| 1. |
- Sendova-Vassileva, M, et al.
(författare)
-
Depth dependence of photoluminescence and chemical bonding in porous silicon
- 1999
-
Ingår i: Journal of Luminescence. - 0022-2313 .- 1872-7883. ; 80:1-4, s. 179-182
-
Tidskriftsartikel (refereegranskat)abstract
- Porous silicon (PS) is studied by stepwise peeling of the surface layer to clarify the non-uniformity in the photoluminescence (PL) and correlate it with the in-depth chemical bonding and structure of the 30 μm thick layer. The PL intensity grows by an order of magnitude after the peeling off of the first 10 μm and decreases five times in the next 5 μm while the peak maximum position shifts from 730 to 800 nm. X-ray photoelectron spectroscopy (XPS) measurements show that Si–Si and Si–O bonds are present both on the surface and below, and the preferential oxidation state of silicon changes from 3+ and 4+ on the surface to 1+ and 2+ below 10 μm. Using Raman spectroscopy silicon nanocrystals are shown to exist. Their mean size can be estimated at about 3 nm. These results show that the strongest PL comes from a region in the PS layer where silicon nanocrystallites are surrounded by oxides with a low level of oxidation and not from the strongly oxidized surface layer.
|
|
| 2. |
- Tzolov, M, et al.
(författare)
-
Modification of the structure of ZnO : Al films by control of the plasma parameters
- 2001
-
Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 396:1-2, s. 274-279
-
Tidskriftsartikel (refereegranskat)abstract
- ZnO:Al films were deposited by RF magnetron sputtering in triode configuration applying an external DC electric field to the substrates. Reflection high-energy electron diffraction measurements characterized the different films as consisting of randomly-oriented zinc blende crystallites or randomly and texture-oriented wurtzite crystallites, as well as of the amorphous phase. The non-resonant Raman spectra are strongly influenced by the presence of a built-in electric field at the grain boundaries and they do not depend on the symmetry of the microcrystallites. The Raman spectra taken at resonant excitation are more sensitive to the presence of the amorphous phase in the films. (C) 2001 Elsevier Science B.V. All rights reserved.
|
|
| 3. |
- Tzolov, M., et al.
(författare)
-
Vibrational properties and structure of undoped and Al-doped ZnO films deposited by RF magnetron sputtering
- 2000
-
Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 379:1-2, s. 28-36
-
Tidskriftsartikel (refereegranskat)abstract
- Highly conductive and transparent in the visible range Al-doped ZnO (ZnO:Al) and undoped ZnO films have been deposited by RF magnetron sputtering. Reflection high-energy electron diffraction observations characterized them as textured. The habitus of the microcrystallites forming the texture depends on the Al doping. The layer texture of undoped ZnO films has texture axis parallel to the substrate. The ZnO:Al films, instead, show a columnar texture with texture axis perpendicular to the substrate. The Raman spectra of the films obtained by non-resonant excitation are completely different from those of the target material which is polycrystalline ZnO. For the interpretation of the different bands in the Raman spectra the existence of a depletion region near the grain boundaries has been assumed. The most intensive band in the Raman spectra at approximately 570 cm-1 has been assigned to electric field-induced Raman scattering on longitudinal optical phonons. The built-in electric field in the depletion region induces the Raman activity of the B2 modes and a band at 276 cm-1 appears in the spectra. Phonon modes highly localized near the grain boundaries have been detected at 516 cm-1 and 468 cm-1 which are well pronounced in the Raman spectra for the doped samples. Localized modes were observed also in the infrared reflection spectra of the doped films. Surface enhanced Raman scattering has been applied and the band in the range 830-920 cm-1 has been interpreted as due to adsorbates from the ambient air. It has been shown that the non-resonant Raman scattering can be used for qualitative study of some details of the microstructure of the zinc oxide films like the built-in electric field and the adsorbates in the films.
|
|
