Stable Oxygen Incorporation in Superconducting TaN: An Experimental and Theoretical Assessment

Oxide formation in superconducting TaN thin films is analyzed through experimental measurements and computational simulations. TaN was synthesized in an ultrahigh vacuum (UHV) system by reactive pulsed laser deposition and characterized in situ by X-ray photoelectron spectroscopy; it was also characterized ex situ by X-ray diffraction, transmission electron microscopy, and the four-point probe method. Despite being grown in an UHV chamber with a base pressure of 5 × 10-9 Torr, TaN contains a significant amount of oxygen (up to 20 at. %) attributed to residual gases containing O atoms. Several TaN1-x O x models, with different amounts of O atoms incorporated into N sites, were simulated using ab initio calculations to assess the feasibility of oxide formation. Thermodynamic stability analysis reveals that TaN1-x O x stability increases with oxygen addition, indicating that its incorporation is thermodynamically favorable. The oxygen-impurified TaN exhibits a face-centered cubic structure and is a superconductor (R = 0 Ω) at 2.99 K. The results discussed here highlight the importance of considering stable oxygen impurities when studying superconductivity in TaN films. The formation of TaN1-x O x regions in the compound may be key to understanding the variation in critical temperature reported in the literature.

Resistive Switching and Synaptic Characteristics in ZnO/TaON-Based RRAM for Neuromorphic System

We fabricated an ITO/ZnO/TaON/TaN device as nonvolatile memory (NVM) with resistive switching for complementary metal-oxide-semiconductor (CMOS) compatibility. It is appropriate for the age of big data, which demands high speed and capacity. We produced a TaON layer by depositing a ZnO layer on a TaN layer using an oxygen-reactive radio frequency (RF) sputtering system. The bi-layer formation of ZnO and TaON interferes with the filament rupture after the forming process and then raises the current level slightly. The current levels were divided into high- and low-compliance modes. The retention, endurance, and pulse conductance were verified with a neuromorphic device. This device was stable and less consumed when it was in low mode rather than high mode.

Modification and Characterization of Interfacial Bonding for Thermal Management of Ruthenium Interconnects in Next-Generation Very-Large-Scale Integration Circuits

Ruthenium may replace copper interconnects in next-generation very-large-scale integration (VLSI) circuits. However, interfacial bonding between Ru interconnect wires and surrounding dielectrics must be optimized to reduce thermal boundary resistance (TBR) for thermal management. In this study, various adhesion layers are employed to modify bonding at the Ru/SiO₂ interface. The TBRs of film stacks are measured using the frequency-domain thermoreflectance technique. TiN and TaN with high nitrogen contents significantly reduce the TBR of the Ru/SiO₂ interface compared to common Ti and Ta adhesion layers. The adhesion layer thickness, on the other hand, has only minor effect on TBR when the thickness is within 2-10 nm. Hard X-ray photoelectron spectroscopy of deeply buried layers and interfaces quantitatively reveals that the decrease in TBR is attributed to the enhanced bonding of interfaces adjacent to the TaN adhesion layer, probably due to the electron transfer between the atoms at two sides of the interface. Simulations by a three-dimensional electrothermal finite element method demonstrate that decreasing the TBR leads to a significantly smaller temperature increase in the Ru interconnects. Our findings highlight the importance of TBR in the thermal management of VLSI circuits and pave the way for Ru interconnects to replace the current Cu-based ones.

Development of tantalum with highly hydrophilic surface and antimicrobial properties obtained by micro-arc oxidation process

Tantalum (Ta) and its application in biomaterials has been attracting more and more attention recently. It can be considered as a material for hard tissue implants. This study focuses on antimicrobial and surface characterization of micro-arc oxidized (MAO) nanocrystalline Ta compared with its microcrystalline equivalent. For the purposes of the investigation, x-ray diffractometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), wetting analysis, optical profilometry, corrosion resistance measurement, and antimicrobial tests were performed. Nanocrystalline Ta was fabricated using high-energy ball milling (HEBM) and pulse plasma sintering (PPS). The MAO process done at 250 V results in the formation of a porous oxide surface. An XRD analysis confirmed the presence of a Ta2 O5 oxide layer. Based on the SEM pictures, the obtained oxide layer was approximately 3-4 μm thick for nanocrystalline Ta substrate. For microcrystalline Ta, the oxide layer was thinner, in the range of 0.3-0.6 μm. The analysis of polarization curves showed a significant improvement of corrosion resistance for MAO nanocrystalline Ta (2.62 × 10-8 A/cm2 ) versus not oxidized nanocrystalline Ta (1.20 × 10-5 A/cm2 ). The surface roughness of MAO nanocrystalline Ta proved to be several times higher than that of unoxidized Ta. Wetting analysis showed that the oxide layer on the nanocrystalline substrate is hydrophilic. This research provides detailed information about MAO microcrystalline and MAO nanocrystalline Ta antimicrobial activity against Staphylococcus aureus and Pseudomonas aeruginosa. A significant decrease of S. aureus for MAO nanocrystalline Ta (control 10,435 ± 981 vs. sample 3,453 ± 130) was noticed. No significant difference was noticed for MAO microcrystalline and nanocrystalline Ta tested for P. aeruginosa.

Sol-gel-assisted micro-arc oxidation synthesis and characterization of a hierarchically rough structured Ta-Sr coating for biomaterials

Tantalum (Ta) is an element with high chemical stability and ductility that is used in orthopedic biomaterials. When utilized, it can produce a bioactive surface and enhance cell-material interactions, but currently, there exist scarce effective methods to introduce the Ta element onto the surface of implants. This work reported a sol-gel-assisted approach combined with micro-arc oxidation (MAO) to introduce Ta onto the surface of the titanium (TC4) substrate. Specifically, this technique produced a substrate with a hierarchically rough structured topography and introduced strontium ions into the film. The films were uniform and continuous with numerous crater-like micropores. Compared with the TC4 sample (196 ± 35 nm), the roughness of Ta (734 ± 51 nm) and Ta-Sr (728 ± 85 nm) films was significantly higher, and both films (Ta and Ta-Sr) showed increased hydrophilicity when compared with TC4, promoting cell attachment. Additionally, the in vitro experiments indicated that Ta and Ta-Sr films have the potential to enhance the recruitment of cells in the initial culture stages, and improve cell proliferation. Overall, this work demonstrated that the application of Ta and Ta-Sr films to orthopedic implants has the potential to increase the lifetime of the implants. Furthermore, this study also describes an innovative strategy to incorporate Ta into implant films.

Improved Osteogenesis of Selective-Laser-Melted Titanium Alloy by Coating Strontium-Doped Phosphate With High-Efficiency Air-Plasma Treatment

Surface treatment and bioactive metal ion incorporation are effective methods for the modification of titanium alloys to be used as biomaterials. However, few studies have demonstrated the use of air-plasma treatment in orthopedic biomaterial development. Additionally, no study has performed a direct comparison between unmodified titanium alloys and air-plasma-treated alloys with respect to their biocompatibility and osteogenesis. In this study, the biological activities of unmodified titanium alloys, air-plasma-treated titanium alloys, and air-plasma-treated strontium-doped/undoped calcium phosphate (CaP) coatings were compared. The strontium-doped CaP (Sr-CaP) coating on titanium alloys were produced by selective laser melting (SLM) technology as well as micro-arc oxidation (MAO) and air-plasma treatment. The results revealed that rapid air-plasma treatment improved the biocompatibility of titanium alloys and that Sr-CaP coating together with air-plasma treatment significantly enhanced both the biocompatibility and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Overall, this study demonstrated that low temperature air-plasma treatment is a fast and effective surface modification which improves the biocompatibility of titanium alloys. Additionally, air-plasma-treated Sr-CaP coatings have numerous practical applications and may provide researchers with new tools to assist in the development of orthopedic implants.

Tantalum boride as a biocompatible coating to improve osteogenesis of the bionano interface

A proper biological microenvironment conducive to tissue repair and regeneration, while the bioimplant interface directly affects the local microenvironment. In this study, to improve the biological microenvironment, a nanosized tantalum boride (Ta-B) was coated on a titanium alloy substrate (Ti6Al4V, TC4) using magnetron cosputtering. The sample surface was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). To investigate the effects of tantalum boride coating on the microenvironment, rabbit bone marrow stromal cells (BMSCs), and RAW 264.7 cells were respectively seeded on the sample surface and relevant experiments were conducted in vitro. The pure tantalum coating (Ta) and naked TC4 were prepared as controls. Our results showed that the Ta-B coating enhanced cell proliferation and adhesion and inhibited the inflammatory response. Findings of alkaline phosphatase (ALP) staining, alizarin red staining and real-time PCR for osteoblastic gene expression indicated that Ta-B and Ta coating improve the osteogenesis, in which Ta-B coating showed higher osteogenesis than Ta coating. Thus, this study suggests that Ta-B coating with excellent biocompatibility could have new applications for wound healing in bone tissue engineering.

Preparation, Microstructure, Mechanical Properties and Biocompatibility of Ta-Coated 3Y-TZP Ceramic Deposited by a Plasma Surface Alloying Technique

A Ta coating has been successfully fabricated on the surface of zirconia polycrystals ceramic (3 mol% yttria, 3Y-TZP) by a plasma surface alloying technique. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that a α-Ta coating with a continuous and compact surface morphology which consisted of a deposited layer with a thickness of 390 nm and a diffusion layer with a thickness of 200 nm covered the 3Y-TZP. Due to the effect of inhabitation the t→m transformation by the deposited Ta coating, the biaxial flexural strength caused by the phase transformation during hydrothermal aging is reduced e.g. p < 0.05 after 20 h and/or 100 h. In addition, the Ta coating shows non-cytotoxicity and improved proliferation ability of osteoblasts.

Antibacterial effects of silver incorporated zeolite coatings on 3D printed porous stainless steels

Functionalization of porous metals with antibacterial coatings is hotly pursued in recent decade. Here we fabricated a highly porous stainless steel component by selective laser melting and then coated with silver incorporated zeolite by in situ hydrothermal crystallization method. The morphology of their surface was investigated by scanning electron microscopy. The inhibition of Escherichia coli and Staphylococcus aureus were identified by bacterial viability studies after 24 h of incubation. More importantly, the obtained coatings show better osteointegration by spreading bone marrow stromal cells (BMSCs) after cultured with different scaffold extract solutions for 1, 3, and 5 days. These results suggest that silver incorporated zeolite coatings on 3D printed porous stainless steels exhibit better antibacterial activity and biocompatibility, showing potential application in the field of medical implant materials.

Fabrication and In Vitro Evaluation of 3D Printed Porous Polyetherimide Scaffolds for Bone Tissue Engineering

For bone tissue engineering, the porous scaffold should provide a biocompatible environment for cell adhesion, proliferation, and differentiation and match the mechanical properties of native bone tissue. In this work, we fabricated porous polyetherimide (PEI) scaffolds using a three-dimensional (3D) printing system, and the pore size was set as 800 μm. The morphology of 3D PEI scaffolds was characterized by the scanning electron microscope. To investigate the mechanical properties of the 3D PEI scaffold, the compressive mechanical test was performed via an electronic universal testing system. For the in vitro cell experiment, bone marrow stromal cells (BMSCs) were cultured on the surface of the 3D PEI scaffold and PEI slice, and cytotoxicity, cell adhesion, and cell proliferation were detected to verify their biocompatibility. Besides, the alkaline phosphatase staining and Alizarin Red staining were performed on the BMSCs of different samples to evaluate the osteogenic differentiation. Through these studies, we found that the 3D PEI scaffold showed an interconnected porous structure, which was consistent with the design. The elastic modulus of the 3D PEI scaffold (941.33 ± 65.26 MPa) falls in the range of modulus for the native cancellous bone. Moreover, the cell proliferation and morphology on the 3D PEI scaffold were better than those on the PEI slice, which revealed that the porous scaffold has good biocompatibility and that no toxic substances were produced during the progress of high-temperature 3D printing. The osteogenic differentiation level of the 3D PEI scaffold and PEI slice was equal and ordinary. All of these results suggest the 3D printed PEI scaffold would be a potential strategy for bone tissue engineering.