Direct atomic scale analysis of the distribution of Cu valence states in Cu/γ-Al2O3 catalysts

Sun, Kai; Liu, Jingyue; Browning, Nigel D.

doi:10.1016/s0926-3373(02)00055-3

Cited by 22 publications

(17 citation statements)

References 37 publications

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“…27 The shapes of the L-transitions (2p to 3d shell) near 931 eV and 951 eV and their intensity ratio (L 3 -to-L 2 ) can be used to fingerprint the oxidation state of metallic copper and its compounds. 25 The shapes of the EELS edges agree well with those reported elsewhere 28 and, together with HAADF images [ Fig. 3(a)] and SAED patterns [ Fig.…”

Section: A Structure Of the Copper-oxide Coatingsupporting

confidence: 88%

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A neutron scattering and electron microscopy study of the structure, wetting, and freezing behavior of water near hydrophilic CuO-nanostructured surfaces

Torres

Buck

Kaiser

et al. 2019

Journal of Applied Physics

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Oscillating heat pipes (OHPs) provide a promising heat transfer device for a variety of applications, including the cooling of electronic devices. Recently, it has been shown that a hydrophilic, nanostructured cupric oxide (CuO) coating can significantly enhance the thermal performance of copper OHPs that use water as the working fluid. Motivated by these results, we report neutron scattering and electron microscopy (EM) measurements to investigate the interaction of water with copper-oxide surfaces on the nanoscale. Our measurements confirm earlier observations of a thin cuprous oxide (Cu 2 O) layer growing on a bare copper substrate followed by "grass-like" CuO nanostructures. New evidence of the nanostructure hydrophilicity is provided by EM measurements of wetting and by our high-energy-resolution elastic neutron scattering measurements, showing a continuous freezing and melting of the water in our samples over a temperature range of ∼80 K. In addition, our neutron diffraction measurements are consistent with water closest to the CuO nanostructures freezing into an amorphous solid at low levels of hydration and hexagonal ice at higher hydration. In short, our findings support a strong interaction of water with the CuO nanostructures, which could significantly affect the operation of an OHP.

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Section: A Structure Of the Copper-oxide Coatingsupporting

confidence: 88%

“…3(b) shows Bragg spots indicative of single-crystal domains, which could be indexed to bulk copper and cuprous oxide (Cu 2 O). 25 26 EELS scans, collected simultaneously with STEM images, were used to identify chemical composition within each layer Fig. 3(c).…”

Section: A Structure Of the Copper-oxide Coatingmentioning

confidence: 99%

A neutron scattering and electron microscopy study of the structure, wetting, and freezing behavior of water near hydrophilic CuO-nanostructured surfaces

Torres

Buck

Kaiser

et al. 2019

Journal of Applied Physics

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“…It seems that the mobility of Cu on SiO film is suppressed dramatically due to the strong reaction of Cu with SiO film [18], which results in the formation of Cu-rich silicides as shown in Cu/SiO/Si system [18]. At elevated temperature, Cu oxide can also be formed [19][20] as demonstrated in deficient γ-Al 2 O 3 substrate [21]. Both processes suppress Cu mobility in SiO film.…”

Section: Discussionmentioning

confidence: 99%

Behaviour of TEM metal grids during in-situ heating experiments

Zhang

2009

Ultramicroscopy

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The stability of Ni, Cu, Mo and Au TEM grids coated with ultra-thin amorphous carbon or silicon monoxide film is examined by in-situ heating up to a temperature in the range 500~850°C in a transmission electron microscope. It is demonstrated that some grids can generate nano-particles either due to the surface diffusion of metal atoms on amorphous film or due to metal evaporation/redeposition. The emergence of nano-particles can complicate experimental observations, particularly in in-situ heating studies of dynamic behaviours of nanomaterials in TEM. The most widely used Cu grid covered with amorphous carbon is unstable, and numerous Cu nano-particles start to form once heating temperature reaches 600°C. In the case of Ni grid covered with α-C film, a large number of Ni nano-crystals occur immediately when the temperature approaches to 600 °C, accompanied by the graphitization of amorphous carbon. In contrast, both Mo and Au grids covered with α-C film exhibit good stability at elevated temperature, for instance, up to 680°C and 850°C for Mo and Au, respectively, and no any metal nano-particles are detected. Cu grid covered Si monoxide thin film is stable up to 550 °C, but Si nano-crystals appear under intensive electron beam. The generated nano-particles are well characterized by spectroscopic techniques (EDXS/EELS) and high-resolution TEM. The mechanism of nano-particle formation is addressed based on the interactions between the metal grid and the amorphous carbon film and on the sublimation of metal.

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“…near 931 eV and 951 eV and their intensity ratio (L3-to-L2) can be used to fingerprint the oxidation state of copper [107]. The shapes of the EELS edges agree well with those reported elsewhere [108]; and, together with the HAADF images and SAED patterns, confirm the identities of the layers labeled in Fig.…”

Section: Properties Of Nanostructured Cuosupporting

confidence: 86%

Neutron scattering and microscopy studies of the structure and dynamics of water near a nanostructured hydrophilic copper oxide surface

Torres¹

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Recently, it has been shown that superhydrophilic coatings of "grass-like" cupric oxide (CuO) nanostructures can significantly improve the thermal performance of heat transfer devices known as oscillating heat pipes (OHPs). The origin of this enhanced performance is currently unknown, but it is believed to be attributed to the thin film of interfacial water supported by the nanostructures that coat the OHP's interior surface. The aim of this work is to investigate the microscopic origin of enhanced heat transfer at the CuO surface by studying the structure, morphology, freezing/melting behavior, and dynamics of the water in proximity to the CuO coating over time and length scales that span picosecond-to-seconds and angstroms-to-millimeters, respectively . ... Our results demonstrate that water near superhydrophilic CuO nanostructures exhibits low-temperature anomalies in its structure and dynamics at the molecular level-a direction of research that has both applied and fundamental interest. The significantly altered structure and dynamics of the interfacial water could affect the boundary conditions for bulk water motion inside of an OHP during its operation. To test this hypothesis, we have proposed time-resolved neutron imaging experiments to characterize the kinetics of water oscillations in CuO-coated OHPs.

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Direct atomic scale analysis of the distribution of Cu valence states in Cu/γ-Al2O3 catalysts

Cited by 22 publications

References 37 publications

A neutron scattering and electron microscopy study of the structure, wetting, and freezing behavior of water near hydrophilic CuO-nanostructured surfaces

A neutron scattering and electron microscopy study of the structure, wetting, and freezing behavior of water near hydrophilic CuO-nanostructured surfaces

Behaviour of TEM metal grids during in-situ heating experiments

Neutron scattering and microscopy studies of the structure and dynamics of water near a nanostructured hydrophilic copper oxide surface

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