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- Odén, Magnus, 1965-, et al.
(författare)
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Growth of single-crystal CrN on MgO(001) : Effects of low-energy ion-irradiation on surface morphological evolution and physical properties
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:6, s. 3589-3597
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Tidskriftsartikel (refereegranskat)abstract
- CrN layers, 0.5 ╡m thick, were grown on MgO(001) at Ts=570-775░C by ultrahigh vacuum magnetically unbalanced magnetron sputter deposition in pure N2 discharges at 20 mTorr. Layers grown at Ts=700░C are stoichiometric single crystals exhibiting cube-on-cube epitaxy: (001)CrN(001)MgO with [100]CrN[100]MgO. At higher temperatures, N2 desorption during deposition results in understoichiometric polycrystalline films with N fractions decreasing to 0.35, 0.28, and 0.07 with Ts=730, 760, and 775░C, respectively. The surface morphologies of epitaxial CrN(001) layers were found to depend strongly on the incident ion-to-metal flux ratio JN2+/JCr which was varied between 1.7 and 14 with the ion energy maintained constant at 12 eV. The surfaces of layers grown with JN2+/JCr=1.7 consist of self-organized square-shaped mounds, due to kinetic roughening, with edges aligned along orthogonal <100> directions. The mounds have an average peak-to-valley height =5.1 nm and an in-plane correlation length of =0.21 ╡m. The combination of atomic shadowing by the mounds with low adatom mobility results in the formation of nanopipes extending along the growth direction. Increasing JN2+/JCr to 14 leads, due to increased adatom mobilities, to much smoother surfaces with =2.5 nm and =0.52 ╡m. Correspondingly, the nanopipe density decreases from 870 to 270 ╡m-2 to <20 ╡m-2 as JN2+/JCr is increased from 1.7 to 6 to 10. The hardness of dense CrN(001) is 28.5▒1 GPa, but decreases to 22.5▒1 GPa for layers containing significant nanopipe densities. The CrN(001) elastic modulus, 405▒15 GPa, room-temperature resistivity, 7.7╫10-2 cm, and relaxed lattice constant, 0.4162▒0.0008 nm, are independent of JN2+/JCr. ⌐ 2002 American Institute of Physics.
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- Shin, C.-S., et al.
(författare)
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Epitaxial NaCl structure d-TaNx(001) : Electronic transport properties, elastic modulus, and hardness versus N/Ta ratio
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:6, s. 2879-2885
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Tidskriftsartikel (refereegranskat)abstract
- While metastable Bl-NaCl-structure d-TaNx. is presently used in a variety of hard coating, wear-resistant, and diffusion barrier applications, it is a complex material exhibiting a wide single-phase field, x?0.94-1.37, and little is known about its fundamental properties. Here, we report physical properties of epitaxial d-TaNx. layers grown as a function of x on MgO(00) by ultrahigh vacuum reactive magnetron sputter deposition. The room-temperature resistivity (? = 225 µO cm), hardness (H = 30.9 GPa), and elastic modulus (E = 455 GPa) of d-TaNx(001) are independent of x over the range 0.94-1.22. However, changes in the electronic structure associated with increasing x>1.22 lead to an increase in ? with a decrease in H and E. All d-TaNx(001) layers exhibit negative temperature coefficients of resistivity between 20 and 400 K due to weak carrier localization. d-TaNx is superconducting with the highest critical temperature, 8.45 K, obtained for layers with the lowest N/Ta ratio, x=0.94. Based upon the above results, combined with the fact that the relaxed lattice constant a0 shows only a very weak dependence on x, we propose that the wide phase field in d-TaNx is due primarily to antisite substitutions of Ta on N (and N on Ta) sites, rather than to cation and anion vacancies. To first order, antisite substitutions in TaNx are isoelectronic and hence have little effect on charge carrier density. At sufficiently high N/Ta ratios, however, simple electron-counting arguments are no longer valid since large deviations from stoichiometry alter the character of the band structure itself. © 2001 American Institute of Physics.
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- Wilson, A. N., et al.
(författare)
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Magnetic dipole bands in 190Hg : First evidence of excitations across the Z = 82 sub-shell in Hg nuclei
- 2001
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 505:1-4, s. 6-14
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Tidskriftsartikel (refereegranskat)abstract
- An experiment aimed at studying high-spin states in 190Hg was performed with the Eurogam II array. The data have revealed the presence of cascades of magnetic dipole transitions with some unexpected properties. Unlike the MI bands previously observed in the heavier Hg isotopes, these structures have extremely large B(M1)/B(E2) ratios, The observation of a third dipole band with much lower B(M1)/B(E2) values in the same spin/excitation energy regime suggests that the bands may represent configurations occurring in different minima in the potential energy surface. Configuration-dependent Cranked Nilsson-Strutinsky calculations predict the presence of a minimum in the nuclear potential energy surface at a deformation of ε ≅ 0.2, γ ≅ -90°, occurring when a proton is excited across the Z = 82 shell-gap into an h9/2 orbital. It is suggested that the bands exhibiting anomalously large B(M1)/B(E2) ratios may be associated with this minimum.
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