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[en] In this work, we demonstrate that grain boundaries (GBs) in multicrystalline silicon solar cells may be easily grooved using porous silicon (PS). We then use this interesting property to try reducing the area of these highly recombining regions. To reach this objective a thin PS layer was formed on both front and back sides of the multicrystalline material. After removing the PS films, conventional phosphorus diffusion was achieved. Grooved GBs enable deep penetration of phosphorus and metallic contacts. As a result, we found an improvement of the I-V characteristics under the dark and at AM1.5 illumination. The light-beam-induced current was found to be improved of approximately 16% resulting from an enhancement of the bulk minority carrier collection probability. The internal quantum efficiency was also found to be enhanced by approximately 15% in a rather wide spectral range, approximately between 600 and 1100 nm. These results are discussed and compared to solar cells based on untreated multicrystalline silicon wafers
[en] Thirty-four radio-induced malignancies of the scalp following irradiation for tinea capitis are reported. Patient age at the time of the discovery of the malignancy varies from 20 to 83. Basocellular carcinomas (24 cases) and spinocellular carcinomas (5 cases) are the most common: two other cases of annexial tumors, two malignant non-hodgkin's lymphomas and one malignant melanoma are also present. The average age at irradiation is 11, and the cancerization interval is 35 years. In 60% of the cases, the scalp appeared normal and in 40 more or less severe radiodermitis is noted. Radiotherapy was used in the treatment of these cancers in 32 cases; only two patients had surgical exicision alone. Out of the evaluable patients, 6 developed local and/or nodal recurrence, 5 of which were recovered with surgery
[en] There is a small quantity of participants in the global market of silicon, mainly from the developed countries. It should be noticed also that production of metallurgical silicon Mg-Si is among the most important steps to produce solar grade silicon and photovoltaic panels. Therefore, in this paper we focused on the growth of Mg-Si by carbothermal reduction of silica. An investigation was made using FT-IR characterization to study the effect of process conditions (temperature, atmosphere, duration) in Mg-Si production. Raman spectroscopy was used to investigate the produced Mg-Si. Based on these results, we established a pilot line production of metallurgical silicon at the 'CRTEn' in Tunisia
[en] Introduction. - The induction of malignant diseases is one of the most concerning late effects of ionizing radiation. The topic of this study deals with skin tumors developed in the irradiated areas in children given X-ray therapy for tinea capitis. Material and methods. - All patients with malignant tumors of the scalp referred to Salah Azaiz Institute between 1970 and 2001 have been questioned in order to determine if there had been a prior X-ray irradiation for tinea capitis, its modality, and its consequences. The first scalp irradiation goes back to 1922 and the last was performed in 1963. Results. - Ninety-eight patients with 150 radio-induced cancers of the scalp following irradiation for tinea capitis are reported (1.5 lesion per patient). The patients were irradiated in various hospitals and dispensaries throughout the country. Eighty-one patients (82%) had only one session of radiation. The average age at irradiation was 12 (±6) years, the latent period for radiation-induced skin cancers was 36 (±14) years. In 61 patients (62%), the scalp appeared normal and in 38% radiodermatitis was noted. Patient age at diagnosis of malignancy varied from 20 to 83 years with an average of 47 years. Basal cell carcinomas (125 cases) and spino-cellular carcinomas (16 cases) were the most common. three other cases of annex tumors, two malignant non-Hodgkin's lymphomas and four melanoma lesions are also present. Radiotherapy was used for the treatment of 74 patients (alone in 42 and associated with surgery in 32 patients); 14 patients had exclusive surgical excision. Conclusions. - Basal cell carcinomas are the most frequent tumors arising on chronic radiodermatitis. In spite of the long latency period, patients' young age at irradiation explained the occurrence of these cancers at a relatively young age. Literature review is suggesting recessive mutation of tumor-suppressor genes as the characteristic abnormality in radio-induced cancer. (author)
[en] This paper presents a new method to produce porous silicon which derived from the conventional stain etching (SE) method. But instead of one etching step that leads to formation of porous layer, the substrate is subjected to an initial etching step with a duration Δt0 followed by a number of supplementary short steps that differs from a layer to another. The duration of the initial step is just the necessary time to have a homogenous porous layer on the whole surface of the substrate. It was found that this duration is largely dependent of the doping type and level of the silicon substrate. The duration of supplementary steps was kept as short as possible to prevent the formation of bubbles on the silicon surface during silicon dissolution which leads generally to inhomogeneous porous layers. It is found from surface investigation by atomic force microscopy (AFM) that multistep stain etching (MS-SE) method allows to produce homogeneous porous silicon nanostructures compared to the conventional SE method. The chemical composition of the obtained porous layers has been evaluated using Fourier transform infrared spectroscopy (FTIR). Photoluminescence (PL) measurement shows that porous layers produced by SE and MS-SE methods have comparable spectra indicating that those layers are composed of nanocrystallites with comparable sizes. But the intensity of photoluminescence of layer elaborated by MS-SE method is higher than that elaborated by the SE method. Total reflectance characteristics show that the presented method allows the production of porous silicon layers with controllable thicknesses and optical properties. Results for porous silicon layers elaborated on heavily doped n-type silicon show that the reflectance can be reduced to values less than 3% in the major part of the spectrum.
[en] SPECT is a well established tool in neurology. This functional imaging method is preponderantly used in the field of stroke, epilepsy and dementia. Cerebral blood flow (CBF) is visualized and/or measured by HMPAO or 133Xe. Sequential SPECT investigations allow the detection of changing CBF patterns. Relying on PET results, these SPECT data can be interpreted in a correct way and have some prognostic relevance. Alzheimer's disease shows a characteristic HMPAO distribution pattern, which allows separation from other forms of dementia. Receptor studies can be performed with new ligands. D2-Dopamine receptors can be visualized with lodobenzamide (IBZM). It was found, that parkinsonian patients have a normal D2-Dopamine receptor binding capacity. No relationship between disease duration or symptoms and D2-receptor occupancy was observed. In contrast, patients suffering from multisystem atrophy show a decreased binding capacity. Normal subjects and parkinsonian patients have a significant decrease of D2-Dopamine receptor binding capacity with increasing age. Benzodiazepine receptors can be investigated with lomazenil SPECT. However, the clinical value of such studies is yet not clear, since visual interpretation of lomazenil SPECT images has no advantage over HMPAO SPECT in the field of epilepsy. Dynamic lomazenil SPECT studies will perhaps increase the possibilities of the clinical application for this compound. (orig.)
[de]Die SPECT wird bei verschiedenen neurologischen Erkrankungen eingesetzt, wobei es moeglich ist, einerseits regionale Hirndurchblutungsveraenderungen routinemaessig mit HMPAO oder 133Xe zu untersuchen, andererseits bestimmte Rezeptoren im Gehirn mit neuen Liganden darzustellen. Hauptsaechtliche Anwendungsgebiete fuer die HMPAO SPECT sind der Schlaganfall, die Epilepsie und die Demenz. Serielle Untersuchungen zeigen unterschiedliche Durchblutungsmuster, die man in Anlehnung an PET-Ergebnisse weitgehend richtig interpretieren kann und daher auch eine prognostische Aussage haben. Bei den Demenzen ist die Abgrenzung zur Alzheimerschen Erkrankung moeglich, da letztere meist ein typisches Durchblutungsmuster zeigt. Fuer D2-Dopaminrezeptorstudien eignet sich vor allem das lodobenzamid (IBZM). Es wurde in verschiedenen Studien gesehen, dass bei Parkinsonpatienten keine Abhaengigkeit zwischen Rezeptorbindungskapazitaet und Dauer bzw. Schweregrad der Erkrankung besteht. Im Gegensatz dazu ist die D2-Dopaminrezeptorbindungskapazitaet bei Multisystematrophien und bei der Chorea Huntington erniedrigt, was die Abgrenzung solcher Erkrankungen zum Parkinsonsyndrom erleichtert. Bei normalen Probanden und bei Parkinsonpatienten besteht eine signifikante Abnahme der D2-Dopaminrezeptoren mit zunehmendem Alter. Benzodiazepinrezeptoren lassen sich mit lomazenil darstellen. Die klinische Wertigkeit der Benzodiazepinrezeptorstudien ist noch unklar, vor allem in der Diagnostik der Epilepsie. Hier koennten moeglicherweise dynamische SPECT-Studien einen Fortschritt bringen. (orig.)
[en] The use of low cost silicon wafers seems to be very attractive for photovoltaic and microelectronic devices. However, this material is widely contaminated by different impurities particularly transitions metals, which deteriorate the lifetimes and the bulk diffusion lengths of the minority charge carriers. One possible way to overcome this undesirable behavior is to include an efficient purification technique in the process of device fabrication. In this work, we present the effect of photothermal treatments of monocrystalline Czochralski silicon substrates under SiCl4/N2 atmosphere using a thin sacrificial porous silicon layer. The main results show a decrease of the resistivity over 40 μm depth. The Hall mobility of the majority charge carriers is improved from 300 to 1417 cm2 V-1 s-1. The capacitance-voltage (C-V) characteristics of metal/SiO2/Si (MIS) structures indicate a decrease of carrier concentration which confirms the results obtained by Hall Effect and Van Der Pauw method. The reduction of boron concentration in Czochralski silicon may reduce boron- and oxygen related metastable defect centers
[en] Highlights: • ZnO and ZnO:Ni thin films are prepared by spray pyrolysis technique. • We have studied the effects of the pulverization time on the physical properties. • We optimize the most suitable duration of pulverization of ZnO thin films. • Amelioration on optical and electrical properties of ZnO:Ni films was noticed. - Abstract: In this study, undoped and nickel-doped zinc oxide thin films (ZnO:Ni) were deposited on glass substrates using a spray pyrolysis technique. The effects of the Zn concentration in the initial solution and the substrate temperature on the physical properties of the thin films are studied. The results show that the optimum Zn concentration and substrate temperature for preparation of basic undoped ZnO films with n-type conductivity and high optical transparency are 0.02 M and 350 °C, respectively. Then, by using these optimized deposition parameters, nickel-doped zinc oxide films are prepared. Surface morphology and crystalline structure of the films are investigated by atomic force microscopy (AFM) and X-ray diffractometer. X-ray diffraction (XRD) patterns show that the films are polycrystalline. The structural analysis shows that all the samples have a hexagonal structure. The crystallite size and the preferred orientation were calculated from the XRD data. From AFM investigations, the surface morphology of the nanostructured films is found to depend on the concentration of Ni. Optical measurements have shown that an increase in the Ni doping results in a reduction in the optical transmission of the layer, but it remains higher than 80% for Ni doping greater than 8 wt%. At the same time, the optical gap increases from 3.4 to 4 eV when the Ni ratio increases. The electrical measurements show that the resistance of the films varies with the duration of pulverization and the nickel content of the film. Low values for the electrical resistivity (around 103 Ω cm) were obtained for Ni-doped ZnO thin films
[en] A simple and inexpensive spray pyrolysis technique was employed to deposit nickel oxide (NiO) thin films from hydrated nickel chloride salt solution onto amorphous glass substrate. The as-deposited films were transparent, uniform and well adherent to the glass substrate. The effect of the substrate temperature, the volume and the concentration of the sprayed solution on the structural, optical and electrical properties was studied using X-ray diffraction, optical transmittance, four point probe, scanning electron microscopy and atomic force microscopy. The structural analyses show that all the samples have a cubic structure. It was found that the increase in the volume of sprayed solution leads to an increment in the crystallite size of NiO and improves the homogeneity of the film. Optical measurements have shown that an increase in the thickness of the layer results in a decrease in the optical transmission, but it remains higher than 70% even if the thickness exceeds 600 nm. At the same time, the optical gap decreases from 3.7 to 3.55 eV when the thickness increases from 133 to 620 nm. Low values of the electrical resistivity (less than 10 Ω cm) were obtained for thin films with thicknesses less than about 240 nm, but for higher thicknesses the resistivity increases linearly to reach about 170 Ω cm for a thickness of 620 nm.
[en] Un-doped and lithium doped nickel oxide thin films have been prepared on glass substrates by the sol–gel spin coating technique using nickel acetate and lithium chloride as source materials. The thickness of the films was increased by increasing the number of layers successively deposited on the same substrate. The effect of the number of layers on the structural, optical and electrical properties of NiO thin films was studied. The results of investigations of the samples show that four is the most suitable number of layers of undoped NiO films with high optical transparency. Then, by using these optimized deposition parameters, lithium doped nickel oxide films are prepared. The surface morphology and crystalline structure of the thin films were investigated by atomic force microscopy and X-ray diffraction (XRD), respectively. A modification in the morphology of the films was observed while increasing the Li amount in the solution. XRD patterns show that the films are polycrystalline. The preferred orientations were evaluated from XRD data. The average transmittance of the NiO films in the visible region increases with the increase of Li concentration. The electrical measurements show that the resistance of the films decreases as the lithium content increases. - Highlights: • NiO and NiO:Li thin films are prepared on a glass substrate by sol–gel technique. • The effects of thickness on the physical properties of NiO are studied. • Effect of Li doping on the structural, optical and electrical properties of the films. • Li doped NiO films can be used as transparent conductors