Trapping a Photoelectron behind a Repulsive Coulomb Barrier in Solution

Multiply charged anions (MCAs) display unique photophysics and solvent-stabilizing effects. Well-known aqueous species such as SO42– and PO43– experience spontaneous electron detachment or charge-separation fragmentation in the gas phase owing to the strong Coulomb repulsion arising from the excess of negative charge. Thus, anions often present low photodetachment thresholds and the ability to quickly eject electrons into the solvent via charge-transfer-to-solvent (CTTS) states. Here, we report spectroscopic evidence for the existence of a repulsive Coulomb barrier (RCB) that blocks the ejection of “CTTS-like” electrons of the aqueous B12F122– dianion. Our spectroscopic experimental and theoretical studies indicate that despite the exerted Coulomb repulsion by the nascent radical monoanion B12F12–•aq, the photoexcited electron remains about the B12F12–• core. The RCB is an established feature of the potential energy landscape of MCAs in vacuo, which seems to extend to the liquid phase highlighting recent observations about the dielectric behavior of confined water

High-Performance Mid-IR to Deep-UV van der Waals Photodetectors Capable of Local Spectroscopy at Room Temperature

The ability to perform broadband optical spectroscopy with sub-diffraction-limit resolution is highly sought-after for a wide range of critical applications. However, sophisticated tip-enhanced techniques are currently required to achieve this goal. We bypass this challenge by demonstrating an extremely broadband photodetector based on a two-dimensional (2D) van der Waals heterostructure that is sensitive to light across over a decade in energy from the mid-infrared (MIR) to deep-ultraviolet (DUV) at room temperature. The devices feature high detectivity (> 10^9 cm Hz^1/2 W^-1) together with high bandwidth (2.1 MHz). The active area can be further miniaturized to submicron dimensions, far below the diffraction limit for the longest detectable wavelength of 4.1 um, enabling such devices for facile measurements of local optical properties on atomic-layer-thickness samples placed in close proximity. This work can lead to the development of low-cost and high-throughput photosensors for hyperspectral imaging at the nanoscale

Persistent Photogenerated State Attained by Femtosecond Laser Irradiation of Thin <i>T</i>_d‑MoTe₂

Laser excitation has emerged as a means to expose hidden states of matter and promote phase transitions on demand. Such laser-induced transformations are often rendered possible owing to the delivery of spatially and/or temporally manipulated light, carrying energy quanta well above the thermal background. Here, we report time-resolved broadband femtosecond (fs) transient absorption measurements on thin flakes of the Weyl semimetal candidate Td-MoTe2 subjected to various levels and schemes of fs-photoexcitation. Our results reveal that impulsive fs-laser irradiation alters the interlayer behavior of the low temperature Td phase as evidenced by the persistent disappearance of its characteristic coherent 1A1 ≈ 13 cm–1 shear phonon mode. We found that this structural transformation is likely related to lattice strain formation, withstands thermal cycling, and can be reverted to the 1T′ phase by fs-laser treatment at room temperature. Since interlayer shear strain was encountered to lead to a topologically distinct phase in an analogous compound, our work opens the door to the reversible optical control of electronic properties in this class of materials

High-Performance Mid-IR to Deep-UV van der Waals Photodetectors Capable of Local Spectroscopy at Room Temperature

The ability to perform broadband optical spectroscopy with subdiffraction-limit resolution is highly sought-after for a wide range of critical applications. However, sophisticated near-field techniques are currently required to achieve this goal. We bypass this challenge by demonstrating an extremely broadband photodetector based on a two-dimensional (2D) van der Waals heterostructure that is sensitive to light across over a decade in energy from the mid-infrared (MIR) to deep-ultraviolet (DUV) at room temperature. The devices feature high detectivity (>109 cm Hz1/2 W–1) together with high bandwidth (2.1 MHz). The active area can be further miniaturized to submicron dimensions, far below the diffraction limit for the longest detectable wavelength of 4.1 μm, enabling such devices for facile measurements of local optical properties on atomic-layer-thickness samples placed in close proximity. This work can lead to the development of low-cost and high-throughput photosensors for hyperspectral imaging at the nanoscale