Role of surface strain in the subsurface migration of adsorbates on silicon

Abstract

Modification of silicon surfaces through the insertion of atoms or even small molecular fragments of an adsorbate into a silicon-silicon bond can be affected tremendously by the effects of surface strain. This process takes place as either surface insertion or subsurface insertion, depending on whether the inserted species remains within the topmost layer or undergoes migration into subsurface layers, respectively. Using densityfunctional-theory cluster calculations, we show that insertion can be both thermodynamically and kinetically favorable if it takes place in such a way that surface strain is mitigated by neighboring surface sites. By considering the thermal decomposition of ammonia ͑NH 3 ͒ adsorbed on a Si͑100͒-2 ϫ 1 surface, we find that insertion mainly depends on the initial distribution of adsorbates and the orientation taken by inserted species with respect to neighboring structures along the surface. These factors seem to greatly affect the subsurface insertion, which can therefore be considered a long-range process. On the other hand, for surface-insertion processes the factors mentioned above are less influential, and insertion has more of a local character. Understanding the factors governing insertion mechanisms may lead to development of more approaches to surface functionalization, where the adsorbates decorating the surface can decompose in a controllable fashion.

Reactivity of selectively terminated single crystal silicon surfaces

“…7 suggest that the surface exposed to ammonia at room temperature likely has both types of expected configurations: aligned (where -NH 2 groups are located on the same edge of the silicon dimer row) and alternate (where -NH 2 and -H species alternate along the edge of the silicon dimer row); however, lowering the temperature seems to lead to the production of more alternate configuration. 27,66,67 In the room temperature low coverage STM studies of the inter-dimer row effects of NH 3 dissociation on Si(100)-2 Â 1 summarized in Fig. 8, Chung et al observed all the possible combinations of structures related to the dissociation of ammonia on the dimers of the neighboring rows.…”

Reaction of Hydrazine with Solution- and Vacuum-Prepared Selectively Terminated Si(100) Surfaces: Pathways to the Formation of Direct Si–N Bonds

“…Reactions of nitrogen-containing molecules with silicon surfaces have been a subject of substantial research over several decades (see, for example, references ,, and multiple references therein). In addition to the fundamental intricacies of surface reactions in ultrahigh vacuum, − more recently, a number of condensation processes on selectively terminated silicon surfaces with nitrogen-containing compounds have been investigated by solution-based approaches. The condensation reactions included investigations of the reactivity of nitro- and nitroso-compounds with H-terminated silicon and amine reactions with halogen-terminated silicon surfaces. , Both efforts have been inspired by surface functionalization; however, the key target has been the formation of a direct Si–N bond for the ultimate formation of silicon nitride (SiN) layers.…”

Competing reactions during metalorganic deposition: Ligand-exchange versus direct reaction with the substrate surface

“…47,50,58,[73][74][75][76] While atoms representing the third layer of the surface and below are held at fixed positions to simulate lattice conditions, the two topmost layers of the cluster model are allowed to fully relax. 47,50,58,[73][74][75][76] While atoms representing the third layer of the surface and below are held at fixed positions to simulate lattice conditions, the two topmost layers of the cluster model are allowed to fully relax.…”