| 1. |
- Birch, J., et al.
(författare)
-
Structural characterization of precious-mean quasiperiodic Mo/V single-crystal superlattices grown by dual-target magnetron sputtering
- 1990
-
Ingår i: Physical Review B. - 1098-0121. ; 41:15, s. 10398-10407
-
Tidskriftsartikel (refereegranskat)abstract
- A class of quasiperiodic superlattice structures, which can be generated by the concurrent inflation rule A→AmB and B→A (where m=positive integer), has been studied both theoretically and experimentally. Given that the ratios between the thicknesses of the two superlattice building blocks, A and B, are chosen to be γ(m)=[m+(m2+4)1/2]/2 (known as the ‘‘precious means’’), then the x-ray- and electron-diffraction peak positions are analytically found to be located at the wave vectors q=2πΛ−1r[γ(m)]k, where r and k are integers and Λ is an average superlattice wavelength. The analytically obtained results have been compared to experimental results from single-crystalline Mo/V superlattice structures, generated with m=1, 2, and 3. The superlattices were grown by dual-target dc-magnetron sputtering on MgO(001) substrates kept at 700 °C. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) showed that the analytical model mentioned above predicts the peak positions of the experimental XRD and SAED spectra with a very high accuracy. Furthermore, numerical calculations of the diffraction intensities based on a kinematical model of diffraction showed good agreement with the experimental data for all three cases. In addition to a direct verification of the quasiperiodic modulation, both conventional and high-resolution cross-sectional transmission electron microscopy (XTEM) showed that the superlattices are of high crystalline quality with sharp interfaces. Based on lattice resolution images, the width of the interfaces was determined to be less than two (002) lattice-plane spacings (≊0.31 nm).
|
|
| 2. |
- Cheng, Y.F., et al.
(författare)
-
TEM study of the early stages of the precipitation process in strip-cast Al3003 alloys
- 1992
-
Ingår i: Journal of Materials Research. - 0884-2914. ; 7, s. 3235-3241
-
Tidskriftsartikel (refereegranskat)abstract
- The precipitation behavior, especially the early nucleation stages, of the industrial strip-cast Al3003 alloys was investigated by using transmission electron microscopy (TEM). An icosahedral quasicrystalline phase was found as secondary particles in these strip-cast alloys after heat treatment for a few seconds. Three different nucleation paths are proposed based on the TEM observations. They have the same origin, viz. (Mn, Fe)-containing Mackay icosahedra, and are governed by the composition of alloys, especially the Mn and Si content.
|
|
| 3. |
- Ferrow, EA, et al.
(författare)
-
Compositional control of plane group symmetry in tourmalines : an experimental and computer simulated TEM, crystallographic image processing and Mossbauer spectroscopy study
- 1993
-
Ingår i: European Journal of Mineralogy. - 0935-1221. ; 5:3, s. 479-492
-
Tidskriftsartikel (refereegranskat)abstract
- Tourmalines with different compositions show different plane group symmetries in experimental high resolution transmission electron microscopy (HRTEM) when projected along the c-axis. Fe-poor elbaite shows p31m symmetry, while Fe-bearing elbaite shows p3m1 symmetry. Rubellite shows p6 symmetry, while Fe-Mg-Al-bearing tourmaline shows a `pseudo' p6 type of symmetry. Symmetries p3m1 and p6 are not compatible with the space group R3m assigned to tourmaline from X-ray structural determination studies. The perturbations of symmetry from p31m to p6 and `pseudo' p6 depend on the magnitude of the scattering amplitude of the atoms occupying the 3a and 9b sites. Furthermore, computer simulations of elbaite, schorl and dravite show different projected potentials for images down the c-axis. Regions with high mean concentration of light or heavy elements a few unit cells apart are common in Fe-poor elbaite. This results in a marked difference of the distribution contrast in the HRTEM image of elbaite. The Mossbauer effect (ME) spectra of tourmaline are different with different Mossbauer parameters, reflecting the difference in composition. Experimental HRTEM, computer simulation and ME indicate that composition controls symmetry, ME parameters and atomic coordinates in tourmaline, an observation not recorded in other minerals.
|
|
| 4. |
- Hultman, L., et al.
(författare)
-
Formation of polyhedral voids at surface cusps during growth of epitaxial TiN/NbN superlattice and alloy films
- 1992
-
Ingår i: Journal of Vacuum Science and Technology A. - : American Vacuum Society. - 0734-2101. ; 10:4, s. 1618-1624
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial TiN/NbN(001) superiattice thin films with periods A between 0 (alloy) and 9.6 nm have been grown by ultrahigh vacuum reactive magnetron sputter deposition on MgO(OOl) substrates in mixed Ar/N2 discharges. Cross-sectional transmission electron microscopy was used for characterizing layer and defect structure. Coherency strain relaxation close to the film/substrate interface resulted in nonplanar growth with surface cusps and the creation of apparent column boundaries at which TiN and NbN layers curved towards the substrate, but across which the basic lattice was ordered. Also, a fraction of the boundaries were associated with threading defects along the growth direction. The column boundaries and threading defects were decorated by voids that exhibited an orthorhombohedral shape, were elongated in the growth direction, and typically had flat surfaces on {100} planes. The origin of voids is suggested to be through self-shadowing at surface cusps in combination with limited adatom mobility. The voids subsequently attained equilibrium shape as the result of surface and bulk diffusion. The void density varied withλ and the void length in the growth direction was generally an integer number of periods, indicating that the void formation was influenced by the superiattice layers. The formation of limited voids is suggested to be characteristic of thin film growth close to the epitaxial temperature.
|
|
| 5. |
- Håkansson, G., et al.
(författare)
-
Ion irradiation effects during growth of Mo/V(001) superlattices by dual-target magnetron sputtering
- 1992
-
Ingår i: Journal of Crystal Growth. - 0022-0248. ; 121:3, s. 399-412
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial (001)-oriented Mo/V superlattice films with wavelengths of ≈ 5 nm have been grown on MgO(001) substrates, kept at 700°C, by dual-target unbalanced magnetron sputter deposition in Ar discharges. Low-energy (15-250 eV) Ar ion irradiation with incident ion-to-metal flux ratio of ≈ 1 during film growth was obtained through the application of a negative potential Vs to the substrate. The effects of ion bombardment on interface roughness and mixing, resputtering rates, and defect structure were investigated using a combination of cross-sectional transmission electron microscopy (XTEM), X-ray diffraction (XRD), and simulation of XRD patterns. High-resolution XTEM images showed that the interfaces were relatively sharp for Vs ≤ 100 V while higher Vs values resulted in more diffuse interfaces indicating ion-induced intermixing. By using a kinematical model of diffraction, and comparing with experimental XRD results, it could be concluded that the intermixing increased from ≈ 0.3 nm (2 monolayers) at Vs = 15 V to & 0.9 nm (6 monolayers) at Vs = 250 V. The inhomogeneous strain showed a large increase for Vs & 50 V. This is explained by an incorporation of point defects. Coherency strain relaxation between layers is suggested to take place through the formation of edge dislocations with Burgers vector 〈110〉 by climb processes. Finally, increasing Vs also resulted in resputtering, preferentially from the V layers.
|
|
| 6. |
- Ni, W.-X., et al.
(författare)
-
δ-function-shaped Sb-doping profiles in Si(001) obtained using a low-energy accelerated-ion source during molecular-beam epitaxy
- 1992
-
Ingår i: Physical Review B. - 0163-1829. ; 46:12, s. 7551-7558
-
Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) buried delta-function-shaped Sb-doping profiles have been obtained in Si using a low-energy accelerated Sb-ion source during molecular-beam epitaxy. A combination of secondary-ion mass spectrometry (SIMS), capacitance-voltage (C-V) measurements, and cross-sectional transmission electron microscopy (XTEM) was used to investigate dopant distributions and to determine profile widths. The 2D-sheet Sb-doping concentration N(Sb), obtained by integrating SIMS delta-doping profiles in samples grown with substrate temperature T(s) = 620-degrees-C and Sb-ion acceleration potentials V(Sb) = 200 and 300 V, was found to vary linearly with the product of the Sb-ion flux and the exposure time (i.e., the ion dose) over the N(Sb) range from 5 X 10(12) to 2 X 10(14) cm-2. The full width at half maximum (FWHM) concentration of 8-doping profiles in Si(001) films was less than the depth resolution of both SIMS and C-V measurements (approximately 10 and 3 nm, respectively). High-resolution XTEM lattice images show that the FWHM was less-than-or-equal-to 2 nm. This is consistent with dopant incorporation simulations, based upon a multisite transition-state dopant incorporation model, which show that accelerated-beam dopant species are trapped in near-surface substitutional sites with atomic mobilities between those of surface and bulk atoms. Dopant surface segregation during growth is strongly suppressed, and the dopant distribution is determined primarily by the straggle in ion trapping distributions. The present results are compared with profile broadening observed in 8-doped layers obtained by solid-phase epitaxy of amorphous Si containing a buried Sb layer.
|
|
| 7. |
- Selinder, T.I., et al.
(författare)
-
Structural characterization of yttria (Y2O3) inclusions in YBa2Cu3O7−x films : Growth model and effect on critical current density
- 1993
-
Ingår i: Thin Solid Films. - 0040-6090. ; 229:2, s. 237-248
-
Tidskriftsartikel (refereegranskat)abstract
- A higher critical current and enhanced pinning was obtained in c-axis-oriented YBa2Cu3O7−x (YBCO)films having a higher density of semicoherent yttria (Y2O3) inclusions. The films were grown by sputtering and the inclusion density depends on the fraction of N2O in the sputtering gas. The inclusions were studied by transmission electron microscopy, both in planar sections and in cross-sections. They are embedded in the YBCO matrix without disturbing its structure appreciably, and the inclusion density is up to about 1017 cm−3, comprising about 4% of the film volume. From the appearance of moiré fringes and from high resolution transmission electron micrographs, it is concluded that the inclusions are highly oriented and have coherent or semicoherent interfaces towards matrix. A model for formation of the yttria inclusions during film growth is presented, which includes nucleation of epitaxial coherent yttria islands, layer-by-layer growth and finally overgrowth by advancing steps of the YBCO film. The enhanced pinning and transport critical current densities, relation to film microstructure and the possible flux-pinning mechanisms by these yttria inclusions are discussed.
|
|
| 8. |
- Selinder, T.I., et al.
(författare)
-
Yttrium oxide inclusions in YBa2Cu3Ox thin films : Enhanced flux pinning and relation to copper oxide surface particles
- 1992
-
Ingår i: Physica C: Superconductivity and its Applications. - 0921-4534. ; 202:1-2, s. 69-74
-
Tidskriftsartikel (refereegranskat)abstract
- Semi-coherent Y2O3 (yttria) inclusions are identified in high quality epitaxial YBa2Cu3Ox (YBCO) thin films by using transmission electron microscopy and energy dispersive X-ray analyses. Magnetization measurements show enhanced flux pinning in films containing an increasing number density of inclusions. The inclusions are incorporated into the films without disturbing the YBCO structure appreciably. The number density is ≈ 1017 cm-3 in films having transport critical currents of 4x106 A cm-2 at 77 K. Nucleation of the yttria inclusions is suggested to occur spontaneously during film growth. The abundance of yttria inclusions is connected to the occurrence of large Cu-rich surface particles in films that have optimum superconducting properties.
|
|
| 9. |
- Selinder, TI, et al.
(författare)
-
Microstructure and microwave loss studies on epitaxial YBa2Cu3Ox thin films
- 1992
-
Ingår i: High Tc superconductor thin films. - 0444893539 ; , s. 219-224
-
Konferensbidrag (refereegranskat)abstract
- Thin YBa2Cu3Ox films were grown on SrTiO3 or LaAlO3 single crystals by dc-magnetron reactive sputtering in argon/oxygen gas mixtures. Deposition temperatures ranged from 540 °C to 780 °C. After deposition and subsequent cool down, films grown above 680 °C are superconducting below 86–88 K. All films are oriented with the [001] direction parallel to the [001] substrate normal. The best films have critical current densities well above 106 A/cm2, and effective 6 GHz surface resistance values below 300 μω, at 77 K. Despite good electrical properties, the films are littered with copper rich particles on a smooth and epitaxial single crystalline surface. Cross-section Transmission Electron Microscopy (X-TEM) was used to study the crystalline quality on a microscopic level, and the nature of particles occurring on/in the as grown film. Small misaligned YBa2Cu3Ox grains often occur in the films. The large copper rich particles on the film surface seem to have nucleated at such grains on the film surface. Their occurrence can, at least partly, be explained by a nonstoichiometric flow to the substrate. The number density of the particles decreased with increasing growth temperature but the volume density seemed to be constant in the investigated temperature interval.
|
|
| 10. |
- Sjostrom, H., et al.
(författare)
-
Characterization of interfaces between hydrogenated amorphous carbon films and steel substrates using high resolution cross-sectional transmission electron microscopy
- 1993
-
Ingår i: Diamond and Related Materials. - 0925-9635. ; 2:2-4, s. 562-566
-
Tidskriftsartikel (refereegranskat)abstract
- Cross-sectional transmission electron microscopy, including high resolution microscopy, was employed to characterize the interfaces between hydrogenated amorphous carbon (a-C:H) films and steel substrates. Films were deposited both by ion beam decomposition of large hydrocarbon molecules and by magnetron plasma decomposition of C2H2. The latter method was also used to deposit Mo- and W-containing a-C:H films onto steel substrates with interlayers of the pure metals between the steel substrate and the a-C:H films. The films were found to be amorphous except for the metal-containing films where 1–4 nm crystalline clusters were present in an a-C:H matrix. The metal interlayers had a columnar microstructure with column widths of ∼30 nm. The interfaces between the a-C:H films and the Mo or W interlayers were found to extend over 20–40 nm with a gradual crystalline-to-amorphous transition. In most of the a-C:H film-substrate interface regions a thin (less than 10 nm) layer was observed which was predominantly amorphous, but contained a small fraction of crystalline grains. Additional analyses carried out using Auger electron spectroscopy showed an increase in both O and N close to the interface. However, for the cases with Mo and W interlayers, the substrate surface contaminants were less localized and on some parts of the substrate surface the lattice fringes were continuous across the atomically sharp interface.
|
|
| 11. |
- Sjöström, H., et al.
(författare)
-
Microstructure of amorphous C:H and metal-containing C:H films deposited on steel substrates
- 1993
-
Ingår i: Thin Solid Films. - 0040-6090. ; 232:2, s. 169-179
-
Tidskriftsartikel (refereegranskat)abstract
- Cross-sectional transmission electron microscopy (XTEM), including high-resolution microscopy (HREM), was employed to characterize the interface between different amorphous hydrogenated carbon (a-C:H) films and steel substrates. Additional analyses using Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were also performed. Films were deposited both by high-energy (50 keV) nitrogen ion-beam decomposition of large hydrocarbon molecules and by magnetron plasma decomposition of C2H2 in mixed Ar-C2H2 discharges. The latter method was also used to deposit Mo- or W-containing a-C:H films (Me-C:H films) onto steel substrates with interlayers of the pure metals between the substrate and Me-C:H film. The films were found to be truly amorphous except for the cases of the metal-containing films, where 1–2 nm crystalline clusters were present in an a-C:H matrix. In the case of Mo the clusters were identified from HREM micrographs to have a bcc-like structure, characteristic of metallic Mo. The metal interlayers had a columnar microstructure with column widths of ∼ 30 nm. The interfaces between the Mo and W interlayers and the a-C:H films were found to extend over 20–40 nm with a gradual crystalline-to-amorphous transition. In most of the a-C:H film-substrate interface regions a thin layer ( < 10 nm) was observed which was predominantly amorphous but contained a small fraction of crystalline grains. AES showed an increase of both O and N close to the interface. However, for the cases with Mo and W interlayers, the substrate surface contaminants were less localized, and on some parts of the substrate surface the lattice fringes of the substrate and metal interlayer phase were continuous across a sharp interface.
|
|
| 12. |
- Sjöström, H, et al.
(författare)
-
Reactive magnetron sputter deposition of CNx films on Si(001) substrates : film growth, microstructure and mechanical properties
- 1994
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 246:1-2, s. 103-109
-
Tidskriftsartikel (refereegranskat)abstract
- There is currently considerable interest in producing new materials with extreme combinations of mechanical properties such as high hardnesses and moduli. One example of such a material is crystalline C3N4, which has been predicted to have a bulk modulus higher than that of diamond. In this paper we report on experiments carried out to synthesize CNx thin films. The films were grown in an unbalanced magnetron-sputtering system by reactive sputtering of C in N2 discharges. Si(001) substrates with the native oxide removed by thermal desorption and then kept at temperatures ranging from 150 to 600°C and substrate bias voltages Vs between 7.5 and -200 V were used. The films were analysed using X-ray diffraction, transmission electron microscopy (TEM). Auger electron spectroscopy, Rutherford backscattering and nano-indentation tests. Typically the films were grown at rates of 5 nm s-1 to total thicknesses of 300 nm. Owing to an extensive re-sputtering, only low negative bias voltages (-80
|
|
| 13. |
- Vavra, I, et al.
(författare)
-
The influence of thermal processing on structural and electrical properties of WxSi1−x/Si multilayers
- 1994
-
Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0168-9002. ; 350:1-2, s. 379-390
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal stability of WxSi1−x/Si multilayers (MLs) with x varying from 1 to 0.11 is studied by TEM and LAXS. The structure of the prepared samples is amorphous. Doping of W sublayers with silicon affects the interdiffusion process as well as the crystallization in these sublayers. We investigated these two processes (which have a detrimental influence on e.g. X-ray mirror stability) by annealing our samples at 400°C for 40 min. The structural changes were monitored by resistance measurement in the temperature range of 1.5–300 K. A correlation between structural and electrical characteristics was found, which is based on the comparison between three different R(T) curves. It is shown in our paper that the R(T) curve of a ML lies between the R(T) curves of two extreme types of single layers. The first single layer is the analogue of a fully intermixed ML and the second one represents a parallel connection of all conductive sublayers. Thus, a simple resistance measurement can give additional information about the quality of interfaces. We claim that in MLs with ultrathin sublayers the reported highest thermal stability of the amorphous mixture W0.72Si0.28 cannot be utilized because interdiffusion dominates over crystallization so that the superlattice structure is not retained.
|
|
