Mass-spectroscopy and modeling of capacitive coupled hydrogen plasmas

This work presents the characterization of a radio-frequency, capacitively coupled, symmetric, hydrogen plasma. Both steady-state operation and the time-prole of the afterglow when RF power is terminated are investigated. Fluxes of the hydrogen ions, H+ , H+2, H+3, at the grounded electrode are measured with an energy-resolved mass spectrometer. Spatial proles of the electron density are measured using a hairpin probe. Particle-in-cell simulations including a complex hydrogen chemistry are performed which enable direct comparison to the experiment. In the steady-state operation, the electron density increases with both power and pressure, and the ion flux magnitudes and energy distributions are found to vary with power. The H+3 ion flux decreases with power and pressure, whereas the H+ and H+2 ion fluxes increase with power and pressure, with approximately equal fluxes at the highest pressure/power combination of 30.0 Pa and 750V peak-to-peak. In conjunction with the PIC results, it is determined that the H+3 ion remains the dominant ion in the plasma for all investigated parameter space, and that the strong variation in ion flux magnitudes and energy-distributions are due to fast-ion induced chemistry occurring in the sheath at the grounded electrode. A simple theoretical model is developed in order to estimate the electron temperature at the sheath edge if the IEDFs and electron density are known. Investigations of the afterglow include time-evolution of the H+3 ion energy distribution, spatio-temporal proles of the electron density, and particle-in-cell simulations. The measured H+3 ion flux energy distribution persists substantially longer into the afterglow than is seen in the PIC simulations. This unusual result is explained in the hypothesis of super elastic collision of vibrationally excited hydrogenmolecule with an electron resulting in energy transfer to the electron. The mechanics such super-elastic collisions are not included in the PIC simulation, and this is consistent with the discrepancy between the simulation and the experiment. Electron density measurements show a substantial increase in the density, as much as a factor of four, sharply rising immediately after the RF voltage is switched off. Small density rises, of order 10%, are seen in the simulation. An analysis showing the validity of the measurements, and two hypothesis to explain the density rise are presented. A method for determining the electron temperature time-prole in the afterglow is introduced

Pulsed plasma physical vapour deposition approach towards the facile synthesis of multilayer and monolayer graphene for anticoagulation applications

We demonstrate the growth of multilayer and single layer graphene on copper foil using bipolar pulsed direct current (DC) magnetron sputtering of a graphite target in pure Ar atmosphere. Single layer and few layer graphene films (SG and FLG) are deposited at temperatures ranging from 700-920 °C in less than 30 minutes. We find that the deposition and post-deposition annealing temperatures influence the layer thickness and quality of the graphene films formed. The films were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), High resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and optical transmission spectroscopy techniques. Based on the above studies, a diffusion controlled mechanism was proposed for the graphene growth. A single step whole blood assay was used to investigate the anticoagulant activity of graphene surfaces. Platelet adhesion, activation and morphological changes on the graphene/glass surfaces compared to bare glass were analysed using fluorescence microscopy and SEM techniques. We have found significant suppression of the platelet adhesion, activation and aggregation on the graphene covered surfaces compared to the bare glass, indicating the anticoagulant activity of the deposited graphene films. Our production technique represents an industrially relevant method for the growth of single and few layer graphene for various applications including the biomedical field

Real-time Plasma Controlled Chemistry in a Two-Frequency, Confined Plasma Etcher

The physics issues of developing model-based control of plasma etching are presented. A novel methodology for incorporating real-time model-based control of plasma processing systems is developed. The methodology is developed for control of two dependent variables (ion flux and chemical densities) by two independent controls (27 MHz power and O2flow). A phenomenological physics model of the nonlinear coupling between the independent controls and the dependent variables of the plasma is presented. By using a design of experiment, the functional dependencies of the response surface are determined. In conjunction with the physical model, the dependencies are used to deconvolve the sensor signals onto the control inputs, allowing compensation of the interaction between control paths. The compensated sensor signals and compensated set–points are then used as inputs to proportional-integral-derivative controllers to adjust radio frequency power and oxygen flow to yield the desired ion flux and chemical density. To illustrate the methodology, model-based real-time control is realized in a commercial semiconductor dielectric etch chamber. The two radio frequency symmetric diode operates with typical commercial fluorocarbon feed-gas mixtures (Ar/O2/C4F8). Key parameters for dielectric etching are known to include ion flux to the surface and surface flux of oxygen containing species. Control is demonstrated using diagnostics of electrode-surface ion current, and chemical densities of O, O2, and CO measured by optical emission spectrometry and/or mass spectrometry. Using our model-based real-time control, the set-point tracking accuracy to changes in chemical species density and ion flux is enhanced

Pulsed-Plasma Physical Vapor Deposition Approach Toward the Facile Synthesis of Multilayer and Monolayer Graphene for Anticoagulation Applications

We demonstrate the growth of multilayer and single-layer graphene on copper foil using bipolar pulsed direct current (DC) magnetron sputtering of a graphite target in pure argon atmosphere. Single-layer graphene (SG) and few-layer graphene (FLG) films are deposited at temperatures ranging from 700 °C to 920 °C within <30 min. We find that the deposition and post-deposition annealing temperatures influence the layer thickness and quality of the graphene films formed. The films were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and optical transmission spectroscopy techniques. Based on the above studies, a diffusion-controlled mechanism was proposed for the graphene growth. A single-step whole blood assay was used to investigate the anticoagulant activity of graphene surfaces. Platelet adhesion, activation, and morphological changes on the graphene/glass surfaces, compared to bare glass, were analyzed using fluorescence microscopy and SEM techniques. We have found significant suppression of the platelet adhesion, activation, and aggregation on the graphene-covered surfaces, compared to the bare glass, indicating the anticoagulant activity of the deposited graphene films. Our production technique represents an industrially relevant method for the growth of SG and FLG for various applications including the biomedical field