Fig. 2: Non-oxidized surface of Cu NPs with a negatively charged state in air.
From: Non-oxidized bare copper nanoparticles with surface excess electrons in air
a,b, TEM images of Cu NPs; as prepared (a) and as a function of exposure time in air (b). c, EELS data from positions 1–4 shown in a and the surface for each position shown in b. The separated NP from the oxidized electride (position 4) is also metallic Cu, indicating that excess electrons are transferred in the growth process of Cu NPs. d, Cu NP exposed to air for 158 days. The enlarged image (top inset) confirms the absence of a surface layer of Cu oxide and the interplanar distance of 0.21 nm of the Cu{111} plane. EELS data (bottom inset) also prove that the Cu NPs persist against oxidation. e, HR-TEM image of Cu NPs exposed to air for 219 days showing the interatomic distance of 0.25 nm for fcc Cu(110) (top inset). f, HR-TEM image of Cu NPs exposed to air for 219 days showing the interplanar distance of 0.21 nm for fcc Cu(111) (top inset). The invariable interplanar distance profiles (bottom insets) of the surface regions (positions 1, 2, 4 and 5) and bulk regions (positions 3 and 6) clearly indicate that Cu NPs survive without oxidation for more than seven months.
