| 1. |
- Dezelah, Charles L., et al.
(författare)
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A low valent metalorganic precursor for the growth of tungsten nitride thin films by atomic layer deposition
- 2007
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 17:11, s. 1109-1116
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Tidskriftsartikel (refereegranskat)abstract
- The atomic layer deposition growth of tungsten nitride films was demonstrated using the precursors W-2(NMe2)(6) and ammonia with substrate temperatures between 150 and 250 degrees C. At 180 degrees C, surface saturative growth was achieved with W-2(NMe2)(6) pulse lengths of >= 2.0 s. The growth rates were between 0.74 and 0.81 angstrom cycle(-1) at substrate temperatures between 180 and 210 degrees C. Growth rates of 0.57 and 0.96 angstrom cycle(-1) were observed at 150 and 220 degrees C, respectively. In a series of films deposited at 180 degrees C, the film thicknesses varied linearly with the number of deposition cycles. Films grown at 180 and 210 degrees C exhibited resistivity values between 810 and 4600 mu Omega cm. Time-of-flight elastic recoil detection analysis on tungsten nitride films containing a protective AlN overlayer demonstrated slightly nitrogen-rich films relative to W2N, with compositions of W1.0N0.82C0.13O0.26H0.33 at 150 degrees C, W1.0N0.74C0.20O0.33H0.28 at 180 degrees C, and W1.0N0.82C0.33O0.18H0.23 at 210 degrees C. In the absence of an AlN overlayer, the oxygen and hydrogen levels were much higher, suggesting that the films degrade in the presence of ambient atmosphere. The as-deposited films were amorphous. Amorphous films containing a protective AlN overlayer were annealed to 600 - 800 degrees C under a nitrogen atmosphere. X-Ray diffraction patterns suggested that crystallization does not occur at or below 800 degrees C. Similar annealing of films that did not contain the AlN overlayer afforded X-ray diffraction patterns that were consistent with orthorhombic WO3. Atomic force microscopy showed root-mean-square surface roughnesses of 0.9, 0.8, and 0.7 nm for films deposited at 150, 180, and 210 degrees C, respectively.
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| 2. |
- Pavlov, Dmitriy A., 1976-
(författare)
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Synthesis and properties of substituted Hg-based superconductors
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is focused on studies of substituted Hg-based superconducting copper oxides ((Hg1-xMx)Ba2Can-1CunO2n+2+δ). These compounds are promising objects of investigation, not only from a fundamental point of view but also because of their high values of superconducting transition temperature (Tc) and irreversibility field (Hirr).The first part of the thesis is devoted to optimization of the synthesis procedure for Hg-based cuprates. The influence of different parameters (T, t, p(Hg), p(O2)) on the synthesis of these compounds in sealed silica tubes was studied. Optimal conditions yielded samples containing up to 95% of HgBa2Ca2Cu3O8+δ (Hg-1223). The formation of solid solutions with the formula (Hg1-xCux)Ba2Ca2Cu3O8+δ (where x <= 0.5) was also established. Another technique was developed, using LiF as a flux, for synthesis of samples containing up to 90% of the HgBa2CaCu2O6+δ (Hg-1212) phase.The second part concerns synthesis and studies of oxyfluorides using Hg-1212 and Hg-1223 as starting materials together with XeF2 as a fluorinating agent. It was found that oxyfluorides of both phases have a parabolic dependence of Tc vs. a parameter as well as enhanced Tc values (ΔT ≈ 3-4 K) in comparison with optimally doped non-fluorinated analogues. The crystal structure of Hg-1223 oxyfluoride was studied by X-ray powder and neutron diffraction methods. It is suggested that chemical modification of the crystal structure leads to a decrease in Cu-O distance without noticeable change in Cu-O-Cu angle (in the (CuO2) layers), which may be the significant factors influencing this Tc increase. Hg-1223 oxyfluoride was also studied under high pressure for first time. It was found that this compound has a record-high Tc value (≈ 166 K) at P ≈ 23 GPa.The last part describes the investigation of substituted Hg-based superconductors in the series (Hg0.9M0.1)Ba2CuO4+δ {(Hg,M)-1201}, where M = Tl, Pb, W, Mo, Nb and V. A comprehensive study of these compounds by various methods (X-ray powder diffraction, EDX, IR-, EXAFS- and XANES -spectroscopy) indicated that the change of charge carrier doping level is a crucial factor determining the irreversibility line. (Hg0.9Mo0.1)Ba2CuO4+δ showed the most improved irreversibility line position among the (Hg,M)-1201 compounds studied in this series.
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| 3. |
- Törndahl, Tobias, 1974-
(författare)
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Atomic Layer Deposition of Copper, Copper(I) Oxide and Copper(I) Nitride on Oxide Substrates
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films play an important role in science and technology today. By combining different materials, properties for specific applications can be optimised. In this thesis growth of copper, copper(I) oxide and copper(I) nitride on two different substrates, amorphous SiO2 and single crystalline α-Al2O3 by the so called Atomic Layer Deposition (ALD) techniques has been studied. This technique allows precise control of the growth process at monolayer level on solid substrates. Other characteristic features of ALD are that it produces films with excellent step coverage and good uniformity even as extremely thin films on complicated shaped substrates.Alternative deposition schemes were developed for the materials of interest. It was demonstrated that use of intermediate water pulses affected the deposition pathways considerably. By adding water, the films are thought to grow via formation of an oxide over-layer instead of through a direct reaction between the precursors as in the case without water.For growth of copper(I) nitride from Cu(hfac)2 and ammonia no film growth occurred without adding water to the growth process. The Cu3N films could be transformed into conducting copper films by post annealing. In copper growth from CuCl and H2 the water affected film growth on the alumina substrates considerably more than on the fused silica substrates. The existence of surface -OH and/or -NHx groups was often found to play an important role, according to both theoretical calculations and experimental results.
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