Near-surface generation of negative ions in low-pressure discharges

Formation processes of negative ions in low-pressure plasmas are not yet fully understood: as a rule experiments reveal higher negative ion density than predicted by the models. In this work we report near-surface generation of negative ions. This hitherto neglected formation mechanism appears to be important in low-pressure discharges and can have large impacts on the bulk plasma chemistry. We monitor energy-resolved positive and negative ion fluxes arriving at the electrodes in an oxygen parallel-plate radio-frequency ~rf, 13.56 MHz! and dc glow plasmas by means of a quadrupole mass spectrometer. Negative ions formed in the plasma volume are observed by extracting them through an orifice in the anode of a dc glow discharge. Unexpectedly, we record large negative ion signals at the cathode of a dc discharge and at the grounded electrode of an rf discharge. These ions are formed in the plasma sheath, in collision processes involving high-energy species. We propose an efficient mechanism of negative ion generation due to ion pair formation in the sheath

Near-surface generation of negative ions in low-pressure discharges

Formation processes of negative ions in low-pressure plasmas are not yet fully understood: as a rule experiments reveal higher negative ion density than predicted by the models. In this work we report near-surface generation of negative ions. This hitherto neglected formation mechanism appears to be important in low-pressure discharges and can have large impacts on the bulk plasma chemistry. We monitor energy-resolved positive and negative ion fluxes arriving at the electrodes in an oxygen parallel-plate radio-frequency ~rf, 13.56 MHz! and dc glow plasmas by means of a quadrupole mass spectrometer. Negative ions formed in the plasma volume are observed by extracting them through an orifice in the anode of a dc glow discharge. Unexpectedly, we record large negative ion signals at the cathode of a dc discharge and at the grounded electrode of an rf discharge. These ions are formed in the plasma sheath, in collision processes involving high-energy species. We propose an efficient mechanism of negative ion generation due to ion pair formation in the sheath

Atmospheric pressure plasma analysis by modulated molecular beam mass spectrometry

Fractional no. d. measurements for a radiofrequency plasma needle operating at atm. pressure were obtained using a mol. beam mass spectrometer (MBMS) system designed for diagnostics of atm. plasmas. The MBMS system comprises three differentially pumped stages and a mass/energy analyzer and includes an automated beam-to-background measurement facility as a software-controlled chopper mechanism. The automation of the beam modulation allows the neutral components in the plasma to be rapidly and accurately measured using the mass spectrometer by threshold ionization techniques. Data are reported for plasma generated by a needle plasma source operated using a He/air mixt. In particular, data for the conversion of atm. O and N into nitric oxide are discussed with ref. to its significance for medical applications such as disinfecting wounds and dental cavities and for microsurgery. [on SciFinder (R)

When the going gets tough, the tough get going: Social identification and individual effort in intergroup competition.

Based on social identity theory, the authors predicted that in ongoing intergroup competition, people’s strength of social identification will have a positive impact on their behavioral efforts on behalf of an ingroup when its current status is low, whereas this will not be the case when its current status is high. In a first experiment, male participants showed the expected pattern of behavior. Female participants, however, tended to display opposite reactions. As a possible explanation, it was argued that the experimental procedure may have inadvertently evoked a gender-based stereotype threat for female participants. In an attempt to obtain more consistent support for their hypothesis, the authors therefore replicated the experiment with modifications to avoid such a threat. These changes proved to be effective in the sense that this time the predicted interaction effect between ingroup identification and current group status was obtained for both male and female participants