Stephen Daniels

Cold Air Plasma To Decontaminate Inanimate Surfaces of the Hospital Environment

ABSTRACT The hospital environment harbors bacteria that may cause health care-associated infections. Microorganisms, such as multiresistant bacteria, can spread around the patients inanimate environment. Some recently introduced biodecontamination approaches in hospitals have significant limitations due to the toxic nature of the gases and the length of time required for aeration. This study evaluated the in vitro use of cold air plasma as an efficient alternative to traditional methods of biodecontamination of hospital surfaces. Cultures of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), extended-spectrum-β-lactamase (ESBL)-producing Escherichia coli, and Acinetobacter baumannii were applied to different materials similar to those found in the hospital environment. Artificially contaminated sections of marmoleum, mattress, polypropylene, powder-coated mild steel, and stainless steel were then exposed to a cold air pressure plasma single jet for 30 s, 60 s, and 90 s, operating at approximately 25 W and 12 liters/min flow rate. Direct plasma exposure successfully reduced the bacterial load by log 3 for MRSA, log 2.7 for VRE, log 2 for ESBL-producing E. coli, and log 1.7 for A. baumannii. The present report confirms the efficient antibacterial activity of a cold air plasma single-jet plume on nosocomial bacterially contaminated surfaces over a short period of time and highlights its potential for routine biodecontamination in the clinical environment.

Detecting Clostridium difficile Spores from Inanimate Surfaces of the Hospital Environment: Which Method Is Best?

ABSTRACT The recovery of Clostridium difficile spores from hospital surfaces was assessed using rayon swabs, flocked swabs, and contact plates. The contact plate method was less laborious, achieved higher recovery percentages, and detected spores at lower inocula than swabs. Rayon swabs were the least efficient method. However, further studies are required in health care settings.

What is the best method? Recovery of methicillin-resistant Staphylococcus aureus and extended-spectrum β-lactamase-producing Escherichia coli from inanimate hospital surfaces.

Environmental sampling in hospitals, when required, needs to be reliable. We evaluated different methods of sampling methicillin-resistant Staphylococcus aureus and extended-spectrum β-lactamase-producing Escherichia coli on 5 materials of the hospital setting. Petrifilms and contact plates were superior to swabs for all of the surfaces studied.

Real-time control of electron density in a capacitively coupled plasma

Reactive ion etching (RIE) is sensitive to changes in chamber conditions, such as wall seasoning, which have a deleterious effect on process reproducibility. The application of real time, closed loop control to RIE may reduce this sensitivity and facilitate production with tighter tolerances. The real-time, closed loop control of plasma density with RF power in a capacitively coupled argon plasma using a hairpin resonance probe as a sensor is described. Elementary control analysis shows that an integral controller provides stable and effective set point tracking and disturbance attenuation. The trade off between performance and robustness may be quantified in terms of one parameter, namely the position of the closed loop pole. Experimental results are presented, which are consistent with the theoretical analysis.

Attenuation of wall disturbances in an electron cyclotron resonance oxygen–argon plasma using real time control

Present practice in plasma-assisted semiconductor manufacturing specifies recipes in terms of inputs such as gas flow rates, power and pressure. However, ostensibly identical chambers running identical recipes may produce very different results. Extensive chamber matching, i.e., initial iterative, empirical tuning of the process recipe, which entails time-consuming, ex situ statistical analysis of process metrics such as etch depth, uniformity, anisotropy and selectivity, is required to ensure acceptable results. Once matched, chambers are run open loop and are thus sensitive to disturbances such as actuator drift, wall seasoning and substrate loading, which may impact negatively on process reproducibility. An alternative approach, which may obviate the need for chamber matching and reduce the sensitivity of process metrics to exogenous disturbances, would be to specify a recipe in terms of quantities such as active species densities, and to regulate these in real time by adjusting the inputs with a suita...

Similarity Ratio Analysis for Early Stage Fault Detection with Optical Emission Spectrometer in Plasma Etching Process

A Similarity Ratio Analysis (SRA) method is proposed for early-stage Fault Detection (FD) in plasma etching processes using real-time Optical Emission Spectrometer (OES) data as input. The SRA method can help to realise a highly precise control system by detecting abnormal etch-rate faults in real-time during an etching process. The method processes spectrum scans at successive time points and uses a windowing mechanism over the time series to alleviate problems with timing uncertainties due to process shift from one process run to another. A SRA library is first built to capture features of a healthy etching process. By comparing with the SRA library, a Similarity Ratio (SR) statistic is then calculated for each spectrum scan as the monitored process progresses. A fault detection mechanism, named 3-Warning-1-Alarm (3W1A), takes the SR values as inputs and triggers a system alarm when certain conditions are satisfied. This design reduces the chance of false alarm, and provides a reliable fault reporting service. The SRA method is demonstrated on a real semiconductor manufacturing dataset. The effectiveness of SRA-based fault detection is evaluated using a time-series SR test and also using a post-process SR test. The time-series SR provides an early-stage fault detection service, so less energy and materials will be wasted by faulty processing. The post-process SR provides a fault detection service with higher reliability than the time-series SR, but with fault testing conducted only after each process run completes.

Investigation of O2 and SF6 plasma interactions on thermally stable damage resistant poly phenyl-methyl silsesquioxane low-k films

The need for improved device performance has led the microelectronics industry to consider alternate materials to use as interlayer dielectrics. Thermally stable low dielectric constant (low-k) materials, with minimal dielectric constant variation during plasma exposure are essential for microelectronic applications. Here we report on the deposition and characterisation of low-k poly phenyl-methyl silsesquioxane films having less k-variation upon interaction with O2 and SF6 plasmas compared to the other reported silsesquioxane materials. Structural transformation and thermal stability of the films during annealing was studied using Fourier transform infrared spectroscopy (FTIR). Even though significant removal of the film occurred with SF6 plasma exposure, no considerable variation of the k-value was observed with both O2 and SF6 plasma exposures. X-ray photoelectron spectroscopic (XPS) analysis was used to investigate the surface modification of the films resulting from plasma exposure. The higher dielectric stability is due to the insignificant moisture intake of the films after plasma treatment which is clear from the FTIR and XPS analysis.