Stacking Polymorphism in PtSe₂ Drastically Affects Its Electromechanical Properties

Abstract

PtSe 2 is one of the most promising materials for the next generation of piezoresistive sensors. However, the large‐scale synthesis of homogeneous thin films with reproducible electromechanical properties is challenging due to polycrystallinity. It is shown that stacking phases other than the 1T phase become thermodynamically available at elevated temperatures that are common during synthesis. It is shown that these phases can make up a significant fraction in a polycrystalline thin film and discuss methods to characterize them, including their Seebeck coefficients. Lastly, their gauge factors, which vary strongly and heavily impact the performance of a nanoelectromechanical device are estimated.

Edge Conductivity in PtSe2 Nanostructures

“…We employ a data set that includes PtSe 2 structures in the octahedrally coordinated 1T O , 2H O , and 3R O stacking phases, as discussed in our previous work, [ 30 ] as well as bulk phases, ribbons, and surfaces. [ 44 ] All trajectories have been calculated at the same level of theory (see Experimental Section for details).…”

“…For example, varying the layer thickness from 2–3 layers gives rise to a semiconductor‐to‐semimetal transition, [ 24–26 ] point‐ and edge‐defects cause magnetic behavior, [ 27–29 ] and stacking faults lead to semiconducting instead of semimetallic behavior. [ 30,31 ] All of those factors may contribute to varying observations of PtSe 2 characteristics, such as mobilities below 1 cm 2 V −1 s −1 , [ 32 ] p– or n–type behavior depending on the selenization process, [ 33 ] and a 35% reduction of the crossplane thermal conductivity due to polycrystallinity. [ 34 ]…”

“…For example, varying the layer thickness from 2-3 layers gives rise to a semiconductor-to-semimetal transition, [24][25][26] point-and edge-defects cause magnetic behavior, [27][28][29] and stacking faults lead to semiconducting instead of semimetallic behavior. [30,31] All of those factors may contribute to varying observations of PtSe 2 characteristics, such as mobilities below 1 cm 2 V À1 s À1 , [32] p-or n-type behavior depending on the selenization process, [33] and a 35% reduction of the crossplane thermal conductivity due to polycrystallinity. [34] In this study, we investigate how electrical conductivity depends on the lateral width of PtSe 2 nanostructures, namely, ribbons, surfaces, nanoflakes, and nanoplatelets, with different edge terminations using density functional theory (DFT).…”

“…To this end, we train a deep neural network to obtain an interatomic potential for PtSe 2 nanostructures. The training data includes three different stacking phases in their bulk form and for up to nine layers (from our previous work) [30] and differently terminated ribbon and surface models (see Figure 1a-d). We employ the DeePMD-kit framework [35] which implements the smooth version of the deep potential (DP) model by E et al [36,37] The DP model has been successfully used to represent the potential energy surface (PES) of complex systems in materials science, such as the formation of defects from radiation exposure under fusion reactor conditions [38] or the behavior of water confined between graphene nanocapillaries.…”

Interfacial electronic properties between PtSe2and 2D metal electrodes: a first-principles simulation

“…[26][27][28][29][30][31][32] It has applications in optoelectronics, gas sensors, and catalysis and possesses thermoelectric properties which are at the forefront of research in physics, chemistry, engineering, and materials science. [33][34][35][36][37][38][39][40][41] High-performance PtSe 2 FETs with ON/OFF ratios of up to 10 8 and good gate modulation properties at room temperature and air stability have been fabricated. [27][28][29][30][31] However, owing to the lack of effective doping, Fermi level pinning(FLP) occurs when the metal and the material are in direct contact, resulting in a Schottky barrier at the interface that hinders carrier transport.…”