Effects of oxygen atoms and oxygen molecules on the electronic properties of modified black phosphorus

The effect of the oxygen dangling on the thermoelectric properties of organic Thienoisoindigo single-molecule junction

CONTEXT

Theoretical investigation for thermoelectric characteristics of organic Thienoisoindigo single-molecule is carried out using the first-principles calculations based on the density functional theory. It reveals that modifying the position or removing oxygen atoms significantly alters the thermoelectric properties. Transmission coefficient calculations show that the lowest unoccupied molecular orbital (LUMO) dominates across all molecular configurations. Repositioning oxygen atoms increases the bandgap from 1.14 to 1.53 eV, while the complete removal of oxygen further increases to 1.8 eV. This change leads to the disruption of constructive quantum interference, which is replaced by destructive one. The electrical conductance is similarly affected by changes in oxygen atom positioning, with values shifting from - 1.06 to - 1.63. Molecules without oxygen atoms exhibit lower conductance compared to those with dangling oxygen, resulting in reduced semiconductor-like behavior and enhanced insulating properties. The Seebeck coefficient remains stable at - 2.99 μ V/K when oxygen atoms are repositioned. However, the removal of one oxygen atom changes the coefficient to a positive value (290.14 μ V/K), causing the molecule to transition from n-type to p-type behavior. The complete absence of oxygen atoms returns the Seebeck coefficient to a negative value ( - 256.08 μ V/K), switching the molecule back to n-type conduction.

METHODS

This investigation was achieved by applying the SIESTA software through density functional theory (DFT) computations. To account for exchange and correlation effects, we use a double-zeta polarized (DZP) basis set in conjunction with the generalized gradient approximation (GGA-PBE) to determine the ideal ground-state atomic locations. By combining the Hamiltonian of each system with the quantum transport code GOLLUM, we can calculate the transmission coefficient, projected density of states, electrical conductance, and Seebeck coefficient to examine the thermoelectric characteristics of the molecular junction.

Graphdiyne-Based All-Solid-State Passively Q-Switched Tm:YAP Laser at 2 μm

All-solid-state Tm lasers have a wider wavelength range and higher output power compared to other types of lasers. In this work, we demonstrate an all-solid-state, high repetition, Tm:YAP laser Q-switched by a graphdiyne (GDY) saturable absorber. The high-quality optical nonlinear material GDY, synthesized by a cross-coupling method, exhibits a strong nonlinear optical response. The application of GDY as a saturable absorber in the passively Q-switched (PQS) Tm:YAP of an all-solid-state laser has been realized with the shortest pulse duration of ~785 ns and repetition frequency of ~199.6 kHz at a central wavelength of 1985.8 nm. This represents the shortest pulse duration and the highest repetition frequency achieved from GDY in a solid-state Tm laser to date. Our work demonstrates the remarkable nonlinear optical properties of GDY, which holds promising potential in the field of optoelectronics.

Molecular-level degradation pathways of black phosphorus revealed by mass spectrometry fingerprinting

Understanding the molecular mechanism of material transformation raises a great challenge for material characterization techniques. As a promising 2D material, the application potential of black phosphorus (BP) is seriously compromised by its environmental instability. However, until now, the degradation mechanism of BP remains ambiguous. Here we show that by using laser desorption ionization mass spectrometry (LDI-MS) fingerprinting it is possible to unravel the degradation pathways of BP at the molecular level without any chemical labeling. We found that BP-based materials can generate intrinsic phosphorus cluster (Pn+ or Pn-) fingerprint peaks in LDI-MS in both positive-ion and negative-ion modes, which allows the degradation processes of BP materials to be monitored by providing abundant mass information about intermediates and products with the sample-to-sample RSDs in the range of 1.0-28.4%. The stability of BP or cerium-encapsulated BP was monitored under ambient and increased temperature conditions for up to 20 or 180 days. Notably, by using LDI-MS fingerprinting, we reveal an unreported BP degradation pathway, i.e., nitrogen (N2)-addition oxidation, in addition to the direct oxidation pathway. Our results not only enable an in-depth understanding of the chemical instability of BP, but also, importantly, demonstrate a new powerful platform for monitoring and characterization of material transformation.