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Nitrogenation of highly sp2 bonded amorphous carbon
Sunglyul Maeng,A Tagliaferro,John Robertson,W. I. Milne,Soonil Lee 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.1
Amorphous carbon with a high sp2 bonding content is considered to be a poor electronic material due to its very narrow band gap and its excessive density of defect states in the gap, both of which pin the Fermi level. This paper describes the ability of nitrogen to improve the semiconducting properties of highly sp2 bonded ( 80 90 % sp2) amorphous carbon. The electron spin resonance shows a reduction in the density of gap states in nitrogenated amorphous carbon (a-C : N) with increasing nitrogen content. Photo-thermal deflection spectroscopy and ultraviolet-visual spectroscopy measurements show that the opening of the gap and clearing of the gap states occur through nitrogen incorporation into the amorphous carbon film.
Amorphous Oxide Semiconductor TFTs for Displays and Imaging
Nathan, Arokia,Sungsik Lee,Sanghun Jeon,Robertson, John IEEE 2014 Journal of display technology Vol.10 No.11
<P>This paper reviews the mechanisms underlying visible light detection based on phototransistors fabricated using amorphous oxide semiconductor technology. Although this family of materials is perceived to be optically transparent, the presence of oxygen deficiency defects, such as vacancies, located at subgap states, and their ionization under illumination, gives rise to absorption of blue and green photons. At higher energies, we have the usual band-to-band absorption. In particular, the oxygen defects remain ionized even after illumination ceases, leading to persistent photoconductivity, which can limit the frame-rate of active matrix imaging arrays. However, the persistence in photoconductivity can be overcome through deployment of a gate pulsing scheme enabling realistic frame rates for advanced applications such as sensor-embedded display for touch-free interaction.</P>
Lee, Sungsik,Nathan, Arokia,Alexander-Webber, Jack,Braeuninger-Weimer, Philipp,Sagade, Abhay A.,Lu, Haichang,Hasko, David,Robertson, John,Hofmann, Stephan American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.13
<P>A positive shift in the Dirac point in graphene field-effect transistors was observed with Hall-effect measurements coupled with Kelvin-probe measurements at room temperature. This shift can be explained by the asymmetrical behavior of the contact resistance by virtue of the electron injection barrier at the source contact. As an outcome, an intrinsic resistance is given to allow a retrieval of an intrinsic carrier mobility found to be decreased with increasing gate bias, suggesting the dominance of short-range scattering in a single-layer graphene field-effect transistor. These results analytically correlate the field-effect parameters with intrinsic graphene properties.</P> [FIG OMISSION]</BR>
Martin, Marie-Blandine,Dlubak, Bruno,Weatherup, Robert S.,Yang, Heejun,Deranlot, Cyrile,Bouzehouane, Karim,Petroff, Fré,dé,ric,Anane, Abdelmadjid,Hofmann, Stephan,Robertson, John,Fert, Alb American Chemical Society 2014 ACS NANO Vol.8 No.8
<P/><P>We report on the successful integration of low-cost, conformal, and versatile atomic layer deposited (ALD) dielectric in Ni–Al<SUB>2</SUB>O<SUB>3</SUB>–Co magnetic tunnel junctions (MTJs) where the Ni is coated with a spin-filtering graphene membrane. The ALD tunnel barriers, as thin as 0.6 nm, are grown layer-by-layer in a simple, low-vacuum, ozone-based process, which yields high-quality electron-transport barriers as revealed by tunneling characterization. Even under these relaxed conditions, including air exposure of the interfaces, a significant tunnel magnetoresistance is measured highlighting the robustness of the process. The spin-filtering effect of graphene is enhanced, leading to an almost fully inversed spin polarization for the Ni electrode of −42%. This unlocks the potential of ALD for spintronics with conformal, layer-by-layer control of tunnel barriers in magnetic tunnel junctions toward low-cost fabrication and down-scaling of tunnel resistances.</P>