Light management with quantum nanostructured dots-in-host semiconductors

Insightful knowledge on quantum nanostructured materials is paramount to engineer and exploit their vast gamut of applications. Here, a formalism based on the single-band effective mass equation was developed to determine the light absorption of colloidal quantum dots (CQDs) embedded in a wider bandgap semiconductor host, employing only three parameters (dots/host potential barrier, effective mass, and QD size). It was ascertained how to tune such parameters to design the energy level structure and consequent optical response. Our findings show that the CQD size has the biggest effect on the number and energy of the confined levels, while the potential barrier causes a linear shift of their values. While smaller QDs allow wider energetic separation between levels (as desired for most quantum-based technologies), the larger dots with higher number of levels are those that exhibit the strongest absorption. Nevertheless, it was unprecedently shown that such quantum-enabled absorption coefficients can reach the levels (104–105 cm−1) of bulk semiconductors.

The Effects of Molecular Packing Behavior of Small-Molecule Acceptors in Ternary Organic Solar Cells

Herein, two diketopyrrolopyrrole (DPP)-based, small-molecule isomers, o- and p-DPP-PhCN, were introduced as acceptors in ternary organic solar cells (OSCs). The isomers have the same molecular backbone but differ in the positions of the cyanide (CN) substituents (ortho and para), which greatly affects their packing behavior. Ternary solar cells composed of poly(3-hexylthiophene) (P3HT):DPP-PhCN:phenyl-C61-butyric acid methyl ester (PCBM) were fabricated, and the effects of the different packing behaviors of the third component on the device performance and the working mechanism of the ternary cells were investigated. The addition of o-DPP-PhCN with a relatively high-lying lowest unoccupied molecular orbital energy level resulted in an increase in the open-circuit voltage (VOC) in the ternary devices, demonstrating the alloy-like structure of the two acceptors (o-DPP-PhCN and PCBM) in the ternary system. However, the p-DPP-PhCN-based ternary cells exhibited VOC values similar to that of a P3HT:PCBM binary cell, irrespective of the addition of p-DPP-PhCN, indicating a cascade energy-level structure in the ternary system and an effective charge transfer from the P3HT to the PCBM. Importantly, by increasing the addition of p-DPP-PhCN, the short-circuit current density increased substantially, resulting in pronounced shoulder peaks in the external quantum efficiency responses in the long-wavelength region, corresponding to the contribution of the photocurrent generated by the light absorption of p-DPP-PhCN. Despite sharing the same molecular backbone, the two DPP-PhCNs exhibited substantially different packing behaviors according to the position of their CN substituents, which also greatly affected the working mechanism of the ternary devices fabricated using the DPP-PhCNs as the third component.

Influence of SERS Activity of SnSe2 Nanosheets Doped with Sulfur

The application of 2D semiconductor nanomaterials in the field of SERS is limited due to its weak enhancement effect and the unclear enhancement mechanism. In this study, we changed the surface morphology and energy level structure of 2D SnSe2 nanosheets using different amounts of S dopant. This caused the vibration coupling of the substrate and the adsorbed molecules and affects the SERS activities of the SnSe2 nanosheets. SERS performance of the 2D semiconductor substrate can effectively be improved by suitable doping, which can effectively break the limitation of 2D semiconductor compounds in SERS detection and will have very important significance in the fields of chemical, biological, and materials sciences. In this work, the intensities of SERS signals for R6G molecules on SnSe0.93S0.94 are 1.3 to 1.7 times stronger than those on pure SnSe2 substrate. It not only provides a new way to effectively improve the SERS activity of a semiconductor SERS substrates but also helps to design more efficient and stable semiconductor SERS substrates for practical application.

Identification of molecular quantum states using phase-sensitive forces

Quantum-logic techniques used to manipulate quantum systems are now increasingly being applied to molecules. Previous experiments on single trapped diatomic species have enabled state detection with excellent fidelities and highly precise spectroscopic measurements. However, for complex molecules with a dense energy-level structure improved methods are necessary. Here, we demonstrate an enhanced quantum protocol for molecular state detection using state-dependent forces. Our approach is based on interfering a reference and a signal force applied to a single atomic and molecular ion. By changing the relative phase of the forces, we identify states embedded in a dense molecular energy-level structure and monitor state-to-state inelastic scattering processes. This method can also be used to exclude a large number of states in a single measurement when the initial state preparation is imperfect and information on the molecular properties is incomplete. While the present experiments focus on N$${}_{2}^{+}$$ 2 + , the method is general and is expected to be of particular benefit for polyatomic systems.

Bose–Einstein condensation of dilute alpha clusters above the four-α threshold in 16O in the field theoretical superfluid cluster model

Observed well-developed $\alpha$ cluster states in $^{16}$O located above the four-$\alpha$ threshold are investigated from the viewpoint of Bose–Einstein condensation of $\alpha$ clusters by using a field-theoretical superfluid cluster model in which the order parameter is defined. The experimental energy levels are reproduced well for the first time by calculation. In particular, the observed 16.7 MeV $0_7^+$ and 18.8 MeV $0_8^+$ states with low-excitation energies from the threshold are found to be understood as a manifestation of the states of the Nambu–Goldstone zero-mode operators, associated with the spontaneous symmetry-breaking of the global phase, which is caused by the Bose–Einstein condensation of the vacuum 15.1 MeV $0^+_6$ state with a dilute well-developed $\alpha$ cluster structure just above the threshold. This gives evidence of the existence of the Bose–Einstein condensate of $\alpha$ clusters in $^{16}$O. It is found that the emergence of the energy level structure with a well-developed $\alpha$ cluster structure above the threshold is robust, almost independently of the condensation rate of $\alpha$ clusters under significant condensation rate. The finding of the mechanism that causes the level structure that is similar to $^{12}$C to emerge above the four-$\alpha$ threshold in $^{16}$O reinforces the concept of Bose–Einstein condensation of $\alpha$ clusters in addition to $^{12}$C.