| 1. |
- Landälv, Ludvig, 1982-, et al.
(författare)
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Phase evolution of radio frequency magnetron sputtered Cr-rich (Cr,Zr)(2)O-3 coatings studied by in situ synchrotron X-ray diffraction during annealing in air or vacuum
- 2019
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Ingår i: Journal of Materials Research. - : CAMBRIDGE UNIV PRESS. - 0884-2914 .- 2044-5326. ; 34:22, s. 3735-3746
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Tidskriftsartikel (refereegranskat)abstract
- The phase evolution of reactive radio frequency (RF) magnetron sputtered Cr0.28Zr0.10O0.61 coatings has been studied by in situ synchrotron X-ray diffraction during annealing under air atmosphere and vacuum. The annealing in vacuum shows t-ZrO2 formation starting at similar to 750-800 degrees C, followed by decomposition of the alpha-Cr2O3 structure in conjunction with bcc-Cr formation, starting at similar to 950 degrees C. The resulting coating after annealing to 1140 degrees C is a mixture of t-ZrO2, m-ZrO2, and bcc-Cr. The air-annealed sample shows t-ZrO2 formation starting at similar to 750 degrees C. The resulting coating after annealing to 975 degrees C is a mixture of t-ZrO2 and alpha-Cr2O3 (with dissolved Zr). The microstructure coarsened slightly during annealing, but the mechanical properties are maintained, with no detectable bcc-Cr formation. A larger t-ZrO2 fraction compared with alpha-Cr2O3 is observed in the vacuum-annealed coating compared with the air-annealed coating at 975 degrees C. The results indicate that the studied pseudo-binary oxide is more stable in air atmosphere than in vacuum.
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| 2. |
- Broekhuijsen, Sjoerd, 1993-, et al.
(författare)
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Synthesis and characterization of 11B4C containing Ni/Ti multilayers using combined neutron and X-ray reflectometry
- 2023
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Ingår i: Optical Materials Express. - : Optica Publishing Group. - 2159-3930. ; 13:4, s. 1140-1149
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Tidskriftsartikel (refereegranskat)abstract
- The performance of multilayers in optical components, such as those used in neutron scattering instruments, is crucially dependent on the achievable interface width. We have shown how the interface width of Ni/Ti multilayers can be improved using the incorporation of B4C to inhibit the formation of nanocrystals and limit interdiffusion and intermetallic reactions at the interfaces. A modulated ion-assistance scheme was used to prevent intermixing and roughness accumulation throughout the layer stack. In this work we investigate the incorporation of low-neutron-absorbing 11B4C for Ni/Ti neutron multilayers. Combined fitting of neutron reflectivity and X-ray reflectivity measurements shows an elimination of accumulated roughness for the 11B4C containing multilayers with a mean interface width of 4.5 Å, resulting in an increase in reflectivity at the first Bragg peak by a factor of 2.3 and 1.5 for neutron and X-ray measurements, respectively.
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| 3. |
- Dorri, Samira, 1988-, et al.
(författare)
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Enhanced quality of single crystal CrBx/TiBy diboride superlattices by controlling boron stoichiometry during sputter deposition
- 2024
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584.
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Tidskriftsartikel (refereegranskat)abstract
- Single-crystal CrB2/TiB2 diboride superlattices with well-defined layers are promising candidates for neutron optics. However, excess B in sputter-deposited TiBy using a single TiB2 target deteriorates the structural quality of CrBx/TiBy (0001) superlattices. We study the influence of co-sputtering of TiB2 + Ti on the stoichiometry and crystalline quality of 300-nm-thick TiBy single layers and CrBx/TiBy (0001) superlattices on Al2O3(0001) substrates grown by DC magnetron sputter epitaxy at growth-temperatures TS ranging from 600 to 900 °C. By controlling the relative applied powers to the TiB2 and Ti magnetrons, y could be reduced from 3.3 to 0.9. TiB2.3 grown at 750 °C exhibited epitaxial domains about 10x larger than non-co-sputtered films. Close-to-stoichiometry CrB1.7/TiB2.3 superlattices with modulation periods Λ = 6 nm grown at 750 °C showed the highest single crystal quality and best layer definition. TiB2.3 layers display rough top interfaces indicating kinetically limited growth while CrB1.7 forms flat and abrupt top interfaces indicating epitaxial growth with high adatom mobility.
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| 4. |
- Eriksson, Fredrik, 1975-, et al.
(författare)
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Interface engineering of short-period Ni/V multilayer X-ray mirrors
- 2006
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 500:1-2, s. 84-95
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Tidskriftsartikel (refereegranskat)abstract
- Low-energy ion-assisted magnetron sputter deposition has been used for the synthesis of highly reflective Ni/V multilayer soft X-ray mirrors. A low ion energy and a high ion-to-metal flux ratio were employed in order to stimulate the adatom mobility while minimizing ion-induced intermixing at the interfaces. An analytic model, based on the binary collision approximation, was used in order to gain insight into low-energy ion-surface interactions as a function of ion energy and ion-to-metal flux ratio. The model predicted a favorable region in the ion energy-flux parameter space where only surface atomic displacements are stimulated during growth of Ni and V for multilayers. For a series of Ni/V multilayer mirrors with multilayer periods about Λ = 1.2 nm, grown with a continuous ion assistance using energies in the range 7-36 eV and with ion-to-metal flux ratios ΦNi = 4.7 and ΦV=20.9, specular and diffuse X-ray scattering analyses revealed that ion energies of ∼27-31 eV produced the best trade-off between reduced interfacial roughness and intermixing. However, it was also concluded that an interface mixing of about ± 1 atomic distance is unavoidable when a continuous flux of assisting ions is used. To overcome this limitation, a sophisticated interface engineering technique was employed, where the first 0.3 nm of each layer was grown with a high-flux low-energy ion assistance and the remaining part was grown with a slightly higher ion energy. This method was demonstrated to largely eliminate the intermixing while maintaining the smoothening effect of ion assistance. Two Ni/V multilayer soft X-ray mirror structures, one with 500 periods designed for near-normal incidence and one 150 periods reflecting polarizer at the Brewster angle, were grown utilizing the interface engineering concept. Both the near-normal incidence reflectivity as well as polarizability were improved by a factor of 2 as compared to previously reported data for an X-ray energy of E = 511 eV. © 2005 Elsevier B.V. All rights reserved.
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| 5. |
- Eriksson, Fredrik, 1975-, et al.
(författare)
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Morphology control in Ni/Ti multilayer neutron mirrors by ion-assisted interface engineering and B4C incorporation
- 2023
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Ingår i: Optical Materials Express. - : Optica Publishing Group. - 2159-3930. ; 13:5, s. 1424-1439
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Tidskriftsartikel (refereegranskat)abstract
- The optical contrast and minimum layer thickness of Ni/Ti broadband neutron multilayer supermirrors is usually hampered by an interface width, typically 0.7 nm, caused by nanocrystallites, interdiffusion, and/or intermixing. We explore the elimination of nanocrystallites in combination with interface smoothening by modulation of ion assistance during magnetron sputter deposition of 0.8 to 6.4 nm thick Ni and Ti layers. The amorphization is achieved through incorporation of natural B4C where B and C preferably bond to Ti. A two-stage substrate bias was applied to each layer; -30 V for the initial 1 nm followed by -100 V for the remaining part, generating multilayer mirrors with interface widths of 0.40-0.45 nm. The results predict that high performance supermirrors with m-values as high as 10 are feasible by using 11B isotope-enriched B4C combined with temporal control of the ion assistance.
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| 6. |
- Ghafoor, Naureen, 1975-, et al.
(författare)
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Impact of B4C co-sputtering on structure and optical performance of Cr/Sc multilayer X-ray mirrors
- 2017
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 25:15, s. 18274-18287
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Tidskriftsartikel (refereegranskat)abstract
- The influence of B4C incorporation during magnetron sputter deposition of Cr/Sc multilayers intended for soft X-ray reflective optics is investigated. Chemical analysis suggests formation of metal: boride and carbide bonds which stabilize an amorphous layer structure, resulting in smoother interfaces and an increased reflectivity. A near-normal incidence reflectivity of 11.7%, corresponding to a 67% increase, is achieved at λ = 3.11 nm upon adding 23 at.% (B + C). The advantage is significant for the multilayer periods larger than 1.8 nm, where amorphization results in smaller interface widths, for example, giving 36% reflectance and 99.89% degree of polarization near Brewster angle for a multilayer polarizer. The modulated ion-energy-assistance during the growth is considered vital to avoid intermixing during the interface formation even when B + C are added.
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| 7. |
- Lorentzon, Marcus, 1993-
(författare)
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Nanostructured TiN/ZrAlN and HfAlN Thin Films : Effect of Structure on Mechanical Properties
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transition metal nitrides are a remarkable group of ceramic materials that offer exceptional properties such as high hardness, low tribological wear, excellent thermal stability, and high oxidation resistance. Alloys such as TiN, CrN, VN, ZrN, and HfN have been identified as ideal candidates for protective coatings on cutting tool inserts in the metal processing industry. While TiAlN has been widely accepted, ZrAlN and HfAlN alloys have much unexplored potential. With a melting point of HfN at 3300 °C, approximately 400 °C higher than TiN, HfAlN shows great potential for age-hardening at even higher temperatures. These remarkable materials inspire us to push the limits of what is possible, and to continue to innovate materials science.The work performed in this thesis focuses on the development of hard coatings using ionassisted reactive magnetron sputtering. The coatings are based on group IV TM-Al-N, where TM is either Ti, Zr, or Hf. The aim is to enhance the performance of these ceramic coatings by simultaneously increasing their hardness and toughness. To achieve this, the growth mechanisms, structure, and mechanical properties of the films were studied in detail. The coatings were deposited onto single crystal Si(001) and MgO(001) substrates.The first study describes the development of a multilayer structure, consisting of alternating layers of TiN and Zr0.37Al0.63N1.09, with a bilayer period of 20 nm, with the aim of combining the unique properties of the constituent materials. Cubic rocksalt TiN is known for its high hardness and unfortunate brittleness. Hexagonal wurtzite Zr0.37Al0.63N1.09 is less hard, but also more ductile. The crystal structure of the multilayers varied depending on the substrate temperature during growth. At temperatures below ~350 °C, the ZrAlN layers grew near amorphous, while they were nanocrystalline between 500 °C and 800°C. At 900 °C, the ZrAlN segregated into a nanolabyrinthine structure consisting of w-AlN and c-ZrN. The hardness of the films increased significantly with increasing deposition temperature, from 24 GPa to 36 GPa. The films also showed superior fracture stress compared to the available literature, increasing from 6.1 to 7.7 GPa. The fracture toughness of the films was also improved compared to the binary constituents, up to 2.8 MPa√m. These findings illustrate the potential of combining diverse materials, to create new structures with enhanced properties and highlight the importance of optimizing the growth conditions to achieve the desired film functionality.In a second study, single-crystal Hf1-xAlxNy films were grown at high temperatures on MgO(001) substrates. Excess nitrogen in HfNy (y=1.22, 1.33) film created ordered nanosized domains of variations in the nitrogen composition, leading to the formation of a compositionally modulated superstructure. In Hf0.93Al0.07N1.15, the immiscibility of the constituents (c-HfN and c-AlN) causes the formation of a superstructure consisting of isostructural Al-rich and Hf-rich domains due to surface initiated spinodal decomposition. Micropillar compression tests reveal a ductile HfN1.22 and substantial strain hardening upon deformation. Hf0.93Al0.07N1.15 exhibited a brittle nature, although at a substantially increased yield stress in comparison, consistent with the improved hardness from 26 GPa to 40.5 GPa, measured by nanoindentation.
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| 8. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Interface bonding of Zr1−xAlxN nanocomposites investigated by x-ray spectroscopies and first principles calculations
- 2020
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Ingår i: Physical Review Research. - College Park, MD, United States : American Physical Society. - 2643-1564. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure, chemical bonding, and interface component in ZrN-AlN nanocomposites formed byphase separation during thin film deposition of metastable Zr1−xAlxN (x = 0.0, 0.12, 0.26, 0.40) are investigatedby resonant inelastic x-ray scattering, x-ray emission, and x-ray absorption spectroscopy and compared to firstprinciples calculations including transitions between orbital angular momentum final states. The experimentalspectra are compared with different interface-slab model systems using first principles all-electron full-potentialcalculations where the core states are treated fully relativistically. As shown in this work, the bulk sensitivity andelement selectivity of x-ray spectroscopy enables one to probe the symmetry and orbital directions at interfacesbetween cubic and hexagonal crystals. We show how the electronic structure develops from local octahedralbond symmetry of cubic ZrN that distorts for increasing Al content into more complex bonding. This results inthree different kinds of bonding originating from semicoherent interfaces with segregated ZrN and lamellar AlNnanocrystalline precipitates. An increasing chemical shift and charge transfer between the elements takes placewith increasing Al content and affects the bond strength and increases resistivity.
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| 9. |
- Thörnberg, Jimmy, et al.
(författare)
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Microstructure and materials properties of understoichiometric TiBx thin films grown by HiPIMS
- 2020
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 404
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Tidskriftsartikel (refereegranskat)abstract
- TiBx thin films with a B content of 1.43 <= x <= 2.70 were synthesized using high-power impulse magnetron sputtering (HiPIMS) and direct-current magnetron sputtering (DCMS). HiPIMS allows compositions ranging from understoichiometric to overstoichiometric dense TiBx thin films with a B/Ti ratio between 1.43 and 2.06, while DCMS yields overstoichiometric TiBx films with a B/Ti ratio ranging from 2.20 to 2.70. Excess B in overstoichiometric TiBx thin films from DCMS results in a hardness up to 37.7 +/- 0.8 GPa, attributed to the formation of an amorphous B-rich tissue phase interlacing stoichiometric TiB2 columnar structures. We furthermore show that understoichiometric TiB1.43 thin films synthesized by HiPIMS, where the deficiency of B is found to be accommodated by Ti-rich planar defects, exhibit a superior hardness of 43.9 +/- 0.9 GPa. The apparent fracture toughness and thermal conductivity of understoichiometric TiB1.43 HiPIMS films are 4.2 +/- 0.1 MPa root m and 2.46 +/- 0.22 W/(m.K), respectively, as compared to corresponding values for overstoichiometric TiB2.70 DCMS film samples of 3.1 +/- 0.1 MPa root m and 4.52 +/- 0.45 W/(mK). This work increases the fundamental understanding of understoichiometric TiBx thin films and their materials properties, and shows that understoichiometric films have properties matching or going beyond those with excess B.
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| 10. |
- Zubayer, Anton, 1995-
(författare)
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Enhanced Polarizing Neutron Optics with 11B4C Incorporation : SLD Tunability, Interface Refinement, and Elimination of Magnetic Coercivity
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis explores novel strategies for improving Fe-based polarizing neutron optics, a critical part for improving neutron scattering methods to study materials science, physics, biology, medicine, chemistry and cultural heritage. Polarization analysis is important in uncovering data on magnetic domains, protein structures, molecular composition and orientation in biological systems, and ion-diffusion mechanisms that would otherwise be inaccessible. However, conventional methods, particularly state-of-the-art multilayer polarizing neutron optics, are hindered by low specular reflectivity, low polarization at higher scattering vectors/angles, high diffuse scattering and the need for high external magnetic fields for polarizer magnetization. The outcomes leading to this thesis, introduces the concept of scattering length density tuning, strategies to decrease the interface width, the diminishing of lateral correlation and magnetic coercivity. All improvements realized by introducing 11B4C in clever ways.The multilayers were deposited using ion-assisted DC magnetron sputter deposition (DCMS). Our improvement of Fe-based multilayer mirrors all revolves around the use of 11B4C. 11B4C in various concentrations can be used together with other materials to tune the scattering length density contrasts. It can amorphize the interfaces and layers to achieve smaller interface width, diminish lateral correlations and eliminate magnetic coercivity. In other words, increase reflectivity, increase polarization, decrease diffuse scattering and saturate at lower fields. The multilayers were mainly characterized using X-ray reflectivity (XRR), X-ray diffraction (XRD), grazing incidence small/wide angle X-ray scattering (GISAXS/GIWAXS), elastic recoil detection analysis (ERDA), magneto-optical Kerr effect (MOKE), vibrating sample magnetometry (VSM), transmission electron microscopy (TEM) and polarized neutron reflectivity (PNR). All results prove the benefit of using 11B4C in Fe-based polarizing neutron optics.
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| 11. |
- Ghafoor, Naureen, 1975-
(författare)
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Growth and Nano-structural Studies of Metallic Multilayer for X-ray Mirrors
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A part of the Ph.D. project focused on growth and characterization of metal multilayers is presented in this licentiate thesis. The main interest in carrying out this research is to develop highly reflective normal-incidence condenser mirrors for soft X-ray microscopy studies in the water window (λ=2.4-4.2 nm) wavelength regime.Transition metals like Sc, Ti V, etc. have been considered because of the presence of their 2p-absorption edges within the water window. An anomalous dispersion at absorption edges has been utilized to get enhanced reflectance of soft X-rays. Since a single surface exhibits a very poor X-ray reflectivity, Cr/Sc, Cr/Ti, and Ni/V multilayers were grown in order to coherently add many reflections from several interfaces. The selection of Cr and Ni, as spacer layer, was made on the basis of their X-ray optical contrasts with the above-mentioned transition metals. The multilayer design, i.e., the individual layer thicknesses and the total number of bilayers, directly influences the resultant reflectance and careful determination was therefore made with the aid of computer simulations.All multilayers were grown on chemically cleaned Si substrates by ion-assisted dual target magnetron sputtering under high vacuum (~10-7 Torr) conditions. The effect of low and high ion-flux bombardment of low energy (<50 eV) Ar ions, on growing surfaces was studied for all material systems. Furthermore, a two-stage deposition of each individual layer with modulated ion-energies was applied in order to obtain smooth and abrupt interfaces with as small intermixing as possible. Ion-surface interactions were also theoretically considered for estimating an appropriate ion-flux and ion-energy range desired for sufficient ad-atom mobilities.X-ray reflectivity and transmission electron microscopy have been the main probes for multilayer characterization in this work. For the Cr/Ti multilayer designed for normal incidence and grown with optimized two-stage ion-energy modulation, a peak reflectance of 2.1% was achieved at the Ti-2p absorption edge (λ=2.74 nm). For a multilayer mirror designed for the Brewster angle a maximum reflectance of 4.3% was accomplished. These measurements were made at the synchrotron radiation source BESSY in Berlin. Specular reflectivity and diffuse scattering scans were utilized for quantitative and qualitative analysis of the vertical and lateral structure of the multilayers. At-wavelength measurements of a series of Cr/Ti multilayers revealed the accumulation of roughness with increasing number of bilayers (N>100) for this material system. Hard X-ray reflectivity and diffractometry were used for quality checks of the multilayers for rapid feedback to the deposition. In-situ annealing using hard X-ray reflectivity was also performed to assess the thermal stability of Cr/Ti multilayers. It was found that probably due to a strong thermal diffusion the degradation of multilayers (with bilayer period of 1.37 nm) in this material system occurs just above the growth temperature (~40°C). The accumulation of a low spatial frequency "waviness" with increasing number of layers in Cr/Ti multilayers was investigated by transmission electron microscopy. The influence of process conditions on multilayer structure with different periodicities was investigated by TEM analyses of a series of three samples for each of the above-mentioned material system. The Cr/Sc multilayers have shown the most flat and abrupt interface structure without any significant roughness evolution when grown with optimum process parameters.
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| 12. |
- Ghafoor, Naureen, 1975-
(författare)
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Materials Science of Multilayer X-ray Mirrors
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis treats the reflective and structural properties of multilayer structures. Soft X-ray multilayer mirrors intended as near-normal incidence reflective optics and polarizers in the water window (λ=2.4-4.4 nm) are the main focus. Such mirrors require multilayer periodicities between 1.2-2.2 nm, a large number ~600of multilayer periods (N), and atomically flat interfaces. Bi-metallic multilayers were deposited by dual-target magnetron sputtering on Si(001)Geometrical roughness and intermixing/interdiffusion at the interfaces were investigated in connection with the impact of ion-surface interactions during growth of Cr/Ti, Cr/Sc, and Ni/V multilayers. This was achieved by comparing multilayers grown with or without high-flux low energy (Eion<30 eV) ion assistance. The use of modulated ion assistance resulted in a substantial improvement of interface flatness and abruptness in each of theAb-initio calculations indicate that the stabilization of the amorphous layer structure is due to a lowering of the total energy of the system by eliminating high energy incoherent interfaces between crystalline Sc and Cr.Light element incorporation in Cr/Sc multilayers was investigated through residual gas pressure variation. It is shown that multilayers retain their structural and optical properties within the high vacuum range of 2×10-7-to-2×10-6 Torr. The incorporation of 34 at.% nitrogen at a higher residual gas pressure ( ~2×10-5 Torr) resulted in highly textured understoichiometricx/ScNy multilayers. As a result of nitrogen incorporation, interface widths as small as 0.29 nm, and near-normal incidence reflectivity enhancement (at λ=3.11 nm) by 100 % (compared to pure Cr/Sc multilayers) was achieved. Light element incorporation was also found to be advantageous for the thermal stability of the multilayers. In-situ hard X-ray reflectivity measurements performed during isothermal annealing in thex/ScNy are stable up to 350 °C. As an alternative route to metallic multilayers, single crystal CrN/ScN superlattices, grown by reactive sputtering in N atmosphere onto MgO(001), were also investigated. The superlattice synthesis at 735 °C, resulted in highly abrupt interfaces with minimal interface widths of 0.2 nm. As-deposited superlattices with only 61 periodsλ=3.11 nm as well as very high thermal stability up to 850 °C.
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