Competing interactions in molecular adsorption: NH₃on Si(001)

Abstract

Ammonia is a good model system for the study of co-adsorption interactions, including indirect effects such as charge and strain-induced local effects on adsorption sites, and direct interactions such as hydrogen bonding. On the Si(001) surface, it adsorbs molecularly, via a dative bond from the N atom to the down atom of a buckled dimer, and is therefore very sensitive to the local charge conditions. It will then dissociate into -H and -NH(2) groups, adsorbed on the dangling bonds of the Si dimers. The NH(2) groups do not diffuse, so any correlations deriving from interactions during adsorption are preserved, and can be derived by analysis of the arrangements of the NH(2) groups. Hydrogen-bonding interactions are crucial in understanding the behaviour of this system, with significant co-adsorption interactions occurring both along and across rows, outweighing the electrostatic or buckling-related effects. In recent years, there have been several scanning tunnelling microscopy studies and extensive computational modelling of the NH(3) on Si(001) system, attempting to determine a dominant mechanism governing co-adsorption effects. In this review, I will discuss both experimental and theoretical results, make a comparison with similar molecules such as phosphine (PH(3)), and review the different ways in which experimentalists and modellers have approached this complex system.

Separation of the attractive and repulsive contributions to the adsorbate–adsorbate interactions of polar adsorbates on Si(100)

“…Also listed are hydrogen bond length between an electronegative O (or N) atom and proton in two nearest neighboring adsorbates. d α , d βm and d βp indicate the mean length and dispersion of H-bonds for relevant Structures (3,4,7,8), (2,4) and (6,8) …”

“…Taking the adsorption of organic molecules for example, several different origins of adsorbateadsorbate interactions (AAIs) have been identified [1,2]. They include direct adsorbate-adsorbate steric repulsion, dipole-dipole interaction and hydrogen bonding.…”

Building Organic Monolayers Based on Fluorinated Amines on the Si(111) Surface

“…Several monolayer formation processes have been developed for N-containing compounds on silicon surfaces leading to the formation of Si-N linkages. For example, ammonia reacts with Si(100) surface in ultra-high vacuum (UHV) conditions [8][9] by forming Si-NH 2 and…”

“…[10][11][12] A number of studies focus on the surface reactions of clean silicon surfaces with amines, including dimethylamine (DMA), trimethylamine (TMA), [13][14][15][16] triethylamine(TEA), 17 aniline, 18 and aryl amines [19][20] , performed in UHV conditions. However, UHV surface preparation and interface processing are time-consuming and expensive, and for most chemistries described to date, the formation of Si-N bonds is accompanied by the processes leading to other surface species (such as Si-H).…”

Dissociative adsorption of CH3X (X = Br and Cl) on a silicon(100) surface revisited by density functional theory

“…As the flipping motion of silicon dimer is intrinsic to Si(100) that operates even in the absence of adsorbates, the effect of this motion on dissociation dynamics, as we describe in this work, should be general for a wide class of molecules. [14][15][16][17][18][19][20] Central to our current work is the effect of flipping silicon dimer on the barrier height of a single dissociative adsorption reaction on Si(100), rather than its effect on the branching of multiple reaction pathways examined in early work. 16,19 We also examine how the dissociative adsorption is altered on a heterodimer in a Si(100) surface.…”