Browsing by Subject "Amorphous silicon"
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Item Open Access Alteration of spontaneous emission in hydrogenated amorphous silicon nitride microcavities(Elsevier BV, 1998) Serpengüzel, A.; Aydınlı, Atilla; Bek, A.A Fabry-Perot microcavity is used for the alteration of the spontaneous emission spectrum in hydrogenated amorphous silicon nitride. The modified photon density of states of the Fabry-Perot microcavity are responsible for the alteration of the spontaneous emission spectrum. The Fabry-Perot microcavity enhances the intensity of the spontaneous emission signal by a factor of 4 at the photon energies corresponding to the microcavity resonances. The 0.075 eV wide spontaneous emission linewidth of the Fabry-Perot microcavity resonances is 7 times smaller than the 0.5 eV wide spontaneous emission linewidth of the bulk hydrogenated amorphous silicon nitride. © 1998 Elsevier Science B.V. All rights reserved.Item Open Access Analysis of strain fields in silicon nanocrystals(American Institute of Physics, 2009) Yilmaz, D. E.; Bulutay, C.; Çaǧın, T.Strain has a crucial effect on the optical and electronic properties of nanostructures. We calculate the atomistic strain distribution in silicon nanocrystals up to a diameter of 3.2 nm embedded in an amorphous silicon dioxide matrix. A seemingly conflicting picture arises when the strain field is expressed in terms of bond lengths versus volumetric strain. The strain profile in either case shows uniform behavior in the core, however, it becomes nonuniform within 2-3 Å distance to the nanocrystal surface: tensile for bond lengths whereas compressive for volumetric strain. We reconcile their coexistence by an atomistic strain analysis.Item Open Access Compositional homogeneity in a medical-grade stainless steel sintered with a Mn-Si additive(Elsevier, 2012-06-09) Salahinejad, E.; Hadianfard, M.J.; Ghaffari, M.; Mashhadi, S.B.; Okyay, Ali KemalIn this paper, chemical composition uniformity in amorphous/ nanocrystallization medical-grade stainless steel (ASTM ID: F2581) sintered with a Mn-Si additive was studied via scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy. The results show that as a result of sintering at 1000 °C, no dissociation of Mn-Si additive particles embedded in the stainless steel matrix occurs. In contrast, sintering at 1050 °C develops a relatively homogeneous microstructure from the chemical composition viewpoint. The aforementioned phenomena are explained by liquation of the Mn-Si eutectic additive, thereby wetting of the main powder particles, penetrating into the particle contacts and pore zones via capillary forces, and providing a path of high diffusivity.Item Open Access Fabrication of nanostructured medical-grade stainless steel by mechanical alloying and subsequent liquid-phase sintering(Springer, 2012-05-10) Salahinejad, E.; Hadianfard, M. J.; Ghaffari, Mohammad; Mashhadi, S. B.; Okyay, Ali KemalThis article focuses on the microstructure of medical-grade P558 (ASTM F2581) stainless steel produced by mechanical alloying and liquid-phase sintering. Rietveld X-ray diffraction and transmission electron microscopy reflect that the mechanically alloyed stainless steel powder is a nanocrystal dispersed amorphous matrix composite.Mn-11.5 wt pct Si eutectic alloy as additive improves densification of the synthesized P558 alloy via liquid-phase sintering mechanism. X-ray mapping shows that after sintering at 1323 K (105°C) for 1 hour, a uniform distribution of dissolved Mn and Si is achieved. Moreover, the development of a nanostructured, fully austenitic stainless steel after sintering at the same temperature is realized by X-ray diffraction and transmission electron microscopy.Item Open Access Germanium for high performance MOSFETs and optical interconnects(2008-10) Saraswat, K. C.; Kim, D.; Krishnamohan, T.; Kuzum, D.; Okyay, Ali Kemal; Pethe, A.; Yu H.-Y.It is believed that to continue the scaling of silicon CMOS innovative device structures and new materials have to be created in order to continue the historic progress in information processing and transmission. Recently germanium has emerged as a viable candidate to augment Si for CMOS and optoelectronic applications. In this work we will first review recent results on growth of thin and thick films of Ge on Si, technology for appropriate cleaning of Ge, surface passivation using high-κ dielectrics, and metal induced crystallization of amorphous Ge and dopant activation. Next we will review application of Ge for high performance MOSFETs. Innovative Si/Ge MOS heterostructures will be described with high on current and low off currents. Finally we will describe optical detectors and modulators for on-chip and off-chip interconnect. Successful integration of Ge on Si should allow continued scaling of silicon CMOS to below 22 nm node. ©The Electrochemical Society.Item Open Access Improved efficiency of thin film a-Si:H solar cells with Au nanoparticles(Institute of Electrical and Electronics Engineers Inc., 2013) Islam, K.; Alnuaimi, A.; Okyay, Ali Kemal; Nayfeh, A.In this work, the effect of Au nanoparticles on the performance of a-Si:H solar cells is investigated experimentally. Au nanoparticles of 10, 20, 50, 80, 100, 200 and 400 nm are spin coated on ITO before metallization. The results show an increase in the Jsc and efficiency with increasing nanoparticle size. The Jsc increases from 9.34 mA/cm2 to 10.1 mA/cm2. In addition, the efficiency increases from 4.28% to 5.01%. © 2013 IEEE.Item Open Access Microcavity effects in the photoluminescence of hydrogenated amorphous silicon nitride(SPIE, 1998) Serpengüzel, Ali; Aydınlı, Atilla; Bek, AlpanFabry-Perot microcavities are used for the alteration of photoluminescence in hydrogenated amorphous silicon nitride grown with and without ammonia. The photoluminescence is red-near-infrared for the samples grown without ammonia, and blue-green for the samples grown with ammonia. In the Fabry- Perot microcavities, the amplitude of the photoluminescence is enhanced, while its linewidth is reduced with respect to the bulk hydrogenated amorphous silicon nitride. The microcavity was realized by a metallic back mirror and a hydrogenated amorphous silicon nitride - air or a metallic front mirror. The transmittance, reflectance, and absorbance spectra were also measured and calculated. The calculated spectra agree well with the experimental spectra. The hydrogenated amorphous silicon nitride microcavity has potential for becoming a versatile silicon based optoelectronic device such as a color flat panel display, a resonant cavity enhanced light emitting diode, or a laser.Item Open Access Microcavity enhanced amorphous silicon photoluminescence(IEEE, 1997) Serpengüzel, Ali; Aydınlı, Atilla; Bek, AlpanA microcavity enhancement of room temperature photoluminescence (PL) of a hydrogenated amorphous silicon (a-Si:h) was performed. A quantum confinement model was developed to describe the occurrence of the PL in the bulk a-Si:H. According to the model, small a-Si clusters are in a matrix of a-Si:H. The regions with Si-H, having larger energy gaps due to strong Si-H bonds, isolate these clusters, and form barrier regions around them. The PL originates from these a-Si clusters.Item Open Access Synthesis, characterization, and wear and friction properties of variably structured SiC/Si elements made from wood by molten Si impregnation(2012) Dhiman, R.; Rana, K.; Bengu, E.; Morgen P.We have synthesized pre-shaped SiC/Si ceramic material elements from charcoal (obtained from wood) by impregnation with molten silicon, which takes place in a two-stage process. In the first process, a porous structure of connected micro-crystals of β-SiC is formed, while, in the second process, molten Si totally or partly infiltrates the remaining open regions. This process forms a dense material with cubic (β-)SiC crystallites, of which the majority is imbedded in amorphous Si. The synthesis of preshaped "sprocket" elements demonstrates that desired shapes of such a dense SiC/Si composite ceramic material can be achieved, thus suggesting new industrial applications. The structure and composition of numerous as-synthesized samples were characterized in detail by using a wide range of techniques. Wear and friction properties were also investigated, with polished samples. The properties found for the present samples are very promising for abrasive applications and for new generation brake systems. © 2011 Elsevier Ltd.