Crystalline Ice Research Articles

The growth process of first water layer and crystalline ice on the Rh(111) surface

The adsorption states and growth process of the first layer and multilayer of water (D(2)O) on Rh(111) above 135 K were investigated using infrared reflection absorption spectroscopy (IRAS), temperature programed desorption, spot-profile-analysis low-energy electron diffraction, and scanning tunneling microscopy (STM). At the initial stage, water molecules form commensurate ( radical3x radical3)R30 degrees islands, whose size is limited for several hexagonal units; the average diameter is approximately 2.5 nm. This two-dimensional (2D) island includes D-down species, and free OD species exist at the island edge. With increasing coverage, the D-up species starts to appear in IRAS. At higher coverages, the 2D islands are connected in STM images. By the titration of Xe adsorption we estimated that the D-down domain occupies about 55% on Rh(111) at the saturation coverage. Further adsorption of water molecules forms three-dimensional ice crystallites on the first water layer; thus, the growth mode of crystalline water layers on Rh(111) is a Stranski-Krastanov type. We have found that an ice crystallite starts to grow on D-down domains and the D-down species do not reorient upon the formation of a crystalline ice.

A computational study on the X-ray absorption spectrum of proton-ordered crystalline ice IX

The cluster model commonly used in the simulation of X-ray absorption spectra is examined for water in a crystalline environment. The proton-ordered crystalline ice IX was chosen as an example. Effects of the size of the quantum cluster, long-range electrostatic interactions and the quality of the atomic basis sets are examined in detail. It is found that both the size of the quantum cluster and the Madelung potential due to long-range electrostatic interactions in the ordered crystal strongly influence the calculated spectrum while the quality of the basis set only has a very minor effect. For ice IX, it is shown that the features observed in the pre- and near edge region are described reasonably well but the main and post-edge absorption profile is more difficult to reproduce.

Reactivity of water–electron complexes on crystalline ice surfaces

The interactions between long-living electrons trapped in defects of crystalline D2O and electronegative molecules have been investigated using two-photon photoemission spectroscopy. When covered by a Xe adlayer, the spectroscopic signature of the trapped electrons vanishes, which provides evidence that the trapping sites are located on the surface of the crystalline ice. The reactive character of these surface-trapped electrons with molecules has been studied. In the case of CFCl3 adsorbed on top of the ice, we show that the trapped electrons induce the dissociation of the molecules, via a dissociative electron attachment process, resulting in *CFCl2 and Cl(-) formation. The latter species are responsible for the observed increase of the work function and presumably for the deactivation of the surface trapping sites with respect to subsequent light-induced population by excited electrons. This process is thought to be of high efficiency since it is observed for a very low CFCl3 coverage of only approximately 0.004 monolayer (ML). In the case of exposure of the crystalline ice to a partial pressure of gaseous O2, the deactivation of the trapping site has also been observed. The mechanism is thought to involve the formation of the O2*(-) transient anion by electron attachment, followed by its reactive interaction with the water molecules of the defect. In both cases, the mechanisms are triggered by negative ion resonances which are known from experiments using a primary electron beam to be effective for isolated molecules for ballistic electrons of approximately 0 eV. We thereby demonstrate a similarity between the processes induced by these primary, very low kinetic-energy electrons and by the long-living surface electrons on the crystalline ice surface. These results suggest that the photoexcited trapped electrons can play an important role in the heterogeneous chemical processes on condensed water surfaces and could be relevant in the polar stratosphere chemistry.

A Dynamic Landscape from Femtoseconds to Minutes for Excess Electrons at Ice−Metal Interfaces

Stabilization of excess electrons is studied at crystalline ice−metal interfaces by femtosecond time-resolved two-photon photoelectron spectroscopy and ab initio calculations. Following optical excitation into delocalized image potential states, electrons localize at pre-existing defects which are located at the ice−vacuum interface. Remarkably, the stabilization of these trapped electrons is monitored continuously from femtoseconds up to minutes. By first principle calculations we identify defect structures, that support excess electrons in front of crystalline ice surfaces, and suggest that the stabilization proceeds through subsequent conformational substates. The excess electron wave functions are efficiently screened from the underlying bulk and explain the long residence times observed in the experiment. Thereby, we shed light on the collective character of the nuclear rearrangement that determines the energetics over all timescales.

Desorption of H2O from Flat and Stepped Pt(111)

To investigate the effect of steps on H2O binding on a nominal Pt(111) surface, we used thermal desorption spectroscopy of water adsorbed on purposefully nanostructured surfaces: a rippled surface containing densely packed (100)-microfaceted and (111)-microfaceted steps was created using grazing incidence ion bombardment, and a surface with triangular mounds mainly consisting of (111)-microfaceted steps was fabricated through homoepitaxial growth. These morphologies are determined by scanning tunneling microscopy. We find two additional high-temperature H2O desorption peaks using the rippled surface, whereas only the peak with the highest desorption temperature is present on the (111)-microfaceted mound. Thus, water preferentially binds to steps and especially favors (111)-microfaceted ones. Furthermore, the large step concentration on our nanostructured surfaces precludes the coexistence of a condensed and a diluted phase in a monolayer of water and suppresses the formation of crystalline ice multilayers...

A Possible Icy Kuiper Belt around HD 181327

We have obtained a Gemini South T-ReCS Qa-band (18.3 micron) image and a Spitzer MIPS SED-mode observation of HD181327, an F5/F6V member of the ~12 Myr old beta Pictoris moving group. We resolve the disk in thermal-emission for the first time and find that the northern arm of the disk is 1.4x brighter than the southern arm. In addition, we detect a broad peak in the combined Spitzer IRS and MIPS spectra at 60 - 75 micron that may be produced by emission from crystalline water ice. We model the IRS and MIPS data using a size distribution of amorphous olivine and water ice grains (dn/da proportional to a^{-2.25} with a_{min} consistent with the minimum blow out size and a_{max} = 20 micron) located at a distance of 86.3 AU from the central star, as observed in previously published scattered-light images. Since the photo-desorption lifetime for the icy particles is ~1400 yr, significantly less than the estimated ~12 Myr age of the system, we hypothesize that we have detected debris that may be steadily replenished by collisions among icy Kuiper belt object-like parent bodies in a newly forming planetary system.

INFRARED SPECTRA AND THERMODYNAMIC PROPERTIES OF CO2/METHANOL ICES

Ices of mixtures of carbon dioxide and methanol have been studied in a range of temperatures relevant for star-forming regions, comets, polar caps of planets and satellites, and other solar system bodies. We have performed temperature-programmed desorption measurements and recorded IR spectra of various types of samples. The presence of two slightly different structures of CO2 is manifest. A distorted CO2 structure is characterized by bandshifts between 5 cm–1 (ν3) and 10 cm–1 (ν2) with respect to normal CO2. If the samples are heated above 130 K, the distorted CO2 sublimates and only the normal structure remains. The latter can stay trapped until the sublimation of crystalline methanol (150 K). The desorption energy (E d ~ 20 kJ mol–1) of CO2 from methanol ice, and the specific adsorption surface area (6 m2 g–1) of amorphous CH3OH ice, have been determined. CO2 does not penetrate into crystalline ice. Whereas the desorption energy is similar to that of CO2/H2O samples, the specific surface of methanol is much smaller than that of amorphous solid water (ASW). The interaction of CO2 molecules with water and methanol is similar but ices of CH3OH are much less porous than ASW. The inclusion of CO2 into previously formed ices containing these two species would take place preferentially into ASW. However, in processes of simultaneous deposition, methanol ice can admit a larger amount of CO2 than water ice. CO2/CH3OH ices formed by simultaneous deposition admit two orders of magnitude more CO2 than sequentially deposited ices. These findings can have direct relevance to the interpretation of observations from protostellar environments (e.g., RAFGL7009S) and comet nuclei.

The Mesoscale Morphologies of Ice Films: Porous and Biomorphic Forms of Ice under Astrophysical Conditions

We present the results of experiments in which we grow submicrometer- to millimeter-thick ice films at temperatures of 6-220 K at low pressures in situ in a cryo environmental scanning electron microscope. We find that ice films show pronounced morphologies at the mesoscale similar to those previously described in films of ceramics, semiconductors, and metals; materials with quite different material properties to ice. Our experiments are aimed at revealing the mesoscale morphologies of amorphous and crystalline ice with regard to astrophysical environments, as the conditions in which the ice films grow in our experiments are those under which exists most extraterrestrial ice. The porosity on the mesoscale of many of the morphologies is notable in this regard; a further intriguing finding is that these ice films can emulate biological forms.

Electron Damage to Supported Ice Investigated by Scanning Tunneling Microscopy and Spectroscopy

We study the interaction of low-energy electrons with crystalline ice (D2O) on Cu(111) by low-temperature scanning tunneling microscopy and spectroscopy. Electrons induce dissociation of the molecules with a threshold of approximately 3 eV. The large dissociation yield of the order of 10(-8)/electron and the extended area of dissociation are attributed to a shift in conduction band during the dissociation. Voltage dependent differences in imaging of ice and dissociated ice are reflected in the spectroscopic signature.

Ground-State Properties of Crystalline Ice from Periodic Hartree-Fock Calculations and a Coupled-Cluster-Based Many-Body Decomposition of the Correlation Energy

Ground state properties of crystalline ice Ih are investigated by combining periodic Hartree-Fock calculations with a many-body expansion for the electron correlation energy using second-order many-body perturbation theory and coupled-cluster techniques. Very good agreement with experimental data can already be achieved by considering two-body correlation contributions up to the third coordination shell in crystalline ice. This hints at the possibility to accurately simulate ab initio water by using periodic Hartree-Fock calculations together with a parametrized two-body correlation potential.

Fingerprints of Amorphous Icelike Behavior in the Vibrational Density of States of Protein Hydration Water

The low-frequency modes of protein hydration water are investigated by inelastic neutron scattering. Experiments on both protonated and fully deuterated maltose binding protein samples allow us to unambiguously single out the contribution from water. The low-energy vibrational density of states of hydration water at 100 K is similar to the density of states of high- and low-density amorphous ice, and quite different from that of simple forms of crystalline ice. This result can be related to the picture of hydration water mass density depending on the protein surface curvature, which supports its glassy behavior.

HK-band imaging polarimetry and radiative transfer modeling of the massive young stellar object CRL 2136

Aims. We investigate the physical properties of the dust environment of the massive proto-stellar object CRL 2136 by means of two-dimensional radiative transfer modeling, which combines fitting of the spectral energy distribution, the intensity images, and the polarization images. Methods. We obtained polarimetric images of CRL 2136 in the H and K bands using the CIAO instrument on the 8 m Subaru telescope. We developed a new Monte Carlo code which can deal with multiple-grain models and computes the SED, the dust temperature, and the Stokes IQUV images. With this code, we performed two-dimensional modeling of CRL 2136’s circumstellar disk and envelope. Results. Our images show a compact infrared source, two bright lobes extending towards the south and east, and two faint lobes extending towards the northwest and west. The polarization images show a polarization disk near the central star with a position angle of ∼−135 ◦ , a polarization vector alignment approximately parallel to the polarization disk, and a region with low polarization between the eastern and the southern lobes. In our modeling, we assume three grain models: bare grains, warm grains with a crystalline water ice mantle, and cold grains with an amorphous water ice mantle. We obtained a maximum grain core size of 0.45 μm. We found that the CRL 2136 disk has a low disk mass of 0.007 M� , a large radius of 2000 AU, a scale height of 1.0, and a low accretion rate of ✭

Adsorption of water on JSC‐1A (simulated moon dust samples)—a surface science study

AbstractJSC‐1a (a simulated lunar dust sample) supported on a silica wafer (SiO2/Si(111)) has been characterized by scanning electron microscopy (SEM), energy dispersive x‐ray (EDX) spectroscopy, and Auger electron spectroscopy (AES). The adsorption kinetics of water has been studied primarily by thermal desorption spectroscopy (TDS) and in addition by collecting isothermal adsorption transients. Blind experiments on the silica support have been performed as well. JSC‐1a consists mostly of aluminosilicate glass and other minerals containing Fe, Na, Ca, and Mg, as characterized in detail in prior studies, for example, at NASA. The particle sizes span the range from a few micrometers up to 100 µm. At small exposures, H2O TDS is characterized by broad (100–450) K structures; at large exposures, distinct TDS peaks emerge, which are assigned to amorphous solid water (ASW) (145 K) and crystalline ice (CI) (165 K). Water dissociates on JSC‐1a at small exposures but not on the bare silica support. Coadsorption TDS data (alkane–water mixtures) indicate that rather porous condensed ice layers form at large exposures, with the mineral particles acting most likely as nucleation sites. At thermal impact energies, the initial adsorption probability amounts to 0.92 ± 0.05. It is evident that the drop‐and‐dry technique, developed in studies about nanoparticles/tubes, can be extended to obtain samples for surface science studies based on powders consisting of particles with rather large diameters. Copyright © 2008 John Wiley & Sons, Ltd.

Structural transformations in amorphous ice and supercooled water and their relevance to the phase diagram of water

Arguably the most important liquid in our existence, water continues to attract enormous efforts to understand its underlying structure, dynamics and thermodynamics. These properties become increasingly complex and controversial as we progress into and below the ‘no man's land' where bulk water can only exist as crystalline ice. Various, so far unconfirmed, scenarios are painted for this region, including the second critical point scenario, the singularity-free scenario, and most recently the ‘critical point-free’ scenario [C.A. Angell, Science 319, 582 (2008)]. In this article the structural aspects of water in its supercooled, amorphous and confined states are explored, to the extent that these are known, and related to the water phase diagram. An important issue to emerge is the extent to which structural measurements on a disordered material can tell us about its phase.

Thermodynamic, structural, and dynamic properties of supercooled water confined in mesoporous MCM-41 studied with calorimetric, neutron diffraction, and neutron spin echo measurements

Thermodynamic, structural, and dynamic properties of heavy water (D(2)O) confined in mesoporous silica glass MCM-41 C10, C12, and C14 were investigated by differential scanning calorimetry, neutron diffraction, and neutron spin echo (NSE) measurements, respectively. The DSC data showed that no crystallization of D(2)O confined in C10 occurs in a temperature range between 298 and 180 K, and that crystalline ice is formed at 204 and 221 K for C12 and C14, respectively. For C10, the neutron radial distribution functions of confined D(2)O suggested a structural change in the supercooled state between 223 and 173 K. For C10 sample, it has been found that the tetrahedral-like water structure is partially enhanced in the central part of pores at 173 K. For all the samples, the intermediate scattering functions from the NSE measurements are fitted by the Kohlrausch-Williams-Watts stretched exponential function which implies that confined supercooled D(2)O exhibits a wide distribution of relaxation times. For C10, C12, and C14 samples, between 298 and 240 K, the relaxation times of supercooled D(2)O follow remarkably well the Vogel-Fulcher-Tamman equation; for C10 sample, below 240 K, the relaxation times of nonfreezing D(2)O show an Arrhenius type behavior. From the present experimental results on calorimetric, structural, and dynamic properties, it has been concluded that supercooled D(2)O confined in MCM-41 C10 experiences a transition from high-density to low-density hydrogen-bonded structure at around 229 K.

Experimental Evidence for Ice Formation at Room Temperature

The behavior of water under extreme confinement and, in particular, the lubrication properties under such conditions are subjects of long-standing controversy. Using a dedicated, high-resolution friction force microscope, scanning a sharp tungsten tip over a graphite surface, we demonstrate that water nucleating between the tip and the surface due to capillary condensation rapidly transforms into crystalline ice at room temperature. At ultralow scan speeds and modest relative humidities, we observe that the tip exhibits stick-slip motion with a period of 0.38+/-0.03 nm, very different from the graphite lattice. We interpret this as the consequence of the repeated sequence of shear-induced fracture and healing of the crystalline condensate. This phenomenon causes a significant increase of the friction force and introduces relaxation time scales of seconds for the rearrangements after shearing.

Cryocrystallography in capillaries: critical glycerol concentrations and cooling rates

Capillary tubes have many advantages over multi-well plates for macromol-ecular crystal growth and handling, including the possibility of in situ structure determination. To obtain complete high-resolution X-ray data sets, cryopreservation protocols must be developed to prevent crystalline ice formation and preserve macromolecular crystal order. The minimum glycerol concentrations required to vitrify aqueous solutions during plunging into liquid nitrogen and liquid propane have been determined for capillary diameters from 3.3 mm to 150 microm. For the smallest diameter, the required glycerol concentrations are 30%(w/v) in nitrogen and 20%(w/v) in propane, corresponding to cooling rates of approximately 800 and approximately 7000 K s(-1), respectively. These concentrations are much larger than are required in current best practice using crystals in loops or on microfabricated mounts. In additon, the relation between the minimum cooling rate for vitrification and glycerol concentration has been estimated; this relation is of fundamental importance in developing rational cryopreservation protocols.

Dielectric relaxation of the amorphous ices

The dielectric properties of the low and high density amorphous ices are discussedin terms of those for supercooled water and crystalline ices, and also used toevaluate the transition behaviour upon pressure cycling at 130 K. The dielectricrelaxation of the high density amorphous ice is described well by the symmetricalCole–Cole function with an almost pressure independent relaxation timeτ∼2 s at 133 K and a relaxation time distribution factor of 0.7. At the high to low density amorphousice transition, the dielectric relaxation time increases by about two orders of magnitude despite a∼30% decrease indensity, and τ of the low density amorphous ice is in the range102–103 s at 130 K. The relaxation time behaviour of the high densityamorphous ice is similar to that of supercooled liquid water, whereasτ of the low density amorphous ice appears to be prolonged by the ice rules, incorrespondence to that of the crystalline ices.

Resolving the Optical Spectrum of Water: Coordination and Electrostatic Effects

The optical absorption of small water clusters, water chains, liquid water, and crystalline ice is analyzed computationally. We identify two competing mechanisms determining the onset of the optical absorption: Electronic transitions involving surface molecules of finite clusters or chains cause a redshift upon molecular aggregation compared to monomers. On the other hand, a strong blueshift is caused by the electrostatic environment experienced by water monomers embedded in a hydrate shell. Concerning the recent dispute over the structure of the liquid, the present results support the conventional fourfold coordinated water, as obtained from ab initio molecular-dynamics simulations.

Growth of multilayer ice films and the formation of cubic ice imaged with STM

Ice films as many as 30 molecular layers thick can be imaged with scanning tunneling microscopy (STM) when negative sample biases $<\ensuremath{-}6(\ifmmode\pm\else\textpm\fi{}1)\text{ }\text{V}$ and subpicoamp tunneling currents are used. We observe that water deposited onto Pt(111) below 120 K forms amorphous films, whereas metastable cubic ice appears between 120 and 150 K. To determine the mechanisms of ice growth, we investigate the thickness-dependent film morphology. Cubic ice emerges from screw dislocations in the crystalline ice film that are caused by the mismatch in the atomic Pt- step height and the ice-bilayer separation.