Passivation and activation: How do monovalent atoms modify the reactivity of silicon surfaces?

Hamers, Robert J.

doi:10.1016/j.susc.2006.05.025

Cited by 12 publications

(8 citation statements)

References 16 publications

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“…Although H-terminated silicon surfaces are often considered to be relatively unreactive, Dai et al found that a Cu amidinate precursor, a precursor similar to Cu(hfac)VTMS, reacts with the H-terminated silicon surface as well as with several other differently terminated silicon crystals in an ALD-like reaction. 8 The studies presented here, of a reaction on hydrogen-covered silicon surfaces, suggest that the reaction begins at defects, which is similar to previous studies by Kelly et al 12 Other reactions have also been observed on H-terminated Si(100) to initiate at a silicon dangling bond and to continue consuming the rest of the surface hydrogen; 14,17,[33][34][35][36][37][38][39][40] however, this reaction leads to the formation of metallic nanoparticles with sizes determined by the amount of surface hydrogen available. Thus, copper chemical vapor deposition and nanoparticle formation proceed by a self-limiting surface reaction.…”

Section: Introductionsupporting

confidence: 88%

“…70 Although our density functional theory (DFT) calculations predict a high reaction barrier of 120-127 kJ/mol for a Cu(hfac) fragment to remove a hydrogen atom from the surface (shown in detail in Supporting Information), it is possible that metal centers already present on a surface catalyze the reaction of Cu(hfac) with H-terminated silicon surfaces by lowering its barrier. 12,39,71 The Si-H stretching band loss, shown in Figure 2, on chemically prepared H-Si(100) (b) is not as welldefined compared to that of H-Si(111) because of the presence of a larger number of defects and multiple types of hydrogen sites on H-Si(100) prior to the reaction, as was previously documented by STM and FTIR studies. 40,41,43,49,50,54 Our XPS studies further indicate that the majority of copper grown on H-terminated silicon surfaces is metallic.…”

Section: Discussionmentioning

confidence: 70%

“…A recent computational study of the interaction of copper with a variety of terminated silicon surfaces suggested that copper atoms may migrate freely on the H-terminated Si(111) surface but would adhere strongly to hydroxyl species . Although our density functional theory (DFT) calculations predict a high reaction barrier of 120−127 kJ/mol for a Cu(hfac) fragment to remove a hydrogen atom from the surface (shown in detail in Supporting Information), it is possible that metal centers already present on a surface catalyze the reaction of Cu(hfac) with H-terminated silicon surfaces by lowering its barrier. ,, The Si−H stretching band loss, shown in Figure , on chemically prepared H−Si(100) (b) is not as well-defined compared to that of H−Si(111) because of the presence of a larger number of defects and multiple types of hydrogen sites on H−Si(100) prior to the reaction, as was previously documented by STM and FTIR studies. ,,,,, …”

Section: Discussionmentioning

confidence: 90%

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Metallic Nanostructure Formation Limited by the Surface Hydrogen on Silicon

Perrine

Teplyakov

2010

Langmuir

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Constant miniaturization of electronic devices and interfaces needed to make them functional requires an understanding of the initial stages of metal growth at the molecular level. The use of metal-organic precursors for metal deposition allows for some control of the deposition process, but the ligands of these precursor molecules often pose substantial contamination problems. One of the ways to alleviate the contamination problem with common copper deposition precursors, such as copper(I) (hexafluoroacetylacetonato) vinyltrimethylsilane, Cu(hfac)VTMS, is a gas-phase reduction with molecular hydrogen. Here we present an alternative method to copper film and nanostructure growth using the well-defined silicon surface. Nearly ideal hydrogen termination of silicon single-crystalline substrates achievable by modern surface modification methods provides a limited supply of a reducing agent at the surface during the initial stages of metal deposition. Spectroscopic evidence shows that the Cu(hfac) fragment is present upon room-temperature adsorption and reacts with H-terminated Si(100) and Si(111) surfaces to deposit metallic copper. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to follow the initial stages of copper nucleation and the formation of copper nanoparticles, and X-ray energy dispersive spectroscopy (XEDS) confirms the presence of hfac fragments on the surfaces of nanoparticles. As the surface hydrogen is consumed, copper nanoparticles are formed; however, this growth stops as the accessible hydrogen is reacted away at room temperature. This reaction sets a reference for using other solid substrates that can act as reducing agents in nanoparticle growth and metal deposition.

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Section: Introductionsupporting

confidence: 88%

Section: Discussionmentioning

confidence: 70%

Section: Discussionmentioning

confidence: 90%

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Metallic Nanostructure Formation Limited by the Surface Hydrogen on Silicon

Perrine

Teplyakov

2010

Langmuir

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“…20 Unlike the reaction of ammonia with the clean Si(100) surface discussed above, the mechanism by which chlorine atoms activate the Si(100) surface for amine formation is not yet fully understood. It was suggested 30 that the reactivity of the chlorinated surface could arise from the ability of silicon to redistribute electron density 25 that favors the formation of datively bonded complexes with amines. 31 Finstad et al 18 suggested that NH 3 could form datively bonded adducts because the chlorine-terminated surface polarizes the silicon atoms, inducing a slight positive charge.…”

Section: ' Introductionmentioning

confidence: 99%

On the Mechanism of Silicon Activation by Halogen Atoms

2011

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Despite the widespread use of chlorinated silicon as the starting point for further functionalization reactions, the high reactivity of this surface toward a simple polar molecule such as ammonia still remains unclear. We therefore undertook a comprehensive investigation of the factors that govern the reactivity of halogenated silicon surfaces. The reaction of NH3 was investigated comparatively on the Cl-Si(100)-2 × 1, Br-Si(100)-2 × 1, H-Si(100)-2 × 1, and Si(100)-2 × 1 surfaces using density functional theory. The halogenated surfaces show considerable activation with respect to the hydrogenated surface. The reaction on the halogenated surfaces proceeds via the formation of a stable datively bonded complex in which a silicon atom is pentacoordinated. The activation of the halogenated Si(100)-2 × 1 surfaces toward ammonia arises from the large redistribution of charge in the transition state that precedes the breakage of the Si-X bond and the formation of the Si-NH2 bond. This transition state has an ionic nature of the form Si-NH3(+)X(-). Steric effects also play an important role in surface reactivity, making brominated surfaces less reactive than chlorinated surfaces. The overall activation-energy barriers on the Cl-Si(100)-2 × 1 and Br-Si(100)-2 × 1 surfaces are 12.3 and 19.9 kcal/mol, respectively, whereas on the hydrogenated Si(100)-2 × 1 surface the energy barrier is 38.3 kcal/mol. The reaction of ammonia on the chlorinated surface is even more activated than on the bare Si(100)-2 × 1 surface, for which the activation barrier is 21.3 kcal/mol. Coadsorption effects in partially aminated surfaces and in the presence of reaction products increase activation-energy barriers and have a blocking effect for further reactions of NH3.

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“…The covalent attachment of active molecules to surfaces is now an important item in the surface scientist's toolbox. Such tools include thiol-modified DNA probes on gold, , alkane thiols on gold, , silanes on silica − and on metal oxides, , diazonium salts on glassy carbon, alkylation of chlorinated silicon surfaces, and the modification of hydrogen-terminated silicon surfaces. − The majority of these methods suffer from the irreversibility of the surface attachment, although alkane thiols on gold do exhibit some limited exchange with sluggish diffusion of the attached molecule. We were intrigued by the possibility of using the strong tetra-hydrogen-bonding group, ureido-[2-(4-pyrimidone)], developed by Meijer and co-workers − as a reversible point of attachment.…”

Section: Introductionmentioning

confidence: 99%

Reversible Attachment of Perylenediimide Fluorophore to Glass Surfaces via Strong Hydrogen-Bonding

2007

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Chemical immobilization of a triethoxysilyl-functionalized hydrogen-bonding ureido-[2-(4-pyrimidone)] tetraplex produced interaction sites on a glass substrate that allowed association with a perylenediimide-functionalized tetraplex, providing noncovalent links of the fluorophore to the surface. The association between the self-complementary molecules was exceptionally strong, both in solution and at the surface, such that effective hydrogen-bonding was retained after repeated solvent washes.

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Passivation and activation: How do monovalent atoms modify the reactivity of silicon surfaces?

Cited by 12 publications

References 16 publications

Metallic Nanostructure Formation Limited by the Surface Hydrogen on Silicon

Metallic Nanostructure Formation Limited by the Surface Hydrogen on Silicon

On the Mechanism of Silicon Activation by Halogen Atoms

Reversible Attachment of Perylenediimide Fluorophore to Glass Surfaces via Strong Hydrogen-Bonding

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