| 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. |
- CHAKAROV, DV, et al.
(författare)
-
WATER-ADSORPTION ON GRAPHITE(0001)
- 1995
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 46:8-10, s. 1109-1112
-
Tidskriftsartikel (refereegranskat)abstract
- Wafer adsorption on the clean graphite (0001) surface has been studied by high-resolution electron-energy-loss spectroscopy (HREELS) and temperature-programmed desorption (TPD). At 85 K H2O adsorbs non-dissociatively forming hydrogen-bonded aggregates. The structure and the growth mode of water clusters depend on the substrate temperature and the coverage. At all coverages, above a few per cent of a monolayer (ML), the desorption is characterized by zero-order kinetics, while the HREEL spectra reveal a threshold coverage approximately 1 ML when the average co-ordination of the H2O molecules changes. Isothermal measurements of the desorption rate and HREELS measurements at elevated temperatures suggest an irreversible phase transition from amorphous to crystalline ice at approximately 135 K.
|
|
| 3. |
|
|
| 4. |
- 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.
|
|
| 5. |
- 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.
|
|
| 6. |
- 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.
|
|
| 7. |
- Eriksson, Mats, 1963-, et al.
(författare)
-
The water-forming reaction on thin, SiO2 supported, palladium films
- 1990
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 41:1-3, s. 137-138
-
Tidskriftsartikel (refereegranskat)abstract
- The water-forming reaction has been studied on thin Pd films, evaporated on planar SiO2 substrates. The nominal film thickness varied between 5 and 100 Å. The studies were performed in uhv by means of mass spectrometry, UPS and work function measurements in the temperature range 323–523 K. The film structure was also studied with TEM. The results are compared with previous measurements on 1000 Å, thick, homogeneous Pd films. The structure of the thin Pd films changed dramatically during cyclic H2 and O2 exposures, from that of a continuous film with cracks to that of drop-like metal particles. These structural changes are not observed on the thick (1000 Å) Pd films. Even though there are large structural changes, the water-forming reaction looks qualitatively the same as on a thick Pd film. The total water production however, decreases with decreasing film thickness. We believe that some minor qualitative differences in the water-forming reaction for different nominal Pd film thicknesses, are due to the increasing PdSiO2 boundary as the thickness is reduced.
|
|
| 8. |
- Fogelberg, J., et al.
(författare)
-
A hydrogen sensitive palladium metal-oxide-semiconductor device as sensor for dissociating NO in H2-atmospheres
- 1990
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 41, s. 705-
-
Tidskriftsartikel (refereegranskat)abstract
- A Pd-MOS structure can be used as a sensitive analytical tool in the study of dissociating oxygen containing molecules. Nitric oxide has been studied as a test case. Initially NO adsorbs very effectively and dissociatively on polycrystalline Pd at temperatures above 473 K. At this temperature H2O, N2O and N2 desorbs during an NO exposure in a hydrogen background. After such exposure the surface is probably left with only residual nitrogen atoms adsorbed on the surface. Below 390 K the dissociation probability is insignificant.
|
|
| 9. |
- Jonsson, Lars, et al.
(författare)
-
Controlled topography production - True 3D simulation and experiment
- 1995
-
Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 46, s. 971-975
-
Tidskriftsartikel (refereegranskat)abstract
- A true 3D computer program, named DINESE, has been developed to simulate the evolution of real 3D structures during erosion and deposition. It is based on the generalized Huygens reconstruction formalism of surface evolution and can predict the evolution of any surface of the form z = f(x,y) resulting from any erosion or deposition process. True 3D computer simulations of a number of cases are presented and compared with experiment. The powers of the simulation method are further demonstrated by a series of sequential predictive simulations resulting in a desired topography which is then verified experimentally under the same sequence of conditions. Specifically, the evolution of different Si3N4 structures during ion beam etching with Ar ions under different erosion conditions has been studied both numerically and experimentally.
|
|
| 10. |
- Mankefors, S., et al.
(författare)
-
Theoretical investigation of soft x-ray emission from a Si(100) layer buried in GaAs
- 1998
-
Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 49:3, s. 181-184
-
Tidskriftsartikel (refereegranskat)abstract
- Calculations of the soft x-ray emission spectrum have been carried out on a buried Si(100) layer in GaAs and compared with experimental data. We find that Si occupies Ga- as well as As-sites and that the local density of states is different for these two cases.
|
|
