Changes In Hole Density Research Articles

Parameter modulation on p-type doping of AlGaN nanowires

The p-type doping process during the growth of AlGaN nanowires directly influences the optoelectronic properties of the related devices. However, research on the p-type ionization mechanism in AlxGa1-xN nanowires remains limited. In this work, we utilize first principles calculations to investigate p-type doping in AlxGa1-xN nanowires under different structural variables (Al component, doping element, doping site, and doping concentration). Our results demonstrate that p-type doping in AlxGa1-xN nanowires is an endothermic process, and increased dopant concentration leads to a decrease in system stability. Moreover, we found that dopant atoms are easier to substitute for Ga atoms than Al atoms. Among the three doping elements (Zn, Be and Mg), Zn exhibits the most challenging doping difficulty, while Be shows the easiest doping process, with Mg falling in between. Crystal Orbital Hamilton Population (COHP) and bond population calculations reveal the mechanism for the variation in doping structure stability. Doping induces a rearrangement of energy level orbitals, resulting in changes in the band gap. Specifically, the valence band exhibits an overall upward trend crossing the Fermi level, showing the p-type conductive properties. Notably, a significant decrease in electron density near Mg and Be leads to the formation of p-type conductive properties. The changes in hole density and effective mass further confirm the formation of p-type conductivity after doping. Additionally, structures with lower Al composition exhibit higher doping ionization degrees. This study is expected to provide a theoretical basis for the growth, preparation, and application of optoelectronic devices based on p-type AlGaN nanowires.

Temporal Persistence of Red Grouper Holes and Analysis of Associated Fish Assemblages from Towed Camera Data in the Steamboat Lumps Marine Protected Area

AbstractThe Red Grouper Epinephelus morio is an ecologically and economically important Gulf of Mexico reef fish species. The well‐documented excavation behavior of this species generates several‐meter‐wide holes that serve as habitat in otherwise structureless areas. These mesohabitats are notably dense within the Steamboat Lumps (SL) Marine Protected Area (MPA) in the eastern Gulf of Mexico. Previous work in the SL‐MPA used high‐resolution multibeam bathymetry to analyze changes in hole density and structure (width, height, and slope) between 2006 and 2009. The present study utilizes additional multibeam data collected in 2017 to further these analyses. Overall, the density of holes within the SL‐MPA continued to increase, but no definite trend in structural changes could be identified. Additionally, a towed camera was used to directly observe 95 holes, of which 63 had detectable reef fishes. Within the occupied holes, approximately 46% had a Red Grouper or other grouper species (Epinephelidae) present. The most frequently observed species within the occupied holes were invasive lionfish Pterois spp., which were present in 84% of the holes. The increasing density of Red Grouper holes in the SL‐MPA indicates that the closure of the area may be resulting in a more robust local population of this species. However, quick colonization of the holes by lionfish has occurred, and additional studies are necessary to determine the impact of this on grouper and other native reef fish populations found within this type of uniquely created habitat.

Effects of Ge Doping on Micromorphology of MnSi in MnSi∼1.7 and on Their Thermoelectric Transport Properties

MnSi layers in Ge-doped MnSi∼1.7 increased with increasing Ge content up to x=0.00133, began to break at x=0.00265 and finally disappeared at x=0.00530. An experimental equation for the growth of MnSi was proposed for the interval between the MnSi layers and amount of doped Ge content. The crystallinity of Ge-doped MnSi∼1.7 increased initially with increasing doped Ge content and saturated at high Ge content. Thermoelectric transport properties along the c-axis of Ge-doped MnSi∼1.7 were measured as a function of Ge content at room temperature. Electrical conductivity and thermoelectric power of Ge-doped MnSi∼1.7 were compared to those of Al-doped MnSi∼1.7 in our previous work. A maximum in the electrical conductivity and a minimum in the thermoelectric power of Ge-doped MnSi∼1.7 were observed at x=0.00133, reflecting a change in hole density which was influenced by the volume ratio of MnSi. Hole mobility depended on the existence of MnSi layers and/or of interfaces between MnSi∼1.7 and MnSi and on the crystallinity of MnSi∼1.7. The thermal conductivity of Ge-doped MnSi∼1.7 had a maximum at x=0.00053. The increase in thermal conductivity at low Ge doping can be explained by the increase in the amount of MnSi segregated in doped MnSi∼1.7, while the decrease at high Ge content was caused by the increase in phonon scattering of Ge. A maximum figure of merit of Ge-doped MnSi∼1.7 was obtained at x=0.00974, reflecting a maximum power factor.

錯体重合法によるＳｒ‐置換ＹＢａ２Ｃｕ３Ｏ７−ｄの複素帯磁率

We measured complex susceptibilities of Sr-doped YBa2Cu3O7-d superconductors, YBa2-xSrxCu3O7-d (x=0-1.0) and determined the onset temperature of the superconducting transition. The samples were synthesized by the modified polymerized complex method. With increasing x, the onset temperature decreased, although the depletion was not large as those for Sr-doped YBa2Cu4Oy. Measurements of the phonon Raman spectra have revealed that with increasing x the frequencies of the Ba, Cu(2) and apex oxygen O(4) vibrational modes along c-axis change. Besides, at about 570 cm-1, a small growth of a peak was observed with increasing x, which may be caused by oxygen disorder in the CuO chains. But no appreciable changes in hole density were found from optical absorption spectra.

Electronic structure and correlations of CuO3 chains in YBa2Cu3O7.

The correlated ground state of ${\mathrm{CuO}}_{3}$ chains in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ is determined by using a tight-binding model and local-ansatz method. The holes in the chains are found to be delocalized and strongly correlated. Hole correlations are dependent on the hole density in the chains and are somewhat stronger than those in the ${\mathrm{CuO}}_{2}$ planes, being similar at Cu(1) and O(4) sites. The distortions of apical oxygens lead to strong changes in hole density at these atoms.

Optimization of hole density and Tc in Bi 2(Sr,Ca) 3Cu 2O 8+ y by lithium electrochemical reduction

Pellets of BiSrCaCuO with cation ratios 2−1.75−1.25−2 and 2.10−1.67−1−2 have been partially reduced electrochemically in lithium cells to x( Li)=0.20. The reaction is partially reversible only (0.14 Li/formula unit) and proceeds further via a two-phase reaction, possibly involving Cu/Li substitution. The net effect on T c (increasing with x(Li), i.e. with decreasing hole density) and on the c-parameter is consistent with the effect of changes in hole density induced in other ways (quenching, annealing at variable oxygen pressure, alkaline-earth cation substitutions) and confirms that Bi-2212 annealed in air or oxygen and not quenched has a hole density in excess of that corresponding to the maximum T c.