Wafer-Scale Growth of 2D PtTe₂ with Layer Orientation Tunable High Electrical Conductivity and Superior Hydrophobicity

Abstract

Platinum ditelluride (PtTe2) is an emerging semimetallic two-dimensional (2D) transition-metal dichalcogenide (TMDC) crystal with intriguing band structures and unusual topological properties. Despite much devoted efforts, scalable and controllable synthesis of large-area 2D PtTe2 with well-defined layer orientation has not been established, leaving its projected structure–property relationship largely unclarified. Herein, we report a scalable low-temperature growth of 2D PtTe2 layers on an area greater than a few square centimeters by reacting Pt thin films of controlled thickness with vaporized tellurium at 400 °C. We systematically investigated their thickness-dependent 2D layer orientation as well as its correlated electrical conductivity and surface property. We unveil that 2D PtTe2 layers undergo three distinct growth mode transitions, i.e., horizontally aligned holey layers, continuous layer-by-layer lateral growth, and horizontal-to-vertical layer transition. This growth transition is a consequence of competing thermodynamic and kinetic factors dictated by accumulating internal strain, analogous to the transition of Frank–van der Merwe (FM) to Stranski–Krastanov (SK) growth in epitaxial thin-film models. The exclusive role of the strain on dictating 2D layer orientation has been quantitatively verified by the transmission electron microscopy (TEM) strain mapping analysis. These centimeter-scale 2D PtTe2 layers exhibit layer orientation tunable metallic transports yielding the highest value of ∼1.7 × 106 S/m at a certain critical thickness, supported by a combined verification of density functional theory (DFT) and electrical measurements. Moreover, they show intrinsically high hydrophobicity manifested by the water contact angle (WCA) value up to ∼117°, which is the highest among all reported 2D TMDCs of comparable dimensions and geometries. Accordingly, this study confirms the high material quality of these emerging large-area 2D PtTe2 layers, projecting vast opportunities employing their tunable layer morphology and semimetallic properties from investigations of novel quantum phenomena to applications in electrocatalysis.

Wafer‐Scale Van der Waals Assembly of Free‐Standing Near Atom Thickness Hetero‐Membranes for Flexible Photo‐Detectors

“…[30] The surface energy of the PtS film at the moment of its delamination is calculated to be ≈44.37 mN m −1 . [16] The air-exposure driven increase of hydrophobicity has also been observed with other vdW layered 2D TMD materials, [31,32] while its exact origin needs to be clarified with further investigations. The illustrations in Figure 2e compare the efficacy of the water-assisted delamination for the samples of low (left) versus high (right) hydrophobicity.…”

“…Figure 1b-g present the characterization data of these materials which were grown by a chemical vapor deposition (CVD)-based thermal sulfurization or tellurization of Pt thin films, similar to the growth of other 2D TMDs. [13,16,[18][19][20][21][22][23][24][25][26] Specific details regarding the growth conditions are found in the Experimental Section. Figure 1b displays a low-magnification cross-sectional transmission electron microscopy (TEM) image of a non-layered PtS thin film (left) as well as its corresponding high resolution TEM (HR-TEM) image (right).…”

“…We then studied the structural/chemical structures of 2D PtTe 2 layers whose CVD growth method and characterization were previously discussed in our earlier works. [16,19,20,24] Figure 1f shows a cross-sectional HR-TEM image of 2D PtTe 2 layers exhibiting well-resolved horizontally-aligned layers. The identified interlayer spacing of 5.2 Å well matches the dimension of the vdW gap between individual 2D layers along the [001] direction, consistent with the atomic model illustration shown in the inset.…”

“…The EDS spectrum in Figure 1g confirms the stoichiometric composition of Pt:Te ≈ 1:2, consistent with our previous studies. [16,20,24] Figure 2 demonstrates the water-assisted vdW delamination/assembly method and studies the underlying mechanism. Figure 2a illustrates the adopted step-by-step process in the vdW assembly of 2D PtTe 2 layers and 3D PtS films.…”

“…Herein, we report on a wafer-scale vdW integration of layered 2D TMDs and non-layered 3D membranes realizing 2D/3D heterojunctions on flexible substrates. We fabricated waferscale 2D platinum ditelluride (PtTe 2 ) metallic [16] multi-layers and 3D platinum sulfide (PtS) non-layered semiconductors via a modified chemical vapor deposition (CVD) method. We then precisely delaminated both materials in water and sequentially integrated them onto the plastic substrates, creating large-area (>cm 2 ) 2D/3D heterostructures of near atom thickness.…”