Christopher E. Mead

Ferroelectric semiconducting field-effect transistors (FeS-FETs) based on two-dimensional materials exhibit nonvolatile resistive switching, making them promising candidates for next-generation memory and neuromorphic computing. However, the mechanisms governing resistive switching in α-In₂Se₃ lateral devices remain unresolved, particularly regarding the relative contributions of channel and contact resistance. In this study, Kelvin probe force microscopy (KPFM) was employed to spatially resolve the gate-poling-dependent contact and channel resistances in α-In₂Se₃ FeS-FETs, while scanning photocurrent microscopy (SPCM) was used to quantify changes in effective Schottky barrier height at the metal contacts. Both contact and channel resistances were found to increase (decrease) with positive (negative) poling, with the contact resistance modulation correlating with changes in Schottky barrier height. Control experiments on as-exfoliated multidomain flakes confirmed that spontaneous polarization influences both channel and contact resistances. However, typical clockwise resistive switching characteristics can be observed even in the absence of detectable ferroelectric polarization switching. Furthermore, typical gate-poling conditions lead to the formation of stacking defects observed by ex situ high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The observed defects can impede domain wall motion, providing a rationale for the lack of an abrupt switching threshold and a possible mechanism of coupling in-plane fields to out-of-plane polarization. We conclude that resistive switching in α-In₂Se₃ lateral channel devices is often influenced by both reversible polarization switching and irreversible defect formation, highlighting the need for improved domain wall control and defect mitigation strategies to enhance FeS-FET performance for reliable memory applications.

The growth of layered 2D compounds is a key ingredient in finding new phenomena in quantum materials, optoelectronics, and energy conversion. Here, we report SnP ₂ Se ₆ , a van der Waals chiral ( R 3 space group) semiconductor with an indirect bandgap of 1.36 to 1.41 electron volts. Exfoliated SnP ₂ Se ₆ flakes are integrated into high-performance field-effect transistors with electron mobilities >100 cm ² /Vs and on/off ratios >10 ⁶ at room temperature. Upon excitation at a wavelength of 515.6 nanometer, SnP ₂ Se ₆ phototransistors show high gain (>4 × 10 ⁴ ) at low intensity (≈10 ⁻⁶ W/cm ² ) and fast photoresponse (< 5 microsecond) with concurrent gain of ≈52.9 at high intensity (≈56.6 mW/cm ² ) at a gate voltage of 60 V across 300-nm-thick SiO ₂ dielectric 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/cm ² at 20.6 W/cm ² .

Tin monosulfide (SnS) is a two-dimensional layered semiconductor that exhibits in-plane ferroelectric order at very small thicknesses and is of interest in highly scaled devices. Here we report the epitaxial growth of SnS on hexagonal boron nitride (hBN) using a pulsed metal-organic chemical vapor deposition process. Lattice matching is observed between the SnS(100) and hBN{11̅0} planes, with no evidence of strain. Atomic force microscopy reveals superlubricity along the commensurate direction of the SnS/hBN interface, and first-principles calculations suggest that friction is controlled by the edges of the SnS islands, rather than interface interactions. Differential phase contrast imaging detects remnant polarization in SnS islands with domains that are not dictated by step-edges in the SnS. The growth of ferroelectric SnS on high quality hBN substrates is a promising step toward electrically switchable ferroelectric semiconducting devices.

Control over the distribution of dopants in nanowires is essential for regulating their electronic properties, but perturbations in nanowire microstructure may affect doping. Conversely, dopants may be used to control nanowire microstructure including the generation of twinning superlattices (TSLs)—periodic arrays of twin planes. Here the spatial distribution of Be dopants in a GaAs nanowire with a TSL is investigated using atom probe tomography. Homogeneous dopant distributions in both the radial and axial directions are observed, indicating a decoupling of the dopant distribution from the nanowire microstructure. Although the dopant distribution is microscopically homogenous, radial distribution function analysis discovered that 1% of the Be atoms occur in substitutional-interstitial pairs. The pairing confirms theoretical predictions based on the low defect formation energy. These findings indicate that using dopants to engineer microstructure does not necessarily imply that the dopant distribution is non-uniform.

French architect. He studied with Charles Percier c. 1793, and in 1813 he succeeded Jacques Cellerier as the architect responsible for restoring the royal abbey church of Saint-Denis, near Paris. Debret’s restorations revealed his ignorance of Gothic architecture and included a structurally dangerous trimming of stone from the church’s buttresses, the removal of authentic ornament and such ill-conceived additions as the historically implausible Gallery of Kings on the west façade. Already under attack by medievalists, Debret then rebuilt the spire of the façade’s north tower (which had been struck by lightning in ...