Influences of 1-Propanol and Methanol Additives on Crystallization of Thin Amorphous Solid Water Films.

In general, randomly oriented ice crystallites are formed by heating amorphous solid water (ASW) films at ∼160 K via homogeneous nucleation. Here, we demonstrate that monolayers of methanol and 1-propanol additives incorporated in the multilayer ASW film lead to heterogeneous nucleation at the substrate interface of Pt(111), as evidenced by the occurrence of epitaxial ice growth. The mobility of water in direct contact with the Pt(111) substrate is decreased relative to that in the bulk, but it can be increased via interactions with hydrophobic moieties of alcohols that are segregated to the interfacial region.

A temperature programmed desorption study of interactions between water and hydrophobes at cryogenic temperatures.

It is considered that hydrophobic solutes dissolve in water the formation of icelike cages in the first hydration shell. However, this conventional picture is currently under debate. We have investigated how hydrophobic species, such as D, Ne, Ar, Xe, CH, and CH, interact with water in composite films of amorphous solid water (ASW) based on temperature programmed desorption (TPD).

Nucleation and growth of water ice on oxide surfaces: the influence of a precursor to water dissociation.

We have investigated how nucleation and growth processes of ice are influenced by interfacial molecular interactions on some oxide surfaces, such as rutile TiO2(110), TiO2(100), MgO(100), and Al2O3(0001), based on the diffraction patterns of electrons transmitted through ice crystallites under the experimental configuration of reflection high energy electron diffraction (RHEED). The cubic ice Ic grows on the TiO2(110) surface with the epitaxial relationship of (110)Ic//(110)TiO2 and [001]Ic//[11[combining macron]0]TiO2. The epitaxial ice growth tends to be disturbed on the TiO2(110) surface under the presence of oxygen vacancies and adatoms.

Reflection high energy electron diffraction (RHEED) study of ice nucleation and growth on Ni(111): influences of adspecies and electron irradiation.

How interfacial molecular interactions influence nucleation and growth processes of water ice is explored using pristine, oxygenated, and CO-adsorbed Ni(111) substrates based on RHEED, together with the effects of high-energy electron irradiation on the crystallization kinetics. A monolayer of amorphous solid water deposited onto the pristine Ni(111) substrate crystallizes into ice Ic at ca. 150 K, whereas ice Ih (Ic) is formed preferentially during water vapor deposition at 135 K (125 K).

Crystallization kinetics of thin water films on Pt(111): effects of oxygen and carbon-monoxide adspecies.

This paper describes nucleation, epitaxial growth, and wettability of water on Pt(111) and how they are influenced by oxygen and carbon-monoxide adspecies, based on reflection high energy electron diffraction (RHEED), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and temperature-programmed desorption (TPD). Amorphous solid water deposited onto the pristine Pt(111) substrate crystallizes into ice Ih together with a 2D layer at 150 K, whereas ice Ic (stacking disordered ice or a mixture of ice Ic and Ih) is formed preferentially onto oxygenated Pt(111) (CO-adsorbed Pt(111)) at 155-160 K (150 K). The ice nucleation and epitaxial growth tend to be hampered on the oxygenated Pt(111) surface via hydrogen bond formation with chemisorbed oxygen.

Crystallization kinetics of water on graphite.

Graphite is hydrophobic in nature, but the crystallization kinetics and dewetting transition of thin water films deposited onto graphite are distinct from those on typical hydrophobic substrates. To clarify the origin of these behaviors, we investigated the crystallization kinetics of thin water films on graphite in terms of the initial film thickness, deposition temperature, and template effects of adspecies based on reflection high-energy electron diffraction (RHEED) images; the film morphology change was analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The water monolayer nucleates after surface diffusivity occurs at ca.

Interactions of methanol, ethanol, and 1-propanol with polar and nonpolar species in water at cryogenic temperatures.

Methanol is known as a strong inhibitor of hydrate formation, but clathrate hydrates of ethanol and 1-propanol can be formed in the presence of help gases. To elucidate the hydrophilic and hydrophobic effects of alcohols, their interactions with simple solute species are investigated in glassy, liquid, and crystalline water using temperature-programmed desorption and time-of-flight secondary ion mass spectrometry. Nonpolar solute species embedded underneath amorphous solid water films are released during crystallization, but they tend to withstand water crystallization under the coexistence of methanol additives.

Decomposition of multilayer benzene and n-hexane films on vanadium.

Reactions of multilayer hydrocarbon films with a polycrystalline V substrate have been investigated using temperature-programmed desorption and time-of-flight secondary ion mass spectrometry. Most of the benzene molecules were dissociated on V, as evidenced by the strong depression in the thermal desorption yields of physisorbed species at 150 K. The reaction products dehydrogenated gradually after the multilayer film disappeared from the surface.

Interfacial reaction of water ice on polycrystalline vanadium and its effects on thermal desorption of water.

Thermal desorption and decomposition of water ice deposited onto a polycrystalline V surface were investigated using temperature-programmed desorption and secondary ion mass spectrometry. The water molecules in multilayer films dissociate preferentially at the interface, whereas water desorption from the surface is depressed considerably. The oxygen atoms (hydrogen molecules) formed at the interface are incorporated into the substrate (released into the gas phase) sequentially at temperatures higher than 140 K.

On sub-T(g) dewetting of nanoconfined liquids and autophobic dewetting of crystallites.

The glass transition temperature (T(g)) of thin films is reduced by nanoconfinement, but it is also influenced by the free surface and substrate interface. To gain more insights into their contributions, dewetting behaviors of n-pentane, 3-methylpentane, and toluene films are investigated on various substrates as functions of temperature and film thickness. It is found that monolayers of these molecules exhibit sub-T(g) dewetting on a perfluoro-alkyl modified Ni substrate, which is attributable to the evolution of a 2D liquid.

Adsorption, diffusion, dewetting, and entrapment of acetone on Ni(111), surface-modified silicon, and amorphous solid water studied by time-of-flight secondary ion mass spectrometry and temperature programmed desorption.

Interactions of acetone with the silicon surfaces terminated with hydrogen, hydroxyl, and perfluorocarbon are investigated; results are compared to those on amorphous solid water (ASW) to gain insights into the roles of hydrogen bonds in surface diffusion and hydration of acetone adspecies. The surface mobility of acetone occurs at ∼60 K irrespective of the surface functional groups. Cooperative diffusion of adspecies results in a 2D liquid phase on the H- and perfluorocarbon-terminated surfaces, whereas cooperativity tends to be quenched via hydrogen bonding on the OH-terminated surface, thereby forming residues that diffuse slowly on the surface after evaporation of the physisorbed species (i.

Translational diffusion of cumene and 3-methylpentane on free surfaces and pore walls studied by time-of-flight secondary ion mass spectrometry.

Mobility of molecules in confined geometry has been studied extensively, but the origins of finite size effects on reduction of the glass transition temperature, T(g), are controversial especially for supported thin films. We investigate uptake of probe molecules in vapor-deposited thin films of cumene, 3-methylpentane, and heavy water using secondary ion mass spectrometry and discuss roles of individual molecular motion during structural relaxation and glass-liquid transition. The surface mobility is found to be enhanced for low-density glasses in the sub-T(g) region because of the diffusion of molecules on pore walls, resulting in densification of a film via pore collapse.

Structural relaxation of vapor-deposited water, methanol, ethanol, and 1-propanol films studied using low-energy ion scattering.

Glassy thin films of water, methanol, ethanol, and 1-propanol were prepared by deposition from the gas phase at 20 K. Relaxation of their surface and bulk structures was investigated by measuring temperature evolutions of H(+), H(-), and total yields in low-energy H(2)(+) scattering. The surface structure of a methanol film changes at temperatures of about 20 K below the glass transition temperature (T(g) = 103 K) because of enhanced diffusivity of molecules at the surface.

Roles of individual and cooperative motions of molecules in glass-liquid transition and crystallization of toluene.

Deeply supercooled fragile liquid is known to be dynamically heterogeneous, where super Arrhenius behavior of shear viscosity and alpha and beta relaxation processes have been observed. To clarify origins of these behaviors, we have investigated correlations between microscopic molecular diffusion and macroscopic hydrodynamics of vapor-deposited toluene films by using time-of-flight secondary ion mass spectrometry. The molecules are intermixed gradually at around 70 K on the film deposited at 15 K, which is followed by an abrupt film morphology change at around the calorimetric glass-transition temperature (T(g)) of 117 K.

Glass transition and crystallization dynamics of thin CCl(2)F(2) films deposited on Ni(111), graphite, and water-ice films.

The glass-liquid transition and crystallization of thin CCl(2)F(2) films, as well as the influence of substrates on the phase transition of a monolayer, have been investigated using temperature-programmed time-of-flight secondary ion mass spectrometry. The multilayer films of CCl(2)F(2) dewet a Ni(111) substrate abruptly at 57 K, which is explainable as immediate crystallization of supercooled liquid. The morphology of the crystalline CCl(2)F(2) film changes at 85 K; the molecules permeate through porous D(2)O films at temperatures higher than 70 K.

Liquidlike nature of crystalline n-butane and n-pentane films studied by time-of-flight secondary ion mass spectrometry.

Crystallization of vapor-deposited thin films of n-butane and n-pentane has been investigated using temperature-programmed time-of-flight secondary ion mass spectrometry. The morphology of thin n-butane (n-pentane) films changes at around the calorimetric crystallization temperature of 65 K (85 K) as a result of crystallization of the supercooled liquid. The morphology of the crystal grains of n-butane changes at 85 K; the butane molecules permeate through porous amorphous-solid-water films above this temperature.

Comparative study of electron stimulated positive-ion desorption from LiCl and 1-ethyl-3-methylimidazolium bis[trifluoromethylsulfonyl]imide.

The mechanism of electron stimulated desorption (ESD) from LiCl has been investigated in comparison with that from a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis[trifluoromethylsulfonyl]imide, [emim][Tf(2)N]. The bonding natures of these materials are discussed based on the matrix effect in positive-ion yields. The [emim](+) and fragment ions are emitted from the [emim][Tf(2)N] molecule unless it is in direct contact with a metal surface, suggesting that the ions are emitted provided that the electronic excitation can be localized in each molecule.

Phase transition of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide thin films on highly oriented pyrolytic graphite.

Thin glassy films of a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis[trifluoromethylsulfonyl]imide ([emim][Tf(2)N]), were deposited by thermal evaporation onto a substrate of highly oriented pyrolytic graphite. Their crystallization and fusion kinetics are discussed on the basis of results of time-of-flight secondary-ion mass spectrometry (TOF-SIMS) by measuring sputtered secondary-ion intensities as a function of temperature. Multilayer films crystallize at 205 K and then fuse at 255 K, as determined from temperature-programmed TOF-SIMS measurements, whereas crystallization occurs at around the glass-transition temperature (175-180 K) within 10 min, as shown by isothermal TOF-SIMS measurements.

Matrix effects on secondary ion emission from a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis[trifluoromethanesulfonyl]imide.

The ionization mechanism of room-temperature ionic liquids has been investigated using time-of-flight secondary ion mass spectrometry in the temperature range of 15-300 K. Analyses of 1-ethyl-3-methylimidazolium bis[trifluoromethanesulfonyl]imide ([emim][Tf(2)N]) deposited on a Ni(111) substrate revealed that the [emim](+) and [Tf(2)N](-) yields increase together with the Ni(+) yield at monolayer coverage; no such increase was observed for the films deposited on a D(2)O spacer layer. Results indicated that the [emim][Tf(2)N] molecule is not perfectly ionized; the Ni(111) surface accepts (for [emim](+)) or donates (for [Tf(2)N](-)) an electron with higher efficiency than the counterion because of the metal band effect.

The glass-liquid transition of water on hydrophobic surfaces.

Interactions of thin water films with surfaces of graphite and vitrified room-temperature ionic liquid [1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)])] were investigated using time-of-flight secondary ion mass spectrometry as a function of temperature and annealing time to elucidate the glass-liquid transition of water at the molecular level. Surface diffusion of water occurs at temperatures higher than 120 K, thereby forming three-dimensional clusters (a two-dimensional layer) on the [bmim][PF(6)] (graphite) surface. The hydrophobic effect of the surface decreases with increasing coverage of water; the bulklike properties evolve up to 40 ML, as evidenced by the occurrence of film dewetting at around the conventional glass transition temperature (140 K).

Temperature-programed time-of-flight secondary ion mass spectrometry study of 1-butyl-3-methylimidazolium trifluoromethanesulfonate during glass-liquid transition, crystallization, melting, and solvation.

For this study, time-of-flight secondary ion mass spectrometry was used to analyze the molecular orientation of 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([bmim][OTf]) and its interaction with the adsorbed Na and LiI species at temperatures of 150-300 K. A glassy [bmim][OTf] film crystallizes at around 230 K, as observed from the increase in the [bmim](+) yield. LiI and Na adsorbed on the glassy film are solvated, whereas they tend to form islands on a crystalline film.

Glass-liquid transition, crystallization, and melting of a room temperature ionic liquid: thin films of 1-ethyl-3-methylimidazolium bis[trifluoromethanesulfonyl]imide studied with TOF-SIMS.

To discuss the relationship between liquid, crystalline, and glassy states of ionic liquids, TOF-SIMS was used to analyze the glass-liquid transition, crystallization, and melting of 1-ethyl-3-methylimidazolium bis[trifluoromethanesulfonyl]imide ([emim][Tf(2)N]) at the molecular level at temperatures of 150-280 K. The [emim][Tf(2)N] molecules can be deposited thermally on a Ni(111) surface without decomposition. LiI was adsorbed onto the thin film in order to investigate the glass-liquid transition; it was incorporated in deeper layers at temperatures higher than 180 K.

Glass-liquid transition of vapor-deposited hexane studied using TOF-SIMS.

Thermodynamic connection between liquid and glass is not obvious for poor glass formers. In this study, microscopic molecular diffusivity and macroscopic fluidity of vapor-deposited thin films of n-hexane were investigated using TOF-SIMS to elucidate the mechanism of the glass-liquid transition. The C 6H 14 film deposited at 15 K is characterized by a porous structure, as inferred from the intermixing with adsorbed C 6D 14 and D 2O molecules, as well as the formation of D 2O nanoclusters on the surface.

Dewetting of thin amorphous solid water films and liquid-cubic ice coexistence in droplets studied using infrared-absorption and secondary-ion-mass spectroscopy.

The infrared absorption band of decoupled OD stretching vibration (4 mol% HOD in 20-monolayer H2O) of amorphous solid water is red-shifted and sharpened at around 160 K because of spontaneous nucleation. The crystal grows in a fluidized liquid that forms droplets on a Ni(111) substrate. The shape change and red-shift of a coupled OH band during crystallization are elucidated by a Mie particle scattering model, indicating that nanometer-size droplets are formed preferentially.

Roles of deeply supercooled ethanol in crystallization and solvation of LiI.

The mechanisms of glass-liquid transition and crystallization of amorphous solid ethanol were investigated through detailed analyses of the interaction with LiI using time-of-flight secondary ion mass spectrometry and reflection absorption infrared spectroscopy. The LiI species adsorbed on the surface are incorporated into the bulk of ethanol at temperatures higher than 100 K, concomitantly with the reorganization of the ethanol molecules at the surface. This behavior is explicable by self-diffusion of the ethanol molecules as a consequence of the glass-liquid transition.