Tyndall National Institute - Journal Articles

Patterning optically clear films: co-planar transparent and color-contrasted thin films from interdiffused electrodeposited and solution-processed metal oxides

Tue, 28 Nov 2017 00:00:00 GMT

Patterning optically clear films: co-planar transparent and color-contrasted thin films from interdiffused electrodeposited and solution-processed metal oxides Glynn, Colm; Geaney, Hugh; McNulty, David; O'Connell, John; Holmes, Justin D.; O'Dwyer, Colm Transparent thin films can now be site-selectively patterned and positioned on surface using mask-defined electrodeposition of one oxide and overcoating with a different solution-processed oxide, followed by thermal annealing. Annealing allows an interdiffusion process to create a new oxide that is entirely transparent. A primary electrodeposited oxide can be patterned and the secondary oxide coated over the entire substrate to form high color contrast coplanar thin film tertiary oxide. The authors also detail the phase formation and chemical state of the oxide and how the nature of the electrodeposited layer and the overlayer influence the optical clearing of the patterned oxide film.

Interface chemistry of contact metals and ferromagnets on the topological insulator Bi2Se3

Mon, 02 Oct 2017 00:00:00 GMT

Interface chemistry of contact metals and ferromagnets on the topological insulator Bi2Se3 Walsh, Lee A.; Smyth, Christopher M.; Barton, Adam T.; Wang, Qingxiao; Che, Zifan; Yue, Ruoyu; Kim, Jiyoung; Kim, Moon J.; Wallace, Robert M.; Hinkle, Christopher L. The interface between the topological insulator Bi2Se3 and deposited metal films is investigated using x-ray photoelectron spectroscopy including conventional contact metals (Au, Pd, Cr, and Ir) and magnetic materials (Co, Fe, Ni, Co0.8Fe0.2, and Ni0.8Fe0.2). Au is the only metal to show little or no interaction with the Bi2Se3, with no interfacial layer between the metal and the surface of the TI. The other metals show a range of reaction behaviors with the relative strength of reaction (obtained from the amount of Bi2Se3 consumed during reaction) ordered as: Au < Pd < Ir < Co ≤ CoFe < Ni < Cr < NiFe < Fe, in approximate agreement with the behavior expected from the Gibbs free energies of formation for the alloys formed. Post metallization anneals at 300°C in vacuum were also performed for each interface. Several of the metal films were not stable upon anneal and desorbed from the surface (Au, Pd, Ni, and Ni0.8Fe0.2), while Cr, Fe, Co, and Co0.8Fe0.2 showed accelerated reactions with the underlying Bi2Se3, including inter-diffusion between the metal and Se. Ir was the only metal to remain stable following anneal, showing no significant increase in reaction with the Bi2Se3. This study reveals the nature of the metal-Bi2Se3 interface for a range of metals. The reactions observed must be considered when designing Bi2Se3 based devices.

Ab initio study of the atomic level structure of the rutile TiO2 (110) – titanium nitride (TiN) interface

Fri, 22 Sep 2017 00:00:00 GMT

Ab initio study of the atomic level structure of the rutile TiO2 (110) – titanium nitride (TiN) interface Gutiérrez Moreno, José Julio; Nolan, Michael Titanium nitride (TiN) is widely used in industry as a protective coating due to its hardness and resistance to corrosion and can spontaneously form a thin oxide layer when it is exposed to air, which could modify the properties of the coating. With limited understanding of the TiO2 – TiN interfacial system at present, this work aims to describe the structural and electronic properties of oxidized TiN based on a density functional theory (DFT) study of the rutile TiO2 (110) – TiN (100) interface model system, also including Hubbard +U correction on Ti 3d states. The small lattice mismatch gives a good stability to the TiO2 – TiN interface after depositing the oxide onto TiN through the formation of interfacial Ti – O bonds. Our DFT+U study shows the presence of Ti3+ cations in the TiO2 region, which are preferentially located next to the interface region as well as the rotation of the rutile TiO2 octahedra in the interface structure. Although the vacancy formation energies for Ti in TiN (Evac (Ti) ≥ 4.03 eV) or O in the oxide (Evac (O) ≥ 3.40 eV) are quite high relative to perfect TiO2 – TiN, defects are known to form during the oxide growth and can therefore be present after TiO2 formation. Our results show that a structure with exchanged O and N can lie 0.82 eV higher in energy than the perfect system, suggesting the stability of structures with interdiffused O and N anions at ambient conditions. The presence of N in TiO2 introduces N 2p states localized between the top edge of the O 2p valence states and the mid-gap Ti3+ 3d states, thus reducing the bandgap in the TiO2 region for the exchanged O/N interface EDOS. The outcomes of these simulations give us a most comprehensive insight on the atomic level structure and the electronic properties of oxidised TiN surfaces.

In situ investigation of methane dry reforming on metal/ceria(111) surfaces: metal-support interactions and C-H bond activation at low temperature

Tue, 05 Sep 2017 00:00:00 GMT

In situ investigation of methane dry reforming on metal/ceria(111) surfaces: metal-support interactions and C-H bond activation at low temperature Liu, Zongyuan; Lustemberg, Pablo; Gutiérrez, Ramón A.; Carey, John J.; Palomino, Robert M.; Vorokhta, Mykhailo; Grinter, David C.; Ramírez, Pedro J.; Matolín, Vladimír; Nolan, Michael; Ganduglia-Pirovano, M. Verónica; Senanayake, Sanjaya D.; Rodriguez, José A. Studies with a series of metal/ceria(111) (metal=Co, Ni, Cu; ceria=CeO2) surfaces indicate that metal–oxide interactions can play a very important role for the activation of methane and its reforming with CO2 at relatively low temperatures (600–700 K). Among the systems examined, Co/CeO2(111) exhibits the best performance and Cu/CeO2(111) has negligible activity. Experiments using ambient pressure X-ray photoelectron spectroscopy indicate that methane dissociates on Co/CeO2(111) at temperatures as low as 300 K—generating CHx and COx species on the catalyst surface. The results of density functional calculations show a reduction in the methane activation barrier from 1.07 eV on Co(0001) to 0.87 eV on Co2+/CeO2(111), and to only 0.05 eV on Co0/CeO2−x(111). At 700 K, under methane dry reforming conditions, CO2 dissociates on the oxide surface and a catalytic cycle is established without coke deposition. A significant part of the CHx formed on the Co0/CeO2−x(111) catalyst recombines to yield ethane or ethylene.