English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Recently, atomically thin PdSe$_2$ semiconductors with rare pentagonalSe-Pd-Se monolayers were synthesized and were also found to possess superiorproperties such as ultrahigh air stability, and high carrier mobility, thusoffering a new family of two-dimensional (2D) materials for exploration of 2Dsemiconductor physics and for applications in advanced opto-electronic andnonlinear photonic devices. In this work, we systematically study the nonlinearoptical (NLO) responses [namely, bulk photovoltaic effect (BPVE),second-harmonic generation (SHG) and linear electric-optic (LEO) effect] ofnoncentrosymmetric bilayer (BL) and four-layer (FL) PdS$_2$ and PdSe$_2$ byapplying the first-principles density functional theory with the generalizedgradient approximation plus scissors-correction. First of all, the shiftcurrent conductivity is in the order of 130 $\mu$A/V$^2$, being very highcompared to known BPVE materials. Similarly, their injection currentsusceptibilities are in the order of 100$\times$10$^8$A/V$^2$s, again beinglarge. Secondly, the SHG coefficients ($\chi^{(2)}$) of these materials arealso large, being one order higher than that of the best-known few-layer group6B transition metal dichalcogenides. For example, the maximum magnitude of$\chi^{(2)}$ can reach 1.4$\times$10$^3$ pm/V for BL PdSe$_2$ at 1.9 eV and1.2$\times$10$^3$ pm/V at 3.1 eV for BL PdS$_2$. Thirdly we find significantLEO coefficients for these structures in the low photon energy. All theseindicate that 2D PdX$_2$ semiconductors will find promising NLO applications.Fourthly, we find that the large BPVE and SHG of the few-layer PdX$_2$structures are due to strong intralayer directional covalent bonding and also2D quantum confinement.

Large bulk photovoltaic effect and second-harmonic generation in few-layer pentagonal semiconductors PdS$_2$ and PdSe$_2$