Electron induced restructuring of crystalline ice adsorbed on Pt(111)

Harnett, J.; Haq, S.; Hodgson, A.

doi:10.1016/s0039-6028(02)02604-3

Cited by 57 publications

(33 citation statements)

References 27 publications

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“…As reported by Kimmel et al (36) and confirmed by our previous STM work (31), water deposited at 135-150 K onto Pt(111) first forms a one-molecule-thin wetting layer (37)(38)(39)(40). Then, isolated 3D ice crystallites emerge and eventually, at thicknesses of ∼3-10 nm, coalesce into a continuous multilayer film.…”

Section: Resultssupporting

confidence: 77%

Formation of hexagonal and cubic ice during low-temperature growth

Thürmer

Nie

2013

Proc. Natl. Acad. Sci. U.S.A.

106

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From our daily life we are familiar with hexagonal ice, but at very low temperature ice can exist in a different structure--that of cubic ice. Seeking to unravel the enigmatic relationship between these two low-pressure phases, we examined their formation on a Pt (111) substrate at low temperatures with scanning tunneling microscopy and atomic force microscopy. After completion of the onemolecule-thick wetting layer, 3D clusters of hexagonal ice grow via layer nucleation. The coalescence of these clusters creates a rich scenario of domain-boundary and screw-dislocation formation. We discovered that during subsequent growth, domain boundaries are replaced by growth spirals around screw dislocations, and that the nature of these spirals determines whether ice adopts the cubic or the hexagonal structure. Initially, most of these spirals are single, i.e., they host a screw dislocation with a Burgers vector connecting neighboring molecular planes, and produce cubic ice. Films thicker than ∼20 nm, however, are dominated by double spirals. Their abundance is surprising because they require a Burgers vector spanning two molecular-layer spacings, distorting the crystal lattice to a larger extent. We propose that these double spirals grow at the expense of the initially more common single spirals for an energetic reason: they produce hexagonal ice.ice growth mechanisms | molecular surface steps | molecular-layer nucleation | scanning probe microscopy | spiral growth O wing to its ubiquity in nature, ice and its structural properties have inspired widespread interest (1, 2). Not long after the introduction of X-ray diffraction in 1912, the structure of the most common modification of ice, hexagonal ice Ih, had already been investigated extensively (1-6). In 1942, König (7) discovered that at low temperatures water occasionally crystallizes into a different modification, cubic ice Ic. Subsequently, cubic ice has been produced in the laboratory, e.g., by condensing water vapor onto cooled substrates (7-11), by heating amorphous solid water (7-9), by supercooling liquid water droplets (12-14) or clusters (15), or by freezing high-pressure phases of ice and reheating them at atmospheric pressure (16)(17)(18)(19). Cubic ice has been proposed to also occur naturally, e.g., in the earth's atmosphere (13,(20)(21)(22)(23)(24) and in comets (25,26). However, even after thousands of articles dedicated to ice formation have appeared, important questions regarding fundamental growth mechanisms of ice remain. Some of these questions concerning the competition between the two lowpressure crystalline phases ice Ih and ice Ic are addressed in this paper.Ice Ih and ice Ic have been observed to coexist at temperatures up to 240 K (10-12, 18, 27, 28). When ice Ic is heated above 170 K it transforms irreversibly into ice Ih. The release of a measurable amount of heat (on the order of 35 J/mol) (17-19) establishes hexagonal ice as the equilibrium structure above 170 K. Below 170 K no phase transformation has been observed, allowing for the poss...

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Section: Resultssupporting

confidence: 77%

Formation of hexagonal and cubic ice during low-temperature growth

Thürmer

Nie

2013

Proc. Natl. Acad. Sci. U.S.A.

106

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“…The same unit cell has been reported for H 2 O on Pt͑111͒, and a hydrogen-bonded structure was proposed. [47][48][49] However, the proposed structure does not match the features in our STM images, indicating that the molecular arrangement within the unit cell may be different for H 2 S than for H 2 O. Indeed, one would expect the molecular arrangement to be different, given the large difference in the O-O and S-S bond lengths in the solid ices ͑0.40-0.42 and 0.28 nm, respectively͒.…”

Section: B Molecular Interactionsmentioning

confidence: 66%

Low-temperature adsorption of H2S on Ag(111)

Russell

Liu

Kawai

et al. 2010

The Journal of Chemical Physics

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H 2 S forms a rich variety of structures on Ag(111) at low temperature and submonolayer coverage. The molecules decorate step edges, exist as isolated entities on terraces, and aggregate into clusters and islands, under various conditions. One type of island exhibits a (×)R25.3° unit cell. Typically, molecules in the clusters and islands are separated by about 0.4 nm, the same as the S-S separation in crystalline H 2 S. Density functional theory indicates that hydrogen-bonded clusters contain two types of molecules. One is very similar to an isolated adsorbed H 2 S molecule, with both S-H bonds nearly parallel to the surface. The other has a S-H bond pointed toward the surface. The potential energy surface for adsorption and diffusion is very smooth. KeywordsAmes Laboratory, adsorption, density functional theory, diffusion, hydrogen bonds, intermolecular forces, island structure, molecular clusters, potential energy surfaces, silver, sulphur compounds H 2 S forms a rich variety of structures on Ag͑111͒ at low temperature and submonolayer coverage. The molecules decorate step edges, exist as isolated entities on terraces, and aggregate into clusters and islands, under various conditions. One type of island exhibits a ͑ ͱ 37ϫ ͱ 37͒R25.3°unit cell.Typically, molecules in the clusters and islands are separated by about 0.4 nm, the same as the S-S separation in crystalline H 2 S. Density functional theory indicates that hydrogen-bonded clusters contain two types of molecules. One is very similar to an isolated adsorbed H 2 S molecule, with both S-H bonds nearly parallel to the surface. The other has a S-H bond pointed toward the surface. The potential energy surface for adsorption and diffusion is very smooth.

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“…Electron-induced damage has been discussed in LEED studies of molecularly thin water films [10,11]. Starke et al found that to circumvent beam damage, incident beam currents had to be reduced to about 1 pA [10].…”

mentioning

confidence: 99%

“…Starke et al found that to circumvent beam damage, incident beam currents had to be reduced to about 1 pA [10]. Harnett et al reported that total electron doses even as low as 0:02e ÿ per water molecule (4 C cm ÿ2 ) induced cluster formation of multilayer ice [11]. In the structural LEED study by Held and Menzel [4], electron beam currents in the 100 -300 nA range were used, adding up to a total electron dose of 3-9e ÿ per water molecule (0:5-1:5 mC cm ÿ2 ) at each spot used on their sample.…”

mentioning

confidence: 99%

Water Dissociation on Ru(001): An Activated Process

et al. 2004

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It is shown using x-ray photoelectron spectroscopy that water is adsorbed either nondissociatively or partially dissociatively on Ru(001) under ultrahigh vacuum conditions. We found an activated dissociation process with a barrier slightly larger than that of desorption. A difference in dissociation barriers is found between H2O and D2O that explains the anomalous isotope effects in the thermal desorption. Previous theoretical and experimental disagreements can be rationalized based on electron or x-ray beam-induced dissociation of the water overlayer and an earlier underestimation of the dissociation barrier.

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Electron induced restructuring of crystalline ice adsorbed on Pt(111)

Cited by 57 publications

References 27 publications

Formation of hexagonal and cubic ice during low-temperature growth

Formation of hexagonal and cubic ice during low-temperature growth

Low-temperature adsorption of H2S on Ag(111)

Water Dissociation on Ru(001): An Activated Process

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