Hydrogen passivation of the n-GaN nanowire/p-Si heterointerface.

The influence of hydrogen plasma treatment on the electrical and optical properties of vertical GaN nanowire (NW)/Si heterostructures synthesized via plasma assisted molecular beam epitaxy is studied. The effect of the treatment is thoroughly studied via variation of the passivation duration. Photoluminescence investigation demonstrates that the passivation affects the doping of the GaN NWs. The samples were processed as photodiodes with a top transparent electrode to obtain detailed information about the n-GaN NWs/p-Si heterointerface under illumination. The electron beam induced current measurements demonstrated the absence of potential barriers between the active parts of the diode and the contacts, indicating ohmic behavior of the latter. I-V characteristics obtained in the dark and under illumination show that hydrogen can effectively passivate the recombination centers at the GaN NWs/Si heterointerface. The optimum passivation duration, providing improved electrical properties, is found to be 10 min within the studied passivation regimes. It is demonstrated that longer treatment causes degradation of the electrical properties. The discovered phenomenon is discussed in detail.

Effects of the surface preparation and buffer layer on the morphology, electronic and optical properties of the GaN nanowires on Si.

The role of Si (111) substrate surface preparation and buffer layer composition in the growth, electronic and optical properties of the GaN nanowires (NWs) synthesized via plasma-assisted molecular beam epitaxy is studied. A comparison study of GaN NWs growth on the bare Si (111) substrate, silicon nitride interlayer, predeposited AlN and GaO x buffer layers, monolayer thick Ga wetting layer and GaN seeding layer prepared by the droplet epitaxy is performed. It is demonstrated that the homogeneity and the morphology of the NW arrays drastically depend on the chosen buffer layer and surface preparation technique. An effect of the buffer and seeding layers on the nucleation and desorption is also discussed. The lowest NWs surface density of 14 µm-2 is obtained on AlN buffer layer and the highest density exceeding the latter value by more than an order of magnitude corresponds to the growth on the 0.3 ML thick Ga wetting layer. It is shown, that the highest NWs mean elongation rate is obtained with AlN buffer layer, while the lowest elongation rate corresponds to the bare Si (111) surface and it is twice as lower as the first case. It is found, that use of AlN buffer layer corresponds to the most homogeneous NWs array with the smallest length dispersion while the least homogeneous array corresponds to the bare Si substrate. Vertically aligned GaN NWs array on the wide bandgap GaO x semiconductor buffer layer grown by plasma-enhanced chemical vapor deposition demonstrates its potential for electronic applications. Photoluminescence (PL) study of the synthesized samples is characterized by an intense optical response related to the excitons bound to neutral donors. The highest PL intensity is obtained in the sample with AlN buffer layer.

Effect of nonselective beta-adrenoblockers on the state of sympathoadrenal system and ratio of neuroactive amino acids in rat medulla oblongata.

Experiments on rats showed that injection of propranolol into the medulla oblongata increased the contents of epinephrine, norepinephrine, dopamine, and L-DOPA by 3.76, 1.4, 2.0, and 1.7 times, respectively. These propranolol-induced changes in the levels and ratio of neurotransmitters were not accompanied by variations in serotonin content. Propranolol had no significant effects on the content of excitatory amino acids, except marked increase in aspartate content. The level of inhibitory amino acids increased mainly due to an increase in GABA content. The balance between excitatory and inhibitory amino acids was shifted towards inhibitory compounds.

Effects of bradysole and dibasole on cerebral bloodflow under experimental conditions.

Bradysole (1 mg/kg intravenously) induced a moderate increase in cerebral bloodflow and a minor decrease in systemic blood pressure in narcotized rats. These effects were less pronounced compared to the effects of dibasole (bradysole structural analog) in the same dose.

Effect of imidazobenzoimidazole derivatives RU-353, RU-563, and lidocaine on cerebral circulation in rats.

We demonstrated a dose-dependent inhibitory effect of novel imidazobenzoimidazole derivatives RU-353 and RU-563 on cerebral blood flow and systemic blood pressure in narcotized rats. The effects of RU-353 increased, while the effect of RU-563 decreased with increasing the dose.

Effect of cyclic GABA derivative TZ-146 on the content of neurotransmitters in rat brain stem.

The effect of cyclic GABA derivative TZ-146 on the content of catecholamines, serotonin, their metabolites, and neurotransmitter amino acids in rat hypothalamus and brain stem was studied by high-performance liquid chromatography with electrochemical detection. Opposite changes in the content of homovanillic acid, aspartate, glutamate, and glycine in the examined structures were accompanied by inhibition of dopamine metabolism. Possible participation of cerebral glutamatergic system in the effect of TZ-146 is discussed.