Search for: All records

We report the two-dimensional (2D) bimetallic selenophosphate, LiGaP2Se6, prepared through direct combination reactions and P2Se5 flux methods. The material is a member of the broad class of van der Waals 2D materials of the type M2P2Q6 (M = metals). The structure was determined using single-crystal X-ray diffraction and refined in the chiral space group P3̅1c, with lattice parameters a = b = 6.2993(9) Å, c = 13.308(3) Å, α = β = 90°, γ = 120°. Differential thermal analysis indicated a congruent melting point at ∼458 °C. Optoelectronic properties were assessed using ultraviolet–visible (UV–vis) spectroscopy, showing a band gap of 2.01 eV, and photoemission yield spectroscopy in air (PYSA), which determined a work function of 5.44 eV. Notably, stability studies on LiGaP2Se6 revealed remarkable resilience despite its Li content, showing no structural changes after 2 weeks in ambient air or after soaking in a water/ethanol bath. 

The growth of layered 2D compounds is a key ingredient in finding new phenomena in quantum materials, optoelectronics, and energy conversion. Here, we report SnP₂Se₆, a van der Waals chiral (R3 space group) semiconductor with an indirect bandgap of 1.36 to 1.41 electron volts. Exfoliated SnP₂Se₆flakes are integrated into high-performance field-effect transistors with electron mobilities >100 cm²/Vs and on/off ratios >10⁶at room temperature. Upon excitation at a wavelength of 515.6 nanometer, SnP₂Se₆phototransistors show high gain (>4 × 10⁴) at low intensity (≈10⁻⁶W/cm²) and fast photoresponse (< 5 microsecond) with concurrent gain of ≈52.9 at high intensity (≈56.6 mW/cm²) at a gate voltage of 60 V across 300-nm-thick SiO₂dielectric layer. The combination of high carrier mobility and the non-centrosymmetric crystal structure results in a strong intrinsic bulk photovoltaic effect; under local excitation at normal incidence at 532 nm, short circuit currents exceed 8 mA/cm²at 20.6 W/cm². 

Two recent strands of the structural vector autoregression literature use higher moments for identification, exploiting either non-Gaussianity or heteroskedasticity. These approaches achieve point identification without exclusion or sign restrictions. We review this work critically and contrast its goals with the separate research program that has pushed for macroeconometrics to rely more heavily on credible economic restrictions. Identification from higher moments imposes stronger assumptions on the shock process than second-order methods do. We recommend that these assumptions be tested. Since inference from higher moments places high demands on a finite sample, weak identification issues should be given priority by applied users.