Complete Wetting of Pt(111) by Nanoscale Liquid ... - ACS Publications

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Complete Wetting of Pt(111) by Nanoscale Liquid Water Films Yuntao Xu, Collin J. Dibble, Nikolay G. Petrik, R. Scott Smith, Bruce D. Kay,* and Greg A. Kimmel* Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States ABSTRACT: The melting and wetting of nanoscale crystalline ice films on Pt(111) that are transiently heated above the melting point in ultrahigh vacuum (UHV) using nanosecond laser pulses are studied with infrared reflection absorption spectroscopy and Kr temperature-programmed desorption. The as-grown crystalline ice films consist of nanoscale ice crystallites embedded in a hydrophobic water monolayer. Upon heating, these crystallites melt to form nanoscale droplets of liquid water. Rapid cooling after each pulse quenches the films, allowing them to be interrogated with UHV surface science techniques. With each successive heat pulse, these liquid drops spread across the surface until it is entirely covered with a multilayer water film. These results, which show that nanoscale water films completely wet Pt(111), are in contrast to molecular dynamics simulations predicting partial wetting of water drops on a hydrophobic water monolayer. The results provide valuable insights into the wetting characteristics of nanoscale water films on a clean, wellcharacterized, single-crystal surface. it is energetically costly to cover the surface with a water film; thus, the surface is hydrophobic. However, the converse, that a strong water−surface interaction leads to wetting, is not necessarily the case. In the simulations discussed above and on other surfaces,9 strong water−substrate interactions led to the formation of a tightly bound water monolayer that effectively turned it into a hydrophobic surface.5,11 Experimental measurements of macroscopic drops of water on Pt have produced a range of results for the contact angle (0 ≤ θc ≤ 40°).4,12 However, the connection between macroscopic contact angles and the structure of nanoscale films is unclear. Experiments in ultrahigh vacuum (UHV) have shown that thin crystalline ice films on Pt(111) only partially wet a water monolayer at cryogenic temperatures.13−16 For small coverages, the ice grows as isolated islands that are ∼10−20 layers thick and tens of nanometers across.15,16 In contrast to crystalline ice films, thin amorphous solid water (ASW) films completely wet Pt(111) and grow nearly layer-by-layer.17 Here we use pulsed laser heating, infrared reflection absorption spectroscopy (IRAS), and Kr temperature-programmed desorption (TPD) to investigate the wetting of nanoscale liquid water drops on clean, well-characterized Pt(111) in UHV. The liquid water films are produced by transiently heating crystalline ice (CI) or amorphous solid water (ASW) films above the melting point with a pulsed nanosecond laser. For each pulse, temperature jumps of ∼200 K with heating rates of ∼1010 K/s lead to rapid melting of the CI films. The subsequent rapid cooling (at ∼5 × 109 K/s)

W

etting is one of the most basic aspects of water’s interaction with a surface, representing a balance between adhesive and cohesive forces.1 A common way to measure the wettability of a surface is to measure the contact angle, θc, of a macroscopic liquid drop on that surface. Thermodynamic considerations lead to Young’s equation for the contact angle: γsl + γlv cos θc = γsv, where γsl, γlv, and γsv are the surface tensions of the solid−liquid, liquid−vapor, and solid−vapor interfaces, respectively.1 A surface is considered to be hydrophobic (hydrophilic) if θc > 90° (θc < 90°). For complete wetting, θc = 0°. The contact angle in Young’s equation is relevant for macroscopic drops. However, it does not necessarily apply to nanoscale drops or at the nanometer scale for the contact line of macroscopic drops.1−3 While experimental measurements of θc on the nanometer scale are challenging, this scale is wellsuited for molecular dynamics simulations, and several groups have simulated nanoscale water drops on a variety of surfaces,4−10 including platinum.4,5,7,11 Kimura and Murayama found that water completely wet Pt(111) with one water− platinum potential, while another potential predicted the formation of a partially wetting drop on a water monolayer with θc ∼ 20°.11 Shi and Dhir7 also found a water droplet on top of a water monolayer with θc ∼ 25°. Limmer et al.5 showed that the strong water−Pt interaction led to the formation of a water monolayer that relaxed more slowly than, and formed few hydrogen bonds with, the liquid drop above it. An important conclusion from the simulations of water on platinum and other surfaces is that small differences in the water−substrate potential can lead to relatively large changes in the predicted wetting behavior. Typically, when the water− surface interaction is weaker than the water−water interaction, © 2016 American Chemical Society

Received: December 10, 2015 Accepted: January 19, 2016 Published: January 19, 2016 541

DOI: 10.1021/acs.jpclett.5b02748 J. Phys. Chem. Lett. 2016, 7, 541−547

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Figure 1. Melting and wetting of a 10 ML CI film by pulsed laser heating to 280 K. (a) IRAS spectra of the as-grown CI film (black line) and after 1 (dark green line), 2, 3, 5, and 10 (red lines) laser pulses. The CI film was completely melted after ∼5 pulses. The blue dashed line shows the spectrum of a 10 ML ASW. (b) IRAS spectra of a 10 ML initially ASW film (black line) and after heating with up to 10 pulses. Essentially no changes are observed in the transiently heated ASW spectra. Kr TPD of the transiently heated 10 ML CI (c) and ASW (d) films: as-grown film (black line) and these films after heating with 1 (dark green line), 2, 3, 5 (red lines), and 10 (blue line) laser pulses. Schematic of a 10 ML CI film before (e) and after pulsed heating (f−h). For the as-grown film (e), the ice crystallites (black) initially cover ∼60% of the substrate, with the rest covered by 1 ML of water (dark blue). One ML of Kr (brown spheres) adsorbs on the ice crystallites and on the water monolayer. After pulsed heating to 280 K (f− h), the CI melts, spreads over the surface, and quenches to ASW (light blue). Schematic of Kr adsorbed on multilayer ASW (h) and 1 ML of water (j).

1a shows the IRAS spectrum of the as-grown 10 ML CI film. The spectrum has peaks at ∼3240 cm−1 and ∼3350 cm−1 and a shoulder at 3140 cm−1. For the ASW film (Figure 1b), the IRAS spectra are less structured, less intense, and shifted to higher wavenumbers. Figure 1a also shows the spectra after heating with 1 (dark green line), 2, 3, 5, and 10 laser pulses (red lines). After the first pulse, the CI is partially converted into ASW, indicating substantial melting of the film during the heat pulse. In particular, the peaks at ∼3240 and 3350 cm−1 decrease and the spectrum shifts to higher wavenumbers. As Np increases, the extent of melting increases. After 10 pulses, the film has completely melted and the spectrum is essentially identical to that of the ASW after pulsed heating (Figure 1a, dashed blue line). Note that some water desorption occurs during the pulsed heating leading to a slight loss of intensity.22 The small peak at ∼3693 cm−1 in Figure 1a is due to molecules that have a hydrogen atom that is not forming a bond with another molecule (i.e., “dangling OH” bonds). These dangling OH bonds are on the surface of the (nonporous) water films. The IRAS spectra for the dangling OH of CI and ASW are different.18,19 As a result, the dangling OH peak provides information about the surface of the thin

quenches these films to form ASW. Nanoscale ice crystallites, which do not wet the water monolayer at cryogenic temperatures, melt upon heating to approximately room temperature. The resulting nanoscale water drops subsequently spread out and completely wet the surface. The rate of spreading of the liquid drops increases with increasing temperature. These results provide new insights into the dynamics of thin liquid films on metal surfaces. CI and ASW films have been shown to exhibit distinct infrared line shapes in the OH stretching region.18,19 As a result, IRAS has been used for investigating the crystallization kinetics of ASW films.20,21 Here, we will use IRAS to track the melting kinetics of nanoscale ice films. Figure 1a shows a series of IRAS spectra for a 10 ML film of CI on Pt(111) before and after transiently heating the film to 280 K via pulsed laser heating. For these experiments, the 10 ML CI film was deposited at T = 140 K. The temperature was then set to Ti = 90 K for the pulsed heating experiment. After the desired number of laser pulses, IRAS spectra were measured at 90 K, and as described below, Kr TPD spectra were also obtained. Figure 1b shows a corresponding series of IRAS spectra where the initial film was ASW instead of CI. The black line in Figure 542

DOI: 10.1021/acs.jpclett.5b02748 J. Phys. Chem. Lett. 2016, 7, 541−547

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The Journal of Physical Chemistry Letters water films. In contrast, the OH-stretch region provides information on the water molecules in the entire film. Figure 2 shows an expanded view of the dangling OH region for the

1c shows the Kr TPD from 1 ML of water on Pt(111).25 For the transiently heated 10 ML film, the Kr TPD change systematically as the number of heat pulses increases. After the first pulse, the peak at ∼37 K due to Kr desorbing from ice crystallites has largely disappeared (Figure 1c, green line) and the peak at ∼43 K has significantly decreased. As the number of heat pulses increases, the TPD peak at ∼43 K completely disappears, as does the peak due to Kr desorbing from CI (Figure 1c, red lines). These features are replaced by Kr TPD spectra characteristic of multilayer ASW on Pt(111) (see Figure 1d). As depicted schematically in Figures 1e−h, the changes in the Kr TPD are consistent with an initially non-wetting CI film that melts during the pulsed heating and wets the water monolayer. The rapid cooling following each laser pulse prevents significant recrystallization and leads to the formation of ASW. For a film that is initially ASW, the Kr TPD spectra undergo relatively modest changes after pulsed heating (Figure 1d). The main change is a small loss of intensity on the high-temperature “tail” of the spectra, which suggests that pulsed heating removes some structures within the ASW film (e.g., surface roughness) that led to higher binding energy for the Kr on the as-grown ASW film. The fraction of the CI films that have melted and the extent to which they wet the surface can be quantified from their IRAS and TPD spectra, respectively. For partially melted films, the IRAS spectra, S(ν), is fit by a linear combination of the spectra for the pure CI and ASW films, SCI (ν) and SASW (ν), respectively.26

Figure 2. IRAS spectra for the dangling OH peak in 10 ML water films for the experiments shown in Figure 1a. (a) As-grown CI film (black line) and that film after and 2 heat pulses (green and red lines, respectively). (b) The CI film after 2, 3, 5, and 15 heat pulses. In both panels a and b, the dashed blue line shows the spectrum of an ASW film for comparison.

IRAS spectra in Figure 1a. For the CI film and ASW film, the dangling OH peaks are at 3690 and 3696 cm−1, respectively (Figure 2a, black and blue lines, respectively). For the transiently heated films, the dangling OH peak has changed from CI to mostly ASW after two heat pulses (Figure 2a), but the intensity is reduced. As the number of pulses increases, the intensity of the dangling OH peak increases, becoming comparable to the intensity of the dangling OH peak for an ASW film (Figure 2b). The results in Figures 1 and 2 show that the transiently heated CI films melt during the short time (∼6 ns) that they are above the melting point. Furthermore, the cooling rate is large enough to quench these liquid water films into an amorphous solid without appreciable recrystallization. The lack of recrystallization is consistent with recent measurements of the homogeneous nucleation rate for crystalline ice and the fact that ASW forms when liquid drops are quenched on a cold surface with cooling rates >105 K/s.23,24 Because thin CI films initially grow as isolated crystalline islands embedded in a hydrophobic water monolayer on Pt(111)13−16 and laser heating can transiently create nanoscale liquid water films, we can explore the wetting characteristics of these films. Previous research has shown that desorption of rare gas atoms can be used to investigate the morphology of thin water films.13,14,17 The basic idea is that the desorption temperature of a rare gas atom from a water film is related to the distance of the atom from the substrate. For example, a monolayer of Kr desorbing from 0, 1, 2, and 3 (or more) monolayers of ASW on Pt(111) have distinct peaks in their corresponding TPD spectra, as does Kr desorbing from nanoscale CI films.13,17 For the transiently heated thin water films shown in Figure 1a, the Kr TPD spectra for 1 ML of Kr were also obtained after each heating pulse (Figure 1c). The solid black line shows the Kr TPD for the as-grown 10 ML CI film. The peak at 43 K and the small broad shoulder from ∼47−53 K are due to Kr desorbing from a single layer of water, while the peak at 37 K results from Kr desorbing from multilayer ice crystallites (see Figure 1e).13,14 For comparison, the gray dashed line in Figure

S(ν) = αCISCI(ν) + βASW SASW (υ)

(1)

The coefficients αCI and βASW are determined by a leastsquares fitting procedure. The crystalline fraction of the film, f CI, is then given by fCI = αCI/(αCI + βASW )

(2)

This procedure can be applied to both the OH-stretch (Figure 1a) and dangling OH (Figure 2) regions of the IRAS spectra, giving the crystalline fraction of the entire film, f CI, and the crystalline fraction of the surface of the film, fCI(dOH), respectively. The light green dashed line in Figure 1a shows the fit obtained for Np = 1. In addition to f CI, the fraction of the surface covered with a single layer of water, Φ1ML, can be determined from the area of the 1 ML peak in the Kr TPD after pulsed heating relative to the TPD peak area for a 1 ML water film. Figure 3a shows f CI (red triangles) and Φ1ML (black circles) versus Np determined from the IRAS and Kr TPD spectra shown in panels a and c of Figure 1, respectively. For the asgrown film, f CI = 1 and the ice crystallites cover about 60% of the surface (i.e., Φ1ML ∼ 0.4). After the first pulse, approximately half the film has melted ( f CI = 0.53) and Φ1ML has decreased to ∼0.2. Additional heating pulses lead to further melting and spreading of the multilayer water film across the Pt(111). Note that the spreading of the water droplets is also responsible for the increase in the intensity of the dangling OH peak for the ASW films seen in Figure 2b. For a 10 ML film, the normalized area covered by 1 ML, Φ1ML/Φ1ML(Np = 0) versus Np is very similar to f CI (not shown). However, this is not true for other coverages. For example, for 3 ML initially CI films, f CI decreases more quickly than Φ1ML /Φ1ML(Np = 0) (not shown). This is plausible given that at lower total coverages the 543

DOI: 10.1021/acs.jpclett.5b02748 J. Phys. Chem. Lett. 2016, 7, 541−547

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would likely be melting from the sides (the prism faces), leaving a crystalline center with its basal plane exposed to the vacuum (e.g., see Figure 1f). Alternatively, the melting of the individual crystallites could be a statistical process such that some crystallites completely melt after a given number of pulses, but others remain crystalline. In that case, intermediate values of f CI and f CI(dOH) would be due to an ensemble average over a surface with a mixture of melted droplets and crystalline islands. The ensemble average case would also explain the close similarity between f CI and f CI(dOH) that is observed in Figure 3a. Further research is needed to clarify this issue. We have investigated the melting of CI films and the subsequent wetting of the liquid films for several initial coverages (3 ≤ θ0 ≤ 20 ML) and a range of temperatures (275−330 K). In all cases, the films rapidly melt upon heating, the liquid water films wet the water monolayer, and the rapid cooling after each heat pulse quenches the film. For example, Figure 3b shows Φ1ML versus the number of heating pulses for 3 ML initially CI films for several different temperatures. In this case, the ice crystallites in the as-grown films cover 20% of the surface and with the rest covered by only one layer of water. Qualitatively the behavior of these films is similar to the that of the 10 ML film heated to 280 K (Figure 3a). However, for these thinner films, melting occurs more quickly relative to the spreading of the liquid drops (data not shown). The results also show that at higher temperatures, the water films wet the surface in fewer laser pulses. Because the total amount of water that is deposited in the CI films and the fraction of the surface covered by the ice crystallites are known, the average thickness, hCI, of the ice crystallites (in monolayers) is hCI = 1 + (θ0 − 1)/(1 − f1ML). For θ0 = 10 ML, f1ML = 0.4; therefore, the ice crystallites are, on average, 16 ML thick (i.e., hCI = 16 ML). For θ0 = 3 ML, f1ML = 0.8; thus, hCI = 11 ML. Using the interlayer spacing of 0.367 nm for CI (along the c-axis),31 these crystallites are ∼4−6 nm high. This height estimate agrees well with STM images of thin CI films on Pt(111).15,16 In addition, the STM images suggest that the lateral dimensions of the ice crystallites are typically ∼20−60 nm. Therefore, if these crystallites were to melt without spreading, then the corresponding contact angle would be ∼20−35° assuming the liquid drop had the shape of a spherical cap. As the number of heat pulses increases, the liquid drop spreads out, the contact angle decreases toward 0°, and multilayer water films completely wet the surface. As discussed above, several recent simulations of nanoscale water drops on Pt(111) suggest a contact angle in the range of 20−40°.5,7 Thus, the approximate “starting point” in the current experiment corresponds to the predicted equilibrium configuration in the simulations. Because water films that are heated near the bulk melting point in UHV are rapidly desorbing (at ∼106 ML/s!), it is not possible with our approach to study the long-time or equilibrium behavior of these films. However, even at these high desorption rates, the average lifetime of a water molecule on the surface of the film prior to desorption is long compared to molecular time scales. As such, we expect that while the films are hot, they will locally maintain (quasi)equilibrium as they evolve toward the energetically preferred, wetting configuration. Furthermore, the observation that transiently heated ASW films return to their as-grown configuration (i.e., wetting and amorphous, see panels b and d of Figure 1) suggests that the equilibrium configuration for the nanoscale liquid water films is to completely wet the surface. We also note that previous

Figure 3. (a) f CI (red triangles), f CI(dOH) (green diamonds), and Φ1ML (black circles) versus Np for a 10 ML CI film heated to 280 K. (b) Φ1ML versus Np for 3 ML CI films heated to various temperatures. At higher temperatures, fewer pulses are required for the multilayer water films to completely cover the surface.

ice crystallites are further apart (on average), so the water droplets have to spread further to wet the surface. For the 10 ML film heated to 280 K, an important observation is that during the first heat pulse about half the film melts. Therefore, there is more than enough liquid water to cover the entire surface with more than 1 layer of water. Because some of the surface remains covered by just 1 layer of water, this indicates that the rate at which the nanoscale liquid water drops spread is the rate-limiting step for the wetting, not the rate at which the ice crystallites melt. The evolution of the surface dangling bonds provides valuable insight into the melting and wetting of the water film. Figure 3a shows that f CI(dOH) versus Np (green diamonds) is very similar to f CI. For 1 ML of water on Pt(111), there are very few dangling OH bonds.27−29 Therefore, most of the dangling OH signal comes from portions of the surface covered with multilayers of water or ice. Also, STM images show that the nanoscale ice crystallites on Pt(111) are typically much broader than they are high,15,16 and this will also be true for the melted droplets. Therefore, f CI(dOH) from the partially melted films should be similar to the fraction of the surface of the nanoscale droplets that is crystalline or amorphous.30 From Figure 3a, we see that after the first pulse, approximately 45% of the total surface area of the nanoscale islands is still crystalline. This could indicate that individual crystallites are partially melted. In that case, they 544

DOI: 10.1021/acs.jpclett.5b02748 J. Phys. Chem. Lett. 2016, 7, 541−547

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(i.e., melting of CI films without significant recrystallization) is difficult to assess. Because those experiments used shorter laser pulses, the cooling rates should be even greater than those found in our system. As a result, one might expect that quenching the liquid water to ASW would be even more effective in the ultrafast experiments (i.e., the opposite of the observations). Interestingly, for the experiments on Pt(111), transient melting of the CI films was not observed when it was adsorbed directly on Pt(111) without the intervening CO layer,36 suggesting that the CO influenced the melting kinetics in some way. The role of CO and other adsorbates on the melting and wetting of nanoscale crystalline ice films will be the subject of future investigations. In conclusion, nanosecond pulsed laser heating was used to explore the properties of thin water films on Pt(111) at high temperature (280−330 K). Initially nonwetting CI films rapidly melt and the nanoscale liquid drops that are formed spread out and completely cover the surface in a multilayer liquid water film. Heat transfer into the bulk of the platinum crystal produces rapid cooling of the adsorbed water film and quenches it into ASW. As expected, the spreading of the liquid drops occurs more rapidly at higher temperatures. The results provide valuable insights into the wetting kinetics on a clean, well-characterized, single-crystal surface. The results also indicate that using nanosecond pulsed lasers to transiently heat an adsorbed film is a valuable technique for studying the properties of nanoscale liquid films and supercooled liquids in ultrahigh vacuum.

experiments in our laboratory showed that ASW films can grow nearly layer-by-layer on Pt(111).17 Thus, it is possible that these wetting, low-temperature ASW films are simply a metastable extension of the wetting behavior observed for liquid water films above the melting point. An important question is how much spreading occurs during the time the film’s temperature is below 273 K. While the results in Figure 3b show that wetting takes longer at lower temperatures, a potential scenario is that for T > 273 K the liquid water films do not wet the water monolayer and that the observed wetting occurs during the time the films are cooling below 273 K. However, control experiments show that this is not the case: For those experiments, we used a single hightemperature pulse (Tmax = 311 K) to almost completely melt a 3 ML initially CI film (f CI = 0.04). As seen in Figure 3, the wetting increases after a single pulse, but some portion of the surface was still covered by a single layer of water (i.e., Φ1ML ∼ 0.3). The maximum temperature was then reduced for subsequent pulses, and the wetting kinetics were measured at lower temperatures. These experiments showed that even for Tmax < 273 K, the films continued to spread on the sample and they could eventually completely wet the surface. However, the rate at which these films spread was significantly reduced compared to the rate for T > 273 K and could not explain the observations at the higher temperatures. These and other experiments exploring the wetting behavior of supercooled liquid water films on Pt(111) will be the subject of a future publication. While simulations have suggested that water drops do not wet the first water monolayer on Pt(111),5,7,11 the results presented here show that nanoscale water drops do completely wet the monolayer. The simulations5 provide a likely explanation for this disagreement: For water on Pt(100), very few hydrogen bonds were formed with rest of the water film, and the water monolayer was strongly hydrophobic. In contrast for the simulations on Pt(111), more of the water molecules in the first layer formed a hydrogen bond with the rest of the water film, resulting in a mildly hydrophobic first layer. Therefore, small differences between the actual water−Pt interaction and those used in the simulations could account for the differences. At cryogenic temperatures, the water monolayer on Pt(111) is also a mixture of “H-down” and “flat lying” molecules.32 However, recent experiments in our laboratory showed that even at temperatures as low as 25 K, weakly bound adsorbates (such as N2 and CO) can flip some “H-down” molecules in the water monolayer to “H-up.”33 Thus, flipping to an “H-up” configuration to form a hydrogen bond to a water molecule in the second layer in liquid water films is quite reasonable and likely accounts for the wetting of the nanoscale liquid water films that is observed. Several groups have used pulsed laser heating to investigate various physical and chemical processes in nanoscale water films on Pt(111) and other surfaces.34−42 Most of these experiments have used femtosecond to picosecond duration laser pulses where excitation of the substrate electrons can lead to electron-induced reactions in the adsorbed water,39,42 different temperatures for the electrons and the phonons in the substrate,39,40 and very large temperature jumps.39 Melting of transiently heated CI films has been reported for water adsorbed on CO-covered Pt(111)36 and chlorine-terminated Si(111).38 In both cases, partial melting occurred in less than 200 ps, followed by recrystallization in about 1 ns. The connection between those experiments and the current results

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EXPERIMENTAL SECTION The experiments were conducted in a UHV chamber with a base pressure of ∼1 × 10−10 Torr. The chamber, which has been described previously,29 was equipped with a molecular beam dosing system, a closed-cycle helium cryostat, a Fourier transform infrared (FTIR) spectrometer, and a quadrupole mass spectrometer (QMS). The sample, a Pt(111) single crystal, was cleaned by sputtering with 2 keV Ne+ and annealing at 1000 K. Thin CI or ASW films were deposited at temperatures of 140 and 90 K, respectively. After the water films were deposited, the sample was typically held at an initial temperature, Ti, of 90 K, a temperature at which many kinetic processes such as desorption, diffusion, and crystallization are negligible on experimental time scales. An optical system that used the fundamental (1064 nm) of a nanosecond Nd:YAG laser (Continuum DLS 8000) and a custom beam homogenizer (Silios Technologies) was used to produce a laterally uniform heat pulse in the platinum crystal and adsorbed water films. The IR laser pulses, which were not absorbed by the water films, heated the metal substrate. However, due to efficient heat transfer, the temperature of the thin water films closely tracked the temperature of the Pt(111) surface.8 Subsequent diffusion of the heat into the metal crystal led to rapid cooling of both the metal surface and the adsorbed water film. The resulting heat pulse was approximately 10 ns long. After the samples were heated with the desired number of laser pulses (Np), IRAS and Kr TPD were used to characterize the adsorbed water films. We have performed extensive characterization, calculations, and calibration tests of the time- and distant-dependent temperature profiles within the Pt(111) and adsorbed water films. These results will be described in a future publication. For the results presented here, the key points regarding the laserinduced heating were that (1) the results were observed for a 545

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Structure and the Underlying Lattice Constant. Phys. Rev. Lett. 2013, 110, 126101. (11) Kimura, T.; Maruyama, S. In Proceedings of the 12th International Conference on Heat Transfer, Grenoble, Switzerland, 2002; pp 537− 542. (12) Bewig, K. W.; Zisman, W. A. Wetting of Gold and Platinum by Water. J. Phys. Chem. 1965, 69, 4238. (13) Kimmel, G. A.; Petrik, N. G.; Dohnalek, Z.; Kay, B. D. Crystalline Ice Growth on Pt(111) and Pd(111): Nonwetting Growth on a Hydrophobic Water Monolayer. J. Chem. Phys. 2007, 126, 114702. (14) Kimmel, G. A.; Petrik, N. G.; Dohnálek, Z.; Kay, B. D. Crystalline Ice Growth on Pt(111): Observation of a Hydrophobic Water Monolayer. Phys. Rev. Lett. 2005, 95, 166102. (15) Thurmer, K.; Bartelt, N. C. Growth of Multilayer Ice Films and the Formation of Cubic Ice Imaged with STM. Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 77, 195425. (16) Thurmer, K.; Bartelt, N. C. Nucleation-Limited Dewetting of Ice Films on Pt(111). Phys. Rev. Lett. 2008, 100, 186101. (17) Kimmel, G. A.; Petrik, N. G.; Dohnalek, Z.; Kay, B. D. Layer-byLayer Growth of Thin Amorphous Solid Water Films on Pt(111) and Pd(111). J. Chem. Phys. 2006, 125, 044713. (18) Bergren, M. S.; Schuh, D.; Sceats, M. G.; Rice, S. A. OH Stretching Region Infrared-Spectra of Low-Density Amorphous Solid Water and Polycrystalline Ice Ih. J. Chem. Phys. 1978, 69, 3477−3482. (19) Hagen, W.; Tielens, A.; Greenberg, J. M. The Infrared-Spectra of Amorphous Solid Water and Ice Ic between 10 and 140 K. Chem. Phys. 1981, 56, 367−379. (20) Smith, R. S.; Matthiesen, J.; Knox, J.; Kay, B. D. Crystallization Kinetics and Excess Free Energy of H2O and D2O Nanoscale Films of Amorphous Solid Water. J. Phys. Chem. A 2011, 115, 5908−5917. (21) Smith, R. S.; Petrik, N. G.; Kimmel, G. A.; Kay, B. D. Thermal and Nonthermal Physiochemical Processes in Nanoscale Films of Amorphous Solid Water. Acc. Chem. Res. 2012, 45, 33−42. (22) The measured desorption rate for a water film heated to 280 K is ∼0.024 ML per heat pulse. (23) Johari, G. P.; Hallbrucker, A.; Mayer, E. The Glass-Liquid transition of Hyperquenched Water. Nature 1987, 330, 552. (24) Laksmono, H.; et al. Anomalous Behavior of the Homogeneous Ice Nucleation Rate in ″No-Man’s Land″. J. Phys. Chem. Lett. 2015, 6, 2826−2832. (25) Transiently heating a 1 ML water film to T > 273 K does not result in any appreciable changes to the Kr TPD compared to the Kr TPD from an as-grown water monolayer. (26) The total IRAS spectra also have contributions from those portions of the surface covered by a single layer of water. However, the amount of water in the monolayer is typically small compared to the total amount of water (e.g., 4% for the results in Figures 1 and 2a). Also, the IRAS spectrum of a single layer is, on a per molecule basis, less intense than the signal for multilayer ASW or CI. Thus, the contributions to the total spectra from the 1 ML areas are modest. (27) Nie, S.; Feibelman, P. J.; Bartelt, N. C.; Thurmer, K. Pentagons and Heptagons in the First Water Layer on Pt(111). Phys. Rev. Lett. 2010, 105, 026102. (28) Ogasawara, H.; Brena, B.; Nordlund, D.; Nyberg, M.; Pelmenschikov, A.; Pettersson, L. G. M.; Nilsson, A. Structure and Bonding of Water on Pt(111). Phys. Rev. Lett. 2002, 89, 276102. (29) Feibelman, P. J.; Kimmel, G. A.; Smith, R. S.; Petrik, N. G.; Zubkov, T.; Kay, B. D. A Unique Vibrational Signature of Rotated Water Monolayers on Pt(111): Predicted and Observed. J. Chem. Phys. 2011, 134, 204702. (30) For prism faces of the ice crystallites, the dangling OH should be parallel to the Pt(111) surface and would therefore have a very weak signal due to the surface dipole selection rule for IRAS. (31) Petrenko, V. F.; Whitworth, R. W. Physics of Ice; Oxford University Press: Oxford, 1999. (32) Nie, S.; Feibelman, P. J.; Bartelt, N. C.; Thurmer, K. Pentagons and Heptagons in the First Water Layer on Pt(111). Phys. Rev. Lett. 2010, 105, 026102.

wide range of temperatures (280−311 K), and this range is much broader than the uncertainty in our temperature calibration. As a result, the conclusions we draw are independent of the details of the temperature calibration. (2) The relative temperature versus time, Trel(t), for the Pt(111) surface was obtained from time-resolved measurements of the optical reflectivity43−45 and compared to detailed calculations of the heat transfer. (3) The absolute temperature versus time, T(t), was determined by comparing measured and calculated desorption rates from thin CI and ASW films during pulsed heating. (4) The heating and cooling rates for the surface of the metal and adsorbed films were ∼1010 K/s. (5) For a temperature jump, ΔT = Tmax(t) − Ti, of ∼200 K, the lateral variation in the laser pulse energy across the sample was ± ∼3%, and this led to a lateral variation in the maximum temperature, Tmax(t), of ± ∼6 K.46 (6) For water films heated above the melting point of ice, the subsequent rapid cooling quenched the films in an amorphous state without significant crystallization (or recrystallization).

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Phone: 509-371-6134. *E-mail: [email protected]. Phone: 509-371-6143. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. The work was performed using EMSL, a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated for DOE by Battelle.

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REFERENCES

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