Characterization Of An Ambient Low-Temperature Plasma Probe On Thin Polymeric Films

The Plasma Pencil Atmospheric Mass Spectrometer (PPAMS) is a new surface analysis device which allows mass spectrometry (MS) to be conducted on samples under normal atmospheric conditions. This enables surface analysis that could previously not be analyzed under the current vacuum-based techniques. However, characterization of this method of surface analysis is necessary to maximize the benefits of the PPAMS device and to determine the extent to which the vacuum-based methods can be replaced.  This process of characterization involves determining the ionization rate of the plasma pencil probe, performing various experiments while changing parameters (i.e. sample concentration, thickness, and gas type), and comparing results to established methods. Our current investigation is focused on the determination of the ionization rate of the PPAMS device. Initial experiments were performed using polyurethane-based samples dissolved in dimethyl acetamide and polystyrene-based samples dissolved in toluene. These samples were spun-coated onto a gold-coated silicon wafer and probed by the PPAMS over controlled time intervals. A multivariate statistical method, Principal Components Analysis (PCA), was used to evaluate whether the MS signals obtained varied as a function of exposure time.  We hypothesized that the signal would resemble our bare gold background signal within two to three minutes, once the entire polymer surface being probed had been ionized. Instead, the MS signal was found to stay constant over the first 15 minutes. The results of our device characterization will provide valuable insight into the limits of the PPAMS device that will enable improved experimental design.