| 1. |
- Agnarsson, Björn, et al.
(author)
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Influence of initial surface reconstruction on nitridation of Al2O3 (0001) using low pressure ammonia
- 2007
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:1, s. 013519-
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Journal article (peer-reviewed)abstract
- The purpose of this study is to investigate the effect of initial surface reconstruction on the nitridation process of Al2O3 (0001). This was done by exposing differently reconstructed sapphire substrates at different temperatures to low pressure ammonia (NH3). Structural and chemical analysis were carried out using low-electron energy diffraction and x-ray photoelectron spectroscopy. The experiments revealed that using low pressure ammonia (P-NH3 < 1 X 10(-5) Torr), no nitridation takes place on (1x1) unreconstructed surfaces. However, when the unreconstructed surface starts to change to a (root 31 x root 31) R +/- 9 degrees reconstructed surface, with increasing substrate temperature, the nitridation becomes successful. When using the initially reconstructed surface, the nitridation is successful even from the lowest temperature used. These results suggest that the initial surface reconstruction has a major effect on the nitridation process. This kinetic behavior has not been reported before, with most nitridation studies mainly focusing on the effect of surface temperature on the resulting surface morphology, rather than the actual kinetics of the process itself.
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| 2. |
- Agnarsson, Björn, et al.
(author)
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The effect of hard nitridation on Al(2)O(3) using a radio frequency operated plasma cell
- 2011
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:22, s. 7796-7802
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Journal article (peer-reviewed)abstract
- We report on an atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) investigation of hard nitridation of sapphire (alpha.-Al(2)O(3)) substrate, using an Epi UNI-Bulb RF plasma cell at substrate temperatures ranging from 250 to 600 degrees C. Our results show that an AlN(1-x)O(x) layer forms on sapphire after extended nitridation at all temperatures, following a Stranski-Krastanov growth mode, with less islands forming at higher temperatures. We also observe a layer-dependent charging shift in XPS, separating smooth AlN(1-x)O(x) layers from rough AlN(1-x)O(x) islands due to their different electronic coupling to the substrate. Although the island growth is suppressed at higher temperatures, the surface roughness increases at higher temperatures as seen by AFM. We also observe sputtering effects with protrusions and pits.
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| 7. |
- Qi, B., et al.
(author)
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A micro-spectroscopy study on the influence of chemical residues from nanofabrication on the nitridation chemistry of Al nanopatterns
- 2012
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 258:10, s. 4497-4506
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Journal article (peer-reviewed)abstract
- We applied spatially resolved photoelectron spectroscopy implemented with an X-ray photoemission electron microscopy (XPEEM) using soft X-ray synchrotron radiation to identify the compositional and morphological inhomogeneities of a SiO2/Si substrate surface nanopatterned with Al before and after nitridation. The nanofabrication was conducted by a polymethylmethacrylate (PMMA)-based e-beam lithography and a fluorine-based reactive ion etching (RIE), followed by Al metalization and acetone lift-off. Three types of chemical residues were identified before nitridation: (1) fluorocarbons produced and accumulated mainly during RIE process on the sidewalls of the nanopatterns; (2) a thick Al-bearing PMMA layer and/or (3) a thin PMMA residue layer owing to unsuccessful or partial lift-off of the e-beam unexposed PMMA between the nanopatterns. The fluorocarbons actively influenced the surface chemical composition of the nanopatterns by forming Al-F compounds. After nitridation, in the PMMA residue-free area, the Al-F compounds on the sidewalls were decomposed and transformed to AIN. The PMMA residues between the nanopatterns had no obvious influence on the surface chemical composition and nitridation properties of the Al nanopatterns. They were only partially decomposed by the nitridation. The regional surface morphology of the nanopatterns revealed by the secondary electron XPEEM was consistent with the scanning electron microscopy results.
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| 8. |
- Qi, BingCui, et al.
(author)
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Characterisation of high-temperature annealing effects on alpha-Al2O3(0001) substrates
- 2008
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In: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY. - : IOP Publishing.
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Conference paper (peer-reviewed)abstract
- High temperature annealing in air has been applied as an effective ex-situ surface treatment for the alpha-Al2O3(0001) substrates used in molecular beam epitaxy (MBE) growth of III-nitrides. The method is based on the criterion that atomically smooth surface of terrace-and-step like structure, which is considered to be crucial in obtaining a high quality epilayer, could be produced upon high temperature annealing. The annealed surface was mostly studied by atomic force microscopy (AFM) imaging. In this work, the effects of high temperature annealing on the surface morphology, crystalline quality, optical quality and surface reconstruction behaviour of alpha-Al2O3(0001) substrates were fully studied using AFM, triple-axis high resolution X-ray diffraction (THRXRD), spectroscopic ellipsometry (SE) and insitu reflection high-energy electron diffraction (RHEED). A new strategy, H-2 thermal cleaning at 1100 degrees C followed by O-2 annealing at 1300 degrees C was proposed as an efficient surface treatment for alpha-Al2O3 (0001) substrates for MBE growth.
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| 9. |
- Qi, B., et al.
(author)
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Formation and nitridation of InGa composite droplets on Si(111) : In-situ study by high resolution X-ray photoelectron spectroscopy
- 2014
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 303, s. 297-305
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Journal article (peer-reviewed)abstract
- We demonstrate applying synchrotron radiation based high resolution X-ray photoelectron spectroscopy as a versatile in-situ tool to study the step-wise formation and nitridation of indium gallium (InGa) composite droplets on Si(1 1 1) 7 x 7. This includes analysis of initial interactions of Ga and In with Si(1 1 1)7x7, and characterization of formation and nitridation of InGa droplets. The results show that after stabilization of Si(1 1 1) 7 x 7 structure with Ga and In at 750 degrees C and formation of Ga nanodroplets as the bases, the InGa composite droplets (In:Ga approximate to 3:1) were formed at RT and 200 degrees C in a coverage range 3-14 monolayers. The nitridation efficiency and structure of the droplets/Si(1 1 1) with NH3 were temperature dependent. At or below 350 degrees C, the droplets were hardly nitridated. At 670 degrees C, the nitridation of InGa was more completed, which however caused an unavoidable nitridation of Si surface. The optimum nitridation occurred around 480 degrees C and proceed in a 2D mode. Further simultaneous growth and nitridation of the InGa droplets on the 2D nitridated surface at 400 degrees C resulted in a complex surface composition and structure. An ex-situ atomic force microscopy reveals both the aligned metallic droplet-island assemblies and the fractured nitridated island bases with small droplets on top for the final surface.
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| 10. |
- Qi, B., et al.
(author)
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High-resolution X-ray photoemission spectroscopy study of AlN nano-columns grown by nitridation of Al nano-squares on Si(111) substrates with ammonia
- 2010
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 518:14, s. 3632-3639
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Journal article (peer-reviewed)abstract
- The growth of AlN nano-columns by ammonium nitridation of Al nano-squares embedded in SiO2 on Si(111) substrates was studied by high-resolution X-ray photoemission spectroscopy from a synchrotron radiation source and scanning electron microscopy (SEM). Selective nitridation of the Al nano-squares on the SiO2 mask was obtained in the temperature window of 600 degrees C-700 degrees C. The well-shaped AlN nano-column arrays with diameters confined by the lateral size of the Al nano-squares (similar to 100 nm) were observed in SEM.
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