Deep transcranial magnetic stimulation (TMS) is a technique of neuromodulation and neurostimulation based on the principle of electromagnetic induction of an electric field in the brain. The coil (H-coil) used in deep TMS is able to modulate cortical excitability up to a maximum depth of 6 cm and is therefore able not only to modulate the activity of the cerebral cortex but also the activity of deeper neural circuits. Deep TMS is largely used for the treatment of drug-resistant major depressive disorder (MDD) and is being tested to treat a very wide range of neurological, psychiatric and medical conditions. The aim of this review is to illustrate the biophysical principles of deep TMS, to explain the pathophysiological basis for its utilization in each psychiatric disorder (major depression, autism, bipolar depression, auditory hallucinations, negative symptoms of schizophrenia), to summarize the results presented thus far in the international scientific literature regarding the use of deep TMS in psychiatry, its side effects and its effects on cognitive functions.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Self heating during long-term DC-aging is found to be responsible for the degradation of the electrical and optical characteristics of blue p-GaN/p-AlGaN/InGaN/n+-GaN/SiC LEDs. Electroluminescence and Cathodoluminescence studies reveal an additional large optical band, not observed in unstressed devices, on the p-type side of the LEDs. Deconvolution procedures shows the band, peaked at about 3.1 eV, is due to three main emissions at 2.93, 3.08 and 3.23 eV. Deep Level Transient Spectroscopy reveals the presence of four traps for majority carriers in p-type GaN. A comparison with the optical spectra suggests three of them (at 0.12, 0.22 and about 0.5 eV) are responsible for the additional emissions after stress, while a further trap at 1.21 eV is considered non-radiative in nature. A thermally activated mechanism inducing the dissociation of native Mg-H complexes and the subsequent formation of metastable Mg-H2 complexes is considered responsible for the LED degradation. The hypothesis is supported by high power electron beam irradiation during Cathodoluminescence studies which induced a complete disappearance of the band at 3.1 eV as a consequence of the dissociation under energetic electron beam of the metastable Mg-H2 complexes.

In this work we describe a novel system for photovoltaic applications which combines InGaAs based strain-balanced multiple quantum wells (MQWs) with a “virtual substrate”, designed to extend the absorption edge of the photovoltaic devices to about 1 eV. The virtual substrate is designed by properly choosing a sequence of InGaAs layers having different In content, in order to obtain the desired lattice parameter at the topmost layer and to confine at the deepest interfaces the misfit dislocations, well away from the QW active region.

A series of InGaAs p-i-n junctions, containing a strain balanced MQW in the intrinsic region, were deposited by metallorganic chemical vapor deposition on different virtual substrates. In all the samples the virtual substrates were proved to be successful to grow zero net strain MQW and to confine defects at the buffer/substrate interface. Transmission electron microscopy observation shows that no defects propagate from the strain accommodating layers to the active region. The total density of threading dislocations reaching the surface was found to be less than 1*E5/cm2.

The confined misfit dislocation network, however, results in marked cross-hatched morphology that was found to affect the lateral strain distribution in the whole structure. By optimizing the growth condition of the structures, the influence of the surface roughness induced by CH pattern is partially suppressed.

The results of a systematic investigation by transmission electron microscopy (TEM), cathodoluminescence (CL), Rutherford backscattering (RBS), X-ray diffraction and topography and scanning force microscopy (SFM) techniques on several InGaAs/InP compressive and tensile strained layers covering the misfit range from −2.3 to 1.5×10−2 and grown by the metal organic vapor phase epitaxy (MOVPE) technique are reported. In compressively strained films the same dependence for the residual strain vs the film thickness as for the InGaAs/GaAs is found whereas a different strain release rate and different extended defects are found in tensile stressed InGaAs alloy. In particular in tensile stressed samples, grooves, planar defects and cracks are present in addition to the interfacial network of misfit dislocations. The correlation between the observed planar defects and the mechanisms of strain relaxation in the case of tensile strained layers is discussed.

Low temperature monochromatic cathodoluminescence (CL) spectral analyses and imaging were used to determine the widths of resistive regions (due to Fe diffusion) in multi-quantum-well (MQW) InP-based laser devices and to detect the different amount of damage induced by alternative In-situ Etching (ISE) and Reactive Ion Etching (RIE) techniques. The widths of the resistive regions were estimated by comparing the 5 K CL emission width from the MQW and the actual width as obtained by SEM investigations. Monochromatic CL also did not reveal any emission from the InP:Sn layer between semi-insulating material (Fe-doped lnp) and p-type layer (Zn-doped InP), indicating interdiffusion of Fe and Zn laterally the MQW, and the presence of substantial Sn diffusion (up to 2500 nanometers) into the substrate.

We correlate structure analyzed by transmission electron microscopy with photo- and cathodoluminescence studies of GaN/Al2O3(0001) and GaN/SiC(0001) and show that an additional UV line at 364nm/3.4eV can be connected to the occurrence of stacking faults. We explain the occurrence of this line by a model that is based on the concept of excitons bound to stacking faults that form a quantum well of cubic material in the wurtzite lattice of the layer material. The model is in reasonable agreement with the experimental observations.

We investigate the structure, growth morphology and the related electro-optical properties of gallium nitride (GaN) films deposited on (0001) sapphire substrates by gas source molecular beam epitaxy (GSMBE) and use transmismission electron microscopy, atomic force microscopy and scanning tunneling microscopy, photoluminescence (PL) and cathodoluminescence (CL). We find two types of specimens: one type which shows a strong UV luminescence (band-to-band transition at 358nm/3.46eV) in CL and PL and only faint yellow luminescence (Gaussian shaped CL/PL peaks at around 528nm/2.35eV), specimen ‘B’, and another type, which shows a strong UV and a comparably strong yellow luminescence, specimen ‘Y’. These two types of specimens have a rough layer surface, specimen ‘Y’ even an islanded one with, facetted hexagonal islands with a width of 1-2μm at a height of 50nm. A correlation of spectrally resolved CL images to the observed defect structure shows: (i) the yellow luminescence is homogeneously distributed over the complete specimen for ‘B’ and ‘Y’ specimens. Our investigations strongly suggest the yellow luminescence to be related to screw dislocations with , which are found randomly distributed in ‘B’ and ‘Y’ specimens with a high density of 1.3·109cm−2; (ii) the strong UV luminescence in ‘Y’ specimens is located in the troughs between adjacent surface islands, where dislocations essentially in small angle grain boundaries of edge type, i.e. with or are located; (iii) in the case of the ‘B’ specimens these dislocations are randomly distributed and so is the luminescence.

InAs single layers were grown by Molecular Beam Epitaxy on nominally (001) oriented GaAs substrates at growth temperatures ranging from 350 °C to 500 °C and thicknesses between 1 nm and 6 μm. A systematic study of the influence of growth temperature and thickness on crystal defects and surface morphology is discussed by comparing High Resolution X-Ray Diffraction, Transmission Electron Microscopy and Atomic Force Microscopy investigations.

Surface hexagonal shaped holes were observed to develop at the lowest temperatures starting from an heterolayer thickness of 50 nm. Both misfit and threading dislocations were revealed; moreover the correlation between hexagonal shaped surface holes and mixed dislocations, with the component of the Burgers vector (b) along the growth axis larger than the minimum interatomic distance, is discussed. The holes increase in size and decrease in density by increasing the layer thickness. An almost complete surface planarization is observed at a thickness of 6 μm by increasing the growth temperature up to 500 °C.