ANSTO :: Browsing by Author "Stampfl, APJ"

Browsing by Author "Stampfl, APJ"

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The adsorption of glycine on alumina: surface complexation and polymerisation
(Australian Institute of Physics, 2009-02-05) Murison, JL; Asquith, NL; Stampfl, APJ; Pi, TW; Tang, YW; Lee, YC; Hwu, YK
Not available
Artificially modulated chemical order in thin films: a different approach to create ferro/antiferromagnetic interfaces
(American Physical Society, 2010-10-06) Saerbeck, T; Klose, F; Lott, D; Mankey, GJ; Lu, Z; LeClair, PR; Schmidt, W; Stampfl, APJ; Danilkin, SA; Yethiraj, M; Schreyer, A
We report on a unique magnetic exchange interaction in a thin film of FePt3, comprising an artificially created ferromagnetic (FM)/antiferromagnetic (AFM) modulation, but homogeneous chemical composition and epitaxy throughout the film. The chemical order, on the other hand, is modulated resulting in the formation of alternating FM/AFM layers. To determine the existence and form of the magnetic structure within the monostoichiometric thin film, we use a unique combination of polarized neutron reflectometry, x-ray/neutron diffraction, and conventional magnetometry. This artificial stratified AFM/FM FePt3 exhibits a high magnetic exchange bias thus opening up possibilities to study such magnetic phenomena in a perfectly lattice-matched system. © 2010, American Physical Society
Bacterial nano-particle uptake under extreme white-beam irradiation conditions
(Australian Institute of Physics, 2009-02-05) Wilde, KL; Asquith, NL; Graham, SM; Holden, PJ; Stampfl, APJ; Kempson, I; Yang, BW; Hwu, YK
Not available
Bio-molecule adsorption studied using micro-beam photoemission spectroscopy
(Australian Institute of Physics, 2005-01-31) Stampfl, APJ; Cheng, CH; Wang, SC; Huang, ML; Klauser, R
The idea that some functioning bio-surfaces may be built-up using dry (in-vacuum) techniques is interesting because of the compatibility with existing dry-fabrication technologies and that completely novel bio-surfaces not seen in nature may be created. Adsorption chemistry and surface bonding of simple bio-molecules at metal and semiconductor surfaces is probed using synchrotron-based photo-emission techniques. Cysteine, for example, appears to adsorb intact onto Pt{111} in its zwitterionic form. Other examples of in-situ amino-acid and peptide deposition onto metal surfaces are given with a discussion on surface damage due to radiation exposure. © 2005 Australian Institute of Physics
Central-atom size effects on the methyl torsions of group XIV tetratolyls
(Wiley-V C H Verlag GMBH, 2012-10-01) Ng, MCC; Harper, JB; Stampfl, APJ; Kearley, GJ; Rols, S; Stride, JA
The Group XIV tetratolyl series X(C6H4-CH3)4 (X=C, Si, Ge, Sn, Pb) were studied by using inelastic neutron scattering to measure the low-energy phonon spectra to directly access the methyl-group torsional modes. The effect of increased molecular radius as a function of the size of the central atom was shown to have direct influence on the methyl dynamics, reinforced with the findings of molecular dynamics and contact surface calculations, based upon the solid-state structures. The torsional modes in the lightest analogue were found to be predominantly intramolecular: the Si and Ge analogues have a high degree of intermolecular methylmethyl group interactions, whilst the heaviest analogues (Sn and Pb) showed pronounced intermolecular methyl interactions with the whole phonon bath of the lattice modes. © 2012, Wiley-VCH Verlag GmbH & Co. KGaA
Comparison between calculated and measured photoelectron diffraction patterns for Cu (001)
(Australian Institute of Physics, 2008-01-30) Cousland, GP; Smith, AE; Riley, JD; Homolya, S; Stampfl, APJ; King-Lacroix, J
We compare the results of X-ray photoelectron diffraction experiments with simulations obtained using the EDAC multiple scattering computer simulation package. Comparisons are presented for Cu (111) at photon energies of ~ 600eV. With an intention to study Cu3Mn, our initial work considers experimental and simulated data for Cu (001) at photon energies from 100 to 380eV.
Data-processing technique for the Taipan “Be-filter” neutron spectrometer at the Australian Nuclear Science and Technology Organisation
(American Institute of Physics (AIP), 2021-07-09) Iles, GN; Rule, KC; Peterson, VK; Stampfl, APJ; Elcombe, MM
There are five filter-analyzer neutron spectrometers available worldwide for scientists to use in order to measure the vibrational density of states in various samples. While Taipan, the thermal spectrometer, has been operated as a triple-axis spectrometer at the Australian Centre for Neutron Scattering since 2010, a beryllium filter analyzer spectrometer was added in 2016. Due to the complex nature of the data post-processing, it has thus far been impossible to fully treat experimental data from scientific measurements taken over the last five years. We have successfully created a robust method of treating data from the Taipan filter-analyzer and present the method on three different samples. The data-treatment process includes correction for the non-linear energy variation of a particular monochromator, removal of higher-order wavelength contamination, and estimation of low-energy multiple-scattering. The steps described here can be utilized by all users of the Australian Nuclear Science and Technology Organisation “Be-filter”—past, present, and future. © 2021 Author(s). Published under an exclusive license by AIP Publishing.
Does local disorder occur in the pyrochlore zirconates?
(American Chemical Socity, 2012-12-17) Blanchard, PER; Clements, R; Kennedy, BJ; Ling, CD; Reynolds, EM; Avdeev, M; Stampfl, APJ; Zhang, Z; Jang, LY
The zirconates Ln2Zr2O7 (Ln = lanthanoid) have been studied using a combination of Zr L-edge X-ray absorption near edge structure (XANES) and synchrotron X-ray and neutron powder diffraction methods. These studies demonstrate that as the size of the lanthanoid cation decreases, the local structure evolves smoothly from the ideal pyrochlore toward the defect fluorite rather than undergoing an abrupt transformation. The Zr L-edge spectrum is found to be extremely sensitive to changes in the local coordination environment and demonstrates an increase in local disorder across the pyrochlore oxides. The sensitivity of the XANES measurements enables us to identify the progressive nature of the transition that could not be detected using bulk diffraction techniques. © 2012, American Chemical Society.
Elastic constants of oriented Ti3AlC2 and Ti3SiC2 obtained via coherent inelastic neutron scattering
(International Conference on Neutron Scattering, 2017-07-12) Kirstein, O; Gray, V; Stampfl, APJ; Kisi, EH
Effort has gone into understanding the properties of MAX phases and their archetypes, Ti3SiC2,and Ti3AlC2, is as these materials exhibit a desirable combination of metallic and ceramic properties [1]. Single crystal elastic constants(SEC), usually obtained using ab-initio calculations in combination with crystallographic information, indicate the materials to be isotropic [2]. While it is difficult to obtain single crystals it is possible to produce highly textured specimens. Using a method developed by Buchenau [3] allows using coherent inelastic neutron scattering to obtain an estimation of the SEC, and such an experiment was performed using the three-axis spectrometer TAIPAN at ANSTO [4]. Results for Ti3AlC2 agree with ab-initio calculations and the assumption of isotropy. For Ti3SiC2 experimental results of c44 = 402.7 GPa do not support isotropic values obtained from ab-initio calculations. Molecular dynamics simulations combined with inelastic neutron scatteringexperiments support the initial diffraction experiment and hence themicromechanical model that was used [5]. We present here a self-consistentdescription of the mechanical properties of the MAX phases Ti3SiC2and Ti3AlC2. [1] M. W. Barsoum et al. Annual Rev.Mat. Res. 41(2011); [2] M. F. Cover et al., J. Phys.Conds. Matt., 21(2009) 305403; [3] U. Buchenau, Sol. St. Comm.,Vol.32(12), 1979 ; [4] V. Gray et al.. J. Am. Ceram. Soc.1-6, 2016; [5] E.H. Kisi et al, J. of Phys.: Cond.Matter 22 (2010) 162202
Electronic and vibrational properties of yttria-stabilised zirconia from first-principles for 10–40 mol% Y2O3
(Elsevier, 2014-11) Cousland, GP; Cui, XY; Ringer, SP; Smith, AE; Stampfl, APJ; Stampfl, CM
Density-functional theory calculations are performed to investigate the electronic and vibrational density-of-states (DOS) for a series of recently predicted stable and metastable structures of yttria-stabilised zirconia (YSZ) with yttria (Y2O3) concentrations of 14, 17 and 20 mol%. Analogous quantities are also studied for the so-called δ-phase, which forms for 40 mol% yttria, as well as for model structures with ≈10.3 mol% yttria. These calculated results, together with those for the cubic, tetragonal and monoclinic phases of ZrO2, afford a comparison of structural, electronic and vibrational properties as a function of yttria concentration. With increasing yttria content, the electronic DOS exhibit a decrease in the valence band-width (of about 2.0 eV relative to the cubic phase) and a corresponding increase of the band-gap of 0.73 eV (from cubic to 40 mol% yttria containing ZrO2). Regarding the vibrational DOS (vDOS), the addition of yttria causes the peaks in the vDOS of ZrO2 to become less distinct, reflecting the more dense occupation of states due to the larger number of atoms in each primitive cell, and to the lower symmetry. The vDOS of the various YSZ structures appear qualitatively similar with contributions from O atoms spanning the whole frequency range and cation related contributions present for frequencies View the MathML source. With increasing yttria content, more Zr atoms become seven-fold coordinated as in monoclinic ZrO2, concominantly the vDOS increasingly resembles that of m-ZrO2, but with notable contributions from Y atoms, which has a main peak at about 17 meV, similar to that of Zr atoms. © 2014 Elsevier Ltd.
The electronic structure of S-layer proteins from Lactobacillus brevis
(IEEE, 2008-07-28) Graham, SM; Asquith, NL; Wilde, KL; Short, KT; Holden, PJ; Stampfl, APJ; Holmes, AJ; Ruys, AJ; Stojanov, P; Riley, JD; Fang, LJ; Yang, YW; Hwu, YK
The valence electronic structure of the S-layer of Lactobacillus brevis is determined using synchrotron-based photoelectron spectroscopy and soft X-ray absorption spectroscopy. Spectra are compared to experimental work on amino-acids and S-layers of Bacillus sphaericus. While it is indeed possible to identify energy levels with those of natural amino-acids, distinct energy shifts are indeed observed which cannot be reconciled using such simple comparisons. Furthermore a strong nitrogen signal observed in both the occupied and unoccupied energy levels suggests that the Lactobacillus brevis protein is amine-terminated. A discussion of the surface of this protein is given. © 2008 IEEE
The fermi surface of Cu3Mn {100} and spinglass magnetism
(Australian Institute of Physics, 2009-02-05) Stampfl, APJ; Loh, NA; Hsieh, KY; Yu, DH; Brigden, P; Stojanov, P; Riley, JD; Stamps, RL; Yuh, JY; Pi, TW; Chang, J; Hwu, YK
Not available
The fluorite-pyrochlore transformation of Ho2-yNdyZr2O7
(Elsevier, 2011-08-01) Clements, R; Hester, JR; Kennedy, BJ; Ling, CD; Stampfl, APJ
Twelve members of the Ho2-yNdyZr2O7 series, prepared using conventional solid state methods, have been characterised by neutron powder diffraction. Ho2Zr2O7 has a defect fluorite structure whereas Nd2Zr2O7 is found to adopt the ordered pyrochlore structure with the composition induced fluorite-pyrochlore transformation occurring near y=1. Rietveld analysis on the neutron data for all the compositions reveals an increase in lattice parameter as a function of y across the entire series, with a small discontinuity associated with the transformation. The neutron profile results suggest that domains of pyrochlore-type initially begin to form before crystallising into a separate phase, and therefore that anion and cation ordering processes are distinct. There is a strong correlation between the extent of disorder in the anion sublattice and the x-parameter of 48f oxygen. These results point the way to a better understanding of the stability observed in pyrochlore structures.(C) 2011 Elsevier Inc.
High resolution synchrotron XPS study of L-cysteine and S-benzyl-L-cysteine on platinum: adhesion mechanisms and radiation damage
(Australian Institute of Physics, 2006-12-07) Wong, L; Yayebjee, M; Stampfl, APJ; Chen, CH; Wang, SC; Huang, ML; Klauser, R
Key to the development of functional biomaterials and innovative technologies behind medical implants and biosensors is a deep understanding of the interaction between inorganic surfaces and biological systems at the molecular level. Amino acids adhered onto inorganic substrates are model systems which may be analysed at a fundamental level using x-ray photoelectron spectroscopy (XPS) [1]. L-cysteine has been proposed as a potential anchor for larger molecules, e.g. proteins, to adhere onto metals such as Au, due to cysteine’s reactive thiol group [2]. This paper presents a related but unexplored system: in-situ prepared L-cysteine on Pt{111}. Pt{111} is an atomically flat surface and is a relevant material, used in biosensors and medical implants. To compare the adhesion characteristics of small and large molecules, S-benzyl-L-cysteine on Pt{111} is also analysed. Core level binding energies are examined using high resolution XPS at the National Synchrotron Radiation Research Centre (NSRRC) in Taiwan. Analysis of S 2p binding energies indicates cysteine adsorption via the thiol group. Two N 1s peaks in the spectra suggest that cysteine is present in both neutral and zwitterionic forms. Analysis of S-Benzyl-L-Cysteine core level shifts demonstrates similar adhesion characteristics. An important consideration in the application of biosurfaces is the impact of x-ray irradiation. XPS, using an excitation energy of 480eV, is used to examine the damage to each surface, due to exposure from the x-ray beam. The dramatic evolution of the N 1s spectra from both molecules suggests cleavage of the amine group. In addition, C 1s spectra from L-cysteine and S-benzyl-L-cysteine show cleavage of the carboxyl group due to prolonged irradiation. [1] B. Kasemo, Surf. Sci., 500, 2002, 656. [2] O.Cavalleri, L. Oliveri, A. Daccà, R. Parodi and R. Rolandi, App. Surf. Sci., 175, 2001, 357
In situ monochromator alignment on ANSTO’s thermal spectrometer, TAIPAN
(Australian Institute of Physics, 2018-01-30) Sutton, C; Rule, KC; McIntyre, GJ; Danilkin, SA; Stampfl, APJ
TAIPAN is the thermal triple axis spectrometer at ANSTO and also hosts an alternate secondary spectrometer called the Be-filter. Both instruments use a common graphite monochromator (PG002) to select a single wavelength or energy of the neutrons. By rotating the monochromator with respect to the incident beam of neutrons from the reactor, the energy of the neutrons from the monochromator can vary between 5-70 meV. The PG002 monochromator is made from 63 individual crystals of highly oriented pyrolytic graphite and the neutrons are scattered from the 002 lattice planes. The benefit of separate crystals is that they can be oriented to allow for vertical focusing of the neutron beam, or horizontal focusing or double focusing, depending on the experimental requirements. Recent measurements at TAIPAN have indicated that the crystals may not be well aligned on the double focusing mechanism, leading to broad peaks that indicate an increased mosaicity. We will present our work to develop a rapid in situ laser alignment-checking procedure for the 63-crystal TAIPAN graphite monochromator. Due to the small aperture, translation, rotation and tilt of the laser, as well as rotation and tilt of the monochromators would be needed, which will involve derivation of the geometrical mathematics, construction from what we have available of a stage with the large translations needed, testing ex situ, then in situ.
Investigation of field-induced ferromagnetism in Pd-Ni-Fe-P metallic glass by x-ray magnetic circular dichroism
(American Institute of Physics, 2009-01-12) Yu, DH; Duriavig, J; Loh, NA; Woodward, RC; Lin, HJ; Chang, FH; Kilcoyne, SH; Stampfl, APJ; Robinson, RA
We have applied x-ray magnetic circular dichroism to investigate the field-induced ferromagnetism in Pd40Ni22.5Fe17.5P20 alloy. The experiment revealed that both Ni and Fe were in a divalent state and that the magnetic properties of the material were determined by the localized 3d electrons of the transition metals. No clear evidence of Ruderman–Kittel–Kasuya–Yosida-type interaction among magnetic clusters was observed. It is believed that the detailed balance of fundamental spin-orbit and exchange interactions as a function of temperature and applied magnetic field determine the different magnetic properties of the alloy. © 2009, American Institute of Physics
Investigation of the vibrational properties of cubic yttria-stabilized zirconia: a combined experimental and theoretical study
(Elsevier, 2014-03) Cousland, GP; Mole, RA; Elcombe, MM; Cui, XY; Smith, AE; Stampfl, CM; Stampfl, APJ
A combined experimental and theoretical investigation into the vibrational properties of cubic 8–9 mol% yttria-stabilized zirconia (YSZ) is presented. Measurements of acoustic phonon dispersion curves have been obtained from inelastic neutron scattering investigations using a triple axis spectrometer, as well as calculations of the vibrational density-of-states (vDOS) using density-functional theory. The present measurements agree closely with, and extend, previously published results. The phonons become broader and decrease in intensity as the Brillouin zone boundary is approached, particularly in the Γ–Δ–X direction. Interestingly, there is evidence of a previously unreported low energy phonon band (8–9 meV) in the Γ–Σ–X direction, which could possibly be related to the stabilization (by yttria doping) of the imaginary mode of cubic ZrO2 about the X-point. Compared to pure cubic ZrO2, the vDOS of YSZ are broader and extend to higher frequency. Furthermore, the prominent Zr-related feature in the vDOS of c-ZrO2 at ≈14 meV is shifted to higher energy in the vDOS of YSZ. This behavior is consistent with the measured dispersion bands (first acoustic branch in the Γ–X direction, about the X-point) of YSZ which is higher in energy by a similar amount relative to that of c-ZrO2, thus providing support for the structural model considered. Crown copyright © 2013 Published by Elsevier Ltd.
Low energy photoelectron diffraction analysis at high angular resolution of Cu and Mn/Cu surfaces
(American Institute of Physics, 2009-11-01) Cousland, GP; Smith, AE; Riley, JD; Stampfl, APJ
X-ray photoelectron diffraction simulations using a real-space approach are Shown to accurately produce the extraordinarily detailed photoelectron diffraction pattern from Cu{111} at an electron kinetic energy of 523.5 eV. These same simulations show that most sensitivity is obtained when using low energy electrons at high angular resolution Structural differences are observed to be greatest around a kinetic energy of similar to 100 eV and many of the features observed in the photoelectron diffraction patterns may be directly related to phenomena observed in low energy electron diffraction patterns from the same Surface. For Cu{100}. simulations of buckled surfaces with a Mn overlayer predict that low energy photoelectron diffraction can easily discriminate chemical and structural differences. Even the effects of the relaxed Surface of Cu{100} is indeed observable along azimuthal scans around a kinetic energy of 100 eV Our results show that low energy photoelectron diffraction is extremely sensitive to changes in Surface Structure If high resolution patterns are acquired. © 2009, American Institute of Physics.
The magnetic structure of an epitaxial BiMn0.5Fe0.5O3 thin film on SrTiO3 (001) studied with neutron diffraction
(American Institute of Physics, 2012-10-22) Cortie, DL; Stampfl, APJ; Klose, F; Du, Y; Wang, XL; Zhao, HY; Kimura, H; Cheng, ZX
High-angle neutron diffraction was used to directly reveal the atomic-scale magnetic structure of a single-crystalline BiMn0.5Fe0.5O3 thin film deposited on a SrTiO3 (001) substrate. The BiMn0.5Fe0.5O3 phase exhibits distinctive magnetic properties that differentiate it from both parent compounds: BiFeO3 and BiMnO3. A transition to long-range G-type antiferromagnetism was observed below 120K with a (1/2 1/2 1/2) propagation vector. A weak ferromagnetic behavior was measured at low temperature by superconducting quantum interference device (SQUID) magnetometry. There is no indication of the spin cycloid, known for BiFeO3, in the BiMn0.5Fe0.5O3 thin film. The neutron diffraction suggests a random distribution of Mn and Fe over perovskite B sites. © 2012, American Institute of Physics.
The magnetism of CrO2 under high pressure
(Australian Institute of Physics, 2009-02-04) Loh, NA; King-Lacroix, J; Yu, DH; Robertson, R; Stampfl, APJ; Tseng, YC; Haskel, D
Not available

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