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R. G. Buckley

Bio: R. G. Buckley is an academic researcher from MacDiarmid Institute for Advanced Materials and Nanotechnology. The author has contributed to research in topics: Raman spectroscopy & Sea ice. The author has an hindex of 25, co-authored 110 publications receiving 2997 citations. Previous affiliations of R. G. Buckley include Simon Fraser University & Industrial Research Limited.


Papers
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Journal ArticleDOI
TL;DR: In this paper, annealing results for several Tl-superconductors in the series Tlm(Ba, Sr)2Can−1CunO2n+m+2+δ, for both m=1 and 2, revealing two general results for this class of Bi or TI superconductors: (1) effects on Tc due to labile oxygen occur for all m=2 compounds but are absent in m = 1 compounds with Sr.
Abstract: We have previously shown that Tc for Bi2 (Sr, Ca)n+1CunO2n+4+δ (n=1, 2 and 3) varies with oxygen stoichiometry δ determined by annealing in a variety of oxygen partial pressures and temperatures. Annealing results are now also presented for several Tl-superconductors in the series Tlm(Ba, Sr)2Can−1CunO2n+m+2+δ, for both m=1 and 2, revealing two general results for this class of Bi or TI superconductors: (1) effects on Tc due to labile oxygen occur for all m=2 compounds but are absent in m = 1 compounds with Sr. m=1 compounds with Ba do have variable oxygen but the effects on the c-axis are the opposite to m=2 compounds. This suggests for the latter that the labile oxygen resides in interstitial sites within the Bi2O2 or Tl2O2 bi layers; (2) the hole concentration per Cu decreases in progressing from n = 1 to 2 to 3 in either class so that the parent n = 3 and n = 2 compounds lie respectively on the low- and high-hole concentration sides of the peak in Tc while the n = 1 compounds extend out into the non-superconducting domain at very high hole concentration.

712 citations

Journal ArticleDOI
01 May 1988-Nature
TL;DR: In this paper, three distinct phases in the homologous series Bi2.1 were identified and indexed on a pseudo-tetragonal subcell with a = b = 5.4 A and c = 24.6 A. The critical temperature for these phases is sharply dependent on the Sr/Ca ratio and oxygen stoichiometry, as determined by heat treatment.
Abstract: Following the report of Maeda et al.1 on high-Tc superconductivity in samples of nominal composition BiSrCaCu2Ox we have identified three distinct phases in the homologous series Bi2.1(Ca, Sr)n+lCunO2n+4+δ with n = 1,2 and 3. These have zero resistance Tcs of 80 K, 91 K and 105 K respectively. The structures in the homologous series appear to be based on alternating double bismuth Bi2O2 layers and perovskite (Sr, Ca)O–CuO2 layers, with higher members obtained by intercalating additional 3.1 A Ca-CuO2 bilayers. The structures can be indexed on a pseudo-tetragonal subcell with a = b = 5.4 A and c = 24.4 A (n = 1), 30.76 A (n = 2) or 36 A (n = 3). We were unable to prepare the n =4 member. In each structure a 2× superlattice structure in the c-direction arises as a natural consequence of a 19/4 incommensurate structure in the b direction, which accounts for 2.1 Bi atoms in the unit formula. The critical temperature, Tc, for these phases is sharply dependent on the Sr/Ca ratio and oxygen stoichiometry, as determined by heat treatment.

271 citations

Journal ArticleDOI
TL;DR: In this article, the authors measured the thermoelectric power and conductivity as a function of temperature of a wide range of polypyrrole samples, including a film of soluble poly pyrrole synthesized chemically, and wrinkled films synthesized using indium-tin oxide electrodes.
Abstract: We have measured the thermoelectric power and conductivity as a function of temperature of a wide range of polypyrrole samples, including a film of soluble polypyrrole synthesized chemically, and wrinkled films synthesized using indium–tin oxide electrodes; other samples investigated include high-conductivity polypyrrole films synthesized at different temperatures and current densities, films grown on nonconducting substrates, and polypyrrole gas sensors. The thermoelectric powers are remarkably similar and metal-like for the medium and high conductivity samples but show nonzero extrapolations to zero temperature for wrinkled samples. The temperature dependence of conductivity tends to be greater for samples of lower conductivity. In contrast to polyaniline and polyacetylene, a crossover to metallic sign for the temperature dependence of conductivity at higher temperatures is not observed in any of our samples; the fluctuation-induced tunnelling and variable-range hopping expressions account for nearly all our conductivity data except for low-temperature anomalies. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 953–960, 1999

130 citations

Journal ArticleDOI
TL;DR: The sensitivity of Tc to oxygen sorption and the Ca to Sr ratio has been studied for the homologous series Bi2 in this article, where single phase n=2 samples were equilibrated under a fixed partial pressure of oxygen at temperatures between 300 and 850°C and quenched in liquid nitrogen.
Abstract: The sensitivity of Tc to oxygen sorption and the Ca to Sr ratio has been studied for the homologous series Bi2.1(CaχSr1−χ)n+1CunO2n+4+δ for n=1, 2 and 3. The n=0 and n=∞ members have been produced as single phase samples but are found to be semiconducting. While single phase n=2 material has been prepared, the n=1 member always displays a small n=2 contribution to the X-ray diffraction pattern. n=3 is only found in multiphase samples. Single phase superconducting samples were equilibrated under a fixed partial pressure of oxygen at temperatures between 300 and 850°C and quenched in liquid nitrogen. It is shown that Tc can be controlled in a reversible and systematic way by varying the oxygen partial pressure and the annealing temperature and consequently the oxygen stoichiometry. The site energy per oxygen sorbed for n=2 is 3.24 eV, only a little less than that for YBa2Cu3O7. However, the volume change on sorption is ten times smaller than that for YBa2Cu3O7, and is manifested as a changing c-axis with the a-axis invariant. This can be interpreted as implying that oxygen sorption occurs within the Bi-O layers. Tc is found to be maximised for a Ca to Sr ratio of 1 to 2 for both n=1 and 2. Thermal expansion data for n=2 material is also reported to illustrate that oxygen sorption does effect the physical properties of these materials.

121 citations

Journal ArticleDOI
TL;DR: In this article, a Raman study of diamond films prepared by the filament assisted chemical vapor deposition technique from a methane-hydrogen gas mixture was performed and it was shown that Raman spectroscopy is a useful probe of both the phase of carbon present and of the diamond component in the films.
Abstract: Results are presented on a Raman study of diamond films prepared by the filament‐assisted chemical vapor deposition technique from a methane‐hydrogen gas mixture. It is shown that Raman spectroscopy is a useful probe of both the phase of carbon present and of the quality of the diamond component in the films. The study entailed varying the total gas pressure, but holding the ratio of CH4 to H2 constant. It is clearly demonstrated that as the pressure is decreased, the density of defects within the diamond phase increases. The increase in defect density as the pressure is lowered leads eventually to disordered forms of carbon. This result can be understood in terms of the relatively higher electron and ion fluxes at the substrate for films prepared at low pressure.

119 citations


Cited by
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TL;DR: A review of the most recent ARPES results on the cuprate superconductors and their insulating parent and sister compounds is presented in this article, with the purpose of providing an updated summary of the extensive literature.
Abstract: The last decade witnessed significant progress in angle-resolved photoemission spectroscopy (ARPES) and its applications. Today, ARPES experiments with 2-meV energy resolution and $0.2\ifmmode^\circ\else\textdegree\fi{}$ angular resolution are a reality even for photoemission on solids. These technological advances and the improved sample quality have enabled ARPES to emerge as a leading tool in the investigation of the high-${T}_{c}$ superconductors. This paper reviews the most recent ARPES results on the cuprate superconductors and their insulating parent and sister compounds, with the purpose of providing an updated summary of the extensive literature. The low-energy excitations are discussed with emphasis on some of the most relevant issues, such as the Fermi surface and remnant Fermi surface, the superconducting gap, the pseudogap and $d$-wave-like dispersion, evidence of electronic inhomogeneity and nanoscale phase separation, the emergence of coherent quasiparticles through the superconducting transition, and many-body effects in the one-particle spectral function due to the interaction of the charge with magnetic and/or lattice degrees of freedom. Given the dynamic nature of the field, we chose to focus mainly on reviewing the experimental data, as on the experimental side a general consensus has been reached, whereas interpretations and related theoretical models can vary significantly. The first part of the paper introduces photoemission spectroscopy in the context of strongly interacting systems, along with an update on the state-of-the-art instrumentation. The second part provides an overview of the scientific issues relevant to the investigation of the low-energy electronic structure by ARPES. The rest of the paper is devoted to the experimental results from the cuprates, and the discussion is organized along conceptual lines: normal-state electronic structure, interlayer interaction, superconducting gap, coherent superconducting peak, pseudogap, electron self-energy, and collective modes. Within each topic, ARPES data from the various copper oxides are presented.

3,077 citations

Journal ArticleDOI
TL;DR: The pseudogap is seen in all high-temperature superconductors and there is general agreement on the temperature and doping range where it exists as discussed by the authors, and it is also becoming clear that the superconducting gap emerges from the normal state pseudogaps.
Abstract: We present an experimental review of the nature of the pseudogap in the cuprate superconductors. Evidence from various experimental techniques points to a common phenomenology. The pseudogap is seen in all high-temperature superconductors and there is general agreement on the temperature and doping range where it exists. It is also becoming clear that the superconducting gap emerges from the normal state pseudogap. The d-wave nature of the order parameter holds for both the superconducting gap and the pseudogap. Although an extensive body of evidence is reviewed, a consensus on the origin of the pseudogap is as lacking as it is for the mechanism underlying high-temperature superconductivity.

1,721 citations

Journal ArticleDOI
TL;DR: It is shown that conducting polymers might be capable of meeting the demands of electricity production from waste heat (co-generation) and natural heat sources and to generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs.
Abstract: Thermoelectric generators (TEGs) transform a heat flow into electricity. Thermoelectric materials are being investigated for electricity production from waste heat (co-generation) and natural heat sources. For temperatures below 200 °C, the best commercially available inorganic semiconductors are bismuth telluride (Bi(2)Te(3))-based alloys, which possess a figure of merit ZT close to one. Most of the recently discovered thermoelectric materials with ZT>2 exhibit one common property, namely their low lattice thermal conductivities. Nevertheless, a high ZT value is not enough to create a viable technology platform for energy harvesting. To generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs. This requires thermoelectric materials that are readily synthesized, air stable, environmentally friendly and solution processable to create patterns on large areas. Here we show that conducting polymers might be capable of meeting these demands. The accurate control of the oxidation level in poly(3,4-ethylenedioxythiophene) (PEDOT) combined with its low intrinsic thermal conductivity (λ=0.37 W m(-1) K(-1)) yields a ZT=0.25 at room temperature that approaches the values required for efficient devices.

1,470 citations

Journal ArticleDOI
07 Mar 2007-Sensors
TL;DR: In this article, a review of gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers has been reviewed.
Abstract: The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

1,333 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compare and contrast the advantages of two limiting perspectives on the high-temperature superconductor: weak coupling, in which correlation effects are treated as a perturbation on an underlying metallic (although renormalized) Fermi-liquid state, and strong coupling, where the magnetism is associated with well defined localized spins, and stripes are viewed as a form of micro phase separation.
Abstract: This article discusses fluctuating order in a quantum disordered phase proximate to a quantum critical point, with particular emphasis on fluctuating stripe order. Optimal strategies are derived for extracting information concerning such local order from experiments, with emphasis on neutron scattering and scanning tunneling microscopy. These ideas are tested by application to two model systems---an exactly solvable one-dimensional (1D) electron gas with an impurity, and a weakly interacting 2D electron gas. Experiments on the cuprate high-temperature superconductors which can be analyzed using these strategies are extensively reviewed. The authors adduce evidence that stripe correlations are widespread in the cuprates. They compare and contrast the advantages of two limiting perspectives on the high-temperature superconductor: weak coupling, in which correlation effects are treated as a perturbation on an underlying metallic (although renormalized) Fermi-liquid state, and strong coupling, in which the magnetism is associated with well-defined localized spins, and stripes are viewed as a form of micro phase separation. The authors present quantitative indicators that the latter view better accounts for the observed stripe phenomena in the cuprates.

1,081 citations