Control of ion energy distribution functions ͑IEDF͒ at the substrate during plasma processing is achieved using a specially tailored voltage waveform for substrate bias, consisting of a short voltage spike in combination with a slow ramp. A much narrower IEDF is possible compared to the conventional approach of applying a sinusoidal waveform to the substrate electrode. Measurements in a helicon plasma combined with a time-dependent spherical-shell plasma fluid model demonstrate the benefits of this method in producing a narrow IEDF of precisely controllable energy, independent of ion mass.

Excitation and ionization of atoms out of the 4 energy levels of the excited np 5 (n + 1)s configuration of rare gases play an important role in many low temperature rare-gas plasmas. We compare two optical methods for measuring the number densities of atoms in these excited levels in an inductively coupled plasma under a variety of operating conditions (600 W, 1-25 mTorr). The first method is a standard white light absorption technique, whereas the second method exploits changes in the effective branching fractions of np 5 (n + 1)p → np 5 (n + 1)s emissions brought about by radiation trapping of atoms in np 5 (n + 1)s levels. The branching fraction method was found to produce results that agree well with the direct white light absorption method for both argon and neon plasmas using little more than a low-resolution spectrum of the plasma glow.

Topographic features are generally accepted as being capable of modulating cell alignment. Of particular interest is the potential that topographic feature geometry induces cell alignment indirectly through impacting adsorbed proteins from the cell culture medium on the surface of the substrate. However, it has also been reported that micron-scale feature depth significantly impacts the level of alignment of cellular populations on topography, despite being orders of magnitude larger than the average adsorbed protein layer (nm). In order to better determine the impact of biomimetic length scale topography and adsorbed protein interaction on cellular morphology we have systematically investigated the effect of combinations of sub-micron to nanoscale feature depth and lateral pitch on corneal epithelial cell alignment. In addition we have used the unique properties of a serum-free media alternative in direct comparison to serum-rich medium to investigate the role of culture medium protein composition on cellular alignment to topographically patterned surfaces. Our observation that increasing groove depth elicited larger populations of corneal epithelial cells to align regardless of culture medium composition and of cell orientation with respect to the topography, suggests that these cells can sense changes in topographic feature depths independent of adsorbed proteins localized along ridge edges and tops. However, our data also suggests a strong combinatory effect of topography with culture medium composition, and also a cell type dependency in determining the level of cell elongation and alignment to nanoscale topographic features.

Optical modeling of emissions from low-temperature plasmas provides a non-invasive technique to measure the electron energy distribution function (EEDF) of the plasma. While many models assume the EEDF has a Maxwell-Boltzmann distribution, the EEDFs of numerous plasma systems deviate significantly from the Maxwellian form. In this paper, we present an optical emission model for the Ar(3p 5 4p → 3p 5 4s) emission array which is capable of capturing details of non-Maxwellian distributions. Our model combines previously measured electron-impact excitation cross sections with Ar(3p 5 4s) number density measurements and emission spectra. The model also includes corrections for radiation trapping of the Ar(3p 5 4p → 3p 5 4s) emission lines. Results obtained with this optical technique are compared with corresponding Langmuir probe measurements of the EEDF for Ar and Ar/N 2 inductively coupled plasma systems operating under a wide variety of source conditions (1-25 mTorr, 20-1000 W, %N 2 admixture). Both the optical emission method and probe measurements indicate the EEDF shapes are Maxwellian for low electron energies, but with depleted high energy tails.

The β-decay half-lives of 110 neutron-rich isotopes of the elements from 37 Rb to 50 Sn were measured at the Radioactive Isotope Beam Factory. The 40 new half-lives follow robust systematics and highlight the persistence of shell effects. The new data have direct implications for r-process calculations and reinforce the notion that the second (A ≈ 130) and the rare-earth-element (A ≈ 160) abundance peaks may result from the freeze-out of an ðn; γÞ ⇄ ðγ; nÞ equilibrium. In such an equilibrium, the new half-lives are important factors determining the abundance of rare-earth elements, and allow for a more reliable discussion of the PRL 114, 192501 (2015) P H Y S I C A L R E V I E W L E T T E R S week ending 15 MAY 2015 0031-9007=15=114(19)=192501 (7) 192501-1 © 2015 American Physical Society r process universality. It is anticipated that universality may not extend to the elements Sn, Sb, I, and Cs, making the detection of these elements in metal-poor stars of the utmost importance to determine the exact conditions of individual r-process events. Introduction.-The origin of the heavy elements from iron to uranium is one of the main open questions in science. The slow neutron-capture (s) process of nucleosynthesis [1,2], occurring primarily in helium-burning zones of stars, produces about half of the heavy element abundance in the universe. The remaining half requires a more violent process known as the rapid neutron-capture (r) process [3][4][5][6]. During the r process, in environments of extreme temperatures and neutron densities, a reaction network of neutron captures and β decays synthesizes very neutron-rich isotopes in a fraction of a second. These isotopes, upon exhaustion of the supply of free neutrons, decay into the stable or semistable isotopes observed in the solar system. However, none of the proposed stellar models, including explosion of supernovae [7][8][9][10][11][12] and merging neutron stars [13][14][15][16], can fully explain abundance observations. The mechanism of the r process is also uncertain. At temperatures of one billion degrees or more, photons can excite unstable nuclei which then emit neutrons, thus, counteracting neutron captures in an ðn; γÞ ⇄ ðγ; nÞ equilibrium that determines the r process. These conditions may be found in the neutrino-driven wind following the collapse of a supernova core and the accreting torus formed around the black hole remnant of merging neutron stars. Alternatively, recent r-process models have shown that the r process is also possible at lower temperatures or higher neutron densities where the contribution from ðγ; nÞ reactions is minor. These conditions are expected in supersonically expanding neutrino-driven outflow in low-mass supernovae progenitors (e.g., 8 − 12 M ⊙ ) or prompt ejecta from neutron star mergers [17]. The final abundance distribution may also be dominated by postprocessing effects such as fission of heavy nuclei (A ≳ 280) possibly produced in merging neutron stars [18].New clues about the r process have come from the discovery of de...