Henry J. Ramos

Characterization of Ni thin films following thermal oxidation in air

The authors study the thermal oxidation of nickel thin films (50 nm) fabricated by conventional thermal evaporation, resulting from annealing in air at 300, 325, 350, 400, and 700 °C. The characterization is performed by x-ray diffraction, Raman spectroscopy, superconducting quantum interference device magnetometry, and scanning electron microscopy. These techniques show that the oxidation increases with annealing temperature. The formation of granular films of coexisting Ni and NiO is confirmed after annealing at 400 °C. The magnetic measurements indicate coexisting ferromagnetism and antiferromagnetism, corresponding to Ni and NiO contributions. The magnetic hysteresis loops reveal exchange bias in the samples annealed at 235, 350, and 400 °C due to the competition between the exchange interactions at the Ni/NiO interfaces.

Neutral beam probe spectroscopy for edge plasma diagnostics

Abstract A new method of neutral beam probing combined with spectroscopic and laser-induced fluorescence techniques has been developed in order to measure electron density profiles of the boundary layer plasma. The feasibility of this method using two kinds of Li0-beams of thermal and several eV energies is demonstrated with an ECR test plasma. The obtained electron density profile agrees well in form with that measured by a Langmuir probe. The absolute values are about one third of those obtained by the Langmuir probe but agree with results from a microwave interferometer. The applicability of this method to the TEXTOR tokamak is discussed.

Optimization and enhancement of H− ions in a magnetized sheet plasma

Several schemes to improve the efficiency of extraction of H− ions from a magnetized sheet plasma source are reported. Parameters that affect the optimization of the extraction process such as plasma electrode position relative to the core plasma, plasma electrode bias, extraction electrode bias, neutral gas pressure, and discharge current were investigated. The negative hydrogen ion current density extracted from pure hydrogen plasma under optimum conditions was 0.15 A/m2. Enhancement of the H− current density has been observed by as much as 73.3% when argon was mixed with hydrogen at a 10%/90% ratio. The addition of argon raised the electron density by ten times and increased the electron temperature by 40% at the center of the sheet plasma. These plasma parameters were of comparable value with and without argon at the periphery of the sheet. The existence of high-energy electrons at the core and the presence of cold electrons at the periphery of the sheet plasma conform to ideal conditions of H−product...

Surface Modification of Narra Wood (Pterocarpus indicus) by Ion Shower Treatment

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 this particular monatomic ion in the surface modification process. Low energy irradiation (600–700 eV) produced hydrophobic surfaces with scanning electron micrographs showing partial closure of surface pores. Whereas, a reversion to hydrophilicity was observed for higher energy irradiation (>900 eV), with surface images showing exterior degradation believed to be the etching effects of the chemically active H+ species. The irradiated samples absorbency was quantified via the wetting model wherein the contact angles time rate equation was numerically solved and fitted onto experimental data. The change rate proportionality constant K with value 0.0015 corresponding to 600 eV beam energy, exhibited the longest moisture absorptive inhibition time of more than 10 min. An increasing value of K indicates increased wetting behavior.

Extraction characteristics of ions in a magnetized sheet plasma

A sheet plasma of thickness several millimetres was produced by a combination of a pair of strong dipole magnets with opposing fields and a pair of Helmholtz coils producing a magnetic mirror field. A ferrite magnet and a coreless magnetic coil encased within the limiters add to the mirror field, enhancing quiescence in the plasma. The negative hydrogen ions produced in the peripheral region of the sheet plasma were extracted with a deflection mass spectrometer. Maximum negative ion current of about 0.9 A for an initial gas filling pressure of 3 mTorr was observed when the plasma electrode was negatively biased near the value of the plasma potential and when the mass spectrometer coil current generated a B field intensity equal to 691 G. The ratio of the negative ion density and the electron density near the extraction electrode was relatively high at 0.276. The measured electron temperature showed the existence of high-energy electrons in the sheet plasma. The extracted negative hydrogen current density of is higher than what has been obtained from similar sources. The bulk electron temperature and density at the centre of the sheet plasma were measured to be 11.06 eV and , respectively.

A real-time method for monitoring the work function of a surface conversion negative ion source

Abstract An in-situ method to monitor the work function of the converter surface of a self-extraction negative ion source using photoelectron emission from the surface has been developed. The method uses two lasers. The photoelectron current induced by an Ar+ laser serves as a monitor of the overall coverage by Cs of the Mo surface, while that due to a dye laser is used to confirm that the Cs surface coverage corresponds to the work function minimum.

Design and operational characteristics of a cast steel mass spectrometer

A cast steel magnetic sector mass analyzer is developed for studies of hydrogen and helium ion beams generated by a gas discharge compact ion source. The optimum induced magnetic flux density of 3500 G made it possible to scan the whole spectrum of hydrogen and helium ion species. Analysis of beam characteristics shows that the mass spectrometer sensitivity, and resolving power are approximately inversely proportional. The resolution is enhanced at higher pressures and lower current discharges. In contrast, the instrument sensitivity increased at higher current discharges and decreased at higher pressures. Calculations of the ultimate resolving power with reference to analyzer dimensions yield a numerical value of 30. System anomaly in the form of spherical aberrations was also analyzed using the paraxial beam envelope equation. Beam divergence is most significant at high discharge conditions where angular spread reaches an upper limit of 8.6°.

Extraction and profile analysis of hydrogen-like helium ions in a magnetized sheet plasma

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.

Correlation of surface production of negative ions and the work function measured by laser‐induced photoelectron current

Dynamic change of a negative‐ion production surface in an ion source due to cesium introduction and plasma ion bombardment has been studied by simultaneous measurements of photoelectron current by laser irradiation and negative‐ion current. Strong dependences of production rates for negative ions by desorption (H−) and by sputtering (Au−) on the work function monitored by photoelectron current were observed. Peaks on mass spectra corresponding to He− were observed only when the monitoring signal indicated that the work function of a molybdenum‐cesium surface was near the minimum.

Gas discharge plasma treatment of poly(ethylene glycol-co-1,3/1,4 cyclohexanedimethanol terephthalate) for enhanced paint adhesion

Low-energy hydrogen-ions and tetrafluoromethane-ions produced from a gas discharge ion source were irradiated to poly(ethylene glycol-co-1,3/1,4 cyclohexanedimethanol terephthalate) (PETG) sheets for enhancing paint adhesion. The ion beams were characterized using a cast steel mass spectrometer, while the untreated and treated samples were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, contact angle measurements, and profilometry. The paint adhesion was determined by using the standard method for evaluating adhesion by knife [ASTM D6677-07, Standard Test Method for Evaluating Adhesion by Knife (ASTM International, West Conshohocken, PA, 2012)] and was correlated with the calculation of the work of adhesion derived from the Young–Dupre equation. After plasma treatment, a significant decrease in the contact angle was observed in all samples, except for the CF4 ion-treated samples with the discharge current of 3 mA and an irradiation time of 30 min. At longer irrad...