| 1. |
- Håkansson, G., et al.
(författare)
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Ion irradiation effects during growth of Mo/V(001) superlattices by dual-target magnetron sputtering
- 1992
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Ingår i: Journal of Crystal Growth. - 0022-0248. ; 121:3, s. 399-412
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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.
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| 2. |
- Cerreta, M.K., et al.
(författare)
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Contact nuclei formation in aqueous dextrose solutions
- 1990
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 102:4, s. 869-876
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Tidskriftsartikel (refereegranskat)abstract
- A laser Raman microprobe was used in situ to observe the growth of alpha dextrose monohydrate on alpha anhydrous dextrose crystals. The Raman spectra indicate growth of the monohydrate below 28.1°C, but the presence of only the anhydrous form above 40.5°C. Contact nucleation experiments with parent anhydrous crystals yielded only monohydrate nuclei below 28.1°C, while contacts in solutions between 34.5 and 41.0°C produced both crystalline forms, and contacts in solutions above 43.5°C produced only anhydrous nuclei. The inability of the monohydrate to grow on anhydrous crystals in the same solution that forms the two crystalline phases with a single contact precludes a simple attrition mechanism of nuclei formation. For the same reason, the hypothetical mechanism involving parent crystal stabilization of pre-crystalline clusters, allowing the clusters to grow into nuclei, is also contradicted. A third, mechanism, which may be a combination of the two, is believed to apply.
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| 3. |
- Chakraborty, Reena, et al.
(författare)
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Steady state fluorescence spectroscopy of pyranine as a trace extrinsic probe to study structure in aqueous sugar solutions
- 1992
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 125:1-2, s. 81-96
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Tidskriftsartikel (refereegranskat)abstract
- The steady state fluorescence behavior of pyranine has been monitored in aqueous solutions of sucrose, glucose, fructose, and lactose. In each case it is possible to use the ratio of peak intensities at 440 and 511 nm (the PIR) as an indicator of the degree of supersaturation of the sugar solutions. We observed both bulk water and water of solvation in all solutions examined, regardless of degree of sapersaturation. In each case the amounts of bulk water and water of solvation per molecule of sugar appear to be nearly equal at saturation. We did not observe any evidence of solvent exclusive clusters in any of the systems we studied
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| 4. |
- Dunuwila, Dilum D., et al.
(författare)
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An investigation of the applicability of attenuated total reflection infrared spectroscopy for measurement of solubility and supersaturation of aqueous citric acid solutions
- 1994
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 137:3-4, s. 561-568
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Tidskriftsartikel (refereegranskat)abstract
- Currently applied methods for measurement of solubility and supersaturation based on viscometry, refractometry, interferometry and density require the separation of phases prior to measurement. ATR (attenuated total reflection) infrared spectroscopy provides a unique configuration in which the infrared spectrum of a liquid phase can be obtained in a slurry without phase separation. The applicability of the technique was investigated using a micro Circle® open boat cell equipped with a ZnSe (zinc selenide) ATR rod. Experiments conducted with aqueous citric acid proved that ATR infrared spectroscopy can be successfully employed to determine solubility and supersaturation.
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| 5. |
- Guo, S.J., et al.
(författare)
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Improved single crystal growth in the Bi-Sr-Ca-Cu-O system using a sealed cavity technique
- 1990
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 100:1-2, s. 303-308
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Tidskriftsartikel (refereegranskat)abstract
- Bi-Sr-Ca-Cu-O single crystals obtained thus far commonly have a very small thickness in the c-axis because of the weak bonding between two adjacent BiO layers and the high vapour pressure of Bi2O3 at high temperature. To overcome these difficulties a presintered SrCaCu4O6 was used to seal the Bi-Sr-Ca-Cu-O melt from which the single crystals grew during slow cooling. In the SrCaCu4O6 sealed cavity the Bi loss through vaporization was prevented and Sr and Ca were enriched in the superconducting crystals. The resulting single crystals have a dimension of up to 3.0×1.5×0.7 mm3, which is two orders of magnitude thicker than those grown from alkali chloride flux. The composition of the crystals is Bi2.2Sr1.8Ca0.75Cu1.8Ox and they possess a zero resistance at temperature above liquid nitrogen
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Pan, Borlan, et al.
(författare)
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Time resolved fluorescence and anisotropy of 1-pyrene butyric acid and pyranine as probes of solvent organization in sucrose solutions
- 1993
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 130:3-4, s. 587-599
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Tidskriftsartikel (refereegranskat)abstract
- The microenvironment of solute-solvent interactions in aqueous sucrose solutions, ranging from 0 to 80 wt% in concentration, was investigated using time resolved fluorescence techniques. The fluorescence lifetimes and rotational correlation times of the trace fluorescent probes, PBA (1-pyrene butyric acid) and pyranine (trisodium 8-hydroxy-1,3,6-pyrenetrisulfonate), were measured in sucrose solutions. The behavior of the fluorescence lifetimes and the increase in the rotational correlation times with increasing sucrose concentration provided no evidence for the formation of water exclusive solute clusters in the metastable solutions. Instead, the results indicated the formation of a network of hydrogen bonding interactions between dispersed sucrose molecules.
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| 10. |
- Vaitkus, J., et al.
(författare)
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Scanning tunneling microscopy of CdSe single crystal cleaved and "real" surface
- 1994
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 138:1-4, s. 545-549
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Tidskriftsartikel (refereegranskat)abstract
- Ultrahigh vacuum-cleaved and as-grown surfaces of CdSe single crystals were investigated by scanning tunneling microscopy. The single crystals were grown by Reynolds-Green method. Striations and terrace-step structure have been found. The surface atomic geometry was found and investigated. The (1120) face geometry (structure formed by elementary cell of 0.75 × 0.7 nm2) as well as other type structures (e.g., 2.1 × 0.75 nm2 elementary cell) have been determined. The variations of the band gap at the surface have been found. The band values in the range 2.0-2.6 eV on a cleaved surface and 1.1-2.0 eV on an as-grown surface were measured and explained as being the influence of surface relaxation and gas adsorption. © 1994.
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