| 1. |
- Birch, Jens, et al.
(författare)
-
Recent advances in ion-assisted growth of Cr/Sc multilayer X-ray mirrors for the water window
- 2002
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 68:3, s. 275-282
-
Tidskriftsartikel (refereegranskat)abstract
- Cr/Sc multilayer X-ray mirrors intended for normal incidence reflection in the water window wavelength range, lambda=[2.4-4.4 nm], have been grown by ion-assisted sputter deposition and characterized using soft and hard X-ray reflectivity. By extracting low-energy ions, with energies, E-ion, ranging from 9 to 113 eV and with ion-to-metal flux ratios, Phi, between 0.76 and 23.1, from the sputtering plasma to the growing film, the nano-structure of the multilayer interfaces could be modified. A significantly increased soft X-ray reflectivity, using lambda = 3.374 nm, for Cr/Sc multilayers with layer thicknesses in the range 0.4-2.8 nm, was obtained when high ion-to-metal flux ratios, Phi(Cr) = 7.1 and Phi(Sc) = 23.1, and low energy ions, E-ion = 9eV, were used. An experimental reflectivity of 5.5% was obtained at 76degrees for a multilayer with 400 bi-layers. Simulations of the reflectivity data showed that the interface widths are < 0.425 nm. It could be concluded that roughness of low spatial frequency is reduced at lower ion energies than the high spatial frequency which was eliminated at the expense of intermixing at the interfaces at higher ion energies. The predicted performance of normal incidence multilayer mirrors grown at optimum conditions and designed for lambda = 3.374 and 3.115 nm indicates possible reflectivities of 6.5% and 14%, respectively.
|
|
| 2. |
- Donchev, V., et al.
(författare)
-
High-temperature excitons in GaAs quantum wells embedded in AlAs/GaAs superlattices
- 2000
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 58:2, s. 478-484
-
Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence (PL) spectra of GaAs quantum wells embedded in short-period AlAs/GaAs superlattices have been measured at 2 K and at room temperature. Two approaches have been applied in order to investigate the mechanisms of radiative recombination in these structures. In the first one, we studied the excitation density dependence of the PL intensity. In the second approach a line-shape analysis of the PL spectra is performed by means of a statistical model, which includes both free exciton, and free carrier recombinations. The fit based on this model reproduces with high accuracy the experimental spectra and allows to assess the relative contributions of excitons and free carriers to the radiative recombination process. The results of both approaches indicate the predominance of free excitons in the radiative recombination at room temperature.
|
|
| 3. |
- Ehiasarian, A.P., et al.
(författare)
-
Influence of high power densities on the composition of pulsed magnetron plasmas
- 2002
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 65:2, s. 147-154
-
Tidskriftsartikel (refereegranskat)abstract
- The application of high power pulses with peak voltage of -2 kV and peak power density of 3 kWcm-2 to magnetron plasma sources is a new development in sputtering technology. The high power is applied to ordinary magnetron cathodes in pulses with short duration of typically some tens of microseconds in order to avoid a glow-to-arc transition. High plasma densities are obtained which have been predicted to initiate self-sputtering. This study concerns Cr and Ti cathodes and presents evidence of multiply charged metal ions as well as of Ar ions in the dense plasma region of the high power pulsed magnetron discharge and a substantially increased metal ion production compared to continuous magnetron sputtering. The average degree of ionisation of the Cr metal deposition flux generated in the plasma source was 30% at a distance of 50 cm. Deposition rates were maintained comparable to conventional magnetron sputtering due to the low pressure of operation of the pulsed discharge - typically 0.4 Pa (3mTorr) of Ar pressure was used. Observations of the current-voltage characteristics of the discharge confirmed two modes of operation of the plasma source representing conventional pulsed sputtering at low powers (0.2 kWcm-2) and pulsed self-sputtering at higher powers (3 kWcm-2). The optical emission from the various species in the plasma showed an increase in metal ion-to-neutral ratio with increasing power. The time evolution within a pulse of the optical emission from Ar0, Cr0, Cr1+, and Cr2+ showed that at low powers Cr and Ar excitation develops simultaneously. However, at higher powers a distinct transition from Ar to Cr plasma within the duration of the pulse was observed. The time evolution of the discharge at higher powers is discussed. © 2002 Elsevier Science Ltd. All rights reserved.
|
|
| 4. |
- Engstrom, C., et al.
(författare)
-
Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil
- 2000
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 56:2, s. 107-113
-
Tidskriftsartikel (refereegranskat)abstract
- An original design and solution to the problem of magnetic field interactions in a vacuum chamber between two unbalanced magnetron sputtering sources and a solenoid coil serving to increase plasma density in near substrate position, is presented. By changing the solenoid coil current strength and direction, plasma growth conditions in an argon discharge and Ti-magnetron cathodes were found to vary in a broad region. Langmuir probe analysis shows that an increase in the coil current from 0 to 6 A caused plasma and substrate floating potentials to change from -7 to -30 V and from +1 to -10 V, respectively, as well as increasing the ion densities to a biased substrate from 0.2 to 5.2 mA cm-2 for each of the magnetrons. By using a ferro-powder magnetic field model, as well as finite element method analysis, we demonstrate the interference of the three magnetic fields - those of the two magnetrons and the solenoid coil. X-ray diffraction and transmission electron microscopy were used to study the microstructure and morphology of Ti-films grown under different ion bombardment conditions. At low Ar-ion-to-Ti-atom arrival rate ratios, Jion/Jn to approximately 1.5, at the substrate, variations of the ion energy, Eion, from 8 to 70 eV has only a minor effect on the microstructure and film preferred crystallographic orientation, resulting in an open/porous structure with defect-rich grains. At a higher Jion/Jn value of approximately 20, films with a well-defined dense structure were deposited at ion energies of 80 eV. The increase in ion flux also resulted in changes of the Ti film preferred orientation, from an (0 0 0 2) preferred orientation to a mixture of (0 0 0 2) and (1 0 1¯ 1) orientations.
|
|
| 5. |
- Philipps, V., et al.
(författare)
-
Erosion and redeposition of wall material in controlled fusion devices
- 2002
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 67:04-mar, s. 399-408
-
Tidskriftsartikel (refereegranskat)abstract
- Processes of erosion and redeposition and their impact on plasma facing materials in devices for magnetically confined fusion are discussed. Volatile molecules formed in the erosion process are partly pumped out but the majority of species released from the wall components returns to the surface causing the modification of its morphology. Prompt redeposition and redeposition after global transport reduce the gross erosion at any surface. Detailed analysis shows that erosion and deposition can coexist on otherwise erosion-dominated surfaces due to local inhomogenities. The erosion yield of redeposited material of sub-monolayer thickness significantly differs from that observed for thick targets. On deposition dominated areas one observes the formation of thick co-deposits containing a mixture of trapped fuel atoms (hydrogen isotopes) and species removed originally from the wall. This leads to a large and long-term fuel accumulation (tritium inventory) in a device. Reduced mechanical integrity of such layers stimulates their flaking and peeling-off if a critical thickness has been reached. This, in turn, results in the formation of hydrogen-rich dust particles.
|
|
| 6. |
- Rubel, Marek J., et al.
(författare)
-
Ion beam analysis methods in the studies of plasma facing materials in controlled fusion devices
- 2003
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 70:03-feb, s. 423-428
-
Tidskriftsartikel (refereegranskat)abstract
- Application of ion beam analysis techniques in the studies of material transport and fuel inventory in the controlled fusion devices is exemplified. Enhanced proton scattering on the carbon isotopes C-12(p,p)C-12, C-13(p,p)C-13 and secondary ion mass spectrometry allowed for determination of carbon erosion and re-deposition on the wall components following the experiments with a tracer ((CH4)-C-13) injection into the plasma edge at the TEXTOR tokamak. For the assessment of the deuterium fuel accumulation in the plasma facing components depth profiling by means of nuclear reaction analysis, He-3(d,p)He-4, was performed. Advantages and limitations of those nuclear methods in solving experimental problems are addressed.
|
|
| 7. |
- Shtinkov, N., et al.
(författare)
-
Effect of non-abrupt interfaces in AlAs/GaAs superlattices with embedded GaAs quantum wells
- 2000
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 58:2, s. 561-567
-
Tidskriftsartikel (refereegranskat)abstract
- In the present paper, we investigate the effect of the non-abrupt interfaces on the electronic and optical properties of short-period AlAs/GaAs superlattices with embedded GaAs quantum wells. The lateral disorder and the component interdiffusion at the interfaces are averaged over the layer planes and are effectively represented by a diffusion concentration profile in the growth direction. The diffusion length LD is used as a parameter characterizing the degree of interface broadening. The electronic structure calculations are made using the sp3s* spin-dependent empirical tight-binding Hamiltonian, the virtual crystal approximation, and the surface Green function matching method. The dependencies of the lowest electron (E1), heavy hole (HH1), and light hole (LH1) bound states on the diffusion length are calculated for LD from 0 to 4 monolayers. It is found that the energies of the transitions (E1-HH1) and (E1-LH1) increase as LD increases. The results obtained are compared with photoluminescence data for MBE-grown samples. It is found that the degree of interface broadening depends on the growth temperature and on the sample geometry. The diffusion lengths calculated from the experimental data follow the expected trends, revealing a good qualitative agreement between theory and experiment.
|
|
| 8. |
- Toneva, A, et al.
(författare)
-
FeSi2 thin films investigated by X-ray photoelectron and infrared spectroscopy
- 2000
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 58:2-3, s. 420-427
-
Tidskriftsartikel (refereegranskat)abstract
- Thin films of iron silicide prepared by ion-beam and by electron-beam evaporation of iron on silicon substrates and following rapid thermal processing are investigated. Low-energy argon ion sputtering of surface layer is used for depth profile XPS analysis. The Si2p, Fe2p3/2, O1s and C1s electron spectra are recorded. On the basis of established binding energies and infrared transmission spectra (200–600 cm−1) conclusion are made about the effect of the annealing temperature and duration on the chemical bond type and phase composition of the iron silicide films.
|
|
| 9. |
- Wronkowska, A.A., et al.
(författare)
-
Characterisation of Cd1-xMgxSe solid solutions by spectroscopic ellipsometry
- 2001
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 63:1-2, s. 233-239
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Optical properties of bulk Cd1-xMgxSe mixed crystals, grown from a CdSe, Mg, and Se melt by the Bridgman method, are presented. The alloys have a wurtzite type structure in the investigated range of composition, i.e. for 0 = x = 0.4. Measurements of the complex pseudo-dielectric function, = + ie2(?)>, were performed at room temperature in the photon energy range of 1.25-4.5 eV, using a computer-controlled variable angle of incidence ellipsometer. The spectral dependence of the effective refractive index and the absorption coefficient were also derived. The structure observed in the dielectric functions, attributed to the interband transitions E0, E0 + ?0 and E1, have been analysed by fitting the and d2/d?2 spectra to the damped harmonic oscillator and critical-point line shapes, respectively. For all critical points, the energy increases with increasing Mg concentration. The ellipsometric results of a fundamental band-gap shift due to Mg content are compared with the rate of increase of the excitonic energy, derived from photoluminescence spectra. © 2001 Elsevier Science Ltd.
|
|
| 10. |
- Atanassov, A, et al.
(författare)
-
Grazing incident asymmetric X-ray diffraction of beta-FeSi2 layers, produced by ion beam synthesis
- 2004
-
Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 76:02-Mar, s. 277-280
-
Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of beta-FeSi2 phase, prepared by ion beam synthesis (IBS) method, followed by rapid thermal annealing (RTA) is investigated by grazing incident asymmetric X-ray diffraction (GIAXRD). The X-ray spectra, obtained at different grazing angles, indicated that the beta-FeSi2 phase is formed in the whole implantation range. From the comparison of the reflections intensities ratios, it is found that in the metal-deficient regions, where the beta-FeSi2 phase is present in the form of precipitates, the crystallites orientation is influenced by the one of the silicon substrates, while the orientation in the metal-rich region is different and depends on the annealing temperature. (C) 2004 Elsevier Ltd. All rights reserved.
|
|
| 11. |
- Beshkova, Milena, et al.
(författare)
-
Low-pressure sublimation epitaxy of AlN films - growth and characterization
- 2004
-
Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 76, s. 143-146
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial layers of aluminum nitride have been grown at temperatures 1900-2400degreesC on 10 x 10 mm(2) 4H-SiC substrate via sublimation recondensation in an RF heated graphite furnace. The source material was polycrystalline sintered AlN. A maximum growth rate of about 100 mum/h was achieved at 2400degreesC and seed to source distance of 1 mm. The surface morphology reflects the hexagonal symmetry of the seed suggesting an epitaxial growth. This was confirmed by X-ray diffraction (XRD). The spectra showed very strong and well-defined (0002) reflection position at around 36.04degrees in symmetric Theta-2Thetascans for all samples. Micro-Raman spectroscopy reveals that the films have a wurtzite structure. It is evidenced by the appearance of the A(1) (TO) (at 601 cm(-1)) and E-2((2)) (at 651 cm(-1)) lines in the spectra. Secondary-ion mass spectroscopy (SIMS) results showed a low concentration of carbon incorporation in the AlN films. A correlation between the growth conditions and properties of the AlN layers was established.
|
|
| 12. |
- Hultman, Lars
(författare)
-
Thermal stability of nitride thin films
- 2000
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 57:1
-
Forskningsöversikt (refereegranskat)abstract
- This paper is a review of the thermal stability of state-of-the-art transition metal nitride thin films synthesized by physical vapour deposition techniques. Nitrides are successfully applied as wear-protection coatings for tools and mechanical components, decorative coatings, electrical contacts, and diffusion barriers in electronic devices. The aspects for thermal stability are on phase equilibrium, metal, nitrogen and impurity diffusion, recrystallization, phase separation, interfacial reactions, and oxidation. Microstructurally engineered structures are considered including single-crystals, nanolaminates, metastable alloys, and films in a state of compressive intrinsic stress. Titanium nitride is discussed in detail as a model system for the studies, but results are given also for NbN, AlN, BN, CNx, CrN, TiN-TiB2, Ti(C,N), and (Ti,Al)N films. More than 150 references are included. (C) 2000 Elsevier Science Ltd. All rights reserved.
|
|
| 13. |
- Hellborg, Ragnar, et al.
(författare)
-
Accelerator mass spectrometry - an overview
- 2003
-
Ingår i: Vacuum. - 0042-207X. ; 70:2-3, s. 365-372
-
Tidskriftsartikel (refereegranskat)abstract
- The technique of accelerator mass spectrometry (AMS) has spread worldwide since its first demonstration 25 years ago. The equipment used today is very diverse and dedicated accelerators as well as old "nuclear physics machines" can be found in the nearly 50 AMS laboratories today. The most widely spread application of AMS is for radiocarbon dating. However, AMS with C-14 as well as with other long-lived isotopes have also found applications in many other fields in physics and beyond.
|
|
| 14. |
- Popok, Vladimir, 1966, et al.
(författare)
-
Surface nanostructuring by implantation of cluster ions
- 2004
-
Ingår i: Vacuum. - : Elsevier BV. - 0042-207X. ; 76:2-3, s. 265-272
-
Tidskriftsartikel (refereegranskat)abstract
- A brief state-of-the-art review in the field of cluster ion implantation is presented. Ionised cluster beams are considered as a controllable and versatile tool for modification and processing of surfaces and near-surface layers on an atomistic scale as an alternative to ion implantation and ion assisted deposition. The main effects occurring under cluster-surface collisions as well as advantages in the application of cluster ion beams are reviewed. The problem of surface erosion under impact of energetic cluster ions is emphasised in the paper. A model explaining crater and hillock formation on target surfaces with relation to the thermal-transfer effect and local target melting at the collision spot is discussed.
|
|
| 15. |
|
|
