Cu interactions with α-Al2O3(0001): effects of surface hydroxyl groups versus dehydroxylation by Ar-ion sputtering

Niu, C.; Shepherd, K; Martini, D.; Tong, J.; Kelber, J. A.; Jennison, D. R.; Bogicevic, Alexander

doi:10.1016/s0039-6028(00)00728-7

Cited by 97 publications

(114 citation statements)

References 46 publications

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“…However, the very best quality factors were achieved with high temperature (850 • C) anneals in O * 2 , yielding significantly higher Q i even though RHEED and AFM are nearly identical to other MBEannealed samples. These results are consistent with microscopic theories attributing TLS to surface-bound hydroxyl groups 14 , which can saturate the sapphire (0001) surface 15 , and remain even after annealing at 1100 • C in UHV 15,16 . Carbon and hydrogen have also been observed on sapphire after similar annealing processes 16 .…”

supporting

confidence: 89%

“…These results are consistent with microscopic theories attributing TLS to surface-bound hydroxyl groups 14 , which can saturate the sapphire (0001) surface 15 , and remain even after annealing at 1100 • C in UHV 15,16 . Carbon and hydrogen have also been observed on sapphire after similar annealing processes 16 . The highly reactive activated oxygen used here may remove such surface-bound molecules, more effectively than a simple anneal, and with less damage than with ion milling, although we cannot at present verify these hypotheses.…”

supporting

confidence: 89%

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Planar superconducting resonators with internal quality factors above one million

Megrant¹,

Neill²,

Barends³

et al. 2012

Applied Physics Letters

419

373

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We describe the fabrication and measurement of microwave coplanar waveguide resonators with internal quality factors above 10 7 at high microwave powers and over 10 6 at low powers, with the best low power results approaching 2 × 10 6 , corresponding to ∼ 1 photon in the resonator. These quality factors are achieved by controllably producing very smooth and clean interfaces between the resonators' aluminum metallization and the underlying single crystal sapphire substrate. Additionally, we describe a method for analyzing the resonator microwave response, with which we can directly determine the internal quality factor and frequency of a resonator embedded in an imperfect measurement circuit.High quality factor microwave resonators provide critical elements for superconducting electromagnetic radiation detectors 1 , quantum memories 2,3 , and quantum computer architectures 4 . Good performance and stability can be achieved for such applications using aluminum resonators patterned on sapphire substrates. Aluminum is a favored material due to its robust oxide and reasonable transition temperature, and sapphire provides an excellent substrate due to its very low microwave loss tangent 5 δ ∼ 10 −8 and its chemical inertness. However, the quality factors measured in such resonators is lower than expected; recent simulations 6 and experiments 7 suggest that the unexplained loss arises mostly from imperfections at the metal-substrate interface. Using an experimental apparatus with minimal stray magnetic fields and infrared light at the sample 8 , here we show that careful substrate preparation and cleaning yields aluminumon-sapphire resonators with significantly higher internal quality factors Q i . We also introduce a new method for evaluating the resonator microwave response.The aluminum for the resonators was deposited on cplane sapphire substrates in one of three deposition systems: A high vacuum DC sputter system (base pressure P base = 6 × 10 −8 Torr), a high vacuum electron-beam evaporator (P base = 5 × 10 −8 Torr) or an ultra-high vacuum (UHV) molecular beam epitaxy (MBE) system (P base = 6 × 10 −10 Torr) with electron-beam deposition. The sapphire substrates were first sonicated in a bath of acetone then isopropanol followed by a deionized water rinse. For the sputter-deposited and e-beam evaporated samples, we further cleaned the substrates prior to Al de-

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supporting

confidence: 89%

supporting

confidence: 89%

Planar superconducting resonators with internal quality factors above one million

Megrant¹,

Neill²,

Barends³

et al. 2012

Applied Physics Letters

419

373

View full text Add to dashboard Cite

show abstract

“…XPS studies have been interpreted to show that with an increasing degree of hydroxylation, copper starts to wet an alumina surface. 13,14 The experiment cannot, however, distinguish between actual wetting where a monolayer ͑or more͒ spreads over the surface, and a significant increase of the metal island density. Atomic scanning tunneling microscopy ͑STM͒ suggests the latter situation.…”

Section: Discussionmentioning

confidence: 99%

“…8,10 Hydroxylation of the alumina surface dramatically influences the interaction with metals. In the case of rhodium 11 a large increase of the metal island density on alumina thin films was observed by Heemeier et al 12 For copper on thin alumina films, XPS studies by Kelber et al 13,14 suggest that hydroxylation of the surface significantly increases the ability of the oxide surface to be wetted by Cu.…”

Section: Introductionmentioning

confidence: 88%

Adsorption of Cu and Pd on α-Al2O3(0001) surfaces with different stoichiometries

Łodziana

Nørskov

2001

The Journal of Chemical Physics

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We report density functional theory calculations of the interaction of Cu and Pd with the ͑0001͒ surface of ␣-Al 2 O 3 . The interaction of those metals with the oxide surface varies from covalent-like for the aluminum rich surface to ionic-like for the oxygen terminated surface. Stoichiometric hydroxylation of the surface does not increase the metal-oxide interaction significantly. We suggest that defects created upon hydroxylation are the main mechanism to explain the observed metal wetting of the oxide.

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“…24 Niu et al showed that the reaction is even more severe in the presence of absorbed oxygen and water on the substrate. 25 Although the real components still remain unknown, the existence of composite layer is obvious. Therefore the present device possesses two different interfacial layers: composite interfacial layer and alumina interfacial layer.…”

Section: -4mentioning

confidence: 99%

Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

Xia

Wang

et al. 2017

AIP Advances

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A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM) Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF) state to low resistance (ON) state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

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Cu interactions with α-Al2O3(0001): effects of surface hydroxyl groups versus dehydroxylation by Ar-ion sputtering

Cited by 97 publications

References 46 publications

Planar superconducting resonators with internal quality factors above one million

Planar superconducting resonators with internal quality factors above one million

Adsorption of Cu and Pd on α-Al2O3(0001) surfaces with different stoichiometries

Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

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