Gene Blantocas

Helium beams in a compact gas discharge source lose their transverse symmetry when the extracting electrode is biased at high potentials. Further, this condition gives rise to excessive formation of electrons within the vicinity of the beam line of propagation. A plausible explanation for these abnormalities is explained via the effects of the source extractor’s lens property on the beams’ physical configuration. The optical relation of the extractor shows that when the extraction voltage (Ve) exceeds half the discharge voltage (Vd), its focal length extends backward pass the discharge region’s emitting orifice. As a consequence, beam divergence is increased akin to light beams expanding when the source is positioned between a negative lens and its principal focus. Numerical simulations of the beams’ envelopes at different discharge and biasing conditions provide further proof of the theory’s validity. When Ve>Vd/2, the construct shows exiting beams to have waists greater than the diameter of the drift tube suggesting increased interaction between beam edge and the tube’s interior walls resulting in secondary electron emissions. The presence of electrons inexorably leads to charge neutralization thus creating asymmetric beams downstream. Mass spectroscopic detection of O- ions most likely from surface oxides, and increased electron densities obtained by way of Langmuir measurements are phenomenological evidences to this effect. This work intends to establish the explicit causality relation between secondary electron emission and the formation of asymmetric beams in miniaturized ion sources.

The extraction of He+ ions from a magnetized sheet plasma source is reported. Optimum detection and extraction of He+ ions were conducted using an E×B probe as a mass analyzer. The effect of the probe's extraction potential, its position relative to the center of the core plasma, gas filling pressure, and discharge conditions in the production and extraction of He+ ions were investigated. The He+ ion current density yield of 8 μA/cm2 was optimum at plasma discharge current of 1.5 A within the vicinity of 5-7 cm from the sheet plasma core. Investigations also show the predominance of detected He++ species. At higher pressures, the formation of molecular helium ions He2+ were observed. The He+ current yield decreases as the plasma current is increased according to the modified Saha population density equation of the collisional-radiative model.

Helium beams in a compact gas discharge source lose their transverse symmetry when the extracting electrode is biased at high potentials. Further, this condition gives rise to excessive formation of electrons within the vicinity of the beam line of propagation. A plausible explanation for these abnormalities is explained via the effects of the source extractor's lens property on the beams'

The enhancement and optimization of H - extraction through argon and magnesium seeding of hydrogen discharges in a magnetized sheet plasma source are reported. The paper first presents the modification of the production chamber into a hexapole multicusp configuration resulting in decreased power requirements, improved plasma confinement and longer filament lifetime. By this, a wider choice of discharge currents for sustained quiescent plasmas is made possible. Second, the method of adding argon to the hydrogen plasma similar to the scheme in Abate and Ramos [Y. Abate, H. Ramos, Rev. Sci. Instr. 71 (10) (2000) 3689] was performed to find the optimum conditions for H - formation and extraction. Using an E × B probe, H - yields were investigated at varied argon-hydrogen admixtures, different discharge currents and spatial points relative to the core plasma. The optimum H - current density extracted at 3.0 cm from the plasma core using 3.0 A plasma current with 10% argon seeding increased by a factor of 2.42 (0.63 A/m 2) compared to the measurement of Abate and Ramos [Y. Abate, H. Ramos, Rev. Sci. Instr. 71 (10) (2000) 3689]. Third, the argon-hydrogen plasma at the extraction chamber is seeded with magnesium. Mg disk with an effective area of 22 cm 2 is placed at the extraction region's anode biased 175 V with respect to the cathode. With Mg seeding, the optimum H - current density at the same site and discharge conditions increased by 4.9 times (3.09 A/m 2). The enhancement effects were analyzed vis-à-vis information gathered from the usual Langmuir probe (electron temperature and density), electron energy distribution function (EEDF) and the ensuing dissociative attachment (DA) reaction rates at different spatial points for various plasma discharges and gas ratios. Investigations on the changes in the effective electron temperature and electron density indicate that the enhancement is due to increased density of low-energy electrons in the volume, conducive for DA reactions. With Mg, the density of electrons with electron temperature of about 3 eV increased 3 orders of magnitude from 2.76 × 10 12 m -3 to 2.90 × 10 15 m -3.

An E × B probe (a modified Wien filter) is constructed to function both as a mass spectrometer and ion implanter. The device, given the acronym EXBII selects negative hydrogen ions (H -) from a premixed 10% argon-seeded hydrogen sheet plasma. With a vacuum background of 1.0 × 10 -6 Torr, H - extraction ensues at a total gas feed of 1.8 mTorr, 0.5 A plasma discharge. The EXBII is positioned 3 cm distance from the sheet core as this is the region densely populated by cold electrons ( Te ˜ 2 eV, Ne ˜ 3.4 × 10 11 cm -3) best suited for H - formation. The extracted H - ions of flux density ˜0.26 A/m 2 are segregated, accelerated to hyperthermal range (<100 eV) and subsequently deposited into a palladium-coated 1.1 × 1.1 cm 2, n-type Si (1 0 0) substrate held at the rear end of the EXBII, placed in lieu of its Faraday cup. The palladium membrane plays the role of a catalyst initiating the reaction between Si atoms and H - ions simultaneously capping the sample from oxidation and other undesirable adsorbents. AFM and FTIR characterization tests confirm the formation of SiH 2. Absorbance peaks between 900-970 cm -1 (bending modes) and 2050-2260 cm -1 (stretching modes) are observed in the FTIR spectra of the processed samples. It is found that varying hydrogen exposure time results in the shifting of wavenumbers which may be interpreted as changes in the frequencies of vibration for SiH 2. These are manifestations of chemical changes accompanying alterations in the force constant of the molecule. The sample with longer exposure time exhibits an additional peak at 2036 cm -1 which are hydrides of nano-crystalline silicon.

Narra ( Pterocarpus indicus) wood chips were irradiated with positive hydrogen ions H + and H2+ to make them hydrophobic. The ions were produced and extracted from a gas discharge ion source. The extracted beam current ranges from 0.01 to 0.07 μA for discharge currents of 1.0-4.0 mA, discharge potential between 600 V and 1000 V. The chips, positioned at 70 mm downstream from the ion source, were processed for different time periods and discharge currents. The wettability was characterized by the contact angle of the liquid droplet with respect to the wood surface. Surface modifications were assessed with by measurements of the water contact angle. Tests indicate retarded absorption characteristics for ion-irradiated samples compared to controlled samples. The longest absorptive inhibition were exhibited by samples irradiated for 30 min, at discharge current of 1.0 mA, 720 eV ion energy and 0 V extraction potential. Scanning electron micrographs reveal the difference in morphologies of treated and untreated samples. The results prove that low energy beams of hydrogen from a gas discharge ion source are suitable in transforming surfaces of wood chips to be water resistant.

A gas discharge ion source (GDIS) was used as test facility to produce and study the characteristics of diffused, low-energy hydrogen ion showers. Narra wood samples were then exposed to the showers to investigate topographical effects of ion irradiation. Analysis of beam constituents by mass spectroscopy shows H+ ions to be the dominant species suggesting an essential participatory role for

The wettability and optical transmittance properties of hydrogen ion treated polytetrafluoroethylene (PTFE) materials were evaluated using contact angle, laser irradiation, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) tests. The materials were processed using low-energy hydrogen ion shower (LEHIS) produced by a gas discharge ion source (GDIS). The duration of treatment and ion shower energy were varied to determine their effects on the PTFE specimens. Mass spectrometry showed the ion shower constituents to be H + and H 2+ species. Within the bounds of the discharge conditions, flux density for the H n+ beam measured a minimum of 0.06 A/m 2 and a maximum of 0.25 A/m 2. Both one- and two-way analysis of variance were employed to assist in the interpretation of the empirical data. Results showed that treatment using lower plasma discharge currents ( Id) improved material hydrophobicity with contact angles measuring a high of 115° while higher Id resulted in enhanced hydrophilicity reducing contact angles down to 61°. Transmittance and wettability were found to correlate, i.e., a surface made more wettable became optically transmissive allowing as much as 99% signal transmittance. Conversely, a surface made more hydrophobic reduced light leakage to as low as 60%. As the material showed increased surface striations, its optical transmittance, wettability, and surface tension also increased. With no observable shifting of the IR-absorption peaks, the surface modification was essentially morphological in character.

An E×B probe (a modified Wien filter) is constructed to function both as a mass spectrometer and ion implanter. The device, given the acronym EXBII selects negative hydrogen ions (H−) from a premixed 10% argon-seeded hydrogen sheet plasma. With a vacuum background of 1.0×10−6Torr, H− extraction ensues at a total gas feed of 1.8mTorr, 0.5A plasma discharge. The EXBII is