Oxygen Plasma Techniques Research Articles

Comparison of Al and Cu masks used for patterning boron-doped diamonds in oxygen plasma

In this paper we investigate the influence of different metallic (or metal-based) masking materials and plasma techniques for etching and patterning polycrystalline boron-doped diamond thin films. Lift-off technique was used to prepare various testing mask patterns with dimensions ranging from 1 μm to 15 μm. The results of plasma etching utilizing 100 nm Al and Cu masks are compared. Radio frequency and inductively coupled pure oxygen plasma techniques were used to obtain the fine etched structures. A simple etching scheme describing the obtained results is presented for each type of plasma technique and mask type. Although the Al mask is widely believed to have outstanding properties over other metallic materials, we found that the Cu mask exhibits lower side edge etching for both types of plasma techniques. A formation of thick and crystalline copper oxide layer in contrast with thin amorphous aluminum oxide is believed to be the reason for this behavior. Consequently, the etched structures also possessed much better side wall angles which is a key parameter for micro-fabrication of boron doped diamond microelectrodes, microfluidics, sensors and microelectromechanical devices in general.

Different types of electrospun nanofibers and their effect on microfluidic‐based immunoassay

Protein capturing on polymeric substrate of microfluidic devices is a key factor for the fabrication of immunoassay with high sensitivity. In this work, simple and versatile technique of electrospinning was used to produce electrospun nanofibrous membranes (e.NFMs) with high surface area as a substrate for microfluidic‐based immunoassay to increase sensitivity. It was found that the simultaneous use of e.NFM and 1‐Ethylethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide/N‐Hydroxysuccinimide hydroxysuccinimide as coupling agent has synergic effect on antigen immobilization onto the microchannels. It was found that the oxygen plasma technique for the creation of oxygen containing functional group like carboxyl and hydroxyl causes extreme leakage of solution through the microchannels. Thus, due to capillary effect, it is impossible to use hydrophilic substrate to modify microchannels. In order to compensate this problem, it is propose to utilize other type of polymer for the fabrication of nanofiber to answer this important question that if it is possible to enhance the sensitivity of immunoassay just by changing the polymer type? For this purpose, four different polymers, namely, polycaprolactone, poly lactic‐co‐glycolic acid, poly L‐lactic acid, and polyethersolfone were used as the based material for e.NFM fabrication. Results showed that compared with plain poly (dimethylsiloxane) surface of microchannels, poly lactic‐co‐glycolic acidand poly L‐lactic acid, which inherently contain end‐group of carboxyl in their chemical structure, can improve the protein immobilization, which leads to immunoassay signal enhancement through 1‐ethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide/N‐hydroxysuccinimide coupling chemistry, significantly.

Oxygen plasma-fragmented KMnF3 nanoparticle benefits contrast enhancement for MRI of a patient-derived tumor xenograft model

Magnetic nanoparticles (NPs) are emerging as promising candidates for the next generation of image contrast agents and their performance is largely dependent on physicochemical properties. In this paper, a new type of ‘top-down’ fabrication technique was developed to synthesize ultrasmall magnetic NPs as a contrast enhancer. In a detailed, home-made oxygen plasma generator, fragments of larger KMnF3 NPs (22 nm) were broken down into smaller (<5 nm) particles with enhanced hydrophilicity. As massive activated oxygen species were produced during the process, the plasma was able to severely etch the NPs, and vacuum UV light irradiated them heavily as well, leaving them with weak crystallinity, splitting them into ultrafine particles. Also their surface transformed from hydrophobic to hydrophilic by oxidizing the passivated ligand, evidenced by the spectroscopy and microscopy results. The fragmented NPs are characteristic of unprecedented high longitudinal relaxivity (r1 = 35.52 mM−1.s−1) and appropriate biocompatibility. In a healthy mouse, the ultrafine NPs did not exert observable toxicity, this was evaluated by histology of the main organs and hemogram analysis, including kidney and liver function analysis. More interestingly, the ultrasmall NPs had a very long circulation time, as its blood half-life was around 20 h. When applied as a contrast enhancer for MRI of the patient-derived tumor xenograft model, the accumulation of KMnF3 NPs within the tumor had an average of 12.13% ID per gram, which greatly shortened the relaxation time of the tumor. Therefore the control-to-noise ratio was significantly enhanced, relative to the same dosage of Gadopentetetic acid (Magvenist) (P < 0.001). Our primary results demonstrate that fragmentation of the NPs via our home-made oxygen plasma technique might be an effective route for fabricating ultrasmall NPs, and benefit their contrast effect when applied as MRI enhancers for clinical diagnosis of tumors.

Flexible electrochemical biosensors based on graphene nanowalls for the real-time measurement of lactate

We demonstrate a flexible biosensor for lactate detection based on l-lactate oxidase immobilized by chitosan film cross-linked with glutaraldehyde on the surface of a graphene nanowall (GNW) electrode. The oxygen-plasma technique was developed to enhance the wettability of the GNWs, and the strength of the sensor’s oxidation response depended on the concentration of lactate. First, in order to eliminate interference from other substances, biosensors were primarily tested in deionized water and displayed good electrochemical reversibility at different scan rates (20–100 mV s−1), a large index range (1.0 μM to 10.0 mM) and a low detection limit (1.0 μM) for lactate. Next, these sensors were further examined in phosphate buffer solution (to mimick human body fluids), and still exhibited high sensitivity, stability and flexibility. These results show that the GNW-based lactate biosensors possess important potential for application in clinical analysis, sports medicine and the food industry.

Clusters of α-LiFeO2 nanoparticles incorporated into multi-walled carbon nanotubes: a lithium-ion battery cathode with enhanced lithium storage properties

We report the preparation of a novel nanocomposite architecture of α-LiFeO2-MWCNT based on clusters of α-LiFeO2 nanoparticles incorporated into multiwalled carbon nanotubes (MWCNTs). The composite represents a promising cathode material for lithium-ion batteries. The preparation of the nanocomposite is achieved by combining a molten salt precipitation process and a radio frequency oxygen plasma for the first time. We demonstrate that clusters of α-LiFeO2 nanoparticles incorporated into MWCNTs are capable of delivering a stable and high reversible capacity of 147 mA h g(-1) at 1 C after 100 cycles with the first cycle Coulombic efficiency of ~95%. The rate capability of the composite is significantly improved and its reversible capacity is measured to be 101 mA h g(-1) at a high current rate of 10 C. Both rate capability and cycling stability are not simply a result of introduction of functionalized MWCNTs but most likely originate from the unique composite structure of clusters of α-LiFeO2 nanoparticles integrated into a network of MWCNTs. The excellent electrochemical performance of this new nanocomposite opens up new opportunities in the development of high-performance electrode materials for energy storage application using the radio frequency oxygen plasma technique.

Effects of laminin‐coated carbon nanotube/chitosan fibers on guided neurite growth

This study assesses the ability and potential of carbon nanotube (CNT)/chitosan to guide axon re-growth after nerve injuries. The CNT/chitosan fibers were produced via the coagulation and hydrodynamic focusing method. Fiber width and morphology were adjusted using such parameters as syringe pumping rate and the coagulant used. The CNT/chitosan fiber diameters were 50-300 μm for syringe pumping rates of 6-48 mL/h. Polyethylene glycol/NaOH (25%, w/w) solution was a suitable coagulant for forming fibers with small diameters. Physical property tests demonstrate that the CNT/chitosan composites had superior tensile strength and electrical conductivity compared with those of chitosan alone. The MTT and LDH tests reveal that CNT/chitosan composites were not cytotoxic. To improve the neural cell affinity of CNT/chitosan fibers, laminin was incorporated onto fiber surfaces via the oxygen plasma technique; cell adhesion ratio increased significantly from 3.5% to 72.2% with this surface modification. Immunofluorescence staining and SEM imaging indicate that PC12 cells adhered successfully and grew on the laminin (LN)-coated CNT/chitosan films and fibers. Experimental results show that PC12 grown on LN-coated CNT/chitosan fibers in vitro extend longitudinally oriented neurites in a manner similar to that of native peripheral nerves. With the inherent electrical properties of CNTs, oriented CNT/chitosan fibers have a potential for use as nerve conduits in nerve tissue engineering.

Surface Modification of COC Microfluidic Devices: A Comparative Study of Nitrogen Plasma Treatment and its Advantages Over Argon and Oxygen Plasma Treatments

AbstractControl of surface properties is very important in high performance microfluidic devices because appropriate functionalization of the surface of the microchannel helps to minimize adsorption of certain analytes thus improving its performance. In this regard, both the argon and oxygen plasma techniques have been used to improve the adaption of polymer surfaces to biological environments. However, the less common nitrogen plasma technique has not been used for surface modification of cyclic olefin copolymer (COC) in microfluidic applications. This paper presents a comparative study between the argon, oxygen, and nitrogen plasma treatments with the aim to identify the most suitable process for the development of a smart, disposable chip for the Bio‐MEMS application. The chemical and morphological changes of the plasma modified COC surfaces were characterized using X‐ray photoelectron spectroscopy, atomic force microscopy, and water contact angle measurements. The effect of plasma treatment on the strength of thermally bonded lap‐shear specimens was studied. The influence of plasma treatment on the integrity of thermally sealed microdevices was assessed using burst pressure tests. The plasma treatments had a significant impact on the electroosmosis flow mobility in the microchannels. The hemocompatibility of the various plasma‐modified COC surfaces was determined using the static platelets adhesion experiment. It was shown that the nitrogen plasma treatment was more effective than the argon and oxygen treatments for the modification of COC based microfluidic devices. magnified image

Processing and characterization of yttrium-stabilized zirconia thin films on polyimide from aqueous polymeric precursors

Low-temperature deposition of dense, nanocrystalline yttrium-stabilized zirconia (YSZ) thin films on polyimide (PI) substrates is illustrated using an aqueous polymeric precursor spin-coating technique. The polymeric precursor uses low-cost materials, is water-soluble and the viscosity and cation concentrations can be easily adjusted in order to vary the film thickness from 0.02 to 0.3 μm. Due to the use of water as the solvent in the YSZ precursor and the hydrophobic nature of the PI surface, surface modification processes were utilized in order to improve the wetting characteristics. Surface modification of PI substrates using wet chemical and oxygen plasma techniques led to a decrease in the precursor contact angle, and ultimately allowed for uniform film formation on both bulk and thin film PI substrates. Scanning electron microscopy, transmission electron microscopy and UV/Vis absorption illustrate that near full-density nanocrystalline thin films of YSZ can be produced at temperatures as low as 350 °C. Thermogravimetric analyses illustrate that the PI substrate does not undergo any weight loss up to these temperatures.

Comparison of the removal efficiency for organic contaminants on silicon wafers stored in plastic boxes between UV/O 3 and ECR oxygen plasma cleaning methods

When wafers are stored in a plastic storage box to protect them from airborne contaminants, volatile organics from the polymeric construction material adsorb onto the wafer surface. Both UV/O 3 and ECR oxygen plasma techniques have been found to completely remove these organic contaminants adsorbed on the silicon surfaces up to the detection limit. After cleaning, Si wafers were characterized using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and atomic force microscopy (AFM). Organic contaminants were eliminated more efficiently by the ECR oxygen plasma technique than the UV/O 3 technique when they were employed under optimum process conditions.

Functional nanostructures by organized macromolecular-metallic hybrid systems

Stabilization of nanoparticles by block copolymers does allow accurate control of particle size and inter particle distance, and offers the possibility of producing thin optically transparent films and a new technique for lithography in the nanometer range. The approach is based on micelles of diblock copolymers with a polar core, which are formed in organic solution and whose core is able to bind a transition-metal compound. Chemical conversion of the inorganic species within the nanocompartment is employed to prepare sterically stabilized inorganic crystallites or clusters. The particle size and interparticle distance of these crystallites or clusters can be controlled exclusively by the film forming block copolymer. Controlled coagulation of spherical block copolymer micelles allows to agglomerate several clusters of equal size in one compartment and to prepare strings of the clusters. After film formation the polymer shell can be removed entirely by using an oxygen plasma technique resulting in the deposition of the naked clusters on different substrates without destroying the former particle organization.

Hydrodesulphurization of thiophene by coal mineral matter and a cobalt-molybdate catalyst in a pulse reactor

A pulse reactor was used to compare the catalytic activity of a commercial desulphurization catalyst (Nalco 471) and of mineral matter from Western Kentucky coal. Hydrodesulphurization of thiophene, a model coal sulphur compound, was the reaction studied. Mineral matter was obtained from the coal in its least altered state by a low-temperature, oxygen-plasma technique commonly referred to as low-temperature ashing. Conversion is determined from the C 4 gases which are separated in a two-column Chromatographic system. At 748 K it was found that thiophene conversion with mineral matter was 12% of that with the commercial catalyst. Relative activities of hydrogenation of intermediate butenes to butane, the effect of presulphiding, and that of pyridine poisoning were also determined.