Large grain-sized FeSi2 films by micro-channel epitaxy for infrared detectors

科学研究費助成事業(科学研究費補助金)研究成果報告書：基盤研究(B)2009-2011課題番号：2136000

Energetic stability and magnetic moment of tri-, tetra-, and octa- ferromagnetic element nitrides predicted by first-principle calculations

Formation energies and magnetic moments of tri-, tetra-, and octa- ferromagnetic element nitrides have been calculated using spin-polarized Perdew–Wang generalized gradient approximations of the density functional theory. From the energetic point of view, Fe4N are more stable compared to Fe and N2 gas. Ni4N may be a metastable phase since mixture of Ni3N and Ni would be more energetically stable. Fe4N may be also a metastable from energetic point of view but effect of configurational entropy caused by N-vacancy and of disregarded random occupation of interstitial sites by N observed in Fe3N must be evaluated so as to make precise evaluation, which is beyond the scope of the present work. Co4N are not stable compared to Co metal with the hcp structure and N2 gas, but more stable in case Co metal with the fcc structure is used as a reference state. Only Fe8N with the α″-Fe16N2 type structure would be stable among octa-metal nitrides with the assumed structure of the α″-Fe16N2 type and the Ni32N4 type structure. All of Fe3N, Co3N, and Ni3N are stable, but Ni3N would be non-magnetic in contrast to ferromagnetism of other tri-metal nitrides

Effects of Sr addition on crystallinity and optical absorption edges in ternary semiconducting silicide Ba1-xSrxSi2

Polycrystalline Ba1-xSrxSi2 films with the Sr composition x varying from 0 to 0.77 were grown on transparent fused silica substrates by molecular beam epitaxy, and the effects of Sr addition on the indirect optical absorption edge Eedge were investigated. It was found that the Eedge value increases almost linearly with increasing x and reached approximately 1.40 eV when x was 0.52. When x>0.6, the Eedge value almost saturates, and the formation of homogeneous Ba1-xSrxSi2 films became difficult. Phase separation was observed for x=0.77

On the Mechanism of BaSi2 Thin Film Formation on Si Substrate by Vacuum Evaporation

AbstractWe report on the formation mechanism of BaSi2 thin film on Si substrate grown by vacuum evaporation using BaSi2 granules as source materials. Since the vapor flux at the initial stage of evaporation is known to be Ba-rich, Si supply from the substrate is of crucial importance to obtain homogeneous BaSi2 thin film. In fact, low substrate temperature and/or thick film deposition led to formation of rough film with voids, and the oxidation proceeded upon exposure to air. We revealed that appropriate choice of substrate temperature, film thickness, and post-growth in-situ annealing can provide enough diffusion of Si and Ba, leading to realization of homogeneous BaSi2 thin film

結晶Siタンデム型太陽電池に向けたSi系ワイドギャップ新材料の探索

科学研究費助成事業 研究成果報告書：基盤研究(A)2015-2017課題番号 : 15H0223

Multilayer graphene on insulator formed by Co-induced layer exchange

The direct synthesis of multilayer graphene (MLG) on arbitrary substrates is essential for incorporating carbon wirings and heat spreaders into electronic devices. Here, we applied the metal-induced layer exchange (MILE) technique, developed for group-IV semiconductors, to a sputtered amorphous carbon (a-C) thin film using Co as a catalyst. MLG was formed on a SiO2 substrate at 800 °C for 10 min; however, it disappeared during wet etching for removing Co. This behavior was attributed to the small contact area between MLG and SiO2 caused by the deformation of the Co layer during annealing. By preparing the Co layer at 200 °C, its thermal stability was improved, resulting in the synthesis of MLG on the substrate through MILE. Raman measurements indicated good crystal quality of the MLG compared with that obtained by conventional metal-induced solid-phase crystallization. MILE was thus proven to be useful not only for group-IV semiconductors but also for carbon materials on insulators

Minority-carrier diffusion length, minority-carrier lifetime, and photoresponsivity of β-FeSi2 layers grown by molecular-beam epitaxy

We have epitaxially grown undoped β-FeSi2 films on Si(111) substrates via atomic-hydrogen-assisted molecular-beam epitaxy. β-FeSi2 films grown without atomic hydrogen exhibited p-type conduction with a hole density of over 1019 cm−3 at room temperature (RT). In contrast, those prepared with atomic hydrogen showed n-type conduction and had a residual electron density that was more than two orders of magnitude lower than the hole density of films grown without atomic hydrogen (of the order of 1016 cm−3 at RT). The minority-carrier diffusion length was estimated to be approximately 16 μm using an electron-beam-induced current technique; this value is twice as large as that for β-FeSi2 prepared without atomic hydrogen. This result could be well explained in terms of the minority-carrier lifetimes measured by a microwave photoconductance decay technique. The 1/e decay time using a 904 nm laser pulse was approximately 17 μs, which is much longer than that for β-FeSi2 prepared without atomic hydrogen (3 μs). The photoresponsivity reached 13 mA/W at 1.31 μm, which is the highest value ever reported for β-FeSi2 films

Usefulness and complications of computed tomography-guided lipiodol marking for fluoroscopy-assisted thoracoscopic resection of small pulmonary nodules: Experience with 174 nodules

ObjectiveSeveral techniques have been reported for the localization of small pulmonary nodules in thoracoscopic resection. In the present study we examined the usefulness and complications of computed tomography-guided lipiodol marking for thoracoscopic resection in our experience of 174 nodules.MethodsComputed tomography-guided lipiodol marking was performed on 174 nodules less than 30 mm in size. Of these nodules, 45 showed ground-glass opacity images and 129 showed solid images on computed tomography. The mean size of the nodules was 10 ± 6 mm (range, 2-30 mm), and their mean depth from the pleural surface was 10 ± 7 mm (range, 0-30 mm). One to 7 days before thoracoscopy, all of the nodules were marked with 0.4 to 0.5 mL of lipiodol by using computed tomography. The marked nodules were grasped with a ring-shaped forceps during fluoroscopy and resected by means of thoracoscopy.ResultsAll the nodules could be marked and localized by means of fluoroscopy as a clear spot during thoracoscopic surgery. Complications of the marking were chest pain requiring analgesia in 16 (11%) patients, hemosputum in 11 (6%) patients, pneumothorax in 30 (17%) patients, and hemopneumothorax in 1 (0.6%) patient. Eleven (6%) patients with pneumothorax required drainage, and the patient with hemopneumothorax required an emergency operation. No other complications were observed.ConclusionLipiodol marking is a useful, safe, and inexpensive procedure for localizing ground-glass opacity lesions, small pulmonary nodules, or both for thoracoscopic resection