Influence of environmental conditions and surface treatments on the photoluminescence properties of GaN nanowires and nanofins

Due to their intrinsically large surface-to-volume ratio, nanowires and nanofins interact strongly with their environment. We investigate the role of the main air constituents nitrogen, oxygen and water on the efficiency of radiative recombination in GaN nanostructures as a function of different surface treatments and at temperatures up to 200 °C. Oxygen and water exposures exhibit a complex behavior as they can both act quenching and enhancing on the photoluminescence intensity dependent on the temperature. For oxygen, these characteristics are already observed for low concentrations of below 0.5% in nitrogen. While the photoluminescence intensity changes induced by oxygen occur independently of illumination, the influence of water is light-induced: it evolves within tens of seconds under ultraviolet light exposure and is heavily influenced by the nanostructure pre-treatment. In contrast to observations in dry atmospheres, water prevents a recovery of the photoluminescence intensity in the dark. Combined measurements of the electrical current through GaN nanofins and their photoluminescence intensity reveal the environmental influence on the interaction of non-radiative recombination processes and changes in the surface band bending of the nanostructures. Several investigated solvents show an enhancing effect on the PL intensity increase, peaking in c-hexane with a 26-fold increase after 6 min of light exposure. Stabilization of the PL intensity was achieved by a passivation of the GaN surface with Ga_xO_y, and ZnO shells. Surprisingly, Al₂O₃coatings resulted in a highly instable PL intensity during the first minutes of illumination. Our findings reveal the high importance of controlled environmental conditions for the investigation of nanostructures, especially when aimed at their applications in the fields of environmental sensing, photo-catalysis and light-emitting diodes.

Surface-Anisotropic Janus Silicon Quantum Dots via Masking on 2D Silicon Nanosheets

Surface-anisotropic nanoparticles represent a new class of materials that shows potential in a variety of applications, including self-assembly, microelectronics, and biology. Here, the first synthesis of surface-anisotropic silicon quantum dots (SiQDs), obtained through masking on 2D silicon nanosheets, is presented. SiQDs are deposited on the 2D substrate, thereby exposing only one side of the QDs, which is functionalized through well-established hydrosilylation procedures. The UV-sensitive masking substrate is removed through UV-irradiation, which simultaneously initiates the hydrosilylation of a second substrate, thereby introducing a second functional group to the other side of the now free-standing SiQDs. This renders surface-anisotropic SiQDs that have two different functional groups on either side of the particle. This method can be used to introduce a variety of functional groups including hydrophilic and hydrophobic substrates, while the unique optoelectronic properties of the SiQDs remain unaffected. The anisotropic morphology of the QDs is confirmed through the aggregation behavior of amphiphilic Janus SiQDs at the interface of water and hexane. Additionally, anisotropic SiQDs are used to produce the first controlled (sub)monolayer of SiQDs on a gold wafer.

Anapole Excitations in Oxygen-Vacancy-Rich TiO2-x Nanoresonators: Tuning the Absorption for Photocatalysis in the Visible Spectrum

Research on optically resonant dielectric nanostructures has accelerated the development of photonic applications, driven by their ability to strongly confine light on the nanoscale. However, as dielectric resonators are typically operated below their band gap to minimize optical losses, the usage of dielectric nanoantenna concepts for absorption enhancement has largely remained unexplored. In this work, we realize engineered nanoantennas composed of photocatalytic dielectrics and demonstrate increased light-harvesting capabilities in otherwise weakly absorptive spectral regions. In particular, we employ anapole excitations, which are known for their strong light confinement, in nanodisks of oxygen-vacancy-rich TiO_2-x, a prominent photocatalyst that provides a powerful platform for exploring concepts in absorption enhancement in tunable nanostructures. The arising photocatalytic effect is monitored on the single particle level using the well-established photocatalytic silver reduction reaction on TiO₂. With the freedom of changing the optical properties of TiO₂ through tuning the abundance of V_O states, we discuss the interplay between cavity damping and the anapole-assisted field confinement for absorption enhancement. This concept is general and can be extended to other catalytic materials with higher refractive indices.

Photo-induced selective etching of GaN nanowires in water

Nanowire (NW) based devices for solar driven artificial photosynthesis have gained increasing interest in recent years due to the intrinsically high surface to volume ratio and the excellent achievable crystal qualities. However, catalytically active surfaces often suffer from insufficient stability under operational conditions. To gain a fundamental understanding of the underlying processes, the photochemical etching behavior of hexagonal and round GaN NWs in deionized water under illumination are investigated. We find that the crystallographic c-plane remains stable, whereas the m-planes are photochemically etched with rates up to 11 nm min-1, depending on the applied UV light intensity. By investigating nanowalls, we achieve control of the exposed crystallographic facets and find an enhanced stability of the a-plane compared to the m-plane. Photo-excited holes, which drift to the side facets due to the upward surface band bending in nominally n-type (not intentionally doped) GaN, are identified as the driving force of the process, which allows the development of concepts for the stabilization of the nanostructures. A geometrically enhanced absorption of periodic NW arrays is correlated with a dependence of the etch rate on the NW pitch and diameter. Further, we find selective photochemical etching of the NW base in the presence of sub-band gap illumination, which is attributed to defect-related absorption in this region. These results provide improved understanding of the roles of inhomogeneous defect distribution, light excitation profiles, and different surface facets on the photochemical stability of nanostructures and provide viable strategies for improving stabilities under light-driven reaction conditions.

Double-blind multicenter study of paroxetine and amitriptyline in depressed inpatients

Paroxetine is a new compound in the group of the selective serotonin-reuptake inhibitors. The results of several open and double-blind control-group studies demonstrate clear antidepressive efficacy of paroxetine. However, most data were collected in samples of outpatients. To overcome this restriction, a six-week double-blind control-group study, comparing 30 mg paroxetine with 150 mg amitriptyline per day, was performed in a sample of inpatients suffering from major depression. Generally speaking, the efficacy analysis of 160 patients was not able to demonstrate statistically significant differences in the antidepressive activity of paroxetine or amitriptyline, either with respect to the total score on the Hamilton Depression Scale (HAMD) and the Clinical Global Impressions or with respect to the subscores of the HAMD. One exception was the retardation subscore, in which amitriptyline showed a greater degree of reduction. Both drugs had a characteristic side-effect profile. Paroxetine was characterized by a lack of anticholinergic side-effects and a higher rate of nausea.

[Cerebral insufficiency--treatment with Ginkgo-biloba extract. Time of onset of effect in a double-blind study with 60 inpatients]

Sixty inpatients with cerebral insufficiency and the leading symptom depressive mood, were treated in a double-blind study for 6 weeks with a daily dose of 160 mg Ginkgo biloba extract or placebo. After 2, 4 and 6 weeks, changes in 12 typical symptoms in comparison with the last examination, were evaluated. In the group receiving placebo, small, but progressive improvements were observed. In the Ginkgo-biloba group, the overall number of improvements was significantly larger. After 2 weeks the differences were marked for only a few of the symptoms; after 4 and 6 weeks in contrast, in 11 of the 12 symptoms. The largest number of improvements in the Ginkgo-biloba group was observed between the 2nd and 4th weeks of treatment. In this period, about two-thirds of the patients on Ginkgo-biloba, and about one-fifth of the patients on placebo showed improvements.

[Mortality of hospitalized psychiatric patients--results of a 10-year study]

The mortality rate of 1239 psychiatric patients--609 men and 639 women, aged between 40 and 70 years, permanently hospitalized in 6 different German clinics--was registered, ten years after they had been examined for the incidence of cardiac risk factors in 1971 and 1972. The death rate figures were compared with the corresponding figures of the total population of the Federal Republic of Germany. In all age-groups mortality among psychiatric patients, both male and female, was higher than the average rate at Federal level. The gap narrowed with increasing age. With male patients the most frequent cause of death were cardiovascular diseases, followed by respiratory diseases and malignant growths, whereas with women respiratory diseases were the primary cause of death. In comparison to the population of the Federal Republic of Germany considerably more patients died of respiratory diseases--according to age and sex the death rate was up to ten times higher. This was due to the high percentage of lethal pneumonia. The number of deaths in which the cause was unknown was also higher than the national average. A remarkably high percentage of the patients (27%) died suddenly and unexpectedly. In some age-groups fewer patients died of malignant growths than at Federal level. Death caused by cardiovascular diseases was only more frequent among younger patients. Among men acute ischaemic heart diseases were the most frequent cause of cardiac failure. Death due to cerebral sclerotic diseases was remarkably reduced among older patients, probably as a result of a less high incidence of hypertension.

Self-rating data as a selecting factor in clinical trials of psychotropic drugs

In psychiatry the relationship between rating by others and self-rating has been discussed again and again. The question has been raised as to the influence of complete data material (all patients with self-rating and rating by others) on results, in comparison to results where patients without self-rating are not taken into evaluation. This question was answered by conducting a double-blind study which included two pharmacologically active substances (amitriptylinoxide and trazodone) and two sub-samples of patients (patients with rating by others and self-rating, and patients with rating by others alone). The trial was performed in a total of 57 in-patients suffering from endogenous depression (ICD 296.1) who received drug treatment for 21 days. The effect was assessed multi-methodically. While no differences between the two drugs were seen in the sub-sample "self-rating and rating by others", amitriptylinoxide proved to be superior to trazodone in the sub-sample "rating by others". On the basis of these findings the use of rating by others and self-rating procedures will be considered.

[Mortality in hospitalized psychiatric patients (results from a 5-year study) (author's transl)]

During 5 years we have registered mortality in 1239 chronic hospitalized psychiatric patients (609 men and 630 women) aged between 40-70 years in 6 German hospitals. We examined this patients on incidence of cardial riskfactors. The death rates were compared to the others of BRD. In this connection we found out an intensified mortality in all age groups of psychiatric patients as against to BRD average. The mortality of respiratory system diseases surpassed death rates of BRD many times better. Also psychiatric patients died by cardiovascular diseases more than expected. The death rates from ischaemic heart diseases in men were approximately twice as much than at BRD statistic. Patients who died in arteriosclerotic diseases had more often riskfactors than the other deceased. The great number of sudden and unexpected deaths was remarkable.

[ECG changes in psychiatric patients under long-term therapy with psychopharmaca (author's transl)]

Within the scope of an epidemiologic study on risk factors and coronary heart diseases, 1726 mentally ill, aged 40-69, under permanent hospitalization were examined electrocardiographically. There were few pronounced indications of a relationship between pathological ECG findings and psychopharmaca. ECG changes were rarest among patients treated exclusively with non-tricyclic drugs, and most often among those patients who received tricyclics and non-tricyclics simultaneously. Statistically ascertained, however, was only the connection with lesser pathological changes in the rest and load ECG's (T-flattening). In this connection, these disturbances appeared more often among women. A reciprocal effect between sex and the influence of psychopharmaca appeared on the ECG. Contrary to males, females under treatment with tricyclica or with several psychopharmaca simultaneously showed more ECG changes than those treated without medication.

[The mortality from ischaemic heart diseases in hospitalized psychiatric patients (author's transl)]

In 1357 chronic hospitalized psychiatric patients (641 men and 716 women) aged between 40 and 69 years the mortality during 30 months was registered, referring for a prevalent study about riskfactors. The death rates for ischaemic heart diseases in hospitalized patients were 2,5-3,5 times as high as states in the statistic for total population of BRD. The majority of dead patients had two or more of the known riskfactors, more as the half of the dead patients had a manifest diabetes mellitus or a disorder of oral glucose tolerance test.

[Are neuroleptic drugs anticarcinogenic? (author's transl)]

Statistical methods seem to confirm the impression that a connection exists between the administration of neuroleptic drugs and a lowered cancer mortality rate. However, further analysis shows that the neuroleptic group and the controls represent two distinct populations which cannot be compared with each other.

[Psychotropic agents and pathological ECG changes (author's transl)]

1. An epidemiological research programme was carried out on a collective of 1752 psychotic patients from eight psychiatric hospitals during the period from October 1970 until February 1973. The possible relationships as to the intensity of pathological ECG changes and such factors as sex, age, the administration of tricyclic and non-tricyclic psychotropic agents with or without the combination of glycosides, the potency of neuroleptics and their clinical structure, were investigated. 2. No statistical significance could be established between pathological ECG changes and such factors as administration of tricyclic and non-tricyclic psychotropics with or without the combination of glycosides, or the potency of neuroleptics and their chemical structure. With a higher age the frequency of ECG changes increases independent on psychotropics. 3. The difficulties of interpretation, in particular regarding a generalisation of the results, are discussed.