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Contact Design and Attachment
Published in Paul G. Slade, Electrical Contacts, 2017
Gerald J. Witter, Guenther Horn
The almost total chemical resistance of gold against reactions with surrounding atmospheric constituents under conditions experienced during its use as a switching, sliding or connector contact is its outstanding property. Gold oxide decomposes at low temperatures above 200°C and is not retained in a solidified melt produced under normal air atmosphere. The only reported chemical reactions occur when gold comes into contact with mercury forming an amalgam which ultimately can lead at temperatures above 400°C to the gold almost completely dissolving in the mercury [24]. Another reaction of practical importance is the attack of liquid lead and tin, mostly in the form of tin-lead solders, onto gold surfaces, leading to alloying and the formation of brittle phases.
Application of RF discharge in oxygen to create highly oxidized metal layers
Published in Surface Engineering, 2018
A. I. Stadnichenko, L. S. Kibis, D. A. Svintsitskiy, S. V. Koshcheev, A. I. Boronin
The O1s spectrum analysis showed the presence of several oxygen electronic states (Figure 3(b)). Two of them with Eb(O1s) at 529·2 and 530·2 eV were assigned to the oxygen in Au2O3 oxide. Most probably, these oxygen species originated from surface and bulk gold oxides. However, the presence of two non-equivalent oxygen types in the structure of bulk gold oxide was previously shown [38]. For unambiguous interpretation of these oxygen states, further experiments should be performed. The low intensity peak at 532·0 eV could be interpreted as surface hydroxyl groups [19]. The oxygen form with Eb(O1s) = 535·3 eV was observed only after a prolonged plasma treatment of the gold surface. The binding energy of this species (535·3 eV) is anomalously high for a thermostable oxygen form, since only weakly adsorbed or physisorbed oxygen species have such high binding energies Eb(O1s) [39]. Thus, it could be interpreted as molecular oxygen occluded by intergrain voids of the oxide film or stabilised by the metal–oxide interface layer.
Probing the electronic absorption spectrum of single gold nanoparticles in the gas phase
Published in Molecular Physics, 2023
Benjamin Hoffmann, Sophia Leippe, Knut R. Asmis
We find reasonable agreement between our cryo-SNAS spectrum and the simulated spectrum of a spherical core–shell NP with a 23 nm radius Au core and a 5.5 nm thick gold oxide shell, if we use the values n = 3.3 and k = 1.1 reported by Kim et al. [42] for a gold oxide thin film at a wavelength of 600 nm (see Figure 8(a)). The dimensions of the core and shell were chosen such to yield the same mass as the experimentally determined value M0 and assuming a gold oxide density of 6 g·cm−3 [43].
Photoacoustic analysis and imaging techniques: Sound of light
Published in Particulate Science and Technology, 2018
For an effective photothermal therapy, the passive or active accumulation of the photoabsorbers inside the tumor region should be confirmed; in addition, the spatial location and size of the tumor should be determined before the treatment. Also, localized temperature elevation should be noninvasively monitored during treatment. Shah et al. (2008) investigated the usability of photoacoustic imaging combined with ultrasound imaging in order to detect photoabsorbers and monitor the temperature increase for guiding the photothermal treatment. Researchers utilized gold-oxide nanoparticles to enhance the contrast of ex vivo photoacoustic imaging. Overlapping ultrasound and photoacoustic images reflect the complementary characteristics of both imaging techniques. In other words, the ultrasound imaging shows the structure of the tissue, while photoacoustic imaging demonstrates the optical contrast differences increased by the photoabsorbers. The photothermal treatment during the study was performed by a continuous laser and gold-oxide nanoparticles absorbing within NIR optical range. The ultrasonic imaging system was interfaced with a nanosecond pulsed laser to display the tissue-like phantoms and the pre/post photothermal treatment ex vivo animal tissue. Before applying the treatment, photoacoustic imaging had determined the presence and spatial localization of the nanoparticles. Thermal maps during the thermal treatment were computed via the temperature-induced changes in the photoacoustic signals and these were compared with the temperature estimations from the ultrasound imaging. The increase of temperature caused a stable increase in the photoacoustic signal density in the study. For a 90°C change in temperature, 42% increase was observed in the photoacoustic signal density. When compared with the photoacoustic signal, the measured strain in the ultrasound image for the same temperature increase was less than 1%. All these results indicated that the photoacoustic imaging enhanced by ultrasound imaging is a suitable method to guide the photothermal treatment developed with photoabsorbers.