Direct Evaluation of the Quantum Confinement Effect in Single Isolated Ge Nanocrystals

To address the yet open question regarding the nature of quantum confinement in Ge nanocrystals (Ge NCs) we employed scanning tunneling spectroscopy to monitor the electronic structure of individual isolated Ge NCs as a function of their size. The (single-particle) band gaps extracted from the tunneling spectra increase monotonically with decreasing nanocrystal size, irrespective of the capping ligands, manifesting the effect of quantum confinement. Band-gap widening of ∼1 eV with respect to the bulk value was observed for Ge-NCs 3 nm in diameter. The picture emerging from comparison with theoretical calculations and other experimental results is discussed

Fullerene-Like (IF) Nb<i>_x</i>Mo₁_-<i>_x</i>S₂ Nanoparticles

IF-Mo1-xNbxS2 nanoparticles have been synthesized by a vapor-phase reaction involving the respective metal halides with H2S. The IF-Mo1-xNbxS2 nanoparticles, containing up to 25% Nb, were characterized by a variety of experimental techniques. Analysis of the powder X-ray powder diffraction, X-ray photoelectron spectroscopy, and different electron microscopy techniques shows that the majority of the Nb atoms are organized as nanosheets of NbS2 within the MoS2 host lattice. Most of the remaining Nb atoms (3%) are interspersed individually and randomly in the MoS2 host lattice. Very few Nb atoms, if any, are intercalated between the MoS2 layers. A sub-nanometer film of niobium oxide seems to encoat the majority of the nanoparticles. X-ray photoelectron spectroscopy in the chemically resolved electrical measurement mode (CREM) and scanning probe microscopy measurements of individual nanoparticles show that the mixed IF nanoparticles are metallic independent of the substitution pattern of the Nb atoms in the lattice of MoS2 (whereas unsubstituted IF-MoS2 nanoparticles are semiconducting). Furthermore the IF-Mo1-xNbxS2 nanoparticles are found to exhibit interesting single electron tunneling effects at low temperatures

Mobility–Lifetime Products in MAPbI₃ Films

Photovoltaic solar cells operate under steady-state conditions that are established during the charge carrier excitation and recombination. However, to date no model of the steady-state recombination scenario in halide perovskites has been proposed. In this Letter we present such a model that is based on a single type of recombination center, which is deduced from our measurements of the illumination intensity dependence of the photoconductivity and the ambipolar diffusion length in those materials. The relation between the present results and those from time-resolved measurements, such as photoluminescence that are commonly reported in the literature, is discussed

Fullerene-Like (IF) Nb<i>_x</i>Mo₁_-<i>_x</i>S₂ Nanoparticles

IF-Mo1-xNbxS2 nanoparticles have been synthesized by a vapor-phase reaction involving the respective metal halides with H2S. The IF-Mo1-xNbxS2 nanoparticles, containing up to 25% Nb, were characterized by a variety of experimental techniques. Analysis of the powder X-ray powder diffraction, X-ray photoelectron spectroscopy, and different electron microscopy techniques shows that the majority of the Nb atoms are organized as nanosheets of NbS2 within the MoS2 host lattice. Most of the remaining Nb atoms (3%) are interspersed individually and randomly in the MoS2 host lattice. Very few Nb atoms, if any, are intercalated between the MoS2 layers. A sub-nanometer film of niobium oxide seems to encoat the majority of the nanoparticles. X-ray photoelectron spectroscopy in the chemically resolved electrical measurement mode (CREM) and scanning probe microscopy measurements of individual nanoparticles show that the mixed IF nanoparticles are metallic independent of the substitution pattern of the Nb atoms in the lattice of MoS2 (whereas unsubstituted IF-MoS2 nanoparticles are semiconducting). Furthermore the IF-Mo1-xNbxS2 nanoparticles are found to exhibit interesting single electron tunneling effects at low temperatures

Electrical and Optical Properties of γ‑SnSe: A New Ultra-narrow Band Gap Material

We describe the unusual properties of γ-SnSe, a new orthorhombic binary phase in the tin monoselenide system. This phase exhibits an ultranarrow band gap under standard pressure and temperature conditions, leading to high conductivity under ambient conditions. Density functional calculations identified the similarity and difference between the new γ-SnSe phase and the conventional α-SnSe based on the electron localization function. Very good agreement was obtained for the band gap width between the band structure calculations and the experiment, and insight provided for the mechanism of reduction in the band gap. The unique properties of this material may render it useful for applications such as thermal imaging devices and solar cells

Hydroxyl Functional Groups in Two-Dimensional Dion–Jacobson Perovskite Solar Cells

In this work we demonstrate a new diammonium spacer molecule with hydroxyl functional groups forming a Dion–Jacobson perovskite. Polarization modulation infrared reflection absorption spectroscopy reveal hydrogen bonding between the iodide to the spacer molecule and in between the OH groups. As a result, we were able to demonstrate n = 5 low dimensional perovskite solar cell (LDPSC) with an efficiency of 10%. Photoconductivity measurements and scanning tunneling spectroscopy draw the band structure of this low dimensional perovskite (LDP) revealing in-gap states adjacent to the conduction band edge, consistent with Shockley–Reed–Hall modeling of the temperature-dependent photoconductivity. The LDPSC based on the diammonium spacer H3N–C4H6(OH)2–NH3 shows enhanced stability under a relative humidity of more than 50% over 1030 h. Evaluating the mechanism of the cell shows a misalignment of the hole selective contact with the LDP. Improving this interface can increase further the photovoltaic performance, demonstrating the potential of this new type of diammonium spacer in LDP