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Nanostructured GaN surfaces sputtered with Au provide very promising and reproducible platforms for surface enhanced Raman scattering (SERS). The enhancement factor (EF) in SERS is expected to depend strongly on the local metal (Au) surface structure (size, distribution and morphology). Herein we show how temperature-induced coalescence followed by recrystallization of Au on GaN nano-columns occurs well below the melting point of gold. This process is reflected in SEM, TEM images and SERS spectra of Au/GaN – bound p‐mercaptobenzoic acid (4-MBA), a model Raman scatterer. SERS signals of 4-MBA bound to Au/GaN reach minimum for platforms exposed to t = 350 °C before regaining the intensity when annealed in the range of 450–900 °C. The results have been discussed in the light of the nature of SERS active sites – so called “hot spots” and structure of Au nanoparticles.

We describe surface patterning as a method to obtain discrete regions of different local miscut angles, δ, in semipolar ( 20 2 ¯ 1 ) GaN substrates. During patterning the region angle δ was varied between 0° and ±2° with respect to the growth plane. We chose two nonequivalent miscut directions: a 〈 1 ¯ 2 1 ¯ 0 〉 and c ׳ 〈 1 ¯ 01 4 ¯ 〉. On such patterned substrates In x Ga 1− x N/GaN quantum wells were grown by a Metalorganic Vapor Phase Epitaxy method. Angled regions were not planarized during growth and their initial miscut angles remained. We studied structural, morphological and optical properties of In x Ga 1− x N/GaN quantum wells as a function of δ . The intended In concentration, x , was about 13% on exact oriented ( 20 2 ¯ 1 ) planes. For miscut towards the a -direction, indium content decreases and luminescence energy increases with δ . For miscut towards c ׳, we observe quite different behaviors, indium content and quantum well width are constant and luminescence energy increases with δ . We propose the explanation of these effects on the basis of sample morphology, In-content and built-in electric field. The obtained results are important for understanding the role of miscut (intentional and unintentional) in basic properties of semipolar InGaN/GaN quantum well structures. It is also worth to note that, the spectral width of luminescence was the smallest for regions miscut 2° towards c ׳ direction, which can be important for semipolar optoelectronic devices.

GaN bulk crystals grown by Hydrate Vapor Phase Epitaxy (HVPE) contain regions with non-homogenous electrical properties. Kelvin Probe Force Microscopy (KPFM) was used for revealing and analysis of these defects in thick GaN layers grown by this method on top of GaN on sapphire templates. Such layers initially grow in the form of separate pyramids, which are later overgrown, creating microscopically flat crystallization front. Cross-sectional KPFM images, made just above the template surface, revealed a series of inverted dome-like features of significantly lower potential, indicating regions of high electron concentration. Inside the thick HVPE-grown layer the changes of surface potential are much smaller and indicate the existence of minor fluctuation in carrier concentration during bulk growth of GaN. Subsequent photo-etching, sensitive to carrier concentration, and measurements of etch depth supported this findings. Both KPFM and photo-etching confirmed the known preferential incorporation of impurities at sides of the overgrown pits (pinholes) during initial phase of HVPE growth. During subsequent HVPE growth the changes of the surface potential and of the etch depth are small and may be related to non-uniform incorporation of impurities due to rotation of the growing sample.

Objective Infantile spasms are one of the most frequent disorders affecting the children up to 1 year of age. The drug of the first line is Vigabatrine (VGB) which is considered to cease the seizures or causes the significant reduction in seizure frequency. The well described adverse event occurring during the treatment with VGB is visual field defects. Less is known about its impact on white matter although there are several papers where VGB is considered to cause the reduction in density of white matter easily detected on diffusion tensor imaging (DTI). The aim of our study was to observe functional measurements like fractional anisotropy (FA) and apparent diffusion coefficient (ADC) of white matter before and during treatment with VGB. Methods We have studied 9 patients with infantile spasms (5 boys, 4 girls). Age range 7 months–1 year. The diagnosis was made by detailed case history and was proved by electroencephalography (EEG). VGB with dosage 120 mg/kg was given to all patients and MRI with DTI was performed before and during the treatment. MRI was performed on a 1.5T Siemens system (TR/TE=500/11 ms, slice thickness=3 mm). Neuroradiologist blinded to patients' treatment status reviewed the MRI including DTI. Results We have observed the significant reduction of white matter density during treatment with VGB compared to those before treatment. This result was proved by decreasing of FA and increasing of ADC values. Conclusion VGB causes changes on MRI signal and diffusion restriction. Cryptogenic cases are less vulnerable than symptomatic. The future direction is to study if these changes are dose or age related or if seizure frequency affects on white matter functional measures.

Mechanisms of optical detection of magnetic resonance in wide band gap II-Mn-VI diluted magnetic semiconductor (DMS) are discussed based on the results of photoluminescence (PL), PL kinetics, electron spin resonance (ESR) and optically detected magnetic resonance (ODMR) and optically detected cyclotron resonance (ODCR) investigations. Spin-dependent interactions between localized spins of Mn 2+ ions and spins/magnetic moments of free, localized or bound carriers are responsible for the observed ODMR signals. We conclude that these interactions are responsible for the observed rapid shortening of the PL decay time of 4 T 1 → 6 A 1 intra-shell emission of Mn 2+ ions and also for the observed delocalization of excitons in low dimensional structures.

The temperature dependence of the dielectric loss (tgδ) in β-B was studied at temperatures ranging from −196 to 350 °C and at frequencies of 1–104 Hz. The curve of the temperature dependence of dielectric loss in an electric field with a frequency of 50 Hz showed two relaxation maxima at −65 and −45 °C characterized by activation energies of 0.18 eV and 0.23 eV respectively. It was established that by annealing boron in H2 at 700 °C for 1 h the peak of dielectric loss found at −65 °C increased whereas the relaxation maximum observed at −45 °C completely disappeared. In an electric field of 10 kHz, a relaxation maximum with an activation energy of 0.6 eV appeared at 100 °C. The height of this peak correlated to the change in the carbon content of the samples investigated. A non-relaxation peak of tgδ was observed at 300 °C. Around this temperature, the temperature dependence curve of the capacitance passed through a maximum. It was assumed that the processes of absorption of the a.c. electric field energy are caused by the redistribution of the electrically active gas admixtures and of carbon under the effect of the electric field voltage.

Diffraction phase analysis of the structure of near-eutectic alloys in the Ti-B system obtained by quenching from the melt has been carried out. It is shown that the alloy consists of heavily distorted phases of α titanium and titanium monoboride in a finely dispersed state. Intensive maxima are observed in the temperature spectrum of the low frequency internal friction in the temperature region 20–750 °C, a part of them being of a non-relaxational nature. This is also confirmed by the internal friction measurements within the acoustic frequency range of flexural oscillations. On the basis of the comparative analysis of the structural investigation data and the properties of the observed internal friction maxima, mechanisms are proposed taking into account structural changes in the intermediate phases and on the boundaries under continuous heating.