ORCID Profile
0000-0001-5200-727X
Current Organisations
Uppsala University
,
University of Oslo
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Publisher: Elsevier BV
Date: 12-1994
Publisher: Elsevier BV
Date: 11-1994
Publisher: Oxford University Press (OUP)
Date: 08-2008
DOI: 10.1093/RPD/NCN162
Abstract: In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where (209)Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the (209)Pb atoms were implanted into the glass with an energy of 39 keV. The diffusion profiles and the diffusion coefficients were determined after annealing at 470-620 degrees C and serial sectioning by ion sputtering. In addition, the effect of surface cleaning on diffusion was tested. From the Arrhenius fit, the activation enthalpy (H) was determined, which is equal to 3.2 +/- 0.2 eV, and also the pre-exponential factor D(0), in the order of 20 m(2)s(-1). This result confirms the assumption that over a time period of 50 y (209)Pb (and (210)Pb) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of (209)Pb in the topmost surface at high temperatures.
Publisher: Elsevier BV
Date: 06-2009
Publisher: IOP Publishing
Date: 26-11-2003
Publisher: Elsevier BV
Date: 05-2008
Publisher: Elsevier BV
Date: 08-2020
Publisher: Elsevier BV
Date: 12-1994
Publisher: Elsevier BV
Date: 10-2006
Publisher: American Vacuum Society
Date: 05-2009
DOI: 10.1116/1.3117257
Abstract: Collimators are widely used to define MeV ion beams. Recent studies have shown the capability of collimators to define beams of MeV ions with sub-100nm dimensions. Such nanometer beams have potential applications in MeV ion-beam lithography, which is the only maskless technique capable of producing extremely high aspect-ratio micro- and nanostructrures, as well as in high-resolution MeV ion-beam-based tomography. The ion scattering from the collimator edges that define the beam can be a resolution-restricting factor in these applications. Scattering processes at edges are difficult to study using conventional simulation codes because of the complicated geometry. In this part of the work, the authors used the GEANT4 toolkit as a simulation tool for studying the behavior of ions impinging onto, or in close proximity to, a single straight aperture edge. Results from simulations are presented for realistic beams of 3MeV He ions with 0.2–1mrad ergence incident on a 100-μm-thick Ta plate. The contribution from grazing scattering of ions impinging under glancing angles of incidence & ° on the slit-edge surface plane can degrade the beam spot size and shape. Ray-tracing simulations were also performed to investigate the trajectories of ions impinging on the aperture edge and in close proximity to it.
Publisher: AIP Publishing
Date: 15-03-1995
DOI: 10.1063/1.358770
Abstract: CoSi2 exhibits the features of low resistivity and stability at elevated temperatures which make it interesting to employ for metallization on GaAs. The interfacial reactions in GaAs s les with thin film overlayers of Si and Co [Si(220 nm)/Co(50 nm)/(〈100〉-GaAs)] were studied using x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy, and mass and energy dispersive recoil spectrometry. S les were vacuum furnace annealed for time periods between 1 and 8 h at temperatures ranging from 300 to 700 °C. It was found that a CoSi2 layer formed without observable reaction with the substrate at 500 °C and above. The excess Si (Si/Co atomic ratio of 2.41) remained near the surface as elemental Si and as SiO2 for the 500 and 600 °C annealings. For the 700 °C annealing the excess near-surface Si was not observed.
Publisher: Springer Science and Business Media LLC
Date: 03-1995
DOI: 10.1007/BF01244430
Publisher: Elsevier BV
Date: 03-1994
Publisher: Elsevier BV
Date: 07-2007
Publisher: Elsevier BV
Date: 07-1995
Publisher: Elsevier BV
Date: 06-2009
Publisher: American Vacuum Society
Date: 05-2009
DOI: 10.1116/1.3117281
Abstract: The capability of collimators to define beams of MeV ions with sub-100nm dimensions has recently been demonstrated. Such nanometer beams have potential applications in MeV ion-beam lithography, which is the only maskless technique capable of producing extremely high aspect-ratio micro- and nanostructrures, as well as in high resolution MeV ion-beam imaging. Ion scattering from the collimator edges can be a resolution-restricting factor in these applications. Scattering processes at edges are difficult to study using conventional simulation codes because of the complicated geometry. In this part of our work, the authors used the GEANT4 toolkit as a simulation tool for studying the behavior of beams of 3MeV He ions with 0.2–1mrad ergence impinging onto the programmable proximity aperture comprising four 100-μm-thick Ta plates. The transmission and scattering from the aperture are asymmetric due to the aperture design. For a perfectly parallel beam, the fluence of ions scattered from the aperture edges is spread over large areas. The enhancement of the fluence from the edge-scattered ions is two to three orders of magnitude smaller compared to the incident-beam fluence. Therefore, the edge scattering is not a resolution-restricting factor, and the sub-100nm resolution is achievable. However, for erging beams, the significant penumbra broadening of the beam spots restricts the attainable resolution. In lithography applications, the halo associated with penumbra broadening causes pattern edge roughening by producing single ion tracks in close vicinity to the pattern element edges.
Publisher: Elsevier BV
Date: 07-2013
Publisher: Elsevier BV
Date: 07-1995
Publisher: Elsevier BV
Date: 07-2007
Publisher: Elsevier BV
Date: 05-2008
Publisher: American Vacuum Society
Date: 09-2200
DOI: 10.1116/1.2978173
Abstract: A novel MeV ion beam programmable proximity aperture lithography system has been constructed at the Accelerator Laboratory of the University of Jyväskylä, Finland. This facility can be used to fabricate three dimensional microstructures in thick (& μm) polymer resist such as polymethylmethacrylate. In this method, MeV ion beams from the 1.7 MV pelletron and K130 cyclotron accelerators are collimated to a beam spot of rectangular shape. This shape is defined by a computer-controlled aperture made of a pair of L-shaped Ta blades which are in close proximity to the s le to minimize the penumbra broadening. Here the authors report on development of the system, the controlling software, the calibration procedures, investigations of multiple scattering effects, and present illustrative results using 3MeV He2+4 ion beams for lithography and 56MeV N3+14 ion beams for creating patterns of regions with ion tracks.
Publisher: Elsevier BV
Date: 03-1994
Publisher: Elsevier BV
Date: 06-2009
Publisher: Elsevier BV
Date: 07-2013
Publisher: Elsevier BV
Date: 08-2001
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Harry James Whitlow.