-type groups on the carbon support. Furthermore, the high relative content of COO-type groups on the carbon support is correlated with the presence of well-dispersed Co₃O₄ nanoparticles. The results obtained indicate that to achieve a better dispersed and thus more catalytically active material, it is more important to control the speciation of the oxygen functional groups rather than to maximize their total concentration.

Promotion of bone formation and antibacterial properties of titanium coated with porous Si/Ag-doped titanium dioxide

Implant materials are mainly used to repair and replace defects in human hard tissue (bones and teeth). Titanium (Ti) and Ti alloys are widely used as implant materials because of their good mechanical properties and biocompatibilities, but they do not have the ability to induce new bone formation and have no antibacterial properties. Through surface modification, Ti and its alloys have certain osteogenic and antibacterial properties such that Ti implants can meet clinical needs and ensure integration between Ti implants and bone tissue, and this is currently an active research area. In this study, bioactive Si and Ag were introduced onto a Ti surface by plasma oxidation. The surface morphology, structure, elemental composition and valence, surface roughness, hydrophilicity and other physical and chemical properties of the coating were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), a profiler and a contact angle meter (CA). Adhesion and extensions of osteoblasts on the surface of the material were observed by scanning electron microscopy, and mineralization of osteoblasts on the surface of the material were observed by alizarin red staining. The antibacterial properties of the material were tested by culturing Staphylococcus aureus on the surface of the material. The osteogenic properties of Ti implants with porous Si/Ag TiO₂ (TCP-SA) coatings were evaluated with in vivo experiments in rats. The results showed that Si and Ag were successfully introduced onto the Ti surface by plasma oxidation, and doping with Si and Ag did not change the surface morphology of the coating. The osteoblasts showed good adhesion and extension on the surfaces of Si/Ag coated samples, and the porous Si/Ag TiO₂ coating promoted cell proliferation and mineralization. The bacterial experiments showed that the porous TiO₂ coatings containing Si/Ag had certain antibacterial properties. The animal experiments showed that Si/Ag-coated Ti implants promoted integration between the implants and the surrounding bone. It was concluded that the porous Si/Ag TiO₂ coating on the Ti surface had good osteogenic and antibacterial properties and provides an optimal strategy for improving the osteogenic and antibacterial properties of Ti implants.

Steep Subthreshold Swing and Enhanced Illumination Stability InGaZnO Thin-Film Transistor by Plasma Oxidation on Silicon Nitride Gate Dielectric

In this paper, an InGaZnO thin-film transistor (TFT) based on plasma oxidation of silicon nitride (SiN_x) gate dielectric with small subthreshold swing (SS) and enhanced stability under negative bias illumination stress (NBIS) have been investigated in detail. The mechanism of the high-performance InGaZnO TFT with plasma-oxidized SiN_x gate dielectric was also explored. The X-ray photoelectron spectroscopy (XPS) results confirmed that an oxygen-rich layer formed on the surface of the SiN_x layer and the amount of oxygen vacancy near the interface between SiN_x and InGaZnO layer was suppressed via pre-implanted oxygen on SiN_x gate dielectric before deposition of the InGaZnO channel layer. Moreover, the conductance method was employed to directly extract the density of the interface trap (D_it) in InGaZnO TFT to verify the reduction in oxygen vacancy after plasma oxidation. The proposed InGaZnO TFT with plasma oxidation exhibited a field-effect mobility of 16.46 cm²/V·s, threshold voltage (V_th) of −0.10 V, I_on/I_off over 10⁸, SS of 97 mV/decade, and V_th shift of −0.37 V after NBIS. The plasma oxidation on SiN_x gate dielectric provides a novel approach for suppressing the interface trap for high-performance InGaZnO TFT.

Nanoscale-Precision Removal of Copper in Integrated Circuits Based on a Hybrid Process of Plasma Oxidation and Femtosecond Laser Ablation

Copper (Cu) is the main interconnect conductor for integrated circuits (IC), and its processing quality is very important to device performance. Herein, a hybrid process of plasma oxidation and femtosecond laser (fs-laser) ablation was proposed for the nanoscale precision removal of Cu in integrated circuits. In this hybrid process, the surface layer of Cu was oxidized to the copper oxide by plasma oxidation, and then the fs-laser with a laser fluence lower than the Cu ablation threshold was used to remove the copper oxide without damaging the underlying Cu. Theoretically, the surface temperature evolutions of Cu and copper oxide under the femtosecond laser were studied by the two-temperature model, and it was revealed that the ablation threshold of copper oxide is much lower than that of Cu. The experimental results showed that the ablation threshold of copper oxide is lower than that of Cu, which is consistent with the theoretical analysis. Using the hybrid process, a surface roughness of 3 nm and a removal accuracy of 4 nm were obtained in the process of Cu film processing, which were better than those obtained by fs-laser ablation. This demonstrated that the hybrid process has good application potential in the field of copper micromachining.

A DLC-Punch Array to Fabricate the Micro-Textured Aluminum Sheet for Boiling Heat Transfer Control

A diamond-like carbon (DLC) film, coated on an SKD11 (alloy tool steel) substrate, was shaped by plasma oxidation to form an assembly of DLC macro-pillars and to be used as a DLC-punch array that is micro-embossed into aluminum sheets. First, the SKD11 steel die substrate was prepared and DLC-coated to have a film thickness of 10 μm. This DLC coating worked as a punch material. The two-dimensional micro-patterns were printed onto this DLC film by maskless lithography. The unprinted DLC films were selectively removed by plasma oxidation to leave the three-dimensional DLC-punch array on the SKD11 substrate. Each DLC punch had a head of 3.5 μm × 3.5 μm and a height of 8 μm. This DLC-punch array was fixed into the cassette die set for a micro-embossing process using a table-top servo-stamper. Furthermore, through numerically controlled micro-embossing, an alignment of rectangular punches was transcribed into a micro-cavity array in the aluminum sheet. The single micro-cavity had a bottom surface of 3.2 μm × 3.2 μm and an average depth of 7.5 μm. A heat-transfer experiment in boiling water was also performed to investigate the effect of micro-cavity texture on bubbling behavior and the boiling curve.

Binder-Free N- and O-Rich Carbon Nanofiber Anodes for Long Cycle Life K-Ion Batteries

Carbon nanofibers produced by electrospinning of polyacrylonitrile polymer and subsequent carbonization were tested as freestanding potassium-ion anodes. The effect of oxygen functionalization on K-ion carbon anode performance was tested for the first time via plasma oxidation of prepared carbon nanofibers. The produced materials exhibited exceptional cycling stability through the amorphous carbon structuring and one-dimensional architecture accommodating significant material expansion upon K⁺ intercalation, resulting in a stable capacity of 170 mAh g^-1 after 1900 cycles at 1C rate for N-rich carbon nanofibers. Excellent rate performance of 110 mAh g^-1 at 10C rate, as compared to 230 mAh g^-1 at C/10 rate, resulted from the K-ion surface storage mechanism and the increased K⁺ solid diffusion coefficient in carbon nanofibers as compared to graphite. Plasma oxidation treatment augmented surface storage of K⁺ by oxygen functionalities but increased material charge transfer resistance as compared to N-rich carbon fibers. Ex situ characterization revealed that the one-dimensional structure was maintained throughout cycling, despite the increase in graphitic interlattice spacing from 0.37 to 0.46 nm. The carbon nanofibers demonstrate great potential as an anode material for potassium-ion batteries with superior cycling stability and rate capability over previously reported carbon materials.

Effective Schottky Barrier Height Lowering of Metal/n-Ge with a TiO2/GeO2 Interlayer Stack

A perfect ohmic contact formation technique for low-resistance source/drain (S/D) contact of germanium (Ge) n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) is developed. A metal-interlayer-semiconductor (M-I-S) structure with an ultrathin TiO₂/GeO₂ interlayer stack is introduced into the contact scheme to alleviate Fermi-level pinning (FLP), and reduce the electron Schottky barrier height (SBH). The TiO₂ interlayer can alleviate FLP by preventing formation of metal-induced gap states (MIGS) with its very low tunneling resistance and series resistance and can provide very small electron energy barrier at the metal/TiO₂ interface. The GeO₂ layer can induce further alleviation of FLP by reducing interface state density (D_it) on Ge which is one of main causes of FLP. Moreover, the proposed TiO₂/GeO₂ stack can minimize interface dipole formation which induces the SBH increase. The M-I-S structure incorporating the TiO₂/GeO₂ interlayer stack achieves a perfect ohmic characteristic, which has proved unattainable with a single interlayer. FLP can be perfectly alleviated, and the SBH of the metal/n-Ge can be tremendously reduced. The proposed structure (Ti/TiO₂/GeO₂/n-Ge) exhibits 0.193 eV of effective electron SBH which achieves 0.36 eV of SBH reduction from that of the Ti/n-Ge structure. The proposed M-I-S structure can be suggested as a promising S/D contact technique for nanoscale Ge n-channel transistors to overcome the large electron SBH problem caused by severe FLP.

Carbon Nanotube Interconnects Realized through Functionalization and Sintered Silver Attachment

Carbon nanotubes (CNTs) in the form of interconnects have many potential applications, and their ability to perform at high temperatures gives them a unique capability. We show the development of a novel transfer process using CNTs and sintered silver that offers a unique high-temperature, high-conductivity, and potentially flexible interconnect solution. Arrays of vertically aligned multiwalled carbon nanotubes of approximately 200 μm in length were grown on silicon substrates, using low-temperature photothermal chemical vapor deposition. Oxygen plasma treatment was used to introduce defects, in the form of hydroxyl, carbonyl, and carboxyl groups, on the walls of the carbon nanotubes so that they could bond to palladium (Pd). Nanoparticle silver was then used to bind the Pd-coated multiwalled CNTs to a copper substrate. The silver-CNT-silver interconnects were found to be ohmic conductors, with resistivity of 6.2 × 10(-4) Ωm; the interconnects were heated to temperatures exceeding 300 °C (where common solders fail) and were found to maintain their electrical performance.