Melting and Wetting Behavior in Oxygen Films

Awschalom, D. D.; Lewis, Gilbert N.; Gregory, Stephen

doi:10.1103/physrevlett.51.586

Cited by 56 publications

(9 citation statements)

References 6 publications

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“…This response is due to the γ–β antiferro-to-paramagnetic transition of S = 1 O 2 . Magnetic susceptibility studies of adsorbed O 2 (denoted O 2ads ) on vycor glass, graphite, and zeolites identified this transition and presented similar χ( T ) behavior ,− that is observed herein. Also, χ( T ) from O 2ads broadens depending on the amount of O 2ads surface coverage.…”

Section: Resultssupporting

confidence: 72%

Predicting NO_x Catalysis by Quantifying Ce³⁺ from Surface and Lattice Oxygen

Paidi

Savereide

Childers

et al. 2017

ACS Appl. Mater. Interfaces

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Our work introduces a novel technique based on the magnetic response of Ce and molecular oxygen adsorbed on the surface of nanoceria and ceria-based catalysts that quantifies the number and type of defects and demonstrates that this information is the missing link that finally enables predictive design of NO catalysis in ceria-based systems. The new insights into ceria catalysis are enabled by quantifying the above for different ceria nanoparticle shapes (i.e., surface terminations) and O partial pressure. We used ceria nanorods, cubes, and spheres and evaluated them for catalytic reduction of NO by CO. We then demonstrated the quantitative prediction of the reactivity of nanomaterials via their magnetism in different atmospheric environments. We find that the observed enhancement of reactivity for ceria nanocubes and nanorods is not directly due to improved reactivity on those surface terminations but rather due to the increased ease of generating lattice defects in these materials. Finally, we demonstrate that the method is equally applicable to highly topical and industrially relevant ceria mixed oxides, using nanoscale alumina-supported ceria as a representative case-a most ill-defined catalyst. Because the total oxide surface is a mixture of active ceria and inactive support and ceria is not likely present as crystallographically well-defined phases, reactivity does not easily scale with surface area or a surface termination. The key parameter to design efficient NO reduction in ceria-based catalysts is knowing and controlling the surface localized excess Ce ion areal density.

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Section: Resultssupporting

confidence: 72%

Predicting NO_x Catalysis by Quantifying Ce³⁺ from Surface and Lattice Oxygen

Paidi

Savereide

Childers

et al. 2017

ACS Appl. Mater. Interfaces

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“…Clear jumps in the -T curve of F ) 1.3 (d ) 0.35 nm and f ) 0.82) are observed at 24 and 44 K, which correspond to the transition temperatures of R-and -γ of the bulk oxygen, respectively, as shown in the inset of Figure 2a, whereas either phase corresponding to the bulk oxygen does not appear below F ) 3.5 in the O 2 /graphite system. 3 This result shows that even trimolecular layers in the micropore can form the dense structure identical to the bulk solid, since the pore width of ACF-0.96 is almost 3 times as long as the collision diameter of O 2 . This phenomenon may be ascribed to the strong micropore field which offer a high-pressure effect.…”

Section: Resultsmentioning

confidence: 83%

“…It is well-known that the bulk α-phase shows antiferromagnetism. The magnetic interactions of O 2 adsorbed on the graphite surface have been extensively studied. − The mono- or bilayer of O 2 molecules adsorbed on the two-dimensional graphite surface has its own phases such as δ, ε, and ζ different from the bulk α, β, and γ phases; the phase change depends on both the temperature and the coverage (Figure ). The α and β phases appear in the multiadsorbed O 2 layer on the flat graphite surface.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Spin States of O₂ Confined in a Graphitic Slit-Shaped Nanospace at Low Temperature

and

Kaneko

1996

J. Phys. Chem.

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The magnetic susceptibility of O 2 molecules confined in slit-shaped graphitic micropore systems with the slit pore width w of 0.75, 0.96, and 1.45 nm was measured at diffrent coverages F and over the temperature range of 1.7-100 K. For all micropore systems, the adsorbed O 2 at a very low coverage showed the paramagnetism without any obvious magnetic transition, which is quite close to the paramagnetism of bulk gaseous oxygen. An antiferromagnetic behavior appeared with an increase in F. This behavior was caused not by the formation of 2D lattices or bulk solid phases but by the random magnetism for the systems of w ) 0.75 and 0.96 nm. The random magnetism indicates the cluster formation of the O 2 molecules in the nanospace. The paramagnetism and the random magnetism arise from an enhanced intermolecular interaction of O 2 in the unique potential field of the narrow slit space. The O 2 assembly in the micropores showed a different magnetic behavior dpending on the pore width. Besides the cluster formation, a phase like the θ phase, which appears in the O 2 bilayer on the 2D graphite surface, was observed for 0.4 < F < 0.8 in the micropores of w ) 1.45 nm. This suggest that the micropores with w ) 1.45 nm provide an enhanced formation of the specific 2D phase. These unusual magnetic behaviors were presumed to be caused by the special critical phenomenon in the nanospace.

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“…In the last two decades this system has been extensively investigated by many experimental methods, namely, x-ray diffraction ͑XRD͒, 7-10 neutron diffraction ͑ND͒, [11][12][13][14][15][16] susceptibility (), [17][18][19][20][21] heat capacity, [22][23][24][25] low-energy electron diffraction ͑LEED͒, [26][27][28][29] reflection high-energy electron diffraction ͑RHEED͒, 30,31 electron energy-loss spectroscopy ͑EELS͒, 32-34 photoelectron spectroscopy ͑XPS and UPS͒, [35][36][37] resonance electron scattering ͑RES͒, 38,39 nearedge x-ray-absorption fine structure ͑NEXAFS͒ 40 and many theoretical works. [41][42][43][44][45][46][47] From the structural studies it was found that this system has many phases depending on temperature and O 2 coverage C. The coverage Cϭ1 is defined in this paper so as to form the triangular ͱ3ϫͱ3 superlattice referred to the graphite lattice.…”

Section: Introductionmentioning

confidence: 99%

Magnetic and melting transitions of oxygen monolayers and multilayers physisorped on exfoliated graphite

Murakami

Suematsu

1996

Phys. Rev. B

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The magnetic susceptibility () and magnetization of oxygen ͑O 2 ) monolayers and multilayers physisorped on exfoliated graphite have been investigated in order to elucidate the magnetic and melting transitions in the two-dimensional ͑2D͒ system. An anisotropy of in the dense monolayer phase has been observed below T N ϭ11.9Ϯ0.1 K. The magnetization process shows the precursor of the spin-flop transition, which is estimated to occur in the magnetic-field region 6ϽHϽ7 T at Tϭ5.0 K. These experimental results confirm the existence of magnetic long-range order below T N . The exchange field between nearest-neighbor O 2 molecules in a monolayer is estimated as 70% of that of bulk O 2 . The anisotropy in the fluid-II phase has also been observed, which means that O 2 molecules in this phase have orientational order. In the bilayer region, the second O 2 layer is not only ordered magnetically, but the magnetic ordering of the first layer is also destroyed in a magnetic field when the second layer coverage exceeds 65% of the full coverage of the second layer. These results are discussed in relation to a random-exchange field effect between the first and second layers, which are incommensurate to each other. The feature of melting transitions in the multilayer region is described in terms of surface melting.

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Melting and Wetting Behavior in Oxygen Films

Cited by 56 publications

References 6 publications

Predicting NO_x Catalysis by Quantifying Ce³⁺ from Surface and Lattice Oxygen

Predicting NO_x Catalysis by Quantifying Ce³⁺ from Surface and Lattice Oxygen

Magnetic Spin States of O₂ Confined in a Graphitic Slit-Shaped Nanospace at Low Temperature

Magnetic and melting transitions of oxygen monolayers and multilayers physisorped on exfoliated graphite

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Melting and Wetting Behavior in Oxygen Films

Cited by 56 publications

References 6 publications

Predicting NOx Catalysis by Quantifying Ce3+ from Surface and Lattice Oxygen

Predicting NOx Catalysis by Quantifying Ce3+ from Surface and Lattice Oxygen

Magnetic Spin States of O2 Confined in a Graphitic Slit-Shaped Nanospace at Low Temperature

Magnetic and melting transitions of oxygen monolayers and multilayers physisorped on exfoliated graphite

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Predicting NO_x Catalysis by Quantifying Ce³⁺ from Surface and Lattice Oxygen

Predicting NO_x Catalysis by Quantifying Ce³⁺ from Surface and Lattice Oxygen

Magnetic Spin States of O₂ Confined in a Graphitic Slit-Shaped Nanospace at Low Temperature