Steve M. Heald

Bio: Steve M. Heald is an academic researcher from Argonne National Laboratory. The author has contributed to research in topics: Extended X-ray absorption fine structure & XANES. The author has an hindex of 56, co-authored 323 publications receiving 10054 citations. Previous affiliations of Steve M. Heald include Pacific Northwest National Laboratory & University of Washington.

Intrinsic Ferromagnetism in Insulating Cobalt Doped Anatase TiO2

Abstract: Using complementary experiments we show that the room temperature ferromagnetism observed in anatase $\mathrm{Co}\ensuremath{\mathbin:}{\mathrm{TiO}}_{2}$ films is not carrier mediated, but coexists with the dielectric state. TEM and x-ray absorption spectroscopy reveal a solid solution of Co in anatase, where Co is not metallic but in the $+2$ state substituting for Ti. Measurements at 300 K yield a ${M}_{\mathrm{S}}$ of $1.1\text{ }\text{ }{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Co}$ atom, while all films are highly insulating. The evidence of intrinsic ferromagnetism in the dielectric ground state of $\mathrm{Co}\ensuremath{\mathbin:}{\mathrm{TiO}}_{2}$ leads to new considerations for the origin of ferromagnetism in transition metal doped oxides.

(De)Lithiation Mechanism of Li/SeSx (x = 0–7) Batteries Determined by in Situ Synchrotron X-ray Diffraction and X-ray Absorption Spectroscopy

Abstract: Electrical energy storage for transportation has gone beyond the limit of converntional lithium ion batteries currently. New material or new battery system development is an alternative approach to achieve the goal of new high-energy storage system with energy densities 5 times or more greater. A series of SeSx–carbon (x = 0–7) composite materials has been prepared and evaluated as the positive electrodes in secondary lithium cells with ether-based electrolyte. In situ synchrotron high-energy X-ray diffraction was utilized to investigate the crystalline phase transition during cell cycling. Complementary, in situ Se K-edge X-ray absorption near edge structure analysis was used to track the evolution of the Se valence state for both crystalline and noncrystalline phases, including amorphous and electrolyte-dissolved phases in the (de)lithiation process. On the basis of these results, a mechanism for the (de)lithiation process is proposed, where Se is reduced to the polyselenides, Li2Sen (n ≥ 4), Li2Se2, an...

Direct kinetic correlation of carriers and ferromagnetism in Co2+: ZnO.

Abstract: In only a few cases have the key factors controlling long-range magnetic ordering in diluted magnetic semiconductors (DMSs) been unambiguously identified. In Ga1� xMnxAs, the identification and variation of critical experimental parameters has culminated in a testable microscopic model describing hole-mediated magnetic ordering in this and several related manganese-doped III-V semiconductors [1]. The recent discovery of high-Curietemperature (TC) ferromagnetism in doped oxide semiconductors has stimulated intense experimental and theoretical interest in these materials [2]. In contrast with Ga1� xMnxAs, a clear consensus has not yet been reached about the relationship between carriers (bound or free) and ferromagnetism in these doped oxides. Only through identification and systematic variation of key compositional parameters will a significant advance in the understanding of high-TC ferromagnetism in doped oxides be realized. In this Letter, we demonstrate that the native shallow donor interstitial zinc (Zni) is capable of activating high-TC ferromagnetism in Co 2� -doped ZnO (Co 2� : ZnO). The Zni concentration in an oriented epitaxial thin film of Co 2� : ZnO was systematically varied by controlled oxidative removal of these shallow donors at elevated temperatures. A direct correlation between the 300 K ferromagnetic saturation moment (MS) and the concentration of Zni was observed. The experimental activation barriers clearly identify the diffusion of Zni as the rate-determining process in the oxidative quenching of ferromagnetism in Co 2� : ZnO. These results provide conclusive evidence that the high-TC ferromagnetism in Co 2� : ZnO is mediated by

X-ray filter assembly for fluorescence measurements of x-ray absorption fine structure.

Abstract: Fluorescence detection, in principle, permits the detection of the extended x-ray absorption fine structure (EXAFS) of more dilute atoms than can be obtained in absorption. To take advantage of this it is necessary, in practice, to eliminate the background that normally accompanies the fluorescence signal. We describe an x-ray filter assembly that accomplishes this purpose. The unique characteristic of the assembly is a slit system that minimizes the fluorescence background from the filter. The theory of the slit assembly is presented and is found to agree with measurements made on the Fe EXAFS of a dilute sample. The filter assembly has a better effective counting rate in this case than that of a crystal monochromator design.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Diamond-like amorphous carbon

Abstract: Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).