Morphological Changes at a Silver Surface Resulting from Exposure to Hyperthermal Atomic Oxygen

Abstract

Bulk single crystals of Ag(100) and Ag(111) at a sample temperature of 220 °C were exposed to a beam containing hyperthermal atomic oxygen with a nominal translational energy of 5.2 eV. The resultant oxide scales and interface structures were characterized by cross-sectional (scanning) transmission electron microscopy ((S)TEM) and scanning electron microscopy (SEM). The oxide scales formed on Ag(100) and Ag(111) were more than 10 microns thick and contained numerous micropores, microchannels, grain boundaries, and defects (e.g., twins), which can provide pathways for the rapid transport of oxygen atoms through the thick oxide scales to the oxide/Ag interface. Energy dispersive X-ray spectroscopy (EDS) and nanoarea electron diffraction pattern (NA-EDP) investigations revealed that the oxide scales were predominately polycrystalline silver, containing only ∼3−5 atom % of oxygen, which is mainly in the form of Ag2O. Additional low-fluence exposures of thin foils of single-crystal Ag followed by analysis with TEM and NA-EDP identified crystalline grains of Ag, with dimensions of 500−800 nm, imbedded in a porous region of nanometer-sized Ag2O grains during the initial stages of surface transformation by hyperthermal atomic oxygen. A mechanism based on the rapid oxidation of Ag by atomic oxygen followed by thermal reduction of the Ag2O at 220 °C is proposed to explain the formation of the thick and unique polycrystalline silver “oxide” scales that were observed.

Changes in the structure and tribological property of Ag film by LEO space environment exposure

“…This phenomenon has been simulated by the ground based experiments [9,[17][18][19]25]. It is found that that Ag surface is easy to be oxidized as exposed in the AO environment, resulted in the formation of an oxide layer at initial stage.…”

Atomic Oxygen Effect on Sputtered MoS2-Ag Composite Film

“…Compared to the Au and Sb 2 O 3 , the Ag is an active element, and can be oxidized by the AO irradiation and space exposure. It was found that that Ag surface is easy oxidized as exposed in the AO environment and causes the formation of an oxide layer [26][27][28][29][30][31] . Due to the mismatch in volume between the Ag oxides and Ag, the internal stress would occur in the oxide layer and result in the flaking and cracking of the oxide layer [27] .…”

Initial stages of nickel oxide growth on Ag(001) by pulsed laser deposition

“…On the other hand, hyperthermal atomic oxygen can penetrate and form Ag 2 O grains down to the depth of several m in a Ag single crystal. 60 Oxygen projectile with kinetic energy higher than ϳ10 eV, which was formed by the laser ablation during PLD, should have penetrated into the deep region of the Ag substrate. Also, it is known that single crystalline Ag can store atomic oxygen, and that annealing processes above 400°C in UHV will cause the subsurface oxygen to easily diffuse to the surface region.…”