BYU Physics and Astronomy

Selected Publications

Application of nuclear-reactions for quantitative hydrogen analysis in a variety of different materials problems
BYU Authors: D. D. Allred, published in Nucl. Instr. Meth.
The application of nuclear reaction techniques to hydrogen analysis problems in metallurgical, mineralogical and semiconductor areas is described. Hydrogen analyses and profiles obtained with both the 1H(19F, αγ)16O and 1H(15N, αγ)12C reactions are presented. The advantages and disadvantages of the two techniques are discussed. Particular emphasis will be given to interpretive problems associated with analyzing the data. Various corrections to the data will be discussed, including off-resonance cross-section corrections and lower energy resonance corrections. Both crystalline and amorphous materials are examined. The hydrogen content of electrodeposited hard gold films has been determined as a function of plating conditions. Hydrogen contents as high as 9 atom % have been measured. The hydrogen profile of natural and synthetic SiO2 samples was determined. Hydrogen was found to be quite stable in amorphous silica samples but highly mobile in crystalline quartz samples under the analysis conditions. A hydrogen depth profile for a film of glow discharge deposited amorphous silicon () has been obtained and will be compared with a profile measured by secondary ion mass spectrometry (SIMS) on the same sample.
Profiling hydrogen in materials using ion-beams
BYU Authors: D. D. Allred, published in Nucl. Instr. Meth.
Over the last few years many ion beam techniques have been reported for the profiling of hydrogen in materials. We have evaluated nine of these using similar samples of hydrogen ion-implanted into silicon. When possible the samples were analysed using two or more techniques to confirm the ion-implanted accuracy. We report the results of this work which has produced a consensus profile of H in silicon which is useful as a calibration standard. The analytical techniques used have capabilities ranging from very high depth resolution () and high sensitivity (< 1 ppm) to deep probes for hydrogen which can sample throughout thin sheets (up to 0.2 mm thick).
Hydrogen concentration profiles in quartz determined by a nuclear-reaction technique
BYU Authors: D. D. Allred, published in Phys. Chem. Miner.
The nuclear reaction 19F(1H, αγ) 16O has been used to determine the hydrogen concentration in natural and synthetic quartz samples. The depth-profile of the hydrogen concentration in these samples has been determined in detail for the smoky and X o quartzes. These profiles exhibit a region of high hydrogen concentration in the near surface region (down to a depth of ∼2000Å), with a lower concentration in the bulk of the sample. The results provide a plausible explanation for the substantial disagreement between previous hydrogen analysis in these quartzes by other techniques. Evidence for hydrogen mobility in crystalline quartz under ion beam bombardment is presented and discussed.
The use of nuclear reactions and SIMS for quantitative depth profiling of hydrogen in amorphous silicon
BYU Authors: D. D. Allred, published in Appl. Phys. Lett.
Depth profiles for hydrogen in amorphous silicon have been determined by the use of resonantnuclear reactions [1H(15N,αγ)12C and 1H(19F,αγ)16O] and by secondary ion mass spectroscopy(SIMS). Independent calibration procedures were used for the two techniques. Measurements were made on the same amorphous silicon film to provide a direct comparison of the two hydrogen analysis techniques. The hydrogen concentration in the bulk of the film was determined to be about 9 at.% H. The SIMS results agree with the resonantnuclear reaction results to within 10%, which demonstrates that quantitative hydrogen depth profiles can be obtained by SIMSanalysis for materials such as amorphous silicon.
β-Delayed Proton Decay of C9
BYU Authors: David Allred, published in Phys. Rev. C
The delayed-proton spectrum following the β decay of C9 (τ12=126.5±1.0 msec) was found to consist primarily of a continuum extending from 13 to 1.5 MeV, the latter being the lowest energy observed. In addition to the previously observed peaks at 9.28 and 12.30 MeV (c.m.), possible peaks between 3 and 7 MeV have been tentatively identified.
A carbon nanotube structure for an EUV window with differential pumping
BYU Authors: Scott Olsen, Richard Vanfleet, David Allred, Steve Turley, and Robert Davis, published in Proc. SPIE

We report on a large-area, high-aspect-ratio, carbon nanotube (CNT) forest structure produced at BYU acting as a window/separator for a hollow cathode EUV lamp. The structure has large-surface-area, high light trans-mission, and differential pumping. CNT fabrication allows for variable dimensions, which allows various EUV distributions and pressure gradients to be possible. Theory is presented for predicting such distributions and gradients. Several structures have been fabricated; their dimensions, properties, and predicted distributions and gradients are given.