| 11. |
- Doyle, James P.
(författare)
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Copper germanide schottky contacts to silicon and electrically active defects in n-type 6H-SiC and 4H-SiC epitaxial layers
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metallization for contacts to silicon devices presents amajor challenge as the linewidths are further reduced into thesub-micron regime. Copper germanide due to its relatively lowroom temperature resistivity ( ~ 10 µΩ - cm) has beenexamined as a potential contact metallixation. In addition, dueto the growing interest in silicon carbide as a potentialwide-bandgap semiconductor candidate for high voltage, power,and frequency devices, a characterization of electricallyactive deep levels was conducted on as-grown and electron andion irradiated layers as such defects can influence theelectrical behaviour of active devices. N-type 6H- and 4H-SiChave been characterized by deep level transient spectroscopy(DLTS) in conjunction with MeV electron beam irradiation andkeV hydrogen and deuterium implantation. Intrinsic levels havebeen identified in both polytypes through an examination ofas-grown and irradiated samples.It is demonstrated that silicon outdiffusion into the coppergermanide contact causes an increase in the electricalresistivity. Additionally, deviation from ideal behaviour isobserved in current-voltage (IV) measurements an indicationthat this outdiffusion of silicon produces recombinationcenters primarily in the upper part of the bandgap near to thecontact-semiconductor interface. Additionally, copper germanideis found to be morphologically unstable during theamorphous-to-crystalline transformation. The high diffusivityof copper in amorphous germanium at temperatures as low as 200°C coupled with the independence of the barrier height onthe germanium fraction used during contact formation indicatesthat the interface between copper germanide and silicon issimilar to that of copper silicide and silicon.A number of electrically active deep levels have beencharacterized in both the 4H- and 6H-SiC polytypes. In 6H-SIC,many of the defects are found to be intrinsic as they areobserved to grow as a function of increasing irradiation dose.In contrast, as-grown 4H-SiC epitaxial layers, exhibit only asingle acceptor-like level at 0.70 eV below the conduction bandedge (Ec). After irradiation the level is not observed toincrease in concentration, but two new levels are found. Theselevels are found to be unstable at room temperature in contrastto the 6H-SiC defects. In 6H-SiC, the defect concentration isfound to limit the average carrier lifetime. Through the use ofthermal annealing, SIMS, and electron irradiation, a model oftheir Origin is proposed.Keywords:Deep level transient spectroscopy (DLTS),secondary ion mass spectrometry (SIMS), amorphous germanium,electron irradiation, ion irradiation, wide-bandgap
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| 12. |
- James, P, et al.
(författare)
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Calculated magnetic properties of binary alloys between Fe, Co, Ni, and Cu
- 1999
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Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - : AMERICAN PHYSICAL SOC. - 0163-1829. ; 59:1, s. 419-430
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present a detailed theoretical investigation of the magnetic properties of all the binary alloys between the 3d elements Fe, Co, Ni, and Cu, in the fee, bcc, and hcp structures using the coherent-potential approximation in combination with a linear muf
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Leblanc, James P., et al.
(författare)
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Fractionally spaced CMA equalizers under periodic and correlated inputs
- 1995
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Ingår i: Conference proceedings ICASSP-95. - Piscataway, NJ : IEEE Communications Society. ; , s. 1041-1044
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Konferensbidrag (refereegranskat)abstract
- CMA fractionally spaced equalizers (CMA-FSEs) have been shown, under certain conditions, to be globally asymptotically convergent to a setting which provides perfect equalization. Such a result relies heavily on the assumptions of a white source and no channel noise (as is the case in much of the literature's analysis of CMA). Herein, we relax the white source assumption and examine the effect of source correlation on CMA. Analytic results are meshed with examples showing CMA-FSE source correlation effects. Techniques for finding all stationary and saddle points on the CMA-FSE error surface are presented using recent developments in the algebraic-geometry community.
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| 17. |
- Lorber, Christian, et al.
(författare)
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Synthesis, Structures and Oxo Transfer Reactivity of bis(Dithiolene) Tungsten(IV,VI) Complexes Related to the Active Sites of Tungstoenzymes
- 1998
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 120:32, s. 8102-8112
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Tidskriftsartikel (refereegranskat)abstract
- A series of bis(dithiolene)tungsten(IV,VI) complexes derived from benzene-1,2-dithiolate (bdt) has been prepared as an synthetic approach to pterin dithiolene-bound active sites of tungstoenzymes, one example of which, a archaeal oxidoreductase, has been established crystallographically (Chan et al. Science 1995, 267, 1463). With [WIVO(bdt)2]2- (2) as the starting compound, silylation with RR'2SiCl afforded [WIV(bdt)2(OSiRR'2)]1- (4). Oxidation of 4 with Me3NO gave [WVIO(bdt)2(OSiRR'2)]1- (5), also accessible by silylation of [WVIO2(bdt)2]2- (3). Reaction of 3 or 5 with Me3SiCl resulted in [WVIO(bdt)2Cl]1- (6), from which the unstable species [WVIO(bdt)2L]1- (L = ButO-, PhS-) were generated in solution. Reductive oxo transfer of 6 with L' = P(OEt)3 or ButNC/P(OEt)3 gave [WIV(bdt)2L'2] (8 and 9). Sulfido complex [WVIS(bdt)2(OSiRR'2)]1- (12) was obtained in the reaction systems 4/(PhCH2S)2S and 5/(Me3Si)2S. Structures of [WO(SPh)4]1- and [W(bdt)3]2- and eight complexes of types 4-6, 8, 9, and 12 were determined by X-ray crystallography. Complexes 4 and 5 are tungsten analogues of the desoxo Mo(IV) and monooxo Mo(VI) states of Rhodobacter sphaeroides DMSO reductase. Six types of reactivity, including oxygen atom transfer, are recognized by the synthesis and interconversion of the set of complexes. The potential biological relevance of these complexes to the structure and function of active sites in two families of tungstoenzymes is considered (RR'2 = Me3 (4); ButMe2 (4 and 5), ButPh2 (4, 5, and 12)).
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| 18. |
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| 19. |
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| 20. |
- Thapper, Anders, et al.
(författare)
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The Unperturbed Oxo-Sulfido Functional Group cis-Mo(VI)OS, Related to that in the Xanthine Oxidase Family of Molybdoenzymes: Synthesis, Structural Characterization and Reactivity Aspects
- 1999
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 38:18, s. 4104-4114
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Tidskriftsartikel (refereegranskat)abstract
- The oxo-sulfido functional group cis-MoVIOS is essential to the activity of the xanthine oxidase family of enzymes but has proven elusive to synthesis in molecules containing no other four-electron ligands. A direct route to molecules containing this group has been achieved. The reaction system [MoO2(OSiPh3)2]/L in dichloromethane yields the complexes [MoVIO2(OSiPh3)2L] (L = phen (1), Me4phen (2), 4,4'-Me2bpy (3), 5,5'-Me2bpy (4), 2 py (5)) (74-96%), which are shown to have a distorted octahedral structure of crystallographically imposed C2 symmetry (1, 5) with cis oxo and trans silyloxy ligands. The related reaction system [MoO3S]2-/2Ph3SiCl/L in acetonitrile affords the complexes [MoVIOS(OSiPh3)2L] (L = phen (6), Me4phen (7), 4,4'-Me2bpy (8), 5,5'-Me2bpy (9)) (36-69%). From the collective results of elemental analysis, mass spectrometry, 1H NMR, and X-ray structure determinations (6, 7), complexes 6-9 are shown to contain the cis-MoVIOS group in molecules with the same overall stereochemistry as dioxo complexes 1-5. The crystal structures of 6 and 7 exhibit O/S disorder, which was modeled in refinements with 50% site occupancies. The Mo=O (1.607(5) (6), 1.645(5) (7) Å) and Mo=S (2.257(3) (6), 2.203(2) (7) Å) bond distances obtained in this way are somewhat shorter and longer, respectively, than expected. Distances obtained by molybdenum EXAFS analysis using the GNXAS protocol for 6-9 (Mo=O 1.71-1.72 Å; Mo=S 2.18-2.19 Å) are considered more satisfactory and are in good agreement with EXAFS values for xanthine oxidase. Molybdenum K-edge data for 1 and 6-9 are reported. Reaction of 7 with Ph3P in dichloromethane results in sulfur abstraction and formation of [MoVOCl(OSiPh3)2(Me4phen)] (10), which has a distorted octahedral structure with cis O/Cl and cis silyloxy ligands. Sulfur rather than oxygen abstraction is favored by relative Mo=O/Mo=S bond strengths. Complexes 6-9 should allow exploration of the biologically significant cis-MoVIOS group.
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