Substitutional doping of Cu in diamond: Mott physics with pp orbitals

Discovery of superconductivity in the impurity band formed by heavy doping of boron into diamond (C:B) as well as doping of boron into silicon (Si:B) has provided a rout for the possibility of new families of superconducting materials. Motivated by the special role played by copper atoms in high temperature superconducting materials where essentially Cu $d$ orbitals are responsible for a variety of correlation induced phases, in this paper we investigate the effect of substitutional doping of Cu into diamond. Our extensive first principle calculations averaged over various geometries based on density functional theory, indicates the formation of a mid-gap band, which mainly arises from the $t_{2g}$ and $4p$ states of Cu. For impurity concentrations of more than $\sim 1$2p$bands of neighboring carbon atoms can be ignored. Based on our detailed analysis, we suggest a two band model for the mid-gap states consisting of a quarter-filled hole like$t_{2g}$band, and a half-filled band of$4p$states. Increasing the concentration of the Cu impurity beyond$\sim 5%, completely closes the spectral gap of the host diamond.Comment: 5 figure

Investigation of bias current and modulation frequency dependences of detectivity of YBCO TES and the effects of coating of Cu-C composite absorber layer

Bolometric response and noise characteristics of YBCO superconductor transition edge IR detectors with relatively sharp transition and its resulting detectivity are investigated both theoretically and experimentally. The magnitude of response of a fabricated device was obtained for different bias currents and modulation frequencies. Using the measured and calculated bolometric response and noise characteristics, we found and analyzed the device detectivity versus frequency for different bias currents. The detectivity versus chopping frequency of the device did not decrease following the response strongly, due to the decrease of the noise at higher frequencies up to 1 kHz, resulting in maximum detectivity around the modulation frequency of 100 Hz. We also improved the responsivity of the device through the increase of the surface absorption by using a novel infrared absorber, which is made of a copper-carbon composite, coated in a low-temperature process. Within the modulation frequency range studied in this paper, comparison of device detectivity before and after coating is also presented. © 2009 IEEE

Ni nanoparticle catalyzed growth of MWCNTs on Cu NPs @ a-C:H substrate

NiCu NPs @ a-C:H thin films with different Cu content were prepared by co-deposition by RF-sputtering and RF-plasma enhanced chemical vapor deposition (RF-PECVD) from acetylene gas and Cu and Ni targets. The prepared samples were used as catalysts for growing multi-wall carbon nanotubes (MWCNTs) from liquid petroleum gas (LPG) at 825 °C by thermal chemical vapor deposition (TCVD). By addition of Cu NPs @ a-C:H thin layer as substrate for Ni NPs catalyst, the density of the grown CNTs is greatly enhanced in comparison to bare Si substrate. Furthermore the average diameter of the grown CNTs decreases by decreasing of Cu content of Cu NPs @ a-C:H thin layer. However Cu NPs @ a-C:H by itself has no catalytic property in MWCNTs growth. Morphology and electrical and optical properties of Cu NPs @ a-C:H thin layer is affected by Cu content and each of them is effective parameter on growth of MWCNTs based on Ni NPs catalyst. Moreover, adding of a low amount of Ni NPs doesn’t vary optical, electrical and morphology properties of Cu NPs @ a-C:H thin layer but it has a profound effect on its catalytic activity. Finally the density and diameter of MWCNTs can be optimized by selection of the Cu NPs @ a-C:H thin layer as substrate of Ni NPs