Developing High Performance GaP/Si Heterojunction Solar Cells.

To improve the efficiency of Si-based solar cells beyond their Shockley-Queisser limit, the optimal path is to integrate them with III-V-based solar cells. In this work, we present high performance GaP/Si heterojunction solar cells with a high Si minority-carrier lifetime and high crystal quality of epitaxial GaP layers. It is shown that by applying phosphorus (P)-diffusion layers into the Si substrate and a SiNx layer, the Si minority-carrier lifetime can be well-maintained during the GaP growth in the molecular beam epitaxy (MBE). By controlling the growth conditions, the high crystal quality of GaP was grown on the P-rich Si surface. The film quality is characterized by atomic force microscopy and high-resolution x-ray diffraction. In addition, MoOx was implemented as a hole-selective contact that led to a significant increase in the short-circuit current density. The achieved high device performance of the GaP/Si heterojunction solar cells establishes a path for further enhancement of the performance of Si-based photovoltaic devices.

Synthesis and quality control of 68Ga citrate for routine clinical PET.

INTRODUCTION AND AIM: Scintigraphic imaging of infection and inflammation with 67Ga-citrate is an established and powerful diagnostic tool in the management of patients with infectious or inflammatory diseases. 68Ga is a short-lived positron-emitting radionuclide (half-life 67.6 min, positron energy 2.92 MeV), which allows better imaging qualities than 67Ga using the high spatial resolution and the quantitative features of PET. The aim of this study was to develop a method of synthesis for 68Ga citrate with high and reproducible radiochemical yield using a commercial 68Ga-labelling module. The resultant 68Ga citrate would be suitable for use in the detection of infectious or inflammatory diseases in routine clinical practice. METHODS: A simplified method of producing 68Ga citrate is described. Radiochemical purity, pyrogen testing were performed as per the standard protocols. RESULTS: After performing 10 syntheses of 68Ga citrate, the radiochemical yield was 64.1+/-6.0% (mean+/-standard deviation) with an average activity of 971.2+/-103.4 MBq available for labelling. Radiochemical purity determined by instant thin-layer chromatography-silica gel was higher than 98%. All the synthesized products were found to be sterile and pyrogen-free. In this study, the quality control step provided good and reproducible results. This is worth noting, especially in view of the stringent new rules adopted in most European countries for the in-house good manufacturing practice (GMP) synthesis of radiopharmaceuticals. CONCLUSION: The high radiochemical yield and purity showed that this method is a reliable tool for the production of 68Ga citrate to be used in the detection of inflammatory and infectious diseases using high resolution and qualitative PET.

Standardization of 67Ga by 4pigamma (NaI) and 4pibeta-gamma coincidence methods.

The nuclide 67Ga is widely used in nuclear medicine for diagnostic purposes. It decays with a half-life of 3.259 days to 67Zn, a stable nuclide. The decay mode is electron capture with several branches followed by gamma-de-excitation. One of the excited levels of 67Zn with energy 93 keV has a half-life of 9.1 micros, which makes its absolute standardization by coincidence methods difficult. Two methods were used to standardize a solution of this nuclide: (a) 4pi-EC(PPC)-gamma(NaI) coincidence counting with efficiency extrapolation to infinite dead time and (b) high-efficiency 4pigamma counting with a well-type NaI detector.

A 3-year clinical evaluation of a gallium restorative alloy.

Several alternative materials have been suggested to take the place of amalgam, because of the environmental toxic effects of its mercury component. One such material is gallium-based alloy restoratives. The aim of this in vivo study was to compare the long-term clinical performance of a commercial gallium alloy with an admixed high copper amalgam alloy. For this purpose, 32 gallium and 32 amalgam restorations were placed in molar teeth in 14 human subjects. All the selected patients had at least two molar teeth that required restoration. In this way both restoratives were used in the same oral cavity. The restorations were examined at baseline, 6 months, 1, 2 and 3 years. At baseline, six teeth restored with gallium alloy showed post-operative sensitivity, whereas none of the amalgams were sensitive. At the end of 3 years, only a few amalgam restorations showed slight surface tarnish and marginal integrity loss. None of them needed replacement. Of the 32 gallium restorations placed, five had to be removed because of sensitivity, corrosion and tooth fracture. Also dramatic surface roughness and corrosion were noticed in 12 gallium restoration. According to the results of this clinical study, gallium-based restoratives should not be used before their physical properties are improved.