Cluster Nucleation and Growth from a Highly Supersaturated Adatom Phase: Silver on Magnetite

Abstract

The atomic-scale mechanisms underlying the growth of Ag on the (√2×√2)R45°-Fe3O4(001) surface were studied using scanning tunneling microscopy and density functional theory based calculations. For coverages up to 0.5 ML, Ag adatoms populate the surface exclusively; agglomeration into nanoparticles occurs only with the lifting of the reconstruction at 720 K. Above 0.5 ML, Ag clusters nucleate spontaneously and grow at the expense of the surrounding material with mild annealing. This unusual behavior results from a kinetic barrier associated with the (√2×√2)R45° reconstruction, which prevents adatoms from transitioning to the thermodynamically favorable 3D phase. The barrier is identified as the large separation between stable adsorption sites, which prevents homogeneous cluster nucleation and the instability of the Ag dimer against decay to two adatoms. Since the system is dominated by kinetics as long as the (√2×√2)R45° reconstruction exists, the growth is not well described by the traditional growth modes. It can be understood, however, as the result of supersaturation within an adsorption template system.

Dual role of CO in the stability of subnano Pt clusters at the Fe 3 O 4 (001) surface

“…Fig. 1B), the configuration commonly observed for other metal adatoms at this surface (31,35,36,39,40). DFT+U calculations find an adsorption energy ΔE ads (Pt 1 ) of 3.89 eV compared with free Pt atoms in vacuum and little charge transfer to the surface (<0.5 e − ).…”

Co on Fe3O4(001): Towards precise control of surface properties

“…27 Foreign metal atoms deposited onto this surface adsorb in an oxygen-bridging site in one specific location of the unit cell. 39,[41][42][43] The force-relaxed structure of a Co adatom (Co 2+ ) in such site is shown in Figure 6(a).…”

“…Among them, based on reported work 39,[41][42][43] and our DFT calculations, we have considered the adatom site on top of two surface oxygen cations in a bridge configuration, the surface octahedral positions, and the subsurface octahedral positions. The latter, as described in the Sec.…”

A multi-technique study of CO2 adsorption on Fe3O4 magnetite

“…7(b) highlights the region of the unit cell without a light-grey 2nd layer Fe atom; this is the preferred adsorption site for many metal adatoms and hydrogen. [42][43][44][45][46] Figure 7(c) shows an STM image acquired following saturation exposure of 2 Langmuir (L; 1 L = 10 6 Torr s) CO 2 at a nominal sample temperature of 82 K. Note that this temperature is within the 2nd ML desorption peak in Fig. 3(a), so only the 1st ML molecules should be present on the surface when the STM experiment is conducted.…”