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D Teehan

Publications and source records attributed to D Teehan.

5 recordsLinked to original sources
PubMed1998

Higher-order suppression in diffraction-grating monochromators using thin films.

Although a continuously tuneable source of photons is a very desirable feature of synchrotron radiation it has one main drawback: the contamination of the photon beam by higher-order diffracted light. Several elements have absorption edges which lie between 10 and 200 eV, a range prone to high second- and third-order content in XUV monochromators. They can, therefore, be used as transmission filters to reduce this higher-order content. This paper describes the use of thin filters to reduce the higher-order content in diffraction-grating monochromators. Their suppression efficiency, transmission and ageing have been characterized using photoelectron spectroscopy and compared with calculated values. The effect of oxide contamination on their performance has been assessed. Filters are now installed on eight XUV beamlines and have been in routine use for several years.

Journal Article↗
PubMed1998

Development of high-throughput flexible multichannel electron detectors at Daresbury Laboratory.

Continuing demands from Synchrotron Radiation Source (SRS) end-users for higher throughput and improved reliability in photoelectron spectroscopy experiments have driven an intensive development programme for new multichannel electron detectors. The development philosophy focuses on high throughput to match present and future source intensity, flexible structures to allow increased mobility of designs and modular design for easy maintenance and repair. Developments include parallel readout electronics and innovative detector heads for the hemispherical deflection analysers currently in use on the SRS. Novel anode arrays have been implemented in the detector heads and extensive microchannel plate (MCP) characterization has been undertaken to source the MCPs most suited to this application. The present multichannel detection systems provide a significant enhancement to single-channel detection systems. They have also surpassed previous multichannel detection systems due to their high throughput, flexible structure and modular design. Information on these developments and experimental results obtained at Daresbury Laboratory are presented.

Journal Article↗
PubMed1995

Resonant photoemission from complex cuprates and nickelates.

Synchrotron-excited resonant-photoemission measurements at rare-earth 4d --> 4f and transition-metal 3p --> 3d thresholds have been carried out using a variety of complex cuprates and nickelates on stations 6.1 (grazing-incidence monochromator) and 6.2 (toroidal-grating monochromator) at the SRS CLRC Daresbury Laboratory. The systems studied are Nd(2)Ni(1 - x)Cu(x)O(4), La(2 - x)Sr(x)Ni(1- y)Fe(y)O(4 + delta) and Bi(2)Sr(2)Ca(1 - x)Y(x)Cu(2)O(8 + delta). A combination of EDC and constant-initial-state data is used to examine the 4f and 3d contributions to the valence-band density of states and their binding-energy positions relative to the Fermi energy. This allows the study of the valence states of the transition-metal ions and their modulation on doping. For La(2 - x)Sr(x)Ni(1 - y)Fe(y)O(4 + delta), this approach is used to infer a valence state of >/= 3.0 for Fe. In the case of Bi(2)Sr(2)Ca(1 - x)Y(x)Cu(2)O(8 + delta), the effect of Cu valence modulation on the 3p resonance is observed as x is varied. This is discussed in the light of controversy surrounding shifts in core-level photoemission with doping for this system.

Journal Article↗