Electric-field control of single-molecule tautomerization.

The electric field is an important parameter to vary in a single-molecule experiment, because it can directly affect the charge distribution around the molecule. Yet, performing such an experiment with a well-defined electric field for a model chemical reaction at an interface has proven to be extremely difficult. Here, by combining a graphene field-effect transistor and a gate-tunable scanning tunneling microscope (STM), we reveal how this strategy enables the intramolecular H atom transfer of a metal-free macrocycle to be controlled with an external field. Experiments and theory both elucidate how the energetic barrier to tautomerization decreases with increasing electric field. The consistency between the two results demonstrates the potential in using electric fields to engineer molecular switching mechanisms that are ubiquitous in nanoscale electronic devices.

Structural Evolution of Metal (Oxy)hydroxide Nanosheets during the Oxygen Evolution Reaction.

Metal (oxy)hydroxides (MO xH y, M = Fe, Co, Ni, and mixtures thereof) are important materials in electrochemistry. In particular, MO xH y are the fastest known catalysts for the oxygen evolution reaction (OER) in alkaline media. While key descriptors such as overpotentials and activity have been thoroughly characterized, the nanostructure and its dynamics under electrochemical conditions are not yet fully understood. Here, we report on the structural evolution of Ni1-δCoδO xH y nanosheets with varying ratios of Ni to Co, in operando using atomic force microscopy during electrochemical cycling. We found that the addition of Co to NiO xH y nanosheets results in a higher porosity of the as-synthesized nanosheets, apparently reducing mechanical stress associated with redox cycling and hence enhancing stability under electrochemical conditions. As opposed to nanosheets composed of pure NiO xH y, which dramatically reorganize under electrochemical conditions to form nanoparticle assemblies, restructuring is not found for Ni1-δCoδO xH y with a high Co content. Ni0.8Fe0.2O xH y nanosheets show high roughness as-synthesized which increases during electrochemical cycling while the integrity of the nanosheet shape is maintained. These findings enhance the fundamental understanding of MO xH y materials and provide insight into how nanostructure and composition affect structural dynamics at the nanoscale.

Morphology Dynamics of Single-Layered Ni(OH)2/NiOOH Nanosheets and Subsequent Fe Incorporation Studied by in Situ Electrochemical Atomic Force Microscopy.

Nickel (oxy)hydroxide-based (NiOxHy) materials are widely used for energy storage and conversion devices. Understanding dynamic processes at the solid-liquid interface of nickel (oxy)hydroxide is important to improve reaction kinetics and efficiencies. In this study, in situ electrochemical atomic force microscopy (EC-AFM) was used to directly investigate dynamic changes of single-layered Ni(OH)2 nanosheets during electrochemistry measurements. Reconstruction of Ni(OH)2 nanosheets, along with insertion of ions from the electrolyte, results in an increase of the volume by 56% and redox capacity by 300%. We also directly observe Fe cations adsorb and integrate heterogeneously into or onto the nanosheets as a function of applied potential, further increasing apparent volume. Our findings are important for the fundamental understanding of NiOxHy-based supercapacitors and oxygen-evolution catalysts, illustrating the dynamic nature of Ni-based nanostructures under electrochemical conditions.

TiO2 anatase with a bandgap in the visible region.

TiO2 anatase plays a central role in energy and environmental research. A major bottleneck toward developing artificial photosynthesis with TiO2 is that it only absorbs ultraviolet light, owing to its large bandgap of 3.2 eV. If one could reduce the bandgap of anatase to the visible region, TiO2-based photocatalysis could become a competitive clean energy source. Here, using scanning tunneling microscopy and spectroscopy in conjunction with density functional theory calculations, we report the discovery of a highly reactive titanium-terminated anatase surface with a reduced bandgap of less than 2 eV, stretching into the red portion of the solar spectrum. By tuning the surface preparation conditions, we can reversibly switch between the standard anatase surface and the newly discovered low bandgap surface phase. The identification of a TiO2 anatase surface phase with a bandgap in the visible and high chemical reactivity has important implications for solar energy conversion, photocatalysis, and artificial photosynthesis.

Atomic-scale observation of multiconformational binding and energy level alignment of ruthenium-based photosensitizers on TiO2 anatase.

Dye-sensitized solar cells constitute a promising approach to sustainable and low-cost solar energy conversion. Their overall efficiency crucially depends on the effective coupling of the photosensitizers to the photoelectrode and the details of the dye's energy levels at the interface. Despite great efforts, the specific binding of prototypical ruthenium-based dyes to TiO2, their potential supramolecular interaction, and the interrelation between adsorption geometry and electron injection efficiency lack experimental evidence. Here we demonstrate multiconformational adsorption and energy level alignment of single N3 dyes on TiO2 anatase (101) revealed by scanning tunnelling microscopy and spectroscopy. The distinctly bound molecules show significant variations of their excited state levels associated with different driving forces for photoelectron injection. These findings emphasize the critical role of the interfacial coupling and suggest that further designs of dye-sensitized solar cells should target a higher selectivity in the dye-substrate binding conformations in order to ensure efficient electron injection from all photosensitizers.

Molecular orbital gates for plasmon excitation.

Future combinations of plasmonics with nanometer-sized electronic circuits require strategies to control the electrical excitation of plasmons at the length scale of individual molecules. A unique tool to study the electrical plasmon excitation with ultimate resolution is scanning tunneling microscopy (STM). Inelastic tunnel processes generate plasmons in the tunnel gap that partially radiate into the far field where they are detectable as photons. Here we employ STM to study individual tris-(phenylpyridine)-iridium complexes on a C60 monolayer, and investigate the influence of their electronic structure on the plasmon excitation between the Ag(111) substrate and an Ag-covered Au tip. We demonstrate that the highest occupied molecular orbital serves as a spatially and energetically confined nanogate for plasmon excitation. This opens the way for using molecular tunnel junctions as electrically controlled plasmon sources.

Trauma and PTSD in patients with alcohol, drug, or dual dependence: a multi-center study.

BACKGROUND: We investigated (1) the prevalence of posttraumatic stress disorder (PTSD) in treatment-seeking subjects with substance use dependence (SUD), (2) the association between comorbid PTSD and the severity and course of addiction and psychopathology, and (3) this association in patients with subsyndromal PTSD, and in trauma exposure without PTSD. METHODS: In this cross-sectional study, 459 subjects in 14 German addiction treatment centers participated with alcohol-dependence (A) in 39.7%, drug-dependence (D) in 33.6%, or both (AD) 26.8%. The diagnostic measures included the International Diagnostic Checklists (IDCL), Posttraumatic Diagnostic Scale (PDS), Addiction Severity Index (ASI), and the Brief Psychiatric Rating Scale (BPRS). Associations between independent characteristics and outcomes were analysed by univariate and multivariate statistics. RESULTS: 25.3% of the subjects had PTSD confirmed by both IDCL and PDS with higher rates in the AD (34.1%) and D (29.9%) groups compared with group A (15.4%, p < 0.001). In 22.8%, PTSD was subsyndromal (either IDCL or PDS positive) without significant differences between SUD groups, and 18.3% met PTSD trauma criteria A without PTSD (exposure). After controlling for SUD and gender, trauma subgroups significantly differed regarding the onset of alcohol-related symptoms (p < 0.02), numbers of previous admissions (p < 0.03), severity of SUD (p < 0.001), current craving (p < 0.02), and psychopathology (p < 0.001). We observed the worst outcome in PTSD, while trauma exposure had no effects. CONCLUSIONS: The prevalence of PTSD is higher in drug than in alcohol dependence. The more strictly PTSD is diagnosed (by interviewer and questionnaire) the more clearly are associations with characteristics of SUD. PTSD seems to be an independent risk factor for an unfavorable outcome of SUD.