Exploring the air stability of PdSe2 via electrical transport measurements and defect calculations

Abstract

In this work we investigate the effects of ambient exposure on CVD grown PdSe 2 and correlate density functional theory calculations of various physisorption and chemisorption binding energies and band structures to the observed changes in the electrical transport. Pristine PdSe 2 is n-type due to intrinsic selenium vacancies, but shows increased p-type conduction and decreased n-type conduction as a function of ambient aging during which various aging mechanisms appear to be operative. Short term aging (<160 h) is ascribed to an activated chemisorption of molecular O 2 at selenium vacancies; first-principles calculations suggest a~0.85 eV activation energy and adsorption geometries with binding energies varying between 1.3-1.6 eV, in agreement with experimental results. Importantly, this chemisorption is reversible with a low temperature anneal. At long term aging (>430 h), there is a total suppression of n-type conduction, which is attributed to a dissociative adsorption/reaction of the O 2 molecules to atomic O and subsequent PdO 2 formation. XPS confirms the presence of PdO 2 in long term aged flakes. At these extended aging times, the low temperature anneal restores low n-type conduction and suppresses p-type conduction due to the low thermal stability of PdO 2 which, in agreement with XPS measurements, sublimates during the anneal. Thus PdSe 2 devices can be processed into device architectures in standard laboratory environments if atmospheric exposure times are limited to on the order of 1 week. npj 2D Materials and Applications (2019) 3:50 ; https://doi.

Two‐Dimensional Palladium Diselenide with Strong In‐Plane Optical Anisotropy and High Mobility Grown by Chemical Vapor Deposition

“…[5] PdSe 2 has excellent optical and electrical properties including high carrier mobility with ambipolar behavior and thickness-dependent bandgaps that range from 0 eV (bulk) to 1.3 eV (monolayer). These properties, along with high air stability make PdSe 2 a promising candidate for next generation optoelectronic devices, [5,[20][21][22][23][24] such as highly efficient and sensitive broadband photodetectors with long-wavelength infrared detection. [5,25,26] In addition, the highly anisotropic structure of PdSe 2 , with its unique puckered pentagons and strong interlayer coupling, also allows the formation of many polymorphic phases including the pyrite phase that results in Dirac fermions and superconductivity, [27] as well as the recently observed monoclinic Verbeekite phase [28] and its high-pressure-induced derivatives.…”

“…In addition, the observed changes in transfer curves, threshold voltage, and electron mobility of the devices after annealing were attributed to the desorption of surface adsorbates during the anneal treatment. [20,24] As shown in Figure S14 (Supporting Information), the thickness-dependent electrical properties of 2D PdSe 2 were also measured. As the thickness increases, the gate control becomes negligible, which is consistent with a decrease in bandgap.…”

Molybdenum Disulfide Field Effect Transistors under Electron Beam Irradiation and External Electric Fields

“…We note that the effect of air pressure on the channel conductance, which could result in the dramatic transformation of n-type to p-type conduction when passing from high vacuum to atmospheric pressure, has been reported also for other 2D TMDs materials such as WSe2 or PdSe2 (REF). The effect is usually reversible although it has been found that an aging can occur in specific TMDs, such as PdSe2, after a long (>20 days) air exposure at atmospheric pressure [32].…”

“…It has been reported that the adsorbed gases on the MoS2 channel of FETs result in degradation of device conductance, in enhanced hysteresis and in threshold voltage shifting [10,31,32]. Conversely, vacuum annealing can increase the MoS2 device conductance by desorbing the gas molecules.…”

Defect Engineering in Ambipolar Layered Materials for Mode‐Regulable Nociceptor

“…On the one hand (Figure 3di), the atmospheric oxygen molecules that are initially adsorbed on the PdSe 2 channel surface are regarded as the electron acceptor and are stabilized by the Se vacancies through electron transfer from PdSe 2 host to oxygen. [42][43][44] On the other hand ( Figure 3dii), under laser irradiation, the oxygen-adatom clusters desorption process is boosted greatly, resulting in the reverse charge transfer from the oxygen to the PdSe 2 host and the increase of electron concentration. Besides, according to the recently reported experiments and first-principle calculations, the exposed Se vacancies would introduce localized electronic states near the conduction band of PdSe 2 , thus collaboratively contributing to the n-doping effect and raised Fermi level (E F ) in the PdSe 2 channel of around 0.022 eV.…”