Oxygen Plasma Processing Research Articles

Carbon Nanotube Reinforced Natural Fibers for Biodegradable Nanocomposites

Natural fiber-reinforced nanocomposites (NFRCs) are proved as the best alternative for synthetic composites in view of cost and environmental effects. NFRCs have been produced from agro-waste such as banana tree fiber (BFs), because BF are strong, light-weight, and have smaller elongation. To improve the quality of BF, multiwall carbon nanotubes (MWCNTs) are used as reinforcing filler. MWCNTs are functionalized by an ecofriendly radio frequency oxygen plasma processing method. Cellulose nano-crystals (CNC) are extracted from BFs by double hydrolysis process and a simple dip-drying technique has been used to produce NFRCs. Field emission scanning electron micrographs and transmission electron microscopy conform the well functionalization of MWCNTs and also ensure homogeneous incorporation in the BF matrix. The composites continue thermally stable corresponding to BFs. Mechanical strength of the NFRCs are improved owing to the incorporation of MWCNTs. Functional groups in the BFs, CNC and NFRCs are investigated by Fourier transform infrared spectroscopy. The current density of the sample is increased 1000 times than the raw fibers and conductivity increases up to 17 Sm^-1, which increases with temperature under the applied voltage 100 V and shows the linier characterization. Therefore, these light-weight biodegradable NFRCs encourage its ability as cost effective industrial conductive composite as usable in electronic devices.

Defect Engineering for Quantum Grade Rare-Earth Nanocrystals.

Nanostructured systems that combine optical and spin transitions offer new functionalities for quantum technologies by providing efficient quantum light-matter interfaces. Rare-earth (RE) ion-doped nanoparticles are promising in this field as they show long-lived optical and spin quantum states. However, further development of their use in highly demanding applications, such as scalable single-ion-based quantum processors, requires controlling defects that currently limit coherence lifetimes. In this work, we show that a post-treatment process that includes multistep high-temperature annealing followed by high-power microwave oxygen plasma processing advantageously improves key properties for quantum technologies. We obtain single crystalline Eu3+:Y2O3 nanoparticles (NPs) of 100 nm diameter, presenting bulk-like inhomogeneous line widths (Γinh) and population lifetimes (T1). Furthermore, a significant coherence lifetime (T2) extension, up to a factor of 5, is successfully achieved by modifying the oxygen-related point defects in the NPs by the oxygen plasma treatment. These promising results confirm the potential of engineered RE NPs to integrate devices such as cavity-based single-photon sources, quantum memories, and processors. In addition, our strategy could be applied to a large variety of oxides to obtain outstanding crystalline quality NPs for a broad range of applications.

Surface Engineering of Low-Temperature Processed Mesoporous TiO2 via Oxygen Plasma for Flexible Perovskite Solar Cells.

A major problem in the application of mesoporous TiO2 as an electron transport layer for flexible perovskite solar cells is that a high-temperature sintering process is required to remove organic additives from the TiO2 layer. A facile oxygen plasma process is herein demonstrated to fabricate mesoporous-structured perovskite solar cells with significant photovoltaic performance at low temperatures. When the low-temperature processed TiO2 layer is modified via oxygen plasma, the organic additives in the TiO2 layer that hinder the charge transport process are successfully decomposed. The oxygen plasma treatment improves the wettability and infiltration of the perovskite layer and also passivates the oxygen vacancy related traps in TiO2. Hence, the oxygen plasma treatment evidently enhances charge extraction and transport, thereby improving photovoltaic performance and decreasing hysteresis.

Long optical coherence times of shallow-implanted, negatively charged silicon vacancy centers in diamond

The creation of single, negatively charged silicon vacancy (SiV−) centers in well-defined diamond layers close to the host surface is a crucial step for the development of diamond-based quantum optic devices with many applications in nanophotonics, quantum sensing, or quantum information science. Here, we report on the creation of shallow (10 nm below the surface), single SiV− centers in diamond using low energy Si+ ion implantation with subsequent high temperature annealing at 1500 °C. We show transition linewidths down to 99 MHz and narrow inhomogeneous distributions. Furthermore, we achieved a reduction of homogeneous linewidths by a factor of 2 after removing subsurface damage using oxygen plasma processing. These results not only give insights into the formation process of SiV− centers but also indicate a favorable processing method to fabricate shallow single quantum emitters in diamond perfectly suited for coupling to nanostructures on the diamond surface.

Effects of oxygen and tetravinylsilane plasma treatments on mechanical and interfacial properties of flax yarns in thermoset matrix composites

This work is focused on the assessment of the effect of oxygen and polymer plasma tetravinylsilane (pp-TVS) treatments on the adhesion of flax yarns with epoxy and vinylester thermoset matrices. These low temperature plasma processes have been selected as more environmentally friendly alternatives to traditional chemical treatments. Tensile tests performed on single flax yarns revealed a reduction in their mechanical properties after plasma treatments. In particular, a tensile strength reduction of 36.4% was detected after the oxygen plasma treatment using 100 W of plasma power. The morphological analysis highlighted that this result is mainly ascribed to the ablation action produced by oxygen plasma process. In the case of pp-TVS, both morphological and Fourier transform infrared spectroscopy analysis confirmed the presence of a homogeneous tetravinylsilane film on the surface of the yarns. The interfacial adhesion of untreated, oxygen plasma treated, and plasma-polymer coated flax yarns has been determined by single fibre fragmentation test. The plasma polymer deposition can produce a significant improvement of the adhesion property of flax yarns with both epoxy and vinylester matrices. An increase of the interfacial shear strength values of 114% and 71% was found after the TVS film deposition in epoxy and vinylester composites, respectively. These results were confirmed by high-resolution micro-CT, photoelasticity analysis and FE-SEM observations.

Facile Functionalization via Plasma-Enhanced Chemical Vapor Deposition for the Effective Filtration of Oily Aerosol.

With the growing concern about the health impacts associated with airborne particles, there is a pressing need to design an effective filter device. The objective of this study is to investigate the effect of plasma-based surface modifications on static charges of electrospun filter media and their resulting filtration performance. Polystyrene (PS) electrospun web (ES) had inherent static charges of ~3.7 kV due to its electric field-driven process, displaying effective filtration performance. When oxygen species were created on the surface by the oxygen plasma process, static charges of electret media decreased, deteriorating the filter performance. When the web surface was fluorinated by the plasma-enhanced chemical vapor deposition (PECVD), the filtration efficiency against oily aerosol significantly increased due to the combined effect of decreased wettability and strong static charges (~−3.9 kV). Solid particles on the charged media formed dendrites as particles were attracted to other layers of particles, building up a pressure drop. The PECVD process is suggested as a facile functionalization method for effective filter design, particularly for capturing oily aerosol.

Surface plasmon-enhanced UV-emission from ZnO by aluminum bowtie nanoantenna arrays

Aluminum bowtie nanoantenna arrays fabricated by colloid lithography followed by oxygen plasma processing were used to demonstrate the localized-surface-plasmon enhancement of UV light emission from ZnO grown by atomic layer deposition. 4-fold photoluminescence enhancement in the peak of the near band edge emissions was obtained by introducing Al nanotriangles with the gap distance of 31 nm by accurate control of the time of oxygen plasma treatment. Extinction spectra and theoretical simulations showed that this improvement benefited from the resonance coupling between the surface plasmons and the excitons of ZnO and the tremendously elevated local electromagnetic fields across the gaps. This cost-effective and facile approach paves an attractive way for high performance optoelectronic devices.

Surface modification of polypropylene mesh devices with cyclodextrin via cold plasma for hernia repair: Characterization and antibacterial properties

Light weight polypropylene (PP) mesh is the most widely used implant among all other synthetic meshes for hernia repair. However, infection is the complication associated to all synthetic meshes after hernia repair. Thus, to manage mesh related infection; antibacterial drug is generally loaded to surgical implants to supply drug locally in mesh implanted site. Nevertheless, PP mesh restricts the loading of antibacterial drug at operated area due to its low wettability. The aim of this study was to introduce a novel antimicrobial PP mesh modified with β-cyclodextrine (CD) and loaded with antimicrobial agent for infection prevention. A cold oxygen plasma treatment was able to activate the surfaces of polypropylene fibers, and then CD was incorporated onto the surfaces of PP fibers. Afterward, triclosan, as a model antibacterial agent, was loaded into CD cavity to provide desired antibacterial functions. The modified polypropylene mesh samples CD-Tric-1, CD-Tric-3 exhibited excellent inhibition zone and continuous antibacterial efficacy against E. coli and S. aureus up to 6 and 7 days respectively. Results of AFM, SEM, FTIR and antibacterial tests evidenced that oxygen plasma process is necessary to increase chemical connection between CD molecules and PP fibers. The samples were also characterized by using EDX, XRD, TGA, DSC and water contact angle.

Method for Measurement of Multi-Degrees-of-Freedom Motion Parameters Based on Polydimethylsiloxane Cross-Coupling Diffraction Gratings

This work presents a multi-degrees-of-freedom motion parameter measurement method based on the use of cross-coupling diffraction gratings that were prepared on the two sides of a polydimethylsiloxane (PDMS) substrate using oxygen plasma processing technology. The laser beam that travels pass the cross-coupling optical grating would be diffracted into a two-dimensional spot array. The displacement and the gap size of the spot-array were functions of the movement of the laser source, as explained by the Fraunhofer diffraction effect. A 480 × 640 pixel charge-coupled device (CCD) was used to acquire images of the two-dimensional spot-array in real time. A proposed algorithm was then used to obtain the motion parameters. Using this method and the CCD described above, the resolutions of the displacement and the deflection angle were 0.18 μm and 0.0075 rad, respectively. Additionally, a CCD with a higher pixel count could improve the resolutions of the displacement and the deflection angle to sub-nanometer and micro-radian scales, respectively. Finally, the dynamic positions of hovering rotorcraft have been tracked and checked using the proposed method, which can be used to correct the craft’s position and provide a method for aircraft stabilization in the sky.

A top-down approach for fabricating three-dimensional closed hollow nanostructures with permeable thin metal walls.

We report on a top-down method for the controlled fabrication of three-dimensional (3D), closed, thin-shelled, hollow nanostructures (nanocages) on planar supports. The presented approach is based on conventional microelectronic fabrication processes and exploits the permeability of thin metal films to hollow-out polymer-filled metal nanocages through an oxygen-plasma process. The technique is used for fabricating arrays of cylindrical nanocages made of thin Al shells on silicon substrates. This hollow metal configuration features optical resonance as revealed by spectral reflectance measurements and numerical simulations. The fabricated nanocages were demonstrated as a refractometric sensor with a measured bulk sensitivity of 327 nm/refractive index unit (RIU). The pattern design flexibility and controllability offered by top-down nanofabrication techniques opens the door to the possibility of massive integration of these hollow 3D nano-objects on a chip for applications such as nanocontainers, nanoreactors, nanofluidics, nano-biosensors and photonic devices.

Macroporous Calcium Phosphate/Chitosan Composites Prepared via Unidirectional Ice Segregation and Subsequent Freeze-Drying.

Calcium phosphate chitosan-based composites have gained much interest in recent years for biomedical purposes. In this paper, three-dimensional calcium phosphate chitosan-based composites with different mineral contents were produced using a green method called ice segregation induced self-assembly (ISISA). In this methodology, ice crystals were used as a template to produce porous structures from an aqueous solution of chitosan (CS) and hydroxyapatite (Hap) also containing acetic acid (pH = 4.5). For better characterization of the nature of the inorganic matter entrapped within the resulting composite, we performed either oxygen plasma or calcination processes to remove the organic matter. The nature of the phosphate salts was studied by XRD and NMR studies. Amorphous calcium phosphate (ACP) was identified as the mineral phase in the composites submitted to oxygen plasma, whereas crystalline Hap was obtained after calcination. SEM microscopy revealed the formation of porous structures (porosity around 80–85%) in the original composites, as well as in the inorganic matrices obtained after calcination, with porous channels of up to 50 µm in diameter in the former case and of up to 20 µm in the latter. The biocompatibility of the composites was assessed using two different cell lines: C2C12GFP premyoblastic cells and MC3T3 preosteoblastic cells.

A silk-fibroin-based transparent triboelectric generator suitable for autonomous sensor network

In recent years, a new electrification-based mechanism called triboelectric generator (TEG) has been demonstrated as a stable and renewable power source to convert ambient energy into remarkable electrical output. Various TEG configurations have been proposed to enhance the output performance focusing on improvements to its working principle and structural geometry. In order for TEG to make an impact in real life applications, further improvement is needed in particular in the choice of the pair of electrification materials beyond the choice of traditional materials that have been employed in the construction of TEGs. Here, we investigate silk fibroin as a novel material for TEG that occupies a top-tier position in the triboelectric series and possesses the outstanding ability of losing electrons easily. Several technical challenges have been successfully addressed and are shown herein. For instance, an oxygen plasma process is employed to improve the interfacial energy between silk fibroin film and substrate by chemical modification and nanoscale roughness increase, which allows for the reliable switching mechanism needed to generate the electric power. The comprehensive study and the systematical measurement were carried out to study the fabricated TEG, including electrical output test, stability and reliability, humidity effect, and performance comparison with traditional materials. The silk fibroin is proven to be a promising material to construct TEG, and the fabricated TEG exhibits stable high-output performance, with maximum voltage, current, and power density of 268V, 5.78μA, and 193.6μW/cm2, respectively, to a load of 40MΩ. Furthermore, this silk fibroin film has two advantageous potentials for the development of TEGs: higher than 90% transmittance in the visible spectrum region and controllable solubility in aqueous solutions. The former property preserves the intrinsic optical property of TEG and enables the realisation of an ultra-transparent device, while the latter moves us closer to the attractive future vision of realising TEG systems that biodegradable for environmental sensing or implantable for biomedical applications. Additionally, we demonstrate that this silk-fibroin-based TEG can directly produce energy to power two 4-bit liquid crystal displays (LCDs) and to actuate a microscale cantilever. As the first demonstration of TEG applied to power a mechanical micro-device, this TEG-micro-cantilever microsystem shows an attractive potential to realise fully integrated smart transducers that are needed for autonomous sensor networks.

Theoretical study of defect impact on two-dimensional MoS2

Our theoretical findings demonstrate for the first time a possibility of band-gap engineering of monolayer MoS2 crystals by oxygen and the presence of vacancies. Oxygen atoms are revealed to substitute sulfur ones, forming stable MoS2−xOx ternary compounds, or adsorb on top of the sulfur atoms. The substituting oxygen provides a decrease of the band gap from 1.86 to 1.64 eV and transforms the material from a direct-gap to an indirect-gap semiconductor. The surface adsorbed oxygen atoms decrease the band gap up to 0.98 eV depending on their location tending to the metallic character of the electron energy bands at a high concentration of the adsorbed atoms. Oxygen plasma processing is proposed as an effective technology for such band-gap modifications.

(Invited) Integration of 2-D Materials for Electronic Device Application

In this work, we present our recent progresses on the integration of 2-d materials (TMD, BP, TMC) for the electronic device application. In spite of the recent heightened interest in molybdenum disulfide (MoS2) as a two-dimensional material with substantial bandgaps and reasonably high carrier mobility, a method for the layer-controlled and large-scale synthesis of high quality MoS2 films has not previously been established. Here, we demonstrate that layer-controlled and large-area CVD MoS2 films can be achieved by treating the surfaces of their bottom SiO2 substrates with oxygen plasma process. In addition, by using various polymers, we present that the doping level of MoS2 layers can be controlled for realization of electronic devices.Black phosphorous (BP) is known as a most stable allotrope of phosphorous. Recent studies have shown that BP is an elemental layered material, making it possible to obtain layered structures through mechanical cleavage. In this study, we report the preparation of thickness-controlled few-layer black phosphorus (BP) films through the modulated plasma treatment of BP flakes. Not only does the plasma treatment control the thickness of the BP film, it also removes the chemical degradation of the exposed oxidized BP surface, which results in enhanced field-effect transistor (FET) performance.

Low temperature temporal and spatial atomic layer deposition of TiO2 films

Titanium dioxide films were grown by atomic layer deposition (ALD) using titanium tetraisopropoxide as a titanium precursor and water, ozone, or oxygen plasma as coreactants. Low temperatures (80–120 °C) were used to grow moisture barrier TiO2 films on polyethylene naphthalate. The maximum growth per cycle for water, ozone, and oxygen plasma processes were 0.33, 0.12, and 0.56 Å/cycle, respectively. X-ray photoelectron spectrometry was used to evaluate the chemical composition of the layers and the origin of the carbon contamination was studied by deconvoluting carbon C1s peaks. In plasma-assisted ALD, the film properties were dependent on the energy dose supplied by the plasma. TiO2 films were also successfully deposited by using a spatial ALD (SALD) system based on the results from the temporal ALD. Similar properties were measured compared to the temporal ALD deposited TiO2, but the deposition time could be reduced using SALD. The TiO2 films deposited by plasma-assisted ALD showed better moisture barrier properties than the layers deposited by thermal processes. Water vapor transmission rate values lower than 5 × 10−4 g day−1 m−2 (38 °C and 90% RH) was measured for 20 nm of TiO2 film deposited by plasma-assisted ALD.

Photoelectric characteristics of metal-Ga2O3-GaAs structures

We investigate the effect of thermal annealing in argon and of oxygen plasma processing on the photoelectric properties of GaAs-Ga2O3-Me structures. Gallium-oxide films are fabricated by photostimulated electrochemical oxidation of epitaxial gallium-arsenide layers with n-type conductivity. The as-deposited films were amorphous, but their processing in oxygen plasma led to the nucleation of β-Ga2O3 crystallites. The unannealed films are nontransparent in the visible and ultraviolet (UV) ranges and there is no photocurrent in structures based on them. After annealing at 900°C for 30 min, the gallium-oxide films contain only β-Ga2O3 crystallites and become transparent. Under illumination of the Ga2O3-GaAs structures with visible light, the photocurrent appears. This effect can be attributed to radiation absorption in GaAs. The photocurrent and its voltage dependence are determined by the time of exposure to the oxygen plasma. In the UV range, the sensitivity of the structures increases with decreasing radiation wavelength, starting at λ ≤ 230 nm. This is due to absorption in the Ga2O3 film. Reduction in the structure sensitivity with an increase in the time of exposure to oxygen plasma can be caused by the incorporation of defects both at the Ga2O3-GaAs interface and in the Ga2O3 film.

Morphological and spectroscopic analysis of argon- and oxygen-ions treated thin ferritin films

Ferritin is the main iron storage protein in living systems. Recent studies demonstrated that the chemical species present in the ferritin core and their chemical coordination can be different between physiological and pathological ferritin proteins. Therefore it is of paramount importance revealing the presence of metals other than iron and their oxidation state in the protein core.In this work we investigated and compared the use of argon and oxygen plasma processes for the erosion of the protein shell surrounding the mineral core, which is necessary for the chemical analysis of the ferritin core by surface sensitive technique such as X-ray photoelectron spectroscopy. We find that both the proposed etching processes are effective in the disruption of the protein shell and in the exposure of the Fe inside the core of the molecules. Neither oxygen nor argon plasma induced significant artifacts in the samples nor produce dramatic roughening in the surface allowing for a controlled thinning of the ferritin film. In the plasma treated samples X-ray photoelectron spectroscopy detected the Fe(III) oxidation state of metal present inside the ferritin cavity.

Layer-controlled CVD growth of large-area two-dimensional MoS2 films.

In spite of the recent heightened interest in molybdenum disulfide (MoS2) as a two-dimensional material with substantial bandgaps and reasonably high carrier mobility, a method for the layer-controlled and large-scale synthesis of high quality MoS2 films has not previously been established. Here, we demonstrate that layer-controlled and large-area CVD MoS2 films can be achieved by treating the surfaces of their bottom SiO2 substrates with the oxygen plasma process. Raman mapping, UV-Vis, and PL mapping are performed to show that mono, bi, and trilayer MoS2 films grown on the plasma treated substrates fully cover the centimeter scale substrates with a uniform thickness. Our TEM images also present the single crystalline nature of the monolayer MoS2 film and the formation of the layer-controlled bi- and tri-layer MoS2 films. Back-gated transistors fabricated on these MoS2 films are found to exhibit the high current on/off ratio of ∼10(6) and high mobility values of 3.6 cm(2) V(-1) s(-1) (monolayer), 8.2 cm(2) V(-1) s(-1) (bilayer), and 15.6 cm(2) V(-1) s(-1) (trilayer). Our results are expected to have a significant impact on further studies of the MoS2 growth mechanism as well as on the scaled layer-controlled production of high quality MoS2 films for a wide range of applications.

Study on the Manufacturing Process of Polymer Microfluidic Chip with Integrated Cu Micro Array Electrode

To produce perfect polymer microfluidic chip with integrated metal micro array electrode, an oxygen-plasma assisted manufacturing process was developed. The Cu micro array electrodes on the poly substrate was formed by photolithography, sputtering and wet etching; the micro channels on the polymer plate were hot-embossed using metal master; the bonding of cover plate and substrate using thermal bonding. The surface of the polymer plate with micro channels was treated by oxygen-plasma before thermal bonding. The oxygen-plasma treatment could decrease thermal bonding temperature from 100 °C to 85 °C. The bonding of this chip is complete, the micro electrode array keeps its integrity, and the micro channel is not distorted obviously.

Integration of tungsten layers for the mass fabrication of WO3-based pH-sensitive potentiometric microsensors

(W/WO3–Ag/AgCl) and (Pt/IrO2–Ag/AgCl) potentiometric microdevices were developed for pH measurement in liquid phase using a (Pt–Pt–Ag/AgCl) electrochemical microcells (ElecCell) silicon-based technological platform. A special emphasis was placed on the mass fabrication of the W/WO3 microelectrode using sputtering deposition and oxygen plasma processes. Compared to the Pt/IrO2-based one, the W/WO3-based microelectrodes showed lower performances regarding the pH measurement. Nevertheless, since W/WO3 microelectrodes yielded quasi-Nernstian sensitivity (around 55mV/pH) in the [2–12] pH range, tungsten oxide WO3 can be considered as a good candidate for the mass fabrication of pH microsensors using silicon technologies, even if important temporal drift (at least 6mV/h) and high hysteresis (around 50mV) were also evidenced.