Papers by Author: Gholam Reza Yazdi

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Authors: Gholam Reza Yazdi, Mikael Syväjärvi, Remigijus Vasiliauskas, Rositza Yakimova
Abstract: In this report we present results on growth and characterization of AlN wires and thin films on SiC substrates. We have employed PVT technique in close space geometry for AlN deposition on SiC off oriented substrates, most of which were prepared to have scratch-free smooth as-grown surface by SiC sublimation epitaxy. By manipulating the surface kinetics we have been able to determine growth conditions yielding discontinuous or continuous morphologies corresponding to nanowires and thin films, respectively. A particular feature of the latter experiments is the fast temperature ramp up at the growth initiation. The AlN surface morphology was characterized by optical, AFM and XRD tools, which showed good crystal quality independent of the growth mode.
Authors: Mikael Syväjärvi, L. Nasi, Gholam Reza Yazdi, Giancarlo Salviati, M. Izadifard, I.A. Buyanova, W.M. Chen, Rositza Yakimova
Abstract: Ferromagnetic phases in as-grown SiC have been studied. An interpretation about the formation based on details of the phase appearance in the layers from optical microscopy, AFM, and TEM investigations is related to the growth. Some phases were found to have a nucleation at the edge of the phase and detailed TEM investigations show that the phases have an increased grain density at the edge while the main part of the phase is monocrystalline.
Authors: Gholam Reza Yazdi, Konstantin Vassilevski, José M. Córdoba, Daniela Gogova, Irina P. Nikitina, Mikael Syväjärvi, Magnus Odén, Nicolas G. Wright, Rositza Yakimova
Abstract: Free standing AlN wafers were grown on pre-patterned and in situ patterned 4H-SiC substrates by a physical vapor transport method. It is based on the coalescence of AlN microrods, which evolve from the apex of SiC pyramids grown on the SiC substrate during a temperature ramp up for in situ patterned substrate and SiC pyramids formed by reactive ion etching (RIE). This process yields stress-free (according XRD and Raman results) AlN single crystals with a thickness up to 400 µm and low dislocation density.
Authors: Mikael Syväjärvi, Rositza Yakimova, Gholam Reza Yazdi, Arul Arjunan, Eugene Toupitsyn, Tangali S. Sudarshan
Abstract: Thick layers have been grown on (1120) and (1 1 00)6H-SiC substrates. The thicknesses are up to 90 #m obtained with growth rate of 180 #m/h. Even in such thick layers the surfaces are smooth and only disturbed by polishing scratches. The surfaces contain steps which facilitate reproduction of the substrate polytype.
Authors: Rositza Yakimova, Gholam Reza Yazdi, Nut Sritirawisarn, Mikael Syväjärvi
Abstract: We report on growth of 3C-SiC by sublimation process in vacuum with the aim to ultimately select conditions for single polytype growth of bulk crystals. The 3C polytype occurrence, growth mechanism and structure evolution have been in the focus of the study. To gain understanding of the initial formation of the cubic polytype, growth was performed on various substrates, such as 6H- and 4H-SiC (on-axis and vicinal), as well as freestanding 3C-SiC wafers. The growth configuration used allowed a high growth rate, e.g. up to 200 (m/h, respectively very thick layers. The grown material was studied by means of optical microscopy, AFM and HRTEM. 6H-SiC (0001) Si-face substrates may be a good choice if the 3C nucleation is well controlled, which can be achieved by selecting the initial temperature ramp up and substrate orientation. These growth conditions limit the number of nucleation centers and decrease the defective boundaries.
Authors: R.M. Petoral Jr., Gholam Reza Yazdi, C. Vahlberg, Mikael Syväjärvi, Anita Lloyd Spetz, K. Uvdal, Rositza Yakimova
Abstract: SiC is a biocompatible material and a candidate as a transducer for biosensors. Here we have investigated the possibility to functionalize SiC with biomolecules. We have also processed very simple devices and performed electrical characterization. Double polished SiC samples with a C-face substrate and Si-face low doped epilayer have been functionalized on both sides. The SiC was first treated by HF in order to remove the native oxide, partly successful on the Si-face side but probably not on the C-face side. MPTMS, 3-mercaptopropyl trimethoxysilane, was chosen as the biomolecule since it has both a silanol group to be used as an anchoring group to the substrate and a thiol group available for further linking possibilities. The functionalization was evaluated by XPS, contact angle experiments, AFM and electrical measurements. The MPTMS molecules attached with the thiol (or sulphur containing) group pointing out from the surface on both faces of the SiC. Interesting differences between the two faces are however revealed by the analysis.
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