Publications by authors named "David Halley"

Article Synopsis
  • - The study investigates the magnetic properties of epitaxial clusters made of chromium and chromium-vanadium oxides through various techniques, revealing that these clusters exhibit a small magnetic moment with super-paramagnetic behavior.
  • - The magnetization arises primarily from a unique magnetic phase of chromium oxide, contrasting with the bulk form of CrO, which is usually anti-ferromagnetic.
  • - Analysis of the magnetic properties at different temperatures suggests that the magnetic dipoles observed may be associated with short-range coupling between chromium and vanadium ionic spins, resembling the behavior in one-dimensional spin chains.
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Large assemblies of self-organized aluminum nanoclusters embedded in an oxide layer are formed on graphene templates and used to build tunnel-junction devices. Unexpectedly, single-electron-transport behavior with well-defined Coulomb oscillations is observed for a record junction area of up to 100 µm containing millions of metal islands. Such graphene-metal nanocluster hybrid materials offer new prospects for single-electron electronics.

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Article Synopsis
  • - We studied how temperature affects a second order magnetic phase transition in tiny Cr2O3 clusters embedded in an insulating MgO layer, using tunnel magneto-resistance to examine them.
  • - The Cr2O3 clusters transition from an anti-ferromagnetic state, which has no net magnetic moment at near absolute zero, to a weak ferromagnetic state that reaches saturation around 10 K.
  • - Additionally, we found that the temperature at which this magnetic phase transition occurs can be influenced by applying an electric field, showing a linear relationship between the two.
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The near-field Coulomb interaction between a nanoemitter and a graphene monolayer results in strong Förster-type resonant energy transfer and subsequent fluorescence quenching. Here, we investigate the distance dependence of the energy transfer rate from individual, (i) zero-dimensional CdSe/CdS nanocrystals and (ii) two-dimensional CdSe/CdS/ZnS nanoplatelets to a graphene monolayer. For increasing distances d, the energy transfer rate from individual nanocrystals to graphene decays as 1/d(4).

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Epitaxial growth of electrodes and tunnel barriers on graphene is one of the main technological bottlenecks for graphene spintronics. In this paper, we demonstrate that MgO(111) epitaxial tunnel barriers, one of the prime candidates for spintronic application, can be grown by molecular beam epitaxy on epitaxial graphene on SiC(0001). Ferromagnetic metals (Fe, Co, Fe20Ni80) were epitaxially grown on top of the MgO barrier, thus leading to monocrystalline electrodes on graphene.

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Highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is increasingly used as a bearing material in total hip replacements. Cross-linking of UHMWPE has been shown to increase wear resistance but decrease its fracture resistance. We analyzed the clinical fracture failure of four cross-linked UHMWPE total hip replacement components of four different designs via microscopic observation of the fracture surfaces, and found that in all cases fractures initiated at stress concentrations in an unsupported region of the component (termed the elevated rim).

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This is a retrospective radiographic study at 20 to 26 years of follow-up of a single surgeon's consecutive series of patients operated on at 50 years of age or younger with Charnley low-friction arthroplasty. Loosening, osteolysis, and wear were evaluated. Fifty-four patients underwent 68 low-friction arthroplasties.

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