Quasi-liquid layers on ice crystal surfaces Sazaki, et al., 2012: Quasi-liquid layers on ice crystal surfaces are made up of two different phases, PNAS, 109, Asakawa, et al., 2015: Prism and Other High-Index Faces of Ice Crystals Exhibit Two Types of Quasi-Liquid Layers, CGD, 15,

Quasi-liquid layers: why do we care? Because they’re really cool.

Introduction: measurements of surface properties Different ways to measure surface properties – X-ray diffraction – Neutron backscattering – Electron scattering – Low-energy electron scattering – Infrared spectroscopy – Voltammetry – Tunneling electron microscopy – Atomic force microscopy

Introduction: measurements of surface properties Different ways to measure surface properties – X-ray diffraction – Neutron backscattering – Electron scattering – Low-energy electron scattering – Infrared spectroscopy – Voltammetry – Tunneling electron microscopy – Atomic force microscopy Penetrates surface

Introduction: measurements of surface properties Different ways to measure surface properties – X-ray diffraction – Neutron backscattering – Electron scattering – Low-energy electron scattering – Infrared spectroscopy – Voltammetry – Tunneling electron microscopy – Atomic force microscopy Penetrates surface

Introduction: measurements of surface properties Different ways to measure surface properties – X-ray diffraction – Neutron backscattering – Electron scattering – Low-energy electron scattering – Infrared spectroscopy – Voltammetry – Tunneling electron microscopy – Atomic force microscopy High vacuum

Introduction: measurements of surface properties Different ways to measure surface properties – X-ray diffraction – Neutron backscattering – Electron scattering – Low-energy electron scattering – Infrared spectroscopy – Voltammetry – Tunneling electron microscopy – Atomic force microscopy High vacuum

Introduction: measurements of surface properties Different ways to measure surface properties – X-ray diffraction – Neutron backscattering – Electron scattering – Low-energy electron scattering – Infrared spectroscopy – Voltammetry – Tunneling electron microscopy – Atomic force microscopy – Ellipsometry – Grazing-incidence x-ray diffraction – Confocal laser scanning microscopy – Nuclear magnetic resonance – Interference microscopy – Interferometry

Introduction: measurements of surface properties Different ways to measure surface properties – X-ray diffraction – Neutron backscattering – Electron scattering – Low-energy electron scattering – Infrared spectroscopy – Voltammetry – Tunneling electron microscopy – Atomic force microscopy – Ellipsometry – Grazing-incidence x-ray diffraction – Confocal laser scanning microscopy – Nuclear magnetic resonance – Interference microscopy – Interferometry Ice destroys AFM tips Difficult and questionable precision Poor resolution Ice is mostly transparent

Introduction: measurements of surface properties Different ways to measure surface properties – X-ray diffraction – Neutron backscattering – Electron scattering – Low-energy electron scattering – Infrared spectroscopy – Voltammetry – Tunneling electron microscopy – Atomic force microscopy – Ellipsometry – Grazing-incidence x-ray diffraction – Confocal laser scanning microscopy – Nuclear magnetic resonance – Interference microscopy – Interferometry Ambiguous results n ice ≈ n water Very difficult interpretation

Introduction: so who’s tried this? Faraday (1840’s) (1860, PRSL) Several clever experiments showing that “water particles” on ice can briefly turn to liquid before freezing again (experimental) Thomson and Lord Kelvin ( ’s) “Faraday must be daft.” The surface of ice is just melting because the extra pressure lowers the melting point Fletcher (1962, Phil. Mag.) First theoretical treatment of QLL, used thermodynamics and kinetics to show QLL’s are possible and probable (theoretical) Jellinek (1967, JCIS)First literature review in the field of water ice QLL Kuroda and Lacmann (1982, JCG) QLL’s modulate vapor depositional growth at high temperatures with different temperature dependence for the two different facets (theoretical) Elbaum, et al. (1993, JCG)Optical measurements (ellipsometry and interference microscopy) detected possible QLL

Introduction: so who’s tried this? Knight (1996, JGR) QLL’s don’t make physical sense, they’re not thermodynamically possible, and even as a conceptual model they’re useless (comment) Baker and Dash (1996, JGR) Charlie Knight is applying macroscopic thermodynamics to a nanoscale system (reply) Nelson and Knight (1998, JAS) “There is little doubt that the ice surface is rather badly disturbed at temperatures not far below zero…” but Kuroda and Lacmann are wrong about QLL. (theoretical) Ewing (2004, JPCB) QLL is difficult to measure, but IR can tell us some things. QLL kind of appears to be a different phase (experimental review) Nunes, et al. (2007, Solid State NMR) No evidence of QLL, but proving NMR as a possible technique (theoretical) Sazaki, et al. (2012, PNAS) First unambiguous observation of two types of QLL on basal facets Asakawa, et al. (2015, CGD)First unambiguous observation of two types of QLL on prism facets

0.37-nm vertical resolution Creates images by scanning the laser across the crystal Allows video imaging of individual step growth (Sazaki, et al., 2012: Quasi-liquid layers on ice crystal surfaces are made up of two different phases, PNAS.) Fig S2 (Asakawa, 2015) Fig S2 (Sazaki, 2012) Laser confocal microscopy-differential interference microscopy (LCM-DIM)

Round droplet-like features formed at -1.5 to -0.4°C: α-QLLs Interference measurements give heights of approximately 0.5 μm for a width of 50 μm Indicates high wettability of ice surface by QLL (Sazaki, et al., 2012: Quasi-liquid layers on ice crystal surfaces are made up of two different phases, PNAS.) Round liquid-like droplets -0.4°C -0.3°C -0.6°C -0.3°C Figure 1. each band is 317 nm

Coalescence of α-QLLs shows they cannot be solid They appear to serve as step sources (Sazaki, et al. say they nucleate steps) (Sazaki, et al., 2012: Quasi-liquid layers on ice crystal surfaces are made up of two different phases, PNAS.) Coalescence of α-QLLs temperature: -0.3°C duration: 38 seconds Movie S1

Thin layers form at -1.0 to -0.2°C: β-QLLs Clearly thicker than steps, but too thin for interferometry: thickness < 100 nm Droplets and thin layers (not shown here) eventually coalesce (Sazaki, et al., 2012: Quasi-liquid layers on ice crystal surfaces are made up of two different phases, PNAS.) Formation of thin layers temperature: -0.1°C duration: 88 seconds Movie S2

Adjusting image settings shows steps underneath the β-QLL Either β-QLL deforms over steps, or QLL refractive index is different than ice Thin layers cannot be solid ice (Sazaki, et al., 2012: Quasi-liquid layers on ice crystal surfaces are made up of two different phases, PNAS.) Seeing “through” β-QLLs temperature: -0.1°C duration: seconds Movie S3

Temperature decreased -0.5 to -1.0°C β-QLL “decomposed and changed into α-QLLs” and many bunched steps Shows reversibility and phase stability of the transitions between α- and β-QLLs α-QLLs are more stable than β-QLLs in the measured case (Sazaki, et al., 2012: Quasi-liquid layers on ice crystal surfaces are made up of two different phases, PNAS.) Refreezing of QLLs temperature: -0.5 to -1.0°C duration: seconds Movie S4

According to classical thermodynamics: β-QLLs are more thermodynamically favorable: high wettability means low interaction energy with ice α-QLLs are more stable: lower appearance temperature β-QLLs always appear after α-QLLs (Sazaki, et al., 2012: Quasi-liquid layers on ice crystal surfaces are made up of two different phases, PNAS.) Other notes from Sazaki, et al. Figure S1.

Roughening transition on prism/high-index facets Screw dislocation growth at -4.4°C (A) Distances between steps decrease at ≈-3.0°C (B; 42.1 seconds later) Surface becoming rounded (C; seconds later) Almost no reflection off surface (D; seconds later) (Asakawa, et al., 2015: Prism and Other High-Index Faces of Ice Crystals Exhibit Two Types of Quasi-Liquid Layers. CGD.) Figure 1.

QLL’s on prism/high-index facets Prism facet experiencing a roughening transition/becoming rounded Liquid-like droplets appear (little lumps on face) (Asakawa, et al., 2015: Prism and Other High-Index Faces of Ice Crystals Exhibit Two Types of Quasi-Liquid Layers. CGD.) Figure 2.

Liquid-like coalescing on a a prism/high-index facet Two liquid-like droplets coalescing to form one droplet (Asakawa, et al., 2015: Prism and Other High-Index Faces of Ice Crystals Exhibit Two Types of Quasi-Liquid Layers. CGD.) Figure 3. Movie S °C

(Asakawa, et al., 2015: Prism and Other High-Index Faces of Ice Crystals Exhibit Two Types of Quasi-Liquid Layers. CGD.) Figure 4. Thin liquid-like layers on a prism/high-index facet Thin layers coalescing to cover the surface Liquid-like layer appearing underneath liquid-like drop Liquid-like drops apparently “condensing” in to a growing liquid-like layer

(Asakawa, et al., 2015: Prism and Other High-Index Faces of Ice Crystals Exhibit Two Types of Quasi-Liquid Layers. CGD.) Figure 5. Thin liquid-like layers coalescing again

(Asakawa, et al., 2015: Prism and Other High-Index Faces of Ice Crystals Exhibit Two Types of Quasi-Liquid Layers. CGD.) Figure 6. Summary of overall findings β-QLLs are less stable (probably) α-QLLs always form first Both are difficult to observe on prism/high-index faces