David Sprouster

Ending Aging in Super Glassy Polymer Membranes

Aging in super glassy polymers such as poly(trimethylsilylpropyne) (PTMSP), poly(4-methyl-2-pentyne) (PMP), and polymers with intrinsic microporosity (PIM-1) reduces gas permeabilities and limits their application as gas-separation membranes. While super glassy polymers are initially very porous, and ultra-permeable, they quickly pack into a denser phase becoming less porous and permeable. This age-old problem has been solved by adding an ultraporous additive that maintains the low density, porous, initial stage of super glassy polymers through absorbing a portion of the polymer chains within its pores thereby holding the chains in their open position. This result is the first time that aging in super glassy polymers is inhibited whilst maintaining enhanced CO2 permeability for one year and improving CO2/N2 selectivity. This approach could allow super glassy polymers to be revisited for commercial application in gas separations.

Energy dependent saturation width of swift heavy ion shaped embedded Au nanoparticles

P.K. and M.C.R. thank the Australian Research Council for support. P.K., R.G., D.J.S., and M.C.R. were supported by the Australian Synchrotron Research Program, funded by the Commonwealth of Australia via the Major National Research Facilities Program.

Structural and vibrational properties of Co nanoparticles formed by ion implantation

This work was financially supported by the Australian Synchrotron and the Australian Research Council. ChemMatCARS Sector 15 is principally supported by the National Science Foundation/Department of Energy under Grant No. NSF/CHE-0822838. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Swift heavy-ion irradiation-induced shape and structural transformation in cobalt nanoparticles

This work was financially supported by the Australian Synchrotron and the Australian Research Council with access to equipment provided by the Australian Nanofabrication Facility. ChemMatCARS Sector 15 is principally supported by the NSF/ DOE under Grant No. NSF/CHE–0822838.

Structural modification of swift heavy ion irradiated amorphous Ge layers

Swift heavy ion (SHI) irradiation of amorphous Si (a-Si) at non-perpendicular incidence leads to non-saturable plastic flow. The positive direction of flow suggests that a liquid phase of similar density to that of the amorphous solid must exist and accordingly a-Si behaves like a conventional glass under SHI irradiation. For room-temperature irradiation of a-Si, plastic flow is accompanied by swelling due to the formation of voids and a porous structure. For this paper, we have investigated the influence of SHI irradiation at room temperature on amorphous Ge (a-Ge), the latter produced by ion implantation of crystalline Ge substrates. Like a-Si, positive plastic flow is apparent, demonstrating that liquid polymorphism is common to these two semiconductors. Porosity is also observed, again confined to the amorphous phase and the result of electronic energy deposition. Enhanced plastic flow coupled with a volume expansion is clearly responsible for the structural modification of both a-Si and a-Ge irradiated at room temperature with swift heavy ions.

Formation and structural characterization of Ni nanoparticles embedded in SiO2

This work was financially supported by the Australian Synchrotron and the Australian Research Council with access to equipment provided by the Australian Nanofabrication Facility.

Amorphization of Cu nanoparticles: Effects on surface plasmon resonance

Crystalline copper nanoparticles (NPs) were formed in silica by multi-energy MeV ion implantations and then transformed to amorphous NPs by irradiation with 5 MeV Sn3+ ions. Optical absorption spectra of both the phases were evaluated in the ultra-violet to near-infrared regions. Compared with corresponding crystalline NPs of the same mean diameter, the amorphous NPs showed a low-energy shift of the surface plasmon resonance around 2.2 eV and less prominent absorption structure around 4 eV. These differences are explained by a strongly reduced electron mean-free-path in the amorphous NPs due to the loss of lattice periodicity.

The influence of annealing conditions on the growth and structure of embedded Pt nanocrystals

We thank the Australian Synchrotron Research Program and the Australian Research Council for financial support.

Defect complexes in fluorine-implanted germanium

In the present article we employ positron annihilation lifetime spectroscopy and secondary ion mass spectrometry to study the thermal evolution of vacancy related defects in fluorine-implanted germanium. We find that fluorine enriches the germanium matrix with various vacancy-like clusters that show both concentration and annealing temperature-dependent behaviour. We demonstrate that low fluorine concentrations saturate the Ge matrix with large concentrations of divacancy-like complexes that are effectively removed after moderate annealing. High fluorine concentrations, however, appear to stabilize a large component of monovacancy-like complexes in the near-surface region of the Ge substrates. These monovacancy-like complexes also appear to be thermodynamically stable, even after high-temperature annealing. The nucleation and thermal evolution of these vacancy-like defects may have particular importance in the fabrication and control of future germanium electronic devices.

Swift heavy ion irradiation of Pt nanocrystals: I. shape transformation and dissolution

We report on the effects of swift heavy ion irradiation of embedded Pt nanocrystals (NCs), which change from spheres to prolate spheroids to rods upon irradiation. Using a broad range of ion irradiation energies and NC mean sizes we demonstrate that the elongation and dissolution processes are energy and size dependent, attaining comparable levels of shape transformation and dissolution upon a given energy density deposited in the matrix. The NC shape transformation remains operative despite discontinuous ion tracks in the matrix and exhibits a constant threshold size for elongation. In contrast, for ion irradiations in which the ion tracks are continuous, the threshold size for elongation is clearly energy dependent.