Figure 1

Surface topography of crystalline ice. This $750\times 750{\text{nm}}^2$ STM image shows a continuous 4 nm thick ice film grown onto Pt(111) at 140 K. STM is able to nondestructively investigate ice multilayers and routinely resolve surface steps of bilayer height $\left(3.7\text{Å}\right)$.Reuse & Permissions

Figure 2

Surface topography of amorphous ice grown at $T=100\text{K}$. $200\times 200{\text{nm}}^2$ STM images showing amorphous ice films for mean film thicknesses of (a) $d=1.7$, (b) 2, and (c) 20 bilayers (6 nm).Reuse & Permissions

Figure 3

(Color) Surface topography of crystalline ice grown at 140 K. This image sequence shows the evolution of a crystalline ice film, which was deposited at $T=140\text{K}$, with increasing mean film thickness (indicated above the individual images). [(a) and (b)] $150\times 150{\text{nm}}^2$ STM images of the wetting layer. (c)–(f) $1\times 1\mu {\text{m}}^2$ images of multilayer films. In (e), the letter “S” marks a growth spiral, which has formed above a buried substrate step. In (f), the buried substrate steps are marked with yellow-red ellipses. The yellow rectangle marks the area that corresponds to Fig. 5a.Reuse & Permissions

Figure 4

(Color) Influence of substrate steps on the morphology of crystalline ice films. (a) $13\times 13{\text{nm}}^2$ STM image of the Pt substrate. The atom positions on both sides of the atomic step are used to obtain the crystallographic orientations of the sample. The crystallographic orientations indicated in the lower left corner are valid for all STM images herein. (b) $1\times 1\mu {\text{m}}^2$ STM image of an ice film with a mean thickness of 0.8 nm grown at 140 K. In this image, the individual substrate terraces are colored differently. The ice crystallites avoid crossing a substrate step. (c) Image size: $3.5\mu \text{m}\times 3.5\mu \text{m}$; mean thickness: 3 nm; deposition temperature: 150 K. The large elongated crystallites follow the substrate steps, which circle around a shallow surface protrusion. [(d)–(f)] Triangular growth spirals produced by screw dislocations. Most spirals develop above substrate steps (some are marked by yellow ellipses). [(d) and (e)] 4 nm thick film grown at 140 K. (e) Example of a spiral that is not obviously related to a substrate step. (f) 6 nm thick film grown at 145 K. The fastest film growth in this $800\times 800{\text{nm}}^2$ area had occurred at a growth spiral labeled S.Reuse & Permissions

Figure 5

(Color) Ice layers connecting across a buried substrate step. (a) Enlarged $440\times 340{\text{nm}}^2$ detail of the 9 nm thick film shown in Fig. 3f. Crossing the buried Pt step marked by red-yellow ellipses from left to right, the surface either drops (profile 1) or rises (profile 2) by roughly half the ice-bilayer spacing of $3.7\text{Å}$. The yellow rectangle marks the area that corresponds to the schematic in (c). [(b) and (c)] Schematics of how ice layers connect across a Pt step. (c) Connecting two domains, separated by the boundary labeled db, to one domain on the other side of a Pt step creates a screw dislocation.Reuse & Permissions

Figure 6

(Color) Mechanism for cubic ice formation. (a) Schematic top view of an ice bilayer (blue) partially covered by a bilayer (green) bounded by a surface step with A-step and B-step sections. The oxygen atoms (circles) are connected via H bonds (lines). Within each bilayer the higher oxygen atoms are surrounded by three lower-lying oxygen atoms forming triangles (green or blue) whose upward or downward orientation reflects the two possibilities for intrabilayer stacking. [(b) and (c)] Schematic side views of four ice bilayers in the equilibrium hexagonal ice 1h configuration and in the metastable cubic ice 1c configuration. The triangles at the right indicate the intrabilayer stacking. (d) Same configuration as in Fig. 5c viewed along the domain boundary db toward the Pt step. Overgrowing the boundary db between two ice 1h domains (black) by new material (red) creates a growth spiral surrounding the screw dislocation with a Burgers vector $b$.Reuse & Permissions

Figure 7

(Color) STM image of a 4 nm thick ice film. The surface regions are labeled with triangles according to their intrabilayer stacking. Some stacking-domain boundaries appear as small crevices. Two buried substrate steps are marked yellow-red. Nucleating the triangular 2D islands labeled 1 and 2 produced the stacking sequence of hexagonal ice 1h. Ice attaching to a screw dislocation as occurring in the feature labeled 3 leads to the stacking sequence of cubic ice 1c.Reuse & Permissions

Figure 8

(Color) Scenario summarizing key processes leading to growth of cubic ice. Individual ice crystals grow (a) and expand laterally until (b) they coalesce or encounter a substrate step (crystal 4). (c) Crystals merge if their bilayer stacking matches or, else, form a domain boundary labeled db. (d) Layers bend upward or downward to join layers of equal intralayer stacking across a substrate step, producing a screw dislocation. After overgrowing the domain boundary, (e) the top layer can easily expand and form a growth spiral (f). Here, ice of uniform intralayer stacking (blue in this case), i.e., cubic ice 1c is being generated.Reuse & Permissions

Figure 9

(Color) Modified scenario with the configuration in (a) being equivalent to that of Fig. 8c but with the stackings of crystals 1 and 2 reversed. Now, (b) connecting matching layer across the Pt step creates two surface ice steps in addition to a screw dislocation. [(c) and (d)] The ice layers bounded by these two steps expand. After overgrowing the domain boundary, (e) the top layer starts a growth spiral of opposite chirality and different intralayer stackings (green) than in the scenario of Fig. 8.Reuse & Permissions

Figure 10

(Color) Imaging ice-multilayer films on Pt(111). (a) First, the dark $1\times 1\mu {\text{m}}^2$ square in the center was carved out by scanning this area with a positively biased sample $V_{\text{sample}}=7\text{V}$ injecting electrons into the ice. Then, the STM imaged a larger $2\times 2\mu {\text{m}}^2$ area with $V_{\text{sample}}=-7\text{V}$, extracting electrons from the ice. (b) shows the same method used on a 6 nm thick amorphous film. Image area: $1\times 1\mu {\text{m}}^2$. (c) Schematic of the energy levels for the imaging mode. Due to a strong polarization of the ice, most of the applied voltage drops in the vacuum gap. As a consequence, the highest occupied ice states line up with the lowest empty states of the W tip—a precondition for electrons to tunnel from the sample into the tip. (d) Energy diagram for the case of weak polarization. A significant portion of the voltage drop occurs within the ice film. The shortest distance $l$ for which filled states in the ice line up with empty states in the W tip is too large $\left(>3\text{nm}\right)$ for electrons to tunnel through the gap of width $l$ from the ice into the tip.Reuse & Permissions

Figure 11

Tip-induced removal and spontaneous regrowth of a molecular ice layer. At a sample bias of $V_{\text{sample}}=-0.9\text{V}$ and a tunnel current $I_{\text{tunnel}}$ ramped from 0.7–1.2 pA, the STM tip scrapes away the uppermost bilayer of a three bilayer high ice crystal. The time sequence [(a)–(c)] shows the cumulative result of continuous scanning across the imaged crystal. The images were acquired (a) after 30 min scanning at $I_{\text{tunnel}}=0.7\text{pA}$. (b) After additional 20 min scanning at $I_{\text{tunnel}}=0.8\text{pA}$ and (c) after one more hour at $I_{\text{tunnel}}=1.2\text{pA}$. (d) Upon reducing $I_{\text{tunnel}}$ to 0.5 pA, the top layer spontaneously started to regrow.Reuse & Permissions